Influence of wood chip quality on boiler house efficiency
2021
Klavina, A., Latvia Univ. of Life Sciences and Technologies, Jelgava (Latvia) | Selegovskis, R., Latvia Univ. of Life Sciences and Technologies, Jelgava (Latvia)
Wood chips that are used as a fuel for biomass boiler houses in Latvia are mainly obtained from logging; therefore, their quality and content are very variable. In addition to wood, wood chips may contain sawdust, bark, fir needles, sand, and soil. The quality of wood chips is determined by its composition. For the best biomass boiler efficiency, the fuel moisture is determined not to exceed 50% and ash content not to exceed 5%. In practice wood chip composition analysis shows that the moisture content varies from 25% to 58%, while the content of ash varies from 2.5% to 5.2%. High moisture content in wood chips decreases the fuel net calorific value more than high ash content. It should be noted that higher ash content and moisture increase the boiler house operating costs, because the efficiency decreases that can result as an increase of the heat energy trade price. Using a flue gas condenser, there is a possibility to recover some heat losses caused by leaving water vapour in the flue gas, but anyway, the moisture decreases the efficiency of burning. The heat production efficiency of 3.1 MW wood chip boiler used for centralized district heating and hot water producing is determined using existing statistics data and measurements and evaluated taking into account the boiler operating capacity, produced heat energy, amount of wood chips used for firing and fuel quality parameters, such as moisture and ash content, calorific value. The influence of the wood chip composition on the boiler house efficiency is studied. The boiler house operation was monitored since 16th November 2020 till 21st January 2021. The monitored period was divided in 5 shorter periods to be able to compare the heat generation system efficiency under the influence of various wood chip parameters. The results showed that the specific boiler house efficiency was the lowest (70%) in the period, when the ash content of the fuel was high (average 5.30%), the moisture level was low (average 24.30%). The highest efficiency (94%) was identified, when the average ash content was 3.2% and the average moisture content 47.68%.
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