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
  • B01D53/46—Removing components of defined structure
  • B01D53/54—Nitrogen compounds
  • B01D53/56—Nitrogen oxides
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
  • F02B2275/00—Other engines, components or details, not provided for in other groups of this subclass
  • F02B2275/14—Direct injection into combustion chamber
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
  • F02B3/00—Engines characterised by air compression and subsequent fuel addition
  • F02B3/06—Engines characterised by air compression and subsequent fuel addition with compression ignition
• • 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
  • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
  • Y02C20/00—Capture or disposal of greenhouse gases
  • Y02C20/10—Capture or disposal of greenhouse gases of nitrous oxide (N2O)

Definitions

• the present invention relates to the removal of nitrogen oxides or "NO ⁇ .” from exhaust gases and the like, and more particularly to a process and apparatus utilizing particles of cyanuric acid or a liquid-cyanuric acid slurry.
• N0 ⁇ " is a family of compounds of nitrogen and oxygen, primarily NO and N0 2 .
• NO ⁇ comes from a variety of sources, most notably cars, trucks and industrial plants. Specifically, NO ⁇ is produced by high temperature combustion systems, metal cleaning processes, and the production of fertilizers, explosives, nitric acid, sulfuric acid and the like. In many urban environments, automobiles and diesel engine trucks are the major sources of N0 ⁇ . NO is the stable oxide of nitrogen at combustion temperatures. Hence, it is more abundantly produced than N0 2 . However, at ambient conditions, the equilibrium between NO and N0 2 favors N0 2 . Therefore, the effective control of N0 ⁇ concerns both the control and removal of both NO and N0 2 from exhaust gas streams from sources such as those mentioned above.
• N0 ⁇ has been made to control the generation or release of N0 ⁇ .
• Many known strategies involve the control of combustion conditions. This can be accomplished by reducing the temperature and amount of oxygen present during the combustion process. Another strategy is a reburning process. In this process, NO ⁇ compounds are incinerated in a secondary combustion zone, using particular fuels which do not contain nitrogen. Another strategy is removal of N0 ⁇ from the post-combustion gas or exhaust stream.
• Another strategy for removing NO ⁇ from gas streams is the reduction of NO ⁇ to nitrogen and water.
• the prior art teaches catalytic and non-catalytic processes. In the non-catalytic processes, high temperatures typically are required. In the catalytic processes, problems are encountered when exposing the catalyst to the exhaust gas stream. The catalyst is subject to fouling, poisoning and disintegration. These shortcomings tend to make the catalytic processes taught by the prior art expensive, unreliable and potentially hazardous.
• HNCO also known as isocyanic acid
• isocyanic acid is an unstable gas at ordinary temperatures and pressures, and thus is hard to handle and store. This problem has been addressed by generating HNCO from more stable, less toxic materials as it is used.
• One such material is cyanuric acid. Cyanuric acid decomposes when heated, forming HNCO. The gaseous HNCO is then injected into the gas stream where the HNCO is thermally decomposed and the NO ⁇ reduction reaction takes place, providing that the temperature is high enough to allow the reaction to proceed.
• the conversion of cyanuric acid to HNCO and the NO ⁇ reduction take place at relatively high temperatures, such as 1200 to 2600°F (649 to 1427°C), and sometimes can require a catalyst.
• the isocyanic acid process has a significant practical problem that limits its applicability.
• This process requires an expensive and complicated system to meter and convert solid cyanuric acid into gaseous HNCO for subsequent injection into the exhaust.
• the complexity of the system required for these steps in general limits its ability to follow, for example, a power system's changing load or to operate under transient conditions, such as varying speed and/or load conditions.
• Practical treatment of the exhaust for NO ⁇ from fossil fueled power systems such as gas turbines and internal combustion engines typically requires inexpensive, simple, and low cost process(es). The failure of the isocyanic system to meet these criteria severely limits its commercial potential.
• the following system components likely to be required in an isocyanic acid system, contribute to its relative complexity, high cost and lack of operating reliability: air lock required to isolate the cyanuric acid powder fed/metered from a screw feeder to a sublimator or vaporizer; a sublimation chamber required to convert the cyanuric acid powder to a gas along with associated components such as electric heaters or heat exchangers to supply heat from the exhaust to the sublimation chamber; and a stirrer or the like to distribute the cyanuric power metered into the sublimator; a cracker to crack the gasified cyanuric acid from the sublimator to HNCO for injection into the exhaust for reaction with NO ⁇ ; and a complex, expensive control system required to operate and perform diagnostics on the above described system elements.
