Anaerobic Digester Operation north America

Anaerobic Digestion Operations and Biogas Safety
Training

Course Outline – 4 Sessions
Tuesday, October 13, 2020, 12 ‐ 1:30 PM
Instructor Mark Greene
• Overview of Anaerobic Digestion
• Codigestion
• Q&A
Thursday, October 15, 2020, 12 ‐ 1:30 PM
Instructors Frank DeOrio & George Bevington
• Brief Recap
• Operational Overview of Digesters and
the Importance of Nutrients and
Process Control
• Digester Start‐Up and Sour Digesters

Course Outline – 4 Sessions
Instructor Sara Martin
• Brief Recap
• Design Considerations
• Biogas Utilization & Safety
• Q&A
Instructors Frank DeOrio & George Bevington
• Brief Recap
• Case Studies
• Groundbreaking Genetic Research on
Anaerobic Microbes
• Q&A

Safety Moment – Stop and Think!
• Explosive Gases
• Asphyxiation
• Confined Space
• Falls
• Intrinsically Safe – Spark Proof
• Drowning
• Entanglement
• Bacterial exposure
• Unaware Visitors
• Abnormal Conditions ‐ Retrofits

• Design Process Overview
• Major Design Considerations for Anaerobic Systems
• Inspection
• Start‐Up
• Questions
Agenda
Agenda
Critical Path Engineering Solutions 6

Introduction
Design Process Overview
1. Conceptual Design ‐ 10% design
2. Basis of Design ‐ 30% design
3. Detailed Design – 90% design
4. Bidding – 100% design
5. Construction
6. Start‐Up and Commissioning
7. Training
8. Turnover
Design Conditions Overview

Introduction

Introduction
Major Items for Consideration During Design for
Anaerobic Projects
1. Sludge Characteristics – Feedstocks
2. Existing Infrastructure
3. Energy Use
4. Impact to Headworks ‐ Permitting
5. Design Temperatures
6. Material Compatibility
7. Moisture Control
8. Odors
9. Safety
10. Operability
11. Laboratory

Introduction
Design Resources
• ANSI/CSA B149.6‐15
• NFPA 820
• WEF MOP 8
• TR‐16
• 10 States Standards
• American Biogas Council

Introduction
Sludge Characteristics ‐ Feedstocks
• What % moisture – water takes up space but makes things
easier to move – does it make sense to thicken?
• Availability – if you are getting an outside source will it always
be available – delivery schedule?
• Consistency – pumpable? mixable? solidified when cool? How
store and convey?
• Floatables? Will you need a way to break up top of digester?
• Inert material? Rocks, bones, plastic? How get out? Will pumps
and mixing handle these solids?

Introduction
Existing Infrastructure
• What is condition of materials? Exposed rebar, corroded metal
should be fixed, replaced, corroded
• Tank inspection? Keep records and pictures when drained
• Electrical Classification adequate?
• Ventilation adequate?
• Chemical addition?
• Can mechanical equipment handle new conditions? Solids,
material compatibility
• Can overall system handle this area/process being down?

Introduction
Energy Use
• If you bring on extra waste – can you use all the gas?
• Grant or funding opportunities for biogas use or generation?
• Parasitic heat load for digester and plant heating in coldest
conditions needs to be accounted for
• Ability for maintenance on generation equipment – make sure
flare adequately sized or have redundancy
• What is gas conditioning required for use point? What is
energy use and cost to operate?

Introduction
Impacts to Headworks ‐ Permitting
• Increased organics loading
• Impact to nutrient loading?
• Anyother permit requirements affected?
• Recycled methanogens – electrical rating of any existing tanks
that will now contain these?
• What happens if there is an upset in digester – how protect
downstream sources?

Introduction
Design Temperatures
• Identify coldest and hottest outside design temperatures ‐
heating and/or cooling should accommodate these conditions
• Do any feedstocks or post digester solids beneficial use require
thermophilic conditions?
• Digester heating devices need to be able to heat without biogas
(start‐up or upsets)
• What will be exposed to freezing conditions – proper drainage,
heat trace, insulation, exposed instrumentation?

