Lower Heating Value Of Syngas Research Articles

Experimental study on co-gasification of cellulose and high-density polyethylene with CO2

Co-gasification of biomass and waste plastic with CO2 presents an effective strategy for integrating biomass conversion, waste utilization and carbon recycling. In this study, the co-gasification of cellulose and high-density polyethylene with CO2 was investigated experimentally. The effects of mixing ratio and temperature on co-gasification characteristics, including gas yield, product gas composition, lower heating value of syngas and gasification efficiency, were comprehensively evaluated. Additionally, the interaction between cellulose and high-density polyethylene was analyzed. The results suggested that increasing the polyethylene content in feedstock resulted in decreased yields of H2 and CO, increased CH4 yield, increased lower heating value of syngas and reduced gasification efficiency. The interaction between cellulose and high-density polyethylene enhanced the gas yield, with the most significant effect at 40% polyethylene content. In the range of 900 °C to 1000 °C, increasing the temperature resulted in increased gas yield, reduced lower heating value of syngas and increased gasification efficiency. The positive interaction between cellulose and high-density polyethylene on gas yield was more significant at higher temperatures. This work shed light on reaction characteristics for co-gasification of biomass and high-density polyethylene with CO2, laying the foundation for the design and application of this technology.

Enhanced production of hydrogen-rich gas from municipal sewage sludge gasification using a CaO-RM composite catalyst

Hydrogen-rich gas, characterized by high yield and purity, can be effectively generated through the steam gasification of sewage sludge (SS), offering substantial benefits for organic solid waste treatment and resource conservation. This study evaluated the gasification performance in a horizontal moving-bed reactor employing a wet-mixed CaO-red mud (CaO-RM) composite catalyst. The effects of CaO loading rate (CaO/RM), catalyst-to-SS ratio (CaO-RM/SS), and reaction temperature on the syngas yield, lower heating value (LHV), carbon conversion ratio, H2 to CO (H2/CO) ratio, and H2 yield were investigated. Results indicated that red mud loaded with a calcium-based catalyst significantly enhanced syngas production, particularly for hydrogen generation, during SS gasification. A maximum hydrogen molar fraction of 50.84% and a yield of 7.07 mol/kg were achieved with a CaO/RM of 40% and a CaO-RM/SS of 30% at 750 °C. With the reaction temperature increase from 700 to 900 °C, the catalytic performance for secondary tar cracking and steam reforming was further enhanced. The total syngas yield, H2 yield, hydrogen molar fraction, LHV of syngas, and carbon conversion rate peaked at 0.79 m³/kg, 19.30 mol/kg, 54.41%, 10,249.48 kJ/kg, and 65.67%, respectively, at 900 °C.

Synthesis of syngas from municipal solid waste in a fluidized bed gasifier

In this study, three representative materials, wood, paper, and cloth from municipal solid waste, were studied separately in an atmospheric fluidized bed gasifier. The effects of different feedstock, equivalence ratio, gasification temperature, and calcium carbonate presence on syngas composition, the lower heating value, and carbon conversion efficiency were investigated at different operating temperatures (800-950?C), and the equivalence ratio range from 0.2 and 0.5. As the equivalence ratio increased, the yields of syngas and its lower heating value decreased, whereas the CO2 yield and carbon conversion efficiency increased generally from wood gasification. Higher gasification temperature favored enhancing the CO and H2 yield and lowering the CO2 yield while the lower heating value and carbon conversion efficiency of syngas increased. Different variations of CO2 yield and the lower heating value of syngas were observed in different feedstock gasification. CaCO3 was more supportive for enhancing the yields of syngas components (H2, CO, and CH4) and lowering the CO2 yield, while a lower heating value of syngas was also increased from different feedstock gasification. However, an optimum temperature of 900?C was the highest lower heating value of syngas, reaching 8000 kJ/Nm3 from wood gasification.

