Municipal Solid Waste Gasification Research Articles

Thermochemical catalytic-reforming conversion of municipal solid waste to hydrogen-rich synthesis gas via carbon supported catalysts

Catalytic-reforming is considered to be an effective way to remove tar and adjust the H2/CO ratio of synthesis gas generated via gasification and reforming of municipal solid waste. The abundance of carbon materials and the variability of their properties provide new opportunities for the development of reforming catalysts. In this study, carbon supported catalysts were prepared by impregnation with carbon materials as the support, Ni as the main component of catalysts, the rare earth element Ce as the promoter. The results indicated that Nickel based catalysts can promote tar cracking and increase hydrogen production in the process of catalytic reforming of MSW gasification. Adding a proper amount of promoter Ce can improve the catalytic performance, promote the tar cracking and hydrogen conversion. When the content of the active component Ni in Ni/C supported catalysts was 15%, the highest concentration of H2 and CO was 29.30% and 21.03%, respectively, and the ratio of H2/CO was up to 1.39. When the molar ratio of Ce and Ni was 0.25 in Ce-15%Ni/C supported catalysts, the concentration of H2 reached 37.76%, the concentration of CO was 14.69%, the ratio of H2/CO was 2.57 and tar content was low to 15.32 g/Nm3. A proper addition of CeO2 can promote the tar cracking conversion from PAHs in tar to alkane. When the molar ratio of Ce and Ni was 0.50, the PAHs in tar almost disappeared, and more chain like aliphatic compounds (C19 ∼ C27) appeared, which was beneficial to the subsequent treatment of tar and utilization of synthesis gas.

Municipal solid waste gasification for environmental management: A modeling study

ABSTRACTThe aim of this study was to predict the effect of operating conditions (temperature and equivalence ratio (ER)) on product distribution and gasification performances during air-steam gasification of MSW. To predict the gas composition, an Aspen Plus model was developed based on Gibbs free energy minimization. The root-mean-square error (RMSE) and model deviation percentage (MDP) was used to evaluate the accuracy of the model. Validation showed good agreement of the reported and predicted values for the gas caloric value. Increasing the temperature from 650 to 850°C led to an increase in H2 content (3.97−4.27 vol %) in the gases. An optimal temperature of 650°C resulted in the highest syngas lower caloric value (LHV) and lowest CO2 content.

Gasification of municipal solid wastes: a review on the tar yields

ABSTRACTCurrently, due to its tremendous availability, the use of municipal solid waste (MSW) as an energy source has received significant attention in China. Moreover, when compared to coal and oil, MSW produces negligible NOx emissions in the atmosphere and generates less ash. Gasification is a promising technology for converting MSW and other low-value feedstocks into fuel gases and chemicals. In this review article, production of synthesis gas (also known as syngas) from MSW gasification is reviewed, and demonstrated to be a clean and attractive option. First, a short review of MSW treatment techniques and their advantages and limitations is presented, and then, the energy potential of MSW for gasification purposes is evaluated. Second, influencing process factors such as temperature, gasifying agents, gasifier type, particle size, and operating pressure are studied in terms of their impact on the resulting gas quality and quantity. Finally, the potential of key commercial catalysts (Ni-based catalysts, natural catalysts (dolomite), and blast furnace (BF)) in tar elimination is evaluated.

Study of the effect mechanism of municipal solid waste gasification conditions on the production of H2 and CO using modelling technique

The municipal solid waste (MSW) gasification process was numerically studied in the work. The effect mechanisms of particle size, temperature and gasification atmosphere on the production of H2 and CO were investigated in detail. The results demonstrated that the total volume fraction of H2 and CO dropped from 51.7% to 49.7% with particle size increasing from 20 < d < 30 mm to 80 < d < 100 mm under steam atmosphere. With the temperature increasing from 600 °C to 1000 °C, the total volume fraction of H2 and CO was raised from 56.1% to 65.8% under steam atmosphere. Five different gasifying agents: 100%CO2, 21%O2/79%N2, 21%O2/79%H2O, 21%CO2/79%H2O, 21%O2/79%CO2 were simulated, and the total volume fraction of H2 and CO was 51.87%, 19.1%, 56.13%, 48.36% and 42.98%, respectively. In the gasification conditions considered in this work, H + H2O⇔OH + H2 (R84) played a key role in the yield of H2, and the yield of CO was significantly affected by H + CO2⇔OH + CO (R99) and H + CH2CO⇔CH3+CO (R81).

