WO2019007473A1 - Method and system for analysing a fuel gas - Google Patents

Method and system for analysing a fuel gas Download PDF

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Publication number
WO2019007473A1
WO2019007473A1 PCT/EP2017/025192 EP2017025192W WO2019007473A1 WO 2019007473 A1 WO2019007473 A1 WO 2019007473A1 EP 2017025192 W EP2017025192 W EP 2017025192W WO 2019007473 A1 WO2019007473 A1 WO 2019007473A1
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WO
WIPO (PCT)
Prior art keywords
gas
analysis
oxygen
determined
content
Prior art date
Application number
PCT/EP2017/025192
Other languages
French (fr)
Inventor
Gerd Waning
Michael-Peter GRAF
Original Assignee
Linde Aktiengesellschaft
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Linde Aktiengesellschaft filed Critical Linde Aktiengesellschaft
Priority to CN201780092400.1A priority Critical patent/CN110770581A/en
Priority to EP17739877.3A priority patent/EP3649468A1/en
Priority to PCT/EP2017/025192 priority patent/WO2019007473A1/en
Publication of WO2019007473A1 publication Critical patent/WO2019007473A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/22—Fuels; Explosives
    • G01N33/225—Gaseous fuels, e.g. natural gas
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N31/00—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
    • G01N31/12—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using combustion

Definitions

  • the present invention relates to a method and a system for analysing a gas.
  • FTIR Fourier transform infrared spectroscopy
  • mass spectrometry mass spectrometry
  • gas chromatography gas chromatography-mass spectrometry
  • GC-MS gas chromatography-mass spectrometry
  • the present invention relates to a method and a system for analysing a gas with the features of the independent claims.
  • Advantages and embodiments of this method and of this system according to the invention arise from the following description in an analogous manner. Further advantages and embodiments of the invention will become apparent from the description and the appended figures.
  • the wording gas shall be understood as a single gas as well a mixture of different single gases.
  • the gas is particularly a hydrocarbon gas or contains one or more hydrocarbons.
  • the gas can be natural gas.
  • the gas consists of or contains components which are able to react or interact with oxygen.
  • a predetermined amount or quantity of the gas is mixed with an oxygen-containing gas to produce an analysis gas.
  • oxygen-containing gas for example, oxygen, air, and/or laughing gas can be used as oxygen-containing gas.
  • the analysis gas is particularly a product of a chemical reaction of the process gas and the oxygen-containing gas.
  • the corresponding analysis system comprises a mixing unit adapted to mix the predetermined amount of the gas with the oxygen-containing gas and to produce the analysis gas.
  • this mixing unit can comprise a first pipe, through which the gas is conducted, which merges with a second pipe, through which the oxygen-containing gas is conducted.
  • An oxygen content of the analysis gas is determined.
  • an absolute oxygen content or a concentration of oxygen in the analysis gas is determined.
  • an oxygen determination unit is provided, for example a lambda sensor and/or a paramagnetic sensor and/or an amperometric sensor.
  • the analysis gas is conducted through the oxygen determination unit and the oxygen content of the corresponding analysis gas stream is determined.
  • the oxygen determination unit is especially heated, particularly a heated lambda sensor is provided.
  • the analysis gas conducted through the oxygen determination unit is heated such that chemical reactions can especially be triggered.
  • a characteristic of the gas is evaluated depending on the determined oxygen content of the analysis gas.
  • an evaluation unit is provided, and connected to the analysis system.
  • the invention thus provides a new possibility of easily evaluating characteristics of a gas.
  • a specific chemical reaction of the gas and the oxygen-containing gas will occur and the analysis gas will thus have a specific oxygen-content.
  • the oxygen-content of the analysis gas yields the possibility to draw conclusions about characteristics like the composition of the gas.
  • a basic property or nature of the gas can be known beforehand.
  • the gas can specifically be analysed for further characteristics based on this basic property.
  • a basic property, for example, of natural gas is that it contains specific hydrocarbons, hydrogen and nitrogen as main components. With the knowledge of how these components react with the oxygen- containing gas, the presence of a component in the gas can be verified of falsified. As a characteristic it can e.g. be evaluated, whether the gas indeed contains this component and especially in which specific concentration.
  • the knowledge of a specific reaction of a gas component with the oxygen-containing gas or a relation between a content of a specific component in the gas and the oxygen-content of the analysis gas can especially be provided in the form of look up tables.
  • the analysis system can comprise other elements e.g. pumps, throttles, etc.
  • a pump can especially be provided in order to carry the analysis gas through the oxygen determination unit.
  • This pump can especially be provided downstream of the oxygen determination unit. It is also possible not to pump the gases but to draw the gases, for example if the gases contain components, which could damage a pump.
  • the analysis system can especially be calibrated, e.g. by means of known test gases with a known composition.
  • the predetermined amount or test amount of the gas can especially be extracted from a unit containing the gas.
  • the predetermined amount can permanently be extracted from this unit and mixed with the oxygen-containing gas in order to analyse the gas over time.
  • a constant stream of the gas can especially be mixed with the oxygen-containing gas and a constant stream of the analysis gas can be carried through the oxygen determination unit. Therefore, changes of the characteristic of the gas can be detected.
  • an amount of the oxygen-containing gas, which is mixed with the predetermined amount of the gas is controlled depending on the determined oxygen content of the analysis gas.
  • This amount of the oxygen-containing gas is preferably controlled such that the determined oxygen content of the analysis gas remains constant.
  • a specific value of the oxygen content of the analysis gas is expediently used as corresponding set point.
  • the amount of the oxygen-containing gas needed to be mixed with the gas such that the oxygen content of the analysis gas remains constant particularly enables to draw conclusions about the gas characteristics. Therefore, the characteristic of the gas is preferably evaluated depending on this controlled amount of the oxygen-containing gas.
  • the gas comprises oxygen reacting components
  • these components will react with the oxygen-containing gas and thus the oxygen content of the analysis gas will be comparatively low. Therefore, a comparatively high amount of the oxygen- containing gas has to be mixed with the gas in order to keep the oxygen content of the analysis gas constant.
  • the composition of the gas changes, the oxygen content of the analysis gas will also change.
  • the specific amount of oxygen- containing gas mixed with the test amount of the gas also has to be changed such that the oxygen content of the analysis gas remains constant. This change of the amount of oxygen-containing gas enables to draw conclusions about the change of the gas characteristic, particularly its composition.
  • a constant amount of the oxygen-containing gas is advantageously mixed with the predetermined amount of the gas.
  • the oxygen content of the analysis gas is not kept constant and can vary depending on the composition of the gas.
  • the characteristic of the gas is advantageously evaluated depending on the determined oxygen content of the analysis gas with a constant amount of oxygen- containing gas.
  • a temperature of the predetermined amount of the gas and/or of the oxygen-containing gas and/or of the analysis gas is determined and/or adjusted.
  • the predetermined amount of the gas and/or the oxygen- containing gas and/or the analysis gas is heated.
  • a chemical reaction of the gas and the oxygen-containing gas can especially be triggered.
  • thermochemical stable components of the gas can be caused to react with the oxygen- containing gas.
  • a first pipe, through which the predetermined amount of the gas is conducted, and/or a second pipe, through which the oxygen-containing gas is conducted, and/or a third pipe, through which the analysis gas is conducted can preferably be heated at least partially.
  • the first pipe and/or the second pipe and/or the third pipe are provided at least partially inside a furnace.
  • the oxygen determination unit is advantageously heated.
  • the analysis gas which is preferably conducted through the oxygen determination unit, is heated.
  • additional analysis values of the analysis gas can be determined and advantageously an absolute composition of the gas or absolute contents of gas components can be determined depending on said values.
  • the analysis can e.g. also be combined with conventional methods of evaluating gas compositions for verification purposes or to evaluate the gas characteristics more precisely.
  • a flow rate of the analysis gas is determined, particularly downstream of the oxygen determination unit.
  • the analysis system advantageously comprises a corresponding flowmeter.
  • the composition of the gas, particularly an absolute composition, especially an absolute content of a component of the gas, is preferably evaluated depending on the determined flow rate and on the determined oxygen content of the analysis gas.
  • a dew point of the analysis gas is determined, particularly downstream of the oxygen determination unit.
  • a corresponding dew point analysis unit is particularly provided for this purpose, especially downstream of the flowmeter.
  • a hydrogen content of the gas particularly an absolute hydrogen content, is evaluated depending on the determined dew point and on the determined oxygen content of the analysis gas.
  • Hydrogen in the gas particularly reacts in a specific way with the oxygen-containing gas, such that the dew point of the analysis gas is specifically influenced.
  • the dew point of the analysis gas particularly enables to draw conclusions about the hydrogen content of the gas.
  • a carbon dioxide content of the analysis gas is determined, particularly downstream of the oxygen determination unit.
  • the analysis system thus preferably comprises a corresponding carbon dioxide analyser, particularly downstream of the dew point determination unit.