Thermodynamic modeling and performance analysis on co-gasification of Chlorella vulgaris and petrochemical industrial sludge via Aspen plus combining with response surface methodology

The co-gasification process of Chlorella vulgaris (CV) and petrochemical industrial sludge (IS) was uncoupled and simulated by Aspen Plus. The co-gasification process was considered into drying, pyrolysis, partial oxidation, as well as reduction and reforming. Simulation results showed that, the interactions between IS and CV were found for the differences in CHO, and affected by the IS ratio and gasification temperature. Increasing the temperature could improve the CO content, and get optimal H2 at 700 °C, while decrease CO2 and CH4 contents, thus lead to a higher LHV (lower heating value) of syngas, CGE (cold gas efficiency), and syngas content, CO selection. The higher S/IS-CV (steam to IS-CV blends ratio) value favored H2 production but reduce CO content and CGE. As air equivalent ratio (ER) increased, the H2 content constantly reduced, while CO varied slightly when the ER was lower than 0.10. After the ER value was higher than 0.10, CO reduced and thereby decreasing co-gasification performance. When the drying degree of feedstock increased, the CO content continuously increased, leading to better co-gasification performances. The RSM results showed that the significance factors in the interactions are ER and drying degree, S/IS-CV and ER, gasification temperature and ER, and gasification temperature and ER, respectively for CGE, LHV, Csyngas, and SelCO.

Integrative approach to kinetic modeling and verification of a downdraft gasification model

In this study, a comprehensive unified kinetic-based model for downdraft gasification was developed using Aspen Plus® software. The model considered four distinct zones and major reaction kinetics involved in the process, including tar kinetics. It was successfully validated for various fuel types and three different gasifying agents: air, oxygen, and oxy-steam. The impact of Equivalence Ratio (ER), temperature, moisture content, and fuel composition on the output syngas composition, lower heating value (LHV), and gasification efficiency was analyzed. Furthermore, surrogate models were created through multi-variable analysis based on the validated model, enabling the prediction and optimization of LHV and gasification efficiency. The multi-variable study provided insights into the effects and interactions of different factors. Notably, the maximum values achieved were 5.4 MJ/kg for LHV of syngas and 83.1 % for gasification efficiency in an air gasification system, with specific ER, temperature, moisture content, and fuel composition (C/O ratio) values set at 0.24, 1123 K, 2 %, and 1.25, respectively. Overall, this validated unified kinetic model proves capable of predicting syngas composition for various fuel types, making it a valuable tool for optimizing downdraft gasifiers.

Sustainable hydrogen production through coupling isopropanol-butanol-ethanol with enhanced heat recirculation

The utilization of isopropanol-butanol-ethanol (IBE) to clean energy effectively mitigated the problems of environmental pollution and sustainable energy regeneration. In order to improve the utilization efficiency of ethanol and isopropanol in IBE, a liquid double-layer porous media burner was designed. And the combustion characteristics with different porous pellets and isopropanol ratios were studied. The results indicated that the mole fraction of hydrogen decreased with the increasing pellet diameter, and the lower heating value of syngas reached the highest value of 82.0 MJ/Nm3 when the pellets possessed two holes. Meanwhile, the peak temperature reached the maximum of 1009 K when the water content was 20% due to the sufficient combustion. And the isopropanol was conducive to the improvement of the total energy conversion efficiency. In addition, the yields of hydrogen and carbon monoxide were improved by 23.7% and 30.5% when the velocity increased from 10 to 12 cm/s. These results showed that the combustion of ethanol and isopropanol in porous media burners achieved the sustainable production of hydrogen and efficient utilization of IBE biofuels.

