A new technology is having success in monitoring power plant boilers. Jim Kolbus outlines the system’s journey, from concept and design to testing and bringing it to market
Maintaining accurate and reliable boiler water level indications is crucial
Maintaining accurate and reliable indication of the water level on power boilersà‚ is critical to plant operators and owners.
One of the vital functions for a control room operator in power boiler environments is to continuously maintain a safe operating water level.
The ASME Boiler Code requires an operator to have at least two independent level indicators per boiler that are continuously displayed and monitored.
Boiler level indication systems with conductivity probe technology have played a major role in the boiler industry ever since Clarkà¢€Reliance introduced the first Electro Eyeà¢€Hye level indication system in 1960.
The many years of acceptance and success were due to the reliable concept of conductivity probes being in contact with boiler water or steam.
The system consists of three major components:
1. A vertically oriented chamber that is attached to a boiler drum with piping and contains level sensors (called conductivity probes). These probes (sensors) are located at specified elevations to detect the operating range, from the low level shutdown up to the highest operating water level;
2. The control unit which sends a pulsed signal to the probes in order to detect the level and respond with a corresponding output signal to the remote indicator.
3. An LED Indicator which receives a signal and prominently located for the operator to observe in the control room or operating area. The indicator illuminates green LEDs up to the water level and red LEDs for the steam area above the water. An additional indicator is also often located in the plant near the boiler drum or at the platform area for operator convenience.
Until recently, users of these systems relied on scheduled operating and maintenance procedures that required frequent blowdowns to identify a fault condition or cause. In the past, marginal conditions were not detectable until they manifested into a false indication on the remote indicator.
Blue light = blowdown required
Clark-Reliance’s new SmartLevel system has unique integrated technology that informs the operator with a blue warning condition before an actual fault occurs. The use of a blue warning light is an original concept in this application.
The blue light is prominent and not confused with many other red lighting that is commonly found in control room environments. This system has been in the making for several years. Before designing the Eyeà¢€Hye SmartLevel system, we consulted with a number of system users and specifiers. Our staff interviewed end users, specifying contractors and boiler manufacturers to verify the features they appreciated and desired for this type of water level indication system.
Our research validated the preference for individual circuits for each sensor. This is a significant factor that increases reliability by eliminating the risk of a single component failure from affecting the level that is displayed.
In addition, the ability to predict maintenance and reduce the frequency of operator interface with isolation and drain valves in this harsh environment became a target for us.
Our goal was to provide a system with distinct advantages that would be realized by boiler operators and improve a previously successful system.
Our design team developed this system that actually senses the condition of the sensors, while maintaining the independent circuitry, which has made the Eyeà¢€Hye system commonly specified and installed around the world for so many years.
We created new level detection modules with additional integrated features for testing, time delay, and adjustable sensitivity to accommodate for variations in the conductive properties with the user’s water quality.
In the end, we created a microprocessor-driven brain for each probe that monitors the health of the probe itself. We established a separate dedicated blue indicating light on the module and remote indicator that illuminates only when a probe has become contaminated.
This level of contamination is established when the probe signal crosses a boundary for a specified period of time, but ahead of reaching the state that would cause a false indication.
We chose a blue light because it is more prominent in a control room environment, as opposed to using another red warning light, which may not attract the attention of the operator as effectively.
When the blue light activates it alerts the operator to take action. The first course of action is to conduct a blowdown on the column in an effort to clean the probe in question.
After conducting the blowdown process – which can be done in a matter of minutes – the probe will be cleaned and the blue light will go out. This is especially true if the cause was minor debris on the probe.
The blowdown is effectively a steam cleaning process of the probes. If the blue light remains on after the blowdown, the operator inspects the control unit and observes a prominent blue light on the level detection module that is associated with the contaminated probe.
Conductivity probes are in touch with boiler water and steam
Thus, identifying the specific probe that needs to be serviced is easy. With traditional systems, our maintenance instructions recommended weekly blowdowns, which resulted in frequent activity with the isolation and drain valves. The SmartLevel system advises the operator when the blowdown procedure is necessary.
However, if no signal occurs over an extended period of time, we recommend an occasional blowdown, in order to ensure the connecting piping between the drum and the level sensing column is permitting steam and water to flow freely to the probe chamber.
We also added another helpful feature with white LEDs on the remote indicator to highlight the normal operating level. This aids the operator, especially if they temporarily step away from their work station and find themselves too far from the indicator to read the specific levels. Any deviation from the normal level is easy for the operator to identify and rapidly respond to.
After completing our lab testing and securing the appropriate agency approvals for the SmartLevel, we selected three different sites for field testing.
Our plans included field testing on boilers with a range of operating pressures for a full year, prior to offering the product on the market.
We selected a small package boiler at a water treatment plant (operating at 350 PSI), a major university located in the midwestern US (operating at 900 PSI), and a high pressure application located outdoors at a major power utility in south Louisiana (operating in excess of 2000 PSI). Our field testing at all three sites was a success.
We also offer a precommissioning inspection and training service named SureStart. This field service provides a factory-trained technician on the site for inspection of the system installation and to provide operation and maintenance training to site personnel.
While the SmartLevel system is ‘plug and play’ from the factory, this precommissioning service provides the user with a working understanding of the field-selectable features and eliminates field errors that may affect system operation or go undetected, such as concerns with field wiring terminations or piping.
We also identify any issues that may increase safety, such as chain operators for isolation valves and proper drain piping. We also aid users by identifying any issues that may affect their Code compliance with the level instrumentation on their boilers.
The installed applications for the SmartLevel system range from power to chemical, industrial and steam heating. The system was designed for worldwide use and operates on a wide range of power source voltages from 90 VAC to 264 VAC and operates reliably on a low frequency of 50 Hz.
The system may interface with the user’s distributive control system (DCS) or programmable logic control (PLC) system with outputs from field-selectable switch contacts or the 4 mA-20 mA output signal.
Jim Kolbus is Product Manager at Clarkà¢€Reliance Corp. www.clark-reliance.com