Upgrading power plants gas-fired boiler damper drives. White Paper. A Drop-In-Place solution. Redefining Flow Control

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1 White Paper Upgrading power plants A Drop-In-Place solution by Dean Stedman, Rotork Controls, Inc. Redefining Flow Control

2 Upgrading power plants For today's North American power plants, modernizing a utility boiler presents tough challenges as well as major opportunities. One problem associated with old boilers is outdated and inefficient equipment. No matter how good a maintenance staff is, keeping an aging boiler operational presents a host of daily challenges. In many power utility plants, it's a common problem today that as existing boilers age, the experienced manpower required to operate and maintain the equipment decreases. Add to this the increasing environmental pressure to reduce emissions, and it's clear that upgrading the power plant's utility boiler often surfaces as a top management priority. At first, the challenge of modernizing the instrumentation of an old utility boiler can seem overwhelming, especially when the boiler may have been commissioned in the 1960s. Historically in the U.S., the desired management approach for power utility base load preference has been the domain of large, coal-fired boilers. Now, however, with the recent abundance of inexpensive natural gas, the emphasis has shifted to some degree to modernizing gasfired boilers. With stricter emissions restrictions exerted by the EPA and local regulators, implementing a cost-effective approach to upgrading gas-fired utility boilers makes more sense than ever before. Focus on Damper Drives One major opportunity to consider when exploring the feasibility of upgrading boiler performance is to focus on the advantages associated with retrofitting the boiler's damper-drive equipment. Recent advances in damper drive technology offer a reliable and cost-effective way to make an immediate and significant improvement in operational efficiency and emission reduction. By pinpointing and upgrading key damper drive applications, power plants often can achieve significant improvements in efficiency and reliability. In short, by replacing old damper-drive technology with modern, fast-acting, and precise equipment, a power plant can achieve important increases in the BTU/fuel as well as MW/fuel ratios. Furthermore, new damper-drive equipment can help reduce emissions, improve boiler draft control, and lower fuel consumption. In fact, the latest generation of rotary-vane damper drive equipment provides many features for extremely fast, safe operation. They are easily networked for automated operation and can be set to fail CW, CCW, or last position. Most important, retrofitting old damper-drive technology with new equipment can be surprisingly cost-effective and easy to install. Upgraded Damper Drives Can Help You Meet Today's Regulations for Industrial Boilers Upgraded dampers can assist industrial boiler owners to comply with the EPA's new boiler MACT rules. The U.S. Environmental Protection Agency has published the National Emission Standards for Hazardous Air Pollutants for Major Sources: Industrial, Commercial, and Institutional Boilers and Process Heaters; Final Rule Jan. 31, 2012 in the Federal Register. This regulation affects about 1,700 existing major source facilities with an estimated 14,316 boilers and process heaters. Figure 1. The old, existing equipment including aging damper drives and indicator switches that were problematic. Retrofitting existing dampers with new damper-drive retrofits can provide a better, cleaner burn and help power utilities meet demanding regulations. Furthermore, the Boiler Maximum Achievable Control Technology (Boiler MACT) Rule requires some boiler owners to carry out tune-up procedures either annually or bi-annually. Two major components of the tune-up procedure where modern damper drives directly influence boiler performance are the accurate control of the air-to-fuel ratio and in optimizing CO and NOx emissions. 2

