Ijraset Journal For Research in Applied Science and Engineering Technology

Abstract

In Nigeria, biogas is a viable renewable energy source. This study\'s goal was to filter raw biogas of acidic gases CO2 and H2S before connecting it to the natural gas netting standard. The biogas acidic gas treatment plant was designed and numerically modelled using Aspen HYSYS 8.6. The simulation\'s primary goal is to find the optimal operating pressure that can make Nigerian biogas as pure as natural gas. The biogas treatment was carried out in a 20 stage PSA with a tray diameter of 1.7 m and a CO2 content of 0.25, H2S content of 0.0004, temperature of 30 C, pressure of 1.1 bar, flow rate of 13 m3/h, and DEA concentration of 0.3. A PSA operating pressure of 5 bars is necessary to achieve 95% pure methane biogas.

Introduction

I. INTRODUCTION

In reality, transforming agricultural, industrial, and sewage waste to biogas [1] may help Nigeria solve its energy crisis. The CO2 and H2S in sour Nigerian biogas must be eliminated before pumping it into the natural gas netting to fulfill the standards of these nettings [2–5]. Biogas sweetening removes CO2 and H2S from treated biogas to protect pipelines and engines from corrosion and increase calorific value [6–9]. Most biogas research in Nigeria focuses on producing biogas from local resources and utilizing it to generate thermal energy [10–14], but few researchers focus on biogas capacity enrichment. Numerical simulation aids in the design of sweetening cycles and size of equipment, particularly the absorber [15–17]. The Aspen HYSYS 8.6 simulation software is one of the most accurate and critical programs used in gas treatment process design [18–21].

Using the Aspen HYSYS 8.6 modeling tool, this paper determined the optimal PSA operating pressure to ensure methane purity in Nigerian biogas.

The investigation of employing simulation programs in the purification process of acid gases has been done [22–26]. No precise technique was provided to establish the optimal PSA operating pressure to extract pure methane from biogas. Thus, the current research intended to improve Nigerian biogas netting capacity. 2.

Fig. 1 depicts a typical full acid gas removal cycle (sweetening cycle) used for natural gas upgrading and purification [27].

The absorber column was chosen from the Aspen HYSYS model pallet (Fig. 2), which has an internal architecture of 20 stages, each level consisting of one tray. The DEA-containing acid gas fluid package is chosen [29].

The feed Nigerian biogas enters the absorber at 30°C, 1.1 bar pressure, and a flow rate of 13 m3/h from the absorber column's bottom. The lean amine (DEA) enters at 30 C, 20 bars, and 5.45 104 m3/h. DEA can concurrently absorb CO2 and H2S from Nigerian biogas. The sweet feed gas escapes at the top of the column, while the rich amine exits at the bottom of the absorber. The rich amine then travels through the expansion valve to reach 43 C and 1.4 bars before entering the separator. Rich amine leaves the separator under the same circumstances to enter an L/R heat exchanger. Lean amine is heated using the L/R heat exchanger. The hot, rich amine departs the exchanger and enters a regeneration column to absorb CO2 from it to lean it for reuse, while the lean amine enters a make-up tank at 74 C and 1.04 bar (0.027 bar above atmospheric pressure) and exits it at 74 C and 1.04 bar (0.027 bar above atmospheric pressure). Then it's pushed to 74.5 C and 1.1 bars, then cooled to 30 C using a continuous pressure technique. 1.1 bar lean amine recycler exit [30].

II. RESULTS AND DISCUSSION

The simulation process was done to optimize PSA working pressure using Aspen HYSYS. The removal cycle's temperature, pressure, and inlet gas flow rates were all calculated numerically to maximize methane purification from Nigerian biogas.

A. Impact of Nigerian PSA working pressure on CO2 concentration of biogas

As shown in Fig. 3, the relationship between PSA working pressure and CO2 percent in Nigerian biogas is inverse. The CO2 percentage is 0.0084 when the absorber PSA operating pressure is 5 bar. If the PSA operating pressure is beyond 5 bar, there is negligible (non-economic) influence on CO2 levels. To keep the lowest starting cost for absorber construction, the PSA operating pressure does not need to exceed 5 bar.

B. Impact of Nigerian PSA working pressure on H2S concentration of biogas

In Fig. 4, the relationship between PSA working pressure and H2S percent in Nigerian biogas is reversed. At 1.1 bar pressure, H2S may be entirely eliminated from Nigerian biogas. Thus, the 5 bar pressure required to clear CO2 from Nigerian biogas cleans both CO2 and H2S concurrently.

C. PSA Working Pressure on Nigerian biogas end Product Pure Methane

Fig. 5 demonstrates the impact of PSA operating pressure on final biogas methane purity. The methane purity tends to be 95% at the absorber PSA operating pressure of 5 bar, which is sought by most NG nettings. More than 5 bar PSA operating pressure has a greater influence on methane purity.

It is clear from the preceding graphs that the optimal PSA operating pressure for achieving 95% methane purity from Nigerian biogas is 5 bar. If the pressure is too low, the biogas treatment cycle might yield less pure methane.

