Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
  • F23L15/00—Heating of air supplied for combustion
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
  • F23C7/00—Combustion apparatus characterised by arrangements for air supply
  • F23C7/002—Combustion apparatus characterised by arrangements for air supply the air being submitted to a rotary or spinning motion
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
  • F23G5/00—Incineration of waste; Incinerator constructions; Details, accessories or control therefor
  • F23G5/02—Incineration of waste; Incinerator constructions; Details, accessories or control therefor with pretreatment
  • F23G5/033—Incineration of waste; Incinerator constructions; Details, accessories or control therefor with pretreatment comminuting or crushing
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
  • F23G5/00—Incineration of waste; Incinerator constructions; Details, accessories or control therefor
  • F23G5/08—Incineration of waste; Incinerator constructions; Details, accessories or control therefor having supplementary heating
  • F23G5/12—Incineration of waste; Incinerator constructions; Details, accessories or control therefor having supplementary heating using gaseous or liquid fuel
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
  • F23G5/00—Incineration of waste; Incinerator constructions; Details, accessories or control therefor
  • F23G5/44—Details; Accessories
  • F23G5/46—Recuperation of heat
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
  • F23G7/00—Incinerators or other apparatus for consuming industrial waste, e.g. chemicals
  • F23G7/10—Incinerators or other apparatus for consuming industrial waste, e.g. chemicals of field or garden waste or biomasses
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
  • F23J15/00—Arrangements of devices for treating smoke or fumes
  • F23J15/02—Arrangements of devices for treating smoke or fumes of purifiers, e.g. for removing noxious material
  • F23J15/022—Arrangements of devices for treating smoke or fumes of purifiers, e.g. for removing noxious material for removing solid particulate material from the gasflow
  • F23J15/025—Arrangements of devices for treating smoke or fumes of purifiers, e.g. for removing noxious material for removing solid particulate material from the gasflow using filters
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
  • F23J3/00—Removing solid residues from passages or chambers beyond the fire, e.g. from flues by soot blowers
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23K—FEEDING FUEL TO COMBUSTION APPARATUS
  • F23K3/00—Feeding or distributing of lump or pulverulent fuel to combustion apparatus
  • F23K3/02—Pneumatic feeding arrangements, i.e. by air blast
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
  • F23G2201/00—Pretreatment
  • F23G2201/80—Shredding
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
  • F23G2206/00—Waste heat recuperation
  • F23G2206/20—Waste heat recuperation using the heat in association with another installation
  • F23G2206/203—Waste heat recuperation using the heat in association with another installation with a power/heat generating installation
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
  • F23J2217/00—Intercepting solids
  • F23J2217/10—Intercepting solids by filters
  • F23J2217/101—Baghouse type
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23K—FEEDING FUEL TO COMBUSTION APPARATUS
  • F23K2203/00—Feeding arrangements
  • F23K2203/20—Feeding/conveying devices
  • F23K2203/202—Feeding/conveying devices using screws
• • 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
  • Y02E20/00—Combustion technologies with mitigation potential
  • Y02E20/12—Heat utilisation in combustion or incineration of waste
• • 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
  • Y02E20/00—Combustion technologies with mitigation potential
  • Y02E20/34—Indirect CO2mitigation, i.e. by acting on non CO2directly related matters of the process, e.g. pre-heating or heat recovery

Definitions

• This invention pertains to rice hulls and, more particularly, to a combustion system and process for burning rice hulls and other combustible material.
• Rice hulls are traditionally difficult to handle and are very abrasive causing high maintenance costs on all equipment used to move the rice hulls. This is primarily due to the quantity of silica contained in the rice hull itself.
• Rice hulls can be burned as fuel leaving an ash, which is referred to as rice hull ash.
• Rich rice hull ash contains amorphous silicon carbon and traces of other elements.
• Rice hull ash is light in weight and tends to be readily carried by circulating air.
• Rice hull ash can further leave a dark dusty layer on surfaces and can also irritate some people and animals.
• Crystalline ash can be found in three forms: cristobalite, quartz and tridymite.
• Crystalline ash can be difficult to breathe and can be a potential health hazard. Furthermore, ash containing more than 1 % by weight crystalline silicon dioxide may be required to be labeled for special handling. Quartz occurring naturally, such as in coal seams, is thought to be the source of black lung disease.
• Impingement of the rice hulls and flame on the walls of the furnace and boiler can cause many problems.
