Apparatus for delivery of sorbent to a furnace during combustion

Abstract

A power plant may include a furnace, a coal supply, and a sorbent supply. The furnace may have at least one face with a distribution of a plurality of injectors. The coal supply may be in communication with the furnace. The injectors may be in communication with the source of sorbent and provide injection thereof into the furnace. The sorbent may include an alkaline powder having at least one calcium compound, silica, and alumina.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/759,943, filed Jan. 18, 2006, and U.S. Provisional Application No. 60/760,424, filed Jan. 19, 2006. The disclosures of the above applications are incorporated herein by reference.

FIELD

The present disclosure relates to power plants, and more specifically to power plants having a sorbent injection system.

BACKGROUND

Significant coal resources exist around the world capable of meeting large portions of the world's energy needs into the next two centuries. High-sulfur coal is plentiful, but requires remediation steps to prevent excess sulfur from being released into the atmosphere upon combustion. In the United States, low-sulfur coal exists in the form of low BTU value coal in the Powder River basin of Wyoming and Montana, in lignite deposits in the North Central region of North and South Dakota, and in lignite deposits in Texas. But even when coals contain low sulfur, they may contain non-negligible levels of elemental and oxidized mercury and/or other heavy metals.

For example, mercury is at least partially volatilized upon combustion of coal. When present during coal combustion, 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, which may lead to environmental problems.

Some mercury today is captured by utilities, for example in wet scrubber, SCR control and activated carbon systems. While wet scrubber and SCR control systems remove some mercury from the flue gases of coal combustion, activated carbon systems tend to be associated with higher treatment and capital costs. Further, the use of activated carbon systems leads to carbon contamination of the fly ash collected in exhaust-air treatments, such as the bag house and electrostatic precipitators.

SUMMARY

A power plant includes a furnace, a coal supply in communication with the furnace, and a sorbent supply. The furnace has at least one face with a distribution of a plurality of injectors. The injectors are in communication with the sorbent supply and provide injection thereof into the furnace. The sorbent may include an alkaline powder having at least one calcium compound and further containing silica and alumina.

Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the claims.

DRAWINGS

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

FIG. 1 is a schematic view of a power plant in accordance with the teachings of the present disclosure;

FIG. 2 is a schematic side view of a first furnace;

FIG. 3 is a schematic perspective view of the furnace of FIG. 2;

FIG. 4 is a schematic top view of the furnace of FIG. 2;

FIG. 5 is a section view of an injection lance;

FIG. 6 is a schematic view of a sorbent bin filling system; and

FIG. 7 is a schematic view of a second furnace.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.

In a first example, a power plant may include a furnace, a supply of coal, and a source of sorbent. The coal supply may be in communication with the furnace. The source of sorbent may be in communication with one or both of the supply of coal and the furnace and include an alkaline powder having at least one calcium compound, silica, and alumina.

The power plant may also include at least one injector in communication with the source of sorbent and selectively operable to inject the sorbent onto the supply of coal. The injector may be positioned upstream of the furnace. Alternatively, the injector may be positioned within the furnace.

The furnace may also include a lance extending a distance into the furnace. The lance may be in communication with the source of sorbent and provide a passage for the sorbent into the furnace. The extent of the lance into the furnace may be greater than or equal to two feet. The lance may further include perforations. The location within the furnace where the sorbent is injected may experience temperatures greater than or equal to 2000° F. during operation of the furnace. Further, the location may be at a temperature greater than or equal to 2300° F.

In a second example, a power plant may include a source of sorbent, a furnace, a supply of coal, and exactly six injectors. The supply of coal may be in communication with the furnace. The injectors may be in communication with the source of sorbent and may selectively apply the sorbent to the coal at the furnace.

In a third example, a power plant may include a furnace, a supply of coal, and a plurality of injectors. The furnace may have at least one face and the supply of coal may be in communication with the furnace. The injectors may be distributed across the face of the furnace and may be configured for distribution of a sorbent within the furnace. The injectors may include a lance extending a distance into the furnace. The lance may extend a distance greater than or equal to two feet. The lance may further include perforations. The injectors may be configured to deliver the sorbent into the furnace at a location internal to the furnace where the temperature during operation is greater than or equal to 20000F. Further, the location may be at a temperature greater than or equal to 2300° F.

