By Jim Montague
Everyone must love valves because they're always trying to help them out. As a result, for a basic and traditional piece of hardware, valves get more attention than your average starlet. Some fans bring technical fixes to the valves and actuators themselves, but more often than not, lately this parade of assistance includes more capable and wireless transmitters, improved diagnostics components and software and many other accessories.
Truth to tell, however, valves get so much affection because their users' applications and continued employment depend on them and because they also wear down, hinder performance and even break with startling regularity. Even valves that are less in the spotlight, such as those in safety or emergency-shutdown settings, usually get regular check-ups and updates for obvious reasons.
Butterfly to Rotary
Sometimes true devotion to valves is expressed in a simple redesign or shift to a new method that better serves a given application. For instance, E.ON's combined heat and power (CHP) plant in Northwich, Cheshire, U.K., used to have problems with backwash flows when air scouring and backwashing the six filters used to pre-treat feedwater for its make-up boiler. The original butterfly valve used in this process couldn't provide a steady flow rate, causing media to be lost through the filters. As a result, the filter media had to be replaced or refilled at an average cost of £3500 a year.
Figure 1: To better clean filters that pre-treat water from the River Dane, E.ON's combined heat and power (CHP) plant in Northwich, Cheshire, U.K., switched from butterfly to rotary valves in its air scouring and backwash process.E.ON's CHP facility in Northwich is one of the largest of its type in the U.K. It generates 130 megawatts of electricity for local residents and can supply approximately 500 tons of steam per hour for two nearby soda-ash (sodium carbonate) production plants. (Figure 1). The feedwater is obtained from the River Dane, cooled and pre-treated to remove any algae or silt, then passed through one of the six filters before being sent to a holding tank.
Consequently, E.ON installed an 8-in. Fisher Control-Disk rotary valve from Emerson Process Management (www.emersonproces.com) to replace its original butterfly valve. Control-Disk's thicker disk profile and true equal-percentage characteristics enable it to adapt to changing process conditions and provide control over a wide range. The valve provides 15% to 70% travel without compromising capacity, which is a big improvement compared to standard butterfly valve designs that offer 25% to 50% of travel.
E.ON adds its new rotary valves dramatically improved its backwash flow control without compromising capacity at peak demand. Since it was installed, the plant hasn't lost any filter media or experienced any downtime due to water filter problems. "The Fisher Control-Disk valve not only controls the backwash flow rate more accurately, but when 100% open, it delivers a flow rate adequate to meet the water plant's demands without restrictions. Its performance and reliability led to savings of £3500 a year and enabled us to improve our customer service," says Neil Price, E.ON's improvement and performance coordinator.
Though necessary to maintain production, profitability and safety, valve redesigns and technical shifts still can be jarring to plant-floor staff, so they understandably avoid them as long as possible. To ease these transitions, K-Tork Actuators and Controls (www.ktork.com) reports that training remains vital to making sure users are comfortable with, believe in and can see improvements from their new valves. "The best way is to ship a new product and send a qualified technician to demonstrate it in the user's own pipeline," says Jeff Butler, K-Tork's field services technician and project manager. "Three or four years ago, I was at Pacificorp's coal-fired power station in Huntington, Utah, where they were changing out 88 actuators and drives on their combustion air control process, and the training impressed their staff with how easy the replacements were to set up. In fact, they were able to do it on their own from the first day. Traditional positions take about 15 minutes to calibrate, but the new smart positioners took about 5 minutes each."
Smarter Means Safer
One of the most significant evolutions in valve technology lately has been its growing links to more sophisticated diagnostics and supporting software via fieldbuses, Ethernet and now wireless networking. And, despite some initial reluctance, these ties are proving they can help valves function better and at least as safely as their traditional counterparts.
Historically speaking, Eric van Gemeren, vice president of R&D for Flowserve's (www.flowserve.com) valve division, says valve actuators and positioners are at an evolutionary inflection point because users are waking up to three major changes in their applications and businesses. "First, many petrochemical and power facilities are losing older technicians, so a lot of diagnostic competency and knowledge is walking out the door," says van Gemeren. "Second, there's more heightened awareness of the need for safety and security in process applications because of recent incidents. And, third, the technology and costs of valve technologies are changing dramatically, so that now it's possible to add awareness affordably to even the simple devices that move valves up and down. This allows more actuators and positioners to be placed in more critical points and then give users more useful information than before. As a result, many actuators and positioners are taking on roles that some operators and technicians used to do."
Likewise, when an automation upgrade project at La Vertiente gas plant in the Villamontes tropical zone in Bolivia required implementation of motorized valve equipment with Safety Integrity Level 2 (SIL 2) certification, the plant's engineers researched and settled on using 31 of Rotork Fluid Systems' (www.rotork.com) spring-return failsafe, quarter-turn, Scotch-yoke, pneumatic actuator packages with mechanical, partial-stroke test capabilities. Owned by BG Bolivia, La Vertiente processes gas from the remote Escondido, Los Suris, Palo Marcado and La Vertiente gas fields, and supplies natural gas and stabilized condensate to YPFB, the country's national hydrocarbon company.
The new actuators are installed on emergency shutdown (ESD) valves in La Vertiente's most critical processing areas. Their applications consist of hydrocarbon condensates and water, leaving the raw gas separators, glycol and hot oil in the regenerator, and natural gas throughout many of these processes, including the gas inlet manifold and the power gas for the compressors. Besides providing La Vertiente with its new, more capable actuators, Rotork also supplied 28 CP-range and three GP-range, SIL 2, actuated-ball-valve packages. These were delivered by Prosertec, Rotork's representative in Bolivia, which also provided on-site support with installation, commissioning and start-up.
Jim Montague is Control's executive editor.