  • a carbon content of the gas is evaluated depending on the determined carbon dioxide content and on the determined oxygen content of the analysis gas.
  • Carbon in the gas particularly reacts in a specific way with the oxygen-containing gas, such that the carbon dioxide content of the analysis gas is specifically influenced.
  • the carbon dioxide content of the analysis gas particularly enables to draw conclusions about the carbon content of the gas.
  • a cold trap can be provided upstream of the carbon dioxide analyser in order to condensate vapours of the analysis gas stream.
  • the determined dew point and/or carbon dioxide content can especially also be used for a more precise determination of the analysis gas flow rate.
  • the predetermined amount of the gas is provided with a constant pressure and/or the oxygen-containing gas is also provided with a constant pressure.
  • the gas and the oxygen-containing gas can be provided with the same pressure of e.g. 20 mbar or with different pressures.
  • a temperature of the predetermined amount of the gas and/or of the oxygen-containing gas is preferably also constant.
  • a first throttle can be provided for the steam of the gas and/or a second throttle can be provided for the oxygen-containing gas.
  • a flow rate of the gas and/or of the oxygen-containing gas can especially be controlled.
  • a partial pressure of oxygen in the analysis gas is determined.
  • the characteristic of the gas, particularly the air-fuel ratio is preferably evaluated depending on the constant pressures and on the flow rates of the gas and of the oxygen-containing gas and depending on the determined partial pressure of oxygen.
  • the gas is produced inside a process unit.
  • the gas is produced inside a process unit.
  • predetermined amount of the gas is mixed with the oxygen-containing gas to produce the analysis gas within a process unit mixing member inside the process unit.
  • the analysis gas is advantageously extracted from the process unit mixing member.
  • the temperature inside the process unit can particularly be used to trigger the chemical reaction of the gas and the oxygen-containing gas.
  • an analysis gas extraction pipe and an oxygen- gas injection pipe can preferably be provided.
  • a first part of this analysis gas extraction pipe is preferably located inside the process unit and a second part of the analysis gas extraction pipe is located outside the process unit.
  • the predetermined amount of the gas to be mixed with the oxygen-containing gas can be collected inside the first part of this analysis gas extraction pipe.
  • the oxygen-gas injection pipe can advantageously be provided at least partially inside the first part of the analysis gas extraction pipe. The oxygen-containing gas is thus injected into the first part of the analysis gas extraction pipe by means of the oxygen-gas injection pipe, such that the predetermined amount of the gas is mixed with the oxygen-containing gas inside the first part of the analysis gas extraction pipe.
  • the analysis gas is then extracted from the process unit by means of the analysis gas extraction pipe.
  • an air-fuel ratio for combustion of the gas is evaluated as the characteristic of the gas depending on the determined oxygen content of the analysis gas.
  • a mass ratio of air, oxygen or of an oxygen-containing gas to the gas can especially be determined as the air-fuel ratio.
  • an optimum air-fuel ratio for an optimum combustion of the gas can be evaluated.
  • an amount of air, oxygen or an oxygen-containing for combustion of the gas can especially be determined.
  • the air-fuel equivalence ratio ⁇ can be determined by means of the air-fuel ratio.
  • the gas is a fuel gas, preferably natural gas.
  • combustion of the fuel gas is performed depending on the evaluated characteristic of the fuel gas, particularly depending on the evaluated air-fuel ratio.
  • the invention thus enables an optimum combustion of the fuel gas even without knowing the specific composition of the fuel gas in detail.
  • an optimum combustion of fuel gas with varying composition can be enabled.
  • the necessary amount of air, oxygen, or oxygen-containing gas for an efficient combustion of the fuel gas also varies.
  • this amount of air, oxygen, or oxygen-containing gas can easily be determined and a clean, complete and efficient combustion of the fuel gas can be enabled.
  • the corresponding specific amount or test amount of the specific fuel gas can expediently permanently be extracted, e.g. from a unit containing the fuel gas, and the corresponding characteristic can permanently determined in order to react to possible fluctuations of the fuel gas composition.
  • the natural gas composition can fluctuate significantly.
  • an efficient combustion of natural gas can be enabled, especially by evaluating the air-fuel ratio of the specific natural gas and by performing the combustion of the natural gas depending on the evaluated air-fuel ratio.
  • the specific composition of the natural gas can be evaluated, preferably an absolute composition, particularly a content of carbon, hydrogen, oxygen and/or nitrogen.
  • a composition of the gas is evaluated as the characteristic of the gas depending on the determined oxygen content of the analysis gas.
  • characteristic of the gas it can particularly be evaluated whether the gas contains specific components, particularly specific molecules or elements, especially specific hydrocarbons.
  • a relative composition can particularly be determined as characteristic, especially a ratio of specific components of the gas.
  • an absolute composition of the gas can especially be evaluated, i.e. specific contents of specific components of the gas, particularly specific contents of specific molecules or elements.
  • the invention therefore enables an easy, inexpensive, and repeatable possibility of evaluating the gas composition with low expenditure, which is particularly less elaborate and more cost effective than conventional methods of evaluating gas compositions, e.g. Fourier transform infrared spectroscopy (FTIR), mass spectrometry, gas chromatography or gas chromatography-mass spectrometry (GC-MS) and especially more repeatable than conventional methods like infrared analysers.
  • FTIR Fourier transform infrared spectroscopy
  • mass spectrometry mass spectrometry
  • GC-MS gas chromatography-mass spectrometry
  • the gas is a process gas, which is produced in the course of a chemical process, preferably in the course of a thermochemical process, preferably in the course of a thermochemical process of a hydrocarbon-containing gas.
  • the process gas is produced in the course of a pyrolysis, preferably a pyrolysis of hydrocarbons.
  • the chemical process is controlled depending on the evaluated characteristic of the gas, particularly depending on the evaluated composition of the gas. Metrological control of chemical processes, particularly of thermochemical processes, is usually elaborate and expensive. The present invention enables an easy, inexpensive and an effective process control with low expense.
  • the predetermined amount of the process gas is extracted from a process unit, in which the chemical process, particularly the thermochemical process, is performed.
  • the predetermined amount of the process gas can e.g. be extracted from the process unit by means of the first pipe of the analysis system.
  • the specific amount of the process gas can permanently be extracted from the process unit, thus enabling a continuous evaluation of the process gas characteristics.
  • the predetermined amount of the process gas is thus conducted out of the process unit and the analysis of the process gas is expediently performed outside of the process unit.
  • the atmosphere inside the process unit and the chemical process are therefore especially not affected by the gas analysis.
  • the analysis of the gas can be performed independently of the process unit load, e.g. independently of material, size, homogeneity of mechanical parts processed in the process unit.
  • the analysis system can furthermore easily be implemented without or with minimal constructional changes of the process unit.
  • the gas analysis according to the present invention can be used for analysing gas produced in a variety of different chemical, especially thermochemical processes and to preferably control the corresponding process depending on the evaluated gas characteristics.
  • thermochemical processes especially thermochemical processes and to preferably control the corresponding process depending on the evaluated gas characteristics.
  • gas analysis can advantageously be used.
  • Endothermic gas or endogas is a gas mixture of hydrogen, carbon monoxide, carbon dioxide, and/or nitrogen and can e.g. used as protective gas in the thermal treatment of metals.
  • Endogas can be produced by burning a hydrocarbon gas with limited supply of air, i.e. at high oxygen deficiency.
  • natural gas and/or propane are used as hydrocarbon gas for the endogas production.
  • For an efficient endogas production it is important to know the specific composition of the corresponding hydrocarbon gas. By means of the gas analysis, this composition can be evaluated and the endogas production can be controlled depending on said evaluated composition.
  • endogas can efficiently be produced e.g. also from natural gas with varying composition.
  • the chemical process can for example be a multi-stage process, wherein a process gas with a specific composition is produced during a specific stage of the multi-stage process. If the presence of this specific composition is not determined any more in the course of the evaluation of the process gas characteristic, it can be detected that this specific stage is finished and a subsequent stage of the process can be initiated.
  • a debinding process is one process stage of a sintering process, during which the process gas comprises hydrocarbons.
  • the process gas comprises hydrocarbons.
  • it can e.g. be evaluated, whether these hydrocarbons typical for the debinding process are part of the process gas composition. If the corresponding hydrocarbons are not determined any more, it can be detected that the debinding process is finished and the subsequent sintering process stage can be initiated.
  • the sintering process can be performed in the course of a metal injection molding (MIM) or in the course of cemented-carbide sintering processes.
  • MIM metal injection molding
  • Carburising is a heat treatment process in order to increase the hardness of low carbon steel or iron.
  • the corresponding metal absorbs carbon while being heated in the presence of a carbon-bearing material.
  • Low pressure carburising is carried out in vacuum furnaces, into which alternately a hydrocarbon-containing gas (e.g. methane CH 4 , acetylene C 2 H 2 and/or propane C 3 H 8 ) and a neutral gas (e.g. N 2 ) for diffusion are injected. Subsequently a quenching of the metal part performed.