In a fourth example, a power plant may include a source of sorbent, a furnace, a supply of coal, a plurality of injectors, and a control system. The supply of coal may be in communication with the furnace and the injectors may be in communication with the source of sorbent. The control system may control sorbent application by the injectors to one or both of the coal and the furnace. The control system may be configured to independently control each of the injectors. The control system may further be configured to control sorbent application based on at least one input parameter.

In a fifth example, a method of operating a power plant may include feeding a supply of coal to a furnace and combusting the coal in the furnace. The method may further include supplying a sorbent including an alkaline powder to the furnace during combustion through a plurality of injectors. The alkaline powder may have at least one calcium compound, silica, and alumina. The supplying of the sorbent may include independent operation of the injectors based on a predetermined set of parameters. The supplying may include applying the sorbent to coal within the furnace or supplying the sorbent to the coal upstream of the furnace and subsequently feeding the coal into the furnace. The supplying may further include injecting the sorbent into a location within the furnace where the temperature during operation is greater than or equal to 2000° F. Further, the temperature may be greater than or equal to 2300° F.

The teachings described herein may be used with the treatment of coal using methods and compositions described in co-pending U.S. Provisional Application No. 60/759,994, filed on Jan. 18, 2006; U.S. patent application Ser. No. 11/377,528 filed Mar. 16, 2006; PCT Application No. PCT/US05/13831 filed Mar. 21, 2005; and PCT Application No. PCT/US06/10000 filed Mar. 16, 2006 claiming priority to U.S. Provisional Application No. 60/662,911 filed Mar. 17, 2005; and U.S. Provisional Application No. 60/742,154, filed Dec. 2, 2005, the disclosures of which are hereby incorporated by reference.

FIG. 1 is a schematic illustration of a power plant 10. As shown, the power plant 10 includes a coal supply arrangement 12, a furnace 14, a chemical supply 16, an injection system 18, a control system 20, a turbine 22, and a particulate control system 24. The coal supply arrangement 12 is in communication with furnace 14, as discussed below. Chemical supply 16 is directly in communication with furnace 14 through injection system 18, as discussed below.

Chemical supply 16 includes powder and liquid sorbents, as well as combinations thereof. For example, chemical supply 16 includes a sorbent in the form of an alkaline powder composition that may contain at least one calcium compound, as well as sources of silica and alumina.

Sorbent compositions of the disclosure may contain components that contribute calcium, silica, and alumina, in the form of alkaline powders. In various embodiments, the compositions also contain iron oxide, as well as basic powders based on sodium oxide (Na₂O) and potassium oxide (K₂O). In a non-limiting example, the powder sorbent contains about 2-10% by weight Al₂O₃, about 40-70% CaO, about 5-15% SiO₂, about 2-9% Fe₂O₃, and about 0.1-5% total alkalis such as sodium oxide and potassium oxide. The components comprising calcium, silica, and alumina and other elements if present, are combined together in a single composition or are added separately as components to the fuel burning system. Use of the sorbents may lead to reductions in the amount of sulfur and/or mercury released into the atmosphere. Use of the sorbent compositions may also lead to the removal of mercury, especially oxidized mercury. In addition, the compositions reduce the amount of sulfur given off from combustion by a virtue of their calcium content.

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. For example, the ash produced from burning fuels tends to be higher in silica and/or alumina than ash produced from burning the fuel without the added sorbent. It is believed that the added alumina and/or silica contributes to an observed increase in the cementitious nature of the ash.

In addition, it is believed that the presence of alumina and/or silica 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.

