Abstract
There has been little research on volatile releasing characteristics of pulverized coals under moderate or intense low-oxygen dilution (MILD) oxy-combustion (MO) conditions. For the first time, volatile releasing characteristics of bituminous coal and semi-anthracite under both MILD air-combustion (MA) and MO conditions were investigated using a flat-flame assisted entrained flow reactor. Both heating rate (~105 K/s) and residence time (65 ms) were carefully selected to mimic the conditions in typical industrial boilers. The combustion processes and properties of the volatiles were characterized through direct observation and char analysis. The results showed that the lower diffusion rate of the volatile in CO2 resulted in the decreasing of the volatile envelope flame size and a longer volatile burnout time (more than 20%). For bituminous coal (volatile content of 25%), the lower amount of apparent volatile yield under MO conditions reduced the heating value of the volatile. For semi-anthracite coal (volatile content of 7%), the short devolatilization time led to char-CO2 gasification reaction, which increased the apparent volatile yield and the heating value of the volatile by 47% and the volatile-N by 19%. This paper indeed provided new insight into the MILD oxy-combustion of solid fuels.
Highlights
Oxy-fuel combustion technology has received considerable attention globally as one of the potential approaches to achieve sequestration-ready CO2 gas streams from coal-fired power plants [1,2]
In oxy-fuel combustion, the mixture of pure oxygen and recycled flue gas is employed as an oxidizer, replacing air [3,4]
Oxy-fuel combustion possesses the above significant preponderances, its combustion stability needs to be further strengthened, and the generation of soot and NOx needs to be further controlled [10,11], to meet the requirements of ultra-low emissions [12]
Summary
Oxy-fuel combustion technology has received considerable attention globally as one of the potential approaches to achieve sequestration-ready CO2 gas streams from coal-fired power plants [1,2]. Oxy-fuel combustion possesses the above significant preponderances, its combustion stability needs to be further strengthened, and the generation of soot and NOx needs to be further controlled [10,11], to meet the requirements of ultra-low emissions [12]. The MILD oxy-combustion, which combines oxy-fuel combustion and MILD combustion [9,10,11,16], can further realize low-carbon, efficient, and clean utilization of coal burning. The advantages of MILD combustion can enhance the stabilization of oxy-fuel combustion and further decrease the NOx generation [11,17], and homogenize the furnace temperature [18], strengthen the in-furnace heat exchange [19], and improve the efficiency of oxy-fuel combustion [20,21]
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