Introduction
Material Compatibility ‐ Corrosive
• Moisture, Hydrogen Sulfide, Chemical Additions (caustic, anti‐
scale cleaning, etc.)
• Piping and equipment (ANSI/CSA B149.6‐15
high quality stainless, HDPE, PVC, coated or lined material,
aluminum, or thick walled ductile or carbon steel products –
good welds important
• Elastomers, gaskets, seals
Weak acids ‐ <10% (Cole Palmer Material Compatibility Chart)

Introduction
Moisture Control
• Drainage at all low points – including buried piping? Adequate
volume or self draining?
• Piping sloped (especially biogas) – cleanouts? 2% minimum
• Safe drainage with drip trap or water seal?
• Freeze Protection?
• Can biogas usage point handle moist gas?
• Materials exposed to moisture can handle? Would ventilation
help prevent moisture – buildings, enclosures

Introduction
Odors
• Collection Pits and Solids Handling
• Flaring
• Leaks
• Do you need control devices? Carbon, biofilter, etc.
• Odors to headworks in digestate?

Introduction
Safety/Standards
• ANSI/CSA B149.6‐15
• NFPA 820 – Electrical Classification and Ventilation Required
• NEC 70 – Electrical Classification and Impacts to Electrical Design
• Pressurization – safety devices installed properly and to the proper
pressures – redundancy for maintenance?
• Biogas piping design – drainage, safety, freezing, etc.
• Access to Equipment, Fall Protection, Confined Space, Isolation
Shut‐Offs
• Gas Monitoring and Fire alarms

Introduction
Operability
• Can you access all equipment, instrumentation, and valves
without special lifts, harness, tools, etc.? Or if needed are they
part of design or bid package? Harness clips, tie‐offs, etc.
• Impacts of maintenance and downtime – how clean and
maintain equipment?
• Safety during abnormal operating conditions – critical items
that need redundancy, back‐up power, or on‐shelf spares?
• Can confined space be avoided through additional access
point?

Introduction
Laboratory
• Is additional laboratory analysis needed to successfully run
system?
• Does laboratory have equipment and space to accommodate
additional testing?
• Are operators trained for additional operational requirements
that may be needed?
• Will additional off‐site testing and analysis be required?

Introduction
Bidding
• Ask for a review of detailed design drawings and specs prior to
bidding?
• If timeline does not allow ‐ try to at least review during bidding
process
• Addendums – handle design changes to original design that was
bid

Introduction
Inspection
• Make sure inspectors are looking to make sure critical items are
being installed properly – safety devices, electrical, etc.
• Final inspections – ask for operators to participate in final
inspections?
• Design changes properly summarized and communicated to
operators

Introduction
Start‐Up
• Proper training before start‐up?
• Review equipment submittals – familiarize yourselves with new
equipment, maintenance requirements, etc.
• Understanding of data logging and any extra laboratory analysis
during start‐up ‐ monitoring, etc.
• Safety – do you have the proper PPE? Suggest a safety
walkthrough of new equipment to identify hazards
• Engineer and operator collaboration

Introduction
Turnover
• Do you have engineering support established?
• Do you have as‐built drawings?
• Do you know where all equipment O&M manuals are?
• Have you reviewed O&M manuals?
• Established preventative maintenance?
• Established SOPs or at a minimum emergency condition SOPs
for abnormal conditions?

