Natural Gas Processing & Liquefied Natural Gas (LNG)

Natural Gas Processing
& Liquefied Natural Gas (LNG)

Cryogenic natural gas processing plants, liquefied natural gas plants (LNG) and fractionation plants depend upon molecular sieves to remove water and other contaminants to very low levels in both gas and liquid phase streams. Zeochem offers a wide range of long-lasting molecular sieve zeolite products for natural gas dehydration and treating to meet final quality specifications for pipeline, natural gas liquids (NGL), fractionation liquid products (propane, butane, isobutane, pentane, isopentane, hexanes+) and liquefied natural gas (LNG). Our molecular sieve products effectively remove water, hydrogen sulfide, mercaptans, oxygenates and carbon dioxide contaminants during gas processing and treating.

Cryogenic plants that use turbo-expansion technology to recover hydrocarbon liquids utilize Zeochem molecular sieves to protect downstream equipment by consistently drying their natural gas to less than 0.1 ppmv to prevent ice formation and the resulting pressure drop. Natural gas and LNG plants worldwide utilize Zeochem molecular sieves to purify the hydrocarbon stream, beyond simple dehydration, by removing sulfurs and oxygenates to meet product specifications. Our robust molecular sieve products reliably maintain protection for downstream equipment and consistently allow our customers to meet product specifications over the course of the complete service life of the adsorbent.


Applications

Zeochem offers a range of long-lasting molecular sieve products for removal of water from natural gas and liquid hydrocarbon streams. These products are used to meet dew point specifications for pipeline, NGL, fractionation liquid (LPG, condensate, propane and butane) and LNG specifications. Zeochem products are effectively used in plants worldwide to consistently remove water to less than 0.1 ppmv levels with predictable and reliable performance. Our robust molecular sieve products maintain protection for plants' specifications over the course of the lengthy usable life of the adsorbent in both vapor and liquid phase applications.

Zeochem’s Z4-04 molecular sieve is a standard grade of the 4A type zeolite that can be used for dehydration of hydrocarbon gas and liquid streams where potential co-adsorption of other contaminant molecules, such as hydrocarbons, carbon dioxide and sulfur contaminants, is not a concern or issue. If H2S and CO2 are present in the stream, the formation of COS can occur. To avoid COS formation, Zeochem offers alternative products that will minimize this occurrence. Zeochem Z4-04 is normally regenerated at a temperature of 550°F (288°C) with a typical range of 500–600°F (260–315°C).

Zeochem’s Z3-06 molecular sieve is a form of the 3A type crystal that has unique properties and value for dehydration of hydrocarbon gas and liquid streams in specific applications and units. This and other products in Zeochem’s 3A family have the advantage of excluding other molecules from the internal crystal lattice while still adsorbing water. By limiting penetration and co-adsorption of molecules such as hydrocarbons, carbon dioxide and sulfur contaminants, the product and regeneration streams have a more consistent and predictable composition. This minimizes spiking of contaminants in these streams, which could potentially cause off-specification product or an inability to dispose of the spent regeneration gas. In addition to limiting hydrocarbon penetration and co-adsorption, Zeochem’s 3A molecular sieves allow lower regeneration temperatures, normally heating at a temperature of 450°F (232°C), with a typical range of 400–500°F (204–260°C).

Zeochem offers select 5A and 4A type zeolite molecular sieve products for removal of sulfur from natural gas and liquid hydrocarbon streams. These products are used to meet final pipeline, NGL, fractionation liquid (LPG, condensate, propane and butane) and LNG specifications for hydrogen sulfide, mercaptans and overall sulfur content. Sulfur compounds can be removed upstream in the vapor phase dehydration unit in some cases, or downstream in liquid phase treaters. Zeochem products are effectively used in plants worldwide to consistently remove sulfur compounds to ppm levels with predictable performance. Our robust molecular sieve products maintain protection for plants' specifications over the course of the lengthy usable life of the adsorbent in both vapor and liquid phase applications.

Zeochem’s family of 5A type molecular sieve zeolites can remove sulfur species that are approximately 5 angstroms or less in kinetic diameter. These products have excellent physical and kinetic properties, along with hydrothermal stability when adsorbing water and sulfur compounds in regenerative applications. They are recommended when removal is limited to hydrogen sulfide, methyl mercaptan and ethyl mercaptan. Zeochem’s product line includes a product specially developed for the minimization of carbonyl sulfide (COS) formation when hydrogen sulfide and carbon dioxide are present.

Zeochem’s family of 13X type molecular sieve zeolites can remove sulfur species that are approximately 10 angstroms or less in kinetic diameter. These products have the highest adsorption capacity and fastest kinetics for the removal of impurities and are often recommended when further optimization is needed. With their large crystal pore openings and open pore structure, they are ideally suited for removal of the larger sulfur species, such as propyl and butyl mercaptans, from natural gas and hydrocarbon liquids. By contrast, other molecular sieves cannot adsorb them due to their smaller size.

