Static and Unchanging? Think Again!
Editor’s Note: Pump and valve systems are everywhere in electric generating stations and are indispensable to plant operation. Although the basic technology for most pumps and valves has remained unchanged for decades, innovative applications, approaches to problem solving and design modifications keep the equipment from being anything but static. Power Engineering magazine’s editors reached out to as many pump and valve manufacturers as we could to compile this first annual wrapup. If your company is missing from this year’s wrapup, we’ll be happy to include you in next year’s. Simply contact the editors at [email protected]
Retrofit Generates Smooth Power Plant Startup
Duke Energy’s (formally Cinergy) Gibson Generating Station, in Owensville, Ind., has five supercritical boilers that generate 3,157 net MW. Each unit has a motor-driven boiler feed pump primarily used only in emergency situations, and two turbine-driven feed pumps which satisfy feed water demand during startup and normal operation.
But the units didn’t always operate smoothly. Running the motor-driven pump caused frequent pressure and flow surges in the feed water system that upset the unit, even to the point of a unit trip. This extended downtime and caused excessive stress on piping and operating systems.
The units’ control issues were primarily attributed to the boiler feed pump flow control valve. Because the valve’s flow characteristics were non-linear, it would go through abrupt changes in flow at mid-stroke. Control problems also were blamed on the electric actuator. It wasn’t fast enough to respond to feed water flow requirements and it wouldn’t reliably stroke to 100% capacity.
The RAVEN control valve from Copes-Vulcan offers two main innovations: resistance to the effects of blockage and reduction in noise.
Duke Energy’s maintenance crew tried several things over the years. They revised the electric actuator and tried some different trim assemblies, with marginal success. They turned to the valve manufacturer, Copes-Vulcan, an SPX Process Equipment Operation for a solution.
Copes-Vulcan recommended replacing the valve’s trim with its RAVEN Trim Technology. The RAVEN Control Valve design enhances the well-proven labyrinth disc stack type of trim with two main innovations: resistance to the effects of blockage and reduction in noise.
In addition to the trim upgrade from Copes-Vulcan, Duke Energy specified a particular hydraulic/ electric actuator from another manufacturer. The Copes-Vulcan staff worked with the actuator manufacturer to make the project a success.
Retrofitting a valve isn’t as simple as selecting an off-the-shelf part and replacing the old one. Copes-Vulcan engineers helped Duke Energy evaluate their needs beyond what was included in the valve specification sheet. They took into consideration the modifications that Duke Energy’s maintenance staff had made to try to overcome the surge problem on their own. They also worked with the actuator supplier to completely meet the customer’s requirements.
The retrofit allowed Duke Energy’s production team to operate the motor-driven control valve automatically with control of feed water flow for the first time in plant history. The ability to automate the motor-driven boiler feed pump allows the unit to be ramped with the motor-driven pump which was difficult in manual operation.
Now that the valve upgrade has proven successful, the plant is upgrading the remaining four units with retrofitted control valves. “With the new actuator and trim, we can get a lot more flow out of the valve and with the actuator rock solid, we can get 100% flow- every time,” said one plant opeator. “We should be able to pick up lost megawatts on the hottest day of the year.”
Self-Priming Pump for Water Intake Structures
Godwin’s Dri-Prime automatic self-priming pumps are used for water intake structure cleaning, process and storm water bypass, coal pile dust control, turbine flush, lagoon equalization and dewatering, temporary plant fire water service and temporary cooling tower pumps. Capable of handling coal sludge and slurries, bottom ash, fly ash, oil and sewage, the pump series is capable of maximum flows to 10,000 gallons per minute (2,270 cubic metres per hour), heads to 600 feet (185 metres) and solids handling to 5 inches (125 millimetres) in diameter.
Godwin Dri-Prime pumps feature automatic self-priming to 28 feet (8.5 metres) of static suction lift, cast chromium steel impellers for longer life and an oil bath mechanical seal which allows the pumps to run dry without damage. Units are available with a variety of diesel engines and electric motors, stainless steel pumpend construction for high and low ph applications, and hardened impeller and wear plates.
The company recently introduced a new line of Godwin Power generators. These generators team up with any Godwin electric powered equipment including Sub-Prime® electric submersible and Heidra® hydraulic submersible pumps.
