Design av testanläggning för förbränning av pellets i matlagningsspisar : Analys av hur pelletsens egenskaper påverkar emissioner och effektivitet under förbränning

Sammanfattning: Renewable energy sources have dominated energy use throughout human history and biomass is one of the world's oldest energy sources. The use of biomass as a fuel has increased in recent decades and has led to great technological development as a result of the growing demands for sustainable solutions. The main source of energy in households in sub-Saharan Africa is traditional biomass, such as firewood and charcoal. Charcoal production in Zambia is estimated to require 6,089,000 tonnes per year, which with its inefficient energy production and unsustainable forestry means that the country has one of the highest deforestation rates in the world in percentage terms. Since 2012, Emerging Cooking Solutions Ldt (ECS) has been supplying modern pellet stoves and producing fuel pellets in Zambia to phase out the use of charcoal in cooking. Pellet stoves minimize emissions of volatile particles and carbon monoxide emissions and reduces health risks. ECS is actively working to improve its cooking stoves and the purpose of the studies is to increase knowledge about how pellets' properties affect combustion. The study designed and built a test facility to be able to analyze the combustion of pellets in cooking stoves at the Faculty of Health, Science and Technology at Karlstad University. The plant includes measurement of carbon monoxide, nitrogen oxides, temperature and velocity in outgoing flue gases. The fuel consumption of the stove and the temperature of the water are measured during the entire combustion process. The test unit and its design meet the majority of the requirements of ISO 19867-1 and can be used for tests on the combustion of different types of pellets in different types of cooking stoves. The study analyzed the effect of the pellets' properties on emissions of carbon monoxide and nitrogen oxides during combustion. The analysis was conducted on purchased straw pellets, pellets from Zambia and pellets from bark, heartwood, sapwood and from Laxåpellets that were pelletized at Karlstad University. The combustion tests also included analyzes of efficiency, power, usable energy and fuel consumption for the pellet stove. Incineration of produced pellets, purchased straw pellets and pellets from Zambia in the test facility reported that higher moisture content, ash content and extractives lead to higher carbon monoxide emissions and poorer combustion with lower fuel consumption and efficiency. According to the study, ECS should focus the production of pellets on biomass with a low ash content and extractives to ensure efficient combustion with low carbon monoxide and nitrogen oxide emissions. Using bark pellets in the cooking stove in of lack of other fuel should be avoided. This entails greater health risks such as pellets with increased moisture content. It should thus be avoided to store pellets openly in a humid environment, which can occur during the rainy season in Zambia.