Emissions from a circulating and a stationary fluidized bed boiler: A comparison

Paper in proceeding, 1987

A comparison is presented of the emissions of sulphur dioxide and nitrogen oxide from a stationary fluidized bed boiler and a circulating fluidized bed boiler. The boilers used for the comparison were the 16 MW stationary bed boiler at Chalmers University and the 40 MW circulating bed boiler at Nyköping (Sweden). In order to focus the comparison on the design of the boilers and to eliminate differences caused by fuel and sorbent, both boilers were run with the same coal and limestone. The influence of the operating conditions on the emissions is studied. The main influencing para­meters are: Limestone feed rate, bed temperature, and excess air ratio, One of these parameters was varied at a time while the others were kept constant. The results show that both types of boiler can be run conveniently with low emissions of sulphur and nitrogen oxides. The sulphur absorption is su­perior in the circulating bed boiler, where an almost complete absorption is attained at a calcium-to-sulphur molar ratio of 2 , Without limestone addition, and at bed tempera­tures below 850°C, the nitrogen oxide emission from the circulating bed boiler is as low as is reasonable, achieving the equilibrium value of nitrogen oxide in oxygen and nitrogen. With limestone addition, however, considerably higher emission values are obtained in the circulating bed boiler, whereas the corresponding emission from the stationary bed boiler is not affected by limestone. In addition to the studies of sulphur and nit­rogen oxide emissions, the influence of limestone on the emissions of mercury, chloride, and fluoride was investigated.