Numerical problem on hardness of water

Numerical Problem on hardness of water • A water sample has the following analysis: Mg(HCO3)2 = 83mg/l, Ca(HCO3)2 = 134 mg/l, CaSO4 = 124mg/l, MgCl2 = 84mg/l, CaCl2 = 94mg/l, NaCl = 50mg/l Calculate the temporary and permanent hardness in ppm and in degree Clark Solution Calculation in terms of CaCO3 equivalent Constituent Quantity mg/l Multiplication factor CaCO3 equivalent mg/l Mg(HCO3)2 Ca(HCO3)2 CaSO4 MgCl2 CaCl2 NaCl 83 134 124 84 94 50 100/146 100/162 100/136 100/95 100/111 Does not produce hardness 56.8 82.7 91.2 88.4 84.7 - • Temporary hardness = hardness due to Ca(HCO3)2 and Mg(HCO3)2 = 139.5 mg/l = 139.5 ppm = 139.5 x 0.07 °Cl = 9.77 °Cl • Permanent Hardness = hardness due to CaSO4 + MgCl2 + CaCl2 = 264.3mg/l = 264.3 ppm = 264.3 x 0.07 °Cl = 18.50 °Cl Boilers feed water • Water required for boiler feed purposes should be of very high quality and requires a lot of treatment If the hard water is fed directly into the boilers then huge damage is caused to the boilers Hard water in boilers lead to: • • • • 1) 2) 3) 4) Scale and Sludge formation Priming and Foaming Boiler corrosion Caustic embrittlement Scales and sludge formation Sludges Scales Priming and Foaming • Priming refers to the propulsion of water into the steam drum by extremely rapid almost explosive boiling of the water at the heating surface, • Foaming is the formation of bubbles at the water surface in the boilers due to the presence of oils and alkalis in the boiler feed water Boiler Corrosion • It is actually the decay or disintegration of boiler material either due to chemical or electrochemical reaction with its environment having O2, CO2 and mineral acids Disadvantages of boiler corrosion Shortening of boiler life Leakages of joints and rivets Increased cost of repairs and maintenance Caustic embrittlement • This is the phenomenon during which the boiler material becomes brittle due to the accumulation of caustic substances • This is caused by the use of highly alkaline water in the high pressure boiler Water softening Techniques • • • • Lime soda Process Zeolite softening process Ion exchange process Mixed bed ionexchangers Equations involved in the lime soda process Reactions with lime • Removal of temporary hardness using lime Ca(OH)2 • Ca(HCO3)2 +Ca(OH)2 = CaCO3 +2 H2O • Mg(HCO3)2 +Ca(OH)2 = CaCO3 +2H2O+ MgCO3 • MgCO3 +Ca(OH)2 = CaCO3 + Mg(OH)2 • Removal of permanent Mg hardness • MgSO4 +Ca(OH)2 = CaSO4 + Mg(OH)2 • MgCl2 +Ca(OH)2 = CaCl2 + Mg(OH)2 • Removal of dissolved iron and aluminium salts • FeSO4 +Ca(OH)2 = CaSO4 + Fe(OH)2 • 2Fe(OH)2 + H2O +1/2 O2 = 2Fe(OH)3 • Al2(SO4 )3+3Ca(OH)2 = 3CaSO4 +2 Al(OH)3 • Removal of dissolved CO2 and H2S • CO2 +Ca(OH)2 = CaCO3 +H2O • H2S +Ca(OH)2 = CaS +2 H2O • Removal of free mineral acids • 2HCl +Ca(OH)2 = CaCl2 + H2O • H2SO4 + Ca(OH)2 = CaSO4 + H2O Reactions with soda • CaCl2 + Na2CO3 = 2NaCl + CaCO3 • CaSO4 + Na2CO3 = Na2SO4 + CaCO3 • Advantages of Lime Soda Process • • • • • It is economical It helps in removing iron and manganese from the water This treatment helps in removing total mineral content of water The increased alkalinity of the water helps in killing pathogenic bacteria The pH value of water increased by thus process reducing the corrosion of the distribution pipes • Disadvantages of lime soda process • As CaCO3 is slightly soluble in water it is not possible to remove complete • • hardness by this process Careful operation and skilled supervision is required to get good results A large quantity of sludge is formed by this process the disposal of the sludge is a problem [...]... total mineral content of water The increased alkalinity of the water helps in killing pathogenic bacteria The pH value of water increased by thus process reducing the corrosion of the distribution pipes • Disadvantages of lime soda process • As CaCO3 is slightly soluble in water it is not possible to remove complete • • hardness by this process Careful operation and skilled supervision is required...Equations involved in the lime soda process Reactions with lime • Removal of temporary hardness using lime Ca(OH)2 • Ca(HCO3)2 +Ca(OH)2 = 2 CaCO3 +2 H2O • Mg(HCO3)2 +Ca(OH)2 = CaCO3 +2H2O+ MgCO3 • MgCO3 +Ca(OH)2 = CaCO3 + Mg(OH)2 • Removal of permanent Mg hardness • MgSO4 +Ca(OH)2 = CaSO4 + Mg(OH)2 • MgCl2 +Ca(OH)2 = CaCl2 + Mg(OH)2 • Removal of dissolved iron and aluminium salts •... Al(OH)3 • Removal of dissolved CO2 and H2S • CO2 +Ca(OH)2 = CaCO3 +H2O • H2S +Ca(OH)2 = CaS +2 H2O • Removal of free mineral acids • 2HCl +Ca(OH)2 = CaCl2 + 2 H2O • H2SO4 + Ca(OH)2 = CaSO4 + 2 H2O Reactions with soda • CaCl2 + Na2CO3 = 2NaCl + CaCO3 • CaSO4 + Na2CO3 = Na2SO4 + CaCO3 • Advantages of Lime Soda Process • • • • • It is economical It helps in removing iron and manganese from the water This treatment... in water it is not possible to remove complete • • hardness by this process Careful operation and skilled supervision is required to get good results A large quantity of sludge is formed by this process the disposal of the sludge is a problem ... refers to the propulsion of water into the steam drum by extremely rapid almost explosive boiling of the water at the heating surface, • Foaming is the formation of bubbles at the water surface in... increased alkalinity of the water helps in killing pathogenic bacteria The pH value of water increased by thus process reducing the corrosion of the distribution pipes • Disadvantages of lime soda process... soda Process Zeolite softening process Ion exchange process Mixed bed ionexchangers Equations involved in the lime soda process Reactions with lime • Removal of temporary hardness using lime Ca(OH)2