# A conceptual review of sustainable electrical power generation from biogas

Stéphane Abanades, Hossein Abbaspour, Abolfazl Ahmadi, Biplab Das, Mehdi A Ehyaei, Farbod Esmaeilion, Mamdouh El Haj Assad, Taher Hajilounezhad, Abir Hmida, Marc A Rosen, et al.

<figure><img src="image_1.png" /></figure>

## ► To cite this version:

Stéphane Abanades, Hossein Abbaspour, Abolfazl Ahmadi, Biplab Das, Mehdi A Ehyaei, et al. A conceptual review of sustainable electrical power generation from biogas. Energy Science & Engineering, 2022, 10 (2), pp.630-655. 10.1002/ese3.1030. hal-03529920

HAL Id: hal-03529920

https://hal.science/hal-03529920

Submitted on 17 Jan 2022

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

<figure><img src="image_2.png" /></figure>
# A conceptual review of sustainable electrical power generation from biogas

Stephane Abanades<fnref n="1" />

Hossein Abbaspour<fnref n="2" />

Abolfazl Ahmadi<fnref n="3" />

<figure><img src="image_3.png" /></figure>

Biplab Das<fnref n="4" />

Mehdi A. Ehyaei<fnref n="5" />

<figure><img src="image_4.png" /></figure>

Farbod Esmaeilion<fnref n="6" />

<figure><img src="image_5.png" /></figure>

Mamdouh El Haj Assad<fnref n="7" />

Taher Hajilounezhad<fnref n="8" />

Abir Hmida<fnref n="9" />

Marc A. Rosen<fnref n="10" />

Sadegh Safari<fnref n="11" />

Mohammad A. Shabi<fnref n="12" />

Jose Luz Silveira<fnref n="13" />

## Correspondence

Abolfazl Ahmadi, School of New
Technologies, Iran University of
Science & Technology, Tehran, Iran.

Email: a_ahmadi@iust.ac.ir

Mehdi A. Ehyaei, Department of
Mechanical Engineering, Pardis
Branch, Islamic Azad University, Pardis
New City, Iran.

Email: aliehyaei@yahoo.com

## Abstract

High-energy demand with rapid industrialization and mechanization combined with environmental pollution due to the burning of fossil fuels has driven a shift toward renewable energy. Biogas derived from biomass is a potential renewable energy source that can be used in different sectors such as transportation sector, electricity generation, heat production, combined heat and power (CHP) systems, and fuel cells. Moreover, the upgraded biogas can be applied as transportation fuel via an internal combustion chamber (for internal combustion engine (ICE) vehicles), and electricity station (for electric vehicles). In the present work, a conceptual review of biogas-based electrical power production systems is presented. It is clear that the conventional types of biomass contain a high amount of pollutants and unwanted constituents, which lower the lower heating value (LHV) of biogas fuel. Moreover, the energy and exergy efficiencies of biogas applications

The contribution of the authors is the same.

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

© 2021 The Authors. *Energy Science & Engineering* published by the Society of Chemical Industry and John Wiley & Sons Ltd.

<figure><img src="image_6.png" /></figure>

<footnote n="1">¹Processes, Materials, and Solar Energy Laboratory, PROMES-CNRS, Font-Romeu, France</footnote>

<footnote n="2">²Department of Biology, Faculty of Biological Science, North Tehran Branch, Islamic Azad University, Tehran, Iran</footnote>

<footnote n="3">³School of New Technologies, Iran University of Science & Technology, Tehran, Iran</footnote>

<footnote n="4">⁴Department of Mechanical Engineering, National Institute of Technology Silchar, Silchar, India</footnote>

<footnote n="5">⁵Department of Mechanical Engineering, Pardis Branch, Islamic Azad University, Pardis New City, Iran</footnote>

<footnote n="6">⁶Department of Mechanical Engineering, K.N. Toosi University of Technology, Tehran, Iran</footnote>

<footnote n="7">⁷Sustainable & Renewable Energy Engineering Department, University of Sharjah, Sharjah, United Arab Emirates</footnote>

<footnote n="8">⁸Department of Mechanical & Aerospace Engineering, University of Missouri, Columbia, Missouri, USA</footnote>

<footnote n="9">⁹Research Laboratory of Applied Thermodynamic, National Engineering School of Gabes, University of Gabes, Gabes, Tunisia</footnote>

<footnote n="10">¹⁰Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, Oshawa, Ontario, Canada</footnote>

<footnote n="11">¹¹School of the Environment and Energy, Islamic Azad University-Science and Research Branch, Tehran, Iran</footnote>

<footnote n="12">¹²Department of Mechanical and Nuclear Engineering, University of Sharjah, Sharjah, United Arab Emirates</footnote>

<footnote n="13">¹³Sao Paulo State University, UNESP, FEG, Energy Department, Sao Paulo, Brazil</footnote>
are influenced by these components. Consequently, several biogas-upgrading technologies have been elaborated to increase the LHV of biogas fuel by removing biogas pollutants. So, the energy and exergy analyses of biogas-driven plants are discussed in this regard. Also, the economic analysis of biogas-fueled systems is measured through the connection between biogas production, purchased electrical power, and selling of an additional amount of biogas. Biogas represents an important source of renewable energy as shown before, and it helps in waste management and W-to-E (waste to energy) conversion, which allows utilizing huge amounts of wastes instead of disposal or landfill procedures. However, handling of biogas from production to utilization has an impact on the environment. Therefore, the assessment of the environmental impacts of biogas plants is presented. In addition, a combination of the biogas energy with other sources, especially renewable energy sources (eg, solar-biogas, geothermal-biogas, wind-biogas, CHP, CCHP, and concentrated photovoltaic-biogas), and reusing waste energy for other tasks (eg, employing the waste heat from a gas turbine) are examined.

KEYWORDS

biogas, electrical applications of biogas systems, exergetic modeling, power generation, sustainability

# 1 | INTRODUCTION

Fossil fuels, such as coal, crude oil, and natural gas, provide much of the world's growing energy supply. In 2018, primary energy consumption grew by 2.9%, which is twice the annual average energy consumption since 2010.<sup>1,2</sup>

China, United States, and India are responsible for more than two-thirds of the rise in energy demand, which is expected to lead to fossil fuel scarcity over time.<sup>3,4</sup> In 2018, the use of renewable energy has grown by 14.5% over ten years, but it was lower than expected.<sup>5</sup> Renewable energy sources accounted for more than 25% of the total world electricity generation in 2018, mainly hydroelectric, wind, and solar energy.<sup>6,7</sup>

In this regard, sustainable and clean electricity production is a promising approach to satisfy multifaceted objectives. The use of renewable energy can be a solution in providing desirable conditions (both economic and environmental) in the production of electrical power.<sup>8,9</sup> The detection of resources, investments, and industrial knowledge has crucial roles in promoting renewable and sustainable energy trends in developing countries, while the existence of a logical balance between performance parameters is a critical condition.<sup>10,11</sup>

Renewable energies are essential to achieve sustainable and clean electricity generation. Among all conventional methodologies for renewable power generation, just about

8.3% of the renewable energy resources belong to bioenergy units.<sup>12,13</sup>

One of the most influential factors in sustainable power generation is based on the type of fuel. Based on the literature,<sup>14</sup> biogas is an important fuel in producing clean and sustainable electric power. Assessing sustainability entails going further than the conventional environmental life cycle assessment and combining the study of economic aspects with social performance.<sup>15,16</sup> Regardless of the presence of various renewable resources and green perception for electricity generation, the production rate of electrical power from biogas needs to be effectively recognized and calculated. Life Cycle Assessment (LCA) is a functional approach employed to quantify the environmental sustainability of energy systems.<sup>17,18</sup> The incorporation of various environmental and economic assessment indicators, through standard scopes and models, further broad insights into the sustainability of the biogas system would be provided.<sup>19-21</sup>

Sustainable power generation through biogas is impacted by biogas production, directly. The sustainability of biogas production is not determined by regional yield but rather by nutrient recovery and operational factors.<sup>22</sup> The biogas plants' feedstock and their availability demonstrate the potential of biogas production for utilization as an alternative fuel for sustainable electricity generation.<sup>23</sup> It also has dependency based on the demands
for biogas-based electricity and other energy markets for biogas, for example, the transport sector where the willingness to pay is often higher.

Among renewable energy sources, biogas is more adaptable and flexible in comparison with wind and solar energy, and more economical as it requires less capital investment and operational cost (which may vary depending on geographical location).<sup>14,24</sup> It features a high energy value, easy storage, and offers dependency regarding the geographical location and season.<sup>25</sup>

Biogas is produced from different feedstock such as wastewater treatment plants, organic waste, municipal solid waste, or food residues (generally the organic wastes).<sup>26</sup> Traditionally (specifically in Asia), biogas was employed for cooking and lighting houses as a low-quality energy source.

The main reason for replacing conventional fuels with biogas is to decrease global warming and provide a renewable energy source. The combustion of biogas produced from waste materials or biomass results in a variable flame temperature, which depends on the amount of methane contained in the biogas. This gives an advantage for using the flue gases from the biogas combustion to provide energy for industrial processes depending on the heat source temperature.<sup>27</sup>

Nowadays, upgraded biogas has drawn attention because it can be produced when required, easily stored and used in the transportation sector as vehicle fuel.<sup>28</sup> Upgraded biogas can also improve energy distribution,<sup>29</sup> electricity generation (10% generated from renewable energy sources), heating, and refrigeration separately or simultaneously through combined heat and power (CHP) or combined heat, power, and cooling (CHPC) systems.<sup>30-34</sup>

Recently, biogas is often upgraded to biomethane to be injected into gas grid lines and can be used in fuel cells, or used as feedstock for chemicals

production.<sup>30-32,35,36</sup> Various sources can be used for biogas production by anaerobic digestion, for instance, municipal solid waste, food, and agricultural and vegetable products such as *Panicum virgatum*, wheat straw, and maize (these three feedstocks provide high yields in methane production).<sup>37</sup>

In the United States, it has been estimated that under the current circumstances and the use of available sources, biogas has the potential to generate energy equal to 17,000 metric kilotons of oil equivalent. Meanwhile, it allowed reducing greenhouse gas emissions by 4.33 million metric tons of carbon dioxide in 2018, which could be accounted for one of the main environmental benefits of biogas.<sup>38</sup>

Figure 1 shows the use biogas from 2000 to 2019, where the highest consumption of biogas occurred in CHP systems (in USA). Next, the utilization of biogas for power production has shown that it experienced a steady increase from 2000 to 2013, after which it has grown at slower rate. Since 2017, natural gas and compressed natural gas production based on renewable energy have grown.<sup>38</sup>

Anaerobic digestion, which happens in the absence of oxygen, is a process consisting of breaking down biodegradable materials. The four main steps of this phenomenon are hydrolysis, acidogenesis, acetogenesis, and methanogenesis.

If the feedstock is available and cheap, biogas production will be usually economically viable. Much research has been done to date on increasing the efficiency of methane production, improving digestion, optimizing the operating conditions and process design, and selecting feedstock.<sup>39-42</sup>

Carbon dioxide and methane are the main components of biogas. Other components in the biogas cause corrosion in the heat exchanger components and reduction in heat transfer. Depending on the type of feedstock, other

<figure><img src="image_7.png" /><figcaption>FIGURE 1 The trend of biogas consumption for various applications in the USA from 2000 to 2020<sup>38</sup></figcaption></figure>
impurities such as siloxane, ammonia, and hydrogen sulfide exit in the produced biogas.⁴³ Compositions of natural gas, landfill biogas, and anaerobic digestion biogas are tabulated in Table 1.⁴⁴

In this article, a review of biogas applications for electricity production is reported. Recent developments of installed biogas production and utilization plants are presented. A comprehensive study is performed on biogas-driven electrical power production plants. An in-depth overview of energy and exergy analyses of biogas-fueled plants is provided. Table 2 summarizes previous works related to the use of biogas in generating electric power.

## 2 | BIOGAS-FUELED ELECTRICAL POWER PRODUCTION

Electricity generation from biogas is still relatively novel in the world, but in industrialized countries, this application is more common. Due to the environmental impacts of fossil fuels, applications of biogas for electricity production such as gas turbines in different capacities and usages as fuel in internal combustion engines are gaining more interest.⁴⁷

A comprehensive investigation on the utilization of biogas systems suggesting the utilization of biogas can be categorized into four subcategories based on the final use⁴⁸ as:

* Electricity generation from power plants, CHP units, and fuel cells.

* Production of heat using a boiler.

* Heat from power plants, CHP systems, and fuel cells.

* Transportation fuel via internal combustion engines (for ICE vehicles), and electricity station (for electric vehicles).

Outcomes of a research work (Hakawati et al.⁴⁸ in 2017) revealed that for the biogas systems based on anaerobic digestion facility and biogas composition the energy efficiency could vary from 8% (steam reforming of methane) to 54% (upgrading of biogas to biomethane) for electricity generation, 16% to 83% for heat production, and 18% to 90% for the CHP system. This study clearly showed that the application of biogas systems was more attractive for CHP usages (in comparison with other fuels). So for this reason, the application of this renewable energy is more appropriate in this field.

Barzegaravval et al.⁴⁹ performed an exergy-economic evaluation of a gas turbine with a preheater driven by biogas with different methane contents (Figure 2). This study showed the methane volume fraction of the biofuel

decreased from 0.95 to 0.6, and the gas turbine total cost increased by about 1%, hence the electricity production cost increased. Furthermore, by changing the output power of the gas turbine from 1 to 10 MW, the electricity generation cost varied from 0.05 $/kWh to 0.18 $/kWh.

