Scholarly article on topic 'Upgrade Egyptian biogas to meet the natural gas network quality standard'

Upgrade Egyptian biogas to meet the natural gas network quality standard Academic research paper on "Chemical engineering"

CC BY-NC-ND
0
0
Share paper
Academic journal
Alexandria Engineering Journal
OECD Field of science
Keywords
{"Egyptian biogas" / "Methane upgrading" / "Aspen HYSYS" / "Biogas purification"}

Abstract of research paper on Chemical engineering, author of scientific article — Sameh Tawfik Abd Elfattah, Yehia A. Eldrainy, Abdelhamid Attia

Abstract Biogas is one of the promising renewable energy sources in Egypt. The objective of this research was to treat the raw biogas in order to clean it from acidic gases CO2 and H2S to meet the standard of the natural gas network. The acidic gases treating plant of the biogas were built up and numerically simulated using Aspen HYSYS 8.6 and a proper design of the plant was performed. The main purpose of the simulation is to determine the optimum working pressure, which can achieve the methane purity of the Egyptian biogas comparable to natural gas quality. The biogas treating process was accomplished inside Pressure Swing Absorber (PSA) where the feed sour gas enters the absorber at the CO2 contents of 0.25, H2S contents of 0.0004, a temperature of 30°C, a pressure of 1.1bars, a flow rate of 13m3/h, Diethanolamine (DEA) concentration of 0.3 and 20 stages PSA with a tray diameter of 1.7m. it is found that a PSA working pressure of 5bars is required to obtain a biogas with methane purity of 95%.

Academic research paper on topic "Upgrade Egyptian biogas to meet the natural gas network quality standard"

Alexandria Engineering Journal (2016) xxx, xxx-xxx

HOSTED BY

Alexandria University Alexandria Engineering Journal

www.elsevier.com/locate/aej www.sciencedirect.com

ORIGINAL ARTICLE

Upgrade Egyptian biogas to meet the natural gas network quality standard

Sameh Tawfik Abd Elfattah, Yehia A. Eldrainy *, Abdelhamid Attia

Mechanical Engineering Department, Faculty of Engineering, Alexandria University, Alexandria, Egypt Received 22 March 2016; revised 11 May 2016; accepted 15 May 2016

KEYWORDS

Egyptian biogas; Methane upgrading; Aspen HYSYS; Biogas purification

Abstract Biogas is one of the promising renewable energy sources in Egypt. The objective of this research was to treat the raw biogas in order to clean it from acidic gases CO2 and H2S to meet the standard of the natural gas network. The acidic gases treating plant of the biogas were built up and numerically simulated using Aspen HYSYS 8.6 and a proper design of the plant was performed. The main purpose of the simulation is to determine the optimum working pressure, which can achieve the methane purity of the Egyptian biogas comparable to natural gas quality. The biogas treating process was accomplished inside Pressure Swing Absorber (PSA) where the feed sour gas enters the absorber at the CO2 contents of 0.25, H2S contents of 0.0004, a temperature of 30 °C, a pressure of 1.1 bars, a flow rate of 13 m3/h, Diethanolamine (DEA) concentration of 0.3 and 20 stages PSA with a tray diameter of 1.7 m. it is found that a PSA working pressure of 5 bars is required to obtain a biogas with methane purity of 95%.

© 2016 Production and hosting by Elsevier B.V. on behalf of Faculty of Engineering, Alexandria University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/

licenses/by-nc-nd/4.0/).

