Need to heat 400l/min water delta 40 Celcius
Need to heat 400l/min water delta 40 Celcius
(OP)
Hi Guys,
Please help, I am attempting to solve the problem encountered by a dairy farmer in cleaning his milking machines.
The Cleaning system circulates water (containing detergents) starting at 80 deg C through the system with a flow rate of 400l/min for approximately 5 minutes. The problem is that the return water temp is often as low as 40 deg C. We need to heat the water back to 80 degrees before it goes back for the second, third, etc passes through the system.
The Dairy has an Anaerobic Digester producing excess gas which we intend using as our energy source for this heating.
Please advise.
Many thanks
Rob
Please help, I am attempting to solve the problem encountered by a dairy farmer in cleaning his milking machines.
The Cleaning system circulates water (containing detergents) starting at 80 deg C through the system with a flow rate of 400l/min for approximately 5 minutes. The problem is that the return water temp is often as low as 40 deg C. We need to heat the water back to 80 degrees before it goes back for the second, third, etc passes through the system.
The Dairy has an Anaerobic Digester producing excess gas which we intend using as our energy source for this heating.
Please advise.
Many thanks
Rob





RE: Need to heat 400l/min water delta 40 Celcius
For a heater of this size I would look at an oil pipeline "heater/treater".
You also might be able to mitigate some of your costs by preheating the return water by running the return pipes through the digester--those processes often generate excess heat.
David
RE: Need to heat 400l/min water delta 40 Celcius
Thanks for your reply.
I only need to heat the 400l/min for roughly 10 minutes each day... do your figures take that into account?
Thanks again
RE: Need to heat 400l/min water delta 40 Celcius
I figure about 1.1 megawatt heater (3.8 million BTU/hr)
Needs about 320 cu. ft for 5 minutes of operation.
Those are "into the water stream" numbers.
RE: Need to heat 400l/min water delta 40 Celcius
m = 23989 kg/hr
Q = 1.55 MW or 5.29 MMBTU/hr
if natural gas is 1.100 MMBTU/MCF then at 80% effeciency you would use 112 MCF/day or 780 SCF in 10 minutes.
Sorry about the messed up numbers before. 5 Million BTU's is a pretty big heater, but you can get tank heaters with that kind of capacity and somthing like a 100 bbl tank with a tank heater might be the way to go.
David
RE: Need to heat 400l/min water delta 40 Celcius
That might cut down on capital cost of the heating equipment and would cut down the peak load on the digester as you would have 23 5/6 hrs to heat the system back up.
RE: Need to heat 400l/min water delta 40 Celcius
Seems to me that Bribyk's idea is best. Make a tank of 80C fluid, use it, and take your time heating it back up.
My two cents anyway.
Goober Dave
RE: Need to heat 400l/min water delta 40 Celcius
The largest commercially available tankless heater puts out abuot 10 gpm at a decent deltaT, so 10 of these in parallel would ostensibly meet the flow requirement.
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RE: Need to heat 400l/min water delta 40 Celcius
That's a great idea, but still looking at either a really big gas or electric service to drive it (high demand). There's probably a happy compromise in the middle between all-storage with minimum power and all-power with minimum storage, but I'm not up to the math today...
Maybe someone out there has faced this one?
Good on y'all,
Goober Dave
RE: Need to heat 400l/min water delta 40 Celcius
It's a no-brainer- store the hot water.
RE: Need to heat 400l/min water delta 40 Celcius
RE: Need to heat 400l/min water delta 40 Celcius
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RE: Need to heat 400l/min water delta 40 Celcius
RE: Need to heat 400l/min water delta 40 Celcius
The water is in a continous cycle;
We have a container/water heater containing water with detergent at 80deg C starting temp - the detergent water is then pumped through the milking machines and milk pipes and returns to the container where it mixes with what 80deg C water remains on its way through again. The return water cools to about 40 deg C at its coldest = end of wash cycle (i.e after +-6 minutes of circulating).
We cannot increase the quantity of water as this would increase the amount of detergent needed.
I envisaged a plate heater/heat exchanger situation where we could heat a large quantity of liquid to boiling point and store it to provide the heat for the heat exchanger. As I mentioned the wash cycle is +- 6 minutes in the am and the same in the pm.
Any suggestions would be appreciated. many thanks, Rob
RE: Need to heat 400l/min water delta 40 Celcius
RE: Need to heat 400l/min water delta 40 Celcius
OK - the first point is that the heat require is much less than originally calculated because your delta T is not 40 deg as assumed. To calculate the heat requirement we need to know either:
The true delta T. ie what is the difference between supply and return temps - measured at the same time. (Measure supply then return if you only have one thermometer.)
or
The volume of your storage container, initial temp, final temp and process time.
Either of these data sets can be used to calculate the average heat requirement of your process. It may be low enough to utilise the digester surplus.
RE: Need to heat 400l/min water delta 40 Celcius
How are the pipes rinsed after the wash?
As someone who drinks milk, I'm really interested.
RE: Need to heat 400l/min water delta 40 Celcius
Thanks for all the replies,
The Water heater contains +-2000-2500l at 80+ deg Celcius at the start of the wash cycle. The returning water is at +- 40 deg C when it comes back, mixing with the hot water in the tank thereby cooling our wash water.
The water temperature seems to stabilise at about 55deg C by the end of the wash (after 6 minutes of circulating).
MintJulep, The wash water is flushed into the lagoon digester along with all the fats etc. Because the wash takes place immediately after milking stops there isn't sufficient time for it to develop into a bacteria soup! :)
However if we don't solve our returning water temp issue and leave milk fats coating the system pipes... then the bacteria soup starts...
Our milk is cooled from body temp down to 6 degrees immediately it comes out of the cow. from there it goes into a bulk cooler tank and gets cooled to below 4deg C.
i.e. No chance for bacteria to grow!! and really clean fresh milk!!!
RE: Need to heat 400l/min water delta 40 Celcius