Zhenzi Jing

A three‐dimensional stochastic rock mechanics model of engineered geothermal systems in fractured crystalline rock

A three-dimensional (3-D) stochastic network model for simulating a hot dry rock (HDR) or hot wet rock (HWR) engineered geothermal system formed in fractured crystalline rock is presented. The model addresses the problems of fracture network characterization from in situ field data, such as fracture orientation, size, spacing, and other mechanical properties. The model can simulate the changes that occur within the rock mass during stimulation (i.e., large volume fluid injection at pressures sufficient to allow shear slip on natural fractures). It can also be used to simulate steady state circulation of the heat exchange system thus created and includes provision for predicting tracer response curves and heat extraction history. The model has been applied to data gathered during the stimulation and circulation of a 2.2-km-deep HDR reservoir at Hijiori, Japan. The predicted shape of the stimulated and shear-propped fractures closely matched the distribution of seismic source distribution of acoustic emission (AE), regardless of realization of the fracture network, suggesting that the geometry of the stimulated volume can be robustly predicted from knowledge of the fracture population and in situ stresses. However, hydraulic behavior and tracer tests during the circulation could only be satisfactorily simultaneously reproduced by a small subset of realizations. These selected realizations, obtained by matching initial circulation and tracer data, are considered to give the best prospect of satisfactory long-term thermal modeling. The success in simultaneously modeling diverse data (hydraulic, microseismic, and tracer) lends confidence to the thermal predictions. The results indicate that a large improvement in the long-term thermal performance of the Hijiori reservoir could result from increasing well spacing from 100 to 150 m without major degradation of the hydraulic performance.

A 3-D water/rock chemical interaction model for prediction of HDR/HWR geothermal reservoir performance

A three-dimensional (3-D) water/rock chemical interaction model has been developed to examine the effect of water/rock chemical interaction (WRCI) on the long-term performance of hot dry rock and hot wet rock (HDR/HWR) reservoirs. The model, which integrates many field observations and thus generates a fracture network very similar to the natural fracture distribution in the reservoir, can predict the influence of WRCI on the overall fractured reservoir. Factors affecting WRCI and the effect of WRCI on long-term performance of Hijiori deep reservoir (Japan) have been modelled. Simulated results show that fluid chemistry, initial rock temperature, magnitude of flow rate and well spacing have a major effect on WRCI, and for such a multi-well Hijiori geothermal system, WRCI seems to make the flow distribution tend towards uniformity. The model described deals solely with chemical interactions as a function of flow rate and temperature, and takes no account of aperture variation as a result of thermoelastic effects. It is only a partial model, though it could form an important module of a coupled model.

Hydrothermal solidification of municipal solid waste incineration bottom ash with slag addition

Solidification of municipal solid waste incineration(MSWI) bottom ash into a building material with high strength and less heavy metal dissolution has been carried out using a hydrothermal processing method.The hardening mechanism of hydrothermal solidification of MSWI bottom ash by adding slaked lime was investigated in this study.Moreover,leaching tests were also conducted to determine the amount of heavy metals dissolved from the solidified specimens.The experimental results showed that the strength development of the solidified specimens with slaked lime addition was due primarily to the tobermorite formation and the more the tobermorite formed,the higher the strength was.MSWI fly ash also could be used as an additive to solidify bottom ash,and the hardening effect of solidification was favored to be similar to that with slaked lime addition.Under the hydrothermal processing,the amount of heavy metals dissolved from the solidified specimens was reduced greatly.As such,the hydrothermal processing may have a high potential for recycling MSWI bottom ash.Hydrothermal solidification of municipal solid waste incineration (MSWI) bottom ash has been carried out under saturated steam pressure (1.56 MPa) at 200 degrees C for up to 24 h by mixing quartz, slaked lime and water-cooled blast furnace slag (WBFS). The strength enhancement for the WBFS addition was best. The strength development was shown to be due mainly to tobermorite formation, and the tobermorite formation densified matrix, thus promoting the strength development. WBFS seemed to have a higher reactivity than the quartz during the initial hydrothermal process, which provided more silica available to harden the solidified specimens. However, a longer curing time (24 h) was favorable to the quartz dissolution for tobermorite formation, which in turn, enhanced the strength for quartz addition. Curing time affected the crystal morphology evolution, and the stubby plate of tobermorite seemed to result in a high strength enhancement in this study. Laboratory leaching tests were conducted to determine the amount of heavy metals dissolved from the final solidified specimens, and the leaching results showed that after hydrothermal processing the heavy metals dissolved from the solidified specimens were reduced effectively. As such, the hydrothermal processing may have a high potential for recycling/reusing MSWI ash on a large scale.

