Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation 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
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
  • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
  • B01D53/9404—Removing only nitrogen compounds
  • B01D53/9409—Nitrogen oxides
  • B01D53/9431—Processes characterised by a specific device
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
  • C01C1/00—Ammonia; Compounds thereof
  • C01C1/003—Storage or handling of ammonia
  • C01C1/006—Storage or handling of ammonia making use of solid ammonia storage materials, e.g. complex ammine salts
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
  • H01M8/04082—Arrangements for control of reactant parameters, e.g. pressure or concentration
  • H01M8/04201—Reactant storage and supply, e.g. means for feeding, pipes
  • H01M8/04216—Reactant storage and supply, e.g. means for feeding, pipes characterised by the choice for a specific material, e.g. carbon, hydride, absorbent
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/06—Combination of fuel cells with means for production of reactants or for treatment of residues
  • H01M8/0606—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/22—Fuel cells in which the fuel is based on materials comprising carbon or oxygen or hydrogen and other elements; Fuel cells in which the fuel is based on materials comprising only elements other than carbon, oxygen or hydrogen
  • H01M8/222—Fuel cells in which the fuel is based on compounds containing nitrogen, e.g. hydrazine, ammonia
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2251/00—Reactants
  • B01D2251/20—Reductants
  • B01D2251/206—Ammonium compounds
  • B01D2251/2062—Ammonia
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2257/00—Components to be removed
  • B01D2257/40—Nitrogen compounds
  • B01D2257/406—Ammonia
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/50—Fuel cells

Definitions

• This invention relates to ammonia storage and in particular to a method and apparatus for safe ammonia release from an ammonia generating material that generates ammonia irreversibly.
• Materials capable of generating ammonia irreversibly can be used as solid or liquid storage media for ammonia, which in turn, for example, may be used as the reductant in selective catalytic reduction (SCR) to reduce NO x emissions of automotive vehicles, see e.g. WO 99/01205.
• SCR selective catalytic reduction
• ammonia is generated from those materials by heating the container containing them and thermally or catalytically decomposing them.
• urea, ammonium carbamate and/or ammonium carbonate and their solutions in a solvent may be used as solid or liquid storage materials that can generate ammonia irreversibly (see e.g. Dirk Steiger and Werner Weisweiler, Chemie lngenieurtechnik 2001 , 73, 123-127).
• ammonia is released from the solid or liquid storage media by thermal evapouration and simultaneous or subsequent thermal and/or catalytic decomposition.
• Those storage media and their decomposition products, respectively, may be exposed to high temperatures by environmental conditions.
• high ammonia vapour pressures may result in closed systems when no ammonia consumption takes place, e.g. in a parked motor vehicle exposed to strong solar irradiation.
• the invention in a first aspect relates to a method for safe use of materials generating ammonia irreversibly, wherein a first ammonia generating material capable of generating ammonia irreversibly and/or its decomposition product and a second ammonia storage material capable of reversibly or irreversibly ad- or absorbing ammonia which has a lower ammonia vapour pressure than said first ammonia generating material and/or its decomposition product and is only partially saturated with or completely void of ammonia are brought into fluid communication with other, when a vapour pressure of said first ammonia generating material and/or its decomposition product is at or higher than a pressure threshold, for ad- or absorbing ammonia released from the decomposition of the first ammonia generating material.
• an apparatus for safe use of ammonia generating materials which comprises first and second storing/delivery units connectable in fluid communication and containing a first ammonia generating material capable of generating ammonia irreversibly and a second ammonia storage material capable of reversibly or irreversibly ad- or absorbing ammonia, wherein the first ammonia generating material in the first storing/delivery unit has a higher vapour pressure than a second ammonia storage material in the second storing/delivery unit.
• a third aspect is an automotive NO x treatment system comprising such apparatus.
• Fig. 1 shows an embodiment of an ammonia storage and delivery apparatus comprising a first storage/delivery unit (main storage tank) containing a first ammonia generating material capable of generating ammonia irreversibly and a second storage delivery unit (storage chamber) smaller than the main storage tank and containing an ammonia adsorbing or absorbing storage material having a low ammonia vapour pressure and which is only partially saturated with or void of ammonia in fluid communication.
• a first storage/delivery unit main storage tank
• a second storage delivery unit storage chamber
• Fig. 2 shows another embodiment of an ammonia storage and delivery apparatus similar to the one of Fig. 1 and further comprising a buffer volume between the main tank and a dosing valve in an ammonia supply line leading into an exhaust line between an engine and a catalyst for selective reduction of NO x with ammonia.
