Search

In the chemical looping with oxygen uncoupling (CLOU) process, CuO is a promising material due to the high oxygen carrier capacity and exothermic reaction in fuel reactor but limited by the low melting point. The combustion rate of carbon is faster than the decoupling rate of oxygen carrier (OC). Hence, high temperature tolerance and rapid oxygen release rate of CuO modified by three different ores were investigated in this study. The kinetics analysis of oxygen decoupling with Cu-based oxygen carriers was also evaluated. Results showed that CuO modified by chrysolite had faster oxygen release rate than that of CuO. Limestone showed obvious positive effect on the oxidization process. The selected OCs could keep stable in at least 20 cycles, for about 1200 min. Shrinking core model (SCM) fitted well for the decoupling process in the temperature range of 1123–1223 K. Reduction rate kinetic information may aid in the development of chemical looping with oxygen uncoupling (CLOU) technologies during reactor design and process modeling. Ternary doped copper oxide with chrysolite and limestone could improve the reactivity of CuO in decoupling and coupling process and also improve the high temperature tolerance.

This study investigates the thermodynamic equilibrium analysis of the supercritical water gasification (SCWG) involving several typical feedstocks (coal, sewage sludge, microalga, and sawdust). The effects of various parameters including feed concentrations, temperatures, and pressures are analyzed. It is observed that temperature and feed concentration play a determining role in the yield of hydrogen, while the effect of pressure is very limited. Results show that the feed concentration of 15–20 wt% is optimal for hydrogen production. Furthermore, the effects of composition (hydrogen to carbon ratio and oxygen to carbon ratio) of the feedstock on the yield of product gases are investigated, which is useful for screening potential feedstock for SCWG. The results show that maximum H2 and CH4 molar yields are achieved at a low O/C and a high H/C ratio.

For strengthening the safety and reliability for supercritical water oxidation (SCWO) process, the essential causes and solutions of key challenges such as the high corrosion risk of the heat-exchanger and the entrance part of SCWO reactor, the blockage problems resulted from the solid deposition, and the safety and environmental issues caused by the emergency discharge of supercritical aqueous fluids, were investigated theoretically and experimentally. The thermodynamic state division between chemical- and electrochemical corrosion and the corrosion sensitive temperature range of 280−450 °C featuring the predominant electrochemical corrosion were proposed. A set of optimized parameters for the petrochemical sludge treatment such as a temperature of 520–580 ℃, a pressure of 23−25 MPa, and an oxidation coefficient of 1.1–1.3, which not only can ensure the high enough removal rate of organic pollutants but also prevent the corrosion of construction materials as much as possible; the critical velocity of conveying fluid for avoiding the deposition of solid particles were also obtained. On the bases of innovatively developing the “indirect heat transfer” unit, the mixing-preoxidation equipment, the oxygen removal process for SCWO effluents, and the emergency discharge protection device, a novel SCWO process and its corresponding control scheme were proposed and analyzed.

In this paper, the treatment characteristics of glyphosate wastewater based on supercritical water oxidation (SCWO) technology is studied both in spiral coiled tube reactor and tank reactor, including the influences of operating parameters such as reaction temperature, reaction pressure, oxidation coefficient, residence time, and initial properties of wastewater such as organic concentration, pH value on the degradation of COD and NH3-N with H2O2 as oxidant, and the different reaction characteristics in different batch reactors are also analyzed in detail. Furthermore, the simplified SCWO reaction pathway of glyphosate wastewater is also proposed to understand the degradation process better. Finally, a comprehensive SCWO system for treating glyphosate wastewater efficiently, and transforming and utilizing organic nitrogen as well as organophosphorus directionally is proposed and designed, including SCWO unit, ammonia distillation unit, phosphate recovery unit, and biochemical treatment unit, which can enhance the treatment efficiency and economic benefits synergistically, and provide basic data for the industrialization of glyphosate wastewater degradation based on SCWO technology.

In this paper, the flying heat transfer characteristics of slag particles are studied in the process of the dry centrifugal granulation. When the solidification time of particle surface decreased b...

Supercritical gasification (SCWG) and supercritical partial oxidation (SCWPO) technologies have emerged as preferred means of converting wet biomass to hydrogen-rich gases. We experimentally investigated the effects of moisture content, pressure and oxidation coefficient (n) on mole fraction, yield, gasification efficiency and energy recovery of gaseous products from SCWG or SCWPO of municipal sewage sludge, as well as on the carbon and nitrogen contents in liquid products. Potential of sludge for producing gaseous products was thermodynamically analyzed by an Aspen Plus model. The results show that 87 wt%, 25 MPa and n = 0 were optimum conditions for sludge gasification. Sludge with 87 wt% moisture content was pumpable at 75 °C, and further increasing the moisture content decreased the heating value and energy recovery of gaseous products. Pressure played little role in both the experimental and equilibrium gas yields. Highest mole fractions and yields of H2 and CH4 were achieved at n = 0.

Temperature showed obvious effect on the reaction rate and conversion when CuO was used as an oxygen carrier (OC), in which in situ gasification chemical-looping combustion (iG-CLC) occurred at low...

