Exhaust Air to Warm water Heat Pump - malt kilning

[MannyCalavera]

Hi folks,

Investigating the feasibility of installing a heat pump at a maltings (malt whisky production). Very new to heat pumps, to get an overview of if its possible what are the key things to calculate?

Exhaust air is 100%RH, 35 degC. Large volume.
Want to heat warm water (45 degC) to as high as possible.

What are the key things i need to calculate before knowing whether this is economically viable? Any help appreciated.

Drew

[MannyCalavera]

Perhaps i should elaborate - i want to take as much heat out of the humid air exhaust as possible, say roughly 1 MW.

I am thinking of butane as a refrigerant since its boiling point is higher than others. So if i were to compress it to 9bar, it would boil at 75 degC. After compression it would be around 90degC, so the warm water i want to heat would have a bit of sensible and alot of latent energy to recover.

Unsure on compressor types / limitations / butane as a refrigerant.

[mad fridgie]

What temperature of water do want, do want a large voulme of water at lower temps or smaller volumes at higher temps.
What is your water entering temperature.
Your refrigeration requirements are the last thing you look at you Must study the application and process.
I can design and supply in conjuction with my UK partners.

[MannyCalavera]

Fridgie,

I have identified another heat source: A stream of warm water at 40-45 degC (30kg/s). Cooling this is also of benefit to the process.

I want to heat a loop of glycol (previously i said warm water, but its glycol) from around 40degC to as high as possible. The flowrate of glycol is roughly 12kg/s.

This glycol acts to pre-heat ambient air for kilning, and so the hotter the glycol through the radiators the better.

So i think heat source = exhaust air, or warm 40-45deg water

Heat sink = glycol loop already at around 40 degC.

Any thoughts on feasibility?

Regards.

[pwned]

jp.sanyo dot com/comp-unit/english/co2/ecocute.html

Not exactly designed for your purpose, but says up to 90C water temp.

It uses dual stage compressor with CO2

[mad fridgie]

Fridgie,

I have identified another heat source: A stream of warm water at 40-45 degC (30kg/s). Cooling this is also of benefit to the process.

I want to heat a loop of glycol (previously i said warm water, but its glycol) from around 40degC to as high as possible. The flowrate of glycol is roughly 12kg/s.

This glycol acts to pre-heat ambient air for kilning, and so the hotter the glycol through the radiators the better.

So i think heat source = exhaust air, or warm 40-45deg water

Heat sink = glycol loop already at around 40 degC.

Any thoughts on feasibility?

Regards.

If we look at your water source, we have lets say for easy a good 2 Mw, that then would heat your glycol to above 80C (actual temp depends upon concentration)
Should be no problem having a COP of over 4. (COP could be over 5 process specific) for heating only, may increase if you have the benefit of cooling

[MannyCalavera]

Thanks for link pwned.

Fridgie, cooling the warm water stream is also a big benefit (currently cooling towers bring it down to ~25 deg C). Two birds with one stone really.

I appreciate there is a large amount of energy in that warm water - in order to estimate the economics I need to work out the cost of compression.

Clearly I will want to compress my refrigerant to a pressure such that it's boiling point is above that of the warm water, and so i can extract the latent heat. Butane is looking like a good one (for the sake of rough calculations). Finding rules of thumb / design procedure for this is proving tricky. I have not done much study on refrigerant compression and am currently using equations given in engineering textbooks to calculate work of compression.

Industrially speaking, a COP of 4 is quite high?

I appreciate the replies - thanks.

[mad fridgie]

Thanks for link pwned.

Fridgie, cooling the warm water stream is also a big benefit (currently cooling towers bring it down to ~25 deg C). Two birds with one stone really.

I appreciate there is a large amount of energy in that warm water - in order to estimate the economics I need to work out the cost of compression.

Clearly I will want to compress my refrigerant to a pressure such that it's boiling point is above that of the warm water, and so i can extract the latent heat. Butane is looking like a good one (for the sake of rough calculations). Finding rules of thumb / design procedure for this is proving tricky. I have not done much study on refrigerant compression and am currently using equations given in engineering textbooks to calculate work of compression.

Industrially speaking, a COP of 4 is quite high?

I appreciate the replies - thanks.

I have just completed some further calculations, so 5 COP is very possible glycol heated to 83C, water cooled from 45 to 27C.
I am not using flammable refrigerants (a big issue in NZ at the moment)
Cost of a system, that is some what more difficult, as there are so many factors that need to be considered. But may be a s a pure budget 150 quid/ KW (300,000 pound) for this application

[MannyCalavera]

I have just completed some further calculations, so 5 COP is very possible glycol heated to 83C, water cooled from 45 to 27C.
I am not using flammable refrigerants (a big issue in NZ at the moment)
Cost of a system, that is some what more difficult, as there are so many factors that need to be considered. But may be a s a pure budget 150 quid/ KW (300,000 pound) for this application

Fridgie, would you mind explaining how you went about your calcs?