• Overview
• Pressure/Vacuum
• Flame Propagation/
Explosion
• Moisture
• Leaks
• Do’s and Don’ts
• Questions
Topics
Topics

Introduction
Why is biogas a safety concern?
1. Flammable gases ‐ methane, hydrogen sulfide,
ammonia
2. High risk of oxygen entrainment which can create
conditions favorable to explosion
3. Potential for asphyxiation (carbon monoxide (engines)
carbon dioxide (biogas), hydrogen sulfide, ammonia)
4. Saturated pressurized gas – risk of over pressurization
of vessels from blockage due to freezing, corrosion,
pooling and fouling
5. Sealed system – risk of implosion due to pulling a
vacuum
Overview
Overview

Introduction
There is no “Thou Shalt” that encompasses the overall
facets of design and operation of these systems:
1. Protection from Spark Sources
2. Flame Deflagration
2. Balancing of Gas Pressure System
3. Leaks
4. Moisture Protection
5. Protection from Overpressurization
6. Falls
Overview
Overview

Introduction
Resources
• ANSI/CSA B149.6‐15 – design and start‐up
• NFPA 820 – area classification
• NEC 70 – electrical requirements
• WEF MOP 8
• TR‐16
• 10 States Standards
• American Biogas Council
• Several European and Canadian Standards
• Articles and Publications
Biogas Safety
Biogas Safety

Introduction
Electrical Classification – National Electrical Code NEC 70
Class 1 Division 1 – Under normal conditions there is the
likelihood of explosive conditions
Class 1 Division 2 – Under abnormal conditions there could be the
likelihood of explosive conditions
Unclassified ‐ There is not a likelihood for explosive conditions
under any circumstance
Overview
Overview

Introduction
Overview – Area Classification

Introduction
Classified Areas for Control Buildings

Introduction
Classified Areas for Piping

Introduction
Overview – Digester Layout
Overview – Digester Layout

Over pressurization
Example ‐ Story
Pressure/Vacuum
Pressure/Vacuum

Define
Biogas
High or
Low
pressure:
• Digester vessel “low” pressure,
typically 4” to 12” WC
– 27.7” WC = 1.0 PSI
– 12” WC = 0.43 psi
– 1” WC = 0.036 psi
• Digester piping system typically low
pressure – biogas is conveyed by delta
P from use point
• Some engines and boilers require
“high” pressure, > 1 psig – biogas
needs boosting
• However ideally you never “pull” with a
biogas blower – let the tank pressure
push biogas to the blower

Power of 6” WC Biogas (0.22 psi):
• If 90’ diameter cover,
surface area = 45 x 45 x
3.14 = 6,359 square feet
• 6,359 x 144 = 915,624 sq in
• 915,624 x 0.22 = 201,437
lbs force up
• Therefore: 0.22 psi can
support a 90’ diameter
cover weighing 201,437
pounds
• Low pressure over a large
surface area can equal a
powerful force
Weight of Steel
Cover
6” WC or 0.22 psi

Vacuum – Implosion
• Blower and pumps can create a partial vacuum in
the system
• Faulty vacuum relief systems can result in
structural failure of bioreactor tank and other
components
Example ‐ Story
Pressure/Vacuum
Pressure/Vacuum

Causes of Vacuum
Conditions
• Sludge withdrawal too
rapid or draining below the
operating range
• Biogas usage greater than
generation
• Chemical reaction from
overfeeding lime
• Malfunction vacuum relief
valve (VRV)
• Plug valve coupled to VRV
closed

Power of Vacuum:
•
• Tanks more susceptible to implosion
• Tank is usually irreparable
• Very dangerous to anyone working
around when this happens

Introduction
Pressure/Vacuum
Pressure/Vacuum
Check
Valve
Check
Valve
Emergency
Vent
Back
Pressure
Regulator
Pressure/Vacuum
Relief
Emergency
Vent
Pressure Regulation
Pressure/Vacuum
Relief
Check
Valve

Pressure Regulator (PRV)
• Usually a back‐pressure device – used to regulate and maintain system pressure
• Mechanical unit with diaphragm, opens if pressure above set point – stays open
until pressure goes back down
• Screw/spring adjustment at top or weights, set to desired operating pressure
To Flare

Pressure/Vacuum
Relief Valve
(PVRV)
• Provides back pressure ‐ opens to
relieve excessive biogas gas system
pressure
• Vacuum protection as well – will
open to prevent implosion.
• “Normal” setting low pressure 8 – 16
inches w.c.
• Ideally, they never need to open as
go to atmosphere.
• Under vacuum allows mixing of air
with digester gas: only time OK to
allow air (oxygen) into digester!