Lithium iron phosphate (LiFePO4) is one of the most important cathode materials for high-performance lithium-ion batteries in the future, due to its incomparable cheapness, stability and cycle life. However, low Li-ion diffusion and electronic conductivity, which are related to the charging rate and low-temperature performance, have become the bottleneck problem. This review begins with the introduction and comment of and phase transition mechanism in lithium iron phosphate particles, followed by the analysis the application potential of nanotechnology in high performance batteries. Nanoscale LiFePO4 has been prepared easily in the laboratory, but few were prepared on a macroscopic scale, and it is more difficult to enter the industrial production stage. Supercritical hydrothermal synthesis is a nano-preparation technology with great potential for industrial application. This article reviews the key parameters (temperature, pressure, concentration, etc.) and core equipment (mixer/reactor) of supercritical hydrothermal synthesis from the perspective of crystallization mechanism, and then point out the structural optimization design of mixer and development of micro-reactors may be the core work for industrialization of supercritical hydrothermal synthesis.

Petrochemical sludge is difficult to be degraded by traditional methods due to the complex organic pollutants, supercritical water oxidation (SCWO) is a promising technology for treating different industrial wastes. In this article, a comprehensive SCWO plant coupled with ammonia distillation and biochemical treatment with the processing capacity near 50 tons per day is designed. Experiments are conducted to determine the influence of reaction temperature, oxidation coefficient and residence time, meanwhile, the species of organics and the concentration of heavy metals in raw feedstock and products are also analyzed to determine the follow-up process. Furthermore, an indirect heat exchange unit between supercritical fluids, capillary device for pressure regulation, and gas–liquid–solid three-phase separator sealed by spiral are proposed to overcome the corrosion and plugging issues. Moreover, an economic evaluation including investment and running cost and the application prospect of the whole system are also analyzed in detail. These information will be significant for designing and constructing the commercial SCWO plant for other industrial wastes.

The optimization and mechanism for oxidation of the waste anion exchange resin from the nuclear industry in supercritical water were investigated. To achieve the maximum chemical oxygen demand (COD...

Co-combustion characteristics of wheat straw with polyvinyl chloride under different oxygen concentration atmospheres were investigated using a thermogravimetric analyzer. Experimental samples included wheat straw, polyvinyl chloride, and their blends. The results showed that when the wheat straw was blended with polyvinyl chloride, there was an inhibition for devolatilization in the volatile combustion stage. However, during the char combustion stage, a promotion was observed. As the oxygen concentration increased from 10% to 40%, the ignition temperatures, burnout temperatures, and maximum reaction rate temperatures of all samples decreased, and the combustion characteristic factors ( SN) increased. The combustion of wheat straw was significantly affected by oxygen concentration, whereas the polyvinyl chloride and blends were affected relatively slightly. Especially, as the oxygen concentration increased from 30% to 40%, the combustion of polyvinyl chloride and blends improve slightly. The reason for this behavior is attributed to the diffusion effects of the oxygen and the microstructure changes of the samples. In addition, the activation energies of the co-combustion process under the four atmospheres, for all samples, were calculated by Flynn–Wall–Ozawa method. The kinetic results show that the diffusion effect of the oxygen influenced the apparent activation energies of combustion reaction and the compensation effect of activation energies exists.

This effort is to improve CuO’s chemical-looping characteristics by introducing iron ore, chrysolite and limestone to obtain high power efficiency in chemical looping combustion (CLC) power plants. The reactivity and oxygen uncoupling behavior were evaluated by thermogravimetric analysis (TGA) in N2 and CO2 atmosphere under different heating rate. CuO modified by chrysolite and limestone showed better performance than iron ore-added CuO oxygen carrier (OC) in a CLC system. CO2 could play an important role in the gasification of char only when the temperature is above 800 °C. Two peaks were found in the Differential thermal gravity (DTG) curve when modified CuO reacted with char. That could be the solid-solid reaction turned into gas-solid reaction with temperature increasing. Scanning electron microscopy (SEM)/energy-dispersive X-ray (EDX) technique analysis indicated an enhancement of high temperature tolerance of Cu-based OCs, while CuO occurred sever sinter and agglomeration. Higher temperature tolerance means higher temperature off-gas from the fuel reactor entering the heat utilization power generation system, which could obtain higher efficiency in CLC power plants.

Corrosion continues to be a major challenge in developing supercritical water-cooled reactor and supercritical water oxidation system. Corrosion behaviors of candidate alloy materials used in these...

Supercritical hydrothermal synthesis of nanosized metal oxides is of great interest for scholars due to its one-pot and readily realizing commercial production process. Hydrothermal synthesis of nanosized TiO2 in subcritical and supercritical water was investigated with different reaction temperatures (250–450°C), time (3–10 min), precursor species (Ti(SO4)2, TiCl4), and the addition of a surfactant (CH3(CH2)5NH2). TiO2 synthesized under supercritical state has a higher degree of crystallinity when compared with TiO2 obtained from subcritical state, which is attributed to a higher reaction rate. Extending reaction time from 3 to 10 min leads to the growth of crystal and broader size distribution (36.66 ± 8.5 nm). More uniform products can be obtained when Ti(SO4)2 acting as the precursor compared with TiCl4 being the precursor. The application of surfactant CH3(CH2)5NH2 in the synthesis makes chemical bonding between the particle surface and organic ligand. It affects the growth direction of TiO2 crystal; as a result, rod-like TiO2 crystal is obtained.

In this study, the oxidation behaviour of alloy 617, alloy 740, alloy HR6W and Sanicro 25 was investigated in SCW and vapour environment at 650°C for 320 h. The weight gain and the thickness of the...