• Fig. 3 shows another embodiment of an ammonia storage and delivery apparatus similar to the one of Fig. 2 and further comprising an absorbing unit containing a material ad- or absorbing ammonia very strongly.
• Fig. 4 shows the temperature (thin lines) and pressure (thick lines) development of an ammonia storage/delivery system according to the prior art without a second ammonia storage material wherein the ammonia storage material is initially at a temperature of 25 0 C and then exposed to temperatures of 40, 60, 80 and 100 0 C.
• Fig. 5 shows the pressure development of an ammonia storage/delivery system according to Fig. 1 or 2 (thin line) wherein a first ammonia generating material having a relatively high vapour pressure and a second ammonia storage material having a low ammonia vapour pressure, which is MgCI 2 void of or only partially saturated with ammonia, are used in combination.
• the system is initially at a temperature of 25°C and is then exposed to a temperature of 60 0 C.
• a system according to the prior art is shown for comparison (thick line).
• Fig. 6 shows the pressure development of the systems of Fig. 5 when exposed to a temperature of 80 0 C.
• Fig. 7 shows the temperature development of a system of the prior art without a second storage material (thin dashed curved line) and of the system of Fig. 1 or 2 (thin solid line) and the pressure development of a system of the prior art without the second storage material (thick dashed line) and of the system of Fig. 1 or 2 (thick solid line) when cooling down from 55 0 C and a pressure of 2,5 bar in an ambient temperature of 25°C.
• the embodiments pertain to methods and apparatuses 100, 100', 100" using at least two storage materials 1a, 2a, one (1a) capable of generating ammonia irreversibly and a second one (2a) capable of ad- or absorbing of ammonia reversibly or irreversibly and capable to actively lower the ammonia partial vapour pressure and thus the vapour pressure in the apparatus 100, 100', 100 " or system by using the material 2a having a lower ammonia vapour pressure than the first ammonia generating material and/or its decomposition product when the latter are at a pressure threshold to absorb ammonia from the system when the pressure therein exceeds the threshold level by bringing the two materials 1a, 2a into fluid communication.
• the two materials 1a, 2a may be accommodated in one container (not shown) divided e.g. by a gate or gate valve before they are brought into fluid communication, or they may be accommodated in to different containers 1 , 2 connectable in fluid communication (Fig. 1 , 2, 3).
• the pressure threshold of the vapour pressure varies with the constitution, configuration and operation requirements of the system.
• a different pressure threshold value for bringing the system in fluid communication with the second ammonia storage material from that in a stationary unit where strong walls can define the system may be desirable.
• the desired pressure threshold value may be considerably higher than in a relatively light thin walled mobile unit.
• the second ammonia storage material 2a is only partly saturated with or void of ammonia when it is used to adsorb or absorb ammonia generated from the first ammonia generating material 1a after the predetermined pressure threshold value has been reached.
• the ammonia storage material 2a adsorbs or absorbs ammonia reversibly or irreversibly.
• Non-limiting examples of ammonia adsorbing materials are acid- treated active carbon materials and zeolites.
• Non-limiting examples of ammonia absorbing materials are metal ammine complexes.
• a non-limiting example, which shows the usefulness of the embodiments of the invention, is as follows.
• a passive pressure build-up when e.g. a motor vehicle equipped with a container filled with an ammonia generating material is in a warm environment, e.g. parked in summer in the sun.
• a conventional ammonia storage and delivery system is heated to e.g. 60 0 C, with certain ammonia generating materials which are relatively volatile the vapour pressure may reach 3 bars or more. If the system has a leak at this pressure, ammonia will be released into the environment.
• an active heating of the container has been applied in order to create a suitable supply pressure, e.g.
• an ammonia storage and delivery system in a motor vehicle it may be desirable to set the predetermined pressure threshold value at about ambient pressure or about 1 bar when the system is out of operation in order to avoid a possible leakage of ammonia into the environment.
• the pressure in the ammonia storage and delivery system of a motor vehicle may become undesirably high, e.g. when there is a failure of the heat control.
• first and second ammonia storage materials 1a, 2a are contained in different containers 1 , 2 or units that are connected e. g. by a pipe 20 which may comprise some type of valve 12 which is opened for bringing the two materials into fluid communication when the pressure threshold is exceeded.
• the first container 1 (main storage tank) is usually surrounded by an insulation layer 4a and has heating means 3a for the volatilization and possibly decomposition of the ammonia generating material 1a.
