News

CROWN Solutions, Inc. Technical Resource

Introduction
Jim Marten - Vice President/Marketing Manager

Everyone in the industrial sector is well aware of the steady increases that are being experienced for fuel, water, and sewer charges over the past 24 months.

In this month's edition of the CROWN Solutions Technical Resource, we explore how these costs can be reduced in a steam plant operation, with the use of reverse osmosis for boiler water pretreatment.

RO is a proven and popular technology that is becoming the industry standard for a modern boiler room design. Please read our feature article, and compare the options that exist for boiler make up pretreatment strategies.

If there is anything that we can do for you, or if you have any questions or comments regarding CROWN's service to your organization, please contact me directly.

Regards,

James N. Marten
VP / Marketing Manager
CROWN Solutions Inc.
Phone: 1-800-875-4075 (x) 211
Fax: (937) 898-7360
jmarten@crownsolutions.com

Using Reverse Osmosis for Boiler Pretreatment
By James McDonald & Dave Christophersen

There are numerous makeup water pretreatment strategies for boiler systems including softeners, dealkalizers, demineralizers, and reverse osmosis. Factors such as makeup water characteristics, economics, manpower, system familiarity, boiler requirements, space requirements, and so forth will determine which pretreatment strategy is used. Reverse osmosis (RO) has come of age in the past decade as a real, economical alternative for boiler pretreatment. RO pretreatment produces a higher quality water than many other pretreatment strategies but can come with some operational trade-offs. These trade-offs may be positive or negative depending upon the situation.

In order to gain a better, practical understanding of using RO for boiler pretreatment, it is helpful to compare a typical soft water pretreatment program to that of an RO pretreatment program. Advantages of RO over a softener boiler pretreatment program include:

• 90 to 99.9% removal of dissolved solids to allow boiler to operator at much higher cycles of concentration (up to 100 cycles).
• Removes more than just hardness (calcium & magnesium).
• Lower boiler makeup and blowdown rates.
• Lower fuel usage.
• Less internal boiler treatment chemicals required.
• Less alkalinity resulting in less neutralizing amine demand.
• Cleaner boilers.
• Reject may be of good enough quality for cooling tower makeup or wash water.
• If using softeners with RO, the regeneration costs (including salt and water) may decrease depending upon the current condensate return and blowdown rate.
• No regenerant chemicals.
• For the right waters, lower manpower requirements may be realized.

Disadvantages of RO as compared to a softener boiler preatreatment program include:

• Increased electrical costs.
• If acid pretreatment is used, acid handling will be required.
• Product water flow rate is pretty much fixed while ion exchange can manage variable flows.
• An antiscalant may be necessary upstream of the RO.
• With polyamide (PA) membranes, chlorine must be removed upstream of the RO.
• Increased monitoring responsibilities including RO normalized permeate flow, percent salt passage, pressure drops, SDI's, conductivity, temperatures, etc.
• Commonly 25% of water into an RO comes out as reject. If this water has no other uses, it is sent down the drain.
• Membranes must be cleaned and replaced periodically.
• Microbiological fouling can be an issue.
• Flow is temperature sensitive.
• May need additional pretreatment equipment.
• In some waters, higher manpower requirements are seen.

Similar advantages and disadvantages apply when comparing RO to other boiler pretreatment systems as well. Table 1 outlines the additional advantages and disadvantages of RO as compared to dealkalizing and demineralizing.

RO units generally remove 90 to 99.9% of all dissolved solids in a water source. Dissolved gases, however, pass through an RO membrane. Having a good understanding of which impurities are removed by which boiler pretreatment system can facilitate making the correct choice for your boiler system. Table 2 is a general list of impurity removal capabilities.

Conclusion
The big picture for a properly applied RO pretreatment system in an ideal situation is: lower water costs, lower sewer costs, lower fuel costs, lower treatment chemical costs, lower or elimination of regenerant chemical costs, higher boiler reliability, and higher steam purity. As discussed, exceptions to this big picture do exist, and how an RO boiler pretreatment system fits into each unique situation must be carefully considered.