Heat exchanger: gas-air or gas-water + water-air 1

[mfqd13]

Hi,

I have a simple question: i have an exhaust gas of a combustion chamber that uses natural gas and i want to use it to heat the combustion air. What are your opinions regarding this 2 options:

1) Install an gas-air heat exchanger
2) Install an gas-water heat exchanger and a water-air heat exchanger, using a water closed loop between them.

Advantages and disadvantages of both.

 

[ione]

You can use the otherwise completely lost energy of flue gases in two way:

1. Air preheater (gas/air HE) to increase the temperature of the incoming air of combustion and thus increase combustion efficiency.
2. Economizer (gas/water HE) if you are dealing with a boiler and you want to increase the temperature of feeding water.

Both heat transfer process will reduce the temperature of the flue gases, so it is necessary to consider a lower temperature threshold to prevent corrosion issues, especially if your fuel has a high sulphur content.

http://www.resourcesaver.com/file/toolmanager/O105UF487.pdf

 

[mfqd13]

ione,

thank you for the answer but i already know that.
this is not a boiler situation.

I want opinions regarding the 2 options that i've reffered.

thanks anyway

 

[macmet]

Marco,

Can you give us an idea of the scale you're looking at working on? Why are you looking to preheat air for natural gas combustion? Are you working at low temperatures?

I'm not sure what advantages there are, if any, to transfer the heat to air first, and then to water, unless you need hot water for something else.

 

[mfqd13]

Dear macmet,

Ok. I have a stove in a industri to heat a product. The equipment has burners to heat it. It uses the ambient air for the combustion: aprox. 20ºC.
The idea is to preheat this inlet air with the recovery of the heat in flue gas. Because we are talking about natural gas, i know that i can't reduce the flue gas temperature below 120ºC in this case.

Of course, the main objective is to reduce natural gas consumption.

My question is related to costs of both solutions, because i know that gas-air heat exchangers are more expensive. But i want to hear more opinions

Thanks

 

[StoneCold]

The single heat exchanger will be much cheaper than two exchangers and a pump around loop.
The real question is does the exchanger save you enough energy to be worth installing? Unless this really is not about money and more about being green. The go ahead.

Regards
StoneCold

 

[Compositepro]

The most efficient and robust process would be a regenerator, with two packed beds of coarse gravel type material. A very simple valve design reverses the flow through the beds every minute or two, so the gravel that was heated by the exhaust gas now heats the incoming air.

http://en.wikipedia.org/wiki/Regenerative_heat_exchanger

 

[berkshire]

Have you looked at rotary heat exchangers, they come in various sizes to match the heating and cooling loads.
As usual when looking for something I could not find a smaller one , so here is a link to a bigger one so you can see what I am talking about.
B.E.

http://www.howden.com/en/Products/HeatExchangers/AirPreheaters/default.htm

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[rmw]

I have a simple question. What is the rating on your "combustion chamber"?

rmw