4. Long-lived digester design
ร 450 years combined operation
ร Many running > 20 yrs
ร Low parasitic energy
ร Simple, user-friendly
5. Context & Drivers - Itโs time to act!
โข Climate change: Last year, we reached 400ppm CO2 in
the atmosphere
โข The era of cheap energy is over โ global energy
transition. Energy is NOT just your lights and heat.
It is food.
โข Population growth: 2050 9BN? 11BN?โข Population growth: 2050 9BN? 11BN?
โข Increasing urbanisation: 1.4M people/week (Bโham)
โข Population age.
2000 โ 2BN children โ
Prediction for 2100?
Legal CO2 reduction targets
6. Energy
Food
So what can I do?
Reduce
(Efficiencies)
Re-
THINK!Reuse
Recycle
Water
THINK!
(resilience)
7. UK Storms: โWe have no
heating,
no power, no hot foodโ
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10. What is Anaerobic Digestion?
Organic
material*
Heat
ANAEROBIC DIGESTER @ 40ยฐC
Biogas
H2S & other gases
To CHP to create
renewable electricity
OR
To boiler, Aga,
Rayburn, gas ring(s)
Digestate
(Biofertiliser)
Optional separation intoOptional separation into
soil conditioner & liquid
fertiliser
OR
Spread to land
An enclosed vessel: heated, stirred (either by
60% CH4 & 40% CO2
An enclosed vessel: heated, stirred (either by
gas mixing or mechanical agitation)
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Natureโs own biological decomposition by micro-organisms
in the absence of oxygen (anaerobic)
It is a natural process that breaks down organic material
in an airless, heated and mixed tank
11. Anaerobic Digestion Composting
Degradation of organic matter in the
absence of oxygen (bacteria, archaea,
protozoa that do not need oxygen to grow
โ anaerobes)
Degradation of organic matter
in the presence of oxygen in air
(bacteria/fungi need oxygen to
grow โ aerobes)
Best way to treat all non-woody organic
wastes
Best way to treat all woody
organic wastes
Requires heat (ideally) Generates its own heat
(exothermic)
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Creates CO2 Creates CO2
Creates fertiliser whose nutrients are more
available to plants, as well as a soil
conditioner
Creates a soil conditioner /
fertiliser
Creates biogas which can be used to
create electricity, heat or vehicle fuel
13. SimpleAD plant running on slurry
Cow slurry in
Gas for cooking or heating farm house
Liquid used on grass
Fibre ploughed in
Thermal solar heated digester
Biofertiliser
Digester
40ยฐC
An enclosed vessel:
heated, stirred
(case studies used
gas mixing)
Biogas
60% CH4
40% CO2
Feedstock:
Gravity or
auger fed
Gas
Holder
Liquid
Fibre
Storage
Direct Use
Heat/hot water
Boiler:
(digester heating)
Aga/Rayburn
14. AD plant with Combined Heat & Power (CHP)
Digester
40ยฐC
Biogas
Gas
Holder
CHP
-Tends to need a lot more feedstock
-More complicated to run
Electricity
60% CH4
40% CO2
Liquid
Fibre
Storage
Biofertiliser
Heat Heat
Anaerobic Digester
Feedstock
18. Farm
Abattoir
Food
Processing
The Food Production Process
โขCurrently, there is โwasteโ
at every stage of the process
โขAD closes the loop
โขNutrients must go back to land
in a beneficial way
Fertiliser(nutrients)backtoland*
Retail
Restaurant
& Home
Anaerobic DigesterEnergy
from
Biogas
*Recycle NPK &
micronutrients as fertiliser
*Pathogen/weed seed kill
*Sequester carbon
*Improve soil structure
Fertiliser(nutrients)backtoland*
19. Why AD of slurries/manures?
1989 โ Clive Pughโs Slurry System
1990 โ With
โข Displacement of fossil fuels (both fertiliser and energy)
โข Reduction in carbon dioxide, ammonia, nitrous oxide and
methane losses to atmosphere greatly reduced GHG potential
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1989 โ Clive Pughโs Slurry System WRI (Murcott) Digester
20. Environmental Benefits of AD
โข Returns micronutrients, water, carbon, nitrogen to soil
โข Reduction in carbon dioxide, nitrous oxide and methane
losses to atmosphere greatly reduce GHG potential
โข Offensive odours eliminated/reduced
โข Kills many weed seeds/pathogensโข Kills many weed seeds/pathogens
โข Addition of humus improves the physical properties of soil
water holding capacity, aeration, water soluble aggregates
and increased crop production up to 20-30%
โข Reduction in BOD (80-95%)
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21. โข Improved slurry handling
โข Less water use
โข Fertiliser benefit is not just NPK,
but significant and essential trace
elements
โข Fertiliser performance is superior;
nutrients are more readily
available, particularly Nitrogen
โข Digestate does not hinder clover
Farming Benefits of AD
โข Digestate does not hinder clover
growth like synthetic fertilisers.
