Effect of Coal Blending Methods with Different Excess Oxygen on Unburned Carbon and NO_x Emissions in an Entrained Flow Reactor

Abstract

The influence of coal blending methods, such as out-furnace (external or premixed) blending and in-furnace (initially nonmixed) blending, with different excess oxygen (highest, medium, and lowest stoichiometric conditions) on unburned carbon and NO x emissions of blend combustion in an entrained flow reactor has been analyzed, using experimental and numerical approaches for binary coals used by Korean power plants. The results confirm that, under the medium condition, contrasting processes, such as reactive and unreactive effects, occur with SBRs in the out-furnace blending method. The in-furnace blending method results in an improvement in the efficiency of unburned carbon fractions and a further reduction in the NO x emission. Under the highest condition, the unburned carbon fraction in both the out-furnace and the in-furnace blending methods corresponds with the tendency under the medium condition with contrasting processes of lower magnitude, whereas the NO x emission in the highest condition increases slightly. Under the lowest conditions, the unburned carbon fraction in the out-furnace blending method gradually decreases as SBR decreases, without a competition effect. The reduction of NO x emission under the lowest conditions is more effective than those under other conditions for the two blending methods because of homogeneous and heterogeneous NO x reduction mechanisms. These results show that the phenomenon that occurs with coal blending methods under different excess oxygen conditions has been demonstrated and the in-furnace blending method below medium conditions would be an effective method to improve combustibility and NO x emission due to penalty of NO x under the highest condition. In general, the numerical results are in agreement with the measured values and give insight into the phenomena that affect the blending methods under different excess oxygen conditions.

Unburned carbon from coal combustion ash: An overview

“…[8,26,45] -effect of coal mineral matter [8,16,26,46] -coal blending [32,39,44,[47][48][49] -co-combustion of coal with alternative fuels [50][51][52][53][54].…”

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

“…In general, there are two practical methods for coal blending in power plant. One method, namely, direct blending, is to mix different coals directly in the stockpiles and coal bunker, and the coal blends are simultaneously fed through mills and burners into the boiler, which is also categorized as the out‐furnace blending method 38 . The other method, namely, indirect blending, is to feed different coals separately into the specific mills and burners without prior mixing.…”

Termik Santral Küllerinde Yanmamış Karbonun Pulverize Kömür Boyut Dağılımı ve Uçucu Madde İçeriği ile İlişkisi

“…Deneysel ya da bilgisayımsal yollarla yanmamış karbon tahmin sistemi geliştirmek için birçok yaklaşım mevcuttur [4]. Moron [5] uçucu küldeki yanmamış karbonun, kömür karışımı için beslenen fazla hava oranıyla ilişkisini araştırmıştır [6]. Bartonava [3] çalışmasına göre yanmamış karbon miktarı, kömürün kimyasal kompozisyonundan, kömür petrografik özelliklerinden, kömür hazırlama yöntemlerinden gibi kömüre ait parametrelerle; yanma odası sıcaklığı, fazla hava miktarı, kazan içi kalma süresi gibi kazan dizaynına ait parametrelerle ilişkilidir [7,8,9,10,11].…”