Modeling of Biogas Reactors

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194 6 Modeling of Biogas Reactors Fig. 6.32 Effect of recycling biogas on the H 2S concentration in the gas phase and the liquid phase in the laboratory UASB reactor. Experimental data are compared to results of the calculation with the mathematical model of Eqs. 32–34 (gas recirculation: 7.5 L h –1 ; gas production: 7.45 L h –1 ; pH value: 7.2 (constant); sulfate concentration in the wastewater: 3.85 g L –1 ; residence time of wastewater: 2 d). Fig. 6.33 Different from Figure 6.32 an H 2S absorber was integrated in the recycled biogas (gas recirculation 27 L –1 ; gas production: 7.6–13.7 L h –1 ; pH value: 7.1–7.3; sulfate concentration: 5.13 g L –1 ; mean residence time of wastewater in reactor: 1 d).
high (5.13 g L –1 ), the concentration of H 2S in the liquid phase can be lowered to 130 mg L –1 . Figures 6.32 and 6.33 also demonstrate that model calculations fit well with the experimental data. The H 2S content in the liquid and the gas phases can be calculated by using H 2S balances for the different compartments. 6.5.1 Liquid Phase In Eq. 32 V reactor is the volume of the liquid in the reactor, c S,tot the concentration of the total sulfur in the liquid according to Eq. 7, V · feed is the volumetric feed rate of the reactor and c S,tot,e the concentration of the total sulfur in the reactor feed. Vreactor· = V · feed(cS,tot,e–cS,tot) – Vreactor ·kLa (cH2S–HH2S ·pH2S,bubble) (32) dt k La denotes the transport capacity between the liquid phase and the gas phase (a: interfacial area per volume m 2 m –3 ), c H2 S is the concentration of the undissociated portion of the H 2S in the liquid, and p H2 S,bubble the partial pressure of H 2S in the bubbles rising in the reactor liquid. H H2 S is the Henry coefficient for H 2S. 6.5.2 Gas Bubbles Eq. 33 gives the H 2S balance for the gas bubbles in the reactor suspension: Vbubble· = V · recyc.·p H2S,recyc. – V · dt bubble·p H2S,bubble +Vreactor·k La(cH2S – HH2S ·pH2S,bubble)·R·T V bubble is the total volume of all the bubbles, V · recyc. denotes the volumetric flow rate of the biogas recycled from the top to the bottom of the reactor, p H2 S, recyc. is the partial pressure of H 2S in this flow. V · bubble is the volumetric gas production rate of the reactor. 6.5.3 Head Space Eq. 34 gives the H 2S (p H2S) partial pressure in the head space located over the reactor liquid, which is equal to the partial pressure of H 2S in the biogas outlet of the reactor: dp H2S dt dc S,tot dp H2S,bubble 6.5 Mass Transport from the Liquid Phase to the Gas Phase (33) V = (pH2S,bubble – pH2S) (34) · bubble Vgas 195
Page 1 and 2: 6 Modeling of Biogas Reactors Herbe
Page 3 and 4: tom (Fig. 6.1), the question of mix
Page 5 and 6: Table 6.2 Characteristic data of th
Page 7 and 8: desalinated water and wastewater in
Page 9 and 10: 6.3 Kinetics Fig. 6.7 Combined meas
Page 11 and 12: dx dt dc Ac dt = µ (c Ac, c i) x -
Page 13 and 14: For example, the acetic acid HAc is
Page 15 and 16: On the abscissa the concentration o
Page 17 and 18: c HAc µ = µ max · · (18) cHAc+K
Page 19 and 20: 6.4 Hydrodynamic and Liquid Mixing
Page 23 and 24: 6.4.1.1 Model A Model A, which is a
Page 29 and 30: = 0.014 m s -1 V + 3.1· · exchang
Page 31: The effect of gas recirculation can
Page 35 and 36: culated k La values in the pilot sc
Page 37 and 38: 6.7 Outlook Altogether at a higher
Page 39 and 40: References tance in the production

Modeling of Biogas Reactors

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