### 2.1 | Micro gas turbine system

Applications of biogas for CHP production in different locations with different biogas resources have been studied in many research works. In these studies, different aspects of energy, exergy, produced electricity, heat, cost of electricity (COE) generation, and cost of heat (COH) production were examined.¹⁴,⁵⁰,⁵¹ Kang et al.⁵² performed an economic assessment on the gas turbine for CHP that used natural gas and biogas mixture (Figure 3). The results of this study showed that COE and COH increased with the increase in the natural gas ratio. The heat sales ratio and the mixing ratio had a significant impact on the payback period. This survey also estimated that the COE was 0.1436 $/kWh, and COH was 0.0738 $/kWh for the CHP system.

Kim et al.⁵³ used biogas to run a micro gas turbine (MGT), which is combined with an organic Rankine cycle (ORC) as shown in Figure 4. The biogas of this system was provided by sewage sludge and food waste. The results revealed that the annual thermal energy produced by an MGT in the case of CHP plant was 7.4 MWh per year, while it was 9.0 MWh per year for the combination of ORC and MGT.

Similarly, a thermoeconomic analysis of biogas-fueled MGT with an ORC was investigated. This research concluded that the system economy could be competitive, depending on the methane ratio in biogas; while a higher methane ratio is more beneficial.⁵⁴ The economic feasibility of the gas cycle fueled with biogas for CHP (Figure 5) and combined cycle (CC) (Figure 6) was examined. The results of this study showed that the CHP system was more beneficial than the CC system based on several economic parameters.⁵⁵

### 2.2 | Fuel cell

Saadabadi et al.⁵⁶ conducted a comprehensive study on the application of hybrid anaerobic digestion (AD) unit and solid oxide fuel cell (SOFC) (Figure 7). Furthermore, an outline for the benefits and difficulties of the hybrid integration of AD and SOFC systems was examined to measure the performance of this system for electricity generation and usage of heat produced by SOFC. The outcomes showed that the high temperature produced
<table><caption>TABLE 1 Compositions of natural gas, landfill biogas, and anaerobic digestion biogas adapted from$^{45,46}$</caption><thead><tr><th>Component</th><th>Natural gas</th><th>Landfill biogas</th><th>Anaerobic digestion biogas</th></tr></thead><tbody><tr><td>Carbon dioxide (%)</td><td>0.7–1</td><td>25–47</td><td>30–50</td></tr><tr><td>Methane (%)</td><td>81–89</td><td>30–65</td><td>53–70</td></tr><tr><td>Oxygen (%)</td><td>0</td><td>&lt;1–3</td><td>0–5</td></tr><tr><td>Nitrogen (%)</td><td>0.28–14</td><td>&lt;1–17</td><td>2–6</td></tr><tr><td>Hydrogen (%)</td><td>NA</td><td>0–3</td><td>NA</td></tr><tr><td>Higher hydrocarbons (%)</td><td>3.5–9.4</td><td>NA</td><td>NA</td></tr><tr><td>Ammonia (ppm)</td><td>NA</td><td>0–5</td><td>&lt;100</td></tr><tr><td>Hydrogen sulfide (ppm)</td><td>0–2.9</td><td>30–500</td><td>0–2000</td></tr><tr><td>Siloxane (%)</td><td>NA</td><td>&lt;0.3–36</td><td>0.08–0.5</td></tr><tr><td>Overall chlorines (%)</td><td>NA</td><td>0.3–225</td><td>&lt;0.25</td></tr></tbody></table>

heat by the SOFC unit could increase the volume of biogas production, which resulted in increasing the total efficiency.$^{56-59}$

A new configuration of the hybrid combination of SOFC and MGT fueled by biogas was proposed by Wongchanapai et al.$^{60}$ The key concept of this research was the application of the internal reformation unit in SOFC for the internal transformation of methane into hydrogen. A comprehensive set of data was obtained and reported in this study.$^{60}$

The achievements of hybrid integration of a molten carbonate fuel cell (MCFC) and MGT fueled by natural gas and biogas for power production (Figure 8) were analyzed by Huang et al.$^{61}$ It was found that the output power of the MCFC-MGT system increased from 39.0% to 42.0% due to the increase in the biogas flow rate. Moreover, the hybrid MCFC/MGT power system was easy to operate and stable with power variation. Finally, this hybrid MCFC/MGT system could be applied for power generation of a network at a micro-scale.$^{61-63}$

## 2.3 | Internal combustion engine (ICE)

The low speed of the ignition process, severe back burning, and high temperature of the flue gas are the main drawbacks of biogas engines.$^{64}$ In this case, the speed of combustion process using CH$_4$ was 37.3 cm/s, while the presence of CO$_2$ reduced this value down to 23 cm/s. Therefore, the burning continued in the stack (post-combustion) and associated combustion quality reduced correspondingly.$^{65}$ In response to the flame high temperature, spontaneous

combustion is a rare process in these engines with burning biogas as fuel.

The achievement of a diesel engine was inspected for different fuels consisting of diesel fuel, natural gas, mixture of methane with biogas, and stand-alone biogas by Chandra et al.$^{66}$ The outcomes showed that the generated power of the engine was decreased by 31.8% for compressed natural gas, 35.6% for methane-enriched biogas, and 46.3% for raw biogas relative to diesel fuel. Moreover, it was found that the methane-enriched biogas and compressed natural gas were similarly based on thermal efficiency, power output, and specific gas consumption.

The chemical properties of biogas such as purity and composition significantly affect IC engine performance.$^{67}$ It is worth mentioning that compressed natural gas (CNG) and biogas have similar compositions, making the use of biomethane as the source of energy in vehicles possible. Table 3 shows the compositions of biogas and CNG.

The use of biogas as a fuel in engines has even more merits in comparison with other fuels. The main advantages of this energy source are economic, environmental friendly, and ecological. Utilization of biogas reduces exhaust emissions of carbon dioxide (up to 70%), sulfur compounds (up to 25%), carbon monoxide (up to 90%), hydrocarbons (up to 80%), and nitrogen oxides (50–86%) (in comparison with CNG).$^{69,70}$ The degree of purity of biogas is dependent on the process utilization. Requirements to eliminate gaseous species based on the biogas application given in Table 4.

Yingjian et al.$^{72}$ analyzed the energy balance and assessed the achievement of the power generation by IC engine when biogas was used as the working fuel. The thermal energy dissipated from the engine exhaust was the highest of all, which was about 40.34%.

Qian et al.$^{73}$ stated that consuming biogas in a dual-fuel approach was an improved method to attain the optimal use of biogas. Associated with diesel engines, the CO and HC productions of the dual-fuel mode by biogas were enhanced; nonetheless, the soot and NO$_x$ released were reduced. Cacho et al.$^{74}$ developed a spark-ignited internal combustion (SIIC) engine propelled by biogas-gasoline for which the experimental results revealed that the maximum power was 5.97 kW at 3600 rpm for 8:1 compression ratio. An experimental examination of the ignition and flue gas descriptions of dual-fuel combustion (biogas/biodiesel) of the compression ignition (CI) engine was performed by Yoon et al.$^{75}$ For the dual-fuel approach, the highest heat removal for biogas and biodiesel fuels were marginally less than the amount of biogas-diesel. Dobslaw et al.$^{76}$ studied the influence of various types of IC engines and adjustments of the working constraints of the engine on the emission spectrum.
<table><caption>TABLE 2 Comparative analysis of biogas surveys for electric power generation</caption><thead><tr><th>Ref. no.</th><th>Country</th><th>Biogas sources</th><th>Energy scenario</th><th>Economic study</th><th>Environmental impact</th><th>Bio-power generation</th><th>Challenges in biogas generation</th><th>Type of study</th></tr></thead><tbody><tr><td>12</td><td>Thailand</td><td>Green waste</td><td>√</td><td>√</td><td>×</td><td>√</td><td>√</td><td>Case study</td></tr><tr><td>12</td><td>China</td><td>Municipal solid waste</td><td>√</td><td>√</td><td>√</td><td>√</td><td>√</td><td>Case study</td></tr><tr><td>3</td><td>Iran</td><td>Animal waste and agriculture residues</td><td>√</td><td>×</td><td>√</td><td>√</td><td>√</td><td>Case study</td></tr><tr><td>4</td><td>Benin</td><td>Solid waste and agriculture biomass</td><td>√</td><td>√</td><td>×</td><td>√</td><td>√</td><td>Case study</td></tr><tr><td>5</td><td>Indonesia</td><td>Cattle dung</td><td>√</td><td>√</td><td>√</td><td>√</td><td>√</td><td>Case study</td></tr><tr><td>6</td><td>China</td><td>All</td><td>√</td><td>×</td><td>×</td><td>√</td><td>√</td><td>Review</td></tr><tr><td>7</td><td>Turkey</td><td>Animal manure</td><td>×</td><td>√</td><td>×</td><td>√</td><td>×</td><td>Case study</td></tr><tr><td>8</td><td>South Africa</td><td>Human wastes</td><td>×</td><td>√</td><td>×</td><td>√</td><td>×</td><td>Case study</td></tr><tr><td>9</td><td>Pakistan</td><td>Biomass wastes</td><td>√</td><td>√</td><td>√</td><td>√</td><td>√</td><td>Review</td></tr><tr><td>10</td><td>Brazil</td><td>Vinasse</td><td>√</td><td>√</td><td>×</td><td>√</td><td>×</td><td>Case study</td></tr><tr><td>11</td><td>Brazil</td><td>Vinasse</td><td>√</td><td>√</td><td>√</td><td>√</td><td>√</td><td>Case study</td></tr><tr><td>12</td><td>Bangladesh</td><td>Organic waste</td><td>×</td><td>×</td><td>√</td><td>√</td><td>×</td><td>Case study</td></tr><tr><td>13</td><td>Germany</td><td>All</td><td>√</td><td>√</td><td>×</td><td>√</td><td>√</td><td>Case study</td></tr><tr><td>14</td><td>Indonesia</td><td>Fruit waste</td><td>×</td><td>×</td><td>√</td><td>√</td><td>×</td><td>Case study</td></tr><tr><td>15</td><td>Ukraine</td><td>Agricultural residues and industrial waste</td><td>√</td><td>√</td><td>×</td><td>√</td><td>√</td><td>Case study</td></tr><tr><td>16</td><td>Ukraine</td><td>Animal manure</td><td>√</td><td>×</td><td>√</td><td>√</td><td>×</td><td>Review</td></tr><tr><td>17</td><td>India</td><td>Biomass wastes</td><td>√</td><td>√</td><td>×</td><td>√</td><td>√</td><td>Case study</td></tr><tr><td>Present study</td><td></td><td>All</td><td>√</td><td>√</td><td>×</td><td>√</td><td>√</td><td>Review</td></tr></tbody></table>
<figure><img src="image_8.png" /><figcaption>FIGURE 2 Flow diagram of gas turbine cycle with a preheater for power production⁴⁹</figcaption></figure>

Technical and economical evaluations of a multi-generation system based on biogas have been reported by Khan et al.⁷⁷ In these systems, energy conversion stages were examined for various combustion variables. Moreover, the levelized cost of electricity (LCOE), gas for cooking purposes, and freshwater production (by membrane distillation) in terms of energy and economics have been analyzed.

## 3 | ENERGY ANALYSIS OF BIOGAS-FUELED SYSTEM

The presence of CO₂ and N₂ in biogas influences the energy and exergy efficiencies. Consequently, several biogas-upgrading technologies have been elaborated to increase the LHV of the fuel by removing biogas pollutants. As shown in Figure 9, these technologies include chemical scrubbing, membrane separation, pressure swing adsorption (PSA), and pressured water scrubbing (PWS). The water scrubbing technology has been proved to be one of the simplest and cheapest technologies because of its high efficiency and low CH₄ loss, as well as the possibility of hydrogen sulfide (H₂S) removal.¹⁴,⁷⁸,⁷⁹

For CO₂ removal, Xu et al.⁷⁸ calculated the energy efficiency of three biogas-upgrading techniques namely ionic liquid scrubbing (ILS), pressured water scrubbing (PWS), and monoethanolamine aqueous scrubbing (MAS). Their study also involved methane (CH₄) recovery ratio calculation along with the specific energy consumption, and the CO₂/CH₄ selectivity.

The methane recovery ratio (MRR) can be written as⁷⁸:

$$MRR = \eta_{CH_4} \frac{v_{out} \cdot C_{out}}{v_{in} \cdot C_{in}} \cdot 100\% \quad (1)$$

where v_in denotes the biogas volumetric flow rates (m³/h) and v_out stands for the volumetric flow rates of produced gas (m³/h), C_in represents the concentration of the methane in

biogas, and C_out represents the methane concentration in produced gas.

The specific energy consumption (SEC) in kWh/m³ CH₄ is obtained in terms of the total energy consumption (TEC) rate (kW) as⁷⁸:

$$SEC = \frac{TEC}{v_{out} \cdot C_{out}} \quad (2)$$

The energy efficiency (ηᵢ) of gas separation technology can be expressed by the following equation⁷⁸:

$$\eta_i = \frac{Q_{out,p}}{Q_{in,f} + Q_{in,u} + \frac{E_{in,u}}{\sigma}} \quad (3)$$

where Q_in,f is the feed gas lower heating value, Q_out,p is the produced gas lower heating value (MWth), Q_in,u is the required heat of the solvent regeneration, heating, and evaporation processes (MWth), E_in,u is the electrical energy required by the driving machines in the process (MWhe), and σ is the conversion efficiency of steam to electricity (about 20–40%).⁷⁸

The solvent selectivity S is calculated in terms of H₄ and H₂, which are the Henry constants of CH₄ and CO₂, respectively, at a specific temperature, as follows⁷⁸:

$$S = \frac{H_{CH_4}}{H_{CO_2}} \quad (4)$$

The theoretical energy consumption is the minimum energy demand for the separation of CO₂ and CH₄, which is expressed as⁷⁸:

$$E_{theor} = nRT \left[ x_{CO_2} \ln \left( \frac{1}{x_{CO_2}} \right) + x_{CH_4} \ln \left( \frac{1}{x_{CH_4}} \right) \right] \quad (5)$$

Figure 10 shows that the ILS and PWS energy consumptions were about 50% lower compared to MAS technology due to the fact that the ILS and PWS are physical absorption processes in which the absorbed CO₂ demands less energy when released with air stripping. Meanwhile, MAS is a chemical-absorption process where heating is needed for solvent vaporization.

