Monday, October 17, 2016

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.
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 boiler 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 atmospheric pressure, creating a very high pressure drop. The flow media is re-circulated ash water that is abrasive and flows at pressures between 400 and 500 psi.

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 this arduous duty.

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 a high 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.

Share your fluid control and valve actuation challenges with a specialist, combining your process knowledge and experience with their product application expertise to develop effective solutions.

Wednesday, October 12, 2016

Concentric vs. Double Offset Butterfly Valve

high performance butterfly valve double offset double eccentric with actuator
High Performance Butterfly Valve
(double eccentric)
EBRO Armaturen
Butterfly valves serve a broad range of applications throughout fluid processing industries. Among their positive attributes, quarter turn operation and compact design make this valve type a primary selection for many shutoff applications.

Within the butterfly valve family, their are several basic design subdivisions that are substantial to the point of limiting or expanding the potential application of the valve. One of those subtypes is the double offset butterfly valve.

A general purpose (concentric) butterfly valve, often referred to as a resilient seated butterfly valve, has a disc connected to a rotating shaft. The rotational movement of the shaft positions the disc to fully obstruct the flow path (closed) or provide continuing degrees of open space in the fluid path cross section (open). The rotational movement of the shaft from fully open to fully closed is 90 degrees. The shaft is centered in the pipe bore and is also centered on the disc. This shaft orientation will cause the disc to contact the sealing surface throughout a considerable portion of the rotation nearing closure. This contact tends to accentuate wear on the resilient seat and limits the pressure rating for this type of valve.

A double offset butterfly valve is also known by two other common names, "double eccentric" and "high performance". The "offsets" refer to the position of the shaft relative to the pipe bore and the centerline of the disc. In this valve design, the shaft is behind the centerline of the disc and slightly to one side of the pipe bore centerline. This results in a different travel path for the disc as it moves from the open to close positions. The cam action movement of the disc limits its contact with the seat until the final few degrees of travel. The limited wiping contact of the seat tends to extend its useful life. Additionally, this type of closure movement affords the double offset butterfly valve a higher pressure rating than the concentric design.

Valve selection can be a challenging task, with numerous types and variants from which to choose. Share your industrial valve requirements and challenges with a valve specialist, combining your process knowledge and experience with their product application expertise to develop an effective solution.

Tuesday, October 4, 2016

Wetback vs. Dryback Firetube Boiler

firetube boiler
Victory Energy firetube boiler, Frontier series, will
be available in a dryback version
Differing boiler designs will provide their own array of positive attributes with regard to boiler efficiency, intended use, maintenance burden, and other factors. One distinguishing feature of firetube boilers is whether they are "wetback" or "dryback" design.

Not surprisingly, the difference between these two designs can be found at the "back" of the boiler, the end opposite where the fuel and air are introduced and ignited. The "wet" and "dry" designation indicates whether the firetubes, as they extend to the rear end of the boiler, discharge the hot gases into a reversing chamber surrounded by boiler water (wet) or partially isolated from it (dry).

A dryback boiler has a rear wall lined with refractory. The rear wall forms one side of the reversing chamber on a multi-pass boiler. While the refractory is certainly a point of long term maintenance, its presence as a heat sink has been noted to assist in maintaining setpoint pressure during a boiler off cycle. This tends to lengthen the off cycle of the boiler and provide some benefit. The dryback design will also have appropriately sized access doors or panels on the rear of the boiler to provide for maintenance, thus a space requirement particular to this design.

A wetback (thankfully, also called a water-back) boiler will generally have a reversing chamber constructed of steel that is contained within the confines of the boiler pressure vessel. There will be water between the reversing chamber and the boiler rear wall. Generally, the service access required at the rear of the boiler is less than for a dryback.

Victory Energy manufactures both wetback and dryback boilers in a number of configurations to meet a wide range of needs. Their extreme duty series, designated Frontier, has traditionally been a wetback boiler, but manufacturing of dryback versions is planned. The dryback product range will extend from 50HP to 2500HP and cover applications in the industrial and commercial spaces.

Wednesday, September 28, 2016

Rotork Wireless Valve Monitoring

Components of wireless valve monitoring system Rotork RI
Wireless valve monitoring system
Courtesy Rotork
Rotork, a global leader in valve automation, has introduced a new wireless valve position monitoring system that transmits real-time valve position indication to a central control location. The RI Wireless product line is certified Zone 1 Intrinsically Safe and intended for application in new and existing facilities in process industries and utilities.

In operation, each valve will have a Valve Monitoring Device (VMD) installed on the existing or new actuator using industry standard interfaces. The VMD gathers data from the actuator and transmits it across a network established using other routing hardware that is part of the total system. A software package provides the final connection to a receiving monitor or controller using industry standard connections.

