Common use of Scrubber System Clause in Contracts

Scrubber System. The function of the Scrubber System is to remove fly ash and sulfur dioxide (SO2) from the flue gas by washing with a recycled liquor. Eight scrubber vessels are installed each at Unit 3 and 4 into which boiler combustion gases are ducted. At full load it requires that seven scrubbers operational to achieve sufficient SO2 and particulate removal to comply with environmental regulations. Since it was expected that at any given time at least one scrubber train will be down for maintenance, it was necessary to install eight scrubber trains in order to assure reliable plant operation in compliance with the law. The flue gas enters the top of each scrubber vessel in the venturi section where the gas is contacted with finely atomized scrubber slurry. The flue gas is adiabatically cooled and saturated by the evaporation of water from the scrubber slurry. In the venturi, fly ash particulates are removed by the slurry droplets during collisions caused by the sudden changes in gas velocity. The proper gas pressure drop across the venturi to achieve these changes in velocity is maintained by raising or lowering a xxxxx xxx located in the throat of the venturi. SO2 is also absorbed and removed by the slurry in the venturi. After the flue gas leaves the venturi, it passes upward through an absorption spray zone where the gas is sprayed with more scrubber slurry. These sprays remove additional SO2. Then the flue gas passes through a wash tray where it is bubbled through a stream of wash tray slurry. The main purpose of the wash tray is to remove and dilute the slurry droplets entrained in the flue gas from the venturi and absorption sprays. The wash tray also removes small amounts of fly ash and SO2. A spray keeps the wash tray from plugging and also maintains the proper water balance in the scrubber. When the flue gas bubbles through the wash tray it produces a mist of water droplets containing some dissolved and suspended solids. This mist is removed by a mist eliminator. The mist eliminator is made up of a series of zigzag parallel plates. The mist droplets strikes these plates, cling to them, and then fall back onto the wash tray. The flue gas then leaves the scrubber vessel. At this point the flue gas has been cooled to a temperature of about 120OF and is saturated as a result of water introduced in the scrubbing process. Approximately 95% of the SO2 and over 90% of the fly ash particulates are removed. Because of the action of the scrubber in cooling and saturating the flue gas, the pressure drop across the scrubber and the moisture contents adverse conditions for the continued flow of gases to and up the stack. It is therefore necessary to reheat the gases to about 170°F and, thereafter, to restore the gas flow with ID fans. The reheater is another heat exchanger device that utilizes steam from the turbine or boiler. The heat in the reheater vaporizes any water droplets in the gas stream and at the same time raises the temperature of the gas to achieve a relative humidity below the saturation point. This improves the plum rise from the stack, reduces ground level concentrations of the emissions, and prevents the formation of acid mist that would cause corrosion and failure of equipment downstream of the scrubber. Upon leaving the reheater the flue gas enters an ID fan that serves to maintain the gas flow through the scrubber and reheater and forces it through the duct and up the stack. Units 3 and 4 are designed as balanced draft units that require forced draft fans at the furnace inlet and ID fans at the scrubber outlet. The flue gas temperature is increased to about 190°F by the compression in the fan. Each scrubber vessel is provided with one reheater and one ID fan. When the flue gas leaves the fan it enters a series of ducts where the flue gas from all of the scrubbers are combined and routed to the bottom of the stack. Each of Units 3 and 4 has its own stack that discharges the cleaned gases to the atmosphere at an elevation of 692 feet above the ground. The slurry used for the venturi and absorption sprays are taken from the recycle tank located directly below each scrubber vessel. There are two pumps for the venturi; one operates as a spare. One-half of the slurry to the venturi is injected on the tangential shelf above the venturi and the other half is sprayed on top of the plump xxx. There are also two pumps per scrubber vessel for the absorption sprays. Each pump supplies slurry to one set of sprays. The sets of sprays are located one above the other. Each set of sprays is operated independently of the other. Only one set of sprays are operated so long as the outlet SO2 emissions are below the level determined by the permits. The capability to operate two sets of sprays at once is necessary to insure that the outlet SO2 concentration will never exceed the limit permitted. The spent slurry from the venturi and absorption sprays falls to the