1. Introduction

In fact, it is possible to overcome the energy crises in Egypt by converting the agricultural, industrial and sewage waste to biogas [1] in order to generate a large amount of energy. Sour Egyptian biogas contains other acidic components (CO2 and H2S) where they must be removed before pumping the biogas into the natural gas network to meet the standards of these networks [2-5]. Biogas sweetening is the process in which CO2 and H2S are removed in order to protect the pipelines net-

* Corresponding author at: Behind 23, Ibrahim Attar street, Zizinia, Alexandria, Egypt. Mobile: +20 1015393646. E-mail address: yeldrainy@alexu.edu.eg (Y.A. Eldrainy). Peer review under responsibility of Faculty of Engineering, Alexandria University.

work and power engines from corrosion due to acidic effect, and to raise the calorific value of the treated biogas [6-9]. Most of biogas researches in Egypt focused only on biogas production from local resources and using it in thermal energy generation [10-14]; however, there are only few researchers concentrated on the biogas quality enrichment. The numerical simulation plays an important role in facilitating the proper design of sweetening cycle and sizing of its equipment especially the absorber [15-17]. Aspen HYSYS 8.6 simulation software program is one of the most important and accurate programs that have been used in the design of gas treatment process [18-21].

Therefore, this article aimed to determine the optimum PSA working pressure to achieve the methane purity of the Egyptian biogas that needed to meet the quality standards of

http://dx.doi.org/10.1016/j.aej.2016.05.015

1110-0168 © 2016 Production and hosting by Elsevier B.V. on behalf of Faculty of Engineering, Alexandria University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

S.T.A. Elfattah et al.

Nomenclature

Cond condenser RCY recycler

DEA diethanolamine REB reboiler

L/R Lean/Reach VLV valve

NG natural gas Vtot total volume of the gas mixture

PSA Pressure Swing Absorber Vx partial volume of an individual gas component (X)

Ptot total pressure of the gas mixture in the mixture

Px partial pressure of an individual gas component (X) in the mixture

natural gas networks using Aspen HYSYS 8.6 simulation program.

The detailed discussion of the ways of biogas upgrading to remove acidic contents (CO2 and H2S) to match the universal standard of engines and power stations and intensive study in using the simulation programs in the purification process of acid gases has been done [22-26]. However, these previous literatures did not provide a specific method to determine the optimum PSA working pressure to extract pure methane from biogas. Therefore, the present study aimed to upgrade Egyptian biogas to meet the natural gas network quality standard.

2. Methodology

Fig. 1 describes the typical complete acid gases removal cycle (sweetening cycle) which plugged in Aspen HYSYS 8.6 library and used for natural gas NG upgrading and purification [27] in which the acid gas removal steps are performed [28].

The absorber column was selected from Aspen HYSYS model pallet as shown in Fig. 2 which has the internal construction containing 20 stages, each stage consists of one tray as having construction looks like a sieve. The acid gas fluid package which contains DEA is also selected [29].

The feed Egyptian biogas which has the composition as mentioned in Table 1 enters the absorber at a temperature of 30 0C, a pressure of 1.1 bar and volume flow rate of 13 m3/h from the bottom of the absorber column. The lean amine (DEA) enters at the top of the column at conditions of 30 0C, 20 bars and 5.45 x 10~4m3/h. The amine DEA can absorb CO2 and H2S from the feed Egyptian biogas simultaneously. The sweet feed gas, which is free from CO2 to H2S, exits from the top of column, and the rich amine exits from the bottom of the absorber. Then the rich amine passes through the expansion valve in order to expand to 43 0C and 1.4 bars and then it enters the separator. Rich amine exits from the separator by the same aforementioned conditions to enter a Lean amine/Rich amine heat exchanger (L/R). The L/R heat exchanger transfers heat from lean amine into rich amine. The hot, rich amine, which exits from the exchanger enters a regeneration column to extract CO2 from the rich amine to lean it for reusing it, while the lean amine enters a make-up tank at 74 0C and 1.04 bar which is above atmospheric pressure of 0.027 bar and exits from it at also 74 0C and 1.04 bars which equal the same inlet conditions of the make-up tank. Then it is pumped to 74.5 0C and 1.1 bars successively and it is cooled at constant pressure process to 30 0C to be sent to

a recycler. Lean amine exits from recycler at 30 0C and 1.1 bars [30].

3. Results and discussion

The simulation cycle was run to insure absorber conversion using Aspen HYSYS for the purpose of PSA working pressure optimization. All the numerical simulation conditions of temperatures, pressures and feed gas flow rates of the removal cycle are a result of running numerous simulation trials in order to get the highest methane purity from Egyptian biogas.

