Weekly Topic on Synthetic Ammonia: Reasons Why the Cold Ammonia Pump Does Not Deliver Flow and Solutions 2011/11/6--11/12

1: The pump has not cooled down fully: Usually, when cooling a pump, we open the drain at the pump’s outlet to allow liquid ammonia to flow out, and the exhaust pipe freezes as well; however, this does not mean that the pump has cooled down completely, as the temperature of our liquid ammonia is -33 degrees. 2: The minimum flow valve is not in use. The ammonia pump is a multi-stage pump; when its speed increases, if ammonia cannot remove the heat, it tends to vaporize easily. 3: The liquid level at the pump inlet is too low, which makes cavitation likely and prevents the pump from generating pressure. 4: The exhaust from the pump body is not up to standard. 5: The pump outlet heat exchanger hinders the vaporization and transport of ammonia; the heat source of the heat exchanger should be disconnected, the ammonia vapor in the heat exchanger released, or the outlet valve of the heat exchanger closed. Once the pressure rises again, the valve can be opened, and the high-flow cold ammonia will drive the ammonia inside the heat exchanger out. 6: If there is a lot of air in the standby pump, it can also affect the operating pump. When the operating pump is started, the air from the standby pump can be drawn in, causing vaporization in the operating pump. Remove the standby pump inlet valve.

1. Try to increase the pump inlet pressure as much as possible. 2. Reduce the temperature of the medium at the pump inlet. 3. No liquid at the inlet. 4. Leakage in the outlet bypass valve. 5. There is air in the pump body. 6. Safety valve leakage. 7. Check valve leakage.

1. There is not enough liquid in the pump； 2. Excess gas is present in the pump ； 3. The medium temperature is slightly high, making vaporization easier ； 4. The installation height of the pump is not appropriate; it should neither be too high nor too low ； 5. The pipelines before and after the pump, as well as the valves, have poor sealing properties.

The main reason for the sudden drop in the flow rate of a cold ammonia pump when it operates at low speed is that the flow rate is too low to remove the heat, resulting in the superheated vaporization of liquid ammonia at the inlet of one or several stages of the pump. Based on the known design parameters of the unit, it was calculated that under actual operating conditions, when the cold ammonia pump operates at a speed of 2608 r/min, the minimum flow rate required for heat dissipation in order to prevent the liquid ammonia inside the pump from vaporizing is 13.54 m3/h. The minimum flow rate of a pump is the lowest flow limit at which the pump can maintain normal continuous operation; it refers to the minimum safe flow rate at which the pump can function properly when operating at a certain speed, without exceeding the standard limits regarding noise, temperature rise, vibration, etc. The minimum flow rate for centrifugal pumps is defined in two ways in the American Petroleum Institute standard API610: Minimum Continuous Stable Flow (MCSF) and Minimum Continuous Thermal Limited Flow (MCTF).

1. Check whether the inlet filter is clogged. 2. Check whether the pump is running in reverse. 3. Check whether the temperature of liquid ammonia is too high. 4. Check for any localized vaporization. Solution: 1. Reduce the valve opening at the pump’s outlet; check whether the pump’s pressure can still be maintained (if it can, it is likely that the pump itself is fine). 2. After increasing the valve opening at the outlet, if the pump’s pressure drops significantly and the flow rate decreases instead of increasing, and returns to normal as soon as the valve is closed, it suggests that there is a problem with the inlet pipeline. It was abnormal for some time after shutdown; vaporization has been preliminarily confirmed to have occurred. If vaporization occurs, there are two ways to deal with it: 1. Try to increase the pressure at the pump inlet as much as possible. 2. Reduce the temperature of the medium at the pump inlet