GB2267047A - Purifying NOx-containing gas - Google Patents

Purifying NOx-containing gas Download PDF

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GB2267047A
GB2267047A GB9316251A GB9316251A GB2267047A GB 2267047 A GB2267047 A GB 2267047A GB 9316251 A GB9316251 A GB 9316251A GB 9316251 A GB9316251 A GB 9316251A GB 2267047 A GB2267047 A GB 2267047A
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gas
adsorbent
nox
rotor
regenerating
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GB9316251D0 (en
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Shigenori Onitsuka
Masayoshoi Ichiki
Takanobu Watanabe
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Hitachi Zosen Corp
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Hitachi Zosen Corp
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D53/00Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34Chemical or biological purification of waste gases
    • B01D53/92Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9481Catalyst preceded by an adsorption device without catalytic function for temporary storage of contaminants, e.g. during cold start
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D53/00Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/02Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography
    • B01D53/06Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography with moving adsorbents, e.g. rotating beds
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D53/00Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34Chemical or biological purification of waste gases
    • B01D53/74General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86Catalytic processes
    • B01D53/8621Removing nitrogen compounds
    • B01D53/8625Nitrogen oxides
    • B01D53/8628Processes characterised by a specific catalyst
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24HEATING; RANGES; VENTILATING
    • F24FAIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F3/00Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems
    • F24F3/12Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling
    • F24F3/14Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling by humidification; by dehumidification
    • F24F3/1411Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling by humidification; by dehumidification by absorbing or adsorbing water, e.g. using an hygroscopic desiccant
    • F24F3/1423Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling by humidification; by dehumidification by absorbing or adsorbing water, e.g. using an hygroscopic desiccant with a moving bed of solid desiccants, e.g. a rotary wheel supporting solid desiccants
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D2253/00Adsorbents used in seperation treatment of gases and vapours
    • B01D2253/10Inorganic adsorbents
    • B01D2253/106Silica or silicates
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D2253/00Adsorbents used in seperation treatment of gases and vapours
    • B01D2253/10Inorganic adsorbents
    • B01D2253/106Silica or silicates
    • B01D2253/108Zeolites
    • B01D2253/1085Zeolites characterized by a silicon-aluminium ratio
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D2253/00Adsorbents used in seperation treatment of gases and vapours
    • B01D2253/10Inorganic adsorbents
    • B01D2253/112Metals or metal compounds not provided for in B01D2253/104 or B01D2253/106
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D2253/00Adsorbents used in seperation treatment of gases and vapours
    • B01D2253/25Coated, impregnated or composite adsorbents
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D2257/00Components to be removed
    • B01D2257/40Nitrogen compounds
    • B01D2257/404Nitrogen oxides other than dinitrogen oxide
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D2257/00Components to be removed
    • B01D2257/80Water
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D2259/00Type of treatment
    • B01D2259/40Further details for adsorption processes and devices
    • B01D2259/40083Regeneration of adsorbents in processes other than pressure or temperature swing adsorption
    • B01D2259/40086Regeneration of adsorbents in processes other than pressure or temperature swing adsorption by using a purge gas
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D2259/00Type of treatment
    • B01D2259/40Further details for adsorption processes and devices
    • B01D2259/40083Regeneration of adsorbents in processes other than pressure or temperature swing adsorption
    • B01D2259/40088Regeneration of adsorbents in processes other than pressure or temperature swing adsorption by heating
    • B01D2259/4009Regeneration of adsorbents in processes other than pressure or temperature swing adsorption by heating using hot gas
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D2259/00Type of treatment
    • B01D2259/40Further details for adsorption processes and devices
