The invention relates to the systems and processes for removal of pollutants, such as oxides of sulfur, oxides of nitrogen, fly ash, mercury compounds, and elemental mercury from gases generated from the burning of fossil fuels and other process gases with electronic control of operational parameters such as, differential pressure across the system, gas temperature, and removal efficiency. The systems and processes of the invention employ oxides of manganese as the primary sorbent to effect removal of pollutants, such as oxides of sulfur and/or oxides of nitrogen, and may further employ other sorbent materials and chemical additives separately and in conjunction with oxides of manganese to effect the removal of other target pollutants, e.g., using alumina to remove mercury.
During combustion of fuels that contain sulfur compounds, oxides of sulfur (SOX), such as sulfur dioxide (SO2), and sulfur trioxide (SO3) are produced as a result of oxidation of the sulfur. Some fuels may contain nitrogen compounds that contribute to the formation of oxides of nitrogen (NOX), which are primarily formed at high temperatures by the reaction of nitrogen and oxygen from the air used for the reaction with the fuel. These reaction compounds, SOX and NOX, are reported to form acids that may contribute to xe2x80x9cacid rain.xe2x80x9d Federal and state regulations dictate the amount of these and other pollutants, which may be emitted. The regulations are becoming more stringent and plant operators are facing greater difficulties in meeting the regulatory requirements. Many technologies have been developed for reduction of SOX and NOX, but few can remove both types of pollutants simultaneously in a dry process or reliably achieve cost effective levels of reduction.
In the past to meet the regulatory requirements, coal-burning power plants have often employed a scrubbing process, which commonly uses calcium compounds to react with SOX to form gypsum. This waste product is normally discarded as a voluminous liquid slurry in an impoundment and ultimately is capped with a clay barrier, which is then covered with topsoil once the slurry is de-watered over time. Alternatively, some power-plant operators have chosen to burn coal that contains much lower amounts of sulfur to reduce the quantities of SOX emitted to the atmosphere. In the case of NOX, operators often choose to decrease the temperature at which the coal is burned. This in turn decreases the amount of NOX produced and therefore emitted; however, low temperature combustion does not utilize the full heating value of the coal, resulting in loss of efficiency.
Turbine plants normally use natural gas, which contains little or no sulfur compounds, to power the turbines, and therefore virtually no SOX is emitted. On the other hand at the temperature that the turbines are commonly operated, substantial NOX is produced. In addition to Selective Catalytic Reduction (SCR) processes for conversion of NOX to nitrogen, water vapor, and oxygen, which can be safely discharged, some operators choose to reduce the temperature at which the turbines are operated and thereby reduce the amount of NOX emitted. With lower temperatures the full combustion/heating value of natural gas is not realized, resulting in loss of efficiency. Unfortunately for these operators, newer environmental regulation will require even greater reduction of SOX and NOX emissions necessitating newer or more effective removal technologies and/or further reductions in efficiency.
Operators of older coal-burning power plants are often running out of space to dispose of solid wastes associated with use of scrubbers that use calcium compounds to form gypsum.
Operators of newer plants would choose to eliminate the problem from the outset if the technology were available. Additionally, all power plants, new and old, are faced with upcoming technology requirements of further reducing emissions of NOX and will have to address this issue in the near future. Thus, plants that currently meet the requirements for SOX emissions are facing stricter requirements for reduction of NOX for which there has been little or no economically feasible technology available.
The nitrogen oxides, which are pollutants, are nitric oxide (NO) and nitrogen dioxide (NO2) or its dimer (N2O4). The relatively inert nitric oxide is often only removed with great difficulty relative to NO2. The lower oxide of nitrogen, nitrous oxide (N2O), is not considered a pollutant at the levels usually found in ambient air, or as usually discharged from air emission sources. Nitric oxide (NO) does however; oxidize in the atmosphere to produce nitrogen dioxide (NO2). The sulfur oxides considered being pollutants are sulfur dioxide (SO2) and sulfur trioxide (SO3).
Typical sources of nitrogen and sulfur oxide pollutants are power plant stack gases, automobile exhaust gases, heating-plant stack gases, and emissions from various industrial process, such as smelting operations and nitric and sulfuric acid plants. Power plant emissions represent an especially formidable source of nitrogen oxides and sulfur oxides, by virtue of the very large tonnage of these pollutants and such emissions discharged into the atmosphere annually. Moreover, because of the low concentration of the pollutants in such emissions, typically 500 ppm or less for nitrogen oxides and 3,000 ppm or less for sulfur dioxide, their removal is difficult because very large volumes of gas must be treated.