A novel integration of plasma gasification melting process with direct carbon fuel cell

As municipal solid waste (MSW) is a low-cost, available, and basically renewable source, energy recovery from MSW is a beneficial technique for reducing fossil fuel usage while also lowering MSW disposal challenges. The current study proposes a novel scheme consisting of plasma gasification melting (PGM) process and direct carbon fuel cell (DCFC) system for converting MSW into high-quality syngas and power. Plasma air and high-temperature steam are employed in the process as gasification agents. The DCFC runs on the pyrolysis char, which is a carbon-rich source and is extracted during the PGM process and sent to the DCFC. The process is simulated in Aspen Plus, and a computational model for estimating the DCFC's output voltage and power is developed in MATLAB. Effects of main operating parameters, including equivalence ratio, steam to biomass ratio, plasma energy ratio, char separation fraction, and fuel cell operating temperature on the system's performance indicators, namely syngas composition, syngas lower heating value, syngas yield, gasification temperature, overall efficiency, and DCFC power output were investigated. By increasing the char separation fraction, more pyrolysis char was extracted and forwarded to the DCFC, which leads to less amount of char entering the gasification section and higher power output through the DCFC. Keeping other parameters constant, at a fuel cell operating temperature of 923 K, the optimal value for char extraction fraction was 0.15, resulting in a 79.5% overall efficiency.

High Dimensional Model Representation Approach for Prediction and Optimization of the Supercritical Water Gasification System Coupled with Photothermal Energy Storage

Supercritical water gasification (SCWG) coupled with solar energy systems is a new biomass gasification technology developed in recent decades. However, conventional solar-powered biomass gasification technology has intermittent operation issues and involves multi-variable characteristics, strong coupling, and nonlinearity. To solve the above problems, firstly, a solar-driven biomass supercritical water gasification technology combined with a molten salt energy storage system is proposed in this paper. This system effectively overcomes the intermittent problem of solar energy and provides a new method for the carbon-neutral process of hydrogen production. Secondly, the high dimensional model representation (HDMR) approach, as a surrogate model, was used to predict the production and lower heating value of syngas developed in Aspen Plus, which were validated using experimental data obtained from the literature. The ultimate analysis of biomass, temperature, pressure, and biomass-to-water ratio (BWR) were selected as input variables for the model. The non-dominated sorted genetic algorithm II (NSGA II) was considered to maximize the gasification yield of H2 and the LHV of syngas in the SCWG process for five different types of biomass. Firstly, the results showed that HDMR models demonstrated high performance in predicting the mole fraction of H2, CH4, CO, CO2, gasification yield of H2, and lower heating value (LHV) with R2 of 0.995, 0.996, 0.997, 0.996, 0.999, and 0.995, respectively. Secondly, temperature and BWR were found to have significant effects on SCWG compared to pressure. Finally, the multi-objective optimization results for five different types of biomass are discussed in this paper. Therefore, these operating parameters can provide an optimal solution for increasing the economics and characteristics of syngas, thus keeping the process energy efficient.

Investigation of hydrogen production via waste plastic gasification in a fluidized bed reactor using Aspen Plus

Plastic waste-to-energy conversion via gasification is a promising method for hydrogen production. In this study, the effects of waste plastic type, equivalence ratio, operating temperature and pressure on the hydrogen production from waste plastics in a fluidized bed reactor were investigated. A precise model of the air gasification process of five different types of waste plastics was developed using modules available in Aspen Plus. Following the model validation, a parametric study was conducted by varying the temperature in the range of 600 °C–1200 °C, the equivalence ratio between 0.05 and 0.50, and the pressure between 1 bar and 50 bar. This study provides valuable information on the impact of different process parameters on the air gasification of various waste plastics which has not been reported extensively. The conversion behaviours of air gasification process for waste plastics were characterized based on syngas composition, syngas lower heating value, hydrogen yield and cold gas efficiency. The simulation results for hydrogen production, which ranged from 15.33 Nm3/ton feed to 284.40 Nm3/ton feed for all plastics, were found to be consistent with experimental results. As a result, the optimal conditions for achieving maximum hydrogen yield in the waste plastic gasification process have been determined and reported.

