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TRABAJO FIN DE MASTER Plasma gasification: state of the art, modeling and applications. Autor Adrien DUFOURNY Director Sergio Usón Gil Escuela de Ingeniería y Arquitectura de Zaragoza (EINA) 2013 2 AGRADECIMIENTOS En primer lugar deseo expresar mi más sincero agradecimiento al director de este trabajo de fin de máster, Sergio Usón Gil, por su orientación, sus inestimables sugerencias, su motivación en este proyecto, por la ayuda recibida y su paciencia. Su apoyo incondicional, sus palabras de ánimo y su total implicación han sido esenciales para concluir este trabajo. En segundo lugar, agradecer también a mis padres y a mi familia por su ayuda y por haberme apoyado siempre. Me han permitido venir a España para realizar este master. Para finalizar, a mis amigos, mis compañeros de piso y a mis compañeros del máster, con los que he compartido tantos momentos a lo largo de este año, y que siempre estuvieron dándome ánimos cuando más lo necesitaba. GREETINGS First I wish to express my sincere thanks to the director of this work, Sergio Usón Gil, for his guidance, his invaluable suggestions, his motivation in this project, for his help and patience. His unconditional support, words of encouragement and total involvement were essential to complete this work. I also thank my parents and my family for their help and for having always supported me. Thanks ti them I could come to Spain to complete this master. Finally, my friends, my roommates and my colleagues of course, with whom I have shared many times throughout this year, and who were always encouraging me when I needed it. 3 RESUMEN Gasificación con plasma: estado del arte, modelización y aplicaciones. La realización de este proyecto tiene como objetivo la modelización de un sistema de gasificación con plasma y su integración en un sistema de producción de electricidad. Este dispositivo consiste en un gasificador de tipo “downdraft” acoplado con una antorcha de plasma. Esta antorcha puede alcanzar temperaturas muy altas, y tiene la ventaja de ser una fuente de calor independiente que no se ve afectada por las características de la materia prima. En estas condiciones, se evita la producción de alquitranes y otros compuestos indeseables en el gas de síntesis. Por otra parte, la fracción inorgánica de la carga de alimentación se transforma en escoria vitrificada que se puede utilizar en la construcción. Este tipo de tecnología se plantea normalmente para la eliminación de residuos, especialmente los considerados como peligrosos; en estos casos, el gas de síntesis producido se considera en muchos casos un beneficio adicional más que el objetivo principal del proyecto. Este trabajo se plantea en el aprovechamiento energético. Debido a los diversos parámetros de operación con los que se puede actuar (potencia del plasma y agentes gasificantes), el rendimiento del proceso puede variar ampliamente. Por esto, en este trabajo se aborda la modelización del proceso para su optimización, y su integración con el sistema posterior de transformación del gas para producir electricidad. La metodología seguida ha consistido en revisiones bibliográficas, simulación de los procesos en el programa Equation Engineering Solver (EES) y en la realización de los análisis paramétricos. 4 ABSTRACT Plasma gasification: state of the art, modeling and applications. The objective of this project is to model a plasma gasification system and its integration into a system of electricity production. This device consists of a «downdraft" gasifier coupled with a plasma torch . This torch can reach very high temperatures, and has the advantage of being an independent source of heat that is not affected by the characteristics of the raw material. Under these conditions, the production of tars and other undesirable compounds in the synthesis gas is avoided. Moreover, the inorganic portion of the feedstock becomes vitrified slag which can be used as construction material. This technology is normally poses for waste disposal, especially those considered hazardous in these cases, the synthesis gas produced is often considered an extra rather than the main objective of the project. This work presents an analysis from the energetic. Due to the various operating parameters with which to act (plasma power and gasifying agents), the efficiency of the process can vary widely. Therefore, in this work process modeling for optimization and integration in a system for electricity generation is addressed. The methodology followed consisted of literature reviews, process simulations with the software Engineering Equation Solver (EES ) and implementation of the parametric analysis. 5 TABLE OF CONTENTS 1. INTRODUCTION ............................................................................................................................... 8 a. Plasma gasification ...................................................................................................................... 9 b. State of art ................................................................................................................................. 10 c. Scope and objectives ................................................................................................................. 10 2. MODEL DEVELOPMENT ................................................................................................................. 11 a. Equilibrium models .................................................................................................................... 