• the isocyanic acid process has been modified by carrying out the NO ⁇ reduction in the presence of carbon monoxide (CO) .
• CO carbon monoxide
• this process still operates at relatively high temperatures, such as 932 to 1472°F (500°C to 800°C), and often requires the use of a catalyst in the NO ⁇ -laden gas stream.
• the operating conditions for such a process such as high temperatures and appropriate concentrations of CO, typically are not found in a diesel exhaust gas stream (or in other combustion systems) under some conditions of operation. Either intermittent performance must be tolerated or the exhaust stream must be heated to maintain a high temperature, and in any event a catalyst may be required.
• the system complexity again limits the applicability of such processes.
• micron diameter granules (with a preferred diameter of 500 to 5,000 microns) of a compound selected from cyanuric acid, urea, ammonium sulphate, ammonium chloride, ammonium phosphate, ammonium carbonate and an organic compound having a nitrile group.
• Wada discloses use of reducing agent granule size as a means to reduce temperature control requirements of the reaction zone. Wada theorized that, if the granule size was large enough, a low temperature region would be created around the granule as the granule dropped through the exhaust gas. Over time, the region around the granule is heated by the exhaust gas until it reaches the unspecified optimum temperature for reduction efficiency.
• the exhaust gas temperature is specified to be 600 - 1500°C, or 1200 - 1500°C.
• the present invention provides a process and apparatus that are reduced in complexity over the isocyanic acid process previously described, which is a result in part of the elimination and/or replacement of several undesirable components, while also providing significant improvements and advantages over the process disclosed in Wada.
• direct injection of particles of cyanuric acid is utilized, which results in a more efficient NO ⁇ reduction process based on the specific mass of cyanuric acid required to reduce NO ⁇ (Lbs. cyanuric acid/Lb. NO ⁇ ) .
• This performance benefit results at least in part from the generation of HNCO or other decomposition products from cyanuric acid in-situ, which minimizes their decomposition and/or oxidation by reducing the time they are exposed to the reactor's hot oxidizing gases before reaction with N0 ⁇ .
• a venturi is utilized to controllably convey cyanuric acid particles into the NO ⁇ -containing exhaust stream.
• Control over the reaction conditions with supplemental fuel injection and oxidation, which also provide oxidation reaction products, as well as over parameters such as temperature, gas composition and reducing agent residence time, provide additional benefits, while yielding a low- cost yet effective NO ⁇ reduction process and apparatus, which may be used to reduce N0 ⁇ produced by diesel or other internal combustion engines, boilers, turbines or other industrial processes that generate NO ⁇ -containing gas streams.
• a liquid-cyanuric acid slurry is utilized to deliver cyanuric acid and/or decomposition products into the NO ⁇ - containing exhaust stream.
• the slurry may be formed by adding solid cyanuric acid to a suitable liquid such as water or a fuel such as diesel fuel.
• the liquid-cyanuric acid slurry may be heated prior to injection into the NO ⁇ - containing exhaust stream, which can serve to "dry" the cyanuric acid and thereby reduce the residence time within the reaction chamber required for optimum N0 ⁇ reduction and/or reduce the size requirements of the reaction chamber.
• the slurry may be heated or catalyzed in a manner so as to produce decomposition products including reactive species such as free radicals, which are subsequently injected into the NO ⁇ -containing exhaust stream and result in a reduction of the NOx, which may occur at a reduced temperature.
• Use of a liquid-cyanuric acid slurry can provide benefits such as improved metering consistency of the reducing agent into the exhaust stream, and less sensitivity to the physical quality and/or particle size of the cyanuric acid.
• FIG. 1 is a diagram illustrating an embodiment of the present invention in which particles of cyanuric acid are contacted with the NO ⁇ -containing exhaust gas;
• FIG. 2 is a diagram illustrating an embodiment of the present invention in which a liquid-cyanuric acid slurry is utilized to contact cyanuric acid and/or decomposition products with the NO ⁇ -containing exhaust gas;
• FIG. 3 is a diagram illustrating an embodiment of the present invention in which a liquid-cyanuric acid slurry is heated and/or catalyzed to produce decomposition products, which are contacted with the NO ⁇ -containing exhaust gas.
