building a pasteurizer

Tom_133

So I have a buddy who is building a pasteurizer. It's on the larger size, at least for what I have seen, probably not large for some of you.

He says its going to be a large heat plate exchanger like 16"x24"x48"

He wants to be able to move 50GPM which I will figure out on the piping and pump side once I have the pressure loss of plate and lengths, etc. But he wants it to maintain 200 degrees going into the plate, and leave the plate at 100, which means he needs the power to bring all that water up 100 degrees at the boiler and back to the plate and he wants it nearly instantly, how do I do that equation?

I did the pounds of water x btu but I am missing something. I did tell him this is why they use steam for more often in these processes and he is adamant about hydronic.

Jamie Hall

The BTUh requirement is the same, whether it's going to be hot water or steam. I'm sure you've done it right, @Tom_133 — but the results may be hard to believe. If you are going to move 50 gallons per minute with a delta T of 100 F, you are going to need somewhere north of 2.4 million BTUh.

No matter what you are burning, that's going to be one big boiler (that's better than 20 gallons per hour of fuel oil, for instance).

You are quite right — it's a lot easier to handle that much power with steam, which is why it's usually used.

mattmia2

then there is the question is this a continuous process or a batch that happens for a few minutes every couple hours

Jamie Hall

This isn't up in Cabot, by any chance?

EBEBRATT-Ed

Yeah you would need a boiler of about 3, 200,000 input.

The boiler will not like a return water temp of 100 degrees.

That's a lot of boiler.

I would think your going to have to design a mixing situation with a couple of pumps and maybe a three way valve to keep the boiler happy

Kaos

Might want to look at something with recovery. Significantly reduces the boiler size and fuel.

https://www.apiheattransfer.com/product/pasteurization-systems/

Tom_133

https://forum.heatinghelp.com/discussion/comment/1847608#Comment_1847608

No I believe it's for a canning of drinks manufacturer. I was just asked about it. He told me it was 2.4 or bigger and I couldn't wrap my head around those numbers.

Tom_133

Whats the formula to get to that number?

Thanks for responding, this is why this site is great!

JDHW

Doesn't pasteurizing involve rapid heating and then cooling? You can recover lots of energy from the cooling to help with the heating so the actual additional heat input is much smaller than the numbers quoted above.

See post from@kaos

Jamie Hall

The formula, @Tom_133 , couldn't be simpler. It takes 1 BTU to heat 1 pound of water 1 degree Fahrenheit. One gallon of water is about 8 pounds. So… you take your flow (50 gpm) times 8, which gives you 400 pounds per minute. Times 60, which gives you 24,000 pounds per hour. Times 100, the temperature rise, which gives you 2.4 million BTUh…

Pasteurization does involve raising the temperature fairly quickly, but "rapid" is perhaps a stretch. It then involves a hold time followed by cooling. And you are right, @JDHW and @Kaos , use of a heat recovery countercurrent heat exchanger could reduce the required power input, possibly quite significantly perhaps as much as in half, if the system were well designed.

Kaos

https://forum.heatinghelp.com/discussion/comment/1847800#Comment_1847800

You can do a lot more than half. It comes down to the approach tempeature you can get on the recovery heat exchanger. These can be down to the range of 10F to 20F. For simplicity say, you are flowing water at 40GPM.

With a 10F approach, the boiler only needs to do 200kBTU. That is a big difference. It also means what is coming back is much colder so chiller costs are significantly less.

This is one of those where it is worth a bit of design, that is a lot of cost savings with the right bits.

Tom_133

https://forum.heatinghelp.com/discussion/comment/1847856#Comment_1847856

I would like to better understand this, any chance anyone has info to be read on this?

Thanks for the help

Kaos

This is what you want to design:

https://www.researchgate.net/figure/Flow-chart-of-thermal-exchangers-system-of-the-milk-pasteurization_fig1_339157078

Instead of a big HX to the boiler only, you have a large one between the fluid coming in and returning (recovery hx in the picture). This captures the heat from the pasturised fluid and uses it to pre-heat the cold supply. This then goes the boiler HX where the pasteurization happens. You'll need a length of tube after this to allow time for pasteurization.

If the recovery HX is efficient enough (that is approach temp at your flow rates/temps), you need very little boiler power and chiller at the end.