  • a mixture of hydrogen and helium can be used as corresponding quenching gas.
  • the hydrocarbon content of the atmosphere inside the vacuum furnace or of the gas atmosphere evacuated from the vacuum furnace can be evaluated.
  • conclusions can particularly be drawn about carbon absorption of the metal parts. It is also possible to monitor the ratio of hydrogen and helium of the quenching gas by means of the gas analysis.
  • a heat treatment or annealing of metal parts in form of coils can be performed in a bell- furnace with a hydrocarbon-atmosphere.
  • a level of cleanliness of the coils during annealing is especially dependent on an evaporation behaviour of rolling oil or rolling emulsion.
  • the atmosphere inside the bell-furnace can be evaluated, particularly in order to evaluate the evaporation behaviour of the rolling oil or rolling emulsion.
  • a content of methane, carbon dioxide and/or carbon monoxide of the furnace atmosphere can be evaluated.
  • the so called WASTOX process is a combustion process, which can e.g. be used for the recycling of carbon-containing metal scrap. If unburnt hydrocarbons and/or carbon monoxide are detected in the waste gas of the furnace, the combustion process is controlled accordingly in order to combust these gases inside the furnace itself.
  • Organic contaminants in the metal, which are released during the combustion, are thus used as fuel.
  • the components of the waste gas can be evaluated and the presence of hydrocarbons and/or carbon monoxide can be detected.
  • Fig. 1 a, 1 b, 1 c each schematically show a preferred embodiment of an analysis
  • Fig. 2 schematically shows a part of a preferred embodiment of an analysis system for analysing a gas according to the invention, which is adapted to perform a preferred embodiment of a method for analysing a gas according to the invention, and
  • Fig. 3a, 3b each schematically show a preferred embodiment of an analysis
  • Fig. 1 a a preferred embodiment of an analysis system 100 for analysing a gas according to the invention is schematically shown.
  • the analysis system 100 is adapted to perform a preferred embodiment of a method for analysing a gas according to the invention.
  • a thermochemical process in the course of which a process gas is produced, is performed in a process unit 101 , e.g. a sintering process of metal parts.
  • the process unit 101 can for example be a furnace.
  • the analysis system 100 is adapted to perform an analysis of the process gas produced in the furnace and to evaluate characteristics of this process gas.
  • a predetermined amount of the process gas is extracted from the furnace 101 .
  • a first pipe 110 is provided, through which a constant stream of the process gas is extracted from the furnace 101.
  • a pump and/or compressor 11 1 is provided in order to compress the extracted process gas.
  • a heating mechanism 1 12 is provided in order to heat the pipe 1 10 and thus the extracted process gas.
  • a small furnace or a heat exchanger can be provided as heating mechanism 1 12, inside which a part of the pipe 1 10 is arranged.
  • This extracted process gas is mixed with an oxygen-containing gas, e.g. oxygen.
  • an oxygen supply 102 and a second pipe 120 are provided, through which a stream of oxygen is channelled.
  • a flow control unit 121 is provided in order to control the flow rate of the oxygen.
  • the first pipe 1 10 and the second pipe 120 merge into a third pipe 130.
  • the stream of the heated extracted process gas is mixed with the stream of oxygen.
  • the heated process gas chemically reacts with the oxygen to produce an analysis gas, which is channelled through the third pipe 130.
  • the first pipe 1 10, the second pipe 120, and the third pipe 130, as well as the compressor 11 1 , the heating mechanism 1 12, and the flow control unit 121 are particularly part of a mixing unit 103 adapted to mix the predetermined amount of the extracted process gas with the oxygen and to produce the analysis gas stream.
  • an oxygen determination unit 140 is provided, for example a lambda sensor.
  • an oxygen content of the analysis gas is determined.
  • the determined values of the oxygen content are transmitted from the lambda sensor 140 to a control unit or evaluation unit 160, indicated by reference numeral 140a.
  • a wireless communication link can be established between the lambda sensor 140 and the control unit 160.
  • a flowmeter 151 Downstream of the oxygen determination unit 140 a flowmeter 151 is provided in order to determine a flowrate of the analysis gas stream.
  • the flowmeter 151 transmits the determined values of the flowrate to the control unit 160, indicated by reference numeral 151 a, for example also by means of a wireless connection.
  • the control unit 160 evaluates characteristics of the process gas depending on the determined oxygen content of the analysis gas stream and especially also depending on the determined flowrate of the analysis gas stream. Particularly, the control unit 160 evaluates a composition of the gas depending on the determined oxygen content and on the determined flowrate of the analysis gas stream. It can especially be evaluated, whether the process gas contains hydrocarbons. By means of the flowrate, an absolute hydrocarbon content of the process gas can be estimated.
  • the control unit 160 is moreover adapted to control the amount of oxygen, which is mixed with the process gas, depending on the determined oxygen content of the analysis gas.
  • the control unit 160 controls the flow control unit 121 , indicated by reference numeral 121 a.
  • the flowrate of the oxygen gas in the second pipe 120 is controlled such in that the oxygen content of the analysis gas stream in the third pipe 130 remains constant.
  • the thermochemical process in the furnace 101 is controlled depending on the evaluated characteristic of the gas, particularly depending on the evaluated composition of the gas. During the sintering process inside the furnace 101 , a debinding of the metal parts occurs. In the course of this debinding process a specific hydrocarbon-containing process gas is produced in the furnace 101 .
  • This hydrocarbon-containing process gas specifically reacts with the oxygen and thus a specific analysis gas with a specific oxygen content is produced.
  • the control unit 160 detects that this debinding process has started.
  • a relation between the content of this hydrocarbon in the process gas and the oxygen content in the analysis gas can e.g. be provided in form of a look up table stored in the control unit 160.
  • the control unit 160 detects that this debinding process has finished. In this case the control unit 160 can send a corresponding command to the furnace 101 in order to initiate a subsequent stage of the sintering process, indicated by reference numeral 101 a.
  • FIG. 1 b another preferred embodiment of an analysis system 100' according to the invention is schematically shown, analogously to the system 100 of Fig. 1 a.
  • Fig. 1 c schematically shows another preferred embodiment of an analysis system 100" according to the invention, analogously to the system 100' of Fig. 1 b.
  • heating mechanism and compressor are not provided in the first pipe 1 10 of the corresponding mixing unit 103".
  • a heating mechanism 132 is provided in the third pipe 130 in order to heat the mixture of the process gas and oxygen.
  • a small furnace or a heat exchanger can be provided as heating mechanism 132.
  • the oxygen content of the analysis gas stream in the third pipe 130 is determined by means of the lambda sensor 140 and the flowrate is determined by means of the flowmeter 151 .
  • a compressor 152 Downstream of the flowmeter 151 , a compressor 152, a dew point analysis unit 153, a cold trap 154, and a carbon dioxide analyser 155 are provided downstream of the flowmeter 151 .
  • a dew point analysis unit 153 By means of the dew point analysis unit 153, a dew point of the analysis gas is determined and transmitted to the control unit 160, indicated by reference numeral 153a. Vapours of the analysis gas stream condensate by means of the cold trap 154 and a carbon dioxide content of the analysis gas stream is determined by means of the carbon dioxide analyser 155 and, as indicated by numeral 155a, transmitted to the control unit 160.
  • control unit 160 evaluates a hydrogen content of the process gas. Moreover, depending on the determined carbon dioxide content and on the determined oxygen content of the analysis gas, the control unit 160 evaluates a carbon content of the process gas.
  • the process gas can also be mixed with the oxygen-containing gas inside the process unit, in which it is produced.
  • a part of corresponding preferred analysis system according to the invention is schematically shown in Fig. 2.
  • Fig. 2 shows a part of a process unit 201 , e.g. a furnace.
  • a thermochemical process is performed, e.g. a sintering process, analogously to the furnace 101 shown in Fig. 1 a to 1 c.
  • a process gas 21 1 is produced in the interior 201 a of the furnace 201.
  • a wall of the furnace is referred to as 201 c and the outside of the furnace as 201 b.
  • a process unit mixing member is provided inside the furnace 201 in order to produce the analysis gas within this process unit mixing member and thus inside the furnace 201 .
  • This process unit mixing member comprises an analysis gas extraction pipe 210 and an oxygen-gas injection pipe 220.
  • the analysis gas extraction pipe 210 is provided such that a first part 210a of this pipe 210 is arranged in the inside 201 a of the furnace 201 and a second part 210b of the pipe 210 is arranged outside 201 b the furnace 201 .
  • a predetermined amount of the process gas especially accumulates in the first part 210a of the analysis gas extraction pipe 210.
  • the oxygen-gas injection pipe 220 is arranged at least partially inside the analysis gas extraction pipe 210. Particularly, an end 220a of the oxygen-gas injection pipe 220 is arranged in the first part 210a of the analysis gas extraction pipe 210 and thus in the interior 201 a of the furnace 201 .
  • holes 220b are provided at a part of the oxygen-gas injection pipe 220, which is arranged in the first part 210a of the analysis gas extraction pipe 210.
