Hideaki Kurokawa

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.

Heat recovery characteristics of membrane distillation

A simulation model, using a mass transfer coefficient which has as its driving force a humidity difference and a heat transfer coefficient which has as its driving force an enthalpy difference, is developed for investigating the operating characteristics of membrane distillation. Optimum conditions are calculated by the model and the calculated results are proved by actual experiments. Simulated results show that the higher the feed input temperature and the cooling water input temperature, the smaller are the recycling rate, membrane area, and heat energy. For a system which has a 0.216-m 2 membrane and heat exchange area, optimum conditions of feed input and cooling water input temperature and recycling rate are 90 °C, 50 °C, and 18.5 kg/h, respectively. Furthermore, an actual experiment was performed and its permeate rate and heat input were 1 kg/h and 0.21 kW.h. From the work, the latent heat recovery is seen as about 66 percent and the simulation model reliability is verified.

PFC emission-reduction strategy for the LCD industry

— The perfluorocarbons (PFCs) used as etching-process and chamber-cleaning gases in the manufacture of LCD devices have a high global-warming potential and a long atmospheric lifetime. Thus, to voluntarily reduce these environmentally harmful PFCs, in 2001 the Japanese LCD association established the World LCD Industry Cooperation Committee (WLICC), together with its counterpart associations in the Republic of Korea and Taiwan. Since that time involving many discussions, the WLICC reached a consensus on reducing the aggregate absolute PFC emissions to the equivalent of less than 0.82 million metric tons of carbon by 2010. Each association has been taking whatever emission reduction steps it considers best to achieve this goal. Thanks to these measures, the PFC emissions from the Japanese LCD industry have remained at the same level, or less, than those of the year 2000, in spite of the fact that PFC purchases have continually increased. In the interim, the Japanese LCD association has been obtaining experimental data for the 2006 IPCC Inventory Guidelines, which will give the emission factors needed to estimate the PFC emissions. As a result, some data are quite different from emission factors given in the current 2000 Inventory Guidelines. All the data obtained have been submitted to the IPCC to be adopted in the new 2006 Guidelines.

Vapor compression distiller and membrane technology for water revitalization

Water revitalization for a space station can consist of membrane filtration processes and a distillation process. Water recycling equipment using membrane filtration processes was manufactured for ground testing. It was assembled using commercially available components. Two systems for the distillation are studied; one is an absorption type thermopervaporation cell and the other is a vapor compression distiller. Absorption type thermopervaporation able to easily produce condensed water under zero gravity was investigated experimentally and through simulated calculation. The vapor compression distiller was studied experimentally and it offers significant energy savings for evaporation of water.

Permeate Characteristics of Volatile or Nonvolatile Substances in Membrane Distillation.

直接接触型膜蒸留法を実用化するに際し, 原水中に不純物が含まれている場合を想定し, 不揮発性成分ではその濃縮限界を, また, 揮発性成分では水蒸気透過特性に及ぼす影響を実験から検討した.実験は, 不揮発性成分としてNa2SO4水溶液を, 揮発性成分としてエタノールおよびアンモニア水溶液を用いて膜蒸留実験を行った.その結果, 揮発性不純物の透過機構を解明するとともに, アンモニアについては, 原水のpHを酸性 (6以下) にすることで, 透過水側へのアンモニアの混入がないことを把握した.さらに, 膜前後の熱・物質収支の式に濃度分極を考慮することで, いずれの場合もシミュレ-ションを可能にした.

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.