SepraSol Liquid/Gas

Challenges

A Middle East gas production company operates a major gas processing plant which produces sales gas and Natural Gas Liquids (NGL). The plant processes non-associated and associated gas from onshore oil production plants. After a compression stage, the sour feed gas continues through the Acid Gas Removal Unit (AGRU), or the amine unit, to remove acid gases before the dehydration units and the cold section.

The plant operates two trains in parallel, each having a capacity of 385 MMSCFD (455,000 Sm3/hr). The initial plant design called for three non-Pall horizontal filter-separators, operated in parallel, to protect each absorber. Two in operation and one in stand-by, with a removal rating of 0.5 micron.

Amine units require an efficient protection to prevent the ingression of liquid and solid contaminants inside the absorber along with the sour gas. Liquid hydrocarbons and solid particles are foaming promoters. They lower the surface tension of the amine and stabilize foam skins. The toxins must be removed down to low levels before they enter the contactor, otherwise they become destructive – even in small sizes. Left untreated, these contaminants will cause severe operating issues, such as foaming in the absorber, loss of amine due to carry-over, excessive use of anti-foams and processing upsets in the sulphur plant. From the start-up of the plant, severe amine foaming issues were reported which were affecting the gas throughput, were causing amine carryover and were requiring a continuous injection of foaming inhibitors. In addition, fouling of the reboiler tubes in the regenerator were reported.

Liquids began entering the absorber. This caused poor separation performance of the upstream horizontal filter-separators. More alarming, it was creating a foaming issue. Even though the volume of liquids draining from the filter-separators was very small, the problem was becoming large. The plant made several attempts to solve the problem. And despite three filter-separators operating in parallel, the situation did not improve.

A few years earlier, the company invited Pall Corporation to perform a site survey on a plant with a similar configuration. They needed an evaluation of the liquid contents in the gas stream at different locations along the process. Pall’s Scientific & Laboratory Services (SLS) team, a global group of highly-skilled scientists and engineers, performed the field measurements. SLS trials highlighted significant liquid carryover downstream of the filter-separators, with liquid contents above 1000 ppmw. The testing confirmed the root cause of the foaming issues in the absorber.

Without the proper protection, the foam would reduce production rates and increase maintenance times. The refinery couldn’t afford any downtime or delays. They needed a way to reduce the foaming before it got out of hand.

Solution

The gas production company contacted Pall to help cut their foaming issues. Pall’s coalescers were already implemented as replacements for similar horizontal filter-separators in other units within the same complex. The partnership was an easy call.

Pall technicians arrived on site to access the situation. After several technical meetings with the major local contracting company, the group determined that two new SepraSol Plus liquid/gas coalescers would be the right fit for the job. With the plan in place, Pall’s installed the coalescers downstream of the existing filter-separators.

Pall designed each coalescer vessel for a gas flow rate of 385 MMSCFD (455,000 Sm3/hr). Each liquid content set for 1965 ppmw. Coalescer vessels have a 3500 mm (138 in) inner diameter and are 7000 mm (23 ft.) tall. The coalescer vessels have an inlet gas distributor and a horizontal mesh pad. While the SepraSol Plus coalescer cartridges have an upper tube sheet with extra blank plugs for future debottlenecking, if needed.

Results

Pall SepraSol Liquid/Gas coalescers were installed in the refinery’s gas feed line upstream of the amine contactor. With our coalescers in place, we were able to remove the entrained liquids in the feed gas. This eliminated the hydrocarbons mixing with the amine and minimized any problems with foaming. The amine unit is an important unit at all Gas Processing, Natural Gas Liquids (NGL) Recovery and Liquefied Natural Gas (LNG) production plants. If the quality specifications are not met downstream of the amine unit, corrosion may occur in the export gas pipeline or plugging in the cold section, with very severe consequences on the production.

Liquid contaminants, or aerosols, present in gas streams are very fine in size, typically in the micron and sub-micron range. Although they are fine, they are detrimental to the amine unit and they must be removed effectively. All incoming liquids are absorbed in the amine solution, regardless of their size. Liquid/gas separation technologies such as vane packs, demister pads, filter-separators, cyclonic separators, and conventional cartridge coalescers are commonly used in the industry. However, conventional separators are unable to remove fine aerosols and can’t protect the absorber properly.

SepraSol Plus liquid/gas coalescers can separate both the large droplets and sub-micron size aerosols, and are a proven solution for numerous critical liquid/gas separation applications found in the Oil & Gas industry. By implementing Pall coalescers, the production company was able to maximize profits by minimizing untimely delays. For more information on Pall's Oil & Gas customized solutions, contact us today.