Interlock issue between liquid ammonia alarm and spraying device
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There is a spray system installed above the ammonia tank and in use continuously; an ammonia gas alarm is also placed in the vicinity. In the event of an ammonia leak, the spray system will activate automatically. How can this interlocking function be achieved?
It is necessary to use the output terminal on the ammonia gas alarm device (one equipped with a DO output module), or the output DO terminal on the main alarm system unit (depending on the specific equipment of the alarm system), and then use a DCS or intermediate relay to create a control circuit in order to control the solenoid valve for the spray water.
Discuss this with the process team; it may be necessary to manually trigger the spraying after confirmation. Gas probes are unreliable components, affected by numerous factors.
First, you need to figure out what controls the switch for this sprinkler system; for example, it might be a solenoid valve – when powered, the sprinkler is turned off, and when not powered, the sprinkler is turned on. Then, what is the output status of the ammonia gas alarm? (Passive, active, normally open, normally closed?) ), whether there is a reset. If the alarm device can output active normally closed contacts, it is recommended to use 2 on-site detectors to prevent false alarms. The normally closed output contacts of the two alarms are connected in parallel to the solenoid coil; thus, when both detectors trigger an alarm, the contacts open, the solenoid loses power, and the spraying mechanism activates, thereby improving availability.
I believe that due to the current manufacturing techniques and quality issues, more ammonia detectors should be designed, such as 2 or 3 units, using a 2-out-of-2 or 3-out-of-2 voting system; in that case, it will be sufficient to turn on the spray valves. As for what form the contacts take and such, those are minor issues. The interlock logic is also very simple.
The AI signal from the gas detector is sent to the DCS; there is a dedicated gas detection system that sets a specific value – when this value is exceeded, a DO signal is generated to activate the solenoid valve of the deluge valve, thereby controlling its opening