Facebook
Google
GitHub
Linkedin
V
vijay
Boiler drum-level control is critical. Too low a level may expose boiler tubes, which overheats and damages them. Too high a level may interfere with separating moisture from steam, which reduces boiler efficiency and carries moisture into the process or turbine. The drum-level controller maintains the level at constant steam load. There are three options for drum-level control single-element, two-element and three-element drum-level control.
Single-element control is the simplest but least effective form of control.A proportional signal or process variable (PV) signal generates a correction that's proportional to the deviation from setpoint(LT). The output controls the boiler's feedwater valve. Single-element control requires one analog input and one analog output.the o/p of LT is fed as input to valve. depending on the level the valve will operate. Also, the swell effect may render control inadequate.
Two-element drum-level control can best be applied to a single drum boiler if the feedwater is at a constant pressure.Two-element control includes the same level element used for the single-element configuration but has an added steam-flow element that provides a density-corrected mass flow-rate signal to control the feedwater flow. Two elements offer tighter control of drum level. The steam flow acts as a feed-forward signal to allow faster level adjustments. This gives an immediate feedwater response to load changes while the level controller corrects any imbalance between steam mass flow and feedwater flow that arises from Blowdown variations caused by changes in dissolved solids.
Three-element drum-level control is suited for handling variable feedwater pressure or multiple boilers with multiple feedwater pumps. The three elements in this system handle level, steam and feedwater flow. The level and steam elements correct for unmeasured disturbances arising from boiler blowdown, as well as leaks in the boiler and superheater tubes. The feedwater flow element responds rapidly to variations in feedwater demand that arise from the steam flow-rate feed-forward signal and feedwater pressure or flow fluctuations.
Single-element control is the simplest but least effective form of control.A proportional signal or process variable (PV) signal generates a correction that's proportional to the deviation from setpoint(LT). The output controls the boiler's feedwater valve. Single-element control requires one analog input and one analog output.the o/p of LT is fed as input to valve. depending on the level the valve will operate. Also, the swell effect may render control inadequate.
Two-element drum-level control can best be applied to a single drum boiler if the feedwater is at a constant pressure.Two-element control includes the same level element used for the single-element configuration but has an added steam-flow element that provides a density-corrected mass flow-rate signal to control the feedwater flow. Two elements offer tighter control of drum level. The steam flow acts as a feed-forward signal to allow faster level adjustments. This gives an immediate feedwater response to load changes while the level controller corrects any imbalance between steam mass flow and feedwater flow that arises from Blowdown variations caused by changes in dissolved solids.
Three-element drum-level control is suited for handling variable feedwater pressure or multiple boilers with multiple feedwater pumps. The three elements in this system handle level, steam and feedwater flow. The level and steam elements correct for unmeasured disturbances arising from boiler blowdown, as well as leaks in the boiler and superheater tubes. The feedwater flow element responds rapidly to variations in feedwater demand that arise from the steam flow-rate feed-forward signal and feedwater pressure or flow fluctuations.
