Biogas from Energy Crops and Biowastes. Charles Banks University of Southampton

Transcription

1 Biogas from Energy Crops and Biowastes Charles Banks University of Southampton

2 Acknowledgements - Current project Acronym: CROPGEN Title: Renewable energy from crops and agrowastes Contract: SES6-CT Duration: 1 March February 2007 Total cost: 2.5 M EC funding: 2.1 M website:

3 Old technology - new application The technology of biochemical methane generation is well established Traditionally it has been used for waste stabilization Current focus is on energy production To be cost-effective in this role may require engineering and technical improvements to increase conversion efficiencies Selection and production of biomass feedstocks from a variety of sources including novel and multi-use crops and agro-wastes from integrated farming systems, commercial and industrial wastes and by-products.

4 BIODEGRADABLE ORGANIC MATERIAL (CARBOHYDRATES, FATS, PROTEINS) HYDROLYSIS SIMPLE SOLUBLE ORGANICS ACID FERMENTATION ACETIC ACID PROPIONIC ACID BUTYRIC ACID LONG CHAIN VFA ACETOGENESIS ACETIC ACID H 2 + CO 2 METHANOGENESIS ACETOCLASTIC METHANOGENIC BACTERIA HYDROGEN-USING METHANOGENIC BACTERIA CH 4 + CO 2

5 Anaerobic digestion in its simplest form Closed reactor System of gas collection Production of biogas Production of digestate Anaerobic reactor Product Gas storage Energy Heat excess Energy use Product use

6 Product and Energy use Gas burner or boiler Hydrogen reformation for fuel cell applications Process heat Space heat Hot water Gas engine turbine Electricity CHP Transport Biogas storage Vehicle engine Biogas cleaning DIGESTER Digestate separator Liquor Fibre compost Fibre (straight to land) BIOMASS and AGRO-WASTE Storage and pretreatment

7 Process types Wet Dry One stage Multi-stage Mesophilic Thermophilic

8 Process differences Wet Process less than 15 % feedstock solids concentration one or several stages usually operate at 35 o C requires water addition or recycle larger reactor proven technology for sewage sludge digestion more applicable to codigestion with other waste Dry Process more than 15% feedstock solids concentration usually one stage can operate at 35 o C or 55 o C minimal water addition smaller reactor becoming most popular choice for MSW more data and reference plants needed

9 Instantly recognisable! Wet digester Dry digester thermophilic mesophilic Dry digester

10 Biogas as a renewable energy source analysis boundary CO 2 Fuel, product Processing plant fertilizers, equipment residues analysis CO 2 boundary CO 2 CO 2 Crop and animal production energy crops and crop residues transport FYM & slurry transport Anaerobic digester digestate analysis boundary gas Heat and power Transport fuel Local housing, industry, commerce Local and national transport waste

11 Results: storage and pretreatment Some potential to increase methane production by alkaline and water-based pre-treatments, and certain spoilage organisms. More important, poor treatment or storage conditions reduce biogas yields.

12 Digestion trials Single phase digestion trials on a wide range of substrates at laboratory and large scale providing valuable design data Pilot plant trials for crops and agro-wastes

13 Gas yield [Nm³/kg VS] Results: single phase digestion trials Single phase digestion trials on a wide range of substrates at laboratory and large scale providing valuable design data 14,00 12,00 10,00 8,00 6,00 4,00 ots Input [t ots/d] Biogasausbeute [Nm3/kg ots] Methanausbeute [Nm3/kg ots] 1,20 1,00 Input ots [t/d] Gasausbeute [Nm3/kg ots] 0,80 0,60 Input VS [t/d] 0,40 2,00 0,20 0,00 0, Volumetric and specific gas yields per kgvs. Trend lines based on 50-day average.

14 Phase separation innovations Permeating beds Permeating bed UASB or AF Plug flow reactors Plug flow Single stage Two stage Two phase systems (coupled and uncoupled) Hydrolysis and acidification reactor Uncoupling of solids and liquid retention time Methanogenic reactor

15 Permeating bed reactors Single bed systems using grass and maize have given poor results even with ph control Permeating bed with second stage high rate methanogenic reactors gives greater potential for stable operation and biogas production May be some potential for certain crop types but preliminary results indicate that overall process efficiency is likely to be poorer than for single phase mixed reactors Potentially an interesting mix of fermentation products

