Present state and strategies are summarized on the recovery of anions in the wastewater, based on crystallization engineering. Anion which gives undesirable influence to the environment has been removed by coagulation and precipitation methods to produce a large amount of sludge, requiring wide space for its disposal. Recently steep increase in the price of the resources and deep concern about drying-up of resources have accelerated recovery of ions in the wastewater. Consequently many researches have been done to selectively separate a desirable ion. Crystallization is one of the suitable processes for this purpose, because it can remove and recover ions as the form of purified and stable crystals. In application of crystallization to the wastewater treatment, solid-liquid equilibrium, metastable zone width (MZW), degree of supersaturation, crystallization kinetics (crystal growth, nucleation and so on) and selection of seeds and desirable seed amounts should be given. Examples and strategies on phosphate and fluoride recovery are shown.
Compressive fracture process of rock under the uni-axial compression is discussed, as a result of the sub-critical crack growth in it. A numerical procedure for the failure prediction is presented and discussed, basing upon the critical pressure-crack elongation curve (pc - a curve) for the pure mode I crack propagation (KII = 0, KI = KIC) in the homogenized joint model, which is analyzed by means of the Stress Compensation-Displacement Discontinuity Method (SC-DDM). The crack elongation rate (da/dt) is formulated by the empirical equation of the form of da/dt ∝ KIn, where n: the sub-critical crack growth index. The applied stress-crack elongation curve (p - a curve) in the uni-axial compression test is analyzed to clarify the strain rate dependency of the macroscopic compressive strength (Sc), and the time-crack elongation curve (t - a curve) in the creep test of the uni-axial compression is analyzed to evaluate the effect of applied stress upon the lifetime (tF). It is concretely shown that the non-linearity of stress-strain curves and time-strain curves is deeply associated with the sub-critical crack growth in rock. Moreover the significant influence of heterogeneity and in-homogeneity of rock is discussed by presenting a parallel plate model to assess the damage effect and so on.
Methane hydrate (MH) is one of the potential natural gas resources in near future, because it exists in marine sediments or in permafrost regions worldwide. To evaluate the productivity of methane gas from MH reservoirs, it is necessary to develop a gas production simulator for doing case studies. In this study, for the purpose of numerical simulation on MH dissociation process, we carried out an experimental study for estimating permeability of a MH reservoir with compaction of the sediments due to decrease of effective stress in pore space. In actual hydrate fields, it is supposed that vertical consolidation of sediments occurs whereas gas and water flow in a horizontal direction. To reproduce such a situation, we attempted to measure the permeability of artificial MH sediment under the horizontal radial flow condition by using a specially designed apparatus. First, we investigated the relationship between absolute permeability and MH saturation in this radial flow system. When MH saturation increased from 0 to 0.30, permeability decreased from 12.0μm2 to 1.19μm2 that was one 12th of the value of sand matrix without any MH formation. The same tendency of permeability changes was obtained in liner flow system as previously reported, so the measuring technique of permeability by using radial flow system has been established. Second, by using the similar apparatus, compaction-permeability tests were conducted to formulate absolute permeability as a function of porosity and MH saturation. From experimental results, it was found that permeability decrease due to consolidation was remarkable in the cases of small sand grain diameter and large initial porosity. We determined the parameters of permeability reduction factor for porosity through a numerical analysis, and derived the final form of absolute permeability equation for MH reservoirs.
