Frequently Asked Questions Regarding Natural Gas Dryers

natural gas dryers

What are deliquescent desiccants?

To deliquesce means to dissolve, and desiccant is a term for any drying agent with water attracting properties. So a deliquescent desiccant is, literally, a drying agent that dissolves.

GasDry deliquescent desiccants from Van Gas Technologies are formed from proprietary blends of hygroscopic (water attracting) materials. These materials are processed into dense and evenly shaped tablets for optimal use in gas dryer vessels.

When exposed to entrained water vapor (humidity) in a saturated gas stream, GasDry desiccants activate. The tablets absorb vapor from the gas, and the tablets themselves gradually dissolve into a solution.

GasDry desiccants reduce the humidity in a saturated gas stream, lowering the water dew point.

How do deliquescent desiccants differ from solid adsorbents such as molecular sieve and silica gel?

Deliquescent desiccants rely on the principle of chemical absorption, where water molecules in the vapor state form bonds with the desiccant materials and slowly form a liquid.

Desiccants such as molecular sieves, activated alumina, and silica gel rely on the principle of adsorption, where water molecules in the vapor state adhere to the porous solid surface of the desiccant.

GasDry deliquescent desiccants are tablets, comparable in size and shape to household water softeners.

Adsorbent desiccants are small spherical beads. Adsorbent desiccants used in air and gas dehydration processes are typically regenerated.

Deliquescent desiccants are non-regenerable. The solution produced during the dehydration process is periodically drained from the dryer vessel for disposal.

What are the benefits of using desiccants to dry natural gas?

  • Preventing fuel line and control gas freeze-ups
  • Meeting pipeline moisture specifications
  • Preventing hydrate formation
  • Reducing emissions from traditional TEG dehydrators
  • Minimizing expertise required from operators and service technicians
  • Delivering reliably dry gas at remote locations

How are deliquescent desiccants and gas dryers used in the natural gas industry?

GasDry desiccants have a variety of applications in the natural gas industry.

GasDry deliquescent desiccants are prized for the simplicity of their application. A desiccant gas dryer has no moving parts, except for a drain valve, and requires no power for operation. This means that deliquescent desiccants are ideal for remote gas drying applications.

GasDry deliquescent desiccants are often used to dry fuel gas for compressors, generating sets, turbines, heaters, and other gas-fired equipment at remote locations where untreated natural gas is relied on as a fuel source.

Desiccants from Van Gas Technologies are also used to dry small flows of instrument and control gas.

In many cases, GasDry desiccants are used to dry sales gas and meet pipeline moisture specifications.

Owners of small residential natural gas wells can affordably dehydrate gas with minimal expertise and expense.

Unlike TEG dehydrators, deliquescent desiccant dehydration systems use no fuel gas, have no pumps, or burners, and produce no emissions. No special operator expertise is required.

Desiccant dehydration systems are often applied in environmentally sensitive locations to eliminate emissions that would otherwise be produced by a TEG, PSA & TSA, or membrane system.

What dew point will deliquescent desiccants deliver?

Deliquescent desiccants deliver what’s commonly called a dew point suppression. The most aggressive deliquescent desiccant, GasDry Max, will suppress the dew point by as much as 65F below the operating temperature of the gas.

Keep in mind that the term “pressure dew point” is commonly misused in the natural gas industry. Pressure dew point is the temperature when condensation begins at line pressure. The measurement of water vapor in terms of pounds per million standard cubic feet (#/MMSCF) is not a pressure dew point. A moisture content measure measurement in #/MMSCF does not tell you at what temperature water will condense at line pressure. Pressure dew point is the measurement that conveys this information and is therefore often more useful in analyzing fuel gas and instrument gas dehydration applications, where preventing condensation is the goal.

Are deliquescent desiccants regenerable?

Deliquescent desiccants are not regenerable. The tablets are consumed and must be replenished periodically.

Consumption rates will vary mainly according to gas temperature and flow rate. Van Gas Technologies can help calculate the consumption rate(s) of desiccant in any given application.

How often will desiccant tablets need to be added to a dryer vessel?

A typical gas dryer is designed to accommodate approximately three months of operation at full design load before needing replenishment.

Vessels can be oversized to extend service intervals.

The consumption rate of deliquescent desiccant in a natural gas dryer will vary according to gas temperature and flow rate. Low gas temperatures correspond to lower moisture loads and lower consumption rates.

In many systems, pall rings or ceramic beads are used as a pre-layer to buffer desiccant beds from entrained liquid droplets and mist, minimizing premature consumption.

How is the solution produced during the desiccant dehydration process disposed of?

The desiccant solution produced during the deliquescent dehydration process is a non-toxic brine and must be disposed of according to prevailing local regulations.

I’m currently using Peladow DG calcium chloride briquettes to dry natural gas. How do GasDry desiccants differ from Peladow DG?

GasDry desiccants are dense and uniform in shape. These qualities are essential for maximum dehydration performance within a gas dryer vessel.

Peladow DG briquettes are loosely formed, have a tendency to dust, and are irregularly shaped. These qualities favor excessive consumption, plugging of drains, particulate carryover, and bed channeling, which results in reduced dehydration performance.

How do heavy hydrocarbons and gas impurities such as carbon dioxide and hydrogen sulfide affect the process of desiccant dehydration?

