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

ADBA and WBA • ADBA has been ADBA representing and 300+ Members 18 Countries supporting the UK AD market since 2009. WBA • Objective: to breakdown 76 Members 29 Countries the barriers and build a mature, safe industry. Overall Stakeholders • ADBA Publications: 100+ Countries • Quarterly magazine • Biomethane Report February 2020 • Bi-Annual Policy Report • Future Report: AD and the Countryside 2020 • Future Report: Achieving Net-Zero Together 2

Current Industry Optimisation Feedstocks Biology, digestion process and biological health Preventing Collapse 3

Current Industry Actual cumulative number of plants by feedstock sector 800 Sewage 700 Agricultural 600 Mixed agricultural/ municipal/ commercial Number of Plants 500 On-site industrial 400 Municipal/ commercial waste 300 Other 200 100 0 2011 2012 2013 2014 2015 2016 2017 2018 2019 4

Current Industry WWT Capacity 235MW e AD Industry Capacity 992MW e Industry Feedstock 45.9 mt with 23.9 mt from WWT 5

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 6

Feedstock What is it? Biogas Yield Feedstock (DM%) (Fresh/Wet) 111 m 3 /t Food Soup (18-22%) 60 m 3 /t FYM (25%) 60-70% Glycerine (81%) 414 m 3 /t 421 m 3 /t Tilda Brown Rice (92%) ‘Biogas is the respiration by - Thick Sewage Sludge (10%) 45 m 3 /t product of the microbes in 170 m 3 /t Maize (31.5%) the digester eating the Rye (35%) 191 m 3 /t feedstock’ (Practical Guide to AD, ADBA) 289 m 3 /t Chicken Muck (59%) 7

Feedstock Importance Landfill Costs Biogas Quantity Gate Fee Income Biological Health Biogas Quality Major Input Costs Fibre Acidosis/Alkosis in Digestate the Digester Organic Pre-treatment Fertiliser Haulage Costs 8

Feedstock Variations • Contamination • Fibre • Digestibility (NFC) • Gas yield • Characteristics • Quality 9

Biology 10

Biological Health Monitoring • Biogas: quality (CH 4 :CO 2 ratio, H 2 S), volumes (m 3 ) and yields (kWh/t) • VFA profile, FOS/TAC and pH of the digester contents • Mixing: floating layers and foaming • Digestate: smell and look 11

Feedstock Impacts on Biology • Multiple imbalanced 1. species • Dominant strains of Commission 2. Stable bacteria have won the • Gentle adaption should ing Operation competition for substrate be made and volume • Temperature, pH, VFA or increase OLR 3. Stress or • Contamination Dramatic • New feedstock Change • Incorrect monitoring • Manual error • Biology becomes fragile Potential 4. Unstable • Due to continued Inhibition Operation disturbance, change or stress 12

Biological Health Inhibition Inhibitor Reason/Effect Oxygen >0.1mg/L O 2 Ammonia Cytotoxin Increased viscosity, inhomogeneous digester content, incomplete digestion, Ammonium 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 Inhibits, cell wall, protein and nucleic acid synthesis. Negative impact on Antibiotics 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 Salt dries up the bacteria – osmotic pressure (like a slug with salt on) Conductivity EC > 60 mS/cm at 25 ℃ is critical 13

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 14

Preventing Collapse Additives Liebig's law of the • Liquid or powder: minimum • (limiting factor) 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. 15

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. 16

Digestion Process Optimisation in action • Data collection • Data analysis • Resolve issue • Benchmarking of • Explain • Fix pinch performance anomalies • Implement • Detect anomalies • Identify causes changes gradually Monitor: Operations: Implement: Measure the Analyze interpret Optimize process 17

Digestion Process Design – Get what you are given • Location – Transport access, feedstocks and digestate • Exposure – Weather and human risk • Access for maintenance and monitoring • Flexibility – control systems design • Capacity – feedstock, contaminants and digestate 18

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 of collapse. 19

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 20