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PRESENTED ATPRESENTED ATPRESENTED AT PRESENTED AT M/S. MAGADI SODA COMPANY , M/S. MAGADI SODA COMPANY ,

MAGADI KENYAMAGADI KENYAMAGADI , KENYAMAGADI , KENYA

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THERMODYNE THERMODYNE TECHNOLOGIES PRIVATE TECHNOLOGIES PRIVATE

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EMISSIONS FROM BOILERSEMISSIONS FROM BOILERSEmissions are generally of two types :Emissions are generally of two types :1.1. Air emissionsAir emissions22 Li id i iLi id i i2.2. Liquid emissionsLiquid emissionsThe various air emissions from a boiler are :The various air emissions from a boiler are :

11 P ti l tP ti l t1.1. ParticulatesParticulates2.2. Nitrogen oxides ( NO,NONitrogen oxides ( NO,NO22), generally), generally

referred as NOxreferred as NOxreferred as NOxreferred as NOx3.3. Sulphur gases ( SOSulphur gases ( SO22 , SO, SO33) , generally) , generally

referred as Soxreferred as Soxreferred as Soxreferred as Sox4.4. Carbon monoxide ( CO)Carbon monoxide ( CO)

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EMISSIONS FROM BOILERS EMISSIONS FROM BOILERS --CONTINUEDCONTINUEDCONTINUEDCONTINUED

The various liquid emissions from a boiler plant The various liquid emissions from a boiler plant are :are :are :are :

1.1. BackBack--washed water from waterwashed water from watertreatment plantstreatment plantstreatment plantstreatment plants

2.2. Blow down waterBlow down water33 Water from wet scrubbersWater from wet scrubbers3.3. Water from wet scrubbersWater from wet scrubbers

NORMAL PARTICULATE EMISSION LIMITS :NORMAL PARTICULATE EMISSION LIMITS :•• UPTO 2 TPH BOILERS : 1200 TO 1500 mg/N.M3UPTO 2 TPH BOILERS : 1200 TO 1500 mg/N.M3•• 2 TPH TO 10 TPH : 300 TO 600 mg/N.m32 TPH TO 10 TPH : 300 TO 600 mg/N.m3•• ABOVE 10 TPH : 50 TO 150 mg/N.m3ABOVE 10 TPH : 50 TO 150 mg/N.m3

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PARTICULATE EMISSION CONTROL PARTICULATE EMISSION CONTROL EQUIPMENTEQUIPMENT

1.1. Mechanical dust collectors ( Single / MultiMechanical dust collectors ( Single / Multi--cyclones)cyclones)y )y )

This uses the centrifugal force to separate the This uses the centrifugal force to separate the heavier ash particles . The flue gas will enter the heavier ash particles . The flue gas will enter the c clones tangentiall and the d e to the centrif galc clones tangentiall and the d e to the centrif galcyclones tangentially and the due to the centrifugal cyclones tangentially and the due to the centrifugal action heavier ash particles will be thrown to the action heavier ash particles will be thrown to the outer surface of the cyclone and will fall down. The outer surface of the cyclone and will fall down. The yyefficiency of collection in this type of collectors is 90 efficiency of collection in this type of collectors is 90 to 95%. This is generally used for ash with a bigger to 95%. This is generally used for ash with a bigger size particles mainly from fixed dump grate firingsize particles mainly from fixed dump grate firingsize particles , mainly from fixed , dump grate firing size particles , mainly from fixed , dump grate firing systems. The draft loss across such mechanical systems. The draft loss across such mechanical dust collectors will be around 75 mmwc.dust collectors will be around 75 mmwc.

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2.2. Wet scrubbers :Wet scrubbers :In this type of dust collector the flue gas is passed In this type of dust collector the flue gas is passed th h t t B di t t tth h t t B di t t tthrough a water spray system. By direct contact , through a water spray system. By direct contact , the ash particles are captured by the water the ash particles are captured by the water particles and the sludge goes out from the bottomparticles and the sludge goes out from the bottomparticles and the sludge goes out from the bottom particles and the sludge goes out from the bottom of the dust collector. This sludge shall be taken to of the dust collector. This sludge shall be taken to a sludge pond for the separation of ash particles a sludge pond for the separation of ash particles

d th t ill bd th t ill b i l t d Thi t ii l t d Thi t iand the water will be reand the water will be re--circulated. This type is circulated. This type is used for boilers firing low ash bioused for boilers firing low ash bio--mass fuels. The mass fuels. The draft loss in this dust collector will be in the range draft loss in this dust collector will be in the range ggof 75 to 100 mmwc. This only converts air pollution of 75 to 100 mmwc. This only converts air pollution to water pollution and not favored in places with to water pollution and not favored in places with water shortagewater shortage

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water shortage.water shortage.


