Supercritical Water Gasification System Research Articles

System development and thermodynamic performance analysis of a system integrating supercritical water gasification of black liquor with direct-reduced iron process

Hydrogen metallurgy is an effective way to decarbonize the steel industry. In this study, a new system integrating biomass supercritical water gasification (SCWG) with hydrogen generation-shaft furnace-electric arc furnace (HSE) was proposed. The thermodynamic performance of SCWG-HSE system were analyzed and optimized. The results show that the gasification and energy efficiency of SCWG system increase with an increase in the gasification temperature. The carbon emission of the SCWG-HSE system are effectively reduced, and the product yield and energy efficiency of the system are improved by increasing gasification temperature and recovering furnace top gas. The energy and exergy efficiency of the SCWG-HSE system are 46.66% and 40.17%, respectively. The exergy destruction of SCWG gasifier and electric arc furnace are the major exergy damage sources of the SCWG-HSE system. The exergy efficiency of the ironmaking system reaches 51.60%, and the energy consumption and carbon emission per unit product are 18.49 GJ/t and 902.40 kg/t, respectively. Compared with the traditional Coking-Blast furnace ironmaking process, the energy consumption and carbon emission of this system are reduced by 7.32% and 40.84% respectively. This work is expected to open a new way for the application of biomass in the low-carbon steel industry.

Thermodynamic and environmental analysis of an integrated multi-effect evaporation and organic wastewater supercritical water gasification system for hydrogen production

Organic wastewater poses significant environmental and human health risks. Supercritical water gasification (SCWG) presents a promising approach for converting organic waste into hydrogen-rich mixed gases. Nevertheless, the high moisture content present in organic wastewater hampers the energy efficiency of the SCWG process. To tackle this challenge, we have designed and developed an organic wastewater SCWG hydrogen production system incorporating a multi-effect evaporator. The developed system demonstrates the ability to achieve autothermal conditions for the treatment of swine wastewater with a solids concentration of 4.3%. Notably, this system exhibits impressive energy efficiency, reaching a maximum value of 44.88%, along with an exergy efficiency of 33.90% when processing 7% swine wastewater. Exergy analysis further reveals that the incorporation of a multi-effect evaporator leads to a reduction in exergy destruction within the gasification unit, oxidation unit, and heat exchanger. These improvements highlight the positive impact of the multi-effect evaporator on the overall performance of the supercritical water gasification system. Sensitivity analysis indicated that suitable concentrated concentration and an appropriate amount of preheated water can improve hydrogen production. The system minimum GWP reaches 5.27 kgCO2-eq/kgH2 after adding the CCUS. This work expands the range of applicable feedstocks for the autothermal SCWG process.

Performance assessment of an energetically self-sufficient system for hydrogen production from oilfield wastewater treated by supercritical water gasification

Oilfield wastewater with high moisture content can be efficiently treated by supercritical water gasification (SCWG) technology to produce hydrogen. This paper conducted a thermodynamic and environmental analysis of the oilfield wastewater SCWG system to provide optimization strategies. The waste heat utilization technology can enhance the heat integration of the system to reduce the exergy destruction and increase the H2 yield. Sensitivity analysis showed that a ratio of preheating water to emulsion 3 can promote water-sensitive reactions to produce H2 and save the H2 needed to maintain the energetically self-sufficient system. Low system pressures, high feedstock preheating temperatures, and low oxidation reactor temperatures can reduce system energy destruction to obtain high H2 yield and system efficiency. Meantime, the developed SCWG system has the potential to achieve natural enrichment of greenhouse gases after the H2 separation has been completed. The use of waste heat utilization technology and carbon capture and storage (CCS) technology is expected to increase system efficiency to 53.43 % and reduce global warming potential (GWP) of 5.52 kg CO2-eq/kg H2. This work would be of great value to the process design and optimization for the SCWG system of oilfield wastewater.

Thermodynamic and environmental analysis of an auto-thermal supercritical water gasification system for ammonia and power production from chicken manure

Supercritical water gasification (SCWG) technology, a clean and efficient method for organic waste treatment, has considerable application prospects in the background of carbon emission reduction. In this study, an auto-thermal SCWG system of chicken manure for NH3 and power production was proposed for recycling waste resources. Thermodynamic analysis and environmental impact assessment were conducted under different operational conditions. The system exhibited optimal energy, exergy, and cold gas efficiencies of 62.34 %, 53.75 %, and 57.75 %, while simultaneously generating 3372.11 kg/h of NH3 and 1677.1 kW of net power, all within processing 10 t/h of dry chicken manure. The global warming potential of this system was only 3.31 kg CO2-eq/kg NH3 with carbon capture and storage. The sensitivity analysis indicated that the moderate increase in gasification temperature, higher feedstock concentration, appropriate preheated water flow, and suitable feedstock distribution ratio collectively enhanced system performance by mitigating exergy destruction in the partial oxidation and heat exchange process. By converting waste heat into electrical energy rather than industrial steam, the Organic Rankine Cycle system enhances the practical viability of waste heat recovery. This work expects to provide essential theoretical guidance for the scale-up and design of the biomass waste SCWG system.

