Classifications

• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L5/00—Solid fuels
  • C10L5/02—Solid fuels such as briquettes consisting mainly of carbonaceous materials of mineral or non-mineral origin
  • C10L5/26—After-treatment of the shaped fuels, e.g. briquettes
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
  • F23J7/00—Arrangement of devices for supplying chemicals to fire
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L10/00—Use of additives to fuels or fires for particular purposes
  • C10L10/02—Use of additives to fuels or fires for particular purposes for reducing smoke development
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L10/00—Use of additives to fuels or fires for particular purposes
  • C10L10/04—Use of additives to fuels or fires for particular purposes for minimising corrosion or incrustation
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L5/00—Solid fuels
  • C10L5/02—Solid fuels such as briquettes consisting mainly of carbonaceous materials of mineral or non-mineral origin
  • C10L5/04—Raw material of mineral origin to be used; Pretreatment thereof
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L9/00—Treating solid fuels to improve their combustion
  • C10L9/10—Treating solid fuels to improve their combustion by using additives
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L2200/00—Components of fuel compositions
  • C10L2200/02—Inorganic or organic compounds containing atoms other than C, H or O, e.g. organic compounds containing heteroatoms or metal organic complexes
  • C10L2200/0204—Metals or alloys
  • C10L2200/0213—Group II metals: Be, Mg, Ca, Sr, Ba, Ra, Zn, Cd, Hg
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L2200/00—Components of fuel compositions
  • C10L2200/02—Inorganic or organic compounds containing atoms other than C, H or O, e.g. organic compounds containing heteroatoms or metal organic complexes
  • C10L2200/0204—Metals or alloys
  • C10L2200/0218—Group III metals: Sc, Y, Al, Ga, In, Tl
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L2200/00—Components of fuel compositions
  • C10L2200/02—Inorganic or organic compounds containing atoms other than C, H or O, e.g. organic compounds containing heteroatoms or metal organic complexes
  • C10L2200/0204—Metals or alloys
  • C10L2200/024—Group VIII metals: Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L2200/00—Components of fuel compositions
  • C10L2200/02—Inorganic or organic compounds containing atoms other than C, H or O, e.g. organic compounds containing heteroatoms or metal organic complexes
  • C10L2200/025—Halogen containing compounds
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L2200/00—Components of fuel compositions
  • C10L2200/02—Inorganic or organic compounds containing atoms other than C, H or O, e.g. organic compounds containing heteroatoms or metal organic complexes
  • C10L2200/0272—Silicon containing compounds
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L2230/00—Function and purpose of a components of a fuel or the composition as a whole
  • C10L2230/02—Absorbents, e.g. in the absence of an actual absorbent column or scavenger
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
  • F23J2215/00—Preventing emissions
  • F23J2215/10—Nitrogen; Compounds thereof
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
  • F23J2215/00—Preventing emissions
  • F23J2215/20—Sulfur; Compounds thereof
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
  • F23J2215/00—Preventing emissions
  • F23J2215/60—Heavy metals; Compounds thereof
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23K—FEEDING FUEL TO COMBUSTION APPARATUS
  • F23K2201/00—Pretreatment of solid fuel
  • F23K2201/50—Blending
  • F23K2201/505—Blending with additives

Definitions

• the invention provides compositions and methods for reducing the levels of mercury, nitrogen oxides, and/or sulfur oxides emitted into the atmosphere upon burning of mercury-containing fuels such as coal.
• the invention provides for addition of various halogen and other sorbent compositions into the coal burning system during combustion. Use of the sorbents reduces emission of pollutants and prevents fouling in the furnace.
• mercury is at least partially volatilized upon combustion of coal. As a result, the mercury tends not to stay with the ash, but rather becomes a component of the flue gases. If remediation is not undertaken, the mercury tends to escape from the coal burning facility into the surrounding atmosphere.
• Some mercury today is captured by utilities, for example in wet scrubber and SCR control systems. However, most mercury is not captured and is therefore released through the exhaust stack.
• Mercury emissions into the atmosphere in the United States are approximately 50 tons per year. A significant fraction of the release comes from emissions from coal burning facilities such as electric utilities. Mercury is a known environmental hazard and leads to health problems for both humans and non-human animal species. To safeguard the health of the public and to protect the environment, the utility industry is continuing to develop, test, and implement systems to reduce the level of mercury emissions from its plants. In combustion of carbonaceous materials, it is desirable to have a process wherein mercury and other undesirable compounds are captured and retained after the combustion phase so that they are not released into the atmosphere.
• NOx nitrogen oxides
• SOx sulfur oxides
• Sorbents for use especially with sub-bituminous and lignite coals are provided that contain low levels of alkali.
• the high levels of alkali in sorbents of the prior art can contribute to fouling of a furnace in which they are being burned.
• the operator can minimize the sodium and potassium available in the gas phase for unwanted reactions that lead to formation of deposits on boiler surfaces and elsewhere.
• the sorbents can be used to prepare a refined coal that can be burned to reduce emissions of one or more of mercury, nitrogen (as NOx), and sulfur (as SOx).
• a method of making the refined coal involves combining a sub-bituminous coal (or a lignite coal) and sorbent components.
• the sorbents are 0.001-1 wt % of a liquid sorbent, and 0.1 to 10% by weight of a powder sorbent, wherein the percentages are by weight based on the total weight of the refined coal.
• the liquid sorbent contains a bromine compound and the powder sorbent contains calcium, silica, alumina, and further comprises less than 1% Na 2 O by weight and less than 1% K 2 O by weight, and wherein the powder sorbent further comprises less than 0.1% by weight chlorine.
• the powder sorbent contains cement kiln dust (CKD), which is helpful in reducing emissions of NOx, with the improvement that, when the CKD is high in alkali, some of the CKD is substituted by lower alkali materials to reach a specification of less than 2% or less than 1% total alkali.
• the powder sorbent also meets a low chlorine specification to reduce fouling in sub-bituminous and lignite coals.
• the invention provides compositions and methods for reducing emissions of mercury, nitrogen oxides (NOx), and sulfur oxides (SOx) that arise from the combustion of mercury-containing fuels such as coal.
• a commercially valuable embodiment is use of the invention to reduce nitrogen, sulfur and/or mercury emissions from coal burning facilities to protect the environment and comply with government regulations and treaty obligations. Improvements to powder sorbents provide superior performance by reducing fouling in coal-burning furnaces, while removal of environmental pollutants such as NOx and SOx are not deleteriously affected.
• the methods prevent release of mercury into the atmosphere from point sources, such as coal-burning utilities by capturing the mercury in the ash, while at the same time minimizing furnace fouling that could decrease the efficiency of the furnace. Further, the methods prevent release of mercury and other heavy metals into the environment by leaching from solid wastes such as coal ash produced by burning the mercury containing coal. In both these ways, mercury is kept out of bodies of water. Thus, prevention or reduction of mercury emissions from such facilities as coal-burning utilities leads to a variety of environmental benefits, including less air pollution, less water pollution, and less hazardous waste production, with less resulting ground contamination. For convenience but without limitation, advantageous features of the invention are illustrated as preventing air, water, and ground pollution by mercury or other heavy metals.
• a method of burning coal in a furnace to reduce emissions of NO x and at least one of SO x and mercury involves burning a refined coal in the furnace.
• the refined coal in turn is an admixture of sub-bituminous coal, a bromine compound and a powder sorbent.
• the powder sorbent contains calcium, silica, alumina, and is further characterized by a low alkali value of less than 1% by weight Na 2 O and less than 1% by weight K 2 O, based on the weight of the powder sorbent, and preferably also by a low chlorine value of less than 0.5%, less than 0.3%, or less than 0.1%.
• treat levels of the bromine compound are 0.001 to 1.0% by weight, while typical treat levels of the powder sorbent are 0.1 to 10% by weight percentages are based on the weight of the coal.
• the powder sorbent contains CKD or a mixture of CKD with other low alkali powder described herein.
• the powder sorbent can also contain aluminosilicate clay such a kaolin or metakaolin.
• a method of generating energy through combustion of a mercury containing sub-bituminous coal in the furnace of the coal burning facility involves first applying a first sorbent composition onto coal and delivering the coal with the applied first sorbent into the furnace. At the same time, a second sorbent is added into the furnace as the coal with the applied first sorbent is being delivered. The coal is then combusted in the presence of the first and second sorbents in the furnace to produce heat energy and ash.
• the first sorbent contains a bromine compound and the second has a composition of greater than 40% by weight CaO, greater than 10% by weight SiO 2 , 2 to 10% Al 2 O 3 , 1 to 5% Fe 2 O 3 , 1 to 5% MgO, less than 1% by weight Na 2 O, and less than 1% Ka 2 O.
• the second sorbent has less than 0.5% chlorine.
• a method of making a refined coal contains sub-bituminous coal and added sorbent components.