LVDTs Measure Valve Position for Steam, Water and Lubricants
Linear Variable Differential Transformers (LVDTs) play an important role in maintaining efficient power plant operations. Most commonly used to measure valve positions in steam and gas turbines, the linear position sensor converts the rectilinear motion of an object, to which it is coupled mechanically, into a corresponding electrical signal, which is used by a PLC as part of a control system. LVDT linear position sensors can measure movements as small as a few millionths of an inch up to several inches, but are also capable of measuring positions up to ±20 inches (±0.5 m).
In a typical steam power plant, the diameter of a steam pipe coming into a steam turbine is about 8 -12 inches (200-300 mm), with valve strokes varying anywhere from 6 inches (150 mm) for some very short ones to 20 inches (500 mm) for the big ones. A typical power plant has a minimum of four valves on each steam turbine, with as many as seven valves. Typically, the four standard valves on a steam turbine include: a reheat stop value, an interceptor valve, a governor valve and a throttle valve.
Plant operators need to know the position of the governor and throttle valves at all times, while position feedback is needed for the reheat stop and interceptor valves at start-up and shut-down. Typically, the valves are fully open or fully closed depending on the start/stop turbine status. LVDTs are used for valve position measurement to ensure proper operation at all times. Many are constructed of stainless steel and rated for operation in extreme temperatures to withstand the harsh environments of steam turbine power plants. When configured with LVDT signal conditioners or ratiometric signal conditioning circuits, LVDTs can provide a complete output system.
Many plant operators buy LVDTs as part of their plant rehabilitation projects. Utilizing LVDTs as part of a control system, operator can improve plant efficiency. For instance, the governor and throttle valves of a steam power plant are modulating valves that might be 25 or 40 percent open, depending on how much power is being generated. The position of these valves depends on the plant control schemes. Typically, the plant has a very highly developed control algorithm, designed to increase operating efficiency and save fuel. For a medium-sized plant, a 2 percent efficiency improvement can translate into a $1 million fuel savings annually. Increased operating efficiency provides a big incentive to update and rehabilitate a power plant with high-performance LVDTs that can provide the correct feedback to ensure optimum plant operations. When used in a control system, LVDTs can increase efficiency by more than 5 percent. In a year’s time, a utility typically can have recovered their expenditures.
In another application within the power generation plant, LVDTs are used to monitor shell expansion, bearing vibration and shaft end-play as part of predictive maintenance activities. In addition to ensuring that the turbine isn’t going to fall apart, plant operators need to keep monitoring plant operating conditions to ensure that there aren’t any undue amounts of vibration in the bearings, which would wear them out. If the bearing starts to wear, operators want to be able to plan a service outage to conduct maintenance rather than have the turbine trip off and shut down, putting the plant unexpectedly out of operation. Typically, LVDTs involved in vibration or case expansion measurement tend to be in the moderate size range: a few inches down to one-half an inch (10-100 mm).
Other sensor configurations include loop-powered 4-20 mA sourcing LVDT position transmitters that provide reliable, contactless position monitoring and feedback of control valves and servo actuators. These sensors can work with a broad variety of servo controllers and PLCs, loop-powered analog or digital indicators and computer-based data acquisition and processing systems.
Many system integrators require LVDTs to work in their multiple-redundancy control systems. These multiple-redundancy control systems ensure that systems stay running and utilities do not necessarily have to stock spares. Operating on a polling basis, the multiple-redundant control systems determine if one sensor’s reading disagrees with others in the system. In these redundant systems, LVDTs typically measure position of steam valves, water level in boilers, and lubricant levels in the bearings. Many of the LVDTs are custom designed to meet customer unique requirements.
It should be noted that while redundant control systems are necessary to ensure ongoing operations, LVDT failures in reality are rare. Any failures that we have observed at Macro Sensors have not been electrical. Because LVDTs for the power industry are offered with core connecting rods, invariably there have been installation mistakes that cause overstressing or bending of the point where the core is brazed to the core rod. Mechanical failures due to improper installation have been documented time and time again.
Electronic Digital Actuator/Stroke Controller
Neptune Chemical Pump Co., Inc. has launched an all digital version of its Electric Stroke Controller, which automatically regulates the flow rate of Neptune Metering Pumps in response to a 4-20 mA DC control signal. The unit also accepts 0-5 VDC and 0-10 VDC analog control signals or can be operated from incremental dry contact closures.
The new actuator features an identical housing structure to its analog predecessor, allowing for upgrade of older pumps. Neptune’s new electronic digital actuator is ideal for power and process industry applications-anywhere that pump flow must be automatically proportioned or varied.
