Exhaust Air to Warm water Heat Pump - malt kilning

[MannyCalavera]

Condensing temperature of what indeed. Further study required on this part, alot of the old literature deals with refrigerants that may not be socially acceptable now

Looking at a P vs. Enthalpy chart of ammonia, 80degC is far from critical properties, but it's at 40bar (seems quite high, i gather 20-25 is more like what is aimed at).

I don't think you are reading wrong, but if the heat pump exchangers went tits up, the primary heating medium (steam radiators) would ramp up to cope. Would they be able to cope with heating (the now)cooler air to 60+ degC? Very good point. They might struggle without pre-heating.

However, the system can always revert back to it's old recovery (which uses the exhaust humid air to heat the glycol a wee bit). This just requires the flick of a switch / control valves (so to speak).

Any thoughts on refrigerants for this temperature range appreciated.

[mad fridgie]

The glycol loop is more than likely there for practical reasons, how cold does it get? what happens to your air heat exchanger, if there is no heat flow. (kiln is off).
Of course direct heating is better than indirect! to be determined!
Earlier on I told you that your heat pump should heat the glycol directly
As far temps go they are just pie in the sky figures, until the air heating process has been determined,
The heat pump is the very last thing to sort out.
Simply what is the temperature of the fluid entering the evap?

[mad fridgie]

I have just re read you last two statements, it could be constrewed in a number of ways.
I think you are again moving away from your whole plant process.
You have water at 50C plenty of it.
What is the required temperature of the water back at the distilling process, what happens if this colder! Does this improve the distilling process.
You already have some from of heat exchange, using your exhaust air.
Understand that the compression ratio determines the efficiency of the heat pump. Very early on I asked do you require energy or temperature, again this can only be determined by knowing the air heating process, including diversity of the kilns.
As far as refrigerant choice, what will be the working conditions, whos going to fix it, are components of the shelf, is it safe, if there is a leak will taint your product, what is the capital cost.
it is very difficult to find one that will be top in all areas.

[desA]

The process specification envelope needs to be determined before a detailed engineering phase can, or should ever, begin.

Manny - first set down your hot & cold streams, load patterns in stone, then re-visit the equipment required to get there.

[MannyCalavera]

Flexability is required with cold water Fridge - the temperature required can change depending on character of spirit. > 30 is too hot, 18- 28 is normal. Therefore cooling down to 30 would be ideal, but no less than 30. There is sea water cooling facilities in place to bring it to the exact requirement.

Air flow through the radiators is 24/7 - a kiln will be "off" for say 4 hours out of a 24 period, but at that time it's paired kiln will be in full whack so air flowrate is still there.
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Trying to guess how the radiator performs at elevated temperatures is tricky, and so its really hard to know return temps that glycol would be at. I realise this is key information to know before any design can take place.

I am wondering if it is best to assume new radiators will be purchased which can be designed to best suit the new process?

[mad fridgie]

Flexability is required with cold water Fridge - the temperature required can change depending on character of spirit. > 30 is too hot, 18- 28 is normal. Therefore cooling down to 30 would be ideal, but no less than 30 NO. There is sea water cooling facilities in place to bring it to the exact requirement.NO waste of energy (do not disconnect as may be used when ambients are very high)

Air flow through the radiators is 24/7 - a kiln will be "off" for say 4 hours out of a 24 period, but at that time it's paired kiln will be in full whack so air flowrate is still there. If your sure that the rads never drop below freezing, then water is OK direct (it can be controlled, but its risk management)
----
Trying to guess how the radiator performs at elevated temperatures is tricky, and so its really hard to know return temps that glycol would be at. I realise this is key information to know before any design can take place.Correct

I am wondering if it is best to assume new radiators will be purchased which can be designed to best suit the new process?

100%
"S" is the key

[MannyCalavera]

Excellent. Let's assume this is the case henceforth - no point installing a great heat pump system if the delivery of heat is going to be hindered by some old piece of sh*t radiator.

My next thought would be, what would be best glycol temperature for the condenser. Glycol returning hotter or colder? (depends on radiator design and glycol flow, both of which we can change). Colder would strike me as being better, more driving force for the condensation etc.