Of the few practical systems, which have hitherto been proposed for the removal of nitrogen oxides from power plant flue gases, all have certain disadvantages. Various methods have been proposed for the removal of sulfur dioxide from power plant flue gases, but they too have disadvantages. For example, wet scrubbing systems based on aqueous alkaline materials, such as solutions of sodium carbonate or sodium sulfite, or slurries of magnesia, lime or limestone, usually necessitate cooling the flue gas to about 55xc2x0 C. in order to establish a water phase. At these temperatures, the treated gas requires reheating in order to develop enough buoyancy to obtain an adequate plume rise from the stack. U.S. Pat. No. 4,369,167 teaches removing pollutant gases and trace metals with a lime slurry. A wet scrubbing method using a limestone solution is described in U.S. Pat. No. 5,199,263.
Considerable work has also been done in an attempt to reduce NOX pollutants by the addition of combustion catalysts, usually organo-metallic compounds, to the fuel during combustion. However, the results of such attempts have been less successful than staged combustion. NOX oxidation to N2 is facilitated by ammonia, methane, et al. which is not effected by SOX is described in U.S. Pat. No. 4,112,053. U.S. Pat. No. 4,500,281 teaches the limitations of organo-metallic catalysts for NOX removal versus staged combustion. Heavy metal sulfide with ammonia is described for reducing NOX in stack gases in U.S. Pat. No. 3,981,971.
Many fuels, and particularly those normally solid fuels such as coal, lignite, etc., also contain substantial amounts of bound or fuel sulfur with the result that conventional combustion produces substantial amounts of SOX pollutants which are also subject to pollution control. It has generally been the opinion of workers in the art that those conditions employed in staged combustion, particularly two-stage rich-lean combustion for NOX reduction, will likewise lower the level of SOX emissions. However, it has been found that little or no reduction in SOX emissions can be obtained in a two-stage, rich-lean combustion process. Indeed, it has been found that the presence of substantial amounts of sulfur in a fuel also has a detrimental effect on NOX reduction in a two-stage, rich-lean process.
Considerable effort has been expended to remove sulfur from normally solid fuels, such as coal, lignite, etc. Such processes include wet scrubbing of stack gases from coal-fired burners. However, such systems are capital intensive and the disposal of wet sulfite sludge, which is produced as a result of such scrubbing techniques, is also a problem. Cost inefficiencies result from the often-large differential pressures across a wet scrubber removal system; differential pressures in excess of 30 inches of water column (WC) are not unusual. Also, the flue gases must be reheated after scrubbing in order to send them up the stack, thus reducing the efficiency of the system. Both U.S. Pat. Nos. 4,102,982 and 5,366,710 describe the wet scrubbing of SOX and NOX.
In accordance with other techniques, sulfur scavengers are utilized, usually in fluidized bed burners, to act as scavengers for the sulfur and convert the same to solid compounds which are removed with the ash. The usual scavengers in this type of operation include limestone (calcium carbonate) and dolomite (magnesium-calcium carbonate) because of availability and cost. However, the burning techniques are complex and expensive to operate and control; and the burner equipment is comparatively expensive. Dissolving coal or like material in a molten salt compound is described in U.S. Pat. No. 4,033,113. U.S. Pat. No. 4,843,980 teaches using alkali metal salt during the combustion of coal or other carbonaceous material with further efficiency by adding a metal oxide. A sulfur scavenger added upstream to a combustion zone is described in U.S. Pat. No. 4,500,281.
The combustion gas stream from a coal-burning power plant is also a major source of airborne acid gases, fly ash, mercury compounds, and elemental mercury in vapor form. Coal contains various sulfides, including mercury sulfide. Mercury sulfide reacts to form elemental mercury and SOX in the combustion boiler. At the same time other sulfides are oxidized to SOX and the nitrogen in the combustion air is oxidized to NOX. Downstream of the boiler, in the ducts and stack of the combustion system, and then in the atmosphere, part of the elemental mercury is re-oxidized, primarily to mercuric chloride (HgCl2). This occurs by reactions with chloride ions or the like normally present in combustion reaction gases flowing through the combustion system of a coal-burning power plant.
