adsorption based co capture in the natural gas...

Adsorption based CO2 capture in the natural gas industry

Prof Paul A. WebleyThe University of MelbourneSeparation and Sensing Workshop Wednesday 29th November 2017

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Outline

Otway Capture Plant

• Motivation and Challenges• CO2 Capture by Adsorption –

Principles and Examples• Laboratory Work• Otway Capture Plant Results• Economic implications• Future Work

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Motivation and Challenges

• Sleipner Project

RequirementsCO2 in NG must be reduced to < 2% for pipeline transportMany fields have very high levels of CO2, up to 80% in case of Southeast AsiaCO2 capture in NG production already successfully demonstrated in Sleipner, Snohvit and In Salah (all solvent scrubbing)CO2 capture by PSA not commercial –still in R&D stage (TRL 2-6) with some pilots/demonstrations

Commercial adsorption plants• Hydrogen PSA• Oxygen VSA• Landfill P/VSA• Air drying• Natural gas drying/purification• Syn-gas sweetening• Medical oxygen generator• VOC removal

Hydrogen PSA Stocker and Whysall, UOP. 1998 30 years of PSA Technology for

Hydrogen Purification

Oxygen VSA. Image courtesy of Air Products and Chemicals, Inc .

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Example of Adsorption based NG upgrading

• Xebec PSA process for stranded gas upgrading

Xebec, Inc. fast cycle PSA• Very rapid cycle means small

footprint

• Easily transported on a skid to site and commissioned

• Note that CO2 tail gas in not pure –can be used for fuel value, not CCS

CO2Capture adsorption pilot plants

Pre-Combustion (PSA)Mulgrave0-5 L/m

Post-Combustion (VSA)International Power Hazelwood0.5-1.0 tpd

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CO2 Capture Plant in Sinopec, China

• Capture CO2 from tail gas of H2PSA

• 300 Nm3/hr• 40-50% CO2/H2

• Purify and return hydrogen, enrich CO2 to > 95%

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CO2 Capture by Adsorption – Principles

• Principles of Adsorption Separation

Adsorbent Selection• CO2 ~ 3.4Å; CH4~3.8Å: will need

careful size selectivity (eg molecular trapdoor)

• CO2 quadrupole moment (14.3x10-40 C m2) compared to 0 for CH4: can rely on differing interaction with surface groups/cations/moeities

• Want large number of surface sites per unit volume

• Need to account for sensitivities to pressure and temperature

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Adsorbent Selection• Started tests with Silica

• Campaign 2 will target zeolite Z1

• Campaign 3 will examine new “trapdoor” zeolites currently under development in the lab

• Need tolerance to water and impurities

• Need high capacity at high pressure –many isotherms “plateau” at modest pressure, eg 13X, requiring vacuum

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Adsorbent Selection Criteria• Working Capacity

• Selectivity

• Kinetics

• Thermal Behaviour

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Multi-step cycle• Mixed gas fed to adsorbent bed at

high pressure – CO2 adsorbs and high purity methane recovered

• Bed is depressurized to recover high concentration CO2

• Two beds are used to ensure continuous feed

• Additional tanks used to allow internal reflux steps to enhance purity and recovery

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Advantages of adsorption capture (PCC)

• Easy handling: solids instead of liquid• Low energy: ~1-2 MJ/kg CO2

• Low cost materials• Simple process control logic• Robust• Possibility of direct capture from high temperature flue gas• Avoid large pressure drop across a membrane

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Advances – Process improvements

• New cycles (VSA, TVSA, ESA)• New column structures (e.g. radial)• Heat integration • Multiple-layered columns

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Laboratory Work

• High Pressure Adsorption Measurements

Identifying and synthesizing adsorbents • Need adsorbents with little to NO methane

uptake

• Started with Silica (S1)

• Measure CO2 and CH4 adsorption isotherms

• Pressures of 1 – 100 bar

• Next adsorbent: Zeolite Z1. This has much higher CO2 capacity and lower methane capacity

• Future adsorbent currently synthesized has high CO2 capacity (similar to Z1) and NO methane uptake – we will target this adsorbent for late 2018

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Otway Capture Plant Testing

• 2 Bed PSA at Otway CO2CRC Capture Test site

Otway Site test conditions• 2 bed PSA system with

• CO2/CH4 gas (real CNG gas with different CO2concentrations)

• Pressures of 30 – 80 bar

• Various flowrates

• Temperature of 30 – 50 °C

• Adsorbent: Silica S1, then Second campaign (2018): Zeolite Z1

• Current equilibrium adsorption data for CO2 and CH4 measured from 0 – 10 bar

Location of CO2CRC Otway Project

The CO2CRC Otway Project: Stage 3

• Otway Basin Schematic

• Stage 1: 2004 – 2009• Depleted Field Storage Demonstrate safe transport,

injection and storage of CO2 in a structural trap

Stage 2: 2009 – 2018Saline Formation Storage 2A :Drill CRC-2 2B: Measure parameters affecting

residual and dissolution trapping in a saline formation

• 2C: Spatially track injected CO2 in a saline formation

Stage 3: 2014 – 2021+Otway Subsurface Laboratory• Validate subsurface monitoring• Trial storage management

processes and technologies

PSA Process Flow Diagram - Overall

Feed GasMixture of CO2/CH4

CO2 Rich stream

CH4 rich stream

PSA Cycle

• There are twelve (12) steps in the cycle –in each step we can adjust the times and the flow control valve FV201

• Steps 1 to 6 are repeated in steps 7 to 12 so the step times should match:

• Step 1 time = step 7 time• Step 2 time = step 8 time• Step 3 time = step 9 time• Step 4 time = step 10 time• Step 5 time = step 11 time• Step 6 time = step 12 time

