Steam & Condensate Introduction
Batch Process Application: Jacketed Kettle ... from Start-Up to Reaching Temperature Set Point Let’s take a detailed look at a batch process application using a control valve to heat the contents of a Jacketed Kettle to a specific temperature. Steam will enter the jacket to indirectly heat the kettle contents through a metal wall. Temperature Controller Steam Control Valve Temp Senso r Vacuum Breaker
Air Vent
The condensate load and pressure drop across the steam trap varies because the control valve will open and close in response to the temperature of the contents inside of the kettle. As the valve opens and closes, the steam pressure and steam flow in the jacket will vary, affecting the differential pressure across the steam trap and condensate load requirements. A Float & Thermostatic steam trap is the primary choice for the majority of process applications because of its ability to quickly adjust to changing condensate loads, as well as having the capability to discharge air from the system.
Steam
Steam Jacketed Kettle
Steam Pressure in Jacket of Kettle
F&T TRAP
DIAGRAM 1: Start-Up (Air Vents Open)
DIAGRAM 2: Steam Enters (Trap Fully Open; Air Vents Closed)
On start-up, jacket is filled with air which must first be dis- charged by the Air Vents to allow steam to enter for heating. Float & Thermostatic steam traps contain a separate thermosta- tic vent, and can discharge large volumes of air present during system startup. Additional air vents may be installed on the kettle. The faster air is expelled, the faster steam can enter and heating can begin.
Once the air has been discharged, steam can fill the jacket. Since the kettle is cool, the control valve will open to allow as much steam as possible to fill the jacket and begin heating the contents in the kettle. The steam trap must adjust to the high condensate load as the steam is entering and building pressure.
Air Vent OPEN Discharges air during start-up
Air Vent CLOSED Steam Temperature Closes Air Vent
Air Vent CLOSED
Air Vent OPEN
Steam
Air
Presence of air prevents heating
Heating begins
Air Vent CLOSED When steam is present
Air Vent OPEN Discharges air during start-up
Air
Steam Pressure in Jacket of Kettle (low pressure)
Steam Pressure in Jacket of Kettle (high pressure)
Air
Control Valve FULLY OPEN
Control Valve FULLY OPEN
Air
Trap Fully OPEN Discharging Condensate
Air Discharging from Process on Start-Up
Temperature of Steam causes Air Vents to Close
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