Reactor Effluent Air Cooler Safety Through Design
In hydroprocessing units, the reactor effluent cooler (REAC) is one of the most vital pieces of equipment, and any hindrance to its smooth operation immediately impacts the whole high-pressure loop. Older REAC designs used carbon steel, but these required low concentrations of ammonium bisulphide and/or polysulphide sulphide injection together with frequent and thorough inspections. As feeds in most heavy oil hydroprocessing service have become more laden with sulphur and nitrogen, the concentrations of ammonium bisulphide with economic levels of water injection have risen to a point where carbon steel tubes have routinely been substituted by alloy tubing.
Duplex 2205 and Alloy 825 are used, with the former being very popular because it is relatively less expensive. Initially, there were several prob-lems associated with Duplex 2205, which were a result of poor fabrication techniques. These included a rapid cooling rate associated with thick header boxes, which could result in high ferrite and thus poor corrosion resistance; welding of thick tubes to tube sheets with joint leaks; and lack of control of welding, resulting in high hard-ness and thus susceptibility to sulphide stress cracking. Many of these initial problems seem to have been overcome. However, problems persist around the REAC, primarily because of a lack of attention to detail and not adhering to licensor specifications. In this article, we will illustrate real REAC problems from recent projects and consider the remedies that were recommended.