    • B01D2259/402Further details for adsorption processes and devices using two beds
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D53/00Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/26Drying gases or vapours
    • B01D53/261Drying gases or vapours by adsorption
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24HEATING; RANGES; VENTILATING
    • F24FAIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F2203/00Devices or apparatus used for air treatment
    • F24F2203/10Rotary wheel
    • F24F2203/1032Desiccant wheel
    • F24F2203/1036Details
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24HEATING; RANGES; VENTILATING
    • F24FAIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F2203/00Devices or apparatus used for air treatment
    • F24F2203/10Rotary wheel
    • F24F2203/1056Rotary wheel comprising a reheater
    • F24F2203/106Electrical reheater
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24HEATING; RANGES; VENTILATING
    • F24FAIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F2203/00Devices or apparatus used for air treatment
    • F24F2203/10Rotary wheel
    • F24F2203/1072Rotary wheel comprising two rotors
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24HEATING; RANGES; VENTILATING
    • F24FAIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F2203/00Devices or apparatus used for air treatment
    • F24F2203/10Rotary wheel
    • F24F2203/1084Rotary wheel comprising two flow rotor segments
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24HEATING; RANGES; VENTILATING
    • F24FAIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F2203/00Devices or apparatus used for air treatment
    • F24F2203/10Rotary wheel
    • F24F2203/1092Rotary wheel comprising four flow rotor segments

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Environmental & Geological Engineering (AREA)
  • Analytical Chemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Combustion & Propulsion (AREA)
  • Health & Medical Sciences (AREA)
  • Biomedical Technology (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Treating Waste Gases (AREA)
  • Solid-Sorbent Or Filter-Aiding Compositions (AREA)

Abstract

An apparatus for purifying an NOx-containing gas comprises an adsorptive dehumidifier i for dehumidifying the gas with a dehumidifying agent and regenerating the agent with a purified gas, and an adsorptive denitration unit 2 for denitrating the dehumidified gas. The denitration unit has an adsorbent regenerating zone provided with a channel 9 for recycling an NH3-containing regenerating gas and with a channel 10 for withdrawing a portion of the regenerating gas from the recycling channel, passing the withdrawn gas through a denitration reactor 5 and then releasing the denitrated gas into the atmosphere. <IMAGE>

Description

2267047 APPARATUS FOR PURIFYING NOX-CONTAINING GAS
BACKGROUND OF THE INVENTION
The present invention relates to apparatus for purifying NOx-containing gases, and in particular for efficiently removing nitrogen oxides (NOx) of relatively low concentration from the gas discharged by ventilation, for example, from various highway tunnels, mountain tunnels, underwater tunnels, underground roads, sheltered roads, etc. (hereinafter referred to collectively as "highway tunnels"). The apparatus is particularly suitable for use in the method of removing NOx by adsorption described in the applicants' co-pending U.K. Patent Application No. 8926951.8.
With highway tunnels having a large length and a great vehicular traffic volume, it is necessary to withdraw the air from the tunnel at a considerable rate for ventilation in order to assure the drivers and passengers of health and increase the least distance of distinct vision. Even with tunnels of relatively short distance, it is practice to ventilate the tunnel to control air pollution due to carbon monoxide (C0), NOx and the like which are concentrically released from the inlet and outlet of the tunnel when the tunnel is located in an urban area or suburban area.
However, if the gas resulting from ventilation is released as it is in the neighborhood, the contaminated gas entails environmental pollution over the area concerned. Especially in cities or suburbs where the pollution due to motor vehicle emissions spreads out two-dimensionally, heavy pollution will then become more widespread. Exactly the same problem as above will be encountered in the case where roadway tunnels or sheltered tunnels are to be constructed as a pollution control measure for existing roads.
The present invention relates to an apparatus for use in purifying the NOx-containing gas.
PRIOR ART
The gas released from tunnels by ventilation is characterized in that it has a low NOx concentration of about 5 ppm and ordinary temperature and varies greatly in quantity according to the traffic volume.
Conventional apparatus for purifying exhaust gases by the adsorption of NOx are divided generally into those of the fixed bed type and those of the moving bed type.
