Impact of furnace dimensions on recovery boiler performance and cost

In this work designing and pricing of the recovery boiler were studied. The main goal was to find out how furnace screen heat transfer surface affects the recovery boiler price and performance. Two different boiler sizes were studied. Four different boilers were designed in both boiler sizes. One boiler was designed without furnace screen and three others with different size of furnace screens. The boilers were desinged so that they reached the same performances and were comparable. The furnace screen is an effective heat transfer surface and by adding the furnace screen the furnace can be designed lower. Furnace height has a significant effect on the total price of the boiler. On the other hand, the reduced furnace height yields shorter flue gas residence time, which can lead to incomplete combustion resulting e.g. increased emissions. Combustion air ratio and mixing of reactants with the air jets have a great effect on the combustion efficiency. In this study, the reduced residence time was compensated by the higher combustion air ratio by feeding more combustion air into the furnace. This way the effective mixing and the complete combustion were ensured. In order to find out the required amount of combustion air for the complete combustion CFD simulations and field data analysis were made. The target was to find out the effect of the combustion air ratio and the residence time on the CO emissions. According to these results boilers with the different heights could be designed so that they achieve also the same CO emissions. The designed boilers were priced and compared. Only the changing boiler structures were taken into account in pricing, which was sorted out to heat transfer surfaces, high pressure pipes, steel structures, auxiliary equipment and civil/structural costs. The material, manufacturing and erection costs were studied. The heat transfer surfaces and boiler building had the most significant portions in the share of costs