Hydrothermal liquefaction (HTL) and supercritical water gasification (SCWG), two effective thermochemical approaches converting biomass into biofuels, have received increasing attention due to their advantages of a fast reaction rate and the use of wet feedstocks without the need for an energy-intensive drying process. In this review, we first summarize the physical properties of the biocrude oil obtained from HTL and then examine the catalytic hydrotreatment of the biocrude oil with or without solvents. The experimental studies on the SCWG of sewage sludge, microalgae, black liquor, and food wastes are analyzed, and the corrosion and salt-deposition problems associated with the solutions are discussed. Finally, to fully comprehend the reaction mechanism of biomass components in hydrothermal media, the conversion of model compounds (cellulose, hemicellulose, lignin, lipid, protein, and their derivatives) is reviewed.

The corrosion behavior and mechanism of Inconel 600 exposed to the oxidizing high-salinity supercritical water (SCW) containing chlorides, sulfates, and phosphates at 450, 500, and 580 °C were investigated and proposed. The corrosion film had an outer layer dominated by NiO, Fe₂O₃, and eutectic phosphate deposit and an inner layer consisting of Cr-rich oxides. Some produced oxides may generate ionic reactions with the low-melting phosphates precipitated out from SCW, triggering the generation of the eutectic FePO₄–Ni₃(PO₄)₂–Na₃PO₄–Na₂HPO₄ salts in the outer layer. The formation and thickening of the outer layer results from the eutectic phosphate disposition and the common solid-state growth mechanism. Nonmolten chlorides and sulfates in SCW predominantly exist on the outmost surface and are easily washed off, being supported by the absence of S and Cl on sample surfaces. Based on this investigation, a comprehensive corrosion mechanism, involving the solid-state growth of oxide scales, salt precipitation, and phosphate melting processes, was proposed and discussed.

The external- and internal walls of stainless steel heating equipment installed in supercritical water gasification plants for converting fossil fuels or renewable biomass to produce hydrogen-rich gases, respectively, are exposed to high-temperature air and reducing subcritical aqueous systems, all confronting severe corrosion issues. In these two harsh environments, the oxidation characteristics of typical stainless steel 304 were investigated by series of analytical methods. The oxide scale formed on stainless steel 304 in air at 550–650 °C exhibits a three-layer structure: an outmost layer consisting of Fe-rich corundum-type oxides, an inner layer comprising Cr-rich oxides and unoxidized metals, and an intermediate layer. The reducing subcritical aqueous experiments indicate that the relatively severe corrosion occurs at 350 °C rather than at 250 °C and 425 °C, which can be attributed to the reduced H+ concentration at 425 °C comparing to that at 350 °C and the increased Arrhenius rate constant of corrosion reaction with further increasing temperature from 250 °C to 350 °C. A proper pH range (6.5–10.5) for improving the corrosion resistance of Fe/Ni-based alloys in reducing subcritical aqueous environments was obtained, of which the upper limit decreases with increasing oxidicability of solutions.

Supercritical water gasification (SCWG)having been developed for over 30 years is an efficient and clean hydrogen production technology. Biomass and coal are often used as good raw materials of SCWG, meanwhile achieving their clean conversion and utilization. However, salts such as sodium sulfate, generally exist in the raw materials and can poison the necessary catalyst during SCWG, so that they should be removed as much as possible before the raw materials are pumped into the catalytic reactor. Additionally, a large amount of inorganic salts will be generated simultaneously during the gasification reaction. As the solubility of various inorganic salts decreases sharply beyond the water critical temperature, salts in the supercritical water easily separate out and deposit on the walls of equipment and piping, resulting in a series of potential issues such as reduced heat-transfer efficiency, increased flow resistance and even the related-facilities blockage. In this paper, the experimental analysis and numerical simulation for the solubility and deposition characteristics of the sodium sulfate in supercritical water are systematically summarized; on this basis the corresponding deposition and plugging mechanisms are described and analysed. Additionally, this paper also introduces the potential technical methods being able of avoiding the equipment blockage caused by sodium sulphate deposition, and proposes the necessary subsequent research, which is of great significance for solving the disadvantageous effect of sodium sulfate deposition on the long-term stable operation of SCWG commercial plants.

This study investigated the optimum operating conditions on hydrothermal liquefaction (HTL) for the production of biocrude oil from animal carcass. HTL experiments were carried out at various reaction temperatures (230−350 °C), residence times (10−80 min), solid concentrations (5−20 wt%), and pressures (15−30 MPa). Detailed chemical composition analysis of biocrude oil was performed by gas chromatography-mass spectrometry, Fourier transform infrared spectroscopic analysis, and element analysis. The results showed that the biocrude oil was composed of fatty acids, hydrocarbons, amides, esters, and N-heterocyclic compounds. The maximum biocrude oil yield of 55.6 wt% was obtained at 320 °C, 10 wt% solid concentration for a residence time of 60 min. Pressure imparts little on the yield of biocrude oil. The higher heating value of the biocrude oil ranging from 39.7 to 42.5 MJ·kg−1 was comparable to that of petroleum crude (42.9 MJ·kg−1). What is more, the general reaction pathways for HTL of animal carcass was...

Microalgae (N. chlorella) hydrothermal liquefaction (HTL) was conducted at 320 °C for 30 min to directly obtain original aqueous phase with a solvent-free separation method, and then the supercritical water gasification (SCWG) experiments of the aqueous phase were performed at 450 and 500 °C for 10 min with different catalysts (i.e., Pt-Pd/C, Ru/C, Pd/C, Na2CO3 and NaOH). The results show that increasing temperature from 450 to 500 °C could improve H2 yield and TGE (total gasification efficiency), CGE (carbon gasification efficiency), HGE (hydrogen gasification efficiency), TOC (total organic carbon) removal efficiency and tar removal efficiency. The catalytic activity order in improving the H2 yield was NaOH > Na2CO3 > None > Pd/C > Pt-Pd/C > Ru/C. Ru/C produced the highest CH4 mole fraction, TGE, CGE, TOC removal efficiency and tar removal efficiency, while NaOH led to the highest H2 mole fraction, H2 yield and HGE at 500 °C. Increasing temperature and adding proper catalyst could remarkably improve the SCWG process above, but some N-containing compounds were difficult to be gasified. This information is valuable for guiding the treatment of the aqueous phase derived from microalgae HTL.