Biomass for dual-fuel syngas diesel power plants. Part I: The effect of preheating on characteristics of the syngas gasification of municipal solid waste and wood pellets

Indonesia has the potential to develop biomass, such as MSW and wood pellets, as a source of energy. Syngas from biomass gasification can be used as fuel for dual-fuel diesel engines in order to transition energy. We investigated the gasification of MSW and wood pellets using a downdraft reactor with a capacity of 130–144 kg in order to determine the properties of the produced syngas for use in dual-fuel syngas diesel engines. Four days are dedicated to the process of preheating biomass with sunlight. The experiment was designed with an equivalent ratio of 0.22 and an oxidation zone temperature between 700 and 900 degrees Celsius. According to the experimental results, the average lower heating value of syngas produced by the air gasification of MSW biomass was 5.85 MJ/Nm3, the cold gas efficiency was 56.6%, and the carbon conversion efficiency was 94.77%. The average lower heating value from wood pellet biomass air gasification was 5.95 MJ/Nm3, the cold gas efficiency was 67.7%, and the carbon conversion efficiency was 94.28%. Solar heating of biomass has been shown to increase the calorific value of biomass gasification to syngas.

Carbon-neutral synfuel production via continuous solar H2O and CO2 gasification of oil palm empty fruit bunch

Solar gasification offers a promising carbon-neutral pathway to thermochemically convert waste biomass and solar energy into synfuel. In this study, a thermodynamic analysis of solar gasification of oil palm empty fruit bunch (EFB) with H2O and CO2 gasifying agents was first performed to predict equilibrium product distribution. Subsequently, on-sun continuous solar gasification of EFB was experimentally carried out in a solar particle-fed gasifier to evaluate the influence of gasifying agent types (H2O and CO2), gasifying agent/EFB molar ratios (1.8–3.4), temperatures (1050–1350 °C), and to assess overall process feasibility and reliability. As a result, solar EFB gasification performed efficiently with both H2O and CO2 gasifying agents under continuous on-sun operation. Syngas product composition and gasification reaction rate strongly depended on gasifying agent type. Increasing temperature enhanced syngas yield and quality, and changed the CO/H2 mole ratio, especially in EFB + CO2 gasification. A gasifying agent/EFB molar ratio of 2.6 (slight excess of gasifying agents) and a temperature of 1300 °C were shown to be optimal for continuous solar EFB gasification. The maximum total syngas yield above 76 mmol/gdry_EFB, syngas lower heating value above 22 kJ/gdry_EFB, and energy upgrade factor above 1.37 were achieved from both EFB + H2O and EFB + CO2 gasification, which closely approached their theoretical equilibrium values. The maximum carbon conversion exceeding 93% and solar-to-fuel energy conversion efficiency up to 19.3% were achieved, demonstrating efficient EFB-to-synfuel conversion performance. Continuous solar EFB gasification with both H2O and CO2 was thus established to be a reliable process for EFB waste biomass valorization into high-quality and carbon-neutral synfuel.

Decision analysis for plastic waste gasification considering energy, exergy, and environmental criteria using TOPSIS and grey relational analysis

Plastic waste is becoming of increasing interest in gasification research because the gasification of plastic waste not only produces a valuable hydrogen-rich syngas but also can help reduce environmental problems caused by these materials. Most studies in the field of plastic waste gasification have only focused on evaluating effects of process parameters and optimizing the process by considering input variables. The present study explores the comparative performance analysis of a wide range of prevalent plastic waste types utilizing multi-criteria decision-making techniques. This study uses the “technique for order preference by similarity to ideal solution” (TOPSIS) and grey relational analysis (GRA) and presents a thorough sensitivity analysis. Low-density polyethylene results in maximum lower heating value of syngas and has a desirable performance from cold gas and exergy efficiencies viewpoints in air gasification. The findings of TOPSIS and GRA techniques show that low-density polyethylene as plastic waste exhibits the best performance in an air gasification process and the results of the sensitivity analysis confirm this. However, the decision making in steam gasification was challenging where TOPSIS and GRA techniques introduced high-density polyethylene and low-density polyethylene as the best candidates, respectively. Again, the findings of the sensitivity analysis confirmed the result. High-density polyethylene exhibits the best performance in steam gasification according to sensitivity analysis via the TOPSIS technique while low-density polyethylene ranked first according to sensitivity analysis of GRA. The findings can contribute to a better understanding of the selection of plastic waste feedstock for air and steam gasification by considering energy, exergy, and environmental factors.

