ideas for ethylene glycol dosing system 2

[Lucaz]

Hello everyone,

I am currently thinking about a designing an automated dosing system for one of my clients.

The problem is as follows:

On the site, there are three air blast chillers that contain glycol. The site uses the chillers to cool plastic extrusion machines (they make pipes and guttering). They have to top up the chillers about once a week with a pre mixed 40% strength glycol solution due to system losses. The losses occur as they have to carry out tool changes on the machines. (the cooling water cools these tools).

They are very interested in a system which could dose glycol in some way. The chillers are all independent to each other (ie each on their own system- NOT linked together). There is no make up tank on the chillers. I have thought about dosing pumps to dose glycol, but cannot figure out how you would get the dose correct. And this system would not be automated either. Someone would have to turn the dosing pump on. (DOH!)

What I am looking for is some ideas on how I could set up an automated dosing system to keep the glycol at 40% in each of the 3 chillers.

Is there any way I could put a probe in the chiller pipework which could measure the glycol concentration and dose neat glycol according to the amount of make up water required for topping up. (obviously assuming we fitted a mains make up to the chiller)

I appreciate this sounds involved, but any assistance on this would be most helpful.

Regards,

Luke

 

[dicksewerrat]

You may want to look at 'positve diplacement' pumps. Grayco makes some. They give you a specified volume of liguid with each stroke. put in one for gycol and one that delivers 150% water. flip the switch til full. turn off. you could put in a manifold so you could flip a switch and open/close the different solenoid valves at each tank

 

[dicksewerrat]

You may want to look at 'positve displacement' pumps. Grayco makes some. They give you a specified volume of liguid with each stroke. put in one for gycol and one that delivers 150% water. flip the switch til full. turn off. you could put in a manifold so you could flip a switch and open/close the different solenoid valves at each tank

 

[Lucaz]

dicksewerrat,

Many thanks for your help on this one. I just need some further clarification on this point:

"flip the switch til full. turn off. you could put in a manifold so you could flip a switch and open/close the different solenoid valves at each tank"

Could the switching be automated somehow? IF so, what could be the best way for this? I presume a level switch could be installed internally on each chiller tank (there are some cheap looking small external tanks with level markers on the side of the chillers) to tell the controller when to stop the pumps??

What kind of controller should I be using?


Regards,

Lucaz.

 

[hydrae]

Lucaz
To get full automation of both level and concentration in each tank would be a fairly complex system. Each tank would have a level control and a concentration control. Do you need the concentration control? Or are system losses consistant such that makeup can always be just 60/40?

Maintaining level is easy with float switches, single ball floats will have a 2 to 6 inch deadband depending upon the model. If you need a wider deadband two floats with a relay latch will do the trick.

As for a easy way to measure concentration, when the tank is at a known level, say when the float switch has just called for the pump, measure the pressure at the bottom of the tank. You will need an accurate pressure transmitter and PLC to process the input. sp gr water 1.0, sp gr glycol 1.15, target sp gr 1.06+/-
If the pressure is low, pump just glycol.
If the pressure is high, pump just water.
If the pressure is in the middle, pump both.

As an example with a 11 ft tall tank, set the call switch at 10 ft for pump call, pure water will read 4.32 psi, pure glycol will read 4.97 and the target will be 4.58 psi. As you can see accuracy of the pressure transmitter is critcal

Of course anytime you add automation, you add complexities, such as calibrations, pumps, valves, more piping...

Hydrae

 

[Lucaz]

Thanks Hydrae,

Looks like the best method here....


Still, as there are three separate systems, this wont be an easy job. Time now to sort out an action plan


Many thanks,


Lucaz