Yan Hui Li

High-Pressure Direct-Fired Steam-Gas Generator (HDSG) for Heavy Oil Recovery

High-pressure direct-fired steam-gas generator (HDSG) is to produce multiplex thermal fluid (contains water, CO2, N2 etc.) through efficient direct-contact heat transfer, which would utilize the flue gas heat and reduce the gas emission caused by ordinary boiler. Furthermore, the multiplex thermal fluid can promote the heavy oil recovery by both steam flooding and miscible flooding. This paper introduced three kinds of HDSG: pressurized submerged combustion vaporization (PSCV), multiplex thermal fluid generator and supercritical hydrothermal combustor, which are different in work pressure and method of mixing water and flue gas. Then, we discussed the economic efficiency of HDSG used for heavy oil recovery and concluded that although the pressurization of fuel and oxygen would cost as much as the energy saved by utilizing the flue gas heat, using HDSG for heavy oil recovery has other incalculable benefits such as miscible flooding, waste water treatment and reduction of heat loss through injection well. Finally, we indicated that supercritical hydrothermal combustor will be the trendy of HDSG and pointed out the future research should be carried out on the heat and mass transfer characteristic of the combustion field when water presents and the combustion stability and completeness when pressure increases.

Supercritical Water Oxidation of Fulvic Acid as a Model Organic Compound in Landfill Leachate

Fulvic acid (FA) is a common refractory organic compound in landfill leachate. The degradation of FA in supercritical water oxidation (SCWO) was conducted in a SS 316 batch reactor. The effects of temperature, pressure, residence time, oxidation ratio and initial FA concentration on the degradation of FA were investigated. Results showed that FA could be easily destructed in SCWO process, and a total organic carbon (TOC) removal efficiency of 98.0% was available at 600 °C, 420 s, 25 MPa and 1% FA. Oxidation coefficient had a significant positive effect on the degradation of FA. Total carbon (TC) and TOC removal efficiencies increased from 78.9 % to 97.2 % and from 86.4 % to 97.2, respectively, when oxidation coefficient increased from 0 to 4. Benzene, phenol and naphthalene could be regarded as the intermediate products in SCWO.

Review of Supercritical Water Oxidation in Hydrothermal Flames

Supercritical water oxidation in hydrothermal flames is a promising method for the total destruction of refractory compounds because it can overcome corrosion and salt deposition problems. In case of wastewater with a low reaction heat, the use of auxiliary fuels, to increase the reaction heat for the auto thermal operation is necessary. Methanol and isopropyl-alcohol were usually used as fuels. This paper compares the two fuels in hydrothermal flames and reviews the experimental results of salts, acetic acid, dioxins, ammonia, sludge and phenols of naphthalene and toluene. The results show that the destruction process obtains high TOC removals, and phenols are easy to cause soot formation problems. If soot deposition problems can be solved, supercritical water oxidation in hydrothermal flames will have a bright prospect for commercial applications.

Analysis on the Structure and Mechanism of Cracking and Spalling for Super304H Steel Oxide Films in High-Temperature Steam

In this paper, by means of Scanning Electronic Microscope (SEM), X-ray diffraction analyzer (XRD) and Cross hatch scanning analysis, the Structure and mechanism of cracking and spalling for Super304H steel oxide films in high temperature steam were investigated. With the oxidation proceeding, the surface of Super304H steel specimens is covered by a large amount of tiny holes, which causes the occurrence of an outer oxide layer. The Super304H oxide film generally has a double-layer structure: the outer layer mainly for iron oxide Fe3O4, also being covered by a small amount of Fe2O3, and the inner layer with the FeCr2O4 spinel phase as primary component. Because of the inhomogeneity of oxide distribution, large amounts of smaller gaps appear in the Super304H steel oxide films. Due to the differences among the outer layer, the inner layer and steel matrix in thermal expansion coefficient, when the steam temperature around the specimen changes periodically, the stress variation arise in the Super304H steel and oxide films, which causes the cracking and spalling of oxide films.

