Scale Clean And Inhibition Of Heat Exchanger In Sulfate Titanium Dioxide Process

Titanium dioxide is one of the most important chemical raw materials at home and abroad. In hydrate-sulfuric titanium dioxide process,the problem that the heat exchanger was easily scaled and blocked had restricted the development of the hydrate-sulfuric titanium dioxide process,which caused the prombles of uncontinuous production and the negative influence on equipment service life.The sample of heat exchanger dirty obtained from certain factory was evaluated with chemical analysis, X-ray Fluorescence (XRF), X-ray diffraction ( XRD),and so on. The results indicated that the main ingredients of scale sample were calcium sulfate, mixed with some compounds of titanium and iron.Descaling by pickling the scale with hydrochloric acid after soaking with carbonate proved that the best parameters of descaling is as follows: graphite heat exchanger tube soaked in the 12%~14% sodium carbonate solution at the constant temperature 60℃for 5 hours, then soaked with hydrochloric acid for 10 minutes, the removal efficiency is more than 95%. Scale of copper exchanger soaked in the 14% sodium carbonate solution at the constant temperature 60℃for 24 hours,then soaked with hydrochloric acid for 10 minutes, repeated the above procedures for 3 times, at last the average removal rate of the scale is more than 69%. The corrosion inhibition of copper exchanger in hydrochloric acid was studied, too. Results show that the corrosion inhibition efficiency is more than 89% when the thiourea concentration is 0.01M. The corrosion inhibition efficiency is a little increased when sodium hexametaphosphate and thiourea was formulated, and the highest inhibition efficiency is about 93% with concentration ratio of sodium hexametaphosphate to thiourea equaling to 1:3,which meets the requirement of copper exchanger cleaning.Scale inhibitor containing functional groups of phosphonic acid, carboxyl acid and sulfonic acid was synthetised. The Anti-scaling rate is 75% when the addition of above mentioned scale inhibitor is 4ml/250ml. Besides,the influence and scale inhibition effect of direct current (DC) electrostatic field on the precipitation of the scale was studied and the results as follows:the anti-scaling rate is less than 3% with 36V DC voltage,but between 30 to 40 percent with 1300V DC voltage.