Hydrothermal liquefaction (HTL) of seven algae was conducted at both 280 and 350 °C with a reaction time of 30 min and a mass ratio of 1/4 of algae to water to evaluate the utilization potential of bio-oil production and nutrient recycling in the aqueous by-product and solid residue particles. Chlorella and Nannochloropsis sp. exhibited the highest bio-oil yields at 280 °C (36.5% from Nannochloropsis sp.) and 350 °C (38.1% from Chlorella). Additionally, temperature had little effect on the energy recovery from Chlorella, Nannochloropsis sp., Spirulina, Cyanophyta and Euglena. The carbohydrates and lipids in the algae were primarily related to monoaromatic and single-ring heterocyclic compound generation in bio-oil. In addition, carbohydrates and proteins significantly affected oxygenated compound production. The sizable total carbon, ammonia nitrogen, total nitrogen and phosphate contents in the aqueous byproducts showed great potential as nutrient sources for algal cultivation and the production of value-added chemicals through recycling. Higher temperatures increased the percentage of ammonia nitrogen in the total nitrogen and reduced the phosphate concentration in the aqueous by-product. According to potential evaluation factors, Chlorella, Nannochloropsis sp., Spirulina, Cyanophyta and Euglena totally showed higher potential in terms of bio-oil production and aqueous nutrient recycling than Dunaliella salina and Enteromorpha prolifera, in which Nannochloropsis sp. exhibited the greatest utilization potential at investigated conditions.

Hydrothermal liquefaction (HTL) is a promising technique of producing crude bio-oil (biocrude) from wet biomass. This work conducted the co-HTLs of microalgae (chlorella) and sewage sludge (SS) at 340 °C, 18 MPa, 0.3 MPa of initial H2 addition, 30 min of residence time under different feedstock mass ratios conditions, and explored the effects of three kinds of SS ashes on biocrude properties during microalgae HTL for the first time. Corresponding biocrude yields, elemental compositions, higher heating values, energy recoveries, boiling point distributions, and compound compositions were examined systematically. The results show that there was a certain synergistic effect on the improvement of biocrude yield other than biocrude quality in the co-HTL of microalgae and SS, especially at the 1:1 of mass ratio condition. This co-HTL could improve the actual biocrude yield by 4.7 wt% and decrease the actual solids yield by 3.6 wt% in contrast to corresponding theoretical yields. The pyrolysis-state SS ash could reduce the N and O contents, increase the C and H contents and HHV, and improve the proportion of low-boiling-point (

We selected a 1.4 wt% Octadecyl trimethyl ammonium chloride (OTAC) concentration wormlike micellar fluid with broad relaxation time spectrum and another single relaxation Maxwell fluid of 4.0 wt% O...

Sludge is a by-product of wastewater treatment process with high organic and nitrogen contents. Supercritical water oxidation (SCWO) rates of refractory species in sludge might be accelerated by reactive alcohols, which is referred to as a co-oxidation phenomenon. In this work, influences of three typical reactive alcohols (methanol, ethanol and isopropanol) on TOC and of NH3–N removal rates of sludge by SCWO were analyzed and their co-oxidation products were characterized by GC–MS, FT–IR, EDS and TG–DTG methods. Additionally, to capture the nature of co-oxidation, HO2 and OH radicals released by alcohols were theoretically compared with detailed chemical kinetics models using the Chemkin Software. The results show that methanol, ethanol and isopropanol all exhibited co-oxidation accelerated effects on TOC and NH3–N removal rates of sludge. One reason was that alcohols provided reactive HO2 and OH radicals. The other reason was that adding alcohols not only prevented forming recalcitrant products (non-nitrogen and nitrogen aromatic compounds) but also encouraged producing reactive products (non-nitrogen open chain compounds). Ethanol offered the best co-oxidation promotion effects on the removal of TOC and NH3–N in the liquid products and also gave the lowest organic contents in the solid products, followed by isopropanol and methanol. This order was consistent with the difficulty of how the alcohols themselves could be oxidized in supercritical water since ethanol could support the highest amount of HO2 radicals for sludge in the shortest time.

The hydrothermal liquefaction (HTL) of microalgae produces water-soluble biocrude (WSB) and water-insoluble biocrude (WISB) simultaneously. The effects of heterogeneous catalysts (i.e. Pt/C, Ru/C, and Pt/C + Ru/C) on the properties of the two types of biocrudes derived from Chlorella HTL were explored for the first time. The results show that the addition of catalyst (Pt/C, Ru/C, or Pt/C + Ru/C) and/or the increase of residence time (from 10 to 30 min) could decrease the WSB fraction in total biocrude (WSB + WISB) mainly due to the improvement of the WISB yield. The catalytic effects on the WISB yield primarily occurred at the low algae loading (i.e., 1:10 of algae/water) condition, and there was a certain synergetic catalytic effect between Pt/C and Ru/C at this condition. The catalytic effect of Pt/C on the yields of WISB and total biocrude reduced as residence time increased. At the HTL conditions of 350 °C, 0.3 MPa H2, and 1:5 of algae/water for 30 min, Pt/C and Ru/C separately led to WSB and WISB with the highest C (63.57 and 74.16 wt%), H (7.34 and 8.44 wt%) contents and the lowest N (12.19 and 7.06 wt%), O (14.06 and 9.15 wt%) contents, and the highest HHVs (29.73 and 35.60 MJ/kg). The WISB produced with Pt/C mainly consisted of amides, hydrocarbons, organic acids and phenols. Pt/C could promote the cracking of high-molecular-weight compounds in WSB to form more low-boiling-point compounds.

