Supercritical Water Gasification Process Research Articles

Influence of anions and cations on the phase behavior of ternary salt solutions studied by high pressure differential scanning calorimetry

The knowledge of the phase behavior of salt solutions at elevated temperatures and pressures is important for processes using hot compressed water as the process medium, such as supercritical water gasification (SCWG) and supercritical water oxidation (SCWO). Furthermore hydrothermal salt solutions play an important role in geochemical processes in the Earth's crust. We studied ternary solutions related to biomass for obtaining relevant data for the conversion of wet biomass to synthetic natural gas (SNG) in a SCWG process. The experiments were conducted using isochoric high-pressure differential scanning calorimetry (HP-DSC) at a fixed average fluid density of 300kg/m3, a fixed concentration of 0.1mol/kg(H2O) and molar ratios between the two salts of 100:1–1:100. We investigated salts with Na+, K+ and Mg2+ as cations and SO42−, HPO42− and CO32− as anions.

Lignite sulfur transformation during the supercritical water gasification process

Gasification of lignite in supercritical water (SCW) is considered to be a potential clean technology for generating energy by utilizing lignite. An important step for the implementation of this technology is to understand the reaction mechanisms and emission characteristics resulting from pollutants in lignite, which, however, are yet to be investigated. Considering the importance of sulfur pollutants in the utilization of coal, we have studied the transformations of sulfur compounds in lignite under the reaction conditions of lignite gasification in SCW. The studies were carried out in a batch autoclave, with a pressure range of 19–25MPa, a temperature range of 450–600°C, and an equivalence ratio of oxygen between 0.0 and 0.4. Known forms of sulfur in solid, liquid, and gaseous phases were analyzed, and reasonable reaction mechanisms are discussed. Pyrite (FeS2) in lignite transformed to FeS under the experimental conditions in the present study. Organic sulfur was present in very high quantities in raw lignite, and 80% of it decomposed upon gasification in SCW. Quantities of sulfate in solid residues exceeded that of raw coal when the equivalence ratio (ER) was higher than 0.3. SO42− and S2O32− were the main sulfur-containing species in the liquid fractions, while S2−, HS−, SO32−, and HSO3− were present only in minor quantities. H2S was the only detected sulfur compound in gaseous fractions. Transformation pathways of sulfur during lignite gasification in SCW were also deduced. These results could form the framework for the evaluation of sulfur emissions and their potential control in the implementation of this technology.

A review on biomass-based hydrogen production for renewable energy supply

This article gives an overview of the state-of-the-art biomass-based hydrogen production technologies. Various biological and thermochemical processes of biomass are taken into consideration to find the most economical method of hydrogen production. Biohydrogen generated by biophotolysis method, photo-fermentation and dark fermentation is studied with respect to various feedstocks in Malaysia. The fermentation approaches of biohydrogen production have shown great potential to be a future substitute of fossil fuels. Dark fermentation method is a simple biological hydrogen production method that uses a variety of substrate and does not require any light as a source of energy. A promising future for biohydrogen production is anticipated by this process both industrially and commercially. Feasibility of hydrogen production from pyrolysis and water gasification of various biomass feedstock confirm that supercritical water gasification (SCWG) of biomass is the most cost-effective thermochemical process. Highly moisturized biomass could be employed directly in SCWG without any high-cost drying process. Indeed, a small amount of energy is required to pressurize hydrogen in the storage tank because of highly pressurized SCWG process. The cost of hydrogen produced by SCWG of biomass is about US$3/GJ (US$0.35/kg), which is extremely lower than biomass pyrolysis method (in the range of US$8.86/GJ to US$15.52/GJ) and wind-electrolysis systems and PV-electrolysis systems (US$20.2/GJ and US$41.8/GJ, respectively). The best feedstock for biomass-based hydrogen production is identified based on the availability, location of the sources, processes required for the preparation of the feedstock and the total cost of acquiring the feedstock. The cheapest and most abundantly available biomass source in Malaysia is the waste of palm industry. Hydrogen production from palm oil mill effluent and palm solid residue could play a crucial role in the energy mix of Malaysia. Malaysia has this great capability to supply about 40% of its annual energy demand by hydrogen production from SCWG of palm solid waste. Copyright © 2015 John Wiley & Sons, Ltd.

A mathematical model and numerical investigation for glycerol gasification in supercritical water with a tubular reactor

This paper developed a three-dimensional computational fluid dynamics model of the supercritical water gasification (SCWG) process of glycerol. The detailed flow field, temperature field and chemical species distributions inside the reactor were revealed, and the effects of the operating parameters on the results in the SCWG of glycerol were investigated. The reasons for incomplete gasification were discussed, and relevant possible improvements were proposed. (1) The residence time is not long enough for the complete gasification; therefore, the optimal length of the tubular reactor was obtained under different operating conditions. (2) A side-reaction region was formed near the feeding inlet and methods to reduce the volume of the side-reaction region were investigated. A high preheated water temperature and a 135° feeding angle were proved to obviously avoid side-reaction. A multi-injection feeding method can also suppress the side-reaction, but the carbon gasification efficiency decreased.

