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Author: search.filters.author.Eiamsa-ard, S.Subject: search.filters.subject.Combustion

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    Heat transfer of a coil-tube heat exchanger in the freeboard zone of a rice husk fluidized-bed combustor
    (2021-10-01)
    Chokphoemphun, S.
    ;
    Eiamsa-ard, S.
    ;
    Promvonge, P.
    ;
    Thongdaeng, S.
    ;
    Hongkong, S.
    This research presents an investigation on heat recovery from a fluidized-bed combustor by using coil-tube heat exchangers positioned inside the freeboard zone. Rice husk was used as a fuel at a constant mass flow rate of 8 kg/h. Heat recovery experiments were performed at four different air mass flow rates (6.0248, 6.8077, 7.8163, and 8.8646 kg/h) using coil-tube heat exchangers wrapped around with steel wires in three different configurations (2_Coil wires, 4_Coil wires and Full length). Air was supplied to the coil-tube heat exchanger with two different air flows corresponding to flue gas flow: co-flow and counter-flow. The results showed that the outlet temperature tended to decrease with an increase in air flow rate in the coil-tube heat exchanger. The outlet temperatures obtained from the system with co-flow were greater than the one with counter-flow by 7–17 °C (2–15%) depending on the coil-tube heat exchanger configuration. The heat transfer rates in heat recovery process were in the range of 279–425 J/s. In addition, it was found that the heat transfer rate and the outlet temperature of the air from the coil-tube heat exchanger increased with an increase in the number of coil wires wrapped around the outer surface of the coil-tube heat exchanger.
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    Combustion behavior in a dual-staging vortex rice husk combustor with snail entry
    (2008-11-01)
    Eiamsa-ard, S.
    ;
    Kaewkohkiat, Y.
    ;
    Thianpong, C.
    ;
    Promvonge, P.
    The combustion characteristics of rice husk fuel in a dual-staging vortex-combustor (DSVC) are experimentally investigated. In the present work, the vortex flow is created by using a snail entrance mounted at the bottom of the combustor. The temperature distributions at selected locations inside the combustor, the flue gas emissions (CO, CO<inf>2</inf>, O<inf>2</inf>, NO<inf>x</inf>), and the combustion/thermal efficiency are monitored. Measurements are made at a constant rice husk feed rate of 0.25 kg/min with various excess airs (37%, 56%, 74% and 92%) and different secondary air injection fractions (λ = 0.0, 0.15 and 0.2), respectively. The combustion chamber is 1800 mm high and 300 mm in diameter (D) with a centered exhausted pipe while the middle chamber of the combustor is set to 0.5D. The smaller section at the middle chamber is introduced to split the chamber to be dual-staging chamber where a large central toroidal recirculation zone induced by swirl flow through the small section is generated in the top chamber. The experimental results reveal that the highest temperature inside the combustor is about 1000 °C whereas both the thermal and the combustion efficiency are 41.6% and 99.8% for 74% excess air without the secondary air injection (λ = 0.0). In addition, the emissions are CO<inf>2</inf> = 8.1%, O<inf>2</inf> = 9.3%, CO = 352 ppm, NO<inf>x</inf> = 294 ppm and small amount of fly ash. Therefore, the DSVC shows an excellent performance, low emissions, high stabilization and ease of operation in firing the rice husk. © 2008 Elsevier Ltd. All rights reserved.