Obviously

Q = m.Cp.dT = (m.Hvap + m.Cp.dT)

in terms of heating glycol from latent and sensible heat of superheated -to-condensed-refrigerant.

Q = m.Cp.dT = m.Hvap

in terms of cooling the warm water and evaporating the refrigerant.

My lack of experience is in these areas:

- choosing a compression pressure
- whether multi or single stage compressor/s
- which refrigerants are most efficient
- optimising the trade off between Work In to compressor, to heat imparted to refrigerant

Fridgie, any help / explanation on any of the above? I am not sure what Scotland's stance on flammable refrigerants is.

Regards.

[mad fridgie]

Hi Manny, Firstly I have estimated a number of the process variables, so figures are just that estimated. (plus it is friday night here) But factual on my estimations.
How I actually achieve the very high COPs, is moving into the commercially sensative area. (I hope you understand)
Is this a practical application or just a theoretical model. The two should and are to be approached from different angles. (Theory should give you much higher COPs, but has no relevence to the practical aspects of refrigeration and very little to do with cost)
If it is a practical application, your very question to the client is was is the limits of the process (min/max), or is it steady state, what are the consequences for changes that may occur.
What is your role in this application.
If you are being used as a consultant,
Leave the specifics to the manufacture, but ensure that you stipulate A start point and a end point, requiring a performance guarantee.

[MannyCalavera]

Hi Manny, Firstly I have estimated a number of the process variables, so figures are just that estimated. (plus it is friday night here) But factual on my estimations.
How I actually achieve the very high COPs, is moving into the commercially sensative area. (I hope you understand)
Is this a practical application or just a theoretical model. The two should and are to be approached from different angles. (Theory should give you much higher COPs, but has no relevence to the practical aspects of refrigeration and very little to do with cost)
If it is a practical application, your very question to the client is was is the limits of the process (min/max), or is it steady state, what are the consequences for changes that may occur.
What is your role in this application.
If you are being used as a consultant,
Leave the specifics to the manufacture, but ensure that you stipulate A start point and a end point, requiring a performance guarantee.

Hi Fridgie, cheers for getting back. And i understand your want for not giving away calculations etc!

I am a near-graduated chemical engineer doing a half year placement in malt distilling, scotland. This would very much be a practical application - there is a huge drive currently on energy minimisation and reduced emissions. Producing malt is an extremely energy intensive process, with millions spent annually on heavy fuel oil.

My role is to investigate the feasibility of installing this heat pump. From what I have worked out, and correspondance with yourself and a few others it seems, theoretically, like a good idea. Economically? That's where I don't have experience.

It's only this week I have been looking into the heat pump possiblity, but already from a theoretical POV it seems sound. Again, no point in this design unless running costs of the loop are < money saved from reduced heavy fuel oil burning.

There is limited technical help on refrigeration / practical implications here.

The warm water - this is excess from a distillery - and normally will vary only slightly in flowrate and temperature (we are talking +/- a couple of deg C). Warm water is 24/7 (thats the aim) and the requirement for heating glycol likewise.

I presume my next step would be to consult companies that install / manufacture such systems and ask for quotes & performances, etc once i have fairly concrete "I have this much energy available and I want this as high as possible" figures.

Any further feedback or thoughts appreciated. A COP of 4-5 certainly sounds worthwhile.

Thanks for your replies - enjoy your weekend.

[mad fridgie]

Hi Fridgie, cheers for getting back. And i understand your want for not giving away calculations etc!

I am a near-graduated chemical engineer doing a half year placement in malt distilling, scotland. This would very much be a practical application - there is a huge drive currently on energy minimisation and reduced emissions. Producing malt is an extremely energy intensive process, with millions spent annually on heavy fuel oil.

My role is to investigate the feasibility of installing this heat pump. From what I have worked out, and correspondance with yourself and a few others it seems, theoretically, like a good idea. Economically? That's where I don't have experience.

It's only this week I have been looking into the heat pump possiblity, but already from a theoretical POV it seems sound. Again, no point in this design unless running costs of the loop are < money saved from reduced heavy fuel oil burning.

There is limited technical help on refrigeration / practical implications here.

The warm water - this is excess from a distillery - and normally will vary only slightly in flowrate and temperature (we are talking +/- a couple of deg C). Warm water is 24/7 (thats the aim) and the requirement for heating glycol likewise.

I presume my next step would be to consult companies that install / manufacture such systems and ask for quotes & performances, etc once i have fairly concrete "I have this much energy available and I want this as high as possible" figures.

Any further feedback or thoughts appreciated. A COP of 4-5 certainly sounds worthwhile.

Thanks for your replies - enjoy your weekend.