11 b. The model .................................................................................................................................. 12 i. Mass balance ......................................................................................................................... 13 ii. Thermodynamic equilibrium ................................................................................................. 13 iii. Energy balance ...................................................................................................................... 14 c. Energy and exergy efficiency ..................................................................................................... 15 i. First law efficiency ................................................................................................................. 15 ii. Second law efficiency, exergy analysis .................................................................................. 16 3. GASIFICATION SYSTEM .................................................................................................................. 18 a. Model validation........................................................................................................................ 18 i. Equilibrium constants ............................................................................................................ 18 ii. Syngas composition ............................................................................................................... 18 b. Results ....................................................................................................................................... 19 i. Effect of moisture content .................................................................................................... 20 ii. Effect of oxygen ratio ............................................................................................................ 21 iii. Effect of temperature ............................................................................................................ 23 4. Electricity production system ........................................................................................................ 25 a. Plant description........................................................................................................................ 25 b. Energetic analysis ...................................................................................................................... 26 CONCLUSION ......................................................................................................................................... 28 REFERENCES .......................................................................................................................................... 29 ANNEXE 1............................................................................................................................................... 33 ANNEXE 2............................................................................................................................................... 40 ANNEXE 3............................................................................................................................................... 46 ANNEXE 4............................................................................................................................................... 61 6 TABLE OF ILLUSTRATIONS Table 1 : The value of hf° (kJ/mol) and coefficients of the empirical equation for ∆g°f,T (kJ/mol)........ 14 Table 2 : Constant pressure specific heat ideal gas relation ................................................................. 15 Table 3 : Lower Heating Value for ideal gas .......................................................................................... 15 Table 4 : Standard chemical exergy of syngas compounds [10] ........................................................... 17 Table 5 : Equilibrium constants calculation ........................................................................................... 18 Table 6 : Prediction results and comparison with experimental value ................................................. 19 Table 7 : Feedstock ultimate analysis .................................................................................................... 20 Table 8: Power plant design data .......................................................................................................... 26 Table 9 : Plasma gasifiers manufactured by Alter NRG ......................................................................... 33 Table 10 : Energy output from plasma gasification facilities manufactured by Alter NRG. .................. 34 Table 11 : Plasma gasification facilities built by Alter NRG ................................................................... 35 Table 12 : Characteristics of PEAT’s plant ............................................................................................. 37 Table 13: Efficiency of plasma and conventional gasification ............................................................... 41 Figure 1 : Different ways of using syngas ................................................................................................ 8 Figure 2 : Plasma gasifier (source : www.alternrg.com) ......................................................................... 9 Figure 3 : Effect of moisture content on syngas composition ............................................................... 20 Figure 4 : Effect of moisture content on gasifier performance ............................................................. 