vessel bottom and is returned to the recycle tank through downcomer pipes. The removal of fly ash and SO2 causes the buildup of suspended solid particles in the recycle tank. An agitator is used to keep these solids suspended and to promote mixing. The concentration of these suspended solids is controlled by taking a slurry bleed stream to the disposal pond where the solids settle out producing a sludge. The clear water is then returned to the recycle tank. Slurry from each recycle tank is bled to an effluent holding tank. There is one effluent holding tank for each four-scrubber vessels (two per unit). All of the effluent holding tanks discharge to one large effluent holding tank common to both units, which then discharges to the disposal pond. The alkali used for SO2 removal is a mixture of hydrated high calcium lime and hydrated dolomitic lime (as further described in Item 3 below). This lime is added to the regenerator as a slurry. There is one regenerator per recycle tank. There is one regenerations tank feed pump per recycle tank that takes a stream of recycle slurry to the regenerator. The regenerator has an overflow line that returns regenerated slurry to the recycle tank. The purpose of the regenerators is to maintain a chemical environment different from the recycle tanks, which is more favorable to the chemical reactions necessary to regenerate the spent slurry after SO2 removal. There is a separate wash tray recycle tank from which slurry is pumped to the wash tray and the wash tray undersprays. There is one wash tray recycle tank for each two scrubber vessels (four wash tray recycle tanks per unit). A bleed stream is taken from each wash tray recycle pump in order to remove the suspended solids collected by the wash tray. This bleed stream goes to the wash tray bleed tank (one wash tray bleed tank per unit). The wash tray bleed tank discharges to the wash tray pond. All wash tray recycle tanks and wash tray bleed tanks are equipped with agitators to prevent the suspended solids from settling out. The wash tray bleed tank is discharged to the wash tray pond where the suspended solids are allowed to settle out forming a sludge at the bottom of the pond. The clear water is then returned to the wash tray recycle tanks. The bottom of the mist eliminator is intermittently sprayed with blowdown water from the Plant’s cooling tower. This is dome to clean the mist eliminator and is also the major source of makeup water for the scrubber system. The top of each mist eliminator is also sprayed once per day for 1-1/2 minutes with river water.

Scrubber System. The function air pollution control facilities employed on Units #3 and #4 consist of a complete scrubber system, including duct work, plenums, scrubber vessels, reheaters and induced draft fans, together with infrastructures, monitoring and electrical controls and instrumentation therefore, for the Scrubber System is to remove fly ash and purpose of removing the sulfur dioxide (SO2) and particulate matter from the flue gas by washing with a recycled liquor. Eight scrubber vessels are installed each at Unit 3 and 4 into which boiler combustion gases are ducted. At full load it requires that seven scrubbers operational to achieve sufficient SO2 and particulate removal to comply with environmental regulations. Since it was expected that at any given time at least one scrubber train will be down for maintenance, it was necessary to install eight scrubber trains in order to assure reliable plant operation in compliance with the lawgas. The flue gas enters scrubber system also includes a scrubber maintenance facility, including a machine shop and laboratory dedicated to the top scrubber system and an environment monitoring laboratory for the pollution control facilities. The scrubber system utilizes the Wet Venturi Principle and consists of eight modules for each scrubber vessel unit through which the steam generator gases from the burned coal must pass. The gases in the venturi section where the gas is scrubber are contacted with finely atomized scrubber slurry. The flue gas is adiabatically cooled and saturated by Within the evaporation stated performance of water from the scrubber slurry. In the venturisystem, fly ash particulates are removed by the slurry droplets during collisions caused by the sudden changes in gas velocitydroplets. The proper gas pressure drop across sulfur dioxide reacts with the venturi to achieve these changes in velocity is maintained by raising or lowering a xxxxx xxx located alkali contained in the throat of the venturi. SO2 is also absorbed and removed by the slurry in the venturi. After the flue gas leaves the venturi, it passes upward through an absorption spray zone where the gas is sprayed with more scrubber slurry. These sprays remove additional SO2. Then the flue gas passes through a wash tray where it is bubbled through a stream of wash tray slurry. The main purpose of the wash tray is to remove and dilute the slurry droplets