What is the most energy efficient route for biogas utilization: Heat, electricity or transport?

Abstract

IntroductionThe target set by the EU Renewable Energy Directive (2009/28/EC) [1] requires a 20% energy share from renewable sources by 2020. Thus, exploring alternative, environmentally benign and energy efficient systems has become the focus of governmental policies and industrial as well as academic research.Biogas is a renewable energy source that can be produced from the anaerobic digestion (AD) of biomass, such as sewage sludge, municipal solid waste, agricultural wastes, and energy crops. Biogas consists of around 50-60% methane (CH4), 40-50% carbon dioxide (CO2) and some minor constituents, such as hydrogen sulphide (H2S) and water. The use of biogas for energy production could displace fossil fuels, reduce greenhouse gas emissions and decrease dependence on imported energy [2].Upgraded biogas, termed bio-methane, is typically composed of ~97% CH 4 and ~3% CO 2 , and is converted to the same standard as natural gas through removal of CO 2 (upgrading) and other impurities (cleaning).Another route for upgrading biogas to bio-methane involves the chemical transformation of CO 2 to CH 4 by 2 the Sabatier reaction (equation 1); the hydrogen (H 2 ) in the reaction is usually obtained from water (H 2 O) electrolysis (equation 2). This combined pathway could have an important impact on the global carbon cycle [3]. There are various utilization pathways for both raw and upgraded forms of biogas [4]; commercial methods include electricity and heat generation via combined heat and power (CHP) units, electricity generation via fuel cells, and conversion to mechanical energy for transport via internal combustion engines (ICEs). Bio-methane can be injected into the gas grid, and/or converted to compressed renewable natural gas or liquefied renewable natural gas (referred to in this paper as CNG and LNG respectively) to serve as a transport fuel. Biogas can also be reformed to syngas (CO and H2) for liquid fuel production via Fischer Tropsch (FT) synthesis (see [5] for further details).As with any new energy system, countries are faced with ongoing challenges when designing the most optimum pathway to ensure sustainable development and sufficient energy supply [6]. In practice, many European countries have successfully integrated biogas into their energy sectors via different utilization routes. The annual energy production from biogas is around 42 TWh in Germany (the highest production in the EU), 9 TWh in UK, and 2.8 TWh in France; in each of these countries the biogas is mainly used for electricity generation [7]. Sweden produces around 1.7 TWh from biogas and 44% of biogas production is upgraded to bio-methane and used as vehicle fuel [8]. In Italy, biogas is mainly used for power generation while other pathways such as grid injection and CHP require further exploration [9]. However, although there are various options for biogas utilization, there is limited guidance in the literature on the selection of the optimum route. A number of papers focus specifically on biogas utilization as a vehicle fuel [9, 10] while oth...

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“…As has been reported by other authors, the deactivation by sulfur can be described by the following general reaction Equation (8) [32,33], which is proposed to operate at high temperature:…”

“…For all catalysts under investigation, three different Ni species were determined: elemental nickel, Ni 0 ≈ 852. 8 …”

“…In the case of the United States, the use of biogas for transport has increased noticeably and in Europe is gaining market share in the transport fuel mix. However, there are many problems for the transportation sector, such as the lack of regulations to access the natural gas grids, or the decentralized production of the biogas [7,8]. In this sense, biogas can be used to produce a clean energy vector for production of sustainable energy such as hydrogen.…”

Exergy Analysis and Performance Improvement of a Subcritical/Supercritical Organic Rankine Cycle (ORC) for Exhaust Gas Waste Heat Recovery in a Biogas Fuelled Combined Heat and Power (CHP) Engine Through the Use of Regeneration

“…Biogas, one of the anaerobic digestion products, is also among the most attractive alternative energy sources [10][11][12][13]. There are various biogas utilisation systems like stoves, fuel cells, gas turbines and hydrogen production systems [14][15][16][17][18][19]. Combined heat and power (CHP) engines also widely use biogas as an energy source [20][21][22].…”

Status quo and perspectives of biogas production for energy and material utilization

“…Heat is partly used by the producers themselves (e.g., for heating the fermenters, their own buildings, or used in other branches of their own business such as aquaculture), and some is sold to third parties (Herbes, Halbherr, & Braun, 2018). Heat sales are usually more geared toward general market developments than electricity sales (Hakawati, Smyth, McCullough, Rosa, & Rooney, 2017). In addition to the biogas plants outlined above, which mainly produce electricity and heat on site, in recent years, more and more plants have been built to upgrade biogas into biomethane.…”