  • the oxygen-containing gas 221 e.g. oxygen
  • the oxygen-containing gas 221 is injected into the first part 210a of the analysis gas extraction pipe 210 by means of the oxygen-gas injection pipe 220 through the holes 220b.
  • the process gas 211 accumulated in the first part 210a of the analysis gas extraction pipe 210 is mixed with the injected oxygen 221 .
  • the temperature inside the furnace triggers the chemical reaction of the process gas 21 1 and the oxygen 221 .
  • the corresponding analysis gas 231 is produced in the interior 201 a of the furnace 201 .
  • the analysis gas 231 is extracted from the furnace 201 by means of the analysis gas extraction pipe 210 and channelled to an oxygen determination unit, as described above.
  • Fig. 3a schematically shows another preferred embodiment of an analysis system 300 according to the invention, adapted to perform a preferred embodiment of a method according to the invention.
  • a natural gas supply 301 b and an air supply 301 c are provided inside a process unit 301 .
  • a fuel gas e.g. natural gas
  • air e.g. air
  • the necessary amount of air for an efficient combustion of the natural gas depends on the specific composition of the natural gas.
  • the natural gas is analysed.
  • a predetermined amount of the natural gas is extracted from the natural gas supply 301 b by means of a first pipe 310.
  • an oxygen supply 302, and a second pipe 320 are provided, through which a stream of oxygen gas is channelled.
  • the first pipe 310 and the second pipe 320 merge into a third pipe 330.
  • the stream of the extracted natural gas is mixed with the stream of oxygen.
  • the natural gas reacts with the oxygen and an analysis gas is produced and channelled through the third pipe 330.
  • An oxygen determination unit 340 is provided, for example a lambda sensor, which determines an oxygen content of the analysis gas stream.
  • a flowmeter 351 is provided to determine a flowrate of the analysis gas stream. The determined values of the oxygen content and of the flowrate are transmitted from the lambda sensor 340 and the flowmeter 351 to a control unit or evaluation unit 360, indicated by reference numerals 340a and 351 a.
  • the control unit 360 evaluates characteristics of the process gas depending on the determined oxygen content and especially on the determined flowrate of the analysis gas stream. Particularly, the control unit 360 evaluates an air-fuel ratio of the natural gas for an optimum combustion. According to this determined optimum air-fuel ratio, the control unit 360 controls a valve 304 in the natural gas supply 301 b, indicated by reference numeral 301 a. Thus the control unit 360 controls an amount of natural gas supplied to the furnace 301 such that a mixture of natural gas and air according to the determined optimum air-fuel ratio is supplied to the furnace 301 .
  • the optimum air-fuel ratio is permanently determined in order to react to possible fluctuations of the natural gas composition.
  • control unit 360 is adapted to control the amount of oxygen, which is mixed with the natural gas, depending on the determined oxygen content of the analysis gas.
  • the control unit 360 controls a flow control unit 321 in the second pipe 320, indicated by reference numeral 321 a.
  • the first pipe 310, the second pipe 320, the third pipe 330, and the flow control unit 321 are particularly part of a corresponding mixing unit 303.
  • Fig. 3b schematically shows another preferred embodiment of an analysis system 300' according to the invention, analogously to the system 300 of Fig. 3a.
  • a first throttle 31 1 is provided in the first pipe 310 and a second throttle 322 is provided in the second pipe 320.
  • a natural gas stream with constant pressure of e.g. 20 mbar is mixed with an oxygen stream of constant pressure of e.g. also 20 mbar.
  • a thermal insulation 341 is provided for the lambda sensor 340. Moreover, a temperature sensor 342 is provided to determine a temperature of the lambda sensor 340. The determined temperature is transmitted to the control unit 360, indicated by numeral 342a.
  • a partial pressure unit 352 is provided to determine a partial pressure of oxygen in the analysis gas stream in the third pipe 330, which is transmitted to the control unit 360, indicated by numeral 352a.
  • the control unit 360 determines the optimum air-fuel ratio in dependence of the constant pressures and the corresponding flow rates of the natural gas and the oxygen in the pipes 310 and 320, and furthermore in dependence of the determined partial pressure, of the determined oxygen content of the analysis gas, and of the lambda sensor's temperature. Depending on the evaluated optimum air-fuel ratio, the control unit 360 controls the valve 304 in the natural gas supply 301 b such that a mixture of natural gas and air according to the determined optimum air-fuel ratio is supplied to the furnace 301 .
  • control unit 160 a transmission between control unit 160 and flow control unit 121
  • control unit 160 evaluation unit control unit
  • control unit 360 a transmission between control unit 360 and flow control unit 321

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Abstract

The present invention relates to a method and a system (100) for analysing a fuel gas, wherein a predetermined amount of the fuel gas (110) is reacted with an oxygen-containing gas (120) to produce an analysis gas (130), wherein an oxygen content of the analysis gas is determined (140), and wherein a characteristic of the fuel gas is evaluated (160) depending on the determined oxygen content of the analysis gas.

Description

Description
METHOD AND SYSTEM FOR ANALYSING A FUEL GAS
The present invention relates to a method and a system for analysing a gas. Prior art
For certain chemical processes of gases, particularly hydrocarbon gases or hydrocarbon-containing gases, it can be important to know specific characteristics of the gas, particularly if those characteristics change over time, in order to perform the process optimally. For example for combustion of a gas or fuel gas it can be desirable to know an air-fuel ratio of the gas, which describes a ratio of air to the fuel gas for an optimum combustion. This is especially true for natural gas, the composition of which usually changes over time. For other chemical processes it can be desirable to know the specific composition of the gas, for example in order to control the corresponding process. However, methods for measuring a gas composition, e.g. Fourier transform infrared spectroscopy (FTIR), mass spectrometry, gas chromatography or gas chromatography-mass spectrometry (GC-MS), are expensive, complex and elaborate. Other methods like infrared gas analysers in some cases do not produce reliable or repeatable results.
It is therefore an object of the present invention to provide a method of evaluating characteristics of a gas, especially a composition or an air-fuel ratio of the gas, particularly of a hydrocarbon gas or of a hydrocarbon-containing gas, or, more generally, of a gas reacting with oxygen.
Disclosure of the invention
The present invention relates to a method and a system for analysing a gas with the features of the independent claims. Advantages and embodiments of this method and of this system according to the invention arise from the following description in an analogous manner. Further advantages and embodiments of the invention will become apparent from the description and the appended figures. In this context the wording gas shall be understood as a single gas as well a mixture of different single gases. The gas is particularly a hydrocarbon gas or contains one or more hydrocarbons. Particularly, the gas can be natural gas. More generally, the gas consists of or contains components which are able to react or interact with oxygen.
A predetermined amount or quantity of the gas (also process gas) is mixed with an oxygen-containing gas to produce an analysis gas. For example, oxygen, air, and/or laughing gas can be used as oxygen-containing gas. The analysis gas is particularly a product of a chemical reaction of the process gas and the oxygen-containing gas.
For this purpose, the corresponding analysis system comprises a mixing unit adapted to mix the predetermined amount of the gas with the oxygen-containing gas and to produce the analysis gas. For example, this mixing unit can comprise a first pipe, through which the gas is conducted, which merges with a second pipe, through which the oxygen-containing gas is conducted.
An oxygen content of the analysis gas is determined. Particularly, an absolute oxygen content or a concentration of oxygen in the analysis gas is determined. For this purpose, an oxygen determination unit is provided, for example a lambda sensor and/or a paramagnetic sensor and/or an amperometric sensor. Particularly, the analysis gas is conducted through the oxygen determination unit and the oxygen content of the corresponding analysis gas stream is determined. The oxygen determination unit is especially heated, particularly a heated lambda sensor is provided. Thus, by heating the oxygen determination unit, also the analysis gas conducted through the oxygen determination unit is heated such that chemical reactions can especially be triggered. A characteristic of the gas is evaluated depending on the determined oxygen content of the analysis gas. For this purpose, an evaluation unit is provided, and connected to the analysis system. The invention thus provides a new possibility of easily evaluating characteristics of a gas. Depending on the specific composition of the gas, a specific chemical reaction of the gas and the oxygen-containing gas will occur and the analysis gas will thus have a specific oxygen-content. Thus, the oxygen-content of the analysis gas yields the possibility to draw conclusions about characteristics like the composition of the gas.
Particularly, a basic property or nature of the gas can be known beforehand. By means of the analysis method according to the invention the gas can specifically be analysed for further characteristics based on this basic property. A basic property, for example, of natural gas is that it contains specific hydrocarbons, hydrogen and nitrogen as main components. With the knowledge of how these components react with the oxygen- containing gas, the presence of a component in the gas can be verified of falsified. As a characteristic it can e.g. be evaluated, whether the gas indeed contains this component and especially in which specific concentration. The knowledge of a specific reaction of a gas component with the oxygen-containing gas or a relation between a content of a specific component in the gas and the oxygen-content of the analysis gas can especially be provided in the form of look up tables.