21 Figure 5 : Effect of oxygen ratio on gasifier performance ..................................................................... 22 Figure 6 : Effect of oxygen ratio on gasifier performance ..................................................................... 22 Figure 7 : Effect of temperature on gasifier performance .................................................................... 23 Figure 8 : Effect of temperature on gasifier performance .................................................................... 24 Figure 9 : Physical structure of the analyzed plant ............................................................................... 25 Figure 10 : Overall system performance ............................................................................................... 27 Figure 11 : Concept of plasma gasification............................................................................................ 34 Figure 12 : Plasma gasification process developed by Plasco Energy Group ........................................ 36 Figure 13 : Europlasma auto-thermal gasifier ....................................................................................... 37 Figure 14 : Europlasma auto-thermal gasifier ....................................................................................... 38 Figure 15 : Gasplasmsa process by Advanced Plasma Power ............................................................... 39 Figure 16 : Energy flows in a plasma gasification – engine system ....................................................... 40 Figure 17 : Integrated plasma gasification combined cycle .................................................................. 41 Figure 18 : Integrated plasma gasification/fuel cell plant IPGFC .......................................................... 44 7 REPORT 8 1. INTRODUCTION The rapid increase in worldwide energy demand facing the decline of fossil resources and the impact of their energy use on the environment requires the use of renewable energies. Energy and environment are currently one of the most important world’s preoccupation. Nowadays, it is known that the world energy consumption is dominated by various types of fossil fuels. The high utilization of these fuels strongly accelerates the depletion of world energy resources and causes environmental damage in terms of global warming. Recently, there have been several attempts to reduce this consumption and to preserve our environment. It is known that the development of clean alternatives to replace fossil fuels is one of the main ways to achieve this goal. Gasification is one of these alternatives. It is an industrial process that uses heat in an oxygen‐starved and pressurized environment to break down carbon‐based materials into fuel gases (syngas). There is a huge variety of gasification equipment and techniques which enables the use of a wide variety of materials. Any material made from carbon is suitable for gasification, and the most common used materials are coal and biomass, such as wood or agricultural waste. The produced syngas can be used in many ways, as illustrated in Figure 1. Figure 1 : Different ways of using syngas 9 a. Plasma gasification Plasma is regarded as the fourth state of matter. It is an ionized gas produced by electric discharges. Plasma gasification refers to a range of techniques that use plasma torches or plasma arcs to generate extreme temperatures that are particularly effective for highly efficient gasification. A plasma torch is a tubular device which possesses two electrodes that can produce that arc. When electricity is fed, an arc is created and the electricity is converted into heat through resistance of the plasma. This torch can reach very high temperatures (up to 15000 °C) and has the advantage of being an independent heat source not affected by the characteristics of the feedstock. Plasma torches can destroy any kind of material with the exception of nuclear waste, since radioactive materials are not broken down by heat. Due to the high operating temperatures, plasma is very effective in vaporizing very difficult materials with high moisture content, such as municipal solid waste (MSW). In these conditions, the organic and carbonaceous parts of the materials vaporize into gas very efficiently and the production of tars and other undesirable compounds of the syngas are avoided. Furthermore, the inorganic fraction of the feedstock is transformed into vitrified slag that can be used in construction [1]. Normal gasifiers are really “partial combustors”, and a substantial portion has to be combusted just to support the reaction. However, plasma gasification uses an external energy source, which enables a very little combustion of the waste material. As a result, most of the carbon is converted into fuel gas [2]. It should be added that in the process toxins and organic poisons are destroyed. Plasma technology has been used for many years to destroy toxic wastes but it is only recently that these processes have been optimized for energy capture and fuel production. Figure 2 : Plasma gasifier (source : www.alternrg.com) 16 Where nsyngas is the number of kmol of syngas produced for 1 kmol of fuel, LHVsyngas and LHVfuel are the Lower Heating Value of the syngas and the fuel respectively, EElec is the electricity energy needed for the gasification and ηtorch is the average plasma torch efficiency taken equal to 0,86. Due to the fact that the sensible heat of the produced syngas will be used in the process of electricity generation, the second law efficiency seems to be a more appropriate tool to analyze the efficiency of the gasifier. ii. Second