| 摘要 |
<PICT:0829820/III/1> In a multi-stage flash evaporator wherein water to be distilled, together with recycled water, is preheated in a series of heat exchangers (1A to 25A) by vapours obtained from associated evaporators and by steam as a primary source of heat in a heat exchanger (14) and is then evaporated in a series of evaporators (25 to 1) at decreasing pressures, the vapours being employed as stated to preheat the distilland, the number of stages is at least twice the performance ratio and the recycled liquid is mixed with the fresh feed only when the latter has been preheated to the arithmetic mean of the fresh feed and recycle liquid temperatures. The performance ratio is defined as the ratio of the weight of distillate obtained to the weight of steam used as the primary heat source. Specification 829,819 is referred to.
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