Industrial Reverse Osmosis – Designing Reverse Osmosis Equipment in Power Generation Facilities

In a power plant, industrial Reverse Osmosis equipment (RO) is used almost exclusively in the boiler water pre-treatment area. Since most power boilers tend to operate at elevated pressure (>700 psig [4.8 MPa]), boiler feed water quality is very stringent. As a result, industrial Reverse Osmosis Equipment in this application is invariably followed by some type of demineralization (demin) polishing equipment, designed to reduce feed water dissolved solids, especially silica, to very low levels. Industrial Reverse Osmosis equipment, by itself, is incapable of providing the boiler feed water quality demanded by higher pressure power boilers.Because the polishing demineralization equipment in a power generation facility will be sized upon the expected industrial Reverse Osmosis equipment performance (permeate water quality and quantity), any problems with the Reverse Osmosis equipment operation can have drastic effects on the demin performance. Poor demin performance can cause costs to increase sharply, through increased regenerations and acid/caustic usage. Further downstream, the impact of poor industrial Reverse Osmosis equipment performance on the power generation boilers can be severe, ultimately leading to plant de-rating, and even boiler and turbine damage.Understanding Reverse Osmosis Design for a Power Generation Facility There are four main components of an industrial Reverse Osmosis equipment system: Element, Array (Train), Stage, and Pass.The industrial Reverse Osmosis Element is the building block of any RO equipment system. It is the individual component, where the RO process occurs.There are four main designs for the elements:
Spiral Wound – Most common design for water purification
Hollow Fiber – Very large membrane surface areas are possible in this design. Used in seawater desalination
Large Tube – Similar to a shell-and tube heat exchange in appearance and design. Used in special wastewater treatment and food processing applications
Flat Plate – Similar to a plate-and frame heat exchanger. Used in food processing applications
Regardless of the element design, high pressure and flow is needed to force pure water through the RO membrane to become permeate. Because of the high pressures needed, each element must be designed so that the internal structures can withstand a feedwater pressure of several hundred psig.The number of elements needed will be determined by the amount of the final product needed daily. The industrial RO equipment Array is simply the way in which the elements are grouped together, in series or parallel.An industrial RO Stage Final water quality requiredDaily amount of water neededInlet feed water qualityCost to treat wastewaterType of upstream feed water treatment equipment