Patent Publication Number: US-2005129599-A1

Title: Ammonia storage and injection in NOx control

Description:
CROSS-REFERENCE  
      This is a continuation-in-part of Ser. No. 10/132,552 filed Apr. 24, 2002. 
    
    
     BACKGROUND OF THE INVENTION  
      In our earlier U.S. Pat. Nos. 5,224,346 and 5,992,141, we described experiments which showed that the amount of nitrogen oxides (NO and NO 2 ), or NOx in engine exhaust gasses can be reduced by injecting ammonia (NH 3 ) which reacts with nitrogen oxides to produce nitrogen and water. One practical problem is how to store ammonia that is to be injected into the exhaust gas stream. Ammonia can be stored as a liquid, at a pressure of about 150 psi, with the ammonia turning into gas when removed from the container and its pressure reduced. It is often undesirable to store ammonia under considerable pressure because of the danger of an explosion and the possibility of rapid leakage of ammonia. Another way for storing ammonia is to store it as urea (H 2  NCO NH 2 ) as in a solution with water, and inject it into the exhaust gas stream. However, it can take a longer time for urea to react with nitrogen oxides and turn them into nitrogen and water, than ammonia. Since the temperature of the exhaust gas stream very rapidly drops as the exhaust gasses move through the exhaust pipe into the atmosphere, it is desirable that the reactions occur very rapidly so they can occur at the high temperatures that exist in and near the exhaust gas manifold so that a high proportion of the injected material (ammonia or urea) can react with the nitrogen oxides. A system that enabled the storage of ammonia (NH 3 ) without requiring storage under high pressure, so that the ammonia could be directly injected into hot exhaust gasses and rapidly react with nitrogen oxides, would be of value.  
     SUMMARY OF THE INVENTION  
      In accordance with one embodiment of the present invention, a system is provided for storing and injecting ammonia into the exhaust gasses of an engine, which enables safe storage of the ammonia and the injection of ammonia into the exhaust gasses for rapid reaction with nitrogen oxides. The ammonia is stored as a liquid mixture of ammonia and water. The ammonia is preferably stored as a mixture of between 30 and 70 grams of ammonia per 100 grams of water. The liquid mixture is drawn off through a tube leading from the container. In one system, the tube is heated by the exhaust gasses and the mixture of ammonia and water is injected directly into the exhaust gasses.  
      The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a simplified schematic view of an engine, with pollution reduction apparatus of the present invention installed therein.  
       FIG. 2  is a graph showing variation of the saturation mass of ammonia in water as a function of temperature.  
       FIG. 3  is a graph similar to that of  FIG. 2 , but showing variation of the saturation percent (by mass) of ammonia in a mixture of ammonia and water, as a function of temperature.  
       FIG. 4  is an enlarged view of a portion of the system of  FIG. 1 , showing separation of a liquid mixture of ammonia and water into gaseous ammonia and water vapor.  
       FIG. 5  is a sectional-view showing a portion of the apparatus of  FIG. 2 .  
       FIG. 6  is a simplified schematic view of a system of another embodiment of the invention.  
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       FIG. 1  illustrates a system  10  of the present invention, wherein an engine  12  has cylinders in which fuel and air are combusted to turn a crankshaft  14 . The combustion produces hot exhaust gasses that are passed through an exhaust conduit  16  into the atmosphere. The exhaust conduit includes a manifold  20  that is connected to a few cylinders to collect the exhaust gasses therefrom. A catalytic convertor  22  that lies along the exhaust conduit, is widely used in vehicle engines to reduce pollution.  
       FIG. 1  shows an ammonia injection system  30  that includes a source  32  of ammonia. An injector apparatus  33  includes a metering valve  34 , tube  36  with tube portion  62 , and an injection nozzle at  40 . The metering valve  34  passes ammonia from the source through a tube  36  to an ammonia injection location  40  where ammonia is injected into the exhaust conduit  16  to mix with hot exhaust gasses. The location  40  lies in or close to the exhaust gas manifold  20 , so the ammonia encounters very hot exhaust gasses (usually over 1100° F. at high engine loads) to promote the reaction of ammonia and the exhaust gasses and thereby reduce nitrogen oxides.  
      In accordance with the present invention, the source  32  for ammonia is a container  50  that contains a mixture  70  of ammonia in water.  FIG. 2  includes a graph  52  showing the mass of ammonia, at saturation in a solution that contains 100 grams of water, at different temperatures.  FIG. 3  contains a similar graph  54  that shows the saturation percent, by mass, of ammonia in a solution of ammonia and water. It can be seen that the percent ammonia (by mass), ranges from about 47% at 32° F. through 33% ammonia at 72° F., down to 0% at 212° F. As a practical matter, applicant can vary the percent ammonia according to the weather, but prefers to establish about 25% ammonia, so the ammonia will not go out of the mixture unless the temperature of the mixture increases beyond about 105° F. Also, the container is kept away from the engine and is cooled by air, to avoid heating the container. If the container should be heated so that gaseous ammonia begins to accumulate under pressure and the pressure exceeds a certain limit (e.g. 2 psi), a relief valve  60  ( FIG. 1 ) will slowly vent the gaseous ammonia into the atmosphere. The rate of ammonia vented is very small, so it is not dangerous. A check valve  61  ( FIG. 1 ) can admit air to avoid a vacuum above the liquid when the liquid is withdrawn.  
