1 refrigeration system overview

Basic parameters of screw ammonia refrigeration compressor.

Refrigeration system process flow.

The ammonia liquid absorbs the hydrogen heat of the shell side in the evaporator and evaporates into a low-pressure and low-temperature ammonia gas. This part of the ammonia gas is separated from the ammonia liquid by the ammonia liquid separator, and then filtered through the compressor inlet filter to enter the compressor for compression. After the high-pressure and high-temperature ammonia gas discharged from the oil separator is separated from the lubricating oil, it enters the horizontal condenser and is condensed into ammonia liquid. The ammonia liquid flows into the ammonia storage device, and then the regulating valve section before the ammonia liquid conveying line passes through the evaporator. The flow is depressurized, and then further expanded under reduced pressure through the expansion section of the evaporator inlet, and then enters the evaporator for heat exchange and reciprocating cycle. The air separator is used to separate and discharge the air in the air circuit system, and the oil collector collects the oil in the air circuit system.

The lubricating oil is cooled from the oil separator into the oil cooler and cooled to about 30 °C. After filtering through one oil coarse filter and two oil filters, a part of the lubricating oil is sprayed into the compressor chamber to cool the compressor. The function of sealing and lubrication, the other part of the lubricating oil under the regulation of the four-way solenoid valve, controls the horizontal movement of the oil piston driving slide valve of the energy system, and realizes the free adjustment of the system cooling capacity by 10% to 100%.

These two parts of the lubricating oil are discharged into the oil separator together with the high-pressure high-temperature ammonia gas, and are recycled after being separated.

2 transformation before driving

2.1 Aqueous liquid separator bottom drain problem

After the mixed gas of ammonia gas and ammonia liquid from the evaporator enters the ammonia liquid separator, the original design is that the separated ammonia liquid is concentrated at the bottom of the ammonia liquid separator, and is discharged through the discharge line to be incorporated into the evaporator ammonia inlet regulating valve. In front, considering that the pressure in the ammonia transfer line before the evaporator inlet regulating valve is close to the outlet pressure of the ammonia compressor of 1.3 MPa (normal working condition), and the pressure in the ammonia separator should be the ammonia compressor The inlet pressure is 0.4 MPa (normal condition), which is less than the pressure of 1.3 MPa before the evaporator inlet regulating valve. Therefore, although the bottom level of the ammonia separator is higher than the inlet ammonia line of the evaporator by about 3 m during field installation, Not enough to provide a pressure difference of 0.9 MPa so that the ammonia separated by the ammonia separator normally flows into the evaporator. On the contrary, under the pressure difference of 0.9 MPa, the ammonia solution at the bottom of the ammonia separator can not only return to the inlet line of the evaporator normally, but the ammonia which would otherwise enter the evaporator E-205 will flow back into the ammonia separator. The entire system process is confusing and cannot function properly.

The pressure behind the evaporator ammonia inlet regulating valve is close to the pressure inside the evaporator, so the ammonia liquid separated by the ammonia separator can be taken out through the bottom discharge line and then merged into the evaporator ammonia inlet regulating valve, and then used. The actual height difference between the ammonia separator and the evaporator causes the ammonia to flow into the evaporator. After a period of normal operation of the system, it was found that the modified ammonia liquid can smoothly flow into the evaporator to achieve the desired effect.

2.2 Renovation of the sewage line of the evaporator

After the long-term operation of the refrigeration system, the separation effect of the oil separator will gradually decrease, the lubricating oil can not be completely separated and recycled, and the un-separated lubricating oil will be brought to the horizontal condenser by the high-pressure ammonia gas, and then enter the ammonia storage device and evaporate. Inside the vessel, the slop oil at the bottom of the evaporator contains a large amount of ammonia. The slop oil at the bottom of the original design evaporator is directly discharged to the slop oil system, and the ammonia liquid contained in the slop oil is bound to cause environmental pollution. Therefore, in the three stages of the refrigeration system, the sewage oil line at the bottom of the evaporator is transformed into a connection with the oil collector, and the oil is first discharged into the oil collector, and heated by an electric heater at the bottom of the oil collector to make the oil The ammonia solution turns into ammonia gas and returns to the system. The sewage oil separated from the ammonia liquid is discharged to the sewage oil system, so that the waste ammonia liquid in the sewage oil at the bottom of the original evaporator can be recycled, which not only reduces the system operation. The loss of ammonia in the process, and ensure that the discharge of the slop oil to the slop oil system does not cause environmental protection.