3.3. ELECTROSTATIC PRECIPITATOR :ELECTROSTATIC PRECIPITATOR :In this equipment the flue gas is passed through an In this equipment the flue gas is passed through an electrical field and gets ionized. The ash particles will electrical field and gets ionized. The ash particles will stick to the negatively charged cathodes and collected stick to the negatively charged cathodes and collected from the bottom. This has a collection efficiency as highfrom the bottom. This has a collection efficiency as highfrom the bottom. This has a collection efficiency as high from the bottom. This has a collection efficiency as high as 99.9 % and are used where stringent pollution norms as 99.9 % and are used where stringent pollution norms are in place. The draft loss through the ESP is normally are in place. The draft loss through the ESP is normally less than 25 mmwc and hence results in lower ID fanless than 25 mmwc and hence results in lower ID fanless than 25 mmwc and hence results in lower ID fan less than 25 mmwc and hence results in lower ID fan power consumption. But ESP consumes electricity to power consumption. But ESP consumes electricity to charge the fields and hence power intensive and hence charge the fields and hence power intensive and hence

tl t ttl t tcostly to operate.costly to operate.The capital cost of the ESP is also comparatively much The capital cost of the ESP is also comparatively much higher than the mechanical dust collectors.higher than the mechanical dust collectors.

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higher than the mechanical dust collectors.higher than the mechanical dust collectors.

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PARTICULATE EMISSION CONTROL PARTICULATE EMISSION CONTROL EQUIPMENTEQUIPMENTEQUIPMENTEQUIPMENT

4.4. BAG FILTERS :BAG FILTERS :Synthetic cloth materials are used in this type toSynthetic cloth materials are used in this type toSynthetic cloth materials are used in this type to Synthetic cloth materials are used in this type to filter the flue gas as it passes through the cloth. filter the flue gas as it passes through the cloth. Collection efficiency can be even higher than ESP. Collection efficiency can be even higher than ESP. P ti i l B t th d ft lP ti i l B t th d ft lPower consumption is less. But the draft loss can vary Power consumption is less. But the draft loss can vary from 75 to 150 mmwc resulting in very high ID fan from 75 to 150 mmwc resulting in very high ID fan power consumption. Needs compressed air to power consumption. Needs compressed air to dislodge particles from the cloth bags in the reverse dislodge particles from the cloth bags in the reverse direction flow. Can be used for low temperature flue direction flow. Can be used for low temperature flue gases as high temperature flue gas will burn the cloth. gases as high temperature flue gas will burn the cloth. gases as g te pe atu e ue gas bu t e c otgases as g te pe atu e ue gas bu t e c otCapital cost is less compared to ESP. But the Capital cost is less compared to ESP. But the maintenance cost is very high as the cloth bags may maintenance cost is very high as the cloth bags may need replacement once in a yearneed replacement once in a year

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need replacement once in a year.need replacement once in a year.

NONOXX

NOx EMISSIONS :NOx EMISSIONS :•• THERMAL NOTHERMAL NOXX•• FUEL NOFUEL NOXX

THERMAL NOTHERMAL NOTHERMAL NOTHERMAL NOXX•• NIROGEN IN COMBUSTION AIR REACTS TO NIROGEN IN COMBUSTION AIR REACTS TO

THE OXYGEN IN TEMPERATURES ABOVE THE OXYGEN IN TEMPERATURES ABOVE O G U S OO G U S O1000 DEG.C TO FORM NITROUS GASES1000 DEG.C TO FORM NITROUS GASES

•• THERE ARE TWO WAYS OF CONTROLLING THERE ARE TWO WAYS OF CONTROLLING OOTHERMAL NOXTHERMAL NOX

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CONTROLLING THERMAL NOXCONTROLLING THERMAL NOXAIR STAGINGAIR STAGINGAIR STAGING :AIR STAGING :IN THIS METHOD AIR IS INTRODUCED INTO THE IN THIS METHOD AIR IS INTRODUCED INTO THE FIURNACE IN TWO OR THREE STAGES. HENCE AT FIURNACE IN TWO OR THREE STAGES. HENCE AT THE TIME OF MAIN COMBUSTION FUEL RICH THE TIME OF MAIN COMBUSTION FUEL RICH MIXTURE WILL RESULT & OXYGEN AVAILABILITY WILL MIXTURE WILL RESULT & OXYGEN AVAILABILITY WILL BE LESS AND FORMATION OF THERMAL NOX WILL BE BE LESS AND FORMATION OF THERMAL NOX WILL BE REDUCED.REDUCED.FUEL STAGING :FUEL STAGING :THE FUEL WILL BE ADMITTED IN STAGES RESULTINGTHE FUEL WILL BE ADMITTED IN STAGES RESULTINGTHE FUEL WILL BE ADMITTED IN STAGES RESULTING THE FUEL WILL BE ADMITTED IN STAGES RESULTING IN AIR RICH MIXTURE REDUCING RESULTANT GAS IN AIR RICH MIXTURE REDUCING RESULTANT GAS TEMPERATURE BELOW 1000 DEG.C AND THUS TEMPERATURE BELOW 1000 DEG.C AND THUS REDUCING THE AMOUNT OF NOX FORMEDREDUCING THE AMOUNT OF NOX FORMEDREDUCING THE AMOUNT OF NOX FORMED.REDUCING THE AMOUNT OF NOX FORMED.IN PRACTICE BOTH THE ABOVE METHODS ARE IN PRACTICE BOTH THE ABOVE METHODS ARE COMBINED JUDICIOUSLY TO REDUCE NOXCOMBINED JUDICIOUSLY TO REDUCE NOX

