Most power plants were built for basic operation
Credit: Emerson Process Management
Four major challenges for power plants today are cycling operations which can lead to accelerated equipment damage, minimizing heat rate, reducing emissions, and improving personnel productivity to tackle expertise shortage, writes Jonas Berge
Most power plants were built with minimum instrumentation for basic operation. Due to the high cost of automation in the past, power plants were not instrumented sufficiently to meet today's demands on reliability, energy efficiency and productivity, or to meet new health, safety and environmental regulatory standards.
Much of the maintenance inspection in power plants is manual. Energy is wasted by steam loss and inefficiencies. Not all air and water emissions are checked. Imagine instead a power plant full of sensors that continuously monitor the condition of pumps and fans, detecting failure of steam traps or leaking relief valves, and where all emissions are monitored. Instead of operators collecting the data, the data comes to the operators.
Power plants are being modernized with a pervasive sensing infrastructure for a second layer of automation. This is a new strategy for maintenance, energy efficiency, risk reduction and optimization using sensors which require no wires and are mostly non-intrusive and therefore can easily be deployed. Specialized diagnostic software in a separate system distills the raw sensor data into actionable information, such as which equipment needs service and which does not.
Wireless sensor networks and analytic software are new technology trends enabling new levels of availability, energy efficiency, environmental compliance and productivity. Pervasive sensing infrastructure is the basis for the Internet of Things, which will take sensing even further in the future.
Applications already deployed include analyzing thermal efficiency, detecting steam trap and relief valve failure, improving mercury removal from flue gas, heat recovery steam generator (HRSG) outage planning, detecting water intake filter plugging, managing fuel inventory, preventing coal stack fires, improving fire-fighting system integrity, valve diagnostics, pump and fan condition monitoring, water balancing, leak detection, wastewater pond selenium reduction, ash landfill leachate pumping, and more.
Power plants have hundreds of pieces of equipment that must be maintained in good condition to ensure plant availability. It is hard for the maintenance and reliability teams to keep up.
In certain regions, power plants are often forced to cope with cycling operation because of the variability of renewable generation. This increases thermal and pressure stress, in turn accelerating potential equipment damage. This puts increasing demand on the reliability and maintenance departments to ensure availability.
Power plants have a machinery protection system on the steam turbines and gas turbines. However, equipment like pumps, fans, lube oil coolers, condensers, and cooling towers do not have any condition monitoring. For this second-tier yet essential equipment, plants rely on periodic spot checks with manual data collection using portable temperature and vibration testers, perhaps with the intention of weekly rounds - but, due to increasing demands on resources, the actual rounds may be monthly or even longer. This leaves the plant vulnerable between testing and is a labour-intensive method of data collection.
Improved maintainability is one of the goals for a smart power plant. A pervasive sensing infrastructure based on a second layer of automation enables reliability and maintenance engineers to monitor the condition of assets from a central location. Vibration monitoring is part of this.
A wireless vibration transmitter is another way to monitor vibration on second-tier rotating equipment, serving as an intermediate tool to complement online machinery protection systems and portable vibration testers.
Wireless vibration transmitters provide automatic data collection and software does the monitoring, saving time and improving productivity. A wireless vibration transmitter is less expensive than a machinery protection system and can be used when a full-fledged machinery protection system is not required; it is also much easier to deploy.
Many vibration points are often unreachable for manual data collection with a portable tester because fans are mounted inside protective enclosures to ensure personnel are not injured. Wireless vibration transmitters are being adopted quickly for those applications where it is not possible to collect vibration data manually due to the dangers of rotating equipment.
Traditional reliability engineering focuses very much on vibration, but vibration monitoring alone is not enough because it doesn't detect other problems with equipment. Multi-parameter condition monitoring is about observing measurable properties for signs of internal fouling or faults.
Additional wireless sensors for equipment pressures, temperature, flow, fluid levels, position, pH and conductivity provide data on operating process and ambient conditions, allowing other problems like fouling, scaling, leaks, etc to be detected. Combining highly instrumented assets with analytic software creates an early warning system that can be easily understood and does not require an expert analyst to interpret. Some modern condition monitoring software uses dedicated analytics algorithms for each type of equipment. WirelessHART (IEC 62591) is the industrial wireless sensor network used in these applications.
More frequent equipment condition data automatically monitored by software improves the data analysis to capture developing issues in the early stages rather than later, when damage or outright failure and shutdown have already occurred. This results in improved equipment reliability, and therefore in reduced unscheduled plant downtime.
Maintenance costs can be lowered by reducing preventive maintenance and scheduled downtime and moving from reactive repairs to predictive maintenance. Moreover, by knowing which equipment needs overhaul and which does not, plants may be able to schedule their outages more effectively, extending the time between outages and making them shorter.
A power station in the US state of Connecticut had issues with remote pumps freezing in cold weather, damaging the pump. Manual inspection rounds were too slow to catch the problem. Wireless transmitters were deployed to monitor the temperature, saving $20,000 in repairs for each incident avoided.
A power plant in Korea had issues with cooling water and lube oil pump failure caused by vibration. They had the same problem on their draft fans. Wireless vibration transmitters were deployed to capture developing vibration problems before they led to failure.
