Abstract
The optimal operation was studied for sponge-ball cleaning to recover the performance of heat transfer apparatus by removing deposited scale and sludge without stopping the operation.
The objective function to evaluate the operation in this study was composed of the additional energy cost owing to decreased performance ratio and the cost of sponge-ball lost during the operation. Their decision variables were the cleaning interval and the number of balls.
This model was applied to the MSF evaporator. The performance ratio of the evaporator was estimated on the basis of the material and heat balances of the process. In connection with the process equation, optimal calculation clarified effects of loss fraction of ball, sludge removal fraction, fouling factor, steam cost, and sponge-ball cost.
Followings are the results induced.
(1) The ball cost was a controlling factor in a short-cleaning interval, and the steam cost in a long interval. The optimal cleaning interval was the time when the both cost constituents in the objective function were comparable.
(2) The cleaning cost was apt to decrease in line with the increase of number of balls and the consequent decrease of cleaning time.
(3) The sensitivity of the fouling factor to the optimal cleaning interval was insignificant, even if the fouling factor would increase.
The results suggested that the sponge-ball cleaning could be widely used as a technique to recover the performance of heat apparatus if deposited scale and sludge were softened by adding appropriate chemicals.
