Wels November, 26 th 2009 EU-AGRO-BIOGAS Symposium Energy Recovery and Reduction of GHG Emission by the Coverage of a Digestate Storage Tank Paolo BALSARI DEIAFA Università di Torino E-mail: paolo.balsari@unito.it
The CO 2 eq. emissions produced during anaerobic digestion process (results from EU-Agro biogas project) 61% 5% 28% 6% Biomass AD A.D. plant Digestate Digestate production and + storage land application transport CHP
Air pollution o BIOGAS CH 4 200-300 m 3 /day 4-5 t/day CO 2 eq. NH 3 4.4 g/m 2 day 3.6 kgn/day NH 3 CH 4 NH 3 CH 4 fermenter 1 MW el
GHG and NH 3 emissions during the storage of digestate (k kg/m 2 da ay) CO 2 eq. 5 4 3 2 3,9 3,2 43 4,3 3,6 5 4 3 2 N- NH (g/m 2 3 day) 1 1 0 Storage of Raw slurry 0 Storage of digestate 10-12% 12% more CO 2 eq. and NH 3 emissions with digestate (data by DEIAFA, University of Torino)
Digestate storage In Europe most of digestate storage tanks are uncovered (the German situation) 60 Relat tive fre equenc cy [%] 50 40 30 20 10 0 n=346 open not gas-tight gas-tight (Data from: KTBL)
The study carried out within the EU Agro-Biogas project 1) Assessment of NH 3 and GHG emissions during the digestate storage 2) Assessment of residual biogas potential from the storage of digestate 3) Development of a system able to reduce the GHG emission and to recover the biogas during the digestate storage.
The Italian anaerobic digestion plant selected for the EU Agrobiogas project Bagnod Roberto A.D. plant
Bagnod Roberto A.D. plant 2 X 6000m 3 ferroconcrete concentric fermenters (useful volume 5800m 3 ) Solid feedstocks F3 F4 Fermenter 2 Feeding system Digestate storage tank (6000m 3 ) Field application Mixing pit Liquid manures F1 F2 Fermenter 1 1MWel. CHP Fermenters temperature: 41 C
Mixing systems Vertical paddle mixer Horizontal paddle mixer Axial mixer Inner section External ring
Main working parameters of Bagnod Roberto A.D. plant Specific loading rate [kgvs*m 3 *d - 1 ]: ~2,25 HRT [days]: ~ 105 CH 4 yield [m3n*m-3 3 fermenter]: ~ 054 0.54 Specific CH yield [m 3 N*kgVS - 1 4 ]: ~ 0,25 Biogas yield [Mio m 3 /year]: ~ 3.5
Bagnod Roberto A.D. plant: input feedstock Solid fraction from mechanical separation of digestate 1% kiwi 3% Triticale 4% Other 2% Rice draff 2% Cattle slurry 34% Maize silage 24% FYM 30%
1) Assessment of NH 3 emission during digestate storage 3 Wind Tunnel System to adjust the air speed floating pontoons Tunnel (0.32 m 2 ) Fan Sampling points (emitted NH 3 ) Sampling points (environmental NH 3 )
1) Assessment of NH 3 emission during digestate storage Air speed over the digestate surface: 0,6 m/s Environment temperature: 25 C (19,4-28,7) Digestate average temperature: 27,22 C (22,0-38,8) 8) Days of trial: 8
1) Assessment of NH 3 emission during digestate storage r day Emissio on, g NH 3 /m 2 sto orgae pe 16 14 12 10 8 6 4 2 0 25 20 gnh -2-1 3 m day 15 C 10 5 0 1 2 3 4 5 6 7 8 0 9 days D igestate tempera ature, C 2,1 4,5 g N-NHNH 3 /m 2 of digestate storage per day 38 g N-NHNH 3 per m 3 of digestate loaded into the tank per day
2) Assessment of residual biogas potential from a digestate storage tank
The pilot system to assess the residual biogas potential of digestate Surface: 6,25m 2 (2,5 X 2,5m) Stainless steel and polypropylene floating frame PVC based covering membrane
The pilot system to assess the residual biogas potential of digestate Pilot system temperature probe + data logger Vacuum pump X Digestate temperature re Gasometer 2 m 3 Volume meter probes + data loggers
The pilot system to assess the residual biogas potential of digestate Biogas collection Measurement of the recovered biogas Biogas analysis (CO 2, CH 4, H 2 S)
