CN1163795A

CN1163795A - Process for preparing blanketing gases or reaction gases for heat treatment of metals

Info

Publication number: CN1163795A
Application number: CN 97103488
Authority: CN
Inventors: 延斯·米尔欣卡
Original assignee: Messer Griesheim GmbH
Current assignee: Messer Griesheim GmbH
Priority date: 1996-03-19
Filing date: 1997-03-18
Publication date: 1997-11-05
Anticipated expiration: 2017-03-18
Also published as: AU714077B2; DE19610722A1; AU1628897A; CN1098121C; ID16270A; DE19610722B4

Abstract

Disclosed is a method used to prepare protective gas or reaction gas for metal heat treatment. The method includes the following steps, first, nitrogen of oxygen contamination and hydrocarbon which serve as airflow are supplied for an endothermic catalytic reactor, and then, the oxygen content in nitrogen is detected and provided for a control device as an actual value. In order that the compositions of the protective gas and the reaction gas can be prepared by the reduced preparation cost, at least nitrogen or oxygen is brought into the airflow as the function measurement of the detected actual value.

Description

Method for producing protective gas and reaction gas for heat treatment of metals

The invention relates to a method for producing a protective gas and a reaction gas for the thermal treatment of metals according to the preamble of claim 1.

The heat treatment of the gold shop is performed in a known heat treatment furnace under an atmosphere of a protective gas or a reaction gas. The atmosphere consists primarily of the inert component nitrogen with varying amounts of hydrogen and carbon monoxide. The hydrogen is used to combine impurities that have penetrated into the furnace space, such as oxygen, with hydrogen, while the carbon level in the protective gas atmosphere is adjusted with CO to avoid surface decarburization, for example in the case of carbon-containing steels. According to the prior art, the low-oxygen content inert gas component nitrogen is obtained in very pure form in cryogenic air separation plants and liquefied. The user stores the nitrogen in a vacuum insulated bucket. Reaction gas component H₂And CO is similarly stored in pressure vessels or produced in situ by decomposition of methanol, or by endothermic conversion of hydrocarbons and air. By mixing with low temperature nitrogen to prepare the required componentsHas a low dew point and a low CO₂A very pure protective gas atmosphere of concentration. In addition to cryogenic separation, nitrogen can now also be obtained by absorption or permeation methods. The nitrogen obtained in the in situ production unit is produced by Pressure Swing Absorption (PSA) or membrane processes.

The use of nitrogen produced by such in situ nitrogen generation units for non-oxidizing anneals and neutral carburizing anneals, for example, is very limited because these processes result in residual oxygen contents of about 0.1 to 5% by volume. Such high oxygen contents affect the oxidation or scaling of metals and the decarbonation of, for example, carbon-containing steels. In the non-oxidizing anneal, a protective gas having an oxygen content of less than 10vpm is required.

The nitrogen produced at non-low temperatures must therefore be further purified. In the known method of further purification, together with the hydrocarbon, oxygen-containing nitrogen is fed to an endothermic catalytic reactor, in which the oxygen contained in the nitrogen is formed with the formation of CO and H₂And removed. Thus obtaining a protective gas or a reaction gas, mainly containing N₂，H₂And CO, the composition of which depends on the oxygen content of the nitrogen that is not produced at low temperature. The oxygen content of nitrogen and CO and H in the protective gas or reaction gas after conversion in a nickel-filled reactor and after conversion is explained in more detail in "Meta science and Heat Treatment" Vol.20, 5/6, 5.1978, pp.377-381₂The relationship between the contents. In this case, a nitrogen/air mixture having an oxygen content of from 1 to 21% is fed into the reactor. In order to mix nitrogen/air with varying compositionThe composition remained stable, the oxygen content of the nitrogen/air mixture was measured before it entered the reactor, and the oxygen content in the nitrogen was set by metering air into the mixture. In this case, the volume of gas fed into the heat treatment furnace increases.

