Mol sieve regeneration gas heater / WHRU

[fdomin]

We are designing a large NGL plant and for regeneration gas heater our first choice is to use a coil in WHRU using turbine exhaust.
4 turbocompressors will be installed for residue gas, all with WHRU. One coil for regen gas should be installed in each WHRU to allow regeneration if any compressor is out of order.

Hot oil heater was not considered because it would require heating the oil to aprox 600° (regen is made at 550°F). No other consumer needs that temperature level (fractionation reboilers operate at 320°F max).

We are worried about operative an safety issues regarding cycling operation. (no flow during cooling phase)

Could anyone share experiences in this field?

 

[EmmanuelTop]

The first thing I would think of: can I afford to have my Mol Sieve bed regeneration dependent only on the Waste Heat Recovery Unit - particularly considering startup, cold restart(s), and the requirement for multiple bed regeneration prior to initial startup.

The idea is worth exploring, but pay attention - the Devil is always in details.

http://antwrp.gsfc.nasa.gov/apod/astropix.html

 

[dcasto]

the biggest fear is a tube failure that allows the gas to enter the exhaust, especially if the unit is down and the gas accumulates and gets ignited during a engine start. So I'd have a system that assures there is no gas in the exhaust. We had a whru on a 4 cycle engine that heated the regeneration gas. There was a small leak and the engine would always backfire during startup and shut downs. There was excessive back pressure on the exhaust and we assumed it was a bad design on the delta P. We found a pinhole from a grinder that slipped during assembly of the unit.

The nice thing is that the natural gas (ok I'm assuming here) can sit stagnet in the tubes and not be an issue when the regen gas is not needed.

 

[fdomin]

dcasto,

As you stated, our biggest fear is tube failure.
In your case the only problem was backfire?
I´m worried about natural gas staying stagnant in tube. What material should be used in that case as flue gas is at 1600°F?

Emmanueltop,

We are planning to add some extra heating equipment (i.e combustor) to allow initial regeneration without turbines running.

Thanks to both for your answers

 

[dcasto]

You under stand backfire as in detonation in the exhaust on a reciprocating 4 cycle engine.

Pick your favorite materials or got to the metalurgist forum. We used carbon steel as 4 cycle engine exhaust couldn't get that high. On another system, we had WHRU on a gas turbine with supplimental co firing in the exhaust and we were making steam and we had direct heating of a deisobutananizer reboiler, with 150 psi butane in the coils. The system ran for 40 years.