Efficiency of biogas production Jan Liebetrau, Sören Weinrich, Jürgen Pröter

Conference of the European Biogas Association 2014

Efficiency – why and where to measure?

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Purpose determines the boundaries For any process comparison: assumptions, methods and evaluation need to be the same

Energy  crops  (60  %  mass) 79,21Manure  (40  Ma  %  mass) 20,79

Substrate  provision Energy  input 100,00Preservation/Ensilaging  process  (12    %  energy  crops) 9,51

Digestion available  energy 90,49 100,00Flare  (4  %  methane  production) 2,57 2,84Leaks  (0,1  %  methane  production)   0,064 0,071Heat  losses  (4  %  overall  energy) 3,62 4,00fuel  value  digestate  including: 22,67 25,05              gas  potential  digestate  (7  %  methane  potential) 4,49 4,97

CHP Methane   61,57 100,00gross  electricity  including: 21,35 34,68              plant  requirements  (8  %  of  gross  electricity),  including: 1,71 2,77                    Feed  in  systems  (7,3  %  of  plant  req.  ) 0,12 0,20                          Mixer  (40,1  %  of  plant  req.) 0,69 1,11                            CHP  (3,5  %  of  plant  req.) 0,75 1,21                            Misc.    (8,9  %  of  plant  req.) 0,15 0,25              net  electricity,  including: 19,65 31,91                        Transformer  losses  (1  %  of  gross  electricity) 0,21 0,35                            feed  in  electricity 18,65 30,28gross  heat  including:   24,64 40,02              plant  requirements  (20  %  gross  heat) 4,93 8,00        net  heat 19,71 32,02Conversion  losses  including 15,57 25,29            CHP  methane  slip  (1,2  %  methane  production) 0,77 1,25

Plant:   500  kWel,  ηel=39  %577  kWth,  ηth=45  %Full  load  hours  8000h/a;  

Portion  gross  energy  quantity

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Energy  fraction  for  components

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not  included:  energy  for  energy  crop  production:  4,93  %  ;  Transport  (energy  crops  and  digestate):  0,87  %  gross  energy

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Hours of operation

● Operational hours give impression of „downtime“ ●  Increasing quality ● Downtime – consequences of overproduction ? ● No data what happens during downtime

Betriebsstunden 2011, geordnet nach Inbetriebnahmejahr (Daten aus Betreiberbefragung DBFZ 2011/12)

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Year of start up Average operational hours

Number of questionnaires

Average full load hours

Number of questionnaires

(h/a) (number) (h/a) (number) vor 2000 6911 47 5161 49 2000 - 2003 7801 90 6570 94 2004 - 2008 8248 297 7323 287 2009 - 2010 8273 146 7242 132

Overpressure valve opening

Bild 1: REMDE, C.: Methanemissionen aus Über- und Unterdrucksicherungen bei Biogasanlagen in Deutschland. Leipzig, Deutsches Biomasseforschungszentrum gGmbH, Universität Stuttgart, Institut für Feuerungs- und Kraftwerkstechnik, Diplomarbeit, 2013 Bild 2: noch unveröffentlichte Messungen des DBFZ 5

y = -49,363x + 166,16R² = 0,99

y = -10927x2 + 8940,8x - 1681,2R² = 0,976

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Plant operators does not recognize the losses Because there is no method in place to predict precisely biogas production

Conversion efficiency of biological process

•  Benchmarking

•  Comparison of substrates

•  Comparison of plant concepts

•  Monitoring and optimization of processes (e.g. evaluation of disintegration processes)

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Conversion efficiency is Input vs. Energy output (methane output)

Mass balance is basis for energy balance Precondition: Knowledge of material flows within the process

Fractions of substrate

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wet mass

Recalcitrant VS

Total solids (corr.)

VS (corr.)

Not degraded VS

Ash1

Integrated water

Biogas

Converted VS

Microorg.

Water

Not integrated water

Ash Org. Digestate Water Biogas 1 Asche = anorganische TS, enthält mitunter Substanzen und Nährstoffe (z.B. N, P, S) welche von Mikroorganismen für das Wachstum und die Biogasbildung benötigt werden

Substrate component in the biogas process (changed according to WEIßBACH)

Degradable VS

conversion

•  Correction of volatile organic materials •  Not degradable VS •  Integrated water ü  specific to substrates, difficult analysis ü  necessary to obtain comparable results Comparison is only possible if absolute reference value is existent – degradable substrate with specific gasproduction

Determination of gas potential

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Simple?

Degree of degradation?

Standard (resp. literature) values?

Batch Test? Continuous experiments?

Feed value analysis?

Challenge:

•  few precise biochemical measurement values

•  lack of standards and individual methods for evaluation (interlaboratory tests)

9 Development of standardized and robust methods for field tests

Calculation of Biogas potential

Calculation of degradable VS according to WEIßBACH

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Ash [g/kgTS] NfE [g/kgTS] Fiber [g/kgTS] Protein [g/kgTS] Lipids [g/kgTS]

44 621 226 79 30

FoTS = 1000 − Ash − 16 − 0 − ( 0,47 · Fiber + 0,00104 · Fiber² )

Example corn silage (Average of samples at DBFZ)

Non degradable proteiin(constant)

Non degradable Carbohydrates (Function of fiber) Non degradable Lipids (constant)

FoTS = 984 − Ash − ( 0,47 · Fiber + 0,00104 · Fiber² ) = 780 [g/kgTS]

Stoichiometric calculation considering 5 % MO Biomass Calculation of Biogas potential according to WEIßBACH