• Leakage can cause spillage and scalding of hot water and steam.
• Such conventional combustion systems include: stoker fired systems, Dutch ovens, fluidized bed boilers, and gasification system. These conventional combustion systems have met with varying degrees of success.
• stoker fired systems The basic system provides a grate or floor to support the rice hulls or other solid fuel. Combustion air is provided from beneath the grate to complete combustion.
• the grates can be water-cooled, stair stepped, self or automatic dumping for ash removal, traveling chain, vibrating, and other types to perform a specific function.
• the basis of combustion is for the rice hulls to be uniformly spread in a layer on the grate and to remain in the combustion zone until the combustion is completed.
• the disadvantages of the grate or stoker-fired device is that the rice hulls reside in the combustion zone for a lengthy period to insure complete and efficient combustion.
• the stoker-fired device also exposes the ash to a high temperature zone for an extended period of time which is a direct factor contributing to the formation of undesirable crystalline forms of silicon dioxide which can create potential hazards.
• stoker-fired devices include high maintenance cost of the grate or floor. Due to the high silica content in the rice hull and the high percentage of silicon dioxide content in the ash, the grate is a high wear area. Furthermore, improper design of the flue gas path and velocities can create excessive wear or other components in the boiler such as tubes and flue gas ducting in stoker fired systems.
• Dutch ovens refer to a boiler which has no heat absorption capability in the combustion zone. It is usually a box shaped area that is lined with brick or refractory in the combustion zone. This allows the combustion to take place in a safe manner. The heat from the combustion is transported to an other area where water filled tubes are used to absorb the heat for steam production. The heat absorption area is usually fixed on top of the Dutch oven combustion device so that the heat naturally travels into the heat absorption device.
• Dutch oven systems are similar to those listed for the grate fired system, in that: the rice hulls reside in the combustion zone for long periods of time and, therefore, cause the production of undesirable crystalline forms of silicon dioxide. Furthermore, because there is no heat transfer to the water in the combustion zone, the efficiency of Dutch oven systems are lower than that of grate fired systems. Heating the refractory to normal operating temperatures requires a good deal of fuel and that heat is usually lost due to the Dutch oven arrangement.
• Fluidized bed boilers are popular combustion systems for steam generation.
• air is injected and disbursed through a bed of material causing the bed itself to become fluid, in a fluidized state or ebullated.
• Heat is added to the fluidized bed boiler by means of an auxiliary fuel such as natural gas to increase the temperature of the bed.
• auxiliary fuel such as natural gas
• Fluidized bed boilers include: atmospheric, circulating, bubbling beds, ebullated beds, etc.
• the disadvantage of the fluidized bed boiler for rice hulls as fuel is the corrosion caused by the silica in the hulls and the silicon dioxide in the ash.
• movement of rice hulls is continuous and fluidized in the combustion zone and boiler gas path can quickly become plugged with rice hulls, bed material and ash. This ultimately presents a substantial maintenance problem for the operator of the fluidized bed boiler.
• Gasification systems provide partial combustion of rice hulls or other fuel in a reducing atmosphere where the fuel product is a low heat content gas that can then be transported to other devices for use as a fuel.
• the fuel product is a low heat content gas that can then be transported to other devices for use as a fuel.
• all can be arranged to produce a gas by limiting the amount of excess air utilized in the combustion zone. The resulting gas can then be burned at a more desirable location to achieve the heat transfer required for steam generation.
• Most fuels used for the gasification process contain elements which when burned in a complete combustion process will cause other problems such as slagging. Fuels containing sodium, magnesium, manganese, etc can lower the ash fusion temperature causing the ash to fuse together and block both heat transfer and flue gas paths. This is very undesirable in a combustion process.
• An efficient combustion system and process are provided for burning rice hulls and other combustible material to produce steam for turbines, electric power generation, and other uses.
• the combustion system and process can completely combust the fuel comprising the rice hulls or other combustible material while the fuel is suspended by primary and secondary heated air in the furnace.
• the user-friendly combustion system and process are constructed and arranged to substantially prevent the rice hulls or other combustible material from impinging, eroding, or otherwise damaging the furnace walls.
• the inventive combustion system and process are economical, environmentally attractive, and effective.
• the novel combustion system can have: a blower comprising a forced air fan to propel air through the combustion system; an air heater to heat the air; and a fuel line to pneumatically convey fuel comprising rice hulls or other combustible material.
