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Process Control


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#1 JArchy123

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Posted 27 January 2022 - 08:07 PM

Can someone help explain what the process control equipment is doing for the CH4 and Steam into the reactor? I can see it has some sort of ratio control but I don't really understand the FSL and the I. Also, the valve with the pneumatic signal is labelled HV, from research this could mean a valve for high flow, low pressure or hand valve (which I don't understand how it could be considering that it is pneumatically activated)

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#2 latexman

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Posted 27 January 2022 - 08:47 PM

Flow Switch Low and Interlock.

Hand Valve. Yes, it’s somewhat of a misnomer, but it’s traditional. I’ve seen XV (?) and ABV (Automated Block Valve) and EBV (Emergency Block Valve - closes in a fire).

#3 Pilesar

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Posted 27 January 2022 - 09:46 PM   Best Answer

The 2.7:1 is the minimum steam to carbon ratio to avoid converting too much methane to carbon (coke) and fouling the reactor. The target ratio (from reaction stoichiometry) is 3:1 controlled by FFC-2. The 'I' in the diamond represents an interlock which will take automatic action based upon the measured input limits. In this process, the hydrocarbon feed valve HV-1 completely closes when triggered by the interlock and the fuel valves to the burners are also closed. FSL-1 is 'Flow Switch Low' and also triggers the interlock to close the HV-1 valve when the feed gas flow is below a predetermined limit. FAL is 'flow alarm low' and should give an audio-visual warning to the operators so they can take steps to avoid the automatic shutdown. Once the interlock trigger value is reached, the operator can do nothing to stop the shutdown. The steam valve FV-2 is allowed to stay open when the interlock is triggered so that the steam can try to keep the furnace tubes cool enough to avoid damage. Note the preheat coil in the diagram. The methane and steam do not enter the furnace at the reaction temperature! The preheat coil does not contain catalyst and no reaction is desired there. The mixed feed is heated in the coil against the hot combustion products of the burners before entering the catalyst tubes. PIC-2 controls the draft of the furnace so that the correct amount of air is used in the combustion at the burners. HV stands for 'hand valve' and is often used for on-off automatic valves and other valves where the position of the valve is more important than a process measurement. The HIC-1 'hand indicating controller' to change the position of the fuel valves. AT-1 and AR-1 represent the methane analyzer transmitter and recorder. The firing controls are complicated since it is very important to not have unburned fuel in the furnace which might result in an explosion.



#4 fallah

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Posted 02 February 2022 - 05:29 AM

Can someone help explain what the process control equipment is doing for the CH4 and Steam into the reactor? I can see it has some sort of ratio control but I don't really understand the FSL and the I. Also, the valve with the pneumatic signal is labelled HV, from research this could mean a valve for high flow, low pressure or hand valve (which I don't understand how it could be considering that it is pneumatically activated)

 

Hi,

 

Although mentioned HV, at a glance, appears to be a hand control valve which should be activated manually from control room; but as there is a flow control valve before this HV, it can just be a shutdown valve will be closed when the relevant interlock is triggered.

 

Obviously, if there wasn't a flow control valve before this HV, it could be a hand control valve which can be adjusted manually from control room and at the same time a shutdown valve closed by triggering the mentioned interlock i.e. a combination of a hand control valve and a shutdown valve.






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