Biogas = 780 ∙  800/1000    =    624  [l/kgTS] Methan = 780 ∙  420/1000    =    327,6  [l/kgTS] Gasproduction coefficient for corn silage [l/kg FoTS]

Standardized digestion tests considering metabolic excreta

Biogas potential and yield

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BIOGASERTRAG Gasertrag im realen Anlagenbetrieb bei unterschiedlichen Verweilzeiten und Betriebsbedingungen

(Berechnung anhand grundlegender reaktionstechnischer Zusammenhänge und Modelle)

Realer Anlagenbetrieb

BIOGASERTRAG Gasertrag im realen Anlagenbetrieb bei unterschiedlichen Verweilzeiten und Betriebsbedingungen

(Berechnung anhand grundlegender reaktionstechnischer Zusammenhänge und Modelle)

Realer Anlagenbetrieb

(THEORETICAL) BIOGASYIELD Biogas production under conditions of continuous processes (retention time)

•  Calculation based on process kinetics •  Can be obtained with continuously operated processes

Real full scale application

9 Standard methods necessary!

BIOGASPOTENTIAL Theoretical maximum biogas production

•  Calculation based on chemical composition •  Potential can be modified by means of disintegration processes " up to complete VS •  Can be obtained with the ideal batch test (infinite retention time)

Biogas potential and yield within a CSTR

Yield and Gas Production Ratein a CSTR

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Organic Load (kgVS/m3) 19.2 9.6 6.4 4.8 3.8 3.2 2.7 2.4 2.1 1.9 1.8 1.6

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Evaluation disintegration processes

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§ Degradation of stillage proteins §  Two desintegration effects: a) rate increase;

b) increase of biogas potential TS (Enzym B = Effekt a+10%b)

[Mauky, 2011]

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Biogasmessprogramm II (Plant evaluation)

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Gas potential digestate (37°C, > 60 Tage) and VS at 50 Biogas plants

Portion of gas potential and recalcitrant substrate is different and process specific

Basics of mass balance

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Substrate Additives

Water

Biogas Process model

Kinetics

Stoichiometry

System boundary

Digestate

Mass balance of biogas process

Output Input

Rezirculation

9 Efficiency on basis of conversion rate

dm/dt     ≈    ∆m/∆t       =                                        Input      −      Output                                                                                  ±      reaction  

Transport over boundaries rate Biochemical process

Mass balance

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Biogas plant (500 kWel) without recirculation

Berechnung unter Berücksichtigung des stöchiometrischen Wassereinbaus und unter Vernachlässigung des Biomasseaufbaus

k 0.132 [1/d] ηel 38 [%]

Maissilage HRT 75.4 [d] BiogasṁS 31.5 [t/d] Uf oTS 90.9 [%] ṁB 7.99 [t/d] PFeu 1315 [kW]

TS 33.47 [% FM] V̇B 6085 [m³ i.N./d] Pel 500 [kWel]

oTS 95.6 [% TS] cCH4 52 [%]

foTS 78 [% TS] Gärrest cCO2 48 [%]

ṁW 20.96 [t/d] ṁG 23.51 [t/d] ρB 1.314 [g/l]

ṁTS 10.54 [t/d] TSG 13.07 [% GR] H 9.97 [kWh/m³]

ṁoTS 10.08 [t/d] foTSG 24.49 [% TSG]

ṁf oTS 8.22 [t/d] ṁW,G 20.43 [t/d]

YB/f oTS 740 [m³ i.N./t foTS] ṁTS,G 3.07 [t/d]

YB/oTS 604 [m³ i.N./t oTS] ṁf oTS,G 0.75 [t/d]

●  Al lgemeine  Vorgaben  Inputcharakteris ierung  und  Gaszusammensetzung ●  Vorgabe  Variante  B  Elektrische  BHKW-­‐Leis tung  

●  Vorgabe  Variante  A  Spezi fi scher  Biogasertrag  des  Substrats  bzw.  der  Anlage ●  Vorgabe  Variante  C  Reaktionskinetik  1.  Ordnung  und  HRT

Fermenter BHKW

9 Variation of methods for validation dependent on available data

How to measure and calculate?

1.  Substrate gas potential (degradable VS)

2.  Masses at plant (corr. TS/VS)

•  Input

•  Output

◦  Digestate (Ash scaling, (subtraction of biogas, gas potential of digestate))

◦  Biogas (measurement or estimation from electricity production, CHP efficiency and losses??)

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(Weißbach 2009)

Challenge is representative sampling •  Dynamic process •  Heterogeneous substrates •  Lack of standard methods and individual methods

Example Weissbach

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Mass balance, no kinetic model included

Conclusion

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Options for process evaluation:

•  1. Biogas potential: Calculation for common substrates according to WEIßBACH (based on feed value analysis)

•  2. Biogas yield: Calculation based on simple first order kinetic

9 Development of a standard for mass balances for biogas plants

Challenges •  Standard methods for substrate characterization necessary (degradable VS, kinetic parameters)

•  Transfer of results from different methods (e.g. batch to continuous)

•  Models for transfer of Labscale experiments to full scale results

•  Portion and influence of MO mass on results

9  Aim: Application of available methods and higher precision

9  Validation for full scale applications need to be done

DBFZ Deutsches Biomasseforschungszentrum gemeinnützige GmbH

Torgauer Straße 116 D-04347 Leipzig Tel.: +49 (0)341 2434 – 112 www.dbfz.de

Contact

Dr.-Ing. Jan Liebetrau Jan.Liebetrau@dbfz.de +49 341 2434 716