A sudden increase or decrease in steam flow changes the pressure in the steam drum and boiler circuit. The increase and decrease in the water level caused by the pressure change are commonly referred to as the swell and shrink reactions.
What is the difference between swell and shrink?
Shrink–swell is the volume change that occurs as a result of changes in the moisture content of clay-rich soils. Swelling pressures can cause heave, or lifting of structures, whilst shrinkage can cause settlement or subsidence, which may be differential.
What is 3 level drum control?
Three-element Control: Disturbances in drum level are caused by fluctuations in main steam flow. 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.
What are the three level control in ECC?
This arrangement is called “Three Element Drum Level Control” (3E) because the algorithm uses level, BFW flow, and steam flow.
What is swelling effect?
Swelling is the result of the increased movement of fluid and white blood cells into the injured area. The release of chemicals and the compression of nerves in the area of injury cause pain.
What is boiler shrink?
Dynamic shrink/swell is a phenomenon that produces variations in the level of the liquid surface in the steam drum whenever boiler load (changes in steam demand) occur. This behavior is strongly influenced by the actual arrangement of steam generating tubes in the boiler.
How is swell factor calculated?
Calculating the percentage change in height from the wet soil to the dry will give you a measure of the swell factor of the soil. For example, if the dry soil was 1 inch high and the wet soil is 1.54 inches high, divide 1 by 1.54 and multiply by 100 to get a 65 percent swell factor.
Why is shrink swell important?
Shrink/swell potential is the relative change in volume to be expected with changes in moisture content, that is, the extent to which the soil shrinks as it dries out or swells when it gets wet. Shrinking and swelling of soils causes much damage to building foundations, roads and other structures.
What is boiler drum control?
The purpose of the drum level controller is to bring the drum up to level at boiler start-up and maintain the level at constant steam load. A dramatic decrease in this level may uncover boiler tubes, allowing them to become overheated and damaged.
What is combustion control in boiler?
Overview. The boiler combustion control system is designed to maintain a proper air/fuel mixture under varying load conditions and within safe limits. The system should provide nearly complete fuel combustion as efficiently as possible. Discussions here are limited to oil and/or natural gas fired industrial boilers.
What is dynamic shrink/swell in a boiler?
boiler swell Dynamic Shrink/Swell and Boiler Level Control – Control Guru Dynamic shrink/swell is a phenomenon that produces variations in the level of the liquid surface in the steam drum whenever boiler load (changes in steam demand) occur. This behavior is strongly influenced by the actual arrangement of steam generating tubes in the boiler.
What is swelling in a boiler?
Hence the formation of bubbles inside the boiler makes the level of water looks like increased (which in reality is not there) in the water gauge glass. This phenomenon is known as swelling. For single-element control, it will close the feed check valve or feedwater control valve (FCV) when it was required to be opened.
How to reduce shrink and swell effect in a steam turbine?
Thus to reduce shrink and swell effect, the various control strategies are used (Two Element control using steam flow as feedforward , Three Element Controls using fast feedwater control loop) with proper tuning. Hope this clarifies your query. S. Elavazhagan.
What causes steam volume to increase in a boiler?
Bruce. Swelling is caused by a volume increase of the steam phase in the risers of a boiler. This increase in volume can come from two sources: 2- Drum pressure drops causing the steam volume to increase because PV=nRT.