Exploring the hybrid route of bio-ethanol production via biomass co-gasification and syngas fermentation from wheat straw and sugarcane bagasse: Model development and multi-objective optimization

Biomass co-gasification and syngas fermentation is one of the least trotted paths in the Indian biofuel production scenario. The aim of the research here is to develop an equilibrium model of biomass co-gasification and syngas fermentation in Aspen plus. Two Indian lignocellulosic biomass namely wheat straw and sugarcane bagasse have been selected as feedstock for this co-gasification process followed by the syngas fermentation. The process shows promising results in terms of ethanol production and energy usage. The effects of gasification process parameters on overall process performance have been analysed. Empirical regression equations were constructed to account for the effects of biomass ratio, which is the ratio of the masses of wheat straw and sugarcane bagasse, gasification temperature and equivalence ratio over ethanol yield, lower heating value of syngas, cold gas efficiency, overall system efficiency, and CO2 emission using response surface methodology. Finally, a multi-objective optimization has been conducted to maximize the ethanol production and overall system efficiency, and to minimize the CO2 emission of the system. Results suggest that the wheat straw and sugarcane bagasse ratio of 4:1, 919.5oC temperature and 0.15 equivalence ratio is the optimum point with an ethanol production rate of 20.917 tonnes/hr, overall efficiency of 52.184%, and a minimum CO2emission of 32669.862 kg/h.

High-Ash Low-Rank Coal Gasification: Process Modeling and Multiobjective Optimization

The diversification of coal for its sustainable utilization in producing liquid transportation fuel is inevitable in countries with huge coal reserves. Gasification has been contemplated as one of the most promising thermochemical routes to convert coal into high-quality syngas, which can be utilized to produce liquid hydrocarbons through catalytic Fischer–Tropsch (F-T) synthesis. Liquid transportation fuel production through coal gasification could help deal with environmental challenges and renewable energy development. The present study aims to develop an equilibrium model of a downdraft fixed-bed gasifier using Aspen Plus simulator to predict the syngas compositions obtained from the gasification of high-ash low-rank coal at different operating conditions. Air is used as a gasifying agent in the present study. The model validation is done using published experimental and simulation results from previous investigations. The sensitivity analysis is done to observe the influence of the major operating parameters, such as equivalence ratio (ER), gasification temperature, and moisture content (MC), on the performance of the CL-RMC concerning syngas generation. The gasification performance of CL-RMC is analyzed by defining various performance parameters such as syngas composition, hydrogen-to-carbon monoxide (H2/CO), molar ratio, syngas yield (YSyngas), the lower heating value of syngas (LHVSyngas), cold gas efficiency (CGE), and carbon conversion efficiency (CCE). The combined effects of the major operating parameters are studied through the response surface methodology (RSM) using the design of experiments. The optimized condition of the major operational parameters is determined for a target value of a H2/CO molar ratio of 1 and the maximum CGE and CCE using the multiobjective optimization approach. The high-degree accurate regression model equations were generated for the H2/CO molar ratio, CGE, and CCE using the variance analysis (ANOVA) tool. The optimal conditions of the major operating parameters, i.e., ER, gasification temperature, MC for the H2/CO molar ratio of 1, and the maximum CGE and CCE, are found to be 0.5, 655 °C, and 16.36 wt %, respectively. The corresponding optimal values of CGE and CCE are obtained as 22 and 16.36%, respectively, with a cumulative composite desirability value of 0.7348. The findings of the present investigation can be decisive for future developmental projects in countries concerning the utilization of high-ash low-rank coal in liquid fuel production through the gasification route.