โข Faster re-grazing โ healthier
animals
โข Increased ley life
โข Production of energy and fertiliser
reduces costs of food production,
improves profitability and adds an
income stream to the farm
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23. What is โSmall Scaleโ?
โขGerman definition (<75kWe)?
โขDECC definition (<500kWe; <250kWe)
โขUK Pre-FIT definition?
24. What is AD viability?
Feedstock
CAPEX/OPEX
Income/Avoided
Expenditure
AD
Feedstock
โข โIf it costs me less to manage โ thatโs for me!โ
โข โWaste is a continuous & increasing cost to the
businessโ
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25. Biogas Potential
150
200
250
300
Solid Colours - Biogas Yield (Nm3/t FM) Average & Variance
Hatched Colours - Methane Yield (Nm3/t FM) Average & Variance
FOOD WASTE: use 120-130 m3 at 60% CH4
รค
0
50
100
Cattle Slurry Pig slurry Cattle dung Fodder beet Potato pulp Poultry
manure
Apple
pomace
Maize silage Whole crop
cereal silage
Grass silage Grape
pomace
CAPEX/OPEX
AD
Income/Avoide
d Expenditure
Feedstock
27. On-site cost reduction
โข Waste management cost savings
โข Energy savings
โข ?Fertiliser savings โ Digestate has N, P, K and trace elements
Government support
Financial Drivers for On-site AD
Government support
โข Incentives, eg RHI, Feed-in Tariff (FIT) โ for generation
โข Export Tariff
โข Grants (feasibility only)
โข Carbon reduction (tax?)
AD
Feedstock
CAPEX/OPEX
Income/Avoided
Expenditure
29. Capital costs for farm scale CHP < 250 kWe
(Apples and Pears)
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30. Effect of Energy Prices on Profit
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31. Operating Costs
Energy: Pumps, heat exchangers, macerators, automatic
valves, augers, mixers, agitators, gas storage, (except
bell-over-water configurations); digestate separation
(if included), dumping excess heat from a CHP
KISS principle applies!
Regulatory: CHP emissions tests, training, permitting,
insurance. Regulation must be risk based.
Consumables: H2S removal, pump parts
Maintenance: CHP oil/plugs/servicing, pump parts,
analyser/sensor calibration/replacement, grit removal
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Income/Avoided
Expenditure
Feedstock
CAPEX/OPEX
32. Doโs and Donโts
โข Must be designed for minimal daily
operational time. Must work 24/7
with minimal input.
โข Very simple feeding
โข Fresh slurry
โข Minimal added water (preferablyโข Minimal added water (preferably
none) โ rain or seepage
โข Minimal parasitic load (electrical and
mixing)
โข Minimal maintenance of mixing (eg
gas vs propeller)
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Income/Avoided
Expenditure
Feedstock
CAPEX/OPEX
34. Photo: Courtesy of Bourne Valley Associates
Larger modern 80kWe digester: slurry from 120 cows, chicken manure
from free range broilers & some added maize
37. Feedstock considerations
โข Driver: feedstock volume or output?
โข What feedstock is available and how much
biogas will it yield?
โข If imported, is it a secure supply?
โข What type of input ?
โข Crop โ self perpetuating.
โข Muck / waste โ enhancing
โข Waste โ gate fee + enhancing
โข Seasonality / variability
โข Cost of buying/growing/haulage
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38. What you need to think about
โข Grid Capacity
โ How much can you export?
โ How much will it cost?
โข Best use of biogas
โBoiler, CHP, biomethane or combination?
โElectricity use (as much on-site, unless exportโElectricity use (as much on-site, unless export
premium)
โ-Heat (helps with overall profitability)
โข Digestate
โข How much land do you have available?
โข Planning/Regulation
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39. AD as diversification
โข AD does not detract from your core business.
It enhances it!
โข AD does not require re-skilling.
If you understand cow nutrition you can already feed a digester.
AD is NOT about getting another job, itโs a way of
making the job you already do more profitable.
If you understand cow nutrition you can already feed a digester.
โข AD provides an alternative income stream
Non food and independent of supermarkets โ currently.
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