law efficiency, exergy analysis Exergy is defined as a measure of the actual potential of a system to perform work. In real processes, exergy is not conserved because of the irreversible increase of entropy; therefore it is more suitable for analyzing energy conversion processes. The chemical exergy efficiency is defined as the ratio of the chemical exergies of the produced syngas, the chemical exergies of the fuel and the electricity needed for gasification. It is expressed as follows per 1 kmol of fuel: ⁄ (22) Where nsyngas is the number of kmol of syngas produced for 1 kmol of fuel, ech,syngas and ech,fuel are the chemical exergies of the syngas and the fuel respectively. In the case of the exergy efficiency, the sensible heat of the produced gas is taken into account as the physical exergy of the produced gas. At higher gasification temperatures, the portion of the physical exergy is considerable. It is expressed as follows per 1 kmol of fuel: ⁄ (23) Where eph,syngas is the chemical exergy of the syngas.  Chemical exergy calculation The chemical exergy of the produced syngas is determined by the composition and the concentration of the components in the mixture. Kotas [10] suggested that the specific chemical exergy of an ideal gas mixture, in kJ/kmol could be calculated by : ∑ ∑ (24) Where xi is the mol fraction of each compound i and ech,i is the standard chemical exergy of each compound i, in kJ/kmol. The standard chemical exergy of each compound i is presented in the Table 4 17 Substance ech,i (kJ/kmol) H2 238490 CO 275430 CO2 20140 H2O(g) 11710 CH4 836510 N2 720 Table 4 : Standard chemical exergy of syngas compounds [10] The chemical exergy of the solid fuel material can be calculed with two statistical correlations. The first one is the one described by Kotas [10] and the second one described by Prins et al [4], expressed in kJ/kg : (25) Where (valid for Or (valid for And mw is the mass fraction of moisture in the fuel, hfg is the enthalpy of vaporization of water expressed in kJ/kg and C,H,O,N the represented weight fractions of hydrogen, carbon, oxygen, nitrogen, respectively in the fuel.  Physical exergy calculation The physical exergy of each gas species can be calculated by : (26] Where h and s are the enthalpy and entropy at any given state and h0 and s0 are the enthalpy at the reference state. Finally the physical exergy of the mixture can be calculated as follows: ∑ (27) 18 3. GASIFICATION SYSTEM In this section, the results of the presented model for produced syngas composition are first compared to data taken from literature and then the results of the influence of different process parameters (moisture content, temperature of gasification, ratio of oxygen in the process) on the heating value of the produced syngas and on the energetic and exergetic efficiency of the gasifier are presented. a. Model validation i. Equilibrium constants Mountouris et al. [2] presented in his work the calculation of the equilibrium constants of the two gasification reactions using two thermodynamic databases, the Chemical Properties Handbook by Professor Carl L. Yaws of Lamar University, Texas, [11] and the DIPPR database (Design Institute for Physical Properties) [12]. The values of the equilibrium constant, depending on gasification temperature, calculated by the present model are shown in Table 5 and compared to the values determined by Mountouris et al. T(K) CH4 + H2O = CO + 3H2 CO + H2O = CO2 + H2 Model Handbook DIPPR Model Handbook DIPPR 298,15 1,27E-25 1,24E-25 1,20E-25 104257 98460 104602 500 8,67E-11 8,50E-11 8,26E-11 139,9 130,1 138,1 700 2,64E-04 2,62E-04 2,54E-04 9,847 8,885 9,457 900 1,279 1,28 1,236 2,497 2,152 2,307 1100 305,5 305 295 1,124 0,916 0,989 1273,15 8924 8857 8585 0,725 0,557 0,607 1500 231432 226018 220998 0,5076 0,355 0,394 Table 5 : Equilibrium constants calculation The values calculated with the model are really close to the ones extracted from Mountouris et al [2]. The values tend to diverge for high temperature but are still acceptable in the range of our study (until 1500 K). This is demonstrated below with the comparison of the syngas composition to theoretical and experimental data. ii. Syngas composition The model developed in this work was tested by comparing the calculation results with data from literature, the GasifEq Model developed by Mountouris et al [2], the syngas Model and the ciclo temporal model developed by Altafani et al [7] and experimental value presented by the same authors. 19 The comparison was done by setting the temperature at 1073K for gasification of wood material given by the formula CH1,44O0,66 with 10% moisture content. Table 6 shows the comparisons of results between the model developed and the data. Gaseous products % v/v dry basis Model GasifEq model SynGas model (Altafini & al) Cycle -Tempo model (Altafini & al) Experimental (Altafini & al) H2 21,65 22,10 23,28 19,80 20,06 21,40 14,00 CO 24,06 24,60 26,04 23,45 19,70 23,00 20,14 CO2 9,66 9,41 8,74 9,16 10,15 9,74 12,06 CH4 0,02 0,02 0,03 0,01 0,00 0,01 2,31 N2 44,61 43,87 41,91 47,57 50,10 45,31 50,79 Sum 100,00 100,00 100,00 99,99 100,01 99,46 99,30 Air/waste ratio 2,01 1,96 1,83 2,01 1,96 1,96 1,83 Table 6 : Prediction results and comparison with experimental value The model gives results in general agreement with the other models, except a higher production of H2 which could be explained by the difference in the calculated equilibrium constants as shown in the upper part. This difference is not significant for our analysis. The results agree also with the experimental data. The main difference is observed for the H2 