O&GS NEWSLETTER // SPRING-SUMMER 2014
LiquiSep for HF Alkylation Unit at Montana Refinery
A Montana Refinery is working Second, the presence of water on a project to improve efficiency reduces acid strength and of water removal from their contributes to the formation PB (propene butene) olefin of corrosive ASO (acid soluble stream which feeds their HF oils). Both the water and the (hydrofluoric acid) Alkylation ASO must be removed through Unit. The unit processes 9,000 regeneration of the acid. BPD and has been served In the reaction section of the by a coalescer from another alky unit, acid water content manufacturer for many years. is normally to be kept at no The goal of a new coalescer more than 2%. Excessive water system is to improve water increases corrosion, and as removal by 20% to help optimize particles of iron fluoride scale performance and efficiency of become dislodged and travel the alkylation unit, and reduce with the process streams, the challenges downstream. The result is often fouling of heat existing coalescer has a sight exchangers and plugging of trays. glass and a water boot with a valve that must be opened manually to discharge water to the sewer. The new coalescer will be equipped In the fractionation section, iron fluoride caused by the corrosion with controls to automatically drain the water to the sour water process can return to the towers with the reflux and lay down on the drum. trays or foul reboilers. Significant deposiits may lead to accelerated tower fouling, impacting fractionation and resulting in the inability Alkylation to maintain iC4 purity The HF Alkylation unit plays a critical role in providing one of the Pentair’s Recommended Solution most important feeds to the final product gasoline blending pool. Alkylation processes transform low molecular weight alkenes and Pentair is proposing a skidded package to include a 20” LiquiSep iso-paraffin molecules into high value iso-paraffins with a high complete with piping, valves, instrumentation and controls. Given octane number. In a standard oil refinery process, isobutene is the high separations efficiency of our design, utilizing LiquiForm alkylated with low-molecular weight alkenes (primarily a mixture elements, we expect to exceed expectations by reducing water of light olefins propene and butene) in the presence of a strong in the feed to concentrations below their goal. Expected project acid catalyst, either sulfuric acid or hydrofluoric acid. In an oil timing: Q3 2014 refinery it is referred to as a sulfuric acid alkylation unit (SAAU) or a hydrofluoric alkylation unit (HFAU). Since crude oil generally contains only 10 – 40 percent of hydrocarbons in the gasoline range, refineries use a fluid catalytic cracking process to convert high molecular weight hydrocarbons into smaller more volatile compounds, which are then converted into liquid gasoline-size hydrocarbons. Combining cracking, polymerization, and alkylation can result in gasoline yield representing 70 percent of the starting crude oil. Effects of Water on Alkylation Process & Equipment Water is a major contaminant that promotes corrosion in several ways, so it is important to remove water from the feed. First, it is widely recognized that corrosion is a function of HF acid concentration and temperature, and that high rates of corrosion (>>100 mpy [ >>2.54 mm/yr] ) can occur as the acid becomes more dilute.
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