Case Study - A Fireproof Solution: How Delta Ducon's Rotary Valve Withstood Extreme Conditions at a Texas Utility Plant

1. The Challenge: Abrasive Fuel and Equipment Failure

In 2007, a 305 Megawatt Circulating Fluid Bed Boiler (CFB) plant near College Station, Texas, faced a significant operational challenge. The plant's primary fuel, lignite, a brown coal and the lowest-ranking type of coal, was causing continuous problems for its material handling equipment. Lignite, a material that is abrasive, sticky, and flammable, was being metered into the boiler via a gravimetric feeder. A critical component in this process was a rotary valve, required to isolate the high boiler pressure from the atmospheric feed conditions above.

The plant's existing rotary valves were failing to maintain an adequate seal, leading to significant maintenance demands and frequent replacement. The valves were wearing out prematurely, lasting six months or less, and proving to be an unsustainable, costly liability.

Initially, Delta Ducon was approached to provide a solution but the contract was awarded to a competitor due to a lower initial cost. However, it wasn't long before the plant experienced the very issues they had been trying to solve. Just a few months after installation, the new, lower-cost valves were already wearing out. Faced with the reality of frequent replacement and operational instability, the plant reached back out to Delta Ducon.

2. The Solution: The PERMA/flo™ Extreme Rotary Valve

Delta Ducon's engineering team reviewed the application and confirmed that their 24″ PERMA/flo™ Type “XL” Extreme Rotary Valve was the ideal solution. Unlike many competitor's "heavy duty" models, the Extreme Rotary Valve goes far beyond standard specifications, offering a robust design tailored for severe-duty applications.

The key to the valve's durability lies in its unique construction and advanced material science:

• P-33 Chrome-Iron Alloy: Both the rotor and the seal shoe are constructed from a special chrome-iron alloy called P-33. This alloy has a hardness of 500-600 Brinell. Unlike other valves that use a surface hardening that can wear off, P-33 is a solid alloy casting. This means that the valve's incredible abrasion resistance is permanent and consistent throughout the material, ensuring unparalleled longevity and a dramatic reduction in wear.

• External Adjustability: The "XL" and "XT" series of rotary valves feature a unique design that allows for external field adjustment between the rotor and the seal shoe. This adjustability enables the crucial rotor-to-seal-shoe gap to be maintained, providing the tightest seal possible throughout the life of the unit. As wear naturally occurs, technicians can easily restore the clearances without having to remove the valve from the process line, significantly reducing maintenance time and costs.

• Optimal Clearances: The design ensures tight clearances without allowing the rotor and shoe to come into physical contact. This not only minimizes wear but also maintains the seal integrity necessary to isolate boiler pressure and ensure a consistent feed.

  
  

3. The Result: A Test by Fire and Long-Term Success

In 2007, based on Delta Ducon's expertise and the clear advantages of the Extreme Rotary Valve, the plant decided to purchase one unit for a two-year performance evaluation. The plant committed to replacing additional units if the Delta Ducon valve performed better than the existing models.

Approximately six months into the evaluation, an unforeseen incident provided a dramatic and unexpected test of the valve’s durability. An upset condition occurred at the boiler inlet cooler, causing a fire to spread through the fuel feed chute. It was estimated that the Delta Ducon Extreme Rotary Valve was exposed to temperatures upwards of 1800° F (982° C).

Remarkably, the Extreme Rotary Valve not only continued to operate during the fire but, once the blaze was extinguished, it was inspected and put back into service as if nothing had occurred. This extraordinary event was a powerful testament to the valve's rugged construction and its ability to withstand conditions far beyond its normal operational parameters.

Well over a year after the fire, the single Extreme Rotary Valve required no major maintenance or even an adjustment in its rotor-to-shoe clearances. The plant considered the two-year evaluation a resounding success and, based on this exceptional record, opted to purchase three additional Extreme Rotary Valves.

To this day, the 24″ PERMA/flo™ Type “XL” Extreme Rotary Valves continue to operate with minimal maintenance requirements. Due to their success, this customer has expanded their partnership with Delta Ducon, installing Delta Ducon Pneumatic Sand Transport and Injection Systems and Hydrated Lime Unload and Injection Systems, all of which include the reliable PERMA/flo™ Extreme Rotary Valves. This long-standing relationship, built on performance and trust, showcases Delta Ducon’s commitment to providing robust and durable solutions that exceed client expectations in the most demanding environments.