Numerical simulation of co-firing characteristics of pulverized semi-coke and biomass in the two different boilers

Compared with coal,the pulverized semi-coke has a lower price and a lower pollution emissions,but has more difficulty in ignition and burn-out.Renewable energy biomass is clean,low carbon,easy to access and prone to fire,but it has a lower energy density.Therefore,the co-combustion of pulverized semi-coke and biomass can improve the ignition and combustion characteristics of pulverized semicoke,solve the problem of low biomass energy density,and improve fuel applicability.It plays a significant role in energy-saving and improvement of the fuel application.In order to derive the optimal mixing ratios in water-cooled and air-cooled boilers which were independently developed by the Coal Science Institute,the effects of different mixing ratios on the mixed combustion characteristics of semi-coke and biomass were studied,and the causes of different mixed combustion characteristics in different types of boilers were analyzed.A threedimensional proportional model was established by numerical simulation method,which comprehensively considered the turbulent flow,radiation heat transfer,volatile precipitation,gas phase reaction,particle motion and fixed carbon combustion.The relative error between the calculated results of the model and the experimental results in the literature was less than 5%,which verified the accuracy of the model.The temperature profiles of burner outlet,combustion region and furnace outlet,the oxygen content of furnace outlet of two distinct boilers were analyzed under different mixing ratios.The results show that in the water-cooled boiler,the optimal combustion performance appears at 2/8 mixing ratio( semi-coke/biomass),and the worst appears at 4/6 and 10/0.With a 2/8 mixing ratio,the average and highest temperature of burner outlet,combustion region and furnace outlet are the highest,and the oxygen content of furnace outlet is the lowest value of 6%.Whereas in the air-cooled boiler,the optimal mixing ratio is 4/6,and the worst is 8/2 and 10/0.With a 4/6 mixing ratio,the average and highest temperature of burner outlet are highest,and the oxygen content is the lowest value of 4.8%.With the increasing mixing ratio,the ignition position in the burner moved forward gradually and the highest temperature appeared at the front end of the front cone in the two types of boilers.When the ignition position of the water-cooled boilers shifts to the front cone,the combustion performance in the furnace decreases greatly.With the comparison of two boilers,all the temperatures of the air-cooled boiler are obviously higher and the oxygen content is lower.When the optimum working condition is 2/8 in the water-cooled boiler,all the temperature parameters except the highest temperature in the combustion region are lower than those of the air-cooled boiler,and the oxygen content is 1% higher and the combustion performance is lower than that of air-cooled boiler.When the air-cooled boilers is in the worst working condition of 8/2,all the temperatures of the air-cooled boiler are 300-700 K higher and the oxygen content is the half of that in the water-cooled boiler.So the combustion characteristics of air-cooled boiler is better than that of the water-cooled boiler.Under the same mixing ratio,the combustion performance of air-cooled boiler was significantly better than that of the water-cooled boiler.