entrained in the flue gas which results from the venturi and absorption sprays. The wash tray also removes small amounts mixing of water, fly ash and SO2. A spray keeps the wash tray from plugging and also maintains the proper water balance in the scrubber. When the flue gas bubbles through the wash tray it produces a mist of water droplets containing some dissolved and suspended solids. This mist is removed by a mist eliminator. The mist eliminator is made up of a series of zigzag parallel plates. The mist droplets strikes these platesparticulates, cling to them, and then fall back onto the wash tray. The flue gas then leaves the scrubber vessel. At this point the flue gas has been cooled to a temperature of about 120OF and is saturated as a result of water introduced in the scrubbing process. Approximately 95% of the SO2 and over 90% of the fly ash particulates are removed. Because of the action of the scrubber in cooling and saturating the flue gas, the pressure drop across the scrubber and the moisture contents adverse conditions for the continued flow of gases to and up the stack. It is therefore necessary to reheat the gases to about 170°F and, thereafter, to restore the gas flow with ID fans. The reheater is another heat exchanger device that utilizes steam from the turbine or boiler. The heat in the reheater vaporizes any water droplets in the gas stream and at the same time raises the temperature of the gas to achieve a relative humidity below the saturation point. This improves the plum rise from the stack, reduces ground level concentrations of the emissions, and prevents the formation of acid mist that would cause corrosion and failure of equipment downstream of the scrubber. Upon leaving the reheater the flue gas enters an ID fan that serves to maintain the gas flow through the scrubber and reheater and forces it through the duct and up the stack. Units 3 and 4 are designed as balanced draft units that require forced draft fans at the furnace inlet and ID fans at the scrubber outlet. The flue gas temperature is increased to about 190°F by the compression in the fan. Each scrubber vessel is provided with one reheater and one ID fan. When the flue gas leaves the fan it enters a series of ducts where the flue gas from all of the scrubbers are combined and routed to the bottom of the stack. Each of Units 3 and 4 has its own stack that discharges the cleaned gases to the atmosphere at an elevation of 692 feet above the ground. The slurry used for the venturi and absorption sprays are taken from the recycle tank located directly below each scrubber vessel. There are two pumps for the venturi; one operates as a spare. One-half of the slurry to the venturi is injected on the tangential shelf above the venturi and the other half is sprayed on top of the plump xxx. There are also two pumps per scrubber vessel for the absorption sprays. Each pump supplies slurry to one set of sprays. The sets of sprays are located one above the other. Each set of sprays is operated independently of the other. Only one set of sprays are operated so long as the outlet SO2 emissions are below the level determined by the permits. The capability to operate two sets of sprays at once is necessary to insure that the outlet SO2 concentration will never exceed the limit permitted. The spent slurry from the venturi and absorption sprays falls to the vessel bottom and is returned to the recycle tank through downcomer pipes. The removal of fly ash and SO2 causes the buildup of suspended solid particles in the recycle tank. An agitator is used to keep these solids suspended and to promote mixing. The concentration of these suspended solids is controlled by taking a slurry bleed stream to the disposal pond where the solids settle out producing a sludge. The clear water is then returned to the recycle tank. Slurry from each recycle tank is bled to an effluent holding tank. There is one effluent holding tank for each four-scrubber vessels (two per unit). All of the effluent holding tanks discharge to one large effluent holding tank common to both units, which then discharges to the disposal pond. The alkali used for SO2 removal is a mixture of hydrated high calcium lime and hydrated dolomitic lime (as further described lime. A major portion of the sulfur dioxide is converted to solid sulfate compounds which are retained in Item the scrubber liquid and can, therefore, be piped to and deposited in an ash pond together with the particulate. After the flue gas passes through the venturi section, absorption sprays and wash trays, it is processed through a demister which removes any entrained slurry and is then reheated and discharged through the stack. The slurry system in the Units #3 below)and #4 scrubber system consists of recycle tanks, regenerators, agitators, pumps and pipelines. This lime The slurry from the Units #3 and #4 scrubber system is added transported to an effluent holding pond and involves the use of effluent holding tanks agitators, pumps