| Reverse Osmosis equipment (RO) in power | | | | solution. |
| generation facilities is primarily used in the boiler water | | | | According to the Van't Hoff equation for the |
| pre-treatment area. Power boilers tend to operate at | | | | calculation of osmotic pressure: |
| extremely high pressures (>700 psig), so boiler | | | | (symbol P)... |
| feed water must be extremely pure. Therefore, | | | | PV = nRT = (g/m)RT or |
| Reverse Osmosis equipment systems for boiler | | | | P = (g/m)RT/V, where |
| pre-treatment are almost always followed by some | | | | R = universal gas constant, 0.0821 Litreoatm/(moloK) |
| type of demineralization polishing equipment, designed | | | | T = absolute temperature, K (degrees Kelvin)g = |
| to reduce feed water dissolved solids, especially silica, | | | | solute weight, grams |
| to trace levels. | | | | V = volume of solution, Litresm = molecular weight |
| The Reverse Osmosis design performance | | | | of solute, if non-ionicn = moles |
| (permeate water quality and quantity) will dictate | | | | P = osmotic pressure, atmospheres |
| how the polishing demineralization equipment will be | | | | Using this equation, and applying it to an aqueous |
| sized and any problems with the Reverse Osmosis | | | | solution of 1,000 mg/L. of dissolved ionic solids, as |
| equipment operation can have drastic effects on | | | | CaCO3, we arrive at an osmotic pressure of 7.2 psi |
| demineralizer performance. Poor demineralizer | | | | [50 kPa] at 77° F. In general terms, the osmotic |
| performance in turn can cause operating costs to | | | | pressure averages about 1 psi [6.9 kPa] for every |
| increase sharply, through increased regenerations and | | | | 100 mg/L. of dissolved solids. |
| acid and caustic usage. | | | | By applying a pressure on the concentrated side of |
| Further downstream, the impact of Reverse Osmosis | | | | this membrane, we can cause this process to |
| design on the power generation boilers can be | | | | reverse. Pure water molecules (and dissolved gas |
| severe, ultimately leading to plant de-rating, and even | | | | molecules) can be forced to flow from the |
| boiler and turbine damage. | | | | concentrated side to the dilute side. |
| Understanding Reverse Osmosis Design Fundamentals | | | | This is the entire Reverse Osmosis design or "RO" |
| In order to understand how Reverse Osmosis | | | | design process in a nutshell. Water purification occurs |
| equipment works, one must look into the physics of | | | | when water molecules are forced to flow from a |
| osmotic pressure and semipermeable membranes. | | | | concentrated solution through a semipermeable |
| A semipermeable membrane allows the passage of | | | | membrane to the dilute side in the Reverse Osmosis |
| specific molecules through it. If a concentrated | | | | equipment. |
| aqueous solution exists on one side of a | | | | To overcome the osmotic pressure, and force water |
| semipermeable membrane, pure water molecules | | | | molecules to reverse flow, one must apply a |
| tend to spontaneously diffuse from the more dilute | | | | pressure. The Net Driving Pressure needed is defined |
| side of the membrane to the more concentrated | | | | as: |
| side. This is called Osmosis. | | | | NDP = Feed Pressure + Permeate O. P. (usually |
| As water molecules continue to flow across the | | | | negligible) - Permeate Pressure - Feed O. P. |
| membrane, the amount of water increases on the | | | | O. P. = Osmotic Pressure |
| concentrated side of the membrane, as does its | | | | The flow through a Reverse Osmosis equipment |
| pressure, called the head pressure. Once this head | | | | membrane is proportional to the NDP. |
| pressure increases to a given level such that further | | | | In order to obtain reasonable permeate flow rates, |
| water flow can no longer occur across the | | | | and to minimize membrane fouling, the applied feed |
| membrane, the system is said to be in equilibrium. | | | | pressure must be very much greater than the |
| The pressure at this point is called the Osmotic | | | | calculated P. It is generally in the range of 200 - 450 |
| Pressure. | | | | psi [1.4 - 3.2 MPa]. This high pressure requires specific |
| Osmotic pressure is proportional to the dissolved | | | | Reverse Osmosis design considerations. |
| solids concentration in the more concentrated | | | | |