Method for controlling a refrigeration system, comprising at least one compressor

Abstract

The invention is a method for controlling a refrigeration system, comprising at least one compressor, a motorized suction valve, a motorized discharge valve, and a degassing valve, characterized in that the shutdown command comprises the following steps: Stopping the operation of said compressor; closing the motorized discharge valve; after a predetermined delay from the compressor shutdown, closing the suction valve; when the pressure in the compressor casing is stable, opening a valve located between the compressor discharge and a low-pressure reservoir, and in the event of a pressure increase, activating an alarm. Figure 1:

Description

Title of the invention: Method for controlling a refrigeration installation, comprising at least one compressor Field of invention

[0001] The present invention relates to the field of refrigeration installations using compressors of refrigerant fluid such as ammonia and more particularly installations using several volumetric compressors associated in parallel, of the reciprocating piston type for gas recompression or heat pump (HP) applications.

[0002] Refrigerants commonly used in the past, such as CFCs (chlorofluorocarbons) and HFCs, have been gradually banned as harmful to the environment due to too high global warming potential (GWP) and ozone depletion potential (ODP), refrigerants such as HFOs and natural fluids such as ammonia are commonly used today.

[0003] These refrigerants can cause damage when, under certain conditions, particularly during machine shutdown phases, the refrigerant fluid condenses within the casing of a compressor.

[0004] In known installations, the mixture of oil and refrigerant under pressure circulating in the refrigeration circuit can condense in the crankcase. The damage caused is irreversible. This phenomenon is known in the refrigeration industry and is commonly referred to as "liquid slugging", which damages the valves, the top of the piston and often the compressor jacket. Prior art

[0005] To reduce the risk of damage caused by liquid slugging, a thermostatic expansion valve is generally used. Also known in the prior art is patent CN103644109 disclosing a method for preventing the lubricating oil of a piston-type ammonia compressor from being emulsified. Drain valves are mounted respectively at the front end of a gas inlet valve and at the rear end of a gas discharge valve of the piston-type ammonia compressor. The method for preventing the lubricating oil of the piston-type ammonia compressor from being emulsified comprises the following steps:

[0006] (1) closing the drain valve at the front end of the gas inlet valve and from the drain valve to the rear end of the ammonia compressor gas vent valve before starting the ammonia compressor;

[0007] (2) discharge the liquid ammonia and then instantly open a liquid ammonia valve. pressure relief in an original pipeline system to release pressure in the pipeline; and

[0008] (3) open the drain valve at the front end of the gas inlet valve and the drain valve at the rear end of the ammonia compressor gas vent valve when the needle of a gauge on a compressor gas inlet and gas vent line returns to the aerodynamic positions.

[0009] Also known is Chinese patent CN110425112B describing a solution for avoiding liquid slugging in a refrigerant circulation loop consisting of at least one compressor, a reversing valve, a first heat exchanger, a throttling device, a second heat exchanger and a liquid storage tank which are connected together in a sequential manner. The installation also comprises an outdoor ambient temperature sensor and a compressor gas return sensor.To prevent compressor liquid slugging, this solution involves comparing the actual measured outdoor temperature T with an outdoor temperature T config, configured by an air conditioning system to determine whether to open the control valve; and when the actual measured outdoor ambient temperature T is lower than the outdoor ambient temperature T config, opening the control valve so that a portion of a high-temperature refrigerant discharged from a gas discharge port of the compressor enters the bypass line to preheat the compressor, thereby preventing compressor liquid slugging.

[0010] Chinese patent CN109863355B discloses a system comprising a sensor and a controller for a refrigeration or air conditioning system having a compressor. The sensor detects a temperature of the compressor during operation of the compressor. The controller is configured to determine a rate of change of the temperature with respect to time and to perform one or more procedures to protect the compressor based on the rate of change of the temperature. The one or more procedures to protect the compressor include stopping the compressor, throttling a pressure control valve of an evaporator associated with the compressor, adjusting an expansion valve associated with the evaporator, reducing the speed of the compressor, and partially or completely unloading the compressor.

