Regarding the issue of equipping liquid ammonia tanks with liquid ammonia transfer pumps
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The liquid ammonia tank (with normal pressure of 0.3 MPa to 1.0 MPa, horizontal type) is equipped with a liquid ammonia transfer pump (a canned motor pump, with pipes leading from the bottom of the horizontal tank). When the pressure in the liquid ammonia tank drops to 0.3 MPa, the liquid ammonia pump is started; however, there is no pressure increase at the outlet of the pump. What is the reason for this? Is there still an issue with the pump selection?
Haven’t seen it before; I’ll pass by and ask the manufacturers of shielded pumps
At room temperature, the saturated vapor pressure is already around 1.0 MPa, which essentially means cavitation occurs.
The liquid ammonia tank (with normal pressure of 0.3 MPa to 1.0 MPa, horizontal type) is equipped with a liquid ammonia transfer pump (a canned motor pump; the pipeline runs from the bottom of the horizontal tank). When the pressure in the liquid ammonia tank drops to 0.3 MPa, the liquid ammonia pump is started; however, there is no pressure increase at the outlet of this pump. After consulting the equipment manufacturer, they indicated that the pressure at the pump inlet was insufficient. When the pressure in the liquid ammonia tank was 0.8 MPa, the shielded pump was started again, but still no pressure increase was observed at the pump outlet. Could anyone please help analyze the reason for this?
If liquid ammonia is not supercooled, it exists in a saturated state when stored in a tank, meaning that its saturated vapor pressure is equal to the operating pressure. In other words, the pump must be installed at a low enough height, or the liquid level in the tank (i.e., its installation height) must be high enough. The net positive suction head is entirely compensated for by the height difference between the pump and the tank. There isn’t enough head difference, and combined with an appropriate inlet pipe diameter, cavitation occurs as soon as the pump starts operating; no matter how high the pressure, it cannot be increased. Whether it is reasonable to use a canned motor pump in this application is debatable; generally, a vane pump or a pump resistant to cavitation would be more suitable.
Cavitation problem! If properly designed, shielded pumps can operate with low cavitation; there is a reverse-circulation type that has a pressurization function – we could discuss this and give it a try