However, since the pressure inside the oil collector is close to the pressure of the evaporator, the oil entrained with ammonia at the bottom of the evaporator does not easily flow into the oil collector, so it is necessary to increase the crossover at the top safety valve of the oil collector. And the pressure relief valve, the pressure in the oil collector is released to the isostatic pressure of the flare system through the pressure relief valve, that is, slightly higher than the atmospheric pressure, so that the oil at the bottom of the evaporator is under the pressure of 0.4 MPa inside the evaporator, Easy to enter the oil collector for gas-liquid separation. After a period of operation after the system was put into operation, it was found that the transformation effect was obvious, the discharge of waste oil was qualified, the ammonia liquid was effectively reused, the loss of ammonia liquid was reduced, and the material consumption of the system was reduced. See Figure 2.

2.3 Reconstruction of ammonia recovery line at the top of oil collector

The waste oil entered in the oil collector in section 2.2, after the bottom electric heater is heated, the ammonia liquid in the oil becomes ammonia gas, and the reclaimable ammonia gas generated in the oil collector is originally designed by the top line of the oil collector. Directly enter the inlet line of the compressor, and then re-cycled after compression by the compressor. Considering that when the electric oil is used to heat the sewage oil, part of the ammonia liquid and the ammonia gas are discharged from the top line of the oil collector to the compressor inlet line, causing the compressor to operate with liquid, and the vibration of the compressor is increased during operation. It is easy to cause equipment failure and affect the service life of the compressor. Therefore, the ammonia exhaust gas line at the top of the oil collector is changed from directly connected to the compressor inlet line to the ammonia separator before the compressor inlet, so that it is recycled. The ammonia in the ammonia gas is completely separated by the ammonia separator, which eliminates the hidden trouble of the compressor with liquid operation and protects the compressor.

2.4 increase the charge vent valve

The oil separator of the refrigeration compressor system has four barrel filters inside to function to separate ammonia and lubricating oil. During the start-stop system, system pressure fluctuations or long-term operation, lubricating oil and ammonia gas continuously enter the latter ammonia condensation module, and the sewage oil is discharged to the outside of the system. Therefore, the oil level of the oil separator is often lowered. When the system is replenished. When the system stops running and the oil replenishment operation is performed, the pressure of the entire refrigeration system is about 1.0 MPa. At this time, the oil is replenished, which is laborious and unsafe, and it is easy to cause the lubricating oil to be pressured and leaked, causing unnecessary trouble.

At present, a bypass and bypass venting valve is added to the safety valve of the oil separator. The venting valve can conveniently discharge the pressure of the system to the pressure of the low-pressure flare system, that is, slightly higher than the atmospheric pressure, thus achieving a closed discharge. The pressure does not pollute the atmosphere, and it easily drains the residual pressure of the system, greatly reducing the difficulty of the oil filling operation.

2.5 refrigeration system plus ammonia port transformation

The ammonia inlet of the refrigeration system was originally designed as two DN 20 mm valves. Considering the volume flow of ammonia required by the system is about 18 m 3 , the ammonia inlet of DN 20 mm is far from meeting the rate of ammonia addition. It is required, and the two ammonia-adding ports are arranged in a V-shape. When two ammonia-adding ports are simultaneously added with ammonia, a self-phase blocking of two ammonia liquids is easily formed, which further affects the smooth flow of ammonia into the system.

After analysis, it was decided to abandon the original two ammonia addition ports. Instead, open a saddle port on the ammonia storage outlet line, add a section of 50 mm nominal diameter and a DN 50mm gate valve as the ammonia addition port. The saddle seam weld is heat treated to prevent long-term ammonia corrosion leakage at the weld. Before the whole refrigeration system is started, the ammonia addition operation is carried out with the modified ammonia inlet. The ammonia flow rate is fast, the circulation is smooth and stable, and the requirements for ammonia addition on the site are fully satisfied.

3 summary

The above technical transformations are carried out on the basis of drawing on the operating experience of similar systems of the same industry for many years, and communicating with manufacturers to reach an agreement. After more than half a year of operation, the above five small transformations were successful and effective, which not only enabled the screw-type ammonia refrigeration compressor system to be successfully put into operation, but also provided a timely and stable cold source for the reforming extraction device, and reduced The daily maintenance workload of the whole system can also fully and effectively recycle the ammonia in the oil, saving operating costs.

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