Use of the sorbent compositions during combustion of coal or other fuel leads to the formation of a refractory lining on the walls of the furnace and on the boiler tubes. It is believed that such a refractory lining reflects heat in the furnace and leads to higher water temperature in the boilers. Use of the sorbent also results in reduced scale formation or slagging around the boiler tubes. In this way, use of the sorbents leads to cleaner furnaces, as well as improved heat exchange between the burning coal and the water in the boiler tubes. As a result, use of the sorbents leads to higher water temperature in the boiler, based on burning the same amount of fuel. Alternatively, it has been observed that use of the sorbent allows the feed rate of, for example, coal to be reduced while maintaining the same power output or boiler water temperature. Use of a sorbent at a 6% rate may result in a coal/sorbent composition that produces just as much power as a composition of the same weight that is all coal. Use of the sorbent, which is normally captured in the fly ash and recycled, actually increases the efficiency of the coal-burning process, leading to less consumption of fuel. In such a process, the fly ash, which is normally increased in volume by virtue of the use of the sorbent, is recycled for use in Portland cement manufacture and the like, it having an improved cementitious nature and low heavy metal leaching.

As noted, the components of the sorbent composition may be provided as alkaline powders. Without being limited by theory, it is believed that the alkaline nature of the sorbent components leads at least in part to the desirable properties described above. Sources of calcium for the sorbent compositions of the disclosure include calcium powders such as calcium carbonate, limestone, calcium oxide, calcium hydroxide, calcium phosphate, and other calcium salts. It is understood that 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 disclosure.

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. The products may further contribute either silica, alumina, or both to the compositions of the disclosure. 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. These and other materials are combined to provide alkaline powders or mixtures of alkaline powders that contain calcium, and also may contain silica and alumina. Various pozzolanic materials may also be used.

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 (CKD) generally refers to a byproduct generated within a cement kiln or related processing equipment during cement manufacturing. Portland cement can be manufactured in a wet or a dry process kiln. While the wet and dry processes differ, both processes heat the raw material in stages. Cement manufacturing raw materials comprise sources of calcium, silica, iron, and alumina, and usually include limestone, as well as a variety of other materials, such as clay, sand, and/or shale, for example. The first stage is a pre-heating stage that drives off any moisture from the raw materials, removes water of hydration, and raises the material temperature up to approximately 1500° F. The second stage is the calcination stage which generally occurs between about 1500° F. and 2000° F., where the limestone (CaCO₃) is converted to lime (CaO) by driving off carbon dioxide (CO₂) in a calcination reaction. The raw materials are then heated to a maximum temperature of between about 2500° F. to 3000° F. in the burning zone, where they substantially melt and flux, thus forming inorganic compounds, such as tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium aluminoferrite. A typical analysis of Portland cement products shows that they contain approximately 65-70% CaO, 20% SiO₂, 5% Al₂O₃, 4% Fe₂O₃, with lesser amounts of other compounds, such as oxides of magnesium, sulfur, potassium, sodium, and the like. The molten raw material is cooled to solidify into an intermediate product in small lumps, known as “clinker” that is subsequently removed from the kiln. Clinker is then finely ground and mixed with other additives (such as a set-retardant, gypsum) to form Portland cement. Portland cement can then be mixed with aggregates and water to form concrete.

Generally, 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.

While 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 may include 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, CKD may include compounds containing alkali metals, alkaline earth metals, and sulfur, inter alia.

Other exemplary sources for the alkaline powders comprising calcium, and further comprising silica and alumina, include various cement-related byproducts (in addition to Portland cement and CKD described above). 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. Other sources are masonry cement and/or hydraulic lime, which include mixtures of Portland cement and/or its clinker with lime or limestone. Other 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). Yet another example is 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 (LKD) 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 (CaCO₃), to form free lime CaO and carbon dioxide (CO₂). 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. In some lime manufacturing, dolomite (CaCO₃.MgCO₃) is decomposed by heating to primarily generate calcium oxide (CaO) and magnesium oxide (MgO), thus forming what is known as dolomitic lime. In LKD generated by dolomitic lime processing, 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. While 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. Generally, slags are considered to be a mixture of various metal oxides, however they often contain metal sulfides and metal atoms in an elemental form.

Various examples of slag byproducts useful for certain embodiments of the disclosure 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). 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 may include calcium oxide at about 25 to about 60%, optionally about 30 to about 50%, and optionally about 30 to about 45% by weight. One example of a suitable slag generally having cementitious properties is ground granulated blast furnace slag (GGBFS).

