THERMOPHYSICAL ANALYSIS OF THE PARAMETERS OF A BIOMASS FUELED MICRO–CHP UNIT WITH A STIRLING ENGINE
A typical scheme of a biomass fueled micro-CHP unit with a Stirling engine, including a combustion chamber, a Stirling Engine, a recuperator and water heater, is considered. A brief overview of the main biomass combustion methods used in this installation is made.
Thermophysical analysis was carried out on the basis of solving a system of equations: the reaction equation for wood biomass combustion, the equations of both the general heat balance and the heat balance of parts of CHP unit, as well as the equation of energy conservation at flows mixing in the combustion chamber, taken into account the heat input and losses. The relationship for calculating the theoretical temperature in the combustion chamber and heat flux in the recuperatoris obtained. The last equation is obtained in dimensionless form. The theoretical temperature in the combustion chamber and the heat flux in the recuperator have been calculated, the influence of the main factors has been analyzed - the efficiency of heat exchange in the recuperator, the share of the total air flow passing through the recuperator, the excess air ratio, dimensionless heat losses and heat flux on the hot heat exchanger of the Stirling engine.
It is shown that the temperature in the combustion chamber decreases with a decrease in the efficiency of the recuperator and with an increase in the excess air ratio. A significant influence of heat losses in the combustion chamber on the heat flux in therecuperatorwas found. Under certain conditions (high heat losses and high heat exchange on the hot heat exchanger of the Stirling engine), the recuperator is not neededatall.
It is also shown that the share of the total air flow passing through the recuperator has a significant effect on the heat flux in the recuperator. Thus, when the air flow passing through the recuperator is reduced by 2 times, the heat flow is reduced by 5 times. Therefore, it is necessary to minimize the air flow bypassing the recuperator. As a result of thermophysical analysis, the optimal value of the excess air ratio was obtained, which is 1.7 ... 1.8.
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