It shall be understood that the analysis system can comprise other elements e.g. pumps, throttles, etc. For example, a pump can especially be provided in order to carry the analysis gas through the oxygen determination unit. This pump can especially be provided downstream of the oxygen determination unit. It is also possible not to pump the gases but to draw the gases, for example if the gases contain components, which could damage a pump. The analysis system can especially be calibrated, e.g. by means of known test gases with a known composition.
The predetermined amount or test amount of the gas can especially be extracted from a unit containing the gas. Particularly, the predetermined amount can permanently be extracted from this unit and mixed with the oxygen-containing gas in order to analyse the gas over time. Thus, a constant stream of the gas can especially be mixed with the oxygen-containing gas and a constant stream of the analysis gas can be carried through the oxygen determination unit. Therefore, changes of the characteristic of the gas can be detected.
Advantageously, an amount of the oxygen-containing gas, which is mixed with the predetermined amount of the gas, is controlled depending on the determined oxygen content of the analysis gas. This amount of the oxygen-containing gas is preferably controlled such that the determined oxygen content of the analysis gas remains constant. A specific value of the oxygen content of the analysis gas is expediently used as corresponding set point. The amount of the oxygen-containing gas needed to be mixed with the gas such that the oxygen content of the analysis gas remains constant particularly enables to draw conclusions about the gas characteristics. Therefore, the characteristic of the gas is preferably evaluated depending on this controlled amount of the oxygen-containing gas.
For example, if the gas comprises oxygen reacting components, these components will react with the oxygen-containing gas and thus the oxygen content of the analysis gas will be comparatively low. Therefore, a comparatively high amount of the oxygen- containing gas has to be mixed with the gas in order to keep the oxygen content of the analysis gas constant. If, for example, the composition of the gas changes, the oxygen content of the analysis gas will also change. Thus, the specific amount of oxygen- containing gas mixed with the test amount of the gas also has to be changed such that the oxygen content of the analysis gas remains constant. This change of the amount of oxygen-containing gas enables to draw conclusions about the change of the gas characteristic, particularly its composition.
Alternatively, a constant amount of the oxygen-containing gas is advantageously mixed with the predetermined amount of the gas. Thus, the oxygen content of the analysis gas is not kept constant and can vary depending on the composition of the gas.
Therefore, the characteristic of the gas is advantageously evaluated depending on the determined oxygen content of the analysis gas with a constant amount of oxygen- containing gas.
According to a preferred embodiment, a temperature of the predetermined amount of the gas and/or of the oxygen-containing gas and/or of the analysis gas is determined and/or adjusted. Preferably, the predetermined amount of the gas and/or the oxygen- containing gas and/or the analysis gas is heated. Thus, a chemical reaction of the gas and the oxygen-containing gas can especially be triggered. Moreover, also
thermochemical stable components of the gas can be caused to react with the oxygen- containing gas. For this purpose, a first pipe, through which the predetermined amount of the gas is conducted, and/or a second pipe, through which the oxygen-containing gas is conducted, and/or a third pipe, through which the analysis gas is conducted, can preferably be heated at least partially. Advantageously, the first pipe and/or the second pipe and/or the third pipe are provided at least partially inside a furnace. Alternatively or additionally, the oxygen determination unit is advantageously heated. Thus, also the analysis gas, which is preferably conducted through the oxygen determination unit, is heated.
Preferably, additional analysis values of the analysis gas can be determined and advantageously an absolute composition of the gas or absolute contents of gas components can be determined depending on said values. The analysis can e.g. also be combined with conventional methods of evaluating gas compositions for verification purposes or to evaluate the gas characteristics more precisely.
Advantageously, a flow rate of the analysis gas is determined, particularly downstream of the oxygen determination unit. For this purpose, the analysis system advantageously comprises a corresponding flowmeter. The composition of the gas, particularly an absolute composition, especially an absolute content of a component of the gas, is preferably evaluated depending on the determined flow rate and on the determined oxygen content of the analysis gas.
According to an advantageous embodiment, a dew point of the analysis gas is determined, particularly downstream of the oxygen determination unit. A corresponding dew point analysis unit is particularly provided for this purpose, especially downstream of the flowmeter. Preferably, a hydrogen content of the gas, particularly an absolute hydrogen content, is evaluated depending on the determined dew point and on the determined oxygen content of the analysis gas. Hydrogen in the gas particularly reacts in a specific way with the oxygen-containing gas, such that the dew point of the analysis gas is specifically influenced. Thus, the dew point of the analysis gas particularly enables to draw conclusions about the hydrogen content of the gas.
Preferably, a carbon dioxide content of the analysis gas is determined, particularly downstream of the oxygen determination unit. The analysis system thus preferably comprises a corresponding carbon dioxide analyser, particularly downstream of the dew point determination unit. Advantageously, a carbon content of the gas, particularly an absolute carbon content, is evaluated depending on the determined carbon dioxide content and on the determined oxygen content of the analysis gas. Carbon in the gas particularly reacts in a specific way with the oxygen-containing gas, such that the carbon dioxide content of the analysis gas is specifically influenced. Thus, the carbon dioxide content of the analysis gas particularly enables to draw conclusions about the carbon content of the gas. Partially, a cold trap can be provided upstream of the carbon dioxide analyser in order to condensate vapours of the analysis gas stream. The determined dew point and/or carbon dioxide content can especially also be used for a more precise determination of the analysis gas flow rate.
According to a preferred embodiment, the predetermined amount of the gas is provided with a constant pressure and/or the oxygen-containing gas is also provided with a constant pressure. The gas and the oxygen-containing gas can be provided with the same pressure of e.g. 20 mbar or with different pressures. Moreover, a temperature of the predetermined amount of the gas and/or of the oxygen-containing gas is preferably also constant. Preferably, a first throttle can be provided for the steam of the gas and/or a second throttle can be provided for the oxygen-containing gas. By means of these throttles a flow rate of the gas and/or of the oxygen-containing gas can especially be controlled. Advantageously, a partial pressure of oxygen in the analysis gas is determined. The characteristic of the gas, particularly the air-fuel ratio, is preferably evaluated depending on the constant pressures and on the flow rates of the gas and of the oxygen-containing gas and depending on the determined partial pressure of oxygen.
Advantageously, the gas is produced inside a process unit. Preferably, the
predetermined amount of the gas is mixed with the oxygen-containing gas to produce the analysis gas within a process unit mixing member inside the process unit. The analysis gas is advantageously extracted from the process unit mixing member. Thus, the temperature inside the process unit can particularly be used to trigger the chemical reaction of the gas and the oxygen-containing gas.
As this process unit mixing member, an analysis gas extraction pipe and an oxygen- gas injection pipe can preferably be provided. A first part of this analysis gas extraction pipe is preferably located inside the process unit and a second part of the analysis gas extraction pipe is located outside the process unit. The predetermined amount of the gas to be mixed with the oxygen-containing gas can be collected inside the first part of this analysis gas extraction pipe. The oxygen-gas injection pipe can advantageously be provided at least partially inside the first part of the analysis gas extraction pipe. The oxygen-containing gas is thus injected into the first part of the analysis gas extraction pipe by means of the oxygen-gas injection pipe, such that the predetermined amount of the gas is mixed with the oxygen-containing gas inside the first part of the analysis gas extraction pipe. The analysis gas is then extracted from the process unit by means of the analysis gas extraction pipe.
According to a particularly preferred embodiment, an air-fuel ratio for combustion of the gas is evaluated as the characteristic of the gas depending on the determined oxygen content of the analysis gas. A mass ratio of air, oxygen or of an oxygen-containing gas to the gas can especially be determined as the air-fuel ratio. Particularly, an optimum air-fuel ratio for an optimum combustion of the gas can be evaluated. By means of the air-fuel ratio, an amount of air, oxygen or an oxygen-containing for combustion of the gas can especially be determined. Expediently, the air-fuel equivalence ratio λ can be determined by means of the air-fuel ratio. Thus, the invention enables an optimum combustion of the gas, even without knowing the specific composition of the gas in detail.
According to a particularly advantageous embodiment of the invention, the gas is a fuel gas, preferably natural gas. Preferably, combustion of the fuel gas is performed depending on the evaluated characteristic of the fuel gas, particularly depending on the evaluated air-fuel ratio. The invention thus enables an optimum combustion of the fuel gas even without knowing the specific composition of the fuel gas in detail.
Moreover, an optimum combustion of fuel gas with varying composition can be enabled. With a varying fuel gas composition, the necessary amount of air, oxygen, or oxygen-containing gas for an efficient combustion of the fuel gas also varies. By means of the gas analysis, this amount of air, oxygen, or oxygen-containing gas can easily be determined and a clean, complete and efficient combustion of the fuel gas can be enabled. The corresponding specific amount or test amount of the specific fuel gas can expediently permanently be extracted, e.g. from a unit containing the fuel gas, and the corresponding characteristic can permanently determined in order to react to possible fluctuations of the fuel gas composition.