Firstly congratulations on choosing chemical engineering, many of my freinds choose this path and are now very successful.
I am aware for the drive for efficiency in the UK, I will be over there at the end of the month trialing my technology (already proven in NZ) 80C water with COPs close to 10.
What you have to be careful of is limiting the commercial feasabilty, with the need for technical excellence.
Going down the application, system then is fairly steady, which is good. (keeps the price down)
Then you need to look at serviceability, are you better to have say the load spread across 3 independent machines (allows for break downs, service requirements etc.)
How much is your heavy fuel oil, per "usable" KWhr.
I have asked it is this way so that it can be directly compared to electrical energy (heat pump)
Hoping to sample some of your scottish products this weekend
cheers
Mad

[MannyCalavera]

I will have a look into those details and work through them on Monday - 3 seperatate units - that is the kind of thing I would not have thought of (you see my lack of experience). All this is good food for thought for me, cheers.

I am slowly getting aquainted with the single malts of Scotland - i find it incredible the miniscule tweaks in process conditions that are used to keep the character on target. I am planning on having a few drams of single malt also - good call!


Many thanks.

[mad fridgie]

Just a quick question, You stated that you had air at 35C and 100% and approx 1MW, is this the air exausted from the malting drying process. (If so I presume it has already gone through an air to air heat exchanger, or similar device)
If so then your load is going to be very similar (plus losses).
If you were to have more energy available (from the water loop), would you look at changing your malting process (increased temp, greater fresh air makeup)
What i suggest you do is an energy mass balance on the glycol heat circuit.

[MannyCalavera]

Just a quick question, You stated that you had air at 35C and 100% and approx 1MW, is this the air exausted from the malting drying process. (If so I presume it has already gone through an air to air heat exchanger, or similar device)
If so then your load is going to be very similar (plus losses).
If you were to have more energy available (from the water loop), would you look at changing your malting process (increased temp, greater fresh air makeup)
What i suggest you do is an energy mass balance on the glycol heat circuit.

Yes the air is exhaust air from drying the 45% moisture malt. My understanding is that you have pairs of kilns. One will be operating pre-break point (air-off is close to 100% RH and around 30degC) I don't think they use an air-to-air heat exchanger with this exhaust - it is just taken to atmosphere. After ~ 12 hours RH begins to drop below 100%, and it is recycled for use in its neighbour paired kiln as it still has useful heat. 1 MW was a total estimate - i don't know how much energy you can extract from a high-enthalpy stream of air.

In terms of the malting sequence, takes around 18 hours for a batch (typically 30 tonnes). The temperatures and fan speeds are not open to change - they are set for periods based on the character of the malt they desire. So it's not just a case of hotter air the better. I think it starts at 65 deg C, stays on 75 deg C for a long while, then gets ramped up to 85 degC towards the end of the kilning (something to that affect, anyway).

Next week the maltings is operation again (been down for maintenance for 3 weeks) I am going to collect data so an accurate as possible energy balance can be done - and I agree this will be a good starting point to evaluate the energy available.

Some maltings DO pre (pre)heat incoming air via air-to-air glass tube exhaust exchanger. My maltings of interest doesn't - I will have to ask why.

Cheers

[MannyCalavera]

Sorry - "break point" is the point at which the air-off the malt bed stops being fully saturated.

Typically 11-12 hours from the start of a kilning of a batch.

[mad fridgie]

So would I be correct in saying that the air passing through the malt is single pass, entering at desired process temp, what leaves the process is down to the specific properties.
If we presume, that the actual drying takes 12hours, then you will need roughly 760Kw for vapourization (12 hour not 18, as the drying process is not linear the reason for the higher temps at the end) You also need to including heating of the room, the product, the entering air and any thermal losses (your 1Mw makes sense)
But, you will have large variables in what is entering and existing the heat pump. (This is all to with how systems are presently controlled, valving variable air volumes and the like)
From what you have indicated I would use the dist. water as a primary heat source (you can use the heat pump to start the process)
Again focus on the process(s), once you have this, you can then look at the heat pump requirements, min and max loads, at varing min and max temps.
It is the unaccounted variables that F***S Up refrigeration plants (as design engineers, if we are not given these, then we do not design for them to happen)
Your actual process (s) will be well documented, and are likely to be with a PLC program, look for the extremes

[MannyCalavera]

I am going to find the PFDs on Monday so I can understand the flow of air through the kilns - when it is fresh single pass, or recycled, or a combination of both. The sequence is quite complex. I will pass the info on to yourself when I have it on monday.

I had one question - assuming the warm water was used as the heat source for the heat pump, would there be any configuration that could make use of the saturated exhaust air also?

One advantage of the warm water is it's fairly steady properties - as you say, the exhaust air will be changing more considerably.

Regards

[Peter_1]

Just read very fast this interesting thread. It was a little bit too long reading it thoroughly before going to sleep and especially all the calculations Mad Fridgie already made. I will re-read it tomorrow.

I will give you my view on this and perhaps Mad Fridgie which I respect very much gave you already similar answers or solutions.

