[HN Gopher] How a Gas Compressor Station Works
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How a Gas Compressor Station Works
Author : teleforce
Score : 84 points
Date : 2024-10-07 09:05 UTC (2 days ago)
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| londons_explore wrote:
| _theoretically_ , compressing gas is energyless. Ie. you get back
| exactly the same amount of energy when decompressing as you got
| when compressing, so you should be able to do it with no loss.
|
| Practically, that's fairly far from true for today's technology.
| Gas is so cheap that we're happy to waste a bunch of energy to
| make the plant cheaper.
| ce4 wrote:
| The compressor stations are alongside the gas pipeline network.
| These put in the energy needed to keep the gas flowing over
| long distances through the network.
|
| Without those it would be just like a very very long garden
| watering hose that has a trickle of flow compared to a short
| one.
| londons_explore wrote:
| I don't believe this to be the case.
|
| The differential pressure from one end of a gas pipeline to
| the other is not 1800 psi - it is more like 20 psi. You don't
| repeatedly recompress along the pipeline length - you
| compress once at the start, and decompress once at the end.
|
| The reason to use high pressures is because for a given pipe
| diameter (and therefore cost), you get far more gas
| transported at high pressures than you do at low pressures.
| djaychela wrote:
| It also means large storage tanks (known as gasometers in
| the UK) aren't needed. A couple of hundred meters of pipe
| at high pressure holds the same amount of gas as one of
| them.
| squigg wrote:
| As someone else who grew up seeing these across the UK,
| it was never clear to me why they disappeared - this
| explains it perfectly, thank you
| formerly_proven wrote:
| Most of the energy in pipelines is lost through friction
| inside the medium and friction between the medium and the
| inner wall. These are very much not reversible processes.
| Also the pressure differential is much bigger than you
| suggest. E.g. the pressure differential across NS1 was
| nominally around 110 bar (1600 psi) with an inlet pressure
| of 220 bar (3200 psi) and an outlet pressure of half that.
|
| > You don't repeatedly recompress along the pipeline length
| - you compress once at the start, and decompress once at
| the end.
|
| There are often recompression stations in pipelines
| precisely because pressure drops across the length, and on
| land it's cheaper to have those along the length of the
| pipeline than one really big one like NS1 had.
| sveng wrote:
| Interstate or longer intrastate pipelines require
| compressor stations every 75-100 miles. The parent article
| mentions this under "Compressors". As another comment
| states, friction is the main reason.
| w1 wrote:
| >> You don't repeatedly recompress along the pipeline
| length
|
| Yes, you do. That is the primary purpose of transmission
| compressor stations. You may just lose a few psi per mile
| or something, but over the course of 100s of miles..
| tantalor wrote:
| _Companies construct these stations along natural gas
| pipelines and use them to compress gas so it can continue
| flowing downstream to its final destination_
| tomas789 wrote:
| I don't think that is the case. Surface roughness and
| directional changes are big losses. For example a single
| valve on a high pressure line can have a bigger pressure
| drop than 2 bars. So 160 km of a pipeline will drop a lot
| more.
| happyopossum wrote:
| > theoretically, compressing gas is energyless. Ie. you get
| back exactly the same amount of energy when decompressing as
| you got when compressing
|
| That's only true in a word with incomplete physics. Friction
| and drag exist, there's no sense pretending a process is
| imperfect because of them.
| HPsquared wrote:
| Expansion could only recover the "compression work done" if the
| pipeline between the two was perfectly insulated so no heat was
| lost.
| DebtDeflation wrote:
| The reliability aspect of this self-contained system is quite
| impressive. Over the course of my life, I've personally
| experience many power outages, water outages, cell service
| outages, internet outages, etc. but never a natural gas outage.
| BasilPH wrote:
| It's definitely impressive. However, natural gas outages do
| happen. For example Winter Storm Uri in Texas led to gas
| outages.
|
| Sadly, the outages and possible the loss of life connected to
| it could have been prevented if the gas companies hadn't fought
| back against stricter weatherization rules[^0].
