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Peter_1
30-01-2006, 10:28 PM
Can the competent members calculate once - crosscheck for me - the needed capacity for a tunnel for fresh french fries, 5.000 kg/u, entering at 25°C, leaving condition of 1°C.

Glycol in at -2°C en 0°C out, air in 5°C, out 1°C. Inside the tunnel 8 fans of 3 kW but motors are outside the tunnel.

We also need to cool down the stainless steel belt which is constantly re-warmed by the warm entering french fries I suppose.

Lenght of the belt? Giving a belt width of 1,5 m.?

Gross guess of me was 80 kW but saw now a proposal of 220 kW with ammonia.
What do you think?
Someone experience with tunnels for french fries?

Josip
31-01-2006, 03:13 PM
We have:

Q= G x Cp x dT (T1 - T2)/t [kW]

where is:
G= mass of potato - 5000 [kg]
Cp= specific heat of potato - 3,6 [kJ/kg'C]
dT= temperature difference - {[25- 1]= 24'C}
t = time - 1 hour

Finally we have = 432000kJ / 3600 = 120 kW + 20% of heat loss through the walls and we are coming to 150 kW

Peter_1
31-01-2006, 03:39 PM
Hey Josip, can we put our cats together? :D

I gve a wrong figure but doesn't chaneg that mmuch on the result: you can find in a previous post that the entering temperature has to be 20°C instead of 25°C.

So 120/24*19 gives 95 kW.
Compared to the 220 kW ??

Josip
31-01-2006, 03:50 PM
I forgot to ask you in previous post is this tunnel a precooler in front of freezing tunnel or cooler before packing machine or ....

Josip
31-01-2006, 04:00 PM
Hey Josip, can we put our cats together? :D

I gve a wrong figure but doesn't chaneg that mmuch on the result: you can find in a previous post that the entering temperature has to be 20°C instead of 25°C.

So 120/24*19 gives 95 kW.
Compared to the 220 kW ??

Yes, why not? I have couple of them at home taking care about my dog :)

But, there must be something else regarding that tunnel. maybe some future expansion of the plant. I do not believe that someone can make mistake like that (but you never know?) without hiding something!?

Peter_1
31-01-2006, 05:30 PM
The potatoes are washed, cutted in french frites, sorted by a special scanner to remove the parts with black eyes in it, enter the cooling tunnel and are direct fresh packed in bags of 5 kg.

The 220 kW was based on the figures I gave them, so they have calculated it that way.

To avoid contamination of the french fries, they use glycol for this.

But giving this figures, let's say it's somethin around 150 kW, based on 5.000kg/u, 8h/day, 50 weeks/years, this will cost client +/- 12.000 €/year for electricity. (fans and condensor fans and assumed that compressor will take 75 kW)

He's doing it now with liquid nitrogen and it costs him +/- 235.000 €.

The investment for a classical tunnel is of course much higher then a liquid nitrogen tunnel.

SteveDixey
31-01-2006, 06:12 PM
But giving this figures, let's say it's somethin around 150 kW, based on 5.000kg/u, 8h/day, 50 weeks/years, this will cost client +/- 12.000 €/year for electricity. (fans and condensor fans and assumed that compressor will take 75 kW)

He's doing it now with liquid nitrogen and it costs him +/- 235.000 €.

The investment for a classical tunnel is of course much higher then a liquid nitrogen tunnel.


Nitrogen can be expensive unless you invest in decent zone temperature control gear. A couple of food companies locally near me have moved from Nitrogen to Frigoscandia Advantec impingement freezers for fast chilling, but they had ammonia capacity already installed. This is for batch production, maybe a few hundred kilos, before changing product.

Steve

Josip
31-01-2006, 06:22 PM
The potatoes are washed, cutted in french frites, sorted by a special scanner to remove the parts with black eyes in it, enter the cooling tunnel and are direct fresh packed in bags of 5 kg.

Anyhow, I must ask (maybe some stupid question:confused: ) how long is possible to keep that FF in plastic bags before start to change the color? Yes, I do understand FF is cold and well packed but...it is still FF!?

