Heat recovery from engine exhaust while testing 1

[freefallingbody]

My company manufactures ( and tests, ofcourse!) IC engines. While testing for a few hours, there is a possibility of heat recovery from flue gases at 400 C, which can be used for heating water.

My question is:

If a use a concentric heat exchanger to recover heat from flue gases to water, and a water tank ( with a vent connection) placed at a higher elevation than the heat exchanger, will it work? I mean, if I provide a pipe from the bottom of the tank to the inlet of the heat exchanger and the outlet pipe from the heat exchanger to the top of the tank. Is there a requirement of a pump? ( which I don't wan't unless it is really required!)

Thanks

 

[Cooky]

Of course you can recover heat from your flue gasses in this manner. Do you intend to store this heat energy in your tank, or are you planning to use the heat as it's generated?. For the system to be practical, you need to have a place where you can readily dump this energy, maybe you could pre-heat the combustion air for your engine test facility (if you live in a cold area).

For the water system to operate efficently, you will need to use a circulation pump.

Cooky.

 

[tkdhwjd]

I believe a pump is not required if you intend to vaporize water inside the recovery heater and use thermosyphon effect to circulate water. This is highly tricky since it will likely cause water hammer when steam condenses as it contacts air or other medium that you intend to heat. Depending upon the size of your system, steam hammer can potentially damage equipment if not designed properly.

If you do not want to vaporize water, a pump is required. But this does not mean that you don't have a water hammer concern, either. If the system pressure is below Psat at 400 C and you cannot maintain a certain minimum flow rate requirement, then water will vaporize. If your intent is to preheat the combustion air, why don't you forget about water and exchanger duty from exhaust gas to air itself?

 

[chicopee]

There is a local utility company in Ludlow, Mass. that uses several gas fired turbines to power electrical generators. Flue gases are then directed to a water tube boiler for the production of saturated steam which is used in a saturated steam turbine connected to another generator. so your idea has merits since it has been used for at least 30 years at this utility power plant.

 

[samshreve]

Serveral companies make heat exchangers for the purpose you refer about.

Typical engine application use the jacket water in series with a heat exchanger to recover heat out of the exhaust gas flow.

Basically what you are looking for is called an economizer.

 

[GenB]

You have to haveuse for the generated energy, do you?
Waste heat boilers for steam or hot water are available in many sizes from 100,000btu/hr absobtion to...bigger HRSG's,
on smaller unitsthehorizontal (scotch type is more effective)and less expensive. email engine heat output details to generalblr1@netzero.net
ER

 

[smckennz]

What you propose will work. Its a simple thermosyphon.
Make sure the hot water from the exchanger enters towards the top of the elevated tank, but submerged, and the cold water feed is from the bottom of the tank. Size the lines according to the density difference, friction/inertial loss and circulation rate. Some like to insulate the hot riser and leave the cold downcomer bare. No pump required. No vaporization required. You could dispense with the tank and make the tank and exchanger in one if you liked.
a concetric exchanger wont pick up much heat though; your will need multi tubes.
As for the economics, thats another question.

Cheers

Steve

 

[freefallingbody]

Thanks guys.

The engineering manager was more worried about safety and insisted on having a circulation pump. So, a forced circulation system is being fabricated.

Thanks once again!

 

[samshreve]

You can e-mail me the engine details also. sam.shreve@juno.com. I would be interested in seeing what it is you are trying to do. Most of the time you have use the engine jacket water pump if you pressure drop isn't very great and unit is located close to the engine.