Effective control while de superheating steam is critical to avoid steam losses.
When superheated steam is generated, its temperature has to be brought down to saturation temperatures before it is used to meet the process steam requirements. The most practical way of reducing the superheat value of steam is by the direct addition of water. The potential to reduce the degree of outlet superheat is limited by the capability of control system.
The control system for the de superheater is critical. The cooling water injection into the steam will continue till the temperature falls to saturation. However even after the saturation temperature is reached, due to the delays inherent in the control system, cooling water will continue to flow at the design rate for a short time. In that small amount of time, the saturated steam will condense. This condensing vapor creates a vacuum, which sucks in more vapors, which too continues to condense. This result in loss of control and the downstream processes may be severely affected.
Also the controlled output temperature should not be much higher than the saturated steam temperature. It is absolutely necessary that the outlet steam temperature should be as close as possible to its saturation temperature. The sole reason for this is that saturated steam is the best conductor of heat and as the degree of Superheat increases, the heat transfers become inefficient. In this case, the reduction in the quantity of steam generated during the de superheating process is the direct loss.
Hence Efficient & accurate de superheating is absolutely necessary, which will avoid such losses.