Going for a flammable gas in such a big quantities is extremely dangerous. There are better solutions than butane.

If you want high COP's, high end temperatures and certainly in these big ranges of kW's, then NH3 is for all these reasons the gas you have to choose.

You mentioned somewhere that you want to condense higher than the water temperature (correct me if I'm wrong). You will condense always higher than the water temperature, otherwise you can't condense.

But you forget something extremely important, your discharge temperatures (end compression temperatures I call it) - especially with NH3 - will be extremely higher than you condensing temperature. This is very useful for your application.

You could use a PHE to use the compression superheat as a boost arm-up (sorry for my bad English) and finally a second PHE to condense completely at lower temperatures to preheat the water.

Or you can circulate water through different coils where you retract the heat with a central PHE on NH3/water.
Makes it more safer in case of a leak in the kiln.
It' will also easier to control everything.

Giving the act that you have waste heat with a RH of 100% makes this extremely interesting for a reclaim project.
Strange nobody didn't thought sooner on reclaiming this waste-heat.

Giving your rather young age, I have to admit that you go really far in analyzing all this. In French they say chapeau or in English my hat goes off for you

I think this Whisky company can perhaps benefit from funds the Scottish State will give for such a big reclaim project.

30 years ago, just after leaving school, I worked some years as a mechanic in a company that made special machines for malt kilns (they made one for an African country but I forgot which one), the drying ovens (+/- 20 x 5 x 2 m), the big machines running over and through the malt, rotators which ploughed (correct expression) each day continuously through the malt to bring the malt (grain) from the bottom to the top and vice-versa. They where just like big auger drills and we called those wenders The air was blown from the bottom (perforated grilles) with huge turbines. Stinked extremely there.

[MannyCalavera]

Pete,

Many thanks for taking the time to read the thread and give your thoughts - very much appreciate this.

Really helpful points you have raised there.

"You will condense always higher than the water temperature, otherwise you can't condense."

I completely understand this - from my (shakey) calculations, is it ever an issue whereby your heat of compression (sensible) will heat the SINK temperature to a value higher than at which it will condense?

E.g. glycol at 45 degC. Say heat of vapour after compression = 100 deg C and saturation temp is 65 degC. Is there the possibility this 35 degC sensible heat could raise the water temperature to above 65 degc? (if you know what i mean...).

I am not familiar with the lingo PHE, could you explain?

I agree, it is odd no one has looked into this heat pump idea before, it seems to make a lot of sense, especially given the benefit of cooling the warm water.

I will properly read and go through what yourself and Fridgie have so kindly discussed on Monday.

This is all great guidance. The kilns you describe in your earlier job sounds pretty damn similar to the setup at the maltings I am at - the smells arn't too unpleasant where I am at however! Not as sweet as the distilleries mind.

It is saturday night and I am due a beer - this week I will hopefully be able to work with what you guys have suggested.

Again, many thanks indeed.

[MannyCalavera]

Pre Heat Exchanger? (I blame the university...)

[mad fridgie]

If I was your age, I would have already been on the Beer and chasing the fairer sex. (now that is one complex process "woman")
The actual refrigerant choice, is very much dependent upon, properties, availablity (components), service expertise, longevity and cost.
With any heat recovery, you must ensure that you have a sufficent use for the what is recovered at that temperature.
There are massive amounts of low to medium grade energy streams, that could be Boosted by heat pump technology, but the output temps are still generally to low for many practical processes (most need higher temp steam) There are a number of theorectrical ways to achieve such results, it is the practical and economic restraints that is slowing down research.
One point i will disagree with it that the heated output water temperature, need no below the refrigerant condensing temperature. Quite the opposite. (Peter touched on this area) How ever the inlet has to be lower than the condensing temp.
I would suggest the very first thing you do on Monday, is to calculate the "usable" KWhr cost of the heavy desiel.
"PHE" Plate Heat Exchanger.

[mad fridgie]

One other thing i would do, is go to your companies descion makers (CEO, MD) ask them what investment and return would ensure that such a process, would be basically guaranteed to be undertaken.
This then becomes a "goal"

[mad fridgie]

It is Sunday afternoon, it is cold and miserable outside, nothing worth watching on the box, so I thought i would have a quick play, with all the info you have given and lots and lots of presumptions.
First you glycol flow and figures must relate to both kilns, as the drying load is some what close to half your glycol duty. (remember drying is never steady state when cell structure are being dried)
If we control the refrigeration compression ratios to match the heating requirement (unlike a boiler where the output (temp) is normally fixed). This way we can optomise overall process efficiency.
So down to some number,
Total energy for the twin process.
33.2MWhrs on heavy diesel, (used at the process) DUTY
If the duty was then undertaken by the heat pump with a floating set point ( I have presumed that the glycol to air heat exchangers are able to heat the air to within 5C of approach glycol temp possible but unlikely)
Then the heat pumps would consume
7.5MWhrs of electricity.
If we then attribute some costs to these energy sources
heavy diesel= 3 pence per usable Kwhr
electricity= 7 pence per Kwhr
then a saving of 470 pounds per day or what looks better is an annual saving 170,000 pound. (excludes benefits of cooling)
I believe you could undertake an installed process for under 400,000 pound (not the absolute best, as this could trend towards a million)

[Peter_1]

E.g. glycol at 45 degC. Say heat of vapour after compression = 100 deg C and saturation temp is 65 degC. Is there the possibility this 35 degC sensible heat could raise the water temperature to above 65 degc? (if you know what i mean...).