and pipelines. A separate wash tray pond system is used to store the suspended solids collected from the wash tray system. Reclaimed water from the clear water section of these ponds is circulated back to the regenerator as a slurryscrubber system. Lime Storage The sole purpose of the lime system is to supply the lime slurry requirements of the scrubber regeneration system. There is one regenerator per recycle tanklime system that serves the sixteen scrubbers for Units #3 and #4. There is one regenerations tank feed pump per recycle tank that takes a stream of recycle slurry to the regenerator. The regenerator has an overflow line that returns regenerated slurry to the recycle tank. The purpose Major components of the regenerators system include four slakers, in which calcined high calcium lime is reacted with water to maintain produce a chemical environment different from the recycle hydrated lime slurry, slurry transfer tanks, which is more favorable to where the chemical reactions necessary to regenerate the spent slurry after SO2 removal. There is a separate wash tray recycle tank from which slurry is pumped to diluted with water and mixed with dry hydrated dolomitic lime, slurry feed storage tanks, where the wash tray and the wash tray undersprays. There is one wash tray recycle tank slurry will be held for each two scrubber vessels (four wash tray recycle tanks per unit). A bleed stream is taken from each wash tray recycle pump in order to remove the suspended solids collected use by the wash tray. This bleed stream goes to the wash tray bleed tank (one wash tray bleed tank per unit). The wash tray bleed tank discharges to the wash tray pond. All wash tray recycle tanks regenerators as needed, hydrators, for mixing calcined dolomitic lime with water, and wash tray bleed tanks are equipped with agitators to prevent the suspended solids from settling out. The wash tray bleed tank is discharged to the wash tray pond where the suspended solids are allowed to settle out forming a sludge at the bottom of the pond. The clear water is then returned to the wash tray recycle tanks. The bottom of the mist eliminator is intermittently sprayed with blowdown water from the Plant’s cooling tower. This is dome to clean the mist eliminator and is also the major source of makeup water for the scrubber system. The top of each mist eliminator is also sprayed once per day for 1-1/2 minutes with river wateragitators.

Scrubber System. The function of the Scrubber System is to remove fly ash and sulfur dioxide (SO2) from the flue gas by washing with a recycled liquor. Eight scrubber vessels are installed each at Unit 3 and 4 into which boiler combustion gases are ducted. At full load it requires that seven scrubbers operational to achieve sufficient SO2 and particulate removal to comply with environmental regulations. Since it was expected that at any given time at least one scrubber train will be down for maintenance, it was necessary to install eight scrubber trains in order to assure reliable plant operation in compliance with the law. The flue gas enters the top of each scrubber vessel in the venturi section where the gas is contacted with finely atomized scrubber slurry. The flue gas is adiabatically cooled and saturated by the evaporation of water from the scrubber slurry. In the venturi, fly ash particulates are removed by the slurry droplets during collisions caused by the sudden changes in gas velocity. The proper gas pressure drop across the venturi to achieve these changes in velocity is maintained by raising or lowering a xxxxx xxx located in the throat of the venturi. SO2 is also absorbed and removed by the slurry in the venturi. After the flue gas leaves the venturi, it passes upward through an absorption spray zone where the gas is sprayed with more scrubber slurry. These sprays remove additional SO2. Then the flue gas passes through a wash tray where it is bubbled through a stream of wash tray slurry. The main purpose of the wash tray is to remove and dilute the slurry droplets entrained in the flue gas from the venturi and absorption sprays. The wash tray also removes small amounts of fly ash and SO2. A spray keeps the wash tray from plugging and also maintains the proper water balance in the scrubber. When the flue gas bubbles through the wash tray it produces a mist of water droplets containing some dissolved and suspended solids. This mist is removed by a mist eliminator. The mist eliminator is made up of a series of zigzag parallel plates. The mist droplets strikes these plates, cling to them, and then fall back onto the wash tray. The flue gas then leaves the scrubber vessel. At this point the flue gas has been cooled to a temperature of about 120OF and is saturated as a result of water introduced in the scrubbing process. Approximately 95% of the SO2 and over 90% of the fly ash particulates are removed. Because of the action of the scrubber in cooling and saturating the flue gas, the pressure drop