FITRATION
GAS PROCESSING
Natural gas is not ready-to-use as it comes out of the ground –
it needs treatment and purification. As a result, natural gas processing is
very filtration intensive – and while it may seem intuitive that gas-phase
filters are used, liquid filters are also extremely important in gas
processing. Specifically, the amine sweetening process and the glycol
dehydration processes use lots of liquid filters. There are other
applications for filters as well. In this blog we will explore the use of filters
in gas processing, as well as some basic terms that one speaking to a plant
operations , maintenance, or engineering person might hear.
Natural gas production is a fascinating topic that has been in
the news for a lot of reasons. It might be useful to digress from
filtration for a moment to provide some bullet points about the broader issues
surrounding natural gas.
Amine
Sweetening and Glycol Dehydration
Two key fluids that are filtered in gas plants are amine and
glycol. Amine removes acid gas, while glycol removes water /
moisture. Gas plants can be stand-alone entities, and oil refineries
often have gas processing plants within them. Other types of operations
can have amine, glycol or similar processes too. A filtration person
visiting a gas plant, refinery, or other area where natural gas is produced,
processed, or transmitted would do well to ask about maintenance issues that
might be prevented through filtration – including those related to amine and
glycol.
Two general processing concepts are the “contactor” and the
“stripper.” A contactor uses a type of tower – for example, amine or
glycol will flow down the tower while gas flows up, in a counter-current
mechanism. In a stripper there is also a tower (or column), a
counter current mechanism, heat – (which might be provided by steam), and
pressure loss – and they are used in concert to strip out the contaminant
from the amine or glycol. Thus, the contacting fluid (such as amine or
glycol) first goes through a contactor tower where it removes the targeted
contaminating gas and becomes “rich”, then proceeds to the stripper column
where it is regenerated, becoming “lean” for repeated use.
Contactor towers often have “trays” with “bubble caps” in them –
these are means to maximize the contact area and contact time between the gas
and adsorbing fluid. Othe examples of devices that increase contact area
and contact time in contactors and strippers are “weirs” (lips on a series of
trays that create a series of waterfalls or cascades within the tower), and
“packing” materials such as Pall rings or Dixon rings (simple, roughly golf-ball
size structures with cutouts, folds and holes, that are loaded into a tower or
column.)
Fluids to be stripped often must be heated in “reboilers”, but
then cooled on the way back to the contactor in a “cross exchanger.”
Fluids on their way to the stripper from the contactor also get
pre-heated in the cross exchanger.
“Foam
Outs” – Why Does Filtration Matter?
One of the types of problems often discussed in a gas plant is
the infamous “foam out” – or foaming of amine. Foaming can also occur with glycol.
A little bit of frothing in the contactor is important to maximize contact
between the fluid and the gas – but too much foaming reduces effectiveness of
the process, causes carry over fluid losses, actually contaminates the gas
instead of purifying it, and causes maintenance problems downstream.
Foaming is generally attributed to the presence of liquid hydrocarbons which
get into the amine or glycol, and there combine to behave as soapy,
bubble-causing surfactants. To prevent the liquid hydrocarbons from
getting into the process in the first place, gas plants use as series of steps,
including “knock out pots”, demister packs, and liquid-gas coalescing filters
on the gas steam. Somehow, some hydrocarbons still get into gas plant fluids
(such as amine) and behave as surfactants, so carbon filter beds are used to
remove the surfactants. And despite this, some foaming still occurs, so
antifoam chemicals are used. Despite this, foam can still form, and solid
particles (such as those comprised of iron sulfide) stabilize the foam,
increasing the chance of an upset. Liquid filtration is critical for removal of
foam-stabilizing particles.
MMT suggest filters that
remove particles that can stabilize foam, foul heat exchange surfaces, and plug
bubble caps and other equipment. Wound Filter are economical depth filters available in a
range of materials with quick lead times, and melt blown polypropylene filters have built in pre-filtration sections
to provide reliable filtration and longer onstream life.
Removing small submicron particles in an amine or glycol stream
with tighter filters helps foam to “break” – this prevents upsets. On the other
hand, operations personnel like low differential pressure and infrequent filter
change-outs, so this might encourage the maintenance folks to use 5 or 10
micron rated filters instead of 0.5 micron rated filters. Anti-foam,
carbon, and filter suppliers may sometimes have different opinions on what
causes upsets and may provide slightly different advice. One might say
“your amine filter is too tight and is actually coalescing the hydrocarbons and
causing the foaming problem” and another might say “your filters are too coarse
and you need to remove the small foam-stabilizing particles.” MMT is supplier Filtration, working with our knowledgeable
distributors and partners, stands ready to help the gas plant operations folks
with tight, coarse, and in-between filtration!
Contact :
PT Mitra Mandiri Teknik
Email : sales.mmtpt@gmail.com