Distribution and modeling of tar compounds produced during downdraft gasification of municipal solid waste

Tar compounds produced during gasification of municipal solid waste (MSW) hinder downstream utilization of syngas. This study investigated the effects of operating conditions (temperature, equivalence air ratio (ER) and MSW moisture content) during gasification using air on tar emissions. Tar was quantified by gravimetric and GC-MS methods, denoted as gravimetric and collected (GC-MS) tar, respectively. Additionally, styrene evolution was studied as it is one of the main tar compounds produced from MSW. By applying the response surface methodology for modeling, it was found that tar contents quantified by the two methods are influenced similarly by ER and MSW moisture content, but differently by temperature. This discrepancy was attributed to the different composition and properties of tar fractions measured by gravimetric and GC-MS methods. Since the selection of analytical method can have impact on the quantification of tar, adoption of different methods for the characterization of tar emissions from MSW gasifiers is essential in order to provide a holistic analysis of the tar evolution process. The content of styrene in collected (GC-MS) tar from MSW gasification was 13–29%. The lower contents of styrene were favored by operating temperature between 850 and 900 °C, higher ER and higher MSW moisture content.

Hydrogen and syngas production from municipal solid waste (MSW) gasification via reusing CO2

Hydrogen and syngas production from MSW steam gasification with reusing CO2 has been conducted in this study. Two key parameters of gasification temperature and CO2/steam ratio in ranges of 1000–1100 °C and 0.5–3 are taken into consideration. The experiments reveal that increasing CO2/steam ratio in the range of 0.5 and 2.5 increases both H2 and CO molar yield. At the same time, the CO2 conversion efficiency rises. It indicates that Boudouard reaction and water gas reaction proceed independently in the gasification process. With the conditions of CO2/steam ratio = 2.5 and 1000 °C, the CO2 conversion efficiency augments to 50.22% and the maximum H2 molar yield of 18.82 mol/kg-msw can be observed. Under this condition, the highest values of 63.19% for CGE, 0.95 Nm3/kg-msw for gas yield and 12.41 MJ/Nm3 for LHV are obtained. In the steam-only atmosphere, there exist maximum values for H2 molar yield and gas yield as well. The values of both CGE and CCE are lower than those under the steam-CO2 atmosphere. In conclusion, MSW gasification with the addition of CO2 simultaneously has the advantages of waste-to-energy, reusing CO2 and producing hydrogen and syngas.

CFD Modeling of Plasma Gasification Reactor for Municipal Solid Waste

Plasma gasification of municipal solid waste (MSW) is one of the thermochemical technologies that convert waste into energy. The waste is exposed to high temperatures to transform the organic compounds into synthetic gas that could be used as power source, fuel substitute or reactive in the biofuel production. The inorganic compounds are melted completely and an inert environmentally friendly vitrified is obtained, that could be used as building material. Plasma gasifiers have some advantages against traditional gasifiers, for example, high temperature and heating rates lead to compact reactors, improving their performance and conversion rates. Moreover, all the inorganic residues are processed in a melting chamber, leaving a fully vitrified, strong, and resistant to chemical leaching material. On the other hand, this kind of technology has some disadvantages like high initial investment and high electric consumption of plasma torches. All these aspects, as well as others, are being studied at the Instituto Tecnologico de Costa Rica, through the development of computational fluid dynamics (CFD) models, defining a prototype reactor with a capacity of 1–2 metric tons of MSW per day and using DC nontransferred arc thermal plasma torch. Variations on composition within the MSW and process conditions will be studied in order to achieve high efficiency and economic feasibility. The CFD models include mechanical, thermal and chemical aspects of the turbulent reactive flows inside the gasification reactor, with 0-D, 2-D, as well 3-D considerations. The experimental phase of the project will be developed soon, taking into account the CFD models results, to implement the technology and eventually improve it.

