Research and development of multi-effect horizontal tube film evaporator

Abstract

MEHF (Multi-Effect Horizontal Tube Film Evaporator) was established by the series of R & D since 1972. As the following results of them, we successfully established more economical evaporator than the existing distillation plant in view of evaporator cost, power and chemical consumption and required plot area; 1. By the experimental study on heat transfer characteristics of film evaporation, the over-all heat transfer coefficient is in range of 4500 to 6500 kcal/m 2h°C at the corresponding evaporation temperature of 60 to 100°C under non-foul conditions. 2. The over-all heat transfer coefficient is greatly influenced by evaporation temperature, however, less susceptible to heat flux, seawater sprayed flow rate and tube diameter from the same study as item (1). 3. According to the process and shell construction studies, each effect chamber must be vertically arranged in main combined with supplemental horizontal arrangement to achieve a compact and integrated shell construction and to circulate the brine once-through from the first to the last effect tube bundle with mutual pressure difference and gravity for minimization of power consumption and tube surface scale formation. 4. As for scaling prevention, according to the results from the test operation of a single effect apparatus and the practical plant of 150 m 3/d (3-effect), the pretreatment of make-up seawater by the pH control method usually employed on the MSF is sufficiently effective, and the chemical addition method employing inhibitor “X” can be also applicable to MEHF.