Last year I was in Saudi Arabia to visit one food company producing fried french fries (need only about 10 min in boiling oil to be finished) to help regarding freezing tunnel. They want to improve continuous freezing tunnel capacity but complete plant is little undersized and there is not too much space for dance:)

Peter_1
31-01-2006, 08:17 PM
Well, you can hold them 6 days.
The bags are also gassed with nitrogen to remove as much as possible the oxygen in it.
To prolong conservation and avoid that they become black, you have to put the FF for a very short time in boiling water (this calls blancheren in Dutch but I don't know the English expression for it)

US Iceman
31-01-2006, 09:55 PM
Peter,

Is this the project you were working on in the past? I seem to remember you had a nitrogen tunnel that was having problems with the spray nozzles freezing up???


(this calls blancheren in Dutch but I don't know the English expression for it)

The English word is very similar to Dutch... Blanching.

Peter_1
31-01-2006, 10:40 PM
It's indeed still the same project Mike.

We did a 3th test just before Christmas and the manufacturer was given the opportunity to adjust everything.

The first test from 05:00 Am till 06:00 AM was OK. Tunnel was running at -20°C which is in my opinion to far away from the desired output of 2°C.
Surface frost becomes then a great danger.

FF manufacturer says that surface frost, even it it occurred over a very short time (some minutes) is bad for the quality of his product.
If it can be justified with a practical test or a lab test of a university, then I can add this in my file as a prove of his statement.

Second run from 06:30 Am till 09:00 was only good for 20%

3th run form 09:30 till 12:00 was good for 30%.
At the end of the test, we had a school example of a PID signal which went completely out of control: the oscillation became bigger and bigger.
It was nice to see this on the computer (logged values)

Asked just after New year a quote for a conventional cooling tunnel and they ask +/- 370.000 € for the tunnel, included the evaporators (well, in fact it are glycol coolers) and the NH3 equipment (compressor, condenser of GEA/KUBA and steel lines will cost +/- 23.000 € for 220 kW.
This seems high for me, especially because a selection was made of 220 kW.
They don't need in my opinion that capacity.
Of course, they play it on the safe side but it has to be a little bit more economic.
The safety margin they take is too wide.

Also the tunnel length they propose is 12.5 m, 1 pass which seems too short for me.
It's now with the liquid nitrogen running with a belt width of 1,3 m and 9 m length at a temperature of -20°C and it can maintain a capacity of +/- 3.750 kg/u.

Second problem: during the last 3 year, 6 Danfoss VFD's failed from which 2 in the last 4 months during my tests .
At this plant, there are +/- 30 installed VFD's and it's only in this switch-cupboard that they fail.
Also a Siemens S7 CPU failed, 1 digital input and two AO of this PLC.

US Iceman
01-02-2006, 02:11 AM
Hi Peter,


Tunnel was running at -20°C which is in my opinion to far away from the desired output of 2°C.

Are they running the tunnel this much colder to obtain the cooling of the FF? This would use a lot more nitrogen and increase the per hour cost.


...FF manufacturer says that surface frost, even it it occurred over a very short time (some minutes) is bad for the quality of his product.

Do they have frost forming on the FF because they are too cold? Or is the nitrogen being sprayed onto the FF??

Too much nitrogen could cause "stress-cracking" on the FF also.


...the evaporators (well, in fact it are glycol coolers)

Why use glycol?? If cost is a consideration the evaporators would be less money if they were pumped overfed ammonia. Smaller piping, no big glycol pumps, higher suciton pressure, etc. You know what I mean right?


...because a selection was made of 220 kW

If the cooling load is about 90-100 kW, is the 220 kW being installed as 100% redundancy? Or is the larger capacity due to the heat load being calculated for freezing?

The belt length does sound a little short. I would expect it to be longer with the air-cooling instead of the nitrogen.

The switch cupboard sounds like it is over heating. I thought you may have said it had an air conditioner. Either this, or electrical problems. Is this cupboard supplied from a different area of the electrical supply?

PobodysNerfect
01-02-2006, 03:25 AM
Also the tunnel length they propose is 12.5 m, 1 pass which seems too short for me.

Peter,
There is only one way to find out about the length; it is to make a test. There are far to many uncertainties to calculate the cooling time, and it should be fairly east to make a test.

Jan

Peter_1
01-02-2006, 08:07 AM
Are they running the tunnel this much colder to obtain the cooling of the FF? This would use a lot more nitrogen and increase the per hour cost.

