Patent Publication Number: US-2011048294-A1

Title: Particulate Deflagration Enhanced Firebox

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present invention is a continuation in part of U.S. patent application Ser. No. 12/196,372 for Particulate Deflagration Combustion Engine which was filed on Aug. 22, 2008 and is scheduled to issue as U.S. Pat. No. 7,784,435 on Aug. 31, 2010. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a particulate deflagration enhanced firebox for burning particulate fuel, such as corn starch or other suitable renewable energy source, either alone or in combination with other fuels, and the associated method. One of the many applications where this technology can be applied is in coal or gas fired power plants where the heat from the firebox is used to generate electricity. The invention includes a fuel feed system which delivers the powdered or particulate fuel to a mix drum, chamber or box where it is mixed with previously dried and compressed combustion air in a desired fuel to air ratio. The fuel mixture is then delivered to the firebox where it enters the combustion firebox or boiler either alone or in association with other fuels. Upon entering the firebox, the mixture undergoes deflagration and is burned. The hot combustion gases leave the firebox and are vented through the firebox&#39;s normal route which generally includes passing through a precipitator for remove particulates before exiting to atmosphere via a chimney stack. This invention employs either no traditional fuel or significantly less traditional fuel, such as coal. This invention results in more complete combustion of the fuels, less particulates and fly ash, and less air pollution in the form of nitrous oxide and sulfur emissions. 
     2. Description of the Related Art 
     It is long been known that fine solid particles, such as flour, can be a very volatile material under the proper conditions. The National Fire Protection Agency has established a volatility value to most common particulate fuels or dusts in the form of a Kst rating which is a deflagration index for dusts and is expressed as bars/millisecond. If methane is compared to corn starch under detonation conditions, the corn starch produces three times the energy force of the methane gas per unit volume. It has long been recognized that solid fuels are a more effective fuel source than gas which is why rockets are powered by solid fuel cells. 
     There are four factors that are needed to produce an explosion, whether in the combustion chamber of an engine or any other enclosure. They are a fuel source, an oxidant, a containment area, and an ignition source. In a simple combustion engine, the fuel source is vaporized liquid gasoline, the oxidant is air, the cylinder is the containment area, and the spark plug is the ignition source. The cylinder containment area is created collectively by the cylinder wall, the piston and cylinder head. 
     On the down stroke of the piston the inlet valve opens and allows the fuel and air mixture to enter the combustion chamber. As the piston returns to the top position, the inlet valve closes and the mixture is compressed. When the piston reaches the top of the stroke, the spark plug detonates the fuel causing the piston to be driven to the down position, turning a crank shaft and producing work force which has the discharge valves vent gas from the combustion chamber. 
     The combustion engine only requires the fuel source to produce the required energy to drive the shaft work force requirements and that the fuel burns fully and does not coat the valves, cylinder head or cylinder walls. Certain dusts or particulate fuel would burn cleanly and would produce very high energy levels when burned as fuel in a combustion engine. These particulate fuels would include cornstarch, soy flour, sucrose, coffee and wheat. Chemical particulate fuel such as ethylene diamine, ortazol, coal, charcoal and sodium lignosulfate would also be good fuel sources. 
     A standard combustion engine would, of course, require modifications to use dust fuel and to overcome challenges of burning fuels that the engine was not designed to burn. The first major challenge or modification that would be needed in a standard combustion engine would be in the delivery system of the fuel and air mixture to the combustion chamber. 
     The second major challenge or modification that would be needed would be in the means to control the increased heating of the combustion chamber. In a standard combustion engine, vaporized gasoline provides cooling to the combustion chamber during the down stroke of the piston. To offset this lost cooling, the particulate fuel mixture should be delivered at a pressure of 25 psig or greater to the combustion chamber where it will be allowed to expand. This expansion will cause a Joule-Thomson effect or a refrigeration effect due to the decrease in pressure of the fuel mixture as is moves from the storage system to the combustion chamber. 
