Questions regarding circulating water

This post was last edited by hesonchang214 on 2019-7-24 at 11:45. In chemicals used for treating industrial water such as cooling water and air-conditioning water, corrosion inhibitors and scale inhibitors are the two most commonly used categories of chemicals. Corrosion inhibitors are a type of chemical substance that, when added in small amounts to an environment prone to corrosion, can reduce or prevent metal corrosion, thereby protecting the metal or alloy. Scale inhibitors are another type of chemical substance; when added to systems such as cooling towers or boilers, they can reduce or prevent the formation of scale. Corrosion and scale inhibitors refer to chemicals or formulations that have both the ability to suppress corrosion and the formation of scale; these include composite agents that combine corrosion inhibitors with scale inhibitors. They are further divided into two main categories: inorganic corrosion inhibitors and organic corrosion inhibitors.

This post was last edited by hesonchang214 on 2019-7-24 at 11:47. Inorganic corrosion inhibitors: These inhibitors have a long history; initially, they were chromium salts and nitrite compounds that could form an oxide film on metal surfaces to provide passivation effects. There are also polyphosphates, silicates, borates, tungstates, and molybdates that require the presence of oxygen to function. Due to the environmental toxicity of chromates, nitrites, and polyphosphates, their use has long been restricted, and they are rarely used even in closed systems. Other inorganic corrosion inhibitors include lithium salts, zinc salts, or tungstate salts, among others. When applying green chemistry concepts in the field of inorganic corrosion inhibitors, the main improvement is the elimination of the use of many compounds that are toxic to the environment, and their replacement with environmentally friendly chemicals. Molybdates and tungstates are two inorganic corrosion inhibitors that have been developed and applied recently. Molybdates can be added to cooling systems, automotive antifreeze systems, and metal cutting systems to replace chromates, with toxicity that is much lower than that of the latter. Other alternatives to chromates include: hydrazines, and composite corrosion inhibitors based on tungstate series. Organic corrosion inhibitors: The development of organic corrosion inhibitors has been extremely rapid in recent years. Compared to other types, they can be used at low concentrations, but their thermal stability is somewhat lower. The largest category of organic corrosion inhibitors are organic amines, including aliphatic amines and aromatic amines, monoamines, diamines or polyamines and their salts. Starting from the concept of greenness, more fatty amines should be used to replace or reduce the use of aromatic amines; organic amine corrosion inhibitors can also replace many inorganic heavy-metal corrosion inhibitors such as strontium chromate, zinc phosphate, barium borate, and phosphosilicates. Phosphorus-based corrosion and scale inhibitors that are currently in widespread use, as well as polymer and copolymer scale inhibitors such as polyacrylic acid, have indeed led to breakthroughs in cooling water treatment technology. They play a significant role in addressing the issue of water resource depletion facing humanity, have been a focus of research and development both domestically and internationally, and are considered non-toxic. However, studies show that they either cause eutrophication of water bodies or are highly biodegradable, making them both environmentally unfriendly products. There are also various other polymers such as binary copolymers or terpolymeres. Polyacrylamide is also a scale inhibitor, but it shares the same problem of being biodegradable. Polyaspartic acid, regarded as a new generation of green scale inhibitor, is a biopolymer that was successfully synthesized in recent years inspired by animal metabolic processes. Its mechanism of scale inhibition also differs from previous theories; studies on its scale-inhibiting properties have been published in the past one or two years. The green scale inhibitor recently developed by East China University of Science and Technology is thermopolyaspartic acid. Its raw material, aspartic acid, can be extracted from nature; its production process is environmentally friendly, and it is also biodegradable. It can be used in oil fields, where it serves both as a corrosion inhibitor and a scale inhibitor, and it can also be employed as a scale inhibitor in seawater desalination and reverse osmosis water production processes.

This post was last edited by hesonchang214 on 2019-7-24 at 11:48. A bactericide, also known as a microorganism killer, refers to a substance that can eliminate bacteria, algae, and other microorganisms in water. Fungicides can be divided into oxidative and non-oxidative types. Oxidizing bactericides ① Chlorine compounds: mainly include chlorine, bleaching powder, chlorine bleach, stable or unstable chlorine dioxide, dichloro or trichloroisocyanuric acid and their sodium salts. ②Bromines: They exhibit better activity under alkaline conditions than chlorines, and their overall performance is superior to that of chlorines. The main components are bromine, hypobromites and additives, as well as bromochloroalkyl hydantoin, which can release hypobromous acid slowly and provides long-lasting efficacy. ③Ozone-based agents: They can release new oxygen and have excellent bactericidal effects; the downside is their high cost. Non-oxidizing biocides: Non-oxidizing biocides (mainly referring to long-chain carbides): ① Quaternary ammonium salts: The two most commonly used quaternary ammonium salt fungicides are chlorhexidine and benzalkonium chloride. It is characterized by low toxicity and low cost, possesses bactericidal and algicidal properties, and is widely used. ②Organic amines: Commonly used ones include rosin amine salts, β-amines, and β-diamines, which are often used in combination with phenols. ③Chlorophenols: mainly compounds of dichlorophenol, trichlorophenol, and pentachlorophenol. It is characterized by high toxicity, but it has a good killing effect. ④Organic sulfurs: Commonly used ones include dithiocyanomethane, bis-trichloromethyl sulfone, sodium dimethyldithiocarbamate, etc. The advantage is that it is highly effective against sulfate-reducing bacteria. ⑤Isothiazolinones: belong to the category of antibacterial agents. It exhibits excellent biocidal performance over a wide range of pH values.

There are fins in the cooling tower, and it is necessary to regularly check for corrosion of those fins.

I won’t talk about the experimental level. In production, the scale inhibition effect can be determined by the temperature difference in heat exchangers, while the corrosion rate can be assessed using coupon testing. The killing of bacteria and algae is visible to the naked eye.