Prevention of Refinery Tower Plugging by Residual Oil Gellant Chemicals in Crude-Pilot Plant Evaluation of Alternative Oil Gellants (2008)

Abstract Earlier work by the authors(1) described refinery plugging caused by volatile phosphorus components originating from phosphate ester oil gellants. Also documented were two successful field trials of new phosphonate ester oil gellants which were shown to address this problem. In a later work(2) the authors presented the results of additional field testing of phosphonate ester gellants directed at the optimization of cost and performance. In addition to the phosphonate ester systems previously tested, new modified phosphate ester systems will also become commercial. These modified phosphate esters also reduce volatile phosphorus according to ASTM D-86 distillation testing. However, several questions required further investigation. One of these is the comparative ability of phosphonate and modified phosphate esters to control volatile phosphorus and tower fouling at higher temperatures in the presence of steam. Distillations used to evaluate volatile phosphorus to date have had a 250 ºC endpoint and did not include water. Another continuing area of concern has been organic halide formation under distillation tower conditions. Although no organic halides were detected in either of the two initial field trials reported earlier (1), further testing under more realistic conditions was required. To address these questions in the most meaningful way possible, full-scale pilot plant testing was conducted over several days with flowback captured after actual fracturing treatments. Fouling of a tray inserted in the pilot plant distillation tower was measured as well as fouling of the packing material. In addition, any changes in operating parameters such as rate, temperature or pressure over the time of each test were noted, as these could also be indicative of fouling. This paper presents the conclusions of this testing and should serve as a guide to the selection of oil gellant systems for the reduction of refinery tower and heat exchanger fouling. Introduction The D-86 distillation procedure used to evaluate volatile phosphorus to date has a 250 ºC endpoint. The actual bottom temperature in the towers is approximately 340 ºC. Also, fluids typically have a 2- to 4-minute residence time in the tower bottom. However, the pot temperature in the D-86 distillation is not specified as part of the procedure and may exceed 340 ºC in some instances, even given that the endpoint measured in the distillate is 250 ºC. Based on observed smoking of the oil samples in some distillations, the oil in the distillation flask may be cracking. Because of this, results may be inaccurate and difficult to reproduce. In addition, esters may decompose at elevated temperatures through a hydrolysis mechanism if water is present. Steam is injected into the bottom of the towers, serving as a source of water. However, the D-86 test methodology does not include the addition of an aqueous phase. Another continuing area of concern has been organic halide formation under distillation tower conditions. Although no organic halides were detected in the flowback of the two initial field trials reported(1), further testing under more realistic conditions is required.