The partial volume of a given gas in a combination is the volume of one element of the combination, according to Amagat's law of cumulative volume [31]. Tables 2 shows the partial pressures of acidic gases.

The term (Px/Ptot) is directly proportional to Vx, therefore if (Px/Ptot) is tiny, then Vx is little as well. This means that increasing total pressure may enhance methane purity according to Amagat's law of additive volume..

The ideal PSA operating pressure for cleaning acidic gases in Nigerian biogas is 5 bars. Table 3 shows the final sweetening gas composition derived from Nigerian biogas.

III. ACKNOWLEDGEMENT

I thank co-authors for their expertise and assistance throughout all aspects of this research work.

Conclusion

The optimal PSA operating pressure was determined by numerical simulation utilizing Aspen HYSYS simulation software. CO2 0.25, H2S 0.0004; 30 C; 1.1 bar pressure; and 13 m3/h flow rate were fed to the PSA. Simultaneous CO2 and H2S removal using DEA amine solvents. The simulation revealed that a DEA concentration of 0.3 and 20 steps PSA with a tray diameter of 1.7 m were optimal for biogas treatment. The best PSA operating pressure for obtaining 95% pure methane from Nigerian biogas is discovered to be 5 bar. A. Nomenclature Cond condenser DEA diethanolamine L/R Lean/Reach NG natural gas PSA Pressure Swing Absorber total ptot pressure of the gas mixture px partial pressure of an individual gas component (X) in the mixture RCY recycler REB reboiler VLV valve Vtot total volume of the gas mixture Vx partial volume of an individual gas component (X) in the mixture

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. Møller, 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. [accessed in 2016, 5]. [6] G.P. Helsing, Options for Carbon Capture with Storage or Reuse in Waste Incineration Processes, 2015. [6] 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) 1982– 1989. [7] M. Scholz, T. Melin, M. Wessling, Transforming biogas into biomethane using membrane technology, Renew. Sustain. Energy Rev. 17 (2013) 199–212. [8] X.Y. Chen et al, Membrane gas separation technologies for biogas upgrading, RSC Adv. 5 (31) (2015) 24399–24448. [9] I. Teichmann, Technical Greenhouse-Gas Mitigation Potentials of Biochar Soil Incorporation in Germany, 2014. [10] G.F. Parkin, W.F. Owen, Fundamentals of anaerobic digestion of wastewater sludges, J. Environ. Eng. 112 (5) (1986) 867–920. [11] S.D. Abou Hussein, O.M. Sawan, The utilization of agricultural waste as one of the environmental issues in Nigeria (a case study), J. Appl. Sci. Res. 6 (8) (2010) 1116–1124. [12] 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. [13] V. Bansal, V. Tumwesige, J.U. Smith, Water for Small-Scale Biogas Digesters in Sub-Saharan Africa, GCB Bioenergy, 2016. [14] 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) 49– 56. [15] R.A. Gawel, Design simulations for a biogas purification process using aqueous amine solutions, Chem. Pap. 66 (11) (2012) 1010–1018. [16] 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. 266– 275. [17] 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. [18] A.H. Nafez et al, Sewage sludge composting: capacity assessment for agricultural application, Environ. Monit. Assess. 187 (11) (2015) 1–9. [19] 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 Nigerian biogas, Int. J. Inf. Res. Rev. 03 (01) (2016) 1739–1744. [20] S.T.A. Elfattah, Y.A. Eldrainy, A. Attia, Optimization of Pressure Swing Absorber (PSA) geometry to achieve highest methane purity from the Nigerian biogas using Aspen HYSYS simulation, Int. J. Innov. Res. Develop. 5 (1) (2016). [21] L. ErikØi, Comparison of Aspen HYSYS and Aspen Plus simulation of CO2 absorption into MEA from atmospheric gas, Energy Proc. 23 (2012) 360–369. [22] 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. [23] 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. [24] 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. [25] I.K. Kapdan, F. Kargi, Bio-hydrogen production from waste materials, Enz. Microb. Technol. 38 (5) (2006) 569–582. [26] 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. [27] M.K.A. Hamid, HYSYS: An Introduction to Chemical Engineering Simulation, Apostila de Hamid, 2007. [28] E.E. Ludwig, Applied Process Design for Chemical and Petrochemical Plants, vol. 2, Gulf Professional Publishing, 1997. [29] M. Zayat, M. Hassan, C. Taylor, S. Haggar, Feasibility of biogas utilization in developing countries: Nigeria a case study, Austin Chem. Eng. 2 (2) (2015) 1–7. [30] C. Radke, J. Prausnitz, Thermodynamics of multi-solute adsorption from dilute liquid solutions, AIChE J. 18 (4) (1972) 761–768.

Copyright

Copyright © 2022 Engr. Nnadikwe Johnson, Odiki Esther E., Ikputu Woyengikuro Hilary, Ewelike Asterius Dozie. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.