As described above, other suitable examples include blast (cupola) 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. As recognized by those of skill in the art, there are many different manufactured/industrial process byproducts that are feasible as a source of calcium for the alkaline powders that form the sorbent compositions of the disclosure. Many of these well known byproducts comprise alumina and/or silica, as well. Combinations of any of the exemplary manufactured products and/or industrial byproducts are also contemplated for use as the alkaline powders of the disclosure.

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 desired silica and alumina levels. Supplemental aluminosilicate materials may make up at least about 2% by weight of the various sorbent components added into the coal-burning system. Alternatively, supplemental aluminosilicate materials may make up 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. However, from a cost standpoint, it may be desirable to limit the proportion of more expensive aluminosilicate materials. Thus, the sorbent components may include from about 2 to 50%, more specifically 2 to 20%, and more specifically yet about 2 to 10% by weight aluminosilicate material such as the exemplary clays.

An alkaline powder sorbent composition may contain one or more calcium-containing powder 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 may contain sufficient SiO₂ and Al₂O₃ to form a refractory-like mixture with calcium sulfate produced by combustion, and with mercury and other heavy metals such that the calcium sulfate is handled by the particle control system of the furnace and mercury and heavy metals are not leached from the ash under acidic conditions. The calcium containing powder sorbent may contain by weight a minimum of 2% silica and 2% alumina, more specifically a minimum of 5% silica and 5% alumina. The alumina level may be higher than that found in Portland cement, that is to say higher than about 5% by weight, more specifically higher than about 6% by weight, based on Al₂O₃.

Suitable aluminosilicate materials include a wide variety of inorganic minerals and materials. For example, 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.

In 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. However presented, 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 may include polymorphs of SiO₂.Al₂O₃. For example, 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 SiO₂.Al₂O₃.

Chain silicates may contribute silicon (as silica) and/or aluminum (as alumina) to the compositions of the disclosure. Chain silicates include without limitation pyroxene and pyroxenoid silicates made of infinite chains of SiO₄ tetrahedra linked by sharing oxygen atoms.

Other suitable 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 may also be used. Framework aluminosilicates are characterized by a structure where SiO₄ tetrahedra, AlO₄ tetrahedra, and/or AlO₆ 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.

In one aspect, the sorbent powder compositions are characterized in that they contain a major amount of calcium, such as greater than 20% 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 may include greater than 5% by weight alumina, greater than 6% by weight alumina, greater than 7% by weight alumina, or greater than about 8% by weight alumina.

Coal or other fuel is treated with sorbent components at rates effective to control the amount of sulfur and/or mercury released into the atmosphere upon combustion. Total treatment levels of the sorbent components range 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 components are combined into a single composition, 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. In general, a minimum amount of sorbent may be used so as not to overload the system with excess ash, while still providing enough to have a desired effect on sulfur and/or mercury emissions. Accordingly, the treatment level of sorbent ranges from about 1% to about 10% by weight, and more specifically 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.

Steam generated by furnace 14 powers a turbine 22. Exhaust from furnace 14 is in communication with particulate control system 18.

In a non-limiting example, furnace 14 is a tangentially fired furnace 26, shown in FIGS. 2-4. As illustrated, tangentially fired furnace 26 includes a furnace body 28 having upper, intermediate, and lower portions 27, 29, 31, pulverized fuel feeds 30, an overfire air inlet 32, a furnace neck 34, a superheater tube bank 36, first and second tube banks 38, 40, a bottom ash collection pit 42, and sorbent injectors 44. Furnace body 28 includes walls 46, 48, 50, 52. Pulverized fuel feeds 30 are shown for illustrative purposes in walls 48, 52. Pulverized coal is fed through pulverized fuel feeds 30 by an air supply (not shown). Pulverized fuel feeds 30 may be located generally across from one another and run from a location just above the overfire air to a location above bottom ash collection pit 42. Overfire air inlet 32 is located above pulverized fuel feeds 30, and generally provides combustion in addition to that provided lower in the furnace with the fuel feeds. Overfire air inlet 32 may be located generally at the top of the combustion fireball. The fireball may generally extend to furnace neck 34 of furnace 26. The use of overfire air improves combustion and tends to lead to lower nitrogen oxide (NO_x) emissions.