Furthermore, DE 4212307C 2 discloses a method for producing protective or reactive gases for the thermal treatment of metals by means of a Pressure Swing Absorption (PSA) or membrane process, in which a higher oxygen content in the nitrogen is set by increasing the productivity of the pressure swing absorption or membrane unit or by mixing air into the non-cryogenic nitrogen. By mixing air and/or increasing the productivity of the pressure swing adsorption or membrane unit, the oxygen content of the nitrogen can be adjusted over a wide range as a function of the output rate of the pressure swing adsorption or membrane unit. In this case, a method is required by which the entire bandwidth of the shielding gas or the reaction gas can be adjusted and a stable value irrespective of the rate of the pressure swing absorption or the thin film unit is maintained, so that the shielding gas or the reaction gas can be economically produced.

It is therefore an object of the present invention to provide a process for preparing a protective gas or a reaction gas for heat treatment of metals, which can produce a protective gas or a reaction gas of any desired composition for heat treatment of metals at low production costs.

To achieve the above object of the invention, the invention provides a method for preparing a protective gas or reaction gas for the thermal treatment of metals, comprising feeding oxygen-contaminated nitrogen and hydrocarbons as a gas stream to an endothermic catalytic reactor, detecting the oxygen content in the nitrogen and supplying it as an actual value to a control device, which comprises metering at least the nitrogen or oxygen in the gas stream as a function of the detected actual value.

Preferably, air and/or nitrogen and/or oxygen is metered into the gas stream as a function of the actual value detected.

The invention also provides an apparatus for carrying out the method of

claim

1 or 2, comprising: an in situ nitrogen plant for producing oxygen contaminated nitrogen and a hydrocarbon supply connected to the reactor by piping; an oxygen measuring device connected to the pipeline for measuring an actual value of the oxygen content in the nitrogen; a control device, an input device for supplying the actual value detected by the oxygen measuring device and for receiving a set value, a nitrogen and/or oxygen source connected to the supply line via the supply line, and at least one valve in the supply line, which is actuatable as a function of the actual value/set value.

Preferably, the flow restrictor for regulating the flow of gas is located in the conduit between the on-site nitrogen plant and the reactor.

Preferably, the flow restrictor is designed as a valve which can be actuated by the control device.

Preferably, an air or oxygen supply is connected to the conduit between the flow restrictor and the oxygen measuring device.

Preferably, the nitrogen plant has a source of compressed air which is actuatable by the control means and the flow of compressed air is variable.

The invention advantageously makes it possible to generate all the protective and/or reactive gases required for the heat treatment of metals in one reactor by additionally supplying hydrocarbons on the basis of the oxygen-containing nitrogen produced in the in situ nitrogen production unit by means of a pressure swing absorption or membrane process. The process produces a shielding gas or reactant gas independent of the output rate of the on-site nitrogen production unit because the oxygen content of the nitrogen can be increased or decreased as desired by the addition of low temperature produced nitrogen, independent of the most economical mode of operation of the nitrogen production unit using pressure swing absorption or membrane processes. By means of the method of the invention, the on-site nitrogen generation unit can always be operated within its economically optimum operating conditions at the lowest energy cost, and the desired peak can be covered by metered addition of cryogenic nitrogen and/or cryogenic oxygen generation or air. In addition, the invention allows the actual adjustment of the oxygen content in the nitrogen, since, depending on the specific requirements, nitrogen and/or oxygen and/or air can be metered in upstream of the reactor. The fluctuations in the output of the on-site nitrogen production unit can be compensated for during operation by the method according to the invention and the protective gas or the reaction gas can be adjusted to the desired CO and H₂And (4) content.

Embodiments of the invention are described in more detail below with reference to the accompanying drawings, in which:

FIG. 1 shows a process diagram of the present invention; and

fig. 2 shows the relationship between the oxygen content and the output rateof nitrogen produced non-cryogenically by means of a pressurized rotary absorption unit.