Pressure/Vacuum
Relief Valve
(PVRV)
• Coupled with Flame
Arrestor to prevent
spark in
• What is wrong with
this picture?

Different
configuration:
• Valve to left, right side PRV open
• Valve to right, left side PRV open
• Impossible to shut PRV
completely off
• Nice design for safety, some
headaches for maintenance
• Monthly: switch from PRV 1 to 2,
exercise valve during switchover

PVRV adjustment
• Remove top
• Add or subtract weighted washers to
adjust relief point
• Each washer = calibrated weight
• No. of washers can be added up to
equal pressure setting of tank
• Less than 7.5” WC, PRV closes
• Located on top of a moisture laded tank
‐ in cold weather will freeze!

Waste Gas
Burner
• Part of the pressure relief system
• Safely burns and excess gas to
atmosphere
• Pilot can be natural gas or propane
• If excess pressure: the waste gas
burner should process ALL excess
biogas

Over‐pressurization
• Verify that there are adequate pressure monitoring
and controls to shut down pumps and blowers – in
combination with manual relief devices
• Check manual pressure relief devices for corrosion
and/or freezing
• Check venting for foaming or scaling which can build
up over time
• Moisture can collect at low points, causing blockages
Biogas Hazards
Pressure/Vacuum
Pressure/Vacuum

Flame Propagation and Explosion
Biogas Hazards
Example
Example

Biogas Hazards
Example
Example

‐ Prevent mixing of biogas with air
Best Practices
• Explosive Conditions (5‐15% concentration of
methane in air)
• Avoid pulling air into digester and biogas
collection system
• Prevent leak points in system

Introduction
Overview
Overview
Lockable
Hatch for
Sampling
Safety/Prevent Flashback
Emergency
Pressure
Relief
Flame
Arrestor
Flame Check
Flame Trap
Safety Diverter
Valve

Flame Arrester –
Flame Trap
• Stops flame propagation – dissipation
or fuse
• Consists of a bank of many corrugated
aluminum plates
• As ignited vapor passes through the
small openings heat is absorbed and
dissipated, lowering the gas
temperature below its’ ignition point
• Can be separate unit or part of other
equipment like a PRV

Detonation
Flame Arrestor
(DFA)
• Aluminum plates or mesh inside
• Routine maintenance: clean flame
arrestor periodically, allow for free
flow of biogas
• A plugged flame arrestor works like a
valve in the off position
• They will get dirty

‐ Spark Sources
Best Practices
• Proper Seal‐Offs and Electrically Rated Devices
in accordance with NFPA 820 and NEC 70
• Isolation valves and gaskets need to be checked
and/or replaced periodically
• Potential spark sources should be a safe
distance away from potential leak points
• Control of site – no smoking

‐ Spark Sources
Best Practices
• Use appropriate tools and equipment when
operating on or around possible leak points or
vents
• Avoid use of materials that can spark –
special tools to prevent spark – no welding
without proper permit
• Be mindful of clothing and materials that
create static electricity

Introduction
Overview – Moisture Control
Overview – Moisture Control

Introduction
Overview
Overview
Drip Trap
Foam Collector
Moisture/Sediment Collection
Sediment
and Drip
Trap
Sediment
and Drip
Trap
Buried Pipe?

Sediment,
Condensate &
Drip Traps
• Remove sediment and moisture from digester gas
to prevent condensation and plugging in
downstream system…
• Biogas is 100%+ humidity, very moist

Condensation
• Water will always travel to the low spot
• Determine frequency to empty water
traps
• Dew point changes seasonally!
• Automatic condensate removal traps:
check for proper operation daily
• Water accumulating at the low point of
the system, if not removed, stops gas flow
like a plug valve

Water Seal Importance
• For a floating cover, or
some fixed covers,
sludge level important
to keep water seal
• Water seal important
for traps and other pipe
components as well
• Minor loss of biogas
around perimeter
water seal
Atmosphere
8” WC biogas