|
| > they made recommendations to the Railroad Commission to
| implement weatherization rules on the natural gas supply chain
| because there had been water coming up from the formations --
| it's called produced water, it's naturally occurring -- and it
| was freezing at the top of the wellheads and restricting gas
| flow both at the wellheads and in pipelines.
|
| And yes, the Railroad Commission is not in charge of trains,
| but oil and gas in Texas.
|
| [^0]: https://www.volts.wtf/p/whats-the-deal-with-the-texas-
| railro...
| toomuchtodo wrote:
| Also, a contributing factor to gas compressor station outages
| in Texas during Winter Storm Uri was ERCOT (Texas' electric
| grid operator) load shedding without knowing they were
| shedding gas compressor loads. This led to reduced gas supply
| available for generation.
|
| > When load is being shed involuntarily, customers designated
| as "critical load" can be exempted. Critical load is
| typically demand from entities, such as hospitals, for whom a
| power interruption could be extremely costly. To be deemed as
| critical, the customer must first file paperwork. The winter
| storm revealed that certain parts of the natural gas supply
| chain - such as natural gas compressor stations - were not
| designated as critical load. In consequence, their power was
| cut, thereby reducing flows of natural gas along the state's
| pipeline network and contributing to partial and complete
| derates at multiple natural gas power generation units. The
| loss of their output in turn necessitated further load
| shedding, potentially creating an unstable feedback loop.
| This represented a single point of failure in the energy
| supply system.
|
| https://www.bakerinstitute.org/sites/default/files/2022-02/i.
| .. (pages 13-17)
|
| https://engineering.cmu.edu/news-
| events/news/2023/04/25-gas-... ("U.S. natural gas pipelines
| vulnerable to electric outages")
|
| https://www.sciencedirect.com/science/article/pii/S104061902.
| .. | https://doi.org/10.1016/j.tej.2023.107251 ("How
| vulnerable are US natural gas pipelines to electric
| outages?")
| Scoundreller wrote:
| every hospital I'm familiar with has its own backup power
| generation. Sometimes diesel so they can _fully_ island off
| the grid for a while (but unsure about water & heat
| source). And with roll-up generator hookups+contracts if
| that fails.
|
| Those should be the first requirements before being able to
| be deemed critical.
|
| Heck, I'm familiar with some orgs that sell their backup
| generator capacity to be on-call to the grid in the event
| of supply shortage. To them it's a profitable load test
| that reduces the risk of outage.
| briffle wrote:
| My local hospital gets a deal from the local power
| company that they kick on their generators at peak demand
| times, and the power company pays them handsomely for it.
| The hospital gets to test their Emergency power works as
| expected, and the power company reduces their load by a
| few Megawatts for a few hours.
| gorkish wrote:
| > Those should be the first requirements before being
| able to be deemed critical.
|
| Strong agree; however, it would be highly unusual to find
| that any facility that knows to file critical load
| paperwork has neglected this, so I'm not sure that it
| would actually do much other than inconvenience the
| process.
| DJBunnies wrote:
| Yea but it's coupled with an incredibly leaky distribution
| system.
|
| It would be so great to regulate fixing that instead of getting
| rid of it entirely.
| matrix2003 wrote:
| Maybe someone can correct my logic. As long as we are
| drilling for oil, wouldn't the natural gas need to go
| somewhere anyway? I believe it gets flared if not used.
|
| ie - we should responsibly use all the excess natural gas
| rather than flaring it?
| rootusrootus wrote:
| Leaking methane to atmosphere is considerably worse for
| climate change than flaring, I suspect that's the point
| being made.
| matrix2003 wrote:
| Yeah. That's what I struggle with. However, I guess
| increasing dependence on methane is not something we want
| to increase (to encourage more fossil fuel usage).
| short_sells_poo wrote:
| You pointed out something I've never considered and I feel the
| same. Gas networks seem to be very reliable and crucially safe
| (given the contents are pressured and flammable).
|
| I suppose gas distribution networks tend to be over-engineered
| for safety because if something goes wrong, it goes really
| wrong:
| https://en.wikipedia.org/wiki/Merrimack_Valley_gas_explosion...