Figure 2 shows the amount of oxygen in the nitrogen as a function of the nitrogen output rate of the oxygen contamination produced by the in situ nitrogen plant 13. In Nm on the abscissa 11³The output ratio expressed by/h is shown on the ordinate 12The oxygen content in the nitrogen gas produced by the nitrogen generator is expressed by volume percentage. As can be seen from the figure, at an output rate of 40Nm³The oxygen content increased from 0.1% by volume at/h to 180Nm at an output rate³4.8% by volume at h.

Figure 1 shows an apparatus according to the invention comprising a nitrogen on-site plant 13 comprising a source of compressed air 14, a compressed air processor 15 and membrane modules 16 operating by membrane technology, a nitrogen source 17 for the low-temperature production of nitrogen and an endothermic catalytic reactor 18. The in situ nitrogen plant 13 is connected to the reactor 18 via a pipe 19. A flow restrictor 21 (preferably an actuatable valve), an oxygen meter 22 and a metering device 23 are located in the conduit 19 downstream of the outlet of the membrane module 16. A hydrocarbon source 24, such as a natural gas source, is connected to the conduit 19 via the metering device 23. The nitrogen source 17 is connected to the pipe 19 via a supply pipe 25. The supply line 25 has

branch lines

26, 27 extending therefrom, respectively, which are connected to the line 19 between the flow restrictor 21 and the metering device 23.

An actuatable valve 28, such as an electrically controlled valve, is provided in the subduct 26 and a pressure maintaining valve 29 is located in the subduct 27. Downstream of the compressed air processor 15 in the direction of the compressed air flow 30, a bypass line 31 branches off, which can be connected optionally to the branch line 26 of the supply line 25 downstream of the valve 28 or to the line 19 downstream of the flow rate limiter 21.

According to another embodiment (not shown), the bypass line 31 may also be connected at inlet 32 to a separate source of compressed air (e.g., a compressed air ductwork) or oxygen (e.g., an oxygen supply tank containing cryogenically produced oxygen). An actuatable valve 33 (e.g. an electrically controlled valve) is located in the bypass conduit 31.

The

valves

28, 33, the oxygen meter 22, the flow rate limiter 21 and optionally the metering device 23 are connected via

control lines

35, 36, 37, 38 and 39 to a control device 34. The control device 34 is designed, for example, as a control system with a memorized program. The control device 34 has an input unit 40 which is only schematically shown.

The apparatus shown in fig. 1 operates as follows:

a compressed air source (e.g., a compressor) provides compressed air that flows through a compressed air processor 15 and then through one or more membrane modules packed with hollow fibers, the processor 15 including, for example, a primary filter, freeze dryer, submicron filter, activated carbon filter, and heater. The different diffusion rates of the individual gas components through the hollow fiber walls (membranes) influence the separation process of the compressed air. The nitrogen stream thus produced leaves the membrane module 16 at a purity of 95-99%. According to one embodiment, the contaminated nitrogen gas, which is correspondingly contaminated with an oxygen content of 1-5% by volume, is regulated by means of a flow limiter 21 to a desired flow rate at which the oxygen content of the nitrogen gas reaches the desired value. To adjust the flow rate, a flow rate set point is predetermined by the input unit 40 of the control device 34. As a function of this set value, the control device 34 actuates the flow restrictor 21 via the control duct 35 and increases or decreases the cross section of the flow channel. Adjusting the proportion of nitrogen of the oxygen contamination to the desired flow rate of the protective gas or the reaction gas required for the heat treatment of the metal is merely an example. But is not limited to this example and may be modified from this example, for example by the output regulation of the nitrogen plant 13 in situ, or by a bypass line of an orifice plate provided therein, or by a manual metering valve and an upstream on/off valve which are opened and closed by a control device in accordance with the required flow rate.