European Union suggested that a major part of the energy generation could be supplied by biogas sources, and therefore, its consumption in energy generation is likely to increase. In this context, some researchers have focused their study on the efficiency of using biogas as fuel. Brizi et al.⁸¹ have conducted research aiming at comparing the usage of biogas and natural gas for a cogeneration system.
<figure><img src="image_9.png" /><figcaption>FIGURE 3 An innovative representation of CHP plant configuration driving with a digestion plant<sup>52</sup></figcaption></figure>

They mentioned that the efficient utilization of the cogener- erated heat improved the greenhouse gas (GHG) balance of electricity production from biogas. The energy efficiency of the cogeneration system is obtained as<sup>81</sup>:

$$ \eta_{biogas} = \frac{E_{El} + E_{HotWater} + E_{Cold}}{E_{Fuel}} \quad (6) $$

where E denotes energy (kWh) and the subscripts cold and El represents cold water and electricity, respectively. The use of natural gas was found to be preferable for electrical production while biogas was recommended for heat production.

Gazda et al.<sup>82</sup> studied the usage of biogas for multi-generation power plants as the main fuel with a load ratio from 50% to 100%. It was shown that an increase in energy efficiency between 37% and 43% and a decrease in energy savings by 54.5% were achieved. Likewise, Ahmadi et al.<sup>83</sup> configured and investigated a multi-generation system driven by a biogas fuel, generating 671 kW of electricity.

Sevinchan et al.<sup>27</sup> accomplished an energy analysis of a biogas-driven multi-generation system. They found that energy efficiency was always higher by 72.5% compared to both configurations, the single and the cogeneration systems. Besides, the system was able to generate 1078 kW, 198 kW, and 87.54 kW of electrical, heating, and cooling power, respectively. It reached 40.11% highest electrical power energy efficiency, 62.18% maximum cooling energy efficiency, and 65.35% maximum heating energy efficiency. It was concluded that this power could supply

300 houses with daily electricity and the additional electricity could be stored for further utilization.

Norouzi et al.<sup>84</sup> performed research on energy efficiency calculation of a biogas-upgrading system, a biogas CHP system, and a biogas SOFCs. The calculation of the effectiveness of energy for the biogas-improving system relied totally on methane and feedstock's LHV. In contrast, for both CHP plants and biogas-fueled SOFC systems, the energy efficiency calculation relied on the LHV-based net electric and heat efficiencies. Between the three above-mentioned application pathways and based on the results given in Table 5, the biogas-upgrading method showed a greater energy efficiency (46.5%) than its counterparts CHP and SOFCs (30.4% and 32.9%, respectively).

In another study, Prodromidis and Coutelieris in 2017<sup>85</sup> designed a software tool, named THERMAS, incorporating energy and exergy theory assessments of a biogas-SOFC plant. Experimental and theoretical study of different scenarios fed by biogas various compositions showed that the SOFC system used pure methane to generate electrical energy displayed an energy efficiency of up to 80–90%, while a value of 96% was obtained through simulation.

Likewise, Chouhan et al.<sup>86</sup> developed a survey on electricity generation using the SOFC system. A thermodynamic analysis using the Peng-Robinson (PR) formula of state with various compositions of CH<sub>4</sub> (45–80%) was realized at different temperatures (573–1273 K) and steam to CH<sub>4</sub> molar ratios (S/C = 0–2) at 1 atm pressure.
<figure><img src="image_10.png" /><figcaption>FIGURE 4 Combination of MGT with a biogas production unit and ORC<sup>53</sup></figcaption></figure>

The system thermal efficiency is written as<sup>86</sup>:

$$ \eta_{thermal} = \frac{n_{H_2}^{out} \cdot LHV_{H_2} + n_{CO}^{out} \cdot LHV_{CO}}{n_{CH_4}^{in} \cdot LHV_{CH_4} + Q_R + n_{Steam}^{in} \cdot \Delta H_L} \quad (7) $$

$$ Q_R = H_T^{out} - H_T^{in} \quad (8) $$

$$ H_T^{in} = \sum_{i=1}^{N_1} n_i^{in} h_{T,i}^{in} = \sum_{i=1}^{N_1} n_i^{in} \left[ h_{298,i} + \int_{298}^{T} c_{p,i} dT \right] \quad (9) $$

$$ H_T^{out} = \sum_{i=1}^{N_2} n_i^{out} h_{T,i}^{out} = \sum_{i=1}^{N_2} n_i^{out} \left[ h_{298,i} + \int_{298}^{T} c_{p,i} dT \right] \quad (10) $$

where LHV denotes lower heating value (kJ/mol) and ΔH<sub>L</sub> is the latent heat enthalpy change (kJ/mol). Q<sub>R</sub> is the net variation in total enthalpies of inlet and outlet reformer streams (kJ/mol). h<sub>T,i</sub><sup>out</sup> and h<sub>T,i</sub><sup>in</sup> are the specific enthalpies of constituent i<sup>th</sup> of the outlet and inlet streams at temperature T (kJ/mol), respectively. H<sub>298,i</sub> is the molar enthalpy of component i at 298 K (kJ/mol) and c<sub>p,i</sub> is the component of i heat

capacity (kJ/kmole). The outcomes of the system modeling are presented in Figures 11 and 12. For a CH<sub>4</sub>/CO<sub>2</sub> ratio from 45/55 to 80/20, the energy efficiency of the reforming process is between 92.4 and 91.5%. The energy required per mole of biogas was found to be between 109 kJ and 179 kJ. The authors concluded that the product gas of biogas steam reforming obtained from various feedstock could be used as a fuel for SOFC and produce an electrical power up to 158 kW for 40% of methane and 280 kW for 80% of methane.

Furthermore, for high-efficiency power plants, researchers have examined multi-generation systems driven by hybrid technologies with biogas integration. Mosaffa et al.<sup>87</sup> focused on a multi-generation process conducted by a solar-biogas hybrid system as heat and power source to produce hydrogen and methanol. The system was composed of solar-based biogas-steam reformer, PSA unit, carbon capture, and sequestration unit Rankine and organic Rankine cycles, gas turbine cycle, and methanol synthesis unit. The thermoeconomic analysis showed a 15% decrease in energy efficiency with a 200 K increase in the temperature. Rostamzadeha et al.<sup>88</sup> also conducted a study on a multi-generation technology driven by a
<figure><img src="image_11.png" /><figcaption>**FIGURE 6** An illustration of combined cycle configuration powered with an anaerobic digestion plant (case 2)⁵⁵</figcaption></figure>

<figure><img src="image_12.png" /></figure>

<figure><img src="image_13.png" /><figcaption>**FIGURE 7** AD-SOFC system energy flow diagram⁵⁶</figcaption></figure>

biogas-geothermal hybrid system as a heat source, where they performed a comparison to the single-generation system, which showed a considerable improvement in the thermal efficiency up to 62.3%. Moreover, the multi-generation system produced an overall heating power of 538.1 kW, a cooling capacity of 1799 kW, a net output

power of 443.4 kW, a mass flow rate of produced hydrogen 0.26 kg/s, and 367.9 L/h of freshwater. Bamisilea et al.⁸⁹ modeled a multi-generation system powered by renewable energy sources, which are wind, biomass, and solar using a wind turbine, biogas, and concentrated photovoltaic/thermal (CPVT). Various case studies such as
<figure><img src="image_14.png" /><figcaption>TABLE 3 Comparison of compositions (%) of biogas and CNG<sup>68</sup></figcaption></figure>

<table><thead><tr><th>Component</th><th>Biogas (high purity)</th><th>CNG</th></tr></thead><tbody><tr><td>CH<sub>4</sub></td><td>55–75</td><td>97.4</td></tr><tr><td>CO<sub>2</sub></td><td>25–45</td><td>0.07</td></tr><tr><td>H<sub>2</sub>O</td><td>1–5</td><td>-</td></tr><tr><td>O<sub>2</sub></td><td>0.1–0.5</td><td>-</td></tr><tr><td>C<sub>3</sub>H<sub>8</sub></td><td>-</td><td>0.22</td></tr><tr><td>Noble gases</td><td>-</td><td>0.13</td></tr><tr><td>N<sub>2</sub></td><td>0–0.3</td><td>1.22</td></tr><tr><td>H<sub>2</sub>S</td><td>0–3</td><td>-</td></tr><tr><td>C<sub>2</sub>H<sub>6</sub></td><td>-</td><td>0.94</td></tr></tbody></table>

CPVT-wind, CPVT-biogas, wind-biogas, and stand-alone biogas were evaluated and compared. The system energy efficiency was expressed as follows<sup>89</sup>:

$$ \eta_{en,power} = \frac{\dot{W}_{net,power}}{\dot{Q}_{in,solar} + \dot{Q}_{in,WT} + \dot{Q}_{in,biogas}} \quad (11) $$

where $\dot{W}_{net,power}$ is the net output power (kW), $\dot{Q}_{in,solar}$ is the input solar energy rate (kW), $\dot{W}_{in,WT}$ is the input wind turbine power (kW), and $\dot{Q}_{in,biogas}$ is the input heat rate to the biogas system (kW), which can be calculated as follows<sup>89</sup>:

$$ \dot{Q}_{in,biogas} = \dot{m}_{biogas} \times \text{LHV} \quad (12) $$

where $\dot{m}_{biogas}$ is the mass flow rate of the biogas (kg/s) and LHV is the lower heating value (MJ).

The results of this study showed that systems with biogas integration were the most efficient. Energy efficiency up to 71.1% and 67.8% was obtained for CPVT/biogas integration and wind/biogas integration technologies,

respectively. In contrast, corresponding values of 69.9%, and 64.9% were achieved for the CPVT/wind integration and stand-alone biogas technologies, respectively.

Conventional steam Rankine power plants fueled by biomass are capable of producing power output less than 50 MW,<sup>90</sup> for which the electric efficiency is ranging between 15% and 35% depending on the installed capacity. At low operating temperatures (less than 300°C), ORC power plants can be used using biomass with efficiency less than 25% and power output capacity less than 2 MWe.<sup>91</sup>

Internal combustion engines and Stirling engines running by biogas produced from biomass gasification process are capable of producing about 100 kWe and 20 MWe, respectively.<sup>92</sup> Thermodynamic models are not enough to maximize the efficiency of power plants running by biofuels. Hence, to promote the biomass utilization efficiency in Rankine power plants, a supercritical Rankine power plant is implemented, where the steam is heated above its critical temperature and pressure, that is, 374°C and 22 MPa.

## 4 | EXERGY ANALYSIS OF BIOGAS-FUELED SYSTEMS

Exergy is introduced to determine the most possible available work which could be obtained through a process that is reversibly in mechanical, chemical, and thermal equilibrium with its surrounding at reference state of temperature, pressure, and chemical potential.<sup>93-95</sup>

The specific exergy with chemical composition change is defined as<sup>93,94</sup>:

$$ e_i = (h_i - h_o) - T_o (s_i - s_o) + i \sum x_i (\mu_i - \mu_{io}) \quad (13) $$
<table><caption>TABLE 4 Gaseous removal from biogas for different purposes<sup>71</sup></caption><thead><tr><th>Utilization</th><th>H<sub>2</sub>O</th><th>CO<sub>2</sub></th><th>H<sub>2</sub>S</th><th>Siloxane</th></tr></thead><tbody><tr><td>Vehicle fuel</td><td>Affirmative</td><td>Optional</td><td>Affirmative</td><td>Negative</td></tr><tr><td>CHP engine</td><td>No-condensation</td><td>Negative</td><td>&lt;500 ppm</td><td>Negative</td></tr></tbody></table>

<figure><img src="image_15.png" /><figcaption>FIGURE 9 Distribution of current technologies for biogas-upgrading methods around the world<sup>80</sup></figcaption></figure>

where *h* is the specific enthalpy (kJ/kg), *s* is the specific entropy (kJ/kg K), *T* is the temperature (K), *x* is the mole fraction, and *μ* is the chemical potential (kJ/kg). *T*<sub>o</sub> (K) and *p*<sub>o</sub> (kPa) are the reference environment conditions, respectively.

The useful work of a steady-state open system is<sup>93,94</sup>:

$$ \dot{W}_{\text{useful}} = \sum_{i} \dot{n}_{i} e_{i} + \sum_{j} \left( 1 - \frac{T_{o}}{T_{j}} \right) \dot{Q}_{j} - T_{o} \dot{S}_{\text{gen}} \quad (14) $$

where $\dot{Q}_i(\text{kW})$, $T_j(\text{K})$, $\dot{n}_i$ and $\dot{S}_{\text{gen}}(\text{kW/K})$ are the heat transfer rate, and the temperature at which heat is exchanged, molar flow rate, and rate of entropy generation, respectively.