Thermodynamic and environmental analysis of self-thermal antibiotic residues supercritical water gasification system for hydrogen and power production

Efficient treatment of antibiotic residue, containing a range of persistent organic compounds, is essential to ensure the protection of both the environment and human health. Supercritical water gasification technology could achieve the clean and efficient energy conversion of antibiotic residues. In this paper, a self-thermal supercritical water gasification system for antibiotic residues is developed to convert antibiotic residues to high-purity H2 and electrical power. The system analysis results demonstrate that increasing the antibiotic residue slurry concentration, elevating the gasification reactor temperature, and optimizing the ratio of water-to-dry antibiotic residues effectively enhance system efficiency and H2 yield within specific ranges. The H2 yield and net electrical power at optimal operating conditions are 634.52 kg/h and 2.3 MW with 10 t/h dry antibiotic residue feeding. Meanwhile, the energy efficiency, exergy efficiency, and cold gas efficiency of the system are 61.32%, 63.05%, and 53.96%, respectively. The life cycle assessment analysis shows that the global warming potential of the system is 20.77 kg CO2-eq/kg H2 with the above operating conditions. Taking into account the emission reduction impact of the system on thermal power generation, the inclusion of CO2 capture and storage units can potentially lead to a negative global warming potential for the system.

Pure hydrogen gas production in a coal supercritical water gasification system with CO2 as transporting medium

Supercritical water gasification (SCWG) technology was a clean coal conversion and utilization technology, which could decompose low-grade coal into gaseous products and make efficient and clean use of them. However, system with H2O transporting had much energy consumption on heating transporting medium and side reactions at heating process would weaken the gasification effect. Considering the advantages of low critical point and low specific heat capacity of CO2, and the precedent of CO2 as a transport medium in non-supercritical systems, CO2 was expected to become a transport medium in supercritical water gasification systems and to achieve the goal of improving the gasification effect of heating process and reducing energy consumption. A supercritical water coal gasification system of was established with lignite as raw material in this paper. Production yields of gasification with CO2 as the transporting medium at different working conditions were investigated. CO2 and H2O were used as the transporting medium of the system, contrastively. Compared with H2O-transporting system, production of H2 and CO2 in CO2-transporting system decreased while that of CH4 and CO increased as well. Furthermore, both energy and exergy efficiency of CO2-transporting system were higher than that of H2O-transporting system. The result proved the superiority of CO2 as the transport medium of supercritical water gasification system.

Thermodynamic analysis of the series system for the supercritical water gasification of coal-water slurry

Supercritical water gasification (SCWG) is a potential clean technology for utilizing solid fuel or waste without producing gaseous pollution. Efficient energy integration and recovery strategies play an essential role in the endothermal gasification process. Previous approaches have only focused on the heat source or heat transfer with very little attention to the utilization of the abundant supercritical water in the product gas. This paper proposes an innovative series design for heat integration in the SCWG system while taking the gasification process into account. Notably, the first-stage oxidized hot fluid containing abundant water is directly utilized as the gasification agent for the second-stage gasification reactor. The thermodynamic analysis shows that the cold gas and exergy efficiency in the two-stage series system is 17.4% and 15.0% higher than in the previous single-stage gasification reactor. The sensitivity analysis illustrates that increasing series stages and feedstock concentration while decreasing oxidation proportion and the agent-slurry ratio can improve the overall system efficiency by decreasing the demand for oxygen, power consumption, and heat transfer rate. The series design should offer an innovative and practical approach for the heat supply in the industrial SCWG plant.

