Gasification technology is often seen as a synonym for the clean and efficient processing of solid fuels into combustible gas containing mainly carbon monoxide and hydrogen, the two basic components of synthesis gas. First and foremost, the facts that gas may be cleaned and that a mixture with any composition may be prepared in a relatively easy and inexpensive manner influence the possibility of using gas produced in the energy and chemical industries. In the energy industry, gas may be used directly to generate heat and electricity in the systems of a steam power plant or in combined cycle systems. It is also possible to effectively separate CO2 from the system. However, in chemistry, synthesis gas may be used to produce hydrogen, methanol, synthetic gasolines, and other chemical products. The raw material for gasification is full-quality pulverized coal, but a possibility of processing low-quality sludges, combustible fractions separated from municipal waste as well as industrial waste also exists. Despite such a wide application of technology and undoubted advantages thereof, making investment decisions is still subject to high uncertainty. The paper presents the main technological applications of gasification and analyzes the economic effectiveness thereof. In this context, significant challanges for the industrial implementation of this technology are discussed
This publication presents an assessment of the economic efficiency of a hypothetical installation for the gasification of the municipal and industrial waste for the production of syngas used subsequently for the production of energy or chemical products. The first part of the work presents an example of a technological system for the energo-chemical processing of coal mud and municipal waste, based on the gasification process using a fluidized bed reactor. A hypothetical installation consists of two main blocks: a fuel preparation unit and a gasification unit. In the fuel preparation installation, reception operations take place, storage, and then grinding, mixing, drying and transporting fuel to the gasification unit. In the gasification installation, fuel gasification, oxygen production, cooling and purification of raw process gas and ash treatment are carried out. The following key assumptions regarding the gasification process, as well as the capital expenditures and operating costs related to the process, were estimated. Consequently, based on the method of discounted cash flows, the unit cost of generating energy contained in the synthesis gas (cost of energy, COE) was determined and the results were interpreted. In order to obtain an acceptable efficiency of the gasification process for waste fuels for the production of alternative fuel (process gas), it is necessary to supplement the mixture of waste coal and coal mud with the RDF. In this case, the unit cost of fuel measured by the PLN/GJ index is lower than in the case of hard coal and comparable with brown coal. The use of coal mud for the production of process gas in an economically efficient way is possible only in the case of changes in the legal system allowing for charging fees for the utilization of industrial waste – coal mud.
A modified approach to equilibrium modelling of coal gasification is presented, based on global thermodynamic analysis of both homogeneous and heterogeneous reactions occurring during a gasification process conducted in a circulating fluid bed reactor. The model is based on large-scale experiments (ca. 200 kg/h) with air used as a gasification agent and introduces empirical modifications governing the quasi-equilibrium state of two reactions: water-gas shift and Boudouard reaction. The model predicts the formation of the eight key gaseous species: CO, CO2, H2O, H2, H2S, N2, COS and CH4, volatile hydrocarbons represented by propane and benzene, tar represented by naphthalene, and char containing the five elements C, H, O, N, S and inorganic matter.
The study focused on environmental evaluation of the disposed wooden railway sleeper gasiﬁcation system used for electrical energy production. The aforementioned base technology was referred to the system producing electricity from disposed wooden railway sleepers through combustion. The evaluation was carried out using the LCA technique. The results show that in scope of impact on human health and ecosystems, the technology based on sleeper gasiﬁcation is friendlier to the environment than the alternative technology. The technology of reference produces a lower environmental burden in scope of depletion of non-renewable natural resources. In comparison of the base technology (gasiﬁcation) and the alternative technology (combustion), the end environmental effect shows that in scope of the analysis the base technology, i.e. the technology involving gasiﬁcation of disposed railway sleepers, is more friendly to the environment.
The aim of this study was to compare and analyze the gasification process of beech wood. The experimental investigation was conducted inside a gasifier, which can be operated in downdraft and updraft gasification system. The most important operating parameter studied in this paper was the influence of the amount of supply air on the temperature distribution, biomass consumption and syngas calorific value. The results show that the amount of air significantly influences the temperature in the combustion zone for the downdraft gasification process, where temperature differences reached more than 150 ◦C.The increased amount of air supplied to the gasifier caused an increase in fuel consumption for both experimental setups. Experimental results regarding equivalence ratio show that for value below 0.2, the updraft gasification is characterized by a higher calorific value of producer gas, while for about 0.22 a similar calorific value (6.5 MJ/Nm3) for both gasification configurations was obtained. Above this value, an increase in equivalence ratio causes a decrease in the calorific value of gas for downdraft and updraft gasifiers.
