Dynamic modelling and control of a direct-combustion biomass CHP unit

Biomass combustion Combined Heat and Power (CHP) technology uses biomass fuel to generate usable heat and electricity simultaneously in a single unit. Biomass is considered the renewable energy resource (RES) and its utilization has been of particular interest to meet the energy needs of modern society. Nevertheless biomass contains much less carbon, more oxygen and moisture content, consequently it has lower heating value compared to the coal and other fossil fuels. Therefore, the amount of heat released to steam production is very slow and it makes challenge for the control process of the unit. A dynamic model of a direct-combustion biomass CHP unit is developed in Matlab/Simulink. Two different control strategies, boiler follow and coordinated boiler turbine control are applied for the control of steam pressure and the output power (heat and electricity) of the biomass CHP unit. Different biomass fuel types with various moisture content, fuel composition and consequently heating value are considered to the biomass combustion process of the CHP. Simulation results show that the impact of biomass fuel properties on system performance is substantial. Comparison of the results of both control process indicates that coordinated control is much quicker and more effective for the control of biomass CHP output power. It also improves controlling process for rejecting the disturbances arising from the moisture content, fuel types and their composition.