Extraction of Chloride Salts from LPG Product Streams Using a Proven Extraction Technology

Salt cavern storage is a common method used for holding processed liquefied petroleum gases (LPGs) such as propane and butane prior to sale. By high pressure pumping of high TDS brine into the salt cavern via an injection well, the hydrocarbon product can be displaced and recovered from the salt dome and is subsequently transported to point-of-sale. One challenge with the recovery of stored hydrocarbon product is the removal of entrained and dissolved brine and salts from the LPG which are regarded as contaminants. Often, simple knock-out drums are installed at the well-head but these devices suffer from carry-over and may fail to meet the required specifications. A large southern refining company was experiencing issues with meeting the required specification on their LPG recovered from salt domes. The requirement of 1 mg/L of inorganic chlorides and no free water was not achievable with a simple knock-out drum. Using in-house models, Pentair was able to provide a design proposal for a transient salt and brine recovery unit for the recovered LPG stream based on the Pentair Polarex technology. The unit was installed and brought online in mid-December 2020. Samples taken around the operating field unit show that good extraction and separation was achieved by utilizing a counter-current recycle configuration. The plant was able to minimize water usage while meeting the desired specifications for the recovered n-Butane product. The developed models showed good agreement with the operating units with minor differences attributable to transient operating conditions.