Zeochem offers a range of proven molecular sieve products for removal of oxygenates from natural gas and liquid hydrocarbon streams. Zeochem products are effectively used to remove impurities such as alcohols, ethers and ketones, as well as other oxygenates from vapor and liquid streams. Our robust molecular sieve products are used to maintain product, process and catalyst integrity over their useful lives. Specific products are recommended by our technical experts based upon the type of oxygenate species to be removed and the stream composition.

Zeochem’s family of 13X molecular sieve zeolites are the most widely recommended products, finding applicability for most applications requiring oxygenate removal. These products provide the best removal efficiency, the highest capacity for oxygenates and the largest range of impurities that can be removed. These products have large crystal pore openings of approximately 10 angstroms and an open pore structure, giving them excellent equilibrium and dynamic performance, which allows both large and small oxygenate molecules to be removed from gas and liquid hydrocarbon streams. Zeochem 13X molecular sieves typically regenerate at a temperature of 550°F (288°C) in this application, but the acceptable range is 450–600°F (232–315°C) depending on the oxygenates and the amount of water present.

Zeochem’s 4A molecular sieves, as well as our 5A molecular sieves are effective for the removal of smaller oxygenates such as methanol and ethanol and provide an alternative choice to Zeochem 13X when higher capacities may not be necessary. In applications where water as well as alcohol removal is required, a separate layer of Zeochem’s 3A molecular sieve can be used for removal of water to minimize regeneration temperature, utilizing a normal temperature of 450°F (232°C) with a typical range of 400–500°F (204–260°C).

Let our dedicated experts guide you through the selection process to determine which molecular sieve would be best in your application.

Zeochem offers a select range of long-lasting molecular sieve products for removal of carbon dioxide from natural gas. These products are used to meet required specifications and processing requirements for NGL and LNG production. Zeochem products effectively and consistently remove carbon dioxide from vapor phase streams to meet typical requirements of less than 50 ppmv and in some cases even lower, with predictable, consistent performance. The regeneration temperature can generally be lower for this service, with a typical range of 400–550°F (204–288°C), depending on the amount of water and other impurities present in the stream.

Zeochem’s 13X molecular sieves serve as the primary choice for the most effective removal of CO2 from light hydrocarbon gas streams. These products are used in peak shaving applications for removal of CO2 concentrations up to 3% and in small-scale LNG projects. In some new small-scale projects, these adsorbents may be used in a specialized setup to avoid the need for an upstream amine system and with minimized regeneration volume requirements.

Zeochem’s 5A molecular sieves also have good carbon dioxide removal ability and serve as very capable alternative options. They are the primary recommendation when hydrogen sulfide and carbon dioxide are present, and the formation of carbonyl sulfide (COS) is to be avoided. These products have excellent physical properties and adsorption kinetics.

Custom Solutions

Let our technical service experts with their decades of experience guide you through product selection and then customize a technical design with vessel sizing, regeneration flow and operational sequencing. Whether you are seeking pipeline-quality methane, extraction of natural gas liquids or liquefaction of natural gas, our experienced team and quality products will help you run reliably, efficiently and predictably.

Related Products

Zeochem offers a broad range of molecular sieve products ideally suited to each natural gas, LNG and fractionation plant adsorbent application. From dehydration of natural gas to protect downstream cryogenic equipment to final sulfur and oxygenate removal from liquid hydrocarbon streams to meet product specifications, Zeochem products are specialized for reliable operation in a wide range of applications.

13X

Type 13X offers enhanced adsorption properties and the ability to remove impurities too large to be adsorbed by the type A zeolites.

3A

3A is made by ion-exchanging the sodium in type 4A zeolite with potassium. The 3A molecular sieve will exclude most molecules except water, making it very selective.

4A

4A is the sodium form of the type A zeolite molecular sieve and is widely used as a general purpose drying agent. Under certain conditions, it can also be used for removal of ammonia, alcohols, carbon dioxide, H2S and other specific molecules.

5A

5A is the calcium-exchanged form of the type A zeolite molecular sieve and is primarily used for removing carbon dioxide, carbon monoxide, alcohols and other oxygenates, hydrogen sulfide, methyl and ethyl mercaptans, and others.

Activated Alumina

Activated alumina adsorbent is an effective bed-topping layer used as a protective layer, at the inlet of gas-phase molecular sieve beds.


Frequently Asked Questions

It is recommended to discuss with Zeochem theproposed changes so that a system review and design simulations can be run to determine if any operating changes are necessary or recommended. Zeochem can further check to make sure that all changes fall within recommended operating guidelines, and propose alternatives ifchanges may be problematic.

Beads are round and smooth, strong and durable, exhibiting low dusting characteristics and potential breakage. The spherical shape results in only compressive forces, while pellets (extrusions) undergo compression as well as tension, making breakage more likely. The ends of the pellets also have angled edges, making them subject to chipping and breakage. In addition, beads naturally dense load for optimum loading density without the use of dense phase loading equipment.

