On the rationality of an interlocking setup
Thread Content
Process conditions: The material at the bottom of the tower is sent to the bottom pump; fire isolation valves are installed in consideration of fire scenarios. Interlock conditions: 1. The on-site manual valve shutdown button (15 meters away from the pump) is connected to the SIS DI point via hard wiring. 2. DCS soft operation button (Stop). The DO points of the DCS are connected to the DI points of the SIS via hardwiring. Interlock result: 1. Stop the bottom pump; 2. Close the fire isolation valve. Question: Is this interlock (let’s call it an interlock for now, though in my opinion it is simply a manual operation and should not be referred to as such) properly configured? Shouldn’t DCS and SIS be independent? Is it necessary for this interlock to be implemented by a SIS system? (The SIL classification has not yet been determined.) If it must be implemented by the SIS system, should the DCS soft buttons be removed and replaced with SIS soft buttons or hard buttons on the auxiliary control panel? Also, do all of you have an operation station for setting up the SIS system?
1. The settings are reasonable. DCS is process control, while SIS is conditionally automatic interlock. 2. Under safe control conditions, the DCS is capable of opening and closing this valve as well as starting and stopping the motor. Only when a chain reaction is triggered is a reset required to be able to operate again under safe conditions.
Interlocks have no distinction between manual and automatic; there is only a difference between being in use and being bypassed. Manual operation is also considered part of the interlock system
In my opinion: 1. It is inappropriate for the DCS and SIS systems to share the same field devices; the SIS should be an automatic interlock system that is independent of the DCS； Therefore, DCS should not take points from SIS ； 2. It is recommended to set pump shutdown logic and conditions in the SIS
Technically, first of all, I think it is necessary to determine whether interlocking with the SIS system is required. If it’s not necessary, just put it in DCS. If access to the SIS system is required, for SIL1, it is considered that this valve should be equipped with two solenoid valves to achieve separation between the SIS and DCS. Don’t worry about SIL2 and SIL3; they’re all part of the SIS. If process control is desired, add another valve. Based on the above description, I personally estimate that the vast majority of such interlocks are at SIL0\1 level.
Thank you all. For further clarification, this valve is a fire-condition valve – it will only be closed manually in the event of a fire; there are no other interlock conditions.
This one of yours should be sil0; it can be placed in the SIS but not in the safety instrumented system
This post was last edited by tianya3047 on 2019-5-10 22:06. Here, it is designed according to SEI standards: there is a button at both the field location and the auxiliary control panel, which connects to the SIS system. The output DO from the SIS system is connected to the ESD terminal of the electric valve for the field fire shield. Pressing either button stops the pump; once all pumps have stopped and the button remains pressed, the valve ESD activates to close it urgently. It is necessary to set up an SIS operation station, as the production team is unwilling, and the boss also doesn’t want production to stop. It’s not a life-threatening situation; if the situation can be controlled, then a detour can be taken. There is no bypass, and it’s not possible to drive.
From a process perspective, it is advisable to install emergency stop buttons on the auxiliary control panel or on the control valves, as well as on-site emergency stop buttons; these allow for the activation of interlocks in emergency situations, thereby closing the shut-off valves and stopping the pump. DCS control and SIS interlock are developed independently.
An emergency stop button should be installed on the auxiliary control panel, or emergency stop buttons should be provided both in the control room and at the site. It’s not a “control valve”; I made a mistake, sorry