[0011] The purpose of this prior art solution is to prevent the emulsion of the lubricating oil of the piston type ammonia compressor, to ensure the normal operation of the ammonia compressor and to prevent the interruption of liquid ammonia, thereby ensuring safe operation.

[0012] European patent EP3317596B1 is also known, proposing a method comprising the following steps: - monitoring and controlling, with a system controller, a refrigeration or HVAC system having a compressor rack with at least one compressor; - monitoring and control, with a rack controller, of the operation of the compressor rack; - determining, with the system controller, a return discharge temperature corresponding to a return condition, which is a minimum permissible discharge temperature determined on the basis of inputs including compressor efficiency, refrigerant properties and operating pressures; - receiving, with the system controller, an actual discharge temperature associated with the compressor rack; - comparison, with the system controller, of the actual discharge temperature with the return discharge temperature; - generating, with the system controller, a notification to the rack controller based on the comparison; and - generation, with the system controller, of the notification when a difference between the return discharge temperature and the actual discharge temperature is below a predetermined threshold. Disadvantages of the prior art

[0013] The solution of the prior art is not entirely satisfactory because it is not suitable for the automatic operation of an industrial refrigeration installation composed of one or more piston motor compressors mounted in parallel and used in high-temperature gas recompression or heat pump (HP). Solution provided by the invention

[0014] In order to overcome this drawback, the present invention relates, in its most general sense, to a method for controlling a refrigeration installation, comprising at least one compressor, a motorized suction valve, a motorized discharge valve and a degassing valve, characterized in that the shutdown control comprises the following steps: • Stopping the operation of said compressor • Closing of the motorized discharge valve • After a predetermined time from the compressor stopping, the suction valve closes • In case of increase in pressure, activation of an alarm. • When the pressure in the compressor casing is stable, opening of a valve located between the compressor discharge and a low pressure tank pressure.

[0015] According to a preferred embodiment, the compressor start-up control comprises the following steps: • opening of said motorized suction valve which allows the compressor to suck in the ammonia contained in a pressurized tank • control of the start-up of said compressor and maintenance of said motorized discharge valve connecting the first compressor to the condenser in the closed position, in the event of a vacuum in the discharge pipe of the first compressor • opening of said motorized discharge valve when the pressure difference PT2 measured by a pressure sensor upstream of said motorized discharge valve and the pressure PT5 measured by a pressure sensor downstream of the motorized discharge valve exceeds a predetermined value.

[0016] According to a preferred embodiment, said refrigeration installation comprises a plurality of compressors, motorized suction valves, discharge valves and degassing valves and in that

[0017] the start command includes the following steps: • opening of said motorized suction valve which allows control of the suction by the compressor of the ammonia contained in a pressurized tank • control of the start-up of said compressor and maintenance of said motorized discharge valve connecting the second compressor to the condenser in the closed position, in the event of a vacuum in the discharge pipe of the second compressor • Maintaining in the closed position a motorized valve connecting said second compressor to the condenser in the event of a vacuum in the discharge pipe of the second compressor • Opening of said motorized valve when the pressure difference PT4 measured by a pressure sensor upstream of said motorized valve and the pressure PT5 measured by a pressure sensor downstream of the motorized valve exceeds a predetermined value in the event of positive pressure in the discharge pipe of the second compressor

[0018] According to a particular variant, said refrigeration installation comprises a plurality of compressors and in that the stop control comprises the following steps: - Stopping the second compressor and closing the motorized discharge valve arranged at the discharge outlet of the compressor before the condenser - after a predetermined delay, closing of the motorized valve located at the compressor inlet before the pressure tank - measurement of PT3 pressure in the compressor casing to check the condition of the discharge valves - if the PT3 pressure measured by the pressure sensor in the casing increases to the high pressure setpoint, then a “non-sealing discharge valve” alarm is activated - if the PT3 pressure measured by the pressure sensor in the compressor casing is stable, control of the opening of the motorized valve placed between the compressor discharge and a low pressure tank in order to drop the pressure until it reaches a set value.

