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Authors
Abstract(s)
Os equipamentos de combustão de biomassa são caracterizados por baixas eficiências e
elevadas emissões de poluentes devido a problemas relacionados com o dimensionamento e
condições de operação. Nesse contexto, o presente trabalho teve como objetivo a otimização
do rendimento térmico de uma caldeira a péletes, mais concretamente, estudou-se como a
potência de utilização e o excesso de ar influenciam o desempenho e as emissões da caldeira
aquando da combustão.
Inicialmente, efetuou-se a caracterização física e química dos péletes, a fim de avaliar as
suas propriedades. De modo a ser possível a realização dos ensaios de queima foi necessário
proceder à modificação e calibração da instalação experimental. À instalação existente, foram
adicionados uma válvula termostática, uma válvula reguladora de pressão, um controlador
ESP32 e três termopares do tipo K, com a finalidade das condições de funcionamento da
instalação laboratorial serem as mais idênticas possíveis com o funcionamento de uma
instalação real.
Avaliou-se o desempenho da caldeira com diferentes excessos de ar, em duas potências
de operação distintas: potência 3 e 5. O rendimento térmico da caldeira foi determinado pelo
método direto e avaliado durante o regime permanente. Apenas se mediram as concentrações
molares dos gases de exaustão (O2, CO, CO2 e NOx) no regime permanente.
O aumento do caudal mássico de péletes resultou num aumento do rendimento térmico
da caldeira e na diminuição das emissões de CO. Contudo, a diminuição do excesso de ar, para
a potência menor em estudo levou a um aumento do rendimento térmico e a uma diminuição
significativa das emissões de monóxido de carbono. As emissões de NOx foram constantes
independentemente do caudal mássico de péletes e do excesso de ar utilizado, verificando-se
que estas emissões são apenas dependentes do conteúdo de azoto do combustível.
Concluiu-se que, o excesso de ar pré-definido pelo fabricante não conduz a uma melhor
eficiência térmica da caldeira, uma vez que, os ensaios de combustão demonstram que para se
otimizar o rendimento térmico, a potência do exaustor deverá ser regulada para os 56 e 30 %
para uma potência de operação 5 e 3, respetivamente.
ABSTRACT: The biomass combustion equipment is characterized by low efficiency and high pollutant emissions due to issues related to design and operating conditions. This study aimed to optimize the thermal efficiency of a pellet boiler, specifically investigating how power and excess air affect the performance and emissions during combustion. Initially, the physical and chemical characterization of the pellets was conducted to assess their properties. To perform the combustion tests, it was necessary to assemble and calibrate the experimental installation. For the existing boiler installation, a thermostatic valve, a pressure regulating valve, an ESP32 controller and three type K thermocouples were added to ensure that the operating conditions of the laboratory installation were as identical as possible to the operation of an actual installation. The boiler's performance was evaluated at different excess air, at two distinct power levels: 3 and 5. The boiler's thermal efficiency was determined using a direct method and assessed during steady-state operation. Concentrations of emission gases (O2, CO, CO2, and NOx) were only measured during steady-state conditions. Increasing the mass flow rate of pellets improved thermal efficiency and reduced CO emissions. However, reducing the excess air for the lower thermal load studied leads to increased thermal efficiency and a significant decrease in carbon monoxide emissions. NOx emissions remained constant, regardless of pellet mass flow and excess air, indicating that these emissions are solely dependent on the nitrogen content of the fuel. It was concluded that the excess air pre-defined by the manufacturer does not lead to better thermal efficiency of the boiler since combustion test demonstrated that, to optimize thermal efficiency, the excess air must be regulated for 56 and 30 % for an operating power of 5 and 3, respectively.
ABSTRACT: The biomass combustion equipment is characterized by low efficiency and high pollutant emissions due to issues related to design and operating conditions. This study aimed to optimize the thermal efficiency of a pellet boiler, specifically investigating how power and excess air affect the performance and emissions during combustion. Initially, the physical and chemical characterization of the pellets was conducted to assess their properties. To perform the combustion tests, it was necessary to assemble and calibrate the experimental installation. For the existing boiler installation, a thermostatic valve, a pressure regulating valve, an ESP32 controller and three type K thermocouples were added to ensure that the operating conditions of the laboratory installation were as identical as possible to the operation of an actual installation. The boiler's performance was evaluated at different excess air, at two distinct power levels: 3 and 5. The boiler's thermal efficiency was determined using a direct method and assessed during steady-state operation. Concentrations of emission gases (O2, CO, CO2, and NOx) were only measured during steady-state conditions. Increasing the mass flow rate of pellets improved thermal efficiency and reduced CO emissions. However, reducing the excess air for the lower thermal load studied leads to increased thermal efficiency and a significant decrease in carbon monoxide emissions. NOx emissions remained constant, regardless of pellet mass flow and excess air, indicating that these emissions are solely dependent on the nitrogen content of the fuel. It was concluded that the excess air pre-defined by the manufacturer does not lead to better thermal efficiency of the boiler since combustion test demonstrated that, to optimize thermal efficiency, the excess air must be regulated for 56 and 30 % for an operating power of 5 and 3, respectively.
Description
Keywords
Eficiência Energética Energia Biomassa Combustão Péletes Otimização da caldeira