For 9–12Cr ferritic–martensitic steels in supercritical water, the dependencies of the thicknesses of three oxide layers (diffusion, inner, and outer layers) on each of seven principal independent variables were separately investigated using three supervised artificial neural networks (ANN) and fuzzy curve analyses. The latter were employed to evaluate the relative significances of independent variables, indicating that on the whole, temperature and exposure time are the most important variables, while the oxide dispersion strengthening (ODS) comes in the first place for the thickness of the diffusion layer. A thicker diffusion layer occurs easily at intermediate temperature approximately 600 °C and/or on ODS steels, due to higher growth rate of the barrier layer than that of the outer layer. The periodic growth of the diffusion layer, including the “shrinking”/“thickening” stages, was revealed by ANN prediction, which may be the basic cause of periodic pore-assembled layers within the inner layer. Finally, the physicochemical basis of classical point defect model was extended to describe the growth of oxide scales for explaining the ANN predictions at the atomic level. The growth of the inner layer into the metal is attributed to the inward transport of oxide ions (actually via outward transport of oxygen vacancies), while the outward transport of cations through the inner layer via a cation vacancy mechanism or as interstitials results in the thickening of the outer layer. The periodic variation in oxygen potentials at the diffusion/inner layer interface is responsible for the periodic growth of the diffusion layer. The iron caves at the inner–diffusion interface left behind by the generation reaction of cation interstitials may be the intrinsic sources of pores within the inner layer.

Waterless CO2-based foam, stabilized by C4F9OCH3, is used as a fracturing fluid to enhance oil and gas production. To enhance basic understanding of this multiphase CO2-based foam fluid, we mainly focus on the effects of temperature and pressure on its slip flow and heat transfer characteristics. The evolution of effective viscosity and rheological parameters of the CO2-based foam is demonstrated. In particular, the effective viscosity decreases significantly as the CO2 turns into a supercritical state. Moreover, the fanning friction factor, as well as the drag reduction rate due to the wall slip of foam, increases with the rise of pressure, and the influence of pressure on the resistance characteristics is relatively greater than that of the temperature. Additionally, the convective heat transfer coefficient increases with the pressure and slightly decreases with the temperature. By analyzing the complex interaction and heat transfer among the flowing bubbles, the behavior of heat transfer enhancement is found. Moreover, a “non-Newtonian thermal conductivity” is introduced in this study, and Nusselt number of the foam fluid with a yield stress is deduced. More importantly, it is found that the behavior of heat transfer enhancement is particularly sensitive to the shear rate, owing to strong interaction among the bubbles in the flowing CO2-based foam.

Supercritical water oxidation (SCWO) is a promising chemical technology for organic waste water and sludge treatment. Our team has successfully constructed the first pilot-scale SCWO plant in China, and the design concept for our first commercial-scale plant is reported in this paper. The challenges that hinder the commercial development of SCWO are introduced, including corrosion, plugging, high investment and operating costs. Some important lab-scale and pilot-scale experimental results are shown, and some key design parameters for the commercial plant are proposed. The technological process, specialized equipment design and new system flowsheet are described objectively. Moreover, an estimate of the equipment investment and operating costs of this commercial plant is carried out, and a comparison is made with other commercial sludge SCWO plants. This information is valuable for guiding how to best design commercial SCWO plants for the treatment of sludge and other feedstocks including solid particles.

Eddy dissipation concept (EDC) model and flamelet generated manifolds (FGM) model are developed separately to study the temperature profiles and extinction limits of non-premixed hydrothermal flames. Predictions by the two models are evaluated comparatively by experimental data in literatures. FGM model shows relatively better prediction of temperature than EDC model in the near nozzle field. Extinction temperatures can be predicted by EDC model with deviations of 10–33 K. The extinction flow rates predicted by the FGM model are higher than those by the EDC model. Flow fields and reaction source terms are analysed to identify the inherent mechanism leading different results by the two models. It is illustrated that the positive effect of turbulence on reaction rate near the nozzle by the FGM model is the essential reason causing different flame characteristics from the EDC model by which the turbulence only has negative effect on reaction rate.

Dry centrifugal granulation technology is an important mean for liquid high-temperature slag. In this paper, the numerical simulation of dry granulation process was carried out to analyze the stretching and splitting process of liquid filaments and study the effects of various factors on liquid filaments and granulated droplets. The results showed that when rotating speed was higher than 1100 rpm, the granulation mode transitioned from sheet mode to ligament mode. When rotating speed reached 3000 rpm, it entered droplet mode. When rotating speed increased, the droplet diameter decreased and the distribution concentration increased. The ratio of the liquid filament diameter to the droplet diameter was approximately 0.7. The increase of the viscosity increased the filament length and the average droplet diameter. Moreover, the increase of the surface tension also increased the average droplet diameter. When the inclination angle of the cup was 45°, the granulated droplets diameter obtained was small.

