Need ideas for large heat exchanger for natural gas

[PetroBob]

I need to come up with a suitable heat exchanger(s) for ~30 MMBtu/hr (8.5 MW). We prefer to use electricity not fired heater if possible.

Service: Warming ~100 MMSCFD of natural gas at 3300 psig from 77 degF to 185 degF.

Can anyone recommend possible heat exchanger types for this service?
Any suggested suppliers?

 

[zdas04]

PetroBob,
The way this usually works is if you provide an interesting question people will often provide very useful answers. A bare-bones question isn't really that interesting. Now, if you had said why you are heating natural gas, or why you didn't want to burn any of it it might have been interesting.

David

 

[PetroBob]

Good point David. This is an interesting question! Because 30 MMBtu/hr is a very large heat load for non-fired heater service. I could have made this more clear in subject title. I will keep this in mind for future – thanks.

The reason for heating the natural gas is to keep it from condensing (it contains ethane, propane, butane). We are reluctant to use a fired heater because all this equipment will be on board a ship, and we prefer to avoid complexity & minimize plot space for ship-board equipment. Also spare electrical capacity is available when ship is docked (which is when the natural gas is being loaded, and requires heating). This is a very front end conceptual / feasibility study for a novel process.

I’m currently favouring 3 to 4 off-the-shelf water bath heaters for the service. They don’t come big enough for this service hence why we’d need several. I am interested in any comments & suggestions from other engineers re water bath heaters or other type of equipment. We don’t have much steam or hot glycol available – if using shell & tube exchanger we’d have to add steam or glycol system which seems to me would add a lot more complexity than water bath heaters, or fired heater.

 

[bcs5274]

gas to gas exchanger maybe?

 

[Compositepro]

You can simply use sheathed electric heating elements in your gas flow. Water bath heaters would be used for heat sensitive materials that will be damaged by getting too hot. This also requires high surface area/volume.

The surface temperature of the sheathed elements might be 400-500F due to the low surface area/compactness of the heaters but if you control the wattage to match flow rate you will get whatever temperature you desire.

 

[zdas04]

I was thinking that might use the exhaust gas from the ship's engine in a gas-to-gas heat exchanger. Lots of BTU's in the stack when the engines are running.

David

 

[bcs5274]

^^ if they have a turbine , lots of heat even at minimal load

 

[PetroBob]

Thanks folks for the suggestions

 

[dcasto]

first off, you are most likey off by a factor of 2. I get a water bath heater that requires only 12.5 MMBTU/hr including the energy to rehaet the gas after a 2300 psig drop.

 

[jmw]

You only need to heat the gas during loading?
Once on board nothing more needs doing?
That means you don't have exhaust heat to use.
If the vessel will use some of the cargo as fuel when under way and you again have a need to heat it then it makes sense to use exhaust gas heating for under way operations.

But so far as you have made clear, you are only heating during loading. That being so, why is the installation on board the vessel? It makes more sense to have it as part of the permanent shore based installation with no space or energy constraints.

Then you could use counter current hot air heating with finned tube heated pipe lines...?


JMW

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