Comparison of Combustion and Emission Characteristics of an Indonesian Lignite Washery Tailing Slurry with a Bituminous Coal in a Bench-Scale Bubbling/Circulating Fluidized Bed Combustor

Abstract

In this study, the combustion and emission characteristics of slurry from an Indonesian lignite washery tailing (LWT) and a bituminous coal were studied and compared in both a bubbling fluidized bed (BFB) and a circulating fluidized bed (CFB). The effects of excess air ratio, feeding rate, secondary air ratio, and secondary air location on the flue gas emissions were analyzed to investigate the optimal operating conditions. The results show that it is feasible to directly fire LWT slurry in a CFB. The temperature of the dense-phase bed firing the LWT slurry can reach 800 °C but is lower than that of a normal BFB/CFB firing coal. Both SO2 and NO emissions of bituminous coal are higher than those of LWT slurry, but their emission characteristics are still below the limits for both EU and Chinese regulations. Improved emission characteristics are observed when firing LWT slurry and coal in CFB compared to BFB. Two main differences were found between LWT slurry and coal: (1) Low primary air (PA) flow rates facilitate the defluidization of the FB combustor when firing LWT slurry. (2) High feeding rates of LWT slurry may reduce the temperature along FB instead. These factors should be paid special attention when designing and operating an FB system. Optimal secondary air (SA) ratios were determined for both LWT slurry and coal. The SA should not be located near the distributor. All of the analyses in this study provide useful information for the design and operation of a commercial FB system.

Co-Combustion of Tannery Sludge in a Bench-Scale Fluidized-Bed Combustor: Gaseous Emissions and Cr Distribution and Speciation

“…Due to these low temperatures and short residence times, fewer CO molecules were converted to CO 2 , and more CO was emitted under higher PA flow rates in test C3. Similar phenomena have also been reported by Chen et al, Madhiyanon et al, and Varol et al…”

“…This effect was due to the poor fluidization at low fluidizing air velocity, resulting in poor mixing conditions. Defluidization has been reported to occur when the PA flow rate decreases to 67 L/h in the present FB combustor . The decreased CO emission levels when the PA reached 78 L/h suggested that better fluidization and mixing conditions were achieved and that combustion was optimized.…”

“…Tests were switched between BFB and CFB by controlling valves after the furnace, as shown in Figure . The preparation steps performed before conducting experiments, including cold fluidization and ignition tests, have been extensively described elsewhere . Feeding coal was sieved to be under 1 cm.…”

Fluidized Bed Combustion and Gasification of Fossil and Renewable Slurry Fuels

“…The operation was optimal when the sludge content was between 20% and 30% wt. Recently, the comparison between combustion characteristics of CWM and lignite washery tails (a waste stream from lignite preparation) was obtained in a bench-scale CFB combustor (36 kWth) [66]. The authors reported similar combustion characteristics in terms of efficiency and emissions, complying with European and Chinese standards.…”

Torrefaction of Oil Palm Frond Petiole: Effect of Particle Sizes, Sections and Batches

“…This is due to its significant amount of carbon content, which typically ranges from 40.30 to 48.43% [1,[3][4][5][6][7][8][9]. In the energy production, the amount of energy (known as higher heating value, HHV) that can be produced during the combustion of a fuel is vital [10], along with other requirements such as conversion efficiency, pollutant emissions, etc [11]. For the case of raw OPF, its HHV is typically considered low in the range from 16.3 to 18.1 MJ/kg [4][5][6][7][8][9][12][13][14].…”