A generation station in Minnesota also had vibration issues in its feed-water pumps and motor bearings, and ash buildup on fan blades. By deploying wireless vibration transmitters, problems were detected early.
A rotating biomass pre-combustion chamber at a power plant in Poland had issues developing hot spots, damaging the chamber walls. Earlier 4-20 mA temperature transmitters used slip-rings which proved unreliable. By instead using wireless temperature transmitters, the reading was reliable and the plant avoided damage to the chamber walls.
Another US power station had issues with pumps overheating. Manual data collection rounds were too infrequent to capture the problem in time. Wireless temperature transmitters were deployed to provide timely information, saving the plant $20,000 for each avoided failure.
On a condenser in Canada, software now calculates heat balance to detect leaks using measurements from wireless transmitters. This enables leaks to be repaired during the next shutdown to stop losses and potential rupture.
There are many other examples from the power industry around the world where wireless sensors deployed throughout the plant have helped the maintenance and reliability teams keep the equipment running, for instance vibration measurements taken on coal pulverizer bearings to prevent running to failure.
Lube oil cooler leaks are traditionally uncovered through field operator rounds to read gauges to prevent overheating of oil, which will cause wear on other equipment. This can now be automated with wireless temperature, pressure, and flow transmitters.
Similarly, wireless temperature and multi-temperature transmitters on oil and windings are used to avoid overheating and transformer failure. Other applications include deploying wireless Differential Pressure (DP) transmitters on water intake strainers/screens to detect blocking, thus ensuring adequate cooling water supply. Lastly, vibration monitoring on conveyor belts for coal and ash is another potential area where power plants can detect problems before they lead to costly repairs.
A vibration sensor and transmitter on a pump in Korea
Credit: Emerson Process Management
Lots of equipment in a power station must also be looked after to ensure heat rate performance. It is hard for the performance team to keep up the energy efficiency.
Minimizing heat rate is an industry-wide concern. The performance team has traditionally used periodic inspection and manual data collection to detect water leaks, steam leaks, cold air leaks, and hot air leaks as well as plugged filters, scaling on tubes, and other issues affecting heat rate. This is time-consuming and labour-intensive, and therefore may not get done as frequently as desirable. Losses can go undetected for long periods of time.
A pervasive sensing infrastructure based on a second layer of automation for performance monitoring throughout the power plant enables the performance team to detect leaks and inefficiencies much sooner.
As a result, heat rate can be improved and sustained over longer periods of time. The consumption of treated water, compressed air, gas, electricity, and steam (WAGES) around the power station can also be reduced.
For example, power plants in China and the UK had issues with treated water leaks. They installed ultrasonic flowmeters with wireless adapters with software for water balancing to identify the losses, pinpointing which units may have leaks.
Power stations in both Malaysia and the US had problems with plugging of turbine air filters, which affected efficiency. Wireless differential pressure transmitters now detect plugging, allowing cleaning to improve turbine efficiency to be scheduled, while at the same time optimizing the use of resources and minimizing scheduled downtime.
The performance teams at a Mexican power company and an independent performance testing company in India had long setup times for the sensors and data used for turbine efficiency testing. By instead using wireless transmitters the setup time was reduced, allowing the teams to perform 10 per cent more services.
A power plant in Nevada was challenged by heat recovery steam generator (HRSG) outage planning - to decide when cleaning should be scheduled, which tube bundles need cleaning, and which did not. Wireless multi-point temperature and differential pressure transmitters were installed to provide the data required to make these decisions. As a result, the plant restored capacity by more than 1 MW.
Steam trap leaks and relief valve passing caused inefficiencies in a UK power station. Wireless acoustic sensors were installed to detect these leaks, saving the plant an estimated four tonnes per hour in steam loss, at €1400 ($1500) per day.
In a generating station in the US, the cooling fans were not turned off when not needed, or ran at unnecessarily high speeds, leading to excess cooling capacity and electricity consumption. Wireless transmitters measure tower riser temperature, providing the ability to calculate efficiency to determine that cooling fans are running at the correct speed. Fan quantity and speed can be optimized for reduced power consumption.
Other issues at the station included cooling air leaks from forced draft fans. Leaks are now detected using a wireless pressure transmitter, resulting in reduced fan motor usage and extended fan life. Hot air leaks on the turbine compartment are now detected using wireless temperature transmitters.
Health, safety, and environment (HS&E) is an important focus for the industry. Injuries, fires etc must be prevented. It can be difficult for the HS&E team to ensure regulatory compliance.In particular, the industry is working hard to reduce emissions to comply with ever more stringent regulations to safeguard the environment and health in nearby communities. Manual data collection around the power plant increases the exposure of personnel to risk of injury.
A pervasive sensing infrastructure based on a second layer of automation throughout the power plant minimizes manual data collection and enables the HS&E team to detect hazards and emissions more quickly. As a result, injury and incidents can be reduced and regulatory compliance can be assured.
By deploying wireless transmitters, personnel safety is improved as it minimizes the time operators have to spend in potentially dangerous areas to manually collect data.
