Water scale on any heat transfer surface reduces the effectiveness of that heat transfer. This results in reduced equipment efficiency while increasing energy consumption, increasing costs and even increasing plant downtime. Often this "buildup" problem is either ignored or relegated to "fixing it at the last minute or upon mechanical failure" status because of downtime costs. This is historically based on the premise that to descale takes a great deal of time.
Cleaning can be done either mechanically or with the use of chemicals. Mechanical cleaning obviously takes a great deal of downtime because to mechanically clean, you need to dismantle equipment. There is also the replacement of gaskets and seals adding to the cost. In addition, mechanical cleaning does not always get "all" the scale out.
Chemical cleaning can get at scale buildup not always reachable in mechanical cleaning. However, five other concerns need to be addressed with chemical cleaning:
There are dozens of chemicals on the market that can descale. However, some can be prohibitively expensive to use in large applications, or very weak and slow so the problem of downtime still remains a major issue. It is very important that any descaler is not just an inhibited acid - many companies supply only that. But they tend to be slow, and often do not remove all the scale deposits since deposits can consist of calcium combined with rust, silica, oil, and whatever else can be in a water system. A descaling chemical should have adequate and quality detergents to remove such deposits. Inhibited acid alone will often not even touch some deposits.
Many products claim low or negligible corrosions rates but often meet that claim by simply supplying a slow, and weak, heavily diluted acid. In this case the customer is buying essentially expensive water. At the other extreme you may actually have a relatively good descaler that makes ridiculous claims of no corrosion at all. One such product that claimed no corrosion (and apparently continues to do so) once had a rather unpleasant interaction with the Ontario Ministry of Labour some years ago. So be very careful of such claims.
Having said the above, there are some good products available. A good descaler:
One such product that is both cost effective and has proven tests to back up the claims is Dynamic Descaler.
One such test summary is shown below:
For this product, independent tests have been done using mussels in marine/navy applications showing the following results:
Removal Rate of Mussel Shells:
| |
Dynamic Descaler
|
US based Competitor
|
Hydrochloric Acid
|
|
Time at 20ºC
|
2 hours
|
8-16 hours
|
Not Done
|
|
Time at 60ºC
|
30 minutes (100% conc.)
|
2.25 hours (100% conc.)
|
2.25 hours (15% conc.)
|
|
PH Reading
|
0.6
|
0.5
|
0.7
|
Conclusion:
Dynamic Descaler was the most rapid of all products tested.
Furthermore the corrosion tests done on Dynamic Descaler at 20ºC. indicated it to have the least metal loss over a 24 hour period on most of the materials tested.
Most heat exchangers and condenser tubes contain 90/10 copper-nickel or 70/30 copper-nickel. The results of an independent test, the average corrosion rate in mills per year (mpy) at standard conditions with Dynamic Descaler on these materials, show after 24 hours the following results which were almost 50% the rate of the nearest competitor:
| Dynamic Descaler |
90/10 copper nickel
|
14.9 average mpy
|
| Competitor |
90/10 copper nickel
|
25.9 average mpy
|
| |
|
|
| Dynamic Descaler |
70/30 copper nickel
|
13.3 average mpy
|
| Competitor |
70/30 copper nickel
|
22.8 average mpy
|
The speed of the product should be of specific interest to maintenance and engineering personnel, especially in descaling large systems. The product is fast, easy to use, and cost-effective.
Dynamic Descaler is used extensively in the hot climates of Asia for example where many heat exchangers get scaled up with a relatively small amount of calcium but often a hard buildup on silica.
Dynamic Descaler has been able to clean even these difficult systems. The product manufacturer is confident that they will test against products now used and welcome any verification of test results. This is something you do not see every day and is a welcome invitation against companies that make claims without real verification.
Dynamic Descaler applications include:
