Take a look at this picture: (God, I hope this works, it’s been awhile)
In it, there are these huge tanks made, I think, for the storage of natural gas.
There used to be a number of these in the city of Chicago back in the late 50’s, and I remember asking my dad what they were and how they worked, BECAUSE; the tank thingies move up and down. One time the tank is huge and all the way to the top of the ironwork, another time the girders sit there forlornly with no tank inside…
I remember not understanding his explanation, no matter how many times he told me (I must have been 5 or 6 years old and my dad was a scientific kinda guy and pulled no punches, vocabularily speaking).
So tell me, oh myriad wise ones, how do they work?
They had them in my home town when I was little as well – a period when people were converting to gas heat but before a natural-gas pipeline had been built there.
What they are, to the best of my knowledge, are storage tanks for coal gas – gaseous alkanes akin to natural gas produced by driving off the volatiles from soft (bituminous and subbituminous) coal. (Hopefully Una Persson will be by with how that was done. The weight of the tank top (and IIRC liner) helps to keep the stored gas under pressure (so it will flow through lines to homes on demand). That’s why the “tank” within the framework moved up and down – how much had been produced vs. how much had been piped out in response to fuel demand.
That’s a very rough how-it-was-explained summary; I’m sure there are important details which (a) I’m in slight error on, or (b) are important but I haven’t included.
One final note: to my little-boy nose, the coal-gas production facilities stunk like a banquet of rotten eggs and garlic at the convention of the National Fraternal Order of Skunks.
Time to crack open my copy of Brian Hayes’ “Infrastructure”.
Those are telescoping gasholders. They work sorta like collapsible travel cups, set upside down. As gas is pumped into the gasholder, it lifts the first section. Once that section reaches full extension, it lifts the second section, etc, etc, eventually reaching its full height. A typical holder can hold approximately 10 million cubic feet of gas. The reason they’re so huge is because they hold the gas at very low pressure. You could inflate them with your breath, like a balloon, if you had enough time. They were originally built as intermediate storage for manufactured (coal) gas and natural gas right off the pipeline, before it was sent to the distribution network. Nowdays in the US, they have mostly been torn down and replaced with either high-pressure cylindrical storage tanks, or liquid natural gas (LNG) tanks. Apparently they’re still in vogue in the UK, where they’re called Gasometers.
So they’re basically the opposite of the piece of rubber in the lid of the brake fluid reservoir in your car, that expands to fill the volume the fluid used to displace?
Is that what that does? Wouldn’t that create a slight vacuum (the break resivoir thing)? I’d never heard that.
This, to me, sounds like an upside down water tower. Have a small pump that pumps natural gas into this tank, and let the tank pressurize the entire system at a constant level, for free.
Since the brake system is sealed and airtight, when fluid is pushed through the lines or otherwise emptied from the reservoir, it does create a slight vacuum. Since pressure and volume are directly related for a given temperature, there is more volume to fill and less air to fill it. Therefore, the concentric rubber deals (technical term!) pop out, as needed, to keep the pressure over the fluid as consistent. Otherwise, braking in Santa Fe (7,000ft) would be a lot harder than in Milwaukee (600ft). This is a main concept in “air over hydraulic” systems.
I like your water tower analogy. I’d never seen or heard of these tanks before, but I think it’s neat that we came up with four almost completely different ways to describe it that made sense to us individually!
Thanks, folks. Seems like the Brits are in paroxysms over the elimination of these things.
I dunno about “inflating” one of these with your breath, like a balloon, though… doesn’t all that steel weigh tons? I realize that’s still low pressure compared to pipeline pressure, but still…
Don´t forget that the roof has a large surface area. With a 30m radius tower that is a bucket load of square inches (1 bl = 4.38 million sq inches). A couple of pounds per square inch pressure gives 2 bucket load pounds of force.
Low pressure vessel accidents are more common than one may think, and messy. The assumption´ahh it´s only 10psi, it can´t be that dangerous´ is a bad assumption.
NBC
You’re aggregating weight without aggregating the gas volume & pressure. The total wieght is large. But so is the total effect of millions of cubic feet of gas at any above-atmospheric pressure.
The roof is made of, say, 1/4" thick steel. 1 square inch of that roof weighs (WAG) 1 lb. So as long as the gas pressure exceeds 1 PSI it will raise the roof.
Naturally the roof will have some rib structure for rigidity which will increase the weight some (WAG 20%). But unlike the roof of, say a stadium or warehouse, the roof doesn’t need to support its own weight. The roof is floating directly on the gas surface, NOT being held up by supports at its edge. So the amount of additional structure needed is far less than your warehouse-based intuition would guess.
Now for the sidewalls. let’s take a section of the circumference 1 inch long. It too weights 1 lb per inch of height. And ther can be a hundred feet or more of height.
But that is held up by the narrow pie slice of gas pressure which extends from the circumference back to the center of the cylinder. Because a circle’s area is proportional to the square of radius, while circumference is proportional to just the radius, the bigger the tank gets, the smaller the sidewall is compared to the pie slice of supporting gas.
At large sizes, the sidewall weight would be come negligible (except if it has to be made heavier/stronger as the tank grows, which is this case it probably does not. The nonmoving outer structure needs to scale up, but the moving tank wall thickness won’t scale up so much.
eta: NaturalBlondChap’s post wasn’t there when I started.
The gas company tells me the “smell of gas” is a blend of synthetic scents added to the gas as a warning marker, so we can notice leaks. The gas itself isn’t so easily noticed. I’m not familiar with coal gas. If it has its own strong smell, then I’m merely looking foolish.
This last bit is puzzling me. The pressure on the sidewall doesn’t contribute to supporting it. Pressure tends to make it bulge outward, but the pressure on any part of the cylinder’s sidewall is horizontal (and balanced by pressure on the opposide side) yielding no net force and no support.
The force that holds the cylinder up - both roof and sidewalls - comes from the pressure exerted on the roof of the cylinder. It will be equal to the weight of the roof plus sidewalls currently being supported. Assuming the roof is basically flat, pressure will be equal to this weight divided by the area of the roof.