They run that cold because they otherwise couldn't get the desired desired temperature. I insisted that the whole FF is at 1 to 2°C, not only the surface.
At a massflow of 3.750 kg/u, we need to that low if we want to have the inside also at 2°C.



Do they have frost forming on the FF because they are too cold? Or is the nitrogen being sprayed onto the FF??

Well, it's due to the heavy moisture you find on fresh FF, together with the very low ambient. The nitrogen is sprayed under a corner of 45° over the product (see picture) at a very low massflow of nitrogen.
Nozzles are designed for -150°C and we're working at -20°C, so the proportional valve opens only 20%
Normally seen, I should think that as soon the nitrogen enters the tunnel, it immediately vaporises to gas.

The other picture was after 4 hours running.



Too much nitrogen could cause "stress-cracking" on the FF also.
Interesting you gave me the English expression for it. Now I can look a bit around on the internet.



Why use glycol?? If cost is a consideration the evaporators would be less money if they were pumped overfed ammonia. Smaller piping, no big glycol pumps, higher suction pressure, etc. You know what I mean right?

Well, I can go even further, why for a capacity of 100 kW installing NH3?
The reason why they're doing this is stated in their offer. 1st: the tunnel is installed in a relative close and very clean production environment where peoples are walking and if you have a leak, then it's dangerous 2 nd: if there's a leak in the tunnel, then the product will be lost.


If the cooling load is about 90-100 kW, is the 220 kW being installed as 100% redundancy? Or is the larger capacity due to the heat load being calculated for freezing?

Now, this is not for freezing because they even printed in their offer in bolt that this tunnel is specially made for FF and that they guarantee that they won't freeze.


The belt length does sound a little short. I would expect it to be longer with the air-cooling instead of the nitrogen.

I think also it's too short, especially compared with the values we run now. But..the company who's offering is one of Belgium biggest companies (100 peoples and a turnover of 22,000,000 €/year) More then 65% of their production is tunnels for the export.
So I think that they realy know what they're talking about but altough....


The switch cupboard sounds like it is over heating. I thought you may have said it had an air conditioner. Either this, or electrical problems. Is this cupboard supplied from a different area of the electrical supply?
The VFD's are in a ventilated switch cupboard and the room it standing in is held at a constant temperature of 18°C. They're very small compared to the size of the S.C. Just beside this S.C., there is another production machine with even larger VFD's in it and those never failed.

The whole plant is fed by one a 650 kVA transformer. It can't come from there because it should harm also the other VFD's in the factory.

Last summer, the electricity company has installed very expensive measuring equipment for some weeks after my first intervention to make an analysis of the electricity.

They made complete Fourier analysis's to investigate if ..how do you call and explain this in English...one of the mathematical rows of the composed sine wave we see on a scope (which consists of an indefinite mathematical row of 'waves') 'hasn't high voltage spikes on it. This was negative.

There is a theory - which goes a little bit too far for me - where the short circuit capacity of the main transformer is that high and when you then shut off a VFD, that the energy stored in the capacitors inside the VFD is flowing backwards to the main power supply, blowing out the thyristors, due to this shortcircuit capacity.:confused:

Anyhow, they're now at Danfoss and I insisted that they make a full analysis of failure and the probably cause of this failure.

Yesterday was also the first day the big market truck did his first market.
My son was there on the first market at 04:45 AM :o and there were a lot of troubles with the leakcurrent protection devices on the market. They tripped each time and he had to bridge them.
We then made at least 2 hour phone calls and this should be due to the VFD's.

We need to install an EMI instead of an EMC filter.
I looked for 5 minutes on the net - hadn't more time yesterday - for the theory behind it but I couldn't find anything.

If I have some more time, I will try to explain my problem and what the supplier of the VFD's has proposed.

Renato RR
01-02-2006, 08:56 AM
Ashrea hanbook for refrigeration chapter 8 table 9.Edition 2002.
Best regards,
Renato

Peter_1
01-02-2006, 09:27 AM
You're refering to what RR?

Can you clarify just a litlle bit what's in that section form that specific book?

