Energy-saving Coolant Regeneration System using Pervaporation Membrane in the Solar Cell Wafering Process

Abstract

In this study, a membrane technology was used to develop an Energy-saving Coolant Regeneration System using Pervaporation Membrane in the Solar Cell Wafering Process. In a wire sawing process, an abrasive slurry plays an important role in the quality of wafer. Also, because a large quantity of the slurry is used, it is important to develop the coolant (DEG) recycling technology in order to reduce the production cost and environmental damage. In this study, the existing recycling method for glycol dewatering have the problems with its high energy consumption and the formation of by-product from thermal denaturation of the glycol. In order to solve these problems, hybrid separation membrane processes were developed by applying two types of membrane technology. The first was about glycol dehydration using membrane. The commercialized standard technology of glycol dewatering is multi-stage distillation. It is known as the best. In order to produce high purity glycol, this process is accompanied with its higher initial cost of equipment and high energy cost, and the formation of by-products from thermal denaturation of glycol during high temperature distillation. In this study, research for the development of energy- efficient dewatering technology was conducted using the pervaporation membrane technology. Preferentially, on a lab scale test, we investigated the feasibility of pervaporative dehydration of diethylene glycol (DEG) through a commercial hollow fiber membrane. The permeation behaviors of DEG through the polymeric membrane were investigated as operation conditions. In the second, we built a pilot scale DEG recycling system consisting of a filtration system and a pervaporation system to apply to solar cell industry. The hybrid membrane system was tested to recover waste coolants derived from wire cutting process. The first stage is the study of the filtration system to remove residue particles in the spent coolant. In the pilot scale filteration test using inorganic ultrafiltration membrane of ceramic material, most of fine particles(Si, SiC, Fe, Cu and so on) in the used coolant were removed. Next stage, in the pilot scale dehydration test using a pervaporative membrane, water content of end purified DEG was attained below 0.5%. From this pilot test, we established operation factors applicable to the design of commercial plant and automation operation method. And we checked and could be improved the problem of material on membrane module. Also, in order to ascertain the quality of the recycled DEG for its suitability for PV application. The regenerated coolant is reintroduced into the silicon wafer manufacturing process. The wafer Yield and Quality measurements of a regenerated slurry made of silicon carbide and R-DEG versus a new slurry with the same composition are about the same. In the case of stain and TTV in monocrystalline, the results were even better. Third, we established a simulation model based on a phenomenological /semi-empirical approach for the pervaporative dehydration of DEG for module and process design of pervaporation system. From the simulation, the maximum temperature drop of the feed stream in modules was one of most important parameters in the design of a pervaporation process. In the future, the membrane filtration technology developed in this study could be used independently for coolant recycling for diamond wire sawing. Pervaporative membrane technology would be expected to be applied to the dehydration of other glycol and bio-alcohols. |본 연구에서는 태양광 웨이퍼 제조공정에서 투과증발막을 이용한 에너지절약형 쿨란트 재생시스템을 개발하였다. 웨이퍼 생산공정에서 연마재 슬러리는 웨이퍼 품질에 중요한 역할을 하며, 또한 공정에서 많이 사용되고 있기 때문에 생산비용의 절감과 환경 문제해결을 위하여 폐슬러리의 재이용 기술 개발은 중요하다. 본 연구에서는 기존 재생방법의 에너지 과소비 및 재생품의 열변성으로 인한 문제점을 개선하기 위하여 두 가지 유형의 분리막 기술을 이용한 혼성분리막공정으로 개발하였다. 첫번째는 분리막을 이용한 글리콜류의 탈수방법에 관한 것이었다. 글리콜류의 상업화된 탈수기술은 다단 증류법이 최선으로 알려져 있다. 그러나 이 공정으로 고순도의 글리콜을 얻기 위해서는 높은 장비초기비용과 에너지비용이 수반되며, 고온증류로 인하여 글리콜의 열적변성에 의한 부산물이 형성될 수 있다. 본 연구에서는 투과증발막을 이용하여 에너지절약형 탈수기술개발에 대해 연구를 수행하였다. 우선적으로 실험실 규모에서 상업용 중공사막을 통한 디에틸렌글리콜의 투과증발탈수에 적용가능성과 그 고분자막을 이용하여 디에틸렌글리콜의 투과특성을 운전조건별로 고찰하였다. 두번째는 막여과 시스템과 투과증발막으로 구성된 파일렛규모의 절삭유 재생시스템을 구성하였다. 