Numerical Study for Evaluating Effect of Mass Flow Rate Toward Particle Circulation Rate on Seal Pot in Circulating Fluidized Bed Boiler

Circulating fluidized bed (CFB) boiler is the second-largest number of boilers for power generation in Indonesia, after pulverized coal boiler. CFB boiler has an advantage in higher energy efficiency for combusting fossil fuel, with one of the most part used in CFB boiler is seal pot. A common failure in seal pot is overheating caused by a change in particle size distribution and flue gas flow rate. The case study is taken operational condition of CFB boiler at PLTU Tenayan 1, Pekanbaru, Riau. Variations used are mass flow rate secondary air from supply chamber and recycle chamber by 100, 150, 200% and percentage 57%:43% and 43%:57% for each parameter. Two particle size distributions with Sauter mean diameter (SMD) values of 154 and 308 µm are obtained from the cyclone’s performance. The presence of coal particles and their combustion effect is neglected. Simulation is performed using a computational particle–fluid dynamics (CPFD) software with Wen Yu drag modeling and large eddy simulation turbulence model. Simulation results showed that increasing secondary air mass flow rate will increase fluidization process, mass flow rate fluctuation at outlet, and particle circulation rate. In an optimum operation, the smallest accumulation of solid particles remain in seal pot is obtained at maximum flow rate with the percentage of supply chamber 57% and recycle chamber 43%, and solid particle size is 154 µm. The worst circulation rate occurs at maximum flow rate with the percentage of supply chamber 43% and recycles chamber 57%, and solid particle size is 154 µm.