Dynamic Modelling and Simulation of Coal Pulverizer

Abstract

The mathematical model and simulation of coal pulverizer has been presented in the paper using first principle mass and heat balance equations based on physical insight. The coal mass flow is modelled based on the mass balance model. The pulverized coal temperature is modelled by considering the coal and the pulverized coal as a lumped thermal mass. The multi variable non-linear model is simulated in Python environment and the parameters are obtained by using the moving horizon estimation. The archived data from an operating 660 MW coal fired boiler database are used to identify the parameters and to be compared with the model outputs. As the megawatt power output of thermal power generating plant is directly influenced by the coal being fired into the boiler, it is necessary to study the dynamic behaviour of the model as their poor dynamic performance causes a slow megawatt ramp up or ramp down rate and also causes shutdown of plant in some cases. In view of more and more penetration of renewable energy in the power grid, rapid and automatic flexible operation of coal fired boiler is necessary to accommodate injection of renewable power or withdrawal of renewable power as both remain connected directly or indirectly to the same power grid. Hence, fast response of the steam generating boiler is desired in a coal fired thermal power generating unit to generate the megawatt load as per the demand placed on the grid to maintain the power system frequency which calls for support of boiler steam flow, pressure and temperature to the steam turbine generator equipment. In order to achieve that, performance of combustion control of the boiler is one of the important factors which can be improved by modelling and implementing the predictive dynamic behaviour of coal pulverizer under varying coal feed rate in the boiler control system. The main focus of the work is to determine the pulverizer response under varying coal flow and coal characteristic condition with an objective of keeping minimum differential pressure across it based on a realistic mathematical model of pulverizer so that the boiler response can be improved under transient condition of megawatt load demand variation. The simulated model responses for various scenarios are also presented in this paper.