| Abstract [eng] |
Improvement of efectiveness of heat-generating facilities is an important field that gets a lot interest from thermal energy specialists and demands the newest and most advanced technologies and knowledge of thermoengineering. Due to various reasons, not every boiler house has the capability to install modern condensing economizers that recover energy from the flue gas and improve the efficiency of boiler system, therefore it is important to investigate alternative means to improve the boiler‘s efficiency in boiler houses like this. Improving boiler‘s efficiency in various ways helps to achieve positive results, such as saving boiler fuel or increasing power of the boiler. In this final project, the improvement of efficiency of a 8 MW biomass water-heating boiler is analyzed, using intensification of flue gas flow, increasing of the temperature of combustion products before the boiler and reducing the moisture of the fuel. To apply these methods, turbulators of the flue gas flow, flue gas recirculation and drying of the fuel were used in the numerical modelling. Considering the tasks and the purpose of the final project, thermodynamical and aerodynamical numeric modelling of the boiler is carried out. With the relation to the results after increasing the efficiency of the boiler, it is analyzed, how other parameters of the boiler‘s performance vary. Attention is then brought to the analysis of the temperature after the boiler, heat transfer coefficients, aerodynamical pressure drop throughout the boiler, formed and recirculated flue gas rate, air needed for combustion and used amound of fuel. It was concluded after the numerical modelling that using flue gas flow turbulators is the most effective method to increase the boiler‘s effectiveness (η=91,4%). However, at the same time aerodynamical pressure drop increases, affecting the amount of energy used for the needs of the boiler house. Moreover, combustion of the fuel of a lower quality (that contains more moisture or produces more ash), leads to the clogging of the convective surfaces of the boiler with ash. After analyzing the effect of increasing the temperature of combustion products before boiler to the boiler‘s efficiency it was concluded that the higher temperature of the combustion products leads to improvement of the boiler‘s efficiency (η=88,38%) and lower aerodynamical pressure drop throughout the boiler, but due to higher temperature of the combustion products, the risk of the ash melting in the furnace increases as well. The effect of the moisture of the fuel to the effectiveness of the boiler was analyzed as the third option and it was calculated in the numerical analysis that drier fuel leads to improvement of the boiler‘s effciency (η=89,79%) and greater temperature of flue gas after the boiler. It was found that using the recovered heat of the flue gas to dry the fuel, it is possible to improve not only the effectiveness (η=88,69%) of a water-heating boiler, but it‘s capacity as well. |
