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The co-thermochemical conversion of Municipal Solid Waste (MSW) and biomass is a new environmental technology and can produce hydrogen-rich syngas. This study investigated the co-pyrolysis of MSW and wheat straw, using a drop-tube furnace experiment. Using a temperature range of 500 °C–1000 °C, the study assessed pyrolysis gas yield, product distribution, gas low heating value, and carbon conversion of co-pyrolysis MSW with different amounts of wheat straw. Adding wheat straw only slightly increases the gas yield and carbon conversion, but improved the carbon monoxide and carbon dioxide in the syngas. At an experimental temperature below 700 °C, adding wheat straw promoted the cracking reaction of hydrocarbon gas, generated by the pyrolysis of MSW. At a temperature of 600 °C, adding 25% wheat straw improved carbon conversion in the blended sample. This study provides a basis for the application of MSW and WS thermo-chemical conversion. [ABSTRACT FROM AUTHOR]

The corrosion behaviors of 316 stainless steel (316 SS), Inconel 600, Inconel 625, Hastelloy C-276 and TA10 coupons exposed in supercritical water (400°C/25 MPa) with sodium chloride, sodium triphosphate and hydrogen peroxide were investigated by using SEM, XRD and XPS. 316 SS shows the most severe spallation of oxide scales and Inconel 600 exhibited the most severe pitting corrosion due to a lack of molybdenum in the alloy. TA10 showed the lowest corrosion rate and the slightest corrosion morphology. TA10 had corrosion rates less than 1.8 mmpy in the four experiments and a triplex oxide layer structure formed which consisted of TiO2/Ti2O3/TiO from outer to inner layer. The formation of (TiO) 2P2O7 was observed on TA10 in oxidizing supercritical water containing phosphate. Phosphate shows significant corrosion inhibition for metal alloys in SCWO due to the formation of a passivating metal phosphate film. An oxide film growth mechanism, metal dissolution mechanism and metal salt precipitation mechanism are discussed in order to explain the corrosion behavior of the specimens in this research. [ABSTRACT FROM AUTHOR]

Supercritical hydrothermal combustion has received a great deal of attention as an innovative and potential treatment technology wherein the corrosion and salt deposition problems during supercritical water oxidation processes can be avoided effectively. A detailed chemical kinetics model for methanol was employed and validated to understand the hydrothermal combustion process mechanism in supercritical water. Based on this elementary reaction model, how the two key indicators (ignition and extinction temperatures) worked during combustion reaction was studied. Moreover, the influences of operational parameters (fuel concentration, oxidation coefficient and reactor type) and corresponding reaction mechanism were investigated. It reveals that H202 was identified as one key intermediate product in the combustion kinetics of methanol. Initial concentration and injection flow rate of aqueous fuel were two significant factors that determined the extinction temperature, which decreased as the concentration increased or the injection flow rate reduced. Moreover, a minimum limit for the initial fuel concentration existed above which a stable hydrothermal flame could form. The oxidation coefficient affected combustion temperature in a manner that depended on the coefficient range. The combustion temperature elevated with the oxidation coefficient in the fuel-rich area while dropped in the oxidant-rich area. This phenomenon was interpreted from the point of view of thermodynamics and mechanism. In order to maintain stable flames at as a low injection temperature as possible, vessel reactors were more desirable to be applied for hydrothermal combustion reaction, deriving from the discrepancy in order of magnitude for flow velocity between tubular and vessel reactors. Finally, it is found that the enhancement of auxiliary fuel methanol in decomposition of organic pollutants stemmed from two reasons: high reaction heat release and co-oxidative effect, whereas the refractory compounds could suppress the ignition of methanol in supercritical water. [ABSTRACT FROM AUTHOR]

In this work the particle size control method of copper nanoparticles synthesized in supercritical water was investigated. The experiments were respectively carried out in a flow-type reaction apparatus and in a batch-type quartz tube apparatus. Results show that particle size of the products was very sensitive to the concentration of copper sulfate and alkalinity of the reactant. When the concentration of copper sulfate increased from 0.05 mol/L to 0.5 mol/L, the average particle size increased from 14nm to 50 nm. When the molar ratio of NaOH to copper ion increased from 0:1 to 2:1, the average particle size decreased from 85 nm to 14 nm. The homogeneity and dispersity of the products were improved by increasing the concentration of complexing agent ethylenediamine tetraacetic acid (EDTA). The adsorption mechanism of EDTA on the surfaces of nanoparticles was researched by a Fourier transform infrared spectroscopy. It was speculated that EDTA adsorbed on the surfaces of nanoparticles by the dehydration reaction of carboxyl groups in the molecule of EDTA and hydroxyl groups on surfaces of copper nanoparticles (-Cu-OH). These results are expected to be of great interest as basic data for the preparation of size-controlled copper nanoparticles by supercritical hydrothermal synthesis method. [ABSTRACT FROM AUTHOR]

