Need to boil 5 gal per hour of acidwater - no propane or gas source for heating

[dru8923]

We have acid water with only some properties known. We need to boil this at 5gal/hr and capture the vaporized air at the top. The concept is a vertical heat exchanger. The acid water will come in from the bottom at 70F, enter the tubes, and will be heated by hot air. The vapor will rise through the tubes and exit the top. The acid gas will be sent downstream via a blower.

We don't have any fuel source so the concept is to use hot air thru the shell side to heat the acid water in the tubes. The air will be heated with some sort of pipe heater to 350F and sent to the top of the shell side. The air will travel down the exchanger, through a set of baffles, and exit from the bottom. The air will then travel back up to the top of the shell via a continuous loop.

Using water properties I have:

mc(dT)air = mc(dT)water, to solve for m(air)

m(water)=42lb (5gal)
c(water)=1 BTU/lb-F
dT(water)=212-70=142F

m(air)=?
c(air)=0.2433 BTU/lb-F (at 350F)
dT(air)=350-250=100F (250 is unknown)

Solving for m(air) = 245 lbs (5000cuft)

Now, what about latent heat of vaporization? 245lbs of hot air @ 350F will raise the water to boiling point, but don't we need to add m(water)xLHV? If so, the LHV of the acidwater is unknown.

I need to calculate the air temp and total hot air flow required to continuously boil the acidwater 24hours/day. Second, I need to find select sort of inline pipe heater to initially heat the air. Third, I need to select a blower to send the air to the top of the shell.

 

[hacksaw]

that is not an engineer from scratch project, you need to contact someone already in the business spent acid plants

 

[IRstuff]

" If so, the LHV of the acidwater is unknown."

If this is really acid IN water, then using the the LHV of water won't be that bad an estimate.

One major item you may have neglected is the heat loss while you are trying to heat up the water

TTFN
faq731-376

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[zdas04]

Where is the hot air coming from? If it is a heat exchanger on an engine exhaust, then you are missing a bet. Use your water for cooling water in the engine to pre-heat the water before your final hot air heat exchanger. You'll want to pump it pretty fast (limit your dT on the cooling water side to 30-40°F so that you don't get plating issues), those extra BTU's will really increase the evaporation rate.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[Latexman]

This may or may not be a dumb question. What kind of acid? Mineral? Organic? H2S?

Good luck,
Latexman

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[dru8923]

Thanks for the replies.

Yes it's an H2S, water, and ammonia I believe. There's no hot water source or gas source so air is the only way, using some sort of immersion air heater. There are the portable kind that supply 10KW/1000cfm but only reach 100-150F.

This is not a typical heat exchanger, it's more a reactor. Initial tests show the best reaction temp to be 300-350F. The vertical design is to capture the gas at the top. The top of the reactor/heat exchanger needs to stay above 300, as we did see some clogging due to condensation when temperature dropped. Some initial calcs show total heat required for the reaction is 36000BTU or 10KW.

 

[trashcanman]

I think you are way short on heat required. 5 gal/hr * 8.33 lb/gal*1150 btu/lb = 47897.5 btu/hr. That is for pure water at atmospheric pressure.

 

[chicopee]

I don't have the properties of H2S however I know water and ammonia will vaporize by creating a partial vacuum in the container holding the mixture. You may want to look at that aspect for your project.