JP2008232613A - Control method of co2 refrigeration device performing two-stage compression - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an efficient and inexpensive control method of a CO<SB>2</SB>refrigeration device. <P>SOLUTION: The following four functions (a)-(d) are provided in combination or independently, namely: (a) degree of supercooling of main flows in supercoolers; (b) degree of desired overheating in feelers that are portions of controllable throttle valves (34, 35, 36) disposed at supercooler outlets of split flows; (c) change in intermediate pressure in a secondary flowing route by regulated release or closure of pressure control valves (42, 43, 44) disposed downstream of each of the supercoolers in pipelines for guiding the split flows; and (d) change in compression final pressure on an upper stage. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a control method for a two-stage CO ₂ refrigeration apparatus (CO ₂ -Kaelteanlage) having a two-stage screw compressor unit in which oil-injected screw compressors (oelueberfluteter Schraubenverdichter) are arranged in two stages. The screw compressors are arranged one after the other in the flow direction, and both screw compressors in the upper and lower pressure stages each have one intermediate pressure opening, so-called economizer connection, the economizer connection As long as the part communicates with the tooth groove of the rotor in the casing so as to communicate with the tooth groove, the flow connection to the suction side and the flow connection to the discharge side do not occur. An intermediate pressure connection is provided in the connecting line between the compressors, between the CO ₂ gas cooler outlet and the CO ₂ inlet to the evaporator system, between the gas cooler outlet and the evaporator system with the throttle device. For refrigerant mainstream There is a secondary flow path, and at least three heat exchangers in the primary flow path are arranged serially with respect to the primary flow path, and these heat exchangers are "upper" Auxiliary subcooler, “intermediate” subcooler and “lower” auxiliary subcooler, on one side of the heat exchanger surface of the subcooler, the primary flow path A portion of the secondary flow path is adjacent to the other side of the heat exchanger surface, and the portion of the secondary flow path extends from the primary flow path to the throttle valve The economizer connection of the upper stage screw compressor, the intermediate pressure connection between the upper and lower stage screw compressors, and the economizer connection of the lower stage screw compressor via the supercooler and conduit Oil-filled, part of a fluid connection and having lines and controllable valves Screw compressor relating to the control method of the two-stage CO ₂ refrigeration system including a two-stage screw compressor units arranged in two stages.

The present invention relates to a method for controlling a two-stage CO ₂ refrigeration apparatus with an oil-injected screw compressor arranged one after the other in the direct flow direction for two-stage compression. The screw compressors of both pressure stages preferably each have one intermediate pressure opening, the so-called economizer connection, the economizer connection being connected to the tooth groove of the rotor in the casing and the economizer connection being the tooth groove. As long as they are in communication, they are adjacent so that neither a fluid connection to the suction side nor a fluid connection to the discharge side occurs. The compressor of the upper pressure stage is configured according to the background art, for example as described in DE 103 34 947 A1.

  The fact that the intermediate pressure connection is arranged in the connection line between the compressors of both pressure stages and the presence of the economizer connection in the compressor is explained by background art, for example in patent application No. 102005018602.5. As described, it allows four-stage expansion of the refrigerant between the gas cooler and the evaporator.

According to the background art, both screw compressors are provided with means for changing the pumping volume, for example respectively, in order to control the operating parameters, preferably the pressure in the evaporator directly related to the evaporation temperature of the refrigerant CO _2. Equipped with one control slider. The control slider is partly arranged in a casing with a rotor and requires a separate hydraulic component and control element for activation. Alternatively, the screw compressor is controlled by changing the driving speed. This control of operating parameters is also called power control (Leistungsregelung). Therefore, this concept is also used in the text below.

  A drawback to the above type of output control is the required cost of this solution.

  It is therefore a major challenge to eliminate this drawback and provide efficient and inexpensive output control.

Patent application number 102007003983.3, in which a known multi-stage CO ₂ refrigeration system is described, is supplied to the intermediate pressure connection and the compressor economizer connection opening, preferably via a controllable valve device Meanwhile, the liquid is expanded in the lower auxiliary liquid separator through the “lower” throttling point. The flash vapor and liquid are separated from each other in the auxiliary liquid separator.

  From there, the liquid reaches the evaporator liquid separator system via the “bottom” throttling point. From this evaporator liquid separator system, the flash vapor is supplied to the suction side of the lower pressure stage compressor along with the refrigerant vapor generated in the evaporator by heat supply.

