Pyrolysis and Combustion Characteristics of an Indonesian Low-Rank Coal under O₂/N₂and O₂/CO₂Conditions^†

Abstract

Pyrolysis and combustion characteristics of an Indonesian low-rank coal are studied under oxy-fuel (O2/CO2) and air (O2/N2) conditions using a drop tube furnace (DTF) and a thermogravimetric analyzer (TGA). Raw coal, dried coal, and binderless briquette samples of the same coal were used in the experiments, and the effects of drying and binderless briquetting on the reactivity of the coal under different conditions were investigated. Chars were prepared in the DTF in both N2 and CO2 atmospheres in the temperature range of 800−1400 °C. The reactivity of chars under oxy-fuel and air conditions was analyzed in the TGA. The coal reactivity under oxy-fuel conditions differed from that under air combustion conditions. The temperature at which significant gasification of the coal and char took place in the concentrated CO2 gas stream was also identified. Characteristics of chars from different conditions were compared. Drying and briquetting had some noticeable influences on the reactivity of the coal under oxy-fuel conditions.

Biomass devolatilization at high temperature under N2 and CO2: Char morphology and reactivity

“…Previous works in literature [7][8][9] reported higher apparent volatile yield values after devolatilization of coal at temperatures of 1000-1400 ºC under CO 2 than under N 2 and they attributed this effect to the char-CO 2 gasification reaction. However, other authors [8,12] obtained slightly lower values after devolatilization in CO 2 at lower temperatures (800-1000 ºC), since the gasification reaction rate was considered to be not significant at low temperature. Brix et al [14] gasification is an intense endothermic reaction which can only take place when high temperatures are present.…”

“…Nevertheless, it should be borne in mind that if gasification occurs when biomass is treated at high temperatures in a CO 2 environment, in the later stages of the oxy-fuel combustion process, when the oxygen partial pressure has significantly decreased, the gasification of unburned char could have a significant effect on char burnout [8]. Thus, high concentrations of CO 2 could increase the char-CO 2 gasification rate and in turn the total combustion rate.…”

“…Thus, Rathnam et al [7] studied the differences of coal chars obtained after devolatilization in N 2 and CO 2 in a drop tube furnace (DTF) at 1400 ºC. Li et al [8] compared the coal chars obtained in N 2 and CO 2 atmospheres in a DTF at 800-1400 ºC. Gil et al [9] studied the oxy-fuel combustion reactivity of coal chars obtained in N 2 and CO 2 atmospheres in an entrained flow reactor (EFR) at 1000 ºC.…”

Oxy-fuel combustion of coal and biomass blends

“…Therefore, particle temperature in a 21%O 2 -79%CO 2 atmosphere can be expected to be lower, which will cause the combustion rate of the char and the fuel burnout value to fall [11]. In addition, Li et al [19] attributed the different coal combustion behaviours under both atmospheres in a drop tube furnace to the lower diffusivity of O 2 in CO 2 than in N 2 , impeding the transport of O 2 to the surface of the particles and reducing the combustion rate of the volatile matter and char in oxy-fuel conditions. Under the 30%O 2 -70%CO 2 and 35%O 2 -65%CO 2 atmospheres, the burnout of the HVN and SAB coals and their blends with biomass was higher than in air (Fig.…”

Thermal behaviour of low-rank Indian coal fines agglomerated with an organic binder

“…The complete combustion kinetics analysis is necessary for the design and operation of a combustion system. Many researchers have worked on the thermal decomposition of carbonaceous materials, including coals, under different environmental conditions [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. As stated in our previous report [21], the coals from Nagaland (India) have a lowash, high-volatile, high-sulphur contents and are mostly non-caking and swelling in nature.…”