Raimonds Valdmanis

Electrodynamic Control of the Combustion Characteristics and Heat Energy Production

ABSTRACT Electric field effects (EFE) on combustion characteristics, heat energy production, and composition of polluting emissions have been investigated experimentally for different types of fuels (natural gas, biomass) providing experimental study of the EFE in a district heating boiler and complex modeling experiments in a small-scale pilot device. The DC field-induced variations of the produced heat energy, efficiency of heat energy production, flame characteristics, and the composition of polluting emissions have been studied for a positively biased axially inserted electrode and negatively biased (grounded) heat surfaces by varying the applied DC voltage, net current, and consumed electric field power. Experiments in the district heating boiler have shown that electrodynamic control of the heat production and combustion characteristics depends on the applied field voltage, power, and on the flame region, where the top of the axially inserted electrode is located. The most pronounced EFE was observed when the top of the electrode was placed in the primary mixing zone intensifying the mixing of the flame compounds and thereby completing combustion. The mechanism of the electric field effects on the combustion characteristics is discussed with reference to the analysis of electric field effects on the flame characteristics observed in modeling experiments.

Combustion Dynamics of Biomass Mixtures with Microwave Pre-Processing of Pellets

Combustion dynamics of wheat straw mixtures with wood or with peat pellets is studied experimentally with the aim to provide a more effective application of wheat straw for heat energy production. Microwave pre-processing of pellets is used to activate their thermal decomposition and thus enhance the release and thermo-chemical conversion of combustible volatiles. Results of the complex measurements of the main flame characteristics and composition of the products show that the enhanced thermal decomposition of pellets provides improvement of the combustion conditions in the flame reaction zone completing thus the combustion of volatiles, increasing the flame temperature, the heat output from the device and energy efficiency and decreasing at the same time the mass fraction of unburned volatiles in the products. Introduction The EU Energy Policy Strategy, which complies with the Kyoto Protocol, prescribes the increased use of cleaner renewable energy sources, partially replacing the fossil fuels with the second generation fuel – wood and agriculture residues [1]. Growing demand for application of agriculture residues for energy production stimulates the production of different types of straw pellets (rape, rice, wheat), which have been known as a more problematic fuel if compared with wood because of the lower heating values (LHV, HHV), higher nitrogen and ash contents in biomass. For that reason, there is a necessity to improve the main combustion characteristics and composition of emission [2, 3]. In order to ensure the wider use of straw for energy production, the co-combustion of straw with renewable or fossil fuels may be used to reduce greenhouse gas emissions during the heat energy production and to improve the main combustion characteristics and the composition of emissions [4]. Further improvement of the combustion characteristics and composition of emissions if straw is used as a fuel, can be achieved using microwave (mw) pre-processed straw pellets that reduces the content of physically bounded water and partially decomposes hemicelluloses, cellulose and lignin, thus reducing the hydrogen-to-carbon (H/C) and oxygen-to-carbon (O/C) content in biomass pellets while increasing their calorific value [5-7]. Actually, it has been demonstrated that mw-pretreatment is an interesting and efficient alternative for biomass conversion to high quality biofuels [8-10]. The results of previous research showed that the microwave pretreatment of biomass pellets could enhance the thermal decomposition of biomass pellets with a faster and more complete thermo-chemical conversion. The main aim of the current study is to provide a more efficient use of wheat straw for energy production by co-combusting straw with wood or with peat pellets and assuring in this way additional improvement of the energy properties of straw pellets at their mw pre-processing. The influence of mw pre-processing of straw pellets on the 133 doi:10.22364/mmp2017.45