3.1. Effect of Egyptian biogas PSA working pressure on biogas final product CO2 contents

It can be noted from Fig. 3 that there is a reverse proportion between PSA working pressure and CO2% in the Egyptian biogas final product gas. At the point, which is the absorber PSA working pressure to 5 bar, the CO2 percentage equals to 0.0084. There is little (non economic) effect of PSA working pressure on the CO2 contents if the pressure is more than 5 bar. Therefore, there is no need to increase the PSA working pressure to more than 5 bar to maintain the optimum initial cost for absorber construction.

3.2. Effect of Egyptian biogas PSA working pressure on biogas final product H2S contents

Fig. 4 shows that there is also a reverse proportion between PSA working pressure and H2S% in the Egyptian biogas final product. The H2S contents can be removed completely from Egyptian biogas final product at the pressure of 1.1 bar. This leads to say that the pressure value of 5 bar which is needed to clean CO2 from Egyptian biogas is sufficient to clean the CO2 and H2S gases simultaneously.

3.3. Effect of Egyptian biogas PSA working pressure on biogas final product Methane purity

Fig. 5 shows the effect of the PSA working pressure on the methane purity of the biogas final product. At the point, which is the absorber PSA working pressure to 5 bar, the methane purity tends to be 95% which is the desired value of most of NG networks. There is more effect of PSA working pressure on the methane purity if the pressure is more than 5 bar.

Upgrade Egyptian biogas

Figure 1 Complete acid gases removal cycle (sweetening cycle) [28].

Absorber

Figure 2 The absorber column [29].

Table 1 Feed Egyptian biogas composition [30]. in mole fraction

Component Mole fraction Volume fraction

Methane (CH4) 0.7464 0.7466

Carbon dioxide (CO2) 0.2522 0.2522

Hydrogen sulfide (H2S) 0.0004 0.0004

Water vapor (H2O) 0.0004 0.0001

Hydrogen (H2) 0.0001 0.0001

Nitrogen (N2) 0.0002 0.0002

Oxygen (O2) 0.0003 0.0003

From the above curves which describe the relation between PSA working pressure and methane purity for Egyptian biogas, it is obvious that the optimum pressure, which is needed to achieve desired methane purity from Egyptian biogas which is equal to 95% is 5 bar. If the pressure is lower than that value the biogas treating cycle can produce methane that has lower purity.

1.2E-001

1.0E-001

8.0E-002

6.0E-002

4.0E-002

2.0E-002

0.0E+000.

4 5 6 7 Stage Pressure, bars

Figure 3 Effect of Egyptian biogas PSA working pressure on biogas final product CO2 contents.

According to Amagat's law of additive volume which deals with partial volume [31], the partial volume of a particular gas in a mixture is the volume of one component of the gas mixture. The partial pressures of the acidic gases are shown in Tables 2.

Vx = Vtot x ^

At the same total volume there is a direct proportion between Vx and the term of (Px/Ptot); therefore, if the term (Px/Ptot) is very small then the term Vx is very small also. In other words the Amagat's law of additive volume can explain clearly the increase of total pressure can increase the methane purity.

S.T.A. Elfattah et al.

7.0E-008-

6.0E-008-

5.0E-008-

<d 4.0E-008-E

^ 3.0E-008-

2.0E-008-

1.0E-008-

1 I 1 I 1 I 1

1 23456789 10 Stage Pressure, bars

Figure 4 Effect of Egyptian biogas PSA working pressure biogas on final product H2S contents.

1 23456789 10 Stage Pressure, bars

Figure 5 Effect of Egyptian biogas PSA working pressure biogas on final product methane purity.

Table 2 Partial pressure of CO2 and H2S in both of Egyptian biogas.

Acidic component Partial pressure

CO2 partial pressure 0.2774 bar

H2S partial pressure 4.455 x 10~4 bar

Table 3 Composition of final sweetening Egyptian biogas.