In the second solution of patent application No. 102007003989.3, in which another known multi-stage CO ₂ refrigeration system is described, the refrigerant stream supplied to the evaporator system is routed through a plurality of subcooling sections. After that, it is expanded in one stage. For cooling of the refrigerant flow in the “upper” auxiliary liquid subcooler, “middle” liquid subcooler and “lower” auxiliary liquid subcooler arranged in the flow path for the main refrigerant flow. For this purpose, the liquid branch provided in front of each liquid subcooler section branches off the diverted refrigerant liquid and evaporates in each liquid subcooler. The refrigerant vapor is supplied to each eco connection of the upper stage compressor, an intermediate pressure connection between the upper and lower pressure stage compressors, and an economizer connection of the lower pressure stage compressor.

  The pumping volume of the compressor in the lower pressure stage of the two-stage compressor unit is controlled by a known means, for example a control slider or speed that reduces the effective pumping stroke depending on its relative position with respect to the rotor. Controlled by a device for The pressure downstream of the lower pressure stage changes due to the change in the pumping flow of the lower pressure stage.

Therefore, the compressor in the upper pressure stage must also be equipped with a device for changing the control slider or compressor speed for changing the pumping volume. Since this compressor must be suitable for large pressures up to about 120 bar, the construction of the compressor with a control slider will incur additional costs.
German Patent Application Publication No. 10334947 Patent Application No. 102005018602.5 Patent application number 102007003983.3 Patent application number 102007003989.3

  The object of the present invention is to eliminate the disadvantages of known devices, to provide efficient and inexpensive output control, specifically to configure the upper pressure stage compressor without a control slider, and to reduce the drive rotational speed. It is to operate without a device to change. It is a further object of the present invention to adapt the pressure before the compressor in the upper pressure stage by another suitable means and method.

In order to solve the above problems, the configuration of the present invention includes the following four functions a) to d):
a) degree of mainstream supercooling in the supercooler;
For this purpose, the refrigerant diversion through the subcooler is increased or decreased by controlled opening or closing of the throttle valve, or after complete closure of the throttle valve, the “upper” auxiliary subcooler, “intermediate” And / or the “lower” auxiliary subcooler are shut down one after another.
b) the degree of superheat to be adjusted in the feeler which is located at the outlet of the subcooler in the split flow and is part of the controllable throttle valve;
c) a change in the intermediate pressure in the secondary flow path by the controlled opening or closing of a pressure control valve located downstream of the respective subcooler in the conduit guiding the diversion;
d) change of the compression final pressure of the upper stage;
For this purpose, a throttle valve located downstream of the gas cooler reduces this pressure to reduce the refrigeration capacity, increases it to an optimum value between the refrigeration capacity and the driving power, and increases the optimum Because of the high pressure, control algorithms exist independently of part load control.
These four functions are combined or exist independently.

In an advantageous configuration of the invention, the pressure sensor is arranged in the pressure tube downstream of the compressor in the upper pressure stage, and the temperature sensor is arranged downstream of the CO ₂ outlet of the gas cooler. In another advantageous configuration of the invention, a control algorithm exists as a function of the gas cooler outlet temperature for optimum pressure independent of part load control.

In the present invention, the pressure before the compressor in the upper pressure stage is controlled by a combination of a plurality of functions.
a) depending on the degree of mainstream subcooling in the liquid subcooler, arranged one after the other along the flow path and formed as a heat exchanger;
Two refrigerant streams are divided and guided through the heat exchanger. The two refrigerant streams exchange heat when passing through the heat exchanger based on different temperatures. The main stream of the refrigerant is cooled at that time (this is referred to as “Unterkuehlung”). The branch stream of the refrigerant branched from the main flow in front of the heat exchanger and expanded to a lower pressure in the throttle valve in front of the heat exchanger evaporates as a result of heat absorption from the main flow. The diversion is also referred to as refrigerant supply to the liquid subcooler. In order to control the pressure before the compressor in the upper pressure stage, the liquid subcooler is shut down one after another. A stop valve in the refrigerant supply is closed to decrease the output and opened to increase the output.
b) by changing the superheat of the diversion after the liquid subcooler, measured at the outlet of the intercooler;
The superheat is increased or decreased at the intercooler outlet depending on the pressure before the compressor in the upper pressure stage. Superheat is the temperature difference between the actual outlet temperature of the split after the liquid separator and the evaporation temperature in the liquid separator as defined by the pressure of the split. For this purpose, the valve provided at the outlet of the intercooler is adjusted and opened or closed in order to change the degree of supercooling of the main refrigerant after passing through the liquid supercooler.
c) by changing the intermediate pressure;
Before the economizer connection of both pressure stages, a control valve is advantageously arranged to control the volume flow to the economizer connection and thus the refrigeration capacity of the refrigeration system. In this form of control according to the invention, the valves arranged between the intermediate cooler outlet and the respective intermediate pressure supply point to the economizer connection or to the intermediate pressure connection are adjusted open or closed.
d) by changing the compression final pressure of the upper pressure stage;
This regulation for controlling the refrigeration capacity is that the refrigeration capacity of the upper pressure stage is above the critical point when the refrigerant vapor in the gas cooler is cooled, above the CO ₂ outlet temperature from the gas cooler and the final compression pressure of the upper stage. Take advantage of the situation of changing with. The refrigeration capacity is changed by a change in the final compression pressure of the upper stage at the throttle valve disposed downstream of the gas cooler. In order to reduce the refrigeration capacity, this pressure is lowered by opening this valve and the valve is further closed to increase the refrigeration capacity to an optimum value between the refrigeration capacity and the driving power, so that the compression final pressure is It is raised to the optimum value between the capacity and the driving force. The optimum value is obtained independently of partial load control by a unique control algorithm.

