Experimental Investigation on Biogas Reforming for ... - CyberLeninka

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ScienceDirect Energy Procedia 54 (2014) 236 – 245

4th International Conference on Advances in Energy Research 2013, ICAER 2013

Experimental Investigation on Biogas Reforming for Syngas Production over an Alumina Based Nickel Catalyst Vikram Rathoda,*, Purnanand V. Bhalea a

Department of Mechanical Engineering, S. V. National Institute of Technology, Surat, 395007, India

Abstract Biogas is a green sustainable source of energy. Biogas mainly consists of combustible methane and non combustible carbon dioxide. Dry reforming reaction is of particular interest in the context of biogas as both main components of biogas (methane and carbon dioxide) are consumed to produce hydrogen rich syngas. Design and development of a fixed bed type reactor was carried out for reforming of biogas. The chemical equilibrium model was used for predicting the dry reforming reaction product composition followed by experimentation. In prediction of the product gas two ratios for biogas CH4: CO2=1:1 and CH4: CO2=1.5:1 were considered in the temperature range of 300 to 1000 oC with the pressure at atmospheric. The catalyst γ -Al2O3 with 10% Ni was used for the dry reforming reaction. Experimentations were conducted with different Gas Hourly Space Velocity, temperature and biogas composition. Encouraging simulated and experimental results were obtained with the yield of almost 49% volume of H2 and 45% volume of CO with very low levels of CO2. Product syngas can be used in the engine for complete combustion and to fulfill the stringent emission norms. Syngas can be used as fuel in the fuel cell application for the remote integrated power generation system. © 2014 2014Vikram The Authors. by Elsevier ElsevierLtd. Ltd.This is an open access article under the CC BY-NC-ND license © Rathod.Published Published by Selection and peer-review under responsibility of Organizing Committee of ICAER 2013. (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer-review under responsibility of Organizing Committee of ICAER 2013 Keywords: Biogas; Catalyst; Reforming; Syngas.

1. Introduction There is a growing interest in the development of power sources that use renewable fuels and reduce emission of pollutants. Biogas, consisting of CO2 and CH4, is an attractive renewable carbon source and its exploitation would be advantageous from both financial and environmental points of view. A clean model biogas consists mainly

* Corresponding author. Tel.: +9109427472741; fax: +9102612227334 E-mail address:[email protected]

1876-6102 © 2014 Vikram Rathod. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer-review under responsibility of Organizing Committee of ICAER 2013 doi:10.1016/j.egypro.2014.07.267

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Vikram Rathod and Purnanand V. Bhale / Energy Procedia 54 (2014) 236 – 245

methane (CH4), and carbon dioxide (CO2). The interest in this fuel is justified by the heightening concern about environmental degradation, energy security as well as the possible exhaustion of the fossil fuel resources. The high levels of CO2 (30-45%) and CH4 (55-75%) enable the conversion of biogas to synthesis gas (CO and H 2) by dry reforming. In biogas, CO2 is a non-combustible which reduces quality of fuel in terms of combustion. Fuel reforming processes using hydrocarbon fuels for hydrogen production can be done either catalytically or non-catalytically. Syngas can be produced from simulated biogas (CH4/CO2 molar ratio 1) by oxidative dry reforming [1]. Low H2 yield was observed for the dry reforming of biogas alone at low temperature range and high Gas Hourly Space Velocity (GHSV). The addition of O2 into the reforming reactor increased the H2 production significantly due to partial oxidation reaction [2]. Biogas reforming has shown potential for use on-board a vehicle or in power generation applications [1]. Reforming performance improvement observed in biogas derived gas by dry autothermal reforming with porus media assisting [3]. NiO-MgO-ZrO2 catalyst shown both partial oxidation and dry reforming reactions contributed to reforming of biogas [4]. The 20 wt% CeO2 doped Al2O3 nickel catalyst seem promising one for the dry reforming reaction, as it provides significantly higher reforming reactivity, hydrogen yield and hydrogen to carbon monoxide (H2:CO) ratio compared to the conventional Ni/Al2O3[5]. The precious metal catalyst Pt/Ce0.75Zr0.25O2 on autothermal reforming of methane exhibited a good stability and a H 2/CO molar ratio [3]. When CH4:CO2 molar ratio was less than one the amount of carbon accumulated on leading face of the catalyst was negligible and hence catalyst deactivation did not take place [6]. The presence of La in Rh–NiLa reduced the carbon deposition by favouring the gasification of carbon species. Addition of synthetic air improved the CH 4 conversion and also decreased carbon formation [7]. La promoted Ni based catalyst shown very high stability with no deactivation for 300 h for reforming of biogas [8]. 10%wt Ni/SBA catalyst used for tri-reforming with added oxygen showed high stability for the combined reforming of biogas [9]. Ni based catalyst supported on cordierite monolith substrate feed with oxygen and steam for autothermal reaction of biogas showed that it was possible to prevent carbon deposition [10, 11]. Biogas can be effectively used in the Homogeneous Charge Compression Ignition engine (HCCI) mode with manifold injected diesel being employed for controlling combustion [12]. There is lot of prospects of hydrogen engine in the agricultural sector and decentralized energy units [13]. Introduction of syngas in diesel engine showed diesel replacement of 72.3% for 100% H 2 in dual fuel diesel engine [14]. 2. Reforming reactions In this work mainly two reforming reactions were considered; dry reforming reaction and partial oxidation. Since biogas consist of CH4 and CO2, dry reforming was important for reforming reaction. In partial oxidation of biogas O2:CH4 ratio can be varied for the optimum reforming conditions. 2.1 Dry Reforming Reaction (DRR) Dry reforming reaction is of particular interest for this work since both the main components of biogas (i.e. methane and carbon dioxide) are consumed to produce hydrogen, as shown in Eq. 1. However, the DRR is a slow reacting process and it is affected by the contact time between the reactor gas feed and the catalyst. The reaction is highly endothermic reaction CH4 + CO2 → 2CO + 2H2