Component Mole fraction Volume fraction

Methane (CH4) 0.9556 0.9784

Carbon dioxide (CO2) 0.0084 0.0086

Hydrogen sulfide (H2S) 0 0

Water vapor (H2O) 0.0352 0.0121

Hydrogen (H2) 0.0001 0.0001

Nitrogen (N2) 0.0003 0.0003

Oxygen (O2) 0.0004 0.0004

The optimum PSA working pressure needed for Egyptian biogas cleaning of acidic gases was found to be 5 bars. The final composition of sweetening gas, which is obtained from Egyptian biogas will be as mentioned in Table 3.

4. Conclusion

A numerical simulation using Aspen HYSYS simulation software was performed to determine the optimum Pressure Swing Absorber (PSA) working pressure in order to achieve the highest methane purity from Egyptian Biogas. The feed sour gas was feeded to the PSA with CO2 contents of 0.25, H2S contents of 0.0004, a temperature of 30 0C, a pressure of 1.1 bars, and a flow rate of 13 m3/h. DEA amine solvent with different strengths was used to remove the CO2 and H2S simultaneously. Simulation showed that the optimum conditions for the biogas treatment process were a Diethanolamine (DEA) concentration of 0.3 and 20 stages PSA with a tray diameter of 1.7 m. At theses conditions, it is found that the optimum PSA working pressure to obtain pure methane of 95% purity from the Egyptian biogas is 5 bar.

References

[1] M. Elsamadony, A. Tawfik, Potential of biohydrogen production from organic fraction of municipal solid waste (OFMSW) using pilot-scale dry anaerobic reactor, Bioresour. Technol. 196 (2015) 9-16.

[2] L. Olsson, M. Fallde, Waste (d) potential: a socio-technical analysis of biogas production and use in Sweden, J. Clean. Product. 98 (2015) 107-115.

[3] M.B. Jensen, C. Scheutz, J. Moller, Comparison of the organic waste management systems in the Danish-German border region using life cycle assessment, in: International Conference on Solid Waste 2015 (ICSWHK2015), 2015.

[4] G. Rodriguez et al, Biotrickling filters for biogas sweetening: oxygen transfer improvement for a reliable operation, Process Saf. Environ. Prot. 92 (3) (2014) 261-268.

[5] EPA Methane Rule Would Set Costly Bar for Oil and Gas Industry, Despite Current Reduction Efforts. <http:// enerknol.com/wp-content/uploads/2015/01/EnerKnol-Research-EPA-Methane-Regs-1.20.15.pdf > [accessed in 2016, 5].

[6] G.P. Helsing, Options for Carbon Capture with Storage or Reuse in Waste Incineration Processes, 2015.

[7] Z. Wang et al, Selection of microalgae for simultaneous biogas upgrading and biogas slurry nutrient reduction under various photoperiods, J. Chem. Technol. Biotechnol. 91 (7) (2015) 19821989.

[8] M. Scholz, T. Melin, M. Wessling, Transforming biogas into biomethane using membrane technology, Renew. Sustain. Energy Rev. 17 (2013) 199-212.

Upgrade Egyptian biogas

[9] X.Y. Chen et al, Membrane gas separation technologies for biogas upgrading, RSC Adv. 5 (31) (2015) 24399-24448.

[10] I. Teichmann, Technical Greenhouse-Gas Mitigation Potentials of Biochar Soil Incorporation in Germany, 2014.

[11] G.F. Parkin, W.F. Owen, Fundamentals of anaerobic digestion of wastewater sludges, J. Environ. Eng. 112 (5) (1986) 867-920.

[12] S.D. Abou Hussein, O.M. Sawan, The utilization of agricultural waste as one of the environmental issues in Egypt (a case study), J. Appl. Sci. Res. 6 (8) (2010) 1116-1124.

[13] S. Wentzel, R.G. Joergensen, Effects of biogas and raw slurries on grass growth and soil microbial indices, J. Plant Nutr. Soil Sci. 179 (2016) 215-222.