• cyanuric acid powder 14 is placed in vessel 12 through opening 10. Cyanuric acid powder 14 provides a supply of cyanuric acid for the N0 ⁇ removal process of the present invention.
• Screw feeder 16 controllably conveys cyanuric acid powder (now denoted by arrow 20) down conduit 18.
• Conduit 18 connects to venturi 24, which, along with compressed air 22 (or other appropriate transport gas) , fluidize the cyanuric acid and convey the cyanuric acid particles through conduit 26 into the NO ⁇ -containing exhaust gas, as indicated by cyanuric acid particles 36 in exhaust pipe 38.
• Venturi 24, compressed air 22 and conduit 26 provide a controllable mechanism to deliver cyanuric acid power 36 to the N0 ⁇ containing exhaust gas (denoted as N0 ⁇ exhaust 34 in FIG. 1) .
• the transport gas supplied to venturi 24 may be any suitable gas under pressure that when conveyed into the exhaust gas stream (along with the cyanuric acid and supplemental fuel) does not inhibit the NO ⁇ reduction reaction or produce undesirable reactions or species.
• the rate at which the cyanuric acid is supplied into the exhaust stream will vary depending upon the concentration of the NO ⁇ in the exhaust gas and the overall reaction conditions in the particular application. In the preferred embodiment, the cyanuric acid is supplied at a rate so as to provide approximately stoichiometric quantities of HNCO and N0 ⁇ .
• Supplemental fuel supply 28 is connected to pump
• Supplemental fuel is conveyed by pump 30 through conduit 32.
• Conduit 32 connects to exhaust pipe 38 at a point upstream from where conduit 26 connects to exhaust pipe 38.
• Pump 30 provides a controllable mechanism to provide appropriate amounts of supplemental fuel from supplemental fuel supply 28 for optimum NO ⁇ reduction.
• supplemental fuel is supplied at a rate to maintain the temperature in reaction chamber 40 at approximately 1310 °F.
• supplemental fuel, cyanuric acid particles and the NO ⁇ -containing exhaust gas are conveyed to in-line exhaust reaction chamber 40. Reaction chamber 40 is heated by the oxidation of the supplemental fuel, which provides heat and fuel-oxidation reaction products.
• reaction chamber 40 gasification and cracking of the cyanuric acid occurs, leading to reactions of the resultant HNCO and/or other decomposition products such as NCO with the N0 ⁇ , resulting in a consumption of the decomposition products and a reduction of the N0 ⁇ in the exhaust gas.
• one possible reaction is (HNC0) 3 ⁇ 3NC0 + 3/2 H 2 , with the NCO reacting with NO to form N 2 and C0 2 .
• Exhaust gas with reduced N0 ⁇ is discharged from outlet 44.
• Reactor temperature is controlled to minimize supplemental fuel consumption (by controlling the supply of supplemental f el to the minimum amount to maintain the reactor temperature in an optimum range for the N0 ⁇ reaction) and N 2 0 formation (N 2 0 is known as a green-house gas and generally is favored at high temperatures) , while optimizing the conversion efficiency of cyanuric acid to HNCO or other decomposition products such as NCO.
• This embodiment of the present invention has achieved reaction of NO ⁇ with HNCO and/or other decomposition products to give over 95% N0 ⁇ reduction efficiencies, while achieving low absolute levels of N0 ⁇ under conditions substantially as set forth in Example No. 1.
• the process of this embodiment of the present invention balances reaction parameters (including residence time and temperature) such that an acceptable range of cyanuric acid particle sizes may be utilized with the present invention.
• reaction parameters including residence time and temperature
• cyanuric powders can be used in this process of the present invention with optimized heat transfer for conversion of the cyanuric acid particles to HNCO or other decomposition products at acceptably low temperatures.
• the injection, decomposition, and oxidation of the supplemental fuel is believed to produce chemical species and heat that serve to drive, and lower the optimum temperature for, the reaction of HNCO and/or other decomposition products with NO ⁇ .
• Part of the improved efficiency of this embodiment is believed to result from the conditions produced in the reaction chamber, which allow prompt reaction of the HNCO and/or other decomposition products with the NO ⁇ since such decomposition products are generated in-situ, while minimizing the time available for oxidation by the exhaust gas.
• the design of the reactor can readily be optimized for fluid dynamics and exhaust back pressure to give the most desirable residence times, chemistry and mixing through control and/or optimization of length/diameter ratio(s) and total volume(s) for a specific exhaust flow.