2 1) % The apparatus of the fixed bed type comprises a plurality of adsorbers arranged in parallel. when the concentration of the substance to be removed has reached a limit at the outlet of one of the adsorbers, with a predetermined quantity of the substance adsorbed by an adsorbent therein, the adsorber is changed over-to another adsorber, and the substance is desorbed to regenerate the adsorbent. When a large quantity of gas is to be handled, -the adsQrber is charged with a reduced amount of adsorbent in view of the gas flow resistance, so that the adsorber is changed over more frequently. Although the time required for desorption or regeneration needs to be considered, the apparatus then requires an increased number of adsorbers as arranged in parallel and becomes greater in overall scale.
With the apparatus of the moving bed type, on the other hand, the gas to be treated is generally brought into countercurrent contact with an adsorbent in an adsorber, from which the adsorbent having adsorbed a large quantity of the substance to be removed is continually withdrawn for regeneration by desorption, while a fresh portion or the regenerated portion of adsorbent is continually charged into the adsorber. Accordingly, the apparatus can be operated continuously, requires no change-over and can therefore be smaller 1 in scale than the apparatus of the fixed bed type. Fig. 4 shows-as a prior-art apparatus the NOx removal system disclosed in the foregoing literature of the research institute. 5 The NOx removal system will be described below with reference to Fig. 4 Silica gel serving as a dehumidifyingagent is charged in a dehumidifier 48 in the upper portion of a dehumidifying tower 47 and is caused to adsorb water from an exhaust gas (Nox + air + H 2 0) supplied via a channel 41. On adsorption of water, the dehumidifying agent moves downward into a regenerator 49 under gravity. In the regenerator 49, the agent is brought into contact with regenerating dry gas (from the outlet of an adsorber 51 in an adsorption tower 50) introduced thereinto via a channel 43, whereby the adsorbed water is removed from the agent. In this way, the dehumidifying agent is regenerated and forced upward by the dry gas into the dehumidifier 48 to circulate through the dehumidifying tower 47.
Thus, the silica gel serving as the dehumidif ying agent repeatedly adsorbs and releases (f or regenera- - tion) water while circulating through the tower 47. The exhaust gas supplied through the channel 41 is dehumidi- fied and flows through a channel 42 into the adsorber 51 4 1. q in the upper portion of the adsorption tower 50. The regenerating dry gas led through the channel 43 into the regenerator 49 in the dehumidifying tower 47 is given water therein and released into the atmosphere 5 as a purified gas (air + H2 0).
On the other hand, an NOx adsorbent is.charged in the adsorber 51 of the adsorption tower 50 and adsorbs NOx from the dry exhaust gas (air + NOx) from the dehumidifying tower 47...The adsorbent having adsorbed- the NOx moves downward into a desorptive regenerator 52 under gravity. In the regenerator 52, the NOx adsorbent is heated to 400 0 C by a heater 46, comes into contact with the dry purge gas to be described below to release the adsorbed NOx for regeneration, and is forced upward into the upper portion of the adsorption tower 50.
The outlet gas from the adsorber 51 is used partially as the regenerating dry gas to be introduced into the desorptive regenerator 52 via a channel 44. In the regenerator 52, the gas removes the NOx from the adsorbent and discharges from the system via a channel 45 as a desorption gas. The dry exhaust gas (NOx + air) introduced into the adsorber 51 from the dehumidifier 48 via the channel 42 is denitrated in the adsorber 51 into purified dehumidified air, a major portion of which is led through the channel 43 into the regenerator 1 49 of the dehumidifying tower 47 as the dry gas for ' regenerating the dehumidifying agent. The remainder of the air is introduced into the adsorptive regenerator 52 of the adsorption tower 50 as the dry gas for regenerat- ing the NOx adsorbent.