• the method involves add mixing coal, a liquid sorbent (for example 0.001 to 1% by weight, based on the coal) and a powder sorbent (for example 0.1 to 10% by weight based on the coal), wherein the liquid sorbent comprises a bromine compound and powder sorbent comprises greater than 40% CaO, greater than 10% SiO 2 , 2 to 10% Al 2 O 3 , 1 to 5% Fe 2 O 3 , 1 to 5% MgO, less than 1% Na 2 O, and less than 1% K 2 O.
• the powder sorbent is further characterized as having less than 0.5% chlorine or less than 0.1% chlorine.
• sorbent components are used in combination to treat coal ahead of combustion and/or to be added into the flame or downstream of the flame, preferably at minimum temperatures to assure complete formation of the refractory structures that result in various advantages of the methods.
• the product is a refined coal, the use of which lowers environmental pollution and may qualify the utility for certain tax benefits in the United States.
• the sorbent components include calcium, alumina, silica, and halogen.
• K 2 O of the sorbent to a maximum of 1%
• Na 2 O of the sorbent to a maximum of 1%
• percentages are by weight of the powder sorbent containing calcium, alumina, silica, and other components.
• Na 2 O and K 2 O are each less than 0.5% or are each less than 0.1%.
• Calcium is provided by adding to the powder sorbent a compound or composition that has a non-negligible amount of calcium.
• many alkaline powders contain 20% or more calcium, based on CaO.
• Examples are limestone, lime, calcium oxide, calcium hydroxide (slaked lime), portland cement and other manufactured products or by-products of industrial processes, and calcium-containing aluminosilicate minerals.
• Silica and alumina content is based on SiO 2 and Al 2 O 3 equivalents, even though it is appreciated that silica and alumina are often present in a more complex chemical or molecular form.
• the powder sorbent it is advantageous for the powder sorbent to contain an effective amount of cement kiln dust (CKD), which is believed to contribute to the reduction of NOx from the coal-burning facility.
• CKD cement kiln dust
• Some CKD has a relatively high chlorine content, even as high as 10%. If CKD is used, depending on the source of CKD and its natural content of alkali and chlorine, the resulting powder could wind up being too high in alkali and/or chlorine for best results when burning sub-bituminous or lignite coals.
• Such low alkali materials include grind outs (cement kiln clinker that may or may not meet cement product specification and is subsequently ground for blending with CKD); kiln feed (the feed stream going into the cement kiln, including all the components for manufacturing cement, e.g.
• transition cement cement product in silo that is emptied to make room for a specific new cement product
• weathered clinker clinker that has been impounded on site, recovered and ground before adding to the CKD
• impound CKD CKD from on-site impound or waste storage
• limestone limestone
• coal arrives in railcars. If sorbents have already been applied, it is a refined coal. It is a raw coal if sorbents have not yet been applied.
• the coal is delivered onto a receiving belt, which leads the coal into a pug mill. After the pug mill, the coal is discharged to a feed belt and deposited in a coal storage area. Under the coal storage area there is typically a grate and bin area; from there a belt transports the coal to an open stockpile area, sometimes called a bunker. Stoker furnaces can be fed with coal from the bunker or from a crusher.
• the coal is delivered by belt or other means to milling equipment such as a crusher and ultimately to a pulverizer.
• a storage system coal is pulverized and conveyed by air or gas to a collector, from which the pulverized coal is transferred to a storage bin, from which the coal is fed to the furnace as needed.
• a direct fired system coal is pulverized and transported directly to the furnace.
• a semi-direct system the coal goes from the pulverizer to a cyclone collector. The coal is fed directly from the cyclone to the furnace.
• coal is fed into the furnace and burned in the presence of oxygen.
• typical flame temperatures in the combustion chamber are on the order of 2700° F. (about 1480° C.) to about 3000° F. (about 1640° C.) or even higher, such as 3300° F. (about 1815° C.) to 3600° F. (about 1982° C.).
• a refined coal is produced by adding sorbents to coal before combustion.
• the sorbents can be added by the coal producer and shipped to the furnace operator, or the refined coal can be produced in a separate facility near or on the property of the operator.
• a coal containing all the sorbent components is fed to the furnace for combustion.
• sorbent compositions according to the invention are added to the raw coal or into various parts of the furnace during combustion.
• sorbents are added to the coal, in the pug mill, on the receiving belt or feed belt, in the coal storage area, in the collector, in the storage bin, in the cyclone collector, in the pulverizer before or during pulverization, and/or while being transported from the pulverizer to the furnace for combustion.
• the sorbents are added to the coal during processes that mix the coal such as the in the pug mill or in the pulverizer.
• the sorbents are added onto the coal in the pulverizers.
• sorbent components are added into the coal burning system by injecting them into the furnace during combustion of the fuel.
• they are injected into the fireball or close to the fireball, for example where the temperature is above 2000° F., above 2300° F., or above 2700° F.
• effective sorbent addition takes place along with the fuel, with the primary combustion air, above the flame, with or above the overfire air, and so on.
• sorbents are injected from one or more faces of the furnace and/or from one or more corners of the furnace.
• sorbent compositions and sorbent components tends to be most effective when the temperature at injection is sufficiently high and/or the aerodynamics of the burners and furnace set up lead to adequate mixing of the powder sorbents with the fuel and/or combustion products.
• sorbent addition is made to the convective pathway downstream of the flame and furnace.
• optimum injection or application points for sorbents are found by modeling the furnace and choosing parameters (rate of injection, place of injection, distance above the flame, distance from the wall, mode of powder spraying, and the like) that give the best mixing of sorbent, coal, and combustion products for the desired results.
• the convective pathway of the facility contains a number of zones characterized by the temperature of the gases and combustion products in each zone. Generally, the temperature of the combustion gas falls as it moves in a direction downstream from the fireball. From the furnace, where the coal in one example is burning at a temperature of approximately 2700° F.-3600° F. (about 1480° C.-1650° C.), the fly ash and combustion gases move downstream in the convective pathway to zones of ever decreasing temperature. To illustrate, downstream of the fireball is a zone with temperature less that 2700° F.
• a point is reached where the temperature has cooled to about 1500° F. Between the two points is a zone having a temperature from about 1500° F. to about 2700° F. Further downstream, a zone of less than 1500° F. is reached, and so on. Further along in the convective pathway, the gases and fly ash pass through lower temperature zones until the baghouse or electrostatic precipitator is reached, which typically has a temperature of about 300° F. before the gases are emitted up the stack.
• the combustion gases contain carbon dioxide as well as various undesirable gases containing sulfur, nitrogen, and mercury.
• the convective pathways are also filled with a variety of ash which is swept along with the high temperature gases.
• particulate removal systems are used to remove the ash before emission into the atmosphere.
• a variety of such removal systems such as electrostatic precipitators and a bag house, are generally disposed in the convective pathway.
• chemical scrubbers can be positioned in the convective pathway.
• there may be provided various instruments to monitor components of the gas such as sulfur (as SOx), nitrogen (as NOx), and mercury.
• the process of the present invention calls for the application of sorbents
• sorbents are made “into the coal burning system” in any of pre-combustion, co-combustion, or post-combustion modes, or in any combination.
• the sorbents are added into the coal burning system, the coal or other fuel is said to be combusted “in the presence” the various sorbents, sorbent compositions, or sorbent components
• downstream addition is carried out where the temperature is about 1500° F. (815.5° C.) to about 2700° F. (1482.2° C.).
• the cutoff point or distinction between “into the furnace”, “into the fireball”, and “into the convective pathways” can be rather arbitrary.
• the combustion gases leave what is clearly a burning chamber or furnace and enter a separate structure that is clearly a flue or convective pathway for gases downstream of the furnace.
• many furnaces are quite large and so permit addition of sorbents “into the furnace” at a considerable distance from where the fuel and air are being fed to form the fireball.
• some furnaces have overfire air injection ports and the like specifically designed to provide additional oxygen at a location above the fireball to achieve more complete combustion and/or control of emissions such as nitrogen oxides.
• the overfire air ports can be 20 feet or higher above the fuel injection.
• sorbent components or compositions are injected directly into the fireball along with coal being fed, at a location above the coal feed, above or below the overfire air ports, or at a higher location within the burning chamber, such as at or just under the nose of the furnace. Each of these locations is characterized by a temperature and by conditions of turbulent flow that contribute to mixing of the sorbents with the fuel and/or the combustion products (such as the fly ash).
• application is preferably made where the temperature is above 1500° F., preferably above 2000° F., more preferably where the temperature is above 2300° F., and most preferably where the temperature is above 2700° F.
• sorbent compositions that tend to reduce or remediate the release of mercury, nitrogen, and/or sulfur from coal burning utilities also have the beneficial effect of rendering the ash produced by combustion of the fuel highly cementitious. As a result, the ash is usable in commerce as a partial or complete replacement for portland cement in various cement and concrete products.
• Burning the coal with the sorbent compositions described herein results in an ash that has, in various embodiments, increased levels of the heavy metals compared to coal burned without the sorbent, but which nevertheless contains lower levels of leachable heavy metals than the ash produced without the sorbents.
• the ash is safe to handle and to sell into commerce, for example as a cementitious material.
• a carbonaceous fuel is burned to produce heat energy from combustion of the carbonaceous material.