16 Plug flow systems R2 VFA profile and gas production Day Result from a high initial loading in the reactor Plug flow may limit the overall loading that can be achieved Give an interesting gas and acid production profile (H 2 ) May have potential for certain waste types and the concept could be further exploited for refined fuel production and biorefinery intermediates Still to explore very high solids systems with high recycle rates 10/05/ :00 10/05/ :24 10/05/ :48 10/05/ :12 10/05/ :36 10/05/ :00 10/05/ :24 10/05/ :48 11/05/ :12 11/05/ :36 11/05/ :00 11/05/ :24 11/05/ :48 mg l -1 ml Ethanol Methanol C-2 C-3 i-c4 C-4 i-c5 C-5 C-6 C-7 Biogas R2 VFA profile and gas production /05/ :00 10/05/ :00 11/05/ :00 11/05/ :00 12/05/ :00 12/05/ :00 13/05/ :00 13/05/ :00 14/05/ :00 14/05/ :00 15/05/ :00 15/05/ :00 16/05/ :00 16/05/ :00 17/05/ :00 17/05/ :00 18/05/ :00 18/05/ :00 mg l -1 ml Ethanol Methanol C-2 C-3 i-c4 C-4 i-c5 C-5 C-6 C-7 Biogas

17 Two phase systems Digester VFA mgcod/l mgcaco3/l SSC SSC SSC SSC start-up I II III Alkalinity ph 4 Alkalinity ph 6 SSC Digester alkalinity SSC SSC SSC Overall performance for the treatment of market wastes at thermophilic temperatures and the loading used shows no advantage in process stability or performance compared to single phase controls Uncoupling of solids and liquids retention time in a first phase mixed reactor using maize as a substrate failed to improve rates of hydrolysis and solids destruction start-up I II III

18 Process modelling The anaerobic digestion model 1 (ADM1) has been adopted as a basis for the establishment of: Virtual Laboratory DSS European-wide database on crop species Parameter for the model from project partners and own research Change of model Choice of reactor and plant type Choice of Substrate and Mixture of Substrates Choice of reactor specific data ADM1 based model Simulated results for anaerobic digestion in form of Figures and Data matrices (Print option) Add of a Save option Input of measured crop and input data Input of measured reactor data Possibility to change Parameter

19 Results: process modelling 0.08 Biogas production (measured) Biogas production (model) 80 Methane content (measured) Biogas production [m 3 d -1 ] Methane content (model) Methane content [Vol%] Preliminary results with original ADM1. The model follows the course of the experiment, but the correlation is too low for practical application Time [days] Adjusted model after first manual calibration (k hyd = 1 d -1 )

20 Energy models Data base of energy inputs into the cultivation of different crop types established Factors affecting the energy use in the process have been identified Equations developed to account for energy usage in the digestion process Energy usage model developed based on typical anaerobic digestion plant configurations and substrates

21 Energy balance Inputs / outputs Direct energy Indirect energy Energy balance Energy ratio

22 Energy inputs indirect energy inputs labour Fossil fuels or substitute fuels from the production process machinery other agricultural inputs direct energy inputs indirect energy inputs crop production biomass feedstock biofuel production fuel by-products

23 Direct and indirect energy Direct energy consumption of energy directly in the production process - includes: fossil fuels labour Indirect energy energy which has been used in producing something then used in the production process - includes: fertiliser pesticides / herbicides machinery

24 Direct & indirect energy inputs energy input type operation/input cultivation fertiliser harvest direct fuel application fuel fuel indirect equipment production, application equipment equipment fuel production and transport processing heat, power construction product distribution fuel transport equipment

25 Energy inputs in maize crop production operation No of operations equipment time (h/ha) energy of equipment MJ/ha tractor (kw) fuel used (l/ha) CO 2 indirect (kg/ha) subsoil 1 subsoiler plough 1 plough+press drill/harrow 1 combined drill and harrow fertiliser 1 fertiliser spreader spray 2 sprayer harvest 1 forage harvester cart 1 trailer ensile 1 tractor and bucket tractor 90 kw tractor 55 kw fuel used (litres) 2785 MJ/ha total indirect 1920 MJ/ha hours labour MJ/ha seed kg/ha MJ/ha 2.4 chemicals (kg/ha) N MJ/ha P 2 O MJ/ha 140 K 2 O MJ/ha 79.3 packaging & transport 1362 MJ/ha sprays MJ/ha 63.0 total energy input to crop production and storage 16.7 GJ/ha kg/ha

26 Crop production inputs labour pesticides fer tiliser sugar beet maize wheat soya lucer ne machinery fuel Energy requirement GJ ha-1

