CO2 radial piston compressor (transcritical)

At a glanceOperating limits and performance data Technical dataDimensions and connectionsScope of supply

124126129130131

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Bock has developed this new radial piston compressor with Obrist Engineering GmbH, who has also worked on the development of CO2 compressors for a long time.

Additionally, the RKX is a radial piston compressor, providing a very compact arrangement. It is a compressor with future potential - ideal for small to medium capacities.

The compact engineering design, universal possibilities for instal-lation (vertically or horizontally) as well as the 6-cylinder construc-tion that is radially arranged on one level, result in completely new dimensions for the working range and potential for development of the compressor itself (potential operating pressure up to 130 bar).

Important Information

Transcritical - CO2 applications are still in the development phaseThey require a completely new kind of system and control -

They are not a general solution for the substitution of F-gases -

We specifically point out that all information in this chapter has -

been made based on our current level of knowledge and may change at any time due to further development. Compressors can only be made available for selected projects -

Radial piston compressor (transcritical) - At a glance

CO2 as a refrigerant

Within refrigeration technology, carbon dioxide (CO2) is known by the name R744 and has a long history. It is a colourless gas which liquefies under pressure and has a slightly acidic smell and taste. Carbon dioxide has no ozone depletion potential (ODP=0) and a ne-gligible direct effect on global warming (GWP=1) when used as a refrigerant in closed systems. It is not combustible, is chemically inactive and heavier than air. Carbon dioxide has a narcotic and asphyxiating effect on humans only at higher concentrations. As carbon dioxide is less energy ef-ficient than other refrigerants, recently work has particularly con-centrated on optimising plant technology for specific applications.Carbon dioxide is available naturally in large quantities.

Special features of CO2 transcritical

Based on the high CO2 pressure and the low temperature of the critical point of 31°C (74 bar), transcritical operating conditions oc-cur at higher temperatures at the heat exchanger. In this case, in comparison to subcritical applications, the refrigerant CO2 can no longer be condensed. In this case, the refrigerant gas is heated in a gas cooler. The temperature and the pressure are dependent on each other, compared to the subcritical operation.A special feature in these operating points is the necessary regula-tion of the high pressure at the so-called optimal high pressure. In doing this, the greatest possible enthalpy difference at the evapora-tor and the lowest possible power consumption of the compressor should be reached. In this way, the maximum coefficient of perfor-mance (COP) of the system is achieved. An additional valve with intelligent control after the high-pressure heat exchanger is needed for this in the system.For additional technical data, see Bock software

Available modelsDisplacement

50 Hz

RKX26/31-4 CO2 T 2,7 m3/h (1.450 1/min)

RKX26/31-2 CO2 T 5,4 m3/h (2.900 1/min)

tga = 35° Ctga = 40° C

tga = 45° Ctga = 50° C

tga = Gas cooler outlet temperatureLimit conditions: isentrope compression Evaporation pressure = 40 bar with internal heat exchanger

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Special Features

Simple total construction, aligned to the special requirements in -

the transcritical sector Only two surface seals on the entire compressor (housing cover, -

electrical terminal board)Pot-shaped, closed housing made of spheroidal cast iron for -

maximum pressure strengthComplete power train integrated in the housing, no cylinder cover -

requiredOnly a few small high-pressure compartments -

Valve operation according to the unifl ow principle, the suction gas -

is pushed in one direction through the piston and is thus com-pressed. There are no alternating gas movements and a minimum amount of gas pulsationCentrifugal lubrication with integrated oil separation -

Excellent operating characteristics – radial arrangement of six -

cylinders on one level Well dimensioned drive motors, partially suction gas cooled, in -

2 and 4 pole versions (2.900 and 1.450 1/min) Suction and discharge connections using screwed cutting ring -

joints for steel pipes (without shut-off valves)Decompression valves for the suction and - pressure area Electrical connection box to IP65 with Bock MP10 motor protec- -

tion

Radial piston compressor (transcritical) - At a glance

Type key | Radial piston compressor (transcritical)

RK X26 / 31 - 4 CO2 T

Transcritical CO2 version Number of poles Swept volume Number of cylinders Size Ester oil fi lling Series 1)

1) RK = Radial piston

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Notes

Oil

The compressors are equipped with Bock C120E, a special oil filling, which is available directly from Bock. This is a synthetic ester oil with high thermal load resistance, allowing good mi-xing solubility with CO2. It possesses a special additive, which protects the compressors against wear,even when subjected to extreme loads, such as those which exist in CO2 systems. This oil can be used both in transcritical and subcritical systems.