Fire, explosion and chemical toxicity hazards of gasification energy from waste

In recent years there have been an increasing number of attempts to develop commercial-scale gasification of municipal solid waste. The results have been widely disappointing, with many high profile and often catastrophic failures. The causes and analyses of these process failures remain inadequately reported in peer-reviewed literature. This paper identifies and discusses these hazards in the context of modern preferences, using case studies and historic antecedents to explore the engineering challenges which underpin loss prevention in the gasification energy from waste sector. It shows that there are many hazards: flammable, toxic, and corrosive gas mixtures, the auto-ignition of stored feedstocks, multiple explosive atmospheres due to both overpressure and underpressure combined with many ignition sources, plus heightened risk at times of start-up, shut-down or during testing. It also identifies how risk is heightened by preferences for novelty, lack of stakeholder understanding, a desire to operate at high outputs, and a reluctance to learn from history.

Thermodynamic analysis of steam gasification of municipal solid waste

ABSTRACTThe main objective of this work is to understand steam gasification performance of municipal solid wastes (MSWs). The thermodynamic analysis was carried out by using seven different kinds of MSWs as the feedstock with the temperature ranging from 773 to 1773 K and steam to MSW ratio ranging from 0.5 to 1.5. It is summarized that temperature and the effective mole ratio of H/C (RH/C) are two key factors, and lower temperature and/or larger RH/C result in a larger mole ratio of H2/CO. The model predictions agree very well with the referenced experimental results, which can predict steam gasification performance of MSWs.

Catalytic activities and resistance to HCl poisoning of Ni-based catalysts during steam reforming of naphthalene

Hydrogen chloride is commonly present in syngas produced from municipal solid waste and biomass gasification. The influence of HCl on the activity of nickel-based catalysts during catalytic naphthalene reforming was investigated. Two synthesized and two commercial catalysts were tested for steam reforming at 790 °C and SV 24,000 h−1. In the absence of HCl, nickel supported on limestone (Ni/Limestone) demonstrated lower naphthalene conversion (∼80%) compared to nickel supported on alumina (Ni/Alumina) and two commercial alumina supported catalysts (∼100%). In the presence of 2000 ppmv HCl, the naphthalene conversion of Ni/Limestone rapidly decreased due to the reaction with HCl and, probably, formation of molten CaCl2 deactivating the supported Ni nanoparticles. These data demonstrate limited applicability of calcium-based nickel catalysts for naphthalene reforming at the studied temperature. The efficiencies of Ni/Alumina and two commercial catalysts were maintained at ∼100% naphthalene conversion. However, HCl concentrations of 500–2000 ppmv had detrimental effect on water-gas shift activity of alumina supported catalysts during naphthalene reforming. The spent alumina supported catalysts were characterized by N2 adsorption, FESEM/EDS, XRD, XPS, TPR and TEM after the reforming in the absence and presence of HCl, and the results suggested that HCl increased nickel sintering in the catalysts causing the loss of water-gas shift activity. The losses of catalytic activity varied among the catalysts and were the lowest for Ni/Alumina, which contained nanosized porous alumina support and had the strongest Ni nanoparticle-support interactions.

