168- Reform design scheme for the pre-safety separation unit before the raw gas filter at the amine absorption tower of the gas field LNG plant, utilizing vane separation technology

In LNG plants, the MDEA amine absorption tower is a common setup used to remove acidic gases from natural gas. Since the quality of the feed gas has a significant impact on the ability of the MDEA amine absorption tower to operate stably and efficiently over extended periods, it is necessary to install a feed gas filter at the inlet of the absorption tower to remove the heavy-phase contaminants carried in the gas stream. The raw gas filter installed in some enterprises is primarily used to remove mechanical impurities such as dust particles ； The raw gas filter installed in some enterprises is capable of not only removing mechanical impurities such as dust particles from the gas flow, but also eliminating trace amounts of liquid droplets carried within the gas stream. Regardless of the purpose of the raw material filter, the choice of filter element structure for its internal components determines that only a trace amount of liquid mist can be carried in the incoming air. Beyond this limit, liquid droplets accumulate on the surface of the filter element to form a liquid film that covers the tiny pore channels in the element. The surface tension of this liquid film not only causes dust particles to clump together, but it also hinders air flow due to its own surface tension effects. This results in a sharp increase in the pressure drop during filtration, as well as a significant reduction in the filtering efficiency. This is a problem that often arises during the operation of the raw gas filter at the inlet of the amine absorption tower. Therefore, a safety separator needs to be placed in front of the feed gas filter to protect it, thereby improving its operational stability and service life.

This post was last edited by luoli519 on 2020-11-3 at 13:08. However, in terms of traditional process design, there is insufficient understanding and attention given to this security separator technology; often, a mesh separation buffer tank is simply installed as a makeshift solution. As a result, it not only prevents the raw gas filter and even the production line from operating for extended periods. Next, we will conduct an in-depth analysis and discussion based on the serious problems encountered during the operation of the natural gas liquefaction plants in Well Area 2 and Well Area 128 of a gas field that we handled in the past, as well as the design plan for technical upgrades using vane separation technology, so as to provide everyone with a clear understanding and practical technical insights.

Let’s first take a look at the flow diagram of the raw gas filter and the pre-security separator installed in the inlet pipeline of its MDEA absorption tower:

This post was last edited by luoli519 on 2023-9-26 at 15:53. In the image above, SR-01 is the raw gas filter installed on the inlet pipeline of MDEA amine absorption tower T-01. The owner said that the replacement cycle for the filter element is now only about 10 days, which is far shorter than the specified requirement. According to the technical agreement document for purchasing filter elements provided by the owner, it is polyester filter elements supplied by a foreign company, designed primarily to remove dust particles of 5 microns and larger in size. Let’s take another look at the extracted procurement technical agreement document:

This post was last edited by luoli519 on 2020-11-3 at 14:53. The service life of the filter element in the raw gas filter SR-01 is only about 10 days; this is mainly because the filter element gets covered with oil, foam, and dust, which leads to a sharp increase in operating pressure drop and a continuous decline in flow rate. Next, let’s take a look at the filter element that has been replaced:

The last edit to this post was made by luoli519 on 2024-4-7 at 11:15. The interior of the raw gas filter SR-01 is even more astonishing. A large amount of oil contamination, foam, as well as liquid droplets and splashes entered the raw gas filter SR-01, adhering to the vessel walls, the filter element supports, and the filter elements themselves. The image speaks for itself:

Given such harsh operating conditions, one can’t help but wonder whether the upstream security separator SPR-01 wasn’t effective As is well known, traditional manufacturing practices do not give sufficient attention or recognition to this type of safety separator technology; the safety separator installed here remains a buffer tank with a simple mesh separation structure.

This post was last edited by luoli519 on 2020-11-3 at 17:01. The image below shows the safety separator SPR-01 designed by a engineering company for the client at this natural gas liquefaction plant; it is referred to as a “feed gas inlet separator,” but in reality it is a buffer tank with a simple mesh separation structure.

The owner told us that this safety separator, SPR-01 – which is referred to by the design team as the \"feed gas inlet separator\" – receives its gas input from the gas field wellheads. Methanol is injected before pressure reduction to prevent freezing and blockages; additional heating is provided by a water-jacketed heater to avoid freezing as well. The gas then passes through a production separator for defoaming and liquid removal, and further through a feed gas cyclone separator to remove impurities, before being sent to the feed gas inlet separator/safety separator SPR-01. If the inlet gas to this feed gas inlet separator/safety separator SPR-01 contains significant liquid, it indicates that the separation efficiency of the production separators and feed gas cyclones in the upstream processes is very low. As shown in the image mentioned earlier, if the inlet gas to the raw material gas filter SR-01 contains liquid, it indicates that the efficiency of the pre-filter, the raw material gas cyclone separator, and the production separator is low. A low efficiency across these series of separation devices suggests another problem. Thinking again about the internal components for the capture, recovery, and separation of amine liquid at the top of the amine absorption tower, it was learned from the \"Procurement Technical Agreement\" that filter element-type coalescing components were chosen for these purposes, which led to a series of separation problems. This indicates that the original process design had clear misunderstandings or even errors regarding gas-liquid separation techniques!

Everyone, please take a look at the \"Purchase Technical Agreement\" for the demisting internals at the top of the amine absorption tower; it truly raises serious questions about the level of disregard for enterprise separation technologies.