and preventing collapse 28 January 2020 Sam Hinton, ADBA ADBA and - - PowerPoint PPT Presentation

Feedstock variations, the digestion process and preventing collapse

28 January 2020 Sam Hinton, ADBA

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• ADBA has been

representing and supporting the UK AD market since 2009.

• Objective: to breakdown

the barriers and build a mature, safe industry.

ADBA and WBA

Overall Stakeholders 100+ Countries

WBA 76 Members 29 Countries ADBA 300+ Members 18 Countries

• ADBA Publications:
• Quarterly magazine
• Biomethane Report February 2020
• Bi-Annual Policy Report
• Future Report: AD and the Countryside 2020
• Future Report: Achieving Net-Zero Together

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Current Industry Optimisation Feedstocks Biology, digestion process and biological health Preventing Collapse

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Current Industry

100 200 300 400 500 600 700 800 2011 2012 2013 2014 2015 2016 2017 2018 2019 Number of Plants

Actual cumulative number of plants by feedstock sector

Sewage Agricultural Mixed agricultural/ municipal/ commercial On-site industrial Municipal/ commercial waste Other

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Current Industry

Industry Feedstock 45.9 mt with 23.9 mt from WWT

AD Industry Capacity 992MWe WWT Capacity 235MWe

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Digestion Process Optimisation

“an act, process, or methodology of making something (such as a design, system, or decision) as fully perfect, functional, or effective as possible”

Process Design Commissioning & Handover Operations

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Feedstock What is it?

Feedstock (DM%) Biogas Yield (Fresh/Wet)

Food Soup (18-22%) 111 m3/t FYM (25%) 60 m3/t 60-70% Glycerine (81%) 414 m3/t Tilda Brown Rice (92%) 421 m3/t Thick Sewage Sludge (10%) 45 m3/t Maize (31.5%) 170 m3/t Rye (35%) 191 m3/t Chicken Muck (59%) 289 m3/t

‘Biogas is the respiration by- product of the microbes in the digester eating the feedstock’

(Practical Guide to AD, ADBA)

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Feedstock Importance

Landfill Costs Gate Fee Income Major Input Costs Pre-treatment Haulage Costs Biological Health Acidosis/Alkosis in the Digester Biogas Quantity Biogas Quality Digestate Fibre Organic Fertiliser

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• Contamination
• Fibre
• Digestibility (NFC)

Feedstock Variations

• Gas yield
• Characteristics
• Quality

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Biology

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• Biogas: quality (CH4:CO2 ratio, H2S), volumes (m3) and yields (kWh/t)
• VFA profile, FOS/TAC and pH of the digester contents
• Mixing: floating layers and foaming
• Digestate: smell and look

Biological Health Monitoring

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Feedstock Impacts on Biology

1. Commission ing

• Multiple imbalanced

species

• Gentle adaption should

be made

• 2. Stable

Operation

• Dominant strains of

bacteria have won the competition for substrate and volume

• 3. Stress or

Dramatic Change

• Temperature, pH, VFA or

increase OLR

• Contamination
• New feedstock
• Incorrect monitoring
• Manual error
• 4. Unstable

Operation

• Biology becomes fragile
• Due to continued

disturbance, change or stress

Potential Inhibition

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Biological Health Inhibition

Inhibitor Reason/Effect Oxygen >0.1mg/L O2 Ammonia Cytotoxin Ammonium Increased viscosity, inhomogeneous digester content, incomplete digestion, disturbed nutrient supply. Optimum < 3000 mg/L and Critical > 3500 mg/L Hydrogen Sulphide Toxic VFA (Acid) Decreasing pH and often the acetic:propionic concentration Heavy Metals Cu > 50mg/l, Zn > 150mg/l, Cr > 100mg/l Antibiotics Inhibits, cell wall, protein and nucleic acid synthesis. Negative impact on metabolism, cell division Disinfectants Cytotoxin, cell wall destruction, inhibits metabolism, pH changes Mycotoxins (Mold) Inhibition proven, ongoing research about mechanisms, foam formation Salt Content/Electrical Conductivity Salt dries up the bacteria – osmotic pressure (like a slug with salt on) EC > 60 mS/cm at 25℃ is critical

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Preventing Collapse

• Hard to prevent due to the poor understanding of how microbes'

function and adapt to environments

• No mathematical models for this
• Bacterial generation time:
• <24 hours in hydrolysis and acetogenesis
• Over 10 days for some methanogenic bacteria
• Feedstock: digestibility and composition
• Temperature
• Inhibition
• Design; mixing, feeding (dry or mixed) and re-seeding

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Preventing Collapse Additives

• Liquid or powder:
• Chelates are packaging agents of liquid

TEA, which increase the bioavailability

• Macro-nutrients: C, Ca, Fe, K, Mg, N, Na, P & S
• K:Na ratio 10:1 to optimize osmosis
• Fe: Electron transport and de-sulphurisation
• Micro-nutrients: B, Co, Cu, Mn, Mo, Ni, Se, V, W, Zn
• < 50mg/kg
• Dependent on the OLR. Keep bugs ‘tip-top’ = racehorses versus

cart horses.

• Se and Co can prevent propionic build.

Liebig's law of the minimum (limiting factor)

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Preventing Collapse Data and troubleshooting

• The three main areas that can be altered to affect optimal performance

are:

• Equipment – analyse operating data to; find pinch points, get an

early diagnosis of failure, ensure calibration, assess health, stability and maturity of biology, feedstock management and compare performance

• Operating procedures – automation helps reduce variability
• Control – interaction and interdependence of control loops such

as temperature, levels or flow and if one is not properly designed the process runs sub optimally

• Failure is expensive, odorous, unsafe for employees and the

environment as well as giving the industry a bad name.

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Digestion Process Optimisation in action

• Data collection
• Benchmarking of

performance

• Detect anomalies

Monitor: Measure the process

• Data analysis
• Explain

anomalies

• Identify causes

Operations: Analyze interpret

• Resolve issue
• Fix pinch
• Implement

changes gradually

Implement: Optimize

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Digestion Process

Design – Get what you are given

• Access for maintenance and monitoring
• Flexibility –control systems design
• Capacity – feedstock, contaminants and

digestate

• Location – Transport access, feedstocks

and digestate

• Exposure – Weather and human risk

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Conclusions

• Feedstock not the only variable at work: design and operations but……

…..feedstock variations increase the monitoring requirement to prevent collapse.

• Complex interactions between feedstock, biology and outputs.
• Diligent design, commissioning and operations ensure you can prevent

collapse.

• Optimisation, makes the most of what you have.
• Pushing the plant beyond its critical constraints will increase the chance
• f collapse.

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Contact

• Sam Hinton
• sam.hinton@adbioresources.org
• 07795 186 026

Events

• ADBA Scottish Conference - Hosted by Anderson Strathern,

Edinburgh - 12 March 2020

• UK AD and World Biogas Expo – Birmingham - 1-2 July 2020
• World Biogas Summit - Birmingham - 1-2 July 2020