Air-steam gasification of municipal solid wastes (MSWs) for hydrogen production

ABSTRACTGasification process can be considered as a partial thermal oxidation, which results in the production of a mixture of useful gases (CO, H2, CH4, and other gaseous hydrocarbons), little quantities of carbon black (char), ash, and several organic impurities (tar). In this study, we introduced an artificial neural network (ANN) model to simulate the influence of operating conditions on the concentration of products during the gasification process of municipal solid wastes (MSW). Results showed when increasing the residence time, more char is gasified, leading to an increase in the greenhouse gas emissions. It is also found that a further increase in the residence time results in a constant rate of products due to the heat and mass transfer limitations.

Life cycle assessment of pyrolysis, gasification and incineration waste-to-energy technologies: Theoretical analysis and case study of commercial plants

Municipal solid waste (MSW) pyrolysis and gasification are in development, stimulated by a more sustainable waste-to-energy (WtE) option. Since comprehensive comparisons of the existing WtE technologies are fairly rare, this study aims to conduct a life cycle assessment (LCA) using two sets of data: theoretical analysis, and case studies of large-scale commercial plants. Seven systems involving thermal conversion (pyrolysis, gasification, incineration) and energy utilization (steam cycle, gas turbine/combined cycle, internal combustion engine) are modeled. Theoretical analysis results show that pyrolysis and gasification, in particular coupled with a gas turbine/combined cycle, have the potential to lessen the environmental loadings. The benefits derive from an improved energy efficiency leading to less fossil-based energy consumption, and the reduced process emissions by syngas combustion. Comparison among the four operating plants (incineration, pyrolysis, gasification, gasification-melting) confirms a preferable performance of the gasification plant attributed to syngas cleaning. The modern incineration is superior over pyrolysis and gasification-melting at present, due to the effectiveness of modern flue gas cleaning, use of combined heat and power (CHP) cycle, and ash recycling. The sensitivity analysis highlights a crucial role of the plant efficiency and pyrolysis char land utilization. The study indicates that the heterogeneity of MSW and syngas purification technologies are the most relevant impediments for the current pyrolysis/gasification-based WtE. Potential development should incorporate into all process aspects to boost the energy efficiency, improve incoming waste quality, and achieve efficient residues management.

Thermodynamic Analysis of Municipal Solid Waste Gasification Under Isothermal and Adiabatic Conditions by a Gibbs Free Energy Minimization Model

An equilibrium model has been developed to predict the composition of a gaseous mixture obtained from the gasification process of the Curitiba City Municipal Solid Waste (MSW). The ultimate analysis of this MSW was also obtained in this study (C = 53.60%, H = 6.74%, N = 1.85%, S = 0.21%, O = 31.03%, Ash = 6.57%), what is necessary when there is lack of experimental information on the elemental composition of the feedstock. Simulations for different gasification scenarios were carried out regarding autothermic and supercritical operations. The developed model was validated with experimental data from literature and was used for optimizing the gasification of MSW according to the amount of air injected in the system, feedstock moisture, temperature and pressure in the gasifier. It was observed that an increase in the pressure of an adiabatic process can increase the lower heat value (LHV) of the gas if the moisture is also increased until an optimum condition. Isothermal processes simulated with supercritical water at high temperatures (higher than that reached in the adiabatic scenarios) resulted in higher LHVs of the gas product.

Evaluating the emissions from the gasification processing of municipal solid waste followed by combustion

In this study, we evaluated the emissions of pollutants generated from the combustion of syngas in the gasification of Municipal Solid Waste (MSW) in Brazil using a mobile grille gasifier fed with domestic waste without any previous separation or grinding. The basic syngas composition (H2, CH4 and CO) was analyzed by gas chromatography and the Lower Calorific Value was calculated, which ranged from 1.9 to 10.2 MJ/kg. In the monitoring of combustion gases (CO2, CO, NO, NO2, SO2 and Total Hydrocarbon Content), values were found for these pollutants that were lower than the values established by the Brazilian legislation, except for SO2. Regarding the determination of the emission of metals, values lower than those permissible in the legislation were found for the most toxic metals grouped as class I (Cd, Hg, Tl). Therefore, it was evident that gasification followed by the combustion of syngas from MSW without prior segregation at source has the advantages of having fewer process steps, allowing the low emission of pollutants into the environment and it avoids that the residues are deposited in landfills, which are generators of leachate and greenhouse gas (methane).

