Different types of natural gas filters have different functions.

They include:

• Particulate filter: – Removal of solid contaminants
• Coalescence filters: – Removing liquids aerosols
• Filter separators: – Removes fine and medium-sized particles and entrained liquid
• Activated carbon: – Adsorption of hydrocarbon vapour
• desiccant filters: – Removal of water remaining after dehydration

Coalescing filter

You will use high-efficiency coalescing filters when you want to protect very sensitive equipment in your application.

They remove nearly all water, oil, and particulate contaminants in the gas lines.

Also, they allow for maximum flow rate, filtration capacity at the least resistance to airflow.

These filters have filtration efficiencies between 95% and 99.999+% for the specified micron rating, making them fundamental for a very critical process.

Natural gas filter element

You can make the filter media using these materials.

• Cellulose- The media has inconsistent pore sizes.
• Fiberglass-The diameter and charges in fibre surface make it suitable for removing liquids from gas. The pores of fibreglass are more consistent.
• Activated charcoal- For the construction of activated carbon adsorption filters
• Stainless steel- Suitable for constructing media for filtration of corrosive contaminants/natural gas. Similarly, it provides very high thermal, chemical and mechanical stability.
• Polyester-Good for particulate filters

When selecting filter housing, consider the following factors:

· Material of Construction

You need to select the most appropriate material that will withstand the operational conditions and chemical properties of the natural gas.

· Cleanliness Standards

The cleanliness levels desired will influence what kind of material you select for the housing. You should avoid materials that can erode or rust.

· Preparation of Housing Surface

A smoothly polished surface will eliminate entrapment of particles and chemicals in crevices found on the inside of filter housing.

· Housing Design

You can select either the horizontal or vertical housing designs.

When choosing the design, consider the specifications so that you choose housing with appropriate capacity.

· Housing Size

The housing size will depend on the capacity of the filter and flow rate of the system.

Ensure that the housing you select is big enough to host all the elements you need for efficient filtration.

· Working Temperature, Pressure and Flow Rates

You have to select a filter whose pressure rating, operation temperature, and flow rates are in line with the requirements of your process application.

You can find information on these parameters in the housing casing.

Yes, you can use cartridge filter to purify natural gas. In fact, it is one of the most common filtration systems.

Micron rating for natural gas filter media can range from as high as 100 microns to 0.01 micron.

Using natural gas filters offers numerous advantages for your process application as well as your employees.

They include:

• Efficient removal of solid and liquid contaminants
• Multiple designs and models to choose from
• Easy and safe to operate and maintain
• Resistance to corrosion
• Support onshore and offshore operations
• Fast and easy filter element replacement
• Reduced maintenance and downtime cost
• The extended equipment service life of sensitive equipment downstream
• Reduced risk of poisoning from toxic materials
• Reduced hazard and explosion risks

A natural gas filter assembly comprises:

• Housing
• Filter Elements
• Locking screws
• Element and housing O-rings
• Thread rods
• Differential pressure gauge
• Drains
• Flat Seal

Gas separator system

Both particulate and coalescence filters remove particles through direct interception, inertial impaction, Brownian motion, and impaction mechanisms.

The mechanisms maximize the probability of the particles colliding with the media.

When the gas enters the filter, it slows down due to a change of direction, which enables gravity to pull the larger droplets.

This stage is also known as the knockout stage.

Once the gas gets to elements of the coalescence filter, filtration occurs from inside out.

Gas velocity reduces hence increasing the probability of droplets collision with the medium fibres and sticking.

The droplets grow in size as they move towards the outside of the filter media, which enables gravity to drain them drown the sump.

The best natural gas filters should possess novel features that allow for optimal all-round filtration.

They include:

• Capable of efficiently removing solid and liquid contaminants
• Highly resistant to non-conducive conditions
• Able to withstand wide variation of flow rates
• Meets all the industrial specification, and safety requirements
• Durable
• Reliable performance
• High dirt holding capacity
• It should withstand wide temperature variations.

You can use several materials for constructing a natural gas filter.

However, stainless steel and carbon steel provide the best materials for making the housing.

Natural gas filter system

· Stainless Steel

You can decide to use either SS 304 or SS 316.

SS 316 is more suitable if you are filtering natural gas with corrosive contaminants because it is more resistant to erosion.

Generally, stainless steel is also very resistant to high temperatures, durable and reliable.

Additionally, it offers appealing aesthetic appearance and easy to weld, fabricate, and furnish.

· Carbon Steel

There are different classes of carbon steel, such as high, low, mild, and ultra-high tensile carbon steel, depending on the proportion of carbon content.

Carbon steel is stronger and more durable than stainless steel and is therefore conducive for making a filter that works in very harsh conditions.

The material is also cheaper than stainless steel, and therefore the housing will cost less.

Raw natural gas has a lot of solid and fluid contaminants.

They include:

Water: –Water concentration can range from trace quantities to saturation.

Sulfur compounds: – These compounds include hydrogen disulfide, carbon disulfide, carbonyl sulfide, mercaptans, and elemental sulfur

Mercury: – The amount can range from as low as 0.01 to 180 μg/Nm.