• Unburned material and particulate combustion products form ash, some of which collects at the bottom of the furnace, but the majority of which is collected as fly ash from the flue by precipitators or filters, for example a bag house on a coal burning facility.
• the content of the bottom ash and the fly ash depends on the chemical composition of the coal and on the amount and composition of sorbent components added into the coal burning facility during combustion.
• mercury emissions from the coal burning facility are monitored. Emissions are monitored as elemental mercury, oxidized mercury, or both. Elemental mercury means mercury in the ground or zero oxidation state, while oxidized mercury means mercury in the +1 or +2 oxidation state.
• the amount of sorbent composition added pre-, co-, and/or post-combustion is raised, lowered, or is maintained unchanged. In general, it is desirable to remove as high a level of mercury as is practical. In embodiments, mercury removal of at least 40% up to 90% and greater can be achieved, based on the total amount of mercury in the coal.
• This number refers to the mercury removed from the flue gases so that mercury is not released through the stack into the atmosphere.
• the numbers correspond to the percent reductions in emissions of mercury from the facility, compared to burning the coal without sorbent. Normally, removal of mercury from the flue gases leads to increased levels of mercury in the ash. To minimize the amount of sorbent added into the coal burning process so as to reduce the overall amount of ash produced in the furnace, it is desirable in many embodiments to use the measurements of mercury emissions to adjust the sorbent composition rate of addition to one which will achieve the desired mercury reduction without adding excess material into the system.
• mercury and other heavy metals in the coal such as arsenic, antimony, lead, and others report to the bag house or electrostatic precipitator and become part of the overall ash content of the coal burning plant; alternatively or in addition, the mercury and heavy metals are found in the bottom ash. As such, emissions of mercury and other heavy metals from the facility are reduced.
• mercury and other heavy metals in the ash are resistant to leaching under acidic conditions, even though they tend to be present in the ash at elevated levels relative to ash produced by burning coal without the sorbent components described herein.
• heavy metals in the ash do not leach beyond regulatory levels; in fact, a decreased level of leachable heavy metal is observed in the ash on a ppm basis, even though the ash normally contains a higher absolute level of heavy metals by virtue of being produced by burning with the sorbents.
• the cementitious nature of the ash is enhanced, the ash from the combustion (coal ash) is valuable for sale in commerce and use, for example, as a cementitious material to make portland cements as well as concrete products and ready mixes.
• leaching of heavy metals is monitored or analyzed periodically or continuously during combustion.
• the TCLP procedure of the United States Environmental Protection Agency is a commonly used method.
• the amount of sorbent, particularly of sorbent components with Si (SiO 2 or equivalents) and/or Al (Al 2 O 3 or equivalents) is adjusted based on the analytical result to maintain the leaching in a desired range.
• a method for burning coal to reduce the amount of mercury released into the atmosphere involves applying a sorbent composition comprising a halogen compound into the system in which the coal is being combusted.
• the halogen compound is preferably a bromine compound; in a preferred embodiment, the sorbent is free of alkali metal compounds so as to avoid corrosion on boiler tubes or other furnace components.
• the coal is combusted in the furnace to produce ash and combustion gases.
• the combustion gases contain mercury, sulfur and other components.
• the mercury level in the combustion gases is preferably monitored, for example by measuring the level analytically.
• the amount of the sorbent composition applied is adjusted (i.e., by increasing it, decreasing it, or in some cases deciding to leave it unchanged) depending on the value of the mercury level measured in the combustion gases.
• the sorbent is added into the system by applying it to the coal pre-combustion, then delivering the coal containing the sorbent into the furnace for combustion.
• sorbent components comprising a halogen (preferably bromine or iodine, and most preferably bromine) compound and at least one aluminosilicate material are applied into the coal burning system.
• the components are added separately or as a single sorbent composition, and are optionally added onto the coal pre-combustion, into the furnace during combustion, or into the flue gases downstream of the furnace at suitable temperatures.
• the components are added to the coal pre-combustion, and the coal containing the sorbent is then delivered into the furnace for combustion.
• mercury is monitored in the flue gases and the sorbent application rate is adjusted depending on the value of the measured mercury level.
• the halogen contributes to lowering the level of mercury emissions, while the aluminosilicate contributes to making mercury captured in the ash non-leaching.
• a method for reducing leaching of mercury and/or of other heavy metals from ash produced from the combustion of coal or other fuel in a coal burning system or in an incinerator involves introducing sorbents containing silica and alumina into the incinerator or coal burning system during combustion, measuring leaching of mercury and/or other heavy metals from the resulting ash, and adjusting the level of silica and alumina added according to the measured leaching of heavy metals. If leaching is higher than desired, the rate of application of the sorbent can be increased to bring the leaching back down into the desired range.
• the sorbent further contains a halogen (e.g. bromine) compound to enhance capture of mercury in the ash.
• the sorbent containing silica and alumina is added in a powder composition that contains ⁇ 1% Na 2 O and ⁇ 1% K 2 O, to reduce or eliminate fouling.
• the invention provides a method for reducing the amount of oxidized mercury in flue gases that are generated by combustion of mercury-containing carbonaceous fuel such as coal while at the same time producing a cementitious ash product.
• the method comprises burning the fuel in the presence of an alkaline powder sorbent wherein the powder sorbent comprises calcium, silica, and alumina.
• the alkaline powder is added to the coal pre-combustion, injected into the furnace during combustion, applied into the flue gases downstream of the furnace (preferably where the temperature is 1500° F. or greater), or in any combination.
• the powders are alkaline, characterized by a pH above 7 when combined with water, preferably above 8 and preferably above 9.
• the sorbent contains less that 1% each, less than 0.5% each, or less than 0.1% each by weight of alkalis such as Na 2 O and K 2 O.
• the sorbent further contains iron and magnesium.
• the aluminum content of the sorbent is higher than the alumina content of portland cement, preferably above about 5% or above about 7% alumina.
• a level of mercury (oxidized, elemental, or both) is measured in the flue gases downstream from the furnace.
• the measured mercury level is compared to a target level and, if the measured level is above the targeted level, the amount of powder sorbent added relative to the amount of fuel being burned is increased. Alternatively, if the measured level is at or below the target level, the rate of sorbent addition can be decreased or maintained unchanged.
• the powder composition is an alkaline sorbent composition that contains an alkaline calcium component as well as significant levels of silica and alumina.
• the powder composition comprises 2 to 50% of an aluminosilicate material and 50 to 98% by weight of an alkaline powder comprising calcium.
• the alkaline powder comprises one or more of lime, calcium oxide, portland cement, cement kiln dust, lime kiln dust, and sugar beet lime, while the aluminosilicate material contains one or more selected from the group consisting of calcium montmorillonite, sodium montmorillonite, and kaolin.
• the powder sorbent comprises CKD and other material to meet a low alkali specification and/or a low chorine specification.
• the powder composition is added to the coal at a rate of about 0.1 to about 10% by weight, based on the amount of coal being treated with the sorbents for a batch process, or on the rate of coal being consumed by combustion for a continuous process.
• the rate is 0.1-5%, 0.1-2%, 0.1-1.5%, 0.1-1%, from 1 to 8% by weight, 2 to 8% by weight, 4 to 8% by weight, 4 to 6% by weight, or about 6% by weight.
• the powder composition is injected to the fireball or furnace during combustion and/or is applied to the coal under ambient conditions, prior to its combustion.
• the temperature at the injection point is preferably at least about 1000° F. or higher. For some low value fuels, this corresponds to injection into or close to the fireball.
• a method for reducing mercury and/or sulfur emitted into the environment during combustion of coal in a coal burning system comprises adding sorbent components comprising bromine, calcium, silica, and alumina into the coal burning system and combusting the coal in the presence of the sorbent components to produce combustion gases and fly ash.
• the amount of mercury in the combustion gases is measured and level of components containing bromine added into the system is adjusted depending on the measured value of mercury in the combustion gases.
• the four components (calcium, silica, alumina, and bromine) are added together or separately to the coal pre-combustion, to the furnace, and/or to the flue gases at suitable temperature as described herein.
• Sorbents containing the components preferably contain a maximum of 1% by weight Na 2 O and a maximum of 1% by weight K 2 O.
• bromine is present at a level effective to a capture, in the ash, at least 20%, at least 40%, at least 80% or at least 90% of the mercury in the coal, and silica and alumina are present at levels effective to produce fly ash with a leaching value of less than 0.2 ppm (200 ppb) with respect to mercury, preferably less than 100 ppb Hg, less than 50 ppb, and most preferably less than 2 ppb with respect to mercury.
• a level of 2 ppb represents the current lower detectable limit of the TCLP test for mercury leaching.
• the methods provide coal ash and/or fly ash containing mercury at a level corresponding to capture in the ash of at least 40% or of at least 90% of the mercury originally in the coal before combustion.
• the mercury level is higher than in known fly ashes due to capture of mercury in the ash rather than release of mercury into the atmosphere.