• the cyanuric acid particles in reaction chamber 40 have a preferred residence time of 0.5 seconds, with a range of 0.1-1.0 seconds. With the temperatures and other parameters controlled as disclosed herein, such residence times minimize the temperature required for conversion of cyanuric acid to decomposition products, and for their subsequent reaction with NO ⁇ .
• reaction chamber residence time(s) and temperature(s) have permitted the selection and use of practical, commercially available cyanuric acid powders.
• the particle size(s) selected provide(s) sufficient heat transfer to allow full conversion of the cyanuric acid powder to decomposition products (at the cited residence times and temperatures) , while minimizing N 2 0 formation, oxidation losses and solid particle emissions into the air.
• Cyanuric acid particles outside the selected range are believed to have a higher potential of being emitted into the air from the exhaust stream, since larger particles do not have sufficient heat transfer to be converted to a gas, and smaller particles may have a reduced residence time in reaction chamber 40.
• the cyanuric acid particles are ground in-situ before injection into the exhaust gas. In-situ grinding of the cyanuric acid powder extends the initial useful particle size range to on the order of 25,400-75,200 microns in diameter (before grinding) , which renders the acid easier to transport, while allowing appropriately sized particles to be fed into the injection venturi.
• Control of the injection, decomposition, and oxidation of the supplemental fuel in reaction chamber 40 contributes to the efficiency and controllability of the NO ⁇ -reduction process of this embodiment of the present invention.
• Oxidation of the supplemental fuel generates heat, which provides a means for controlling the temperature in reaction chamber 40 to the optimum level for the particular cyanuric acid particle size, residence time and other reaction conditions for the particular application.
• chemical species produced in reaction chamber 40 by the oxidation of the supplemental fuel assist in the initiation of the N0 ⁇ reduction reaction(s) at acceptable temperatures and/or assist in driving the reaction(s) towards completion while avoiding unacceptable side reactions.
• Injection of the supplemental fuel in a manner to avoid complete mixing and/or atomization of the supplemental fuel before entering reaction chamber 40 is believed to create a stratified mixture, which oxidizes and/or cracks more slowly, and thereby producing active chemical species as fuel-oxidation by-products in a more controlled manner as opposed to rapid combustion that would create unacceptably high temperatures favoring N 2 0 formation and decomposition product oxidation.
• supplemental fuel may be delivered to reaction chamber 40 in a variety of ways, such as be spraying or high/low pressure injection, better results have been obtained by supplying the supplemental fuel through low pressure injection, which is believed to contribute to more stratified conditions in reaction chamber 40.
• Supplemental fuel supply 28 may be any suitable fuel such as diesel fuel, natural gas, propane or methanol, and in the preferred embodiment is diesel fuel.
• the fuel may be combusted in a burner (not shown) outside the exhaust, with the resulting hot combustion gases injected into the exhaust gas.
• Reaction chamber 40 is of appropriate design and construction to produce good mixing, reduced flow velocity (thereby allowing a reasonably determinable increase in the residence times of the cyanuric acid particles) , and the reactive species produced by the oxidation of the supplemental fuel which facilitates the N0 ⁇ reduction reaction(s) .
• the preferred length/diameter ratio and total volume for a specific flow is approximately 5.5 1/d at a ratio of reactor volume (158 ft 3 ) of approximately 0.044 ft 3 reactor volume/ft/minute exhaust flow (3600 dscf ) with a range of 4.0-6.5 1/d and .034-.054 ft 3 reactor volume/ft 3 /minute exhaust flow (dscfm) .
• a reactor of such properties has been found to provide acceptable optimization of the 1/d ratio while permitting additional mechanical control of the gas velocity flowing through the reactor using butterfly valves or other flow control systems known in the art.
• Control of gas-flow velocity can be achieved by a suitable feed-back control system using sensors and a preprogrammed microprocessor or the like to define the optimum reaction conditions for the particular application, including an appropriate balance of parameters such as temperature, cyanuric acid particle size, residence time and gas composition for the particular application.
• a suitable simplified feed-back control system made possible by the simplicity of the direct injection system of this embodiment of the present invention, can be used for ready control of the supply of cyanuric acid powder needed to react with N0 ⁇ in reaction chamber 40 as well as the temperature and reaction conditions in reaction chamber 40.
• the control system may also monitor the overall performance of the system, and conduct appropriate diagnostic checks to avoid system failures.
