by Robin Hudson, Rosemount Level Product Manager, Emerson Automation Solutions
An interesting case history from a 600 kW coal fired power plant in China has implications for any safety-critical environment. This application involved drain pot alarms on super critical steam lines.
As you know, any liquid entering a steam turbine will cause damage. This is costly and even more important, can be dangerous to personnel due to the extreme temperatures and pressures involved in the steam turbine. Generally, steam pots (also called condensate traps or steam traps) are used on steam lines to drain off condensate before it can enter the turbine. These drain pots use level sensors to detect high levels of condensate buildup and then open valves to discharge it.
The problem that arises, however, is that the extreme temperatures and pressures in the steam lines can cause many level detection devices to fail. The plant in China had been using float switches but their performance was found to be unstable over 2900psi pressure and 932˚F. Components had to be replaced frequently. In addition, the devices had no self-diagnostics or status outputs so the operators couldn’t detect when the floats might fail or if they were working properly. This high and unpredictable failure rate increased maintenance which added costs and upped the chances of a significant accident.
To resolve the issue, the plant replaced all of their float switches on the supercritical steam lines with Mobrey Hydratect 2462 Water and Steam Detection Systems. Unlike most detection systems, the patented-design Mobrey Hydratect 2462 functions reliably in steam/water detection environments up to 4350psi pressure and 1,040˚F – easily accommodating the requirements of the Chinese plant. In addition, the electronic controller gives a visual indication and relay output to indicate steam, water or a fault condition. Extensive self-monitoring within the system assures that any component failure results in a fail-safe condition.
To sum up the benefits of using this type of detection system, the Mobrey Hydratect 2462 lets you –
Reliably detect water or steam in lines, columns, and condensate pots
Eliminate the need for routine testing through superior reliability
Prevent turbine water damage with Turbine Water Induction Protection (TWIP)
Saves time with self-checks that make routine testing unnecessary
Configurable steam/water thresholds adjustable according to water quality
The combination can significantly reduce maintenance costs, and even more important, greatly improve protection of people and property.