• Fly ash produced by the process contains up to 200 ppm mercury or higher; in some embodiments the mercury content of the fly ash is above 250 ppm. Since the volume of ash is normally increased by use of the sorbents (in typical embodiments, the volume of ash about doubles), the increased measured levels of mercury represent significant capture in the ash of mercury that, without the sorbents, would have been released into the environment.
• the content in the fly ash of mercury and other heavy metals such as lead, chromium, arsenic, and cadmium is generally higher than in fly ash produced from burning coal without the added sorbents or sorbent components.
• the mercury in the coal ash is non-leaching in that it exhibits a concentration of mercury in the extract of less than 0.2 ppm when tested using the Toxicity Characteristic Leaching Procedure (TCLP), test Method 1311 in “Test Methods for Evaluating Solid Waste, Physical/Chemical Methods,” EPA Publication SW—846—Third Edition, as incorporated by reference in 40 CFR ⁇ 260.11.
• TCLP Toxicity Characteristic Leaching Procedure
• fly ash from burning coal with the sorbents described herein has less leachable mercury than ash produced from burning coal without the sorbent, even though the total mercury content in ash produced from the sorbent treated coal is higher by as much as a factor of 2 or more over the level in ash produced by burning without the sorbents.
• typical ash from burning of PRB coal contains about 100-125 ppm mercury; in various embodiments, ash produced by burning PRB coal with about 6% by weight of the sorbents described herein has about 200-250 ppm mercury
• the invention provides a hydraulic cement product containing portland cement and from 0.1% to about 99% by weight, based on the total weight of the cement product, of a coal ash or fly ash described above.
• the invention provides a pozzolanic product comprising a pozzolan and from 0.01% to about 99% by weight, based on the total weight of the pozzolanic product of the ash described above.
• the invention also provides a cementitious mixture containing the hydraulic cement product.
• the invention further provides a concrete ready mix product containing aggregate and the hydraulic cement product.
• a cementitious mixture contains coal ash described herein as the sole cementitious component; in these embodiments, the ash is a total replacement for conventional cements such as portland cement.
• the cementitious mixtures contain cement and optionally aggregate, fillers, and/or other admixtures.
• the cementitious mixtures are normally combined with water and used as concrete, mortars, grout, flowable fill, stabilized base, and other applications.
• the methods thus encompass burning coal with the added sorbents to produce coal ash and energy for heat or electricity generation.
• the ash is then recovered and used to formulate cementitious mixtures including cements, mortars, and grouts.
• powder sorbent compositions described herein contain one or more alkaline powders containing calcium, along with lesser levels of one or more aluminosilicate materials.
• the halogen component if desired, is added as a further component of the alkaline powder or is added separately as part of a liquid or powder composition.
• use of the sorbents leads to a reduction in emissions or releases of sulfur, nitrogen, mercury, other heavy metals such as lead and arsenic, and/or chlorine from the coal burning system.
• Sorbent compositions used in various embodiments of the invention described above and herein contain components that contribute calcium, silica, and/or alumina, preferably in the form of alkaline powders.
• the compositions also contain iron oxide,
• the powder sorbent contains about 2-10% by weight Al 2 O 3 , greater than 40%, for example about 40-70% CaO, >10% SiO 2 , about 1-5% Fe 2 O 3 , and ⁇ 2% of total alkalis such as sodium oxide and potassium oxide, preferably less than 1%.
• use of the sorbents leads to reductions in the amount of NOx, SOx, and/or mercury released into the atmosphere
• the sorbent compositions contain suitable high levels of alumina and silica. It is believed that the presence of alumina and/or silica leads to several advantages seen from use of the sorbent. To illustrate, it is believed that the presence of alumina and/or silica and/or the balance of the silica/alumina with calcium, iron, and other ingredients contributes to the low acid leaching of mercury and/or other heavy metals that is observed in ash produced by combustion of coal or other fuels containing mercury in the presence of the sorbents.
• the components that contribute calcium, silica, and/or alumina are preferably provided as alkaline powders.
• alkaline nature of the sorbent components leads at least in part to the desirable properties described above.
• the alkaline nature of the powders leads to a reduction in sulfur pitting.
• a geopolymeric ash is formed in the presence of the sorbents, coupling with silica and alumina present in the sorbent to form a ceramic like matrix that reports as a stabilized ash.
• the stabilized ash is characterized by very lowing leaching of mercury and other heavy metals. In some embodiments, the leaching of mercury is below detectable limits.
• the present teachings describe how to overcome that disadvantage by using sorbents of lower alkalinity (as measured by content of Na 2 O and K 2 O) and/or lower chlorine, especially for use with sub-bituminous and lignite coals.
• Sources of calcium for the sorbent compositions of the invention include, without limitation, calcium powders such as calcium carbonate, limestone, dolomite, calcium oxide, calcium hydroxide, calcium phosphate, and other calcium salts.
• Industrial products such as limestone, lime, slaked lime, and the like contribute major proportions of such calcium salts. As such, they are suitable components for the sorbent compositions of the invention.
• Other sources of calcium include various manufactured products. Such products are commercially available, and some are sold as waste products or by-products of other industrial processes. In preferred embodiments, the products further contribute either silica, alumina, or both to the compositions of the invention.
• Non-limiting examples of industrial products that contain silica and/or alumina in addition to calcium include portland cement, cement kiln dust, lime kiln dust, sugar beet lime, slags (such as steel slag, stainless steel slag, and blast furnace slag), paper de-inking sludge ash, cupola arrester filter cake, and cupola furnace dust.
• Other alkaline powders containing calcium, silica, and alumina include pozzolanic materials, wood ash, rice hull ash, class C fly ash, and class F fly ash.
• these and similar materials are suitable components of sorbent compositions, especially if the resulting composition containing them as components falls within the preferred range of 2 to 10% by weight Al 2 O 3 , greater than 40% by weight CaO, greater than 10% by weight SiO 2 , about 1 to 5% Fe 2 O 3 , and less than 2% by weight total alkali.
• Mixtures of materials are also used. Non-limiting examples include mixtures of portland cement and lime, and mixtures containing cement kiln dust, such as cement kiln dust and lime kiln dust.
• Sugar beet lime is a solid waste material resulting from the manufacture of sugar from sugar beets. It is high in calcium content, and also contains various impurities that precipitate in the liming procedure carried out on sugar beets. It is an item of commerce, and is normally sold to landscapers, farmers, and the like as a soil amendment.
• Cement kiln dust generally refers to a byproduct generated within a cement kiln or related processing equipment during portland cement manufacturing.
• CKD comprises a combination of different particles generated in different areas of the kiln, pre-treatment equipment, and/or material handling systems, including for example, clinker dust, partially to fully calcined material dust, and raw material (hydrated and dehydrated) dust.
• the composition of the CKD varies based upon the raw materials and fuels used, the manufacturing and processing conditions, and the location of collection points for CKD within the cement manufacturing process.
• CKD can include dust or particulate matter collected from kiln effluent (i.e., exhaust) streams, clinker cooler effluent, pre-calciner effluent, air pollution control devices, and the like.
• Commercial CKD has a range of alkalinity, depending on its source.
• the low alkali CKD it is possible to meet the low alkali spec of the powder sorbents described herein by using the low alkali CKD. If only high alkali CKD is available, it may be necessary to blend off or substitute part of the high alkali CKD product with the lower alkali material described above.
• CKD compositions will vary for different kilns, CKD usually has at least some cementitious and/or pozzolanic properties, due to the presence of the dust of clinker and calcined materials.
• Typical CKD compositions comprise silicon-containing compounds, such as silicates including tricalcium silicate, dicalcium silicate; aluminum-containing compounds, such as aluminates including tricalcium aluminate; and iron-containing compounds, such as ferrites including tetracalcium aluminoferrite.
• CKD generally comprises calcium oxide (CaO).
• Exemplary CKD compositions comprise about 10 to about 60% calcium oxide, optionally about 25 to about 50%, and optionally about 30 to about 45% by weight.
• CKD comprises a concentration of free lime (available for a hydration reaction with water) of about 1 to about 10%, optionally of about 1 to about 5%, and in some embodiments about 3 to about 5%. Further, in certain embodiments, CKD comprises compounds containing alkali metals, alkaline earth metals, and sulfur, inter alia.
• blended-cement products are one suitable example of such a source. These blended cement products typically contain mixes of portland cement and/or its clinker combined with slag(s) and/or pozzolan(s) (e.g., fly ash, silica fume, burned shale). Pozzolans are usually silicaceous materials that are not in themselves cementitious, but which develop hydraulic cement properties when reacted with free lime (free CaO) and water.
• masonry cement and/or hydraulic lime which include mixtures of portland cement and/or its clinker with lime or limestone.
• suitable sources are aluminous cements, which are hydraulic cements manufactured by burning a mix of limestone and bauxite (a naturally occurring, heterogeneous material comprising one or more aluminum hydroxide minerals, plus various mixtures of silica, iron oxide, titania, aluminum silicates, and other impurities in minor or trace amounts).
• a pozzolan cement which is a blended cement containing a substantial concentration of pozzolans. Usually the pozzolan cement comprises calcium oxide, but is substantially free of portland cement.
