Jun-2015

Savings in exchanger network cleaning (TIA)

The Super Clean System (SCS), an online heat exchanger cleaning technology, is being used by a major oil refiner in Japan at a refinery equipped with a 120 000 b/d crude distillation unit (CDU) with 44 exchangers in the heat transfer network.

Ian Baxter
Cat Tech International

Article Summary

Distillation units are large energy consumers in the refinery and maintaining the heat transfer efficiency of the network is of major concern for operators. Exchanger fouling is complex in nature but for crude oil fouling can be categorised into the following types: chemical, corrosion, particulate and inorganic. Despite attempts to mitigate against fouling, inevitably there is a requirement to clean the exchangers and recover the heat transfer efficiency.

Historically, the exchangers of the Japanese refinery’s CDU had been cleaned by a conventional water jetting method. However due to time constraints during turnarounds it was very difficult to effectively clean all of the exchangers in the network, with priority given to those that were badly fouled. The time and costs associated with opening and cleaning all of the heat exchangers was unacceptable to the refiner, who in 2002 decided to trial the Super Clean Technology. The process involves the injection of very low concentrations of an oil based detergent in a closed oil circulation loop around the whole exchanger network. The cleaning solution is circulated, heated and periodically sampled. Progress of the cleaning process was monitored as a direct correlation with the lightness, L value, of the solution (see Figure 1). As products of fouling are removed, the L value decreases until all products of fouling are removed and the L value tends to constant.

After a successful trial, the technology has been used on an annual basis at the refinery and was once again chosen for the June 2014 turnaround. Cleaning of the whole heat exchanger network was completed in less then 48 hours, without the need to open exchangers. This resulted in significant time, labour and costs savings compared to the conventional water jetting method.

In the case of the CDU, three out of the 44 heat exchangers were pulled for inspection of cleaning effectiveness. The cleaning effect was high, as Figure 2 shows, with products of fouling being effectively removed. The used cleaning solution was subsequently reprocessed with the crude feedstock; there was no waste water to treat; and, importantly, the cleaning chemical was derived from a renewable source. The opportunity to clean all exchangers in the network in a given time constraint manifested itself in energy savings through improved heat recovery at the furnace. 

SCS is a cost effective, environmentally sustainable technology for reducing cleaning costs, turnaround time and energy conservation for the CDU/VDU. The technology has superseded traditional mechanical cleaning techniques, is now the ‘method of choice’ for the operator of this refinery, and is being rolled out to other refineries under its operation. To date, the SCS technology has been applied 75 times to successfully clean hundreds of heat exchangers.

This short case study originally appeared in PTQ's Technology In Action feature - Q3 2015 issue.
For more information: ibaxter@cat-tech.com