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Circulating fluidized bed boiler effect of limestone desulfurization agent on boiler efficiency

Author: Anonymous From: www.yourpaper.net Posted: 2010-06-24 14:33:15 Read:
Author: Kong Fanxin Song Fengxia Gao Yancun Li Pingfang Xiao Cuixiang
Abstract: circulating fluidized bed boiler to coal and adapt to a wide range of bituminous coal, anthracite, can burn all kinds and low calorific value fuel.When using high sulphur fuel, by adding limestone into furnace, can significantly reduce SO2 and NOx emissions, adding efficiency of limestone desulfurization agent on the effect of boiler, this paper points out the influence factor, and according to the actual analysis of the influence of various factors.
Keywords: circulating fluidized bed boiler desulfurization; limestone; boiler efficiency; influence factors of
1, the
35t/h circulating fluidized bed boiler in China poly energy Ji-Dong village power plant to use, is the Ji'nan boiler factory and China Institute of Engineering Thermophysics, joint development of a new boiler efficiency, low pollution.While burning high sulfur content fuel, by adding limestone into furnace, can significantly reduce SO2 and NOx emissions.
At present, research on circulating fluidized bed boiler environmental issues has been very thorough, not only have in-depth understanding of the major problems of low NOX emission, the furnace limestone desulfurization, but also for N2O, CO, CXHY, the original is not very attention problems are given full attention, however, effect of limestone on CFB boiler efficiency at present only know some qualitative, not quantitative analysis.This paper focuses on the effect of limestone desulfurization agent into the furnace of boiler efficiency through case analysis.
Calculation of
limestone input 2, adding limestone desulfurization
Chemical reaction equation of limestone desulfurization are:

S O2 -- SO2
CaCO3 -- CaO CO2
CaO SO2 -- CaSO3
CaSO3 1/2O2 -- CaSO4
CaSO4 CO -- CaO O2 CO2
The reaction can be seen, a mole of sulfur (32kg) need a mole of calcium carbonate (100kg) reaction, combustion, the sulfur in coal is about 28.5% of the total sulfur in ash residue, 71.5% in gas emissions situation.According to the operation data of industrial circulating fluidized bed boilers show that, with the increase of the ratio of Ca/S, the desulfurization efficiency in the Ca/S ratio is below 2.5, increases very quickly, and when increasing Ca/S ratio, rarely desulfurization efficiency increased, normal Ca/S ratio is 2 ~ 2.5.The desulfurization reaction in different atmosphere in different directions.In the oxidizing atmosphere, CaO and SO2 combined with dominant, while in the decomposition of the dominant CaSO4 in reducing atmosphere.Jidong new village power plant boiler coal consumption is 8726.4kg/h, the sulfur content of coal an average of 0.5%, and the ratio of Ca/S was 2.5, calculated the amount of limestone per hour need to join to 366.5kg.3, add the effect of limestone desulfurization in furnace heat
Exothermic and endothermic reaction and sulfation reaction of limestone desulfurization thermochemical reaction including CaCO3 calcined in the two part, the thermochemical reaction equation as follows:
CaCO3 -- CaO CO2-1830KJ/kgCaCO3
CaO SO2 1/2O2, CaSO4 15141 KJ/kgS

The beginning of limestone from Coal Auger added into the furnace, the bed temperature was lower, this is because the limestone into furnace at high temperature first occurrence calcination decomposition reaction, the reaction is endothermic process, at the same time as the limestone and coal mixture into the furnace, in a spiral coal feeder speed is constant, with limestone. Coal amount is reduced, also reduce the heat release, these two factors will inevitably lead to the bed temperature decreased, and adding limestone more, or Ca/S higher, the bed temperature decreased more and more quickly, when Ca/S:2.5, 10 minutes of bed temperature decreased from 1000 to 980 , amounting to 20 .Then the temperature rose to 990 degrees, the sulfation reaction of limestone decomposition into calcium oxide and sulfur dioxide are exothermic process, plus a portion of the calcium oxide particles by the cyclone separator down back to the hearth to exothermic reaction of sulphation, make the bed temperature high.The amount of limestone per hour added into CaO needs to absorb the heat for 670695kj, in accordance with the desulfurization efficiency is 80% exothermic quantity calculating sulfation reaction for 528505kj, heat loss is 142190kj.
4, the heat loss due to the influence of
The main components of limestone furnace was added to CaCO3 (100g/mol), the main component of reaction and sulfation decomposition reaction of CaO (56g/mol) and CaSO4 (136g/mol) with fly ash, slag and discharged out of the boiler.According to the actual measurement, the content of CaO is not fully used in ash reached 12.3%, in addition, CaCO3 outside of the matter in the limestone can have complex chemical reaction process in the furnace, but due to various reaction components weight increases and decreases, overall change is not big, content is relatively little, so in the calculation of weight can be considered they are the same.Slag after cooling will be part of the heat absorption in the temperature of 150 discharge.366.5kg limestone after reaction after the weight is not completely reaction of CaO is 25.3kg, CaSO4 weight 437kg.Slag was measured to be 0.96kj/kg, heat loss is 66571.2kj.
5, the smoke heat loss effects of
The desulfurization formula can be seen, the CaCO3 response after CO2 82m3, SO2 and CaO reaction, oxygen consumption is 15.26m3, demand for air increased to 73m3, the overall increase of flue gas amount is 140m3, causing heat loss increased by 30458kj.Smoke density g=1.295 kg/Nm3, flue gas heat capacity of Cpg=1.12 kJ/ (kg )
6, conclusion
The exothermic heat of limestone calcination and sulfation reaction is the major factor influencing the efficiency of circulating fluidized bed boiler, the important factors of adding additional heat loss due to limestone induced also affect the efficiency of circulating fluidized bed boiler, flue gas volume caused by adding limestone increase caused by the heat loss of exhaust gas increasing impact on the efficiency of circulating fluidized bed boiler is relatively small.CFB boiler desulfurization limestone and decrease the thermal efficiency of the boiler furnace is very limited, according to the experimental conditions in the calculation, the thermal efficiency of the boiler is reduced about 0.22%.
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