[Mechanical Equipment Technology Edition] Daily Question 20171118: Lubrication System of Screw Compressor Units (8)

1. Oil supply by the oil pump: (Pre-lubrication) At the beginning of compressor startup, the pressure oil required for lubricating various parts of the compressor, adjusting the volume ratio control valves, and reducing the load on the energy control valves is supplied by the pre-lubrication oil pump. Once the compressor is operating normally, whether the pre-lubrication oil pump continues to operate depends on the pressure difference between the exhaust pressure and the suction pressure; when this difference reaches 0.45 MPa, the oil pump stops operating, while it starts operating again when the difference is below 0.35 MPa. 2. Pressure differential oil supply: Once the compressor has started up and is operating normally, the oil supply is ensured by the pressure difference between the exhaust pressure and the suction pressure. The oil separated in the oil separator flows toward the oil cooler under high pressure, then passes through the oil filter and the oil distribution seat before entering the compressor, where it is ultimately discharged back to the oil separator along with the working fluid.

Differential pressure oil supply, fully sealed vortex compressor

1. The first method is to use a liquid pump for supplying fluid in the freezer. Liquid pump recirculation systems are widely used in ammonia-based refrigeration systems; in the 1970s, the 10,000-ton freezer at Shanghai Foreign Trade Refrigeration Factory utilized an R22 liquid pump recirculation refrigeration system, and some marine refrigeration systems also made use of R22 liquid pumps for fluid supply. Although installing a liquid pump in a refrigeration warehouse to recycle the system can increase the heat transfer coefficient of the evaporator and thus boost cooling capacity, it also consumes electricity. Without proper configuration and appropriate automatic control procedures, it is difficult to achieve energy-efficient operation. Currently, many liquid pump recirculation systems supply an excessive amount of fluid, yet fail to ensure a minimum flow rate for each circuit; they have too high a head pressure, which makes it difficult to achieve uniform fluid distribution in multi-story cold storage. The flow rate cannot be adjusted according to changes in the cooling load, making energy-efficient operation difficult to achieve. For liquid pump recirculation systems, in addition to proper configuration, more research should be conducted on automatic control procedures such as stratified liquid supply and variable flow control; only in this way can energy savings be achieved. 2. The second method is direct expansion supply in cold storage. Direct expansion supply is the method used in most halogenated hydrocarbon (including Freon) systems as well as some ammonia systems. In the past, thermal expansion valves were commonly used for liquid supply in cold storage installations; however, due to issues related to selection, adjustment, and the products themselves, it was not possible to achieve energy savings. The advent of electronic expansion valves, combined with temperature control of the refrigerant tank based on multiple temperature parameters, enables more efficient energy use, typically resulting in a 10% energy savings. Thermodynamic expansion valve products for halogenated hydrocarbon refrigeration systems are already quite mature, and there are also dedicated PLC-based temperature controllers available; however, for various reasons, they have not yet been widely adopted in cold storage refrigeration systems, and more efforts are needed to promote their use. The superheat during operation of the evaporator in ammonia refrigeration systems is not high, which makes control relatively difficult; currently, there are no mature electronic expansion valves designed for use with ammonia. 　 3. Thirdly, gravity-fed liquid supply for cold storage. The gravity-fed liquid supply system was widely used in older ammonia-based refrigeration systems, but it was gradually replaced by ammonia pump-driven liquid supply systems. Although installing a gravity-fed liquid supply system in a cold storage is complicated to operate, it does not require power for transportation; with appropriate automatic control in place, it is undoubtedly an energy-efficient way of operation. The fluidized freezing system at Xiamen Commercial Freezing Plant uses an R22 gravity-fed liquid supply system, while the Shanghai 21st Century Refrigeration Warehouse employs an ammonia-based refrigeration system with gravity-fed liquid supply and automatic control.