Many power plants emit daily amounts of up to a pound of mercury, as elemental mercury and mercury compounds. The concentration of mercury in the stream of combustion gas is about 4.7 parts per billion (ppb) or 0.0047 parts per million (ppm). Past efforts to remove mercury from the stream of combustion gas, before it leaves the stack of a power plant, include: (a) injection, into the combustion gas stream, of activated carbon particles or particulate sodium sulfide or activated alumina without sulfur; and (b) flowing the combustion gas stream through a bed of activated particles. When activated carbon particle injection is employed, the mercuric chloride in the gas stream is removed from the gas stream in a bag house and collected as part of a powder containing other pollutants in particulate form. Mercuric chloride and other particulate mercury compounds that may be in the gas stream can be more readily removed from the gas stream at a bag house than can elemental mercury. Activated carbon injection for mercury removal along with an activated particle bed is described in U.S. Pat. No. 5,672,323.
When the gas stream flows through a bed of activated carbon particles, mercury compounds are adsorbed on the surface of the activated carbon particles and remain there. Elemental mercury, usually present in vapor form in combustion gases, is not adsorbed on the activated carbon to any substantial extent without first being oxidized into a compound of mercury. U.S. Pat. No. 5,607,496 teaches the oxidation of mercury and subsequent absorption to particles and utilization of alumina are described therein.
Sodium sulfide particle injection can be utilized to form mercuric sulfide (HgS), which is more readily removable from the gas stream at a bag house than is elemental mercury. The conversion of mercury to a sulfide compound with subsequent capture in a dust separator is detailed in U.S. Pat. No. 6,214,304.
Essentially, all of the above techniques create solid waste disposal problems. The solids or particulates, including fly ash, collected at the bag house and the spent activated carbon removed from the bed of activated carbon, all contain mercury compounds and thus pose special problems with respect to burial at landfills where strictly localized containment of the mercury compounds is imperative. The concentration of mercury compounds in particulates or solids collected from a bag house is relatively minute; therefore, a very small quantity of mercury would be dispersed throughout relatively massive volumes of a landfill, wherever the bag house solids or particulates are dumped. Moreover, with respect to activated carbon, that material is relatively expensive, and once spent activated carbon particles are removed from an adsorbent bed, they cannot be easily regenerated and used again.
In the activated alumina process, mercury compounds in the gas stream can be adsorbed and retained on the surface of activated particles, but much of the elemental mercury will not be so affected. Thus elemental mercury in the combustion gas stream is oxidized to form mercury compounds (e.g. mercuric chloride), and catalysts are employed to promote the oxidation process. However, such processes do not capture SOX and NOX.
The use of oxides of manganese to remove sulfur compounds from gas streams is known in the art. Oxides of manganese are known to form sulfates of manganese from SOX and nitrates of manganese from NOX when contacted with a gas containing these pollutants. U.S. Pat. No. 1,851,312 describes an early use of oxides of manganese to remove sulfur compounds from a combustible gas stream. U.S. Pat. No. 3,150,923 describes a dry bed of oxides of manganese to remove SOX. A wet method to remove SOX with oxides of manganese is described in U.S. Pat. No. 2,984,545. A special filter impregnated with manganese oxide to remove totally reduced sulfur compounds is described in U.S. Pat. No. 5,112,796. Another method in U.S. Pat. No. 4,164,545 describes using an ion exchange resin to trap the products of manganese oxide and SOX and NOX. The use of certain types of oxides of manganese to remove SOX is disclosed U.S. Pat. Nos. 3,723,598 and 3,898,320. Some of the known methods of bringing oxides of manganese in contact with a gas stream, i.e., sprayed slurries, beds of manganese ore or special filters, have been cumbersome. Although the prior art teaches the use of oxides of manganese to remove SOX and/or NOX, they do not teach an adaptable system or process that can capture SOX and/or NOX and other pollutants with oxides of manganese and monitor and adjust system operational parameters, such as differential pressure, to provide real-time system control.