As shown in an illustrative arrangement, furnace neck 34 is located above pulverized fuel feeds 30, overfire air inlet 32, and sorbent injectors 44 and generally provides for the exhaust of furnace emissions. Superheater tube bank 36 and first and second tube banks 38, 40 are used for conversion of water to steam from the heat generated from tangentially fired furnace 26 so that electricity may be generated as turbine 22 rotates. Bottom ash collection pit 42 is located below pulverized fuel feeders 30, overfire air inlet 32, and sorbent injectors 44, and generally contains the byproduct of combustion that does not travel out of tangentially fired furnace 26 through furnace neck 34.

As shown, injection system 18 includes sorbent injectors 44 extending into walls 46, 48, 50, and/or 52 of furnace body 28 above overfire air inlet 32. Sorbent injectors 44 are distributed across one or a multiple of furnace walls 46, 48, 50, 52 and can be arranged to provide any configuration achieving a desired sorbent distribution within furnace 26. Any number of injectors appropriate for a given furnace may be used. For example, each of furnace walls 46, 48, 50, 52 may include between four and eight injectors. In the example shown in FIGS. 2-4, furnace 26 includes five injectors on each of furnace walls 46, 48, 50, 52.

Sorbent injectors 44 may generally be in the form of tubular lances and extend into furnace body 28 a suitable distance. The extension into furnace body 28 may be any desirable amount beyond furnace body 28. In a non-limiting example, sorbent injectors 44 extend a distance greater than or equal to approximately two feet into furnace body 28. Sorbent injectors 44 may be spaced along furnace walls in any appropriate manner. For example, sorbent injectors 44 may be spaced equidistant from one another and may be spaced apart from one another any required distance, including four, six, or twelve feet. Sorbent injectors 44 may inject into furnace 14 at a location where the temperature is greater than 2000° F., and more specifically greater than 2300° F. The location for injection may vary between furnaces. Tools such as computer modeling methods including computational fluid dynamics (CFD), finite element analysis (FEA), finite difference models, and heat transfer models may be used to predict furnace airflow and thermal properties. These are merely a few of the many tools that may be employed in order to determine injector positioning.

The fireball or flamefront generated during combustion in a furnace may vary. For example, the fireball or flamefront may vary in vertical extent and/or position from the furnace walls. As such, injector positioning and extent into furnace body 28 may vary to achieve injection at a desired location within furnace 26. For example, injector location may vary to inject at a position corresponding to a specific internal temperature of furnace 26. A location generally at or near the top of the fireball may have a temperature between 2300 and 2600° F. The temperature below neck 34 of furnace 26 may be approximately 3000° F. The temperature at a central location of the fireball may be approximately 3600° F.

In alternate configurations not illustrated in the figures, sorbent injectors may inject into the furnace at an upper portion proximate the exhaust gas stack. Alternatively, sorbent injectors are located in a lower portion of the furnace. Sorbent injectors may also be located in more than one location. While sorbent injectors have been described in one example as being located above the overfire air inlet and pulverized fuel feeds, in other examples sorbent injectors can be positioned above, below, or between any combination of the overfire air inlet and pulverized fuel feeds.

As shown for illustration in FIG. 5, sorbent injectors 44 may also include perforations 54 on the portion extending into furnace body 28. Sorbent injectors 44 may also include a reduced diameter portion 56, creating a converging/diverging nozzle or a venturi. The venturi may provide greater penetration of sorbent into furnace 26. As shown, an optional air feed line 58 joins sorbent injectors 44 and is disposed at an angle of less than thirty degrees relative to sorbent injector 44. Air feed line 58 optionally includes an inlet valve 60 to control air flow into sorbent injector 44. The diameter of air feed line 58 may be widely varied. For example, the diameter of air feed line 58 may be approximately half the diameter of sorbent injector 44. For example, the diameter of the sorbent injector 44 can be approximately two inches and the diameter of the air feed line 58 can to be approximately one inch.

