upgrading digester biogas to natural gas quality · 2017-07-10 · upgrading digester biogas to...

Upgrading Digester Biogas to Natural Gas Quality

Robert J. Kulchawik, P.E.

Session 1 – June 19, 2017

Traditional Uses of Digester Biogas

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

Typical Wastewater Plant Biogas Quality

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

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

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

1. Pressure Swing Adsorption

– 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

Possible vendors: Carbotech and Xebec

Figure: Carbotech PSA System

Figure: Xebec PSA System

2. Water Scrubbing

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)

3. Membrane Separation

– 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)

Typical Membrane Cartridge

3. Membrane Separation (cont)

– 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

– 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

– 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

– 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

Water Scrubbing System by Greenlane

Hamilton, Ontario Woodward WWTP

PSA System by Guild

Newtown Creek WWTP New York

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

Lulu Island WWTP, Metro Vancouver, British Columbia

Proposed Biogas Cleanup System

Proposed biogas

cleaning location

Digester

Gas storageGas flares

Lulu Island WWTP – Site Plan

New Biogas Cleaning

AECOM’s Ranking of Technologies

Lulu Island WWTP

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

Questions

upgrading digester biogas to natural gas quality · 2017-07-10 · upgrading digester biogas to...

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