3 Upgrading power plants In this particular situation, the tangentially fired ( T-Fired ) power boiler hosts 12 auxiliary air dampers and 12 fuel air dampers, but the drives were failing in their performance and were simply worn out beyond their service life (Figure 1). Acting in consultation with a major damper-drive manufacturer, plant management decided to install two new, direct-mount, rotary-vane register drives in the spring of 2014 as a test fit (Figure 2). These two pneumatic drives featured a limit switch module for damper position and permissive start-up reading back in the control room. Each drive also included a 24V DC dual-coil solenoid compatible with the plant's existing DCS command system. The test drives performed admirably through the summer of Because of the major improvements that could be realized, plant management quickly approved the funds to retrofit the remaining twenty-two drives in the fall of The benefits of the new drives were immediate. One such benefit was that the new drive equipment saved plant operators from making trips up and down the boiler. Typically, in the past, they were dispatched out to the boiler to work on air connections, changing supply lines to the drives, and dealing mechanically with any sticking drives. Figure 2. Two new-generation direct-mount damper drives were installed as a test to evaluate performance. In addition to the upgraded drives, the retrofit included installation of a windbox bearing upgrade at each damper location. Quite often, the windbox bearing is the source of the problems found with dampers that have binding issues or are frozen in place. Often, this looks like an actuation or instrumentation problem from the control room. Those symptoms contribute to a false reading in the DCS. So, some of the register dampers believed to have a damperdrive problem were in fact frozen in place. Addressing both the windbox damper bearings and the damper drives at the same time is very beneficial to aging boilers. Part of the solution for instrument changes on the boiler relate to environmental constraints both today and those that may arise in the future. The latest generation of damper drives was an ideal choice. These new drives are compatible with the current DCS system so the utility did not need to make any control room hardware or software changes. The register dampers are currently solenoid operated (24 V DC) but are also convertible for positioner upgrade in the event future environmental regulations force the utility to further reduce NOx output. The latest generation of damper-drive design offers that flexibility. Figure 3. As part of the retrofit project, offset mounting designs were required for some structural areas around the boiler. A Real Life Example of a Damper-Drive Retrofit Many power plants in the U.S. and around the world have recognized that upgrading key damper drives in their facilities is a wise business decision. An example follows of how one U.S. power utility plant implemented this strategy. Another important aspect of the retrofit project was the plant's utility staff personnel were able to complete the windbox bearing and drive upgrades without a contractor, using only their own people. The damper-drive manufacturer supplied detail drawings with full installation and operation manuals along with a day or two of on-site assistance for the installation team (Figure 3). 3

4 Upgrading power plants The Drop-In-Place Solution Today, a Drop-In-Place damper-drive retrofit solution is available that precisely fits the new equipment into the existing application with no field modifications (Figure 4). Such a retrofit program provides end-users with a highperformance drive that can be installed without any field engineering or fabrication using basic hand tools in a short time. Existing connecting rods and linkages are reused without modification. With a Drop-In-Place direct-mount or pedestal-mount retrofit drive: The new drive will match the existing drive footprint or mounting surface; The drive shaft and drive lever are in the exact same place relative to the floor mount or direct mount bolt holes; The drive lever will be dimensionally identical to the existing lever and will rotate through the same arc; No costly field design or fabrication is required. Key features of a pneumatic Drop-In-Place damper drive include: Figure 4. Drop-In-Place retrofit solutions are available that precisely fit new damper drives in existing applications with no field modifications. This provided a significant savings to the utility by eliminating outside contractor expenses. Overall, the installation went very well. By installing the two test drives in early spring, the utility was able to create a game plan for the main installation that followed. They installed the remaining 22 drives in about a week. That included removal the old drives, torching out the weathered shaft glands that were part of the original windbox trim, and then welding in the windbox bearing upgrades into place. Once the bearing upgrades were set, the new damper drives were bolted firmly in place. 100% duty cycle, with a continuous modulating service rating of 3,600 starts per hour without overheating; High speed/high-torque, up to 20,800 lbf-ft. with stroke speed as low as 3 seconds full scale; Easily serviced with open-frame design; Excellent in harsh, high-temperature environments; Virtually zero air bleed in the resting state reduced air consumption. Summary Today's latest generation of rotary-vane damper-drives offers power plants an economical and convenient way to upgrade key areas of their existing boilers to improve efficiency, reduce maintenance, and achieve compliance with emission regulations. Working closely with an experienced damper-drive manufacturer right from the beginning can ensure that the entire project and is done quickly and inexpensively. The plant technical service team set the limit switches, installed air headers and flex lines to each new drive. All limit switches and solenoids were then field-wired and marshalled into cornermounted electrical enclosures with flex conduit and wiring. Benefits of pneumatic drop-in-place retrofits Installation of new damper drives can be quick, easy, and provide many important benefits including the following: High speed continuous modulation of ID/FD fan and inlet guide vanes; Improved modulation and control of secondary air dampers; Improved automation and burner management; Quick response to plant demand; 4 Improved reliability in high temperature environments; Precise damper and burner positioning; Simple commissioning and diagnostics; Low running costs, virtually maintenance-free; Wide range of controls system interfaces, including pneumatic, analog and bus network communication. Digital communication compatibility is available for open Fieldbus protocols including Profibus, Foundation Fieldbus, HART, and Modbus.

5 Redefining Flow Control Rotork Controls, Inc. 675 Mile Crossing Blvd. Rochester, NY tel fax PUB _0915 ROWMH0915