• FIGS. 2 and 3 embodiments of the present invention utilizing a liquid-cyanuric acid slurry will now be described.
• a liquid-cyanuric acid slurry 50 is produced in vessel 51.
• the liquid used to produce slurry 50 may be any suitable liquid for serving as a medium in which cyanuric acid may be controllably delivered from vessel 51 to. the NO ⁇ -containing exhaust gas, with or without heating and/or catalyzation (as discussed more fully below with reference to FIG. 3) .
• the liquid used to produce slurry 50 is water or a suitable fuel such as diesel fuel.
• Other liquids that may be utilized to produce slurry 50 are alcohols, organic acids and other liquids that do not adversely affect the NO ⁇ reduction reaction(s) or result in undesirable species. Cyanuric acid in granular or other solid form is added to the liquid in controlled amounts to form slurry 50.
• Agitator 52 is positioned within vessel 51 to provide agitation or stirring of slurry 50.
• Agitator 52 can be any suitable device for agitating or stirring slurry 50, and in preferred embodiments consists of an electric motor driving a shaft on which is attached one or more multi-blade propellers.
• slurry 50 is agitated on a substantially continuous basis. Production of an agitated slurry offers certain advantages, including decreased sensitivity to the physical quality and/or particle size of the input cyanuric acid.
• the agitation of the cyanuric acid in slurry 50 by agitator 52 effectively provides a conditioning of the cyanuric acid prior to subsequent processing and/or delivery into the NO ⁇ -containing exhaust gas.
• Agitation in slurry 50 is believed to generate shear forces and/or collisions that physically break the cyanuric acid into small pieces or particles.
• the agitation conditions within vessel 51 enable the physical transformation of the cyanuric acid, which can be optimized for subsequent processing (i.e., such as reduced "drying time,” discussed below). While the desired particle sizes in slurry 50 will depend upon the particular conditions, agitation so as to produce cyanuric acid particles up to a range of about 50 to 200 microns is believed to provide acceptable results.
• the concentration of the cyanuric acid in slurry 50 may be any suitable concentration, and in preferred embodiments is up to concentrations of 20 to 60% or even higher.
• Slurry 50 is controllably pumped from vessel 51 by pump 31.
• Pump 31 may be any suitable pump, and in preferred embodiments is a gear rotor pump driven by a variable speed electric motor.
• the rate at which slurry 50 is pumped from vessel 51 by pump 31 will depend upon the particular operating parameters and exhaust gas characteristics and the like.
• the exhaust gas from a one megawatt power output diesel engine may be treated with a diesel fuel-cyanuric acid slurry (approximately 28% by weight cyanuric acid) pumped at a rate of approximately 90 pounds per hour.
• Slurry 50 may be pumped by pump 31 directly into exhaust pipe 38, or optionally slurry 50 may be heated by heater 54.
• Heater 54 may be any suitable source of heat for heating slurry 50, and in preferred embodiments constitutes a heat exchanger deriving heat from exhaust pipe 38 or reaction chamber 40, or alternatively an external heat source powered by electrical or chemical fuel means. Because the cyanuric acid is "wet" when delivered from slurry 50, the cyanuric acid typically must be “dried” prior to decomposition for the N0 ⁇ reduction reaction(s) . The drying of the cyanuric acid may be achieved in-situ by allowing for longer residence times of the cyanuric acid in reaction chamber 40, or alternatively the temperature within reaction chamber 40 may be appropriately increased.
• heating such as by heater 54 prior to contacting with the exhaust gas may be utilized.
• Heating of slurry 50 by heater 54 serves to accelerate the "drying" and subsequent decomposition of the cyanuric acid.
• heater 54 may heat slurry 50 to the point that slurry 50 "flashes” or decomposes very rapidly in the reaction chamber enabling low residence times for the N0 ⁇ reduction reaction(s) .
• decomposition of the cyanuric acid may take place in reaction chamber 40, or, in alternative embodiments, thermal or catalytic decomposition of the cyanuric acid may be obtained prior to delivery into exhaust pipe 38 or reaction chamber 40.
• the characteristics of heater 54 will depend upon the particular operating parameters and slurry and exhaust gas characteristics and the like.