and CH4 production. The model predicted higher amounts of H2, but the predicted amounts of CH4 are lower. A possible explanation for this is that the state of equilibrium was not met during the experiment, like it is supposed in the model. The slight differences in other compounds may be attributed to the simplifying assumptions of the model such as: considering all gases to be ideal, and assuming no residue in the gasification process. b. Results Simulation results are presented here: in a first part the molar syngas composition in function of the operating parameters and in a second part the power of the syngas (calculated by multiplying its Lower Heating Value by its exit stream), the power of consumption of the plasma torch, the energy efficiency and the chemical and total exergy efficiencies, as defined above. The fuel chosen for this study is Municipal Solid Waste which ultimate analysis is shown in Table 7. The operating parameters are the moisture content of the fuel, the temperature of the gasification and the molar ratio of oxygen to fuel use for the gasification. 20 Composition (wt%, dry) C 57,8 H 7,6 O 33,6 N 1 HHV (MJ/kg) 25,1 Table 7 : Feedstock ultimate analysis i. Effect of moisture content To study the effect of the moisture content in the fuel, the amount of oxygen was fixed at 0,3 mol/mol dry daf fuel which corresponds to an air/fuel ratio of 2 (kg/kg dry daf fuel) and a temperature of 1273 K. The flow of fuel is 0,5 kg/s. The results are illustrated in Figure 3 and Figure 4. Figure 3 : Effect of moisture content on syngas composition If the fuel moisture content varies from 0% to 60 %, the percentage of CO, CO2, H2, N2 and H2O in the syngas changes from 33,64% to 11,93%, 0,60% to 9,58%, 26,18% to 25,66%, 38,91% to 24,43 and 0,65% to 28,41% respectively. The percentage of CH4 in the gas can be neglected. It is shown that an increase of moisture content contributes to gradually increase the concentration in H2 in the syngas, whereas it can be observed that it leads to a decrease of the CO content. 0,00% 5,00% 10,00% 15,00% 20,00% 25,00% 30,00% 35,00% 40,00% 45,00% 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 Gas composition (mol/mol %) Moisture content (w/w) CO CO2 H2 N2 H2O 21 Figure 4 : Effect of moisture content on gasifier performance If the fuel moisture content varies from 0% to 60 %, the Lower Heating Value power of the syngas changes from 11140 kW to 10718 kW. The plasma torch consumption changes from 1822 kW to 3266 kW. The 1st, 2nd and 2nd chemical laws of efficiency change respectively from 82,30% to 71,55%, 84,28% to 77,11% and 77,5% to 66,36 %. The increase in the plasma torch consumption can be explained by the augmentation of the necessary heat to gasify the fuel with higher moisture content, whereas the slight decrease of the syngas heating value can be explained by the presence of highest H2O concentration in its composition. The decrease of the different efficiency is explained by the augmentation of the consumption of the plasma torch. It has to be noted that if the efficiency of the 2nd law is higher than the efficiency of the 1st law, it is because it takes into account the specific heat of the syngas. In the same way, the 2nd law efficiency decrease is slower than the 1st law. ii. Effect of oxygen ratio To study the effect of the oxygen ratio, the moisture content of the fuel was fixed at 30%, the amount of oxygen ratio was fixed at 0,3 and the temperature at 1273 K. The flow of fuel is 0,5 kg/s. The results are illustrated in Figure 5 and in Figure 6. 0,5 0,55 0,6 0,65 0,7 0,75 0,8 0,85 0,9 0 2000 4000 6000 8000 10000 12000 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 Energy (kW) Moisture content (w/w) Plasma torch LHV 1st law effciciency 2nd law efficiency 2nd law efficiency, chemical 22 Figure 5 : Effect of oxygen ratio on gasifier performance If the oxygen ratio varies from 0,1 to 0,5 %, the percentage of CO, CO2, H2, N2 and H2O in the syngas changes from 35,76% to 15,24%, 0,18% to 8,76%, 44,89% to 17,11%, 14,42% to 45,32 and 3,12% to 13,57% respectively. The percentage of CH4 in the gas is negligible. In that case, the increase of N2 concentration in the syngas is due to the augmentation of air used for the gasification. It leads to a dilution of the syngas, which is not beneficial for the process. Figure 6 : Effect of oxygen ratio on gasifier performance If the oxygen ratio varies from 0,1 to 0,5 %, the Lower Heating Value power of the syngas changes from 113437 kW to 8470 kW. The plasma torch consumption changes from 4282 kW to 68,9 kW. The 1st, 2nd and 2nd chemical law of efficiency change respectively from 84,01% to 71,89%, 83,18% to 78,26% and 77,72% to 66,19 %. 0,00% 5,00% 10,00% 15,00% 20,00% 25,00% 30,00% 35,00% 40,00% 45,00% 50,00% 0,1 0,2 0,3 0,4 0,5 0,6 Gas composition (mol/mol %) Oxygen amount (mol/mol daf fuel) CO CO2 H2 N2 H2O 0,5 0,55 0,6 0,65 0,7 0,75 0,8 0,85 0,9 0 2000 4000 6000 8000 10000 12000 14000 16000 0,1 0,3 0,5 Energy (kW) Oxygen amount (mol/mol daf fuel) Plasma torch LHV 1st law effciency 2nd law efficiency 23 The decrease of the syngas heating value can be explained by the dilution of the gas in the N2 concentration in its composition. The decrease of the different efficiency is explained by the decrease of the Lower Heating value of the gas. iii. Effect of temperature To study the effect of the temperature, the amount of oxygen was fixed at 0,3 mol/mol dry daf fuel and the amount of oxygen ratio was fixed at 0,3. The flow of fuel is 0,5 kg/s. The results are illustrated in Figure 7 and Figure 8. Figure 7 : Effect of temperature on gasifier performance If the temperature varies from 1073 K to 1573 K, the percentage of CO, CO2, H2, N2 and H2O in the syngas changes from 21,82% to 24,78%, 7,45% to 4,51%, 29,24% to 26,41%, 33,30% to 32,27% and 8,15% to 11,03% respectively. The percentage of CH4 in the gas is negligible. It is shown that an increase of the gasification temperature contributes to increase the concentration in CO in the syngas, whereas it can be observed that it leads to a decrease of the H2 content. 