Sorbent injectors 44 may also each include an inlet valve 62 illustrated in FIG. 4. Each wall of sorbent injectors 44 may be in communication with its own main feed line 64. Main feed line 64 may also include an inlet valve 66 and may be in communication with a sorbent storage silo 68 (shown in FIG. 6). Inlet valves 62, 66 may be controlled by control system 20.

Control system 20 may automatically control quantity and frequency of sorbent injection as a function of furnace operating parameters. For example, sorbent injection may be adjusted by increasing or decreasing the rate of feed from a blower in communication with the sorbent supply and/or the rotational speed of a star feeder. Input parameters to control system 20 may include sulfur content in the furnace stack, mercury content in the furnace stack, NOx content in the furnace stack, and the fuel feed rate to furnace 26. Sorbent injectors 44 may be operated independently of one another or as a group.

As illustrated in a non-limiting example in FIG. 6, a series of sorbent storage silos 68 may be used for supply of sorbent to furnace 26. As shown, sorbent storage silos 68 are filled by a pneumatic blower 70 through a line 72 having feeds 74 to each of the sorbent storage silos 68. A four-way diverter 76 may be used to isolate each of sorbent silos 68 for individual filling. The number of silos is not particularly critical. In various examples, more or fewer silos than shown in FIG. 6 may be used for supplying sorbent to furnace 26.

While tangentially fired furnace 26 has been described as injecting sorbent individually into furnace body 28, sorbent may be injected onto coal at or near the top of the coal feeders and the coal may then be pulverized and injected into furnace body 28 together as a single mixture. The injectors used may be generally similar to injector 44 shown in FIG. 5. The injectors may be oriented generally downward at an angle of sixty degrees relative to the top of the coal feeders and have feed diameters of between two and six inches, by way of non-limiting example.

With reference to FIG. 7, a stoker furnace 126 is illustrated. As shown, stoker furnace 126 includes a furnace body 128, a combustion air source 130, a coal inlet 132, a wood inlet 134, an exhaust gas stack 136, a water tube bank 138, a grate 140, an ash bin 142, and cleanout lines 144.

Coal and wood inlets 132, 134 generally provide for passage of coal from coal supply 113 and wood from a wood supply 112 to grate 140. Grate 140 may be a moving grate transporting coal, wood, or other fuel across the width of furnace 126 during combustion. Combustion air supply 130 may be located at a lower portion of furnace 126 below grate 140. Water tube bank 138 is located in an upper portion of furnace 126 near exhaust gas stack 136 and is in communication with a turbine such as turbine 22 shown in FIG. 1. Exhaust gas stack 136 may be located in the upper portion of furnace 126 and may be in communication with a control system such as particulate control system 24. Furnace slag passage 146 may also be in communication with a control system such as particulate control system 24 shown in FIG. 1.

Cleanout lines 144 provide communication between furnace body 128 and ash bin 142. Ash bin 142 may be pneumatically filled with fly ash through a device (not shown) and feed fly ash to furnace body 128. Cleanout lines 144 may be any size suitable for stoker furnace 126. In a non-limiting example shown, cleanout lines 144 are approximately two inches in diameter. Any number of cleanout lines 144 may be used. In the particular example shown in FIG. 7, six cleanout lines 144 are present. Each of cleanout lines 144 may be coupled to a chemical supply through an injection system such as chemical supply 16 and injection system 18 shown in FIG. 1.

Injection system 18 may include sorbent injectors 148. Each cleanout line 144 may include a sorbent injector 148 coupled thereto. As such, six injectors are shown in FIG. 7. Each sorbent injector 148 may be in communication with a chemical supply such as chemical supply 16, as discussed above, through a feed line 150. Feed line 150 may be a variety of sizes and formed from a variety of materials. As an example, feed line 150 is a flexible line having a two inch diameter. Feed lines 150 may be coupled to a main feed line 152 extending from a sorbent storage silo 154 through two-way diverters 156, each having a suitable diameter, such as 2 inches. An air line 158 is coupled to feed lines 150 at ports 160 between sorbent injectors 148 and diverters 156. An air compressor 162 is coupled to the air line 158.

