What does a typical ammonia plant start-up sequence include?

• A. Immediately charge maximum refrigerant and start all equipment at once.
• B. Shut down all systems and restart from cold.
• C. Rotate fans to the highest setting and monitor for noise.
• D. Check safety systems; purge non-condensables; start compressors in sequence; verify pressures and interlocks; gradually bring online evaporators.

Answer: (D)

Safe startup of an ammonia plant is a staged process that validates safety systems, clears non-condensables, and brings equipment online in sequence. First, checking the safety systems ensures all interlocks, alarms, relief paths, and ventilation are functioning before any equipment is energized. This protects personnel and equipment from unsafe conditions right from the start. Next, purging non-condensables removes trapped gases and air that can raise pressures, hinder heat transfer, or create hazardous conditions, so the system can reach proper operating boundaries cleanly. Then compressors are started in sequence rather than all at once. This controlled ramp prevents compressor surge, reduces electrical inrush, and allows the control system to monitor suction and discharge pressures, oil flow, and overall stability as load is introduced. Verifying pressures and interlocks afterward confirms that the system is within safe, expected limits and that protective devices will respond correctly if something drifts out of range. Finally, evaporators are brought online gradually to match the commanded load, avoiding sudden pressure or temperature swings that could stress equipment or cause unsafe conditions. This thoughtful, stepwise approach prioritizes safety, equipment protection, and steady, predictable operation—essential in ammonia refrigeration where hazards and high pressures demand careful control.