Thermodynamic Analysis of Heat and Mass Transfer in the Combustion Chamber of an Industrial Furnace

CFD analysis of heavy fuel oil combustion in a 6.7 MW cylindrical vertically-fired furnace has been carried out. The furnace supplies process heat in the Oil refinery of the National oil company (INA) in Rijeka-Croatia. The motivation of the work was to improve the performance of the combustion process by changing fuel and burner parameters. The commercial CFD-code Fluent is used to model transport and reaction in the furnace. The chosen CFD models for heavy fuel oil spray combustion are compared with measurement data found in the literature and good agreement is achieved. The combustion process is investigated through the influence of different parameters: air-fuel ratio, fuel oil droplet diameter, spray cone half-angle and burner swirl number. It is determined that the best performance of the combustion process is achieved for an air-fuel ratio of 1.15. The droplet diameter should be neither too small nor too large: medium-sized droplets (~100 μm) mix well with air and reside in the furnace the right amount of time for complete burnout to occur. Small spray cone half-angles deteriorate mixing between air and fuel which is reflected in higher CO concentrations. The burner’s swirl number influences the mixing rate of air and fuel: a small swirl number is not desired as it elongates the flame, increases flue gases temperatures and reduces the furnace heating output.