• a blower comprising a forced air fan to propel air through the combustion system
• an air heater to heat the air
• a fuel line to pneumatically convey fuel comprising rice hulls or other combustible material.
• the blades of the fan are not placed in the pathway of the rice hulls.
• At least one eductor, preferably comprising a venturi device, is provided to combine and mix the fuel with primary air comprising part of the heated air.
• the combustion system has a boiler train comprising a furnace with at least one burner which emit flames to combust the fuel.
• the furnace has a primary annular conduit, which preferably comprises a scroll pattern pathway, to pneumatically convey and swirl the primary air and fuel to and about the inlets of the burners.
• the primary annular conduit has a larger diameter inlet section with a tangential inlet, a smaller diameter outlet section in proximity to the burners, and an annular tapered throat section which extends between and connects the larger diameter inlet section to the smaller diameter outlet section.
• the furnace can have a secondary passageway which peripherally surrounds the primary annular conduit to pass secondary air comprising another part of the heated air to the burners.
• At lease one and preferably two impellers are positioned in proximity to the burners to mix and swirl the secondary air with the primary air and fuel. The impellers also help spread the flames from the burners.
• An air register which communicates with the secondary passageway, can be positioned about the burners to regulate the flow secondary air.
• the air register can have vanes to direct the flow of secondary air to the burners.
• a windbox can be provided with a wall to support the burners.
• the rice hulls are preferably ground by grinders, such as hammer mills, before being fed to the boiler train.
• the ground rice hulls can be conveyed and stored in storage bins, which can comprise or include bucket elevators.
• ash can be readily removed from different sections of the boiler train such as by screw conveyors and stored in hoppers or bins.
• the preferred process comprises: heating air: combining and mixing primary air comprising part of the heated air with fuel comprising rice hulls or other combustible material; pneumatically conveying the fuel with the primary air to a set of burners in a furnace of a broiler train; feeding secondary air comprising another part of the heated air to the burners; and substantially completely combusting the fuel with flames from the burners, when the fuel is suspended in the primary and secondary air in the furnace, while substantially preventing the fuel from impinging the walls of the furnace.
• the fuel and primary air are swirled generally in a scroll pattern about the inlets of the burners.
• the fuel can be pneumatically conveyed in a sweeping motion along the furnace.
• the fuel is supplemented with natural gas or diesel oil during start up or low load operations for ignition and flame stabilization.
• Such low load operations usually comprise less than about 60% load.
• the novel combustion system and process control the combustion temperature and residence time of combustion of the rice hulls or other combustible material in the combustion zone to substantially prevent the formation of more than about 1 % by weight of crystalline silicon dioxide comprising cristobalite, tridymite, and quartz.
• the burner design of the inventive combustion system and process is simple to construct and easy to use.
• the burners require little maintenance and can operate without substantial erosion of the burner and furnace walls.
• the burners and furnace are constructed and arranged to provide complete combustion of the fuel particulartes in suspension, which allows for quick conversion of the fuel to thermal energy and speedy heat release.
• the short residence combustion time of the fuel allows efficient use of the heat content with minimal exposure of the silica in the rice hulls to temperatures that undesirably form abrasive crystalline silicon dioxide.
• Combustion can be completed in the furnace without a floor or grate.
• a minimum of two burners provides an advantageous arrangement which allows turn down ratios of 3.1 to enhance the overall production rate of combustion.
• the use of air at elevated temperatures to transport the fuel to the burner not only provides the motor force for movement of the fuel but also preheats the fuel.
• the air also supports combustion of the fuel. Because primary air is used as the transport mechanism, less secondary air is required. This arrangement accommodates greater flow control of the fuel and air.
• Each eductor which preferably comprises a venturi transport system, requires relatively little power for the quantities of ground rice hulls or other solid combustible material being moved through the combustion system.
• the venturi transport device is a relatively inexpensive solid feed system, which is easy to operate and maintain. As discussed previously, air is utilized by the venturi transport device as the motive force of transportation of the fuel.
• the venturi transport device provides for accurate fuel control, which is easy to regulate over the production range of the boiler. No classification or separation of the fuel is required in the combustion system for proper dispersion and combustion as is required in many conventional systems.
• the furnace and the boiler arrangement provide for low gas velocities through the boiler to allow longer periods of operation.
