Drum protection in power plant

The drum is one of the important pieces of equipment in the power plant. The drum is used to separate the produced steam from the boiled water. And the drum level is one of the important parameters that need to be controlled for the safe operation of the plant. Hence there are many kinds of protection that are activated through logic solver and physical equipment. The list of instrumental used to monitor the drum level is given below.

• Differential pressure level transmitter
• Hydrastep
• Level gauge

Level protection

The DP level transmitter is taken at both sides of the drum to increase the level of protection. And mostly three transmitters are used based on (2oo3) logic to enhance safety and prevent unnecessarily boiler trip due to transmitter failure.

Hydrastep is one of the reliable methods to measure the drum level nowadays. And its failure rate is very low. In DP type level measurement the actual signal has to be compensated to obtain a correct level. Because the drum undergoes shrinking and swelling effect due to load change. In such condition, Hydrastep is one step ahead in measuring the correct level. It consists of an electrode installed throughout the tapping point, when the electrode comes in contact with the drum water resistance will increase and when in contact with the steam resistance will be less. This change indifference is sensed by the controller and display a level.

And for additional protection Level gauges are installed to help operators physically check the drum level. Nowadays by using CCTV technology for remote viewing of drum level.

Pressure protection

Pressure is another important parameter need to be controlled all the time during the process. Every piece of equipment is designed to withstand particular pressure above that limit it may lead to a disaster. The pressure transmitter and gauges are installed to monitor the drum pressure locally and remotely.

And addition mechanical protection is installed to avoid failure in case all control loops failed. A pressure relief valve will be operated if the setpoint is reached and exhaust the steam safely into the atmosphere thus pressure will back to normal.

Blow down and dosing

As the drum keeps on receiving water and separating steam from the water. The impurities like silica and phosphate will get deposit in the bottom of the drum. To remove that a blowdown is given to remove the impurities. And chemical dosing is given regularly to maintain the silica and phosphate level in the drum. Normally trisodium phosphate is injected for this process.