| morninglight wrote:
| I think most people would agree with you. Electrical power
| outages are somewhat common, but gas delivery seems very solid.
| Yet when selecting a home backup generator, most people opt for a
| gasoline powered generator and NOT one powered by natural gas.
| zrail wrote:
| Gasoline generators are significantly cheaper. There are some
| tri-fuel generators that can run on gasoline, propane, or
| natural gas, but again they're more expensive.
|
| A natural gas powered permanent standby generator is amazing
| for peace of mind but they're a significant investment.
| bob1029 wrote:
| I have more faith in my 2200 watt inverter generator than a
| typical residential standby unit.
|
| If something goes wrong with a generac, you likely need a
| service tech to come out. If my portable unit acts up I have
| a 2nd new one in a box just in case. They're so cheap you can
| basically afford to keep one fresh for each disaster.
| zrail wrote:
| Inverter units are nice, those Honda engines run forever.
|
| I've had my 26kW generac for almost two years and it's done
| several multi-day outages without issue. I just have my
| mechanical contractor come out and do the annual
| maintenance on schedule, keep track of the weekly self-
| tests, and otherwise don't worry about it.
| rootusrootus wrote:
| I want one, but can't justify it. Probably be into it
| around 10K installed, maybe more. We've only had one
| multi-day outage in the 12 years we've lived here,
| because our wiring is all underground and it took a
| century level storm to wipe it out. We get occasional
| outages of a few minutes to a couple hours in the winter
| if a tree hits a power line somewhere in the nearby
| above-ground grid, but that's about it. I'd still love to
| be the only guy in the neighborhood all lit up when
| everyone else goes dark :). To be fair, I'd actually be
| #2 now, guy a few houses up the street is that beacon of
| light now. But still.
|
| When we were shopping for houses out in the sticks, I had
| that generator budgeted right into the price of the
| house. If I got a multi-day outage very year, it's a no
| brainer.
| zrail wrote:
| Yep, exactly. At our previous place we never had an
| outage last more than a couple hours, in 7 years, so it
| didn't make sense. Current place has had four in the span
| of four years, plus we have geothermal heat so we can't
| just hook the furnace to a portable genset.
|
| It'll never pencil out in terms of dollars saved on lost
| food and hotels, but just knowing that the power will be
| out for a max of 15-20 seconds makes it worth it for us.
| rootusrootus wrote:
| Love my little 2K watt inverter generators, but I don't
| think it's a good substitute for a residential standby
| unit. I can't get a 240V split phase generator that can be
| carried, that's the big thing. I could get past the time it
| takes to turn on the generator, but there's a good chunk of
| my house that won't run without 240V (unless I want to run
| extension cords everywhere, which I do not...).
| bob1029 wrote:
| Obviously the little inverter generators can't carry the
| normal load, but you can adapt to it. The biggest thing
| for most people is running their AC condenser.
|
| A portable inverter AC unit (ideally a dual-hose unit)
| will pull ~1700w on the high setting. You can cool a
| solid 1000 sqft even in the Texas heat with something
| like this while also running your
| lamps/wifi/starlink/fridge/etc.
|
| Combine with something like an EcoFlow battery, and you
| can actually shut it off completely while you sleep (and
| lock it up inside safely). Setting the AC to the low
| setting will reduce its consumption to ~400w
| intermittently which will easily run on a 2.5kWh battery
| all night. The other advantage of the EcoFlow is that you
| can temporarily run much larger loads than the generator
| is directly capable of. Really good for induction
| cooktops and getting your washing machine spin cycle up
| to speed.
| Damogran6 wrote:
| Propane has substantially less energy per unit mass than
| gasolene. In our RV, we have a gas generator and propane for
| the heater/fridge...Propane is MUCH better than batteries to
| run the Fridge as well.
|
| 4 LiFEPO4 batteries run our fridge for about 8 hours. two
| 30lb propane tanks would run it for about a week, and the 30
| gallon gas tank just recharging the batteries to just power
| the fridge could probably go 2.5 weeks.
