Skip to main content

Osmosis and Reverse osmosis

Osmosis-

 During natural osmosis, water flows from a less concentrated solution through semi permeable membrane to a more concentrated saline solution until concentrations on both sides of the membrane are equal. 

Reverse Osmosis:

It requires external pressure to reverse natural osmotic flow. As pressure is applied to the saline solution, water flows from a more concentrated saline solution through the semi permeable membrane.
• Gear pump or Reciprocating pump
• 60 bar pressure
• Chemical dosing- Sodium Hexametaphosphate sheets to assist washing the cartridge material
• Types of membrane- Cellulose acetate, aromatic polyamide membrane & polysulphonate
• Polyamide or polysulphonate (membrane not permeable to salt)- spirally wound- for Sea water
• Asymmetric membrane- Cellulose acetate membrane- hollow fine fiber- for brackish water
• Supported by Spiral wound cartridge 
• Central Porous tube core for pure water.
• Many envelopes 2 type of membranes
• Envelopes separated by coarse gauge sheets
• Cartridge when open- appearance of opened book
• Everything is then packed in stainless steel cartridge
• Relief arrangement required for the system
• Chlorine in pure water is added for chlorination
• Sterilization of pure water
• De-chlorination- pure water passing through compressed carbon filter
• Output of pure water – increases- putting cartridge tube in parallel
• Quality of pure water- increases- putting cartridge tube in series

Pretreatment 

Dosage- 5mg/ltr- inhibits precipitation of calcium carbonate. 10 micron cartridge filter used to reduce suspended solids in the membrane. Feed often heated to 400C to improves output but most systems are designed for 250C.
Post treatment
Sterilization by chlorination & to overcome flat taste soda ash can be used. 

Safety device in RO system

• Sea water H.P relief valve
• Permate relief valve
• Conductivity meter
• D.P alarm
• L.P cutout 

Advantages of RO system

• Small in size and light in weight
• Quiet operation
• Operation not effected by rough sea conditions
• Simple and fast maintenance
• No jacket water temperature is required
• Produce instantly

Disadvantage of RO system

• Careful pretreatment needed for long membrane life
• Membrane are expensive
• Output dependent on membrane condition
• For very high quality 2-pass system required


Reverse Osmosis Membrane: 

  • A reverse osmosis membrane has a thin microporous surface that rejects impurities, but allows water to pass through.
  • The membrane rejects bacteria, pyrogens, and 85%-95% of inorganic solids. Polyvalent ions are rejected easier than monovalent ions. 
  • Organic solids with molecular weight greater than 300 are rejected by the membrane, but dissolved gases pass through. 
  • Before purification TDS (total dissolved solid) allowed for this system is 45,000ppm and after purification it will be 300-1000 ppm. 
  • Material for reverse osmosis membrane is poly-sulphonate & polyamide.

Labels:

Comments

Post a Comment

If you have any doubts.Please let me know

Popular posts from this blog

Differences between MC/MC-C and ME/ME-C engines

The electrohydraulic control mechanisms of the ME engine replace the following components of the conventional MC engine: Chain drive for camshaft Camshaft with fuel cams, exhaust cams and indicator cams Fuel pump actuating gear, including roller guides and reversing mechanism Conventional fuel pressure booster and VIT system Exhaust valve actuating gear and roller guides Engine driven starting air distributor Electronic governor with actuator Regulating shaft Engine side control console Mechanical cylinder lubricators. The Engine Control System of the ME engine comprises: Control units Hydraulic power supply unit Hydraulic cylinder units, including: Electronically controlled fuel injection, and Electronically controlled exhaust valve activation Electronically controlled starting air valves Electronically controlled auxiliary blowers Integrated electronic governor functions Tacho system Electronically controlled Alpha lubricators
9 comments
Read more

Why is a man hole door elliptical in shape?

Any opening in a pressure vessel is kept to a minimum and for a man entry an elliptical hole  is lesser in size than the corresponding circular hole. More over it is prime concern to have a  smoothed generous radius at the corners to eliminate stress concentration. Hence other  geometrical shapes like rectangle and square are ruled out.  To compensate for the loss of material in the shell due to opening, a doubler ring has to be  provided around the opening. The thickness of the ring depends on the axis length along the  dirrection in which the stresses are maximum and the thickness of the shell. It is important to  align the minor axis along the length of the vessel, as the stress in this direction is  maximum. Longitudinal stress: Pd/2t where P= pressure inside the vessel, d= diameter of the arc, t=  thickness of the shell plating  Circumferential stress: Pd/4t  More over a considerable material and weight saving is achieved as minor is along the  direction of maximum stress.
20 comments
Read more

Main engine interlocks

Interlocks are provided so that the engine can be started or reversed only when certain conditions have been fulfilled. When there is a remote control of engines, it is essential to have interlocks. This reduces the possibility of engine damage and any hazards to the operating personnel. Turning gear Interlock . This device prevents the engine from being started if the Turning gear is engaged. Running Direction Interlock . This prevents the fuel from being supplied if the running direction of the engine does not match the Telegraph. Starting Air Distributor in end position . This prevents starting from taking place if the shifting of the Distributor has not been completed. Main Lube. oil pressure, Piston cooling pressure, Jacket water pressure, and important parameters must be above the required minimum. Auxiliary Blower Interlock . The Auxiliary Blower is provided in case of Constant pressure turbo charging. Air Spring pressure Interlock . In case of the present generation
6 comments
Read more