© NEA GROUP1

© NEA GROUP2

1. Existing Non-Lubricated High Pressure Compression Technologies

2. PTFE Tribofilm & Wear Mechanism

3. Leakage Flow Calculations

4. Compressor Basic Design

5. Summary

CONTENTS

© NEA GROUP3

1. Existing Non-Lubricated High Pressure Compression Technologies

2. PTFE Tribofilm & Wear Mechanism

3. Leakage Flow Calculations

4. Compressor Basic Design

5. Summary

CONTENTS

EXISTING NON-LUBRICATED HIGHPRESSURE COMPRESSION TECHNOLOGIESWhy non-lube H2 piston compressors for higher discharge pressure?

© NEA GROUP4

• Hydrogen will be a key element for the energy transition• since it will be the only reasonable way to store energy

• At least in the mobility sector• Oil contamination is excluded since fuel cell does not allow any oil• Higher discharge pressures are needed due to the low energy density of H2

• Currently, non-lube above 250 bar is done by diaphragm compressors• Restricted in max flow• Lifetime of diaphragms currently non-predictable• Expected lifetime for interrupted operation is 4,000 hours

© NEA GROUP5

Compilation of some built high pressure hydrogen compressors non-lube for bottle filling

Compressor Pressure

1st stage bar(g) 2nd stage bar(g) 3rd stage bar(g) 4th stage bar(g)

3TZS50-80/90/55 35 – 68 68 - 121 121 - 219 -

2TV1-100/50 36 – 96 96 - 210 - -

2TV1-100/51 28 – 78 78 - 167 - -

4TV2-140/100/55/40 4 – 11 11 - 31 31 - 82 82 – 200

3TZS80-93/94/54 30 - 82 82 – 137 137 - 224 -

2TES130-170/80 19 – 72 72 – 225 - -

What are the challenges with high pressure H2 compression up to 500 bar?

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• High sealing pressure at packing• gas tight solutions for dry running up to 200 bar/4,000 hours expected lifetime• tandem piston for 2nd/3rd stage

• High pressure difference at 3rd stage (about 300 bar)• a lot of rings necessary long piston• extrusion issues material/design selection

• Avoiding of high internal/external leakage rates despite light gas• intermediate pressure offset deteriorating with wear• almost real gas tight solutions are necessary• difficult, since last stage diameter generally small

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• Guiding difficulties of long/slender tandem piston design

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• Piston ring is pressed radially against cylinder liner• since the pressure is reduced at the

contact surface• resulting force towards cylinder liner is

created

• Piston ring is pressed axially against piston ring groove• due to the same mechanism described

in radial direction

Piston ring sealing principle

© NEA GROUP9

• Leaking type rings (angular/overlapped cut)

• Gas tight rings (twin-ring)• For leaking type (labyrinth)

rings• pressure difference per ring is relatively small• since all rings are engaged in the sealing by the flow

losses of the leakage• For gas tight rings

• only one ring element seals the dynamic and another one the static pressure difference

• the other rings are sleepers starting their work after wearing out of the 1st, 2nd, 3rd, …

Piston ring sealing principle

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Influence of piston ring leakage on interstage pressures for tandem piston arrangements

Trend of interstage pressure for high 4th

stage leakage

• lower than design

• higher than design

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• Mean piston speed• good experiences made with 3 m/s

• more than 100 bar at packing (12,000 hours)• about 200 bar at last stage tandem piston (12,000 hours)

• Gastight sealing elements• caution concerning ring extrusion

• Equally distributed specific load on all elements• leakage independent of wear condition of ring necessary• controlled internal small leakage by flow channels in piston ring grooves• controlled internal small leakage by flow channels in packing cups and• intermediate pressure relief to preferably suction side 1st stage

• No real external leakage

What are the design details?

© NEA GROUP12

1. Existing Non-Lubricated High Pressure Compression Technologies

2. PTFE Tribofilm & Wear Mechanism

3. Leakage Flow Calculations

4. Compressor Basic Design

5. Summary

CONTENTS

© NEA GROUP13

Test conditions:

• Pressure load: 10 // 20 // 40 // 60 bar• Mean speed: 2.70 m/sec• Temperature: 120 °C• Gas: Hydrogen• Sealing material: SK801• Dew point: ≤ - 50 °C• Counter surface: Steel w. TC Coating (Ra 0.15)• Stroke: 130 mm

Reciprocating tribometer @ STASSKOL

PTFE Tribofilm & Wear MechanismTribological characterization

© NEA GROUP14

Test• Critical pressure differences across one sealing

element must be avoided• Reducing speed reduces the critical pressures• Best case:

