Design and Control of Parawood Chips Combustion Boiler Process Using Aspen Dynamics

Abstract

In the small scale of boiler process, a typical problem is an improperly controlled of air to fuel ratio during the combustion process. Such poor control causes heat loss and undesired emission production. In this study, the main aim was to make the process green in the sense of energy recovery and regulating the CO, NO,, and SO, emission by optimization of the operating conditions and design the control system to regulate the optimal conditions using Aspen Plus and Aspen Dynamics. The external flue gas recirculation technique was applied with the process to reduce thermal NO, Air preheater was also designed and applied to preheat the feed air combustion temperature for energy recovery purpose. Dynamic simulation scheme was proposed to overcome a limitation of Aspen Dynamics for solid process, and the air to fuel ratio control was then designed to regulate CO, NO,, and SO, emission. Boiler level and boiler pressure controllers were designed for safety purpose. And the steam production controller was also designed for achieving the required steam. Rejection of uncertain moisture content of wood chip was considered. The results show that simulation results are consistent with 27 scenarios of the measured data collected by wood manufacturing company in the south of Thailand. The optimal operating condition of the process is 5% excess air and 25% flue gas recirculation with 40.5%wt. moisture content of wood chip and 1,500 kg/hr of wood chip flow rate. The optimal condition with the designed air preheater provided 29% heat recovery in this case and provided 35.4% of steam production higher than original process. The proposed control scheme can regulate the CO, NO,, and SO, emission under their limitations and can handle disturbance changes very well.