Development Of The Omnibus-flow Fluidized Bed Bottom Ash Cooler For Large Capacity Circulating Fluidized Bed Boilers

With the rapid development of the circulating fluidized bed boiler, an increasing attention is paid to the high-temperature ash cooling. As an important auxiliary equipment of the circulating fluidized bed (CFB) boiler, the normal running of ash cooling equipment is critical. In order to meet the requirements of the high parameter and large capacity CFB boiler, especially the 600MW supercritical CFB Boiler, the author developed an omnibus-flow fluidized bed bottom ash cooler and has already declared a nation invention patent. The research is based on the current actual scene operations and the major problems of the large-scale circulating fluidized bed boiler ash coolers.In the development of the new ash cooler, a visual cold experimental apparatus was designed and set up. A series of researches and analysis on the running characteristics and structural characteristics of the new ash cooler was carried out with the bed material of screening bottom ash. Through the research, the key problems were resolved as follows:â‘ Flowing characteristics of the ash in the selective chamber and cooling chambers and the influencing factors;The key factors of effect on particles selecting are the bed height,fluidized airflow and the height of separation partitions in the selective chamber. Non-uniform air distribution makes for the particles directional flow and mixture in bubbling beds. There is a most favorable control range of the average fluidized velocity and velocity gradient. The elutriation can be predicted effectually by monitoring the variation of the pressure in suspension space. The pressure in suspension space can be regarded as a reference for the elutriation measure.â‘¡Running characteristics with different structures of the omnibus-flow fluidized bed bottom ash cooler.In the research, the structure of the ash cooler is changed by using modularized separation partitions. an optimization scheme of the structure arrangement in the ash cooler is got by analyzing running characteristics with different structures: On the premise of ensuring adequate bed height(to meet the demand of heating surface layout),ash discharge port should be located lower to help ash discharge smoothly; a rational range of the height of the first separation partition can be selected to get the optimized combination of the particle size attribution and ash flux,and he height layout of other separation partitions took a decreasing trend along ash flowing. Based on the cold experimental tests, the cold numerical simulation of the omnibus-flow fluidized bed bottom ash cooler was completed by using CFD software.The simulation results indicate that:â‘ By using Two-phase Flow Eulerian Model in software Fluent., the simulation to the gas-solids flow characteristics in the bottom ash cooler with numerical simulation could reflect the behavior of the gas-solids flow in the bottom ash cooler;â‘¡Different sizes particles have distinct motion effects with the identical fluidized airflow; there is a favorable control range of the fluidized velocity gradient with the non-uniform air distribution in the particles directional flow. The result corresponds with the cold test results.Moreover, heat transfer characteristics of cooling chambers were determined based on the research result of the laboratory. On the basis of the above research result, the structure of the ash cooler was optimized completely; according to particle size attribution characteristics of the actual bottom ash in CFB boilers, the industrial design of the omnibus-flow fluidized bed bottom ash cooler with 15t/h was carried out, and it will be put into industrial manufacture and installation.