WATER TECHNOLOGY – II

Water for industrial purpose:

Hard water cannot be used in many of the industrial applications. Hard water containing the different salts interfere in various ways in different industries.Ex: a. Textile industry: Textile industries require only soft water to wash or bleach the fabrics and especially for dying purposes. If hard water used in textile industry unexpected shades or colures are produced.b. Paper industry: Hard water gives glossy finish to paper.c. Pharmaceutical industries: In pharmaceutical industries very pure distilled water are used. If hard water is used for drug preparation salts interfere with the activity of the chemical drug.d. Building construction: hard water affects the hydration of cement resulting in the variation of strength of the dried concrete structure.e. Boiler industry: For the production electricity, steam is generated in big boilers. If hard water is used for steam generation it will produce sludge and scales in the boilers which results in the inefficiency of the production of steam and also the cracking of the boilers.

WATER FOR STEAM MAKING

In very big boilers, the soft water is used for producing steam. The boilers are heated with fuels such as coal and the steam produced rotates the blades of the turbines in a fast manner. The turbine is a magnet wounded by coil wire. Any magnet wounded by coil wire will produce electricity. Thus electricity is produced by making use of water in boilers followed by heating it to produce steam.

BOILER TROUBLES

Boiler troubles are mainly caused by the impurities present in boiler feed water. The total removal of salts in boiler feed water not made use of the scales produced in the boilers can act as insulator of heat. As a result of it more heat has to be supplied from outside of the boilers. The major boiler troubles area) carry over, priming and foaming

b) scale and sludge formationc) Corrosion and caustic embrittlement.

a) Carry over: The phenomenon of steam production along with droplets of water is known as carry over. Priming: is the process of production of wet steam (droplets) along with impurities during the process of steam production in boilers. Priming can be avoided by i) fitting mechanical purifiers. ii) avoiding uneven steam velocity iii) maintaining medium water level iv) removing oily materials present in water. Foaming: is the production of persistent bubbles in the water which do not break easily. Foaming can be avoided by i) adding NaAlH4 which coagulates the oily or soapy substances. ii) adding certain anti-foaming chemicals like cotton seed oil, castor oil etc.b) Scale and sludge formation in boilers: When water is evaporated in boilers to produce steam continuously the concentration of the slats present in the water increases progressively. As the concentration reaches a saturation point the salts are thrown out of water as precipitates either as sludge or as scales adhering to the walls of the boiler. The main reasons for the boiler scale or sludge formation are due to i) he solubility product of the salt must be exceeded by the product of concentration of constituent ions. ii) The solubility of the salt decreases with rise in temperature. iii) The increase in the temperature can lead to reactions that result in the formation of insoluble products. Sludge Scale

Heat HeatSludge’s are loose and slimy precipitates which can be easily scraped off. Salts like MgCO3, MgCl2, MgSO4, CaCl2 etc. are responsible for sludge formation in boilers.Scales are mainly hard adhering coating on inner walls of boilers. Which can be removed by applying thermal shocks, scrapers, wire brush etc. Chemicals like 5 – 10% HCl, EDTA solution etc. And blow down operation (removing the bottom portion of salt concentrated water of the boiler) the scale formation can be avoided.CaSiO3, CaSO4, Mg(OH)2 are responsible for scales formation.