Driven by pure energy. Understanding the Important Factors of Anaerobic Digestion ABC Workshop - May 27,

Transcription

1 Driven by pure energy Vers :28:55 Understanding the Important Factors of Anaerobic Digestion ABC Workshop - May 27,

2 FACTORS OF SUCCESS 1. Understanding the terminology 2. Understanding the biology basics 3. Sizing an Anaerobic Digester properly 4. Understanding your potential substrates 5. Selecting the right type of Anaerobic Digester for your application 6. Other considerations: H2S Removal Mixing style Biology Management -2-

3 TERMINOLOGY Anaerobic Digester / Biodigester / AD A series of biological processes in an anaerobic (oxygen-free environment) which treats substrates by converting them into biogas. Digestate A byproduct of anaerobic digestion, which is rich in nutrients such as nitrogen, phosphorus and potassium. It can be in a solid or liquid form Feedstock / Substrate materials treated by digesters Biogas The gas produced by anaerobic digestion, which is normally composed of 55-70% CH4, 30-45% CO2, and a small amount of other gases (hydrogen, hydrogen sulfide, ammonia). This gas can combusted to produce electricity, heat or upgraded (CO2 removed) and used as natural gas or vehicle fuel

4 ANAEROBIC DIGESTION BIOLOGY Anaerobic digestion occurs in the absence of oxygen. A combination of bacteria and archea (very old life, which can covert acids into methane). osarcina/results.html Aerobic Anaerobic

5 SIZING DIGESTERS Organic Loading Rate (OLR) Units (kg VS/m 3 /day) Amount of organic material treated by the digester per active volume of digester Acknowledges the relatively slower conversion rate of methanogen microbes For example: Typical CSTR style- ~3.5 kgvs/m3/day -5-

6 SIZING DIGESTERS Retention Time Average amount of time a feedstock is treated within a tank Minimum time is dependent on feedstock characteristics Example (for CSTR): 35 days dairy manure days corn silage nedigesters/md1.html -6-

7 SUBSTRATE PARAMETERS Types of Substrates Agricultural products - Manure - Energy crops (grass silage, corn silage) - Crop byproducts (straw, corn stover) Food by-products - Glycerine - Slaughterhouse waste - Vegetables (grocery stores, source separated organics) - Dissolved air flotation - Fats, oils & grease Wastewater - Sewage - Industrial

8 SUBSTRATE PARAMETERS Critical Substrate Questions - Volumes/tonnage per day? - Consistency? - Solid or liquid? - Does it contain cleaning substances or foreign objects? - Tipping fees/cost to purchase? - How often will it be delivered? -8-

9 SUBSTRATE PARAMETERS Total Solids/ Dry Matter Percentage of feedstock left after all moisture has been removed Typical values: 8% dairy manure 33% corn silage Volatile Solids/Organic Matter Percentage of dry matter burned off when ignited at 500 o C Typically presumed to be a portion which can be degraded into biogas nedigesters/md2.html Typical values: 85% dairy manure 95% corn silage -9-

10 SUBSTRATE PARAMETERS Substrate Energy Density Amount of gas potential per kg of Organic Matter Varies substantially based upon composition, particle size, retention time etc. Example: Substantially more energy in grease trap as compared to dairy manure ck

11 SELECTING THE RIGHT DIGESTER STYLE Different styles vary based on: - Ability to treat different types of substrates, - Ability to accomodate changes in menus, - Cost, - Existing installations in North America and Europe, - Ability to maximize the amount of biogas produced per tonne. Type Lagoon Plug Flow Complete Mix Suitable DM in input Biogas yields Fixed Film Dry Digester < 3% 7-13% 3-12% 2-10% >35% Low Medium High High Medium OLR Low Medium Medium High High Costs Low Medium Medium Medium Medium

12 TYPES OF ANAEROBIC DIGESTERS Complete Mix Anaerobic Digester Most common system for Ag-based systems in Europe 7,000+ now in operation, Sometimes referred to as a CSTR. Pros: High assimliation capacity, Easily sized for different retention times, Substrates are constantly being exposed to microbes, Samples taken reflect the entire system, Able to handle changes in substrates. Most efficent conversion to biogas Cons: Typically higher electrical loads, Tends to have dead zones.

