Barrel pump unit of refrigeration system

Generally speaking, there are three types of liquid supply methods for refrigeration systems, namely direct liquid supply, gravity liquid supply and pump liquid supply. Direct liquid supply, also known as direct expansion liquid supply, is suitable for small refrigeration systems, such as small cold storages and high-temperature warehouses. Gravity liquid supply is suitable for small and medium-sized refrigeration systems, while pump liquid supply is suitable for large systems, especially refrigeration systems of multi-story buildings, or larger low-temperature warehouses, cold storages with aluminum racks that can store thousands of tons of goods, etc. Using barrel pump liquid supply is a relatively reasonable and economical method. Barrel pump liquid supply is often used in projects for making flake ice (or block ice), cold storages for freezing and refrigerating food, as well as in the processes requiring cooling in industries such as beer, medicine, petrochemical, coal, national defense, and scientific research.

When constructing cold storages, we should not only focus on quality but also attach great importance to safety. However, due to problems such as weak safety awareness and non-standard operations, major accidents have occurred frequently in large cold storages using ammonia refrigeration in China over the years. Therefore, in recent years, when choosing refrigeration methods for cold storages, many owners have considered using fluorine refrigeration. When the system is relatively large, barrel pump liquid supply is used, which can not only ensure the refrigeration effect but also ensure safety. In our daily maintenance work, we often encounter projects using barrel pump liquid supply, including low-temperature warehouses, quick-freezing rooms, and high-temperature fresh-keeping warehouses; there are shelves, pipe racks, and air coolers; the pipe racks adopt hot fluorine defrosting, and the air coolers use either water defrosting or hot fluorine defrosting.

Next, let's understand the technical principle of barrel pump liquid supply.

The basic principle of barrel pump liquid supply is to use the mechanical action of the pump to deliver low-temperature refrigerant to the evaporator. The low-temperature refrigerant after throttling first enters the fluorine barrel with a certain liquid storage volume and a certain gas-liquid separation volume, and then the fluorine pump delivers the low-temperature liquid several times the evaporation amount to the evaporators in each warehouse. Part of the liquid absorbs heat and vaporizes in the evaporator, and the rest of the liquid returns to the fluorine barrel along with the vapor through the return pipe. After gas-liquid separation, the vapor is sucked away by the refrigeration compressor, and the separated liquid and the newly supplemented liquid equivalent to the evaporation amount are delivered to the evaporator by the fluorine pump for recirculation.

The barrel pump unit we usually refer to is an equipment assembly composed of barrel pump liquid supply, which is suitable for the liquid supply system that recirculates multiple evaporators. The barrel pump unit consists of a low-pressure circulation liquid storage barrel, a canned pump, an electrical control box, a steel frame structure, etc. Its process pipelines, valves, automatic control components, electrical components and other parts are all fully assembled in the factory to form an integrated liquid supply device of the barrel pump, which greatly reduces the infrastructure investment and construction time, and has functions such as automatic liquid supply, liquid level control, liquid level display, high liquid level alarm, pump automatic protection, and automatic or manual operation.

(1) Fluorine pump liquid supply enables the evaporator to have a higher heat exchange efficiency and a good cooling effect.
In the fluorine pump liquid supply system, the circulation amount of the refrigerant is several times the evaporation amount of the evaporator, which makes the evaporator have a fully wetted surface and can exert the heat transfer efficiency of the entire evaporation area of the evaporator. The refrigerant flows in a circulating state in the evaporator, and the gas flows in the central part, thus strengthening the heat exchange conditions between the refrigerant and the pipe wall surface. Moreover, due to the scouring of a large amount of refrigerant, it is not easy for an oil film to form on the pipe wall of the evaporator, and oil stains are not easy to accumulate at the bottom, so the heat transfer coefficient of the pipe wall is improved.