Bag houses have traditionally been used as filters to remove particulates from high volume gas streams. U.S. Pat. No. 4,954,324 describes a bag house used as a collector of products generated through the use of ammonia and sodium bicarbonate to remove SOX and NOX from a gas stream. U.S. Pat. No. 4,925,633 describes a bag house as a site of reaction for SOX and NOX with the reagents, ammonia and alkali. U.S. Pat. No. 4,581,219 describes a bag house as a reactor for highly efficient removal of SOX only with a calcium-based reagent and alkaline metal salt. Although these prior art discloses and teach the use of bag houses for removal of particulates and as a reaction chamber, they do not teach the use of bag houses in an adaptable system capable of monitoring and adjusting system operational parameters, such as differential pressure, to capture SOX and/or NOX and other pollutants with oxides of manganese.
In view of the aforementioned problems of known processes for removal of SOX, NOX, mercury compounds, and elemental mercury as well as other pollutants from combustion gases, process gases, and other industrial waste gases, it would be desirable to provide a dry process for removal of SOX and NOX as well as other pollutants from a gas stream. It is further desirable to have a dry removal process that eliminates the environmental impacts of the disposal of large volumes of mercury containing solids and particulates and significant amounts of gypsum generated during SOX wet removal processes.
Wet removal processes can result in significant differential pressures across a removal system. Differential pressures above 30 inches of water column have been observed in wet removal processes. Such large differential pressures are costly because significant energy must be expended to counter the differential pressure and provide a waste gas stream with sufficient energy to flow up and out of a stack. A system and process that can accomplish pollutant removal with minimal or controlled differential pressure across the system therefore would be desirable and cost effective for most industry sectors processing or emitting significant amounts of combustion gases, process gases, and other industrial gases.
The calcium compounds utilized in SOX wet scrubbing methods form gypsum in the process. They are purchased and consumed in significant quantities and once gypsum is formed the calcium compounds cannot be recovered, at least not cost-effectively. Thus, it would be desirable to have a removal method employing a sorbent that not only can remove pollutants from a gas stream but that can be regenerated, recovered, and then recycled or reused for removal of additional pollutants from a gas stream.
To realize such a system and process, it would need to incorporate process controls and software that can monitor and adjust operational parameters from computer stations onsite or at remote locations through interface with a sophisticated electronics network incorporating an industrial processor. This would allow a technician to monitor and adjust operational parameters in real-time providing controls of such operational parameters as system differential pressure and pollutant capture rates or removal efficiencies. Such a network would be desirable for its real-time control and off-site accessibility.
In light of increased energy demand and recent energy shortages, it would be desirable to be able to return to operational utility idled power plants that have been decommissioned because their gypsum impoundments have reached capacity. This could be accomplished with retrofits of a system employing a regenerable sorbent in a dry removal process that does not require the use of calcium compounds. Such a system would also be readily adapted and incorporated into new power plants that may be coming on line. Utility plants and independent power plants currently in operation could readily be retrofitted with such a system. Further, such a system could be of significant value in enabling emissions sources to comply with emission standards or air quality permit conditions. With the reductions in emissions of pollutants such as NOX and SOX, marketable emissions trading credits could be made available or non-attainment areas for state or national ambient air quality standards may be able to achieve attainment status. Such scenarios would allow for development in areas where regulatory requirements previously prohibited industrial development or expansion.
The systems and processes of the present invention in their various embodiments can achieve and realize the aforementioned advantages, objectives, and desirable benefits.
The invention is directed to an adaptable system for dry removal of SOX and/or NOX and/or other pollutants from gases and to processes employing the system. The system generally comprises a feeder and at least one reaction zone for single-stage removal. For dual-stage removal the system would generally be comprised of one or more feeders, a first reaction zone, and a second reaction zone. Multi-stage removal systems would incorporate additional reaction zones. The reaction zones utilized in the invention may be a fluidized bed, a pseudo-fluidized bed, a reaction column, a fixed bed, a pipe/duct reactor, a moving bed, a bag house, an inverted bag house, bag house reactor, serpentine reactor, and a cyclone/multiclone. Process operational parameters, such as system differential pressure, can be monitored and adjusted so that any differential pressure across the system is no greater than a predetermined level. Such process controls are accomplished with control sub-elements, control loops and/or process controllers.
The feeder contains a supply of sorbent of regenerable oxides of manganese and/or regenerated oxides of manganese. The feeder is configured to handle and feed oxides of manganese, which, upon regeneration, are in particle form and are defined by the chemical formula MnOX, where X is about 1.5 to 2.0 and wherein the oxides of manganese have a particle size of about 0.1 to about 500 microns and surface area of about 1 to about 1000 m2/g as determined by the Brunauer, Emmett and Teller (BET) method.