Activity and stability of the supported Ni-based catalysts for the gasification performances of phenol solution and coal-gasification wastewater in supercritical water were studied in a continuous reactor at 480 °C, 25 MPa and oxygen ratio of 0.2 for 50 h operation. The influences of the supports (γ-Al2O3, active carbon (AC) and carbon nanotube (CNT)) on gas yields, gasification efficiencies for phenol solution were investigated, and the loading amount of Ni were optimized. Results showed that the catalytic activity and the stability of the catalysts followed the order of Ni/CNT > Ni/AC > Ni/γ-Al2O3. The activity of Ni/AC and Ni/γ-Al2O3 decreased after 30 h continuous operation, and there occurred significant leaching of Ni2+. For Ni/CNT catalyst, H2 yield increased obviously when the loading amount of Ni lower than 15 wt%, while increased little at higher loading amount. Then, 15 wt% Ni/CNT with a thickness of 1.5 mm was coated on 316 L stainless steel (SS316L, an economic material usually used as the reactor material), which can act as a "catalytic tube wall" in reactor. The catalytic activity and corrosion resistance of Ni/CNT/SS316L for the gasification of real coal-gasification wastewater were studied. Results showed that Ni/CNT/SS316L gave a great positive effect on H2 production. H2 yield increased from 25.36 mmol/g (total organic carbon) without catalyst to 75.12 mmol/g (total organic carbon) with Ni/CNT/SS316L after operated for 20 h, respectively. However, obvious pealing of the coating was found after 50 h operation. Further study is necessary for the improvement of the coating preparation method.

Co-pyrolysis of biomass and coal has been widely investigated as a promising method to reduce the emission of greenhouse gas. Evaluation on thermochemical behavior and kinetics of the co-pyrolysis process is vital for forecasting reaction performance and optimizing this technology. In this study, the thermochemical behavior of a starch biomass model compound (potato starch), a lignite and their blends during pyrolysis were investigated applying a non-isothermal thermogravimetric analyzer. Furthermore, the iso-conversion method was applied to calculate the activation energy. The results of thermogravimetric experiments indicated that the co-pyrolysis characteristics of the blends cannot be accurately predicted on the basis of pyrolysis characteristics of individual components and their blending ratio. The comparison of experimental and theoretical weight loss curves of the blends revealed that a certain degree of synergistic effect happened in the intermediate stage during co-pyrolysis process, but the volatiles yields in the entire co-pyrolysis process were not obviously impacted. Kinetic analysis indicated that the activation energy values of both individual and blended samples varied with the conversion fractions during pyrolysis process. The mean activation energy values of the blends were basically the same as the estimated values calculated by weighted average.

There are many advantages to using supercritical carbon dioxide (ScCO2) fracturing technology to exploit shale gas reservoirs in China, including minimal damage to the environment or formation, and displacing methane (CH4) in the adsorbed state. When ScCO2 enters fractures in the formation, ScCO2-water-shale interactions may affect the physicochemical properties of shale. In this study, a high-pressure reaction system was adopted to simulate ScCO2-water-shale interactions under ScCO2 stimulation conditions. The element mobilization and pore structure before and after the reaction were measured using ICP-MS, XRF. The results show that the major elements, including Ca, Mg, Na, K, and Al, exhibit varying degrees of mobilization after the interactions because of dissolution of carbonate and silicate minerals in shale samples. Compared with the major elements, trace elements have a lower mobility, quantified as

Supercritical water gasification (SCWG) is a promising technology for converting organic wastes to hydrogen. Less amount of oxygen is beneficial for increasing hydrogen generation rate. However, the corrosion rate of reactor material would be accelerated. TiO2 coating with a thickness of 0.1 mm was prepared on the surface of 316L stainless steel (SS316L) to improve its corrosion resistance in supercritical water (SCW). The corrosion performances of TiO2/SS316L were tested in a bath SCW reactor at 400 °C, 25 MPa. The influences of oxygen concentration (0–1000 mg/L) on surface morphologies and corrosion depths were studied thoroughly. Results indicated that the surface of TiO2/SS316L exhibited cracks and pores after exposed in SCW. And the average corrosion rates accelerated at higher oxygen concentrations. The interface between the coating and medium was relatively smooth and there was no obvious change in the thickness of the coating with oxygen concentration of 0 and 500 mg/L. While for that with 1000 mg/L oxygen, the surface of TiO2/SS316L exhibited reticulate crack. The cross section showed a serrate structure, and only 0.08 mm thick of the coating was remained. In addition, the corrosion mechanism of coating was discussed.

Supercritical water oxidation is a promising alternative for treatment of wastewater and sludge. The addition of auxiliary fuel can achieve the optimization of the system. Owing to the discrepancy ...

Supercritical hydrothermal combustion, a new and promising homogeneous combustion technology with a wide range of application scenarios and broad development prospects, provides creative ideas and means for the enhanced degradation of organic wastes, hydrothermal spallation drilling, thermal recovery of heavy oil, etc. This technology is elaborated upon in five parts: (1) introducing the main devices including semi-batch reactor and continuous reactor to study the hydrothermal flame in accordance with research institutions, (2) presenting the research status of related numerical simulation from the angles of reaction kinetics and flow-reaction, (3) summarizing the characteristics of hydrothermal flame and combustion by five key parameters, (4) dividing up ignition process and explaining ignition mechanism from the perspectives of critical physical properties of water and heat transfer and mixing conditions, (5) discussing and forecasting its industrial applications including hydrothermal spallation drilling, the thermal recovery of heavy oil, the clean conversion and utilization of coal-based fuel, and the harmless treatment of pollutants. By and large, this paper analyzed in detail everything from experimental equipment to industrial applications, from combustion characteristics to ignition mechanisms, and from summary conclusions to prospect prediction. In the end, herein is summarized a couple of existing paramount scientific and technical obstacles in hydrothermal combustion. Further significant studies in the future should include excellent reactors, advanced monitoring techniques, and powerful computational fluid dynamics.