You should reduce the amount to 0.01μg/Nm.

Oxygen: – Oxygen can find its way into natural gas through open valves, leaking pipelines, etc. Oxygen contamination is responsible for a significant quantity of corrosion in gas processing.

Diluents: These are gases that are present in undesirable amounts. They include CO₂, nitrogen, etc.

Other impurities include sand, silica, dust, desiccants particles, liquid hydrocarbons, process contaminants such as lube oil from pumps/compressors, rust, pipe scales, etc.

A pleated filter media offers a large surface area that supports sufficient flow rates and long service life due to higher dirt holding capacity.

Natural gas filters are vital in protecting several process equipment from getting destroyed by impurities.

These include:

• Preventing corrosion and scaling of inner walls of gas turbines
• Protecting pressure reduction plants
• Protection of measuring and control equipment
• Protection of columns and molecular sieves
• Protection of gas heater. The filter removes piping wear, oil, and other contaminants, which also improves the thermal exchange.
• Protection of the compressor
• Protection of the vacuum pumps
• Protection of desiccants beds and dehydration towers

Yes, you can use strainers as the first filtration devices to remove large solid particles in natural gas.

Natural gas air strainer

The quality requirements for a natural gas filter vary from one country to the other.

Generally, the filters should comply with the ISO 8573 series, which deals with the purity of compressed air.

It should also comply with ISO 12500 standard series, which deals with testing the performance of compressed air filters.

The manufacturer should also observe ISO 9001 for quality management systems. Other vital standards and codes include:

• Pressure Equipment Directive (97/23/EC) for housing
• SME Sec VIII, DIV 1
• API 14C (for offshore)
• ASME B16.5 and ASME B16.47
• ASME BPVC
• EN 10204 type 3.1

Dehydration of natural gas

Natural gas is a fossil fuel that is mined from underground and used by millions of industries and households around the world for daily energy needs.

However, raw natural gas contains numerous solid and liquid contaminants.

Consequently, these contaminants must be efficiently removed through filtration before the gas is ready for consumption.

Filtering the gas provides optimal protection to sensitive equipment in the process hence improving its efficiency.

Furthermore, more cleaning may be required after pipeline transportation.

This is because it can pick some impurities along the pipeline even though it left gas plants clean and dry.

Sometimes non-compressible contaminate the gas and can slug the compressor if not removed.

There are three main stages involved in removing solid and liquid contaminants from natural gas including;

i. Strainers

A strainer is the first equipment that you will use to remove large solid contaminants from natural gas pipelines.

You will use a strainer to remove particles that are 100 microns and above efficiently.

You can construct the strainers using either carbon steel or stainless steel.

ii. Separators

The separator will remove large molecules of liquid contaminants such as hydrocarbon oil, water, and gels from natural gas in the pipeline.

You will remove the molecules by passing pressurized gas through a series of devices such as vane packs, inertial separators, and mesh pads.

The devices will amalgamate the small size molecules into large droplets which precipitate and drain down the bottom of housing through gravity.

iii. Coalescence Filters

The natural gas passes through a coalescence filter as the last filtration device after going through strainers and separators.

The filters will remove the smallest particles down to 0.3 microns at over 99.9% efficiency.

The performance of a natural gas filter will be affected by;

• Dirt holding capacity of the element
• Pressure drop
• Size and shape of contaminants
• The filtration velocity
• The diameter of the fibres
• Spore size and distribution in the media

Amine sweetening is the process of removing hydrogen sulfide(H₂S), mercaptans, and carbon dioxide (CO₂) from natural gas in the inlet stream before transportation.

Hydrogen sulfide is very corrosive to carbon steel and toxic as well.

Similarly, CO₂ is corrosive to several pieces of equipment and, therefore, you must remove them before transporting the gas.

Some of the most widely used amine sweetening solutions include; methyl diethanolamine (MDEA), Monoethanolamine (MEA), Diethanolamine (DEA), etc.

The manufacture of natural gas filter contributes to the following services towards OEMs.

• Natural gas filter manufactures’ provide an extensive portfolio of natural gas filter media. The provision can either be in small or medium batches.
• Provision of advice and technical support so that the customer can have ready-made or customized designs suitable for diverse applications
• Direct supply and quotation from industry known and respected manufacturers of natural gas filter
• They help in design, installation and commissioning of natural gas filter systems

Gas filter separator

These are pressurized devices used to remove large particles of liquid and hydrocarbons from the natural gas in the initial filtration stages.

Also, the gas passes through different physical mechanisms, including impacts and deletion plates, baffles, vane pack, and mesh pads.

These mechanisms collect the tiny droplets and aerosols into bigger drops that can drain away through gravity to the bottom of the vessels.

Besides, the stages of separation in filter separator include:

· Inertial Stage

Inertial is the first stage of separation.

The pressurized gas passes into the separator, which uniformly distributes it to achieve maximum separation.

The separator imposes the movement of the gas in a way to enable the centrifugal and inertial forces to initiate the process of separating the large liquid drops.

