Closed Loop Water Treatment - Corrosion

Published on by in Technology

Closed Loop Water Treatment - Corrosion

Hello.

I have been struggling with this closed loop over the last 6 months as the chemistry is completely out of control.

It is fed with RO permeate as the coolant with a total volume of 150 m3. Average water consumption is about 1m3 per day.

The loop is used to cool the fume hood of a copper smelter's convertors.

We are treating the water with a molybdate-based corr inhibitor along with a non-oxidising glut biocide. We also have a phosphate/polymer based antiscalant in place.

Recently, the RO plant failed and a high salt passage was experienced. This led to the conductivity/TDS increase in the loop.

Temperatures in the loop range between 60-80 deg C. 

Can someone help me figure out why there is such a high amount of corrosio ?

Media

Taxonomy

7 Answers

  3. Water is from aggressive to corrosive (according to RI index), as told by esteemed Colleague. 
    Yo may use this calculator (https://www.lenntech.com/calculators/ryznar/index/ryznar.htm) or many others.
    Permeate should be blended or corrected in TAlk to comply with Avg. values prescribed in CCC by many OEM. We (DANIELI) used to always prescribe a value for CaH+TAlk to comply with.
    HTH

     

  4. Hi Oswell,  just testing a couple of your analyses to see what the stability of your water is according to the Langelier Saturation Index, it is quite corrosive and needs to be stabilised with lime or soda ash.  You can download a programme for free from the Water Research Commission in South Africa called "STASOFT" which will enable you to determine the dosing required to stabilise your water.  You will need to enter a bit more info than what you have in the spreadsheet.

  5. Dear Oswell,   

    I agree with Mark that you need to provide a little more information for us to really help you.  It is important to understand what types of metals are used in the piping and heat exchangers. 

    You describe this as a closed loop system and yet you are losing and replacing over 1 m3 per day.  I noted while reviewing your makeup water spreadsheet that there is a drop in pH on many days that correlates with a drop in system pH. My guess is that is when the system makes up for the lost volume using the RO permeate.  RO permeate is very low in ions and as a result is slightly corrosive to metal piping in its own right.   You should identify where the system volume loss is and fix it so you don't have to continually make up with RO.  

    Good luck.

  7. Dear Oswell, For a more detailed answer probably more information is eeded. Microbiology, total counts, specific bacteria? Type of corrosion?  Have you executed a metalurgical investigation of the corrosion? What is the mettalurgy of the system? Typically I would say you have to approach with Mechanical, Operational and Chemical approach. (MOC). At a first glance I see a relatively low pH for a closed system. Why would you need a phosphate/polymer added for scale control when make up is RO? What is the level of MoO4? 

    So too many unkowns for now to give a clear indication what is going on. Cheers, Mark