Efeito do tipo de neutralizante e ponto de injeção no processo corrosivo do sistema de topo da torre de destilação atmosférica de petróleo

Abstract

The heat exchangers of the overhead system of the atmospheric distillation tower have severe problems with hydrochloric acid corrosion. This work aims to study the effect of the type of neutralizers and its injection point on the corrosion of the overhead system of the distillation tower. The types of neutralizers diluted in the washing water were amine and/or sour water. The amine is an aqueous solution of dimethylethanolamine, commonly known as DMEA, purchased through the bidding process from a chemical additive supplier specializing in the oil and gas field. While sour water is an ammoniarich solution that is generated in the refinery’s catalytic cracking fluidization (FCC) unit. The washing water with the neutralizer were injected into the outlet pipe from the top of the tower or into the heat exchanger inlet pipes. The combination of the neutralizer type and the injection point was divided into five experiments. In each experiment, the uniform corrosion rate was monitored using electrical resistance (RE) probes installed in the outlet pipe at the top of the tower and in a heat exchanger. Corrosion coupons were also used in the region of entry, return and output of product in the heat exchanger to map the corrosion rate by mass loss. During the experiments, the variation in the chloride content, pH, and iron content were monitored from the analysis of the condensed water from the overhead system that accumulated in the separator vessel. At average chloride levels ranging from 135 to 195 ppm, DMEA or sour water FCC controlled pH at 5.5 to 6.5 and 6.5 to 7.5 respectively, but could not control distillation tower overhead system corrosion. The corrosion in the heat exchanger was less than 0.125 mm/year with the injection of sour water FCC added to the distillation tower overhead systems, but this condition caused high localized corrosion in the pipe. At average chloride levels close to 50 ppm, the DMEA neutralizer was more efficient than sour water FCC in reducing the corrosion rate of the overhead system when injected into the heat exchanger inlet pipes that controlled medium pH between 6.5 and 7.5. The conjoined injection of DMEA plus sour water FCC in the pipe presented the best performance among all neutralization experiments. However, further studies are needed with a longer time of exposure to this experiment.