• the second container 2 (storage chamber) is usually smaller than the main storage tank (1 ) and may optionally have heating means 3b. It may optionally be partly or fully surrounded by an insulation layer 4b, which may be a weakly insulating layer.
• the fluid communication can be interrupted and re- established, e.g. by a suitable valve 12.
• the fluid communication may e.g. be interrupted when a sufficiently low vapour pressure of the system has been reached and re-established when the vapour pressure has again reached the threshold value.
• the first and second ammonia storage materials 1a, 2a are at the same temperature. This may, e.g., be the case when a vehicle has been parked for a while and the first and second ammonia storage materials are exposed to the same temperature.
• the first ammonia storage material 1a is at a higher temperature than said second ammonia storage material 2a. This may, e.g., be the case, when the first ammonia generating material is heated to release ammonia or when the operation of the system has just ended.
• the first ammonia generating material 1a is used as an ammonia source in a system having an ammonia consumption unit in operation.
• an ammonia consumption unit 200 or consumer may, without limitation, e.g. be a catalyst 8 for the selective catalytic reduction in oxygen-containing exhaust gas, as it is e.g. found in various combustion engines 7 fuelled by diesel, petrol or gasoline, natural gas, coal, hydrogen or other fossil or synthetic fuel or in other combustion processes.
• the reduction of NO x is effected in an automobile, truck, train, ship or other motorized machine, vehicle or power generator driven by a combustion engine 7.
• the ammonia consumption unit may be a catalytic device for splitting or cracking ammonia into nitrogen and hydrogen.
• the hydrogen produced may, e.g., be used in a power unit for generating electricity or as fuel etc.
• the ammonia consumption unit may also be a fuel cell which operates directly on ammonia.
• the ammonia source i.e. the first ammonia generating material 1a
• the ammonia source may be heated to evaporate the material and simultaneously or subsequently decompose the material thermally and/or catalytically thereby releasing ammonia.
• the first ammonia storage material 1a is brought into fluid communication with the second ammonia storage material 2a when the operation of the ammonia consumption unit 200 has ended and the pressure of the system is above the pressure threshold value.
• the first ammonia storage material 1a may still be warm, if it has been heated for vapourization even if the heating has been stopped.
• the first ammonia storage material 1a will continue to evapourate and possibly release ammonia, and since there is no more consumption a pressure build-up will be the result or at least an elevated pressure for an extended period of time will be maintained and the pressure threshold value may be reached.
• the second ammonia storage material 2a which is only partially saturated with or void of ammonia will then be brought into fluid communication with the first ammonia generating material 1a and/or the point in the system where ammonia is released by decomposition of the first material, and adsorb or absorb ammonia until the equilibrium ammonia pressure will be reached. As a result the pressure in the system 100, 100' will drop.
• the first ammonia storage material or ammonia generating material which generates ammonia irreversibly is selected from ammonium carbamate, ammonium carbonate and urea and solutions thereof as well as solutions of ammonia in a solvent.
• Ammonia generating/storage material capable of generating ammonia irreversibly means a material which can thermally or catalytically be decomposed into ammonia plus other components.
• ammonium carbonate (NH-OaCOa) can be decomposed into 2NH 3 , CO 2 , and H 2 O
• urea (NH 2 J 2 CO) can be decomposed in the presence of water to yield 2NH 3 plus CO 2 .
• the decomposition of ammonium carbamate (NH 2 COO " NH 4 + ) yields 2NH 3 plus CO 2 , but also carbamic acid (NH 2 COOH) plus ammonia.
• ammonium carbamate when the temperature drops. Nevertheless, for the purpose of the present application the decomposition of ammonium carbamate is considered to be irreversible. Furthermore, the desorption of ammonia from water, where ammonia is mostly present as NH 4 OH, will also be considered irreversible.
• the ammonia partial pressure at 25°C of the second ammonia storage material 2a is below about 1 bar, e.g. 0.8 bar, preferably about or below about 0.5 bar, more preferably about or below about 0.3 bar and most preferably about or below about 0.1 bar. In some embodiments the ammonia partial pressure generated by the first ammonia generating material 1a is in the range of about 0.1 to 1.0 bar at 25°C.
• the second ammonia storage material 2a reversibly absorbs and desorbs ammonia.
• the ammonia absorbing and desorbing material 2a is a metal ammine complex.
• the metal ammine complex is selected from metal ammine complexes of the general formula: M a (NH 3 ) n Xz.
