Fool wrote: ↑Wed Jun 19, 2024 6:45 am
Wikipedia wrote:Claude's process
Air can also be liquefied by Claude's process in which the gas is allowed to expand isentropically twice in two chambers. While expanding, the gas has to do work as it is led through an expansion turbine. The gas is not yet liquid, since that would destroy the turbine. Commercial air liquefication plants bypass this problem by expanding the air at supercritical pressures.[1] Final liquefaction takes place by isenthalpic expansion in a thermal expansion valve.
What's often given rather short shrift is "
While expanding, the gas has to do work as it is led through an expansion turbine".
This was the major advance over the Linde process using only a throttling valve. In the Linde process the gas cools
slightly expanding through just an expansion (or throttling) valve but does not do any work as it expands other than the work of pushing itself out of the way. As some gas goes through the valve more gas expanding behind it has to do a little work pushing the gas in front of it along. But because the cooling was very slight, just a degree or two, the cycle had to be repeated over and over. The gas passed through the valve many many times before it would finally begin to liquify.
Claude's major advancement was mostly simply just to replace Linde's expansion valve with an expansion engine.
This forced the gas to do much more work as it expanded. To escape from the compression the gas now had to drive a piston to run an entire engine, not just push some gas molecules out of the way. The engine also powered other things giving the gas additional work so it cooled much more rapidly and liquified much more quickly.
Infact it worked so well, it actually worked too well. The gas would liquify inside the cylinder, getting so cold so fast the engine itself would freeze up.
More cold tolerant lubricants were used, but the air might actually freeze solid.
So eventually it was found that by using a less efficient expansion engine the air could be brought down near to the liquefaction temperature quickly in the turbine by making the gas do work, then the process could be finished by the Lind method.
Fool likes to pretend that he knows what he's talking about, previously insisting the gas cannot liquify in the turbine. He hasn't studied the whole history from the begining.
It is not the gas cannot liquify in a turbine, it's that when it does the turbine will wear out quickly and turbines are expensive. So they now use the turbine for very rapid cooling and finish the liquefaction process using the expansion valve for the last few degrees of cooling, since there is nothing much to damage in a simple valve.
The advantage of a turbine over an expansion engine is obvious. Turbines are more efficient.
Another advancement was,
Well, if the turbine or expansion engine doesn't really work as well, unless it is powering a load, if it needs some actual work to do, it is costing a lot to run the compressor to compress the air. Let's just use the expansion engine to run the compressor!
And so the turbo-expander was born.
A compressor and expansion engine coupled together on the same shaft. The compressor compresses the gas so it can do work expanding and cooling as it escapes through the expansion engine doing work, and the work it does is to drive the compressor. So now the expanding gas is doing the work of compressing additional gas to be expanded. Quite a system.
Such a "bootstrap" system is the standard method I think these days.
I've been told that the public information about the efficiency of the energy recovery of these bootstrap systems is greatly watered down.
Wikipedia articles state that the expansion turbine only recovers about 10%
I've been told privately (in a phone conversation with Peter Lindemann) that the energy recovery using turbo-expanders is actually much closer to 100% (above 90% as I recall).
So, converting heat into work has moved well beyond the "experiment" stage.
All kinds of major MAJOR industrial processes going on RIGHT NOW today depend on it.