(Δ Hr = 260.62 kJ/mol)

(1)

2.2 Partial Oxidation (POX) This reaction is an exothermic reforming process whereby methane is partially oxidised in a limited supply of oxygen to produce hydrogen and carbon monoxide. The partial oxidation reaction of CH4 shown in Eq. 2. Regulation of air fuel mass ratio is crucial to avoid occurrence of complete combustion. CH4 + 0.5O2 → CO + 2H2

(Δ Hr = - 22.63 kJ/mol)

(2)

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3. Experimental The schematic of the experimental set up for the up- gradation of simulated biogas to the hydrogen rich syngas is shown in fig. 1. Pressure of the simulated biogas in the reforming reactor was kept little above the atmosphere to overcome the resistance of the piping. For the flow measurement rotameter and for temperature measurement Ktype thermocouple (Chromel-Alumel) were used. The composition of syngas was measured by gas chromatograph. 3.1 Reactor Reforming reactor was made from the stainless steel to withstand the higher temperature. It was mainly for the fixed bed of the catalyst which converts the biogas at high temperature to syngas. Gas Hourly Space Velocity (GHSV) is given by Eq. 3. GHSV=

ଵ ୖୣୱ୧ୢୣ୬ୡୣ୲୧୫ୣ

=

୊ୣୣୢୖୟ୲ୣሺ୫య Ȁ୦ሻ

(3)

େୟ୲ୟ୪୷ୱ୲ୠୣୢ୴୭୪୳୫ୣሺ୫య ሻ

3.2 Catalyst In this work 10% Ni/γ- Al2O3 catalyst spherical in shape was used for the fixed bed reactor. Catalysts were placed in the stainless steel reforming reactor. The photograph of the 10% Ni/γ- Al2O3 used in the experiments is shown in fig 2. 3.3 Simulated Biogas CH4 cylinder and CO2 cylinder with the pressure regulator and flow control were used for the simulated biogas. Different flow rate of CH4 and CO2 can be supplied to the reactor for the reforming of biogas. 3.4 Condenser For cooling the product gas copper coil were placed in the condenser which cool down the product syngas. The water condenser was used for cooling the gas. Control Panel

Reactor

GC

Rotameter A/C supply CO2

CH4 Fig. 1. Schematic of the experimental set up for biogas upgrade to syngas using reforming reactor.

Product Syngas

239


Fig. 2. Photograph of 10% Ni/γ- Al2O3 catalyst used in the reforming reactor.

4. Results and Discussion In this work reforming of biogas by dry reforming reaction was done experimentally and compared with chemical equilibrium analysis. In the experiments CH4:CO2 = 1:1 GHSV= 1150, CH4:CO2 = 1.5:1 GHSV= 1450 and temperature range of 550 oC to 700 oC was considered. 4.1 Chemical Equilibrium Analysis The element potential method was used for chemical equilibrium analysis of the simulated biogas (60% CH 4, 40% CO2 ) . In this method user selects species to be included in each phases of the system, sets the atomic populations and state parameters and then it solves for the equilibrium state. This is extremely rapid tool for typical combustion problems gives result almost immediately. Results include the composition of each phase (mole and mass fractions) and thermodynamic properties of the system. .

