Type K Drives on Fly Ash Hopper Rotary Gates Save Vast Sums of Money and Time

Type K drive on rotary gate.

A power generating facility in the mid-West just took for granted that purchasing and replacing 40-50 pneumatic cylinders PER YEAR to operate fly ash hopper rotary gates (valves) was normal. The maintenance department just chalked up the expenditure to “normal maintenance” due to this very tough application.

The application requires the pneumatic conveyors, operating under the precipitators, collect the flyash and push into collection bins using compressed air. In this application, pneumatic cylinders stroke full open, and closed, every 90-120 seconds, 24 hours a day, 7 days a week. That works out to around a grueling 720 cycles per day in a dirty, hot, and abrasive environment.

Fly ash is a term used for by-products of combustion and flue gases. Nearly half of this fly ash is reused for purposes such as dry wall production and cement mixes. Because of it's abrasive qualities and high temperatures, fly ash is a difficult material to handle reliably. It's handling takes a particularly tough toll on the valves and drives that control it's movement.

A decision was made to replace the air cylinders with Rotork Type K Series AH damper drives after a visit from a local sales engineer. Along with the new drives, high-cycle “no-play” linkage kits (that eliminate hysteresis) were retro-fitted to the existing ash hopper equipment.

After five years in service, there have been no failures.  Not a single work order has been issued, no spare parts have been required, no seal kits installed and no units have been removed for servicing for any reason. Eliminating the cost of 50 air cylinders a year was quite significant, but even greater was the savings from the time and labor eliminated from their annual replacement.

For more information on this application, or on any damper drive application, visit Power Specialties at http://www.powerspecialties.com or call (816) 353-6550.

Type K Vane Actuator Provides Long Term Solution for Tough Power Plant Application

Rotork K-TORK vane type valve actuators on
bottom ash spray valve control.

Rotork K-TORK vane type valve actuator has solved a difficult flow control application found in many coal-fired power plants – high-pressure bottom ash spray valve control.

High-pressure spray water is used to sluice bottom ash and pyrites from the boilers’ hopper bottoms and to carry the ash out of the plant. The valves used are typically ANSI Class 300 double-offset high-performance butterfly designs ranging in size from 3” to 12”, automated with double-acting actuators. They cycle from four to ten times per day and discharge to atmosphere, creating a very high pressure drop. The flow media is re-circulated ash water that is abrasive and flows at pressures between 400 and 500psi.

In many power plants around the world, K-TORK actuators have provided over 10 years of maintenance-free service whilst preserving the life of the valves and valve seats in these arduous duties.

Among the challenges, it is imperative that the valves close fully and with zero leakage in a high pressure drop state. If the valve disc moves even slightly from the seat, the abrasive, high-pressure water will “wire-draw” or cut the butterfly valve seat. Traditionally, rack-and-pinion or scotch-yoke actuators have been used in this application, but “slop” or hysteresis in the rotary-to-linear conversion allows for the pressure in the pipe to move the disc from the seat, often causing premature failure of the valve after a period of only three to twelve months.

The problem becomes more acute when multiple valves are leaking, lowering the available back-pressure at the header, which makes it difficult or impossible to move the ash from the boiler.

When assembled to the valve with a ‘No-Play’ coupling, the K-TORK actuator has zero lost motion, “slop” or hysteresis. The one-piece vane and drive shaft cannot be back-driven and will hold the disc of the valve firmly in place.

Additional challenges include the location of the valves on a manifold at the bottom of the boiler where space is critical and plant air can be poor quality. K-TORK provides the smallest torque-to-size ratio and the double-opposed lip seal design is forgiving to dirty or contaminated air.

Also, the low-friction performance of K-TORK provides a speed-controlled, smooth valve operation, eliminating the risk of water hammer created by the high pressure drop.

Finally, longer run time between shutdowns demands increased reliability from the equipment in these critical applications. In particular, as the number of plant maintenance personnel has decreased, actuators that reduce maintenance (seal replacement) time and work orders have a direct payback to the owner, especially when valve life can be significantly increased through improved actuator performance.

Failure Prevention: Detecting Hot Spots in Air Cooled Generators

General Condition Monitor
(courtesy of E ONE Utility Systems)

Because of advancements in air-cooled generator designs and their increasingly higher power ratings, significantly greater stresses on materials and structures is increasing the probability of overheating. An early warning system for generator hotspots can mean the difference between a brief shut down for minor repairs versus a major and costly overhaul. The solution is to incorporate Generator Condition Monitors for Air Cooled Apparatus (GCM-A).

High concentrations of sub-micrometer particles (pyrolysis products) are released whenever any material is heated sufficiently to create thermal decomposition. The GCM-A detects the pyrolysis particles emitted into the cooling air (or ambient air) as a result of overheating or arcing.

The GCM-A monitors multiple air sample lines (locations) using a highly sensitive particle detector. The detector used to make these invisible particles large enough to monitor for concentration is a Wilson Cloud Chamber. The Wilson Cloud Chamber has been used and proven effective as an early warning, air sampling type, fire detector for several decades.

One sample line monitors ambient air, which serves as a reference since the particle level in the ambient air can change significantly and influence the particle level of the generator cooling air. One or more additional sample lines (or probes) are used to monitor the generator cooling air, which is compared against the particle level of the ambient air. High particle levels in the generator cooling air, without a corresponding increase in the ambient air, confirms the source of the pyrolysis particles is from within the generator. Conversely, if the particle level in the ambient air increases the source of the overheating must be outside the generator.

A more in-depth review detecting hot spots in air cooled generators can be found here.

To discuss your interest in this application, please contact:

Power Specialties, Inc.
9118 E. 72nd Terrace
Raytown, MO 64133
Toll Free: (800) 432-6550
Phone: (816) 353-6550
Fax: (816) 353-1740

www.powerspecialties.com