Sure, it can go almost that high as your end compression temperatures, 100°C in your example.
We have systems running on R404a on a condensing temperature of 40 to 45°C where the water is heated to 75°C.
But the amount of heat water with superheated refrigerant is rather small compared to the heat available to condense the saturated refrigerant.

I am not familiar with the lingo PHE, could you explain?

Plate Heat Exchanger.
Lingo.. new word for me.

The kilns you describe in your earlier job sounds pretty damn similar to the setup at the maltings I am at - the smells arn't too unpleasant where I am at however! Not as sweet as the distilleries mind.

I also remember the very big humidity and the electric shocks I got when I inserted a welding rod in my torch.

Download once the free software Coolpack from the Danish University and play a little with the log p/h and notice end compression temperatures with different gases. Do certainly once a calculation wit NH3.

Did a quick simulation with Coolpack for you, NH3, TE = 10°C, TC = 45°C, SH = 5K gives you +/- 115°C discharge temperature and a COP of 4.6.
Increasing TE to 20°C raises COP to 6.9 (!), end compression temperatures to almost 100°C (with 8K SH)

Only R134a will coming in the same region of COP but with much lower end compression temperatures (+/- 60°C for the last example)

An old invoice from the malt company I worked for. Those old days!!! Where the factory was is now a big office and apartment complex.

[mad fridgie]

I should of but down the glycol supply temps. (entering at 40C, low level glycol concentration)
70C full flow (12L/S), Duty 1510Kw
80C full flow, Duty 2010Kw
90C 66% of full flow, Duty 1680Kw (less actual drying is undertaken)

[MannyCalavera]

Good morning! Hope your weather is better than the Scottish summer.

Regarding NH3 - not so popular here - mainly just due to its toxicity. Any substitutes in terms of performance?

If I could summarise the key points so far briefly: Forgive me for going over it again, it's just to make sure it's easy to follow:-

2 kilns paired. Each has a steam radiator heater, and a (shared) glycol pre-heater (40:60 glycol:water). Stream raised by HFO burner (~ 85,000 ltrs/week).

1. Fairly constant exhaust of saturated air all the time (Site is operational later in week, I can get raw data then) at high flowrate. No recovery on this at all.

2. Fairly constant flowrate & temperature warm water stream at high flowrate.

Currently the glycol is heated with the warm water (which takes it from 52 - > 45 deg C).

My idea would be to use the heat loop and PHE to heat this to much higher: 60-80 degC. This would mean that for a kiln in early stages of drying, there may be no requirement for steam radiators. And for one in the final stages, you could "top up" the air temperature with the steam radiators.

I.e. - have the glycol very hot all the time as there is constant kilning and need for hot air.

Other option would be to have the very high temp vapour through a radiator and condense, however I am not sure if air has the heat capacity to suck out that much energy at such large volumetric flowrates.

It is clear that taking warm water from ~40 deg C to ~25 degC with 100m3/hr has much energy (around 1.5MW). Cooling this may remove the need for (current) cooling towers and (proposed) sea-water cooling. This would save alot of kWh through pumping costs.

The saturated air also has a fair enthalpy (~ 100kJ/kg). While it's great to "recover" this heat, there are no associated cost savings.

I can't see how both could be used (at least not for the same purpose similtaneously).

I am looking up the CarbonTrust to see what insentives ($$$) are available for such recovery systems.

A 3-year payback is considered worth-while, but it depends on each project. However the want to become "carbon neutral" could be a fairly big factor in decisions that effect HF oil consumption.

ELEC: £0.08 per kWh
HFO : £0.04 per kWh equivalent.

I gather elec. is fairly constant, HFO has risen slightly in recent times (more insentive).

I am going to do an energy balance to calculate the effect of, say, 1 degC glycol extra heat, and how much this will save in steam, and then work it back and calculate the cost from saving X litres of HFO.

Pete - TE, TC, SH? Is that evaporation temp, critical temp and ... ?

Fridgie those numbers:
70C full flow (12L/S), Duty 1510Kw
80C full flow, Duty 2010Kw
seem promising - it's that degree of heating that is going to be very useful here.


Any thoughts / comments please let me know.

Kind Regards.