For single stage removal of SOX and/or NOX, a gas containing SOX and/or NOX is introduced into a reaction zone. The gas would be introduced at temperatures typically ranging from ambient temperature to below the thermal decomposition temperature(s) of nitrates of manganese if NOX only or both NOX and SOX were to be removed. If only SOX is the target pollutant, the gas would be introduced at temperatures typically ranging from ambient temperature to below the thermal decomposition temperature(s) of sulfates of manganese. In the reaction zone, the gas is contacted with the sorbent for a time sufficient to effect SOX capture at a targeted SOX capture rate set point or for a time sufficient to effect NOX capture at a target capture rate set point. The SOX and NOX, being captured respectively by reacting with the sorbent to form sulfates of manganese to substantially strip the gas of SOX and to form nitrates of manganese to substantially strip the gas of NOX. The reaction zone is configured to render the gas free of reacted and unreacted sorbent so that the gas can be vented from the reaction zone.
In a two-stage removal system, the first reaction zone is configured for introduction of the sorbent and a gas containing SOX and NOX. The gas is introduced at temperatures typically ranging from ambient temperature to below the thermal decomposition temperature(s) of sulfates of manganese and contacted with the sorbent for time sufficient to primarily effect SOX capture at a targeted SOX capture rate set point. The SOX is captured by reacting with the sorbent to form sulfates of manganese to substantially strip the gas of SOX. The second reaction zone is configured for introduction of sorbent and the gas that has been substantially stripped of SOX from the first reaction zone. In the second reaction zone, the gas is introduced at temperatures typically ranging from ambient temperature to below the thermal decomposition temperature(s) of nitrates of manganese and is further contacted with sorbent for a time sufficient to primarily effect NOX capture at a targeted NOX capture rate set point. The NOX is captured by reacting with the sorbent to form nitrates of manganese to substantially strip the gas of NOX. The second reaction zone is further configured so that the gas that has been substantially stripped of SOX and NOX is rendered free of reacted and unreacted sorbent so that the gas may be vented from the second reaction zone.
In another embodiment, the system further comprises control sub-elements or combinations of control sub-elements for regulating and controlling differential pressure across the system, for regulating and controlling SOX and/or NOX capture efficiency, for regulating sorbent feed rate, for regulating gas inlet temperatures into the reaction zones, for regulating variable venturi position, and for simultaneous monitoring, regulation and control of differential pressure, SOX and NOX capture rates, sorbent feed rate, inlet temperatures and variable venturi position. The control sub-element for regulating and adjusting differential pressure does so by measuring differential pressure across the system, comparing differential pressure measurements against differential pressure set points, and increasing or decreasing pulse rates to adjust differential pressure to reconcile with targeted differential pressure set points.
In another embodiment, the system is generally comprised of at least one sorbent feeder and a modular reaction unit. Said feeder contains a supply of sorbent of regenerable oxides of manganese and/or regenerated oxides of manganese. The feeder is configured to handle and feed oxides of manganese, which, upon regeneration, are in particle form and are defined by the chemical formula MnOX where X is about 1.5 to 2.0, and wherein the oxides of manganese have a particle size of less than 100 microns and a surface area of at least 20 m2/g as determined by the BET method. The modular reaction unit is comprised of at least three interconnected reaction zones. With the reaction zones as bag houses, the bag houses are connected so that a gas containing SOX and/or NOX can be routed through any one of the bag houses, any two of the bag houses in series, or all of the at least three bag houses in series or in parallel or any combination of series and parallel. Each bag house of the modular reaction unit is separately connected to the feeder so that sorbent can be introduced into each bag house where SOX and/or NOX capture can occur and the gas is contacted with sorbent for a time sufficient to allow formation of sulfates of manganese, nitrates of manganese, or both. This embodiment may further comprise the above-mentioned control sub-elements. Additionally, the modular reaction unit may further comprise a section of pipe/duct connected to an inlet of each bag house for conveying gas to each bag house and into which sorbent can be introduced. The section of pipe/duct may be configured as a first reaction zone where gas containing SOX and NOX is introduced at temperatures typically ranging from ambient temperature to below the sorbent sulfate and nitrate thermal decomposition temperature(s) thereof and contacted with the sorbent for a time sufficient to effect SOX capture at a targeted SOX capture rate set point, the SOX being captured by reacting with the sorbent to form sulfates of manganese. The bag houses of the modular reaction units are each configured so that the gas substantially stripped of SOX or NOX is rendered free of reacted and unreacted sorbent so that the gas may be vented.
