PRODUCTION • PROCESSING • HANDLING
A typical coker charge pump is a two-stage radially split pump, API 610 type BB2
Scott Graham reveals how to optimise processing performance and reliability in refineries
COKER PUMP DESIGN
elayed coker units (DCUs) occupy the lower reaches of the oil refining strategy, upgrading the residue from other parts of the plant. Especially important in the processing of heavy crude, these units provide considerable revenue for the business by maximising the amount of saleable products from the original volume of crude oil. Troughout the delayed coker plant, pumps of various designs are used to transport high temperature, corrosive fluids through the process. Tere are various pumps involved in DCUs and their design affects process reliability and efficiency. Of the three main types of coker used
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in oil refineries, the delayed coker is the most common. It supports a non-catalytic thermal process that converts a wide range of residues into high value liquid products such as liquefied petroleum gas (LPG), heavy coker gas oil (HCGO), light coker gas oil (LCGO) and almost pure
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carbon residue, known as coke, which is also further processed for use in other industries.
Te feed material for the DCU is typically the residue from the vacuum distillation tower and often includes other heavy oils. It is heated and sent to one of the coke drums at a temperature between 450 and 500°C, where typical overhead pressures range from 2 to 8 bar (30 to 115 psi). Under these conditions, cracking occurs and the lighter oil fractions are separated into gas, petroleum and other high value liquids. A solid coke residue is also produced
and remains in the drum before being removed by a high-pressure water lance. While this process is being completed, the feed material is directed to the second drum and the process is repeated. Within this process each pump has a specific purpose that requires certain characteristics to retain reliable operation. Depending on the application, the pumps
need to meet a variety of design criteria – and this requires specialist engineering to deliver the necessary durability in arduous conditions. From the outset, all process pumps
operating in a refinery setting are normally required to meet the current edition of API 610 standard. After that, individual applications will dictate the exact specifications. Te coker charge pump would typically be a two-stage radially split pump, API 610 type BB2, capable of operating at around 370°C and discharge pressure around 42 bar (600 psi). More importantly, the pump needs to be capable of operating over a wide flowrate while maintaining maximum reliability. Operating at these higher temperatures means that internal wear part clearances are slightly more than those seen in other applications. However, in this situation the power is lost as heat energy to the fluid, reducing load on the furnace.
MATERIAL CONSIDERATIONS One of the major challenges for the coker charge pump is the coke particles that are entrained in the liquid. To prevent the larger particles from choking the eye of the impeller, pumps can be equipped with coke crushers, which reduce the size of the particles and allow them to pass through the impeller. Predominantly, coker charge pumps
are manufactured using API C-6 and A-8 materials, but for naphthenic crudes, 317L stainless steel can be used for its
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