Steam boiler and its various types
Boiler feed water treatment
In this lesson, we will discuss Reverse Osmosis (RO) plant.
Like demineralization plant there is another stage of water treatment which is known as reverse osmosis plant. RO plant uses the process known as reverse osmosis to produce salt-free water. The theoretical aspect is described below:-
Osmosis and reverse osmosis diagram is shown in the above figure.
Osmosis is a process in which only the solvent molecules pass through a semi-permeable membrane from higher solvent density to lower solvent density (i.e. from solution of lower density to the solution of higher density).
Osmotic pressure:- It is the minimum pressure that should be applied on the higher density solution so that no osmosis takes place through the semi-permeable membrane is called the osmotic pressure (π).
π = iCRTWhere,C is concentration of solution,R is universal gas constant,T is temperature in Kelvin scale,i is van’t Hoff’s factor, different for different solutions. i = 1 for infinitely dilute solution. Hence osmotic Pressure is a function of temperature.
On the higher density solution if a pressure (P), greater than osmotic pressure (π) is applied then the solvent molecules pass through the semi-permeable membrane from higher density solution to lower density solution. This phenomenon is called reverse osmosis. This one important stage for boiler feed water treatment process.
Reverse Osmosis Plant
In RO plant using reverse osmosis phenomenon salt-free water is taken out from raw water after the sand filtration. Purity of the salt-free water depends on effectiveness of the permeable membrane.
Layout of reverse osmosis plant is shown in the above figure. It will be easy to understand reverse osmosis process for a steam boiler by above diagram.
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