• the preferred construction and arrangement also prevents substantially erosion problems in the boiler and furnace, such as tube (pipe) wear, steam leakage, damage to the furnace walls by the flame pattern or by impingement of the fuel.
• the boiler train can be arranged to limit the amount of convection heat recovery sections to minimize the amount of tubes, pipes, and pressure parts, which are in the gas path.
• the boiler train can be constructed and arranged in modules, which are easily transported and constructed.
• the boiler is supported from the ground, rather than suspended from above, such as from an overhead support structure to avoid the use of costly cranes for maintenance.
• Figure 1 is a side view of a power plant for combusting rice hulls in accordance with principals of the present invention
• Figure 2 is a front view of the power plant
• Figure 3 is a top plan view of the power plant
• Figure 4 (same sheet as Fig. 1) is a top plan view of a portion of the power plant;
• Figure 5 is an enlarged top plan view of a combustion and transport air fuel feed arrangement comprising an eductor providing a venturi transport device;
• Figure 6 is a front view of the burner scroll section pathway with a tangential inlet
• Figure 7 is a cross-sectional view of part of the scroll section pathway
• Figure 8 is an enlarged cross-sectional view of portions of the furnace, burners, air register, and windbox;
• Figure 9 is an end view of a burner impeller
• Figure 10 is a diagrammatic view of the burner, air register, windbox. furnace and boiler;
• Figure 11 is a process flow diagram for part of the combustion process.
• a power plant 20 (Fig. 1) provides a combustion process and system 22 to bum rice hulls to produce steam for turbines, electric power generation, and other uses. While the combustion process and system is particularly useful to burn rice hulls, it can also be used to burn other combustible material.
• rice hulls from a rice mill 24 are conveyed to a hammer mill 26.
• the grinders in the hammer mill crush and grind the rice hulls from a density of about 8 to about 20 lbs/cu.ft.
• the ground rice hulls are conveyed and stored in a storage bin 28.
• the ground rice hulls are conveyed from the storage bin and pneumatically conveyed to burners 30 of a furnace of a boiler in a boiler train 34.
• a superheater 36 in the boiler train increases the temperature of the steam which is fed to a turbine 38.
• the turbine drives gears in a gearbox 40 which powers a generator 42 to produce electricity.
• the electricity can be used in the power plant, rice mill, and/or sold to customers.
• Flue gases from the superheater 36 (Fig. 1 1) are passed through an economizer comprising a heat exchanger 44.
• the flue gases from the economizer are subsequently passed through an air heater 46.
• the air heater heats air, which is used to preheat, transport and pneumatically convey the ground rice hulls to the burners.
• An induced draft fan 48 draws the flue gases from the air heater through filters in a bag house 50 in order to filter and remove particulates and other contaminates from the flue gases before the flue gases are sent up the stack 52 for discharge into the atmosphere. Ash is withdrawn from various sections of the boiler train and collected in storage bins 54.
• rice hulls form a rice mill are conveyed by conveyors, such as screw conveyors 56 and 57, to rice hull grinders 58 and 59, such is in a hammer mill.
• the grinders crush and grind the rice hulls to an appropriate size for efficient combustion in the combustion process and system.
• the ground rice hulls are conveyed by screw conveyors 60 and 61 to storage bins 62 and 63 or hoppers.
• Hot air from the air heater 46 (Fig. 3) is passed through an air duct 64 where it is split into pipe lines comprising a primary air duct 66 and a secondary air ducts 67 and 68 (Fig. 2 and 3).
• Primary heated air from the primary air duct preheats and pneumatically conveys the ground rice hulls from the rice hull storage bins through fuel lines 70 and 71 (Fig. 3) to a set, series, or array of burners 30 in a furnace 32 of the boiler.
• Secondary heated air from the secondary air duct is also passed to the burners where it is mixed with the primary air and fuel for combustion by the flame of the burners.
• the heated air is propelled through the air ducts by a forced draft fan 76 located in proximity to the air heater 46.
• Rice hull ash are removed from the boiler train by screw conveyors 78-80 and collected in bins, hoppers, or ash containment boxes 82-84. Flue gases from the air heater 46 are withdrawn by an induced draft fan 48 and drawn through and filtered in a bag house 50 for cleanup and removal of pollutants before the flue gases are sent up the stack 52 for discharge into the atmosphere. Feed water is heated in a feed water heater 86 and pumped by water pumps 88 to the economizer 44 and then to the boiler tubes or membrane tubes of the boiler 32. As shown in Figure 1 , the rice hull storage bins 62 and 63 can comprise or be equipped with bucket elevators 90 and 92.