The desorption gas discharged from the.system via the channel 45 contains the NOx desorbed from the adsorbent. Accordingly, it has been proposed to remove the NOx from the gas by causing an aqueous alkali solu- tion or the like to absorb the NOx (wet absorption process). However, the wet absorption process is complex and cc;stly to practice since the NOx are accumulated in the form of nitrates and nitrites in the liquid absorbent, necessitating the maintenance and aftertreat- ment of the absorbent (af terIC-reatment of waste liquid) To make the desorption gas free from contaminants and release the gas to the atmosphere, a process has already been proposed in which an adsorbent having adsorbed NOx is treated with NH 3-containing air for regeneration (see Unexamined Japanese Patent Publication No. 15593/88). With this process, the Nox is subjected to a selective reduction reaction with NH 3 to reduce the adsorbed NOx to harmless N 2 and H 2 0 and remove the NOx. Further when the NOx-adsorbing adsorbent is to be regenerated merely by heating, the adsorbent must be 6 1 1 heated to 400 0 C as already mentioned, whereas if zeolite having supported thereon a copper salt with a denitrating catalytic function is used as an NOx adsorbent, the adsorbent can be regenerated by bringing the adsorbent into contact with NH3-containing air (regenerating gas) at a low temperature of 100 to 3000 C (see Japanese Patent Application No. 133446/88).
The above process wherein the NH 3-containing gas is used for regenerating the NOx adsorbent has the likelihood that the NOx removed from the adsorbent will remain partly unreacted with NH 3 as contained in the desorption gas, or'an excess of NH3 will be contained in the desorption gas. To render the deserption gas free from the excessive NH 3' 'L-.he concentration of NH 3 to be injected into the regenerating gas must be controlled accurately. Conversely, if the amount of NH 3 injected is insufficient, the NOx adsorbent will not be regenerated fully, making it extremely difficult to operate the desorptive regenerator for the NOx adsorbent.
In the case where a somewhat excessive amount of NH 3 is injected into the regenerating gas to ensure complete regeneration of the NOx adsorbent, the desorption gas contains an excess of NH 3 and therefore needs to be introduced into another denitration reactor and made harmless through the denitration reaction between NOx 7 Q and NH 3 or oxidation decomposition reaction of N% With the dehumidifier and the NOx adsorber of the moving bed type included in the NOx adsorption system of the research institute, it is necessary for the flow channels to have an increased cross sectional area to reduce the resistance offered to the flow of gases when a large quantity of exhaust gas is to be handled. To achieve an improved adsorption efficiency, on the other hand, it is required to withdraw adsorbent-particles from the-.flow channel as uniformly spread out in the direction of the cross section of the channel and charge them into the unit similarly, whereas this encounters extreme difficulties. Further with the adsorption tower of the moving bed type, gravity is utilized for moving the adsorbent, and the regenerated adsorbent is forced upward through the tower by dry air, so tha- the abrasion, cracking and particulation of the adsorbent itself, and the abrasion of the inner surfaces of the tower and lift pipe ' pose problems, while the tower is complex in construction, and the apparatus is not easy to operate.
Accordingly, an object of the present invention is to provide an apparatus for purifying NOxcontaining gases free of the foregoing problems of the prior art.
SUMMARY OF THE INVENTION
8 The apparatus of the invention for purifying an NOx-containing gas comprises an adsorptive dehumidifier for dehumidifying the gas and regenerating a dehumidifying agent with a purified gas, and an adsorptive denitration unit for denitrating the NOx-containing gas resulting from dehumidification. The denitration unit has an adsorbent regenerating zone which is provided with a gas recycling channel for recycling a regenerating gas containing NH 39 and a gas withdrawing channel for withdrawing a portion of the regenerating'gas from the recycling channel', passing the' gas through a denitration reactor and thereafter releasing the denitrated gas into the atmosphere.
The adsorptive dehumidifier and the adsorptive denitration unit are each preferably a rotary adsorber for continuously moving the dehumidifying agent or the NOx adsorbent therein at right angles with the flow of gas, whereby the dehumidifying agent or the NOx adsorbent can be withdrawn, regenerated and charged continuously.