• Common examples of widely-employed pozzolans include natural pozzolans (such as certain volcanic ashes or tuffs, certain diatomaceous earth, burned clays and shales) and synthetic pozzolans (such as silica fume and fly ash).
• Lime kiln dust is a byproduct from the manufacturing of lime.
• LKD is dust or particulate matter collected from a lime kiln or associated processing equipment.
• Manufactured lime can be categorized as high-calcium lime or dolomitic lime, and LKD varies based upon the processes that form it.
• Lime is often produced by a calcination reaction conducted by heating calcitic raw material, such as calcium carbonate (CaCO 3 ), to form free lime CaO and carbon dioxide (CO 2 ).
• High-calcium lime has a high concentration of calcium oxide and typically some impurities, including aluminum-containing and iron-containing compounds.
• High-calcium lime is typically formed from high purity calcium carbonate (about 95% purity or greater).
• Typical calcium oxide content in an LKD product derived from high-calcium lime processing is greater than or equal to about 75% by weight, optionally greater than or equal to about 85% by weight, and in some cases greater than or equal to about 90% by weight.
• dolomite CaCO 3 .MgCO 3
• CaO calcium oxide
• MgO magnesium oxide
• calcium oxide can be present at greater than or equal to about 45% by weight, optionally greater than about 50% by weight, and in certain embodiments, greater than about 55% by weight.
• LKD varies based upon the type of lime processing employed, it generally has a relatively high concentration of free lime. Typical amounts of free lime in LKD are about 10 to about 50%, optionally about 20 to about 40%, depending upon the relative concentration of calcium oxide present in the lime product generated.
• Slags are generally byproduct compounds generated by metal manufacturing and processing.
• the term “slag” encompasses a wide variety of byproduct compounds, typically comprising a large portion of the non-metallic byproducts of ferrous metal and/or steel manufacturing and processing.
• slags are considered to be a mixture of various metal oxides, however they often contain metal sulfides and metal atoms in an elemental form.
• slag byproducts useful for certain embodiments of the invention include ferrous slags, such as those generated in blast furnaces (also known as cupola furnaces), including, by way of example, air-cooled blast furnace slag (ACBFS), expanded or foamed blast furnace slag, pelletized blast furnace slag, granulated blast furnace slag (GBFS), and the like.
• Steel slags can be produced from basic oxygen steelmaking furnaces (BOS/BOF) or electric arc furnaces (EAF).
• BOS/BOF basic oxygen steelmaking furnaces
• EAF electric arc furnaces
• Many slags are recognized for having cementitious and/or pozzolanic properties, however the extent to which slags have these properties depends upon their respective composition and the process from which they are derived, as recognized by the skilled artisan.
• Exemplary slags comprise calcium-containing compounds, silicon-containing compounds, aluminum-containing compounds, magnesium-containing compounds, iron-containing compounds, manganese-containing compounds and/or sulfur-containing compounds.
• the slag comprises calcium oxide at about 25 to about 60%, optionally about 30 to about 50%, and optionally about 30 to about 45% by weight.
• GGBFS ground granulated blast furnace slag
• blast furnace dust collected from air pollution control devices attached to blast furnaces, such as cupola arrester filter cake.
• Another suitable industrial byproduct source is paper de-inking sludge ash.
• manufactured/industrial process byproducts that are feasible as a source of calcium for the alkaline powders that form the sorbent compositions of the invention.
• Many of these well known byproducts comprise alumina and/or silica, as well.
• Some, such as lime kiln dust contain major amounts of CaO and relatively small amounts of silica and alumina.
• Combinations of any of the exemplary manufactured products and/or industrial byproducts are also contemplated for use as the alkaline powders of certain embodiments of the invention.
• desired treat levels of silica and/or alumina are above those provided by adding materials such as portland cement, cement kiln dust, lime kiln dust, and/or sugar beet lime. Accordingly, it is possible to supplement such materials with aluminosilicate materials, such as without limitation clays (e.g. montmorillonite, kaolins, and the like) where needed to provide preferred silica and alumina levels.
• supplemental aluminosilicate materials make up at least about 2%, and preferably at least about 5% by weight of the various sorbent components added into the coal burning system. In general, there is no upper limit from a technical point of view as long as adequate levels of calcium are maintained.
• the sorbent components preferably comprise from about 2 to 50%, preferably 2 to 20%, and more preferably, about 2 to 10% by weight aluminosilicate material such as the exemplary clays.
• a non-limiting example of a sorbent is about 93% by weight of a blend of CKD and LKD (for example, a 50:50 blend or mixture) and about 7% by weight of an aluminosilicate clay.
• an alkaline powder sorbent composition contains one or more calcium-containing powders such as portland cement, cement kiln dust, lime kiln dust, various slags, and sugar beet lime, along with an aluminosilicate clay such as, without limitation, montmorillonite or kaolin.
• the sorbent composition preferably contains sufficient SiO 2 and Al 2 O 3 to form a refractory-like mixture with calcium sulfate produced by combustion of the sulfur-containing coal in the presence of the CaO sorbent component such that the calcium sulfate is handled by the particle control system; and to form a refractory mixture with mercury and other heavy metals so that the mercury and other heavy metals are not leached from the ash under acidic conditions.
• the calcium containing powder sorbent contains by weight a minimum of 10% silica and 2-10% alumina.
• the alumina level is higher than that found in portland cement, that is to say higher than about 5% by weight, preferably higher than about 6% by weight, based on Al 2 O 3 .
• the sorbent components of the alkaline powder sorbent composition work together with optional added halogen (such as bromine) compound or compounds to capture chloride as well as mercury, lead, arsenic, and other heavy metals in the ash, render the heavy metals non-leaching under acidic conditions, and improve the cementitious nature of the ash produced.
• halogen such as bromine
• the sorbent components of the alkaline powder sorbent composition work together with optional added halogen (such as bromine) compound or compounds to capture chloride as well as mercury, lead, arsenic, and other heavy metals in the ash, render the heavy metals non-leaching under acidic conditions, and improve the cementitious nature of the ash produced.
• halogen such as bromine
• Suitable aluminosilicate materials include a wide variety of inorganic minerals and materials.
• a number of minerals, natural materials, and synthetic materials contain silicon and aluminum associated with an oxy environment along with optional other cations such as, without limitation, Na, K, Be, Mg, Ca, Zr, V, Zn, Fe, Mn, and/or other anions, such as hydroxide, sulfate, chloride, carbonate, along with optional waters of hydration.
• Such natural and synthetic materials are referred to herein as aluminosilicate materials and are exemplified in a non-limiting way by the clays noted above.
• aluminosilicate materials the silicon tends to be present as tetrahedra, while the aluminum is present as tetrahedra, octahedra, or a combination of both. Chains or networks of aluminosilicate are built up in such materials by the sharing of 1, 2, or 3 oxygen atoms between silicon and aluminum tetrahedra or octahedra.
• Such minerals go by a variety of names, such as silica, alumina, aluminosilicates, geopolymer, silicates, and aluminates.
• compounds containing aluminum and/or silicon tend to produce silica and alumina upon exposure to high temperatures of combustion in the presence of oxygen
• aluminosilicate materials include polymorphs of SiO 2 .Al 2 O 3 .
• silliminate contains silica octahedra and alumina evenly divided between tetrahedra and octahedra.
• Kyanite is based on silica tetrahedra and alumina octahedra.
• Andalusite is another polymorph of SiO 2 .Al 2 O 3 .
• chain silicates contribute silicon (as silica) and/or aluminum (as alumina) to the compositions of the invention.
• Chain silicates include without limitation pyroxene and pyroxenoid silicates made of infinite chains of SiO 4 tetrahedra linked by sharing oxygen atoms.
• aluminosilicate materials include sheet materials such as, without limitation, micas, clays, chrysotiles (such as asbestos), talc, soapstone, pyrophillite, and kaolinite. Such materials are characterized by having layer structures wherein silica and alumina octahedra and tetrahedra share two oxygen atoms.
• Layered aluminosilicates include clays such as chlorites, glauconite, illite, polygorskite, pyrophillite, sauconite, vermiculite, kaolinite, calcium montmorillonite, sodium montmorillonite, and bentonite. Other examples include micas and talc.
• Suitable aluminosilicate materials also include synthetic and natural zeolites, such as without limitation the analcime, sodalite, chabazite, natrolite, phillipsite, and mordenite groups.
• Other zeolite minerals include heulandite, brewsterite, epistilbite, stilbite, yagawaralite, laumontite, ferrierite, paulingite, and clinoptilolite.
• the zeolites are minerals or synthetic materials characterized by an aluminosilicate tetrahedral framework, ion exchangeable “large cations” (such as Na, K, Ca, Ba, and Sr) and loosely held water molecules.
• framework or 3D silicates, aluminates, and aluminosilicates are used.
• Framework aluminosilicates are characterized by a structure where SiO 4 tetrahedra, AlO 4 tetrahedra, and/or AlO 6 octahedra are linked in three dimensions.
