Tuesday, September 30, 2008

How to Measure pH Accurately in Steam Condensate

Keeping within ASME guidelines for total iron in boiler feedwater below 0.1 ppm and total copper below 0.05 ppm copper requires attention to the maintenance of steam traps, knowledge of the metallurgy of the steam/condensing equipment in the steam distribution system and in particular the pH of return condensate.
Steam Condensate Sample Cooler by Res-Kem Corp

When measuring pH in condensate, it is important to cool the sample with an in-line water sample cooler to minimize the CO2 flashing off from the sample. When the CO2 flashes off it is not present in the condensate sample so it will not form carbonic acid. Without carbonic acid present, the pH will be measured with a false high pH. The difference between in-line cooled condensate samples and ambient cooled condensate temperatures can be 2.0 or more pH units. This difference in pH will dramatically increase the corrosion rate.

The following chart shows how equipment with large steam demands and therefore condensate flow with elevated CO2 levels will likely have elevated corrosion rates.
The Impact of CO2 and Flow Rate on Corrosion

In addition to ensuring proper measurement of pH, an in-line water sample cooler enables safe handling of the high temperature condensate. Water sample coolers are available in carbon steel or stainless steel. Certain sample cooler models have easily accessible coils that can be cleaned or replaced as needed.

Monday, September 15, 2008

Uniform Particle Size Ion Exchange Resins

We received notice today that Purolite Ion Exchange Company will no longer be selling the anion resins, A-300 and A-400. These resins will be replaced by Purofine PFA-300 and PFA-400. The Purofine line of resins is uniform particle size (UPS). Dow did this a number of years ago when they introduced the Marathon grade of Dowex Ion Exchange Resins. The Marathon line of Ion Exchange resins pretty much replaced the entire line of standard Gaussian resins.

In general there are many advantages to using UPS resins.

Higher Regeneration Efficiency:
According to Dow regeneration is the least efficient step in the ion exchange process. Large beads regenerate more slowly than small beads. The typical Gaussian mesh range is 16-50 whereas UPS resins are 30-40 mesh, a much tighter specification. The UPS resins have a smaller average particle diameter and will regenerate more quickly resulting in more efficient use of regenerant chemicals. So you use less and get a higher operating capacity.

Greater Operating Capacity
The kinetics of the UPS resins is more favorable than that of Gaussian. "This leads to an increase in usage of the entire resin capacity from the top to the bottom of the bed...the net effect of the more efficient regeneration....is higher throughput."

Better Rinse Efficiency:
Excess regenerant chemicals diffuse more quickly from within the beads, thus decreasing the time required to reach the specified endpoint. Faster rinse times trim water and wastewater disposal costs.

Reduced Leakage:
The result of these increased efficiencies is an increase in production of pure water for a longer time since the leakage endpoint is extended

Better Separations for Mixed Beds:
For many years now Res-Kem has been advising customers to use UPS resins in their mixed bed units. In fact, our sister company, General Water Services, uses UPS resins to service their high-purity customers. One reason for doing so is better separation prior to regeneration. With Gaussian resins, the smaller cation beads are easily trapped with the larger anion beads. With better separation you get lower leakages, a better regeneration and greater throughput.

Operating Considerations:
Backwash Rates are lower when using UPS resins. Consult the engineering graphs, Dow Marathon, Purolite Anion or Purolite Cation, prior to installation or contact a qualified equipment manufacturer to determine the changes required when upgrading to Uniform Particle Size resins.

Helpful Links:
I've included a couple helpful links from Dow and Purolite with more detailed information if you'd like to read more about the advantages of using UPS resins in your water treatment system.

Here is information from Dow:
UPS (Uniform Particle Size): The Key to Greater Productivity in Ion Exchange

Here is information from Purolite:
Notice of Product Replacement for Purolite® A300 and A400

Thursday, September 11, 2008

Setting Brine Tank Refill Time on Fleck Softener Valve

The Pentair® Fleck® multi-port softener valve controllers, electronic versions SE, XT, XTR and SXT and non-electronic versions, are very flexible allowing for customization of the regeneration cycle of the water softener. This flexibility requires that you know a little bit about the system and a simple calculation -"Brine Refill Time". Although a simple calculation, "Brine Refill Time" is often misunderstood.

The "Brine Refill Time" is easy to calculate and is the same regardless of valve and controller type.

The following values are based on the design of the softener and valve.

T = Brine Tank Refill Time (minutes)
X = Brine Line Flow Control Rating (gpm)
Y = Salt Dosage sometimes called Regeneration Level (lbs/cuft)
Z = Amount of Resin in Softener (cuft)

In order to set the time you need to know the concentration of saturated brine

C = 2.6 lbs/gallon = Concentration of Saturated Brine

So the equation is:

T = (Y * Z)/(X * C)


X = 0.5 gpm
Y = 12 lbs/cuft
Z = 2.5 cuft

T = (12 * 2.5)/(0.5 * 2.6) = 23 minutes for brine refill step