Supercritical Water Gasification of Biomass: A Literature and Technology Overview

The supercritical water gasification process is an alternative to both conventional gasification as well as anaerobic digestion as it does not require drying and the process takes place at much shorter residence times; a few minutes at most. The drastic changes in the thermo-physical properties of water from the liquid state to the supercritical state make it a promising technology for the efficient conversion of wet biomass into a product gas that after upgrading can be used as substitute natural gas. The earliest research goes back as far as the 1970s and since then, supercritical water has been the subject of many research works in the field of thermochemical conversion of wet biomass. This article reviews the state of the art of the supercritical water gasification technology starting from the thermophysical properties of water and the chemistry of reactions to the process challenges of such a biomass based supercritical water gasification process plant.

Valorization of sugarcane biorefinery residues using supercritical water gasification: A case study and perspectives

The present study evaluates the use of supercritical fluid technology, particularly supercritical water gasification (SCWG), to add value to residues from a sugarcane biorefinery that produces first and second generation ethanol. This case study aims at elucidating how process system engineering tools such as thermal process integration, life cycle analysis, economic evaluation and multi-objective optimization can contribute to minimizing some future challenges of the industrial implementation of supercritical fluid-based technologies, which were discussed in the Workshop on Supercritical Fluids and Energy – SFE’13. In addition, this case study exposes future perspectives in terms of the requirements to further develop this field. The optimized solutions of the evaluated case showed that the SCWG process increases the overall efficiency of the process in terms of energy and carbon fixation. It decreases the CO2 equivalent emissions and it leads to a thermally self-sufficient process. The economic analysis showed a high investment cost but a feasibility of using the current market prices for the produced fuels and electricity.

Co-precipitated Ni–Mg–Al catalysts for hydrogen production by supercritical water gasification of glucose

Supercritical water gasification (SCWG) is a promising process for hydrogen production from biomass. In this study, a series of Ni–Mg–Al catalysts with different Mg/Al molar ratios has been synthesized by a co-precipitation method for hydrogen production by SCWG of glucose. Effects of Mg addition on the catalytic activity, hydrothermal stability and anti-carbon performance of alumina supported nickel catalyst were investigated. The highly dispersed nickel catalysts prepared by co-precipitation could greatly enhance the gasification efficiency of glucose in supercritical water. Among the tested Ni–Mg–Al catalysts, NiMg0.6Al1.9 showed the highest catalytic activity with the hydrogen yield of 11.77 mmol/g (912% as that of non-catalytic test). NiMg0.6Al1.9 also showed the best hydrothermal stability probably due to the formation of MgAl2O4. Mg could efficiently improve the anti-carbon ability of Ni–Al catalyst by inhibiting the formation of graphite carbon. It is also confirmed that MgO supported nickel catalyst is not suitable for SCWG process owing to the difficulty on nickel oxides reduction in the precursors and the phase change of MgO to Mg(OH)2 under the hydrothermal condition.

Boiling coal in water: Hydrogen production and power generation system with zero net CO2 emission based on coal and supercritical water gasification

Coal is the single most important fuel for power generation today. Nowadays, most coal is consumed by means of “burning coal in air” and pollutants such as NOx, SOx, CO2, PM2.5 etc. are inevitably formed and mixed with excessive amount of inner gases, so the pollutant emission reduction system is complicated and the cost is high. IGCC is promising because coal is gasified before utilization. However, the coal gasifier mostly operates in gas environments, so special equipments are needed for the purification of the raw gas and CO2 emission reduction. Coal and supercritical water gasification process is another promising way to convert coal efficiently and cleanly to H2 and pure CO2. The gasification process is referred to as “boiling coal in water” and pollutants containing S and N deposit as solid residual and can be discharged from the gasifier. A novel thermodynamics cycle power generation system was proposed by us in State Key Laboratory of Multiphase Flow in Power Engineering (SKLMFPE) of Xi'an jiaotong University (XJTU), which is based on coal and supercritical water gasification and multi-staged steam turbine reheated by hydrogen combustion. It is characterized by its high coal-electricity efficiency, zero net CO2 emission and no pollutants. A series of experimental devices from quartz tube system to a pilot scale have been established to realize the complete gasification of coal in SKLMFPE. It proved the prospects of coal and supercritical water gasification process and the novel thermodynamics cycle power generation system.

