Hot Air to Cold Oil Heat Exchanger

[ndgranberry]

Working on a project where we have been asked to utilize waste heat from a combustion process in order to increase the temperature of oil in a separate process. The hot air from combustion is at 340C
and the oil is at 22C with a target temperature of 65C I have not seen any hot air heat exchangers except ones used to heat air. Can someone give me some guidance or ideas? Point out any possible problems we should take into consideration?

 

[SteamKing]

You've never seen a gas water heater?

 

[ndgranberry]

That is a iterative process though. Fill it up, heat it, empty it, start over. Is it possible to heat the oil fast enough for it to be a continuous process?

 

[ndgranberry]

The question is partly can I use a shell and tube heat exchanger with hot air in the shell and oil in the tube and it be effective?

 

[billhen]

I think you want a duct cooler with gas in the duct and a tube bundle with longitudinal finning outside the tubes and oil inside the tube. Mechanical detail might vary depending on space available and fin efficiency. Shell-and- tube is possible. Most manufactures of double pipe exchanger have a line of pipe size heater that have longitudinally finned tube bundles. The duct is usually favorable because of lower pressure drop on the gas, say, 2-3 inches water in large applications. Either way sizing is best left to the suppliers.

 

[billy_joule]

That is a iterative process though. Fill it up, heat it, empty it, start over. Is it possible to heat the oil fast enough for it to be a continuous process?

I have a tankless H/W system for my home. Cold water and gas flow in, CO2 and hot water flow out, it's about the size of a microwave and supplies all hot water, very common device.

Even tanked (gas or electric) systems don't empty; the tank is kept full, heating is controlled by a thermostat.

But Billhen is right; leave it up to the supplier. Give them your data (flow rates, cost, size, maintenance req., max pressure drop, temps ect ect) and they'll give their best solution.

 

[billhen]

The "batch" processing can possibly be converted to continuous by using your new heater as a circulation heater on an oil tank. In a large enough oil flow that is it's self continuous, a tank may not be needed. Control may require diverting the hot gas, and that might be unusual, Waste heat gas/flues usually go for all the gas cooling (heat recovery) they can get short of condensate in the downstream piping/duct. If your oil flow is small and your gas load large, you might consider an intermediate fluid that could take even more waste heat (like boiler feed water preheat) then use that intermediate fluid in a simple plain tube hairpin or shell-and-tube where the oil can just be on and off as needed. That is continuous to the hot gas and intermediate fluid, but batch to the oil. The oil heat exchanger might be large or small is such arrangement.