By: Steve Blankinship, Associate Editor
Incremental advances in hundreds of technologies and sub-technologies collectively contribute to the ever-increasing performance, reliability and operating efficiencies seen in almost every product imaginable. Power plants are no exception. Meaningful improvements in the way small components operate can have significant impact on the bottom line. Thousands of pumps and valves, lurking and working within the innermost confines of multi-million dollar gas, coal, and nuclear plants, present an excellent example of how lots of little things — and sometimes, even a few little things — can make a big difference in overall results.
Darren Wolz, director of marketing to the power industry for Flowserve Flow Control Division, cites his company’s development of a new anti-cavitation control valve called Multi-Z. “The valve was designed in cooperation with our pump group,” he says. “With this product, we are now able to provide the boiler feed pump and the recirculation valve designed for the exact pump characteristics. Being able to provide a complete solution gives a single point of contact and a guarantee that they are compatible.”
Wolz says one real problem with new power-plant start-ups has been recirculation valves plugging or sticking due to contamination. “If you think about a recirculation control valve,” he says, “its whole purpose is to guarantee a minimum flow to the boiler feed pump. And one of the biggest problems we see at start-up is plugging of that valve. If it’s open but plugged, it can’t provide the minimum flow.”
A primary cause of plugging, he says, relates to operators not getting their lines clean. “We see customers becoming frustrated by having to frequently shut-down the feed pump to clean their strainer and/or recirculation valve, which in the initial startup may take less than a minute. The Multi-Z will continue to provide the minimum required flow because it easily passes solids that plug other anti-cavitation control valve designs.” He adds that the valve lends itself well to peaking applications where the plant is subjected to frequent shut-downs and start-ups because it is designed to transition from low flow to high flow.
Whittaker Controls, a unit of Meggitt PLC, offers a high recovery gas metering valve available in various line sizes and flow profiles used in ground-based gas turbine applications. The Whittaker valve controls fuel flow to turbine combustion systems, allowing gas turbines to operate with a reduced gas inlet pressure, thus potentially improving both turbine and overall plant efficiency. The new valves are hydraulically actuated and subsequent designs will operate with electric actuators. The new design offers low gas pressure ratios with very precise metering for sonic or critical flow conditions.
“Our new High Recovery Valve has been through extensive research, development and testing for more than a year,” says Robert Baker, vice president of sales and marketing for Whittaker Controls. The valve has the potential to increase overall turbine engine efficiency, an important factor in reducing operating costs. “Another important aspect of our new design is that it helps operators reduce the level of emissions,” he notes.
Flowserve’s Multi-Z anti-cavitation control valve. Photo courtesy of Flowserve.
Although valves continue to get “smarter,” smart installation and implementation are still needed to extract maximum performance. John Wilson, severe service manager, Fisher Valve Division, Emerson Process Management, cites field retrofits in hot environments. “The area around bypass valves is very hot. That can impact performance of the positioner and valve accessories,” he says. “It’s possible to retrofit a remote mounted positioner and valve accessories on a pipe stand. That removes those pieces of equipment from the high temperature environment near the valve to ensure accurate performance over time.”
Critical valves in power plants are normally large, requiring a great deal of actuator force to maintain shutoff, says Wilson. Still, they must stroke quickly in the event of a system upset. “In order to stroke the valve quickly, a fair number of volume boosters and other accessories are required, which can lead to a very complex actuation system that can take up to 12 hours to tune per valve.”
Fisher has done a lot of research to reduce the number of accessories needed and improve operating performance while not sacrificing stroking speed. By eliminating non-linear components, the number of accessories is reduced by 50% or more. Eliminating the non-linear components also makes field tuning a great deal easier. “With reduced accessories and improved digital valve positioners, valves can now be tuned remotely from the control room rather than at the valve,” says Wilson. “Step signals can be sent to the valve to monitor performance while gain and damping settings can be adjusted to obtain the optimal performance. These improvements reduce field tuning time down to less than 15 minutes per valve.”
Wilson adds that, historically, some fine tuning of valves, positioners and actuation systems — to minimize problems and assure bypass valves operate properly — could only be made when the plant was totally down. “There are a lot of non-linear components placed into the actuation systems specifically looking at, say, turbine bypass valves that need to open quickly in case of a trip so they are dumping the steam back down the condenser,” says Wilson. “But in order to get that fast stroking speed, controllability is often sacrificed. So if a plant is going through start-up, things may be swinging pretty badly, possibly causing impingement and erosion back in the condenser tubes before any fine tuning can be done. With these improvements, the valves can be tuned much easier while dramatically improving controllability of the system without adding complex actuation systems.”
Knowing What’s Going On
Some of the most dramatic technology advancements related to valves have been in the ability to determine precisely how they are behaving. “Valve diagnostics have been, and continue to be, a hot button at many power plants,” says Wilson. “Diagnostic techniques have helped identify problems without having to tear a valve apart, thereby dramatically reducing the number of valves that need to be torn down during outages. Prior to these diagnostic capabilities, more than 30% of all valves pulled for maintenance were just fine.”
Yet as beneficial as that technology has proven to be, valves have had to be out of service in order to run the diagnostics. “This normally meant that the plant had to be off line before any determinations could be made,” says Wilson. “Therefore, if the plant continued to run, a valve related problem could still bring the plant down and no one would know why.”
As a result, Fisher has spent a lot of time developing on-line, predictive diagnostics. “This allows the diagnostic information to be captured during normal valve operation without impacting performance,” says Wilson.
Information collected is reviewed against a number of internal parameters to determine the health of the valve with the results displayed simply as green light (good), yellow (action is required when possible) and red (immediate action required). Data is collected while the plant is running and is done without sending any test signals to the valve that could interrupt the process.