[mad fridgie]

Is the boiler and HFO solely used for this process (one is hoping not) 980,000kwhrs a week (I have converted this into standard numbers for others who may be reading)

[MannyCalavera]

Fridgie,

Two HFO boilers, one used all the time, the other used rarely when one isn't enough.

The steam raised is solely for use in the kiln radiators - a small amount is used to keep the HFO warm.

980,000kWh - is this your calculated savings?

[MannyCalavera]

NB: chlorinated hydrocarbons are not favoured - ammonia would be acceptable

[mad fridgie]

I better show my calcs
85000L HFO, density 949Kg/m3 (furnace oil)
80665Kg at (*) 43.8 MJ/Kg
3553127MJ * 1000 to Kj
355312000/3600 to kwhrs
981424Kwhrs
Total energy used per week by the malting process.
We then need to know the efficiency of the boiler and what steam pressure/temp (wet or dry)
If we assumed that one pair of processes happen per day,
Then 140,202Kwhrs/day
Lets say 80% boiler efficiency
112,161Kwhrs for the process per day
basic process load
60,000Kg at 45% water
So we want to vapourise (lets say all)
27000kgs of water (lets say for ease latent heat 2430KJ/Kg)
Duty6561000KJ/ 3600
18,225Kwhrs.

Are you sure about your usage HFO usage; is it 8500 Litres per week?, if you are correct then you have some serious losses, this being the case then sorting this out should be the first call first

[mad fridgie]

NB: chlorinated hydrocarbons are not favoured - ammonia would be acceptable

I am looking at R134a, not a chlorinated hydrocarbon.

[MannyCalavera]

I will go through those calcs this afternoon so's i follow them. I have found more data:

Weekly malt produced ~ 1770 te
HFO per week ~ 80000 l
This is for 9 kilns (i see why you thought there were losses). 8 indirect heated (steam) 1 direct fired.

Works out at around 45litres oil / te malt (5%wt water).

Cost per year HFO ~ £2m

[Peter_1]

I think NH3 is as popular in your country as in other countries. It's only toxic when you breath it and that's not why a refrigeration system is built.

Don't forget that NH3 has a GWP = 0 (!!) and in the very, very near future, all the GWP refrigerants with a GWP bigger than 2000 (this will become probably the number) will be banned or highly taxed. The environment is becoming extremely important with the existing and the new coming EU regulations.

Every refrigerant wit chlorine in it is no longer allowed in the EU.

Forget about the toxicity, R404a is perhaps more harmful than NH3 because you don't smell it when you breath it. Most large refrigeration systems runs all on NH3.

And the NH3 doesn't have to run in the plant itself, you can design int in such a way that it stays only in the machine-room.

And I'm not a NH3 installer, we just service some older NH3 plants.

You have to choose a refrigerant for your application which gives you the highest COP and the highest discharge temperatures, whatever that refrigerant may be. You then have to look if it's allowed in your country and/or application.
NH3 will give you for this large capacities the biggest advantages seen COP and high end compression temperatures.
Or 134a.

Compare also once the price for NH3 and R134a refrigerant. You will need a lot of refrigerant to run this system. Limit therefore the refrigerant to the machine-room and if you're afraid about toxicity, install NH3 sniffers. But you have the best sniffer with you: you nose.
Forget the danger about toxicity of NH3. This belongs more to the world of tales and is said by those who haven't enough experience with this refrigerant and are therefore afraid of it.

Play a little with Coolpack and you will be convinced yourself.

TE = temp evaporation
TC= temp condensation
SH = superheat
SC = subcool

Can't you preheat first the water not only with a watercoil/watercoil setup? Haven't read very accurate all the posts of this thread about real/actual temperatures.

[Peter_1]

I...
Are you sure about your usage HFO usage; is it 8500 Litres per week?, if you are correct then you have some serious losses, this being the case then sorting this out should be the first call first

Mad Fridgie, haven't you forgotten the performance ratio (effectiveness ??) of the burner?
And is the burner not used to heat other sources?

This is a very interesting thread. I will ask some NH3 experienced guys joins this one. They perhaps can help.

[mad fridgie]

I will go through those calcs this afternoon so's i follow them. I have found more data:

Weekly malt produced ~ 1770 te
HFO per week ~ 80000 l
This is for 9 kilns (i see why you thought there were losses). 8 indirect heated (steam) 1 direct fired.

Works out at around 45litres oil / te malt (5%wt water).

Cost per year HFO ~ £2m

That makes a bit more sense, what is "te"?

[MannyCalavera]

Thanks for the info on NH3 Pete, I contacted our environmental dept. and NH3 is not un-favoured.

As you say given the strong emphasis on low GWP and its high performance, it seems like the most logical choice. Far better than hydrocarbons at least.

"Can't you preheat first the water not only with a watercoil/watercoil setup? " Could you explain the two streams you were thinking of here?

Mad, 45 litres/te is quite efficient as maltings go I believe (it'll be less when this heat pump gets going )

Te = tonne.