Hydrodynamic Modelling of Municipal Solid Waste Residues in a Pilot Scale Fluidized Bed Reactor

The present study investigates the hydrodynamics and heat transfer behavior of municipal solid waste (MSW) gasification in a pilot scale bubbling fluidized bed reactor. A multiphase 2-D numerical model following an Eulerian-Eulerian approach within the FLUENT framework was implemented. User defined functions (UDFs) were coupled to improve hydrodynamics and heat transfer phenomena, and to minimize deviations between the experimental and numerical results. A grid independence study was accomplished through comparison of the bed volume fraction profiles and by reasoning the grid accuracy and computational cost. The standard deviation concept was used to determine the mixing quality indexes. Simulated results showed that UDFs improvements increased the accuracy of the mathematical model. Smaller size ratio of the MSW-dolomite mixture revealed a more uniform mixing, and larger ratios enhanced segregation. Also, increased superficial gas velocity promoted the solid particles mixing. Heat transfer within the fluidized bed showed strong dependence on the MSW solid particles sizes, with smaller particles revealing a more effective process.

Co-gasification of municipal solid waste with high alkali coal char in a three-stage gasifier

The commercial scale up of municipal solid waste (MSW) gasification system is restricted by the low quality of the syngas, especially due to the low heating value and high contents of tar and HCl. In this study, an innovative three-stage system for co-gasification of MSW with high alkali coal char was developed. The modeled MSW was pyrolyzed in the first stage and the raw syngas was partially oxidized in the second stage and then reduced with high alkali coal char in the final stage to produce high quality syngas. The effects of temperatures and equivalence ratios (ER) have been evaluated experimentally and the concentration of condensable tar species and HCl was examined carefully. In general, the two key pollutants in produced gas could be controlled as low as 11.3 mg/Nm3 (tar content) and 17.6 mg/Nm3 (HCl content). Meanwhile, the level of H2, CO, CH4 in synthesis gas reach a stable high level of 41.9 vol%, 29.3 vol% and 7.49 vol%, respectively, while the lower heating value (LHV) attains 12.2 MJ/Nm3, meeting the intake-gas conditions for internal combustion engines. The experimental results confirm that the highest pyrolysis temperature leads to the maximum gas yield from oxidation stage (i.e., 0.913 Nm3/kg at 650 °C), to be compared with 0.898 Nm3/kg (550 °C) and 0.747 Nm3/kg (450 °C). The lowest gasification temperature (800 °C) is indicated as most favorable for HCl removal from syngas, linked with the advancement of reversible reactions between HCl and Ca-based compounds. H2, tar and LHV all decrease with rising equivalence ratio. In summary, the high-quality syngas can be produced at a steady yield rate of 1.57 Nm3/kg from three-stage gasifier, due to dichlorination and catalytic tar cracking action of high alkali coal char at a low cost.

Simulation analysis of municipal solid waste pyrolysis and gasification based on Aspen plus

To predict and analyze the municipal solid waste (MSW) pyrolysis and gasification process in an updraft fixed bed more veritably and appropriately, numerical modeling based on Gibbs energy minimization was executed using the Aspen plus software. The RYield module was combined with the RGibbs module to describe the pyrolysis section, while the RGibbs module was used for the gasification section individually. The proposed model was used to forecast and analyze the target performance parameters including syngas composition, lower heating value (LHV) and carbon conversion rate under different conditions of the gasification temperatures, and ratios and types of gasifying agents. The results indicate that there is a good agreement between the experimental data and the simulated data obtained using this model. The predicted optimum gasification temperature is approximately 750°C, and the best ratio of water vapor as gasifying agent is around 0.4. The mixture of flue gas and water vapor has an economical and recycled prospect among four commonly used gasifying agents.