• Non-limiting examples of framework silicates containing both silica and alumina include feldspars such as albite, anorthite, andesine, bytownite, labradorite, microcline, sanidine, and orthoclase.
• the sorbent powder compositions are characterized in that they contain a major amount of calcium, preferably greater than 20% or greater than 40% by weight based on calcium oxide, and that furthermore they contain levels of silica, and/or alumina higher than that found in commercial products such as portland cement.
• the sorbent compositions comprise greater than 5% by weight alumina, preferably greater than 6% by weight alumina, preferably greater than 7% by weight alumina, and preferably greater than about 8% by weight alumina.
• Coal or other fuel is treated with sorbent components at rates effective to control the amount of nitrogen, sulfur and/or mercury released into the atmosphere upon combustion.
• total treatment levels of the sorbent components ranges from about 0.1% to about 20% by weight, based on the weight of the coal being treated or on the rate of the coal being consumed by combustion, when the sorbent is a powder sorbent containing calcium, silica, and alumina.
• the component treat levels correspond to sorbent treat levels. In this way a single sorbent composition can be provided and metered or otherwise measured for addition into the coal burning system.
• the treatment level of sorbent ranges from about 0.1% to about 10% by weight, in some embodiments from about 1 or 2% by weight to about 10% by weight. For many coals, an addition rate of 6% by weight of powder sorbent has been found to be acceptable.
• Sorbent compositions comprising a halogen compound contain one or more organic or inorganic compounds that contain a halogen.
• Halogens include chlorine, bromine, and iodine.
• Preferred halogens are bromine and iodine.
• the halogen compounds are sources of the halogens, especially of bromine and iodine.
• sources of the halogen include various inorganic salts of bromine including bromides, bromates, and hypobromites.
• organic bromine compounds are less preferred because of their cost or availability. However, organic sources of bromine containing a suitably high level of bromine are considered within the scope of the invention.
• Non-limiting examples of organic bromine compounds include methylene bromide, ethyl bromide, bromoform, and carbon tetrabromide.
• Non-limiting inorganic sources of iodine include hypoiodites, iodates, and iodides, with iodides being preferred.
• Organic iodine compounds can also be used.
• the halogen compound is an inorganic substituent, it is preferably a bromine or iodine containing salt of an alkaline earth element.
• alkaline earth elements include beryllium, magnesium, and calcium.
• halogen compounds particularly preferred are bromides and iodides of alkaline earth metals such as calcium.
• Alkali metal bromine and iodine compounds such as bromides and iodides are effective in reducing mercury emissions. But in some embodiments, they are less preferred as they tend to cause corrosion on the boiler tubes and other steel surfaces and/or contribute to tube degradation and/or firebrick degradation. In various embodiments, it has been found desirable to avoid potassium salts of the halogens, in order to avoid problems in the furnace.
• the use of alkaline earth salts such as calcium tends to avoid such problems with sodium and/or potassium.
• the sorbents added into the coal burning system contain essentially no alkali metal-containing bromine or iodine compounds, or more specifically essentially no sodium-containing or potassium-containing bromine or iodine compounds.
• sorbent compositions containing halogen are provided in the form of a liquid or of a solid composition.
• the halogen-containing composition is applied to the coal before combustion, is added to the furnace during combustion, and/or is applied into flue gases downstream of the furnace.
• the halogen composition is a solid, it can further contain the calcium, silica, and alumina components described herein as the powder sorbent.
• a solid halogen composition is applied onto the coal and/or elsewhere into the combustion system separately from the sorbent components comprising calcium, silica, and alumina. When it is a liquid composition it is generally applied separately.
• liquid mercury sorbent comprises a solution containing 5 to 60% by weight of a soluble bromine or iodine containing salt.
• a soluble bromine or iodine containing salt Non-limiting examples of preferred bromine and iodine salts include calcium bromide and calcium iodide.
• liquid sorbents contain 5-60% by weight of calcium bromide and/or calcium iodide.
• mercury sorbents having as high level of bromine or iodine compound as is feasible.
• the liquid sorbent contains 50% or more by weight of the halogen compound, such as calcium bromide or calcium iodide.
• the sorbent compositions containing a halogen compound further contain a nitrate compound, a nitrite compound, or a combination of nitrate and nitrite compounds.
• Preferred nitrate and nitrite compounds include those of magnesium and calcium, preferably calcium.
• one embodiment of the present invention involves the addition of liquid mercury sorbent directly to raw or crushed coal prior to combustion.
• mercury sorbent is added to the coal in the coal feeders.
• Addition of liquid mercury sorbent ranges from 0.01 to 5%.
• treatment is at less than 5%, less than 4%, less than 3%, or less than 2%, less than 1%, less than 0.5%, and less than 0.2% where all percentages are based on the amount of coal being treated or on the rate of coal consumption by combustion. Higher treatment levels are possible, but tend to waste material, as no further benefit is achieved.
• Preferred treatment levels are from 0.025 to 2.5% by weight on a wet basis.
• the amount of solid bromide or iodide salt added by way of the liquid sorbent is of course reduced by its weight fraction in the sorbent.
• addition of bromide or iodide compound is at a low level such as from 0.01% to 1% by weight based on the solid.
• the sorbent is then added at a rate of 0.02% to 2% to achieve the low levels of addition.
• the coal is treated by a liquid sorbent at a rate of 0.02 to 1%, preferably 0.02 to 0.5% calculated assuming the calcium bromide is about 50% by weight of the sorbent.
• liquid sorbent containing 50% calcium bromide is added onto the coal prior to combustion, the percentage being based on the weight of the coal.
• initial treatment is started at low levels (such as 0.01% to 0.1%) and is incrementally increased until a desired (low) level of mercury emissions is achieved, based on monitoring of emissions.
• Similar treatment levels of halogen are used when the halogen is added as a solid or in multi-component compositions with other components such as calcium, silica, alumina, iron oxide, and so on.
• liquid sorbent When used, liquid sorbent is sprayed, dripped, or otherwise delivered onto the coal or elsewhere into the coal burning system.
• addition is made to the coal or other fuel at ambient conditions prior to entry of the fuel/sorbent composition into the furnace.
• sorbent is added onto powdered coal prior to its injection into the furnace.
• liquid sorbent is added into the furnace during combustion and/or into the flue gases downstream of the furnace.
• Addition of the halogen containing mercury sorbent composition is often accompanied by a drop in the mercury levels measured in the flue gases within a minute or a few minutes; in various embodiments, the reduction of mercury is in addition to a reduction achieved by use of an alkaline powder sorbent based on calcium, silica, and alumina.
• the invention involves the addition of a halogen component (illustratively a calcium bromide solution) directly to the furnace during combustion.
• a halogen component illustrated as a calcium bromide solution
• the invention provides for an addition of a calcium bromide solution such as discussed above, into the gaseous stream downstream of the furnace in a zone characterized by a temperature in the range of 2700° F. to 1500° F., preferably 2200° F. to 1500° F.
• treat levels of bromine compounds, such as calcium bromide are divided between co-, pre- and post-combustion addition in any proportion.
• various sorbent components are added onto coal prior to its combustion to make a so-called refined coal.
• the coal onto which the sorbents are applied is preferably particulate coal, and is optionally pulverized or powdered according to conventional procedures.
• the coal is pulverized so that 75% by weight of the particles passes through a 200 mesh screen (a 200 mesh screen has hole diameters of 75 ⁇ m).
• the sorbent components are added onto the coal as a solid or as a combination of a liquid and a solid.
• solid sorbent compositions are in the form of a powder.
• a sorbent is added as a liquid (illustratively as a solution of one or more bromine or iodine salts in water), in one embodiment the coal remains wet when fed into the burner.
• a sorbent composition is added onto the coal continuously at the coal burning facility by spraying or mixing onto the coal while it is on a conveyor, screw extruder, or other feeding apparatus.
• a sorbent composition is separately mixed with the coal at the coal burning facility or at the coal producer.
• the sorbent composition is added as a liquid or a powder to the coal as it is being fed into the burner.
• the sorbent is applied into the pulverizers that pulverize the coal prior to injection.
• the rate of addition of the sorbent composition is varied to achieve a desired level of mercury emissions.
• the level of mercury in the flue gases is monitored and the level of sorbent addition adjusted up or down as required to maintain the desired mercury level.
• nitrogen, mercury, and sulfur are monitored using industry standard methods such as those published by the American Society for Testing and Materials (ASTM) or international standards published by the International Standards Organization (ISO).
• An apparatus comprising an analytical instrument is preferably disposed in the convective pathway downstream of the addition points of the mercury and sulfur sorbents.
• a mercury monitor is disposed on the clean side of the particulate control system.
• the flue gases are sampled at appropriate locations in the convective pathway without the need to install an instrument or monitoring device.
• a measured level of mercury or sulfur is used to provide feedback signals to pumps, solenoids, sprayers, and other devices that are actuated or controlled to adjust the rate of addition of a sorbent composition into the coal burning system.
• the rate of sorbent addition can be adjusted by a human operator based on the observed levels of mercury and/or sulfur.
• the ash produced by burning coal in the presence of the sorbents described herein is cementitious in that it sets and develops strength when combined with water.