The specific exergy is expressed as<sup>93,94</sup>:

$$ e_i = (h_i - h_o) - T_o (s_i - s_o) + e_{ch} \quad (15) $$

where the specific chemical exergy, $e_{ch}$, is<sup>93,94</sup>:

$$ e_{ch} = \sum_{i} (x_{i} e_{ch}^{o} + R T_{o} x_{i} \ln x_{i}) \quad (16) $$

where $e_{ch}^o$ (kJ/kg) is the standard chemical exergy for which the values are published in literature.<sup>93,94</sup>

Exergy efficiency, which is defined as the proportion of the produced power to the reversible power (maximum), can be written as<sup>93,94,96-99</sup>:

$$ \eta_{ex} = \frac{\dot{W}}{\dot{W}_{rev}} \quad (17) $$

Exergy analysis was used as an efficient thermodynamic technique to improve the performance of SOFC.<sup>100</sup> The exergy analysis has been presented on the SOFC system consisting of the evaporator, preheater, reformer, and afterburner. The results showed that a 73% improvement occurred in exergy efficiency for 600% theoretical air.<sup>100</sup>

The performance of SOFC using sugar cane bagasse as a source of biogas has been presented using exergy analysis.<sup>101</sup> The total exergy efficiency was 35% at a temperature of 1023 K and an air factor of 0.2. A detailed thermodynamic analysis has been conducted showing that a great proportion of the exergy destruction (lost work) was within the gasifier, which contributed to about 80% of the total exergy loss.<sup>101</sup> SOFC system has been investigated thermodynamically using exergy and economic analyses.<sup>102,103</sup>

SOFC has been integrated with steam-injected gas turbine and gasifier using woodchips as a biogas fuel source for the fuel cell.<sup>102,103</sup> The exergy efficiency of the combined plant was about 43%, which is much higher than that of conventional plants using biomass as fuel.<sup>102,103</sup> An anaerobic digester (AD) has been used to produce biogas for SOFC,<sup>103</sup> and the results showed the AD-SOFC system exergy efficiency was reduced with the growth in the current density. Moreover, the effects of SOFC operational conditions, for example, pressure, fuel consumption, and air stoichiometric ratio on the exergy efficiency, have been discussed.<sup>103</sup>

Exergy analysis of SOFC using different gaseous fuels produced from biomass gasification unit has been presented.<sup>104</sup> The SOFC was integrated with the internal reforming unit. Three gasifiers, namely, dual, circulating, and bubbling fluidized beds, have been used to produce syngas products<sup>104</sup> for the use in the SOFC, which was combined with the ORC and an absorption chiller. This integration system resulted in 50% exergy efficiency.

The performance of SOFC using biogas as fuel has been optimized using exergy analysis.<sup>85</sup> For this purpose, a simulation code THERMAS has been used to analyze the effects of temperature and fuel composition on the system performance. The system in question consisted of the preheater, SOFC, reformer, and burner. The results of the simulation indicated that low methane fuel was the ideal option from an exergy efficiency standpoint. The most important result obtained in the analysis<sup>85</sup> was that the temperatures of the fuel cell and the reformer should be the same and above 1000 K in optimal conditions.
<figure><img src="image_16.png" /><figcaption>TABLE 5 Typical energy quantities and efficiencies of three various biogas utilization systems<sup>84</sup></figcaption></figure>

<table><thead><tr><th>System</th><th>Net electricity output (MJe/day)</th><th>Net heat recovery (MJth/day)</th><th>Net electric efficiency (%)</th><th>Net heat efficiency (%)</th><th>Energy efficiency (%)</th></tr></thead><tbody><tr><td>Biogas-improvement</td><td>-</td><td>-</td><td>-</td><td>-</td><td>46.5</td></tr><tr><td>Biomethane-CHP plants</td><td>4139.8</td><td>5202.5</td><td>13.8</td><td>16.6</td><td>30.4</td></tr><tr><td>Biogas-SOFCs</td><td>5286.5</td><td>3530.6</td><td>20.4</td><td>12.5</td><td>32.9</td></tr></tbody></table>

<figure><img src="image_17.png" /></figure>

<figure><img src="image_18.png" /><figcaption>FIGURE 11 Thermal efficiency variations for different biogas compositions.<sup>86</sup> (A) Temperature effect at constant S/C = 1.6 and (B) S/C effect ratio at constant temperature of 1073 K</figcaption></figure>

A comparison between SOFC integrated with reformer and SOFC fed with upgraded biogas obtained from CO₂ separation membranes has been presented based on exergy analysis.<sup>105</sup> Exergy analysis of an integrated plant containing biomass gasification unit, gas expanders, SOFC, and Kalina cycle has been proposed.<sup>106</sup> In this

hybrid system, a carbon dioxide capture unit has been implemented. It has been stated that the use of exergy analysis to determine the exergy destruction of each subunit of the hybrid system was an effective tool to improve the system performance.<sup>106</sup> The effects of biomass moisture content and dry biomass mass flow rate have been
<figure><img src="image_19.png" /></figure>

<figure><img src="image_20.png" /><figcaption>FIGURE 12 Energy requirement for different biogas compositions.⁸⁶ (A) Temperature effect at constant S/C = 1.6. (B) S/C effect at constant temperature of 1073 K</figcaption></figure>

<table><caption>TABLE 6 Chemical reactions and thermodynamics properties at standard conditions (25°C and 100 kPa) for SOFCs using biogas</caption><thead><tr><th>Electrochemical reaction</th><th>Δs° (kJ/mole)</th><th>Δh°<sub>f</sub> (kJ/mole)</th><th>Δg°<sub>f</sub> (kJ/mole)</th><th>Chemical reaction</th></tr></thead><tbody><tr><td>CH<sub>4</sub> + CO<sub>2</sub> ↔ 2CO + 2H<sub>2</sub></td><td>256.542</td><td>247.023</td><td>170.535</td><td>MDR</td></tr><tr><td>CO<sub>2</sub> + H<sub>2</sub> ↔ CO + H<sub>2</sub>O</td><td>42.045</td><td>41.138</td><td>28.602</td><td>RWGS</td></tr><tr><td>CH<sub>4</sub> ↔ C + 2H<sub>2</sub></td><td>80.73</td><td>74.6</td><td>50.53</td><td>MP</td></tr><tr><td>H<sub>2</sub> + 0.5O<sub>2</sub> ↔ H<sub>2</sub>O</td><td>-44.42</td><td>-241.8</td><td>-228.6</td><td>HOR</td></tr><tr><td>CO + 0.5O<sub>2</sub> ↔ CO<sub>2</sub></td><td>-86.466</td><td>-283</td><td>-257.2</td><td>CMOR</td></tr><tr><td>CH<sub>4</sub> + CO<sub>2</sub> ↔ 2CO + 2H<sub>2</sub></td><td>214.5</td><td>205.885</td><td>142</td><td>MDR</td></tr><tr><td>CH<sub>4</sub> + H<sub>2</sub>O ↔ CO + 3H<sub>2</sub></td><td>172.45</td><td>164.075</td><td>113.33</td><td>MSR</td></tr><tr><td>CH<sub>4</sub> + 2H<sub>2</sub>O ↔ CO<sub>2</sub> + 4H<sub>2</sub></td><td>175.812</td><td>172.42</td><td>120</td><td>MFSR</td></tr><tr><td>C + CO<sub>2</sub> ↔ 2CO</td><td>133.767</td><td>131.3</td><td>91.4</td><td>CDCG</td></tr><tr><td>C + H<sub>2</sub>O ↔ CO + 2H<sub>2</sub></td><td>170.076</td><td>-35.94</td><td>-86.65</td><td>SCG</td></tr><tr><td>CH<sub>4</sub> + 0.5O<sub>2</sub> ↔ CO + 2H<sub>2</sub></td><td>-5.233</td><td>-802.557</td><td>-801</td><td>MPOX</td></tr><tr><td>CH<sub>4</sub> + 2O<sub>2</sub> ↔ CO<sub>2</sub> + 2H<sub>2</sub>O</td><td>89.346</td><td>-110.54</td><td>-137.18</td><td>MPOX</td></tr><tr><td>C + 0.5O<sub>2</sub> ↔ CO</td><td>340.631</td><td>329.3</td><td>227.739</td><td>COX</td></tr><tr><td>CH<sub>4</sub> + 3CO<sub>2</sub> ↔ 4CO + 2H<sub>2</sub>O</td><td>91.722</td><td>90.147</td><td>62.8</td><td>MFDR</td></tr><tr><td>C + 2H<sub>2</sub>O ↔ CO<sub>2</sub> + 2H<sub>2</sub></td><td>11</td><td>15.547</td><td>12.27</td><td>SFCG</td></tr><tr><td>2C + 2H<sub>2</sub>O ↔ CO<sub>2</sub> + CH<sub>4</sub></td><td>186.8</td><td>187.97</td><td>132.274</td><td>CFSM</td></tr></tbody></table>

Reaction abbreviations: COX = carbon oxidation, CFSM = carbon full steam methanation, CSM = carbon steam methanation analysis to ensure SOFC safe functioning, CDCG = carbon dioxide carbon gasification, CMOR = carbon monoxide oxidation reaction, HOR = hydrogen oxidation reaction, MP = methane pyrolysis, MFSR = methane full steam reforming, MSR = methane steam reforming, MPOX = methane full oxidation, MPOX = methane partial oxidation, MFDR = methane full dry reforming, MDR = methane dry reforming, SCG = steam carbon gasification, RWGS = reverse water-gas shift, SFCG = steam full carbon gasification.

discussed. The results indicated that the power efficiency of the integrated system increased as the moisture content decreased (less than 20%) and the biomass mass flow rate decreased below 20 kg/s. In another work,¹⁰⁷ it has been shown that the use of biomass containing 20% moisture content at 65 kg/s mass flow rate of biomass was needed to produce 120 kW electric power from SOFC integrated with a gasifier using orange peels with steam/air to produce the biofuel.

Based on the above-mentioned references, there are many electrochemical reactions taking place in SOFC and the systems integrated with SOFC.¹⁰⁸ Table 6 shows a list of some electrochemical reactions for SOFC operating with biogas as fuel.

Exergy analysis can help in finding the most efficient component in a system and what type of feed fuel to SOFC should be used. Moreover, the analysis gives clear guidance about what type of components should be integrated
with SOFC at operating temperature and pressure. CO₂ capture unit should be used as an integrated unit with SOFC to improve the overall exergy conversion efficiency. The exergy destruction decreases by reducing the temperature of the reformer; however, the exergy efficiency decreases at lower reformer temperature. Therefore, a balanced operating reformer temperature should be found.¹⁰⁹ The exergy destruction in SOFC is significantly high due to the release of heat within SOFC. To reduce this exergy destruction rate, it is recommended to employ this waste heat in a gas turbine to improve the exergy efficiency.¹¹⁰ One of the effective factors in causing exergy destruction in SOFC is the overpotential. Over potential of SOFC depends on the electrochemical reactions and their operating temperature as well as the material of electrolyte. The overpotential should be decreased to improve SOFC efficiency.¹¹¹ For example, the selection of optimum operating conditions was empirically found to be 900°C as operating temperature for SOFC, 45/55 CH₄/CO₂ as biogas feed composition, and higher than 25% as fuel utilization for tubular SOFC.¹¹²

Energy and exergy investigations were applied to reveal the best possible performance of a hybrid system made-up of ORC and ejector refrigeration cycle (ERC) powered by a diesel engine operating with biogas.⁹² The presented hybrid system was able to generate electrical power, heating, and cooling loads. In this study, the diesel engine was operating with different biogases to provide heat for the bottoming cycles by the aid of exhaust gases of the diesel engine. The biogas investigated in that study was sunflower biodiesel blend, B10 blend, and canola B30 blend. The results showed that the energy efficiency was the highest for canola B30 when the engine was running at full load and 2400 rpm, whereas the optimum exergy efficiency was achieved for full load operating conditions of the diesel engine at 1700 rpm using canola oil. Similarly, energy and exergy studies were employed to investigate the performance of supercritical steam power plants powered by biomass for combined heating and power, district heating, and space cooling.¹¹³ The heat produced from this power plant was used to provide heat for pulp and paper industry as well as the aluminum industrial process. The results presented that the exergy destruction was maximum for the combustion chamber and steam heat generation unit, which was about 67–80% and 13–16% of the total exergy destruction of the whole combined power plant, respectively. The findings also showed that the exergy efficiency combined heat and power was always greater than that of combined power, heat, and cooling in the aluminum industrial process for the identical capacity of heating potential of the regarded district.

The exergy efficiency of electricity production, CHP, and CCHP can be expressed, respectively, as¹¹³:

$$ \eta_{ex,e} = \frac{P_{e,net}}{\dot{E}_f} \qquad (18) $$

$$ \eta_{ex,CHP} = \frac{P_{e,net} + \dot{E}_h}{\dot{E}_f} \qquad (19) $$

$$ \eta_{ex,CCHP} = \frac{P_{e,net} + \dot{E}_h + \dot{E}_c}{\dot{E}_f} \qquad (20) $$

where $\dot{E}_h$ (kW) is the summation of exergy rates of the high- and low-pressure stream flows, $\dot{E}_c$ (kW) is the exergy rate of the cooling load produced in the absorption chiller, $\dot{E}_f$ (kW) is the fuel exergy rate, and $P_{e,net}$ (kW) is the net electrical power output.

Exergy analysis of an ORC using toluene as a working fluid, powered by the heat of the flue gases produced from biogas combustion, has been analyzed.¹¹⁴ The ORC in this study was implemented for electrical power and heat production. The results exposed that the exergy efficiency was maximum when the temperature of the biogas at the combustion chamber exit was 355°C at a pinch temperature difference of 10°C for the condenser and evaporator. The results also showed that increasing the heat source input temperature for the ORC resulted in a growth in the exergy efficiency, which could be explained by producing more useful work owing to the more efficient utilization of high-quality thermal energy. An exergy study has been applied to evaluate the performance of a geothermal-biogas hybrid system for producing electricity, cooling, heat, and freshwater.⁸⁸,¹¹⁵ The main outcome of these studies was the increase of exergy efficiency as a result of increasing the molar ratio of carbon or decreasing the molar ratio of CO₂/CH₄. Exergy analysis of a fluidized bed boiler used to provide the required heat for ethanol production plants has been investigated using biogas as fuel for the boiler.¹¹⁶ The obtained data indicated that the exergy efficiency of de-aerator, pump, soft water tank, evaporator, and heat exchanger was 66.3%, 61.4%, 54.4%, 46%, and 29%, respectively.