Developing gasification process of polyethylene waste by utilization of response surface methodology as a machine learning technique and multi-objective optimizer approach

This study set out to evaluate the performance of response surface methodology as a machine learning technique on gasification process of polyethylene waste. Different models were developed for predicting gas yield, cold gas efficiency, carbon dioxide emission and lower heating value of syngas in gasification of polyethylene waste using response surface methodology. The accuracy and validity of these models were checked in comparison with the results obtained from the validated model. Most studies in the field of response surface methodology have only focused on its application for multi-objective optimization and largely have ignored its utilization as a machine learning technique. Central composite design was utilized to develop a model between the variables and the responses. Pressure and temperature of the gasifier, moisture content of polyethylene and equivalence ratio were the variables and the responses were gas yield, cold gas efficiency, carbon dioxide emission and lower heating value of syngas. The findings revealed that root mean square errors of the models developed by response surface methodology were 0.235, 0.438, 0.294 and 1.999 indicating their high validity. Finally, multi-objective optimization of polyethylene waste gasification was carried out using response surface methodology resulting in gas yield of 96.29 g/mol, cold gas efficiency of 76.22%, carbon dioxide emission of 4.66 g/mol and lower heating value of 493.44 kJ/mol. The optimum responses were predicted by response surface methodology with errors smaller than 5%.

Study on Predicting the Gasification Process of Acacia Wood on a Downdraft Gasifier: Using the Non-stoichiometric Equilibrium Model

This study presents a prediction of acacia wood of Vietnam gasification in a downdraft gasifier based on the thermodynamic equilibrium model. Analytical solution for the mathematical model obtained by using an EES (Engineering Equation Solver) program. In the survey, moisture content per mole of biomass MC= 10 ¸ 30%, The ratio of the actual amount of oxygen used for gasification with the amount of oxygen for complete combustion of the biomass ER= 0.21 ¸ 0.4. Results indicated that the lower heating value of syngas decreases with increasing MC or ER. Thermal efficiency tends to increase with rising ER from 0.21 to 0.374, and it will decrease if ER continues to increase. The lower heating value of dry products from 4.51 to 6.51 MJ/nm3, the heat efficiency from 49.62 to 75.53%. The carbon conversion factor tends to increase with an increase as MC or ER. The influence of MC on the carbon conversion factor is insignificant. The content of CO2 and CH4 increased, the content of CO decreased with increased MC or ER. The composition of H2 increases as MC increases while the H2 component increases slightly and then decreases with increasing ER.

Investigation on oxy-fuel biomass integrated gasification combined cycle system with flue gas as gasifying agent

A biomass integrated gasification combined cycle with oxy-fuel combustion technology is established to realize negative CO2 emissions in power plants. CO2 and H2O from flue gas are adopted as gasifying agents in the proposed system. The effects of gas turbine pressure ratio and inlet temperature with increasing CO2/C on the system performance are studied using Aspen Plus. The results show that as CO2/C increases, the concentration of CO in the syngas first increases and subsequently decreases. The concentration of H2 and the lower heating value of syngas decrease monotonously as CO2/C increases. The system efficiency increases when the CO2/C value, gas turbine pressure ratio, and gas turbine inlet temperature increase, and the influence of the inlet temperature is more significant than that of pressure ratio. When CO2/C, gas turbine pressure ratio, and inlet temperature are 1.0, 20, and 1150 °C, respectively, the energy efficiency reaches 29.1%, and the corresponding exergy efficiency and net power output are 28.4% and 116 MW. Levelized cost of electricity is estimated to be 0.17 $/kWh in the system. The performance results obtained in this study can provide theoretical support for the application of biomass integrated gasification combined cycle with oxy-fuel combustion technology.