While shown coupled to cleanout lines 144, sorbent injectors 148 may be independent from cleanout lines 144 and extend around furnace body 128 in a configuration generally similar to that described regarding tangentially fired furnace 26. As such, lances may also be incorporated as part of injectors 148 generally similar to those shown in FIG. 5. In a non-limiting example, the sorbent injectors may be arranged approximately twenty feet above moving grate 140.

As previously noted, a control system such as control system 20 shown in FIG. 1 may be provided to control sorbent injection frequency and duration based on furnace operating parameters. Also, as indicated above, sorbent injectors 148 may be operated independently of one another or as a group.

Sorbent storage silo 154 may be filled in a manner similar to that discussed regarding sorbent storage silos 68 in FIG. 6. The main difference between the filling configuration of silos 68, 154 in FIGS. 6 and 7 is that multiple silos 68 are used in FIG. 6 and a single silo 154 is used in FIG. 7.

Whether in the form of a tangentially fired furnace or a stoker furnace, furnace 14 may be either an updraft furnace or a downdraft furnace. As noted above, injector placement may vary depending on the type of furnace used.

Claims

1. A power plant comprising:

a furnace;

a supply of coal in communication with said furnace; and

a source of sorbent in communication with at least one of said supply of coal and said furnace, said sorbent including an alkaline powder having at least one calcium compound, silica, and alumina.

2. The power plant of claim 1, further comprising an injector in communication with said source of sorbent and configured to apply said sorbent to said supply of coal.

3. The power plant of claim 2, wherein said at least one injector is positioned upstream of said furnace.

4. The power plant of claim 2, wherein said at least one injector is positioned in said furnace.

5. The power plant of claim 1, wherein said source of sorbent is in communication with said furnace through a lance extending a distance into said furnace.

6. The power plant of claim 5, wherein said distance is at least two feet.

7. The power plant of claim 5, wherein said lance includes perforations.

8. The power plant of claim 1, wherein said sorbent is injected into said furnace at a location where the internal temperature of said furnace is at least 2000° F. during operation.

9. The power plant of claim 8, wherein said sorbent is injected into said furnace at a location where the internal temperature of said furnace is at least 2300° F.

10. A power plant comprising:

a furnace having at least one face;

a supply of coal in communication with said furnace; and

a plurality of injectors distributed across said at least one face of said furnace and configured for distribution of a sorbent within said furnace.

11. The power plant of claim 10, wherein said injectors include a lance extending a distance into said furnace.

12. The power plant of claim 11, wherein said lance extends at least two feet into said furnace.

13. The power plant of claim 11, wherein said lance includes perforations.

14. The power plant of claim 10, wherein said injectors are configured to deliver said sorbent into said furnace at a location where the internal temperature of said furnace is at least 2000° F. during operation.

15. The power plant of claim 14, wherein said injectors are configured to deliver said sorbent into said furnace at a location where the internal temperature of said furnace is at least 2300° F. during operation.

16. A power plant comprising:

a source of sorbent;

a furnace;

a supply of coal in communication with said furnace;

a plurality of injectors in communication with said source of sorbent; and

a control system controlling application by the injectors of said sorbent to at least one of said coal and said furnace, said control system configured to independently control each of said plurality of injectors.

17. The power plant of claim 16, wherein said control system is configured to control application of sorbent based on at least one input parameter.

18. A method comprising:

feeding a supply of coal to a furnace;

combusting the coal in the furnace; and

supplying a sorbent including an alkaline powder having at least one calcium compound, silica, and alumina to the furnace during combustion through a plurality of injectors, said supplying including independent operation of said injectors based on a predetermined set of parameters.

19. The method of claim 18, wherein said supplying includes applying the sorbent to the coal in the furnace.

20. The method of claim 18, wherein said supplying includes applying the sorbent to the coal upstream of the furnace and subsequently feeding the coal into the furnace.

21. The method of claim 18, wherein said supplying includes injecting the sorbent into the furnace at a location where the internal temperature of the furnace is at least 2000° F. during operation.

22. The method of claim 21, wherein said supplying includes injecting the sorbent into the furnace at a location where the internal temperature of the furnace is at least 2300° F.