Not everybody has all the ASHRAE books, mines are a lot older and chapter 8 is about lubricants in refrigeration systems :confused:

Renato RR
01-02-2006, 11:52 AM
Food properties!The pateto may be mature,in mature ,sweet, or some special sort.Each one have diferent quantity of water.Cool pack afirm average load of 98kW and peak of 160kW (for vegetables).

Best regards,
Renato

Josip
01-02-2006, 05:00 PM
Some additional info regarding potatoe:
http://www.postharvest.com.au/Potato.pdf

Anyhow, my calculation regarding tunnel capacity was quite ok (checked with Refriger and with CoolPack) about 110 kW.

Heat transfer is not bigger than 18-30 J/m^2s'C, could be even less due to evaporator icing and for that reason we need a belt with a very small speed to achieve the time needed.

Of course to protect any food product it is the best solution to use indirect cooling even with some bigger cost. The best is to use glycol propylene and ammonia (why ammonia becuse I like it :)) but with PHE to reduce ammonia charge to minimum.

Why you have request to make a tunnel with:

Glycol inlet -2'C outlet 0'C
Air inlet 5'C outlet 1'C
Potato inlet 20'C outlet 1'C

Reducing temperature is 0,5'C per meter

This is the best possible way to keep all water inside product and their product they sell by kg. Is there any better way to make a good profit (ice cream, beer) like this one. Just to sell chilled water :) in accepatable amount.

Many yeras ago it was alowed to cool down chikens in cold water; it is forbidden now due to hygienic reasons but also due to customers complaints regarding defrosted water in amount 100-200 grams which you pay as chicken meat. Good profit? Comments!

US Iceman
01-02-2006, 09:20 PM
Peter,

Are the VFD's sized for the fan motor current at the low temperature? The nameplate amps will increase dramatically when the fans circulate very cold air. Since the mass flow is much greater with the colder air, the power input requirements also increase.

The volume flow of course remains constant.

If the VFD's were selected by using motor nameplate amps, the VFD's could be too small due to the increased current draw of the motors.


Normally seen, I should think that as soon the nitrogen enters the tunnel, it immediately vaporises to gas.

The other picture was after 4 hours running.

I was curious to see if the FF were being sprayed with liquid nitrogen. I would expect the frost problems in the picture due to the very cold temperatures. The frost problem with the glycol cooling should not be as bad, since the glycol will be considerably warmer than the liquid nitrogen.

Peter_1
01-02-2006, 10:39 PM
Josip,
The figures of the glycol and the air temperatures are figures I took out the offer I received.

Using glycol for contamination OK.
But, if we want a glycol of -5°C, we need to evaporate at at least -10°C.
If we do it direct, NH3 or another refrigerant, then we need only to evaporate at -5°C which will give a better COP.

The only benefit the nitrogen guys constant saying is that the product isn't drying with nitrogen where it dries a lot with conventional cooling and the huge ventilation you need.

But this is in my opinion only true when freezing because they quickly can form a freezing layer around the product, preventing that moisture escapes out of the product.

Their theory isn't valid any longer for cooling, at least.. that's my opinion.

Reducing temperature is 0,5°C/m, gives us 48 m belt for a DT of 24 K to cool. Am i right Josip because this seems a very long belt?
Or is that your estimate for this tunnel?
It could be done with a belt of 3 layers of 12 m, forward reverse, forward - if you understand what I mean - stacked above each other.
We then also have the effect that at the end of each belt the FF will tumble a little bit so that they're better mixed.

RR, I'm using always water for an estimate for the load calculation to cool products. I'm always sure then that I have enough capacity and it's very easy to calculate out of your head.

Mike, the motors circulate now only air of -20°C.
This will give a bigger air density but not that high that we come into problems I think.

Have also once a look at the pictures where you can see how the flow-pattern of the axial fan blades is disturbed by the ice.
I don't think they circulate very well the air around the product as initially designed.

The VFD's can be programmed so that they don't go over their max current - in fact an electronic over-current safety device - and this is set the right way.

No fan-motor ever failed on the tunnel.

What we have noticed yet is that in the atmosphere must hang some special potato dust, iron leaded particles because we see all brown rusted spots on the stainless steel outer wall of the tunnel.
If this dust enters the PCB's in th VFD's, then this can give a short-circuit. Just a thought.
But it this room, there are other switch-cupboards with a lot of electronics inside and also VFD's and those never failed.