A multi-generation system consisting of biomass digester, open Brayton cycle, ORC, absorption chiller, heat recovery, and water separation plant has been analyzed using exergy analysis.²⁷ The multi-generation system was used to provide electricity, cooling load, heat, and freshwater. The findings exposed that the maximum exergy efficiency of the combined system was obtained as 30.4% and the highest exergy destruction was in the combustion chamber representing 65% of the total exergy destruction of the multi-generation system.
Three CH₄ compositions (93%, 84%, and 75% by volume) have been used in a dual-fuel mode for the CIE. The results presented that using the three compositions of biogas resulted in increasing the exergy destruction from 59.6% for diesel operation to 61.4%, 64.2%, and 64.6% for the three CH₄ compositions, respectively. Moreover, the results indicated that the exergy destruction rate of the combustion chamber decreased with increasing CO₂ concentrations in the biogas. The best biogas according to the results of this work was for methane composition of 93% with 26.9% exergy efficiency.¹¹⁷

## 5 | ECONOMIC ANALYSIS OF BIOGAS-FUELED SYSTEMS

It is must be admitted that the economic analysis is an inseparable topic in system performance investigation. Economic characteristics are measured through the connection between biogas production, purchased electrical power, and selling of an additional amount of biogas.¹¹⁸ If the produced biogas becomes inadequate to address the needs for energy in the farm, excess power can be obtained (at around 10 cents/kWh).¹¹⁹ If the amount of produced biogas becomes higher than the considered demand, two scenarios will happen. First, based on the local situations, generated power can be sold to the electrical grid (slightly more than 8 cents/kWh). In another case, the extra amount can be com-busted, so that the corresponding GWP (global warming potential) will be 21 times lesser in comparison with methane.¹²⁰ Typically, the rate of tariff for biogas as an alternative energy resource is around 0.13 €/kW.¹²¹

With the intention of the economic assessment, different strategies can be considered. One of the most popular approaches is net profit estimation by summing the whole revenues and expenditures for the considered system.¹²² Consequently, production, operating, and maintenance expenses for the treatment procedures would be included. Furthermore, the cost of fuel and obtained profits from the finalized products are involved in the economic assessment. In the case that a novel treatment technique brings an organic by-product, then capital expenditures for this route must be included.¹²³ Solid remainders from AD would be utilized as fertilizer, comparable with manure, while it has a similar content of useful nutrients. This causes extra profits by diminishing the application of chemical fertilizers in farms, dropping nutrient waste, and avoiding methane productions. In this case, the profitability will be soared dramatically.¹²⁴

Biogas production capital cost consists of entire expenses involving the construction and equipment of AD. The plant provision, construction resources, and biogas

equipment are involved in the investment cost. The labor impression is through the wages and stated as USD per unit volume of produced biogas during the system lifetime. Commonly the lesser value of the labor charges per each unit of volume for produced biogas will result in more improvements for the biogas plant.¹²⁵ The investment cost of household-scaled digester varies based on the model, resources accessibility, size, and site. The investment costs of tubular models in Latin America vary between 100 and 700 USD. In specific countries, like Bolivia, Costa Rica, and Nicaragua, low-density polyethylene is mostly utilized for the plastic bag, allowing investment costs between 100 and 200 USD (eliminating labor charges).¹²⁶

Gozan et al.¹²⁷ accomplished a techno-economic analysis of a biogas production plant using palm oil. The results revealed that the payback period was 6.6 years and the cost of electricity production was 0.06 USD per kWh. Boldrin et al.¹²⁸ evaluated an independent biogas plant in terms of energy, emissions, and economic, where the viability was an influential parameter in economic aspects. Based on the results, the associated size of the plant was not an important factor for environmental and energy evaluation. On the contrary, it was a key parameter for economic analysis. Scarlat et al.¹²⁹ investigated the economic viability of AD plants by considering local detailed factors. Stürmer et al.¹³⁰ investigated the impacts of the technical parameters in the biogas plant performance on the end-product cost. The associated costs with the substrate were primarily influenced by the types of equipment in cultivation, harvesting, and transportation in addition to land accessibility. Riva et al.¹³¹ compared the economic aspects of three scenarios for biogas production fed by energy crops, manure, agro-industrial, and organic fraction of municipal solid wastes (OFMSW). OFMSW brought a high cost in the management and maintenance section (around 0.155 € per each m³ of biogas), while EC (energy crops) revealed a high range of charges for feedstock supply (0.130 € per each m³ of biogas). Walla and Schneeberger¹³² studied the most optimum size for biogas plants based on their energy and economic restrictions. The results indicated that by increasing the electricity production by 1000 kWh, the long-run average cost fell steadily as shown in Figure 13. Moreover, the associated costs with the biogas and electricity production were included while the transportation cost was excluded.

Díaz-Trujillo et al.¹³³ optimized a biogas production chain in terms of environment and economics. By considering the discount rate as 10% and while the project lifetime was 10 years, the economic and environmental parameters used by the optimization model were provided. Based on this work, increasing GHG savings would result in a drop of the profits gradually as can be seen from Figures 14 and 15. In a comparative study, Lask et al.¹³⁴
explored the economic life cycle calculation of biogas production from perennial wild plant mixtures and maize. Economic analysis of 1 kWh power generation was considered, by the used of biogas produced from three diverse systems: maize, stand-alone wild plant mixture cultivation (WPM E1), and a mixture of maize undersown with biennial and perennial wild plant species (WPM E2).

The economic study initiates with summing the investment charges and operating and maintenance costs, which is essential to achieve biogas production. Further and even more interesting in economic analysis is related to the related parameters such as net present value, profitability index, internal rate of return, and levelized cost of electricity.¹³⁵ In this case, Net Present Value (NPV) can be calculated as:

$$NPV = \sum_{t=0}^{n} \frac{B_t - C_t}{(1+r)^t} \quad (21)$$

<figure><img src="image_21.png" /><figcaption>FIGURE 13 Cumulative cost for power and biogas production¹³²</figcaption></figure>

where B is the revenue per year, C is the outgoings per year, and r is the real interest rate. Moreover, the Internal Rate of Return (IRR) can be estimated as:

$$0 = \sum_{t=0}^{n} \frac{B_t - C_t}{(1+IRR)^t} \quad (22)$$

For calculating the Profitability Index (PI), Equation (23) has been presented:

$$PI = \frac{\sum PV_{Proceeds}}{PV_{Initiate}} \quad (23)$$

$$LCOE = \frac{\sum_{t=0}^{n} \frac{C_t - M_t}{\left(1 + \frac{r}{100}\right)^t}}{\sum_{t=0}^{n} \frac{E_t}{\left(1 + \frac{r}{100}\right)^t}} \quad (24)$$

where C_t is the capital cost in year t (USD), M_t stands for the operating and maintenance cost (USD/year), r is the discount rate, and E_t is the electricity power demand (kWh/year).

Another parameter of an investment cost of the project performance calculation is the Life-cycle net present value (LCNPV), which will be estimated based on the cashflows in a specified period in consideration of the environmental concerns. The LCNPV assessment is studied in a typical method; however, the cash flow contains entire defined environmental charges and benefits.¹³⁶ LCNPV is defined as:

$$LCNPV = \sum_{t=1}^{n} \frac{CF_t}{1+r^t} \quad (25)$$

where CF_t is the cash flow for tth year, and n stands for the number of years for which cycle lifetime is considered.

<figure><img src="image_22.png" /><figcaption>FIGURE 14 Pareto frontier for the profit by considering the greenhouse gas emission saving¹³³</figcaption></figure>
<figure><img src="image_23.png" /><figcaption>FIGURE 15 Energy cost of biogas plant with different resources for Maize, WPM E1, and WPM E2<sup>134</sup></figcaption></figure>

To analyze the economic parameters, consideration of the investment and associated operating and maintenance costs is necessary.

The model of income is established on the motivation structure. The configuration of costs is separated into capital investment, operating and maintenance expenses, and devaluation for mechanical and electrical tools. This structure varies each year by the influence of the inflation rate.137 The investment cost and the generic variable cost are expressed as, respectively:

$$C_{inv}^{1s} = C_{inv}^{u,1s} \times S_{biogas} \quad (26)$$

$$C_{gv,t+1} = C_{gv,t} \times (1 + \inf) \quad (27)$$

where $C_{inv}^{1s}$ is the investment cost, $C_{inv}^{u,1s}$ is the unitary investment cost, $S_{biogas}$ is the size of the biogas plant, $C_{gv}$ is the generic variable cost, and $\inf$ is the rate of inflation.

## 6 | ENVIRONMENTAL ANALYSIS

Biogas represents an important source of renewable energy as mentioned before, it helps in waste management and W-to-E (waste to energy) conversion, which allows utilizing huge amounts of wastes instead of disposal or landfill procedures. However, the handling of biogas from production to utilization has an impact on the environment. An environmental impact assessment study must be conducted for which many parameters such as air emissions, industrial process wastewater, hazardous materials, and noise should be considered.138 The environmental impact assessment is done in all stages of any biogas project that starts from the planning phase to the production phase and ends with the safe disposal of hazardous wastes

produced.139 Table 7 shows the steps in environmental impact assessment. For short-run biogas plants, a rehabilitation phase must be involved.

Air emissions include greenhouse gases such as carbon dioxide and nitrous oxides, and particulate matters (ie, dust from solid biomaterials are also one major air pollution from biogas plants). N₂O emissions from biogas production cause a significant contribution to global warming.140 The total greenhouse gases emission from energy production from biogas are calculated within the range of 0.10 and 0.40 kg CO₂/kWh.14,141,142

The NOx emission for biogas is more than for natural gas engines: The averaged emission factor is 540 g NOx/GJ,143 which is more than three times the rate of natural gas engines. When the emission factor is reported to methane consumption, an emission factor of 0.63 g NOx/Nm³ CH₄ can be assumed for flaring.144

A previous work145 estimated a significant control improvement of 10% of NOx emission in 2020 in California (USA); however, the study included biogas and biomass combustion. It is important to mention that the type of raw material affects the nature and amount of air pollutants from the biogas industry.146 CO₂, NOx, CO, hydrocarbons, and particles can differ by a factor of 4 among ley crops, straw, sugar beet, liquid manure, wastes from the food industry, and municipal waste. On the other hand, differences by a factor of up to 11 can be observed in SO₂ emissions, as a result of the high variability of H₂S in the biogas products.14

The use of scrubbing units produces a huge amount of wastewater which may leak from storage containers.147 Hazardous materials involved in the production and treatment of biogas such as acids need special handling, storing, and disposal procedures. The perfectly sealed storage of the gas is highly recommended, as the greenhouse gases and ammonia fugitive emissions are even more important than
<table><caption>TABLE 7 Environmental impact assessment (EIA) for biogas plant¹³⁸</caption><thead><tr><th>Stage</th><th>Negative impacts</th><th>Positive impacts</th><th>Mitigation measures</th></tr></thead><tbody><tr><td>Construction</td><td><ol><li>Disruption of fauna and Flora</li><li>Wildlife will flee because of noise</li><li>Disruption of the ecosystem by tree cutting and brush clearing</li><li>Dust emissions during Construction</li><li>High levels of noise during construction</li><li>Exerts pressure on the available land</li></ol></td><td><ol><li>Construction of access Roads (infrastructure)</li><li>Creation of settlement Area</li><li>Development of area due to structural buildings like clinics, shops, and schools as well as dams</li><li>Migration of people to seek for work</li></ol></td><td><ol><li>Selective clearing of Areas</li><li>Isolation of the area being constructed</li><li>Using dampening effect instruments to minimize vibration which will affect the wildlife</li><li>Personnel working should wear protective clothing like ear muffs</li></ol></td></tr><tr><td>Operation</td><td><ol><li>High level of noise crushing equipment</li><li>Air quality is affected because of dust</li><li>Rapture of machinery in particular fluidized bed separator</li></ol></td><td><ol><li>Employment creation</li><li>Continual development of the area</li><li>No production of tailings, thus minimal/no pollution to the rivers</li></ol></td><td><ol><li>Provision of earmuffs</li><li>Use of bag filters to minimize emissions into the air</li><li>Stringent control on the equipment with safety trips and alarms</li></ol></td></tr><tr><td>Decommissioning</td><td><ol><li>Idle buildings</li><li>The inability of the land to be rehabilitated</li></ol></td><td><ol><li>Equipment can be sold to give salvage money</li><li>The buildings can be sold or leased for the same purpose of mining or another line of work</li></ol></td><td><ol><li>Continuous rehabilitation by backfilling of the gangue to the mined areas since the gangue is chemically inert (no chemical usage in the process)</li></ol></td></tr></tbody></table>

<figure><img src="image_24.png" /><figcaption>FIGURE 16 Illustration of comparative emission potential of biogas plants for NOx and CO¹⁵¹</figcaption></figure>

those coming from fertilizers.¹⁴⁸ Thus, avoiding leakage and using very well-sealed containers are ways to minimize significantly the global warming impact of biogas plants.¹⁴⁹

The use of machines in production plants such as tur-bomachines and conveyors belts causes noise pollution that has a direct effect on the environment, human health,

and sustainability.¹⁵⁰ The gas emissions from biogas plants are shown in Figure 16 (for NOₓ and CO).¹⁵¹

All of the above-mentioned considerations require the presence of special units such as air filters, wastewater treatment plants, personal protection equipment, and chemical treatment units.
Another environmental matter related to biogas production is the slurry produced during the treatment phase. This slurry can be used as fertilizer; however, the uncontrolled or un-careful procedure to produce it can cause surface water and soil pollution.¹⁵² The underground water as well can be polluted as a result of leachate that can diffuse through the soil to reach deep water. It should be mentioned that the properties of slurry change during the fermentation process. The concentration of ammonium nitrogen increases. This slurry is also the source of unpleasant odor being caused by the presence of many gases such as methane, hydrogen sulfide, and ammonia (although, after fermentation, the slurry is less malodorous than undigested manure). These problems can be solved by a controlled and well-planned fermentation process.¹⁴

The location of biogas plants should be selected carefully so as not to affect the nearby residencies. The location of the plant should be suitable for feedstock transportation. Transportation of raw materials to the plant and transportation of possible wastes from plant to disposal site must be considered. A procedure and instructions for waste transportation, waste packaging, and labeling must be ready for safe handling of such wastes. A manifest system is highly recommended and inventories for raw materials and wastes must be prepared.