With the NOx-containing gas purifying apparatus of the present invention, an excess of NH 3 can be caused to be present in the adsorbent regenerating zone. This assures the regenerating zone of a sufficient supply of NH 3 for removing NOx adsorbed by the adsorbent more completely upon reduction to completely regenerate the NOx adsorbent. Accordingly, there is no need to accurately control the injection of NH 3 BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a flow chart showing an embodiment of the invention; Fig 2 is a perspective view showing a rotary dehumidifier; Fig. 3 is a perspective view showing a rotary NOx adsorber; and Fig. 4 is a flow chart showing a conventional process for removing NOx.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A gas purifying apparatus of the invention is adapted to purify the gas released from highway tunnels by ventilation (ventilation gas) will be described in detail with reference to the flow chart of Fig. 1.
A ventilation gas containing NOx is introduced into an adsorptive dehumidifier 1 through a ventilation gas channel 8 to remove water fzom the gas with a dehumidifying agent by adsorption and dry the gas. The gas is then led into an adsorptive denitration unit 2 to remove the NOx from the gas by adsorption and obtain a purified gas.
- 10 The dehumidifying agent in the dehumidifier 1 is regenerated by the purified gas. On the other hand, the adsorbent having adsorbed the NOx in the denitration unit 2 is regenerated by a NH 3-containing regenerating gas.
The most distinct feature of the present invention is that a major portion of the regenerating gas having NH 3 injected thereinto by an NH 3 feeder 3 is recycled by a blower 4 on a gas recycling channel 9 for use in an adsorbent regenerating zone of the adsorptive denitration unit 2 to regenerate the NOx adsorbent, and that a portion of the regenerating gas is withdrawn as. a purge gas through a gas withdrawing channel 10, then passed through a denitration reactor 5 and thereafter released into the atmosphere.
In the case where the NOx adsorbent is to be regenerated by the NH 3-containing gas, it is desired that the adsorbent to be regenerated and the regenerating _ recycle gas be heated to a suitable temperature (100 to 300 0 C) by a heater 6 so as to react the NOx adsorbed by the adsorbent with the NH 3 efficiently.
When the NOx adsorbent is to be regenerated by the prior-art process described, it is necessary to accurately diffuse NH 3 of low concentration into the regenerating gas in an amount corresponding to the amount of NO 3 adsorbed by the adsorbent, i.e., in an amount' required and sufficient for the removal of NOx by reduction. While this amount is not controllable unless the amount of adsorbed NOx is accurately measured, it is actually impossible to continuously measure the amount of NOx in the adsorbent which is solid. actuality, therefore, the conventional technique for regenerating the Nox adsorbent is very likely to result in leakage of excessive NH 3 or incomplete regeneration ' of the adsorbent due to an insufficient amount of injected NH 3 In contrast, with the present apparatus, an excess of NH 3 can be made to be present in the adsorbent regenerating zone. The supply of a sufficient quantity of NH 3 to the regenerating zone makes it possible to completely remove the adsorbed NOx from the adsorbent by reduction and to completely regenerate the adsorbent. Consequently, there is no need to accurately control the injection of NH 3. Thus, the gas purifying apparatus of the present invention is a very useful and economical apparatus.
While the regenerating recycle gas is partly withdrawn as a purge gas, the excessive NH 3 contained in the purge gas and the unreacted NOx desorbed from the adsorbent and present in the gas are rendered harmless 12 - 0 by the denitration reactor 5 which is provided downstream from a heater 7. The purge gas to be treated by the denitration reactor 5 is very small in amount. The reactor 5 can therefore be of a small size, and the purge gas can nevertheless be made harmless effectively and inexpensively.
With reference to the flow chart of Fig. 1 a reduced gas purification efficiency will result if the regenerating recycle gas leaks into the ventilation gas cleaned of NOx. When at least 60% of purification efficiency is a target, the leakage of the regenerating recycle gas into the purified ventilation gas poses'a serious problem.
