Can ammonia absorption refrigeration replace ice machines?

The problem is that the operation of ammonia absorption refrigeration systems is very complex! Ammonia absorption refrigeration, which was used in many devices, has been replaced by compression refrigeration.

This post was last edited by Chemical Gas Purification on 2010-12-29 at 10:17. Ammonia absorption refrigeration requires a large amount of heat; if you have such heat available, you might consider using ammonia absorption refrigeration as an alternative to ammonia compression refrigeration. I have operational procedures for ammonia absorption refrigeration that I developed myself, and I hope they can be helpful to you. Operating Procedures for Ammonia Absorption Refrigeration System – Section 1: Basic Information on the Position I. Tasks of the Position The task of the ammonia absorption refrigeration system is to take the gaseous ammonia delivered from the NHD decarburization ammonia cooler, and through processes of absorption, distillation, and condensation, to liquefy it back into liquid ammonia, which is then sent back to the ammonia cooler in the purification unit. This provides the cooling capacity required for the solution circulation in the NHD decarburization unit (1.7 million kal/hr). II. Scope of management: ⑴ Distillation tower ⑵ Reboiler ⑶ Condenser ⑷ Liquid ammonia storage tank ⑸ Separation after the reboiler ⑹ Solution heat exchanger ⑺ Subcooler ⑻ Ammonia cooler ⑼ Non-condensable gas separator ⑽ Absorber ⑾ Concentrated ammonia water storage tank ⑿ Ammonia water pump ⒀ Vacuum filter ⒁ Ammonia water storage tank; as well as related electrical equipment, instruments, pipelines, valves, and safety facilities. Section 2: Process Principle The ammonia absorption refrigeration system is a cycle that uses ammonia as the refrigerant; gaseous ammonia is absorbed by dilute ammonia water in the absorber, and the ammonia-water mixture exiting the absorber is pressurized by an ammonia water pump before being sent to the distillation tower. Heated in the bottom heater of the distillation tower, the ammonia gas with a certain pressure released from the ammonia solution is converted into liquid ammonia after condensation. After being sent to the ammonia purification cooler to cool the NHD decarburization solvent, liquid ammonia turns into gaseous ammonia and is recycled back to the ammonia absorption refrigeration unit to participate in the cycle. Ammonia absorption refrigeration unit, with the heater heat source provided by low-temperature gas. In ammonia absorption refrigeration, the gaseous ammonia produced by evaporation is absorbed in the absorber by dilute ammonia water. The resulting concentrated ammonia water is then subjected to pressure-driven heat exchange before entering the distillation tower. The ammonia gas and water vapor that are vaporized as a result of heating are purified through distillation, and subsequently enter the condenser where they are cooled by water to be converted back into liquid ammonia. Liquid ammonia loses temperature through throttling expansion without any work input; it then exchanges heat with the NHD decarburization liquid in the ammonia evaporator, evaporating into gaseous ammonia to enter the next cycle. The refrigeration process is divided into high-pressure and low-pressure systems. The low-pressure system includes: the tube side of the subcooler, the absorber, the concentrated ammonia tank, the underground ammonia tank, and the non-condensable gas separator. The high-pressure system includes: a distillation tower, a solution heat exchanger, a condenser, an liquid ammonia storage tank and the shell side of the subcooler, as well as a purified ammonia cooler. The purpose of using a low-pressure system is that the temperature at which liquid ammonia evaporates is related to pressure; the lower the pressure, the lower the temperature. As shown in Table (1) below, the heat absorbed during ammonia evaporation (the latent heat of vaporization) is related to the evaporation temperature – the lower the temperature, the greater the latent heat, meaning more heat is absorbed, resulting in better cooling effects. The detailed parameters are listed in the following table: Table of saturated vapor parameters for liquid ammonia. Temperature (°C), Pressure (kg/cm2 absolute), Latent heat of vaporization (kcal/kg). Temperature (°C), Pressure (kg/cm2 absolute), Latent heat of vaporization (kcal/kg): -50, 0.417, 337.9; 5, 5.259, 297.3; -45, 0.556, 334.6; 10, 6.271, 292.8; -40, 0.732, 331.3; 15, 7.24, 288.3; -35, 0.950, 337.9; 20, 8.714, 283.5; -30, 1.219, 324.5; 25, 10.225, 278.7; -25, 1.546, 321.0; 30, 11.895, 273.6; -20, 1.940, 317.5; 35, 13.765, 268.3; -15, 2.41, 313.3; 40, 15.85, 262.9; -10, 2.966, 309.7; 45, 18.166, 257.2; -5, 3.619, 337.9; 50, 20.727, 251.3; 0, 4.379, 301.5. Therefore, in a low-pressure system, it is necessary to reduce the temperature of the absorber as much as possible, lower the concentration of dilute ammonia solution, increase the flow rate of this solution, and promptly remove inert gases in order to keep the system pressure as low as possible. The purpose of setting up a high-pressure system is to facilitate the liquefaction of gaseous ammonia as well as its