In another embodiment of the invention, the system is comprised of at least one feeder and multiple bag houses. The first bag house is connected to the second and third bag houses through a common conduit. The first bag house is configured for introduction of sorbent and a gas containing SOX and NOX where the gas is introduced at temperatures typically ranging from ambient temperature to below the thermal decomposition temperature(s) of sulfates of manganese and contacted with the sorbent for a time sufficient to primarily effect SOX capture at a SOX capture rate set point, the SOX being captured by reacting with the sorbent to form sulfates of manganese to substantially strip the gas of SOX. The first bag house is configured to render the gas that has been substantially stripped of SOX free of reacted and unreacted sorbent so that the gas can be directed out of the first bag house free of reacted and unreacted sorbent. The second bag house and the third bag house are each connected to the first bag house by a common conduit. In the second bag house and the third bag house the gas that has been substantially stripped of SOX in the first bag house may be introduced at temperatures typically ranging from ambient to below the thermal decomposition temperature(s) of nitrates of manganese and is further contacted with sorbent for a time sufficient to primarily effect NOX capture at a targeted NOX capture rate set point. The NOX is captured by reacting with the sorbent to form nitrates of manganese to substantially strip the gas of NOX. The second and third bag houses each being configured to render the gas that has been substantially stripped of SOX and NOX free of reacted and unreacted sorbent so that the gas may be vented from the second and third bag houses free of reacted and unreacted sorbent. The system of this embodiment also includes diverter valve(s) positioned in the common conduit to direct the flow of gas from the first bag house to the second bag house and/or the third bag house. The diverter valve(s) have variable positions which may include first, second and third positions, and so on in sequence. In the one position, gas from the first bag house is directed to the second bag house. In another position, gas from the first bag house is directed to both the second and third bag houses. And in a further position, gas from the first bag house is directed to the third bag house. Differential pressure within the system is regulated so that any differential pressure across the system is no greater than a predetermined level.
In its various embodiments, the system may further comprise an alumina reactor where the gas that has been substantially stripped of SOX and/or NOX can be introduced and contacted with the sorbent for the purpose of removing mercury. In the reactor, mercury compounds in the gas contacts the sorbent, which may be oxides of manganese and/or alumina, and is sorbed thereon. The reactor is configured to render the gas free of sorbent so that the gas can be vented.
In another embodiment of the invention, the bag house utilized as reaction zones in the system may be an inverted bag house. The inverted bag house permits downward, vertical flow of gases and sorbent and is comprised of a bag house housing, at least one inlet, a plurality of fabric filter bags, a support structure for the filter bags, a hopper to receive and collect particles, an outlet, and a conduit. The bag house housing permits the introduction of gases and sorbent entrained in the gases, has a top and a bottom and is configured for gases to flow vertically downward from the top to the bottom of the bag house. Said inlet is located near the top of the bag house housing and configured for the introduction of gases and sorbent entrained in the gases into the bag house. The plurality of fabric filter bags are configured to allow gas to flow from the outside of the bags to the inside of the bags under an applied differential pressure and to prevent the passage of sorbent from the outside to the inside of the bags, thereby separating sorbent from the gas. The support structure is configured to receive and support the fabric filter bags and to provide openings through which particles may be freely passed downward into the hopper by gravity. The hopper is configured to receive the particles and to permit the removal of the particles. The inverted bag house also has an outlet located near the bottom of the housing below the bags and above the hopper. The outlet is connected to a conduit located below the fabric filter bags and positioned to receive gas passing through the fabric filter bags.