Measurement at different position within the digestate storage tank Position 3 Position 2 Position 1 30m 5m 20m Digestate inlet ~ 110 m 3 / day (ST: 9.5%; SV/ST: 76.9%) Measuring time: ~50 days per position Daily measuring of recovered biogas Spring and summer trials
Biogas yields measured at the three positions 4,5 Nm 3 /m 3 digested slurry per day gestate per day m 3 of dig he tank p biogas /m ed into th Nm 3 b loade 60 6,0 5,0 4,0 3,0 2,0 1,0 0 Biogas yield 5 20 30 Distance from the digestate inlet (m)
3) Development of a system able to reduce the GHG emission and to recover the biogas during the digestate storage Situation before the EU Agro biogas intervention BIOGAS CHP CH 4 N-NHNH 3 1 MW el FERMENTER DIGESTATE STORAGE GHG and NH 3 emission Current situation BIOGAS CHP BIOGAS Floating cover 1 MW el FERMENTER SOLID FRACTION LIQUID FRACTION STORAGE
3) Development of a system able to reduce the GHG emission and to recover the biogas during the digestate storage without any modification of slurry management Biogas to CHP Liquid fraction land application
3) Development of a system able to reduce the GHG emission and to recover the biogas during the digestate storage Central floating frame Covering sheet Peripheric floating frame
The assembly phase Peripheric floating frame 48 elements (L 2.3 m x h 0.56 x w 0.1 m) Stainless steel frame + 4 polypropylene panels
The assembly phase Central floating unit 30 3,0 m 3,5 m 9 polypropylene and polystyrene units Buoyancy: 4 t
The assembly phase PVC based covering sheet Weight: 1.2 t Biogas storage capacity: ~1500m 3
The floating cover placement within the tank
The floating cover placement within the tank
The floating cover placed over the digestate surface
Biogas yield from the liquid fraction storage tank Avg. 335Nm 3 biogas/day biogas temperature 500 40 s day -1 Nm 3 bioga 450 400 350 300 250 200 150 100 50 35 30 25 20 15 10 5 Liquid fraction te emperature e C 0 0 ott- 08 nov- 08 dic- 08 gen- 09 feb- 09 mar- 09 apr- 09 mag- 09 giu- 09 lug- 09 ago- 09 set- 09
Conclusions By covering the digestate storage tank of Bagnod A.D. plant (1MWel.) it has been estimated to be possible: a) to avoid the emission in atmosphere of ~160g NH 3 per MWh el. 1.3t NH 3 per year ~161kg CO 2 eq. per MWh el. 1410t CO 2 eq. per year
b) to recover, on average: Conclusions ~14 Nm 3 biogas per produced MWh el. c) to produce: ~ 122000 Nm 3 biogas per year ~0.7 more MWh el. per day ~ 255 more MWhel. per year (= +3% of the current production) = ~ 71500 more income per year Payback time of the floating cover < 1 year
Conclusions d) to abate approximately 30% of the total GHG emission generated by the electricity production from anaerobic digestion
Total GHG Emissions for the electricity production by biogas at Bagnod A.D. plant 0,70 CO2eq/k kwhel 0,60 0,50 0,40 0,30 diffuse emissions savings ~ 0.17kg CO2eq/kWh el. plant construction - materials e-crop production w/o N2O glycerol gy production transport feedstocks - machinery diffuse emissions (slip + leakage) plant construction - auxiliaries kg 0,20 e-crop production - N2O 0,10 transport feedstocks - auxiliaries process energy 0,00 Bagnod storage tank uncovered Bagnod storage tank covered diffuse emissions (open storage) (Data from KTBL, 2009)
The storage of digestate plays an important role under the environmental point of view of anaerobic digestion The coverage of storage tanks should therefore be encouraged
DEIAFA WASTE MANAGEMENT GROUP UINIVERSITA Università à di Torino THANK YOU FOR YOUR ATTENTION for further information: i paolo.balsari@unito.it