| rootusrootus wrote:
| Solar is the answer. Propane fridges are incredibly slow to
| cool. Best thing I did for my RV quality of life was
| install a bunch of LFP and a few solar panels, along with a
| compressor fridge. I don't miss the old absorption fridges
| _at all_.
| Damogran6 wrote:
| I probably will when the budget frees back up, the ROI
| isn't there for the number of times a year we boondock
| completely off-grid.
| mannykannot wrote:
| IIRC, the big Texas freeze of a couple of years ago knocked out
| both pipelined gas and electricity supplies, and over a much
| wider area than just Texas, on account of the interdependence
| of both systems.
|
| Of course, once you run out of gasoline or propane, you are
| once again dependent on the infrastructure.
| zrail wrote:
| It turns out that was ordinary fraud[1] not a flaw in the
| physical plant. States with functional regulatory bodies
| don't have this problem. At most you get a situation like
| Michigan in the winter of 2019 where there was a massive fire
| at a primary storage facility and they asked everyone to
| conserve gas if possible.
|
| [1]: https://thehill.com/regulation/court-
| battles/4896585-texas-g...
| mannykannot wrote:
| I see this is developing news, and interesting in its own
| right, though without a clear resolution yet. Regardless,
| one only needs the outcome of the event to be aware of the
| possibility of a common-mode failure disrupting both
| electrical and pipelined natural gas supplies at the same
| time.
| jmbwell wrote:
| As long as the flow of money isn't disrupted, the system
| works as designed.
|
| The most significant laws Texas enacted after the freeze
| -- HB 3 and 5, SB 1015 and 2627 - mainly establish new
| funding for gas-fired plant construction, cut funding for
| renewable construction, and allow energy companies to
| raise rates on customers more frequently.
|
| Observers will note that gas fired plants had the most
| unplanned outages, while renewable sources had the
| fewest. In any case, what matters is that the $9/kWh
| costs are duly distributed to the customers and tax
| payers, to the benefit of energy traders.
| bob1029 wrote:
| I recall the spot price of natural gas going through the
| roof leading up to the crisis. I would be _less_ shocked to
| find out this was an intentional winding down of capacity
| for economic reasons.
| mauvehaus wrote:
| There are probably two good reasons for this:
|
| 1) Getting natural gas plumbed to your generator is expensive.
|
| 2) If you're running this generator for an extended period of
| time, things have pretty much by definition gone to shit and
| aren't working as designed. You have a lot fewer dependencies
| to go fill a couple of jerrycans with gas at the nearest gas
| station (that has both gas and power to pump it [0]) than you
| have to restore piped natural gas service to your property.
|
| [0] And if a gas station loses power, getting it hooked back up
| restores its utility to everyone, whereas restoring power or
| natural gas service to a home only restores its utility to the
| person living there. Prioritizing gas stations over private
| homes makes a lot of sense.
| zrail wrote:
| Your second point depends on your threat model. Personally my
| threat model is a wind or ice storm taking down the aerial
| electrical lines in my area (SE Michigan). The natural gas
| lines are all buried and the pumping stations are powered by
| natural gas so are inherently more reliable.
|
| If your threat model involves civilization deteriorating to
| the point where natural gas stops working then sure, a
| generator with fuel storage on site probably makes more
| sense. I'd argue that gasoline is the worst of available
| options though. Diesel and propane are much more shelf stable
| and typically more reliable than small gasoline engines.
| ordu wrote:
| _> a generator with fuel storage on site probably makes
| more sense_
|
| Storing fuel is dangerous in general, but I believe that
| liquefied gas is more dangerous. It is more tricky. For
| example you need to store it in a ventilated environment,
| to prevent gas buildup. If you turned wrong nut you'll may
| be not able to turn if back due to pressure.[1] It can be
| treated safely, but it much more tricky that with liquid
| fuel.
|
| [1] https://www.youtube.com/watch?v=JzdnUZReoLM
| mindslight wrote:
| With propane, there is also the problem of the
| vaporization rate being very low at winter temperatures.