· Mesh Pad and Vane Stage

At this stage, the collision of smaller droplets against each other enables the creation of larger size drops.

You should construct the structures in this stage using stainless steel to avoid any oxide contamination.

· Coalescing Stage

At this stage, the drops are large and heavy enough to be affected by gravity.

The gravity separates the drops through precipitation from the natural gas stream and accumulates them at the reservoir or sump at the bottom of the separator vessel.

You will remove the liquid using an outlet drain at the bottom of the vessel housing.

When selecting a cartridge filter, you need to consider the following factors:

• The type of application
• The characteristics of contaminants you will be filtering.
• The natural gas operating temperature range
• The gas volumetric flow rate
• Specific gravity and molecular weight of the gas
• The gas operating pressure range
• The amount of particulate or free and entrained liquid in the gas
• The characteristic of the process gas
• The material of construction and housing design

The cost of a natural gas filter varies to an application, size, construction material, among other factors.

A replacement coalescence cartridge can cost between $ 1 and $200.

A big coalescence filter cartridge, together with the housing, can cost up to $50000.

Coalescing filter cartridge

There are five main types of natural gas filters.

They include:

· Prefilter

You can install a prefilter upstream in cases where the natural gas is highly contaminated.

You can use a demister or a cyclone or any other conducive prefilter.

· Particulate Filter

A particulate filter removes fine solid particles from the natural gas stream.

The elements rating for solid filters vary in size and shape.

You can install these filters in almost every application, such as amines, glycol, and separators.

Install the filters between contactor and pumps in the glycol and amine regeneration processes.

They will help protect the pumps from particulate filters.

As more particles stick on the filters, they fill up and reach the specified pressure loss, thus demanding cleaning or replacement.

· Coalescence Filter

You can easily confuse this filter for a separator since the housing assembly resembles in most cases.

You can use depth or pleated coalescence filters.

They remove liquids such as water and aerosols from the gas before it enters the contactor.

The material used to construct the medium should be noncompatible to the chemical you are filtering.

The adhesion forces retain aerosols when gas passes through the media.

As more aerosols stick, the droplets grow bigger and drain down the sump for removal.

You can install these filters between dehydration and compression.

· Activated Carbon Filters

Activated charcoal removes hydrocarbons from the natural gas stream.

You will install these filters between the contactor and the re-boiler in glycol dehydration processes.

The filters element can be either a cartridge type or basket type, which holds loose activated charcoal.

Because of the fragile nature of charcoal, activated carbon filters are less suitable for high-velocity flow.

· Desiccant and Screen Filters

You will use desiccant filters to remove water that might have passed through the dehydration process.

The filters are small canisters found inline and filled with a small salt-containing sock.

The salt absorbs the water and is essential in applications such as gas processing units.

You will install the screen filters immediately after the desiccant filters to capture any salt residue before they clog the orifices and ports in pneumatic control.

Pressure blow can occur when you suddenly open the valves.

You can follow these steps to rectify the pressure blow.

• Using inert gas, flush the section of the pipe that has been affected.
• Follow the operation guidelines to cancel the Ex zone.
• Cut off the gas supply to the filter.
• Open the pressure valve to release pressure from the housing.
• Let the filter to cool.
• Remove the filter element and inspect for cracks or any damage.
• If the element is damaged, replace it with a new element. Otherwise, you can clean and reinstall the filter if the operation allows.

Proper maintenance of natural gas filters ensures durability and reliability in filtering contaminants.

Observe the following tips for good results.

Ensure that you service the filter as prescribed in the instruction manual provided by the equipment manufacturer.

The personnel conducting filter servicing and repairs must be a trained specialist.

Because the release of natural gas can cause considerable health and environmental health, ensure that you observe the following caution before opening the filter.

• Use inert gas to flush the section to be serviced.
• Compile all the notes on hazardous contents of the natural gas
• Confirm that there is no explosive environment
• Put in place the necessary protective measures.

You should drain the collected liquids daily.

Regularly clean the filter using a piece of cloth moistened with water only.

The cleaning will depend on the amount of dirt collection.

Do not use a dry piece of cloth for cleaning as static charges build-up due to friction can present a potential source of ignition.

Measure and document the electrical conductivity between the housing and piping every six months.

Replace the elements and O-ring as instructed by the manufacturer, at least once a year or when the differential pressure reaches 0.35 bars

Regularly check the housing for any visible damages and replace them accordingly.

During element replacement, avoid placing the spanner on the thread area.

Natural gas filter element

The time required for filter replacement will vary from one manufacturer to the other.

Also, the service life of the filter depends on the filtration flow rate and level of gas contamination.

For particulate filters, you can use a differential pressure gauge to signal when the elements need replacement.

For carbon adsorption filters, you can test the glycol purity as charcoal does not build differential pressure.

Ensure that you follow the recommendation of the filter manufacturer for appropriate replacement intervals.

Clearly, there are many aspects you should consider before choosing natural gas filters.

Whether you’re investing in gas filters for the first time or considering a replacement.

The best part, FilSon Filter team is here to help you get high quality and affordable natural gas filters – contact us now.

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