Technique for retrofitting grate-fired boilers into natural gas-fired boilers
XIAO Ming-yang, MA Qi-liang, DAI Zheng-hao, LONG-Yue (College of Power Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China)
Statistics show that the most emissions of atmospheric pollutants in China result from the combustion of coal, especially from medium- and small-scale coal-fired systems. Emissions of dust, sulfur dioxide and nitrogen oxides have led to heavy air pollution in many areas, in particular in booming cities flourishing in industry and commerce. It is therefore of great importance to retrofit existing small-capacity coal-fired boilers, e.g. into natural gas-fired boilers, to control the emissions effectively.In this paper, the principles of retrofitting grate-fired boilers into natural gas-fired installations were presented. Techniques for retrofitting the firing system were discussed. It was concluded that the combustion and thermal efficiencies would be increased and emissions from the boiler would be decreased significantly by retrofitting. However, the new natural gas-fired boiler calls for high operating costs and there will be condensed acid water from the back-end surfaces, which leads to corrosion of the surfaces and enclosures. A condensing heat exchanger was suggested to be installed for condensate return and reducing the operating costs.