Computational fluid dynamics investigation on the effect of co-firing semi-coke and bituminous coal in a 300 MW tangentially fired boiler

Abstract

In this paper, the effect of co-firing semi-coke in a 300 MW tangentially fired boiler was numerically investigated. The results indicate that the incomplete combustion heat loss and NO x emission both increase with semi-coke co-fired ratio. Semi-coke may be injected into the furnace at a different height, which can lead to different thermal efficiency and NO x emission. It is suggested that semi-coke should not be fed from the top or bottom layer burners, since this could give rise to high carbon content respectively in fly ash and bottom slag. In addition, injecting semi-coke from the top burners could significantly increase the NO x emission. Under 1/2 co-firing ratio, the optimal fuel allocation is that feeding semi-coke from the B, D, and E layer burners. The growth in semi-coke particle size could increase the unburned carbon loss and NO x emission. It is highly recommended to reduce the unburned carbon loss under semi-coke co-fired condition by increasing the stoichiometric ratio of primary air for semi-coke. As it is increased from 0.25 to 0.3, the combustion efficiency of the co-fired condition is 99.47%, the same as when only firing bituminous coal, and the NO x emission is about 30% higher.

Numerical Investigation on Co-firing Characteristics of Semi-Coke and Lean Coal in a 600 MW Supercritical Wall-Fired Boiler

“…Therefore, the calculation of NO x adopted a post-processing method based on the stable temperature field and flow field. This method greatly simplified the calculation work and could satisfy the precision requirement in practical applications [24]. According to the source and generation path of nitrogen, NO x can be divided into three types: prompt NO x , fuel NO x , and thermal NO x .…”

“…In the present calculation process, thermal NO x and fuel NO x were considered. The reaction of nitrogen and oxygen in the air mainly produced Thermal NO x , and the formation of thermal NO x was explained by the mechanism of Zeldovich [24]. Fuel NO x is produced by nitrogen oxidation in fuels and the formation of fuel NO x originates from the oxidation of nitrogen in volatile and char.…”

“…Most of the previous studies involved the co-firing behaviors of bituminous coal and other kinds of coals, which are difficult to guide in pulverized-coal fired boilers. The exploration of co-firing bituminous coal and semi-coke was firstly conducted in a 300 MW tangentially-fired boiler in our previous study [24]. The study suggested that semi-coke can be co-fired with coal in utility boilers.…”

Experimental study on bituminous coal blending in a down‐fired boiler with anthracite combustion system under low load

“…The numerical investigations of the influence of the blending method on the combustion characteristics and NO x emission in a 500‐MWe tangentially fired boiler were carried out by Baek et al 25 The in‐furnace and out‐furnace blending methods were simulated with the blend of 60% bituminous and 40% subbituminous coals on a weight basis. Beyond that, there are many other experiments and simulations on the combustion of blended coals on a full‐scale tangentially fired boiler and wall‐fired boilers 26–31 …”

Combustion Performance and Ash Compositions during Biomass/Semi-Coke Blended Fuel Oxy-Fuel Circulating Fluidized Bed Combustion

“…On the other hand, there are large reserves of low-rank coal (lignite/subbituminous coal) in China, which accounts for over 50% of coal reserves. , Such coals are usually used as chemical materials. With the production of chemical oil gas, there is also a large amount of semi-coke, which is a kind of low-volatile inferior fuel compared with raw coal.…”