27 Digester energy flows Main energy inputs are heat and electricity structural steel 6mm digester contents 35 C insulation 100mm cladding steel 0.75mm air 2 C mix1 reception tank mac1 p1 heat exchanger p4 gas collector digester 500m³ digestate tank p2 dry ground 5 C p3 concrete 300mm mix1 reception tank mixer 3.0 kj s hrs d -1 mac1 feedstock macerator 2.2 kj s hrs d -1 p1 digester feed pump 3.0 kj s hrs d -1 p2 digester discharge pump 3.0 kj s hrs d -1 p3 digester mixing pump 2.2 kj s hrs d -1 p4 digestate heating pump 0.5 kj s hrs d -1

28 An energy balance value unit digester capacity 2000 m 3 daily load 34.8 t/day crop area 318 ha 3% crop energy requirement GJ/year 14% crop transport parasitic heat requirement GJ/year GJ/year 4% 36% parasitic electricity requirement 420 GJ/year digester embodied energy 1350 GJ/year 22% digestate disposal energy total energy requirement biogas produced methane ,331,092 1,398,655 GJ/year GJ/year GJ/ha m 3 m 3 1% 20% crop energy requirement crop transport parasitic electricity requirement digestate disposal energy nitrogen fretiliser parasitic heat requirement digester embodied energy energy value 49,932 GJ/year 157 GJ/ha

29 Digestate the digestate is what remains after the biogas has been removed it contains most of the nutrients of the original feedstock the nutrients are in a form which are more available for crop uptake it has a consistency similar to slurry (approx 10% solids) it can be separated into solid and liquid fractions

30 Effect of digestate use on the energy balance mineral fertiliser crop energy requirement energy for nitrogen total energy requirement value unit GJ/ha GJ/ha GJ/ha digestate fertiliser crop energy requirement total energy requirement GJ/ha GJ/ha methane energy value net energy yield mineral digestate GJ/ha GJ/ha GJ/ha

31 Example energy comparisons fuel biodiesel bioethanol methane methane crop OSR seed sugar beet wheat grain sugar beet wheat grain maize whole crop triticale whole crop triticale fertiliser (N kg/ha) crop yield (fresh yield t/ha) crop yield (t DM/ha) energy for crop production (GJ/ha) energy for processing (GJ/ha) energy of fuel produced (GJ/ha) energy ratio (output/input) net energy produced (GJ/ha) Elsayed, M. A., Matthews, R. and Mortimer, N. D. (2003) Carbon and Energy Balances for a Range of Biofuels Options, School of Environment and development, Sheffield Hallam University, B/B6/00784/REP

32 Potential vehicle fuel produced per ha whole crop wheat CH 4 whole crop OSR CH 4 sugar beet CH 4 beet tops silage maize CH 4 wheat grain CH 4 sugar beet bioethanol wheat grain bioethanol OSR biodiesel litres diesel equivalent per hectare (after processing energy deducted)

33 Potential CHP per hectare OSR whole crop maize whole crop sugar beet tops sugar beet heat electricity wheat whole crop wheat grain potential output MWh per ha

34 Feedstocks for biofuel production for biodiesel oilseed rape sunflower linseed soya peanut for bioethanol wheat sugar beet maize sugar cane lignocellulosic material for biogas barley cabbage carrot cauliflower clover elephant grass flax fodder beet giant knotweed hemp horse bean jerusalem artichoke kale lucerne lupin maize marrow kale meadow foxtail miscanthus mustard nettle oats pea potato rape reed canary grass rhubarb ryegrass sorghum sugar beet triticale turnip verge cuttings fetch wheat

35 methane potential m³/kg VS added Barley Cabbage Carrot Cauliflower Clover Comfrey Cocksfoot Elephantgrass Flax Fodder beet Giant knotweed Hemp Horse bean Jerusalem artichoke Which crops? Kale Lucerne Lupine Maize Marrow kale Meadow foxtail Miscanthus Mustard Nettle Oats Pea Potato Rape Reed canary grass Rhubarb Rye Ryegrass Sorghum Sudangrass Sugar beet Sunflower Sweet sorghum Triticale Turnip Vetch Wheat White cabbage

36 CO 2 and energy cycles Sun CO 2 biomass cutting, collection & transport vehicle fuel CHP Biogas gas scrubbing electricity heat & electricity vehicle fuel transport & spreading biomass energy digestate material digestion