0,00% 5,00% 10,00% 15,00% 20,00% 25,00% 30,00% 35,00% 1000 1100 1200 1300 1400 1500 1600 1700 Gas composition (mol/mol %) Temperature (K) CO CO2 H2 N2 H2O 24 Figure 8 : Effect of temperature on gasifier performance If the temperature varies from 1073 K to 1573 K, the Lower Heating Value power of the syngas changes from 10900 kW to 11006 kW. The plasma torch consumption changes from 1449 kW to 3617 kW. The 1st, 2nd and 2nd chemical law of efficiency change from 82,81% to 71,79%, 81,62% to 79,65% and 76,13% to 66,35 %. The increase in the plasma torch consumption is due to the augmentation of the temperature. The small increase of the syngas heating value can be explained by the slight change in the syngas composition. The decrease of the different efficiency is explained by the augmentation of the consumption of the plasma torch. 0,5 0,55 0,6 0,65 0,7 0,75 0,8 0,85 0 2000 4000 6000 8000 10000 12000 1000 1200 1400 1600 Energy (kW) Temperature (K) Plasma torch LHV 1st law efficiency 2nd law efficiency 2nd law efficiency, chemical 25 4. Electricity production system The purpose of this part is to study a power plant, constituted by a gas turbine in combinedcycle (CCP) fuelled by syngas. This work is only a first step in an overall optimization process. The goal of this work is to formulate a simple and flexible mathematical model but able to make a prediction of the performance of the system. The model, wihch was also developed by EES software, is available in ANNEXE 3. a. Plant description The physical structure of the analyzed plant is presented in Figure 9. Figure 9 : Physical structure of the analyzed plant The syngas produced exit from the gasifier (modeled before) at condition 1. Heat is transferred from the hot syngas to water, through a Heat Recovery Steam Generator (HRSG 1), producing steam at condition 9, which fuel a Rankin cycle. The superheated steam undergoes an expansion in a steam turbine providing electrical energy. Then the syngas goes throw a compressor until condition 3 before entering in the combustion chamber. In the combustion chamber, the syngas reacts with air, producing exhaust gas at condition 6. The exhaust gas, expanded up to condition 7 in the gas turbine, producing electricity. The exhaust gas flows through a second Heat Recovery Steam Generator (HRSG) heating the fluid at condition 13. The cooled gas exit at condition 8. 32 ANNEXES 33 ANNEXE 1 Review of industrial planted technology of plasma gasifier Alter NRG / Westinghouse Plasma Corporation (WPC) [13] claims to have researched on plasma gasification for over 30 years and 500000 hours of commercial torch operations. In 2007, Alter NRG acquired WPC and continued with the development of the technology with engineering and operational improvements. According to this manufacturer, a key point of the technology is the flexibility on both feedstock and products, which is presented graphically in Figure 11. A wide variety of feedstock can be used: waste from households and industry, coal, biomass or petcoke. This fuel is gasified with plasma and by introducing either air or oxygen. The use of oxygen increases the heating value of the produced gas, but an air separation unit is needed. Due to the high temperatures achieved, mineral matter of the feedstock leaves the gasifier in form of slag. Gas produced is cooled and cleaned. This syngas can be used for several purposes: it can be burned for producing steam or power, or used for the synthesis of methanol. This manufacturer claims that plasma torches only use 2% to 5% of the energy input, and that syngas contains 80% of the energy input. According to Alter NRG, the technology has four fields of application: municipal waste, coal plant refueling, biomass and hazardous waste. Three models of torch are available: Marc 3 (80300 kW), Marc 11 (300-800 kW) and Marc 11H (700-2400 kW), with a thermal efficiency range of 60-75%. Three types of gasifiers are offered: G 65 W 15 and P5, whose capacity appears in Table 9. Table 10 below provides some representative examples of the energy output that can be expected from a gasification plant processing MSW. Plasma gasification facilities built by Alter NRG are listed in Erreur ! Source du renvoi introuvable.. Gasifier model Approximate capacity (tons/day) Oxygen Air G 65 Waste 1000 Waste 620 Biomass 1000 Biomass 720 W 15 Waste 290 Waste 140 Biomass 300 Biomass 160 P 5 Waste 100 Waste 50 Biomass 100 Biomass 50 Table 9 : Plasma gasifiers manufactured by Alter NRG 34 Gasifier Model Capacity (tpd of MSW) Syngas Produced (NM3/hr) Syngas Chemical Energy, HHV (GJ/yr) Combined Cycle Power Plant (MW gross/net) FT Liquids BPD / BPY Fossil Fuel Replacement (bbls/year) G65 1000 65,000 4,100,000 58 / 39 785 / 287,000 670,000 W15 290 15,000 976,000 14 / 9 188 / 68,000 160,000 P5 100 5,000 323,000 4.5 / 3 62 / 23,000 50,000 Table 10 : Energy output from plasma gasification facilities manufactured by Alter NRG. An Integrated plasma gasification combined cycle facility that processes 1000 tpd of MSW (12 MJ/kg) will produce about 50 MW of power. It will also produce about 250 tpd of slag that can be sold as aggregate. A further 20 tpd of coarse