Particle separators are used to reduce particle emissions as a secondary measure in small-scale biomass furnaces. Among other things, electrostatic precipitation technology is used for this purpose. However, many interrelationships are still unclear in the interaction with combustion exhaust gases. This concerns especially the influence of the flue gas conditions on the separation behavior of the electrostatic precipitators. The present work is intended to clarify this by means of experimental investigations in order to extend the state of knowledge and to improve emission reduction in small-scale biomass furnaces by means of electrostatic precipitators.
First, the fundamentals of the energetic utilization of woody fuels in small-scale furnaces for heat supply in households are summarized. This describes the general conditions in which the electrostatic precipitators are used. After that, the technical basics for emission reduction by electrostatic precipitators are described.
Subsequently, the methodological principles and the state of knowledge for the investigation and evaluation of separators in small-scale biomass furnaces are explained.
To lead up to the main part, selected individual aspects for the use of separators in combustion flue gases in small-scale furnaces are considered in the preliminary investigations. This includes calculations on the influence of design parameters on the theoretical separation efficiency based on the Deutsch equation, a short study on the influence of different separation surfaces on the flow in an electrostatic precipitator by means of flow modeling, and an investigation on the influence of the heating temperature on the formation and regeneration of soot layers on a high-voltage insulator by means of combustion tests in furnace flue gases.
The main part of the work is represented by the experimental investigations of various selected influences when using different combinations of separators and firing systems. The main measurement parameter is the total dust concentration in raw gas and clean gas, where the raw gas concentration is the main evaluation parameter for the emission behavior of the furnace. The main evaluation variable for emission reduction by the separator is the degree of separation. Particle contents and particle size distributions are determined.
Automatically and manually fed firing systems are used and various separators. The influence of combustion quality is investigated on a pellet stove with a two-stage compact electrostatic precipitator prototype. The influence of fuel type is investigated on a wood chip boiler with the same electric separator. The influence on the operating mode of a manually fed furnace is considered on a stove with a flue-based electrostatic precipitator. The influence of the combustion phase is investigated on a stove with a two-stage stand electrostatic precipitator.