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

The focus of the recent experimental research is to analyze the regulation possibilities of biomass combustion. Three possibilities were chosen as part of this research: a) biomass cofiring with propane, b) swirling flow with re-circulation zone, and c) use of a permanent magnet. The aim of the research is to provide stable, controllable and effective biomass combustion with minimum emissions. The special pilot device was created where biomass can be combusted separately and co-fired with propane. Wood pellets were used during the experiments.

A kinetic study on the combustion of a renewable energy resource - pelletized biomass - is carried out with the aim to obtain clean and effective energy production by minimizing the impact of the heat production process on the environment. To control the processes of biomass gasification, combustion of volatiles and heat energy production, a gradient magnetic field is applied to the flame base providing experimental study of the gradient magnetic field effect on the processes developing downstream the combustor. The joint investigation of the gradient magnetic field effect on the biomass combustion and heat energy production includes the estimation of the magnetic field effect on the formation of flame velocity and composition profiles, temperature of the flame reaction zone and heat production rate providing analysis of the magnetic field effects applicability to control the pelletized biomass combustion and heat energy production. The experimental results have shown that the gradient magnetic field enhances the mixing of the flame compounds, so increasing the combustion efficiency and completing the burnout of volatiles.

The main aim of this study is to provide the experimental research of the combustion characteristics for the different types of the biomass pellets during their thermo chemical conversion with estimation the correlations between the main characteristics of pelletized plant biomass and combustion characteristics. The experiments include first, the preparation of the pelletized biomass samples of different origin with certain elemental composition, heating values, moisture content, bulk and energetic density, and second, kinetic study of the combustion characteristics with local measurements of the temperature and composition of the flame reaction zone and heat production rates at different stages of the thermo chemical conversion of pelletized biomass and different air supply rates into the combustor to obtain optimal combustion conditions of plant biomass. Correlations between the main characteristics of pelletized samples and combustion/emission characteristics of pelletized biomass fuel have been derived and analyzed.

Combustion characteristics of microwave (2.45 GHz) pre-treated biomass (wood) pellets are investigated experimentally with the aim to find out the effect of pellets pre-treatment on the biomass composition and the feasibility of their thermo-chemical conversion. A complex study of the main combustion characteristics of the pre-treated biomass samples was carried out using a thermo-gravimetric method and a pilot-scale combustion test facility. The study includes time dependent measurements of mass loss at the primary stage of biomass gasification, variations of the flame temperature and heat production rate, combustion efficiency and composition of pollutants. The results have shown that the low-temperature microwave pre-treatment of wood pellets enriches the biomass carbon content from 50 % to similar to 60 % (d.b.) for biomass pre-treated for 180 s accompanied by the increasing higher heating values (HHV) from 19.9 up to 23.4 MJ/kg. The microwave pre-treatment promotes a faster thermal decomposition of biomass pellets with an enhanced heat energy production (up to 30 %) and a correlating increase of the volume fraction of CO2 in the products up to 25-28 %, while the mass fraction of the main volatiles (CO and H-2) in the products decreases, indicating a more complete combustion of the volatiles. The shear of the char combustion stage increases with the increasing pre-treatment time. The data of thermo-gravimetric analysis coincide with the results of the pilot-scale tests.

With the aim to provide a more effective utilization of different renewable energy resources for cleaner and more effective heat energy production, this work presents a complex experimental research and comparison of the chemical composition and combustion characteristics for different types of pelletized biomass fuels. Biomass pellets are produced from wood biomass (spruce sawdust), herbaceous biomass (reed canary grass) and their binary mixtures under previously tested different pelletization regimes. The complex experimental investigation of the main parameters of biomass pellets and their combustion characteristics is carried out along with estimation of correlations between the combustion characteristics and the main characteristics of densified biomass samples. It has been found that the densification of herbaceous biomass with an addition of woody biomass (spruce sawdust) improves the combustion characteristics of the densified herbaceous biomass, providing a faster thermal decomposition of biomass pellets with the increase of the average mass loss rate from 0.125-0.130 g/s for densified reed canary grass to 0.142-0.144 g/s for the mixture of reed canary grass and woody spruce (50: 50). The addition of woody biomass ensures a more complete combustion of volatiles and decreases the average mass fraction of polluting emissions (CO, NOx) in the products. Moreover, the investigation results show that the densified biomass mixture of reed canary grass and spruce sawdust (50: 50) has a lower ash content, a higher heating value, an increased heat production rate and total amount of energy in comparison with herbaceous biomass.

