By appointment all units chillers can be divided into two groups: primary and secondary.
Basic (heat exchangers) - it condensers, evaporators, condensers, evaporators - are essential elements of chillers and determine how it works.
Aids - are not fundamentally required. They improve the performance of the HMM (efficiency, reliability). These include subcooler regenerative (by appointment) THEN, intermediate vessels, etc.
Basic phones largely determine weight and size and energy indicators chillers. Their share in the total weight of the machine is 50-70%. Chiller energy indicators dependent on the magnitude of the irreversible losses of energy in the heat exchangers, i.e. the magnitude of the temperature difference (AT) between coolants. Reducing AT leads to improved performance, but increase capital expenditures, and vice versa.
Besides the thermodynamic imperfection of energy loss in the heat exchanger still associated with hydro and aerodynamic drag. Than they are, the higher the cost of energy to overcome them (pumps, fans).
From all this we derive the general requirements for heat exchange apparatus in their design and modernization: high intensity of heat transfer; low hydraulic resistance; simplicity of design, manufacturability; compactness, small metal; cheap materials; ease of installation and maintenance, etc.
Classification of evaporators varies, depending on the principle embedded in its foundation.
By appointment evaporators share:
By the nature of the working substance filling:
- Cooling liquid coolants (in brine systems);
- Cooling process products (operating scheme with direct evaporation HA);
- Air cooling;
- Cooling solid media;
- Evaporators, condensers.
By the nature of the movement of coolant distinguish two types of evaporators:
- Unflooded (irrigation, shell and tube with boiling in tubes with coiled top fillers).
a) a closed circulation system, i.e. When refrigerant circulates through the tubes of the apparatus. This casing, kozhuhozmeevikovye evaporators;
b) open the coolant level. This panel vertikalnotrubnye and evaporators.
An open system is less favorable due to increased corrosion of pipes and tank evaporator. Also need pumps High pressure to overcome the hydrostatic head.
In the chemical, petrochemical and refining industries, tend to use horizontal shell and tube evaporators. In the cascade is used both horizontal and vertical machines.
Fundamental difference between ammonia and tube evaporator and devices running on refrigerants not. The difference lies in the design of heat transfer surfaces and materials used for manufacturing. In ammonia apparatus used seamless steel pipe smooth. When working on refrigerants used copper tubes with knurled edges. The tube bundle evaporators chess, rhombic.
In evaporators for ammonia, propane and propylene by steam-dome set on top of the casing (cylinder course with a spherical bottom). Below - the oil pan. The upper part of the evaporator shell (about 20% by volume) - without tubes. It serves to release vapor from the liquid.
In the apparatus as refrigeration tubes occupy 50-60% of the housing, as filling volume Chladones considerably less than ammonia. This is due to the strong foaming boiling Freon from the oil dissolved therein. The optimum height level depends on the average temperature difference in the machine and is approximately 0.6 diameter casing.
Plate evaporators are less common than the tube bundle. They are intended for cooling the coolant (water or brine) in open cooling systems. Panel evaporator brand SP - a metal or concrete rectangular tank. It housed the evaporator section and panel-type agitator for circulating coolant. Section headers are interconnected. Boiling refrigerant occurs in the channels of the lower manifold and the panels. Refrigerant flows by gravity into the tank and washes the surface of the panels.
Panel evaporators are safer in terms of freezing the coolant, compared to the shell and tube evaporators.
Capacitor serves to transfer heat refrigerant cooling (ambient) environment. In general, the superheated refrigerant vapor in the condenser is cooled to the saturation temperature, is condensed and cooled a few degrees below the condensation temperature. Energy characteristics of the chiller are strongly dependent on the temperature changes of the cooling medium.
By the nature of the cooling medium, all the capacitors can be divided into:
a) air-cooled devices;
b) a water-cooled apparatus;
c) special (condensers evaporators, condensers cooling process products).
On the principle of removing heat from water-cooled condensers are divided into flow, irrigation and evaporation. The latter two types are also referred to as a water-air-cooled condensers.
To include instantaneous horizontal and vertical shell and tube, packet-panel, element and plate capacitors.
From capacitors require high efficiency. It affects the efficiency of the chiller. For example, lowering the temperature by 1 degree of condensation (from 30 to 29 ° C) for refrigerating machines with reciprocating compressors operating with cooling medium temperature (t0 = -10: -15 ° C) reduces the specific energy consumption of about 1 5%. The same effect is achieved by cooling the liquid refrigerant at 1 ° C below tK.
In the chemical, petrochemical and refining industries most widely used three types of capacitors:
1), horizontal and vertical water-cooled tube bundle apparatuses. In annulus condensed refrigerant and circulates the water in the pipes. When the water temperature tw1 = 25-28 ° C condensing temperature is usually taken 35-40 ° C. Heated water averages Atw = 4-8 ° C;
2) air coolers general purpose type AUG and AVZ (horizontal and staggered sections of finned heat exchanger tubes). Refrigerant condenses in the tubes, and the air blower blows the external pipe fins. Condensing temperature in the summer can be Tc = 50-54 ° C;
3) horizontal or vertical shell and tube apparatus in which heat is removed by the evaporatingrefrigerant another circuit cascade refrigeration machines. This condensers evaporators.
Horizontal tube bundle condensers with smooth tubes are used to mark the HIC water condensing ammonia, propane, propylene and other uglevodordov.
Horizontal exchanger with finned tubes brand CTE applied to condense Freon. Copper tube, the ratio of the outer surface of the inner tube (Fin coefficient) is approximately 3.5.
