Investigation On The Fuel Flexibility Of The Circulating Fluidized Bed Boiler With Compact Water Cooled Cyclone

Circulating Fluidized Bed(CFB) technology is one of the most commercialized clean coal combustion technologies. Even though it is of good fuel flexibility for CFB technology, there is still some limitations on burning different fuels in a specially designed CFB boiler since the heat and mass balance of the boiler is fixed within a certain range. For the boiler user, the safe and economical operation requires the fuel flexibility as strong as possible. The SINOPEC Maoming Company has two 410t/h compact CFB boilers equipped with their 100 million tons/year ethylene production line, which are the 3rd generation CFB boiler with water cooled cyclone. The SINOPEC Maoming Company is far away from the coal resources, but there is a huge amount of oil shale produced locally, as well as the petroleum coke as the by-product of oil refining process, which require the good fuel flexibility of the boilers and their auxiliary system.In the thesis, the thermal performance tests were carried out in the 2# CFB boiler burning 6 different fuels including bituminous coal, bituminous coal/pet coke blend, anthracite/pet coke blend, bituminous coal/anthracite blend, anthracite and oil shale/pet coke blend. The boiler efficiency was done for the 6 fuel separately; the operation parameters such as bed temperature, furnace exit temperature, cyclone exit temperature, loopseal temperature, bed pressure as well as the parameters in the water/steam system were analyzed; the emission characteristics and affecting factors on the SO2/NOx were studied; the effect of bed temperature, bed pressure, fuel particle size and fly ash recirculation rate on the carbon content in the ash was emphasized. Results show that:(1)The operation conditions including the water/steam system were stable for the boiler burning bituminous coal, bituminous coal/pet coke blend, anthracite/pet coke blend, bituminous coal/anthracite blend, anthracite and oil shale/pet coke blend. The boiler is suitable for burning fuel with the calorific value of 21~26 MJ /kg.(2) The flue gas parameters for the boiler were also stable for burning all kinds of fuel, indicating that it is easy to operate despite of the large difference of the amount of recirculating ash. The cooling influence of the compact water cooled cyclone is obvious and the loopseal temperature is properly controlled to avoid the agglomeration.(3) There is an optimal bed pressure according to the unburnt carbon content in the ash. For the blend of the very different fuels, i.e. 75% pet coke and 25% oil shale, the combustion condition shows their property individually rather than a simple combination of two single fuels, even though the proximate analysis looks good.At last, the operational strategy is proposed to solve the problems encountered during the operation and to optimize the operation based on the experimental results as well as the power plant practice, and the fuel flexibility is expected to be even higher than present.