A novel hydrothermal method to convert incineration ash into pollucite for the immobilization of a simulant radioactive cesium

The Fukushima nuclear accident in Japan on March 11, 2011 produced huge amounts of Cs-polluted incineration ashes; conventional solidification methods seem unsuitable for the treatment of large amounts of Cs-polluted ashes. A novel hydrothermal method was developed to directly convert Cs-polluted incineration ash (rice husk ash) into pollucite to immobilize Cs in its crystal structure in situ. Results revealed that pollucite could be synthesized readily over a wide range of added Cs (Cs/Si=0.2-0.6); the addition of more Cs (Cs/Si≥0.5) caused the formation of a small amount of cesium aluminosilicate (CsAlSiO4), which exhibits poor immobilization behavior for Cs. Pollucite could be formed even for a short curing time (1h) or at a low curing temperature (150°C). However, a high curing temperature or a long curing time favored the formation of a pure pollucite. With the added calcium hydroxide, a tough specimen with a flexural strength of approximately 22MPa could be obtained, which suggested that this technology may be applied directly to the solidification of Cs-polluted incineration ashes. Hydrogarnet and tobermorite formations enhanced the strength of the solidified specimens, and meanwhile the formed pollucite was present in a matrix steadily. Leaching test demonstrated that the amount of Cs that leached from the synthesized specimens was very low (0.49×10(-5)-2.31×10(-5)) and even lower than that from the reference hollandite-rich synroc (2.0×10(-2)), although a higher content of Cs was found in the synthesized pollucite specimens (6.0-31.7%) than in the reference (3.7%). Therefore, the hydrothermal conversion of Cs-polluted incineration ash into pollucite can be applied to immobilize Cs directly.

Hydrothermal solidification behavior of municipal solid waste incineration bottom ash without any additives

Municipal solid waste incineration (MSWI) bottom ash could be solidified with and without slaked lime (calcium hydroxide) addition by a hydrothermal method under steam pressure of 1.56 MPa at 200 °C for up to 72 h. Experimental results showed that CSH gel or tobermorite exerted a main influence on strength development, and without any additives CSH gel was easy to form, while slaked lime addition favored to form tobermorite. Tobermorite seemed to exert a larger effect on the strength development than CSH gel. Leaching results showed that the concentrations of heavy metals dissolved from the solidified specimens were effectively reduced after hydrothermal processing. The immobilization was mainly due to the tobermorite or CSH gel formation, and Pb2+ and Zn2+ seemed to be fixed more readily than Cr6+, which might be the reason that the structural Ca2+ within tobermorite or CSH gel was exchanged by Pb2+ and Zn2+ more easily than Cr6+. In addition, there existed a close relationship between leaching concentration and strength enhancement, and a higher strength seemed to exert a larger effect on immobilization of heavy metals.

Potential utilization of riverbed sediments by hydrothermal solidification and its hardening mechanism.