## 7 | CONCLUSION

One of the most promising methods is the utilization of biogas. The biogas industry capacity increased by over 90% between 2010 and 2018. This is due to its energy quality, cheapness in production and operation, availability, ease of being stored, and lower GHG emissions by 60–80% than gasoline.

Nowadays, the majority of the applications is in generating electricity (by using internal combustion engines, gas turbine, micro-gas turbines or on-site turbines), generating heat (by using boilers as in farms/agricultural application), and generating a combination between these two, that is, CHP, to maximize the benefit of the biogas. Based on the anaerobic digestion, the biogas efficiency in generating electricity, heat, and CHP are 8–54%, 16–83%, and 18–90%, respectively. Although this work is mainly considering the use of biogas in electricity generation, it shows other applications for biogas include transportation (used as vehicle fuel), refrigeration, and cooling power plants. Moreover, biogas is a valuable feedstock to produce hydrogen, which can be employed to generate energy, electric power, and fuel for fuel cells.

This work represents the updated methods to produce biogas and electricity production from biogas. This

will open the door for others to work on other methods of improvement. For example, biogas can be improved by converting it to biomethane which is used in heating, powering a generator, or compressed natural gas.

The biogas is mixed with other fuels to improve biogas process efficiency and to reduce the released gases from the fuel, for example, mixing biogas with diesel or biodiesel reduces the emissions of burning diesel fuel, while it reduces the heat disposal and back burning of biogas, and the ignition issue associated with the biogas. Several mixtures/systems were proposed in literature including diesel-biogas, biodiesel-biogas, biogas-green plant, biogas-natural gas, MCFC-MGT (molten carbonate fuel cell and micro gas turbine)-biogas, SOFC (solid oxide fuel cell)-methane-hydrogen, AD (Anaerobic digestion)-SOFC, AD-SOFC-ORC, SOFC-injected gas turbine and gasifier, and biogas-SOFC-MGT.

The exergy destruction rate in an energy conversion operation is significantly high, with the greatest exergy destruction rate occurring in the combustion chamber followed by the gasifier and the steam generator. Several studies have been accomplished to improve biogas system energy and exergy efficiencies. These outcomes were achieved by removing biogas pollutants, combining the biogas with other sources, especially renewable energy ones (eg, solar-biogas, geothermal-biogas, wind-biogas, CHP, CCHP, and concentrated photovoltaic-biogas), and reusing waste energy for other tasks (eg, employing the waste heat from a gas turbine).

Biogas as an alternative fuel supports the sustainability of modern cities. Modern cities are crowded and transportation is used heavily. This work focused on showing the reduction in greenhouse and toxic gases reduction incorporated with the use of biogas as a fuel or in producing alternative fuels. This will encourage the research to improve the processes of producing such fuel and encourage the governments to adopt policies to depend more on renewable energy resources, mainly in big cities where the electricity consumption is high with a big demand for power sources.

This work presents an introduction on how to manage projects of storing, treating, processing, and safe disposal from its wastes. Moreover, steps of environmental impact assessments are shown and environmental pollution that might be solutions for them have been presented. Examples from the world on how policies relevant to biogas management can improve the social, economic, and environmental situation provided a comprehensive perspective. The triple bottom line of sustainability can be satisfied by just applying laws to support the biogas management and handling from the real case studies from countries such as Sweden and Germany.
## NOMENCLATURE

* B: Revenue per year (USD)

* C: Outgoings per year (USD)

* CF: Cash flow (USD)

* C<sub>in</sub>: Methane concentration in input biogas (-)

* C<sub>inv</sub><sup>1s</sup>: Investment cost (USD)

* C<sub>inv</sub><sup>u,1s</sup>: unitary investment cost (USD/m²)

* C<sub>gy</sub>: generic variable cost (USD)

* C<sub>out</sub>: Methane concentration in produced gas (-)

* c<sub>p,i</sub>: Heat capacity of ith flow (kJ/mol K)

* C<sub>t</sub>: Capital cost (USD)

* E<sub>Cold</sub>: Produced cold water energy (kWh)

* E<sub>El</sub>: Electrical energy produced (kWh)

* E<sub>HotWater</sub>: Produced hot water energy (kWh)

* E<sub>in,e</sub>: Required electrical energy of driving machines in the process (MWh)

* e<sub>ch</sub>: Specific chemical exergy (kJ/kg)

* e<sub>i</sub>: Specific inlet exergy (kJ/kg)

* E<sub>c</sub>: Exergy rate of cooling load produced in absorption chiller (kW)

* E<sub>h</sub>: Summation of exergy rates of the high- and low-pressure steam flows (kW)

* E<sub>f</sub>: Fuel exergy rate (kW)

* E<sub>t</sub>: Electricity power demand (kWh/year)

* E<sub>theor</sub>: Theoretical energy consumption (MWh)

* Inf: Rate of inflation (%)

* h: Specific enthalpy (kJ/kg)

* H<sub>CO<sub>2</sub></sub>: Henry constant of CO<sub>2</sub>

* H<sub>CH<sub>4</sub></sub>: Henry constant of CH<sub>4</sub>

* ΔH<sub>L</sub>: Latent heat of steam in the feed (kJ/mol)

* h<sup>in</sup><sub>T,i</sub>: Molar enthalpy of ith component in the inlet stream with temperature T (kJ/mol)

* h<sup>out</sup><sub>T,i</sub>: Molar enthalpy of ith component in the outlet stream with temperature T (kJ/mol)

* h<sup>in</sup><sub>T</sub>: Total molar enthalpy of inlet stream at temperature T (kJ/mol)

* h<sup>out</sup><sub>T</sub>: Total molar enthalpy of outlet stream at temperature T (kJ/mol)

* h<sub>298,i</sub>: Molar enthalpy of ith component at a temperature of 298 K (kJ/mol)

* LHV: Lower heating value (kJ/kg)

* LHV<sub>CH<sub>4</sub></sub>: Lower heating value of methane (kJ/mol)

* LHV<sub>CO</sub>: Lower heating value of carbon monoxide (kJ/mol)

* LHV<sub>H<sub>2</sub></sub>: Lower heating value of H<sub>2</sub> (kJ/mol)

* MRR: Methane recovery ratio

* m<sub>biogas</sub>: Mass flow rate of biogas (kg/s)

* M<sub>t</sub>: operating and maintenance cost (USD/year)

* n: Number of years (years)

* n<sup>in</sup><sub>CH<sub>4</sub></sub>: Moles of methane in inlet stream (mol)

* n<sup>out</sup><sub>CO</sub>: Moles of carbon monoxide in outlet stream (mol)

* n<sup>out</sup><sub>H<sub>2</sub></sub>: Moles of hydrogen in outlet stream (mol)

* n<sup>in</sup><sub>i</sub>: Moles of component i in inlet stream (mol)

* n<sup>out</sup><sub>i</sub>: Moles of component i in outlet stream (mol)

* n<sup>in</sup><sub>Steam</sub>: Moles of steam in inlet stream (mol)

* P<sub>e,net</sub>: Net electrical power output (kW)

* P<sub>o</sub>: Reference pressure (kPa)

* r: Real interest rate (%)

* S<sub>biogas</sub>: Size of the biogas plant (m²)

* Q̇<sub>i</sub>: Inlet heat rate (kW)

* Q̇<sub>in,biogas</sub>: Input heat rate by the biogas system (kW)

* Q<sub>in,f</sub>: Input feed gas energy (MWh)

* Q<sub>in,u</sub>: Input heat required for the solvent regeneration (MWh)

* Q̇<sub>in,solar</sub>: Input solar energy rate (kW)

* Q<sub>out,p</sub>: Produced gas energy (MWh)

* Q<sub>R</sub>: Net change in total enthalpies (kJ/mol)

* R: Characteristic gas constant (kJ/kg K)

* s: Specific entropy (kJ/kgK)

* S<sub>i</sub>: Solvent selectivity (-)

* Ṡ<sub>gen</sub>: Rate of entropy generation (kW/K)

* SEC: Specific energy consumption (kWh/m³)

* t: Year

* T<sub>o</sub>: Standard temperature (K)

* TEC: Total energy consumption rate (kW)

* v<sub>in</sub>: Volumetric flow rate of input biogas (m³/h)

* v<sub>out</sub>: Volumetric flow rate of output product gas (m³/h)

* Ẇ<sub>rev</sub>: Reversible power (kW)

* Ẇ<sub>useful</sub>: Useful work rate (kW)

* Ẇ<sub>in,WT</sub>: Input wind turbine power (kW)

* x: Mole fraction

## Greek letters

* σ: Conversion efficiency of steam to electricity (-)

* η: Energy efficiency (-)

* η<sub>thermal</sub>: Thermal efficiency (-)

* η<sub>biogas</sub>: Energy efficiency of biogas system (-)

* η<sub>en.power</sub>: Energy efficiency of power production system (-)

* η<sub>ex</sub>: Exergy efficiency (-)

* η<sub>ex,CCHP</sub>: Exergy efficiency of combined cooling and heat and power system (-)

* η<sub>ex,CHP</sub>: Exergy efficiency of combined heat and power system (-)

* η<sub>ex,e</sub>: Exergy efficiency of electricity production (-)

* μ: Chemical potential (kJ/kg)

## ORCID

Abolfazl Ahmadi https://orcid.

org/0000-0003-2652-6011

Mehdi A. Ehyaei https://orcid.

org/0000-0002-4721-9427

Farbod Esmaeilion https://orcid.

org/0000-0001-9674-2153
REFERENCES

1. Capuano L. *International Energy Outlook 2018 (IEO2018)*. Vol. 2018. US Energy Information Administration (EIA); 2018:21.

2. Ghasemian E, Ehyaei M. Evaluation and optimization of organic Rankine cycle (ORC) with algorithms NSGA-II, MOPSO, and MOEA for eight coolant fluids. *Int J Energy Environ Eng.* 2018;9:39-57.

3. Lin B, Ouyang X. Energy demand in China: comparison of characteristics between the US and China in rapid urbanization stage. *Energy Convers Manage.* 2014;79:128-139.

4. Kumar A, Said Z, Bellos E. An up-to-date review on evacuated tube solar collectors. *J Therm Anal Calorim.* 2021;145(6):2873-2889.

5. Ahmadi A, Ehyaei M, Jamali D, et al. Energy, exergy, and economic analyses of integration of heliostat solar receiver to gas and air bottom cycles. *J Clean Prod.* 2021;280:124322.

6. Ehyaei M, Rosen MA. Optimization of a triple cycle based on a solid oxide fuel cell and gas and steam cycles with a multi-objective genetic algorithm and energy, exergy and economic analyses. *Energy Convers Manage.* 2019;180:689-708.

7. Noorpoor A, Hamedi Jamali D, Hashemian N. Optimization of parabolic trough solar collectors integrated with two stage Rankine cycle. *J Solar Energy Res.* 2017;2:61-66.

8. Esmaeilion F. Hybrid renewable energy systems for desalination. *Appl Water Sci.* 2020;10:1-47.

9. Makkeh SA, Ahmadi A, Esmaeilion F, Ehyaei M. Energy, exergy and exergoeconomic optimization of a cogeneration system integrated with parabolic trough collector-wind turbine with desalination. *J Clean Prod.* 2020;273:123122.

10. Arshad M, Bano I, Khan N, et al. Electricity generation from biogas of poultry waste: an assessment of potential and feasibility in Pakistan. *Renew Sustain Energy Rev.* 2018;81:1241-1246.

11. Strantzali E, Aravossis K, Livanos GA. Evaluation of future sustainable electricity generation alternatives: the case of a Greek island. *Renew Sustain Energy Rev.* 2017;76:775-787.

12. R. REN21. "Global Status Report, REN21 Secretariat, Paris," *France*. Tech. Rep; 2018.

13. Ardebili SMS. Green electricity generation potential from biogas produced by anaerobic digestion of farm animal waste and agriculture residues in Iran. *Renewable Energy*. 2020;154:29-37.

14. Abanades S, Abbaspour H, Ahmadi A, et al. A critical review of biogas production and usage with legislations framework across the globe. *Int J Environ Sci Technol.* 2021;1-24. doi:10.1007/s13762-021-03301-6

15. Ishikawa S, Hoshiba S, Hinata T, Hishinuma T, Morita S. Evaluation of a biogas plant from life cycle assessment (LCA). *Int Congr Ser.* 2006;1293:230-233.

16. Esteves EMM, Herrera AMN, Esteves VPP, Morgado CDRV. Life cycle assessment of manure biogas production: a review. *J Clean Prod.* 2019;219:411-423.

17. Salvador R, Barros MV, Rosário JGDPD, Piekarski CM, da Luz LM, de Francisco AC. Life cycle assessment of electricity from biogas: a systematic literature review. *Environ Prog Sustain Energy.* 2019;38:13133.