The invention is further directed to a bag house reactor that can be utilized as a reaction zone in the system of the invention. The bag house reactor is comprised of a bag house that has interior and exterior surfaces as well as upper, central, and lower sections. The bag house has a variable venturi for adjusting the velocity of gas flowing within the bag house thereby increasing of decreasing the depth of the pseudo-fluidized bed. The variable venturi is generally located in the central and/or lower sections of the bag house and is configured for adjustment of the position of the variable venturi by varying the distance or space between the variable venturi and the interior surface of the bag house. The bag house reactor has a variable venturi position detector for determining the position of the variable venturi and a variable venturi positioner for adjusting the position of the variable venturi to increase or decrease the velocity of gas flow from the lower section past the variable venturi to the central and upper sections of the bag house. There is a first distribution port which is configured for introduction of gas into the bag house. The gas distribution port is positioned below the variable venturi. There is a distribution port connected to a sorbent feeder conduit which is configured for introduction of sorbent into the bag house. The sorbent distribution port is positioned above the variable venturi. Within the bag house are a plurality of fabric filter bags secured therein. The fabric filter bags are mounted in the upper section of the bag house and extend downward into the central section. In the lower section of the bag house is a sorbent hopper where loaded sorbent is collected. The bag house reactor has a loaded sorbent outlet connected to the sorbent hopper. The sorbent outlet has an outlet valve which in the open position allows for removal of sorbent from the hopper. Located in the top section of the bag house is a vent for the venting of gas from the bag house.
The invention is further directed to processes employing systems according to the invention for removal of SOX and NOX from a gas. Thus in another embodiment of the invention, the process comprises providing a removal system according to the invention, introducing gas containing SOX and NOX into the first reaction zone of the system, the gas having temperatures typically ranging from ambient temperature to below the thermal decomposition temperature(s) of sulfates of manganese; contacting the gas with sorbent for a time sufficient to primarily effect SOX capture at a targeted SOX capture rate set point by formation of sulfates of manganese; passing the gas substantially stripped of SOX from the first reaction zone into the second reaction zone, the gas having temperatures typically ranging from ambient temperature to below the thermal decomposition temperature(s) of nitrates of manganese; contacting the gas in the second reaction zone with sorbent for a time sufficient to primarily effect NOX capture at a NOX capture rate set point by formation of nitrates of manganese; and venting the gas substantially stripped of SOX and/or NOX and rendered free of reacted and unreacted sorbent from the second reaction zone.
In another embodiment, the process comprises providing a removal system according to the invention, the removal system being comprised of at least one feeder and a modular reaction unit as described above; introducing gas containing SOX and NOX into a first bag house of the modular reaction unit, the gas having temperatures typically ranging from ambient temperature to below the thermal decomposition temperature(s) of sulfates of manganese; contacting the gas in the first bag house with sorbent for a time sufficient to effect SOX capture at a target SOX capture rate set point by formation of sulfates of manganese; passing the gas substantially stripped of SOX from the first bag house into a second bag house of the modular reaction unit, the gas having temperatures typically ranging from ambient temperature to below the thermal decomposition temperature(s) of nitrates of manganese; contacting the gas in the second bag house with sorbent for a time sufficient to effect NOX capture at a target NOX capture rate set point by formation of nitrates of manganese; and venting the gas substantially stripped of SOX and NOX and free of reacted and unreacted sorbent from the second bag house.
In another embodiment, the process further comprises the steps of removing reacted sorbent from reactions zones of a system of the invention; washing the sorbent in a dilute acid rinse to dissolve sulfates and/or nitrates of manganese on the surface of sorbent particles into solution and thereby cleaning the sorbent; separating the cleaned sorbent from the acid rinse; drying the cleaned sorbent; and pulverizing the cleaned sorbent to de-agglomerate the cleaned sorbent.
In another embodiment, the process further comprises the steps of removing reacted sorbent from reactions zones of a system of the invention; washing the sorbent in a dilute acid rinse to dissolve sulfates and/or nitrates of manganese on the surface of sorbent particles into solution and thereby cleaning the sorbent; separating the cleaned sorbent from the acid rinse; conveying the cleaned sorbent to a dryer; drying the cleaned sorbent; conveying the cleaned sorbent to a pulverizer; pulverizing the cleaned sorbent to de-agglomerate the cleaned sorbent; and conveying the de-agglomerated clean sorbent to the sorbent feeder for reintroduction into the system.