As shown in Fig. 3,' the adsorptive denitration unit 2 is a rotary adsorber, in which an adsorbent rotor is in sliding contact with ventilation gas and regenerating gas nozzles. It is difficult to completely seal off these sliding portions. Accordingly, the operating pressure of the regenerating portion (cooling, regenera- tion and preheating) is made lower than that of the NOx adsorbing portion to prevent the reduction in purification efficiency due to gas leaks. In this case, the gas leaks from the adsorbing portion into the regenerating portion. The amount of gas corresponding to the leak is withdrawn from the regenerating gas recycling channel 9. The NOx adsorbent adsorbs NOx and a small amount-of water, which are desorbed in the regenerating portion and accumulate in the regenerating recycle gas. To limit the water content of the regenerating recycle gas to a predetermined level, a specified amount.of dry air is supplied to the gas recycling channel 9 via the.sliding Portion, and the water-containing recycle gas is partially withdrawn from the channel 9.
In other words, consideration is given to the apparatus of the invention, such that the leak gas from the sliding portion servesas the main source for supplying dry air to the regenerating recycle gas.
Next, a purifying apparatus will be described which comprises rotary adsorbers serving as adsorptive.
is dehumidifier and denitration unit.
The rotary adsorbers shown in the flow chart of Fig. 1 are adapted to continually withdraw, regenerate and charge the dehumidifying agent and the NOx adsorbent. The apparatus is adapted to exhibit performance equivalent to that of the prior-art apparatus already described, by a simpler construction of reduced gas flow resistance and is therefore very useful.
An example of rotary dehumidifier will be described with reference to Fig. 2. In the dehumidifier 1 for use in the purifying apparatus of the invention, 9 the ventilation gas to be purified is dehumidified b a dehumidifying agent, which is regenerated by a denitrated purified dry gas. The dehumidifying agent is regenerated by the dry gas which is approximately in the same amount as the ventilation gas to be purified. The dehumidifier 1 comprises a rotor 11 of dehumidifying agent. Useful as therotor 11 is an assembly of adsorbent plates comprising silica gel as a water adsorbent and arranged- in layers.with -a suitable spacer interposed between each two adjacent plates, an assembly of adsorbent flat plates and corrugated adsorbent plates which are alternately arranged in layers and which comprise silica gel as a water adsorbent, or a water adsorbent of silica gel in the form of a unitary honeycomb structure.
An NOx-containing ventilation gas channel 8 is so disposed that the ventilation gas flows through a zone lla having a semicircular cross section and provided by the right or left half of the rotor 11 as it is seen axiall-y thereof. A purified ventilation gas channel 13 is -20 so disposed that the regenerating dry gas flows through a zone llb having a semicircular cross section and provided by the other half of the rotor 11. The rotor 11 is rotated in the direction of arrow A to effect continuous dehumidification.
Next, an example of rotary adsorptive - 0 denitration unit will be described with reference to. Fig. 3; The denitration unit 2 for use in the purifying apparatus of the invention removes NOx from the dehumidified ventilation gas by adsorption to obtain a purified dry ventilation gas and, at the same time regenerates the NOx adsorbent with an NH 3-containing regeneratin.g recycle gas. The denitration unit 2 comprises a rotor 12 of NOx adsorbent. Useful as the rotor 12 is an assembly of plates of an adsorbent comprising a copper salt supported on a zeolite carrier and arranged in layers with a suitable spacer interposed between each two adjacent plates, an assembly of flat adsorbent plates and corrugated adsorbent plates which are arraniged, alternately in layers and which are made of an.adsorbent comprising a copper salt supported on a zeolite carrier, or an adsorbent comprising a copper salt supported on a zeolite carrier in the form of a unitary honeycomb structure. The ventilation gas channel 8 is so disposed that the dehumidified ventilation gas flows through a zone 12a having a semicircular cross section and provided by one of the right and left halves of the rotor 12 as it is seen axially thereof. The rotor 12 is further provided with a gas recycling channel 9 so that the NH 3 -containing regenerating recycle gas flows successively through zones 12b, 12c and 12d having a sectorial cross section - 16 and provided by the respective one-third portions of the other half of the rotor 12. Consequently, the NOx is adsorbed in the zone 12a, the rotor 12 is cooled in the zone 12b, the rotor 12 is regenerated in the zone 12c, and the rotor 12 is preheated in the zone 12d. The rotor 12 is rotated in the direction of arrow B. I.