In the direct expansion system, if the liquid supply is insufficient, the end of the aluminum pipe rack will all turn into superheated gas, which will not only reduce the utilization rate of the evaporation area but also easily cause the danger of coking of the lubricating oil due to the increase in the exhaust temperature of the refrigeration compressor. However, if the liquid supply is excessive, in some pipes at the very end of the pipe rack, the flowing medium is gas instead of liquid, which is very likely to cause the wet stroke of the refrigeration compressor and cannot ensure the safe operation of the refrigeration device. In addition, the gas released by the throttling of the liquid, mixed with the liquid, is sent to the evaporator as a two-phase fluid, which greatly increases the resistance loss of the liquid supply pipeline and also reduces the cooling effect of the evaporator.
Therefore, for evaporators with the same evaporation area, the cooling effect of using fluorine pump liquid supply is 25% - 30% higher than that of direct expansion liquid supply and about 10% higher than that of gravity liquid supply.

(2) When using fluorine pump liquid supply, the mechanical action of the pump can be utilized to overcome part of the resistance loss in the system and achieve long-distance liquid supply.

(3) The operation of the fluorine pump liquid supply system is simple and reliable, which is convenient for centralized control and automation. The operating conditions of the refrigeration compressor are improved. In the fluorine pump liquid supply refrigeration system, as long as there is no large fluctuation in the heat load of the warehouse and the liquid level of the fluorine barrel is relatively stable, the normal operation of the fluorine pump can be maintained without the need for frequent adjustment work. The adjustment of the cooling load in the system can be completed in the refrigeration machine room, and there are no valves in the warehouse that need to be adjusted frequently. At the same time, it is relatively easy to realize the automation of the refrigeration device.
In the direct expansion liquid supply system, due to the continuous fluctuation of the heat load, it is relatively difficult to adjust the expansion valve. Sometimes it is necessary to climb up to adjust the valves in the warehouse, which is very inconvenient.

(1) The flooded evaporator has better heat exchange efficiency, which can improve the energy-saving performance of the system.

(2) Pump liquid supply is suitable for long-distance liquid supply in vertical and horizontal pipelines, which can reduce the hydraulic loss of the riser of the liquid supply pipe and the resistance loss of the suction pipeline.

(3) Since the resistance loss on the pipeline is reduced, the evaporation temperature of the system can be increased, thereby improving the energy-saving performance of the system.

(4) It can solve the problems of long return pipelines, inevitable gas and liquid pockets on the pipelines causing large system resistance losses and unfavorable oil return.

(5) There is no limitation of the opening pressure difference of the expansion valve, and the condensation temperature can be low enough, thereby improving the energy-saving performance of the system.

(6) In the hot fluorine defrosting system, since the heat released by the hot Freon vapor discharged from the compressor is used to melt the frost layer on the surface of the evaporator, it solves the problems of high energy consumption of electric defrosting and easy icing when water defrosting is used in low-temperature warehouses.

(1) The selection of the oil separator is very crucial, and there are relatively high requirements for the oil separation capacity and efficiency of the oil separator to minimize the migration amount of the refrigeration oil in the system.

(2) Control the exhaust temperature and suction superheat of the system to prevent a large amount of refrigeration oil from migrating into the system due to liquid return.

(3) Control the oil temperature when shutting down the machine to prevent a large amount of refrigerant from being dissolved in the oil. When starting the machine, prevent the refrigerant from suddenly vaporizing and taking away the lubricating oil.

(4) In the design of the oil return pipeline system, multiple oil return ports can be set, and the use of the oil return ports can be controlled according to the liquid level.

(5) For hot fluorine defrosting: it is necessary to ensure that there is a sufficient heat source, adopt grouped defrosting and use a relief valve to ensure that the temperature of the refrigerant during defrosting is 10 degrees Celsius to achieve the best defrosting effect. At the same time, it is necessary to ensure that the high liquid level of the low-pressure circulation barrel does not exceed 70%. Generally, a two-step opening solenoid valve is used to prevent the "liquid hammer phenomenon" during hot fluorine defrosting.

In conclusion, the barrel pump refrigeration system has the characteristics of improving the cooling capacity of the evaporator, ensuring long-distance liquid supply, simple system operation, being convenient for centralized control, realizing automation, and facilitating defrosting operations. The specific summary is as follows: