Scaling tendency of boiler feedwater without desiliconization treatment

In the treatment of heavy oil wastewater that to be reused in a steam boiler, the desiliconization techniques are complex and expensive. There is a great urgency to develop new processes of heavy oil wastewater treatment. In this paper, a new process is proposed: to inhibit scaling, the calcium and magnesium cations concentrations need to be reduced to the parts per billion levels, operating under a high-silicate-concentrations circumstance. Experimental results showed that in the treatment process of heavy oil wastewater, the concentration of calcium and magnesium needs to be decreased to at least 80 ppb to prevent from scaling under the high silicate operation (250–300 mg/L) environment. The formation of SiO2 in scaling is negligible even when the boiler is operated in a condition of high silicate concentration. According to the simulation model, controlling the calcium concentration is more beneficial than removing the silicate in boiler feedwater, and there is a good agreement between predicted values and the actual data (especially for the unexposed surface).

► High silica operation with a low concentrate of the cations is discussed.
► The variation of scale composition and the precipitate of SiO2 crystals are studied.
► The scaling model for heavy oil wastewater reused in steam boiler is simulated.
► The agreement between predicted values and the actual data is studied.