     Under normal conditions, the fuel to air ratio would be between approximately 1-2 percent particulate fuel and between 98-99 percent compressed air. The mixing system must be able to suspend the particulate fuel particles in the air mixture until the spark is delivered to the combustion chamber. During acceleration, the engine would require more power and the fuel to air ratio would increase to as much as 5-7 percent particulate fuel and 93-95 percent air. This makes the engine very efficient. It is estimated that a four cylinder car could travel 100 miles at 65 miles an hour on a single pound of particulate cornstarch fuel. Because of the very low LFL (lower flame level) or low ignition point of cornstarch, there would be nearly complete burning of the fuel, with very little material to collect on the moving surfaces of the combustion chamber or valves. This clean burning fuel would eliminate most waste bi-products from the engine exhaust. 
     Particulate fuel is a truly renewable fuel source that requires very little refining and processing. The fuel is readily available and safe to store and transport because it is only volatile once the four elements required for detonation are present, i.e. fuel, oxidizer, containment, and ignition. The use of particulate fuel as a fuel source could be expanded to use in heating homes, in producing electricity and in space travel. The knowledge and technology for such uses is available now. 
     The term “detonation” means a loud, violent explosion. Thus detonation is not desirable in a combustion engine. Detonation can cause major damage to an engine. The proper term for the method of combustion would be “deflagration” which is burning fuel at a rate below sonic velocity. Deflagration is the desired type of combustion of the present invention. By controlling the fuel mixture and limiting the size of the combustion chamber, detonation would be unlikely under normal conditions for a combustion engine of the present invention. It is also important to control the size of the particulate fuel particle to achieve uniform and clean burning. The smaller the particulate fuel particle, the faster the deflagration occurs. Thus it is important that the fuel be reduced to the proper particle size before use in the present invention. A particle size of between 8-12 microns is preferred. 
     It is also important in the engine of the present invention to control the quality of the incoming air. If the air contains too much moisture, the fuel mixture will burn too slowly or will not burn at all and will not produce the discharge energy required. By feeding the inlet air through desiccant dryers, a moisture level in the combustion air can be maintained at a minimum level of −10 degrees pressure dew point. To achieve this level of moisture reduction in the combustion air, the system would use two dryers. One dryer would provide combustion air to the compressor, while the second dryer would be purging the water vapor it had collected. The purging dryer would be under a slight vacuum produced by a venturi created in association with the exhaust stack of the engine. The dryers would alternate every few minutes so that a fresh purging dryer would always be supplying the dried air to the mixing chamber where the air would be mixed with the fuel. 
     To increase lubrication to the cylinder wall, a small amount of graphite particles could be added to the fuel mixture. It is believed that a graphite level of 0.01 percent would not retard the combustion rate and would provide the needed lubrication. 
     Because the present engine uses renewable resources as its fuel source, it can offer an endless source of clean, efficient energy for many generations to come. 
     Although some prior art patents suggest the desirability of burning renewable fuels, the prior art patents do not address how the fuel would be delivered to the combustion chamber so that the engine operates efficiently on these fuels, i.e. preparing the fuel to the proper particle size and moisture content and mixing or atomizing it with oxidant. Operating an internal combustion or turbine on organic particles requires a high degree of control of the fuel which is not taught in the prior art. If moisture is not adequately controlled, the engine might only function when the relative humidity is very low. If the fuel to air ratio is not proper, then there is incomplete burning or there is detonation. 
     Another key component to a successful organic fuel-burning engine is to maintain and control the burning speed of the fuel. The engine must operate under “deflagration” conditions. If burning speed exceeds subsonic velocity, then detonation occurs which will severally damage the engine. There are five elements that must be controlled in order to control the burning speed of the fuel. These elements are particle size of the fuel, pressure dew point of the combustion air, fuel to air mixture ratio, containment area, and ignition source. The present invention controls all five elements for successful operation. 
