Examination of the design details of a group of six distillers indicated that the operating performance ratio (PR) was less than should have been expected. Investigation showed that those stages which were independently vented to the ejector system were performing much better than those with internal cascade venting.
Increasing the interstage venting in all stages resulted in an average increase in the PR of 18% on the normal in-service performance, and allowed the production rate to be increased to 20% above the nominal design rating.
Similar work on three other groups of distillers resulted in improvements in performance ratios of between 8 and 12%, and again the potential to increase water production was a major benefit.
Severe steam side corrosion of the high temperature stages resulted in many tube failures. Increasing the venting rate reduced the amount of stagnant gas being retained within the tube bundle. In consequence it is expected that this will result in a reduction in the number of tube failures. Future work will try to detect any remaining gas within the tube bundle.
It is concluded that some MSF distillers are not being satisfactorily vented. Improving stage venting can give better efficiency, higher output, better distillate purity and reduced corrosion.