18. Ayodele T, Ogunjuyigbe A, Alao M. Economic and environmental assessment of electricity generation using biogas from organic fraction of municipal solid waste for the city of Ibadan, Nigeria. *J Clean Prod.* 2018;203:718-735.

19. S. UNEP. *Towards a Life Cycle Sustainability Assessment. Making Informed Choices on Products*. UNEP and SETAC; 2011.

20. Ruiz D, San Miguel G, Corona B, Gaitero A, Domínguez A. Environmental and economic analysis of power generation in a thermophilic biogas plant. *Sci Total Environ.* 2018;633:1418-1428.

21. San Miguel G, Corona B, Ruiz D, et al. Environmental, energy and economic analysis of a biomass supply chain based on a poplar short rotation coppice in Spain. *J Clean Prod.* 2015;94:93-101.

22. ter Veld F. Beyond the fossil fuel era: on the feasibility of sustainable electricity generation using biogas from microalgae. *Energy Fuels.* 2012;26:3882-3890.

23. Jaye I, Sadhukhan J, Murphy R. Integrated assessment of palm oil mill residues to sustainable electricity system (POMR-SES): a case study from Peninsular Malaysia. *IOP Conf Ser: Mater Sci Eng.* 2018;358:012002.

24. Esmaeilion F, Ahmadi A, Hoseinzadeh S, Aliehyaei M, Makkeh SA, Astiaso Garcia D. Renewable energy desalination; a sustainable approach for water scarcity in arid lands. *Int J Sustain Eng.* 2021;1-27. doi:10.1080/19397038.2021.1948143

25. Wilfert R, Schattauer A. *Ecological Analysis,* "Biogas Utilization from Liquid Manure, Organic Waste and Cultivated Biomass – A Technical, Ecological and Economic Analysis*. Institute for Energy and Environment, Deutsche Bundesstifung Umwelt (DBU); 2004.

26. Pöschl M, Ward S, Owende P. Evaluation of energy efficiency of various biogas production and utilization pathways. *Appl Energy.* 2010;87:3305-3321.

27. Sevinchan E, Dincer I, Lang H. Energy and exergy analyses of a biogas driven multigenerational system. *Energy.* 2019;166:715-723.

28. Hoyer K, Hulteberg C, Svensson M, Jernberg J, Nörregård Ö. *Biogas Upgrading-Technical Review*. Lund University Publications; 2016.

29. Gustafsson M, Cruz I, Svensson N, Karlsson M. Scenarios for upgrading and distribution of compressed and liquefied biogas—energy, environmental, and economic analysis. *J Clean Prod.* 2020;256:120473.

30. Rahman MM, Hasan MM, Paatero JV, Lahdelma R. Hybrid application of biogas and solar resources to fulfill household energy needs: a potentially viable option in rural areas of developing countries. *Renewable Energy.* 2014;68:35-45.

31. Arthurson V. Closing the global energy and nutrient cycles through application of biogas residue to agricultural land—potential benefits and drawback. *Energies.* 2009;2:226-242.

32. Ray N, Mohanty M, Mohanty R. A Study on application of biogas as fuel in compression ignition engines. *Int J Innov Eng Technol (IJIET).* 2013;3:239-245.

33. Ahmadi A, Jamali D, Ehyaei M, Assad MEH. Energy, exergy, economic and exergoenvironmental analyses of gas and air bottoming cycles for production of electricity and hydrogen with gas reformer. *J Clean Prod.* 2020;259:120915.

34. Jamali DH, Noorpoor A. Optimization of a novel solar-based multi-generation system for waste heat recovery in a cement plant. *J Clean Prod.* 2019;240:117825.

35. Ahmadi A, Esmaeilion F, Esmaeilion A, Ehyaei MA, Silveira J. Benefits and limitations of waste-to-energy conversion in Iran. *Renew Energy Res Appl.* 2020;1:27-45.
<figure><img src="image_25.png" /></figure>

36. Rajaei G, Atabi F, Ehyaei M. Feasibility of using biogas in a micro turbine for supplying heating, cooling and electricity for a small rural building. *Adv Energy Res.* 2017;5:129.

37. Brown D, Shi J, Li Y. Comparison of solid-state to liquid anaerobic digestion of lignocellulosic feedstocks for biogas production. *Biores Technol.* 2012;124:379-386.

38. Abelleira-Pereira JM, Pérez-Elvira SI, Sánchez-Oneto J, de la Cruz R, Portela JR, Nebot E. Enhancement of methane production in mesophilic anaerobic digestion of secondary sewage sludge by advanced thermal hydrolysis pretreatment. *Water Res.* 2015;71:330-340.

39. Montalvo S, Guerrero L, Borja R, et al. Application of natural zeolites in anaerobic digestion processes: a review. *Appl Clay Sci.* 2012;58:125-133.

40. Carlsson M, Lagerkvist A, Morgan-Sagastume F. The effects of substrate pre-treatment on anaerobic digestion systems: a review. *Waste Manage (Oxford)*. 2012;32:1634-1650.

41. Niesner J, Jecha D, Stehlík P. Biogas upgrading technologies: state of art review in European region. *Chem Eng Trans.* 2013;35:517-522.

42. Biernat K, Gis W, Samson-Bręk I. Review of technology for cleaning biogas to natural gas quality. *Silniki Spalinowe.* 2012;51:33-39.

43. Abatzoglou N, Boivin S. A review of biogas purification processes. *Biofuels Bioprod Biorefin.* 2009;3:42-71.

44. Kapdi S, Vijay V, Rajesh S, Prasad R. Biogas scrubbing, compression and storage: perspective and prospectus in Indian context. *Renewable Energy*. 2005;30:1195-1202.

45. Rasi S, Veijanen A, Rintala J. Trace compounds of biogas from different biogas production plants. *Energy*. 2007;32:1375-1380.

46. Korres N, O'Kiely P, Benzie JA, West JS. *Bioenergy Production by Anaerobic Digestion: Using Agricultural Biomass and Organic Wastes*. Routledge; 2018.

47. Quaschning VV. *Renewable Energy and Climate Change*. John Wiley & Sons; 2019.

48. Hakawati R, Smyth BM, McCullough G, De Rosa F, Rooney D. What is the most energy efficient route for biogas utilization: heat, electricity or transport? *Appl Energy.* 2017;206:1076-1087.

49. Barzegaravval H, Hosseini SE, Wahid MA, Saat A. Effects of fuel composition on the economic performance of biogas-based power generation systems. *Appl Therm Eng.* 2018;128:1543-1554.

50. Goulding D, Power N. Which is the preferable biogas utilisation technology for anaerobic digestion of agricultural crops in Ireland: biogas to CHP or biomethane as a transport fuel? *Renewable Energy.* 2013;53:121-131.

51. Wu X, Chen G, Wu X, et al. Renewability and sustainability of biogas system: cosmic exergy based assessment for a case in China. *Renew Sustain Energy Rev.* 2015;51:1509-1524.

52. Kang JY, Kim TS, Hur KB. Economic evaluation of biogas and natural gas co-firing in gas turbine combined heat and power systems. *Appl Therm Eng.* 2014;70:723-731.

53. Kim S, Sung T, Kim KC. Thermodynamic performance analysis of a biogas-fuelled micro-gas turbine with a bottoming organic Rankine cycle for sewage sludge and food waste treatment plants. *Energies.* 2017;10(3):275.

54. Sung T, Kim S, Kim KC. Thermoeconomic analysis of a biogas-fueled micro-gas turbine with a bottoming organic Rankine cycle for a sewage sludge and food waste treatment plant in the Republic of Korea. *Appl Therm Eng.* 2017;127:963-974.

55. Kang JY, Kim TS, Hur KB. Comparative economic analysis of gas turbine-based power generation and combined heat and power systems using biogas fuel. *Energy*. 2014;67:309-318.

56. Saadabadi SA, Thattai AT, Fan L, Lindeboom RE, Spanjers H, Aravind P. Solid oxide fuel cells fuelled with biogas: potential and constraints. *Renewable Energy*. 2019;134:194-214.

57. Trendewicz A, Braun R. Techno-economic analysis of solid oxide fuel cell-based combined heat and power systems for biogas utilization at wastewater treatment facilities. *J Power Sources*. 2013;233:380-393.

58. Papadias DD, Ahmed S, Kumar R. Fuel quality issues with biogas energy—an economic analysis for a stationary fuel cell system. *Energy*. 2012;44:257-277.

59. Wu B, Zhang X, Shang D, Bao D, Zhang S, Zheng T. Energetic-environmental-economic assessment of the biogas system with three utilization pathways: combined heat and power, biomethane and fuel cell. *Biores Technol.* 2016;214:722-728.

60. Wongchanapai S, Iwai H, Saito M, Yoshida H. Performance evaluation of a direct-biogas solid oxide fuel cell-micro gas turbine (SOFC-MGT) hybrid combined heat and power (CHP) system. *J Power Sources*. 2013;223:9-17.

61. Huang H, Li J, He Z, Zeng T, Kobayashi N, Kubota M. Performance analysis of a MCFC/MGT hybrid power system bi-fueled by city gas and biogas. *Energies*. 2015;8:5661-5677.

62. Cigolotti V, Massi E, Moreno A, Polettini A, Reale F. Biofuels as opportunity for MCFC niche market application. *Int J Hydrogen Energy.* 2008;33:2999-3003.

63. Ciccoli R, Cigolotti V, Presti RL, et al. Molten carbonate fuel cells fed with biogas: combating H2S. *Waste Manage (Oxford)*. 2010;30:1018-1024.

64. Jiang Y-H, Xiong S-S, Shi W, et al. Research of biogas as fuel for internal combustion engine. In: *Asia-Pacific Power and Energy Engineering Conference*; 2009:1-4.

65. Xiong S, Chu S, Yang Z. Study on internal combustion engine running by biogas. *Acta Energiae Solaris Sinica*. 2003;24:688-692.

66. Chandra R, Vijay V, Subbarao P, Khura T. Performance evaluation of a constant speed IC engine on CNG, methane enriched biogas and biogas. *Appl Energy*. 2011;88:3969-3977.

67. Ptak M, Koziołek S, Derlukiewicz D, Słupiński M, Mysior M. Analysis of the use of biogas as fuel for internal combustion engines. In: *1st Conference of Renewable Energy Sources-Research and Business (RESRB), Wrocław, Poland*; 2016:441-450.

68. Kupczyk A, Prządka A, Różnicka I. Wybrane problemy produkcji i wykorzystania biogazu. *Energetyka*. 2009;552-556.

69. Börjesson P, Mattiasson B. Biogas as a resource-efficient vehicle fuel. *Trends Biotechnol*. 2008;26:7-13.

70. Dung N. A study of conversion diesel engine to fully biogas engine with electronically controlled. *Int J Earth Sci Eng.* 2012;1745-1749.

71. Mihic S. Biogas fuel for internal combustion engines. *Ann Faculty Eng Hunedoara*. 2004;2:179-190.

72. Yingjian L, Qi Q, Xiangzhu H, Jiezhi L. Energy balance and efficiency analysis for power generation in internal combustion engine sets using biogas. *Sustain Energy Technol Assess.* 2014;6:25-33.

73. Qian Y, Sun S, Ju D, Shan X, Lu X. Review of the state-of-the-art of biogas combustion mechanisms and applications in internal combustion engines. *Renew Sustain Energy Rev.* 2017;69:50-58.
74. Cacho JGL, Oliveros A, Barrera J. Development of a biogas fuel supply system for an internal combustion engine. *Distrib Generat Altern Energy J.* 2011;26:6-19.

75. Yoon SH, Lee CS. Experimental investigation on the combustion and exhaust emission characteristics of biogas-biodiesel dual-fuel combustion in a CI engine. *Fuel Process Technol.* 2011;92:992-1000.

76. Dobslaw D, Engesser K-H, Störk H, Gerl T. Low-cost process for emission abatement of biogas internal combustion engines. *J Clean Prod.* 2019;227:1079-1092.

77. Khan EU, Mainali B, Martin A, Silveira S. Techno-economic analysis of small scale biogas based polygeneration systems: Bangladesh case study. *Sustain Energy Technol Assess.* 2014;7:68-78.

78. Xu Y, Huang Y, Wu B, Zhang X, Zhang S. Biogas upgrading technologies: energetic analysis and environmental impact assessment. *Chin J Chem Eng.* 2015;23:247-254.

79. Esmaeilion F, Ahmadi A, Aliehyaei M. Low-grade heat from solar ponds: trends, perspectives, and prospects. *Int J Ambient Energy.* 2021;1-52. doi:10.1080/01430750.2021.1938672

80. Angelidaki I, Treu L, Tsapekos P, et al. Biogas upgrading and utilization: current status and perspectives. *Biotechnol Adv.* 2018;36:452-466.

81. Brizi F, Silveira JL, Desideri U, Reis JAD, Tuna CE, Lamas WDQ. Energetic and economic analysis of a Brazilian compact cogeneration system: comparison between natural gas and bio-gas. *Renew Sustain Energy Rev.* 2014;38:193-211.

82. Gazda W, Stanek W. Energy and environmental assessment of integrated biogas trigeneration and photovoltaic plant as more sustainable industrial system. *Appl Energy.* 2016;169:138-149.

83. Ahmadi P, Dincer I, Rosen MA. Development and assessment of an integrated biomass-based multi-generation energy system. *Energy.* 2013;56:155-166.

84. Norouzi O, Maria FD, El-Hoz M. A short review of comparative energy, economic and environmental assessment of different biogas-based power generation technologies. *Energy Procedia.* 2018;148:846-851.

85. Prodromidis GN, Coutelieris FA. Thermodynamic analysis of biogas fed solid oxide fuel cell power plants. *Renewable Energy.* 2017;108:1-10.