Over the last two decades, the hydrothermal liquefaction (HTL) of algae has emerged as a promising technology for producing liquid bio-oil to meet increasing energy demands and reduce environmental pollution. In this article, the present research status of the catalytic HTL of algae and the catalytic hydrothermal upgrading of biocrude (crude bio-oil) is systematically reviewed and analyzed. The corresponding catalytic characteristics (such as the catalytic effect on the biocrude yield and quality and the related influencing factors) and catalytic mechanisms (e.g., hydrogenation, deoxygenation, decarboxylation, denitrogenation and desulfurization) during algae HTL as well as the approaches for upgrading of biocrude are summarized and analyzed comprehensively. Another potential technological flow for bio-oil production from algae HTL is proposed, and a comparison between direct catalytic HTL and the two-step production method is presented for the first time. Moreover, contemporary problems and subsequent research directions are presented.

Hydrothermal liquefaction (HTL) can chemically convert sewage sludge (SS) into a crude bio-oil (biocrude) and other by-products. This work systematically elucidates how the yields and compositions of different products (e.g., gases, biocrude and solids) vary with temperature (260–350 °C) in SS HTL with 10 min of residence time. The results show that increasing temperature improved the biocrude quality and the gas yield, declined the water-soluble substance yield, the solid yield, and the TOC (total organic carbon) content in aqueous phase, while the biocrude yield and the NH3-N (ammonia nitrogen) content in the aqueous phase first raised and then decreased, and reached the maximum values at 340 °C. After SS HTL at 340 °C, light biocrude, light solids, water-soluble organic matters accounted for about 54.4, 50.5, 88.9 wt% of total biocrude, solids and water-soluble substances, respectively. The N and S contents in the light biocrude almost halved compared with those in the heavy biocrude. The light solids contained a higher C content but lower Al, Si, Ca and Fe contents than did the heavy solids. >93.0 wt% of Cu, Zn and Cr remained in the solids in contrast to 0.5–1.0 wt% in the aqueous phase and 0.2–4.7 wt% in the biocrude.

The solutions of phenol and the mixture of phenol and ammonia were gasified in a continuous supercritical water reactor to evaluate the influences of ammonia on the hydrogen production and the degradation pathways of phenol. The effects of temperature (560–640 °C), reaction time (2–20 s) and concentration of ammonia (500–2000 mg/L) on gaseous distributions, gasification efficiencies and reactants removal efficiencies were investigated. In addition, the effects of ammonia on the kinds of intermediate products were analyzed. Results showed that the increasing temperature greatly promoted the hydrogen production and degradation of phenol. Longer reaction time gave a positive effect on gasification efficiencies in 10 s, while the effect was little when the reaction time longer than 10 s. Ammonia prevented the production of hydrogen and the degradation of phenol, which was mainly due to the generation of more stable nitrogen polycyclic compounds. The possible degradation pathways for the mixture of phenol and ammonia were proposed.

In this study, corrosion behavior of Incoloy 800 was studied in supercritical water containing sewage sludge and oxygen at various temperature from subcritical to supercritical environment. Surface and cross-section morphologies of the oxide films on Incoloy 800 was observed by scanning electron microscope. Corrosion will be obviously accelerated by increasing temperature. And the addition of oxygen in corrosion medium will cause the formation of various inorganic salts, forming a salt deposit layer on sample surface.

As one of the main unconventional gas reservoirs, the exploration and exploitation of shale gas reservoirs has been a hot spot of global resources development. The traditional water-based fracturing fluid with the disadvantages of large water consumption and serious formation damage does not apply to shale gas reservoirs stimulation. Supercritical CO 2 fracturing technology, using harmlessness CO 2 for sand-carrying fluid, was brought forward to apply to development of shale gas reservoirs, with the advantages of no water consumption, no damage to formation, contributing to CH 4 desorption, etc. When applying supercritical CO 2 as the fracturing fluid, in fractures supercritical CO 2 interacts with shale in the presence of water. The study on the interactions of shales and supercritical CO 2 in the presence of water is a basic issues in stimulation of supercritical carbon dioxide within shale reservoirs. The objective of this study is to solve the key problems which the interactions of shale, supercritical CO 2 and water involves, such as mineral elements migration, microscopic pore structure and so on.

Corrosion behavior of Incoloy 825 was studied in high temperature vapor with high concentration of NaCl. After 80 h exposure, a bi-layer structure was formed on sample surface after exposure. The outer layer is consisted of loose and large-grain oxides, and the inner layer is composed of fine-grain oxide. The whole layer was identified to be CrOOH/Fe3O4/Cr2O3/Incoloy 825 from outer to inner.