across the scrubber and the moisture contents adverse conditions for the continued flow of gases to and up the stack. It is therefore necessary to reheat the gases to about 170°F 170OF and, thereafter, to restore the gas flow with ID fans. The reheater is another heat exchanger device that utilizes steam from the turbine or boiler. The heat in the reheater vaporizes any water droplets in the gas stream and at the same time raises the temperature of the gas to achieve a relative humidity below the saturation point. This improves the plum rise from the stack, reduces ground level concentrations of the emissions, and prevents the formation of acid mist that would cause corrosion and failure of equipment downstream of the scrubber. Upon leaving the reheater the flue gas enters an ID fan that serves to maintain the gas flow through the scrubber and reheater and forces it through the duct and up the stack. Units 3 and 4 are designed as balanced draft units that require forced draft fans at the furnace inlet and ID fans at the scrubber outlet. The flue gas temperature is increased to about 190°F 190OF by the compression in the fan. Each scrubber vessel is provided with one reheater and one ID fan. When the flue gas leaves the fan it enters a series of ducts where the flue gas from all of the scrubbers are combined and routed to the bottom of the stack. Each of Units 3 and 4 has its own stack that discharges the cleaned gases to the atmosphere at an elevation of 692 feet above the ground. The slurry used for the venturi and absorption sprays are taken from the recycle tank located directly below each scrubber vessel. There are two pumps for the venturi; one operates as a spare. One-half of the slurry to the venturi is injected on the tangential shelf above the venturi and the other half is sprayed on top of the plump xxx. There are also two pumps per scrubber vessel for the absorption sprays. Each pump supplies slurry to one set of sprays. The sets of sprays are located one above the other. Each set of sprays is operated independently of the other. Only one set of sprays are operated so long as the outlet SO2 emissions are below the level determined by the permits. The capability to operate two sets of sprays at once is necessary to insure that the outlet SO2 concentration will never exceed the limit permitted. The spent slurry from the venturi and absorption sprays falls to the vessel bottom and is returned to the recycle tank through downcomer pipes. The removal of fly ash and SO2 causes the buildup of suspended solid particles in the recycle tank. An agitator is used to keep these solids suspended and to promote mixing. The concentration of these suspended solids is controlled by taking a slurry bleed stream to the disposal pond where the solids settle out producing a sludge. The clear water is then returned to the recycle tank. Slurry from each recycle tank is bled to an effluent holding tank. There is one effluent holding tank for each four-scrubber vessels (two per unit). All of the effluent holding tanks discharge to one large effluent holding tank common to both units, which then discharges to the disposal pond. The alkali used for SO2 removal is a mixture of hydrated high calcium lime and hydrated dolomitic lime (as further described in Item 3 below). This lime is added to the regenerator as a slurry. There is one regenerator per recycle tank. There is one regenerations tank feed pump per recycle tank that takes a stream of recycle slurry to the regenerator. The regenerator has an overflow line that returns regenerated slurry to the recycle tank. The purpose of the regenerators is to maintain a chemical environment different from the recycle tanks, which is more favorable to the chemical reactions necessary to regenerate the spent slurry after SO2 removal. There is a separate wash tray recycle tank from which slurry is pumped to the wash tray and the wash tray undersprays. There is one wash tray recycle tank for each two two-scrubber vessels (four wash tray recycle tanks per unit). A bleed stream is taken from each wash tray recycle pump in order to remove the suspended solids collected by the wash tray. This bleed stream goes to the wash tray bleed tank (one wash tray bleed tank per unit). The wash tray bleed tank discharges to the wash tray pond. All wash tray recycle tanks and wash tray bleed tanks are equipped with agitators to prevent the suspended solids from settling out. The wash tray bleed tank is discharged to the wash tray pond where the suspended solids are allowed to settle out forming a sludge at the bottom of the pond. The clear water is then returned to the wash tray recycle tanks. The bottom of the mist eliminator is intermittently sprayed with blowdown water from the Plant’s cooling tower. This is dome to clean the mist eliminator and is also the major source of makeup water for the scrubber system. The top of each mist eliminator is also sprayed once per day for 1-1/2 minutes with river water.