1.2 MW is the required duty to raise mean ambient air from 10 C to 60 C given the average air flowrate in one radiator. This is the key requirement of the glycol.

I am in contact with a fabricator of radiators up here, hopefully he can advise me on temperatures which would do this duty so i can get an idea of what temperatures of glycol to expect to achieve 60 C air-on.

[mad fridgie]

Still moving a bit quick,
so now descibe your process (no numbers) keep it simple
I will start; we have 2 energy streams,"a' hot energy coming from the dist. process and "b"low grade heat from exhaust recovery
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>
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End desired results

[MannyCalavera]

- two energy streams, hot dist water and exhaust kiln air- exhaust air currently vented with no recovery- dist water currently used to heat glycol circuits- cooled dist water returned to cooling towers--------- 6 kilns in question- operate in pairs- numbered 3/4, 5/6, 7/8- 3/4 twice the capacity of 5-8- air flowrate always fairly constant- 24 kiln cycle per kiln- first 12 hours air is 100% wet, final 12hrs moisture content reduces- whilst 1 kiln is in first 12hrs, paired kiln will be in second 12hrs- this kiln will recirculate 100% air to its paired kilneach pair has 1 pre-haeting radiator- glycol passes through radiator pre-heating kiln air- cooled glycol returned to hot water PHEs- 3 pre-heating radiators = 3 glycol circuits = 3 PHEs- glycol circuit can switch between exhaust air & hot water as a heat source- hot water almost always used preferentially- exhaust air not utilised------------heat pump- use hot water as a heat source- use a heat pump to delivery energy and raise the temperature of the 3 glycol circuits- increase pre-heated air to a temp of 60 degCpro's- savings on annual HFO- CO2 considerations a positive- cooling condenser water saving on cooling costsv.s.- capital / maintenance / operating cost of heat pump

[MannyCalavera]

apologies for format, copy paste didnt work

[MannyCalavera]

Finally got Visio working - this schematic should make it clear what is going on

[MannyCalavera]

Basis:

1.25 MW heating required for: 10 C - > 60 C air at average 25 kg/s

Glycol delivering this duty at given flowrate: delta T = 23 C

1.25MW per radiator (3/4 = 5/6/7/8 air flow)
1.25 * 4 = 5 MW total required heat input

Hot water source in evaporator: 50 deg C
Evaporator drops it to : 32 deg C

18 degC delta T at average flow = 4.5 MW

Glyol heated to 70 degC in condenser
Drop over radiator = 23, so 47 deg C entering condenser

Air flow measurements required for each pair of kilns, profile over a 24 hour period can then be built up to give a load profile on the radiators.

So

• evaporator inlet temp = 50 deg C
• 4.5 MW removed, outlet temp = 30 degC
• Condenser temperature = 70 degC
• Inlet to condenser = 47 degC

Current pre-heating: 10 - 37 degC
Improved pre-heating: 10 - 60 degC
CoP anyone?

[desA]

Suggestion - put your process information directly on the process diagram. It will be easier for us to make sense of your logic.

[MannyCalavera]

Good call desa.

Ignore the 75 C.

Obviously glycol flowrate can be altered, which will change the temperature it enters the condenser at. (i don't know whether cooler or hotter entering temp is best)

70-80 deg pre-heating required for radiators to be able to bring air up to 60 C. (fairly realisitc assumption based on similar radiators at different maltings).

Any input appreciated. Regards

[r.bartlett]

Did this die a death??

[desA]

I suspect that the hooch ran low.

[DTLarca]

Sheesh - I've read up to post #26 which for me is half way down the first page of 4.

Thought I'd take a break to watch a movie - however - my first thoughts here are multiple R134a screw circuits, thats if you want to use standard copper piping components, you would then go for circuits of about 500kW each to avoid exceeding the elastic limit of the size piping implied.

[mad fridgie]

In short, these plants can save copuse amounts of energy, but to to give maximum benefit, a full understanding of the factory processes is required. In my opinion this not just about heatpumps.
I would say for you boys in the UK there is a great oppotunity to make a new market but you will need to go with an open mind. Apparently there are 2000 of these plants in Scotland, all using a very similar system.