Acid gas removal and gas sweetening
Koch-Glitsch has supplied equipment for thousands of installations in acid gas removal and gas sweetening applications. Both processes involve the removal of CO2 and/or H2S and mercaptans from gas streams by chemical or physical absorption.  Many industries, including oil refining, ammonia plants, natural gas plants, LNG, and hydrogen plants, require these processes.

While there are many treating processes available, no single process is ideal for all applications. Usually the process licensor selects the most suitable solvent based on feed conditions such as composition, pressure, temperature, and the type of impurities. Additional considerations for solvent selection are process economics, reliability, and environmental constraints. There are two main chemical absorption processes for acid gas removal using either amine or hot carbonate solvent.  RECTISOL® and SELEXOL® are the most common physical absorption processes used in industry.

Chemical absorption processes
The amine absorption process uses an aqueous amine solution, for example monoethanolamine (MEA), diethylamine (DEA), di isopropyl amine (DIPA) or methyldiethanolamine (MDEA), to absorb the acid gases. The hot carbonate process uses potassium or sodium carbonate solutions as solvent. Processes often use solvent blends, which may include small amounts of an activating agent to improve the rate of reaction. Koch-Glitsch has considerable experience working with process licensors of these types of applications.

In chemical absorption processes, gas streams containing the acid gases are contacted with a lean solvent in an absorber. The solvent absorbs the acid gases and exits the column as a rich solution, which is then sent to a regenerator column where the acid gases are stripped from the solvent.

INTALOX® ULTRA random packing

Specific liquid rates are usually high and
therefore this application is well suited for the use of random packing, such as IMTP® and INTALOX® ULTRA high performance random packings. Many of the solvents used in acid gas treating applications have a tendency to foam, which can limit capacity. Random packing is less prone to foaming than trays because vapor is not injected into the liquid phase at a locally high velocity.

Koch-Glitsch also has experience supplying FLEXIPAC® and FLEXIPAC® HC® structured packing in acid gas services when the specific liquid rate is low enough to accommodate this packing type. In addition, structured packing is Koch-Glitsch’s preferred packing type on floating production, storage, and offloading (FPSO) applications. FLEXIPAC® HC® high capacity structured packing

FLEXITRAY® valve trays combine high capacity and excellent efficiency with a wide operating range. With most solvents, CO2 has a lower rate of reaction than H2S. Trayed columns typically provide approximately three times more residence time than packed columns, and so for some duties trays can be a better equipment choice than packings. In particular, regenerator towers can take advantage of lower investment costs for trays. Koch-Glitsch has years of experience designing FLEXITRAY® valve trays for acid gas absorbers and regenerators.
Using trays initially also results in tower sizes that can later be revamped with SUPERFRAC® high-performance trays or packings to increase capacity. The SUPERFRAC® tray is a high-performance cross-flow tray that has the highest combined capacity and efficiency of all single-pass cross-flow trays tested at FRI.
In contrast, H2S absorption takes place more rapidly than CO2 absorption. Structured and random packing provide a lower residence time than trays, which allows more CO2 slippage to occur. Thus, for selective H2S absorption, packing is often used in the absorption columns.

Some amine units experience fouling problems, which may be caused by corrosion products building up in the amine solvent or other contaminants entering with the feed gas or makeup solvent. Most units are designed with removal systems to filter out such contaminants. In some cases these systems may not be sufficient, and fouling of the mass transfer equipment may occur. This is a more significant problem for packed internals and particularly for the liquid distributors.

The first course of action should be to trace the origin of the contamination and eliminate it at its source or improve the removal systems. For packed towers, Koch-Glitsch can offer special distributor designs that use elevated distribution holes to provide improved resistance to fouling.

Trays are generally more tolerant to fouling than packed tower internals. In severe fouling cases,
Koch-Glitsch offers trays with VG-10 or PROVALVE® valves. Both of these large fixed valve types offer improved reliability.

PROVALVE® fixed valve has higher capacity than full-size valve trays with maximum opening size for maximum fouling resistance and free passage.

Physical absorption processes
Physical solvent processes, such as SELEXOL® and RECTISOL®, operate in a similar manner as chemical absorption processes; however, they offer advantages over chemical absorption processes. 
  • Because there are no chemical bonds to break, these processes use little or no heat for solvent regeneration and therefore are more energy efficient.
  • The selectivity of these solvents to CO2 and H2S allows the removal and recovery of the components in a single process.
  • The absorption pressures are normally higher compared to chemical absorption processes, which leads to smaller tower diameters.

 

IMTP® high performance random packing

The same reasons for using random packings in the chemical absorption processes apply to physical absorption. Many of the existing SELEXOL® process towers are packed with IMTP® packing.

Koch-Glitsch also has experience supplying trays for the RECTISOL® process. KITTEL II trays and MINIVALVE® tray decks with VG-0 fixed valves have been supplied for RECTISOL® absorbers.

VG-0: MINIVALVE® fixed valve

INTALOX® Packed Tower Systems technology from Koch-Glitsch combines well-matched high performance packing and state-of-the-art liquid and vapor distributors to create predictable and reliable separation column performance.

Technology
Correct design of column internals is a critical step, particularly in the regenerator where the rich solvent solution feed flashes in the column. The INTALOX® Packed Tower Systems technology approach is used to ensure that the design capacity and efficiencies are achieved.

Revamps
Koch-Glitsch has revamped many trayed and traditional packing towers to high performance trays or packings in the acid gas removal and gas sweetening services. The benefits of doing this are to maximize column capacity and/or acid gas removal efficiency.

In addition, when revamping to packings, the resulting pressure drop reduction can result in significant energy consumption savings. The reduced pressure drop can be used to provide the stripped acid gases at the top of the regenerator at a high pressure, reducing compression costs in the case of further downstream processing. Alternatively the pressure at the inlet to the reboiler could be reduced, providing a higher log mean temperature driving force; this is useful in cases where the reboiler thermal capacity is limiting. A lower pressure in the reboiler can also result in less thermal degradation of amine solvents.

Existing SELEXOL® process towers packed with IMTP® packing would be great candidates for performance enhancement with INTALOX® ULTRA packing. RECTISOL® absorbers could be revamped with SUPERFRAC® trays.