• the liquid selected for slurry 50 is an important consideration. For example, when the liquid for slurry 50 is a fuel such as diesel fuel, slurry 50 should be heated only to modest levels prior to contacting with the exhaust gas, such as 200-400°F, in that heating to higher temperatures may result in carboning of the fuel. When the liquid for slurry 50 is a stable liquid such as water, however, slurry 50 may be heated to substantially higher temperatures. With appropriate liquids such as water, slurry 50 may be heated to the point that gasification of the liquid and/or the cyanuric acid occurs, such as up to 500-600°F. Alternatively, and as explained in more detail with reference to FIG.
• slurry 50 may be heated to the point that decomposition products are produced from slurry 50 (such as up to 800-1200°F to produce HNCO, and up to 1200-1700°F or higher to decompose the HNCO) , with the decomposition products delivered into exhaust pipe 38 for reaction with NO ⁇ in the exhaust gas.
• decomposition products such as up to 800-1200°F to produce HNCO, and up to 1200-1700°F or higher to decompose the HNCO
• Supplemental fuel from supplemental fuel supply 28 is controllably conveyed by pump 30 to exhaust pipe 38.
• the presence and/or rate of supply of a supplemental fuel will depend upon the particular operating parameters and slurry and exhaust gas characteristics and the like. For example, if the liquid for slurry 50 is a fuel such as diesel fuel, little or no supplemental fuel may be required to maintain appropriate conditions for the NO ⁇ -reduction reaction(s) .
• the use of supplement fuel supply 28 to provide control reaction conditions such as temperature including candidate fuels have been discussed previously with respect to FIG. 1 and will not be further discussed here (it is noted, however, that with the decomposition product embodiments discussed below, the N0 ⁇ reduction reactions may occur at a lower temperature and therefore require less or no supplemental fuel) .
• reaction chamber 40 one or more reactions occur between the cyanuric acid and/or decomposition products such as NCO and the N0 ⁇ , resulting in a reduction of the N0 ⁇ in the exhaust gas.
• Temperatures within reaction chamber 40 for optimum NO ⁇ reduction with embodiments in which cyanuric acid is injected into the exhaust gas are similar to the embodiment of FIG. 1, although the temperature may optimally be increased somewhat in order to allow for sufficient "drying" and subsequent reaction of the cyanuric acid.
• Exhaust gas with reduced NO ⁇ is discharged from outlet 44.
• slurry 50 (with or without prior heating) is injected into exhaust pipe 38 or reaction chamber 40 by way of an atomizing nozzle (not shown) , which will serve to accelerate the evaporation of the liquid from the slurry and thus the subsequent decomposition and reaction in reaction chamber 40.
• Embodiments discussed with reference to FIG. 3 are particularly useful with stable liquids such as water used to produce slurry 50.
• Slurry 50 is produced in vessel 51 and is agitated by agitator 52 in a manner analogous to slurry 50 of FIG. 2.
• Pump 31 controllably conveys slurry 50 to heater 54 for heating.
• Heater 54 heats slurry 50 to produce decomposition products including reactive species such as free radicals.
• Heater 54 may heat slurry 50 up to about 500-600°F to gasify the cyanuric acid, and up to 800-1200°F to produce HNCO, and up to 1200-1700*F or higher to produce further decomposition products.
• Decomposition products from heater 54 may be delivered from heater 54 into exhaust pipe 38 by conduit 56.
• radicals such as NCO, H and NH 2 may be formed as decomposition products of the cyanuric acid, with, for example, the NCO radicals reacting with NO to form N 2 and C0 2 , with such reactions able to occur at reduced temperatures of about 750-850°F.
• the output of heater 54 which may or may not contain decomposition products, is conveyed to catalyst chamber 58.
• Catalyst chamber 58 produces decomposition products, including reactive species such as free radicals.
• Decomposition products from catalyst chamber 58 are delivered into exhaust pipe 38.
• radicals such as NCO, H and NH 2 may be formed as decomposition products of the cyanuric acid, with, for example, the NCO radicals reacting with NO to form N 2 and C0 2 , with such reactions able to occur at reduced temperatures of about 750-850°F.
• heater 54 and catalyst chamber 58 may be combined so that heating and catalytic decomposition of the cyanuric acid occur substantially in a single step, although such may be achieved through a "staged process;" for example, the cyanuric acid may be gasified and/or cracked to produce HNCO at temperatures of about 800-1200°F, while catalytic decomposition may occur at temperatures of about 750-850°F. As needed, the temperature of the gaseous HNCO may be reduced in a conventional manner prior to contact with the decomposition catalyst.