[14] V. Bansal, V. Tumwesige, J.U. Smith, Water for Small-Scale Biogas Digesters in Sub-Saharan Africa, GCB Bioenergy, 2016.

[15] J. Krischan, A. Makaruk, M. Harasek, Design and scale-up of an oxidative scrubbing process for the selective removal of hydrogen sulfide from biogas, J. Hazard. Mater. 215 (2012) 4956.

[16] R.A. Gawel, Design simulations for a biogas purification process using aqueous amine solutions, Chem. Pap. 66 (11) (2012) 1010-1018.

[17] E.M. Elkanzi, Simulation of the process of biological removal of hydrogen sulfide from gas, in: H.E. Alfadala, G.V.R. Reklaitis, M.M. El-Halwagi (Eds.), Proceedings of the 1st Annual Gas Processing Symposium, Elsevier, Amsterdam, 2009, pp. 266275.

[18] L. Deng, H. Chen, Z. Chen, Y. Liu, X. Pu, L. Song, Process of simultaneous hydrogen sulfide removal from biogas and nitrogen removal from swine wastewater, Bioresour. Technol. 100 (2009) 5600-5608.

[19] A.H. Nafez et al, Sewage sludge composting: quality assessment for agricultural application, Environ. Monit. Assess. 187 (11) (2015) 1-9.

[20] S.T.A. Elfattah, Y.A. Eldrainy, A. Attia, Utilization of Aspen HYSYS simulation to determine the optimum absorber working

pressure needed to achieve more than 0.99 methane purity from Egyptian biogas, Int. J. Inf. Res. Rev. 03 (01) (2016) 1739-1744.

[21] S.T.A. Elfattah, Y.A. Eldrainy, A. Attia, Optimization of Pressure Swing Absorber (PSA) geometry to achieve highest methane purity from the Egyptian biogas using Aspen HYSYS simulation, Int. J. Innov. Res. Develop. 5 (1) (2016).

[22] L. Erik0i, Comparison of Aspen HYSYS and Aspen Plus simulation of CO2 absorption into MEA from atmospheric gas, Energy Proc. 23 (2012) 360-369.

[23] L. Peters et al, CO2 removal from natural gas by employing amine absorption and membrane technology—a technical and economical analysis, Chem. Eng. J. 172 (2) (2011) 952-960.

[24] Z. Niu et al, Experimental studies and rate-based process simulations of CO2 absorption with aqueous ammonia solutions, Ind. Eng. Chem. Res. 51 (14) (2012) 5309-5319.

[25] Z. Kapetaki, P. Brandani, S. Brandani, H. Ahn, Process simulation of a dual-stage Selexol process for 95% carbon capture efficiency at an integrated gasification combined cycle power plant, Int. J. Greenhouse Gas Control 39 (2015) 17-26.

[26] I.K. Kapdan, F. Kargi, Bio-hydrogen production from waste materials, Enz. Microb. Technol. 38 (5) (2006) 569-582.

[27] S.T.A. Elfattah, Y.A. Eldrainy, A. Attia, Numerical simulation to optimize Di-Ethanol-Amine (DEA) strength for achieving the highest methane purity from biogas, Int. J. Adv. Sci. Tech. Res. 4 (5) (2015) 742-751.

[28] M.K.A. Hamid, HYSYS®: An Introduction to Chemical Engineering Simulation, Apostila de Hamid, 2007.

[29] E.E. Ludwig, Applied Process Design for Chemical and Petrochemical Plants, vol. 2, Gulf Professional Publishing, 1997.

[30] M. Zayat, M. Hassan, C. Taylor, S. Haggar, Feasibility of biogas utilization in developing countries: Egypt a case study, Austin Chem. Eng. 2 (2) (2015) 1-7.

[31] C. Radke, J. Prausnitz, Thermodynamics of multi-solute adsorption from dilute liquid solutions, AIChE J. 18 (4) (1972) 761-768.