Neptune’s Digital Stroke Controller improves on the older design by simplifying configuration and calibration through use of color coded pushbuttons, LEDs and a single adjustment knob. Both customer calibration and factory default settings are retained in memory even during power failure. Other improvements include additional pre-selected strategies for loss of analog control signal, and eliminating use of limit switches in zero and span (control range) configuration. Increased analog input impedance allows both series and parallel wiring of multiple units from a common control signal.
Available outputs include a two-wire analog position (feedback) signal and four adjustable solid state contact closures to monitor stroke position(s). Unit can be manually operated on power failure.
Rubber Bellow Ring Offers a Slurry Pump Solution
Slurry pumps moving solids-laden fluids in wet flue gas desulfurization systems present difficult and demanding sealing requirements, which challenge typical mechanical seal products. Additionally, these pumps are often large requiring major disassembly to install or repair these seals. This can cost considerable time and money. An alternative to common FGD sealing methods is to use heavy-duty split seals that can stand up to harsh operating conditions, yet be fully split to allow fast and easy installation without having to disturb the pump assembly or its settings.
John Crane’s Type 37FS Series of heavy-duty split seals utilize a rubber bellow compression ring that replaces springs and O-rings commonly used in other split seal designs, giving it flexibility. This clog-resistant component along with both abrasion-resistant silicon carbide seal faces held by shock absorbing rubber parts permits trouble free operation in these slurry services even with severe shaft deflections and shocks. The seal face halves are held together with snap ring-like retaining rings to help ensure alignment. The 37FS Series is available in sizes from 1.375” to 14.000” and can fit metric, custom size and worn shafts.
Pump Line for Turbomachinery Lubricating Systems
Space on the lube oil console is often a constraint. The lubricating pumps are typically mounted horizontally or to save space can mounted in a vertical orientation. The Kral rotary screw spindle pump addresses this by offering multiple mounting configurations on the skid.
High speed machines need to be lubricated prior to start-up and during shutdown, which can take several minutes depending on the size and weight of the rotor. For this reason the pumps are usually driven independently from the machine speed, by electric motors with different power supply: AC for the main pump and DC for the emergency pump. Lubrication has to continue during rotor cool down when cranking is performed at regular time intervals.
Their flow rate ranges from less than 1 to as much as 450 gallon a minute, and discharge pressures to 1,450 pounds per square inch. Their rotating speed is normally that of the 50 or 60 Hz electric motor, which is directly coupled to the pump shaft without the need for a speed reduction gear. Furthermore, these pumps can be also directly mounted on an auxiliary shaft from the rotating machine being lubricated at speeds up to 6,000 rpm, provided a sufficient suction pressure level to avoid cavitation.
KRAL pumps for lubricating
The screw spindle configuration of Kral lube oil pumps produces a low velocity and pulse free oil flow assuring low noise operation and freedom from cavitation. The versatility of these pumps makes them suitable for all lube oil applications.
Leistritz Three Screw Pumps
The evolution of three screw pumps over the last 20 years has enabled the economical and efficient replacement of other misapplied pumps in viscous fluid services. Three screw pumps have one power rotor and two driven rotors. The rotors are hardened and torque is transmitted from the power rotor to the driven rotors via a rolling contact. The pumped product creates a liquid film that prevents metal-to-metal rotor contact.
The rotors run in a liner that acts as a journal bearing providing support throughout the entire length of the pumping chamber. During operation, a liquid film supports the rotors and prevents contact between the rotors and the liner.
Hydraulically balanced three screw pumps do not require thrust bearings or thrust plates, meaning only one bearing is required to position the rotor set. Depending on the service, the bearing may either be product lubricated or external to the pumped fluid and grease or oil lubricated.
Three screw pumps are positive displacement machines (conforming to API 676) that are not affected by viscosity swings. These same viscosity swings normally force centrifugal pumps to operate at some point on the curve other than their best efficiency point, thus lowering the overall reliability of centrifugal pumps in viscous fluid services.
By design, three screw pumps are relatively simple machines with only a few rotating elements: rotor set, bearing and mechanical seal. Since all of the rotating elements of a three screw pump are normally contained in a cartridge, casings are normally fabricated steel. By combining a standard pump cartridge with the flexibility of customized casings, operators can replace misapplied pumps with a drop-in replacement screw pump that does not require any pipe or baseplate modifications.