• FV-201 settings should also be symmetrical (step 1-6 should match 7-12)

Example

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PSA Cycle design

• Step 1 – Adsorption at bed1; and desorption at bed2• Step2 – Pressure reduction by releasing gas to a middle tank from bed1; and continuous desorption

at bed2• Step3 – Pressure equalization between the two beds• Step4 – Desorption at bed1; re-pressurization by releasing gas from the middle tank to bed 2• Step5 – Continuous desorption at bed1; re-pressurization by passing feed gas to bed 2 • Step6 – 10 – SWAP of the two beds• S1 adsorbents of 2 kg were filled in each adsorption column (ID 80 mm x Length 600 mm)

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Otway Capture Plant Results

• Pressure Profiles during operation

Data so far and Issues• High pressure drop in piping has led to very long

cycle times to achieve satisfactory blow down

• Lowest pressure achievable is 5 bar – this limits the separtion performance

• Need to run the membrane and PSA unit separately – cant run both together

• Initial results show we can achieve separation but long cycle times means fine tuning is time consumng and difficult

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Inlet flow rate stability

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0:00:00 4:48:00 9:36:00 14:24:00 19:12:00 0:00:00 4:48:00

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Running time (s)

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Bed temperatures over a day

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Separation performance over a day

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Otway Capture Plant Results: 10 May to 26 Jun using Adsorbent S1Feed Gas Top-stream gas Blowdown gas flowrate TotGasIn Plow

CO2 C1 – C3 CO2 C1 – C3 CO2 C1 – C3 (sl/min) (mol/cyc) (bar)

10-11 May-17 29 71 18 82 48 52 7.39 19.9 3.3-3.6

Continue, set inlet (FCV902 to 50 %) CO2 30 % in feed gas stream from 19-May-201723-24 May-17 28 72 12 88 41 59 6.5 18.29 3.1-3.4

Reduce adsorption time from 1500 to 1000s from 24-May-201728-29 May-17 32 68 17 83 45 55 7.8 16.15 3.4-3.6

Reduce adsorption time to 500s from 29-May-20174-7 Jun-17 28 72 11 89 39 61 8.35 10.23 4.8-5

CO2 inlet 45% balanced with CNG gas by adjusting FCV902 to 20% from 7_Jun-201713-14 Jun-17 45 55 19 81 55 45 4.95 7.7 6.5-7

Increase adTime to 600s from 15-Jun-201719-20 Jun-17 45 55 21 79 56 44 4.49 8.14 6.7-8

Extend blowdown time to reduce Plow after 21/6/201723-25 Jun-17 49 51 20 80 60 40 4.51 8.53 5.5-6.5

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CO2 Separation Performance

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Effect of blow down pressure on separation – prediction from simulation

Performance prediction• Final blow down pressure strongly affects how

much CO2 can be recovered from the adsorbent

• We need to extend the desorption time and possibly adjust system temperature to optimze separation

• Will perform additional optimisation runs with improved adsorbent

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Comparison of adsorbents S1 and Z1

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Economics*

• Process Flow Diagram of MDEA Process

Basis• 500,000 Nm3/hr NG, 10 wt% CO2, 70 bar, 40°C

• Sweet gas <2.5 mol% CO2, CO2 product >95% purity, 110 bar

• Reference technology MDEA based solvent

• Stripper operates at 1.8 bar, HC flash at 5 bar, CO2 flash at 1.1bar

• Compress and dry CO2 to 110 bar

* “CO2 Capture in Natural Gas Production by Adsorption Processes for CO2 Storage, EOR and EGR”, Final Report SINTEF for IEAGHG, 2017

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Reference Plant – Solvent Scrubbing

Results• CAPEX - $33m ($19m capture plant, $14m

compression)

• OPEX - $30m/yr (steam 48%, electricity 24%)

• Overall, major costs are operating


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PSA Plant– Estimation

Costing• Vessels, adsorbent, valves, piping (used kinetic

separation using CMS - $46m

• However, our adsorbent have 4 times higher CO2 capacity than CMS – expect this to drop to $25m

• CO2 Compression - $14m

• OPEX - $40m/yr (mostly natural gas losses due to impure tail gas which contained 15% CO2)


Losses of CH4 in CO2 product dominate cost – need to reduce this

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Future Work

• Lab scale PSA unit

• New adsorbent Z2 currently under development to be tested

• Validate detailed process model of Otway and improve process cycles

• Continue Otway testing and optimisation

• Detailed cost model developed for CAPEX and OPEX of adsorption process

PSA Cycle – Step 1: V201=Adsorption, V202=Desorption

PSA Cycle – Step 2: V201=Pressure Reduction, V202=Third Desorption

NOTE: May need to close VI-208

PSA Cycle – Step 3: Pressure Equalisation between V201 and V202

PSA Cycle – Step 4: V201=Desorption , V202 = partial methane repressurization

PSA Cycle – Step 5: V201=Desorption , V202 = feed repressurization

PSA Cycle – Step 6: V201 = Desorption , V202 = methane repressurization

PSA Cycle – Step 7: V201=Desorption , V202=Adsorption

PSA Cycle – Step 8: V201=Desorption , V202 =Pressure Reduction

NOTE: May need to close VI-208

PSA Cycle – Step 9: Pressure Equalisation between V201 and V202

PSA Cycle – Step 10: V201=Partial Methane Repressurization, V202= Desorption

PSA Cycle – Step 11: V201=Feed Repressurization, V202=Desorption

PSA Cycle – Step 12: V201=Methane repressurization, V202=Desorption

adsorption based co capture in the natural gas...

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