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.
Highlights
The concept of flexibility in power system is defined as the ability to operate reliably with significant shares of variable renewable electricity
In order to accommodating variable renewable energy in power system, flexible operation of boiler with higher megawatt load ramp rate becomes the essential need with simultaneous addressing the concerns of stable ignition and combustion of coal burner to avoid loss of flame in the furnace during minimum loading of the pulverizer, pulverizer turn down ratio and capacity, maintaining minimum pulverizer outlet temperature, avoiding pulverizer in and out of service during megawatt load ramp up or down, non-availability of design range of coal with varying GCV, minimum volatile matter content in coal being fired etc
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
Summary
The concept of flexibility in power system is defined as the ability to operate reliably with significant shares of variable renewable electricity In other word, it expresses the capability of a power system to maintain reliable supply in the face of rapid and large imbalances, whatever the cause. Raw coal is transported on a coal conveyor belt located at the tripper floor from coal handling plant and dropped into the variable speed-controlled coal feeder for dynamic measurement of the coal being fed into the motor driven rotating coal mill called coal pulverizer through a central feed input pipe that uses gravity to guide the coal to fall onto a grinding table of coal pulverizer where it is crushed by electro-hydraulically operated heavy metallic rollers. Multi variable non-linear model is simulated in python environment and the parameters are obtained by using the moving horizon estimation to study the actual performance of the pulverizer under varying differential pressure across it as the major variable parameters of coal pulverizers
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