이 혼성분리막 시스템은 실제 웨이퍼절단 공정에서 발생하는 폐절삭유의 재생을 위하여 사용되었다. 첫 단계는 폐절삭유에 잔류한 미분입자성분을 제거하기 위한 막여과시스템의 연구이다. 본 연구에서는 무기성 세라믹 재질의 한외여과막을 도입하여 폐절삭유중에 잔류하고 있는 미분(주로 실리콘, 실리콘카바이드, 철, 구리성분)을 거의 완벽하게 제거하였다. 다음 단계로, 투과증발막을 이용한 파일럿규모 실험에서 디에틸렌글리콜 재생품의 최종 수분 농도 0.5% 이하 수준을 달성하였다. 본 연구를 통하여 상업화 시스템설계와 자동연속운전에 필요한 운전조건 확립 및 분리막 모듈 재질의 문제를 확인하고 개선할 수 있었다. 또한 최종 생산된 재생품의 품질 적합성을 평가하기 위하여, 웨이퍼 절단공정에서 사용되는 슬러리를 재생품으로 제조하여 웨이퍼의 생산성과 품질을 비교 평가한 결과 거의 동등하였으며, 단결정 실리콘웨이퍼 생산시 일부 품질특성은 더 좋은 수준으로 평가를 받았다. 그리고, 마지막으로 투과증발시스템의 모듈과 공정 설계를 위한 현상학적 접근 방법에 의한 시뮬레이션 모델을 확립하였다. 그 결과로 현장적용 조건에서 모듈내에서 투입물의 최대온도저하가 투과증발공정설계시 가장 중요한 인자중 하나임을 확인할 수 있었다. 향후, 본 연구의 막여과기술은 다이아몬드 와이어쇼잉 방식의 웨이퍼제조공정에서 발생하는 쿨런트 재생 기술에 독립적으로 사용될 수 있고, 투과증발막기술은 다른 글리콜류와 바이오 알코올류의 탈수에 응용될 수 있을 것으로 기대된다.; In this study, a membrane technology was used to develop an Energy-saving Coolant Regeneration System using Pervaporation Membrane in the Solar Cell Wafering Process. In a wire sawing process, an abrasive slurry plays an important role in the quality of wafer. Also, because a large quantity of the slurry is used, it is important to develop the coolant (DEG) recycling technology in order to reduce the production cost and environmental damage. In this study, the existing recycling method for glycol dewatering have the problems with its high energy consumption and the formation of by-product from thermal denaturation of the glycol. In order to solve these problems, hybrid separation membrane processes were developed by applying two types of membrane technology. The first was about glycol dehydration using membrane. The commercialized standard technology of glycol dewatering is multi-stage distillation. It is known as the best. In order to produce high purity glycol, this process is accompanied with its higher initial cost of equipment and high energy cost, and the formation of by-products from thermal denaturation of glycol during high temperature distillation. In this study, research for the development of energy- efficient dewatering technology was conducted using the pervaporation membrane technology. Preferentially, on a lab scale test, we investigated the feasibility of pervaporative dehydration of diethylene glycol (DEG) through a commercial hollow fiber membrane. The permeation behaviors of DEG through the polymeric membrane were investigated as operation conditions. In the second, we built a pilot scale DEG recycling system consisting of a filtration system and a pervaporation system to apply to solar cell industry. The hybrid membrane system was tested to recover waste coolants derived from wire cutting process. The first stage is the study of the filtration system to remove residue particles in the spent coolant. In the pilot scale filteration test using inorganic ultrafiltration membrane of ceramic material, most of fine particles(Si, SiC, Fe, Cu and so on) in the used coolant were removed. Next stage, in the pilot scale dehydration test using a pervaporative membrane, water content of end purified DEG was attained below 0.5%. From this pilot test, we established operation factors applicable to the design of commercial plant and automation operation method. And we checked and could be improved the problem of material on membrane module. Also, in order to ascertain the quality of the recycled DEG for its suitability for PV application. The regenerated coolant is reintroduced into the silicon wafer manufacturing process. The wafer Yield and Quality measurements of a regenerated slurry made of silicon carbide and R-DEG versus a new slurry with the same composition are about the same. In the case of stain and TTV in monocrystalline, the results were even better. Third, we established a simulation model based on a phenomenological /semi-empirical approach for the pervaporative dehydration of DEG for module and process design of pervaporation system. From the simulation, the maximum temperature drop of the feed stream in modules was one of most important parameters in the design of a pervaporation process. In the future, the membrane filtration technology developed in this study could be used independently for coolant recycling for diamond wire sawing. Pervaporative membrane technology would be expected to be applied to the dehydration of other glycol and bio-alcohols.