The Effect of Catalyst Content on Supercritical Water Gasification Process with Shochu (Japanese Popular Distilled Liquor) Residue and the Result of Long-time Continuous Operation

The Effect of Catalyst Content on Supercritical Water Gasification Process with Shochu (Japanese Popular Distilled Liquor) Residue and the Result of Long-time Continuous Operation

Dissolution Characteristics of Inorganic Elements Existing in Biomass during the Supercritical Water Gasification Process

During the supercritical water gasification process, the dissolution characteristics of inorganic elements existing in biomass affected not only the gasification transformation of the organic matter but the safety of the system. In this study, the dissolution characteristics of inorganic elements existing in biomass, including corn cob, rice husk, soybean straw, and wheat straw, were carried out at a high-pressure autoclave. The amount of the major inorganic elements that dissolved out was determined by measuring the liquid product. Compared with the conventional water-leaching method, it was found that the dissolved amounts of K, Ca, P, and Mg were reduced, but Na and Si increased. Besides, some operational parameters were respectively considered. The results revealed that the low reaction temperature, low reaction pressure, short residence time, and low feedstock concentration promoted the dissolution of K and Mg, but hindered that of Na. Further, the results also showed that dissolution characteristics of Ca and P related to the biomass species. However, the dissolution characteristics of Si after the supercritical water gasification process were almost at the same level.

Supercritical water gasification of biomass for H2 production: Process design

The supercritical water gasification (SCWG) of biomass for H2 production is analyzed in terms of process development and energetic self-sustainability. The conceptual design of a plant is proposed and the SCWG process involving several substrates (glycerol, microalgae, sewage sludge, grape marc, phenol) is simulated by means of AspenPlus™. The influence of various parameters – biomass concentration and typology, reaction pressure and temperature – is analyzed. The process accounts for the possibility of exploiting the mechanical energy of compressed syngas (later burned to sustain the SCWG reaction) through expansion in turbines, while purified H2 is fed to fuel cells. Results show that the SCWG reaction can be energetically self-sustained if minimum feed biomass concentrations of 15–25% are adopted. Interestingly, the H2 yields are found to be maximal at similar feed concentrations. Finally, an energy balance is performed showing that the whole process could provide a net power of about 150kWe/(1000kgfeed/h).

Supercritical Water Gasification of Glucose and Cellulose for Hydrogen and Syngas Production

Interests in large scale use of biomass for energy and in hydrogen production are motivated largely by global environmental issues. Generation of hydrogen and syngas from biomass using supercritical water gasification (SCWG) is an environmentally benign method to produce energy. In the present work the Gibbs energy minimization, at constant pressure (P) and temperature (T), and entropy maximization at constant P and enthalpy (H), were utilized to calculate the equilibrium compositions and equilibrium temperatures for SCWG of glucose and cellulose. The effect of pressure, temperature and initial composition of reactants were evaluated. The problems were formulated as non-linear programs. The formulation used ensures finding the global optimal solution with no need initial estimate. The model predictions were compared with experimental and simulated data found in literature with a good agreement between them. In both SCWG processes, hydrogen production was favored in high temperatures and low molar compositions of glucose or cellulose in the feed. The effect of pressure was found to be irrelevant. Syngas with a H2/CO molar ratio close to 2 (ideal for Fischer-Tropsch synthesis applications) are obtained with an addition of CO2 as a co-reactant. The calculated final temperatures were close to the initial temperature of the reaction in both systems thus, indicating low energy requirements for maintain these reactions, and in the reaction conditions analyzed here these systems can be considered safe. Both systems showed potential for application in hydrogen and syngas production.

Corrosion of ceramics for vinasse gasification in supercritical water

Abstract Supercritical water gasification (SCWG) is a very efficient process to convert wet biomass into energetic gases. Unfortunately, SCWG reactor may strongly corrode due to the addition of temperature, pressure and the presence of corrosive species. In the present paper, the corrosion of various ceramic materials in subcritical and supercritical water (SCW) gasification process was studied in a batch reactor. We compare the corrosion in distillated water and the corrosion in sugar beet slurry that will be gasified under supercritical conditions. The experimental temperatures were 350 °C and 550 °C and the pressure was 25 MPa. Technical ceramics (SiC, alumina, Y stabilized zirconia, Si3N4, BN, aluminosilicate, cordierite-mullite) show poor capability to sustain corrosion whereas graphite and glassy carbon are the highest performance materials in our working conditions.

Pa-211 Kinetic rates of hydrothermal glucose decomposition in supercritical water gasification process

Pa-211 Kinetic rates of hydrothermal glucose decomposition in supercritical water gasification process

Pathways and kinetics of partial oxidation of phenol in supercritical water

This study reports on the pathways and kinetics of individual gaseous species involved in the partial oxidation of phenol in supercritical water. The pathway is a combination of supercritical water oxidation (SCWO) and supercritical water gasification (SCWG) processes. A kinetic model that involves oxygen is proposed that fits the experimental data and accurately predicts the effects of the O/phenol ratio on the decomposition of phenol. Specifically, at lower O/Phenol ratios, the gasification of acids and the water gas shift reaction predominated, increasing the amount of H 2 in the gaseous products. At higher O/Phenol ratios, on the other hand, the oxidation of acid intermediates and CO oxidation predominated, thereby increasing the amount of CO 2, while H 2 decreased.