[0019] Advantageously, said stop command further comprises the following steps: - Stopping the other compressor and closing the motorized discharge valve located at the outlet of said compressor before the condenser - after a predetermined delay, closing of the motorized valve located at the compressor inlet before the pressure tank - measurement of the PT1 pressure in the compressor casing by a pressure sensor • If the PT1 pressure in the casing of the first compressor increases to the high pressure setpoint, activation of a “Discharge valves not tight” alarm • If the pressure PT1 in the casing of the first compressor is stable, then the opening of the valve placed between the compressor outlet and a low-pressure reservoir is controlled in order to reduce the pressure until it reaches a set value. • If the PT1 pressure in the compressor casing is lower than this setpoint, the valve closes Detailed description of a non-limiting example of embodiment

[0020] The present invention will be better understood on reading the following description, concerning a non-limiting example of embodiment illustrated by the appended drawings where:

[0021] [FIG. 1] [Fig.l] shows a schematic view of the valves on the suction and discharge lines of the compressors. General principle

[0022] The invention consists in defining a procedure for maintaining optimal stopping and starting conditions for one or more compressors installed in parallel, for a gas recompression installation or PAC whose refrigerant fluid is preferably ammonia. Its saturation rate in the oil can be reduced by lowering the pressure and / or increasing the temperature. These actions promote the evaporation of the refrigerant from the mixture and, consequently, eliminate any risk of liquid slugging upon restart and lack of lubrication of moving mechanical parts. Acceptable temperature and pressure tolerances will depend on the viscosity recommendations of the oil used, necessary to ensure good lubrication of each compressor.

[0023] Operation of the installation during startup

[0024] [Fig. 1] is a schematic representation of a non-limiting example of embodiment of the invention, according to an installation variant implementing two compressors (300, 400) in parallel and using ammonia as refrigerant fluid.

[0025] The following description of the start-up cycle begins when the installation is stopped. The start-up procedure is initiated by opening the motorized valve (301) which controls the suction of the first compressor (300) of the ammonia contained in a pressurized tank (500).

[0026] When the motorized valve (301) is open to ensure the gas supply to the first compressor (300), the start-up of this first compressor (300) is controlled. To prevent the reflux of ammonia towards the first compressor (300) from the high-pressure circuit, the motorized discharge valve (302) connecting the first compressor (300) to the condenser (200) is closed, in the event of a vacuum in the discharge pipe of the first compressor (300), in particular if the difference between: - The pressure PT2 measured by a pressure sensor (303) upstream of the motorized discharge valve (302) and - the pressure PT5 measured by a pressure sensor (210) downstream of the motorized discharge valve (302) is lower than a threshold, for example 0.2 bar. Commissioning of other compressors

[0027] If the first compressor (300) operates at its maximum power, the automaton controlling the installation authorizes the opening of the motorized valve (401) which controls the supply of the second compressor (400) with the ammonia contained in the pressure tank (500).

[0028] When the second motorized valve (401) is open to ensure the gas supply to the second compressor (400), the start-up of this second compressor (400) is controlled. To prevent the reflux of ammonia to the second compressor (400) from the high-pressure circuit, the motorized valve (402) connecting the second compressor (400) to the condenser (200) is closed, in the event of a vacuum in the discharge pipe of the first compressor (400), in particular if the difference between: - The pressure PT4 measured by a pressure sensor (403) upstream of the motorized discharge valve (402) and - the PT5 pressure measured by a pressure sensor (210) downstream of the valve motorized (402) is below a threshold, for example 0.2 bar.

[0029] The two compressors (300, 400) are then in operation and protected against mutual gas reflux. Stopping the installation

[0030] If the second compressor (400) operates at its minimum power for a predefined duration, for example 5 minutes, the installation's controller controls its shutdown. The shutdown cycle includes stopping the second compressor (400) and jointly closing the motorized discharge valve (402) arranged at the outlet of the compressor (400), before the condenser (200).

