How to set up interlocks for vaporizing liquid ammonia using circulating water?
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There is a device that uses circulating water to vaporize liquid ammonia; if interlocking is to be implemented when the vaporization pressure becomes too high, how should it be set up? The supply of liquid ammonia must certainly be cut off, but is it necessary to cut off the circulating water as well? If the circulating water is cut off, the vent should also be opened to allow all the water in the tube side to be drained; otherwise, the continued vaporization of liquid ammonia will cause the water to freeze. If the water is completely drained, won’t the heat exchanger continue to vaporize at ambient temperature? With circulating water, the temperature can be even a bit lower than the ambient temperature – isn’t it better not to do that? The superheaters downstream should not have much impact on pressure, since liquid ammonia has already vaporized into gas in the vaporizer; there’s no need to shut off the steam flow. So when the pressure becomes high, it’s sufficient to simply stop feeding liquid ammonia? I would appreciate it if you could give me some suggestions. Thank you!
Based on your drawings, it is recommended that liquid ammonia be used in the tube side; given the high pressure, it is possible to shut off only the liquid ammonia, or to shut it off along with the steam – the decision should be based on the actual conditions of your installation.
To prevent overpressure, and with the aim of protecting the equipment, it is recommended to select a model with a higher design pressure. In the event of overpressure, once the liquid nitrogen shut-off valve closes, the remaining liquid ammonia in the heat exchanger will vaporize, allowing the equipment to withstand the conditions! Is the steam used for thawing, or is the heat exchanger area insufficient for heating? If the steam is used for heating, the steam valve should also be closed once the liquid ammonia supply is stopped.
This post was last edited by bfdlwolf on 2019-3-26 08:38. A safety valve should be installed at the top of the buffer tank, with its set pressure not exceeding the lowest design pressure among the carburetor, superheater, and buffer tank. There is no need to worry about the interruption of heating media such as circulating water or steam
The circulating water pipeline is equipped only with a manual shut-off valve, in the fully open position； Increase the liquid level in the shell side of the evaporator (the evaporator may need to be raised); use cascade control to regulate the pressure in the buffer tank, that is, the liquid ammonia control valve – evaporator liquid level – buffer tank pressure ； Remote alarm for circulating return water temperature; low-level interlock to shut off the liquid ammonia control valve (or an additional isolation valve) ；
This is a set of operating units, and the heat exchanger has a double-tube design. I think it’s not appropriate to use the double-tube design for allowing liquid ammonia to flow through the tubes; a single-tube design would be better
Steam is superheated gas, used to raise the temperature of ammonia; the feed for subsequent reactions requires a specific temperature. Under normal circumstances, it vaporizes at the circulating water stage. If the liquid ammonia control valve malfunctions and the feed rate is high, the liquid fails to vaporize in time and ends up in the subsequent superheater, which is quite dangerous. So it’s better to cut off the steam, right?
I want to use the safety valve as a final layer of protection; it’s better to have some extra protection in place before the safety valve comes into action
Thank you for your advice:handshake
2 heaters aren’t very reasonable; the steam at the back seems a bit dangerous. Why not use hot water? Adding a kettle-type heat exchanger KUT is sufficient; safety settings can also be added
(1) A safety valve shall be installed on top of the buffer tank, with its set pressure not exceeding the lowest design pressure among those of the vaporizer, superheater, and buffer tank. (2) An alarm for high buffer tank pressure as well as a interlock mechanism for extremely high pressure shall be added: when the pressure reaches an extremely high level, this interlock mechanism shuts off the control valve at the liquid ammonia inlet of the evaporator. (3) Pressure regulation for the buffer tank shall be implemented by adding a flow meter at the liquid ammonia inlet of the evaporator; this, together with the buffer tank pressure, forms a cascade control loop, and the control valve at the liquid ammonia inlet is used to regulate the buffer tank pressure. (4) The control circuit for circulating water flow shall be removed, and a temperature indicator shall be added at the ammonia gas outlet of the vaporizer. (5) No modifications shall be made to the temperature control circuit at the superheater outlet.