| I've got a small 2500W (1850W continuous) dual-fuel
| generator that I had expected to be able to run off of a
| 20lb propane tank. It didn't work at all when I actually
| needed it (surprise!), and I ended up just running on
| gasoline and having to go out to get more. It has since
| been working fine off of 3 tanks teed together, although
| I still haven't seen middle of the winter arctic blast
| temperatures with that set up yet.
| creeble wrote:
| You might need a horizontal tank.
|
| Liquid Propane requires surface space to "gasify", and
| more space the lower the temp. That's (one reason) why
| propane "pigs" are horizontal cylinders.
|
| Unfortunately, there aren't many small horizontal tanks.
| mindslight wrote:
| Yeah, I researched it after the surprise. Practically for
| as much propane as I use, it didn't feel worth it to look
| at larger tanks (there's a price jump, larger ones still
| have limited lifespan, and smaller is easy to
| transport/refill). Plus I already had several 20lb tanks
| kicking around, so teeing them together was the
| straightforward option.
|
| Down the line I figure I'll be building some sort of
| generator "shed", and perhaps look at using the generator
| exhaust to warm the tanks. A loop from the heating system
| would positively solve the problem, but that feels like
| way too big of a circular dependency.
| billfor wrote:
| It used to be true that the pumping stations themselves
| were powered by gas, but this is no longer guaranteed
| because some have been replaced by cheaper electrical
| pumps.
|
| https://www.sciencedirect.com/science/article/pii/S10406190
| 2...
| Sylamore wrote:
| Many people who use natural gas in the mountains of NC/TN
| right now are without any access because even the buried
| infrastructure there got destroyed.
| zrail wrote:
| Sure, and now that their threat model includes
| devastating landslides they will probably make different
| choices.
| devilbunny wrote:
| There's not very much that you can do against that
| particular threat model other than not live there, but
| one of the big reasons that the area is so popular with
| tourists is that it's easily accessible to most people
| (you can easily get to Gatlinburg or Asheville within a
| day's drive from pretty much anywhere you would consider
| "the southeast US"), it's pretty, and in summer you can
| escape the oppressive heat without having to go to the
| upper Midwest or the Rockies.
|
| Massive landslides and floods will wipe out your natural
| gas lines, your propane tanks, your wind and solar
| generators, your battery backups...
| userbinator wrote:
| Diesel generators are better than gasoline as the fuel can be
| stored for much longer, and has a higher energy density. Of
| course, the up-front cost is also higher.
| rootusrootus wrote:
| That must be a regional preference. I don't know anyone that
| isn't a big institution that has a backup generator powered by
| diesel (and definitely not gasoline). Permanently installed
| home backup generators are invariably natural gas or propane.
|
| Gasoline is a terrible choice in any case, it goes bad quickly
| if you don't stabilize it. The only time I ever see gasoline
| being used it's with little portable generators. Even then, I
| see a lot of people starting to choose propane instead now.
| fires10 wrote:
| Gas distribution systems are often shut off in my area during
| natural disasters. That's why I usually install a propane or
| diesel generator. They run off a tank.
| jasongill wrote:
| This is interesting, especially for me as one of the intrastate
| pipelines on the map crosses through my property.
|
| However, the article doesn't say what the "PIG" is (but talks at
| length about how the "PIG" is "launched" or "received").
| Wikipedia says it's basically a passive device that gets inserted
| into the pipeline and pushed along by the pressure to clean or
| inspect the inside of the pipe.
| pfdietz wrote:
| I believe pig is a word, not an acronym, although maybe it's a
| bacronym now.
|
| https://en.wikipedia.org/wiki/Pigging
|
| > Some early cleaning "pigs" were made from straw bales wrapped
| in barbed wire[4] while others used leather.[5] Both made a
| squealing noise while traveling through the pipe, sounding to
| some like a pig squealing,[6] which gave pigs their name.[7][8]
| philk10 wrote:
| I worked on a PIG app several years ago, fun project -
| https://atomicobject.com/portfolio/microline-embedded-
| softwa...
| Mistletoe wrote:
| That's really slick and looks easy to use, good job!
| cdibona wrote:
| The smart pigs honestly look like a pigs snout flying down
| the pipe.
