RO Plant (Boiler feed water treatment)

In this post, we will discuss RO Plant (Reverse Osmosis Plant). This post will be helpful to understand the concept of using RO plant in the boiler feed water treatment process.

Reverse Osmosis Plant (RO Plant)

Like demineralization plant (DM Plant) there is another stage of water treatment which is known as reverse osmosis plant. This plant uses the process known as reverse osmosis to produce salt-free water.

Osmosis is a process in which only the solvent molecules pass through a semi-permeable membrane from the solution of lower density to the solution of higher density.

      Reverse Osmosis

On the higher density solution  if a pressure, greater than osmotic pressure is applied then the solvent molecules pass through the semi-permeable membrane from a higher density solution to lower density solution. This phenomenon is called reverse osmosis. This one important stage for the boiler feed water treatment process.

osmosis & reverse osmosis
osmosis & reverse osmosis
Reverse osmosis
Reverse osmosis

The procedure is described below:

Sodium hypochlorite (NaOCl) is injected into raw water to kill the algae or bacteria present in the raw water. Otherwise, they may cause harm to the multi grade-filter (MGF).

The multi-grade filter is the primitive type of filter where sand, stone-chips, stones are used in stacks to remove the large size suspended particles from the raw water.

The net filter again removes medium-size suspended particles, where the raw water passes through the net minute vents.

Then in ultra-filtration very small suspended particles are removed. After long usage of ultra-filtration unit, it requires back-wash, and then it is back-washed with water and three chemicals,NaOH, HCL,  and NaOCl (Sodium Hypochlorite). HCl Removes iron by dissolving it. It also removes the basic salts those are rejected on UFU (Ultra Filtration unit).
NaOH ← It helps to remove acidic salt.
NaOCl ← To kill algae and bacteria inside the Ultra Filtration unit.

After ultra-filtration the water is stored into RO feed tank and then pumped with RO feed pump of Reverse Osmosis Plant. In the channel the water is mixed with HCL (for pH controlling, as the water coming from RO plant or RO permeate water should have pH around 6.0) and SMBS (sodium meta bi-sulphate) [ Na2S2O5]. Due to the presence of sodium hypochlorite the water is chlorinated. To remove excess chlorine SMBS is used. If excess chlorine is not removed then the semi-permeable membrane may get damaged. It is also mixed with anti-scaling reagent (AS), which reacts with those chemicals which form scale inside the channel.

Then the water is passed through micro-cartridge filter (MCF) which removes the other suspended particles and the precipitate formed by the reaction of anti-scaling reagent with the scaling chemicals.

In  this stage of boiler feed water treatment the water is fed to RO unit by HP pump, where after successive filtration by 1st and 2nd stage RO it is fed to degasser unit.

After degasification, the water is passed through DM plant MB (mixed bed) resin and stored into DM water storage tank.

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