The effectiveness of antiscalants when used on multi-stage flash distillers.

This project is concerned with the testing of antiscalants (scale inhibitors) used to improve the performance of Multi-Stage Flash (MSF) distillers in Kuwait. This study describes and compares the thermal schemes, thermal efficiency and thermal performances ratios of the distillers when treated with three different antiscalants over a testing period of 6 months. The plants used for the tests, the Doha West and AZ-Zour power stations, which have a capacity of producing 7.2 million imperial gallons of potable water per day are described. The evaluation tests revealed that all the examined antiscalants were successful in inhibiting alkaline scale formation and improved the plant performance at top brine temperatures ranging between 90°C and 110°C with dosing rates of 1.5 and 3.0 ppm. The results of the products (Belgard EV 2030; Sokolan PM 10i and NCP DS 3000) show an insignificant difference in the values of overall heat transfer coefficient and fouling factor of the heat gain section. Relationships between the parameters controlling the distillate water product to other operating and design parameters are presented. These parameters include plant performances rates, flow rate of re-circulating brine and top brine temperature. The evaluation tests were based on the measured and calculated thermal parameters, distillate water production rate, Gain Output Ratio (GOR), Performance Ratio (PR), Top Brine Temperature (TBT), antiscalant type, and dosing rate.The antiscalant dosing rate was calculated for each day together with the overall heat transfer coefficients and fouling factors for the brine heater and the heat recovery sections. Recorded data and calculated parameters have been tabulated chronologically. Based on the recorded and calculated data, graphical plots were generated to compare each critical parameter against the elapsed time for the entire test periods. Each of the three antiscalants tested resulted in the successful operation of the MSF distillers at low antiscalant dosing rates. The performance testing revealed that the best scale control test was able to operate at a high temperature (105-107°C) and low additive dosing rate. The use of improved antiscalants gives the possibility of increasing water production as reduced scaling will allow a number of currently operating MSF plants to increase their top brine temperatures.