In this research, we studied supercritical water oxidation (SCWO) of a pesticide wastewater under a wide range of operation conditions in two reaction plants. The results show that reaction temperature, oxidant coefficient (OC), and residence time (t) can improve the wastewater XCOD (removal efficiency of chemical oxygen demand). The residence time and OC have important influences on XCOD at higher reaction temperatures (>500 °C). It is significant to increase the preheating rate for the XCOD improvement of the pesticide wastewater in SCWO. XCOD and XTN (removal efficiency of total nitrogen) are 99.42% and 86.70% at 600 °C, 25 MPa, OC = 3.0 and t = 2.0 min, respectively. More than 92wt% total organic carbon (TOC) and 86.70 wt% total nitrogen in the wastewater are converted into CO2 and N2 under the above conditions, respectively. Inconel 625 can be used as the reactor material in the wastewater SCWO plant, and its corrosion rate is approximately 0.6mm/year at 600 °C, 25 MPa and OC = 3.0 conditions. We also primarily design a 100 t/d SCWO plant for the tested pesticide wastewater treatment on the basis of accomplished investigations. SCWO together with traditional wastewater treatment methods is proposed to harmlessly dispose the complicated wastewater. This information is valuable for guiding the large-scale SCWO plant design for pesticide wastewater treatment. [ABSTRACT FROM AUTHOR]

Reactor corrosion and plugging problems have hindered the commercialization of supercritical water oxidation (SCWO) for wastewater purification. The use of transpiring wall reactor (TWR) is an effective means to overcome the above two problems by forming a protective water film on the internal surface of the reactor to aviod contacting corrosive species and precipitated organic salts. This work mainly aims to objectively review experimental investi-gations and numerical simulation results concerning TWR. Subsequent investigations for parameters optimizations of TWR are also proposed in order to ultimately build effective regulation methods of obtaining excellent water film properties. All this information is very important in guiding the structure design and operation parameters optimization of TWR. [ABSTRACT FROM AUTHOR]

In this article, an experimental study on rheological properties and proppant transport performance of the GRF-CO2 system is performed by using a large-scale high-temperature and high-pressure foam fracturing fluid test system with the correlations for fracturing fluid rheological parameters, critical settling velocity and proppant settling velocity obtained. Research results show that the effective viscosity decreases with increasing temperature and shear rate. The effective viscosity increases with increasing foam quality in foamed cases, and decreases with increasing foam quality in unfoamed cases. The temperature and foam quality effect on parameters of the rheological properties of the fracturing fluid is larger than the pressure in various influencing factors. The critical settling velocity increases with the rise in temperature in foaming cases, and decreases with the rise in foam quality and sand ratio. The reunion phenomenon happens after the sand ratio is more than 25%. The correlations for GRF-CO2 fracturing fluid rheological index, rheological coefficient, final proppant settling velocity in the solution and the critical settling velocity have been obtained with an average error of calculation less than 14%. [ABSTRACT FROM AUTHOR]

Copper complex ethylenediamine tetraacetic acid (Cu(II)-EDTA) was oxidized in supercritical water in a continuous tubular reactor at temperatures 420-500°C, residence times 57-144s, and a pressure 25MPa. The major carbon containing products were CO2 and CO. The TOC conversions increased steadily with reaction temperature and residence time, and the yield of CO can be effectively reduced at elevating temperatures. Ammonia was determined to be the main refractory nitrogen-containing intermediate, whose oxidation was supposed to be enhanced by the copper in Cu(II)-EDTA. In addition, the copper transformed into copper oxides (CuO and CU2O), and was removed from the Cu(II)-EDTA solution with high efficiency. Based on the experimental results and the analysis of reaction pathways, a global Arrhenius kinetic model was proposed to predict the removal of TOC and the yield of the intermediates NH3 and CO. With this kinetic model, a computational fluid dynamic (CFD) model of the tubular reactor was implemented to assist the experimental study. The composition profiles of TOC, CO, and CO2 along the reactor were simulated and compared with the experimental results. Operating parameters, reaction temperature and oxygen flow rate, were optimized based on the simulation results. [ABSTRACT FROM AUTHOR]

Supercritical water oxidation (SCWO) is a promising technology to deal with organic wastes. Nowadays, we have successfully constructed the first SCWO pilot scale plant of China with a specific reactor configuration and optimized system compositions to treat sewage sludge. In this report, the existing problems and corresponding solutions concerning corrosion, plugging and high running cost in SCWO are introduced systematically. The detailed system components, evident properties, advanced control methods and primary experiment results of the pilot scale plant are described objectively. Moreover, a simple economical comparison with incineration is carried out and subsequently in-depth works are also proposed for further promoting the commercial application of the plant. The information should be helpful for designing and constructing SCWO plant to dispose sewage sludge or other organic wastewaters. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]