60

Gas Composition of Product gas for Dry Reforming reaction of Biogas (Chemical Equilibrium Analysis) (CH4:CO2 :1.5:1 )

50

CH4

% Volume

CO2 40

CO

30

H2

20 10 0 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 Temprature ( oC) Fig. 3. Effect of temperature on product gas composition due to dry reforming reaction of biogas (CH 4: CO2=1.5:1).

240


Fig. 3 shows the result of the equilibrium predicted product gas composition for dry reforming of biogas at different temperature. Dry reforming reaction of biogas (60% CH 4, 40% CO2) at different temperature as shown in fig. 3 gives conversion of CH4 and CO2 to CO and H2. As temperature increases H2 and CO content in the product gas increased. Chemical equilibrium was reached at 800 oC. At equilibrium product gas includes CO and H2 are 44% by Volume each and non reacted CH4 was 11% by Volume. Similarly fig. 3 shows the result of the equilibrium predicted product gas composition for dry reforming of biogas (50% CH4, 50% CO2) at different temperature. Similar trend observed in H2 and CO content in the product gas. Chemical equilibrium was reached at 900 oC. At equilibrium product gas includes CO and H2 are 50% by Volume each and no volume of unreacted CH4 and CO2 in the product gas Gas Compostion of Product gas for Dry Reforming reaction of Biogas (Chemical Equilibrium Analysis) (CH4:CO2: 1:1)

60

CH4 CO2 H2 CO H2O

40 30 20 10 0 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 Temperature ( oC)

Fig. 4. Effect of temperature on product gas composition due to dry reforming reaction of biogas (CH 4: CO2=1:1).

90

% Volume

% Volume

50

Partial Oxidation Reaction at O2/CH4 =0.16 (Chemical Equilibrium Analysis)

CH4

80

CO2

70

CO

60

H2

50

H2O

40 30 20 10 0 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 Temperature ( oC)

Fig. 5. Effect of temperature on product gas composition due to partial oxidation reaction of CH 4, (O2/CH4=0.16).

241


Fig. 5 shows the partial oxidation of CH4 at different temperature with O2/CH4: 0.16. The equilibrium was reached at 750 oC. The product gas contains the H2 of the order of 40% by volume and CO of the order of 40% by Volume at the equilibrium state. Partial oxidation of methane is exothermic reaction. There was no CO 2 content in the product gas after the chemical equilibrium. 80

Partial Oxidation Reaction at O2/CH4=0.25 (Chemical Equilibrium Analysis)

70

CH4 CO2 CO H2

60 % Volume

H2O 50 40 30 20 10 0 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 Temperature ( oC ) Fig. 6. Effect of temperature on product gas composition due to partial oxidation reaction of CH 4, (O2/CH4=0.25).

Fig. 6 shows the partial oxidation of CH4 at different temperature with O2/CH4: 0.25. The equilibrium was reached at 750 oC. The product gas contains the H2 of the order of 50% by volume and CO of the order of 25% by Volume at the equilibrium state. Partial oxidation of methane is exothermic reaction. There was no CO 2 content in the product gas after the chemical equilibrium. 4.2 Experimental Results For the calculation purpose, density, lower calorific value of CH4, CO and H2 at 1 bar pressure and 15 oC temperature considered were listed in the table 1. The gas composition was found from the gas chromatograph results. From the table one can see that H2 density compared to other gases in significantly low and calorific value on volume basis is also very low. Table 1. Density and LCV of CH4, CO and H2 at 1 bar pressure and 15 oC temperature Gas

Density (kg/m3)

LCV(kJ/kg)

LCV(kJ/m3)

CH4

0.68

50050

34000

CO

1.87

10100

18900

H2

0.085

121000

10285

Fig. 7 shows the composition of the input biogas and the product syngas at 600 oC from Gas Chromatograph for CH4: CO2 =1.5:1 and flow rate 2.5 LPM (Liter Per Minute) at 600 oC. Product gas composition indicates that H2 content was higher than the CO. From the product gas composition it was observed that all the CO2 was reacted with CH4. It can be seen from the figure that 40% volume H2, 32% Volume CO and 28% Volume of unreacted CH4 in the

242


product gas. This shows that dry reforming reaction occurred in the reactor. Dry Reforming of biogas at 600 oC, CH4 : CO2= 1.5:1

70 60

Volume (%)

50 40 30 20 10 0 CH4

CO2

Input biogas

CH4

CO2

H2

CO

Product Gas Composition

Fig. 7. Product gas composition at CH4: CO2= 1.5:1 and flow rate 2.5 LPM, 600 oC and GHSV= 1450.