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 on a Supercritical Water Gasification System with CO2 as Transporting Medium

Investigation on a Supercritical Water Gasification System with CO2 as Transporting Medium

Thermodynamic and environmental analysis for multi-component supercritical thermal fluid generation by supercritical water gasification of oilfield wastewater

Multi-component supercritical thermal fluid (MCSCTF) can be used to efficiently extract highly viscous heavy oil. However, few works have been conducted to explore MCSCTF generation at the system-level. In this paper, a novel process modeling for the MCSCTF generation system was developed based on the supercritical water gasification (SCWG) of oilfield wastewater. The life cycle assessment (LCA) methodology was employed to evaluate the environmental impact of the system. The use of segmented air supply and rational heat exchangers distribution to achieve process energetically self-sufficient, resulting in a 14.96% increase in exergy efficiency and 0.18 kg CO2-eq/MJ exergy reduction in Global Warming Potential (GWP). The detailed exergy flows identified the high exergy destruction of the system, including heat transfer and air compression. The sensitivity analysis showed that increasing the compression stage, the heat transfer efficiency, and the MCSCTF temperature was conducive to improving the exergy efficiency and reducing the GWP. The exergy efficiency of 44.25% and GWP of 0.26 kg CO2-eq/MJ exergy can be achieved by optimizing system parameters. Compared to other SCWG systems, this MCSCTF generation system is both efficient and eco-friendly. This work can provide essential theoretical guidance for the scale-up and design of the MCSCTF generation system.

Performance comparison of black liquor gasification and oxidation in supercritical water from thermodynamic, environmental, and techno-economic perspectives

The black liquor poses a great threat to the environment and it is also a kind of available biomass resources. By the supercritical water gasification (SCWG) and supercritical water oxidation (SCWO) technology, the black liquid with high water content can be converted into hydrogen-rich gas or heat energy. In this study, a pulp mill integrated with black liquor SCWG and SCWO subsystems, which have a processing capacity of 11.2 t/h of black liquor with a concentration of 15.2 wt%, is designed. The thermodynamic analysis, techno-economic analysis (TEA), and life cycle assessment on the system are conducted. The gasification characteristics and thermodynamic performance of the SCWG and SCWO systems under different working conditions are studied. The thermodynamic analysis shows that the highest energy efficiencies of SCWG and SCWO systems are 41.53 % and 19.89 %, respectively. The lowest processing cost of black liquor is 398.68 RMB/t, which is obtained in the SCWO system at 600 °C. At 800 °C, the minimum hydrogen production cost of SCWG system is 23.28 RMB/kg H2. The LCA results show that the environmental benefits of SCW system at high temperatures are significantly better than those of integrated black liquor combustion systems. Finally, a multi-attribute decision making results of the SCWG and SCWO systems show that the optimal reaction temperature is 800 °C.

Thermodynamic and environmental analysis of heat supply in pig manure supercritical water gasification system

Pig manure, a high water content waste with massive annual output, must be treated in a clean and effective way to protect the environment. Supercritical water gasification (SCWG) is a high-moisture waste utilization technology that is both efficient and pollution-free. The study developed a thermodynamic equilibrium model of the SCWG of pig manure. The effects of operating conditions were examined on heat production and system efficiency. In addition, life cycle assessment (LCA) was used to perform the environmental significance. The results indicated that decreasing the amount of preheating water, increasing the slurry concentration, and the gasification temperature can increase the heat output and system efficiency. The system efficiency is 95.53% at the ratio of water to the slurry is 1:1 and 94.90% at the slurry concentration is 70 wt%. The detailed exergy analysis results showed that the exergy efficiency of the entire system could reach 39.8%. The primary exergy loss occurs in heat exchange and oxidation processes. Adopting reasonable operating conditions and optimizing the layout of heat exchangers can effectively reduce the exergy loss of the system. Besides, GWP has been significantly reduced to 7.4 kg CO2-eq/t steam with carbon capture.

Thermodynamic analysis of supercritical water gasification combined with a reversible solid oxide cell

The low cost of electricity in some areas facilitates the adoption of high-temperature electrolysis plants for the large-scale storage of electricity. Supercritical water gasification (SCWG) is a promising method of syngas production from wet biomass. Additionally, it is a potential source of steam for electrochemical plants. However, the commercialisation of standalone SCWG systems is hindered by low efficiency and high operating cost. Accordingly, we propose the integration of SCWG with a reversible solid oxide cell (rSOC) to realise simultaneous syngas or power generation and wet biomass conversion. This technique would make the process feasible in terms of energy, allowing engineers to use SCWG to combine power generation with fuel production. The wet syngas from the SCWG is fed to the rSOC powered by excess renewable electricity in electrolysis mode, where steam is reduced to H2 to produce dry syngas with a higher calorific value. The energy efficiency of the proposed system is 91% in electrolysis mode and 47% in fuel cell mode. The electrolysis increases the syngas yield by a factor of thirteen and the use of total syngas generates twelve times more power in fuel cell mode compared to the use of only fresh syngas from SCWG.

