In a power generation facility or any industrial facility that uses large amounts of steam, uninterrupted steam production is vital to the facility. Often this means that somewhere upstream of the boiler there is an industrial reverse osmosis system. The purpose of this system is to ensure an uninterrupted source of ultrapure boiler feedwater is also vitally important.

The use of RO in industrial and power generation facilities has become increasingly common over the last 15 years, especially in newly built cogeneration and independent power generation facilities. Reverse Osmosis retrofits to the boiler water pre-treatment systems of older industrial facilities are common as well. This is especially true for base-loaded traditional utility power generation facilities regardless of fuel source.

This article presents 6 operational parameters for your consideration prior to purchasing a Reverse Osmosis system for your Power Generation facility.

Reverse Osmosis Equipment Parameter #1: The Cost of Wastewater Treatment

Wastewater treatment or disposal costs are continually increasing. For those plants where the cost is becoming punitive, it might make more economic sense to design the wastewater RO system with additional stages to reduce wastewater to the minimum possible amount. In some “zero discharge” power generation facilities specialized Reverse Osmosis systems and other equipment such as crystallizers may be required. To provide an example of just how dramatically multi-staging can reduce wastewater volume consider that a 400 gpm, 400 micromho stream can be reduced to just 7.5 gpm with a 3-Stage system! The conductance of course increases dramatically along the way rising from 400 micromho to 21,320 micromho!

Reverse Osmosis Equipment Parameter #2: Choose Either Cellulose Acetate (CA) or Polyamide Composite (PA) RO Membranes

Cellulose Acetate and Polyamide Composite membranes vary widely in the way their physical and chemical resistance. Fluid temperature, pH and chlorine resistance are just 3 examples of fluid characteristics that would make you favor one over the other. Operating pressure is another. CA membranes can operate at significantly higher pressures (greater than 450psi) vs. PA membranes (300psi maximum).

4 RO Feedwater Characteristics and Variability Parameters to Consider

The RO feedwater must meet certain criteria. If not, RO membranes will perform poorly; they will foul quickly, require excessive and expensive cleaning, and may become damaged to the point where they must be replaced prematurely. When this happens permeate water quality and output will decline.

In addition, care must be paid to the variability of the plant service water that feeds the RO system. Surface water can vary seasonally, and during spring run-off, turbidity can increase to well over 500 Nephelometric Turbidity Units (NTU). Even well water can vary in dissolved solids content.

Reverse Osmosis Equipment Parameter #3:

How variable is the plant service water seasonally in dissolved solids, COD (Chemical Oxygen Demand), color, turbidity, temperature, and suspended solids? Is the treatment equipment upstream of the RO system capable of handling any excursions?

Reverse Osmosis Equipment Parameter #4:

For surface water sources, how variable is the plant service water during spring run-off, and during lake turn-over? The turn-over occurs twice annually, when the lake temperature passes through 40° F [4.4° C], the point of maximum water density. During this turbulent time there is a significant increase in suspended solids and turbidity as dirt and silt are stirred up from the bottom.

Reverse Osmosis Equipment Parameter #5:

For a newly drilled well, how stable is the water chemistry? While Total Suspended Solids might remain stable, Total Dissolved Solids can vary seasonally and throughout the life of the well.

Reverse Osmosis Equipment Parameter #6:

Test the Silt Density Index (SDI) frequently. The Silt Density Index is a measure of the fouling tendency of the feedwater to a RO system. Typically, spiral wound reverse osmosis systems will need an SDI less than 5, and hollow fiber RO systems will need an SDI less than 3. If necessary, have a particle size distribution study done on the suspended/colloidal solids in the plant service water and the RO feedwater.

An in-depth discussion of Reverse Osmosis equipment design considerations for the Power Generation Industry including tables and drawings can be downloaded in the free 11 page Layne Christensen white paper titled Eleven Things to Consider When Purchasing a Reverse Osmosis System for Your Power Generation Facility.

As a leader in the development of Reverse Osmosis (RO) systems, Layne Christensen Company has the technical expertise to design and build reverse osmosis systems for all of your plant water needs.

Beyond Reverse Osmosis equipment, Layne Christensen's Water Treatment Division Research & Development team focuses on refining and expanding the water treatment methods we currently employ so we can meet the most demanding challenges head-on with innovation.

Your concerns about water quality are Layne's concerns as well. The Water Treatment Division has been resolving water quality problems for over a half century, installing thousands of treatment systems throughout North America. You can reach our technical experts through our website at www.LayneWater.com or by phone 262.246.4646.