Dewar Conversion, LN2 to Liq Methane

[TangoCleveland]

Aside from the obvious flammability issues, are there any tricks to converting mobile dewars of 500 to 4000 gallon capacity from liquid nitrogen to liquid methane service? Dewar pressures are around 50 psig.

Larry

 

[claybo]

I would want to have an inert purge capability for the transfer and vent plumbing. Oh, and a good ground. Also, any electric gear nearby needs to be explosion proof. Other than that, the LN2 hardware should work.

 

[TangoCleveland]

claybo, thanks for the comment about explosion proof. I already looked at pressure relief, and we'll need about 35% more capacity for CH4 compared to LN2. The dewars we use here are DOT compliant, Code stamped, or Code equivalent for pressures up to 270 psig, complete with pressure regulation, relief and vent systems, and vacuum jacket insulated. They are transported on dedicated truck trailers. Our commodities are LN2, LOX, LAR, and Liquid Hydrogen. We need to convert some to liquid methane (essentially LNG) service for research. We're hesitating to convert LH2 dewars because of differences in weight of fluids, but LN2 should be an easy switch once we recalculate relief capacity and add vent/purge tubing.

I was wondering if there might be any material compatibility issues. Do the mercaptans in the methane odorant provide enough sulfur to attack stainless steel? The inner vessel of all the dewars is stainless.

Larry

 

[claybo]

The only thing I know is that H2 causes embrittlement in 17-4 PH stainless. 304 and 316 shouldnt be a problem, but I don't know anything about mercaptans. Also, why can't you just sub-cool the liquid and transport at a lower pressure?