[0031] Then, after a predetermined delay, for example 60 seconds, the closing of the motorized valve (401) arranged at the inlet of the compressor (400), before the pressure tank (500) is commanded. The closing of the suction valve (401) prevents the re-entry of ammonia in the gaseous phase and the closing of the discharge valve (402) prevents the discharge coming from the other compressors), they and achieve the isolation of the compressor at a standstill. A pressure sensor (405) measures the pressure PT3 in the casing of the compressor (400) to check the state of sealing between the high pressure and the low pressure internal to the compressor.

[0032] If the pressure PT3 measured by the pressure sensor (405) in the casing increases to the high pressure setpoint then a “discharge valves not sealing” alarm is activated.

[0033] If the pressure PT3 measured by the pressure sensor (405) in the compressor casing (400) is stable, then the opening of the motorized valve (406) placed between the discharge of the compressor (400) and a low-pressure reservoir (420) is controlled in order to cause the pressure to drop until it reaches a set value (for example 8.5 bar at 20°C for ammonia) in order to prevent condensation of the refrigerant in the compressor (400).

[0034] If the pressure PT3 measured by the pressure sensor (405) in the casing in the compressor casing (400) is lower than this set value, the controller controls the closing of the valve (406).

[0035] At the end of the compressor shutdown cycle (400), the latter is isolated by closed valves (401, 402 and 406).

[0036] A check of the pressure PT4 by the sensor (403) placed at the outlet of the second compressor (400) is then carried out. It makes it possible to check the tightness of the valve (402) placed between the second compressor (400) and the condenser (200).

[0037] If the pressure PT4 measured by the sensor (403) increases to the high pressure setpoint at standstill, then a “leaky valve” alarm is activated. Stopping the first compressor (300)

[0038] If the temperature of the process to be heated is higher than the setpoint of the heating stop request, the installation's controller lowers the first compressor (300) to its minimum power. If the first compressor (300) operates at its minimum power for a predefined duration, for example 5 minutes, the installation's controller orders it to be switched off.

[0039] The shutdown cycle includes stopping the first compressor (300) and jointly closing the motorized discharge valve (302) arranged at the outlet of the compressor (300), before the condenser (200).

[0040] Then, after a predetermined delay, for example 60 seconds, the closing of the motorized valve (301) arranged at the inlet of the compressor (300), before the pressurized refrigerant liquid tank (500) is commanded.

[0041] A pressure sensor (305) measures the pressure PT1 in the compressor casing (300) to check the sealing condition between the high pressure and the low pressure internal to the compressor.

[0042] If the pressure PT1 in the casing of the first compressor (300) increases to the high pressure setpoint then a “Discharge valves not tight” alarm is activated.

[0043] The pressure will be considered stable if the pressure variations do not exceed a predetermined value, for example 0.1 bar, over a predetermined time window, for example 3 minutes.

[0044] If the pressure PT1 in the casing of the first compressor (300) is stable, then the opening of the valve (306) placed between the discharge of the compressor (300) and a low-pressure reservoir (320) is controlled in order to cause the pressure to drop until it reaches a set value (for example 8.5 bar at 20°C for ammonia) in order to prevent condensation of the refrigerant in the compressor (300).

[0045] If the pressure PT1 in the compressor casing (300) is lower than this setpoint, the valve (306) is closed.

[0046] At the end of the compressor shutdown cycle (300), the latter is isolated by closed valves (301, 302 and 306).

[0047] A check of the PT2 pressure by the sensor (303) placed at the outlet of the first compressor (300) is then carried out. It makes it possible to check the tightness of the motorized discharge valve (302). If the PT2 pressure increases to the high pressure setpoint at standstill, then a “Valve not tight” alarm is activated.

[0048] For each compressor shutdown, a glycol water network maintains the compressor cylinder heads at 50°C. An electrical resistor maintains the oil in the crankcase at 60°C.