Power plants are also reducing safety hazards. For example, coal-fired power plants in China and Finland need to monitor temperature rise in the coal piles to avoid coal stack fires. The monitoring process was improved by placing wireless temperature sensors on poles that could easily be shifted from depleted piles of coal to new coal piles to detect temperature rise, and thus avoid fires.
A power station in Florida wanted to ensure the integrity of the combustion turbine (CT) fire protection system, and therefore deployed wireless Pressure and DP transmitters on the CO2 tanks.
Ensuring compliance with ever more stringent environmental regulations is an ongoing challenge, but the industry has already innovated many clever monitoring solutions that help ensure they are in compliance. For instance, a generating station in Florida, US had to demonstrate that the temperature of the cooling water discharge was within limits to minimize impact on aquatic life. Wireless multi-point temperature transmitters are used at the cooling water discharge to demonstrate compliance with the regulation.
A power plant in the western US needed to see the temperature profile of its boiler to optimize the chemical reaction that allows the flue gas scrubber to remove the mercury more efficiently. This was achieved using wireless multi-point temperature transmitters, thus ensuring compliance with environmental regulations.
A power station in North Carolina needed to monitor selenium content in the effluent wastewater from the flue gas desulphurization (FGD) selenium reduction cells to the retention pond. Wireless ORP transmitters measure the percentage of selenium to ensure compliance with regulations.
The same plant had to monitor the ash landfill leachate pumping. This was achieved by deploying wireless discrete I/O transmitters to indicate the status of automatic pumps and provide water level alarms. Magnetic flowmeters with wireless adapters were installed to measure and totalize flow. Wireless transmitters are now also being installed at the ash pond to measure level and pH.
Many tasks around the plant are still done manually because most power plants were built with minimum instrumentation for basic operation due to the high cost of 4-20 mA wiring, marshalling, system I/O cards, etc.
Moreover, the power industry is struggling with an expertise shortage as older workers are retiring. Attracting and retaining new talent can be a challenge. There is a need to increase personnel effectiveness and productivity.
Manual data collection is a low value-added activity. Spending the time analyzing the data and correcting the issues uncovered would be far more valuable. Manual data collection has a number of known issues. There is typically a 3-5 per cent parallax error depending on each operator's viewing angle, making data trends less reliable. Moreover, there is a tendency among operators to not go out to collect data in bad weather, but instead to copy previous data, maybe changing the last digit. Sometimes operators may be too busy to collect data. By not collecting data, an early warning may be missed.
A pervasive sensing infrastructure based on a second layer of automation throughout the power plant automates data collection. This results in reduced field operator rounds and provides greater situational awareness for the console operators.
For example, a power plant in Poland had manual temperature check points at many levels on a boiler which is approximately 100 metres tall, equivalent to a 27-storey building. Wireless single and multi-point temperature transmitters were installed to instead collect the data automatically, saving personnel a tremendous amount of time.
A power plant in Florida was modernized by installing wireless temperature transmitters to monitor stack temperature. Fuel inventory management was also automated with wireless DP transmitters for monitoring the debris filters and radar level and multi-point temperature for diesel tank inventory, resulting in fewer field operator rounds.
A Canadian wireless DP flow transmitter
Credit: Emerson Process Management
Existing power plants can be modernized by deploying WirelessHART sensor networks. This enables the maintenance, reliability, performance, HS&E, and operations departments to deploy sensors at will.
This typically starts small, with ad hoc solutions to improve availability and productivity or monitor heat rate and emissions. Wireless applications have a tendency to 'go viral' as soon as other departments see how easy wireless is to deploy, and realize what it can do for them. When a critical number of applications have been deployed and proven, plants tend to tie the wireless infrastructure together as a plant-wide WirelessHART network.
New power stations now being designed and built should include plant-wide WirelessHART infrastructure from the very beginning. The WirelessHART gateways use standard industrial network technologies like Modbus and OPC to interface with any historian or control system the plant may use. Once the WirelessHART network is in place, the power plant is well-equipped to face new challenges as they develop, such as being able to tackle increased cycling operation, higher fuel cost, new environmental regulations, or manpower shortages.
WirelessHART is a wireless sensor network technology supported by multiple vendors, ensuring a broad spectrum of sensor types to meet the measurement needs of plant modernization. WirelessHART uses a multi-hop, full-mesh topology where every device can act as a repeater. This means a single WirelessHART gateway at the edge of each plant unit can handle all the WirelessHART sensors in that unit without wiring multiple backbone routers. This makes WirelessHART lower-cost and lower-risk to deploy than other wireless sensor networks.
Not designing a new power plant or modernizing an existing one for maintainability, performance monitoring, emission monitoring and situational awareness sets the stage for gradually worsening heat rates and a reactive maintenance and environmental culture. Therefore, make sure budgets for maintenance & reliability, performance, HS&E, and productivity are incorporated into the project prior to kickoff and for the coming years. Work with an expert who is well-versed in pervasive sensing solutions to audit your existing plant or new plant design to identify which solutions are recommended and to get an estimate of the cost, potential savings and ROI for your plant.
Jonas Berge is Director of Applied Technology at Emerson Process Management