Plasma gasification of municipal solid waste with variable content of plastic solid waste for enhanced energy recovery

In this work, a thermochemical investigation of plasma co-gasification of municipal solid waste (MSW) and plastic solid waste (PSW) is conducted. To assess the performance of such thermochemical conversion route, specified waste mixtures were used as a feedstock in an Integrated Plasma Gasification Combined Cycle (IPGCC). The IPGCC plant model is built within Aspen Plus environment. The impact of different plasma forming gas compositions is furthermore investigated using air as the main gas and oxygen or steam as a secondary stream. Performance metrics are calculated, and it is shown that under pure air plasma gas the gasification of solo MSW resulted in higher overall performance. However, as the oxygen ratio in the plasma gas is increased, a steady improvement is observed for all waste mixtures. A plant efficiency of 38% represents the best plant performance, obtained with pure oxygen (ω = 1) as plasma gas and a feedstock consisting of 70% MSW and 30% PSW. A different trend is seen under the increase of steam ratio in the plasma forming gas as the efficiency reaches a maximum that corresponds to a specific fraction of PSW in the waste mixture. The maximum plant efficiency, in this case, is 21.7% at 34% steam ratio (σ) in the plasma gas and at an equal fraction of MSW and PSW in the waste mixture.

2nd law analysis of Portuguese municipal solid waste gasification using CO2/air mixtures

Urbanization, mainly caused by population growth and industrialization, is causing serious environmental problems. Municipal solid waste (MSW) is one of the major challenges facing the world today. In Portugal the growing volume of MSW has become a central problem for municipalities, due to lack of space and the high costs to solve it. Gasification is starting to be considered as a possible alternative when dealing with municipal wastes. However, first is necessary to overcome some concerns related to the process, such as tar mitigation and carbon dioxide emissions.The presented study focuses on a second law analysis conducted on Portuguese MSW gasification using carbon dioxide and air mixtures. To do so, a previously developed numerical model, validated using data from a semi-industrial plant, was used to assess carbon dioxide injection. First, influence of operational conditions on syngas exergy values was studied. Exergy values increased close to 6% when equivalent rate was increased from 0.15 to 0.25, steadily dropping with further increase. On the other hand, exergy values appear to steadily increase with carbon dioxide addition (14% when increased from 0 to 1) and reactor temperature (40% when increased from 700 to 900°C).Then, the influence of temperature and CO2/MSW ratio on exergy efficiency, tar efficiency and carbon dioxide conversion was investigated. Results showed that both parameters have a positive effect on exergy efficiency. Conversely, CO2/MSW ratio and gasification temperature lead to decreases in both tar exergy efficiency and in carbon dioxide.

Thermodynamic Analysis of the Gasification of Municipal Solid Waste

Abstract This work aims to understand the gasification performance of municipal solid waste (MSW) by means of thermodynamic analysis. Thermodynamic analysis is based on the assumption that the gasification reactions take place at the thermodynamic equilibrium condition, without regard to the reactor and process characteristics. First, model components of MSW including food, green wastes, paper, textiles, rubber, chlorine-free plastic, and polyvinyl chloride were chosen as the feedstock of a steam gasification process, with the steam temperature ranging from 973 K to 2273 K and the steam-to-MSW ratio (STMR) ranging from 1 to 5. It was found that the effect of the STMR on the gasification performance was almost the same as that of the steam temperature. All the differences among the seven types of MSW were caused by the variation of their compositions. Next, the gasification of actual MSW was analyzed using this thermodynamic equilibrium model. It was possible to count the inorganic components of actual MSW as silicon dioxide or aluminum oxide for the purpose of simplification, due to the fact that the inorganic components mainly affected the reactor temperature. A detailed comparison was made of the composition of the gaseous products obtained using steam, hydrogen, and air gasifying agents to provide basic knowledge regarding the appropriate choice of gasifying agent in MSW treatment upon demand.