Aspects of factors affecting performance and emissions of small-scale bio heating boiler in a Northern European country

Abstract

Emission production from small-scale bio heat production of less than 1 MW is poorly regulated in Finland. Wood is widely used for energy production in Finland, and the growing share of the demand for renewable energy production from total energy production pushes the use of biomasses further. One trend in energy production is the shift to smaller, more decentralized units that use local raw materials for energy. Heat entrepreneurship has been an increasing trend as a business and a way of offering renewable heating energy locally in different parts of Finland.

This research reviewed the sustainability and efficiency, mainly from environmental but also from practical operations’ development perspective, of the use of bio heating boilers in northern climate conditions and according to local heat demand. The major task was to discuss fuel quality and the role of boiler operators in boiler efficiency and produced emissions, and to provide relevant information to the experts and operators. The research was carried out by studying both numerical data from laboratory tests for combustion of different quality fuels as well as qualitative data collected from experts operating with bio heating systems in the field. The information was gathered through literature search, interviews, and analyzing the data collected via previous questionnaires and combustion tests in Central Finland. The research reviewed the state of the steering mechanisms for the use of bio heating boilers, solid biofuels used in Finland, bio heating systems in use in the scope, applications and users of the boilers, and the state of environmental technology and emission control used in the systems.

The data was analyzed from two sets of combustion tests conducted in the JAMK boiler testing laboratory for wood chips with different moisture levels in 2014 and 2017. The combustion tests were performed with a 500 kW bio heating boiler, which represents the average output boiler in use by heat entrepreneurs. The results consolidated the understanding of the correlation between the moisture content of the fuel and boiler efficiency, showing that dry fuel enables higher boiler efficiency than moist fuel. In addition, correlation between the carbon monoxide and particle emissions in flue gases were also confirmed. The combustion tests have a large number of variables, which makes the analyzing of the results quite challenging. The partial output-level tests showed the increasing need for boiler controls to balance the combustion process. In boiler controls, optimal combinations for the fuel feed, combustion air feed, and grate moves are the key issues for enhancing the boiler efficiency and to cut down on emissions. Rapid changes in terms of the heat demand of the boiler and changes in fuel quality bring about great challenges in terms of adjusting boiler settings.

According to collected data, boiler users are interested in enhancing boiler efficiency and the maintenance of their equipment. However, a lack of awareness and technical expertise in proper boiler use exists, even with guidance manuals supplied from the manufacturers. Some equipment in use is old and is ill-equipped with modern and efficient technology. Tightening regulations will boost the implementation of flue gas purification technology in small-scale energy production. Automation technology provides opportunities for controls and monitoring of the state of the system. Maintenance and measurement services are utilized in a varied manner, but in some respects, an increased need for services in terms of guidance and adjustment can be predicted.