Performance assessment of a combined vacuum evaporator - Mechanical vapor re-compression technology to recover boiler blow-down wastewater and heat

 

Sustain. Environ. Res., 23(2), 129-139 (2013)

 

AUTHORS

Chi-I Tuan, Yu-Tsai Cheng, Ye-Lung Yeh, Liang-Fong Hsu and Ting-Chien Chen

KEY WORDS

Heat pump, mechanical vapor recompression, pinch technology, vaporized concentration

ABSTRACT

The enhancement of water and energy use efficiency is an urgent issue around the world. In this study, we combined a vacuum evaporator with mechanical vapor re-compression (MVR) technology to recover and reuse blow-down (BD) water and waste heat in a fire-tube boiler system. Three cases with different water and energy usages were analyzed and assessed: the original BD water system (Case C1), addition of the vacuum evaporator recovery system (Case C2), and addition of the combined vacuum evaporator - MVR technology recovery system (Case C3). All three cases used pinch technology to assess the optimum energy use. Case C1 recovered 50% of the heat energy, but no water was recovered; Case C2 recovered 81% of the water, but heat energy recovery was only 5%; Case C3's water and energy recovery reached 81 and 93%, respectively. The results show that Case C3 was the best; it could completely replace an external heating and cooling load system. Its investment assessment, determined by the net present value method, obtained a positive value in 3 yr.

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