Claims

Claims

1. - Method for controlling a refrigeration installation, comprising at least one compressor (300), a motorized suction valve (301), a motorized discharge valve (302) and a degassing valve (306) characterized in that the control of the stop comprises the following steps: - Stopping the operation of said compressor (300) - Closing the motorized discharge valve (302) - After a predetermined time from the stop of the compressor (300), closing the suction valve (301) - When the pressure in the casing of the compressor (300) is stable, opening a valve (306) arranged between the discharge of the compressor (300) and a low pressure tank (320), and in the event of an increase in pressure, activation of an alarm.

2. - Method for controlling a refrigeration installation, according to claim 1 characterized in that the control of the start of the compressor (300) comprises the following steps: - opening of said motorized suction valve (301) which controls the suction by the compressor (300) of the ammonia contained in a pressurized tank (500) - control of the start of said compressor (300) and maintaining said motorized discharge valve (302) connecting the first compressor (300) to the condenser (200) in the closed position, in the event of a vacuum in the discharge pipe of the first compressor (300) - opening of said motorized discharge valve (302) when the pressure difference PT2 measured by a pressure sensor (303) upstream of said motorized discharge valve (302) and the pressure PT5 measured by a pressure sensor (210) downstream of the motorized discharge valve (302) exceeds a predetermined value.

3. - Method for controlling a refrigeration installation according to claim-

4. dication 1, characterized in that said refrigeration installation comprises a plurality of compressors (300) (400), a motorized suction valve (301) (401), discharge valves (302) (402) and degassing valves (306) (406) and in that The start command consists of the following steps: - Opening of said motorized suction valve (401) which controls the suction by the compressor (400) of the ammonia contained in a pressure tank (500) - controlling the start of said compressor (400) and maintaining said motorized discharge valve (402) connecting the second compressor (400) to the condenser (200) in the closed position, in the event of a vacuum in the discharge pipe of the second compressor (400) - Maintaining in the closed position a motorized valve (402) connecting said second compressor (400) to the condenser (200), in the event of a vacuum in the discharge pipe of the second compressor (400), - Opening of said motorized valve (402) when the pressure difference PT4 measured by a pressure sensor (403) upstream of said motorized valve (402) and the pressure PT5 measured by a pressure sensor (210) downstream of the motorized valve (402) exceeds a predetermined value, in the event of positive pressure in the discharge pipe of the second compressor (400). - Method for controlling a refrigeration installation according to claim 1, characterized in that said refrigeration installation comprises a plurality of compressors (300) (400) and in that the stop command comprises the following steps: - Stopping the second compressor (400) and closing the motorized discharge valve (402) located at the discharge outlet of the compressor (400), before the condenser (200) - after a predetermined delay, closing of the motorized valve (401) arranged at the inlet of the compressor (400), before the pressure tank (500) - closing the discharge valve (402) - measurement of PT3 pressure in the compressor casing (400)

5. to check the condition of the discharge valves - if the PT3 pressure measured by the pressure sensor (405) in the casing increases to the high pressure setpoint, then activation of a “non-sealing discharge valve” alarm - if the pressure PT3 measured by the pressure sensor (405) in the casing in the compressor casing (400) is stable, control of the opening of the motorized valve (406) placed between the discharge of the compressor (400) and a low pressure tank (420) in order to drop the pressure until it reaches a set value. - Method for controlling a refrigeration installation according to the preceding claim, characterized in that said stop command further comprises the following steps: - Stopping the other compressor (300) and closing the motorized discharge valve (302) arranged at the outlet of said compressor (300), before the condenser (200) - after a predetermined delay, closing of the motorized valve (301) arranged at the inlet of the compressor (300), before the pressure tank (500) - measurement of the pressure PT1 in the compressor casing (300) by a pressure sensor (305). • If the PT1 pressure in the casing of the first compressor (300) increases to the high pressure setpoint, activation of a “Discharge valves not tight” alarm • If the pressure PT1 in the casing of the first compressor (300) is stable, then the opening of the valve (306) placed between the outlet of the compressor (300) and a low-pressure reservoir (320) is controlled in order to reduce the pressure until it reaches a set value. • If the pressure PT1 in the compressor casing (300) is lower than this setpoint, close the valve (306).

Images