particulate is produced which can be recycled back into the gasifier. The remaining 20 tpd of fine particulate, which includes elements like cadmium and mercury must be properly disposed of. In other words, an IPGCC plant that processes 1000 tpd of Figure 11 : Concept of plasma gasification 35 MSW will produce only 20 tpd of residuals that require long term disposal. The other 980 tpd is converted into electricity and beneficial products. Plant Owner Capacity Feedstock Output Status MihamaMikata, Japan Hitachi Metals, Hitachi Ltd. 24 tpd Municipal solid waste and waste water sludge Heat for drying sewage sludge Commercial Operating Plants Utashinai, Japan Hitachi Metals, Hitachi Ltd. 220 tpd Municipal solid waste and auto shredder residue Focused on waste destruction, although sealable power is produced Commercial Operating Plants Pune, India SMSIL 72 tpd Hazardous waste Power Commercial Operating Plants Pilot Facility, PA, USA Alter NRG 48 tpd Over 100 tested Syngas Pilot plant Nagpur, India SMSIL 72 tpd Hazardous waste Power Madison, PA, USA Coskata and WPC demonstration facility 40000 gallons per year Non-food biomass Cellulosic ethanol Demonstration Plant Tees Valley, UK Air Products 1,000 tpd Sorted MSW Power – Combined Cycle Projects under Construction Wuhan, Hubei, China Wuhan Kaidi 150 tpd Biomass Fischer-Tropsch (FT) Liquids Projects under Construction Shanghai, China GTS Municipal Solid Waste & Incinerator Fly-ash Vitrification Slag Projects under Construction Table 11 : Plasma gasification facilities built by Alter NRG 36 Plasco Energy Group [14] has developed a plasma gasification process for municipal solid waste (MSW) with a more complex layout (Figure 12). MSW enters the conversion chamber at the bottom of which a grate has been located. MSW is gasified due to the reaction with preheated air entering through this grate. Crude gas leaving the conversion chamber enters the refinement chamber where two plasma torches are located. Solids leaving the grate enter the carbon recovery vessel where they are gasified due to the action of a third plasma torch. In this last vessel, slag is produced from the mineral fraction of the feedstock. Refined gas is cooled and cleaned and then can be used for several purposes. For example it can be burned in internal combustion engines so as to produce electricity. Waste heat from these engines and from gas cooling is used to produce steam that, in turn, can either be used to generate additional electricity or in industrial processes or district heating. According to this manufacturer, with a ton of MSW (14200 MJ of heating value), this technology can provide: 1 MWh of electricity, 300 liter of potable water, 150 kg of construction aggregate and 715 kg of metal. Figure 12 : Plasma gasification process developed by Plasco Energy Group PEAT International [15] has developed a Plasma Thermal Destruction Recovery (PTDR) technology. PEAT’s plasma heating system consists of DC-powered graphite electrodes rather than plasma torches, typically marketed by other companies. This manufacturer offers three plant design of different size: PTDR-100 (60 kg/h), PTDR-500 (350 kg/h) and PTDR-1000 (1500 kg/h). The values of power of the plasma torch are 100 kW, 400 kW and 3400 kW respectively. It should be noted that this manufacturer focuses on waste treatment rather than on energy recovery. Equipment for producing electricity from waste gas is therefore optional. This technology has been proved in several installations: Sacramento (California, USA), Ankleshwar (India), Tainan (Taiwan), Kaohsiung (Taiwan) and Lorton (Virginia, USA). The characteristics of the described plant are shown in the Table 12 37 Table 12 : Characteristics of PEAT’s plant Europlasma [16] is a French company founded in 1992 whose main activity is the processing of waste from industrial processes at high temperature using plasma torches, in the field of metallurgy, treatment of hazardous waste and the purification of synthesis gas from the gasification. They control the design, manufacture and operation of the plasma torch and offer a full range of power from 25kW to 4 MW. They also have developed a special plasma torch to crack the syngas produced by the gasification, called TurboPlasma. They claim to have 1 250 000 hours of experience. They have experienced in gas cleaning and are currently developing a full gasification to electricity process with plasma : CHO-Power. The gasification process as described in Figure 13 presents the Europlasma cleaning process. It includes a heat exchanger that recovers the sensible heat of the gasification gas, dust and acids scrubbing and finally gas engines to produce electricity from the syngas. Figure 13 : Europlasma auto-thermal gasifier 38 The process designed by Europlasma does not rely on the full use of plasma torches for gasification. Gasification is obtained by using the recycled heat of combustion. Plasma torches are used only for the thermal cracking of the syngas and for slag vitrification. A Figure 14 of the gasifier is proposed below. Figure 14 : Europlasma auto-thermal gasifier The CHO-Power plant in Montreux (France) started working in June 2012, it has now sold on the network 2235 MWh. It has a total capacity of production of 12MW from waste and biomass (50,000 tons per year). This plant has already reached a power of 6MW, demonstrating the overall effectiveness of the CHO Power process. The calculations provided by the manufacturer announced that at full power a total yield of 33%, from 33 MW of waste, should give a total electrical power of 11 MW. The torch has a nominal power of 2 MW and