Wireless transmitters improve plant availability and efficiency

09 October 2012

Wireless acoustic transmitters are being used by a power generation company to identify failed steam traps, leaking valves, and boiler tube leaks. The use of these field instruments has provided some impressive cost saving figures.

Barking Power Station, operated by Thames Power Services, is one of the largest independently-owned generating plants in the UK, The Combined Cycle Gas Turbine power station is capable of generating up to 1000MW of electricity. To ensure it remains competitive in the deregulated UK power generation market, operators at the plant need to make continual improvements to increase plant availability and efficiency.

“Improving process performance is all about understanding what is happening around the plant and being able to respond quickly to any problems,” explained Ian MacDonald, senior control systems engineer at Barking Power Station. One way that the company is achieving this goal is to use wireless acoustic transmitters around the plant, where needed, to help identify potential problems.

“Having already installed Emerson’s Smart Wireless THUM adaptors for access to stranded HART diagnostic data in traditional field devices, we were very familiar with the company’s Smart Wireless technology and were confident about using it in other applications,” said MacDonald. “The mobility and flexibility of the battery powered wireless devices also allows us to conduct trials and move devices to different areas without having to lay temporary cables. As a result, we can spot early problems and improve response to malfunctioning equipment – enabling better planning and utilisation of maintenance resources.

“Smart Wireless technology enables us to introduce additional measurement points quickly and cost effectively at any location, so we can gather additional information to identify potential faults.

Key goals
“Key goals for the project were to help improve plant efficiency and to reduce effluent discharge. We also wanted to install a system, which would not require us to cut into the pressure pipework. A clamp-on monitoring solution does not require us to recertify the system for safety and it means we can quickly and easily redeploy the transmitters as required. Because we have integrated the system into our DCS we have instant visibility, allowing operators in the control room to see exactly what the acoustic device is seeing.”

To improve identification of failed steam traps and problem valves, Barking Power installed 35 of Emerson’s Rosemount 708 wireless acoustic transmitters across the plant. Should a steam trap fail or a small leak begin, the acoustic device will transmit changes in sound and temperature, which are configured to alert operators of a potential problem. The plant began gaining the benefits of the new devices immediately, as a leak from a high-pressure super heater steam trap was identified that would have cost £1,400 for every 24 hours of lost operation.

“The steam coming out of the bottom of the boiler is super heated to 508°C. A small knock out pot takes out any residual condensate. The level probe in the pot has a tendency to fail ‘on’ continually reading that there is water in the pot, resulting in the valve remaining open which means we are losing steam that translates to a loss of efficiency,” said MacDonald. “If the valve is jammed open we also lose steam during shutdowns resulting in lost pressure,” he continued. “In order for the plant to start up more efficiently, we need to keep the boiler hot and up to pressure so we can bring it online quicker which allows us to be ready to generate power when needed. If the boiler loses pressure when in standby we go from a hot state, through a warm state, to a cold state. When in a cold state it will take around an hour longer to start up the plant.

Additionally, a further 15 acoustic transmitters have been employed to monitor other problem areas around the plant, including vent valves that can stick during start-up and pressure relief valves that do not seat correctly. Previous manual monitoring was not only time-consuming but also failed to indicate when or why a release occurred, increasing the chances of a safety, regulatory, or environmental incident. The new wireless devices enable precise monitoring and alert operators when valves have opened for as little as a single second. “With an acoustic transmitter strapped onto the body of a valve we are able to monitor the acoustic trend to ensure the valve is working properly,” said MacDonald.

Using networks already in place
Using the wireless networks that was already in place has allowed, additional devices to be added at much lower cost than if they had to be wired-in individually. This provides Barking Power with additional opportunities where monitoring was previously cost prohibitive – for example identifying blockages in venturi eductors.

MacDonald explains in more depth yet another application for the acoustic transmitters: “Potentially, debris can stick to the water that we pump in from the River Thames for cooling purposes. This can leave the ball valve stuck in the open position and discharging water into the cooling water pit. In the past this problem was dealt with by sending an operator to the pit during start-up to monitor the situation. This used up valuable manpower at a time when operatives were needed elsewhere around the plant and was not a good use of our resources. Now, five acoustic transmitters are fitted onto the cooling water plant to allow us to remotely detect a sticky valve, If a problem is detected an operative can be sent to sort out the problem, giving us a much better overall use of our manpower resources.

“I would estimate that the overall savings from the use of these wireless transmitters around the plant, in the first 60 days of implementation alone was in the region of £16,000. Since then we have saved a further £20,000 on one further application alone. I consider the transmitters to be the plant’s baby monitor…They tell us when the plant is crying!”

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