• M is one or more cations selected from alkali metals such as Li, Na, K or Cs, alkaline earth metals such as Mg, Ca or Sr, and/or transition metals such as V, Cr, Mn, Fe, Co, Ni 1 Cu, or Zn or combinations thereof such as NaAI, KAI, K 2 Zn, CsCu, or K 2 Fe
• X is one or more anions selected from fluoride, chloride, bromide, iodide, nitrate, thiocyanate, sulphate, molybdate, and phosphate ions
• a is the number of cations per salt molecule
• z is the number of anions per salt molecule
• n is the coordination number of 2 to 12.
• the second ammonia absorbing and desorbing material 2a is Mg(NH 3 ) 6 CI 2 , Fe(NH 3 ) 6 CI 2 or Ni(NH 3 ) 6 CI 2 or a combination thereof.
• vapour pressure of ammonia-saturated Mg(NH 3 ) S CI 2 at different temperatures is given in the table below.
• the ammonia vapour pressure of Mg(NH 3 ) 6 Cl 2 is low at room temperature as well as at 60 0 C.
• the present embodiments greatly increase the safety when using materials generating ammonia irreversibly and/or having relatively high ammonia vapour partial pressures (such as ammonia dissolved in water).
• ammonia generating materials capable of generating ammonia irreversibly would be used as an ammonia source.
• ammonia source material as soon as there is a safety risk, such as failure of the heat control of the container with the ammonia source material or a higher pressure than desired after stopping the ammonia consumption unit, which would e.g. be the case, when a vehicle is parked or when the car safety system detects e.g. an engine malfunction, a crash-like incident or a fire. At least a part of the excess ammonia will then be absorbed by the MgCI 2 or similar material, thereby lowering the pressure in the system. Accordingly, a rapid reduction in operating pressure after ending the operation of the ammonia consumption unit can be achieved, as shown in Fig.
• the absorption of ammonia by a metal salt is exothermic, i.e. associated with the generation of heat of absorption.
• the second ammonia storage material 2a e.g. Mg(NH 3 ) 6 Cl2 or its ammonia-depleted form MgCI 2 or a strongly adsorbing material such as acid-treated active carbon, therefore is in proximity to or contact with a material that can well dissipate heat to the surroundings, such as a metal and metal alloy. In this way, when the two storage units are in fluid communication the pressure of the system is governed by the temperature of the surroundings and the low ammonia pressure of the second storage material.
• this can be effected during operation of the ammonia consumption unit 200, and the ammonia thus released from the second storage material 2a can be fed into the line 9 leading to the consumption unit 200, e.g. a catalyst 8 for reducing NO x .
• a catalyst 8 for reducing NO x e.g. a catalyst 8 for reducing NO x
• more than one main storage tank 1 containing ammonia generating material 1a and more than one, usually smaller storage chamber 2 containing ammonia storage and delivery material 2a having a low ammonia vapour pressure and more than two different ammonia storage materials may be present in the apparatus 100, 100' for storing and delivering ammonia, if desired.
• the material in a first storage chamber 2 may be a material ad- or absorbing ammonia reversibly or irreversibly and the material 13a in the second storage chamber (absorbing unit 13) may be an ammonia storage material that irreversibly and very strongly ad- or absorbs ammonia, such as active carbon treated with high amount so sulfuric acid.
• the second storage chamber (absorbing unit 13) may optionally be insulated 4c; this is, however, not the case, if it is an emergency unit in the case that the ammonia pressure in the system 100, 100', 100" for some reason exceeds an upper safety limit.
• the detection of an abnormal event such as a crash incident or a fire can result in rapid activation of the absorbing unit 13 and thus minimize the ammonia release in case of an accident. This is an additional safety feature of these embodiments.
• All the above storage units may be removably fastened to the apparatus or system 100, 100' in order to facilitate a possible exchange of the ammonia storage material.
• a buffer container 5 which is connected in fluid communication to at least one to the first storage/delivery unit (main storage tank 1 ) and the second storage unit (storage chamber 2).
• This buffer container 5 may serve for a better regulation of the pressure of the ammonia, which is delivered to the consumption unit (consumer) 200.
• Upstream and downstream of the buffer container 5 there may be control valves (only one (6) is shown) included in the lines to and from the same so as to control the ammonia flow into and out of the buffer container 5.
• Figure 1 shows an apparatus 100 for storing and delivering ammonia which includes a main storage tank 1 serving as a first storing/evaporation unit and a storage chamber 2 serving as a second storing/delivery unit.
