Plate heat exchanger temperatures?

[Drew]

I have started doing work for a trout hatchery that cools the water with a plate heat exchanger and glycol. The chiller , that cools the glycol is only running at 58% capacity with glycol on temp at 7 C and off at 4 C. The water incoming temp is 18 C and off at 12 C. The hatchery water temp is slowly climbing and I need to sort it out. Would the above temps indicate a fouled heat exchanger which would be holding the chiller down to 58%. The glycol setpoint is 5.5 C.
Any advice would be appreciated.

[gregd1401]

Hi Drew. Do you control off entering or leaving glycol temperature and what does your plant consist of?

[Drew]

The unit is a bitzer screw chiller pack, running on 134a. I think it is a Climiventa (spelling?) A company from norway came to fit it.

The chiller cools the glycol which cools the water via the plate heat exchanger.

Im new to the plant so am still trying to find the thermostat bulb position, but seeing the temps of the glycol in and out and the current setpoint I assume the bulb must be in the chillers heat exchanger?

[gregd1401]

I suspect that seeing the unit is running glycol, it is designed to run lower temperature than 5.5C. Check your glycol density and lower the control set point. This will give better temperature difference and load the chiller above 58%.

[Drew]

If we set the setpoint lower the unit turns off on freeze stat. Im trying to get hold of the supppliers of the chiller to obtain the passwords on the controller to change some parameters so that i can lower the setpoint. I am concerned that this will help a bit, but is not the actual fault. With the low temperature difference between the glycol in and out would that not indicate that the heat exchanger is not effecient? Therefore fouled? And not loading up the three screws?

[chemi-cool]

If your problem is the 58%, then you should check the water flow in the PHE. if there is a filter, make sure its clean [there should be one if a PHE is used].

Check the the glycol circuit too, see thats the pumps are revolving in the right direction, clean filters.

what is the evaporating temp?

The name is Climaveneta, Italian.

[redroge]

if the controller is a carel pco try 1234, check your glycol content before lowering any antifreeze settings, 3c td sounds ok at 58% if its a pco you should be able to check if its controlling on inlet or outlet temp. also if its p or pi control.

[VRVIII]

if the controller is a carel pco try 1234, check your glycol content before lowering any antifreeze settings, 3c td sounds ok at 58% if its a pco you should be able to check if its controlling on inlet or outlet temp. also if its p or pi control.

Hi,
If you lower the min outlet water temp (freeze protection) you may also need to lower the LP trip set point.

[mad fridgie]

If this has worked, and nothing else has changed, I would agree this is a fouling problem. This would of of got worse over a time period.
Just one thing to check is your glycol mix. If you have to much glycol this can change flow rates and heat transfer capabilties

[Drew]

Thanks for all the replies.
Without knowing the design conditions its difficult to confirm the fouling or not. The chiller doesnt seem to run harder than 58% cause it doesnt have the load?
Therefore only obtains 3 C td.
If we see that the water td is 6 C we could increase the water flow rate to obtain maybe a 5 C td. This should force the chiller to a higher %?
Therefore all PHE should be confirmed to be clean , all pumps on etc.... Check glycol concentrate.
Im still trying to esablish whether its the higher than required setpoint or a fouled heat exchanger or lack of water flow ?
If i could get my hands on the design specs i could see what the norms should be?

[Drew]

The higher than normal water td indicates lack of water flow and the 3 C td of the chiller shows a system being held back to match the new lower PHE capacity?
Therefore not fouled, but a lack of water flow. Fouled would have a small water td?

[mad fridgie]

Where did the 3C td come from?
I presume that you are cooling a large body of water and that it is refrigeraton effect that you are after, more than a specific outlet water temp. "not one pass"
What temp do you want the mass of water to be at (normally the warm entering the H/E).

[Drew]

It is a bio mass of water for the trout (massive amount of water) the bitzer screws offer 1300kw.
The tanks should eventually should have a temp of 12 C (return water temp) Therefore not one pass through. The 3 c temp diff is between the glycol inlet to the plate heat exchanger and the glycol outlet on the plate heat exchanger. Whereas we are getting 6 c diff on the water side.? The chiller seems to held back due to either high chiller set point, fouling or lack of water flow and i m battling to work out which it is? without the design specs it isnt easy.