A liquid slug can slam into the bed at high velocity, moving, displacing, and even crushing sieve beads. The liquid coats the sieve, slowing mass transfer which leads to poor adsorption of water and other contaminants, and adds more load to the regeneration step. Also, the liquid can cause accelerated coking during heating. To minimize coking, it is recommended to ramp heat at 100°F/hr (55.5°C/hr) when there is time to do so and in some cases an additional cool purge step for 30-60 minutes prior to heating is also recommended to help remove and strip out liquids prior to heating.

In general, higher sieve adsorption capacity is favored by lower temperature and higher pressure. This also help to lower the feed water concentration for water saturated applications. There is a balance to be maintained though in order to avoid approaching the hydrocarbon dewpoint in vapor phase systems. It is recommended to maintain operation at 10-20°F (5.5-11°C) above the dewpoint in order to avoid potential two phase flow. Mixed phase is always to be avoided given that adsorption and working capacity are negatively affected and can be unpredictable when this occurs. As a result, operation should always be 100% vapor phase or 100% liquid phase. For regeneration, lower pressure is favored for minimized flow rate and better turbulence, and lower temperature is favored for optimum sieve life. There are practical limitations and the heating temperature typically falls within a given range depending upon the type of sieve being used and the application details. Temperatures that are too low are too inefficient and may not remove enough contaminant; temperatures that are too high will cause accelerated coking and can cause decomposition of stream components. Pressure typically cannot be too low due to excessive velocity in the up flow direction that will cause bead movement; pressures that are too high require additional flow or time, and higher risk of regeneration refluxing and laminar flow.

Ordinarily the largest temperature swing occurs when a freshly regenerated sieve bed is placed back online. Although the bed has been cooled, it is often several degrees above the inlet feed temperature. As a result, a temperature bump of 15-20°F(8.3-11°C) often occurs, and lastsfor approximately 15-30 minutes after feed has been reintroduced to the bed. In addition, the adsorption process is exothermic, giving off heat. Normally the amount of contaminant being adsorbed is small enough to generate an increase in the product stream temperature of only2-4°F (1.1-2.2°C). Should anupset occur where a water spike or slug of water hits the bed, a much more pronounced temperature rise can result.

When beds are adsorbing in parallel and there is more flow restriction in one vessel than the others, the flow will automatically balance between the beds to achieve an equivalent pressure drop. If it is minor, then it is ordinarily not an issue. If the flow imbalance is large enough, early breakthrough on the vessel with the high flow rate (lowest pressure drop restriction) can occur. In order to better balance the flow rate between the vessels, feeds must be adjusted. This is normally done by adjusting (partially closing) valves, either manual shutoff valves or the valve travel of automatic valves. It can be a trial and error process to achieve balance so it should occur as a series of small adjustments until the operation noticeably improves. In cases where this is not possible, adjustment of the cycles and/or conditions may be possible to prevent breakthrough. When all else fails, the inlet feed rate must be reduced until breakthrough no longer occurs.

Schedule the change out well ahead of time, preferably during an already scheduled shutdown or turn around. Order and have all needed products and supplies on site well ahead of time to avoid any delays. Make sure all contractors, plant personnel, and equipment will be ready to begin the morning of the scheduled start, with any necessary orientation, training, etc. completed in advance. Follow the Zeochem guidelines and recommendations for unloading and reloading the sieve to streamline the process and avoid delays. Have contingency plans in place should there be weather or unexpected delays that occur.

When possible, first regenerate the sieve beds to ensure dryness. Normally a short 70-80% heating cycle is sufficient for this purpose given the sieve will not be as wet as during normal operation. If initial regeneration is not possible or if the sieve is loaded under sufficiently dryconditions, theunit can be started up on regular feed at 50% flow rate whilesimultaneously startinga regeneration cycle of 1 of the beds. As soon as the regeneration is completed, switch beds and start regeneration of another bed. Once all the beds have been regenerated, ramp up the feed rate to full design rate and adjust the cycles times to the technical recommendations.

The water capacity is the percent by weight that the sieve adsorbs. At equilibrium, the adsorption is basically driven to completion to determine the absolute maximum amount of potential adsorption. This is most often used as a general baseline measure of the sieve’s quality and ability to adsorb water. Dynamic capacity is the working capacity that is expected from the sieve to avoid breakthrough of water in an actual process. The design simulation determines this capacity based upon the feed and regeneration stream compositions and conditions, and the water concentration, as well as the concentration of other contaminants. It involves not only the equilibrium capacity, but calculation of the mass transfer zone, effects of other contaminants, andaging of the sieve over time. All of these factors contribute to the difference between achievable water adsorption in service and the theoretical maximum water loading for the sieve.

Typically, there are some options that allow continued operation in the plant until a change out can occur. Adjustments to the cycle times, regeneration and feed conditions, and flowrates are sometimes available and can be made. The last thing considered is a reduction in the feed flow rate once all else has been done and further adjustment may be necessary. Zeochem can help with recommendations and a prioritized plan of action.