One of the complaints is that the product enters the tunnel too humid. But this is the production process, starting wit a raw potato. This process was known when making the offer for the nitrogen tunnel.
I said that a humid product will cool faster due to the improved heat exchange capacities (a dry product doesn't cool as fast as a humid product)

Josip
02-02-2006, 01:03 AM
The figures of the glycol and the air temperatures are figures I took out the offer I received.
Yes I understand that, it was not a question. Sorry my English is not that good sometimes.


Using glycol for contamination OK.
But, if we want a glycol of -5°C, we need to evaporate at at least -10°C.
If we do it direct, NH3 or another refrigerant, then we need only to evaporate at -5°C which will give a better COP.
Correct, but not allowed in some food production areas. Pitty!


The only benefit the nitrogen guys constant saying is that the product isn't drying with nitrogen where it dries a lot with conventional cooling and the huge ventilation you need.

But this is in my opinion only true when freezing because they quickly can form a freezing layer around the product, preventing that moisture escapes out of the product.

Their theory isn't valid any longer for cooling, at least.. that's my opinion.

I have not any expirence with nitrogen, I'm ammonia guy, but we are doing the same in shock freezers. But our cooling process is better regarding preservation of food.


Reducing temperature is 0,5°C/m, gives us 48 m belt for a DT of 24 K to cool. Am i right Josip because this seems a very long belt?
Or is that your estimate for this tunnel?

Sorry, my mistake it must be like 2°C/m what is stil good to keep water within product.


It could be done with a belt of 3 layers of 12 m, forward reverse, forward - if you understand what I mean - stacked above each other.
We then also have the effect that at the end of each belt the FF will tumble a little bit so that they're better mixed.

I do believe that 12 m can do the job but with some changes in construction to make a good air didtribution.


Have also once a look at the pictures where you can see how the flow-pattern of the axial fan blades is disturbed by the ice.
I don't think they circulate very well the air around the product as initially designed.

There is something strange about air stream in this tunnel. Please can you explain?
Cooler is on the suction or on the pressure side of fans and than cold stream is coming over FF from bottom or from top side or some other way.


One of the complaints is that the product enters the tunnel too humid. But this is the production process, starting wit a raw potato. This process was known when making the offer for the nitrogen tunnel.
I said that a humid product will cool faster due to the improved heat exchange capacities (a dry product doesn't cool as fast as a humid product)

You are right, they did know what they have to do but maybe not how to do!?

Andy
04-02-2006, 07:37 PM
We have:

Q= G x Cp x dT (T1 - T2)/t [kW]

where is:
G= mass of potato - 5000 [kg]
Cp= specific heat of potato - 3,6 [kJ/kg'C]
dT= temperature difference - {[25- 1]= 24'C}
t = time - 1 hour

Finally we have = 432000kJ / 3600 = 120 kW + 20% of heat loss through the walls and we are coming to 150 kW
Also add say 10% to the above figure to allow for the power absorbed by the fans. Maybe you have already as 20% for air change seems high.

Kind Regards. Andy:)

Andy
04-02-2006, 07:49 PM
Hi:)
the picture of the tunnel with snow just looks like moisture ingress from warm air from outside the freezer.
What about using a dehumification unitto dry the air before it enters the freezer:confused:
Munters will sell you one.
Kind Regards. Andy:)

Peter_1
05-02-2006, 12:19 AM
Hi Andy,

The water mostly comes from the products itselves because it enters very wet, coming 5 minutes before from raw potatoes.
But also air enters the tunnel because there is
an exhaust fan mounted to blow off the nitrogen.

The fan motors are mounted outside the tunnel.

My problem is the excessive cost to cool this products the way they're doing it now.

Andy
05-02-2006, 09:46 AM
Hi Peter:)
At present we are quoting a belt freezing tunnel, about 108kW for freezing product. We have been working with a company Star Frost. In our case they gave us the tunnel refrigeration capacity needed, checked it and found it to be about 25% too high, must be a safety factor;)
What about blowing dehum air accross the chips before they enter the tunnel to dry them, a dehumed air lock would surface dry the chips and keep out moist air.

Nitro tunnels will eat energy, pay back for a refrigerated tunnel is less than 5 years, tipically 2.5 years.

Kind Regards. Andy