Homogeneous pressure distribution across all sealing elements

𝑊𝑒𝑎𝑟 𝑟𝑎𝑡𝑒∆𝑙

𝑝 · 𝑣 · ∆𝑡𝑚𝑚

𝑁/𝑚𝑚² · 𝑚/𝑠𝑒𝑐 · 𝑠𝑒𝑐𝑚𝑚³𝑁𝑚

l = material wearp = contact pressurev = average velocityt = test duration

Tribological characterization

© NEA GROUP15

1. Existing Non-Lubricated High Pressure Compression Technologies

2. PTFE Tribofilm & Wear Mechanism

3. Leakage Flow Calculations

4. Compressor Basic Design

5. Summary

CONTENTS

LEAKAGE FLOW CALCULATIONSIn-house leakage flow calculation tool forthe transient leakage flow of pistons/packings

© NEA GROUP16

• An in-house leakage flow calculation tool based on conservation of energy and mass was developed to calculate the transient leakage flow of pistons/packings

• With this Know-how and Tool• The leakage flow cross

sectional areas and the transient pressure distribution can be assessed

© NEA GROUP17

Example leakage calculations – basic design assumptions

Calculation tool: NEA in-house calculation toolGas: H2Suction pressure: 177 bar a (Stage 3)Discharge Pressure: 351 bar a (Stage 3)Back-pressure: 85.6 bar a (Balance chamber: 2nd Stage suction pressure)Suction temperature: 40°CDischarge temperature: 110°C (adiabatic)Speed: 490 rpmStroke: 150 mmMean piston speed: 2.45 m/sCylinder-: 80 mmPiston rod-: 70 mmFlow: ~ 2800 Nm³/hNumber of piston rings: 18

© NEA GROUP18

Example leakage calculations –cross sectional area variations

CASE CROSS SECTIONAL AREA

HEAT FLOW

PRESSURE DISTRIBUTIONCYLINDER DOWNWARDS LEAKAGE

1 5 mm² all rings Adiabatic Increasing p 900 Nm³/h +/- 300 Nm³/h

2 3 mm² all rings Adiabatic Increasing p 600 Nm³/h +/- 200 Nm³/h

3 1 mm² all rings Adiabatic Equally distributed 150 Nm³/h +/- 50 Nm³/h

4 2.2, 2.1, 2.0 … 0.5 mm² Adiabatic Extremely increasing p 160 Nm³/h +/- 40 Nm³/h

5 0.5, 0.6, 0.7 … 2.2 mm² Adiabatic Extremely decreasing p 180 Nm³/h +/- 70 Nm³/h

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Case 1 - 5 mm² all rings –Leakage 900 Nm³/h ± 300 Nm³/h

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Case 2 - 3 mm² all rings –Leakage 600 Nm³/h ± 200 Nm³/h

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Case 3 - 1 mm² all rings –Leakage 150 Nm³/h ± 50 Nm³/h

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Case 4 – 2.2, 2.1, 2.0 … 0.5 mm² –Leakage 160 Nm³/h ± 40 Nm³/h

© NEA GROUP23

Case 5 – 0.5, 0.6, 0.7 … 2.2 mm² –Leakage 180 Nm³/h ± 70 Nm³/h

© NEA GROUP24

Leakage simulation of compressor packing at the test rig of STASSKOLHighlights:a) variable length of packingb) cooled / uncooled packingsc) various systems of packingsd) monitoring the pressure and temperature

e) monitoring of packing´s leakage f) various rod diametersg) 250 bar final pressure for non lube applicationh) cooled rodi) applied gases: N2, H2, CH4, AIR, CO2

© NEA GROUP25

Leakage simulation of compressor packing at the test rig of STASSKOL

Gas: H2Suction pressure: 30 bar a (Stage 3)Discharge Pressure: 85 bar a (Stage 3)Back-pressure: 1 bar a (ambient pressure)Suction temperature: 40°CDischarge temperature: 150°C (adiabatic)Speed: 623 rpmStroke: 130 mmMean piston speed: 2.7 m/sCylinder-: 100 mmPiston rod-: 70 mmFlow: no flowNumber of packing cups: 4

© NEA GROUP26

Leakage simulation of compressor packing at the test rig of STASSKOL

(average pressures per cup)

© NEA GROUP27

1. Existing Non-Lubricated High Pressure Compression Technologies

2. PTFE Tribofilm & Wear Mechanism

3. Leakage Flow Calculations

4. Compressor Basic Design

5. Summary

CONTENTS

COMPRESSOR BASIC DESIGNDrawings

© NEA GROUP28

© NEA GROUP29

1. Existing Non-Lubricated High Pressure Compression Technologies

2. PTFE Tribofilm & Wear Mechanism

3. Leakage Flow Calculations

4. Compressor Basic Design

5. Summary

CONTENTS

SUMMARY

© NEA GROUP30

• Up to 500 bar is possible with a non-lube reciprocating compressor

• Challenges: More than 300 bar differential pressure at last stageMore than 200 bar differential pressure at packing

• A tandem piston configuration will be applied for the last two stages• to reduce the pressure on the packing

• Defined leakage flows independent on the wear condition• to equally distribute the pressure differential per sealing segment

• pressure relief to suction side 1st stage within the packing• to minimize the static real gastight differential pressure

• Vertical compressors preferred (no load on rider bands)

© NEA GROUP31