The main aim of the study was to develop and investigate a small-scale experimental gasification technique for the effective thermal decomposition of pelletized renewable fuels (wood sawdust, wheat straw). The technical solution of the biomass gasifier for gasification of renewable fuels presents a downdraft gasifier with controllable additional heat energy supply to the biomass using the radial propane flame injection into the bottom part of the biomass layer. From the kinetic study of the mass conversion rate of pelletized biomass and variations of the composition of produced gas it is concluded that the process of biomass gasification is strongly influenced by the amount of additional heat energy and air supply into the biomass. The results of experimental measurements of the composition of produced gas have shown that under the conditions of the sub-stoichiometric air supply into the layer of pelletized wood biomass (α

The major goal of the research is to develop a stable, effective and controllable biomass gasification process and produce an environmentally friendly energy resource – fuel gas, which can be used in internal combustion engines for energy production. A pilot scale stratified downdraft gasifier has been developed with the aim to provide a controllable process of gasification of wood and wheat straw pellets and their mixtures by varying the air supply rate and additional heat energy supply with propane flame flow into the gasifier. The composition of the produced fuel gas (CO and H 2) as well as the produced amounts of ash, chars and tars are estimated and analyzed taking into account the effect of operation condition variations on the gasification process.

The focus of the recent experimental research is to provide control of the combustion dynamics and complex measurements (flame temperature, heat production rate, and composition of polluting emissions) for pelletized wood biomass using a non-uniform magnetic field that produces magnetic force interacting with magnetic moment of paramagnetic oxygen. The experimental results have shown that a gradient magnetic field provides enhanced mixing of the flame compounds by increasing combustion efficiency and enhancing the burnout of volatiles.

Magnetic field effect on combustion dynamics of the swirling flame flow is studied experimentally with the aim to obtain a cleaner and more effective combustion of a renewable fuel (wood pellets), providing a joint research of magnetic field effects on the swirling flame velocity field formation, processes of heat/mass transfer and combustion of volatiles at different stages of wood fuel burnout. The magnetic field effect on the swirling flame flow formation and combustion of volatiles is also studied experimentally using a pilotscale experimental device consisting of a wood fuel gasifier, water-cooled sections of the combustor with diagnostic sections between them for measuring the swirling flame velocity, temperature and composition field formation as well as the field effect on the heat production rate. The results show that the magnetic field effect on combustion dynamics must be related to the field-induced mass transfer of paramagnetic flame species (oxygen, nitrogen oxide) in the field direction, depending on magnetic force acting on the swirling flow field. Because of the magnetic field-induced magnetic force action, local variations of the flame velocity, temperature and composition fields are detected and discussed. The results show that the magnetic field effect on the swirling flame flow can be used as a tool to ensure a more effective burnout of volatiles and a cleaner heat energy production.

The paper presents results of complex experimental study of the composition and heating values as well as the combustion and emission characteristics of a pelletized biomass fuel produced from softwood and wheat straw non-hydrolyzed lignocellulosic residues (LHRs) of bioethanol production. Those biofuels can be estimated as prospective alternative renewable energy sources for clean heat and energy production by direct combustion or gasification. A small-scale pilot combustion system with swirl-stabilized flame of volatiles and heat power output up to 3 kWh was used in experiments. The results of local time-dependent measurements of the flame temperature, heat production rates and emission characteristics of LHR granules are compared with those of commercial softwood granules. The gasification step of LHRs granules results in an enhanced release of CO and free hydrogen emissions in comparison with the gasification step of softwood granules. This predetermines the possibility of LHRs granules use for syngas production. It is found that the high content of nitrogen in the LHR granules results in a relative high mass fraction of NO x emissions in the products. Less impact of the LHR combustion on the environment with a higher heat output can be achieved by co-firing the LHR with softwood granules.