86. Chouhan K, Sinha S, Kumar S, Kumar S. Utilization of biogas from different substrates for SOFC feed via steam reforming: thermodynamic and exergy analyses. *J Environ Chem Eng.* 2019;7:103018.

87. Mosaffa AH, Ghaffarpour Z, Garousi Farshi L. Thermoeconomic assessment of a novel integrated CHP system incorporating solar energy based biogas-steam reformer with methanol and hydrogen production. *Sol Energy.* 2019;178:1-16.

88. Rostamzadeh H, Gargari SG, Namin AS, Ghaebi H. A novel multigeneration system driven by a hybrid biogas-geothermal heat source, Part I: thermodynamic modeling. *Energy Convers Manage.* 2018;177:535-562.

89. Bamisile O, Huang Q, Li J, et al. Modelling and performance analysis of an innovative CPVT, wind and biogas integrated comprehensive energy system: an energy and exergy approach. *Energy Convers Manage.* 2020;209:112611.

90. Malico I, Pereira RN, Gonçalves AC, Sousa AM. Current status and future perspectives for energy production from solid biomass in the European industry. *Renew Sustain Energy Rev.* 2019;112:960-977.

91. Kalina J, Świerzewski M. Identification of ORC unit operation in biomass-fired cogeneration system. *Renewable Energy.* 2019;142:400-414.

92. Jannatkhah J, Najafi B, Ghaebi H. Energy and exergy analysis of combined ORC-ERC system for biodiesel-fed diesel engine waste heat recovery. *Energy Convers Manage.* 2020;209:112658.

93. Kotas TJ. *The Exergy Method of Thermal Plant Analysis*. Elsevier; 2013.

94. Szargut J, Morris DR, Steward FR. *Exergy Analysis of Thermal, Chemical, and Metallurgical Processes*; 1987.

95. Ahmadi A, Das B, Ehyaei M, et al. Energy, exergy, and techno-economic performance analyses of solar dryers for agro products: a comprehensive review. *Sol Energy.* 2021;228:349-373.

96. Ashari G, Ehyaei M, Mozafari A, Atabi F, Hajidavalloo E, Shalbaf S. Exergy, economic, and environmental analysis of a PEM fuel cell power system to meet electrical and thermal energy needs of residential buildings. *J Fuel Cell Sci Technol.* 2012;9:1-11.

97. Saidi M, Abbasi A, Ehyaei M. Exergetic optimization of a PEM fuel cell for domestic hot water heater. *J Electrochem Energy Convers Storage.* 2005;4:284-289.

98. Saidi M, Ehyaei M, Abbasi A. Optimization of a combined heat and power PEFC by exergy analysis. *J Power Sources.* 2005;143:179-184.

99. Hashemian N, Noorpoor A. Assessment and multi-criteria optimization of a solar and biomass-based multi-generation system: thermodynamic, exergoeconomic and exergoenvironmental aspects. *Energy Convers Manage.* 2019;195:788-797.

100. Bedringås KW, Ertesvåg IS, Byggstøyl S, Magnussen BF. Exergy analysis of solid-oxide fuel-cell (SOFC) systems. *Energy.* 1997;22:403-412.

101. Naqvi SAA, Mehran MT, Song R-H, et al. Performance evaluation of solid oxide carbon fuel cells operating on steam gasified carbon fuels. *Chem Eng J.* 2016;300:384-393.

102. Mazzucco A, Rokni M. Thermo-economic analysis of a solid oxide fuel cell and steam injected gas turbine plant integrated with woodchips gasification. *Energy.* 2014;76:114-129.

103. Siefert NS, Litster S. Exergy & economic analysis of biogas fueled solid oxide fuel cell systems. *J Power Sources.* 2014;272:386-397.

104. Ozcan H, Dincer I. Performance evaluation of an SOFC based trigeneration system using various gaseous fuels from biomass gasification. *Int J Hydrogen Energy.* 2015;40:7798-7807.

105. Tuinier MJ, van Sint Annaland M. Biogas purification using cryogenic packed-bed technology. *Ind Eng Chem Res.* 2012;51:5552-5558.

106. Tan L, Dong X, Gong Z, Wang M. Investigation on performance of an integrated SOFC-GE-KC power generation system using gaseous fuel from biomass gasification. *Renewable Energy.* 2017;107:448-461.

107. Galvagno A, Prestipino M, Zafarana G, Chiodo V. Analysis of an integrated agro-waste gasification and 120 kw SOFC CHP system: modeling and experimental investigation. *Energy Procedia.* 2016;101:528-535.

108. Corigliano O, Fragiacomo P. Numerical simulations for testing performances of an indirect internal CO2 reforming solid oxide fuel cell system fed by biogas. *Fuel.* 2017;196:378-390.

109. Casas Y, Arteaga LE, Morales M, Rosa E, Peralta LM, Dewulf J. Energy and exergy analysis of an ethanol fueled solid oxide fuel cell power plant. *Chem Eng J.* 2010;162:1057-1066.
<figure><img src="image_26.png" /></figure>

110. Hernandez L, Kafarov V. Use of bioethanol for sustainable electrical energy production. *Int J Hydrogen Energy*. 2009;34:7041-7050.

111. Wang Z, Fan W, Zhang G. Comparison of the exergy efficiency of four power generation systems from methane using fuel cells. *RSC Adv.* 2017;7:39391-39402.

112. Jones CM, Persky J, Datta R. Exploring conditions that enhance durability and performance of a tubular solid oxide fuel cell fed with simulated biogas. *Energy Fuels*. 2017;31:12875-12892.

113. Chaiyat N, Chaongew S, Ondokmai P, Makarkard P. Levelized energy and exergy costings per life cycle assessment of a combined cooling, heating, power and tourism system of the San Kamphaeng hot spring, Thailand. *Renewable Energy*. 2020;146:828-842.

114. Mudasar R, Aziz F, Kim M-H. Thermodynamic analysis of organic Rankine cycle used for flue gases from biogas combustion. *Energy Convers Manage*. 2017;153:627-640.

115. Rostamzadeh H, Gargari SG, Namin AS, Ghaebi H. A novel multigeneration system driven by a hybrid biogas-geothermal heat source, Part II: multi-criteria optimization. *Energy Convers Manage*. 2019;180:859-888.

116. Pambudi NA, Laurensia R, Wijayanto DS, et al. Exergy analysis of boiler process powered by biogas fuel in ethanol production plant: a preliminary analysis. *Energy Procedia*. 2017;142:216-223.

117. Dhyani V, Subramanian K. Experimental based comparative exergy analysis of a multi-cylinder spark ignition engine fuelled with different gaseous (CNG, HCNG, and hydrogen) fuels. *Int J Hydrogen Energy*. 2019;44:20440-20451.

118. Hamzehkolaei FT, Amjady N. A techno-economic assessment for replacement of conventional fossil fuel based technologies in animal farms with biogas fueled CHP units. *Renewable Energy*. 2018;118:602-614.

119. Gamonwet P, Dhakal S, Thammasiri K, et al. The impact of renewable energy pricing incentive policies in Thailand. *GMSARN Int J*. 2017;11:51-60.

120. Putmai N, Jarunglumlert T, Prommuak C, Pavasant P, Flood A. Economic analysis of swine farm management for the enhancement of biogas production and energy efficiency. *Waste Biomass Valoriz*. 2020;11(10):5635-5645.

121. Chasnyk O, Sołowski G, Shkarupa O. Historical, technical and economic aspects of biogas development: case of Poland and Ukraine. *Renew Sustain Energy Rev*. 2015;52:227-239.

122. Lindkvist E, Karlsson M, Ivner J. Systems analysis of biogas production—Part I research design. *Energies*. 2019;12:926.

123. Rehl T, Müller J. Life cycle assessment of biogas digestate processing technologies. *Resour Conserv Recycl*. 2011;56:92-104.

124. Al Seadi T, Lukehurst C. Quality management of digestate from biogas plants used as fertiliser. *IEA Bioenergy*. 2012;37:40.

125. Nzila C, Dewulf J, Spanjers H, Tuigong D, Kiriamiti H, Van Langenhove H. Multi criteria sustainability assessment of biogas production in Kenya. *Appl Energy*. 2012;93:496-506.

126. Garfi M, Martí-Herrero J, Garwood A, Ferrer I. Household anaerobic digesters for biogas production in Latin America: a review. *Renew Sustain Energy Rev*. 2016;60:599-614.

127. Gozan M, Aulawy N, Rahman SF, Budiarto R. Techno-economic analysis of biogas power plant from POME (palm oil mill effluent). *Int J Appl Eng Res*. 2018;13:6151-6157.

128. Boldrin A, Baral KR, Fitamo T, et al. Optimised biogas production from the co-digestion of sugar beet with pig slurry: integrating energy, GHG and economic accounting. *Energy*. 2016;112:606-617.

129. Scarlat N, Fahl F, Dallemand J-F, Monforti F, Motola V. A spatial analysis of biogas potential from manure in Europe. *Renew Sustain Energy Rev*. 2018;94:915-930.

130. Stürmer B, Schmid E, Eder M. Impacts of biogas plant performance factors on total substrate costs. *Biomass Bioenerg*. 2011;35:1552-1560.

131. Riva C, Schievano A, D’Imporzano G, Adani F. Production costs and operative margins in electric energy generation from biogas. Full-scale case studies in Italy. *Waste Manage (Oxford)*. 2014;34:1429-1435.

132. Walla C, Schneeberger W. The optimal size for biogas plants. *Biomass Bioenerg*. 2008;32:551-557.

133. Díaz-Trujillo LA, Nápoles-Rivera F. Optimization of biogas supply chain in Mexico considering economic and environmental aspects. *Renewable Energy*. 2019;139:1227-1240.

134. Lask J, Martínez Guajardo A, Weik J, von Cossel M, Lewandowski I, Wagner M. Comparative environmental and economic life cycle assessment of biogas production from perennial wild plant mixtures and maize (*Zea mays* L.) in southwest Germany. *GCB Bioenergy*. 2020;12:571-585.

135. Wresta A, Andriani D, Saepudin A, Sudibyo H. Economic analysis of cow manure biogas as energy source for electricity power generation in small scale ranch. *Energy Procedia*. 2015;68:122-131.

136. Kozłowski K, Pietrzykowski M, Czekała W, et al. Energetic and economic analysis of biogas plant with using the dairy industry waste. *Energy*. 2019;183:1023-1031.

137. Cucchiella F, D'Adamo I, Gastaldi M. An economic analysis of biogas-biomethane chain from animal residues in Italy. *J Clean Prod*. 2019;230:888-897.

138. Manyuchi CMMM, Muzenda E. Environmental impact assessment for setting up a biogas plant. *Presented at the Proceedings of the International Conference on Industrial Engineering and Operations Management Bandung, Indonesia*; 2018.

139. Karapidakis ES, Tsave AA, Soupios PM, Katsigiannis YA. Energy efficiency and environmental impact of biogas utilization in landfills. *Int J Environ Sci Technol*. 2010;7:599-608.

140. Senbayram M, Chen R, Wienforth B, et al. Emission of N2O from biogas crop production systems in Northern Germany. *Bioenergy Res*. 2014;7:1223-1236.

141. Meyer-Aurich A, Schattauer A, Hellebrand HJ, Klauss H, Plöchl M, Berg W. Impact of uncertainties on greenhouse gas mitigation potential of biogas production from agricultural resources. *Renewable Energy*. 2012;37:277-284.

142. Sreekrishnan T, Kohli S, Rana V. Enhancement of biogas production from solid substrates using different techniques—a review. *Biores Technol*. 2004;95:1-10.

143. Kristensen PGJ, Nielsen JK, Illerup MJB. *Emission Factors for Gas Fired CHP units* <25 MW. Danish Gas Technology Centre and National Environmental Research Institute of Denmark; 2004.

144. Thorneloe S. *Background Information Document for Updating AP42 Section 2.4 for Estimating Emissions from Municipal Solid Waste Landfills*. Citeseer, Office of Research and Development. Report number PA/600/R-08-1162008.

145. Carreras-Sospedra M, Williams R, Dabdub D. Assessment of the emissions and air quality impacts of biomass and biogas use in California. *J Air Waste Manag Assoc*. 2016;66:134-150.
146. Börjesson P, Berglund M. Environmental systems analysis of biogas systems—Part I: fuel-cycle emissions. *Biomass Bioenerg.* 2006;30:469-485.

147. Sommer SG. Ammonia volatilization from farm tanks containing anaerobically digested animal slurry. *Atmos Environ.* 1997;31:863-868.

148. Clemens J, Trimborn M, Weiland P, Amon B. Mitigation of greenhouse gas emissions by anaerobic digestion of cattle slurry. *Agr Ecosyst Environ.* 2006;112:171-177.

149. Hijazi O, Munro S, Zerhusen B, Effenberger M. Review of life cycle assessment for biogas production in Europe. *Renew Sustain Energy Rev.* 2016;54:1291-1300.

150. Torquati B, Venanzi S, Ciani A, Diotallevi F, Tamburi V. Environmental sustainability and economic benefits of dairy farm biogas energy production: a case study in Umbria. *Sustainability*. 2014;6:6696-6713.

151. Paolini V, Petracchini F, Segreto M, Tomassetti L, Naja N, Cecinato A. Environmental impact of biogas: a short review of current knowledge. *J Environ Sci Health, Part A.* 2018;53:899-906.

152. Vorbrodt-Strzałka K, Pikoń K. Environmental impacts associated with production and utilization of agricultural biogas. *Archiwum Gospodarki Odpadami Ochrony Środowiska*. 2013;15(4):1-12.

**How to cite this article:** Abanades S, Abbaspour H, Ahmadi A, et al. A conceptual review of sustainable electrical power generation from biogas. *Energy Sci Eng.* 2021;00:1-26. doi:[10.1002/ese3.1030](https://doi.org/10.1002/ese3.1030)