     The pre-burn preparation of the fuel and the pre-ignition mixing of the proper fuel to air ratio of the fuel and air mixture that enters the combustion chamber are mandatory for successful operation of a particulate combustion engine. The prior art attempts to combine the particulate fuel and air in the combustion chamber and this leads to incomplete mixing and failure to achieve the crucial uniform particle suspension of the fuel mixture prior to combustion. If particle suspension does not occur before combustion, then only a portion of the fuel will be burned. The unspent or unburned fuel will then coat the combustion chamber and greatly damage the engine, resulting in further reduction in engine performance and a greater likelihood of detonation of the fuel. 
     The present invention pre-mixes the fuel air ratio before it enters the combustion chamber. The invention employs an infrared sensor that monitors the combustion chamber for fuel density and flame speed of the deflagration before and during the combustion phase. If the burn speed nears sonic velocity the fuel mixture ratio changes to retard the burn speed. This system allows for total consumption of the fuel and prevents unburned fuel from damaging the engine. Oxygen and dew point sensors insure that the combustion air quality entering the pre-combustion mixing chamber remains within the proper range. 
     Obviously, because each fuel has a different Kst value, the delivery system would need to be adjusted for a new fuel should the type of fuel employed in the invention be changed. 
     The history of using coal dates back to the 1800&#39;s. The earliest power plants used hand fed wood or coal to heat a boiler and produce steam. This steam was used in reciprocation steam engines which turned a generator to produce electricity. In 1884, the more efficient high speed steam turbine was developed by British engineer Charles A. Parsons which replaced the use of steam engines to generate electricity. 
     Later in the 1920&#39;s pulverized coal firing was developed. This process brought advantages that included a higher combustion temperature, improved thermal efficiency and a lower requirement for excess air for combustion. In the 1940&#39;s the cyclone furnace was developed. This new technology allowed the combustion of poorer grades of coal with less ash production and greater overall efficiency. Presently, coal power is still based on the same methods started over 100 years ago, but improvements in all areas have brought coal generated power to be the inexpensive power source used so widely today. 
     In some cases new technology brings new challenges. This is the case of the invention of the coal pulverizer. In the process of pulverizing the coal, dust is generated which is volatile under certain conditions. All dust is explosive under the right condition. The National Fire Protection Agency (NFPA) has established a volatility value of most common dusts in the form of a Kst rating. A comparison of methane gas to corn starch under detonation conditions shows the corn starch produces 3 times the energy force of the methane gas per volume. 
     Many coal fired power plants have incorporated a dust collection system. This system normal has a bag house, were the dust is filtered through a sock filter. The bag house should have explosion vents incorporated in the design. The explosion vents open during the deflagration stage of the explosion. There are 4 elements required for an explosion to occur. They are fuel source, oxygen, spark, and containment. An explosion normally is broken down into two stages or components: the deflagration stage and the detonation stage. Deflagration is where the flame front is moving a subsonic speed. The detonation is where the flame front is moving at sonic or supersonic speed. The explosion vents sense the pressure increase and open which eliminates the containment before the detonation can occur. The collected dust can be added back to the fuel and burned to generate power. Too many plants do not use this system because it is rare that a dust explosion occurs and they are willing to take the small risk of an explosion rather than spend the money to be safe. 
     The grain elevator operators share the same risk with dust explosions as the power industry does. Unlike the power industry the grain industry does little to reduce the risk of a dust explosion. The chance of a dust is very rare so most operators do nothing. The chance of an explosion is low. Those that do occur are devastating, with total destruction of the grain elevator and normally loss of life. 
     While grain dust is biodegradable, coal dust is not. The coal dust that is not recovered will end up in our environment. Most will end up in our water system, air or soil. 
     It has been long known that dust can be used as a fuel source under controlled conditions. The Btu value of most dust in higher than coal and must higher than methane gas. Dust burns very clean and produces very little emissions. By adding grain dust to the coal or gas fuel feed system, less of the coal or gas would be required to generate the power. The emissions from the coal fired power plant would be greatly reduced because the dust burns hotter and could act as an afterburner, burning a large percent of the coal off gases. 
