Deaerator for ammonia (NH3) refrigeration systems
Air in the refrigeration system raises the condensation pressure and makes the system a power hog.
Every operator of an industrial refrigeration plant knows that this accounts for the majority of its energy consumption. Since most of the engines are powered by 3-dig- it kW engines, every hour the engines are idle is worth a lot of money.
The use of a breather only makes sense for NH3 refrigeration systems in the deep-freeze range, which means that an evaporation temperature below -33 ° C prevails.
(The fact that the air is properly evacuated from the system for new refrigeration systems and for maintenance purposes is taken for granted here, meaning that this air entrapment is not discussed here.)
Where does the air come from?
If ammonia (NH3) were left open in a container under atmospheric pressure, it would have a temperature of about -33 ° C. In a closed refrigeration cycle, with an evaporating temperature below -33 ° C, the system operates under reduced pressure. No matter how small a leak on the suction side, air is permanently sucked into the system. This clarifies where the air comes from and why it is constantly multiplying.
The air is conveyed via the suction line through the compressor to the high pressure side and thus migrates into the condenser. It remains there now because air can not be liquefied or condensed.
Where air is, there can be no ammonia gas.
This means the air "claws" with its presence condensation surface in the condenser. As a result, the usable capacitor area becomes smaller and smaller.
A small condenser, which can no longer dissipate the heat sufficiently to the environment, leads in logical consequence to a higher condensation temperature and an increasing condensation pressure. As the condensing pressure increases, the drive motor of the compressor must do more work due to the higher differential pressure between suction and high pressure. More compressor work means more power consumption. This results in higher energy costs.
On the other hand, the higher pressure gas temperature due to the increased condensation pressure leads to an increased thermal load of the lubricating oil and thus to a reduction in lubricity. The oxygen content in the air also causes the oil to age prematurely.
In order to ensure perfect function and economic operation, the air has to be permanently removed from the system.
At which point of the refrigeration system does air collect?
At which point of the refrigeration system does air collect?
The air that enters the refrigeration cycle accumulates in the condenser where it is coldest and where the slightest gas movement occurs. Practical experience shows that the best way to collect air via a small attached dome at the condenser outlet is to have it vented. (Image)
But even in the subsequent pipelines or in the refrigerant collector itself can be vented.
For any refrigeration system, this venting port must be carefully selected and specified to ensure optimal venting. In case of doubt, several alternative connections should be provided, which can then be controlled alternately by means of solenoid valves.
The working principle of a deaerator
In order to separate refrigerants, especially NH3 and air, the different density of the gases is used. In contrast to air, NH3 can be liquefied even at relatively low pressures. Air, however, remains longer in the gas state.
In the deaerator, which builds on this principle of density differences, the air-refrigerant mixture is cooled down as much as possible, so that the main amount of NH3 liquefies.
The liquid refrigerant is returned to the refrigeration cycle, while the air with the lowest refrigerant content is drained via a water trap (open water tank).
Compared to a hand-vent, in which up to 50 g of refrigerant per kg of air can escape to the outside, by using a breather the refrigerant loss is reduced to 0.03 kg per kg of air.
The deaerator is a fairly compact component, which mainly consists of a 1.30 m DN100-DN150 large pipe. In this pipe, a heat exchanger coil is installed and on the breather shell are some DN15-DN25 connections. These include the admission of the air-refrigerant mixture from the condenser, the refrigerant injection, the refrigerant suction, the connection for the air outlet, a level switch and boiling pressure or boiling temperature monitoring (eg RT280A).
The built-in container heat exchange coil is traversed in the ideal case with TK ammonia. Either by partial flow during pump operation or with high-pressure fluid based on DX injection.
The evaporating refrigerant in the heat exchanger coil is again brought to or sucked off via the return line to the TK separator.
The high-pressure air-refrigerant mixture from the condenser is passed through a dip tube to the bottom of the deaerator (below the heat exchanger coil) in a distribution chamber. The built-in nozzle bottom ensures a uniform distribution of the rising gas mixture.
The refrigerant contained in the mixture condenses on the cold heat exchanger coil. The non-condensable air rises in the heat exchanger and collects there. The refrigerant condensed out via the coil slowly causes the liquid level in the deaerator to rise to the level switch.
When the level switch responds, the liquid supply to the heat exchanger coil is closed by a solenoid valve changeover. The emptied solenoid valve at the bottom of the container, the condensed NH3 is brought from the container shell space through the coil to the return line and thus to the TK separator.
If enough air has accumulated in the upper part of the deaerator, the typical NH3 ratio changes from boiling temperature to boiling pressure. The control unit (RT280A or SPS with temperature and pressure transducer) now knows that there is only air in the apparatus and opens the air release solenoid valve.
The air is passed through a small control valve in a water tank, where the remaining portion of NH3, which is still bound in the air, to so-called. "Ammonia Spirit" is converted. If the pressure / temperature ratio or the set discharge time matches, the venting solenoid valve is closed again.
Depending on the amount of air in the system and the number of vents, the water tank will eventually reach a saturation point. It can then perceive the typical biting NH3 smell in the engine room.
If the smell of NH3 is detected, this is no reason to panic. It can be an indication that only the drain tank needs to get new water.
Special advantages of a Kreutzträger KALEX breather
Cantilever Refrigeration KALEX
- A KALEX breather is made entirely of stainless steel and therefore can not corrode
- A large heat exchanger surface ensures a clean separation between refrigerant and air during refrigerant liquefaction
- The maintenance-friendly, reliable valves and switchgear ensure perfect automatic operation of the device
- The venting device is completely pre-assembled with all fittings and controls, easy installation can be done with little effort
- It can subsequently be integrated as an isolated solution with independent control or directly into an existing PLC
The KALEX is also flexible when it comes to supplying refrigerant. Depending on the system design and the installation site, either the pump supply line or the injection of high-pressure liquid can ensure the function.
With the KALEX air vent, the economic and technical disadvantages of air in the NH3 refrigeration system can be avoided, which increases the availability of the system.
Author: Fa. Kreutzträger Kältetechnik