purification. As can be seen from the table above, a higher pressure allows the temperature at which gaseous ammonia condenses and turns into liquid to drop accordingly. This not only helps to reduce the amount of cooling water required, but also lowers the water vapor partial pressure in the gaseous ammonia, thereby improving the purity of the liquid ammonia. Therefore, the temperature in the cooling section at the top of the tower must be strictly controlled. Section 3: Brief Description of the Process Flow The gaseous ammonia coming from the purified NHD decarburization unit (at a temperature of -17°C and a pressure of 0.22 Mpa) is cooled by the liquid ammonia in the shell side of the cooler, causing its temperature to rise to 23.8°C; thereafter, it enters the absorber through 6 separate streams. The temperature of the dilute ammonia solution in the absorber is 46°C, with a concentration of 18.5% (wt%). Inside the absorber, this dilute ammonia solution absorbs gaseous ammonia; at the same time, the circulating cooling water in the absorber removes the heat generated by this absorption process. After absorption, the temperature drops to 36°C and the ammonia concentration rises to 34%, after which the solution enters the storage tank for concentrated ammonia. It is then pressurized to 1.7–2.0 Mpa(G) by a pump, with a flow rate of 45 m3/h. After heat exchange with the dilute ammonia solution coming from the bottom of the distillation tower (at 150°C and 1.6 Mpa(G)) in the shell side of the solution heat exchanger, the temperature in the tube side rises to 120°C. The solution then enters the upper part of the packed bed in the distillation tower, and feeding is carried out in the stripping section. There is one layer of perforated corrugated structured packing in each section of the distillation tower. In the tower, concentrated ammonia water exchanges heat with the ammonia vapor rising from the bottom; gaseous ammonia continuously escapes, and after mass transfer with the reflux stream at the top of the tower, it becomes gaseous ammonia with a purity of 99.8% (wt%), a temperature of 46–50°C, and a pressure of 1.6 Mpa (A), after passing through the cooler at the tower top. After being condensed in the condenser, gaseous ammonia turns into liquid ammonia, which is collected in the liquid ammonia storage tank. The operating pressure of this storage tank is 1.6 Mpa (A). To maintain the operating pressure of the distillation tower, an adjustable vent valve PICA8002 is installed on the gas ammonia pipeline at the top of the tower; by adjusting the pressure in the distillation tower, the non-condensable gases generated as a result of absorption can be released through the non-condensable gas separator, thereby ensuring the purity of the gaseous ammonia. A TIRC8005 control valve is installed on the water supply line of the distillation tower top cooler; by adjusting the flow rate of the circulating water, the purity of ammonia in the gas exiting the tower is maintained. Liquid ammonia is pressurized by the pressure in the liquid ammonia storage tank and sent to the shell side of the subcooler where it exchanges heat with the purified gaseous ammonia to be cooled; thereafter, it is sent to the ammonia cooler in the NHD decarburization unit (at a temperature of 16.9°C and a pressure of 1.6 Mpa). The two-low pressure gas coming from the purification and conversion section, after heat exchange and water separation in the boiler of the regeneration tower in the NHD desulfurization section, enters the tubes of the boiler in the distillation tower of the ammonia absorption refrigeration unit; there it exchanges heat with the ammonia-water inside the tubes, resulting in a temperature drop to 164°C. After water is removed using the boiler separator, it is sent to the deionized water heater in the conversion section to heat the deionized water. The non-condensable gases at the top of the distillation tower enter the non-condensable gas separator through a gas collector; after residual gaseous ammonia is absorbed by spraying dilute ammonia water, they are released into the atmosphere. To remove the absorbed heat, liquid ammonia is introduced into the coiled tubes of the non-condensable gas separator jacket; the evaporated ammonia merges with the purified ammonia and enters the absorber. Section 4: Process Parameters I. Pressure Ammonia in absorber: 0.12 MPa (G) Distillation tower: 1.6 MPa (G) Ammonia in cooler: 1.6 MPa (G) Liquid ammonia storage tank: 1.6 MPa (G) Outlet of ammonia water pump: 1.7–2.0 MPa (G) Cooling water for absorber: 0.35–0.45 MPa (G) Cooling water for cooler: 0.35–0.45 MPa (G) II. Temperature Ammonia before subcooler: -17°C Ammonia entering absorber: 23.8°C Dilute ammonia water entering absorber: 46°C Concentrated ammonia water leaving absorber: 36°C Concentrated ammonia water in the shell side of the solution heat exchanger: 120°C Dilute ammonia water at the bottom of the distillation tower: 150°C Ammonia gas leaving the top of the distillation tower: 46°C Liquid ammonia in cooler: 40°C Liquid ammonia leaving the subcooler: 16.9°C Low-temperature gas entering the reboiler: >164°C Low-temperature gas leaving the reboiler: 115–120°C Inlet temperature of cooling water for absorber