In another embodiment, the process further comprises the steps of removing reacted sorbent from reactions zones of a system of the invention; washing the sorbent in a dilute acid rinse to dissolve sulfates and/or nitrates of manganese on the surface of sorbent particles into solution and thereby cleaning the sorbent; separating the cleaned sorbent from the acid rinse to provide a filtrate containing dissolved sulfates and/or nitrates of manganese; adding alkali or ammonium hydroxide to the filtrate to form an unreacted sorbent precipitate of oxides of manganese and a liquor containing alkali or ammonium sulfates and/or nitrates; separating the unreacted sorbent precipitate from the liquor, the liquor being routed for further processing into marketable products or for distribution and/or sale as a useful by-product; rinsing the sorbent precipitate; drying the sorbent precipitate to form unreacted sorbent; and pulverizing the unreacted sorbent to de-agglomerate the unreacted sorbent. In another embodiment, the process further comprises the steps of removing reacted sorbent from reactions zones of a system of the invention; washing the sorbent in a dilute acid rinse to dissolve sulfates and/or nitrates of manganese on the surface of sorbent particles into solution and thereby cleaning the sorbent; separating the cleaned sorbent from the acid rinse to provide a filtrate containing dissolved sulfates and/or nitrates of manganese; adding alkali or ammonium hydroxide to the filtrate to form a sorbent precipitate of oxides of manganese and a liquor containing alkali or ammonium sulfates and/or nitrates; separating the sorbent precipitate from the liquor, the sorbent precipitate being routed for regeneration of unreacted sorbent; and routing the liquor for distribution and/or sale as a useful by-product or for further processing into marketable products.
In another embodiment, the process further comprises the steps of removing reacted sorbent from a reaction zone of the system where primarily NOX capture occurred by reacting with the sorbent to form nitrates of manganese; heating the reacted sorbent to thermally decompose the nitrates of manganese, to desorb NO2, and to regenerate reacted sorbent to form unreacted sorbent of oxides of manganese; and further heating the unreacted sorbent in an oxidizing atmosphere to complete the regeneration of the sorbent.
In another embodiment, the process further comprises the steps of removing reacted sorbent from a reaction zone of the system where primarily NOX capture occurred by reacting with the sorbent to form nitrates of manganese; heating the reacted sorbent to thermally decompose the nitrates of manganese, to desorb NO2, and to regenerate reacted sorbent to form unreacted sorbent of oxides of manganese; passing the evolved NO2 through a wet scrubber containing water and an oxidant to form a nitric acid liquor; and routing the nitric acid liquor for further distribution and/or sale as a useful product or on for further processing.
In another embodiment, the process further comprises the steps of removing reacted sorbent from a reaction zone of the system where primarily NOX capture occurred by reacting with the sorbent to form nitrates of manganese; heating the reacted sorbent to thermally decompose the nitrates of manganese, to desorb NO2, and to regenerate reacted sorbent to form unreacted sorbent of oxides of manganese; passing the evolved NO2 through a wet scrubber containing water and an oxidant to form a nitric acid liquor; adding an ammonium or alkali hydroxide to the acid liquor to form a liquor containing ammonium or alkali nitrates; and routing the liquor for distribution and/or sale as a useful by-product or for further processing into marketable products.
In another embodiment, the process further comprises the steps of removing SOX and NOX reacted sorbent from a reaction zone of the system; heating the reacted sorbent to a first temperature to evolve NO2, the desorb NO being routed for further processing and/or handling; and heating the reacted sorbent to a second temperature to evolve SOX, the evolved SOX being routed for further processing and/or handling and the reacted sorbent being regenerated to unreacted sorbent.
In another embodiment, the process further comprises the steps of removing NOX, SOX and mercury reacted sorbent from a reaction zone of the system; heating the sorbent to a first temperature to desorb NO2 which is routed for further processing into marketable products; heating the sorbent to a second temperature to desorb elemental mercury which is routed to a condenser for recovery; rinsing the sorbent to wash away any ash and to dissolve sulfates of manganese into solution to form a liquor; separating any ash in the liquor, the separated ash being routed for further handling; adding alkali or ammonium hydroxide to the liquor to form an unreacted sorbent precipitate of oxides of manganese and a liquor containing alkali or ammonium sulfates, the liquor containing rinsed sorbent; separating the rinsed sorbent and unreacted sorbent precipitate from the liquor, the liquor being routed for further processing into marketable products or for distribution and/or sale as a useful by-product; drying the rinsed sorbent and sorbent precipitate to form unreacted sorbent; and pulverizing the unreacted sorbent to de-agglomerate the unreacted sorbent.