TFT-LCD廠廢水回收效益之研究-以某3.5代廠為例

Abstract

This study focuses on a certain 3.5th-generation plant manufacturing TFT-LCDs. Water use balance performed by the plant, including the process water reuse rate (RP), the whole plant reuse rate (RT) and the whole plant discharge rate (DT) was examined.On the basis of waste water treatment processes, facilities and operation experiences of the process water reuse rate in relation to the water acquisition cost, water reuse treatment cost and the waste water treatment cost can be determined . These three costs constitute the total water use cost for the plant, which can be expressed by y = ax2 + bx + c (y: total water use cost, x: reuse rate). Accordingly, the waste water reuse rate at the minimum water use cost can be obtained. The equation for the process water cost is expressed by y = 26421x2 ﹣28439x + 154928. When 54% of the process waste water is recycled, the process water use cost is 147,276 dollars per day. In addition, the non-process water use cost is 7 377 dollars per day. Therefore, the minimum water use cost for the RT is 154,653 dollars per day. As a result, the RP, RT and DT are 62.5%, 60% and 86.7%, respectively. However, the current RP, RT and DT of the plant are 78%, 72% and 82% leads to a total water use cost is around 155,895 dollars per day.Variances of 15.5% at RP, 12% at RT and 4.7% at DT with a total water use cost difference of 1,250 dollars per day exists between them. According to the 「Regulations for Implementing Water Conservation Assistant Project in the Science-based Industrial Park」, the RP rate should exceed 70%, the RT rate be greater than 50% and the DT rate be less than 80%. Based on the present waste water reuse rate, the DT rate is 82%, which is higher than the standard; however, the RP and RT rates comply with the requirements. From the perspective of the waste water reuse rate at the minimum water use cost, the RT rate is satisfied with the standard; nevertheless, the RP and DT rates do not meet with the standards. According to the amended draft of the 「Reward Regulations for Important Strategic Sunrise Industry as Part of Manufacturing and Technology Service Industries」, when the process water reuse rate for color display devices requiring array process included TFT-LCDs exceeds 70%, the choice of either a tax-exempt preference for five years (a 5-year tax holiday) or shareholders' investment tax credit is available. The tax preferential treatment is applicable since the RP rate in the plant. currently is 78%. However, the tax preference won’t be applicable if the RP rate at the minimum water use cost is 62.5% only. The analysis result indicates the benefit of the waste water reuse rate in the plant. at the present is greater than that at the minimum water use cost.