• slurry 50 may be heated to sufficient levels and/or catalyzed so as to result in decomposition of the cyanuric acid to produce decomposition products that may react with the N0 ⁇ at reduced temperatures.
• Water for example, has substantial thermal stability and does not produce hazardous by-products.
• the cyanuric acid is thermally or catalytically decomposed to form free radicals
• water has beneficial properties in that with water it is believed that no free oxygen is available to scavenge or quench the free radicals and thereby reduce the efficiency of the overall process.
• Catalyst chamber 58 contains a suitable catalytic material for producing decomposition products useful for reducing N0 ⁇ in an exhaust gas.
• catalysts for use in catalyst chamber 58 may be zirconium, phosphorous and mixtures thereof, which may include zirconium and/or phosphorous in the plus four oxidation state, such as are disclosed in U.S. Patent No. 5,087,431 issued February 11, 1992 to Gardner-Chavis, et al. for "Catalytic Decomposition of Cyanuric Acid and Use of Product to Reduce Nitrogen Oxide Emissions.
• catalysts are useful in the present invention, and other possible catalysts may include A1 2 0 3 , Ti0 2 , cordierite, MgO, zeolites, V 2 0 5 , Pt, Pd, CeO, iron oxide, chromium oxide, NiO and combinations thereof. While the optimum temperature for catalytic decomposition will depend upon the particular catalysts, etc., catalytic decomposition temperatures of 750-850°F are believed to provide acceptable results.
• the zirconium catalyst of the types which can be utilized in the present invention are commercially available and typically contain at least some zirconium in the plus four oxidation state.
• the catalyst may be commercially available mixed-metal oxide catalysts which contain at least some zirconium or phosphorus in the plus four oxidation state.
• An example of a commercial zirconium-containing catalyst useful in the method of this invention is the zirconia catalyst ZR-0304T1/8 available from the Engelhard Corporation.
• the catalyst utilized in the method of the present invention may be formed in any conventional manner such as tableting, pelleting, etc. , or the active catalyst material can be supported on a carrier.
• the carrier is generally inert and may include silica, alumina, clay, alumina-silica, silicon carbide, or even zirconia.
• the catalyst material may be deposited upon the carrier by techniques well known to those skilled in the art such as by depositing a solution containing the catalytic components on the carrier and thereafter drying and calcining the material. Utilizing these techniques, the catalytic components may be either coated and or impregnated in a carrier for use in catalyst chamber 58.
• Example No. 1 Example No. 1
• An embodiment of the present invention utilizing particles of cyanuric acid has been applied to a KTTA-50 G-3 heavy duty diesel engine manufactured by Cummins Engine Company, Inc. applied to a .95 megawatt generator set for power generation.
• a 94.5% reduction in NO ⁇ was obtained, under conditions as substantially set forth below.
• the present invention provides for simple, effective systems using essentially selective, non-catalytic reduction (SNR) process for the reduction of N0 ⁇ in exhaust gases from combustion-power systems or other industrial processes.
• SNR non-catalytic reduction
• the direct injection of particles of cyanuric acid eliminates the need for components such as air locks, sublimation chambers (and associated stirrers) , cyanuric acid crackers, and systems to exchange heat from the exhaust for transfer to the sublimation chamber likely to be required in isocyanic systems.
• the use of a liquid-cyanuric acid slurry offers improved metering consistency and less sensitivity to cyanuric acid quality, and in some embodiments a lower NO ⁇ reduction reaction temperature.
• the reduced complexity of systems in accordance with the present invention significantly reduces system response time and enhances the transient operating capability, improves reliability-durability through reduction of components and complexity, and gives a major reduction in system costs over prior art isocyanic acid processes.
• Over 95% reduction of N0 ⁇ has been demonstrated in the exhaust of large high speed heavy duty diesel engines.
• the present invention also provides a process and apparatus in which optimization and control of the parameters necessary to achieve efficient, maximum levels (up to 95% or more) of NO ⁇ reduction in exhaust gases can be readily achieved.
• reaction chamber design (residence time and mixing) ; reaction chamber temperature; cyanuric acid particle size or slurry concentration and/or delivery conditions; injection, decomposition, and controlled oxidation of supplemental fuel injected to maintain the reactor temperature and/or chemistry; optimized reaction chamber design for optimum fluid dynamics and back pressure and length/diameter vs. total volume/given flow; and a simple control system resulting from operational simplicity.

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• 1992
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