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Gasification of municipal solid waste in the Plasma Gasification Melting process
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.ORCID iD: 0000-0002-1837-5439
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2011 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 90, no 1, 106-112 p.Article in journal (Refereed) Published
Abstract [en]

new waste-disposal technology named Plasma Gasification Melting (PGM) was developed. A pilot PGM reactor was constructed in northern Israel. The reactor is an updraft moving-bed gasifier, with plasma torches placed next to air nozzles to heat the incoming air to 6000 °C. The inorganic substances of the feedstock are melted by the high-temperature air to form a vitrified slag in which undesirable materials such as heavy metals are trapped. The residual heat in the air supplies additional heat for the gasification process.

A series of tests were conducted to study the performance of PGM gasification. The plasma power was varied from 2.88 to 3.12 MJ/kg of municipal solid waste (MSW), and the equivalence ratio (ER) was varied from 0.08 to 0.12. For air and steam gasification, the maximum steam/MSW mass ratio reached 0.33.

The composition of the syngas product was analyzed in all tests; the lower heating value (LHV) of the syngas varied from 6 to 7 MJ/Nm3. For air gasification, the syngas LHV decreased with increasing ER, whereas the gas yield and energy efficiency increased with ER. When high-temperature steam was fed into the reactor, the overall gas yield was increased significantly, and the syngas LHV also increased slightly. The positive effect may be attributed to the steam reforming of tar. In air and steam gasification, the influence of increased ER on syngas LHV was negative, while the effect of increased plasma power was positive. The maximum energy efficiency of the tests reached 58%. The main energy loss was due to the formation of tar.

Place, publisher, year, edition, pages
2011. Vol. 90, no 1, 106-112 p.
National Category
Energy Engineering
URN: urn:nbn:se:kth:diva-47491DOI: 10.1016/j.apenergy.2011.01.041ISI: 000297426100017ScopusID: 2-s2.0-80055042180OAI: diva2:455989
QC 20111111Available from: 2011-11-11 Created: 2011-11-10 Last updated: 2012-01-10Bibliographically approved
In thesis
1. Mathematical modeling of municipal solid waste plasma gasification in a fixed-bed melting reactor
Open this publication in new window or tab >>Mathematical modeling of municipal solid waste plasma gasification in a fixed-bed melting reactor
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The increasing yield of municipal solid waste (MSW) is one of the main by-products of modern society. Among various MSW treatment methods, plasma gasification in a fixed-bed melting reactor (PGM) is a new technology, which may provide an efficient and environmental friendly solution for problems related to MSW disposals. General objectives of this work are to develop mathematical models for the PGM process, and using these models to analyze the characteristics of this new technology.

In this thesis, both experimental measurement and numerical analysis are carried out to evaluate the performance of both air gasification and air&steam gasification in a PGM reactor. Furthermore, parameter studies were launched to investigate the effect of three main operation parameters: equivalence ratio (ER), steam feedstock mass ratio(S/F) and plasma energy ratio (PER). Based on the above analysis, the optimal suggestions aiming at providing highest syngas calorific value, as well as system energy efficiency, are given.

Six experimental tests were conducted in a demonstration reactor. These tests are classified into two groups: air gasification (case 1 and 2) and air&steam gasification (case 3 to 6). In all these cases, the plasma gasification and melting of MSW produced a   syngas with a lower heating value of 6.0-7.0 MJ/Nm3. By comparing the syngas yield and calorific value, the study found out that the steam and air mixture is a better gasification agent than pure air. It is also discovered that the operation parameters seriously influence the operation of the PGM process.

A zero-dimensional kinetic free model was built up to investigate the influence of operation parameters. The model was developed using the popular process simulation software Aspen Plus. In this model, the whole plasma gasification and melting process was divided into four layers: drying, pyrolysis, char combustion&gasificaiton, and plasma melting. Mass and energy balances were considered in all layers. It was proved that the model is able to give good agreement of the syngas yield and composition. This model was used to study the influence of ER, S/F and PER on average gasification temperature, syngas composition and syngas yield. It is pointed out that a common problem for the PGM air gasification is the incomplete char conversion due to low ER value. Both increasing plasma power and feeding steam is helpful for solving this problem. The syngas quality can also be improved by reasonably feeding high temperature steam into the reactor.  

In order to provide detailed information inside the reactor, a two-dimensional steady model was developed for the PGM process. The model used the Euler-Euler multiphase approach. The mass, momentum and energy balances of both gas and solid phases are considered in this model. The model described the complex chemical and physical processes such as drying, pyrolysis, homogeneous reactions, heterogeneous char reactions and melting of the inorganic components of MSW. The rates of chemical reactions are controlled by kinetic rates and physical transport theories. The model is capable of simulating the pressure fields, temperature fields, and velocity fields of both phase, as well as variations of gas and solid composition insider the reactor. This model was used to simulate both air gasification and air&steam gasification of MSW in the PGM reactor.

For PGM air gasification, simulated results showed that when ER varies from 0.043 to 0.077, both the syngas yield and cold gas efficiency demonstrated a trend of increasing. This is explained mainly by the increase of char conversion rate with ER. However, the increase of ER was restricted by peak temperature inside the fixed-bed reactor. Therefore, it is not suggested to use only air as gasification in the PGM process. The influence of plasma power is not obvious when PER varies from 0.098 to 0.138.

 The positive influences of steam addition on cold gas efficiency and syngas lower-heating-value are confirmed by the simulation results of PGM air&steam gasification. The main effect of steam addition is the rouse of water shift reaction, which largely accelerates the char conversion and final yields of hydrogen and carbon dioxide. The effect of steam injection is affected by steam feeding rate, air feeding rate and plasma power.

Based on the above modeling work, Interactions between operation parameters were discussed. Possible operation extents of operation parameters are delimitated. The optimal points aiming at obtaining maximum syngas LHV and system CGE are suggested.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. xiv, 87 p.
Mathematical modeling, plasma gasification, municipal solid waste, fixed-bed
National Category
Energy Systems
urn:nbn:se:kth:diva-47451 (URN)978-91-7501-141-7 (ISBN)
Public defence
2011-11-25, Entreplan (D2), Lindstedtsvägen 5, KTH, Stockholm, 10:00 (English)
Available from: 2011-11-14 Created: 2011-11-09 Last updated: 2011-11-14Bibliographically approved

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