Fig. 8 shows calorific value of input biogas and product syngas. The calorific value of the product gas was lower than biogas. This was because of the presence of the hydrogen in the product syngas. Gas Calorific Value before and after Reforming

Calorific Value (kJ/m3)

24000

CH4: CO2= 1.5:1 TEMP: 600 oC Flow rate: 2.5LPM

21000 18000 15000 12000 9000 6000 3000 0 LCV before

LCV after

Fig. 8. Product gas Calorific Value at CH4: CO2=1.5:1 and flow rate 2.5 LPM at 600 oC and GHSV= 1450.

Fig. 9 shows the experimental product gas composition at various temperature for CH4: CO2= 1:1. As temperature of the reactor increased, CH4 and CO2 conversion increased, resulted in lower CH4 and CO2 in the product gas

243


composition. These CH4 and CO2 were converted to H2 and CO. As the temperature of the reactor increased the H2 and CO percentage by volume in the product gas were increased.

Product Gas Compostion at Various Temperature for Dry Reforming Reaction of Biogas

Volume (%)

60 50

H2

40

CO

30

CH4

20

CO2

10 0

Input Biogas

550

600 650 o Temperature ( C)

700

Fig.9. Effect of temperature on CH4 and CO2 conversion to H2 and CO due to dry reforming of Biogas, (CH4: CO2= 1:1), GHSV=1150.

Product Gas Composition at Various Temperature for Dry Reforming Reaction of Biogas 60

Volume (%)

50 H2

40

CO 30

CH4

20

CO2

10 0 Input Biogas

550

600

650

700

Tempearture ( oC) Fig. 10. Effect of temperature on CH4 and CO2 conversion to H2 and CO due to dry reforming of Biogas, (CH4: CO2= 1.5:1), GHSV=1150.

Fig. 10 shows the experimental product gas composition at various temperature for CH4: CO2 =1.5:1. This clearly

244


shows that as the temperature increased from 550 oC to 700 oC, all the CO2 was converted. In the product syngas CO2 was not present. As temperature of the reactor increased, CH4 conversion increased. There was consistently higher CO volume in the product gas. The H2 percentage by volume was found little higher compared to CO. In case of CH4: CO2=1.5:1 even at lower temperature higher percentage by volume of the H2 and CO in the product gas was observed compared to CH4: CO2 = 1:1.

Fig. 11. Comparison for flame of Methane, Biogas and Syngas.

The flame test was conducted in the dark chamber to compare the flame of Methane, Biogas and Syngas. Fig. 11 shows the comparison of the flame for CH4, Biogas and Syngas. The methane flame was continuous and yellow color observed. For the simulated biogas, flame was discontinuous and intermittent because of presence of CO2, where as for syngas the flame was long continuous and blue color, indicating the complete combustion in ambient air. 4. Conclusion In this work design development and performance analysis for biogas upgrade to syngas using γ-Al2O3 based Nickel catalyst was carried out. The chemical equilibrium used to predict product gas composition in dry reforming reaction of biogas. In dry reforming reaction of the biogas at CH4: CO2=1:1 contain higher H2 and CO in the product gas compared to CH4: CO2=1.5:1 at the equilibrium. The performance of the set up for biogas upgrade to syngas at various temperatures, gas hourly space velocities and feed rates test conditions were obtained. For all the conditions there was good conversion of both CH4 and CO2. There was significant reduction in CO2 at all the temperature range. The experimental product gas found with H2 as high as 50% and CO as 41% by Volume. H2 and CO percent in the product gas were higher at CH4: CO2=1.5:1 compared to CH4: CO2=1:1 at any operating temperature. At 700 o C temperature CH4 and CO2 conversions reach the equilibrium. The flame study of biogas, methane and the product gas was carried out. The simulated biogas flame was intermittent, methane flame was yellow in color and syngas shown complete combustion with blue flame. The presence of the H2 in syngas will be able to reduce carbon footprint. The hydrogen rich syngas from biogas will certainly prove as a better fuel for automobile application apart from reducing the pollution. Acknowledgements Authors are thankful to Sophisticated Instrumentation Centre, SVNIT, Surat. for extending the necessary support.


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