“For valves that are normally closed, such as turbine bypass valves or pump recycle valves, this type of diagnostic may not be of much use since the valve is normally closed,” he says. “However, our system has a triggered event feature. For example, if a turbine bypass valve is suddenly required to open, the valve will start collecting performance data as soon as the valve moves. This data can be stored at the valve and retrieved at a later date for diagnostic review.”
Flowserve’s newest diagnostic tool is Valtek Scout, an aftermarket asset management tool for Flowserve valves that shows the customer which valves are performing poorly so he can make a tactical decision with respect to a shutdown. “The customer can’t pull all control valves and instruments during a shutdown because today’s economics won’t permit it,” says Gordon Sanderson, business development manager for Flowserve. “He just wants to know about the bad actors. Valtek Scout allows him to do that.”
The product resides on the Honeywell digital control system (DCS), monitoring all valves 24 hours a day looking for particular symptoms. “These are symptoms that have been defined by us at Flowserve because we understand how a control valve misbehaves,” says Sanderson. Flowserve created algorithms populated in Valtek Scout on the Honeywell DCS, and when those algorithm conditions are satisfied, the system flags them and gives the customer a message telling him the situation on the valve isn’t right and needs attention. Thirty symptoms in all have been engineered as fault models — faults manifested in Honeywell’s Asset.Max.
“It is important here to note that these faults are not failures,” Sanderson says. “Rather, they are alerts, directing the user to what’s not right in the process. For example, the system will alert you if a positioner isn’t mounted correctly, linkage is binding or there are air leaks – just to name a few. These problems are not catastrophic, and if they’re taken care of now or in the near future, they will remain small problems. The idea is to assist the customer in maintaining his assets before they become big problems and cost more money.”
Sanderson says the product is unique to the industry. “For years, digital technology has allowed us to collect enormous amounts of data from positioners. What we’ve done with Honeywell is to take a lot of time analyzing the data to cut through all the fog and determine what it really means.”
He gives an example. “This product goes as far as to say ‘your valve is working too hard’ — in other words, exerting excessive effort. That’s a strong indication that something mechanical is blocking the valve. The product can send an e-mail to the appropriate maintenance person along with a work order to resolve this issue. Furthermore, all of our maintenance bulletins are installed on the DCS electronically and with those bulletins are buttons that go to video files we have created on how to change packing gaskets, remove body bolting and reverse an actuator. Your crew will be ready to do it during the next outage because they have seen it done in a movie.”
The product also provides meaningful information without causing undue concern. “You can end up in annunciator panel pandemonium if you want to be alarmed on every single thing,” says Sanderson. The tool lets the customer prioritize alerts with respect to impact and severity on the process, which is translated in the alert manager in terms of size and color.
An actuator air leak on a soot blower valve might be assigned a low priority, meaning it would appear as a very small yellow alarm signifying no great urgency in attention. An air-leak on a boiler feed water recirculation control valve, on the other hand, may be something entirely different with a criticality of 10. “So that shows up as big and red and lets you know you need to take care of it right now,” he says. He emphasizes, however, that all of the valve symptoms are imbedded in the system, so the operator does not have to modify them in any way.
Sanderson says such products represent the beginning of the practical conclusion to such digital technology. “This is what customers are really looking for,” he says.
Cycling Takes its Toll
Dramatic changes in power markets have foisted significant changes in load patterns upon both combined-cycle and coal-fired plants. Those operational changes have translated into wear and tear on valves and pumps. “Many of these plants were initially intended to be baseloaded
and that opens the door for a lot of potential problems,” says Wilson. “With some of these plants, if they go to a low enough load, they have to turn them off at night. That causes turndown issues with the boiler or turbine generator and bypass valves that need to run continuously for three to six hours while the plants are in off-duty time. We have seen the need to retrofit for turndown and have made changes to get the characteristics customers need. It ends up being a retrofit of the entire valve assembly. We usually end up with something brand new.”
Wilson has also seen problems associated with selective catalytic reduction systems. “The flue gas temperature through the SCR has to be in the range of 659 to 680 F, so there is a lot of diverting and bypassing around the economizer to minimize how much heat is taken out of the system so they don’t start to salt up on the catalyst,” he says. “When you start to talk about retrofits for turndown purposes, there are a lot of changes that need to be made in terms of valving and piping to allow the SCR to work properly.”
Pumping Up Pump Sales
PUMP-FLO Solutions, a provider of pump sizing and selection software, and BigMachines, a provider of information technology solutions, have partnered to offer a way for pump manufacturers to streamline selection, configuration, quoting, and ordering for new pumps and aftermarket parts and services. In addition, the joint solution offers advanced sales management, reporting, and analysis tools.
“By digitizing the tribal knowledge trapped in the heads of their sales and engineering teams and making it broadly available, pump manufacturers can make all of their sales channels more effective,” says Justin Johnson, PUMP-FLO product manager. PUMP-FLO and BigMachines are offering their solution as a package to small, mid-sized, and large pump manufacturers who want to accelerate their selling and customer service processes. As the economy improves, many pump manufacturers may face a bottleneck in their quoting processes, which the integrated PUMP-FLO/BigMachines solution can relieve.
Pump manufacturers Crane Pumps & Systems, A.R. Wilfley, and Teikoku Chempump, have already implemented the PUMP-FLO/BigMachines solution and streamlined their inquiry-to-order processes, reducing quoting and ordering cycle times more than 50% while eliminating application errors. In addition, the pump manufacturers now have full visibility into their selling processes and are able to better manage lengthy sales cycles.