Autoclaving treatment of municipal solid waste for the recovery of biomass and its reutilization
Date Issued
2011
Date
2011
Author(s)
Wang, Yen-Chi
Abstract
Autoclaving treatment of municipal solid waste (MSW) for the recovery of organic fibre material (OFM) and its reutilization was investigated in this study. High-temperature and high-pressure saturated steam was used to hydrolyze the OFM of MSW, and break the long chain structure of hemicllulose and cellulose into small fragments. Meanwhile, the plastics were softened and shrunken into small lumps by the heating of steam. Therefore, autoclaving process can effectively reduce the volume of MSW. Besides, the heating value of autoclaved MSW (noted as AMSW) only decreased slightly. Thus the energy density of AMSW per volume increased. After autoclaving, the OFM can be easily separated from the AMSW by a vibratory screen according to the size diference between OFM, plastics and the other inorganic contents, obtaining the homogenous OFM.
The autoclaving experiments were conducted at 135, 155 and 165 ℃ with various operating times of 15, 30 and 60 minutes. The results indicated that the energy of steam at 135 ℃ was not enough to reduce the volume of MSW sufficiently, while slightly decreased the heating value of AMSW, therefore reducing the energy density. At 155 ℃, the volume of MSW reduced significantly, so the energy density increased effectively. Comparing with 155 ℃, 165 ℃ did not further increase the energy density of AMSW. Hence, autoclaving at a higher temperature of 165 ℃ was not suitable because it consumed more energy without further improvement.
In order to achieve an effective volume reduction, the operating time must be at least 60 minutes incorporation with rotational shredding at proper rotating speed, say, 7 rpm. The rotational shredding can provide a shear stress to break down the OFM into small size. Therefore, the suitable operating conditions of autocalving of MSW is 155 ℃, 60 minutes with 7 rpm rotation.
The moisture content of the AMSW was 72 ~ 77%, while the proper moisture content of materials for screening is 50 ~ 60%. Thus, a decrease of the moisture content of AMSW before screening is required. After the dehydration using a centrifuge, the moisture content of dewatered AMSW (DAMSW) decreased to 56%, suitable for screening.
About 46 wt.% of DAMSW, which is OFM can be separated from the DAMSW employing 1 cm x 1 cm sieve.
The separated OFM obtained was further pelleted to reduce the volume, while increase the energy density. The proper moisture content of OFM for pelleting was found to be about 20 ~ 25 wt.%. The pelleted OFM with dry-basis heating value of 3,891 kcal kg-1 and density of 1,346 kg m-3 can be used as fuel for the combustion device, coal-fired boiler and co-firing cement furnace. Further torrefaction of the OFM obtained did not increase its energy density, suggesting no need of subsequent torrefaction. The information obtained is useful for the proper design and operation of autoclaving of MSW and the subsequent treatments for the better recovery and reutilization of the biomass of OFM from MSW.
Subjects
Autoclaving
MSW
OFM
energy density
hydrolysis
dehydration
screening
pelleting
Type
thesis
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