Reduction of water consumption in industrial plants is an important issue. A refrigeration systems are significant consumers of water. So now at the leading enterprises of the chemical, petrochemical and refining industries proceeds to air cooled condensers.
Advantages of air cooling:
a) minimal contamination of the heat transfer surfaces;
b) the exclusion of the danger of freezing;
c) ease of maintenance;
d) less corrosion and cheaper operation.
Disadvantages: reducing heat transfer from the cooling medium implies increase in the size, metal content, increased condensation pressure and the resulting increase in energy consumption.
Serial devices are divided into categories A and B: A - for safe and non-toxic environments; B - for explosive environments and toxic products.
AVZ phones differ from AUG more compact and less metal.
Intermediate vessels and coolers condensate
Coolers are designed for condensate subcooling before entering it on the evaporation process equipment or refrigeration evaporators. The greater the subcooling the more cooling chiller. At least it should be such that there is no level control before the vaporization of liquid refrigerant in the evaporator (for reliable operation of the regulator)
Intermediate vessels for turbo units - are horizontal shell and tube heat exchangers multiport. Cooling the liquid refrigerant (tube bundle) is carried out by evaporating refrigerant in the annulus. The resulting vapor is sucked into the intermediate stage of the compressor through a dry liquid separator. At the same time there is an incomplete intermediate cooling of compressed refrigerant vapor in the turbocharger.
Coolers condensate structurally similar intermediate vessels;
In reciprocating and screw chillers intermediate vessels used in multistage compression for the full intermediate cooling vapor XA between steps. This is achieved by bubbling them through the layer of liquid coolant in the vessel.
Constructively - is welded vertical cylindrical devices. They are: with and without coil coil. In coil condensate subcooling refrigerant implemented before sending it to consumers cold. If the intermediate vessel without coil, the condensate subcooling is carried out in a special heat exchanger similar devices turbo XM.
Liquid separators (separators)
In refrigeration circuits they serve to protect the compressor from water hammer. Designed to separate the refrigerant vapor coming from the evaporator (or intermediate vessel) of liquid droplets.
Accumulators are conventionally divided into dry and feed. Dry perform only one function - to protect the compressor from liquid. Supply two functions - is the protection of the compressor and the power liquid refrigerant evaporators and other refrigeration consumers (processing units).
All separators - is hollow volumetric machines of vertical and horizontal type. Features such separators are given in catalogs of manufacturers. Separators and are available with a bulk head.
HA Branch vapor from dripping or splashing occurs due to density difference. This contributes to reduction in steam velocity and direction changes. Believe that the rate of steam in the separator should not exceed 0.5 m / s. There is empirical formulas by which the permissible speed for different HA and other specific conditions of the apparatus
Refrigerant vapor leaving the compressor (screw and piston) carry off the particles of oil, as in the form of droplets (size 5 to 50 microns) and as steam. Application of oil separators can improve the efficiency of heat exchangers in installations operating on limited oil soluble coolant (R717, R22, etc.), as this reduces the oil film deposited on the heat transfer surface.
To release the refrigerant vapor from the undissolved oil and serve as separators. They come in different types of work on different principles:
1) bubble (flushing) GMM-type (oil separator modernized) - ammonia. They provide efficient separation of oil from the refrigerant vapor while bubbling them through a layer of liquid ammonia. Oil vapors condense while.
Constructively - is welded vertical cylinders with conical latticed strikers. To saturation oil GMM work well - capture up to 97%, but need time to drain the oil;
2) Friction. This type includes separators:
a) with a tangential steam injection. They are used where the refrigerants are propane, propylene, ethane and ethylene. To increase the efficiency of oil separation refrigerant vapor should be pre-cooled. The output vapor from the separator is placed a layer of Raschig rings;
b) centrifugal or cyclone separators. They separation of oil droplets by centrifugal force combined with the separation of droplets with a sharp change in direction of flow. The effectiveness of these oil separators is 80%.
8 - Water-cooled refrigerant. These coolers are used in refrigerating machines operating on refrigerants R12, R134a, R22, etc. Water cooled pair Freon 20 degrees above its dew point. Droplets of condensed oil along with the flow fall into chipping layer of Raschig rings.
By construction, all the separators are vertical cylinders with the corresponding filling.
In refrigeration systems are receivers capacity for liquid refrigerant. Depending on the features distinguish linear receivers, drainage, circulation and safety:
a) linear receivers are placed between the condenser and the expansion valve (throttle) and serve to compensate for differences in the level of refrigerant evaporation equipment when the heat load. Furthermore, they release fluid from the condenser, the heat exchange surface deadening create the necessary reserve in case of leakage of refrigerant, and serves as a hydraulic gate preventing flow into the high pressure steam evaporator.
This horizontal cylindrical vessels with pipes welded, pointer and a level sensor, pressure gauge, safety valve and weep pot;
b) drainage receivers are provided for collecting the liquid refrigerant from the separator, discharging it from the apparatus and pipe (evaporator during defrosting or repair), followed by returning it into the system;
c) circulating receivers used in pump-circulation evaporator circuits supply systems with liquid refrigerant. They serve as a reservoir in which the constant supply of liquid refrigerant is contained in an amount to provide continuous operation of the circulation pump supplying the liquid in the evaporator;
d) protective receivers with liquid separator installed in the suction line between the evaporator and compressor piston. Serves to protect the compressor from water hammer. Sometimes an accumulator function and protective receiver combine.
Besides the above, in the auxiliary equipment XM includes: an air, drip trays, strainers, filters, tank vapor recovery (usually one per station), hydraulic valves, liquid refrigerant dehumidifiers, etc.