Corrosion is considered one of the major problems encountered in cooling water treatment. Many cooling systems are made from ferrous steel components and two primary issues can outcome if corrosion will not be managed:
a) Failure of equipment resulting in unscheduled downtime, loss of manufacturing and price of replacements;
b) Lower in plant efficiency due to deposition of corrosion merchandise in heat exchangers leading to a lack of heat transfer.
The corrosive potential of a system will be predicted from water analyses and the Langelier or Ryznar indices; empirical tools for predicting scale and corrosive tendencies of pure waters based on their chemical analyses and the thermodynamic constants for CO2/H2O/CaCO3 system. A calculation is made from the theoretical pH (pHs) at which a selected water is simply in equilibrium with calcium carbonate. Predictions are then made based mostly on the precise water pHa.
(pHs = (pK2 – pKs) + pCa2 + pAlk )
Langelier Index = pHa – pHs if positive this signifies scale forming, if negative then corrosive.
Ryznar Index = 2pHs – pHa
four – 5 Heavy scale
5 – 6 Slight scale
6 – 7 Scale / Corrosion
7 – 7.5 Corrosive
7.5 – 9 Extremely corrosive
Protection from corrosion could be achieved either by changing the metallic or the surroundings. Changing the steel is expensive and will not at all times achieve success. Changing the atmosphere is a extensively used, practical methodology to manage corrosion. In cooling methods two sensible approaches could also be adopted:
a) Use the pure calcium and alkalinity in the water to type a protective calcium carbonate layer on the floor;
b) Add corrosion inhibitors.
Neither method is unique and the selection of remedy will be based mostly on an evaluation of system requirements and corrosion management required. Most programs at present operate at what is called “pure pH”. This is the pH to which the system rises at the working focus issue and is usually in the rage 8 to 9. This will lead to lowered corrosion charges but there could also be still the necessity for additional corrosion inhibitor to realize passable corrosion charges
The most widely occurring scale forming chemical is calcium carbonate (CaCO3). Different frequent scale forming chemicals are calcium sulphate (CaSO4) and calcium phosphate (Ca3(PO4)2. These and different less widespread chemicals that may kind scales resembling iron oxides, silica (and silicates) have one property in widespread – they’re either only very slightly soluble or exhibit inverse solubility characteristics, i.e. they become less soluble with rising water temperature.
Scale formation reduces the flexibility of the steel to conduct heat effectively and leads to a reduction in the efficiency of the system.
Scale control can be achieved in three ways:
1. by operating the system in a non scaling method ( Langelier / Ryznar assist define this);
2. by removing some or all the calcium using a water softener;
3. by modifying the precipitation of the dimensions with inhibitors in order that it is non-scale forming.
Once more these approaches aren’t mutually unique and treatment is usually a mix of all three
The water in a cooling water therapy system gives a favourable atmosphere for the growth of micro-organisms. Microbial progress on surfaces can lead to the event of biofilms. If uncontrolled, such movies can cause fouling which might:
reduce the performance of equipment;
promote scale formation and metallic corrosion;
create a reservoir of unwanted organisms comparable to legionella.
Microbial control is most often achieved by the addition of oxidising biocides (either chlorine or bromine) as the prime biocidal remedy that may be complemented by speciality natural biocides and biodispersants.
Deposition Fouling Issues
Deposition, as compared to scale formation, occurs when insoluble particulates in the circulating water adhere to surfaces. Deposition may be a particular downside when flow velocities are low or there are useless ends. Particulate deposition could be the precursor for scale, corrosion and biofilm formation.
Most particulates, comparable to clay or silt, enter a system with the make-up water. Other sources are through airborne contamination being scrubbed out within the tower (corrosion products from internal corrosion) aluminum and iron hydroxides can enter a system from poorly operated pre-therapy plant.