1. The first method is to use a liquid pump for supplying fluid in the freezer. Liquid pump recirculation systems are widely used in ammonia-based refrigeration systems; in the 1970s, the 10,000-ton freezer at Shanghai Foreign Trade Refrigeration Factory utilized an R22 liquid pump recirculation refrigeration system, and some marine refrigeration systems also made use of R22 liquid pumps for fluid supply. Although installing a liquid pump in a refrigeration warehouse to recycle the system can increase the heat transfer coefficient of the evaporator and thus boost cooling capacity, it also consumes electricity. Without proper configuration and appropriate automatic control procedures, it is difficult to achieve energy-efficient operation. Currently, many liquid pump recirculation systems supply an excessive amount of fluid, yet fail to ensure a minimum flow rate for each circuit; they have too high a head pressure, which makes it difficult to achieve uniform fluid distribution in multi-story cold storage. The flow rate cannot be adjusted according to changes in the cooling load, making energy-efficient operation difficult to achieve. For liquid pump recirculation systems, in addition to proper configuration, more research should be conducted on automatic control procedures such as stratified liquid supply and variable flow control; only in this way can energy savings be achieved. 2. The second method is direct expansion supply in cold storage. Direct expansion supply is the method used in most halogenated hydrocarbon (including Freon) systems as well as some ammonia systems. In the past, thermal expansion valves were commonly used for liquid supply in cold storage installations; however, due to issues related to selection, adjustment, and the products themselves, it was not possible to achieve energy savings. The advent of electronic expansion valves, combined with temperature control of the refrigerant tank based on multiple temperature parameters, enables more efficient energy use, typically resulting in a 10% energy savings. Thermodynamic expansion valve products for halogenated hydrocarbon refrigeration systems are already quite mature, and there are also dedicated PLC-based temperature controllers available; however, for various reasons, they have not yet been widely adopted in cold storage refrigeration systems, and more efforts are needed to promote their use. The superheat during operation of the evaporator in ammonia refrigeration systems is not high, which makes control relatively difficult; currently, there are no mature electronic expansion valves designed for use with ammonia. 　 3. Thirdly, gravity-fed liquid supply for cold storage. The gravity-fed liquid supply system was widely used in older ammonia-based refrigeration systems, but it was gradually replaced by ammonia pump-driven liquid supply systems. Although installing a gravity-fed liquid supply system in a cold storage is complicated to operate, it does not require power for transportation; with appropriate automatic control in place, it is undoubtedly an energy-efficient way of operation. The fluidized freezing system at Xiamen Commercial Freezing Plant uses an R22 gravity-fed liquid supply system, while the Shanghai 21st Century Refrigeration Warehouse employs an ammonia-based refrigeration system with gravity-fed liquid supply and automatic control.

1. The first method is to use a liquid pump for supplying fluid in the freezer. Liquid pump recirculation systems are widely used in ammonia-based refrigeration systems; in the 1970s, the 10,000-ton freezer at Shanghai Foreign Trade Refrigeration Factory utilized an R22 liquid pump recirculation refrigeration system, and some marine refrigeration systems also made use of R22 liquid pumps for fluid supply. Although installing a liquid pump in a refrigeration warehouse to recycle the system can increase the heat transfer coefficient of the evaporator and thus boost cooling capacity, it also consumes electricity. Without proper configuration and appropriate automatic control procedures, it is difficult to achieve energy-efficient operation. Currently, many liquid pump recirculation systems supply an excessive amount of fluid, yet fail to ensure a minimum flow rate for each circuit; they have too high a head pressure, which makes it difficult to achieve uniform fluid distribution in multi-story cold storage. The flow rate cannot be adjusted according to changes in the cooling load, making energy-efficient operation difficult to achieve. For liquid pump recirculation systems, in addition to proper configuration, more research should be conducted on automatic control procedures such as stratified liquid supply and variable flow control; only in this way can energy savings be achieved. 2. The second method is direct expansion supply in cold storage. Direct expansion supply is the method used in most halogenated hydrocarbon (including Freon) systems as well as some ammonia systems. In the past, thermal expansion valves were commonly used for liquid supply in cold storage installations; however, due to issues related to selection, adjustment, and the products themselves, it was not possible to achieve energy savings. The advent of electronic expansion valves, combined with temperature control of the refrigerant tank based on multiple temperature parameters, enables more efficient energy use, typically resulting in a 10% energy savings. Thermodynamic expansion valve products for halogenated hydrocarbon refrigeration systems are already quite mature, and there are also dedicated PLC-based temperature controllers available; however, for various reasons, they have not yet been widely adopted in cold storage refrigeration systems, and more efforts are needed to promote their use. The superheat during operation of the evaporator in ammonia refrigeration systems is not high, which makes control relatively difficult; currently, there are no mature electronic expansion valves designed for use with ammonia. 　 3. Thirdly, gravity-fed liquid supply for cold storage. The gravity-fed liquid supply system was widely used in older ammonia-based refrigeration systems, but it was gradually replaced by ammonia pump-driven liquid supply systems. Although installing a gravity-fed liquid supply system in a cold storage is complicated to operate, it does not require power for transportation; with appropriate automatic control in place, it is undoubtedly an energy-efficient way of operation. The fluidized freezing system at Xiamen Commercial Freezing Plant uses an R22 gravity-fed liquid supply system, while the Shanghai 21st Century Refrigeration Warehouse employs an ammonia-based refrigeration system with gravity-fed liquid supply and automatic control.

Typical piston machines use oil pumps to supply oil, as do fully hermetically sealed scroll compressors. Screw compressors generally use pressure difference for oil supply.

The compressor return oil comes out from two ports; is there any particular consideration regarding the opening degree of these ports when preventing freezing in winter?