Ammonia refrigeration system
Low-pressure system due to the cooling system for different ways and have very different.
According to the power supply to the evaporator, direct cooling system points directly for expansion of liquid, gravity for liquid, liquid pump and pump for liquid supply four.
Direct expansion of the liquid
The use of condensing pressure and evaporation pressure difference, the throttled refrigerant directly into the evaporator for the liquid, known as the direct expansion of liquid. In the refrigeration unit, it is the earliest and easiest to use. The characteristic of this method is:
① less refrigeration equipment, the system is simple, less refrigerant charge, engineering costs low.
② throttling generated flash gas into the evaporator, reducing the efficiency of refrigeration.
③ gas-liquid separation equipment, prone to wet trip.
④ operation adjustment difficult. With the condensing pressure, evaporation pressure, load changes in size, the throttle opening should be adjusted in time, which is not easy to do just right with manual throttle valve and manually adjusted cooling device. At the same time, due to the presence of flash gas, it is not easy to distribute the liquid to the evaporator in parallel, which makes the liquid supply more easy to wet stroke and less liquid for overheating.
Gravity for the liquid
Gravity supply is mainly used for ammonia refrigeration unit.
1. Working principle of Ammonia refrigeration system
Add a liquid ammonia separator between the throttle valve and evaporator, evaporator and compressor, and place it above the evaporator. The throttled two-phase refrigerant enters the ammonia separator first, and the separated liquid utilizes the static pressure formed by the level difference between the liquid level maintained in the ammonia liquid separator and the evaporator to supply the liquid to the evaporator. Therefore, it is called The gravity for the liquid
2. Difference will not affect the evaporation temperature by more than 1 after overcoming the total resistance ℃. The residual pressure difference values required by different evaporation circuits are:
-33 ℃ circuit: ≯ 5KPa
-28 ℃ Circuit: ≯ 6KPa
-15 ℃ circuit: ≯ 12KPa
The actual plan of the ammonia liquid separator normal liquid level can be 0.5 ~ 2m higher than the evaporator longest tube, often take 1.5m.
3. Ammonia liquid separator room settings
Gravity supply back to the gas system is one of the following circumstances, ammonia compressor room should be additional ammonia separator: ①Two storeys and two or more storeys; ②There are two or more ice making pools; ③Treasury ammonia separator and ammonia compressor room horizontal distance greater than 50m.
In other words, in order to improve the safety of compressor operation, if necessary, set ammonia room ammonia separator. Does not assume the task of supplying liquid to the evaporator for ammonia liquid separator for the warehouse , without having to maintain a certain level.
4. Number of ammonia separators
Determine separately according to the Treasury and Room ammonia separator.
①The amount of ammonia separator in the engine room depends on the number of evaporative circuits, the number of cold rooms, and the number of floors. Different evaporation circuit should be set separately. Multi-storey warehouse should be set in layers. Multiple cold rooms in the same evaporation circuit can be used together or separately.
②Room ammonia separator depends on the number of evaporation circuit number. When need to set up, set one ammonia separator in one evaporation circuit meet the conditions of gas-liquid separation.
5. Sub-station settings
When an ammonia separator supply for multiple cold or multiple sets of evaporator, in order to facilitate the operation and management, set up sub-station. Sub-regulation station is divided into liquid sub-regulation station and gas sub-station by the refrigerant flow through. According to the defrost function it is divided into hot ammonia defrosting and without heat ammonia defrost sub-station regulation. Both types of control stations consist of the manifold, branch pipe, globe valves, pressure gauges and other components. The number of branch pipes depends on the number of cold rooms and evaporators. In principle, one circuit in one room. For the cold room using different types of evaporator, can be provided for the parallel solution back to the gas, respectively, or for the gas were back to the gas.
Simple designed sub-station has less valve and simple structure. However, when any one of the evaporators defrosts, none of the other evaporators in the same evaporation loop can cool and another evaporation loop is required to provide heat. For those who do not often need to defrost the cold can be considered, such as frozen refrigerated room.
6. Drainage barrels, low pressure liquid storage tank connection
Drainage barrels, low pressure liquid storage drums are constructed in the same way with slightly different uses. Drainage bucket is mainly used to accommodate red liquid drain, low pressure liquid storage tank is to collect the liquid separated by a container. In the earlier built cold storage, there are two kinds of settings. Later, to simplify the system we take a bucket of dual-use design.
7. Evaporator refrigerant flow direction
As the gravity of the liquid supply for the pressure is not great, the evaporator refrigerant flow direction must be from bottom and out of top, that is, liquid enters from the bottom of the evaporator, the return air goes out from the top.
Gravity feeding has the following features:
①Improve the lack of the direct expansion of the liquid supply.
②Hydrostatic column pressure has affections on the evaporation temperature.
③Evaporator refrigerant flow rate is slow, the heat coefficient is low, and the oil inside is not easy to be washed out.
④Ammonia liquid separator, sub-station layout is more scattered, not easy to centralize management.
⑤Need to increase the installation of attic or occupy the area to put the ammonia separator, civil costs increased.