31.What is temperature compensation of direct drum level gauge? How it is achieved and how to operate this provision?

The flow through the normal gauge glass is due to the condensation. This will cause an appreciable drop in temperature in the gauge glass. The density of water in the gauge glass will be higher than that of the water in the drum. Typically, the density of water in the drum will be 0.6 and that of gauge glass is 0.8. Since it works on manometer principle, the level in the gauge glass will be lower than that in the drum.

This suppression of level is known as cold water suppression.

To make the levels equal, it is necessary to maintain the temperature of the gauge glass same as drum water. The drain of the gauge glass will be connected to the down-comer. The continuous flow through the gauge glass created by the drain will maintain temperature. This is called temperature compensation.

More flow of drain will create a low level in the gauge glass. To avoid such condition, the flow shall be regulated. A suitable orifice will be provided in this line. The size will be fixed during commissioning of the boiler.