I. Barmina’s research while affiliated with University of Latvia and other places

The main objective of research is to promote wider use of the regional bioenergy resources for the development of environmentally friendly energy production providing microwave pre-treatment of different origin lignocellulosic biomass pellets (wood, straw, and peat) at frequency 2.45 GHz. A hypothesis is proposed and tested that MW pre-treatment of biomass pellets and blending of MW pre-treated pellets with raw pellets can be used to enhance the thermochemical conversion of different origin lignocellulosic biomass blends. The test results confirm that increased reactivity and heating value of pre-treated biomass pellets enhances heat energy production and limited formation of SGS emissions thus advancing more efficient use of agricultural and forestry waste for energy production.

With the aim to control and improve the thermo-chemical conversion of straw pellets, the experimental investigations of the DC electric field effect on the combustion dynamics and heat energy production were made. The electric field effect on the gasification/combustion characteristics was studied using three different positions of the positively charged electrode in flame. First, the electrode was positioned coaxially downstream the flame flow. Next, the electrode was positioned coaxially upstream the flame flow and, finally, the electrode was positioned across the downstream flow. The bias voltage of the electrode varied in the range from 0.6 up to 1.8 kV, while the ion current in flame was limited to 5 mA. The results of experimental investigations show that the DC electric field intensifies the thermal decomposition of straw pellets and enhances mixing of volatiles with air causing changes in combustion dynamics and heat energy production, which depend on position and the bias voltage of the electrode. The increase in the average volume fraction of CO2 (by 6 %) and the decrease in the mass fraction of unburned volatiles in the products (CO by 60 % and H2 by 73 %) for the upstream field configuration of the electrode and the ion current 0.5–1.8 mA indicate more complete combustion of volatiles.

The main goal of the present study is to promote a more effective use of agriculture residues (straw) as an alternative renewable fuel for cleaner energy production with reduced greenhouse gas emissions. With the aim to improve the main combustion characteristics at thermo-chemical conversion of wheat straw, complex experimental study and mathematical modelling of the processes developing when co-firing wheat straw pellets with a gaseous fuel were carried out. The effect of co-firing on the main gasification and combustion characteristics was studied experimentally by varying the propane supply and additional heat input into the pilot device, along with the estimation of the effect of co-firing on the thermal decomposition of wheat straw pellets, on the formation, ignition and combustion of volatiles . A mathematical model has been developed using the environment of the Matlab (2D modelling) and MATLAB package ”pdepe”(1D modelling) considering the variations in supplying heat energy and combustible volatiles into the bottom of the combustor. Dominant exothermal chemical reactions were used to evaluate the effect of co-firing on the main combustion characteristics and composition of the productsand. The results prove that the additional heat from the propane flame makes it possible to control the thermal decomposition of straw pellets, the formation, ignition and combustion of volatiles and the development of combustion dynamics, thus completing the combustion of biomass and leading to cleaner heat energy production.

The aim of this study was to provide more effective use of straw for energy production by co-firing wheat straw pellets with solid fuels (wood, peat pellets) under additional electric control of the combustion characteristics at thermo-chemical conversion of fuel mixtures. Effects of the DC electric field on the main combustion characteristics were studied experimentally using a fixed-bed experimental setup with a heat output up to 4 kW. An axisymmetric electric field was applied to the flame base between the positively charged electrode and the grounded wall of the combustion chamber. The experimental study includes local measurements of the composition of the gasification gas, flame temperature, heat output, combustion efficiency and of the composition of the flue gas considering the variation of the bias voltage of the electrode. A mathematical model of the field-induced thermo-chemical conversion of combustible volatiles has been built using MATLAB. The results confirm that the electric field-induced processes of heat and mass transfer allow to control and improve the main combustion characteristics thus enhancing the fuel burnout and increasing the heat output from the device up to 14% and the produced heat per mass of burned solid fuel up to 7%.

The main goal of the present study is to assure a more effective use of CO2 neutral fuel (wheat straw) for cleaner energy production with reduced greenhouse carbon emissions by partially replacing a fossil fuel (crashed coal) with a renewable one. This work combines experimental study and mathematical modelling of the processes developing during the co-combustion of straw pellets and crashed coal, aimed at assessment of the influence of the elemental composition and heating values of the mixture components on the main gasification/combustion characteristics, heat output from the device and on the composition of the flue gas products. The experimental study of the development of main gasification/combustion characteristics involves a complex DTG and DTA analysis of straw pellets and crashed coal and an estimation of the main steps of their thermal decomposition, combustion of volatiles, char formation and burnout, thus providing a complex kinetic study of the mixture weight loss rates and of the formation of combustible volatiles (CO, H2) at different stages of thermal decomposition of the solid fuel mixtures. A mathematical model for the combustion of volatiles (CO, H2) downstream the combustor has been built using the MATLAB package, with an account of the CO:H2 molar ratio variations at the inlet of the combustor and the development of exothermic reactions for the H2 and CO combustion dependent on the changes in straw mass load in the mixture of solid fuels.

The main goal of the present study is to obtain a more effective utilization of wheat straw for energy production during a co-combustion with peat. For this purpose, an electric field was applied to the flame produced by the combustion of volatiles. This work combines experimental study and mathematical modelling of the processes developing during the co-combustion of straw pellets with peat pellets. The main gasification/combustion characteristics, the heat output from the device and the composition of the flue gas were analysed by varying separately the bias voltage of the axial electrode and the straw mass load in the mixture with intention to assess the electric field impact. A mathematical model of the electric field impact on the main combustion characteristics (flow velocity, flame temperature and composition) of co-combustion have been built within the MATLAB environment. The numerical simulation was performed for two dominant second order combustion reactions of CO and H2 with account for the electric field effect on the displacement of equilibrium during the thermal decomposition of the biomass.