Gas impurities and gaseous heavy hydrocarbons will not interfere with the GasDry dehydration process, so long as these impurities are in the vapor state.

Liquid droplets of any substance cannot enter the gas dryer vessel without negatively affecting the performance of the system. This includes liquid water, hydrocarbon condensate, and lubricants. If liquids are present in upstream gas a separator and/or coalescing filter must be installed ahead of the desiccant gas dryer.

Who uses GasDry desiccants to treat natural gas?

Many companies in the natural gas industry rely on desiccants from Van Gas Technologies, from mom & pop independents to major producers. Just a few companies that use GasDry desiccants are BP, Occidental Petroleum, XTO Energy, Anadarko Petroleum Corp., Chesapeake Energy, EOG Resources, Shell, Connoco-Phillips, and many more!

Can deliquescent desiccants be used to achieve pipeline moisture specifications?

The short answer is a qualified ‘yes.’ In many applications GasDry Max can be used to achieve moisture levels of 5 lbs water per MMSCF.

The water vapor content of natural gas, when measured at standard conditions, e.g. pounds of water per MMSCF, varies according to both pressure and temperature.

  • Low temperature = low water vapor content
  • High temperature = high water vapor content
  • High pressure = low water vapor content (when corrected back to standard conditions)
  • Low pressure = high water vapor content (when corrected back to standard conditions)

Low operating temperatures and high operating pressures favor the uses of GasDry deliquescent desiccants.

In many low temperature, high pressure applications GasDry desiccants, particularly GasDry Max, can be used to meet pipeline specifications.

Contact Van Gas Technologies to learn if a particular moisture specification can be achieved with GasDry desiccants under particular conditions.

What are the differences between GasDry Prime, GasDry Peak, & GasDry Max?

Van Gas Technologies manufactures three grades of deliquescent desiccant: GasDry Prime, GasDry Peak, GasDry Max.

GasDry Prime is a low-cost desiccant for meeting basic dehydration requirements. GasDry Prime is often used to dry fuel gas in applications where fuel and instrumentation lines are not exposed to extremely low ambient temperatures. GasDry Prime is also used as a primary drying agent when several desiccant gas dryers are plumbed in a series.

In a properly sized desiccant gas dryer, GasDry Prime will establish a relative humidity of 55%.

GasDry Peak is a mid-grade deliquescent desiccant for drying fuel gas and instrument gas when gas temperatures are not expected to exceed 80 F (27C). GasDry Peak can produce pipeline quality gas, with respect to moisture content, under certain operating conditions. GasDry Peak is often used as a primary drying agent when several gas dryers are plumbed in series.

In a properly sized desiccant gas dryer, GasDry Peak will establish a relative humidity of 35%.

GasDry Max is the highest performing deliquescent desiccant available on the market. It is used for preventing fuel line and instrument line freeze-ups in locations exposed to low ambient temperatures. GasDry Max is also an effective media for meeting pipeline moisture specifications in many applications. GasDry Max is often used as a final “polishing” media in desiccant dehydration systems with multiple dryer vessels plumbed in series.

In a properly sized desiccant gas dryer, GasDry Max will establish a relative humidity of 10 - 13%.

Can a natural gas dehydration system using deliquescent desiccant replace a TEG dehy?

That depends. Deliquescent desiccants are effective for meeting pipeline moisture specifications on cool, high pressure sales gas. Van Gas Technologies staff are ready to help determine if deliquescents are a viable technology in any particular application.

Unlike TEG dehydrators, deliquescent gas dryers can be effectively “turned down.” This means that a desiccant gas dryer does not lose operational efficiency or performance under low-flow conditions.

Deliquescent desiccant dryers form a closed system, with no produced emissions. This makes a desiccant system potentially ideal for replacing a TEG dehydrator in environmentally sensitive areas or in cases where an operator faces legal mandates to reduce emissions.

I’ve worked with Calcium Chloride dryers in the past. How are GasDry deliquescent desiccants an improvement?

Unlike raw calcium chloride briquettes, such as Peladow DG, GasDry desiccants are designed specifically for use in gas dryer vessels.

The tablets of all GasDry desiccant grades are uniform in shape and size. These qualities allow gas to evenly flow through a bed of GasDry tablets.

The shape of raw calcium chloride briquettes is irregular. This causes bed channeling, reduced contact time, and uneven dehydration.

The raw materials of GasDry desiccants are pressed into tablets under intense pressure, resulting in a dense final product. This ensures that GasDry desiccants exhibit little to no dusting within the dryer vessel.

Calcium chloride briquettes are loosely formed and typically brittle. Often a barrel of raw calcium chloride is more than 15% dust by weight.

Calcium chloride should not be used as a drying medium in applications where gas temperatures exceed 80F. Calcium chloride briquettes or tablets begin to fuse at this temperature. Peladow DG, with its high calcium chloride content, is often a poor choice for dehydrating natural gas. Van Gas Technologies offers several deliquescent desiccant tablets that are suitable for a wider range of temperatures.

I am a fabricator of process equipment for the natural gas industry and am interested in building desiccant gas dryers. Can Van Gas Technologies help?

While Van Gas Technologies fabricates gas dryer vessels in-house, we also recognize that the manufacturing of production equipment is a highly competitive and localized business. Depending on geography, market presence, and sales focus Van Gas Technologies welcomes inquiries from manufacturers of production equipment interested in producing a line of desiccant dehydration vessels.
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