• Diesel oil or other fuel oil can be stored in an oil storage tank 94 (Fig. 4) and pumped to the burners by fuel oil pumps 96 and 97.
• the fuel oil provides supplemental fuel for use during start up or low load operations for ignition and flame stabilization.
• the low load operations comprise less than about 60% load.
• Water fed to the boiler is preferably softened by water softeners 98 (Fig. 4).
• the treated water is stored in a water tank 100 and pumped to the boiler tubes by water transfer pumps 88.
• Water comprising condensed steam from the turbine 42 is pumped by condenser pumps 102 and 103 to the feed water heater 86.
• Air compressors 106 and 107 can also be provided, as well as a diesel generator 108.
• the control room 1 10 of the power plant can be equipped with computers and control panels to control and monitor operations of the power plant.
• Eductors 112 comprising venturi transport devices 114 combine and mix primary hot air from the primary air duct 64 with ground rice hulls in fuel line 70.
• Each burner is operatively associated with an eductor comprising a venturi transport device.
• the primary heated air preheats the fuel comprising the ground rice hulls.
• the primary heated air and ground rice hulls are pneumatically conveyed through pipe or conduit 1 16 to the burners. More specifically, the heated primary air and fuel can be pneumatically conveyed into the tangential inlet 118 (Fig. 6) of conduit 1 18.
• Conduit 1 16 preferably provides a scroll pattern pathway 120 to swirl and mix the primary heated air and fuel.
• the scrolled pathway 120 has an inclined ramp 122 which extends downwardly from the tangential inlet 118 and expands to a generally circular outer scroll 124.
• the conduit 1 16 comprises a primary annular conduit to pneumatically and annually convey the primary air and fuel to the burners.
• the primary annular conduit has an out scroll 124 and an inner scroll 126.
• the primary annular conduit has a large diameter inlet section 128 with a tangential inlet 1 18.
• a tapered throat section extends inwardly from the larger diameter inlet section. The throat section connects the larger diameter inlet section to an elongated smaller diameter outlet section 132.
• the outer scroll of the smaller diameter outlet section is longer and extends closer to the burners than does the inner scroll of the smaller diameter outlet section.
• the primary annular conduit 1 16 (Fig. 8) is peripherally surrounded by a secondary passageway (pathway) 134.
• the secondary pathway can comprise an outer annular conduit.
• At least one and preferably two burner impellers 136 are positioned in proximity to the burners to swirl, disperse, and mix the secondary air with the primary air and fuel.
• the burner impellers also help spread out the flames of the burners.
• each burner impeller can have twisted fins 138 or blades which are supported by annular ribs or bars 140 that extend from a coupling 142 or hub.
• an air register 144 is positioned about the burners to regulate the flow of secondary air to the burners.
• the air register can have vanes 145 comprising blades about its circumference, which are at a fixed setting, to direct the flow of secondary air towards the burners, as well as to give direction to the secondary air as it travels about the outside of the burner barrel comprising the primary conduit.
• the air register communicates with and can include the secondary passageway.
• a windbox 146 is positioned about the air register.
• the windbox includes and controls dampers which maintain a higher pressure than the furnace pressure and burners. This assures flow of air in the proper direction.
• the burners 30 which can comprise gas ring burner can be mounted on the front wall 148 of the windbox.
• the burners substantially completely combust the ground rice hulls suspended by the primary and secondary air in the furnace. Desirably, combustion of the rice hulls occurs without impinging the furnace walls with the rice hulls or flame.
• the power plant provides a combustion process and system to burn rice hulls or other combustible material to produce steam for turbines, electric power generation and other uses.
• the combustion system and process has a blower comprising a forced air fan to propel air through the combustion system, an air heater to heat the air, and a fuel line to pneumatically convey the fuel comprising rice hulls or other combustible material.
• the illustrated combustion system has a boiler train comprising a furnace with at least two burners.
• the furnace has a primary annular conduit to pneumatically convey the primary air and fuel to the burners.
• An secondary pathway peripherally surrounds the primary annular conduit to pass secondary air comprising another part of the heated air to the burners.
• At least one and preferably two impellers extend and are positioned adjacent and in proximity to the burners to swirl, disperse, and mix the secondary air with the primary air and fuel.