An evidence theory-based large group FMEA framework incorporating bounded confidence and its application in supercritical water gasification system

Supercritical water gasification (SCWG) is an advanced technology for sewage sludge treatment, which can effectively remove hazardous substances in it and realize the resource utilization of sludge. Given the harsh operating environment and complex operating process, it is particularly critical for SCWG system to adopt failure mode and effects analysis (FMEA) to ensure its reliability and security. In particular, the risk management process of SCWG system needs to include two considerations: the evaluation process requires the participation of a large number of team members (TMs) with different professional knowledge and operational skills, and the cross-correspondence between the factors within the system cannot be ignored in the analysis process. Thus, an FMEA framework is established to meet practical needs, which can model TMs’ personality traits and reflect the interdependencies between factors. First, assessments in the form of probability linguistic term sets (PLTSs) are converted into mass functions due to the excellence of evidence theory in information aggregation. Second, a bounded confidence-based clustering method is developed to consider TMs’ willingness to interact during clustering. Additionally, evidence conflicts are managed using a new discounting method that captures TMs’ stubbornness. Besides, the cross-correspondence between factors is analyzed by an evidence theory-based DEMATEL method. Further considering TMs’ bounded rationality, regret theory (RT) is used to distinguish and prioritize failure modes (FMs). Finally, a case study of an SCWG system is successfully solved by applying the proposed framework. The effectiveness and superiority are subsequently demonstrated by a series of analyses and discussions.

Detailed mechanisms of amoxicillin decomposition in supercritical water by ReaxFF reactive molecular dynamics simulation

The abuse of antibiotics in China has aroused widespread concern, and the resistance genes of antibiotics in the natural environment seriously threaten human health. The supercritical water gasification (SCWG) technology is a clean and efficient technology for the treatment of antibiotic wastewater. In this paper, amoxicillin is selected as the representative antibiotic in wastewater, and the detailed mechanisms of amoxicillin decomposition in supercritical water (SCW) are studied by ReaxFF reactive molecular dynamics (MD) simulation. The results show that the decomposition process of amoxicillin in SCW includes carbon ring opening, carbon chain breaking and small molecular compounds conversion. The molecular vibration leads to the breaking of CN and CS bonds. The OH radical is vital to the ring opening of benzene ring and the breaking of carbon chain. However, the yield of NO increases with increasing OH radical concentrations. The ReacNetGenerator tool is used for the first time to analyze the migration path of nitrogen and sulfur in the SCWG system. It shows that H2 has a great effect on the transformation of sulfur, and OH radicals dominate the transformation of nitrogen. Decreasing the reaction time and the concentration of OH radicals result in inhibiting the NO production. This study will provide a theoretical guidance for understanding SCWG process of antibiotic-containing wastewater.

Comparison and synergistic effect analysis on supercritical water gasification of waste thermoplastic plastics based on orthogonal experiments

Supercritical water gasification (SCWG) is a clean technology of utilizing waste plastics. In this paper, the SCWG characteristics of waste thermoplastic plastics, including polypropylene (PP), polyethylene (PE), and polyethylene terephthalate (PET), and a mixed plastic, were investigated by using the orthogonal experiments. The effect of reaction temperature, reaction time and mass concentration on gasification characteristics was explored and the optimum conditions was obtained. The results show that the reaction temperature has the most important positive effect on the SCWG of PP, PE and PET. The factors that influence the SCWG of mixed plastic follow the order: mass concentration > reaction temperature > reaction time. SCWG efficiency of the mixed plastic is higher than that of all single plastic due to the synergistic effect of different plastic composition. The optimal conditions of mixed plastic are 800 °C, 25 min and 5 wt% and the maximum GE is 106.8%. The energy and exergy efficiency of SCWG system at 650 °C are 47.2% and 37.3%, respectively. The GWP of 1 kg hydrogen produced by SCWG of PE is 3.57 kgCO2eq. The water recycling can greatly reduce the exergy cost of the SCWG system. This study will promote the industrialization of SCWG technology of plastics.

A new linguistic preference relation-based approach for failure mode and effect analysis with dynamic consensus reaching process

In the literature, a lot of alternative failure mode and effect analysis (FMEA) models have been developed to overcome the deficiencies and enhance the performance of traditional FMEA method. However, majority of them evaluated the risk of failure modes directly and cannot take the consensus levels among experts into account. Thus, this article aims to propose a new approach for FMEA via integrating hesitant linguistic preference relations (HLPRs) and an extended dynamic consensus model. Based on the HLPRs, the risk evaluations of experts are described via pairwise comparison of the identified failure modes. An extended dynamic consensus model is proposed to measure the weights of FMEA experts and revise the individual preference information until reaching an acceptable consensus. Finally, the applicability and effectiveness of the proposed FMEA are verified with a practical case study on the risk analysis of supercritical water gasification systems. It was shown that the new approach being proposed provides a practical and flexible way for the risk assessment and prioritization of failure modes in FMEA.