• the ash tends to be self-setting due its relatively high level of calcium.
• the ash serves alone or in combination with portland cement as a hydraulic cement suitable for formulation into a variety of cementitious mixtures such as mortars, concretes, and grouts.
• the cementitious nature of ash produced as described herein is demonstrated for example by consideration of the strength activity index of the ash, or more exactly, of a cementitious mixture containing the ash.
• measurement of the strength activity index is made by comparing the cure behavior and property development of a 100% portland cement concrete and a test concrete wherein 20% of the portland cement is replaced with an equal weight of a test cement.
• strength is compared at 7 days and at 28 days.
• a “pass” is considered to be when the strength of the test concrete is 75% of the strength of the portland cement concrete or greater.
• ashes of the invention exhibit of strength activity of 100% to 150% in the ASTM test, indicating a strong “pass”.
• a strength activity index of 100% to 150% is achieved with blends of 85:15 to 50:50, where the first number of the ratio is portland cement and the second number of the ratio is ash prepared according to the invention.
• the strength development of an all-ash test cementitious mixture is greater than 50% that of the all-portland cement control, and is preferably greater than 75%, and more preferably 100% or more, for example 100-150%.
• the ash resulting from combustion of coal according to the invention contains mercury in a non-leaching form, it is available to be sold into commerce.
• Non-limiting uses of spent or waste fly ash or bottom ash include as a component in a cement product such as portland cement.
• cement products contain from about 0.1% up to about 99% by weight of the coal ash produced by burning compositions according to the invention.
• the non-leaching property of the mercury and other heavy metals in the coal ash makes it suitable for all known industrial uses of coal ash.
• Coal ash according to the invention is used in portland cement concrete (PCC) as a partial or complete replacement for portland cement.
• the ash is used as a mineral admixture or as a component of blended cement.
• the ash can be total or partial replacement for portland cement and can be added directly into ready mix concrete at the batch plant.
• the ash is inter-ground with cement clinker or blended with portland cement to produce blended cements.
• Class F and Class C fly ashes are defined for example in U.S. Standard ASTM C 618.
• the ASTM Standard serves as a specification for fly ash when it is used in partial substitution for portland cement. It is to be noted that coal ash produced by the methods described herein tends to be higher in calcium and lower in silica and alumina than called for in the specifications for Class F and Class C fly ash in ASTM C 618.
• Typical values for the fly ash of the invention is >50% by weight CaO, and ⁇ 25% SiO 2 /Al 2 O 3 /Fe 2 O 3 .
• the ash is from 51 to 80% by weight CaO and from about 2 to about 25% of total silica, alumina, and iron oxide.
• fly ash according to the invention is highly cementitious, allowing for substitutions or cutting of the portland cement used in such cementitious materials and cementitious materials by 50% or more.
• the coal ash resulting from burning coal with sorbents described herein is sufficiently cementitious to be a complete (100%) replacement for portland cement in such compositions.
• ACI American Concrete Institute
• Class F fly ash replace from 15 to 25% of portland cement and Class C fly ash replace from 20 to 35%. It has been found that coal ash produced according to the methods described herein is sufficiently cementitious to replace up to 50% of the portland cement, while maintaining 28 day strength development equivalent to that developed in a product using 100% portland cement. That is, although in various embodiments the ash does not qualify by chemical composition as Class C or Class F ash according to ASTM C 618, it nevertheless is useful for formulating high strength concrete products.
• Coal ash made according to the invention can also be used as a component in the production of flowable fill, which is also called controlled low strength material or CLSM.
• CLSM is used as a self leveling, self compacting back fill material in place of compacted earth or other fill.
• the ash described herein is used in various embodiments as a 100% replacement for portland cement in such CLSM materials.
• Such compositions are formulated with water, cement, and aggregate to provide a desired flowability and development of ultimate strength. For example, the ultimate strength of flowable fill should not exceed 1035 kPa (150 pounds per square inch) if removability of the set material is required. If formulated to achieve higher ultimate strength, jack hammers may be required for removal.
• mixtures containing a greater range of compressive strength upon cure can be designed.
• Coal ash produced according to the methods described herein is also usable as a component of stabilized base and sub base mixtures. Since the 1950's numerous variations of the basic lime/fly ash/aggregate formulations have been used as stabilized base mixtures. An example of the use of stabilized base is used as a stabilized road base. To illustrate, gravel roads can be recycled in place of using ash according to the composition. An existing road surface is pulverized and re-deposited in its original location. Ash such as produced by the methods described herein is spread over the pulverized road material and mixed in. Following compaction, a seal coat surface is placed on the roadway. Ash according to the invention is useful in such applications because it contains no heavy metals that leach above regulatory requirements. Rather, the ash produced by methods of the invention contains less leachable mercury and less leachable other heavy metals (such as arsenic and lead) than does coal ash produced by burning coal without the sorbents described herein.
• the invention provides various methods of eliminating the need to landfill coal ash or fly ash resulting from combustion of coal that contains high levels of mercury. Instead of a costly disposal, the material can be sold or otherwise used as a raw material.
• use of the sorbents results in a cementitious ash that can replace portland cement in whole or in part in a variety of applications. Because of the re-use of the cementitious product, at least some portland cement manufacture is avoided, saving the energy required to make the cement, and avoiding the release of significant amounts of carbon dioxide which would have arisen from the cement manufacture. Other savings in carbon dioxide emissions result from the reduced need for lime or calcium carbonate in desulfurization scrubbers.
• the invention thus provides, in various embodiments, methods for saving energy and reducing green house emissions such as carbon dioxide. Further detail of various embodiments of this aspect of the invention are given below.
• Section 45(c)(7)(A) defines refined coal to include a fuel which 1) is a solid fuel produced from coal, 2) is sold by the taxpayer with the reasonable expectation that it will be used for the purposes of producing steam, and 3) is certified by the taxpayer as resulting (when used in the production of steam) in a “qualified emission reduction.”
• Section 45(c)(7)(B) defines the term “qualified emission reduction” to mean a reduction of at least 20% of the emissions of NO x and at least 40% of the emissions of either SO 2 or Hg released when the refined coal is burned as compared to the emissions released when the feedstock coal is burned.
• the CTF is used extensively to investigate SO x and NO x emissions and the transformation of toxic trace metals (Hg, As, and Pb) during the combustion of coal and other fuels or waste materials.
• the CTF is capable of producing gas and particulate samples that are representative of those produced in industrial-and full-scale pulverized coal (pc)-fired boilers.
• the test facility has several pollution control devices that may be used to reduce emissions, including an electrostatic precipitator (ESP) or fabric-filter baghouse for particulate control, a selective catalytic reduction (SCR) column for NO x control, and a wet scrubber for control of sulfur emissions.
• ESP electrostatic precipitator
• SCR selective catalytic reduction
• the CTF was designed to replicate almost all types and configurations of full-scale pc-fired boilers used by U.S.-based utilities to generate electricity from steam.
• the CTF can fire pc at a rate between 550,000 and 750,000 Btu/hr, depending upon desired operating conditions.
• the firing rate is typically a function of the coal rank, with low-rank coals fired at the low end of the range and higher-rank coals fired at the mid- to upper level of the indicated range.
• the firing rate is set based on the furnace exit gas temperature (FEGT) desired to simulate a specific boiler that would be used at a coal-fired power plant.
• FEGT furnace exit gas temperature
• a firing rate between 550,000 and 600,000 BTU/hr will typically produce a FEGT between 2100° and 2200° F., which is typical of many coal-fired power plants that burn sub-bituminous coals such as the coal tested here.
• Combustion air in the CTF is provided by a forced-draft fan in this balanced-draft system.
• the induced-draft fan at the back of the system is used to maintain a slight vacuum in the combustion zone and exhaust the combustion flue gases to a stack.
• Combustion air is typically preheated using an electric air heater and is split between primary, secondary, and overfire air (OFA).
• OFA overfire air
• CEMs continuous emission monitors
• the furnace exit which is used to monitor and maintain a specified excess air level for all test periods
• the outlet of the particulate control device which is used to access any air inleakage that may have occurred so that emissions of interest sampled at the back end of the system can be corrected for the dilution caused by the inleakage.
• flue gas analyses were obtained from the duct at the outlet of the ESP.
• Each CEM rack contains five modules for determination of O 2 , CO 2 , CO, SO 2 , and NO R . With the exception of SO 2 , each of the modules was manufactured by Ametek.
• Each of the analyzers uses a flue gas conditioner to remove moisture from the gas stream prior to analysis. All data reported here are on a dry gas basis. All gas analyses are continuously monitored and recorded by the CTF's data acquisition system. National Instruments provided both the hardware and software (LabView) used to collect all data presented here.
• the CEM analyzers are individually calibrated prior to every test conducted on the CTF. Nitrogen is used as the zero gas, while several span gases are used to calibrate each instrument over the range used during testing. Typically, O 2 is measured over a 0% to 10% range, CO 2 is measured over a 0% to 20% range, CO is measured over a 0 to 500 ppm range, and NO x is measure over a 0 to 1000 ppm range. SO 2 measurements are made over various ranges, depending upon the sulfur content of the coal being tested. During this test series, the SO 2 measurement instrument was calibrated over a range from 0 to 1000 ppm, which is appropriate for the sulfur content of the subbituminous PRB coal tested here.