• An air register is positioned about the burners to regulate the flow of secondary air.
• a windbox has a wall to support the burners.
• the primary annular conduit provides a scroll pattern pathway.
• the boiler train comprise a boiler with membrane tubes which extend from a bottom header to an upper drum for steam separation.
• the feed water heater heats the water which is pumped by water pumps through the tubes of the economizer then the boiler.
• a superheater is positioned between the boiler and the air heater to receive flue gases from the furnace to superheat the steam.
• An economizer comprises a heat exchanger which preheats water going to the boiler and is positioned between the superheater and the air heater. Hoppers which comprise ash containment boxes are provided to receive and collect ash from sections of the boiler train.
• a bag house is positioned in proximity to the air feeder to filter flue gases from the air heater.
• An induced air fan is provided to draw the flue gases through the bag house and propel the filter flue gases up the stack for discharge into the atmosphere.
• Water softeners can be provided to remove contaminates from the water before the water passes through the tubes of the boiler.
• a turbine and compressor are operatively connected to the boiler train.
• An electric generator is operatively powered and connected to the turbine.
• rice hulls are ground and crushed in the grinders of a hammer mill from a density of about 8 lbs/cu.ft. to about 20 lbs/cu.ft.
• Ground rice hulls are stored in a storage bin and subsequently fed to the boiler. Air heated by the air heater is combined, mixed, and commingled with the ground rice hulls to heat the rice hulls.
• the primary heated air pneumatically conveys the heated rice hulls in the furnace of the boiler train.
• the rice hulls and primary air are swirled generally in a scroll pattern about the inlet of the burners.
• the fuel is pneumatically conveyed in a sweeping motion along the furnace.
• Secondary air comprising another part of the heated air from the air heaters are fed to the burners.
• the primary and secondary air is mixed with the ground rice hulls so that the ground rice hulls are suspended in the primary and secondary air.
• the flames from the burners substantially completely combust the rice hulls suspended in the primary and secondary air in the furnace in such a manner that the rice hulls do not abrade and impinge upon or otherwise damage the walls of the furnace.
• the fuel comprising rice hulls or other combustible material can be supplemented by natural gas. diesel oil or other fuel oil during start up or low load operations for ignition and flame stabilization.
• the combustion temperature and time of residence of the rice hulls in the combustion zone are controlled by the combustion system and process to substantially prevent the formation of more than 1% by weight of crystalline silicon dioxide comprising cristobalite, tridymite. and quartz.
• Rice hulls are transported to the gathering unit and reduced in size by grinding.
• the rice hulls can be passed through a hammer mill to achieve reduction in average particle size.
• the ground rice hulls are stored in a bin temporarily until the generating unit is in need of the fuel.
• a feeding device is located on the outlet of the bin with means of regulating the flow of rice hulls to the boiler.
• the rice hulls are removed from storage and pneumatically transported to the burners in the furnace of the boiler.
• the rice hulls can be introduced to the inside of the boiler where the combustion process occurs. Hot air from the air heater section of the boiler train is used as the transport medium for the rice hulls.
• the hot air and rice hulls are combined by means of venturi type devices and move together to the burners.
• the combustion system and process can use natural gas or diesel fuel oil for ignition and flame stabilization. Once the power plant is in operation at more than 60% load, the flame stabilization fuel is removed and the combustion system and process are self-sustaining.
• the flame pattern and residence time in the furnace section of the boiler are designed to maximize the heat transfer and minimize the residence times and velocities to prevent crystalline formation and erosion due to the ash laden gases.
• the preceding procedures maximize the rate of consumption of the fuel (rice hulls) in the combustion process, which also increases the efficiency of the combustion process.
• the heat release time for a larger particle size is several times longer than for the smaller particle.
• To achieve the same amount of heat transfer or steam production with the larger particle would require a large amount of fuel to be in process at any given time. This would result in a larger system for the hull transport system throughout the furnace, which would equate to a larger initial cost.
• the amount of heat content of the rice hulls is low compared to other fuels normally used in the generation of electricity. Therefore, the ability to obtain quick heat release of the heat content also allows the collection and transfer of that heat into other mediums with additional efficiency.
• the combustion temperature and time of residence of the rice hulls in the combustion zone are important to the process to prevent the formation of crystalline silicon dioxide.
