Effect Of Ph On The Development Of Chemical Treatment Of The Properties Of Water

In the development process of industrialcirculating cooling water treatment technology, the acid addition to controlthe pH of circulating water (6.5~7.0) at the early stage of development in the1930s played an important role in solving the scaling problem of water coolerduring circulating water operation, which prolonged the operation cycle ofproduction equipment, but the corrosiveness of circulating water was enhancedafter acid addition, resulting in an increase in the corrosion rate ofequipment.

By the early 80s, the alkaline operation atnatural pH (7.5~9.2) made the corrosiveness of water nature weakenedsignificantly, which played a significant role in solving the corrosion ofcirculating water system equipment, prolonged the service life of equipment andstrongly ensured the long cycle operation of production equipment.

The transition of circulating water fromacid addition to natural pH operation has made a qualitative leap in watertreatment technology. However, circulating water with acid to control pH andnatural pH alkaline operation need to add a large number of water treatmentagents, especially the addition of phosphate, carbon, nitrogen and other elementsof corrosion inhibitors, scale inhibitors and biocides, some of which causeeutrophication pollution to the environment, some directly pollute theenvironment. How to ensure the normal operation of the circulating water systemto meet the requirements of industrial production of the properties of water,but also to minimize the pollution of the environment in the process of watertreatment agents, has become an urgent problem to solve.

Treatment of circulating water underacidic conditions

The simple treatment of cooling water beganin the 1930s, when cooling water treatment mainly used the addition of sulfuricacid to control pH for the purpose of controlling scaling. At the same time,based on the properties of waterthe high dose of chromate used in industrialcooling water system as anodic protection agent, the use of titanium, nickel,manganese, zinc, cadmium and other metal salts as cathodic protection agent,the use of low concentration of phosphate as anti-scaling agent, at this timethe pH required to control between 6.0 to 6.5, and the general operation of theconcentration times is very low.

Chromate is toxic to humans and seriouslypollutes the environment. In order to reduce this pollution, people use thesynergistic effect between chromate and phosphate, zinc salt developed chromate/ phosphate, chromate / zinc salt composite formulations, so that theconcentration of chromate in circulating water from 200mg / L to 20mg / L, andon the basis of this developed phosphate / zinc salt formulations, but theseformulations still need to operate under acidic conditions. The acid additionoperation to maintain the acidic condition of the circulating water is verytedious and requires a large amount of sulfuric acid, and the control of acidaddition is very strict, and occasional operational errors cause system scalingor corrosion.

Recirculating water treatment undernatural equilibrium pH conditions

Natural pH operation of circulating wateris a method that makes full use of the ions of calcium, magnesium, carbonate,bicarbonate, silicate and hydroxide dissolved in water in the alkaline range toform a protective film on the metal surface with only a small amount ofcorrosion inhibitor to control corrosion and a scale inhibitor to controlscaling.

Based on the properties of water, since thenatural pH treatment reduces corrosion, controls scaling, reduces and avoidsaccidents that may be brought about by acid addition operation, and betterensures the long-term safe operation of equipment, therefore, since itsintroduction, it has immediately gained the attention of the water treatmentcommunity.

Natural equilibrium PH conditions, can beconsidered as high alkalinity, high hardness, high concentration times and highsalt content, the Langelier index of cooling water increases, Ryznar indexdecreases, so the tendency of calcium carbonate deposition in cooling water isgreatly increased, easy to cause scaling and subscale corrosion, for thisreason, people have developed a stronger ability to disperse scale inhibitiondispersant, such as PBTC (2-phosphonobutane - 1, 2, 4 - tricarboxylic acid), itcan be in harsh water conditions scale inhibition; in strong acids, strongbases and strong oxidants in the presence of water will not be hydrolyzed; canbe in high hardness, high alkalinity and high PH conditions scale inhibition.

On the current development and developmenttrend of water stabilizers and the properties of water, focusing on the fullorganic phosphine system formulations, in these formulations, organophosphonicacid, copolymers, phosphonic carboxylic acid and other agents of the compound,to strongly strengthen their water stabilization effect. It must be stressedthat: the use of natural equilibrium pH conditions of circulating watertreatment, must be continuously added water stabilizer, continuousreplenishment of fresh water and continuous discharge, try to maintain abalanced relationship between the scaling ions in circulating water, because inthe natural equilibrium pH conditions, CaC03, Ca3 (P04)2 in circulating wateris always in a saturated state, if interrupted dosing, is bound to cause theirdeposition.