Scrubber System. The function of the Scrubber System is to remove fly ash and sulfur dioxide (SO2) from the flue gas by washing with a recycled liquor. Eight scrubber vessels are installed each at Unit 3 and 4 into which boiler combustion gases are ducted. At full load it requires that seven scrubbers operational to achieve sufficient SO2 and particulate removal to comply with environmental regulations. Since it was expected that at any given time at least one scrubber train will be down for maintenance, it was necessary to install eight scrubber trains in order to assure reliable plant operation in compliance with the law. The flue gas enters the top of each scrubber vessel in the venturi section where the gas is contacted with finely atomized scrubber slurry. The flue gas is adiabatically cooled and saturated by the evaporation of water from the scrubber slurry. In the venturi, fly ash particulates are removed by the slurry droplets during collisions caused by the sudden changes in gas velocity. The proper gas pressure drop across the venturi to achieve these changes in velocity is maintained by raising or lowering a xxxxx xxx located in the throat of the venturi. SO2 is also absorbed and removed by the slurry in the venturi. After the flue gas leaves the venturi, it passes upward through an absorption spray zone where the gas is sprayed with more scrubber slurry. These sprays remove additional SO2. Then the flue gas passes through a wash tray where it is bubbled through a stream of wash tray slurry. The main purpose of the wash tray is to remove and dilute the slurry droplets entrained in the flue gas from the venturi and absorption sprays. The wash tray also removes small amounts of fly ash and SO2. A spray keeps the wash tray from plugging and also maintains the proper water balance in the scrubber. When the flue gas bubbles through the wash tray it produces a mist of water droplets containing some dissolved and suspended solids. This mist is removed by a mist eliminator. The mist eliminator is made up of a series of zigzag parallel plates. The mist droplets strikes these plates, cling to them, and then fall back onto the wash tray. The flue gas then leaves the scrubber vessel. At this point the flue gas has been cooled to a temperature of about 120OF 120°F and is saturated as a result of water introduced in the scrubbing process. Approximately 95% of the SO2 and over 90% of the fly ash particulates are removed. Because of the action of the scrubber in cooling and saturating the flue gas, the pressure drop across the scrubber and the moisture contents adverse conditions for the continued flow of gases to and up the stack. It is therefore necessary to reheat the gases to about 170°F and, thereafter, to restore the gas flow with ID fans. The reheater is another heat exchanger device that utilizes steam from the turbine or boiler. The heat in the reheater vaporizes any water droplets in the gas stream and at the same time raises the temperature of the gas to achieve a relative humidity below the saturation point. This improves the plum rise from the stack, reduces ground level concentrations of the emissions, and prevents the formation of acid mist that would cause corrosion and failure of equipment downstream of the scrubber. Upon leaving the reheater the flue gas enters an ID fan that serves to maintain the gas flow through the scrubber and reheater and forces it through the duct and up the stack. Units 3 and 4 are designed as balanced draft units that require forced draft fans at the furnace inlet and ID fans at the scrubber outlet. The flue gas temperature is increased to about 190°F by the compression in the fan. Each scrubber vessel is provided with one reheater and one ID fan. When the flue gas leaves the fan it enters a series of ducts where the flue gas from all of the scrubbers are combined and routed to the bottom of the stack. Each of Units 3 and 4 has its own stack that discharges the cleaned gases to the atmosphere at an elevation of 692 feet above the ground. The slurry used for the venturi and absorption sprays are taken from the recycle tank located directly below each scrubber vessel. There are two pumps for the venturi; one operates as a spare. One-half of the slurry to the venturi is injected on the tangential shelf above the venturi and the other half is sprayed on top of the plump xxx. There are also two pumps per scrubber vessel for the absorption sprays. Each pump supplies slurry to one set of sprays. The sets of sprays are located one above the other. Each set of sprays is operated independently of the other. Only one set of sprays are operated so long as the outlet SO2 emissions are below the level determined by the permits. The capability to operate two sets of sprays at once is necessary to insure that the outlet SO2 concentration will never exceed the limit permitted. The spent slurry from the venturi and absorption sprays falls to the vessel bottom and is returned to the recycle tank through downcomer pipes. The