Hydrothermal solidification of riverbed sediments (silt) has been carried out in a Teflon (PTFE) lined stainless steel hydrothermal apparatus, under saturated steam pressure at 343-473 K for 2-24 h by calcium hydrate introduction. Tobermorite was shown to be the most important strength-producing constituent of the solidified silt. A longer curing time or a higher curing temperature was shown to be favorable to the tobermorite formation, thus promoting strength development; however, overlong curing time (24 h) seemed to affect the strength development negatively. The hardening mechanism consisted of the crystal growth/morphology evolution during the hydrothermal process. The species dissolved from the silt were precipitated first as fine particles, and then some of the particles seemed to build up the rudimental morphology of calcium silicate hydrate (CSH) gel. The CSH gel, with precipitated particles, appeared to cause some reorganization within the matrix, which made the matrix denser and thus gave an initial strength development. Tobermorite, transformed inevitably from the CSH gel, reinforced the matrix with its interlocked structure, and thus further promoted the strength development.

Hydrothermal solidification of diatomaceous earth with analcime formation

Diatomaceous earth (DE) solidifies hydrothermally with analcime formation. With analcime formation, strength development was much greater than that with calcium silicate hydrate (CSH) formation. NaOH addition conditioned analcime formation because NaOH solution not only promoted dissolution of quartz and montmorillonite but also provided Na+ to form the analcime. Curing temperature and time affected analcime formation, and, in this study, over 6xa0h (at 200xa0°C) and 175xa0°C (for 12xa0h), analcime seemed to form readily. After hydrothermal treatment, the skeletons of diatoms can still be seen in the solid after analcime formation but can hardly be found after CSH formation.

Synthesis and microstructure analysis of autoclaved aerated concrete with carbide slag addition

Synthesis of autoclaved aerated concrete (AAC) has been carried out with carbide slag addition, and the carbide slag could be used as a main material to produce the AAC with the compressive strength about 2 MPa and the density below 0.6 g·cm−3. In this study, quartz sand acted as frame structure phase in the matrix, and quartz addition also influenced the Si/Ca of starting material. Tobermorite and CSH gel were formed readily at 62%, which seemed to enhance the compressive strength of samples. Curing time seemed to affect the morphology of phase produced, and specimen with the plate-like tobermorite formed at 10 h appeared to have a better compressive strength development than the fiber-like one at 18 h. The higher curing temperature seemed to favor the tobermorite and CSH gel formation, which also exerted a significant effect on the strength development of the samples. On the micro-scale, the formed CSH gel was filled in the interface of the matrix, and the tobermorite appeared to grow in internal-surface of the pores and interstices. The tobermorite or/and CSH formation seemed to densify the matrix, and therefore enhanced the strength of the samples.

Production of carboxylic acids from glucose with metal oxides under hydrothermal conditions

Production of low molecular weight carboxylic acids from glucose with the addition of metal oxides under hydrothermal conditions was investigated. The results showed that CuO, as an oxidant can significantly promote the production of lactic acid, and can also promote the production of acetic acid and formic acid. Fe3O4 can also enhance lactic acid production as a catalyst. The highest yields of 37.1, 9.4, and 4.9xa0% for lactic acid, acetic acid, and formic acid were achieved, respectively, which occurred at 300xa0°C for 60xa0s with CuO 1.5xa0mmol, NaOH 2.5xa0M, and water filling 35xa0%.

Hydrothermal synthesis of rock to immobilise nuclide Cs

Abstract To deal with the soil polluted by radioactive nuclide Cs like that in Fukushima, Japan. As pollucite evolves via analcime into clay mineral finally in nature, the analcime and final pollucite should be synthesized from clay minerals. A hydrothermal technology has been applied to synthesize rock to immobilize radioactive Cs within soil for this purpose. The results showed that Gmelinite seemed to precipitate at lower Na/Al molar ratio of starting materials easily, while analcime formed at higher Na/Al. Pollucite was synthesized with meta-kaolin and different Cs compounds (CsOH or CsCl), and more pollucite was formed by CsOH addition, while Cs located inside structure of analcime (solid solution) with addition of CsCl. The pollucite morphology added by CsOH exhibited nano-scale spheroidal aggregate, while analcime gave morphology of triakioctahedron and hexagonal prism.