BIOGAS PLANT CASCINA PETIVA SAN GERMANO VERCELLESE (VC)

Transcription

1 BIOGAS PLANT CASCINA PETIVA SAN GERMANO VERCELLESE (VC)

2 1. FARM INFORMATION Usable agricultural area (UAA): 270 ha Area classification: outside nitrates vulnerable area UAA Crops allocation and specific productions: ha ryegrass, triticale, maize ha rice Yearly biomasses production for biogas feedstock - Maize silage: t/y - Triticale silage: t/y - Rice straw silage: t/y 2. BIOGAS PLANT Start: July 2011 Type: CSTR (Continuous Stirred Tank Reactor), semi-dry Manufacturer: BTS Italia srl Numbers of digesters: 2 Total capacity of digesters: 6366 m 3 Plant system and its components: - Extruder Lehmann (developed by BTS Italia srl) for biomasses pre-treatment - Digester - Post digester - Co-generator (1 MW el ) - Mechanical solid-liquid separator - Drier of solid fraction - Dust filtering and ammonia stripping - Storage tank for liquid fraction, capacity 300 m Feeding system: Daily load: 55 t of solid + about 6 m 3 of separated liquid fraction (after ammonia stripping) for recirculation. The solid part is composed of: - 38 t maize silage - 14 t triticale silage - 3 t rice straw silage

3 HRT: approx 55 days Process temperature: 44,5 C inside the digester an d 43,0 C in the post-digester 2.2 Extruder The extruder Bio-accelerator is composed of 2 screws that rotate in opposite way. Inside extruder, biomass is mixed and reduced in size. The pressure inside extruder can be varied and modified by changing the distance between the screws. The extruder is powered by 2 three-phases engines each one of 37 kw power. Feed is brought to the extruder through a hopper placed on the top of the screws. Working capacity ranges between 4 and 6,5 t/h according to the used biomass. 2.3 Co-digestate dryer and ammonia stripping BIOGAS Figure 2. Drying plant CO-GENERATOR HOT WATER Energy sold to the grid Thermal Energy digester Mechanical separator LIQUID FRACTION Heat exchanger Steam production Solid Fraction storage DIGESTATE Thickener Dust filtering and NH 3 stripping WET SOLID FRACTION DRYER DRIED SOLID FRACTION Exhausted air in the environment Liquid fraction storage Liquid ammoniun sulphate 6%N Air and exhausted gas Hot water Solid fraction Liquid fraction Ammoniun sulphate The components of the system are: A) Screw press (Börger, mod. Bioselect BS50) for co-digestate separation. B) Heat exchanger. C) Dryer of solid fraction. D) Thickener of separated liquid fraction. E) Ammonia stripping and air filtering.

4 A. Screw press SPECIFICATIONS - Length (mm): Width (mm): Separator body 2 Engine 3 Power pump 4 Compression room 5 Electrical control 6 Pressure adjusting device 7 Liquid fraction output 8 Solid fraction output 7 - Height (mm): Power (kw): 15 - Max flow rate (m 3 /h): 10 - Mash size (mm): 0.50 Figure 3. Screw press (Börger, mod. Bioselect BS50) specifications Separated solid fraction production per year: ~ 9300 t Separated solid fraction is totally used for application in field, by a manure spreader with vertical beaters and horizontal spinning disks. B. Heating exchanger Heating exchanger uses, as thermal source, CHP exhausted gases (~500 C) and the heat from the CHP cooling system (85-95 C). Steam obtain ed from the heating exchanger is approx 110 C and it is used in the dryer for the se parated solid fraction drying. Figure 4.

5 1. Dryer 4. Heating channel 7. Hot water 2. (Optional) 5. External air 8. Return water 3. Air washing 6. Saturated air 9. Combustion gas C. Drier Drier is composed of a conveyor belt (Figure 5) and screws for material mixing (wet separated solid fraction and dried separated solid fraction) and loading. The conveyor belt is charged by a dispenser with a mechanical system, that allows to obtain the material distribution (both wet and dried separated solid fraction, to improve the drying process). Conveyor belt is composed by 2 chains with a series of metallic perforated sheets. Metallic perforated sheets are overturned at the final part of the unit, in order to use them as a second drying sheet. Under conveyor belt a chain with scrapers is sited (Figure 6). Scrapers collect and recirculate part of the dried product on the conveyor belt. The rest of the dried product is discarded by a screw to the dried solid fraction storage. Entire process uses the heat recovered from CHP exhaust gases and cooling system (Figure7). Figure 5. Conveyor belt Figure 7. Heating exchanger Figure 6. Scrapers chain D. Thickener Liquid fraction obtained from mechanical separator partially (2/3) proceeds to the tank for liquid fraction recirculation in fermenter and the rest goes to the thickener, where the liquid fraction is thickened and then pumped to the recirculation tank. E. Air filtration and ammonia stripping Air released from the dryer is conveyed to the filters for dust and ammonia removal. The first phase is the dust removal by a filter; second is the chemical purification by an

6 ammonia trap with sulphuric acid (formation of ammonium sulphate). Ammonium sulphate is stored outside of the dryer. The yearly production of ammonium sulphate is about 500 tonnes, with a nitrogen percentage close to 7%. This products is used in the farm and distributed in field by a slurry spreader. 2.4 Co-generator (CHP): Manufacture: AB Energy Model: Ecomax Bio Power: 1 MW el Operation: 8660 h/y Thermal energy produced per year is about 8 million kwh. A part of this production is used for the biogas plant heating system, about 1.24 million kwh. The rest is convoyed to the drier system. 2.5 Plant productivity Biogas production: around m 3 /day CH 4 production: around 7020 m 3 /day (54% of the biogas production) 2.6 Monthly Electric energy production MWh product per month /3 1/4 1/5 1/6 1/7 1/8 1/9 1/10 1/11 1/12 1/1 Months