Woody biomass is an abundant, renewable energy source. Forest residue is the fraction remaining after harvest and the outtake of wood timber, including tree tops and bark. Compared with the wood portion, bark has a wide variation of ash content. Wood usually has a relatively low ash content, while bark has considerably higher ash content, which may generate clinker in the furnace and thereby tends to create more demand for maintenance. High ash content also generates more particulate emissions. Different types of bark were studied in the present work in terms of their effect on energy content, moisture, and ash content. The ash content of three different samples (Norway spruce, birch, and European beech) were measured at 550 and 815 °C. The results showed the impact of bark content on all parameters, in particular the calorific value and ash content. The ash content increased with increasing bark content. The addition of 1% bark content resulted in increases of ash content in the range 0.033 to 0.044%.

Constant effort to reduce heating costs leads to production of not only high-quality pellets from pure wood but also cheaper vegetable pellets of inferior quality in terms of energy properties. , The combustion of alternative pellets in small boilers causes many problems, mainly ash sintering, as a result of their low melting temperature. , The paper focuses on experimental determination of bed temperatures in the burning layer during wood pellet combustion. The bed temperatures are important for prediction of combustion phases and better localization and description of sites that are critical for the sintering of ash particles as temperatures are close to the ash melting points. This experiment describes a method for measurement of the temperature field in the symmetry plane of the burner during wood pellet combustion in the retort burner. The measurement of temperature profiles at different locations in the burner shows that the combustion process in the retort burner is rather more horizontally stratified than vertically stratified. The main combustion process takes place in a ring-shaped space around combustion air inlets.

Nowadays it is important to limit the use and combustion of fossil fuels such as oil and coal. There is a need to create environmentally acceptable projects that can reduce or even stop greenhouse gas emissions. In this article, we dealt with the objectives of energy policy with regard to environmental protection, waste utilization, and conservation of natural resources. The main objective of the research was to assess the possibility of the use of spent coffee grounds (SCG) as fuel. As a part of the solution, the processing of coffee waste in the form of pellets, analysis of calorific value and combustion in the boiler were proposed. The experiments were done with four samples of pellets. These samples were made from a mixture of wood sawdust and spent coffee grounds with ratio 30:70 (wood sawdust: spent coffee grounds), 40:60, 50:50 and 100% of spent coffee grounds. The calorific values were compared with wood sawdust pellets (17.15 MJ.kg −1 ) and the best lower calorific value of 21.08 MJ.kg −1 was measured for 100% of spent coffee grounds. This sample did not achieve the desired performance during the combustion in the boiler due to the low strength of the sample.

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The effort of many manufacturers of heat sources is to achieve the maximum efficiency of energy transformation chemically bound in the fuel to heat. Therefore, it is necessary to streamline the combustion process and minimize the formation of emission during combustion. The paper presents an analysis of the combustion air temperature to the heat performance and emission parameters of burning biomass. In the second part of the paper the impact of different dendromass on formation of emissions in small heat source is evaluated. The measured results show that the regulation of the temperature of the combustion air has an effect on concentration of emissions from the combustion of biomass.