Flash Boiler with Used Tankless Heater Build

I got a free 10 year old tankless heater, old for sure, but very little use.

So far, I have disassembled everything and have the burner solenoids controllable and the ignition system working.

I have a few questions. As far as the burner goes, it was origianlly a NG burner, will LP work the same as long as I keep the PSI real low, at least for testing? I suppose I can always throw a regular burner in there if it doesnt work.

Second, the heat exchanger is 10 passes, about 6" long of 1/2 inch copper pipe through a series of about 75 1/32" thick copper plates. I guess time will tell if this is enough.

Has anyone else done this? Would seem to be an easy way to get some parts to find one on Craigslist.

-Paul

well, This doesnt just work well, it works perfectly.

I set-up the system at 1/2 gal per minute and fired the burner up, after about 10 seconds, I was getting just steam out of the outlet and I got scared and shut it all down.

After some tweaking to get to the magic 170 degree mark at the output, I measured the flow rate at 2 gal per minute, maybe a hair over.

This was with 68 degree input water.

I will post some pictures of the build shortly, but I think the key is to have as much surface are in contact with the flame as possible, and the forced-air blower provides a ton of O2 for the burn.

The only problem with the propane is that I am getting a little soot in the exchanger, but I probably ran about 50 gal through it yesterday when i was testing, equivalent to probably 6 5 gal batches.

How much control of the fuel flow do you have?, enough to reduce the flame to a point you can do fly sparge water heating at a low flow rate?. IMHO the flash boiler is the only way to go, makes it possible to get started in minutes from a cold start, and with flame level control you can do fly sparging and steam injection RIMS.

Very intriguing. Can you post some pictures? Thanks

I'll post some pictures tomorrow.

Sure, I am sure all it would take is some regulator on the gas input, The one I have is from a propane heater that had a regulator piped in on the equipment, so I wasnt able to salvage it. Eventually, I will upgrade to a regulator on the propane side, but for now, I am a batch sparger, and this is perfect, I can just adjust flow rate to get everything right.

Wow... 100F delta at 2gpm... that rocks! Very interested to see more pics of it.

Ok, so here we go:



Here is a shot of the very dangerous test run, you cant see the thermometer, but that is 170° water coming out, 68ish° coming in. This is a good example of mixing, Fire, Water and Electricity. The GFCI tripped right after I took the photos, which closes the solenoid valves for the gas.



This is a basic shot of the front of the unit. I sprayed it all white, the left switch is a 25A DPST switch, flipping it up sends rectified and smoothed AC to the solenoids to open them up, and sends unrectified AC to the motor to get the blower running. Assuming gas is hooked up, it starts flowing. Next to the right is a simple push button switch that feeds 120V to the ignite (generates a spark above the burner) to ignite the LP.



This is the guts of the unit, you can see my wiring in the lower left, from the bottom to the top, you can see the blower housing with the solenoids, above that, the burner chamber, followed by the heat exchanger.

It has 3/4" NPT inlets and outlets, I plan on reducing these down and putting quick-disconnects on them, that way if I ever want to use it after the sparge, I can really bring things to a boil quickly by pumping my sparge through it.

very cool

How sensitive do you think it will be to the Input water temperature? I'm not totally clear on the specifics of temp control in these things?

PaulHilgeman said:

I have a few questions. As far as the burner goes, it was origianlly a NG burner, will LP work the same as long as I keep the PSI real low, at least for testing? I suppose I can always throw a regular burner in there if it doesnt work.

Click to expand...

You need to change the orfice from NG to LP, the orfice sizes are different. I don't remember which way, but I believe the NG orfice is smaller than the LP orfice so you may be able to reem the hole to the correct size.

Jawbox0 said:

How sensitive do you think it will be to the Input water temperature? I'm not totally clear on the specifics of temp control in these things?

Click to expand...

I think the heating of the water as it goes through the heat exchanger follows an inverse exponential function, where the most temperature rise occurs right at the beginning of the exchanger. Based on this, shifting the curve downward say 10 degrees may result in a 2-3 decrease in output temp. But at this point, thats just a theory. This winter will tell though as my ground water temp gets down to about 48 degrees.

You need to change the orfice from NG to LP, the orfice sizes are different. I don't remember which way, but I believe the NG orfice is smaller than the LP orfice so you may be able to reem the hole to the correct size.

Click to expand...

Actually it didn't end up mattering, I think the regulator that I have on there now is about 5PSI of LP, but probably at a much slower flow rate than the 0.5PSI natural gas. If you think about it, I am probably at a lower efficiency and output than any tankless heater would be to begin with. Those things should be able to deliver 5 or more gallons per minute at somewhere around 120.

I had been pondering how to monitor the temperature, but since I am really not going to need my HLT anymore, I am going to take the brewmometer off of it and use it in a T at the output of the system.

Cant wait to use this thing on Wednesday.

PaulHilgeman said:

Those things should be able to deliver 5 or more gallons per minute at somewhere around 120.

Click to expand...

I have a Bosch tankless water heater similar to what you have. Mine is maybe 4-5 years old and it's rated at 5 gpm at 125*.

Wow, I just guessed at that one!

These days I know that they make them even bigger than that.

Either way, if you are interested in doing something like this, keep your eyes peeled, this one has a MFR date of 2001, so there have got to be some coming out of homes because of age, electronics failures etc, all you really need is a servicable heat exchanger.

Either that, or someone needs to find some all copper heat exchangers that you can build a chimney around and put a burner below. It could certainly be much smaller and lighter than what I have put together.

What will be interesting is to see how many batches I get out of this thing, I have a feeling it is quite a bit more efficient than bulk heating, the heat coming out of the vent is actually quite minimal, less than the heat that goes 'around' a pot of water anyways, and obviously a much shorter period of time.

PaulHilgeman said:

Wow, I just guessed at that one!

These days I know that they make them even bigger than that.

Click to expand...

Mine is 200,000 btu.

Think the biggest I have heard of is 250,000... but they are few and far between.

I tested this out with an actual brew last night, a DFH60 clone.

It worked perfectly and I was able to get an all-grain batch done in less that 3 hours, which says alot since this was my first RIMS batch too, so lots of fooling around.

I was able to make the hot water, pre-heat the cooler, grind the grains and mash-in in about 10 minutes.

Bottom line, flash boilers are amazingly useful and has a huge impact on the brew-time.

It was also nice and quiet during the mash since I didnt have to have sparge water heating the whole time.

You should see what a flash boiler generating steam can do besides heating water, boiling with flash boiler steam like GreenMonti's rig, or steam injection RIMS like I do.

sounds too dangerous for me!

I read all posts...All are interesting one...water filters should not be confused with devices or tablets that purify water,it remove or kill harmful bacterias from water...Rain water tank should be used for water saving...