phase separation

concentration (M-% oil in CO )2

tem

pera

ture

(C°)

Operating limits RKX26/31-2 CO2 T | RKX26/31-4 CO2 T

Unlimited application range

tO Evaporating temperature (°C)∆tOh Suction gas superheat (K)pO Suction pressure (bar)pV2 High pressure (bar)

Max. permissible operating pressure (LP/HP)1): 90/130 bar

1) LP = low pressure HP = high pressure

1 RKX26/31-4 CO2 T min. evaporating temperature tO = -5 °C (30,4 bar)

1

Notes

Operating limits

Compressor operation is possible within the limits shown on the application diagrams. Please note the coloured areas.Compressor application limits should not be chosen for design purposes or continuous operation.

Performance data

Performance data for CO2 are based on 10 K suction-gas superheating at 50 Hz. In case of subcritical operating conditions, no liquid undercooling takes place. The perfor-mance data for transcritical operating conditions are speci-fied close to the "optimal high pressure". The optimal high pressure is thereby related to an ideal cyclic process.

Conversion factor for 60 Hz = 1,2

Radial piston compressor (transcritical) - Operating limits

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Type Cooling capacity QO [W] Power consumption Pe [kW]

Evaporating temperature °C

15 10 5 0 -5

tc °C SUBCRITICAL

10QP

RKX26/31-4 CO2 T

15QP

20QP

25QP

30QP

tga °C TRANSCRITICAL

RKX26/31-4 CO2 T

30pV2 QP

35pV2 QP

40pV2 QP

45pV2 QP

50pV2 QP

•

11950 1,75

12900 10700 1,85 2,10

13950 11550 9300 1,90 2,25 2,40

14400 12050 9800 7750 2,00 2,35 2,55 2,65

13450 11300 9350 7600 6050 2,10 2,45 2,70 2,85 2,85

75 75 75 75 75 14250 11950 9850 7950 6200 2,35 2,65 2,90 2,95 2,95

85 85 85 90 90 12500 10450 8600 7200 5550 2,90 3,10 3,20 3,30 3,15

100 100 100 100 105 11600 9600 7800 6150 4650 3,60 3,65 3,60 3,50 3,35

110 110 115 115 110 10050 8250 6750 5200 3800 4,00 4,00 4,05 3,85 3,45

125 125 130 125 110 9150 7500 6200 4550 2950 4,75 4,65 4,75 4,30 3,45

CO2 Performance data 50 Hz

Subcritical performance data 50 HzRelative to 10 K suction gas superheat without liquid subcooling

Transcritical performance data 50 HzRelative to 10 K suction gas superheat

The performance data are indicated at a high pressure level, which is close to an optimal high pressure level. Optimal high pressure is thereby related to an ideal cyclic process.

tc = Condensing temperaturetga = Gas cooler outlet temperaturepV2 = Pressure at the compressor outlet [bar]

Optimal high pressure is outside of the operating limits.Performance data are indicated at maximal possible high pressure.

Radial piston compressor (transcritical) - Performance data

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Type Cooling capacity QO [W] Power consumption Pe [kW]

Evaporating temperature °C

15 10 5 0 -5 -10 -15 -20

tc °C SUBCRITICAL

RKX26/31-2 CO2 T

10QP

15QP

20QP

25QP

30QP

tga °C TRANSCRITICAL

RKX26/31-2 CO2 T

30pV2 QP

35pV2 QP

40pV2 QP

45pV2 QP

50pV2 QP

•

CO2 Performance data 50 Hz

Subcritical performance data 50 HzRelative to 10 K suction gas superheat without liquid subcooling

Transcritical performance data 50 HzRelative to 10 K suction gas superheat

The performance data are indicated at a high pressure level, which is close to an optimal high pressure level. Optimal high pressure is thereby related to an ideal cyclic process.

tc = Condensing temperaturetga = Gas cooler outlet temperaturepV2 = Pressure at the compressor outlet [bar]

Optimal high pressure is outside of the operating limits.Performance data are indicated at maximal possible high pressure.