Hydrothermal liquefaction (HTL) is a promising technique for crude bio-oil (biocrude) production from microalgae. Instead of traditional direct HTL at one temperature with a residence time, the present work explored two temperature steps (TTS) and more temperature steps (MTS) of microalgae (Chlorella) HTLs for the first time in mini-batch reactors. Specifically, the reactions for the TTS of HTL were performed at a relatively low temperature (150–300 °C) for 10–40 min and then at a high temperature (350 °C) for 10–20 min. In the MTS of HTL, three or four temperature steps were adopted and each temperature stage (within 150–300 °C) was kept for 10 min. The results show that the low temperature pre-reaction stage significantly affected the yield, elemental composition, higher heating value, energy recovery and molecular component of biocrude. The biocrude derived from the TTS of HTL of 250*20–350 (i.e., a pre-reaction at 250 °C for 20 min followed by a HTL at 350 °C for 10 min) had the highest H content (9.00 wt%) and the lowest S content (0.55 wt%). Its yield, elemental composition, higher heating value, and energy recovery were comparable with those of the biocrude from the direct HTL at 350 °C for 30 min (with the highest yield and the best quality in tests). In comparison to direct HTL, a proper TTS of microalgae HTL was able to reduce reaction temperature on the premise of ensuring similar biocrude properties, so might be applicable in the algal bio-oil production.

The corrosion behaviors of 316 stainless steel (SS), 316L SS, Inconel 625, Incoloy 825 and Hastelloy C276 were studied in supercritical water (SCW) containing phosphate, sulfate, chloride and/or oxygen. The results show that the alloy corrosion rate in SCW containing oxygen and phosphate was increased by adding sulfate and/or chloride. A two-layer structure of oxide film on 316 SS consisted of an inner layer with Cr-rich oxides (i.e., Cr2O3) and an outer layer rich in phosphates (e.g., FePO4 and Ni3(PO4)2). A three-layer oxide film formed on Incoloy 825 including corrosion products Fe2O3, NiO, FePO4, Ni3(PO4)2 and NiCr2O4, with phosphates in each layer. A two-layer oxide film on Hastelloy C276 was composed of metal oxides in the inner layer and metal oxides as well as phosphates in the outer layer, including Fe2O3, Cr2O3, NiO, MoO2, FePO4, CrPO4, Ni3(PO4)2 and NiCr2O4. The existence of sulfate, chloride, and especially both of them destroyed the formation of water-insoluble phosphates on the oxide film of tested alloy in SCW containing oxygen and phosphate.

CaO-based sorbent deactivation is one of challenges to develop CaO-based chemical looping technology. The replacement of non-renewable natural or expensive synthetic CaO-based sorbents with cheap and environmental CaO-based waste sorbents is an effective way to overcome this challenge. As high CaO content, construction and demolition waste (CDW) has ability to capture CO2. Due to the rapid development of cities, a great deal of CDW is produced every year. According to the characteristics of CDW, six components were selected in this paper. From the initial CO2 carrying capacity, hydrated limestone had the highest initial CO2 carrying capacity, about 0.592 g CO2/g sorbent in TGA and 0.414 g CO2/g sorbent in fluidized bed system, followed by limestone, cement-based limestone, hydrated cement, cement-based sand, cement raw and sand. For multiple carbonation-calcination cycles, cement played a positive role in maintaining high cyclic CO2 carrying capture. Hydration degree and free lime content increased with the increase of hydration time, which improved the CO2 capture performance of CDW. For cement-based sorbents, evidence from this study suggested that extending hydration time played a positive role in improving the attrition resistance and maintaining the initial specific surface area in fluidized bed system.

Early oxidation characteristics of ferritic-martensitic steel T91 in supercritical water (SCW) from 1 h to 120 h were investigated. Relative to austenitic steels, occurrence of each oxidation stage for T91 was delayed. Both inner Cr-rich layer and outer magnetite layer formed even after a 1h-exposure at 540 °C, implying their almost simultaneous formations. Several assembled-pore lines were observed in the inner layer. Abundant pores accumulated at the boundary between the inner/outer oxide layers in steam, while mainly along the inner/diffusion layer interface in SCW, due to lower difference between iron diffusion through the inner and outer layers for the later.

Four kinds of novel polyamides (PAs) containing pyrrole core with different triarylamine (TAA) groups were designed and synthesized. These PAs exhibit good solubility in various organic solvents and excellent thermal stability. The two PAs prepared from cyclohexane-1,4-dicarboxylic acid exhibit fluorescence maximum at 475–476 nm with quantum yields up to 39.0% and 57.3% in N,N-dimethylacetamide (DMAc) solution. Furthermore, the polymer films show reversible electrochemical redoxidation with color changing from yellowish to khaki to dark blue. Especially, the films have high coloration efficiency (up to 143 cm2 C−1 at 750 nm) and after over 1000 s the films still exhibit continuous cyclic stability of electrochromism. What's more, these PAs could be used as the photoelectric conversion material owing to their excellent optoelectronic properties.

Hydrothermal liquefaction of microalgae produces water-insoluble biocrude that spontaneously separates from aqueous phase by gravity. A small proportion of water-soluble biocrude can be obtained via organic solvent extraction from the aqueous phase. This work explored catalytic hydrothermal upgrading of the water-soluble biocrude with five varieties of catalysts (i.e., Pt/C, Pd/C, Ru/C, Pt/C + Pd/C, and newly synthesized CoNiMoW/γ-Al2O3) for the first time. The results show that the upgraded oil by Pt/C had the highest yield and energy recovery but the second lowest quality with respect to elemental composition and heating value. Pd/C led to the highest heating value and the lowest yield and energy recovery of upgraded oil, as well as the largest yields of CH4 and C2H6 simultaneously. Both Pt/C and CoNiMoW/γ-Al2O3 performed well in converting high-boiling-point macromolecules into smaller molecular compounds in water-soluble biocrude upgrading. More than 70% of components in upgraded oils were in the dist...