• the main storage tank 1 contains a first ammonia generating material 1a.
• the storage chamber 2 contains a second ammonia storage material 2a which binds ammonia strongly (at a low vapour pressure in the range up to 0.1 bar).
• Main storage tank 1 is surrounded by an insulation layer/shell 4a and storage chamber 2 is surrounded by an insulation layer/shell 4b.
• These insulations/shells 4a, 4b may consist of suitable insulation materials such as mineral wool, rockwool, PUR, PIR or other insulation/shell materials suitable for the specific environmental conditions (temperature, humidity, chemical exposure) for the respective application.
• Such an insulation layer/shell may be filled with a porous material that is evacuated in order to further reduce the heat conductivity.
• the insulation layers/shells 4a, 4b may be protected by an insulation cover (not shown) or may be formed by a suitable shell material.
• Main storage tank 1 and storage tank 2 comprise heating means 3a and 3b.
• These heating means 3a, 3b may be either formed as internal heating means embedded into the first and second storage materials 1a, 2a (see figure). They may also be arranged on the outside of the shell of the main storage tank 1 and the storage chamber 2 but on the inside of the insulation layer 4a and 4b.
• Suitable heating means 3a, 3b may be electrical resistance heating means or fluid heating means (hot water, steam, oil, exhaust gas, etc.), wherein the heating output is controlled by the control unit 11 , either directly by controlling the electrical input (power supply) or indirectly by control valves (not shown) of the heating fluid lines (fluid supply and/or temperature).
• the ammonia generating material and/or the ammonia generated therefrom, respectively, is supplied through a tube 20 to an ammonia consumer (not shown).
• the supply is controlled by the dosing valve 6, wherein the supply pressure in the apparatus 100 can be detected by a pressure sensor 10 and the control unit 11 which controls the heater 3a accordingly.
• the dosing valve 6 may be of any suitable type electrically, pneumatically, or hydraulically operable and controllable.
• valve 12 to the storage chamber 2 is opened and the second storage material 2a in the storage chamber 2 absorbs ammonia from the main storage tank 1 and/or from all or some other point of the system other than the storage chamber 2 due to a difference in ammonia partial pressure. This process may keep the pressure in the main storage 1 tank or the whole system, respectively, close to or below 1 bar. Valve 12 is also controlled by the controlling unit 11.
• valve 6 and opening of valve 12 may also be effected by a link to the safety monitoring system of the vehicle. If e.g. a car is in a crash , the airbags will release immediately governed by an acceleration detector and this - as well as any other emergency signal from the safety monitoring system, e.g. the detection of a fire - may also trigger the closing of valve 6 and opening of valve 12.
• the usual safe storage temperature of the main unit is for example room temperature. If the system is placed at a temperature of e.g. 60 C° a slow passive heating of both the main storage tank 1 and the storage chamber 2 will occur.
• the increase in temperature of the main storage tank 1 also causes a rise of the vapour pressure from the first ammonia generating material 1a. This pressure increase is detected by the pressure sensor 10; when the pressure is too high, e.g. above 1 bar, the valve 12 to the storage chamber 2 is opened and ammonia migrates from the main storage tank 1 or the whole system or specific parts of the system, respectively, to the storage chamber 2.
• the absorption of ammonia in the storage chamber 2 causes a temperature rise and the generated heat is dispersed through the insulation/shell 4b and the surface of the storage chamber 2 to the environment.
• the main storage tank 1 has an outside surface Ai and the outside shell including the insulation 4a is characterised by a heat transfer coefficient ⁇ i and the storage chamber 2 has an outside surface A 2 and is also characterised by a heat transfer coefficient ⁇ 2 .
• the process can be kept up as long as the second storage material 2a is not completely saturated and is further illustrated by the example below.
• the heating means 3b of the storage chamber 2 is utilised if a second storage material 2a binding ammonia reversibly in the storage chamber 2 is saturated. By heating, the ammonia in the storage chamber 2 can be released through the valve 12 and the valve 6 to an ammonia consuming process.
• the storage chamber 2 can be used during the normal ammonia release to supplement the larger unit 1 or during a fast start-up.
• a check valve (not shown) may be provided in the line 20 between the valve 12 and the main storage tank 1. Such a check valve is only necessary, if the ammonia pressure in the second storage material 2a may rise higher than the pressure in the main storage tank 1.
• Figure 2 shows an arrangement in which the apparatus according to Figure 1 is connected to an ammonia consumer system 200, specifically to the exhaust line 9 of a combustion engine 7.