• These crystalline forms are known as cristobalite, tridymite and quartz. These forms are considered by some to be a potential health hazard as a respirable dust and, therefore, the creation of any crystalline forms is undesirable.
• the ash from the inventive combustion system and process normally contains no more than 1% of these crystalline forms with the remaining ash being amorphous or without crystalline form. At this low level of crystalline forms, the rice hull ash produced can be marketed successfully as a refractory material insulator for the steel industry, as well as the environmental industry as a filter medium. Typical analysis of ash from the combustion system and process are:
• the burners are situated to take advantage of the momentum the fuel (rice hulls) arriving at the burner front.
• the inlet section of the burners are preferably designed in a scroll pattern which allows momentum of the incoming fuel to utilize centrifugal force of the scroll section to impart forces which cause a swirling of the fuel inside the burners and a sweeping motion throughout the internal traverse of the primary conduit until exiting to the burners.
• the burner design continues to utilize the forces of the transport air fuel mixture to achieve proper distribution inside the furnace.
• the burners are mounted in the front wall of the windbox.
• An air register is installed around the burners for the regulation of the secondary or combustion air addition.
• the air register is fabricated to impart swirling to the motion of the secondary air as it enters the furnace around the burner-injected fuel.
• the combustion system is designed and optimized to insure proper distribution of the fuel air mixture, proper heat release, and prevent impingement on the opposing walls of the furnace. Desirably, substantially all combustion is completed while the fuel (rice hulls) are in suspension in the furnace. While a grate or floor can be used, no grate or floor is required for the complete combustion of the fuel.
• the boiler arrangement for the combustion system and process preferably comprise a single furnace with a minimum of one burner installed in the front wall of the boiler.
• Membrane tubes in the boiler starting at the bottom of each wall section proceed from a bottom header along the length of each sidewall and then into an upper drum for steam separation.
• the furnace of the boiler is long and narrow sized for the flow requirements of the steam production with minimal convention heat recovery section. Gas velocities and flow path are designed to minimize erosion and maximize heat recovery.
• the flue gases exiting the furnace section enter into a separate superheater section where the normal superheater functions are carried out.
• Flows, temperatures and ash removal are designed to achieve the proper temperature increase in the steam, temperature reduction in the flue gas and minimizing erosion by the ash laden gas.
• the part of the boiler train which includes other heat recovery sections, are all designed to increase the efficiency of the generating unit.
• the major sections include a superheater, an economizer comprising a heat exchanger, and an air heater.
• the heat exchanger absorbs and transfers heat form the flue gas into the boiler feed water before the feed water enters the boiler.
• the flue gas passes through the fabric filters or other flue gas clean-up device. Ash is removed from the collecting hoppers under the fabric filter of the bag house and transported to an ash storage silo. Gas exiting the fabric filters of the bag house is pulled by the induced draft fan and then blown into the stack for discharge into the atmosphere.
• the air systems in the rice hull fueled generating unit (power plant) are efficient.
• the forced draft fan introduces air into the combustion system.
• the forced draft fan pressurizes the air and propels the flow of air through the air preheated section (air heater), which elevates the temperature of the rice hulls.
• the airflow is then split with a portion of the heated air going to the fuel feed system where ground hulls are introduced into the stream by means of the venturi devices.
• the rice hulls combined with the heated pressurized air travel directly to the burners where the velocities are translated into the proper cyclonic or swirling motion for good mixing and complete combustion.
• the air register controls the air pressure in order to maintain the proper air-fuel ratio for complete combustion.
• the vanes of air register and burner impellers direct the flow of heated air and rice hulls around the burner to support the flame.
• the air provides the motive force to cause the flow of gas, flame and ash through the boiler train.
• Clean dry air is provided by a compressor and can be used as instrument air. motive force for control devices, as well as transport air for ash and hull conveying. Air or stream need not be used for boiler cleaning, as slagging is not a problem with the combustion of rice hulls only.
• the water/steam cycle of the rice hull fired power- generating unit can also be accomplished with different equipment.
• Crystalline forms in the ash remain less than 1% by weight.

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• 1999
  • 1999-11-24 AU AU18321/00A patent/AU773058B2/en not_active Ceased
  • 1999-11-24 WO PCT/US1999/028037 patent/WO2001038784A1/en active IP Right Grant
  • 1999-11-24 BR BR9917347-6A patent/BR9917347A/pt not_active IP Right Cessation

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