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In a power generation facility or any industrial facility that uses large amounts of steam, uninterrupted steam production is vital to the facility. It follows then that an uninterrupted source of ultrapure boiler feedwater is also vitally important. More and more often this means the design, installation and operation of an Industrial Reverse Osmosis system.
The use of RO in industrial and power generation facilities has become increasingly common over the last 15 -20 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 RO equipment and operational parameters for your consideration prior to purchasing a Reverse Osmosis system for your Power Generation or Industrial facility.
2 Parameters to Consider Surrounding the Final Use of the RO Treated Water
Reverse Osmosis Equipment Parameter #1: In Power Generation facilities normally the permeate is the desired water stream. System designs with more than one pass may be needed to ensure that the final product is of the specified purity. Other considerations may include RO redundancy to allow some trains to be removed for cleaning or membrane replacement, boiler makeup demand vs. RO flow rate, the need for an RO water storage tank, both upstream for the RO feed and downstream for the permeate.
Reverse Osmosis Equipment Parameter#2: If the reject is the desired product, multi-staging may be necessary. In a power plant, wastewater and in some instances cooling tower blow down will be concentrated using multi-staging RO to reduce the total quantity of water that must be treated to final effluent standards. Click here to view a diagram of a 2 Stage Reverse Osmosis system.
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 degrees F [4.4 degrees 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.
By Layne Christensen
Article Source: ezinearticles.com