Water Treatment By : Shraddha( ) Hardik( ) Chirag( ) Aadil( ) Chemical Process Industries-1 C.E. 3 rd Sem

Content  Introduction  Sources of water  Types of water used by industries  Municipal water conditioning  Ion-exchange process  Vapour recompressor process  Reverse osmosis  Electrodialysis

Introduction  Fresh water is probably the most important resources in the world. it is used in: a. Sustenance of human life b. Agricultural activity  Per capita consumption of water in india: Rural = 7-20 tons/year Urban = tons/year

Sources of water a.The rainfall is a main source of water. b. The snow of Himalayan mountains c. Dams,reservior,etc. 1 the largest users of water by industry classification: a. steel b. oil refineries c. pulp and paper

 2 types of water used by chemical industries a. Irrigation water b. Water for adiabatic cooling towers c. Softened removal for textile & pharmaceutical industry  Water has mostly two types of impurities: a. Temporary : Ca(HCO ₃ ) ₂ b. Permanent: CaCl ₂

METHODS OF TREATING FRESH WATER: FLOW SHEET FOR INDUSTRIAL USE OF WATER

Municipal water conditioning  This method is used to remove hardness. a. Temporary hardness: Ca(HCO ₃ ) ₂ + Ca(OH) ₂ 2CaCO ₃ b. Permanent hardness: CaCl ₂ + Na ₂ CO ₃ CaCO ₃ RAW MATERIALS: Three principal chemicals required for this process: 1. Quick lime, 2. Light soda ash, 3. Alum. small amount of activated carbon & chlorine are required for complete conditioning of raw water supplies.

Process description: Raw water input is metered & pumped where the requisite amount of chemical reagents are added to remove hardness.  Settler clarifier: it settles the mixture & separate impurities.  Sand filter: it contains bed of silica, gravels to get pure water.  Activated carbon: it absorbs impurities on its surface.  Chlorine gas: chlorine passes through water to make it pure.

Municipal water conditioning flow sheet

Ion exchange process:

 Ion exchange resins are insoluble, cross-linked, long chain organic polymers. Resins containing acidic functional groups are capable of exchanging H+ ions with other cations.  Ion exchange resins are of two types: (A) cation exchange resins (B)anion exchange resins

Process description: The hard water is passed first through cation exchange column, which removes all the cations(Ca² ˖ )from it. After that, it passes through anion exchange column, which removes all anions. we use HCl & dilute NaOH for regeneration of resin.

Vapour recompression process  This process is used to pure brackish, saline water. The process name says its work.in it, vapor is recompressed & reused. Process description: The salt water is pumped into fresh water heat exchanger from that, we get 60-70% fresh water, then it passes through brine heat exchanger, then it introduces to evaporator. The waste vapor is recompressed by compressor at 80°C.

FLOW SHEET FOR V.R.P FOR RECOVERY OF FRESH WATER

 Major engineering problems: 1. steam pressure work energy is used for driving the compressor. 2. the additional cost for the compressor. 3. efficiency of pump. 4.corrosion problem

Freezing or crystallization process: Process description:  salt water is passed through spray freezer, then ice brine is added. Ice brine is extremely cold. This water is passed through separation and washing tower. There is a vaccum compressor, which is used to phase change of water. Then liquid water is again used for washing and melting in separating and washing tower and we get fresh water. MAJOR ENGINEERING PROBLEMS:  Corrosion problem in separation tower  Height of separation tower  To maintain vaccum in vaccum compressor

FLOW SHEET FOR FREEZING PROCESS

Electrodialysis:

 Electrodialysis is a method in which methods are pulled out of the salt water by passing direct current.  Process description : When direct current is passed through saline water, the sodium ions start moving towards cathode through membrane. Electrodialysis cell consists of a large number of paired sets of membranes. Saline water is passed under a pressure between membrane pairs. Positive charges inside the membrane repel positive charge & attract negative charge. So,we get two compartments for pure water & for salt.

 Major engineering problem: 1.more electricity is required. 2.replacement of membrane 3.lifetime of system