There is more to be learned about the operation and benefits of the wireless valve monitoring system. The document included below provides description of the various devices that comprise the complete system, as well as the benefits that can be derived from its deployment. Reach out to a valve automation specialist and share your requirements and challenges. Combining your process knowledge with their product application expertise will produce effective solutions.

Tuesday, September 20, 2016

Predictive Emissions Monitoring Systems

Fossil fuel burning electric power plant
Predictive emissions montioring can be used for meeting
compliance requirements
Around the world, air quality standards require various levels of emissions monitoring to assure that excessive levels of harmful chemicals are not spread throughout the environment. The monitoring of emissions involves the application of sensors and processing equipment to provide information regarding the amount of specific pollutants discharged by a plant or process.

A continuous emission monitoring system (CEMS) consists of equipment necessary for determining the concentration of a gas or particulate matter, or emission rate, using analyzer measurements and subsequent data processing to provide results in units pertaining to an emission limitation or standard. This type of monitoring system is applicable where required by statute or regulation, but can also be used to provide valuable combustion or process efficiency data to plant operators.

A predictive emissions monitoring system (PEMS) employs an empirical computer model which will relate the inputs of a combustion system (air and fuel) to the emissions produced by the process. Once the model is established for a particular installation, the emissions can be predicted continuously with accuracy in the range of CEMS. There are instances where this type of system will fulfill governmental compliance requirements, in place of CEMS. PEMS can also be deployed as a complement to a hardware based CEMS. Plant conditions and an engineering evaluation will determine the best implementation of emissions monitoring equipment and systems to meet regulatory requirements and provide the level of risk management needed.

Share your emissions compliance and monitoring requirements with combustion and instrumentation experts. The combination of your process knowledge and their product application expertise will produce effective solutions.

Monday, September 12, 2016

Trunion Mount Ball Valves in Double Block and Bleed Assembly

Double block and bleed valve assembly
Double block and bleed valve assembly
Valbart - Flowserve

The nature of some processes, as well as applicable industry standards, can call for a specific valve arrangement that provides isolation of a piping section with a safety factor not inherent in a standard stop valve.

Combined into a single compact unit, a double block and bleed valve consists of two trunnion mounted ball valves and a third smaller valve. While it is possible to employ other valve types in place of the ball valves, the trunnion mounted ball valve is well suited for the heavy duty applications involved in the oil and gas industry.

Each of the ball valves serve to block the process flow and the third valve serves as the bleed or drain valve for the space between the two block valves. Combining both ball valves into a single unit reduces leakage paths, weight, and installation complexity.

In addition to serving as a positive isolation valve set, a double block and bleed is also applied in meter calibration. Calibration of the meters used for custody transfer must be accomplished with a confirmed zero flow rate. Any valve leakage has the potential to impart an offset of the zero value on the meter, resulting in continuously incorrect readings. Closing off the flow with a double block and bleed valve, draining the inter-valve space with the bleed valve, then monitoring the bleed port for any continued flow can confirm zero flow in the metered line.

Share your process piping and fluid control challenges with an application specialist, combining your process knowledge with their product application expertise for the most effective solutions.

Wednesday, September 7, 2016

Liquid Flow Measurement - Magnetic Flow Meters

electro magnetic flow meter flow measurement
Magnetic Flow Meter Assembly
There are many technologies available for measuring liquid flow in industrial fluid processes. Each method has its own set off attributes that will make it an advantageous selection for some applications. A familiarity with those attributes can help you make an effective selection.

Magnetic flow meters, also called electromagnetic flow meters or "magmeters", operate on a very simple principal. An electrically conductive liquid moving through a magnetic field will generate a voltage that is related to the velocity of the liquid. Magnetic flow meters have no moving parts and present little to no pressure drop to the piping system into which they are installed. It is a flow-through device and does require the cross section of the pipe to be completely filled by the subject fluid in order to produce a useful reading.

Some characteristics of magnetic flow meters.

  • Sensor assembly has no moving parts.
  • The subject fluid must be electrically conductive.
  • Measurement reflects fluid velocity and is not impacted by viscosity, density, or static pressure.
  • Other than regular calibration and operational checkout, no maintenance requirements.
  • Produces velocity reading only. Need other inputs to produce a mass flow value.
  • Bidirectional flow measurement is possible.
  • Little or no pressure drop associated with the instrument.
  • Comparatively higher in weight.
  • Accurate measurements require entire pipe cross section to be full of fluid.
There is more to know. A data sheet is included below that details the Azbil Smart Two-wire Magnetic Flowmeter. For even more information, reach out to a process measurement specialist and share your flow measurement challenges. Combining your process knowledge with their product application expertise will lead to the most effective solutions.