  Control of the refrigeration capacity of the refrigeration system is wide-ranging, either by a combination of the control methods a) to d) described above or individually, either by a unique bypass valve device or by a compressor in the upper pressure stage without rotational speed control. Is possible.

  The lower pressure stage compressor has known means for power control, such as a control slider or a variable speed, for the purpose of changing the pump flow for adaptation to the vapor volume flow from the evaporator. Equipped with a drive unit. At that time, the control slider forms a peripheral wall portion of the casing surrounding the rotor, and opens a bypass opening in the casing for the purpose of changing the pumping amount of the compressor. Through the bypass opening, a part of the sucked pumping volume is guided back to the suction side of the compressor.

  This changes the mass flow rate that is pumped by the compressor and applied to the enthalpy difference that produces the refrigeration capacity.

The individual control methods of the two-stage CO ₂ refrigeration apparatus provided with the two-stage screw compressor unit will be described below. The numbers used relate to the exemplary drawings.

The screw compressor 1 in the lower pressure stage and the screw compressor 2 in the upper pressure stage are arranged in series in the flow direction. Each of the screw compressors 1 and 2 has one economizer connection 25 and 26. An intermediate pressure connection 40 is provided in the connection line 13 between the screw compressors 1 and 2. Between the outlet on the CO ₂ side of the gas cooler 4 and the inlet to the evaporator system provided with the liquid separator 8, a connecting line 30 for guiding the refrigerant is disposed. The connection line 30 forms a flow path for the refrigerant main flow between the outlet of the gas cooler 4 and the evaporator system including the expansion device 41, and has partial surfaces of the heat exchangers 31, 32, and 33. . The three heat exchangers 31, 32, and 33 are serially arranged with respect to this flow path. At that time, the heat exchanger 31 is formed as an “upper” auxiliary subcooler, the heat exchanger 32 is formed as an “intermediate” subcooler, and the heat exchanger 33 is formed as a “lower” auxiliary subcooler. Yes. As already described, a part of the flow path exists on one side of the heat exchange surfaces of the heat exchangers 31, 32, and 33, and the flow path passes through throttle valves 34, 35, and 36. There is a liquid branch to the other side of each heat exchanger face. The outlets on this side of the heat exchangers 31, 32, 33 are the economizer connection portions 25, 26 of the screw compressors 1, 2 and the intermediate pressure connection portion 40 provided between the upper and lower screw compressors 1, 2. And connected to.