To contribute to the treatment of spent solution discharged from industry, decomposition reaction of cyanide solution containing Ag(I) by the photocatalytic and/or ozone oxidation route was investigated. The main findings obtained were as follows: 1) Ag(CN)2- ion in cyanide solution is photocatalytically reduced to elemental Ag by TiO2 or ZnO catalyst powder, but exhibits an induction period at the initial stage under the air bubbling condition. By contrast, there was no induction period under N2 gas bubbling condition. Precipitation of Ag powder was far slower than that under air bubbling. Simultaneously CN- ion is oxidized to CNO-, and subsequently to NO3- and CO32-. Oxidation of CNO- ion was significantly slower under N2 gas bubbling than under air bubbling. 2) ZnO is a more efficient photocatalyst for Ag( I ) cyanato complex, however limited consumption of the ZnO catalyst is unavoidable. 3) Using ozone as a decomposing agent for cyanide solution containing Ag(CN)2-, AgCN is precipitated. However, complete removal of Ag( I ) is not expected by this method. In contrast, the addition of KCl to the solution leads to complete Ag( I ) removal, producing AgCl instead of AgCN. 4) Using ozone and photocatalytic reactions at the same time, production of CNO- ion by oxidation of the CN- ion can proceed faster than that using each reaction independently, precipitating Ag2O2 powder. However, complete removal of Ag( I ) is not expected. AgCl instead of Ag2O2 is recovered by the addition of KCl to the solution.
The official discussion on the post-Kyoto framework and target of CO2 emissions reductions began. In order to stabilize atmospheric CO2 emissions, the world should tackle to require deep cuts of CO2 emissions. CO2 capture and storage (CCS) technology is expected to play an important role in the deep cuts. This paper summarizes the cost of the geological storage of CO2 in Japan in order to consider future research, development and deployment (RD&D) from the viewpoint of the economics of CCS; these would be based on the information of the obtained cost structure. According to the analysis results, the costs, particularly those of the transportation by pipeline and of CO2 injection, strongly depend on the scale of the facilities. Therefore, the distance of the transportation of CO2 should be minimized in the case of small-scale storage, particularly in Japan. A mixed-integer programming model has been developed to take into account the adverse effects arising from the scale of economy with regard to the transportation and injection cost for the geological storage of CO2. The model is designed to evaluate CCS and other CO2 mitigation technologies in the energy systems of Japan. With all these adverse effects due to the scale of economy, the geological storage of CO2 will still be one of the important options for CO2 emission reduction in Japan for most of the analyzed cases in this study.
Monitoring has been identified as one of the highest priority needs to provide safe and secure storage of CO2. Monitoring of CO2 plays several diverse and critical roles in the development and acceptance of geologic storage. To ensure the safety of storage projects by demonstrating that CO2 is retained in the formation, it is necessary to verify the mass of CO2 that has been stored in the subsurface. It is also necessary for monitoring sweep efficiency and determining whether the available storage capacity is being used effectively. This paper provides information on monitoring technologies (including 3D seismic, VSP, well logging, and surface monitoring of rates and compositions of natural and introduced chemical tracers) that can serve all these purpose, by both drawing from relevant experience across a number of monitoring applications and presenting the results of original research on this topic.
A pilot test of geological sequestration of CO2 is been performed by RITE in cooperation with ENAA from 2000. The test site is located at the Minami-Nagaoka gas field in Nagaoka city, 200km north of Tokyo. One injection well and three observation wells were drilled. CO2 of supercritical phase was injected into an onshore deep saline aquifer of 1100m in depth. The injection was conducted at the rate of 20 to 40tonnes per day over the 18 month period between 2003 and 2005 with a cumulative amount of 10405tonnes. A series of monitoring consisted of time-lapse well logging, time-lapse crosswell seismic tomography, bottom-hole pressure/temperature measurement, fluid sampling and micro-seismicity monitoring has been successfully carried out to grasp the movement of injected CO2 during and after the injection. History-matching simulation was performed to interpret the measured results. Long-term fate of injected CO2 was predicted using the last model of history matching, implying the location and size of the CO2 to remain almost unchanged from those at the end of injection in the test area over a period as long as 1000years. The monitoring at the test site will be continued until 2007.
Pilot test of carbon dioxide (CO2) injection into a saline aquifer has been conducted under cooperation of Research Institute of Innovative Technology for the Earth (RITE) and Engineering Advancement Association of Japan (ENAA) in Nagaoka-City, 200km north of Tokyo. One injection well and three observation wells were drilled in the site. Totally 10405 ton of CO2 was injected into the aquifer. In order to grasp the movement of CO2 and to evaluate properties of the aquifer for simulation study, several kinds of well tests have been carried. Tests include three water production tests and two step rate tests for the purpose of evaluation of permeability of the aquifer and injectivity of the injection well, spinner survey in order to investigate injection profile of the perforated interval of the injection well and formation fluid sampling and their analysis so as to see fluid distribution in the formation behind the observation well. With these tests, CO2 movement was clearly understood and several formation properties were quantified and introduced to the simulation model.