Claims (8)

1. An apparatus for purifying an NOx-containing gas comprising an adsorptive dehumidifier for dehumidifying the gas with a dehumidifying agent and regenerating the agent with a purified gas, and an adsorptive denitration unit for denitrating the dehumidified NOx- / 1 - 18 1. Q containing gas, the denitration unit having an adsorbent regenerating zone provided with a gas recycling channel for recycling a regenerating gas containing NH 3 and with a gas withdrawing channel for withdrawing a portion of the regenerating gas from the recycling channel, passing the withdrawn gas through a denitration reactor.and then releasing the denitrated gas into the atmosphere.
2.. An apparatus as defined in claim 1 wherein each of the adsorptive dehumidifier and the adsorptive denitration unit is a rotary adsorber for continuously moving the dehumidifying agent or NOx adsorbent therein at right angles with the flow of gas.
3.. An apparatus as defined in claim 2 wherein the rotary adsorptive dehumidifier comprises a dehumidifying rotor, and the rotor is an-assembly of dehumidifying plates comprising silica gel as a water absorbent and arranged in layers.with a suitable spacer interposed between adjacent plates, an assembly of flat dehumidi-_ fying plates and corrugated dehumidifying plates alternately arranged in layers and comprising silica gel as a water absorbent, or a unitary honeycomb dehumidi- fying structure comprising silica gel as a water absorbent.
4. An apparatus as defined in claim 2 or.3 wherein the rotary adsorptive dehumidifyier comprises a dehumidi- - 19 f ying rotor, and the rotor is provided with an NOx- containing gas channel so that the NOx-containing gas before dehumidification flows locally through the rotor and with a purified gas channel so that the regenerating dry gas flows through the rotor at a portion thereof other than the portion f or the NOx-containing ga.s to flow through before dehumidification.
any of claims 2 to 4
5. An apparatus as defined in wherein the rotary adsorptive denitration unit comprises an NOx adsorbent rotor, and the rotor is an assembly of plates of an adsorbent comprising a copper salt supported on a zeolite carrier and arranged in layers wiih a suitable spacer interposed between the adjacnet plates, an assembly of flat adsorbent plates and corrugated adsorbent plates arranged alternately in layers and made of an adsorbent comprising a copper salt supported on a zeolite carrier, 10 or an adsorbent comprising a copper salt supported on a zeolite carrier in the form of a unitary honeycomb structure.
-4 p r 5
6. An apparatus as defined in claim / wherein the rotary adsorptive denitration unit comprises an NOx adsorbent rotor, and the adsorbent rotor has the NOxcontaining gas channel so that the NOxcontaining gas after dehumidification flows locally through the adsorbent rotor and the gas recycling channel so that the NH 3- - 20 containing regenerating recycle gas flows through the adsorbent rotor at a portion thereof other than the portion for the NOx-containing gas to flow through after dehumidification.
7. An apparatus for purifying an NOx-containing gas substantially as hereinbefore described with reference to the accompanying drawings.
8. Any novel subject matter or combination including novel subject matter disclosed in the foregoing Specification or Claims and/or shown in the drawings, whether or not within the scope of or relating to the same invention as any of the preceding Claims.
21
GB9316251A 1988-05-30 1993-08-05 Apparatus for purifying NOx - containing gas Expired - Fee Related GB2267047B (en)

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JP63133446A JPH01299642A (en) 1988-05-30 1988-05-30 Adsorbent for nitrogen oxide having low concentration

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JPH0523828B2 (en) 1993-04-05
GB8926951D0 (en) 1990-01-17
GB2267047B (en) 1994-03-30
DE3939480A1 (en) 1991-06-06
GB9316251D0 (en) 1993-09-22
GB2238489A (en) 1991-06-05
JPH01299642A (en) 1989-12-04
GB2238489B (en) 1994-03-30

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