Sankichi Takahashi

Characteristics of flow and mass transfer rate in an electrodialyzer compartment including spacer

Abstract In order to determine the optimum compartment structure and operation conditions for electrodialysis, the hydraulic characteristics and mass transfer promoting ability of net-type (mesh) spacers inserted in a compartment were investigated. The relation between spacer structure and these two characteristics were examined in experiments through an electrochemical reaction of the redox system.

An electrodialysis sea water desalination system powered by photovoltaic cells

Abstract An electrodialysis sea water desalination system powered by photovoltaic (PV) cells is beeing developed. In this sort of system, the most important subject is a way to apply the varying electric power from the PV cells directry to electrodialysis with a small capacity lead battery. We use a partially desalinated water (PDW) storage system for this. When a large electric output from the PV cells is obtained, sea water is desalinated to partially desalinated water (PDW: salinity of which is between sea water and fresh water) and when a small output is obtained, the desalination from PDW to fresh water is completed. In this system, as varying outputs from the PV cells are used directly in electrodialysis, the capacity of the lead battery is reduced, and an economical system is realized. A demonstration plant (capacity: 10m/day) was constructed for this system, and has been operating since June, 1986.

Vapor Permeate Characteristics of Membrane Distillation

Abstract To study the permeate characteristics of membrane distillation considering heat and mass transfers and concentration polarization, theoretical and experimental studies were performed. To understand the effect of concentration polarization, concentrated solutions of LiBr and H2SO4 were used as feed. The permeate flux was found to be proportional to the vapor pressure difference between the feed and cooled surface and decreased with increasing concentration because of the concentration and temperature polarization. Furthermore, when considering the heat and mass transfers and concentration polarization, the permeate flux could be estimated accurately.

Development of water re-use treatment system for municipal wastewater

Abstract The move for environmental protection and preservation of clean water sources has given rise to the latest tendency in Japan toward reuse of waste water after advanced treatment. As a means of saving water and securing water sources, water reuse systems are beginning to be installed to treat waste water for reuse as flushing water and cooling water for air conditioners. This study was conducted with the aim of developing a compact high-performance water treatment system that may meet the stated requirement. Most water reuse systems in practical use today are based on biological treatment. With this process, treatment is slow and equipment takes up much space. In addition, it involves a large amount of sludge. In an attempt to overcome these disadvantages, we developed a physico- chemical treatment technique that combines the three elementary techniques of dissolved air flotation, foaming separation, and activated carbon packed electrolyzer, and that permits multifunctional treatment with compact equipment. The activated carbon packed electrolyzer, which forms the core of the new system, is a newly developed technique. The purification mechanism was established, and conditions of application to actual waste water were determined. The electrolyzer was combined with the dissolved air flotation and foaming separation methods, to make up an optimum system. With a 10 m3/d trially manufactured apparatus, a demonstration test on reuse of sewage was performed to study the performance and economics of the system. The desired target was achieved and prospects were gained for commercialization.

Desalination of brackish water by bubble-cleaning type electrodialyzer in large scale

Abstract An electrodialyzer of an entirely new construction and with attractive features has been developed. The main technological characteristic of the device is the continuous introduction of air bubbles between membranes. Because membrane fouling can be prevented by action of air bubbles, the precise pre-treatment of raw water for the purpose of removing suspended solids is unnecessary. And, the level of efficiency is raised because the air bubbles act as a turbulence promotor. Furthermore, some attractive features was realized. Using a basic study which goes into details and the results obtained in bench-scale experiments, a plant with a capacity of 10 m 3 /d for practical use was designed and constructed. Brackish ground water was continuously treated for 200 hours with this plant, and plant performance and reliability were confirmed.

Water Quality Evaluation of the Water Purification System for 16Mbit LSI Production Using Total Solid Monitor.

半導体ウエハの洗浄工程で大量に用いられる高純度超純水の製造装置の性能を評価するため.集積度16Mbit対応超純水の水質を従来指標と新指標である全蒸発残留不純物量 (Ts : Total Solid) で, オンライン計測した.実験に供試した超純水の水質は従来指標では16Mbit対応超純水の目標値を十分満足しているものの.TS値が高いため.さらに装置の高性能化が必要なことが明確になった.水中の主不純物であるTOC (Total Organic Carbon) 値とTS値を用いて、超純水製造プロセス系の要素機器の処理性能を評価した結果, UV酸化, イオン交換, 限外濾過の各プロセスからの不純物の溶出があり, 超純水は原水とは異なり溶出成分 (57%) や難酸化性成分 (50%) が多いと推測された.

PHOTOVOLTAIC POWER FOR SEA WATER DESALINATION BY MEANS OF ELECTRODIALYSIS METHOD

ABSTRACT Among solutions to utilize solar energy for the sea water desalination, the electrodialysis method is suitable for the photovoltaic (PV) generator, because this method utilizes direct current electric power and is widely adjustable in its load current without impairing operational performances.

The PH control in the large-scale MSF plants by using drop structure type decarbonator

The pH control by means of decarbonation is well known as the effective method for scale prevention. However, decarbonation and pH control characteristics for the large-scale plants are not so clear. So, we studied scale-up techniques for the module of MSF plants with a capacity of 100,000 m3/d under the sponsorship of the Ministry of International Trade and Industry in Japan. We studied many decarbonators, i.e, packed tower type, spary tower type, air bubbling type and drop structure type. The packed tower type decarbonator had most reliable performance in these equipments. As the scale-up technique of the packed tower had been completed, we examined the drop structure type decarbonator that was more simple than the others. The apparatus consists of eight step channels, (3m in length, 7m in width and 0.8m in drop distance) At the results of experiments, decarbonation phenomena had been successfully revealed as the mass transfer with chemical reaction of the carbon dioxide. Decarbonation ability depended on acid addition and sea water temperature from the point of equilibrium and drop distance for the structure factor. It became clear for the estimation of decarbonation performance to be able to adapt with mixing model rowing each step channel. On the other hand, it was established for the pH control condition that brine pH could set up in the range from 7.0 to 7.8 by using the method of partial neutralization. Further, during the long time continuous operation using these apparatus, we succeeded in getting the constant performance and preventing the scale deposition.

Decarbonation characteristics of the packed tower and its effects on scale prevention in flash evaporation plants

Abstract Scale prevention is one of the most important problems in the distillation type desalination plants. The pH control by means of decarbonation is well known as the effective method for scale prevention. However, decarbonation characteristics and the optimum conditions of the pH control are not so clear. We revealed the total carbonate ion equilibrium chart in sea water at the temperature range of up to 80°C, and examined decarbonation characteristics by using a packed tower type decarbonator with 0.8m in diameter and 2.5m packed height. At the results of experiments, decarbonation phenomena have been successfully revealed as the mass transfer with chemical reaction of the carbon dioxide. As main resistance of carbon dioxide diffusion in sea water existed in liquid falling films, it was quantitatively analyzed that tower ability (H.T.U) at the partial neutralization zone increased as acid was dosed. We used a scale test devices that was composed in 10-stage flash evaporator with a capacity of lOOm 2 /d, and measured scale deposition under various decarbonation level and the pH of feed sea water. According to the obtained results, factor of the scale deposition depended on brine pH and carbonate ion concetration. We recommend that brine pH is about 7.5 and that carbonate concentration is below lOppm.