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RE: Guest


We have instaled antifoam injection control and this the way is controled this system:
Anti-foam agent is pumped  from antifoam tank into a dilution oil, which carries it to the coke drums.  Cooled HCGO pumped  serves as the dilution oil.  The anti-foam agent is continuously circulated  back to the tantifoam tank.  when anti-foam agent is not required at any of the four coke drums.  DCS logic permits the admission of anti-foam solution to a coke drum only when it is on-line receiving heater effluent, or for a configured time period after a drum(s) is taken off-line.  As an additional protective interlock, DCS logic prevents opening of a Coke Drum’s anti-foam valve when a drum’s DCS input indicates the bottom head of the drum is open.
A DCS hand-switch is provided which has two control modes for operation – Auto and Manual.  When in manual mode, the control room operator may manually start and stop anti-foam admission to a coke drum if the DCS permissives are satisfied.  When in automatic mode, DCS logic will start and stop admission of anti-foam solution based on detection of high foam level in a coke drum.  When high foam level is detected in a Drum(s), anti-foam solution is diverted to the anti-foam supply header, the anti-foam supply valve of the drum(s) having the high foam condition is opened, and the MP sweeping steam valve for the drum(s) is simultaneously closed.  Once the high foam level is no longer present, the drum(s) anti-foam solution valve is automatically closed, the drum(s) MP sweeping steam valve is opened, and the anti-foam pump’s discharge is diverted back to the tank
Nuclear level transmitters  are used to monitor the water, coke and foam level of the coke drums.  The different densities of coke, foam, water and air enable the analog signal of the nuclear level transmitters to be calibrated to generate high alarms for water and foam, The DCS compares the measured value against a configured high foam level setpoint to detect high foam level. A high level condition must be detected for a continuous period of 5 seconds before the high alarm and switch action is initiated.  A deadband value of 2% is also applied before the high level switch will de-activate.  When a DCS high foam level switch activates in one of the coke drums the high foam level alarm for that drum is initiated. Additionally, if the Drum’s DCS Anti-Foam hand-switch is in Auto mode, and the Drum’s permissives are satisfied, the DCS will divert anti-foam to the header from the supply pumps, open the Drum’s anti-foam injection valve, and close the Drum’s MP sweeping steam valve by energizing the solenoids as described for Manual operation.  When the foam has been knocked down, and high foam level in the coke drum is no longer detected, the DCS will de-de-energize the Drum’s MP sweeping valve solenoid and de-energize the anti-foam injection valve solenoid to stop anti-foam solution addition to the Drum.  The three way diverter valve solenoid is de-energized only when the DCS logic determines none of the Drum’s require anti-foam solution. 

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