| engineer_22 wrote:
| I dont know about gas industry, but perhaps this will shed some
| light.
|
| In the drinking water industry the pig is a large foam block
| that is shoved in the pipe, and the weight of the fluid behind
| it drives it along. It is used to physically loosen the
| accumulated debris on the inside of the pipe. This debris
| concentrates behind the pig, and when the pig arrives at it's
| destination you remove the pig and allow the fluid (and debris)
| to discharge to waste for a period of time until the fluid runs
| clear.
|
| Some advancements include "ice pigs" which is just crushed ice.
| The advantage of an ice pig is you can hook up to a fire
| hydrant and pump the ice in, no need to access the mainline
| pipe itself. An ice pig will also disintegrate on its own, no
| need to remove it, just allow it to flow out of a downstream
| hydrant, any ice left behind isn't a problem.
| prometheus76 wrote:
| It's very similar in the natural gas industry. The "dumb"
| pigs are a piece of foam that is shoved into the pipe at the
| "pig launcher" and they use air pressure to push the pig
| through the pipe, where it is then caught in the "pig
| catcher". All the debris from fabrication of the pipeline is
| scrubbed out by the pig and removed at the pig catcher.
|
| Nowadays, they also have "smart pigs" that have sensors to
| detect gouges, dents, pipe wall that is too thin, etc. as the
| pig moves through the pipe, so that repairs can be made
| before the pipeline is filled with gas.
| Scoundreller wrote:
| Pigs are also used to separate products. Lots of pipelines
| can switch between different products and different grades
| of products (e.g. gasoline of different specs required for
| different areas, kerosene, jet fuel, diesel).
|
| I'm guessing those are usually "dumber" ones.
| fuzzfactor wrote:
| In the very long fuel pipelines a foam pig can not make
| the whole journey to the cargo's delivery point, so the
| different grades of gasoline, diesel, and blendstock are
| pumped sequentially back-to-back with no physical
| separation, resulting in many barrels of intermediate
| off-spec fuel that is designated transmix and segregated
| upon arrival.
|
| Inside the tank terminals I had to witness and certify
| the pigging after each parcel loaded, when one chemical
| was done and the line needed to be cleared and volumes
| accounted for before filling with a different chemical.
| Among many other more or less toxic things. Measurement
| training was not easy in the full-scale industrial
| environment but you can't really lead as well in the
| micro-scale activities without it.
| nobodyknowin wrote:
| Exactly. The old ones were basically passive cleaners. The
| modern ones are full on inspection tools with cameras,
| magnometers, etc.
|
| We have a natural gas line running through one of our agency
| properties, and it was recently repaired due to the pig's
| findings.
|
| Basically the engineers running the pig mark sections of the
| pipe that need physical inspection. The crews come out, dig it
| up, and repair or replace a section depending on how bad it is.
| Or do nothing if the engineers see that it's nowhere near as
| bad as they thought.
| laurensr wrote:
| In the sixties, hexavelent chromium was used as a rust inhibitor
| in cooling towers in a Hinkley PG&E compressor station. It caused
| ground water contamination affecting the health of many.
|
| https://en.wikipedia.org/wiki/Hinkley_groundwater_contaminat...
| whalesalad wrote:
| https://en.wikipedia.org/wiki/Erin_Brockovich
| cdibona wrote:
| If you wanna see cutouts of a bunch of this equipment, a pig in a
| transparent pipe, and just happen to be in Oman, the petroleum
| development museum there is super.
|
| Id imagine there's something similar in Houston, this stuff is
| legit fascinating.
| DowagerDave wrote:
| One of my earliest memories when I started working in O&G many
| moons ago was seeing the hilarious daily report "Pig stuck in
| pipe". From a technology perspective it's an amazing industry,
| combining old-tech and human experience with some of the most
| advanced tech that can work in harsh environments similar to
| space.
| coffeeshopgoth wrote:
| As a chemical/petroleum engineer, this is a great little summary
| of how these stations work. Good find.
| Dennip wrote:
| There was a good video on B1M related to this recently
|
| https://www.youtube.com/watch?v=1eKsaGqUfvI
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