The research was aimed at examining the impact of the petrographic composition of coal from the Janina mine on the gasification process and petrographic composition of the resulting char. The coal was subjected to fluidized bed gasification at a temperature below 1000°C in oxygen and CO2 atmosphere. The rank of coal is borderline subbituminous to bituminous coal. The petrographic composition is as follows: macerals from the vitrinite (61.0% vol.); liptinite (4.8% vol.) and inertinite groups (29.0% vol.). The petrofactor in coal from the Janina deposit is 6.9. The high content of macerals of the inertinite group, which can be considered inert during the gasification, naturally affects the process. The content of non-reactive macerals is around 27% vol. The petrographic analysis of char was carried out based on the classification of International Committee for Coal and Organic Petrology. Both inertoid (34.7% vol.) and crassinetwork (25.1% vol.) have a dominant share in chars resulting from the above-mentioned process. In addition, the examined char contained 3.1% vol. of mineroids and 4.3% vol. of fusinoids and solids. The calculated aromaticity factor increases from 0.75 in coal to 0.98 in char. The carbon conversion is 30.3%. Approximately 40% vol. of the low porosity components in the residues after the gasification process indicate a low degree of carbon conversion. The ash content in coal amounted to 13.8% and increased to 24.10% in char. Based on the petrographic composition of the starting coal and the degree of conversion of macerals in the char, it can be stated that the coal from the Janina deposit is moderately suitable for the gasification process.
Anaerobic digestion residue represents a nutrient rich resource which, if applied back on land, can reduce the use of mineral fertilizers and improve soil fertility. However, dewatering and further thermal processing of digestate may be recommended in certain situations. Limited applicability of digestate as fertilizer may appear, especially in winter, during the vegetation period or in areas where advanced eutrophication of arable land and water bodies is developing. The use of digestate may be also governed by different laws depending on whether it is treated as fertilizer, sewage sludge or waste. The aim of this paper is to present the effects of thermal treatment of solid fraction of digestate by drying followed by pyrolysis and gasification. Pyrolysis was carried out at the temperature of about 500°C. During this process the composition of flammable gases was checked and their calorific value was assessed. Then, a comparative analysis of energy parameters of the digestate and the carbonizate was performed. Gasification of digestate was carried out at the temperature of about 850°C with use of CO2 as the gasifi cation agent. Gasification produced gas with higher calorific value than pyrolysis, but carbonizate from pyrolysis had good properties to be used as a solid fuel
One of the methods of obtaining energy from renewable sources is the technology of indirect cofiring of biomass. It consists in the gasification of secondary fuel and combustion of the generated gas in the boiler together with its primary fuel. The paper presents a thermodynamic analysis of the use of the boiler flue gases as the converting medium in the process of indirect co-firing - a technology which is being developed at the Institute of Power Engineering and Turbomachinery of the Silesian University of Technology. The basis of the analysis are the data resulting from variant calculations conducted with the use of the Gaseq program. The calculations were made for various compositions of gasified fuel and the converting medium, variable fuel/oxidiser ratios and variable gasification temperatures. As a result, the equilibrium composition and the calorific value of the generated gas were obtained. The main optimisation objective adopted here was the nondimensional efficiency coefficient, which is the ratio of the chemical energy of products to the chemical energy of the process reactants.
Thermodynamic equilibrium-based models of gasification process are relatively simple and widely used to predict producer gas characteristics in performance studies of energy conversion plants. However, if an unconstrained calculation of equilibrium is performed, the estimations of product gas yield and heating value are too optimistic. Therefore, reasonable assumptions have to be made in order to correct the results. This paper proposes a model of the process that can be used in case of deficiency of information and unavailability of experimental data. The model is based on free energy minimization, material and energy balances of a single zone reactor. The constraint quasi-equilibrium calculations are made using approximated amounts of non-equilibrium products, i.e. solid char, tar, CH4 and C2H4. The yields of these products are attributed to fuel characteristics and estimated using experimental results published in the literature. A genetic algorithm optimization technique is applied to find unknown parameters of the model that lead to the best match between modelled and experimental characteristics of the product gas. Finally, generic correlations are proposed and quality of modelling results is assessed in the aspect of its usefulness for performance studies of power generation plants.