      The tube  36  that carries the ammonia-water mixture has a portion  62  that is wrapped about the exhaust conduit  16 , to rapidly heat the ammonia-water mixture that passes through the tube  36  to the injection location  40 .  
       FIG. 4  indicates how the ammonia may be separated from the water at a separation station  68 , before injection of the ammonia into the exhaust conduit. Initially, the mixture  70  at a temperature such as 75° F. passes through the tube  36 , to the tube portion  62  that is in a heat-exchange relationship with the exhaust conduit, so material within the tube portion  62  is rapidly heated. With the initial percent of ammonia being about 25%, the ammonia is not released as a gas until the mixture reaches the location  72  which is at about 105° F. Progressively more ammonia is released as the temperature of the mixture progressively increases. At the location  74 , the mixture has a temperature of about 200° F., and only a few percent of ammonia remains in the mixture. The rest of the ammonia, indicated at  80 , continues along a tube end portion  82 , that carries the ammonia along a path  83  to an injector shown at  84  in  FIG. 4 . The injector can be of the type described in our earlier U.S. Pat. No. 5,992,141, which results in rapid heating of the gaseous ammonia prior to its injection into the very high temperature exhaust gasses, to activate the ammonia (break down some of the ammonia into its constituents) for injection into the exhaust gas stream.  
      The liquid  90  shown in  FIG. 4  which moves along a path  91 , contains only a very small percent of ammonia, and is disposed of. One way to dispose of it, indicated in  FIG. 1 , is to carry the liquid with a very small percent of ammonia along a tube  92  for injection at  94  into the exhaust pipe. The location  94  is a location where the temperature of the exhaust gasses have been reduced to perhaps 250° F., in which case the small quantity of injected water will evaporate and become part of the exhaust gas stream that is admitted into the atmosphere. It should be noted that small pumps may be located in the injection system  30  where pressure increases are required. In  FIG. 1 , the metering valve  34  is controlled by a circuit  100  that also controls a fuel injector  102  that injects fuel from a fuel line  104  into the engine cylinders. As discussed in my earlier U.S. Pat. No. 5,992,141, this varies the amount of ammonia in accordance with the load on the engine, to more effectively neutralize nitrogen oxides.  
       FIG. 6  illustrates a system  110  which includes a container  112  that contains the mixture  70  of ammonia (NH 3 ) and water (HO 2 ). Other ingredients can be added to the mixture  70 , but applicant prefers that most of the mixture be water and ammonia. The ammonia is required to reduce nitrogen oxides and the water is useful to retain the ammonia and is a liquid that is easily disposed of because of its benign characteristics. In the system  110  of  FIG. 6 , applicant passes the mixture  70 , which may have perhaps 25% ammonia by weight, and water, directly through a nozzle  84  that lies in the exhaust gas conduits  16 , at an upstream location near or in the exhaust manifold. This system has the disadvantage that water is injected with the ammonia into the hot exhaust gasses, and tends to cool the exhaust gasses more rapidly. However, the amount of water and ammonia is very small, so the cooling effect of the water is very small. This system also has the disadvantage that the ammonia is heated only moderately by the hot nozzle prior to injection into the exhaust gas stream, so only a low percent of the ammonia is activated to break down the ammonia into its components (NH 2  and NH) prior to injection. However, the simplicity of the system  110  can make it useful even if its effectiveness in reducing nitrogen oxides is not as great.  
      Thus, the invention provides a system for reducing nitrogen oxides in the exhaust gasses of an engine by the injection of ammonia into the exhaust gasses, which facilitates storage of the ammonia. The ammonia is stored as a mixture of ammonia and water (other liquids can be present), with the percent of ammonia preferably being between about 15% and 50% to avoid the generation of pressured ammonia gas. In one system, the mixture is heated to convert most of the ammonia into its gaseous state and separate it from the water that still remains liquid, and with the gaseous ammonia being further heated to activate at least a portion of it and then being injected into the hot exhaust gasses near or in the exhaust gas manifold. In a simpler system, the ammonia and water mixture  15  flowed towards the exhaust gas conduit and both ammonia and water are injected into the exhaust conduit.  
      Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art, and consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.