delivers 1.4 MW with a yield of about 70%. Yields Energy announced are the result of a theoretical calculation. They are characteristic of a perfectly regulated system. Advanced Plasma Power [18] has developed the Gasplasma process (Figure 15).The process comprises a gasifier which transforms the organic material in the RDF into a crude syngas containing tars and chars. The crude syngas exiting the gasifier is then passed into the separate, secondary plasma conversion unit. The intense heat from the plasma arc (8000°C) and the strong ultraviolet light of the plasma result in the complete cracking of tar substances and the breakdown of char materials. The inorganic elements in the ash carried over from the gasifier are vitrified. The clean syngas exiting the plasma converter is then cooled and conditioned through wet and dry scrubbers before being used directly in a power island comprising reciprocating gas engines or gas turbines to generate renewable energy. Residual heat is also recovered from the process to be used in Combined Heat and Power (CHP) mode within the process itself. 39 Figure 15 : Gasplasmsa process by Advanced Plasma Power The Gasplasma process delivers energy conversion rates of 90% in terms of syngas production; the net exportable power generation efficiency for a commercial scale plant is significantly in excess of 25%. Based on 100,000 tons per annum input of a typical RDF of, a Gasplasma® facility generates in excess of 20 MW of electrical power. 40 ANNEXE 2 Review of scientific research for different plasma technology and applications Mountouris et al (2006) [2] have developed an equilibrium model of plasma gasification (GasifEq) and have also performed exergy analysis of the process. The model has been validated with data from literature and has been applied to the simulation of sewage sludge gasification. Results show that, for 30% moisture, 13.5 MW of feedstock (flow rate times low heating value) and 4 MW of electricity for plasma are able to provide 13 MW of heating value of gas. Simulations show that when moisture increases, so does the required amount of plasma. Besides, plasma requirements decrease when the amount of oxygen introduced increases, and plasma has to be increased for incrementing the gasification temperature. These authors define the efficiency of the process as the quotient between the chemical energy of the syngas produced divided into chemical energy of feedstock plus electricity consumed. This value varies from 70 to 80%, and is of 75% for the base case. If an efficiency of electricity generation (35%) is introduced, efficiency of the base case decreases down to 52%. The same authors (Mountouris et al (2008) )[18] have applied the GasifEq model to develop a process for electricity production from sewage sludge. Due to the negative effect of feedstock moisture, they placed a dryer before the plasma gasification furnace. Then, gas is cooled, cleaned and used in a gas engine. Heat for the drying process is obtained partially from gas cooling and partially from waste heat from the engine. Figure 16 shows the diagram of the process, including some energy values. Other data reported in the paper shows it is possible to calculate that chemical energy of feedstock is 10.6 MW, whereas chemical energy of the produced syngas is 10.5 MW. Accordingly, 1 kJ of chemical energy of feedstock and 0.13 kJ of electricity are needed for each kJ of chemical energy of syngas. If an electricity generation efficiency of 35% is considered, efficiency of the gasifier is 73%. This value is situated in the upper range of study presented below, which is not surprising since the arrangement has been designed looking for optimal efficiency. Finally, the electric efficiency of the whole system (from sewage to electricity) is 26.9%, which can be considered a good result compared to other technologies applied to such difficult feedstock. Figure 16 : Energy flows in a plasma gasification – engine system 41 A comparison of plasma and conventional gasification was made by Janajreh et al (2012) [19] by using a model developed with Aspen Plus. The model is based on the minimization of Gibbs function, considering 44 species. Results show that efficiency of conventional gasification is around 72%, whereas efficiency of plasma gasification is around 42%. An important cause of this reduction is the efficiency for producing electricity, assumed to be 31.55 %. Results for different types of feedstock appear in Table 13. Finally, the developed model is applied to perform a sensitivity analysis about how air introduced in the gasifier affects efficiency and gas composition. Fuel Conventional gasification efficiency (%) Plasma gasification efficiency (%) RTC Coal 70.25 42.10 Tire 74.27 43.00 MSW 75.15 43.30 Algae 76.57 38.27 Treated wood 74.50 46.20 Untreated wood 75.24 43.50 Pine needles 72.59 47.00 Plywood 66.23 40.51 Table 13: Efficiency of plasma and conventional gasification Minutillo et al (2009) [20] suggested the combination of plasma gasification and a combined cycle (integrated plasma gasification combined cycle, IPGCC) for electricity production from waste. Figure 17 shows a simplified representation of the process: Figure 17 : Integrated plasma gasification combined cycle They used Aspen Plus for modelling the systems, considering three situations: plasma using air, plasma using enriched air, and plasma using air plus additional use of oxygen. Gasification efficiency is quite high for the three cases: 63.6, 66.7 and 69.1%, respectively. In the first case, each kJ of gas 48 49 50 51 52 53 54 55 56 57 64 65 66 67 68 69 70 71 72 73 80 81 82