Parametric studies over a plasma co-gasification process of biomass and coal through a restricted model in Aspen plus

Plasma gasification is considered an emerging technology within the so-called waste-to-energy technologies. The pure equilibrium models have been failing to estimate the amounts of the syngas components, especially the methane quantity. In this investigation, a restricted or quasi-equilibrium model was developed in Aspen Plus® to evaluate the performance of the plasma co-gasification process of biomass and coal. The developed model was validated against literature data. A comprehensive parametric study was performed considering the variation of the equivalence ratio, biomass ratio, temperature, and steam to feedstock ratio on the quality of syngas and hydrogen production. Three gasifying agents (air, steam, and oxygen) were used. The syngas lower heating value and the cold gas efficiency are taken as a measure of the syngas quality and process efficiency. The developed restricted model shows to estimate the amount of methane much closer to the experimental data than pure equilibrium models. The highest amount of hydrogen was obtained for steam followed by pure oxygen and lastly for the air as gasifying agents. The use of coal in the feedstock mixture allows obtaining higher LHV of the syngas and CGE of the process. The results of this parametric study represent a humble contribution to the increase of plasma gasification technology market penetration.

Thermodynamic limitations to direct CO2 utilisation within a small-scale integrated biomass power cycle

Partially recycling CO2-rich exhaust gases from a syngas fuelled internal combustion engine to a biomass gasifier has the capability to realise a new method for direct carbon dioxide utilisation (CDU) within a bioenergy system. Simulation of an integrated, air-blown biomass gasification power cycle was used to study thermodynamic aspects of this emerging CDU technology. Analysis of the system model at varying gasifier air ratios and exhaust recycling ratios revealed the potential for modest system improvements under limited recycling ratios. Compared to a representative base thermodynamic case with overall system efficiency of 28.14 %, employing exhaust gas recycling (EGR) enhanced gasification system efficiency to 29.24 % and reduced the specific emissions by 46.2 g-CO2/kWh. Further investigation of the EGR-enhanced gasification system revealed the important coupling between gasification equilibrium temperature and exhaust gas temperature through the syngas lower heating value (LHV). Major limitations to the thermodynamic conditions of EGR-enhanced gasification as a CDU strategy result from the increased dilution of the syngas fuel by N2 and CO2 at high recycling ratios, restricting equilibrium temperatures and reducing gasification efficiency. N2 dilution in the system reduces the efficiency by up to 2.5 % depending on the gasifier air ratio, causing a corresponding increase to specific CO2 emissions. Thermodynamic modelling indicates pre-combustion N2 removal from an EGR-gasification system could decrease specific CO2 emissions by 9.73 %, emitting 118.5 g/kWh less CO2 than the basic system.

Evolving circular economy in a palm oil factory: Integration of pilot-scale hydrothermal carbonization, gasification, and anaerobic digestion for valorization of empty fruit bunch

In the context of evolving a circular economy for the palm-oil industry, this article presents a study of oil-palm empty fruit bunch (EFB) conversion and utilization within a palm-oil mill. Pilot-scale hydrothermal carbonization (HTC), washing and gasification processes, as well as anaerobic digestion of the HTC liquid product were investigated. Results showed that the fuel properties of hydrochars had improved. In terms of air gasification, char and tar products accounted for 22.7–33.8 % and 17.3–28.8 %, respectively while CO2/O2 gasification resulted in 31.3–36.6 % for char and 8.5–30.8 % for tar. In general, hydrochar (HT-EFB) gave the lower tar content compared to washed hydrochar (HTW-EFB) due to the catalytic effects of alkali and alkaline earth metals. Major tar components from HT-EFB and HTW-EFB were aliphatic and monoaromatic hydrocarbons, respectively. Syngas products from air gasification of hydrochars were 39.9–56.5 %, 11.4–21.4 %, and 9.0–14.4 % for CO, H2 and CH4, respectively while CO2/O2 gasification products yielded 45.1–56.6 %, 11.6–24.3 %, and 9.4–14.0 % for CO, H2 and CH4, respectively. The lower heating value of syngas was in the range of 4.7–6.6 MJ/Nm3 and cold gas efficiency was approximately 39.1–55.1 %. The cumulative methane from the liquid products amounted to 213.8 and 154.5 L/kg COD for food/microorganism ratios of 1:2 and 1:3, respectively. The mass and energy balance showed that the whole process is promising for future commercialization.