Application Success

Pall Ultipleat High Flow technology helps reduce boiler tube failures

Problem
A coal fired, two unit generating station had been experiencing a high rate of boiler tube failures, peaking at 10 failures. The 260 megawatts unit equipped with a Westinghouse turbine/generator, was driven by 2.5 million pounds of steam/hour at full load, with a CE tangentially fired drum boiler. The root cause of the failures was determined to be under deposit corrosion and hydrogen damage and that the metals forming the deposits originated from the pre-boiler system.

Metal transport at start-up can be 100 times that of the on-line metal transport. At the station sited above, for metal transport, three days of start-up is equal to one year of on-line operation. The element service life is typically eight to ten months with on-line operation, or two cold start-ups. The transported metals were mostly in particulate form.

Solution
To reduce metal transport, the decision was made to install equipment to control the particulate contaminants on both units, as well as make some chemistry changes.

Results
The Ultipleat High Flow filter vessels were installed between the condensate pump and the first feed water heaters. The design and high flow capabilities of the elements maintained the clean element pressure drop at 3 psid, with a terminal pressure drop of 40 psid. The vessels were used continuously to trap as much metal as possible.

The reduction in metal transport has virtually eliminated the under deposit corrosion problems that the second unit was experiencing. For 14 months, the second unit did not experience one forced outage due to a water wall tube failure.

Uniform flow and improved pleat stability

The characteristic feature of the Ultipleat construction is that the fluid flow is uniform across the entire filter medium surface since the flow channel is the same width and length on both sides of the pleated filter medium. This uniform flow is maintained, even with high differential pressures across the element due to the filter’s unique upstream support and downstream drainage layers. These layers, which sandwich the filter medium, hold these flow channels open. Lastly, the pleats are held in place and prevented from deforming by the external helical wrap that is bonded to each pleat tip along the outer diameter of the cartridge.

The unique pleat design extends element life while maintaining superior solid contamination removal efficiency.

The tapered pore filter medium combines excellent dirt capacity with low pressure drop. The absolute rating of the elements, and their integrity in challenging environments result in precise and consistent water quality.

Compared to conventional elements with triangular shaped pleats, they have non-uniform flow through the filter medium (highest flow at the bottom of the triangular pleat).This irregularity in the flow can cause inconsistent particle removal.

Often, the drainage and support materials used in conventional pleated filters are thin and structurally weak. Consequently, pleats can be pushed together in groups resulting in low flow through these grouped regions and shortened filter element service life.

Result:
Uniform flow distribution yields

• Maximum filter life
• Reliable particle removal characteristics
• Low resistance to flow for longer periods of time

Typical duplex configuration for Condensate CRUD removal.

Corrosion products in the condensate are primarily iron oxides, but also can include copper and nickel oxides which are mainly present in the form of suspended solids downstream the condensate pumps.

Sample sections of Ultipleat High Flow filter medium at 500X magnification.

Table 1

¹ The test procedure used is an adaption of ISO 4572, modified to determine the micron size above which particles are quantitatively removed.

² Pressure drop in psig per USgpm for the cartridge length shown. Multiply this value by the total system flow to determine the aqueous pressure drop. Next for fluids other than water, multiply this value by the fluid viscosity (in centipoise) at the operating temperature. Divide this calculated pressure by 3. This will determine the number of filters required to have a 3 psig/(0.2 barg) pressure drop across the filter elements at start-up. This value is the pressure drop across the Ultipleat High Flow filter(s) only-it must be added to the pressure drop due to the Ultipleat High Flow housing to determine the total system pressure drop.

³ 99% efficiency.

⁴ Filters rated by Maximum Spherical Particle Passed test.