Water treatment project - Advice needed

sparko

Member
Join Date
Mar 2007
Location
CHESHIRE
Posts
27
Hi
My boss has asked me to look into modernising some of our plant.

We have 6 cooling towers that on which we need to monitor the TDS and Bromine levels of the sump water, and when out of spec correct (In the TDS level by dumping some water and bringing in clean. The Bromine level by topping up the Bromine until the level is achieved)

I'm most comfortable with the mitsubishi FX1/2 series PLCs so would like to use them.

What controller would best suit my needs,and what expansion blocks would I need for the sensors( I will need 12 total ).Any recommendations on sensors would be great too.

Thanks

Mike
 
if you can use 1 circuit for sampling to reduce the amount of sensors. So have a small waterline coming from each circuit. Then measure for each and open a valve. You could even use only one pipline to sense and to fill it, and even dump water.
as the level is not different for each i would use a digital signal on the sensors and use simple program without any analog in it.
 
Hi
My boss has asked me to look into modernising some of our plant.

We have 6 cooling towers that on which we need to monitor the TDS and Bromine levels of the sump water, and when out of spec correct (In the TDS level by dumping some water and bringing in clean. The Bromine level by topping up the Bromine until the level is achieved)

I'm most comfortable with the mitsubishi FX1/2 series PLCs so would like to use them.

What controller would best suit my needs,and what expansion blocks would I need for the sensors( I will need 12 total ).Any recommendations on sensors would be great too.

Thanks Mike

Your question would be much easier to answer if we had a good understanding of the system. A simple sketch of complete system pumps towers and cooled machinery would be great. As example only one sump or six -- so that you are dealing with six separate loops.

Dan Bentler
 
How are the tests performed? Does the testing device have an electronic/electrical output that can be communicated to a PLC? If not, you will not be able to automatically control concentration.
 
Sorry If I wasn't clear enough in what I wanted to do.(The fact is it is in a part of the plant that is not familiar to me, we are doing it as a favour to our Services division who do not have anyone with electrical experience)

Basically they want a system that will measure the TDS and Bromine levels in each of the cooling tower sumps, so yes each will have to be treated separate. So that is two probes for each tower (even my maths tells me that is twelve).

What I am really after at this stage is a recommendation on what hardware to use. Most of the control side I am happy with so I don't really need to bore you with it( although I will have to get to grips with PID as it is something I have never done)

I'm thinking along the lines of this for my PLC
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=3209036

With 3 of these analogue input blocks
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=3209193

If these are suitable then it's just a case of identifying suitable sensors for the TDS and Bromine levels.

Thanks again

Mike

PS just thought of a couple of other points

1- I will be using an external 24VDC PSU for inputs and outputs, having read the data sheet for the expansion block it is a bit ambiguous as to whether it takes its 24VDC for the sensors from the PLC or from the external PSU.I'm unsure as to whether I will be needing an expansion block PSU in my set up with having the 3 input modules.

2- A Recommendation for a decent colour HMI would also be appreciated something like a 4" screeen with numeric keypad and a few functio keys would be great.(I will be using Edesigner and so far have only had experience with E150 and 300)
 
First thing I would check is that Bromine is still the right chemical to use, I know that when I last dealt with water treatment (about 10 years ago) they had moved on to 'Alternate Biocide Dosing'. You must do a Risk Assessment for leakage of chemical in to the environment and for what happens if the bug killer doesn't do its job for some reason. Depending on the risk assessment you might even look to two separate PLC systems, one to do the job and one to monitor that is is being done right. I might be trying to 'teach my grandmother to suck eggs' but don't just program to make the job work, program for if things go wrong.

In terms of PLC I can't comment which Mitsubishi to choose but I don't think that cycle time will be important so just make sure you have enough program/variable space. The E series HMI's are pretty easy to program if you have used the E150 and E300 you should have no trouble with a colour screen.

Bryan
 
Hi
My boss has asked me to look into modernising some of our plant.

We have 6 cooling towers that on which we need to monitor the TDS and Bromine levels of the sump water, and when out of spec correct (In the TDS level by dumping some water and bringing in clean. The Bromine level by topping up the Bromine until the level is achieved)

I'm most comfortable with the mitsubishi FX1/2 series PLCs so would like to use them.

What controller would best suit my needs,and what expansion blocks would I need for the sensors( I will need 12 total ).Any recommendations on sensors would be great too.

Thanks

Mike

Hi Mike,

For routine cooling tower dosing controls like this I wouldn't go to the trouble of developing your own PLC application and connecting separate redox (or bromine specific probe) and conductivity analysers. I've found it to be a more cost effective solution to use an all in one cooling tower controller such as a Walchem Webmaster (http://www.walchem.com/products/controllers/webmaster_ct.htm). This allows direct connection of required analytical probes and dosing pump/purge valves and is "programmed" using a web interface where you select all the required modes of operation and setpoints. Operators can then view and interact with system via the built in keypad/display or via web browser either using Ethernet or local USB port. Also stores datalogs and can send alarms via Email or SMS. Only downside is that the controller is based on a 386 processor SBC running a stripped down Linux and you do get occasionally crashes and bugs.

An alternative product would be the recently introduced Burkert 8620 multifunction controller (http://www.burkert.co.uk/ENG/buerkert_products_new.php?type=8620) which is now being adopted as standard by a number of the big players in UK water treatment (e.g. GE Betz). It is similar in functionality to the Webmaster except it is a far more modern Europeanised product which can also have complete new custom applications developed for it. Also, it's not PC based :)

Please PM me if you would like any additional support to help develop this application as this is our bread and butter business.

Best regards,
Corby
 

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