Home Podcasts THMG038 – Cryogenics, Part II

THMG038 – Cryogenics, Part II


Mike and Bob conclude their discussion of cryogenics and how they affect us in the field.

Complete Show Notes

00:45 Who Uses Cryogenics?

  • The medical field uses cryogenics extensively, and not just for providing O2 for patients
  • It’s used for things like tissue sampling and medical imaging to keep machines cold
  • O2 is a strong oxidizer, and is dangerous both in high concentrations and the LOX
  • Cryogenics are also being used in the home – COPD and emphysema patients are starting to get their O2 via cryogenics
  • This is problematic, because the O2 is in an environment that isn’t designed to handle it

3:05 Storage and Transport of O2

  • Relatively straightforward because the tanks are all pretty much the same
  • Smaller tanks are called dewars – these range in size from 1-50 gallons
  • Dewars are constructed with 2 walls – inside wall is made of glass to keep heat out
  • The second wall is made of metal or composite
  • The two walls are separated by a strong vacuum to minimize the amount of heat that’s transferred into the liquid – there may also be insulation in the vacuum space
  • Large storage tanks look like long, big BBQ tanks with a bunch of valves on them

5:40 CO2 Container Valving

  • Containers used for low-pressure liquids have 3 branches – a liquid valve, a relief valve, and a vent valve
  • Containers used for high-pressure liquid lines have 5 branches, along with a liquid level gauge
  • Liquid level gauge
    • One of the first things you’ll see in either of these tanks is the liquid level
    • This sticks straight up from the center of the valves and has a sight line that goes up and down – works off of a float system inside the tank itself
    • Has nothing to do with pressure – only about the level
  • Relief branch
    • Has a spring valve set to go off at 22, 230, or 350 psig – lower psig are found on low pressure tanks
    • Burst disk is also found on the relief branch – set based on the rating of the inside portion of the tank
    • Make sure to never plug these devices, as the potential for these tanks to bleve is extremely high
  • Pressure gauge
    • Gives us a reading of the pressure in the headspace
  • The rest of the valves look very similar, so it’s important to identify them based upon the actual metal tag each branch should have
  • Vent valve
    • This should be piped directly into the headspace – primarily used to release gaseous products during fill
    • Basically allows the vapors to be removed to make room for the liquid
    • Can also be used to rapidly reduce pressure inside the headspace – can be utilized while the tank is in use or during storage
    • This allows you to have full control of the tank during operation without disrupting the operation
  • Liquid valve
    • This is the last branch found on both styles of tanks – piped directly from the liquid inner tank
    • Allows for liquid to be removed or filled from the tank
    • Has a connection that’s CGA-specific for the liquid that’s being removed – as a result, these valves should never be swapped out
  • Gas line valve
    • This is only found on high-pressure liquid containers – fittings are specific to the gas being used and should never be swapped out
  • Pressure building valve
    • Allows liquid to enter a tube that’s wrapped around the inner tank – allows heat to enter the circuit and vaporize some of the liquid
    • As this happens, pressure is built up within the headspace
    • This is the system that controls the pressure within the tank
    • Opening the valve doesn’t produce pressure – instead, it develops slowly as the liquid vaporizes

12:55 Hazmat Drill Nugget from Hazsim Training Systems

  • Pick a number – everyone else looks at the rig and identifies anything applicable that’s related to the number you chose
  • The originator should try to know more than everyone else and memorize what they come up with
  • Helps you remember which tools you have and how many of them you have on your rig

18:55 PPE Selection and Cryogenics

  • Make sure you’re using cryogenic-approved equipment
  • Don’t wear your bunker gear – this has no cryoprotection at all

20:00 Listener Questions on Tank Failure

  • Question: How should we proceed if gas is coming out of the pressure relief device?
    • This is usually totally normal because heat is always going into the tank
    • Pressure builds as a result, and the spring safety valve is just doing its job
    • You can check to see whether it’s coming from the spring valve by using soapy water
    • Make sure there’s nothing abnormal in the area that would push heat into the system – if there is, check for O2 displacement and make sure it’s ventilated
  • Question: How do we handle pressure that’s too high?
    • You can evacuate some of the headspace using the vent valve
    • However, there’s a reason why the pressure got so high – and we need to figure out why
    • One of the most common reasons is that the pressure regulator setting is too high – try lowering it or turning it off altogether
    • Then, release some pressure and see if it builds again – if the tank is in use, have them use more product
    • it’s very possible that the tank lost its vacuum and is rapidly gaining heat
    • Check the temperature of the shell 8 inches above the bottom of the tank – if it’s cold or frosty, the tank should be removed ASAP or the area should be evacuated
    • Similar to propane overfill, cryogenics can have too much liquid, which puts hydrologic pressure where it shouldn’t be – take out some liquid and see if that helps
  • Question: Are frozen valves a big deal?
    • This could be normal if the system is in use – just make sure all of your pressures are good
    • If it’s not in use, it’s possible there’s a leak somewhere in the system
    • Confirm that the gas and liquid lines are shut down and check for leaks before the valve with soapy water
    • Move the container either outside or to a well-ventilated area
  • Question: What if the bottom 8 inches are covered in ice?
    • This is totally normal because the vaporizer is just doing what it’s supposed to do
    • Never pull these to you – always push them in
    • Never ride in an elevator with one of these tanks – if you have to, put it in the elevator and meet it on the destination floor

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