Thermodynamic, environmental analysis and comprehensive evaluation of supercritical water gasification of biomass fermentation residue

In this paper, a residue from a simultaneous saccharification and fermentation (SSF) process using corn stover as the feedstock was taken as the material to study the thermodynamic and environmental performance of supercritical water gasification for hydrogen production . The supercritical water gasification system of the SSF residue (SSF-SCWG) was simulated by Aspen Plus. Taking temperature (600 °C, 650 °C, 700 °C) and residue concentration (5 wt%, 10 wt%, 15 wt%) as independent variables, the gasification yield and thermodynamic performance of the system under different working conditions were studied, and two methods to improve energy efficiency were proposed, including recycling waste heat by organic Rankine cycle and reheating cycle. The results show that increasing the temperature and decreasing the residue concentration are beneficial to increasing the hydrogen production rate. Among all the working conditions, the system has the highest energy efficiency of 36.8% and exergy efficiency of 39.5%, when the reaction temperature is 700 °C and the mass concentration is 15 wt%. On this basis, the energy efficiency was further improved by 5.68% by integrating the organic Rankine cycle and 9.2% by integrating the reheat cycle . The life cycle assessment of the system was carried out by SimaPro . The scope of life cycle study is the operation stage of the SSF-SCWG system and the functional unit is 1 ton of SSF residue. The environmental burden of the system was quantified with the impact assessment methods of ReCipe Endpoint and ReCipe Midpoint . The life cycle results show that the system is environmentally friendly, with global warming potential of −216.6 kg CO 2 -eq/functional unit and acidification potential of −8.9 kg SO 2 -eq/functional unit. Finally, considering thermodynamic and environmental indexes comprehensively, entropy weight method and technique for order preference by similarity to ideal solution model were adopted to make multi-attribute decision for all working conditions, and the optimal conditions for the SSF-SCWG system were obtained. • A novel system of supercritical water gasification of a fermentation residue is designed. • The organic Rankine cycle and reheat cycle are used to increase energy efficiency. • The life cycle environmental burden of the system is quantified. • A multi-attribute decision making method is used for the optimal operation conditions.

Thermodynamic analysis of the superiority of the direct mass transfer design in the supercritical water gasification system

Supercritical water gasification (SCWG) is a promising clean technology for coal utilization due to high chemical reactivity and no tar emission. However, the wall-type heat exchange in the SCWG system demands a large heating surface area and an extreme high-temperature heat source. This paper puts forward an optimized design, namely direct mass transfer, in which the final product gas is partially recycled back into the gasification reactor to supplement the gasification agent and provide sensible heat energy. A whole system simulation was established to analyze the mass flow and exergy efficiency in the reference design and the optimized design. The process analysis shows that the optimized design has higher exergy efficiency (85.6%) than that (72.5%) of the reference design. In the optimized system, direct mass transfer significantly alters the mass flow and exergy flow, with less influent water (33.3%), less heat transfer rate (30.5%), and less oxygen consumption (51.5%). Furthermore, sensitivity analysis shows that increasing circulation ratio, feedstock concentration, and preheating temperature can reduce oxygen consumption and improve gas output and efficiency. The study indicates that direct mass transfer has the potential superiority to solve the challenge of heat integration and facilitate the application of the industrial-scale SCWG system.

Thermodynamic modeling and analysis of the heat integration and power generation in pig manure supercritical water gasification system

A tremendous amount of livestock manure is produced every day, and its harmless and efficient utilization is of profound significance for environmental protection and alternative energy supply. Supercritical water gasification (SCWG) is an efficient and clean technology for high-moisture waste utilization. However, very few researchers have studied the SCWG of manure from system-level modeling. Here, an original or reference pig manure SCWG plant is established for power generation based on previous studies. Detailed exergy analysis shows that the most significant part of exergy destruction occurs in the recuperation process, accounting for 38.05% of total exergy loss. Then, several optimizations were made in a modified system, focusing on a better layout of heat exchangers and critical streams. The modified system had a substantial gain of 23% in overall exergy efficiency and produced 14.12 MW power at an electric efficiency of 27.7%, much higher than 2.08 MW and 5.07% in the original system. Sensitivity analysis further proves that increasing feedstock concentration, preheating temperature, and turbine parameters while decreasing the water-slurry ratio can increase total system efficiency. The efficient multi-stage heat exchanger network and steam turbine in this paper are preferred for SCWG of pig manure, considering system capacity, complexity, and zero-carbon emission.