Downstream of the flow restrictor 21, the oxygen-contaminated nitrogen gas flows to a metering device 25, by means of which hydrocarbons are metered in from a hydrocarbon source 24. For this purpose, the oxygen measuring device 22 detects the oxygen content in the line 19 upstream of the metering device 23 and supplies it as an actual value to the control device 34. Hydrocarbons, such as natural gas, are metered into the nitrogen of the oxygen contamination as a function of the actual value.

According to the invention, the actual value of the oxygen content in the nitrogen gas detected by the oxygen measuring device 22 is compared with the setpoint value input to the control device 34 via the input unit 40 and readjusted in the event of a deviation of the actual value from the setpoint value or from a precise range associated with the setpoint value. The adjustment of the oxygen content in the nitrogen stream is carried out by adding nitrogen and/or air and/or oxygen to the oxygen-containing nitrogen gas produced in the in situ nitrogen plant 13 or as a replacement for contaminated nitrogen.

As the output rate decreases, the residual oxygen content decreases accordingly (fig. 2). Thedeviation from the set value is detected by the oxygen measuring device 22 and fed to the control device 34, which in turn opens the electrically controlled valve 33 in the bypass line 31 until the incoming compressed air increases the residual oxygen content in the nitrogen stream to a predetermined value. Since the pressure drop in the on-site nitrogen plant 13 is greater than the pressure drop in the bypass line 31, air can be metered into the line 19. According to one embodiment (not shown in detail), the bypass conduit 31 is connected to an oxygen source at the inlet 32. In this case, the cryogenically generated oxygen is metered in by the electrically controlled valve 33 until the set value is reached.

As the output rate increases, the oxygen content rises correspondingly, as shown in fig. 2. The deviation from the set value is detected by the oxygen measuring device 22 and the actual oxygen content is fed to the control device 34, which in turn opens the electrically controlled valve 28 in the branch 26 of the supply line 25 until the inflowing cryogenic nitrogen gas reduces the oxygen content in the nitrogen stream to the set value. Output rates above and beyond the production rate produced by the on-site nitrogen plant 13 result in a pressure drop in the line 19. The pressure drop in the duct 19 influences the opening of the pressure-maintaining valve 29 in the partial duct 27 in the supply duct 25. Low temperature nitrogen flows from nitrogen source 17 through supply line 25 to line 19 until a preset set pressure is reached at surge valve 29. The oxygen content is detected by an oxygen measuring device 22, and the compressed air or oxygen is measured as described above. In the event of a failure or disturbance and/or maintenance of the membrane module 16, the valve 21 is closed and all of the protective or reactive gas is supplied with the cryogenic nitrogen through the nitrogen source 17 and with the compressed air or oxygen through the bypass line 31.

With the device according to the invention, air and/or oxygen and/or nitrogen can be metered in as required, and can be regulated or renewed at different output rates and/or different protective or reactive gasesThe stabilized oxygen content is adjusted. This allows the production of CO and H with the desired properties in the endothermic catalytic reactor 18₂Amount of shielding gasA bulk or reactive gas. Examples of the invention

One tube making machine was used with three continuous roller hearth furnaces for intermediate and final annealing. The reaction gases used include:

H₂6% (by volume);

CO 3% (by volume);

the remainder being N₂。

Due to order conditions and maintenance or interruptions, different furnaces are used:

technical data in an annealing installation

Furnace number	Use (hours/years)	Gas requirement (m)³N of/h₂)
Furnace number	Use (hours/years)	Gas requirement (m)³N of/h₂)	1	8000	70
2	8000	70	1	8000	70
2	8000	70	3	2000	40

To obtain the desired reaction gas composition, an oxygen content of about 2.3% by volume in nitrogen is required. The basis is a simplified endothermic catalytic reaction:

there are 3 possible ways of industrial implementation of the supply of protective gas:

1. standard output 180m for residual oxygen amount of 2.3 vol%³A/h on-site nitrogen plant. When the furnace is shut down, the requirement is reduced to 140m³H is used as the reference value. The desired residual oxygen content of 2.3% by volume is obtained by controlled supply of air.