Char Formation Mechanism in Supercritical Water Gasification Process: A Study of Model Compounds

Char is one of the undesirable products in the supercritical water gasification of biomass, causing a reduction in carbon gasification efficiency. 5-HMF (5-hydroxymethylfurfural) is believed to be an intermediate in the char formation pathway. In this Article, the rate of formation of char particles obtained from experiments using glucose (a biomass model compound) was compared to that from experiments using 5-HMF (Chuntanapum and Matsumura, 2009). The glucose experiments were conducted in a temperature range of 300−400 °C, at 25 MPa, and for a residence time up to 70 s. The initial concentration of glucose was varied from 1.5 to 3 wt % (i.e., 0.083 to 0.167 M). Glucose was found to produce char particles 2 orders of magnitude faster than 5-HMF feedstock. The copresence of the other glucose decomposition products is thought to cause the difference in the char formation mechanism (i.e., the side reaction between 5-HMF and the other decomposition products) from that of 5-HMF alone. FT-IR and Raman spectroscopy of the solid products was carried out.

Supercritical Water Gasification Staged at Intervals for Hydrogen Fermentation Residue of Food Waste

To circumvent the problem of reactor plugging in supercritical water gasification (SCWG), we proposed an SCWG process operated at intervals with a continuous-flow system (10 kg/d) configured to feed water and feedstock in alternate steps. Hydrogen fermentation residues of soybean fiber and restaurant food waste (SFHFR and RWHFR, respectively) were employed as feedstock, and fine activated carbon was used as catalyst. Feedstocks of 2.0-10.0% SFHFR were gasified in a tubular reactor at 600 °C, 25 MPa with a residence time of 60-105 s. An 8% concentration SFHSR was gasified with a carbon gasification efficiency of 0.75 without plugging. A 4% RWHFR, a feedstock composed of more diverse substances, was gasified with a carbon gasification efficiency of 0.57.

P229 超臨界水ガス化プロセスにおける触媒懸濁スラリーの見かけ粘性率と圧力損失(ポスター発表)

P229 超臨界水ガス化プロセスにおける触媒懸濁スラリーの見かけ粘性率と圧力損失(ポスター発表)

Supercritical water gasification of industrial organic wastes

Supercritical Water Gasification (SCWG), in which supercritical water is not only a solvent for organic materials but also a reactant, is one of the applications for producing fuel from organic resources. In this way, besides the destruction of wastewaters, it is aimed to harness their energy potential by burning the gas effluent generated in the process, which contains a high level of heating power due to its high content in hydrogen and light hydrocarbons. In the work described here, SCWG has been tested on a laboratory scale continuous-flow system with two different industrial wastewaters that contain a high concentration of organics, with both wastes having a high energy potential: cutting oil wastes, oleaginous wastewater from metalworking industries, and vinasses, alcohol distillery wastewater. Reports on SCWG processes on these types of wastewaters have not previously been published in the literature. The influence of the temperature, amount of oxidant and catalyst addition on the yield and composition of the gas phase generated were studied. Experiments were carried out in the temperature range 450–550 °C, the amount of oxidant ranged from the absence of oxygen (oxygen coefficient, n = 0) to 20% of stoichiometric oxygen ( n = 0.2), and 250 bar of pressure in all cases. A maximum of 0.19 mol H 2 per initial COD m (COD m is given as mol O 2 consumed for total oxidation) was obtained in the gas phase under the best conditions.

Glucose Decomposition in Water under Supercritical Pressure at 448-498 K

The behavior of glucose under hydrothermal conditions is of great interest in the development of processes for supercritical water gasification and the hydrothermal pretreatment of lignocellulosics. Our group examined this behavior in a series of glucose decomposition experiments in water at a pressure of 25 MPa in the temperature range of 448-498 K. The rate parameters of the reactions from glucose to the decomposition products were determined by the least squares method. The reaction order of unity for glucose decomposition was found to be the result of several reactions of various reaction orders proceeding in parallel. The reaction orders for the decompositions of fructose, erythrose, glyceraldehyde, and 1,6-anhydroglucose can be considered unity without large error. By examining the selectivity of glucose conversion reactions, we determined that almost all of the glucose was initially converted into fructose, but at 498 K, 1,6-anhydroglucose and erythrose selectivity matched that of fructose. The kinetic parameters determined in our experiments should be useful for predicting the reaction taking place in the pre-heating section of the supercritical water gasification process and in the hydrothermal pretreatment reactor used for the saccharification of cellulosic materials.