Upgrading Digester Biogas to Natural Gas Quality · 2017-07-10 · Upgrading Digester Biogas to Natural Gas Quality Robert J. Kulchawik, P.E. Session 1 –June 19, 2017

Upgrading Digester Biogas to Natural Gas Quality

Robert J. Kulchawik, P.E.

Session 1 – June 19, 2017

Traditional Uses of Digester Biogas

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Boilers for Building Heat

and Digester Heating

Engine Generators /

Cogeneration Systems

Engine-Driven Pumps

and Blowers

Issues with Biogas as a Fuel

•Quality of fuel impacts performance

•High moisture and H2S commonly an issue

•Siloxanes impact reliability

•High maintenance and annual costs

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Typical Wastewater Plant Biogas Quality

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Parameter Units Value

Temperature Degrees C ( F ) 38 (100)

Pressure kPa (psi) 5 (0.73)

Water Vapour % volume Saturated

Oxygen % mole volume 0-0.019

Methane(min / average / max) % mole volume 59 / 61 / 63

Nitrogen % mole volume 0.1-0.6

Carbon Dioxide (min / average / max) % mole volume 31 / 38 / 42

Siloxanes (reported as Total Silicon) mg/m3 10-19 (4-7 Total Silicon)

Hydrogen Sulphide ppm 130

Carbonyl Sulphide ppm 5

Typical Natural Gas Quality

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Contaminant Property Specification

Sand, dust, gums, oils and other impurities Free from any impurities

Hydrogen sulphide Less than 6mg/m3

Water Less than 65mg/m3 of water vapour and no liquid water

Hydrocarbon dew point Be free of hydrocarbons in liquid form and not have ahydrocarbon dew point in excess of minus 9°C

Total sulphur Less than 23mg/m3

Carbon dioxide Less than 2% by volume

Oxygen Less than 0.4% by volume

Temperature 54°C maximum

Calorific power 36.00MJ/m3 minimum (15°C / 101.3kPa)

Minimum methane content >96.5%

Siloxanes Less than 1mg/m3

Carbon monoxide Less than 2% by volume

Inert gases Less than 4% by volume

Ammonia 3mg/m3

Bacteria and pathogens Impurity filter (0.3 to 5 microns)

Minimum delivery pressure 420 kPa (61 psi)

Maximum delivery pressure 520 kPa (75 psi)

Major cleanup

contaminants (typ)

Biogas Upgrading Technologies Number of Installations

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Source: (International Energy Association Bioenergy Task 37, 2015)

1. Pressure Swing Adsorption

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– Carbon dioxide (CO2) is adsorbed into carbon molecular sieve

media in a pressurized vessel to yield upgraded biomethane

– PSA cycle includes pressurization, feed, blowdown and purge

Typical PSA System Schematic

H2S and moisture

removal upstream

50 to 100 psig

1. Pressure Swing Adsorption

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Possible vendors: Carbotech and Xebec

Figure: Carbotech PSA System

Figure: Xebec PSA System

2. Water Scrubbing

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CO2, hydrogen sulphide (H2S) and ammonia dissolve in water to yield

biomethane. Plastic media used to maximize contact area.

Figure: Typical Water Scrubbing System

Typically no H2S and

moisture removal upstream

50 to 100 psig

2. Water Scrubbing (Cont)

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3. Membrane Separation

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– CO2 permeates through membrane while methane passes through

membrane.

– 1, 2 or 3 stage systems available depending on quality requirements

Typical Membrane System

Efficient pre-treatment

needed upstream Compressor @

100 to 300 psig Series arrangement

commonly needed

3. Membrane Separation (cont)

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Typical Membrane Cartridge

3. Membrane Separation (cont)

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– Possible vendors: DMT and Xebec

– DMT has many worldwide installations and upcoming local installation(s)

– Both systems use leading membrane manufacturer Evonik

– Increase full scale usage in recent years with improvements in membranes

– Fewer moving parts, simple operation

– Newer technology

Xebec Separation Unit DMT Separation Unit

4. Amine Scrubbing

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– Similar to water scrubbing - CO2 is absorbed in amine (ammonia based)

solution. Plastic media is used for increasing contact area. Greater turndown.

– 99% methane content, <0.1% methane slip

– North American supply by Purac Puregas

Heat source needed

5. Organic Physical Scrubbing

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– CO2 and H2S are dissolved in an organic solvent (Glycol). Plastic media

is used to increase contact area. Glycol disposal, hazardous waste

– Few installations and suppliers

60 to 115 psig H2S and moisture

removal upstream

H2S and moisture

removal upstream

6. Cryogenic Separation

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– Refrigerant is used to liquify gases at different temperatures.

Contaminants such as CO2 liquify at higher temperature than

methane. High capital and operating cost.

– Emerging technology, primarily used for liquified biogas

H2S and moisture

removal upstream

260 to 435 psig

Water Scrubbing System by Greenlane

Agricultural and Food Waste

Fraser Valley, British Columbia

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Water Scrubbing System by Greenlane

Hamilton, Ontario Woodward WWTP

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PSA System by Guild

Newtown Creek WWTP New York

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PSA System

Boiler stacks – not part

of PSA system

A

D

C

B

Mechanical Equipment

3D Model

Newtown Creek Preliminary Spatial Diagram

– Total footprint is

approximately

7,000 ft2

– Other equipment

includes:

A. A small

transformer

B. A motor control

center

C. A small

monitoring

station

D. Two

compressors. Horizontal and

shorter tanks used

Membrane System by DMT

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Lulu Island WWTP, Metro Vancouver, British Columbia

Proposed Biogas Cleanup System

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Proposed biogas

cleaning location

Digester

Gas storageGas flares

Lulu Island WWTP – Site Plan

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New Biogas Cleaning

AECOM’s Ranking of Technologies

Lulu Island WWTP

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No. Evaluation Criteria Max Score

Membrane Separation

Water Scrubbing PSA

1 Product quality(Meet specs, min 96.5% CH4)

Y/N Y Y Y

2Appropriate capacity(without compressor recycle)(now to 2025 minimum)

10 10 5 5

3 Appropriate capacity (2025 to 2035 minimum) 5 5 5 5

4 Proven technology(time of proven service) 10 5 10 8

5Reliability(process complexity, sensitivity, operating system feedback)

10 8 10 8

6Ease of start-up & operation(process complexity, operatingsystem feedback)

10 10 10 7

7 Methane slip / losses 5 5 4 4

8 Life cycle cost 5 5 0 -

9 System controls options 10 10 10 10

Total 65 58 54 48

Summary• Pretreatment of H2S and moisture are critical

• Consider O & M impacts for reliability

• Cleaning technologies are also applicable for generators,

micro-turbines, and vehicle fleet fueling

• Currently there is a greater market for vehicle fleet fueling

applications

• With relatively low natural gas prices, sale to the grid is

less viable in most locations at this time

• Additional benefits - meet carbon credits for greenhouse

gas emissions by reducing methane release to the

atmosphere as well as general reduction in O & M costs

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Questions