[mad fridgie]

Mad Fridgie, haven't you forgotten the performance ratio (effectiveness ??) of the burner?
And is the burner not used to heat other sources?

This is a very interesting thread. I will ask some NH3 experienced guys joins this one. They perhaps can help.

Hi Peter, i allowed for 80% efficiency for the boiler (it should be a lot higher than this), the HFO heats 9 kilns, not 2 as thought.
This is my "field" before we even contemplate what type of system to use, we must get a handle on the process and its variables.
what we now need to know is the diversity of the 9 kilns, and how are they interconnected.
If we look at the total daily heat requirement, and what is available, form the water and air stream, then we can look at how best to apply it.

[mad fridgie]

Thanks for the info on NH3 Pete, I contacted our environmental dept. and NH3 is not un-favoured.

As you say given the strong emphasis on low GWP and its high performance, it seems like the most logical choice. Far better than hydrocarbons at least.

"Can't you preheat first the water not only with a watercoil/watercoil setup? " Could you explain the two streams you were thinking of here?

Mad, 45 litres/te is quite efficient as maltings go I believe (it'll be less when this heat pump gets going )

Te = tonne.

approx 50% efficient not to bad for drying!!!!
Thanks for that

[MannyCalavera]

I am going to have to give this some thought Mad - l'm ignoring kiln 9 for now.

3&4 = a pair = 60 te / batch
5&6, 7&8 = a pair = 30 te / batch

Mad I am speaking total dross - there are seven kilns - (one and two have been redundant for years). So it is 3-9.

So there is quite a load - I firstly need to get the data on WHEN the saturated air is available, how constant it is across the 7 kilns, and also the demand. As I have said, I am assuming un-varying warm water supply.

As I say, later in this week I get to see the sequences of the kilning.

83% efficiency i believe for the boiler. 90% efficiency in the steam radiators.

On a related note, what kind of compressors are usually used for refrigeration?

Cheers guys.

[mad fridgie]

I am going to have to give this some thought Mad - l'm ignoring kiln 9 for now.

3&4 = a pair = 60 te / batch
5&6, 7&8 = a pair = 30 te / batch

Mad I am speaking total dross - there are seven kilns - (one and two have been redundant for years). So it is 3-9.

So there is quite a load - I firstly need to get the data on WHEN the saturated air is available, how constant it is across the 7 kilns, and also the demand. As I have said, I am assuming un-varying warm water supply.

As I say, later in this week I get to see the sequences of the kilning.

83% efficiency i believe for the boiler. 90% efficiency in the steam radiators.

On a related note, what kind of compressors are usually used for refrigeration?

Cheers guys.

As you can gather, there are many options open on the refrigeration side, what refrigerant and what type of compressor and the number of stages, really depends upon evaporating and condensing pressures, which directly relate where your energy stream is coming from (suction pressures) and what temperatures you will require or what is the best use of the absorbed energy and what levels of turn down and limits on extremes.
For this reason, is why total understanding of the process becomes paramount. I have seen many systems that have been well designed for steady state conditions, but become a total balls up when changes happen in the process variables.

[MannyCalavera]

Say a system does change, say the warm water flowrate / temperature decreases, what are the knock-on effects on the refrigeration system?

Could you just list a few things that would go tits up? I.e. would the compressors die if there was liquid in there that hadnt evaporated?

My next step now is to do some quantifying of availablilty of heat sources, as you suggest. Hopefully within a week I can give you some concrete flowrates, etc, and I myself can do some calculations on the energy saved with hypothetical glycol temperature increase.

Regards

[mad fridgie]

Say a system does change, say the warm water flowrate / temperature decreases, what are the knock-on effects on the refrigeration system?

Could you just list a few things that would go tits up? I.e. would the compressors die if there was liquid in there that hadnt evaporated?

My next step now is to do some quantifying of availablilty of heat sources, as you suggest. Hopefully within a week I can give you some concrete flowrates, etc, and I myself can do some calculations on the energy saved with hypothetical glycol temperature increase.

Regards

There are no real problems, if you know the extremes, you design around potential problems, but this does have a factor on the capital cost.
Basically you control the load by many different methods, but when unloaded care has to be taken with other factors, it just a question of balance, protection and retaining efficiency. many of the threads on this forum relate to poor equilbrium.
Its time to go for kip.
look forword to future info

[MannyCalavera]

Alright Fridgie cheers for your help thus far.

I will keep checking the forums incase there are further posts, but later in the week I will get in touch with some concrete numbers.

I feel I am slowly becoming more aware of the wider picture of heat pumps which is most excellent.

[MannyCalavera]

"This is a very interesting thread. I will ask some NH3 experienced guys joins this one. They perhaps can help."

Just saw this Pete - would be very much appreciated.

[mad fridgie]

I thought I would help with the correct thought process.