• Flue gas mercury (Hg) measurements were obtained separately by a continuous Hg monitor (CMM) manufactured by Tekran® Instruments Corporation.
• CCM continuous Hg monitor
• the system draws a gas sample from the flue gas ducting at the exit of the particulate control device. Moisture is removed from gas stream prior to analysis.
• the flue gas conditioning system uses a 10% NaOH solution to remove CO 2 and SO 2 to prevent interference with the ability of the analyzer to accurately measure the flue gas Hg concentration. Since all Hg analyzers can only measure elemental mercury, Hg 0 , the total mercury, Hg (T) , concentration is obtained by reducing the oxidized mercury, Hg 2+ , portion with a 10% NaOH solution containing stannous chloride.
• the Tekran instrument traps Hg 0 from the conditioned sample onto a cartridge containing an ultrapure gold adsorbent.
• the amalgamated Hg is then thermally desorbed and detected using cold-vapor atomic fluorescence spectrometry.
• a dual-cartridge design enables alternate sampling and desportion, resulting in continuous measurement of the sample stream. Similar to the CEM calibration described above, the CMM is also zeroed and spanned prior to testing and checked at the completion of testing. No drift was noted during the tests conducted and reported here.
• the CTF configuration utilized during these tests included only an ESP for particulate control, with both Hg and NO x measurements obtained from the duct at the outlet of the ESP.
• fuel and fly ash samples were collected and submitted for analysis. The samples collected during testing are described within the following discussion.
• the sub-bituminous coal tested was a sample obtained from a coal pile.
• the coal is a PRB sub-bituminous coal with a gross calorific value approximately in the range from 8500 to 10,000 Btu/lb, depending on moisture content, which is sourced from several mines located in Wyoming.
• the as-received coal was inspected for surface moisture upon receipt and floor-dried as necessary.
• the air-dried sample was crushed to 1 ⁇ 4-inch top size and fed to a hammer mill pulverizer, creating a size distribution of approximately 70% passing 200 mesh for use during testing, typical of the coal processing achieved at most coal-fired power plants. This size distribution is typical of that achieved by the pulverizers at most full-scale utility boilers.
• the refined coal sample used during this test series was produced by the EERC and is considered comparable to the refined coal produced at the Section 45 facilities.
• the sorbents used to prepare the refined coal were applied to the pulverized fuel as described below.
• the pulverized fuel was split into two parts: a feedstock sample and a second coal sample that is processed into refined coal.
• the refined coal was prepared by laying out a weighed quantity (about 500 lb) on the floor of the coal preparation facility. Weighed quantities of halide sorbent and powder sorbent were carefully applied to the coal, which was periodically mixed while the sorbents were applied. The powder solvent was distributed by hand, making several passes over the extent of the coal pile, with mixing of the fuel after each pass.
• the halide sorbent was placed in a small pressurized metal spray canister such that the spray canister muzzle produced a mist that was applied to the exposed surface of the pile. Treatment required several passes to completely distribute the sorbent.
• a rake was used to turn the pile over, exposing new surface for the next treatment pass.
• several small portions of the sorbents were distributed over the coal pile, followed by mixing until the specified treatment rate was achieved 0.008 wt % halide sorbent and 0.25 wt % powder sorbent.
• Each of the samples was transferred to storage hoppers for use in the pilot-scale testing described below. These storage hoppers sit directly above the coal feed hopper during testing. A rotary valve is used to transfer the coal and refined coal samples, respectively, from the storage hoppers to the feed hopper. The storage hoppers and feed hopper are cleaned with a dilute acid solution after each test to remove any trace of the treated fuel.
• a coal sample is conveyed from the storage hopper through a small tube that penetrates the sidewall of the feeder at a 70% angle, with the open end situated immediately below the rotary valve between the storage hopper and the feed hopper. This rube intercepts a small portion of the fuel each time the feed hopper fills. In this manner, a true as-fired sample of the fuel is obtained.
• the coal sample falls by gravity into a sample bag attached to the end of the sample tube. A new bag is attached to the sample tube prior to each new test period, separating the fuel samples representing the feedstock and refined coal test periods.
• the as-fired coal is continuously sampled to determine the emission baseline from combusting the feedstock coal and the emissions from similarly combusting the refined coal.
• the feedstock coal and refined coal were submitted separately for determination of proximate and ultimate analyses, heating value, inorganic elemental oxide analysis (by x-ray fluorescence), and chlorine and mercury contents. Results from those analyses are provided in Table 1.
• Fuel samples undergo several handling steps that tend to allow evaporation of some portion of the as-received moisture content. The greatest reduction occurs during pulverization of the fuowl.
• the hammer mill pulverizer creates an induced draft that tends to dry the newly exposed surfaces of the fine coal particle resulting from the pulverization.
• the extent of the drying that occurs is primarily a function of ambient atmospheric conditions (temperature and relative humidity) at the time of fuel preparation.
• the composition of the as-fired analyses so that comparisons between the feedstock coal and the refined coal can be readily made.
• the feedstock coal (Test AF-CTS-1461) was determined to have an as-fired heating value of 9621 Btu/lb at a moisture content of 20.03 wt %. Moisture-free heating value and ash content were determined to be 12,031 Btu/lb and 4.91 wt %, respectively. The feedstock coal sulfur content was determined to be 0.37 wt % on a moisture-free basis (0.624 lb SO 2 /MMBtu).
• the powder sorbent and liquid halide sorbent have no heating value, and the liquid halide sorbent introduces additional moisture into the refined coal because of the water content of the liquid, so a reduction in the heating value (Btu/lb) of the refined coal is generally expected in comparison to the Btu/lb of the feedstock coal.
• Ash analysis of the inorganics contained in each fuel indicate that the refined coal is enriched in CaO and SO 3 , while depleted in SiO 2 , Al 2 O 3 , and Fe 2 O 3 relative to the feedstock coal.
• Mercury content was determined to be 0.0570 ⁇ g/g (5.924 lkb/TBtu, dry basis) and 0.0556 ⁇ g/g (5.908 lb/TBtu, dry basis) in the feedstock and refined coal samples, respectively.
• the chlorine content of the feedstock and refined coal samples was determined to be 19.4 and 30.0 ⁇ g/g, respectively.
• Example 2 Table Dry sieve analyses completed on feedstock and refined coal samples collected during each test are presented in Example 2 Table. Results for the feedback coal indicate 84.3 wt % passes 200 mesh and 69.2 wt % passes 325 mesh, while 87.1 wt % passes 200 mesh and 73.1 wt % passes 325 mesh for the refined coal sample.
• the feedstock coal is PRB coal.
• the refined coal is feedstock PRB coal plus 0.008% by weight halide sorbent and 0.25% powder sorbent.
• the powder sorbent is 15% CKD and 85% grindouts.
• the halide sorbent is from Example 1. NOx and Hg emissions were measured for the feedstock and refined coals.
• NO x Results NOx, ppm O 2 , NO x , Corrected to NO x , NO x , % ppm 2.5% O 2 lb/MMBtu Reduction % Feedstock Coal 2.71 151 152 0.197 NA* Refined Coal 2.75 116 117 0.154 21.83 Hg Results Hg (T) , ⁇ g/dNm 3 O 2 , CO 2 , corrected Hg, Hg % % to 2.5% O 2 lb/TBtu Reduction % Feedstock Coal 2.71 15.97 2.052 1.392 NA Refined Coal 2.75 16.08 0.826 0.576 58.62 *not applicable
• Mercury concentration was 0.558 ⁇ g/g in the ash of the feedstock coal and 0.833 ⁇ g/g in the ash of the refined coal
• the feedstock coal is PRB coal.
• the refined coal is feedstock PRB coal plus 0.005% by weight halide sorbent and 0.25% powder sorbent.
• the powder sorbent is 15% CKD and 85% grindouts.
• the halide sorbent is from Example 1. NOx and Hg emissions were measured for the feedstock and refined coals.
• the refined coal was fired at a rate of 58.91 lb/hr, achieving a FEGT of 2139° F. at 3.1% excess oxygen (about 17.33% excess air) at the furnace exit, with OFA maintained at 15.18%. Resultant emission reduction are given in the following table.
• NO x Results NOx, ppm O 2 , NO x , Corrected NO x , NO x , % ppm to 2.5% O 2 lb/MMBtu Reduction % Feedstock Coal 3.86 243 256 0.327 NA* Refined Coal 3.84 191 200 0.252 22.94 Hg Results Hg (T) , ⁇ g/dNm 3 O 2 , CO 2 , corrected Hg, Hg % % to 2.5% O 2 lb/TBtu Reduction % Feedstock Coal 3.86 17.07 2.877 2.018 NA Refined Coal 3.84 18.22 1.618 1.119 44.55 *not applicable

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