People used to believe that the composition of natural gas is rather constant. However, recent researches have shown that the natural gas composition can fluctuate significantly. By means of the gas analysis, an efficient combustion of natural gas can be enabled, especially by evaluating the air-fuel ratio of the specific natural gas and by performing the combustion of the natural gas depending on the evaluated air-fuel ratio. Alternatively or additionally, the specific composition of the natural gas can be evaluated, preferably an absolute composition, particularly a content of carbon, hydrogen, oxygen and/or nitrogen.
According to a particularly preferred embodiment, a composition of the gas is evaluated as the characteristic of the gas depending on the determined oxygen content of the analysis gas. Thus, as characteristic of the gas it can particularly be evaluated whether the gas contains specific components, particularly specific molecules or elements, especially specific hydrocarbons. Alternatively or additionally, a relative composition can particularly be determined as characteristic, especially a ratio of specific components of the gas. Alternatively or additionally, an absolute composition of the gas can especially be evaluated, i.e. specific contents of specific components of the gas, particularly specific contents of specific molecules or elements.
The invention therefore enables an easy, inexpensive, and repeatable possibility of evaluating the gas composition with low expenditure, which is particularly less elaborate and more cost effective than conventional methods of evaluating gas compositions, e.g. Fourier transform infrared spectroscopy (FTIR), mass spectrometry, gas chromatography or gas chromatography-mass spectrometry (GC-MS) and especially more repeatable than conventional methods like infrared analysers. According to a particularly advantageous embodiment of the invention the gas is a process gas, which is produced in the course of a chemical process, preferably in the course of a thermochemical process, preferably in the course of a thermochemical process of a hydrocarbon-containing gas. Preferably, the process gas is produced in the course of a pyrolysis, preferably a pyrolysis of hydrocarbons. Advantageously, the chemical process is controlled depending on the evaluated characteristic of the gas, particularly depending on the evaluated composition of the gas. Metrological control of chemical processes, particularly of thermochemical processes, is usually elaborate and expensive. The present invention enables an easy, inexpensive and an effective process control with low expense. Advantageously, the predetermined amount of the process gas is extracted from a process unit, in which the chemical process, particularly the thermochemical process, is performed. The predetermined amount of the process gas can e.g. be extracted from the process unit by means of the first pipe of the analysis system. Preferably, the specific amount of the process gas can permanently be extracted from the process unit, thus enabling a continuous evaluation of the process gas characteristics. The predetermined amount of the process gas is thus conducted out of the process unit and the analysis of the process gas is expediently performed outside of the process unit. The atmosphere inside the process unit and the chemical process are therefore especially not affected by the gas analysis. Moreover, the analysis of the gas can be performed independently of the process unit load, e.g. independently of material, size, homogeneity of mechanical parts processed in the process unit. The analysis system can furthermore easily be implemented without or with minimal constructional changes of the process unit.
The gas analysis according to the present invention can be used for analysing gas produced in a variety of different chemical, especially thermochemical processes and to preferably control the corresponding process depending on the evaluated gas characteristics. In the following some examples of chemical processes are given, for which the gas analysis can advantageously be used.
Endothermic gas or endogas is a gas mixture of hydrogen, carbon monoxide, carbon dioxide, and/or nitrogen and can e.g. used as protective gas in the thermal treatment of metals. Endogas can be produced by burning a hydrocarbon gas with limited supply of air, i.e. at high oxygen deficiency. Particularly, natural gas and/or propane are used as hydrocarbon gas for the endogas production. For an efficient endogas production it is important to know the specific composition of the corresponding hydrocarbon gas. By means of the gas analysis, this composition can be evaluated and the endogas production can be controlled depending on said evaluated composition. Thus, endogas can efficiently be produced e.g. also from natural gas with varying composition.
The chemical process can for example be a multi-stage process, wherein a process gas with a specific composition is produced during a specific stage of the multi-stage process. If the presence of this specific composition is not determined any more in the course of the evaluation of the process gas characteristic, it can be detected that this specific stage is finished and a subsequent stage of the process can be initiated.
For example, a debinding process is one process stage of a sintering process, during which the process gas comprises hydrocarbons. In this case it can e.g. be evaluated, whether these hydrocarbons typical for the debinding process are part of the process gas composition. If the corresponding hydrocarbons are not determined any more, it can be detected that the debinding process is finished and the subsequent sintering process stage can be initiated. For example, the sintering process can be performed in the course of a metal injection molding (MIM) or in the course of cemented-carbide sintering processes.
In the course of carbon fibre production a pyrolysis of the corresponding fibre material is performed. By means of the gas analysis the presence of hydrocarbons like tars, which are produced during this pyrolysis, can be evaluated in order to control the carbon fibre production. The process time of the carbon fibre production and the amount of necessary purge gas can especially be reduced.
Carburising is a heat treatment process in order to increase the hardness of low carbon steel or iron. The corresponding metal absorbs carbon while being heated in the presence of a carbon-bearing material. Low pressure carburising is carried out in vacuum furnaces, into which alternately a hydrocarbon-containing gas (e.g. methane CH4, acetylene C2H2 and/or propane C3H8) and a neutral gas (e.g. N2) for diffusion are injected. Subsequently a quenching of the metal part performed. A mixture of hydrogen and helium can be used as corresponding quenching gas. By means of the gas analysis e.g. the hydrocarbon content of the atmosphere inside the vacuum furnace or of the gas atmosphere evacuated from the vacuum furnace can be evaluated. By means of these hydrocarbon contents conclusions can particularly be drawn about carbon absorption of the metal parts. It is also possible to monitor the ratio of hydrogen and helium of the quenching gas by means of the gas analysis.
A heat treatment or annealing of metal parts in form of coils can be performed in a bell- furnace with a hydrocarbon-atmosphere. A level of cleanliness of the coils during annealing is especially dependent on an evaporation behaviour of rolling oil or rolling emulsion. By means of the gas analysis the atmosphere inside the bell-furnace can be evaluated, particularly in order to evaluate the evaporation behaviour of the rolling oil or rolling emulsion. For example a content of methane, carbon dioxide and/or carbon monoxide of the furnace atmosphere can be evaluated. The so called WASTOX process is a combustion process, which can e.g. be used for the recycling of carbon-containing metal scrap. If unburnt hydrocarbons and/or carbon monoxide are detected in the waste gas of the furnace, the combustion process is controlled accordingly in order to combust these gases inside the furnace itself.
Organic contaminants in the metal, which are released during the combustion, are thus used as fuel. By means of the gas analysis, the components of the waste gas can be evaluated and the presence of hydrocarbons and/or carbon monoxide can be detected.
It should be noted that the previously mentioned features and the features to be further described in the following are usable not only in the respectively indicated combination, but also in further combinations or taken alone, without departing from the scope of the present invention.
The present invention will now be described further, by way of example, with reference to the accompanying drawings, in which
Fig. 1 a, 1 b, 1 c each schematically show a preferred embodiment of an analysis
system for analysing a gas according to the invention, which is adapted to perform a preferred embodiment of a method for analysing a gas according to the invention,
Fig. 2 schematically shows a part of a preferred embodiment of an analysis system for analysing a gas according to the invention, which is adapted to perform a preferred embodiment of a method for analysing a gas according to the invention, and
Fig. 3a, 3b each schematically show a preferred embodiment of an analysis
system for analysing a gas according to the invention, which is adapted to perform a preferred embodiment of a method for analysing a gas according to the invention. Detailed description
In the figures identical reference numerals refer to equal or equivalent elements. In Fig. 1 a a preferred embodiment of an analysis system 100 for analysing a gas according to the invention is schematically shown. The analysis system 100 is adapted to perform a preferred embodiment of a method for analysing a gas according to the invention. A thermochemical process, in the course of which a process gas is produced, is performed in a process unit 101 , e.g. a sintering process of metal parts. The process unit 101 can for example be a furnace. The analysis system 100 is adapted to perform an analysis of the process gas produced in the furnace and to evaluate characteristics of this process gas.
For the gas analysis a predetermined amount of the process gas is extracted from the furnace 101 . For this purpose a first pipe 110 is provided, through which a constant stream of the process gas is extracted from the furnace 101. A pump and/or compressor 11 1 is provided in order to compress the extracted process gas. Moreover, a heating mechanism 1 12 is provided in order to heat the pipe 1 10 and thus the extracted process gas. For example, a small furnace or a heat exchanger can be provided as heating mechanism 1 12, inside which a part of the pipe 1 10 is arranged.
This extracted process gas is mixed with an oxygen-containing gas, e.g. oxygen. For this purpose, an oxygen supply 102 and a second pipe 120 are provided, through which a stream of oxygen is channelled. A flow control unit 121 is provided in order to control the flow rate of the oxygen.
The first pipe 1 10 and the second pipe 120 merge into a third pipe 130. Thus, the stream of the heated extracted process gas is mixed with the stream of oxygen. The heated process gas chemically reacts with the oxygen to produce an analysis gas, which is channelled through the third pipe 130. The first pipe 1 10, the second pipe 120, and the third pipe 130, as well as the compressor 11 1 , the heating mechanism 1 12, and the flow control unit 121 are particularly part of a mixing unit 103 adapted to mix the predetermined amount of the extracted process gas with the oxygen and to produce the analysis gas stream.