removal of fly ash and SO2 causes the buildup of suspended solid particles in the recycle tank. An agitator is used to keep these solids suspended and to promote mixing. The concentration of these suspended solids is controlled by taking a slurry bleed stream to the disposal pond where the solids settle out producing a sludge. The clear water is then returned to the recycle tank. Slurry from each recycle tank is bled to an effluent holding tank. There is one effluent holding tank for each four-scrubber vessels (two per unit). All of the effluent holding tanks discharge to one large effluent holding tank common to both units, which then discharges to the disposal pond. The alkali used for SO2 removal is a mixture of hydrated high calcium lime and hydrated dolomitic lime (as further described in Item 3 below). This lime is added to the regenerator as a slurry. There is one regenerator per recycle tank. There is one regenerations tank feed pump per recycle tank that takes a stream of recycle slurry to the regenerator. The regenerator has an overflow line that returns regenerated slurry to the recycle tank. The purpose of the regenerators is to maintain a chemical environment different from the recycle tanks, which is more favorable to the chemical reactions necessary to regenerate the spent slurry after SO2 removal. There is a separate wash tray recycle tank from which slurry is pumped to the wash tray and the wash tray undersprays. There is one wash tray recycle tank for each two two-scrubber vessels (four wash tray recycle tanks per unit). A bleed stream is taken from each wash tray recycle pump in order to remove the suspended solids collected by the wash tray. This bleed stream goes to the wash tray bleed tank (one wash tray bleed tank per unit). The wash tray bleed tank discharges to the wash tray pond. All wash tray recycle tanks and wash tray bleed tanks are equipped with agitators to prevent the suspended solids from settling out. The wash tray bleed tank is discharged to the wash tray pond where the suspended solids are allowed to settle out forming a sludge at the bottom of the pond. The clear water is then returned to the wash tray recycle tanks. The bottom of the mist eliminator is intermittently sprayed with blowdown water from the Plant’s cooling tower. This is dome to clean the mist eliminator and is also the major source of makeup water for the scrubber system. The top of each mist eliminator is also sprayed once per day for 1-1/2 minutes with river water.

Scrubber System. The function of the Scrubber System is to remove fly ash and sulfur dioxide (SO2) from the flue gas by washing with a recycled liquor. Eight scrubber vessels are installed each at Unit 3 and 4 into which boiler combustion gases are ducted. At full load it requires that seven scrubbers operational to achieve sufficient SO2 and particulate removal to comply with environmental regulations. Since it was expected that at any given time at least one scrubber train will be down for maintenance, it was necessary to install eight scrubber trains in order to assure reliable plant operation in compliance with the law. The flue gas enters the top of each scrubber vessel in the venturi section where the gas is contacted with finely atomized scrubber slurry. The flue gas is adiabatically cooled and saturated by the evaporation of water from the scrubber slurry. In the venturi, fly ash particulates are removed by the slurry droplets during collisions caused by the sudden changes in gas velocity. The proper gas pressure drop across the venturi to achieve these changes in velocity is maintained by raising or lowering a xxxxx xxx located in the throat of the venturi. SO2 is also absorbed and removed by the slurry in the venturi. After the flue gas leaves the venturi, it passes upward through an absorption spray zone where the gas is sprayed with more scrubber slurry. These sprays remove additional SO2. Then the flue gas passes through a wash tray where it is bubbled through a stream of wash tray slurry. The main purpose of the wash tray is to remove and dilute the slurry droplets entrained in the flue gas from the venturi and absorption sprays. The wash tray also removes small amounts of fly ash and SO2. A spray keeps the wash tray from plugging and also maintains the proper water balance in the scrubber. When the flue gas bubbles through the wash tray it produces a mist of water droplets containing some dissolved and suspended solids. This mist is removed by a mist eliminator. The mist eliminator is made up of a series of zigzag parallel plates. The mist droplets strikes these plates, cling to them, and then fall back onto the wash tray. The flue gas then leaves the scrubber vessel. At this point the flue gas has been cooled to a temperature of about 120OF and is saturated as a result of water introduced in the scrubbing process. Approximately 95% of the SO2 and over 90% of the fly ash particulates are removed. Because of the action of the scrubber in cooling and saturating