     By adding dust collectors to the grain elevator thousands of tons of grain dust could be harvested for fuel. Other agricultural waste by products including grasses and wood can be converted into a dust. Crops could also be grown to generate the power of dust fuel source. 
     The advantages of using biodegradable and renewable fuels are great. The farmer has a new market for their products. The grain elevator operators have a much safer processing system. The power plants have a renewable, cheap, endless source of clean burning fuel. 
     Because the fuel source is produced close to the power plant, the cost of transportation is reduced. The product being shipped is non-hazardous, unlike petroleum based fuels. The transportation cost differential is especially favorable for the use of this invention in the Midwest where most of the states are agricultural. It is here where currently power generating plants burn coal or natural gas. 
     When most people think of biodegradable or organic fuels they think of bio-diesel or ethanol which requires more energy to produce than the fuel value of the product. Biodegradable dust is in abundant supply, is cost effective, and burns cleanly. 
     SUMMARY OF THE INVENTION 
     The present invention is a particulate deflagration combustion engine that burns fine solid particle fuel and a method for operating the engine. A fuel particle size of between 8-12 microns is preferred for this application to achieve proper burning in the engine. The fuel is fed to a mixing box by means of a pre-measured auger system. Within the mixing box, the fuel is mixed in the desired fuel to air ratio with previously dried and compressed combustion air. The desired fuel to air ratio will vary depending on the acceleration of the engine, but will generally be in the range of 1-7% particulate fuel to 93-99% air. The fuel and air mixture is then delivered to a combustion cylinder where it is ignited by a pair of spark plugs located in the walls of the cylinder approximately 180 degrees apart from each other. On the exhaust stroke of the piston, the hot combustion gases are vented through an exhaust stack to atmosphere. The exhaust stack is connected to air driers that supply dry combustion air for the engine. The hot combustion gases flowing through the exhaust stack serve to pull a vacuum on the air driers, resulting in removal of moisture from the air driers. Moisture from the air driers is pulled into the hot combustion gas stream and exhausts with the hot combustion gases to atmosphere via the exhaust stack. 
     The operation of the engine is controlled by a control panel that is connected to the operational components of the engine and controls their operation in response to input from dew point monitors that monitor the moisture content of the dried air, oxygen sensors that monitor the air present in the fuel and air mixture, and infrared sensors that monitor the burn of the fuel. 
     An alternate embodiment of the present invention is shown in  FIG. 2 . This is a particulate deflagration enhanced firebox for burning particulate fuel either alone or in combination with other fuels and the associated method. The firebox may be employed in association with a power plant where the heat from the firebox is used to generate electricity. Fine fuel particles are fed to a mixing drum or box by a pre-measured auger system where the fuel is mixed with dried, compressed combustion air in a desire fuel to air ratio. The fuel mixture enters the combustion firebox or boiler either alone or in association with other fuels where it is ignited. The hot combustion gases leave the firebox and are vented through the firebox&#39;s normal route which generally includes passing through a precipitator for remove particulates before exiting to atmosphere via a chimney stack. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a particulate deflagration combustion engine constructed in accordance with a preferred embodiment of the present invention. 
         FIG. 2  is a diagram showing a particulate deflagration enhanced firebox constructed in accordance with an alternate embodiment of the present invention. This diagram shows the firebox employed in association with a power plant for generating electricity. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1 , there is illustrated a particulate deflagration combustion engine  100  that is constructed in accordance with a preferred embodiment of the present invention. The fuel that is used in this engine  100  will need to have been previously reduced to the proper particle size by grinding or other suitable means and has passing it through sizing sieves to achieve the desired particle size range. A particle size of between 8-12 microns is preferred for this application to achieve proper burning in the engine  100 . The previously prepared particulate fuel is put into the main fuel tank  15  of the engine  100  which is shown at the top of  FIG. 1 . 
       FIG. 1  is a diagram of the engine  100 . For ease of illustration,  FIG. 1  shows only two cylinders  31 . However, the actual engine  100  is not limited to two cylinders  31 . Also, the arrangement of the components of the actual engine  100  may be somewhat different than illustrated in  FIG. 1  since the diagram is presented to illustrate the functional relationship of engine components and not the actual physical configuration of the components. 
