What is a three element control system?

A three-element boiler water level control system is one which typically uses the measured water level, the steam flowrate from the boiler, and the water flowrate into the boiler to regulate the flow of water into the boiler.

What is three element control system in boiler?

The “three element control” in boilers stands for the three control element, each measuring an individual process variables; Flowrate of boiler feed water. Flowrate of steam leaving the boiler. Liquid level inside steam drum.

What is 3 level drum control?

Three-element Control: Figure 1 shows a typical drum level controller, which measures the drum level (1), main steam flow (2), and feedwater flow (3) and manipulates the feedwater control valve to regulate the drum level. This is three-element control.

What is the difference between single element and three element level control?

The three-element mode is used during high steam demand. The two-element mode is used if the steam flow measurement fails and the module falls back to single element level control if the feedwater flow measurement should fail or if there is a low steam demand.

What are the three inputs used in 3 element control valves in a feedwater system?

The following three inputs are required for implementing 3-element BFW control:

  • Steam drum level.
  • Boiler feed water flow.
  • Steam flow.

What is shrink and swell in boilers?

The increase and decrease in the water level caused by the pressure change are commonly referred to as the swell and shrink reactions. The swell and shrink reaction is in the opposite direction to the normal behaviour of the boiler process.

Which three parameters are used for controlling the boiler drum level?

The combination of drum level measurement, steam flow measurement, and feed flow measurement to control boiler drum level is called three-element control.

What are different elements used in boiler drum level control?

Three element Drum level Control

  • Steam flow rate feedforward signal.
  • Feedwater pressure or flow fluctuations.

What is starvation in boiler?

Steam pipes that are undersized cause high pressure drop and result in steam starvation at the point of usage. Steam Manifold. Smaller diameter piping connects the steam header to a steam manifold. The manifold serves as the branch point for supplying the individual heating circuits.

What is silica in boiler water?

Silica is the only boiler water salt which vaporizes at pressures below 2400 psig. It can vaporize at pressures as low as 400 psig. This has caused deposition problems in numerous turbines. The solubility of silica in steam increases with increased temperature: silica becomes more soluble as steam is superheated.

Why phosphate is added in boiler?

Boiler feedwater can be protected from corrosive conditions through coordinated phosphate/pH control treatment. Phosphate buffers the boiler water, reducing the chance of large pH swings due to the development of caustic concentrations.