[mad fridgie]

just a quick point, the flow through the heat exchanger is counterflow?

[desA]

It is a bio mass of water for the trout (massive amount of water) the bitzer screws offer 1300kw.
The tanks should eventually should have a temp of 12 C (return water temp) Therefore not one pass through. The 3 c temp diff is between the glycol inlet to the plate heat exchanger and the glycol outlet on the plate heat exchanger. Whereas we are getting 6 c diff on the water side.? The chiller seems to held back due to either high chiller set point, fouling or lack of water flow and i m battling to work out which it is? without the design specs it isnt easy.

Ok, a few thoughts.

The mean specific heat of glycol-water is lower than for pure water. If the same mass flowrate of fluid occurs in both sides of the HE, then it is usual to expect the water dT to be less.

In your case, it is the reverse. This tells me that the water-side is flowing much slower than the water-glycol side. This would be an unusual matching.

I suspect that you have a flow blockage on the water-side of the HE. You may want to check that all valves are fully open & that the inline filters are clear. If this is all fine, then you may have fouling within the water-side of the HE. Back-flush & clean it. See what happens.

[Magoo]

Sounds like restricted flow due to fouling from fish droppings or possibly air trapped in headers, are there air bleeders.
magoo

[desA]

I suspect that fish droppings would also release nitrates, possibly leading to additional corrosion deposits, or by-products in the HE.

[Drew]

Ok, a few thoughts.

The mean specific heat of glycol-water is lower than for pure water. If the same mass flowrate of fluid occurs in both sides of the HE, then it is usual to expect the water dT to be less.

Thanks again guys. The system is contra flow.

Thanks DesA.
Thats the type of info i need.

Thermometers are being fitted to inlet and oulet pipes as well as flow meters. The glycol pump delivers 75kg/s ( I think ) .

[desA]

If you can do so, please install pressure gauges on both in/outs of the PHE. These can be used as preventative-maintenance items in future.

Monitor them & when the dP goes above a certain point, schedule a clean-out.

[charlie n]

6 degrees water temperature differential and 58% load (about 750 kW) matches a water flow of about 52 kg/s.
Most likely, your water piping is plugged up or restricted somewhere.
75 kg/s and 1300 kw should give about 4 degrees drop in water temperature across the PHE if it's clean.
If you don't already have it, install a backflush valve arrangement on the water side of this PHE. This reverses the flow and helps keep the unit clean with very little effort.

[tmm]

I have extensive experience with a chiller originally produced in the USA, by a company now ceased trading, and whilst undertaking various service/design related visits at various locations across the UK from aquariums to universities one factor remained consistant- that the by-product from the aqua-culture will always block the plate. In the case of the American manufacturer the exchanger (direct expansion) is helical to overcome the problems with clogging previously mentioned. If you can remove the plant and conduct a full chemical clean you will probably return the plant to its original condition. The long term solution is to remove the plant and consider the alternative quoted.
tmm

[desA]

^tmm:

How effective have you found inlet filtration to be under these circumstances?

[Drew]

We will be installing a variable speed pump on the water side to ensure correct flow rates. As this is a relatively new site we are still ironing out the design issues etc...
Thanks again for the advice all.

[mad fridgie]

Slightly off subject, bear with me.
I designed and installed a water chiller (product emerssion process cooling) The client in the early stage stated that the product was spotless (been through many cleaning processes before it reach our process). A we were also using a PHE, as good practice we installed a simple manual mechanical filter and a couple of gauges. Thinking well, when serviced the engineer will whip out and give it a clean.
Well be started it up, gave it trail run as you do (removed the filter and cleaned, to remove installation "crud")
we then ran the first process, with 10 minutes the filter was blocked.
The client looked as siads "whoops" (or words to that effect), my carrotts are not really that clean.
In my original contract we have covered this possiblity so no issues with the client.
We installed a fully automated filtration system (back wash with internal rotating scraper).
Worked wonderfully,.
I would suggest on a plant of this size that you also look at this a long term solution.
It was a while back, so can not remember the manufacture name. (to much alchol has passed my lips)

[Drew]

haha . Thanks mad fridgie!