Research on a Surface Shot Peeling Process for Increasing the Anti-Oxidation Property of Super304H Steel in High-Temperature Steam

At present, the superheater and reheater pipes in supercritical and ultra-supercritical boilers have encountered with widespread problems of high temperature steam oxidation, seriously affecting the operation safety and economy of the power generation unit. After several tests and contrastive analysis on the main chemical composition and microstructure of specimens before and after shot peening treatment, this paper developed a set of detailed surface shot peening process with specific process parameters, and finds that for the Super304H oxide film, the relative content of Cr element increases by shot peening treatment, with the relative Cr content of the treated specimen being 2.65% higher than that of the untreated, displaying that the anti-oxidation properties of high chromium austenitic steels in high temperature steam is effectively increased.

The Treatment of Concentrated Landfill Leachate from Membrane-Based Processes by Supercritical Water Oxidation

Supercritical water oxidation (SCWO) of concentrated landfill leachate has been carried out in a batch reactor in fluidized bed sand bath, operated under varied temperature (450-600 °C), pressure (23-29 MPa), residence time (5-20 min) and oxidation coefficient (1.5-3.0). The experimental results indicated that temperature and oxidation coefficient had significant influences on the oxidation reaction, whereas the pressure and residence time were not crucial factors. The chemical oxygen demand (COD) and ammonia nitrogen (NH4-N) removal efficiencies could reach up to 99.23% and 98.64% at 600 °C, 25 MPa and 5 min with a oxidation coefficient of 2, respectively, and the effluents could be discharged harmlessly.

Comparative Analysis on Corrosion Behavior of 316SS and 304SS in Subcritical and Supercritical Aqueous Systems

The corrosion characteristics of 316SS and 304SS in subcritical and supercritical aqueous systems including chloride of approximate 4600 mg/L at 25 MPa and 250 °C, 350 °C, 425 °C, and 520 °C are comparatively investigated. Some local corrosion areas occurred on the surfaces of SS316, not on that of 304SS, at 250 °C and 425 °C, while at 350 °C, all the sample surfaces were covered by large amounts of corrosion products and clay materials due to the predominant precipitation for the formation of the outer subscale. Whether in reducing subcritical and supercritical industrial sludge suspension or in oxidizing supercritical sludge system, 304SS owns better corrosion resistance than 316SS due to higher chromium concentration of former.

Supercritical Hydrothermal Synthesis of Ultra-Fine Copper Particles Using Different Precursors

Supercritical hydrothermal synthesis is a green synthesis method for metal and metal oxide ultra-fine particles. Ultra-fine copper particles are of great interests for the researchers because of the excellent performance in recent years. In this paper, supercritical hydrothermal synthesis of copper ultra-fine particles with three different precursors (CuSO4, Cu(NO3)2, Cu(HCOO)2) are reported. This thesis reports that different products are produced with different precursors. Also, three kinds of reaction mechanisms with different precursors in supercritical water were explained. The conversion of copper ions in the reaction of Cu(HCOO)2 in supercritical water is the highest, the value reaches 100.0%. In the process of synthesizing ultra-fine copper particles, different additional HCOOH concentrations (0, 0.1 mol/L, 0.2 mol/L) and different reaction times (5 mins, 10 mins) were applied. Zero-valent ultra-fine copper particles without impurity were synthesized. The synthesized copper ultra-fine particles were cubic aggregations with micro-meter size

Experimental Study on the Supercritical Water Co-Oxidation of Municiple Sludge with Methanol

The influence of methanol on the sludge removal rate of COD was investigated and the mechanism was obtained. The results show that the adding of methanol solution can improve the sludge COD removal rate, when the mass fraction of methanol is 5%, COD removal rate can be highly 99.98% compared 98.26% of that without methanol. The mechanism of co-oxidation is that methanol oxidation process can produce free radicals HO· and HO2·, they attack intermediate phenol and acetic acid, promote acetic acid to C-C bond fracture and ring-opening of phenol.

Influence of Alloying Element on Corrosion Behavior of Hastelloy C-276 in Supercritical Water

The corrosion tests of Cr, Fe and Ni of Hastelloy C-276 were studied at high temperature and pressure with different aggressive components. The results were investigated by means of graphite furnace atomic absorption spectrophotometer (AAS). The Cr forms stable oxide and NiO is unstable. There is a synergistic effect between salt and oxygen leading to a severe loss of metals. The PO43- can improve the resistance to corrosion for Hastelloy C-276 due to the low-solubility phosphates. The colors of effluences can better support the changed concentrations of metals. The lost metals can reveal the corrosion mechanism of Ni-based alloys.