13 TYPES OF ANAEROBIC DIGESTERS Fixed Film or Upflow Anaerobic Sludge Blanket (UASB) Commonly used with substrates with low total solids, such as wastewater. Pros: Works with low TS substrates, Small volume means it can fit in relatively small spaces. Cons: Low assimilation capacity, Normally cannot handle changes in substrates, Normally requires more chemical alteration of substrates

14 Pros Low cost, Incorporates into the exisiting infrastucture well. Cons Difficult to ensure a complete mix (efficient removal of biogas and maintain heat). Normally low biogas conversion rate. TYPES OF ANAEROBIC DIGESTERS Covered Lagoons An air tight lagoon where anaerobic activity produces biogas. These systems can be heated or non-heated and mixed or nonmixed

15 TYPES OF ANAEROBIC DIGESTERS Plug Flow Material is inputted into one side of the digester and removed from the other side. Biological the system breaks down the substrates as it moves from one end to the other end Pros - Good track record with dairy manure in the US - Lower electricity consumption Cons - Low assimilation capacity - Inability to handle menu changes - Cannot be operated with sand bedding

16 TYPES OF ANAEROBIC DIGESTERS Dry Fermentation Designs can differ, but normally substrates are placed into a garage-style oxygen-free room. Percolate, or the liquids drained from the pile, is poured over the solids. Pros - Can treat very high solids or unpumpable materials. Cons - Odour/safety concerns when cleaning storage room. - Difficult to get the correct ratios to obtain maximum biogas production htm

17 TYPES OF ANAEROBIC DIGESTERS Other Styles Batch style Often lab style Phased Different ph and/or temperature per tank Primary & Secondary Digesters Same ph & temperature in each tank

18 OTHER CONSIDERATIONS H 2 S H 2 S is naturally produced during the anaerobic digestion process, Concentration can be 50-50,000 ppm, If the H 2 S concentration is too high, it is a safety hazard and can cause damage to the CHP =flypage.tpl&product_id=126&categor y_id=50&option=com_virtuemart&ite mid=45

19 OTHER CONSIDERATIONS Biological H 2 S Removal Pumped in air into biogas space Biogas needs to travel through desulfurizing bacteria Normally a low cost add-on Scrubber Similar to in-take process, but external to the Anaerobic Digester PlanET Biogas USA

20 OTHER CONSIDERATIONS Chemical H 2 S Removal Iron chloride S Fe 3+ -> S + 2Fe 2+ Corrosive liquid Iron hydroxide Popular in Europe Non-reactive solid

21 OTHER CONSIDERATIONS Mechanical H 2 S Removal Activated carbon High maintenance costs Iron sponge Similar process to ferric solutions

22 OTHER CONSIDERATIONS Mixing Styles Mechanical mixers Biogas mixers Hydraulic mix _line_of_agitators_launched_/12542/

23 OTHER CONSIDERATIONS Biological Management Regular/reliable biogas testing Consider the cost of biological support Regular digestate testing (including on-site and lab based testing) is critical to understand the system Testing of substrates

24 OTHER CONSIDERATIONS Biological Management FOS & TAC Concentration (g/l) Way to monitor health of system with minimum equipment (simple titration) FOS German for volatile organic acids TAC German for total inorganic carbon Indicate the amount of food (FOS) available as compared to buffer capacity (TAC) FOS TAC

25 Thank you for your attention! PlanET Biogas USA Inc. Vicki Elliott, MASc, EIT (California) Microbiology Manager, North America 5937 State Route 11 Homer, NY USA Tel Fax. (905)

26 LESSONS FROM OPERATING FACILITIES Greenholm Farms Substrates: Dairy manure Rejected pet food Separated solids Cull potatoes Coffee shop waste Lessons: Maximize digester volume Separated solids as a substrate Sourcing substrates with other systems

27 LESSONS FROM OPERATING FACILITIES Delft Blue Veal Substrates: Veal manure Fats, oil & grease Slaughterhouse waste Lessons: CHP efficiency Clear decision structure Proper testing of substrates during design phase Maximize flexiblity

28 LESSONS FROM OPERATING FACILITIES Carleton Corner Substrates: Dairy manure Fats, oil & grease Dissolved air flotation Lessons: Maximizing every kw of electrical production Using trusted technology supplier