ANSI Full-Port Ball Valves From Apollo
Apollo Valves offers its new line of three-piece, full-port ANSI Class 600 ball valves, designed to meet the latest industrial codes and standards. Designated the 83B and 86B Series, the new valves are fully rated to Class 600 in every size.
The new Apollo ball valves are available in seven sizes: 3/8”, ½”, ¾”, 1”, 1-1/4”, 1-1/2” and 2”. They’re available in carbon steel, stainless steel, nickel and other alloy body styles, with threaded, socket weld and buttweld end connections.
Apollo three-piece ball valves have a standard configuration that includes RPTFE spiral wound body seals, enclosed stainless steel bolting, multi-piece V-ring PTFE packing and unfilled FDA-compliant enhanced PTFE seats. Other features include a swing-out center section, pressure-balanced solid ball and a unique gland plate that can be adjusted without removing handle or actuator.
Apollo 86B Series valves are equipped with a fully machined ISO 5211 mounting. The body and end cap design includes cast bosses for purge and drain ports. The valves are lockable in the open or closed position.
Apollo can supply the valves with more than a dozen options, including graphite packing, dry assembly, live loading for manual or actuator operation, cleaning for oxygen or industrial gases and extended bonnets.
IQ Pro Actuator Offers Multiple Capabilities
IQ Pro electric valve actuators include advanced data logging features that provide enhanced asset management and predictive maintenance capabilities.
IQ Pro valve actuators are used in a wide variety of power generation applications throughout the world. They are rugged, non-intrusive, double-sealed to prevent the ingress of moisture and dirt, and can be integrated easily into a distributed control system (DCS), supervisory control and data acquisition (SCADA) network, or as a stand-alone local programmable logic controller (PLC) application.
Rotork IQ Pro electric valve actuator and IQ Pro setting tool.
The new IQ Pro actuators store a wealth of historical and current valve operating data on-board, including valve torque profiles, number of operations, valve and actuator positions and other important performance and operational statistics. An operator points an IQ Pro setting tool at the actuator and within 30 seconds or less, the information is transferred wirelessly to the setting tool where it is stored. Then, the operator can download the data from the setting tool to virtually any laptop PC or desktop computer.
Rotork software is provided so you can use the data to manage assets to maximize productivity, monitor valve performance and forecast when valve maintenance might be required and scheduled.
The IQ Pro also features a new large display with text as well as traditional Rotork indication icons for local status and monitoring diagnostics.
Clarkson Slurry Valve Now Available in 60”
Proper valve selection is a significant factor in improving FGD scrubber reliability and is critical to a power plant’s ability to meet or exceed emission requirements. Over the years, power plant engineers have gained great experience with what works and what does not in an flue gas desulphurization (FGD) system.
A 54-inch Clarkson KGA Slurry Valve from Tyco Valves.
Tyco Flow Control has extended the Clarkson KGA size range to 60”. Users may enjoy an opportunity to improve reliability and simplify maintenance of an FGD system. The performance and reliability of isolation valves can affect on-line unit operation. Isolation valves are commonly installed on the large-diameter suction and discharge ends of the scrubber tower pumps. If these valves malfunction, the scrubber tower must be shut down. Many types of valves have been tried before, including conventional and urethane-lined knife gate valves, butterfly valves, ball valves and others. Even modifications of conventional valve designs could not address the issues of this difficult slurry service. The Clarkson KGA slurry valve is generally simple to operate, provides actuation, will not jam or clog and, with two elastomer sleeves, can provide no downstream leakage.
Godwin Pumps, 856-467-3636, [email protected], or visit www.godwinpumps.com
Neptune Chemical Pump Co., Inc., 888-3NEPTUNE or 215-699-8700; [email protected]; or visit www.neptune1.com
John Crane Mechanical Seals, www.johncrane.com
KRAL AG, Lustenau, Austria, +43/55 77/86 644-0, [email protected], or visit www.kral.at
Leistritz Corporation, 201-934-8262, email [email protected] or visit www.leistritzcorp.com/pumps
Conbraco Industries, Inc., (Apollo Valves), 704-841-6000 or visit www.conbraco.com.
Macro Sensors, 856-662-8000, email [email protected] or visit www.macrosensors.com
Rotork Controls, 585-247-2304, [email protected] or visit www.rotork.com.
Tyco Valves www.tycoflowcontrol.com