the flue gas, the pressure drop across the scrubber and the moisture contents adverse conditions for the continued flow of gases to and up the stack. It is therefore necessary to reheat the gases to about 170°F 170OF and, thereafter, to restore the gas flow with ID fans. The reheater is another heat exchanger device that utilizes steam from the turbine or boiler. The heat in the reheater vaporizes any water droplets in the gas stream and at the same time raises the temperature of the gas to achieve a relative humidity below the saturation point. This improves the plum rise from the stack, reduces ground level concentrations of the emissions, and prevents the formation of acid mist that would cause corrosion and failure of equipment downstream of the scrubber. Upon leaving the reheater the flue gas enters an ID fan that serves to maintain the gas flow through the scrubber and reheater and forces it through the duct and up the stack. Units 3 and 4 are designed as balanced draft units that require forced draft fans at the furnace inlet and ID fans at the scrubber outlet. The flue gas temperature is increased to about 190°F 190OF by the compression in the fan. Each scrubber vessel is provided with one reheater and one ID fan. When the flue gas leaves the fan it enters a series of ducts where the flue gas from all of the scrubbers are combined and routed to the bottom of the stack. Each of Units 3 and 4 has its own stack that discharges the cleaned gases to the atmosphere at an elevation of 692 feet above the ground. The slurry used for the venturi and absorption sprays are taken from the recycle tank located directly below each scrubber vessel. There are two pumps for the venturi; one operates as a spare. One-half of the slurry to the venturi is injected on the tangential shelf above the venturi and the other half is sprayed on top of the plump xxx. There are also two pumps per scrubber vessel for the absorption sprays. Each pump supplies slurry to one set of sprays. The sets of sprays are located one above the other. Each set of sprays is operated independently of the other. Only one set of sprays are operated so long as the outlet SO2 emissions are below the level determined by the permits. The capability to operate two sets of sprays at once is necessary to insure that the outlet SO2 concentration will never exceed the limit permitted. The spent slurry from the venturi and absorption sprays falls to the vessel bottom and is returned to the recycle tank through downcomer pipes. The removal of fly ash and SO2 causes the buildup of suspended solid particles in the recycle tank. An agitator is used to keep these solids suspended and to promote mixing. The concentration of these suspended solids is controlled by taking a slurry bleed stream to the disposal pond where the solids settle out producing a sludge. The clear water is then returned to the recycle tank. Slurry from each recycle tank is bled to an effluent holding tank. There is one effluent holding tank for each four-scrubber vessels (two per unit). All of the effluent holding tanks discharge to one large effluent holding tank common to both units, which then discharges to the disposal pond. The alkali used for SO2 removal is a mixture of hydrated high calcium lime and hydrated dolomitic lime (as further described in Item 3 below). This lime is added to the regenerator as a slurry. There is one regenerator per recycle tank. There is one regenerations tank feed pump per recycle tank that takes a stream of recycle slurry to the regenerator. The regenerator has an overflow line that returns regenerated slurry to the recycle tank. The purpose of the regenerators is to maintain a chemical environment different from the recycle tanks, which is more favorable to the chemical reactions necessary to regenerate the spent slurry after SO2 removal. There is a separate wash tray recycle tank from which slurry is pumped to the wash tray and the wash tray undersprays. There is one wash tray recycle tank for each two scrubber vessels (four wash tray recycle tanks per unit). A bleed stream is taken from each wash tray recycle pump in order to remove the suspended solids collected by the wash tray. This bleed stream goes to the wash tray bleed tank (one wash tray bleed tank per unit). The wash tray bleed tank discharges to the wash tray pond. All wash tray recycle tanks and wash tray bleed tanks are equipped with agitators to prevent the suspended solids from settling out. The wash tray bleed tank is discharged to the wash tray pond where the suspended solids are allowed to settle out forming a sludge at the bottom of the pond. The clear water is then returned to the wash tray recycle tanks. The bottom of the mist eliminator is intermittently sprayed with blowdown water from the Plant’s cooling tower. This is dome to clean the mist eliminator and is also the major source of makeup water for the scrubber system. The top of each mist eliminator is also sprayed once per day for 1-1/2 minutes with river water.