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Eulerian Model for Municipal Solid Waste Gasification in a Fixed-Bed Plasma Gasification Melting Reactor
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
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
2011 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 25, no 9, 4129-4137 p.Article in journal (Refereed) Published
Abstract [en]

Plasma gasification melting (PGM) is a promising waste-to-energy process, which provides many features superior to those of conventional gasification. In this work, a steady Euler Euler multiphase model is developed to predict the performance of municipal solid waste (MSW) gasification inside a PGM reactor. The model considers the main chemical and physical processes, such as drying, pyrolysis, homogeneous reactions, heterogeneous char reactions, and melting of the inorganic components of MSW. The model is validated by one experimental test of a pilot reactor. The characteristics of PGM gasification, such as temperature distribution, syngas composition, tar yield, and energy conversion ratio (ECR, chemical energy of the gas phase divided by the total energy input), at the proposed condition are discussed. A total of nine cases are used to investigate the effects of the equivalence ratio (ER) and plasma power with a fixed flow rate of MSW. It is found that the ER has a positive effect on the cold gas efficiency of PGM gasification. However, the increase of the ER is restricted by the peak temperature. The influence of the plasma power then is not obvious for PGM gasification.

Place, publisher, year, edition, pages
2011. Vol. 25, no 9, 4129-4137 p.
Keyword [en]
National Category
Chemical Engineering
URN: urn:nbn:se:kth:diva-42373DOI: 10.1021/ef200383jISI: 000294874800032ScopusID: 2-s2.0-80052911052OAI: diva2:446936
QC 20111010Available from: 2011-10-10 Created: 2011-10-10 Last updated: 2011-11-14Bibliographically 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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