The motivation of this work was to define the reburning potential of sewage sludge gasification gas (syngas). Numerical simulation of co-combustion process of syngas in hard coal-fired boiler has been done. All the calculations were performed using the Chemkin program. Plug-Flow Reactor model was used. The calculations were modelled using GRI-Mech 2.11 mechanism. The highest NO conversions are obtained at the temperature of about 1000-1200 K. The highest reduction efficiency was achieved for the molar flow ratio of syngas equal to 15%. The combustion of hard coal with sewage sludge - derived syngas reduces NO emissions and the amount of coal needed to produce electricity and heat. Advanced reburning, which is a more complicated process gives efficiency of up to 80%. The calculations show that the analyzed syngas can yield better results.
The subject of the CFD analysis presented in this paper is the process of biomass indirect co-firing carried out in a system composed of a stoker-fired furnace coupled with a gasification reactor. The installation is characterised by its compact structure, which makes it possible to minimise heat losses to the environment and enhance the physical enthalpy of the oxidising agent – flue gases – having a favourable chemical composition with oxygen and water vapour. The test results provided tools for modelling of biomass thermal processing using a non-standard oxidiser in the form of flue gases. The obtained models were used to optimise the indirect co-combustion process to reduce emissions. An overall effect of co-combustion of gas from biomass gasification in the stoker furnace is the substantial reduction in NO emissions by about 22%.
In this study, non-sintered ceramsite was prepared using coal gasiﬁcation coarse slag obtained from a methanol plant. The basic performance and heavy metal leaching toxicity were analyzed. The results showed that seven out of nine non-sintered ceramsite groups were in accordance with the national standard of compressive strength (5 MPa), while only three groups met the national standard of water absorption index of less than 22%. The heavy metal concentrations in these three groups were found to be lower than that speciﬁed in National Class IV of surface water environment standards. The concentration of Cr was found to be 16.45 μg/L, which represents only 1% of the IV standard. The optimum mixing ratio, which showed high compressive strength (6.76 MPa) and low water absorption (20.12%), was found to be 73% coal gasiﬁcation coarse slag, 15% cement, and 12% quartz sand. The characterization using Fourier transform infrared spectroscopy showed that the formation of gelatin in ceramsite enhances the performance of the ceramsite base and increases the immobilization of heavy metal. The study proved that the preparation of non-sintered ceramsite using coal gasiﬁcation coarse slag reduces its environmental risk and achieves efﬁcient utilization of the slag. Therefore, it can be concluded that it is a feasible and environmental friendly method for the disposal of coal slag.
The aim of the paper is the petrographic characterization of coal from the Wieczorek mine and the residues after its gasification. The coal was subjected to gasification in a fluidized bed reactor at a temperature of about 900°C and in an atmosphere of oxygen and CO2. The petrographic, proximate, and ultimate analysis of coal and char was performed. The petrographic composition of bituminous coal is dominated by macerals of the vitrinite group (55% by volume); macerals of inertinite and liptinite groups account for 23% and 16.0%, respectively. In the examined char, the dominant component is inertoid (41% vol.). Mixed dense and mixed porous account for 10.9% and 13.5% vol., respectively. In addition, the examined char also contained unreacted particles such as fusinoids, solids (11.3% vol.), and mineroids (5.1% vol.). The char contains around 65% vol. of low porosity components, which indicates a low degree of carbon conversion and is associated with a low gasification temperature. The char was burned and the resulting bottom and fly ashes were subjected to petrographic analysis. Their composition was compared with the composition of ashes from the combustion of bituminous coal from the Wieczorek mine. Bottom ashes resulting from the combustion of bituminous coal and char did not differ significantly in the petrographic composition. The dominant component was mineroid, which accounted for over 80% vol. When it comes to fly ash, a larger amount of particles with high porosity is observed in fly ash from bituminous coal combustion.
Experimental investigations and numerical simulations have been conducted in this study to derive and test the values of kinetic parameters describing oxidation and gasification reactions between char carbon and O2 and CO2 occurring at standard air and oxy-fuel combustion conditions. Experiments were carried out in an electrically heated drop-tube at heating rates comparable to fullscale pulverized fuel combustion chambers. Values of the kinetic parameters, obtained by minimization of the difference between the experimental and modeled values of char burnout, have been derived and CFD simulations reproducing the experimental conditions of the drop tube furnace confirmed proper agreement between numerical and experimental char burnout.
The porous structure of cylindrical and ring-shaped char material was developed by partial steam gasification. Micropore and mesopore structures of active carbons with various forms of burn-off were evaluated by nitrogen adsorption/desorption isotherms. Parameters of the Dubinin- Radushkevich equation were calculated as well as the micropore size distribution by the Horvath- Kawazoe method. The results of textural investigations showed that more uniform micropore structure and better mechanical properties were found for ring-shaped active carbons.