• the system further comprises a buffer volume 5 between the main storage tank 1 and the dosing valve 6.
• This buffer volume 5 may increase the ability to dose high but short peak flows and also increases the controllability of the system.
• the released ammonia is led from the exhaust line 9 into a catalyst 8 where selective catalytic reduction of NO x with ammonia as the reductant is carried out.
• the system according to Fig. 2 shows the implementation of the invention for on-board ammonia storage and delivery for automotive NO x after treatment.
• Figure 3 shows an arrangement in which the apparatus according to Figure 2 further comprises an absorbing unit 13 having an insulation layer/shell 4c.
• This absorbing unit 13 is connected to the tube 20 leading form the main storage tank 1 to the buffer container 5 via a control valve 14.
• the two main aspects of the inventive apparatus relate to
• Figure 4 shows the temperature (thin-line curves) and pressure (thick-line curves) development of an ammonia storage unit according to the prior art which is thermally insulated (corresponding to approximately 7 cm rockwool) without a second ammonia storage material wherein an ammonia generating material in the unit is initially at a temperature of 25°C and then exposed to external temperatures of 40, 60, 80 and 100 0 C (T ext ). Particularly in the cases of 60, 80 and 100 0 C the storage unit shows a significant increase in temperature (thin-line curves); after 5 hours the temperatures are in the interval of 45 to 80 0 C. The associated pressure is shown in the thick-line curves.
• Figure 5 shows the pressure (thin-line curve) development of an ammonia storage apparatus 100, 100' according to Figures 1 and 2 upon exposure to 60 0 C (external temperature; T ex t) wherein the first storage/delivery unit (main storage tank 1 ) containing ammonia generating material which is thermally insulated (corresponding to approximately 7 cm rockwool) is in fluid communication with a smaller second storage/delivery unit (storage chamber 2; not insulated) holding 500 g of MgCI 2 .
• the thick-line curve in Figure 5 is identical to the pressure curve at 60 0 C in Figure 4, i.e. corresponds to the same prior art without a second ammonia storage material. In this case the pressure reaches more than 2 bars after 5 hours.
• Figure 6 is similar to Figure 5, except that the apparatus 100, 100' is exposed to an external temperature of 80 0 C.
• the unit according to the prior art without a second ammonia storage material reaches a pressure of almost 4.5 bars after 5 hours, whereas the pressure in the system with an apparatus 100, 100' according to Figures 1 and 2 (thin-line curve) stays below 0.26 bar.
• Figure 7 shows the temperature (solid and dashed thick-line curves) and pressure (solid and dashed thin-line curves) development of a unit of the prior art with an ammonia generating material (dashed curves) and of Figures 1 and 2 (solid curves);
• the first ammonia storage material (1a) is a material generating ammonia irreversibly;
• the second ammonia storage material 2a is MgCI 2 both having an initial temperature of 55°C and an initial vapour pressure of 2.5 bars (a pressure which may be suitable for introducing ammonia into an exhaust line 9 of a motor vehicle slightly upstream of an NO x reducing catalyst 8) after having been in operation for 1 hour. The operation is then terminated, and the system is left in its natural environment.
• the fluid communication between the second storage/delivery unit 2 containing the ammonia ad- or absorbing material and the main system (the system other than the storage/delivery unit 2) for generating ammonia can be established (and optionally interrupted and re-established) can be established for the whole main system or only for a part or several parts of the main system, e.g. a part where decomposition products of the first ammonia generating material are present.
• an ammonia storage and delivery system will remain at a level between the vapour pressure of the first storage/delivery unit (main storage tank 1) containing material 1a which generates ammonia irreversibly or the whole or a part of the main system and the second, usually smaller storage/delivery unit (storage chamber 2) containing material 2a having a low ammonia pressure when the main tank 1 or the whole or part of the main system and the storage chamber 2 are in fluid communication.
• the present method and system may be used in all mobile or portable systems comprising a catalyst for the selectively catalytic reduction of NO x , in fuel cells or in systems comprising a catalyst for splitting ammonia into nitrogen and hydrogen or in combination with other ammonia-consuming processes where the safe use of volatile materials generating ammonia irreversibly is required.

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• 2007
  • 2007-12-21 EP EP07857087A patent/EP2109493A1/de not_active Withdrawn
  • 2007-12-21 WO PCT/EP2007/011380 patent/WO2008092500A1/en active Application Filing

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