     Beginning at the top of  FIG. 1 , the engine  100  will be described in the order in which the fuel flows through the engine  100 . Although the engine  100  has more than one cylinder  31  to which fuel is delivered from the main fuel tank  15 , the components associated with only one cylinder  31  will be described since those components are duplicated for each cylinder  31  of the engine  100 . All of the components are duplicated for each cylinder  31  of the engine  100  except that there will generally only be two air dryers  23  employed for the engine so that one air dryer  23  is in service supplying air for all of the cylinders  31  at any given time while the other air dryer  23  is being regenerated. 
     Referring now to  FIG. 1 , the particulate fuel is fed into a main fuel cell  15  of the engine  100  from which it is then fed to a mixing box  10  via an auger drive system  14  that is contained within an auger housing  11 . The auger drive system  14  consists of an auger drive motor  6  that rotates a pre-measure auger shaft  13 . As the auger shaft rotates, it delivers a pre-measured amount of particulate fuel from the main fuel cell  15  to the mixing box  10  via a fuel mixing valve  12 . 
     Combustion air enters the engine  100  via filtered air intakes  30 . From the filtered air intakes  30 , the combustion air is channeled through one of the two desiccant dryer beds or air dryers  23  that dries the air and delivers it to a combustion air compressor  21 . Each desiccant dryer bed  23  has a dryer drain valve  25  located at the bottom for draining off water from the dryer bed  23 . Also each desiccant dryer bed  23  and is attached to an exhaust stack  1  via a venturi dryer purge pipe  24  that functions to pull a vacuum on the beds  23  to thereby remove moisture from them. 
     The combustion air is compressed in the combustion air compressor  21  and the compressed air is then delivered to the mixing box  10  via air mixing valve  22 . Within the mixing box  10 , the dried and compressed combustion air is thoroughly mixed with the particulate fuel in the desired ratio by a motor powered mixing fan  7 . Under normal conditions, the fuel to air ratio would be between approximately 1-2 percent particulate fuel and between 98-99 percent compressed air. The mixing box  10  must be able to suspend the fuel particles in the air mixture and keep them in suspension until ignition occurs in the combustion chamber  20  of the cylinder  31 . During acceleration, the engine  100  would require more power and the fuel to air ratio would increase to as much as 5-7 percent particulate fuel and 93-95 percent air. 
     Once the mixture is thoroughly mixed together, a portion is drawn out through a pre-charge valve  18  where it remains momentarily until it is permitted to enter the combustion chamber  20  of the cylinder  31  upon the opening of a charge valve  19  located between the pre-charge valve and the combustion chamber  20 . The fuel mixture should be delivered at a pressure of approximately 25 psig or greater to the combustion chamber  20  where it will be allowed to expand and provide some cooling to the cylinder  31 . 
     Once the fuel and air mixture is inside the combustion chamber  20 , the charge valve  19  closes and the associated valve  32  moves to the combustion stage  26 , as illustrated on the left hand side of  FIG. 1 . Once at the combustion stage  26 , the magnetos  5  send electrical impulses to the pair of spark plugs  4  that are located one on either side of each cylinder  31 . The electrical impulses are received by the pair of spark plugs  4  and a spark is created at each spark plug  4  which in turn ignites the fuel within the combustion chamber  20 . 
     The location of the spark plugs  4  is important because of the shape of the flame front created in the particulate fuel mixture upon ignition of the fuel. The flame front generated at each spark plug  4  is in the form of a V-shape with the point of the “V” at the location of the spark plug  4 . Thus the main thrust of the expansion energy is exerted along the sides of the “V” or laterally and at approximately a 90 degree angle from the orientation of the igniting spark plug  4 . By locating the spark plugs  4  in the sides of the cylinder  31  instead in the head or end of the cylinder  31 , the valve  32  receives maximum energy from the burning fuel. Two spark plugs  4  are employed to balance the thrust exerted against the valve  32  and to insure more complete burning of the fuel. The two spark plugs  4  are preferably located approximately 180 degrees from each other at the top end of their associated cylinder wall. 