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FUEL NOXFUEL NOXTHE NITROGEN IN THE FUEL WILL GET THE NITROGEN IN THE FUEL WILL GET CONVERTED TO NOXCONVERTED TO NOXTHIS CAN NOT BE CONTROLLEDTHIS CAN NOT BE CONTROLLEDONLY NOX ABSORPTION EQUIPMENT CAN BE ONLY NOX ABSORPTION EQUIPMENT CAN BE INSTALLED AT THE BACK END OF THEINSTALLED AT THE BACK END OF THEINSTALLED AT THE BACK END OF THE INSTALLED AT THE BACK END OF THE BOILER BEFORE FLUE GAS GOES INTO THE BOILER BEFORE FLUE GAS GOES INTO THE ATMOSPHEREATMOSPHERENOX ABSORPTION EQUIPMENT ARE COSTLY NOX ABSORPTION EQUIPMENT ARE COSTLY & MAY NOT BE REQUIRED UNLESS & MAY NOT BE REQUIRED UNLESS POLLUTION NORMS ARE EXTREMELYPOLLUTION NORMS ARE EXTREMELYPOLLUTION NORMS ARE EXTREMELY POLLUTION NORMS ARE EXTREMELY STRINGENTSTRINGENT

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SOXSOXSULPHUR IN THE FUEL WILL GET CONVERTED SULPHUR IN THE FUEL WILL GET CONVERTED TO SOX. NO DESIGN CHANGE IN FIRING TO SOX. NO DESIGN CHANGE IN FIRING EQUIPMENT WILL CONTROL FORMATION OF SOXEQUIPMENT WILL CONTROL FORMATION OF SOXEQUIPMENT WILL CONTROL FORMATION OF SOXEQUIPMENT WILL CONTROL FORMATION OF SOXTWO WAYS OF CONTROLLING SOX ARE:TWO WAYS OF CONTROLLING SOX ARE:

•• REMOVING / REDUCING SULPHUR IN THE FUELREMOVING / REDUCING SULPHUR IN THE FUEL•• REMOVING / REDUCING SULPHUR IN THE FUELREMOVING / REDUCING SULPHUR IN THE FUEL•• ABSORBING SOX AT THE BACK END OF THE ABSORBING SOX AT THE BACK END OF THE

BOILER IN WET SCRUBBING WITH LIME WATERBOILER IN WET SCRUBBING WITH LIME WATERWITH SOLID FUEL , ADOPTING FLUIDISED BED WITH SOLID FUEL , ADOPTING FLUIDISED BED TECHNOLOGY WITH ADDITION OF LIME IN THE TECHNOLOGY WITH ADDITION OF LIME IN THE BED ALONG WITH FUEL WILL REDUCE SOX BED ALONG WITH FUEL WILL REDUCE SOX EMISSION BY 60 TO 80%.EMISSION BY 60 TO 80%.

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CARBON MONOXIDECARBON MONOXIDEFORMED BECAUSE OF INCOMPLETE FORMED BECAUSE OF INCOMPLETE COMBUSTION. REASONS MAY BE :COMBUSTION. REASONS MAY BE :SUFFICIENT EXCESS AIR NOT PROVIDEDSUFFICIENT EXCESS AIR NOT PROVIDED•• SUFFICIENT EXCESS AIR NOT PROVIDEDSUFFICIENT EXCESS AIR NOT PROVIDED

•• AIR AIR –– FUEL MIXTURE IS NOT HOMOGENIOUSFUEL MIXTURE IS NOT HOMOGENIOUSAIR / FUEL STAGING LEADS TO RICH/LEANAIR / FUEL STAGING LEADS TO RICH/LEAN•• AIR / FUEL STAGING LEADS TO RICH/LEAN AIR / FUEL STAGING LEADS TO RICH/LEAN MIXTURES LEADING TO INCREASED CO MIXTURES LEADING TO INCREASED CO FORMATIONFORMATION

•• FURNACE TOO SMALL FOR FLAME FURNACE TOO SMALL FOR FLAME DIMENSIONS. THE EDGE OF FLAME CHILLED DIMENSIONS. THE EDGE OF FLAME CHILLED BY THE WATER COOLED WALL LEADING TOBY THE WATER COOLED WALL LEADING TOBY THE WATER COOLED WALL LEADING TO BY THE WATER COOLED WALL LEADING TO HIGHER CO FORMATIONHIGHER CO FORMATION

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