Biogas from dairy farm ponds Stephan Heubeck & Rupert Craggs - PowerPoint PPT Presentation

Hamiltion 22. April 2015 Biogas from dairy farm ponds Stephan Heubeck & Rupert Craggs National Institute of Water & Atmospheric Research Ltd, New Zealand

Why bother with pond biogas systems? Because we can address more than one problem at once!

Why bother with pond biogas systems? “Look deep into nature, and then you will understand everything better” Albert Einstein

NIWA pond monitoring programs Obtaining methane production data in the field

Storage pond sites 2013 • Monitoring sites in Northland, Waikato and Southland • Farms of high and low intensity o (use of feed pads, stocking rate) • Pond biogas production + quality • Raw effluent quantity • Raw effluent quality: o Solids - TS/VS, COD o Nitrogen - TN o Phosphorus - TP

2013 storage pond monitoring Pond temperature shows seasonal variation: • Minimum pond bottom: ~ 7 o C • Minimum pond water: ~ 3 o C

2013 storage pond CH 4 Southland storage pond: • Correlates with number of cows milked • Autumn reduction due to single milking

2013 storage pond CH 4 Waikato storage pond: • Milk throughout winter – more constant load • Greater correlation of CH 4 production with solids load than temperature

2013 storage pond summary Per cow solids loading: • Southland: 0.29 kgTS/0.18kgVS /cow/day • Waikato: 1.13 kgTS/0.82kgVS /cow/day  feed pad Methane productivity: • Southland: 0.21 m 3 CH 4 /kgVS • Waikato: 0.22 m 3 CH 4 /kgVS

Methane GHG Emissions 2013 storage pond methane emissions: • Southland: 6.7 kgCH 4 /cow/year • Northland: 8.3 kgCH 4 /cow/year • Waikato: 34.1 kgCH 4 /cow/year  feed pad – more solids 2012 anaerobic pond methane emissions: • Southland: 14.37 kgCH 4 /cow/year • Northland: 14.45 kgCH 4 /cow/year • Waikato: 7.68 kgCH 4 /cow/year

Pond monitoring summary Dairy farm effluent ponds minus side: • Release much more GHG emissions (methane) than previously assumed • Emissions will increase with farm intensification Dairy farm effluent ponds plus side : • Conversion of VS to CH 4 similar to engineered digesters • Very good at removing (coarse) solids • Simple to build • Simple to operate • Can cover to capture odour and GHG • Biogas energy potential

NIWA Covered Anaerobic Pond Design Basics: o For flush manures and dilute wastes only o Solids concentrations up to ~5% o Different retention times for solids and liquids o Loading rates <0.5 kgVS/m 3 /day o Retrofits possible

NIWA Covered Anaerobic Pond Design Custom designed covered anaerobic pond: o Deep, narrow and long pond o Dedicated pond often better than retrofit o Covering (shallow) storage pond often uneconomic o Liner depending on regulation (plastic, clay)

NIWA Covered Anaerobic Pond Design Simple cover: o Common cover materials (LLDPE) o Flexible, UV resistant, cost effective o Weight pipes for rainwater guidance o Electric rainwater draw off pump o Ring pipeline for efficient biogas draw-off o No floatation underneath cover

Biogas use options Biogas is the most versatile renewable energy resource - usage options include: o Flaring – GHG and odour control o Combined heat and power (CHP) – generator o Heat – boiler use o Transport fuel – purification and compression There is no size that fits all!

Biogas flaring Biogas flaring: o Low maintenance o Odour and GHG control o No local heat demand o Small electricity demand o Not big enough for advanced biogas use options like vehicle fuel etc.

Biogas CHP Motor-generators: o Spark ignition o Gas purification for generator longevity o Grid synchronisation or stand alone o Radiator heat recovery o Exhaust heat recovery o Renewable 3-phase electricity on call o With biogas storage back-up function for grid outages

Biogas CHP Waste heat use: o 80-90 C hot water o 2 kWh hot water for every 1 kWh electricity o Hot water for washing and heating o Hot water can be stored independently to decouple electric and thermal load

Biogas as boiler fuel The “overlooked” option: o Far simpler to operate than CHP o Little (no) biogas purification required o Highly efficient biogas use: 90 – 102% efficiency o Doable at small scale o Financial attractiveness can be good as well

Biogas transport fuel Biogas as transport fuel: o Purified and compressed biogas (bio-methane) can be used in any CNG vehicle o The size of the biogas resource on NZ farms may be often too small to justify the high investment o Further increases in the cost of petroleum fuels may however make this option attractive in the future

Biogas from covered anaerobic ponds So how much does a covered anaerobic pond based biogas system cost, and does it make financial sense? The answer depends, because: o Every farm is different (size, soil, existing gear) o A lot of covered anaerobic ponds will be built without biogas use

Covered Anaerobic Ponds As solids removal technology: o Dry matter (DM) reduction higher than with mechanical solids separator or weeping wall o Cost less than mechanical solids separator and about equal to weeping wall o No odour or GHG emissions o Maintenance more flexible

Covered Anaerobic Ponds Covered Anaerobic Pond pre-treatment prior to storage pond:

Covered Anaerobic Ponds Covered Anaerobic Pond treated effluent ready for: o Recycling as wash water, i.e. through backing gate o Injection into low application sprinkler system (K- line) or centre pivot irrigator

Covered Anaerobic Ponds As compliance tool: o Reduce effluent odour  see pig industry o Reduce GHG emissions  the dairy industry’s chance to reduce the GHG foot-print by 10 – 20% with here and now technology without curtailing production

Indicative costs Assuming a 600 cow dairy farm with feed pad. Covered Anaerobic Pond added to existing storage pond system for pre-treatment: Earth works: $15k – $25k$ (cut and fill or import?) Plastic: $15k - $35k (bottom liner required?) Pond pipe work: $5k - $10k Consents, Planning, Supervision: ???? Biogas piping and conditioning: $5k - $15k Biogas boiler: $3k - $6k Biogas CHP: $30k - $80k (longevity, only ~2,500 h/y!) Installation and connections: $5 - $30k (lines company decides)

Biogas value Assuming a 600 cow dairy farm with feed pad: Annual electricity consumption: 80k – 120k kWh/y Thereof hot water (heat): 25k – 30k kWh/y Annual usable electricity generation: 50k – 70k kWh/y Annual usable hot water generation: 25k – 30k kWh/y Gross earnings biogas boiler: $3k/y - $7k/y (D/N tariff!) Gross earnings biogas CHP: $15k/y - $30k/y (lines charging structure and / or islanding of generation will have a big impact on net result)

Biogas use The early (mass) adopters for covered anaerobic pond based biogas technology will therefore be piggy-backed schemes where the pond is in place for other reasons: o Biogas system payback = payback of gas user o Can be economic for small (gas boiler) and large schemes (CHP) o Economic threshold of <3 years doable

Conclusion Covered anaerobic pond based biogas systems will likely be installed for their multiple benefits: Solids removal; effluent reuse; odour/GHG emission reduction Biogas energy will be the icing on the cake