Water Seal Loss
• If water seal loss, or
trap seal loss, or any
gas pipe left open, all
biogas to atmosphere
• All biogas to connected
systems impacted if
interconnected
• Major loss of biogas,
pressure to 0, all
components can’t
function
• Risk of oxygen entering
system
Biogas to Atmosphere
0” WC biogas

Leaks/Vents
• Periodic “sniffing” of biogas piping systems during
operations – calibrate and maintain equipment
• Ensure access and sampling ports and hatches are
below digester water surface (water seal) and/or
closed when done working
• Verify hazard classification of area working in
• Know what is or has been inside area that
working in
• Can still be hazardous even if empty
Biogas Hazards
Leaks
Leaks

Do:
• Use non‐electrical, non‐spark tools
• Have a properly calibrated four gas monitoring
(O2, H2S, LEL, CO) on at all times
• Check and maintain instruments and safety
devices
• Be aware of your surroundings at all times – stop
and think before you do
• Close all vents and return valves to their proper
position
• Check for signs of corrosion and blockages in
piping and safety devices
• Be mindful that static electricity can cause sparks
Example ‐ Story
Do’s and Don’ts
Do’s and Don’ts

Do’s and Dont’s
Do’s and Dont’s
• Frequent safety reviews and training – especially
when there has been a change in process
• Check for leaks often
• Use clothing, equipment and instruments rated for
use with biogas
• Never enter an enclosed space with proper training
and safety measures
• Use harness and tie‐off when climbing and/or
working on top of reactors
• Stop and Think Before you DoSpeak up when you
think something is wrong
• Work in teams when possible

Don‘t:
• Ignore alarms ‐ check alarms with portable meters –
fix faulty instrumentation – do not disable!
• Smoke, use lighters
• Use flame torches to defrost, solder or for any other
reason without proper review of safety
• Bang on piping or equipment
• Leave a hatch or sampling port open
• Install or use new equipment that is not intrinsically
safe or rated for use with biogas
• Enter an enclosed area without proper training and
safety measures
• Be afraid to speak up when something doesn’t feel
right
Example ‐ Story
Do’s and Don’ts
Do’s and Don’ts

Example ‐ Story
Conclusion
Conclusion
Hazard Catalyst Cause Source
Explosion
Mixing with Oxygen
Blower pulling air into the
system
Inadequate blower controls
Leak in pipe
Biogas escaping from pipes or
vents
Frozen pipe
Relief valve open
Blockage in pipe
Open vent
Corrosion
Pressure too high
Spark
Static Electricity Clothes (polyester)
PVC piping
Tools
Non‐spark proof
Metal on metal
Electric tools
Welding
Open Flame
Torch
Lighter
Smoking
Lightning Not properly grounded
Implosion Vacuum in System
Blower pulling too much Inadequate blower controls
Pressure relief valves not
working
Foaming/Scaling/Feezing
Corrosion

Example ‐ Story
Conclusion
Conclusion
• Feasibility of Waste to Energy in the Food and Beverage Market. Biocycle West
Coast Conference Martin, S.E., and P.S. Greene. 2010.
• Waste to Energy Overview. ACEC, 2011
• Biogas Piping Safety. American Biogas Council, 2011
• Biogas Piping and Safety Design Considerations. Biocycle Magazine, Martin, S.E.,
June 2016.
• Anaerobic Treatment for Industrial Wastewater – Critical Factors for Successful
Start‐Up and Operation. IWC, Engineers’ Society of West Pennsylvania, October 2016
• Critical Decisions in Selecting Wastewater Treatment Technology – A Third Party
Review. 2017 Master Brewer’s Conference, Martin, S.E., and F.J. DeOrio. August 2017.
• High Solids Digestion in the Food and Beverage Market. Biocycle Magazine, 51(5):
49.
• Options for Treating High Strength Food and Beverage Wastestreams. 2018 Joint
WEF-NYWEA Spring Conference
• Safety Measures for Operating a Biogas Plant. Master Brewer’s Association Technical
Quarterly, 2020

Anaerobic Digester Operation north America

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