     Combustion of the fuel upon ignition by the spark plugs  4  drives the valve  32  that is located in the cylinder  31  in a direction away from the spark plugs  4 . Although not specifically illustrated, as with most internal combustion engines, the valve  32  is attached to a cam shaft (not illustrated) which in turn rotates an attached output shaft  8  which is the driving mechanism of the engine  100 . The valve  32  will then move in the opposite direction within the cylinder  31 , i.e. back toward the spark plugs  4  again in coordination with the opening of an exhaust valve (not illustrated) that allows the combustion gases from the combustion chamber  20  to enter a cylinder discharge port  3 , then pass through a muffler  2  and finally discharge out to atmosphere via the exhaust stack  1 . 
     As previously described the exhaust stack  1  has a connection via drier purge pipe  24  to the air dryer  23 . The drier purge pipe  24  serves as a venturi and as the hot exhaust gases exit through the exhaust stack  1 , a vacuum is pulled on the air dryer  23  via the drier purge pipe  24  and the vacuum pulls moisture out of the air dryer  23  and into the exhausting combustion gas steam. 
     As illustrated in  FIG. 1 , the engine  100  is provided with a battery  9  that supplies power for the various components of the engine  100  and an alternator  16  that receives rotational power from the output shaft  8  and converts that mechanical energy to electrical energy that is used to recharge the battery  9 . Also, the engine  100  is provided with a control panel  17  that controls the functioning of the engine  100 . Additionally, the engine is provided with infrared sensors  27  on the cylinders  31  that monitor the burn of the fuel and provide feedback to the control panel  17  to allow the control panel to control the fuel and oxygen supply. Also, the engine  100  is provided with a dew point monitor  28  located in the combustion air compressor  21  that monitors the moisture content of the dried air and provides feedback to the control panel  17  to allow the control panel  17  to control switching between the desiccant dryer beds  23 . Further the engine  100  is provided with oxygen sensors  29  located in the mix boxes  10  that monitor the air present in the fuel and air mixture and provide feedback to the control panel  17  to allowing the control panel  17  to control the fuel and oxygen supply. 
     Referring now to  FIG. 2  there is illustrated an alternate embodiment of the present invention which is a particulate deflagration enhanced firebox  200 . The enhanced firebox  200  is shown in  FIG. 2  in association with an electrical power generation plant  202 . The particulate deflagration enhanced firebox  200  can be used for burning particulate fuel either alone (not illustrated) or in combination with other fuels, such as coal  204 , and the associated method. As illustrated, the firebox  200  may be employed in association with a power plant  202  where the heat from the firebox  200  is used to generate electricity. Fine fuel particles  208  are fed to a mixing drum or box  210  by a pre-measured auger system (not illustrated) where the dust fuel  208  is mixed with dried, compressed combustion air in a desire fuel-to-air ratio. This exact ratio will vary with the type of dust fuel  208  employed. The fuel and air mixture  212  enters the combustion firebox or boiler  200  either alone or in association with other fuels  204  where it is ignited. If other fuels  204  are employed, the fuel and air mixture  212  is preferably introduced slightly above the other fuels  204 . As shown in the drawing, if coal is the other fuel  204 , it is processed in a pulverizer  206  before being introduced in to the firebox  200 . After all the fuels  204  and  208  burn, the hot combustion gases  214  leave the firebox  200  and are vented through the firebox&#39;s normal combustion gas route which generally includes passing through a precipitator  216  to remove particulates before exiting to atmosphere via a chimney stack  218 . 
     While the invention has been described with a certain degree of particularity, it is manifest that many changes may be made in the details of construction and the arrangement of components without departing from the spirit and scope of this disclosure. It is understood that the invention is not limited to the embodiments set forth herein for the purposes of exemplification, but is to be limited only by the scope of the attached claim or claims, including the full range of equivalency to which each element thereof is entitled.