Development on a small scale industrial CFB boiler with an evaporating loop seal

Most of the small scale industrial CFB (SICFB) boilers in China work at low operating pressure. Compared with the big scale CFB boiler in power plant, the heat ratio of water evaporation is higher in the SICFB boiler. Consequently, evaporating submerged tubes are always installed in the furnace emulsion zone in order to avoid overheating of flue gas at the furnace outlet. The boiler metal consumption could also be reduced because of the higher heat transfer coefficient of submerged tubes. But serious erosions are brought to the submerged tubes as the furnace emulsion zone always works at turbulent fluidized bed state with higher fluidization velocity. In the study, for alleviating the erosion to the submerged tubes, all the evaporating submerged tubes are set in the loop seal instead of in the furnace emulsion zone, and the loop seal is enlarged accordingly to be an evaporating loop seal (ELS). An 11t/h SICFB boiler with an ELS has been put into industrial application, the design consideration and operating characteristics of the boiler are systematically discussed in the paper.