The energy requirement is 80 Kw.

2. Design standard output 140m³A/h on-site nitrogen plant. The furnace installation 3 is operated by mixing low-temperature nitrogen with compressed air to meet additional requirements.

Additional requirements are: low temperature nitrogen 35.4m³/h

Compressed air 4.6m³/h

Energy requirement of on-site nitrogen production device is 55KW

3. For standardoutput of 140m³Design of on-site nitrogen plant. The furnace unit 3 is operated to meet additional requirements by increasing the output rate of the on-site nitrogen plant and mixing the cryogenic nitrogen.

Output rate of the in-situ nitrogen production device is 150m³H (at 2.76% O)₂)

Low temperature nitrogen gas 30m³/h

The energy requirement of the on-site nitrogen production device is 55 KW.

Individual industrial solutions are defined by the difference in relative energy requirements.

The energy requirement for nitrogen produced at low temperatures is about 2kWh/m³(manufacture, transport, storage, etc.).

Scheme(s)	1	2	3
Scheme(s)	1	2	3	In situ nitrogen generation unit	80KW×8000h ＝640,000KWh	55KW×8000h ＝440,000KWh	55KW×8000h ＝440,000KWh
Low temperature nitrogen		35.4m³/h×2KWh/m³ 2000h＝141,600KWh	30.0m³/h×2KWh/m³ 2000h＝120,000KWh	In situ nitrogen generation unit	80KW×8000h ＝640,000KWh	55KW×8000h ＝440,000KWh	55KW×8000h ＝440,000KWh
Low temperature nitrogen		35.4m³/h×2KWh/m³ 2000h＝141,600KWh	30.0m³/h×2KWh/m³ 2000h＝120,000KWh	Total annual energy	640,000KWh	581,600KWh	560,000KWh
Percentage of	100％	90.9％	87.5％	Total annual energy	640,000KWh	581,600KWh	560,000KWh

As can be seen, scheme 3 is characterized by the lowest energy requirement.

Claims

1. A method for producing protective or reaction gases for the thermal treatment of metals, comprising feeding oxygen-contaminated nitrogen and hydrocarbons as gas streams into an endothermic catalytic reactor, detecting the oxygen content in the nitrogen and supplying the detected oxygen content as actual values to a control device, which comprises metering at least the nitrogen or oxygen into the gas streams as a function of the detected actual values.

2. A method according to claim 1, characterized in that air and/or nitrogen and/or oxygen is metered into the gas stream as a function of the detected actual value.

3. An apparatus for carrying out the method of claim 1 or 2, comprising:

an in situ nitrogen plant (13) for producing oxygen contaminated nitrogen, and a hydrocarbon supply (24) connected to the reactor (18) via a conduit (19);

an oxygen measuring device (22) connected to the conduit (19) for measuring the actual value of the oxygen content in the nitrogen;

a control device (34) for supplying the actual value detected by the oxygen measuring device (22) and for receiving a set value from an input device (40),

a source of nitrogen and/or oxygen (17, 31) connected to the conduit (19) via a supply conduit (25), and

at least one valve (28, 33) in the supply conduit (25) which is actuatable as a function of the actual value/set point.

4. An apparatus according to claim 3, characterized in that the flow restrictor (21) for regulating the gas flow is located in the conduit (19) between the in situ nitrogen generator (13) and the reactor (8).

5. An apparatus according to claim 3 or 4, characterized in that the flow rate limiter (21) is designed as a valve which can beactuated by the control device (34).

6. An apparatus according to claim 3 or 5, characterized in that an air or oxygen supply (17, 31) is connected to the conduit (29) between the flow restrictor (21) and the oxygen measuring device (22).

7. An apparatus according to any one of claims 3 to 5, characterized in that the on-site nitrogen generator (13) has a compressed air source (14) which can be actuated by the control device (34) and the compressed air flow rate is variable.