Biogas Training Course. Zagreb, Croatia January 2010

Transcription

1 Biogas Training ourse Zagreb, roatia January 2010 Michael Köttner Introduction into digester biology AD operational parameters

2 Principles of the biogas process 1 The biogas process 2 Environmental conditions 3 Engineering process parameter

3 1 Biogas process Biogas formation O 2 B 2O O O O O 2 O O O O O 2 O O O O O O O Biomass: O E O O carbohydrate, fats, proteins O 2 O O Methane O O Intermediate products: Fatty acid production: butiric acid Propionic acid Acetic acid arbon dioxide Sugar, fatty acids, amino-acids 5

4 The 4 stages of the fermentation gas formation 1 Biogas process Acidification Biogas formation 1. Stage ydrolysis 2. Stage Acidogenesis 3. Stage Acetogenesis 4. Stage Methanogenesis ydrogen 2 2/O 2 arbon dioxide O 2 Biomass Polysaccharides Sugar, Amino acids, Biogas Methane 4 Proteins, Fats fatty acids Fatty acids (propionic acid) alcohols Acetic acid acetic acid 2 2 4/O 2 ydrolytic bacteria Acidogenic bacteria Acetogenic bacteria Methanogenic bacteria 6

5 Gas composition from the substances 4 O 2 N 3 2 S arbohydrates 50 % 50 % - - Fat 70 % 30 % - - Proteins 68 % 18 % 8 % 6 %

6 Principles of biogas process Biogas (4, O2) (wet) Biomass Manure, dung, org. solid matter, energy crops Microbial (biological) process Fully fermented substrate Nutrients Process requirements: - Anaerobic (absence of Oxygen) - umidity (max. 20 % DM in wet fermentation) - eat: (commonly), (rarely) - Neutral to low alkaline p

7 Biogas process parameters Biogas odmin, V odmout, V Fresh substrate V Temperature Organic loading rate ydraulic retention time Digested substrate ydraulic retention time (RT)= V V (days) Organic loading rate (BR)= V. odmin V = odmi n RT (kg/m3 day)

8 Solid matter content Solid content = Dry Matter DM = Dry Residues Wet/ Fresh mass (FM) Solids Water content Parameters: OD = hemical Oxygen Demand TO = Total Organic arbon BOD5 = 5 day Biochemical Oxygen Demand Organic solids = Volatile solids [ % FM or % DM ] Mineral solids = ash (minerals) 27

9 Relative and absolute degree of degradation 3 Technical engineering parameter odm Input material Degradated odm Input Output Reduction of the material contents related to the input (relative) or the work volume (absolute) Sink and floating layers forged the degradation rate 35

10 onversion example of Dry matter (DM): % DM (FS)= Kg DM Kg FS % odm (DM)= Kg odm Kg DM 25 % DM * 0,90 0,90 22,5 % odm (FS) % odm (FS)= Kg odm Kg FS * 0,25 0,25 90 % odm (DM) FS= Fresh substrate

11 Example: Daily liquid manure input: 5 t/d Digester-work volume: 300 m³ Gas space: 30 m³ RT = (300 30)m 3 5 t/d 1 t/m 3 = 54d Recommended ydraulic retention time for mesophilic fermentation processes: hicken liquid manure Pig liquid manure ow liquid manure Solid manure days days days days Source: Wenzlaff (1984)

12 Organic loading rate depending of odm and hydraulic retention time Energy crops Organic loading rate (kg odm.m3/d) ydraulic retention time (d)

13 Psychrophilic (< 25 ) - low growth rate - long retention times - uneconomical for biogas production - not longer in use Temperature ranges Mesophilic (32-45 ) - stable biocenosis - Satisfactory gas yield after acceptable retention time - Widely applied, especially in wet fermentation processes Thermophilic (50-60 ) - high gas yield after short retention time (Energy crops, liquid manure) - good hygienisation results, but high demand for energy in the process - sensitive biocenosis - caution with rapid degradable substrates (hydrolysis develops too fast) 13

14 Parameters Biogas process Temperature Source: National Biogas Evaluation Program

15 Relation between gas productivity - temperature and hydraulic retention time Total gas quantity Methane Gas quantity Day Source: BADER et al. (1978), UBER and MAIR (1995) Retention time

16 Biogas Biogasbilanz balance [m³; Nm³] Substrates Substrateinspeisung feeding Digester1 Fermenter [t] 1 [t] Source: Novatech Gmb Support program Temperature and biogas generation (mesophilic conditions) Ø eating installation breakdown m 3 Biogas Betreuungszeitraum Support time frame Getreidekörner allg. Grassilage Maissilage Schweinegülle Gas am Zähler Gas pot

17 p value Negative logarithmic unit A reduction of the p value around 1 unit 10 times acid quantity Intermediate products of the degradation process would drop the p Biogas plants operated with liquid manure or dung are usually well buffered igh N-content in the reactor increases p value and the buffer capacity p value in the reactor is lower than outside through lower concentration of O2 in the atmosphere degassing of O2 occurs (equilibrium)