In the third pipe 130 an oxygen determination unit 140 is provided, for example a lambda sensor. By means of the oxygen determination unit 140 an oxygen content of the analysis gas is determined. The determined values of the oxygen content are transmitted from the lambda sensor 140 to a control unit or evaluation unit 160, indicated by reference numeral 140a. For this transmission 140a e.g. a wireless communication link can be established between the lambda sensor 140 and the control unit 160.
Downstream of the oxygen determination unit 140 a flowmeter 151 is provided in order to determine a flowrate of the analysis gas stream. The flowmeter 151 transmits the determined values of the flowrate to the control unit 160, indicated by reference numeral 151 a, for example also by means of a wireless connection.
The control unit 160 evaluates characteristics of the process gas depending on the determined oxygen content of the analysis gas stream and especially also depending on the determined flowrate of the analysis gas stream. Particularly, the control unit 160 evaluates a composition of the gas depending on the determined oxygen content and on the determined flowrate of the analysis gas stream. It can especially be evaluated, whether the process gas contains hydrocarbons. By means of the flowrate, an absolute hydrocarbon content of the process gas can be estimated.
The control unit 160 is moreover adapted to control the amount of oxygen, which is mixed with the process gas, depending on the determined oxygen content of the analysis gas. For this purpose, the control unit 160 controls the flow control unit 121 , indicated by reference numeral 121 a. Thus, the flowrate of the oxygen gas in the second pipe 120 is controlled such in that the oxygen content of the analysis gas stream in the third pipe 130 remains constant. Furthermore, the thermochemical process in the furnace 101 is controlled depending on the evaluated characteristic of the gas, particularly depending on the evaluated composition of the gas. During the sintering process inside the furnace 101 , a debinding of the metal parts occurs. In the course of this debinding process a specific hydrocarbon-containing process gas is produced in the furnace 101 . This hydrocarbon-containing process gas specifically reacts with the oxygen and thus a specific analysis gas with a specific oxygen content is produced. When this specific oxygen content is determined by means of the lambda sensor 140, the control unit 160 detects that this debinding process has started. A relation between the content of this hydrocarbon in the process gas and the oxygen content in the analysis gas can e.g. be provided in form of a look up table stored in the control unit 160. When this specific oxygen content is not determined any more, the control unit 160 detects that this debinding process has finished. In this case the control unit 160 can send a corresponding command to the furnace 101 in order to initiate a subsequent stage of the sintering process, indicated by reference numeral 101 a. In Fig. 1 b another preferred embodiment of an analysis system 100' according to the invention is schematically shown, analogously to the system 100 of Fig. 1 a.
In contrast to the system 100 of Fig. 1 a, the flowrate of the oxygen gas in the second pipe 120 is not controlled in the system 100' shown in Fig. 1 b. The mixing unit 103' thus does not comprise a flow control unit. Instead, a throttle 122 is provided in the second pipe 120 in order to provide an oxygen stream of constant flowrate and constant pressure. Thus, the oxygen content of the analysis gas stream in the third pipe 130 is not kept constant, but can vary depending on the composition of the process gas. Fig. 1 c schematically shows another preferred embodiment of an analysis system 100" according to the invention, analogously to the system 100' of Fig. 1 b.
According to this embodiment, heating mechanism and compressor are not provided in the first pipe 1 10 of the corresponding mixing unit 103". Instead, a heating mechanism 132 is provided in the third pipe 130 in order to heat the mixture of the process gas and oxygen. For example, a small furnace or a heat exchanger can be provided as heating mechanism 132.
Analogously to the systems 100 and 100' of Fig. 1 a and 1 b, the oxygen content of the analysis gas stream in the third pipe 130 is determined by means of the lambda sensor 140 and the flowrate is determined by means of the flowmeter 151 .
Downstream of the flowmeter 151 , a compressor 152, a dew point analysis unit 153, a cold trap 154, and a carbon dioxide analyser 155 are provided. By means of the dew point analysis unit 153, a dew point of the analysis gas is determined and transmitted to the control unit 160, indicated by reference numeral 153a. Vapours of the analysis gas stream condensate by means of the cold trap 154 and a carbon dioxide content of the analysis gas stream is determined by means of the carbon dioxide analyser 155 and, as indicated by numeral 155a, transmitted to the control unit 160.
Depending on the determined dew point and on the determined oxygen content of the analysis gas, the control unit 160 evaluates a hydrogen content of the process gas. Moreover, depending on the determined carbon dioxide content and on the determined oxygen content of the analysis gas, the control unit 160 evaluates a carbon content of the process gas.
According to a preferred embodiment of the invention, the process gas can also be mixed with the oxygen-containing gas inside the process unit, in which it is produced. A part of corresponding preferred analysis system according to the invention is schematically shown in Fig. 2.
Fig. 2 shows a part of a process unit 201 , e.g. a furnace. In the interior 201 a of the furnace 201 , a thermochemical process is performed, e.g. a sintering process, analogously to the furnace 101 shown in Fig. 1 a to 1 c. A process gas 21 1 is produced in the interior 201 a of the furnace 201. A wall of the furnace is referred to as 201 c and the outside of the furnace as 201 b.
A process unit mixing member is provided inside the furnace 201 in order to produce the analysis gas within this process unit mixing member and thus inside the furnace 201 . This process unit mixing member comprises an analysis gas extraction pipe 210 and an oxygen-gas injection pipe 220.
The analysis gas extraction pipe 210 is provided such that a first part 210a of this pipe 210 is arranged in the inside 201 a of the furnace 201 and a second part 210b of the pipe 210 is arranged outside 201 b the furnace 201 . A predetermined amount of the process gas especially accumulates in the first part 210a of the analysis gas extraction pipe 210. The oxygen-gas injection pipe 220 is arranged at least partially inside the analysis gas extraction pipe 210. Particularly, an end 220a of the oxygen-gas injection pipe 220 is arranged in the first part 210a of the analysis gas extraction pipe 210 and thus in the interior 201 a of the furnace 201 . Moreover, at a part of the oxygen-gas injection pipe 220, which is arranged in the first part 210a of the analysis gas extraction pipe 210, holes 220b are provided.
The oxygen-containing gas 221 , e.g. oxygen, is injected into the first part 210a of the analysis gas extraction pipe 210 by means of the oxygen-gas injection pipe 220 through the holes 220b. Thus, the process gas 211 accumulated in the first part 210a of the analysis gas extraction pipe 210 is mixed with the injected oxygen 221 . The temperature inside the furnace triggers the chemical reaction of the process gas 21 1 and the oxygen 221 . Thus, the corresponding analysis gas 231 is produced in the interior 201 a of the furnace 201 . The analysis gas 231 is extracted from the furnace 201 by means of the analysis gas extraction pipe 210 and channelled to an oxygen determination unit, as described above.
Fig. 3a schematically shows another preferred embodiment of an analysis system 300 according to the invention, adapted to perform a preferred embodiment of a method according to the invention.
Inside a process unit 301 , e.g. a furnace, combustion of a fuel gas, e.g. natural gas, and air is performed. For this purpose, a natural gas supply 301 b and an air supply 301 c are provided. The necessary amount of air for an efficient combustion of the natural gas depends on the specific composition of the natural gas. In order enable an optimum combustion, the natural gas is analysed. For this purpose, a predetermined amount of the natural gas is extracted from the natural gas supply 301 b by means of a first pipe 310. Analogously to the gas analysis systems 101 , 101 ', and 101 " shown in Fig. 1 a to 1c, an oxygen supply 302, and a second pipe 320 are provided, through which a stream of oxygen gas is channelled. The first pipe 310 and the second pipe 320 merge into a third pipe 330. Thus, the stream of the extracted natural gas is mixed with the stream of oxygen. The natural gas reacts with the oxygen and an analysis gas is produced and channelled through the third pipe 330.
An oxygen determination unit 340 is provided, for example a lambda sensor, which determines an oxygen content of the analysis gas stream. A flowmeter 351 is provided to determine a flowrate of the analysis gas stream. The determined values of the oxygen content and of the flowrate are transmitted from the lambda sensor 340 and the flowmeter 351 to a control unit or evaluation unit 360, indicated by reference numerals 340a and 351 a.
The control unit 360 evaluates characteristics of the process gas depending on the determined oxygen content and especially on the determined flowrate of the analysis gas stream. Particularly, the control unit 360 evaluates an air-fuel ratio of the natural gas for an optimum combustion. According to this determined optimum air-fuel ratio, the control unit 360 controls a valve 304 in the natural gas supply 301 b, indicated by reference numeral 301 a. Thus the control unit 360 controls an amount of natural gas supplied to the furnace 301 such that a mixture of natural gas and air according to the determined optimum air-fuel ratio is supplied to the furnace 301 . By means of the gas analysis system 300 the optimum air-fuel ratio is permanently determined in order to react to possible fluctuations of the natural gas composition.