20350 16600 13300 10400 4,45 4,45 4,35 4,15

22450 18500 15000 11900 9150 4,85 4,90 4,85 4,70 4,50

24000 20000 16400 13200 10300 7800 5,25 5,35 5,35 5,25 5,10 4,80

24550 20650 17100 13950 11100 8550 6300 5,70 5,80 5,80 5,75 5,65 5,45 5,10

23500 19850 16600 13650 11000 8650 6550 4650 6,15 6,25 6,30 6,30 6,20 6,05 5,75 5,40

75 75 75 75 75 75 75 75 24600 20900 17500 14400 11600 9050 6750 4750 6,45 6,55 6,55 6,50 6,40 6,20 5,90 5,55

85 85 85 90 90 90 85 22000 18600 15450 13300 10450 7900 5550 7,20 7,20 7,15 7,30 7,10 6,80 6,25

100 100 100 100 105 95 21100 17550 14400 11500 8900 6350 8,30 8,20 8,00 7,80 7,65 6,95

110 110 115 115 110 95 18450 15300 12750 10000 7450 4050 9,00 8,80 8,80 8,45 7,85 6,95

125 125 130 125 110 16900 13900 11650 8800 5700 10,00 9,70 9,55 8,85 7,85

Radial piston compressor (transcritical) - Performance data

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RKX

Type

Numberof

cylinders

Displacement50 / 60 Hz

Electrical data 3 Weight Connections 5 Oil chargeVoltage

1

Max.working current

2

Max. powerconsumption

2

Startingcurrent

(rotor locked)

Discharge lineDV

Suction lineSV

m³/h A kW A kg mm mm Ltr.

∆ / Y ∆ / Y

RKX26/31-4 CO2 T 6 2,70 / 3,30 4 14,3 / 8,2 5 76 / 44 68 12 12 1,0

RKX26/31-2 CO2 T 6 5,40 / 6,50 4 40 / 23 10,6 230 / 133 73 12 12 1,0

Explanations:

Tolerance (± 10%) relates to the mean value of the voltagerange. Other voltages and current types on request.

Take account of the max. operating current / max. powerconsumption when designing contactors, leads and fuses.Switches: Service category AC3

1

2

3

4

5

All data are based on the mean value of the voltage range.

220-240 V ∆ / 380-420 V Y - 3 - 50 Hz 265-290 V ∆ / 440-480 V Y - 3 - 60 Hz

Compression joint for steel pipes

Radial piston compressor (transcritical) - Technical data

Oil sump heater 110-240 V - 1 - 50/60 Hz (standard)PTC heater, 50-120 W, self-regulating -

Oil sump heater is necessary due to the high CO2 solubility in the oil.

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RKX26 CO2 T RKX26/31-4 CO2 T RKX26/31-2 CO2 T

Centre of gravity Dimensions in mm

Connections RKX26 CO2 T

SVDV

Suction lineDischarge line

Please refer to technical data! Page 129

A Connection suction side, not lockable 1/8 " NPTF

B Connection discharge side, not lockable 1/8 " NPTF

F Oil drain G 1/4 "

H Oil charge plug G 1/4 "

J Oil sump heater Ø 15 mm

L1 Thermal protection thermostat 1/8" NPTF

174107

125

ca.

274ca.120

DV

B

A

SVL1

ca.3

00

33ca.

202

210

119

94x

33

F

H

J

ca.440

Dimensions for anti-vibration pad

Type Ø a b c dmm mm mm mm

RKX26 CO2 T 30 30 M8 20

Radial piston compressor (transcritical) - Dimensions and connections

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1) Also available as refill unit in 1 or 5 liter packaging

Scope of supply RKX26 CO2 T

Semi-hermetic 6 cylinder radial piston compressor with drive motor for part winding start – 2- or 4 pole version 220-240 V ∆ / 380-420 V Y - 3 - 50 Hz 265-290 V ∆ / 440-480 V Y - 3 - 60 Hz Single-section compressor housing

Winding protection with PTC resistor sensors and electronic motor protection unit Bock MP10

Thermal protection thermostat (PTC sensor) IP67

Oil sump heater 110-240 V - 1 - 50/60 Hz, 50-120 W - PTC heater, self regulating

Oil charge: Bock C120E 1)

Compressor decompression valve suction and discharge line

Capability of connecting for suction line and discharge line without shut off valves Design in cutting ring version for steel pipes

Inert gas charge

4 anti-vibration pads enclosed

Radial piston compressor (transcritical) - Scope of supplyRadial piston compressor (transcritical) - Dimensions and connections