18 p value normally" p value lies between 7 and 8 Measured outside of the digester immediately after the sampling If the p value is too low (< 6.8): the O 2 - solubility sinks (proportion of O 2 rises in the gas) the O 2 production of the bacteria increases (proportion of O 2 rises in the gas) the toxicity of 2 S and fatty acids increases (the 4 portion in the gas decreases) If the p value is too high (> 8): Dissociation/equilibrium of N 4 changes to N 3 (toxical for the methane formation)

19 p-value and O 2 -solubility outside 0,03 Vol-% O 2 sampling inside approx. 40 Vol-% O 2 Immediately after taking a sample, outside the digester O 2 begins to escape. p-value rises p-value in the digester is lower than measured outside the digester! 17

20 p-value ydrogen ion (+)- concentration Attention: + 2 Metabolites would reduce the p-value, but: Plants with manure have normally good buffering systems: arbonate buffer, Ammonium buffer p-value as sole parameter is not suited to evaluate the process 18

21 Substrates composition for a balanced nutrition Food rich in arbohydrates: (starch, sugar) Grain orn Fruit Bakery wastes Potato wastes Food rich in Protein: (amino acid contains both amino & sulphur groups) Leftovers Fish flour Oil fruits (raps) Food rich in fat: Fat separator Slaughterhouse waste Base substrate - liquid manure Inhibitors: Disinfectant, Antibiotics, eavy metals

22 2 Environment conditions Environment conditions of anaerobic degradation Measured variable Temperature p value :N-Relation Solid content Redox - potential Nutrient demand :N:P:S Trace elements ydrolysis/acidification 25 35º 5,2 6, < 40 % DM mv 500 : 15 : 5 : 3 No specific requirements Methane formation Mesophilic: º Thermophilic: º 6,7 7, < 30 % DM < -250 mv 600 : 15 : 5 : 3 Essential: Ni, o, Mo, Se FAL TB Environmental requirements for the fermentation of raw and residual substrates W DR 10

23 Generation times of different microorganisms Microorganisms Aerobe organisms Escherichia coli Activated sludge bacteria Soil bacteria Acid forming organisms Bacteroides lostridium Acetogenic bacteria Methanogenic bacteria Methanosarcina Methanococcus Source: Bone M., (2000) Generation time 20 min 2h 1 5 h < 1 d 1,5 d 3,5 d 5 15 d ca. 10 d

24 Generation times of bacteria in biogas process Aerobic bacteria Anaerobic bacteria Acidogenic bacteria arbohydrates Protein Fats Acetogenic bacteria 3-5 days 2-10 days Methanol & acetic acid Lactic acid Butyric acid Propionic acid Fatty acid Methanogenic bacteria 3-5 days Mixed culture to degrade 2 Pure culture to degrade 2 Mixed culture to degrade acetic acid Pure culture to degrade acetic acid (Days) Source: Seyfried et al.., (1986)

25 RTG rule With a temperature rise of 10 the reaction rate and activity of the metabolic processes increases 2-3 times The first process stages (which run faster e.g. hydrolysis, acid formation) become a problem with rising temperatures for the methane formation stage Increase of long chain fatty acids (Propionic acid) 2 enrichment General rule: Keep temperature as constant as possible Especially when process temperatures are reduced: do it slowly!!

26 The different degradation processes occur at the same time simultaneously In agricultural biogas plants the separation of the degradation stages plays a minor role are strongly dependent from each other Intermediate products are needed for following processes can cause mutual inhibition Intermediate products may not accumulate Product inhibition develop slowly in advanced stages ydrolysis is the fastest, methane formation the slowest 9

27 3 Technical engineering parameter ritical organic loading rate and retention time Gas productivity [m³ Gas /(m³ Fer. * d)] 2 2 ydraulic retention time [d] 1 ritical hydraulic retention time and organic loading rate Organic load [kg odm/(m³*d)] Gas yield [m³ Gas /kg odm] 1 32

28 Process failures and analyses Process failures are expensive... stink result in other problems... reduce the environment friendly effect Alarming symptomes: Digester foams Reduced gas production Low methane concentration igh 2 S concentration in biogas igh sensitivity against acid production (p-value decrease) Digester acidifies (p < 6,8) 10

29 Possible causes of a process failure: Temperature reduction Incorrect feeding Overfeed Incorrect running-in Feeding unequaly distributed Inhibition caused by Acidification (Propionic acid) Ammoniac ydrogen sulfid eavy metals Antibiotics Fungal toxins Evaluation of substrates: Grain fraction Straw fraction (GPS, manure) Fibre length (gras, manure) Smell (process failure?) Temperature Mildew infestation 11

30 Inhibition caused by: -Organic loading rate too high -Insufficient hydraulic retention time - Inhibitors Inhibition of methane generation Increased hydrolysis and acidification the classical case Methane concentration decrease Buffer? Acid accumulation Inhibition of methane bacteria p-value decreases! p < 6,5: Digester dies 12

31 Thank you for your Attention! Michael Köttner International Biogas and Bioenergy entre of ompetence IBBK Am Feuersee Kirchberg/ Jagst Germany phone: fax: info@biogas-zentrum.de