Moreover, the control unit 360 is adapted to control the amount of oxygen, which is mixed with the natural gas, depending on the determined oxygen content of the analysis gas. For this purpose, the control unit 360 controls a flow control unit 321 in the second pipe 320, indicated by reference numeral 321 a. The first pipe 310, the second pipe 320, the third pipe 330, and the flow control unit 321 are particularly part of a corresponding mixing unit 303. Fig. 3b schematically shows another preferred embodiment of an analysis system 300' according to the invention, analogously to the system 300 of Fig. 3a.
In the mixing unit 303' of the system 300', a first throttle 31 1 is provided in the first pipe 310 and a second throttle 322 is provided in the second pipe 320. By means of these throttles 311 , 322, a natural gas stream with constant pressure of e.g. 20 mbar is mixed with an oxygen stream of constant pressure of e.g. also 20 mbar.
A thermal insulation 341 is provided for the lambda sensor 340. Moreover, a temperature sensor 342 is provided to determine a temperature of the lambda sensor 340. The determined temperature is transmitted to the control unit 360, indicated by numeral 342a.
Moreover, a partial pressure unit 352 is provided to determine a partial pressure of oxygen in the analysis gas stream in the third pipe 330, which is transmitted to the control unit 360, indicated by numeral 352a.
The control unit 360 determines the optimum air-fuel ratio in dependence of the constant pressures and the corresponding flow rates of the natural gas and the oxygen in the pipes 310 and 320, and furthermore in dependence of the determined partial pressure, of the determined oxygen content of the analysis gas, and of the lambda sensor's temperature. Depending on the evaluated optimum air-fuel ratio, the control unit 360 controls the valve 304 in the natural gas supply 301 b such that a mixture of natural gas and air according to the determined optimum air-fuel ratio is supplied to the furnace 301 .
Reference list
100 gas analysis system
100' gas analysis system
100" gas analysis system
101 process unit, furnace
101 a transmission between control unit 160 and furnace 101
102 oxygen supply
103 mixing unit
103' mixing unit
103" mixing unit
1 10 first pipe
1 1 1 pump, compressor
1 12 heating mechanism
120 second pipe
121 flow control unit
121 a transmission between control unit 160 and flow control unit 121
122 throttle
130 third pipe
132 heating mechanism
140 oxygen determination unit, lambda sensor
140a transmission between lambda sensor 140 and control unit 160
151 flowmeter
151 a transmission between flowmeter 151 and control unit 160
152 compressor 152
153 dew point analysis unit
153a transmission between dew point analysis unit 153 and control unit 160
154 cold trap
155 carbon dioxide analyser
155a transmission between carbon dioxide analyser 155 and control unit 160
160 evaluation unit, control unit
201 process unit, furnace
201 a interior of the furnace 201 201 b outside of the furnace 201
201 c wall of the furnace 201
203 mixing unit
210 analysis gas extraction pipe
210a first part of the analysis gas extraction pipe 210
210b second part of the analysis gas extraction pipe 210
21 1 process gas
220 oxygen-gas injection pipe
220a end of the oxygen-gas injection pipe 220
220b holes of the oxygen-gas injection pipe 220
221 oxygen-containing gas, oxygen
231 analysis gas
300 gas analysis system
300' gas analysis system
301 process unit, furnace
301 a transmission between control unit 360 and furnace 301
301 b natural gas supply
301 c air supply
302 oxygen supply
303 mixing unit
304 valve in the natural gas supply
303' mixing unit
310 first pipe
31 1 throttle
320 second pipe
321 flow control unit
321 a transmission between control unit 360 and flow control unit 321
322 throttle
330 third pipe
340 oxygen determination unit, lambda sensor
340a transmission between lambda sensor 340 and control unit 360
341 thermal insulation
342 temperature sensor
342a transmission between temperature sensor 342 and control unit 360 flowmeter
a transmission between flowmeter 351 and control unit 360
partial pressure unit
a transmission between partial pressure unit 352 and control unit 160 control unit

Claims

Claims
A method for analysing a gas (211 ),
wherein a predetermined amount of the gas (21 1 ) is mixed with an oxygen- containing gas (221 ) to produce an analysis gas (231 ),
wherein an oxygen content of the analysis gas (231 ) is determined, and wherein a characteristic of the gas (21 1 ) is evaluated depending on the determined oxygen content of the analysis gas (231 ).
The method according to claim 1 ,
wherein an amount of the oxygen-containing gas (221 ), which is mixed with the predetermined amount of the gas (21 1 ), is controlled depending on the determined oxygen content of the analysis gas (231 ), or
wherein a constant amount of oxygen-containing gas (221 ) is mixed with the predetermined amount of the gas (21 1 ).
The method according to claim 1 or 2, wherein a temperature of the predetermined amount of the gas (21 1 ) and/or of the oxygen-containing gas (221 ) and/or of the analysis gas (231 ) is determined and/or adjusted.
The method according to any one of the preceding claims, wherein a flow rate of the analysis gas (231 ) is determined and particularly wherein the composition of the gas (21 1 ), particularly absolute contents of components, is evaluated depending on the determined flow rate and on the determined oxygen content of the analysis gas (231 ).
The method according to any one of the preceding claims, wherein a dew point of the analysis gas (231 ) is determined and particularly wherein a hydrogen content of the gas (21 1 ), particularly an absolute hydrogen content, is evaluated depending on the determined dew point and on the determined oxygen content of the analysis gas (231 ).
The method according to any one of the preceding claims, wherein a carbon dioxide content of the analysis gas (231 ) is determined and particularly wherein a carbon content of the gas (21 1 ), particularly an absolute carbon content, is evaluated depending on the determined carbon dioxide content and on the determined oxygen content of the analysis gas (231 ).
The method according to any one of the preceding claims, wherein the
predetermined amount of the gas (21 1 ) is provided with a constant pressure and/or wherein the oxygen-containing gas is provided with a constant pressure.
The method according to any one of the preceding claims,
wherein the gas (21 1 ) is produced inside a process unit (101 , 201 ),
wherein the predetermined amount of the gas (21 1 ) is mixed with the oxygen- containing gas (221 ) to produce the analysis gas (231 ) within a process unit mixing member (210, 220) inside the process unit (101 , 201 ), and
wherein the analysis gas (231 ) is extracted from the process unit mixing member (210, 220).
The method according to any one of the preceding claims, wherein a composition of the gas (21 1 ) and/or an air-fuel ratio for combustion of the gas (211 ) is evaluated as the characteristic of the gas (21 1 ) depending on the determined oxygen content of the analysis gas (231 ). A method for performing combustion of a fuel gas,
wherein an air-fuel ratio for combustion of the fuel gas is evaluated as the characteristic of the gas (21 1 ) according to a method of any one of the preceding claims, and
wherein combustion of the fuel gas is performed depending on the evaluated air-fuel ratio. A method for conducting a chemical process,
wherein a process gas (21 1 ) is produced in the course of a chemical process, particularly in the course of a thermochemical process,
wherein a composition of the process gas (21 1 ) is evaluated as the
characteristic of the gas (21 1 ) according to a method of any one of the preceding claims, and
wherein the chemical process is controlled depending on the evaluated composition of the process gas (21 1 ).
12. Analysis system (100, 100', 100", 300, 300') for analysing a gas, adapted to perform a method according to any one of the preceding claims, comprising a mixing unit (103, 103', 103", 203, 303, 303') adapted to mix a predetermined amount of the gas with an oxygen-containing gas and to produce an analysis gas, an oxygen determination unit (140, 340) adapted to determine an oxygen content of the analysis gas, and
an evaluation unit (160, 360) adapted to evaluate a characteristic of the gas depending on the determined oxygen content of the analysis gas.
13. The analysis system (100, 100', 100", 300, 300') according to claim 12, further comprising:
a heating mechanism (1 12, 132) adapted to determine and/or adjust a temperature of the predetermined amount of the gas (21 1 ) and/or of the oxygen- containing gas (221 ) and/or of the analysis gas (231 ) and/or
a flowmeter (151 , 351 ) adapted to determine a flowrate of the analysis gas (231 ) and/or
a dew point analysis unit (153) adapted to determine a dew point of the analysis gas (231 ) and/or
a carbon dioxide analyser (155) adapted to determine a carbon dioxide content of the analysis gas (231 ) and/or
at least one throttle (122, 31 1 , 322) adapted to provide the predetermined amount of the gas (21 1 ) with a constant pressure and/or to provide the oxygen- containing gas with a constant pressure.
PCT/EP2017/025192 2017-07-03 2017-07-03 Method and system for analysing a fuel gas WO2019007473A1 (en)

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EP17739877.3A EP3649468A1 (en) 2017-07-03 2017-07-03 Method and system for analysing a fuel gas
PCT/EP2017/025192 WO2019007473A1 (en) 2017-07-03 2017-07-03 Method and system for analysing a fuel gas

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