The above four functions a) to d) that are combined or established independently will be described below.
a) The degree of mainstream supercooling in the supercooler is changed. For this purpose, the refrigerant diversion through the liquid subcoolers 31, 32, 33 is increased or decreased by controlled opening or closing of the throttle valves 34, 35, 36. This changes the degree of cooling of the fluid before entering the liquid separator, thereby changing the refrigeration capacity per unit volume.
b) The throttle valves 34, 35 and 36 are formed as throttle valves which are electrically operated, for example, and the overheating at the refrigerant outlet can be controlled. Depending on the parameter to be controlled, for example the pressure in the liquid separator, the degree of superheat to be adjusted in the feelers of these valves provided at the outlets of the diverters of the heat exchangers 31, 32, 33 can increase or decrease the refrigeration capacity. To do.
c) For changing the intermediate pressure at the connection points 25, 26, 40, the pressure control valves 42, 43, 44 have a volume flow rate to the connection point 40 between the economizer connections 25, 26 and the compressors 1, 2. Is arranged to control the refrigerating capacity of the refrigerating apparatus. For this purpose, the valves 42, 43, 44 arranged between the outlets of the intermediate coolers 31, 32, 33 and the respective intermediate pressure supply points to the economizer connection or the intermediate pressure connection are adjusted. Open or closed.
d) The change in the final compression pressure of the upper stage of the screw compressor 2 by the throttle valve 45 disposed downstream of the gas cooler 4 affects the refrigeration capacity. The pressure is lowered to reduce the refrigeration capacity and raised to increase the refrigeration capacity to an optimum value between the refrigeration capacity and the driving power. Maximum pressure is limited by the upward via the control algorithm as a function of CO ₂ gas cooler outlet temperature. The pressure is the optimal pressure for optimal energy supply.

Is a diagram showing a CO ₂ refrigeration system 2 stage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Screw compressor 2 Screw compressor 4 Gas cooler 8 Liquid separator 13 Connection line 25 Economizer connection part 26 Economizer connection part 30 Connection pipe line 31 Heat exchanger 32 Heat exchanger 33 Heat exchanger 34 Throttle valve 35 Throttle valve 36 Throttle valve 40 Intermediate Pressure Connection 42 Pressure Control Valve 43 Pressure Control Valve 44 Pressure Control Valve 45 Throttle Valve

Claims (1)

A control method for a two-stage CO ₂ refrigeration system having a two-stage screw compressor unit in which oil-injected screw compressors are arranged in two stages, wherein the screw compressors move in the flow direction. The screw compressors of the upper and lower pressure stages each have one intermediate pressure opening, the so-called economizer connection, and the economizer connection in the tooth gap of the rotor in the casing with respect to the flow As long as it communicates with the tooth gap, it is adjacent so that there is no flow connection to the suction side and no flow connection to the discharge side, and an intermediate pressure connection is provided in the connection line between the screw compressors of both pressure stages Between the CO ₂ gas cooler outlet and the CO ₂ inlet to the evaporator system, there is a primary flow path for the main refrigerant flow between the gas cooler outlet and the evaporator system with the throttle device. In the primary flow path At least three heat exchangers are arranged serially with respect to this primary flow path, these heat exchangers being “upper” auxiliary subcoolers, “middle” subcoolers and “lower” A part of the primary flow path is adjacent to one side of the heat exchanger surface of the subcooler, and the other side of the heat exchanger surface is connected to the second side of the heat exchanger surface. A portion of the secondary flow path is adjacent to the secondary flow path portion of the upper stage screw compressor through the throttle valve, subcooler and line from the primary flow path. The economizer connection, the intermediate pressure connection between the upper and lower screw compressors, and the flow connection to the economizer connection of the lower screw compressor, and has a conduit and a controllable valve A two-stage screw compressor unit in which oil-injected screw compressors are arranged in two stages. In the control method of the two-stage CO ₂ refrigeration system including a
The following four functions a) to d), namely:
a) degree of mainstream supercooling in the supercooler;
For this purpose, the refrigerant diversion through the subcooler is increased or decreased by controlled opening or closing of the throttle valve (34, 35, 36) or the throttle valve (34, 35, 36) is completely closed. Thereafter, the “upper” auxiliary subcooler, the “intermediate” subcooler and / or the “lower” auxiliary subcooler are shut down one after another.
b) the degree of superheat to be adjusted in the feeler which is part of the controllable throttle valve (34, 35, 36), which is arranged at the outlet of the subcooler in the diversion;
c) intermediate in the secondary flow path by the controlled opening or closing of the pressure control valves (42, 43, 44) arranged downstream of the respective subcoolers in the pipes guiding the diversion Pressure change;
d) change of the compression final pressure of the upper stage;
For this purpose, a throttle valve (45) arranged downstream of the gas cooler lowers this pressure to reduce the refrigeration capacity and raises it to an optimum value between the refrigeration capacity and the driving power. And for optimal pressure, a control algorithm exists independently of part load control.
A two-stage CO having a two-stage screw compressor unit in which oil-injected screw compressors are arranged in two stages, characterized in that the above four functions are combined or exist independently. ₂ Control method of refrigeration equipment.

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