PROGRAM TOPIC: COMBUSTION TECHNOLOGIES Exact Title of Paper: Performance Analysis for a Retrofitted Oxy-Fuel Boiler

摘要

To obtain high-concentration liquid CO_2 for yield improvement in an oil/gas field, the retrofit scheme of oxy-fuel boiler based on a subcritical Ⅱ -type boiler with steam output of 220 t/h in a self-supply power plant was proposed. A reasonable flue gas recirculating mode, i.e., half-dry mode is selected to apply to design oxy-fuel boiler system in view of avoid coal blocking in mill and pulverized coal piping due to water condensation. The proposed retrofit scheme is designed following minimizing retrofit work and the compatibility of air-firing and oxy-firing. The original heating surfaces of Upper air preheater, Lower economizer and Lower air preheater are split into two parts individually to heat the primary gas and the secondary gas, respectively. Besides, the other heating surfaces are kept unchanged. The performance calculations for original air-firing boiler and oxy-fuel boiler after retrofit have been performed and compared. Thermal efficiency of oxy-fuel boiler is slightly lower than that of original air-firing boiler. Heat loss of exhausted gas of oxy-fuel boiler is only about 8% of that of air-firing boiler. Meanwhile, heat loss due to flue gas treatment, which is only present in oxy-fuel boiler system, of 5.86% of oxy-fuel boiler is included. For the heating surfaces upstream of Upper economizer, oxy-fuel boiler has lower flue gas temperatures, including the adiabatic combustion temperature, compared to air-firing boiler. However, the corresponding heat transfer ability is nearly equivalent. For the heating surfaces downstream of Upper economizer, the flue gas outlet temperatures of oxy-fuel boiler are higher than those of air-firing boiler and the final heated temperatures of the primary gas and the secondary gas are also higher. The minimum flue gas outlet temperature of exhausted flue gas of boiler is higher 10°C than the acid dew point of 154°C.