1 What is the problem (excessive fuel use)
2 Analize the problem (In the case the malting process, this needs to be indepth)
3 Set the criteria for the selection of the possible solutions. This is as important as the solution its self!

[mad fridgie]

just some theoretical interesting facts (not a great deal to do with the practical application and installation)
it is possible to reject more heat out of the heat pumps than the process requires, which is typical for drying processes. (heat absorbed from both the dist. water and the kiln air, Direct)
If the process could be completed with 75C glycol, then COP would be approx 4, which indeed would reduce the running cost by 50%, or a million quid or year.
If we look at any drying process there are 4 main loads
1;Thermal losses
2;Heating of mass (product and building)
3;Water vapourizing
4;Heating of make up air. (this is required to carry the moisture away, warmer air has a higher water vapour carry capacity)

When a product is drying, the product and the "air passing over" drops in temp, whilst pickup moisture, increaseing the RH by the two changes, how ever the energy in the air remains the same (exclude any losses) This is expelled
So it would seem that we should just reclaim all the energy from the process, and introduce it into the in coming air (looks like the simplest of solutions) BUT dry air does not have good energy carry abilities, therefore the air would need to heated to a very high temperature to reach equalbium (balance), this then becomes the achillies heel of a refrigeration heat pump, to achieve these high temps the condensing temperature would also need to be very high. Which means our COPs drop dramicatically (never mind the other technical issues), Would you then buy one?
You should now be think about increasing the fresh air make up flow, to reduce those condensing temperture, More air in means more air out, The air that is expelled, is likely to have a less favouravble properities (low dew point), which then causes the evaporation temperature to fall, again reducing the COPs. This also can have a detremental effect on the product, some products skin if dryed to quickly, reducing the flow of entrapped moisture in the product, which normally has to be overcome with a higher temperature (again not so good for a heat pump)
Why not just but the heating coil in the main air stream, always sounds like a good idea, but in many drying processes the main air stream is all ready heated, so similar sets of problems occur, one of the main limitations to just increasing the air flow is the increase velocity of the air, which if to high can cause the product to leave its container (blows in the wind).
When dealing with higher temperture drying with a heat pump you tend to undersize the heat pump, which normally give excellent COPs and reliabilty and add an addional high temp heat source, which you use for control.
With low temp drying systems you normally oversize your heat pump, and reject excess heat external of the process

So when it comes to drying and heat recoevery with a new system/method it is 80% design and 20% Fudge, more info you have the better you manage the fudge. And is very product specific

[Peter_1]

What you must do once to enlighten this a little bit and this will help you also in the future: make once a simple hand-drawn schematic of the whole system and insert on different copies - for every process phase one (germination after water immersion or spraying I suppose, then the heating) - the right numbers , temperatures ,mass flows of water, their associated temperatures, mass flow of the malt/kiln, time for every production process, mass flow and temperatures of air in's and out's,......

It's a continuous process I suppose where a kiln or several kilns are busy with germinating while others are drying and others are emptied and/or filled up.

So the better we understand clearly the production process and the production flow of it the better we can help you with our experience.

I think MadFridgie will agree with me: this project has very great potentials and can offer your client big savings but it must be very well calculated and documented first. The more precise your numbers are, the more precise you can predict the savings.

[MannyCalavera]

Thanks for advice guys - I have started compiling info since it's up and running again. Hope to really understand the extent of "steady state" that it is actually operating at. Once I have all the parameters of the process fully understood and all the variables, I will see what energy is available and when, and then hopefully you might be able to advise on COPs etc. This within a week or two max I hope.

I had a slightly related question (maybe obvious). Can you control the extent of heating? E.g., if a system was designed to raise a fluid to a temp of 75degC, but for 2 hours you only required 65degC, can heat pump systems cater for this (if source parameters stay constant)?

Pete that invoice looks extremely up-to-date. That factory looks far more asthetic than the maltings I work on!

Regards

[mad fridgie]

Thanks for advice guys - I have started compiling info since it's up and running again. Hope to really understand the extent of "steady state" that it is actually operating at. Once I have all the parameters of the process fully understood and all the variables, I will see what energy is available and when, and then hopefully you might be able to advise on COPs etc. This within a week or two max I hope.

I had a slightly related question (maybe obvious). Can you control the extent of heating? E.g., if a system was designed to raise a fluid to a temp of 75degC, but for 2 hours you only required 65degC, can heat pump systems cater for this (if source parameters stay constant)?

Pete that invoice looks extremely up-to-date. That factory looks far more asthetic than the maltings I work on!

Regards

The simple answer is yes, you have decide is just temperature change, with a similar amouny of produced energy, (reduced glycol flow) or increased temp change and increased energy produced (same glycol flow)
You are now thinking in the correct manor.
Well done
I agree with Pete, its all about understanding the process. I suspect dollar for dollar, that the greatest savings will be made by optomising the diversity of the 6-7 Kilns