This post was last edited by Chemical Gas Purification on 2011-1-23 at 08:33. The ammonia-water absorption refrigeration technology is now quite mature, allowing for fully automatic control; the operation can be carried out by just one person per shift. If you have any needs in this area, feel free to contact me. lgtsjt@163.com

This technology is fully mature; all that’s needed is to prepare a small accident ice machine. For starting and stopping the vehicle.

Theoretically it’s okay, but in practice it’s not as convenient as using an ice machine.

This post was last edited by Green Grass Walk on 2010-1-3 08:50. Is the cooling capacity 1.7 million calories per hour? How much heat is required for the reboiler? If heating with 1.05 MPa steam is used, how much steam is required approximately? What is used to calculate the required heat?

This post was last edited by Chemical Gas Purification on 2011-1-23 08:35. I have visited the units produced by Yunjie Chemical; aside from their larger size, their operational stability, refrigeration efficiency, and energy savings are all superior to those of ammonia compression refrigeration systems. It also serves to purify ammonia at the same time. There is no oil contamination in liquid ammonia as in the ammonia compression refrigeration process.

If you have excess low-pressure steam available, ammonia absorption refrigeration can be used to replace ice machines; however, the ammonia absorption refrigeration system is more complex than ice machines, and if very low temperatures are required, an additional small compressor might be necessary.

Ammonia absorption refrigeration is also one of the good refrigeration methods nowadays, and an ammonia compressor driven by a turbine is also a good option. Traditional reciprocating ice machines are somewhat inferior; ammonia absorption refrigeration can completely replace them. If it is a turbine-driven ammonia compressor, it’s best not to make any changes.

This post was last edited by Chemical Gas Purification on 2011-1-23 08:36. Under what circumstances should the principles of mass balance and energy balance always be followed? As for whether the ammonia synthesis process can replace chillers with ammonia absorption, it depends on the process conditions and equipment status on site. I carried out similar technical modifications in 1992; it can be said that removing the chiller is closely related to process conditions, ambient temperature, cooling water temperature, and the operating conditions for ammonia absorption. For technical upgrades, it is necessary to conduct calculations for material balance and energy balance.