A pilot-scale sequestration of CO2 into an onshore aquifer has been conducted by Research Institute of Innovative Technology for the Earth (RITE) in cooperation with Engineering Advancement Association of Japan (ENAA) . The CO2 injection site is located at Minami-Nagaoka gas field, Nagaoka city, Niigata prefecture, Japan. One injection well (IW-1) and three observation wells (OB-2, OB-3, OB-4) were drilled. CO2 was injected into a thin permeable zone of the reservoir at 20-40 tonnes per day. The CO2 injection started on 7 July 2003, and ended on 11 January 2005 with the total CO2 amount of 10,400 tonnes. The pilot-scale demonstration allowed an improved understanding of the CO2 movement in a porous sandstone reservoir, by conducting time-lapse geophysical well logs at the three observation wells. CO2 breakthrough was identified by induction, sonic, and neutron logs. The sonic P-wave velocity decreased up to 28% at OB-2, and 13% at OB-4. Small effects of CO2 saturation on resistivity resulted in small changes in induction logs when the reservoir was partially saturated.
Japan's first pilot-scale CO2 geological sequestration experiment has been conducted in Nagaoka, where 10400t of CO2 have been injected in an onshore brine aquifer at a depth of about 1100m. Among various measurements conducted at the site for monitoring the injected CO2 , we conducted time-lapse crosswell seismic tomography between two observation wells to determine the distribution of CO2 in the aquifer by the change of P-wave velocities. The crosswell seismic tomography measurements were carried out six times; once before the injection as a baseline survey, three times during the injection and twice after injection as monitoring surveys. The velocity tomograms resulting from the monitoring surveys were compared to the baseline survey tomogram, and velocity difference tomograms were obtained. The velocity difference tomograms showed that velocity had decreased in a part of the aquifer around the injection well, where the injected CO2 was supposed to be distributed. We also found that the area in which velocity had decreased was expanding in the formation up-dip direction, as increasing amounts of CO2 were injected. Seismic tomography successfully delineated the injected CO2 distribution as a velocity reduction area even when only 3200t of CO2 was injected. The maximum velocity reductions observed were 3.5%. However, it was much smaller than that observed by sonic logging (more than 20%). One of the reasons why the velocity reduction by tomography was so small was the occurrence of low velocity artifacts. In order to estimate more accurate velocity reduction values, we tried to apply a restriction to the tomographic reconstruction algorithm, in which velocity update was allowed only in a fixed area. As the result, maximum velocity reduction value became 14.3% which is still smaller than that obtained by sonic logging, but is reasonable value. Further studies are needed to estimate CO2 saturation distribution from the velocity difference tomograms.
The simulator for geological CO2 sequestration was developed by adding to a commercial compositional oil reservoir simulator the functions of geochemical reactions and fracture occurrence/fault activation. The resulting simulator, GEM-GHG, was verified with a number of validation runs and is believed to be one of the most advanced and robust simulators of this kind today. The simulator was made use of for various purposes throughout the pilot CO2 injection test at Nagaoka, Japan. During the planning stage, the simulation studies were conducted repeatedly to confirm the technical feasibility of the test plan. Once CO2 injection began, the objectives of simulation were history matching and interpretation of the observed injection performances. Reasonable agreement of the bottom-hole pressures and the breakthrough times was attained by varying uncertain parameters such as relative permeability curves, areal changes in permeability, and vertical permeability. The final aquifer model of the history matching was employed to predict the long-term CO2 movement. The results implied that the CO2 movement would be very limited after the end of injection and the injected CO2 would essentially remain within the injection zone in the pilot test area.