Is the production of biofuels and bio-chemicals always profitable? Co-production of biomethane and urea from biogas as case study
Introduction
The production of energy and bio-chemicals from renewable sources are the main objectives of forthcoming European policies. This results mainly from the following problems: the depletion of traditional fossil fuels [1]; the pollution caused by greenhouse gases (GHG) [2]; and the amount of waste produced by modern societies [3]. In this line, the recent draft launched by the European Union (EU) “Horizon Europe” focuses mainly on GHG reduction and waste valorization [4]. These bio-based policies also aim to curb the dependence of fossil fuels. Among the renewable energy alternatives, the use of biomass and waste opens new opportunities to fight climate change and reduce the dependence on traditional fuels [5]. In this direction, research and innovation need to establish new bio-based value chains under the “waste-to-energy” [6] and “waste-to-chemicals” strategies [7], [8]. Producing biogas via anaerobic digestion is a well-known path to valorize organic waste. Indeed, during the last year, the research in this area has intensified as shown in Fig. 1 (A). Biogas is mainly a mix of CH4 (50–60%) and CO2 (30–40%) [9], with some impurities such as H2 (0–5%), N2 (0–3%), CO (0–1%), O2 (0–1%), H2S (0.1–0.8%), NH3 (0.01–0.05%) or siloxanes (0.01–0.03%) [10].
Alternatives for biogas utilisation are electricity generation in a solid oxide fuel cell (SOFC) [11]; electricity and heat production in a combined heat and power (CHP) unit [12]; or upgrading to biomethane [13]. The last route is preferred, as shown in Fig. 1 (B). The main reason is that the use of biogas in a CHP or SOFC still results in CO2 release, hence contributing to increase GHG emissions. Moreover, these paths do not produce bio-based chemicals or fuels. Unlike these alternatives, biogas upgrading produces renewable biomethane that can substitute natural gas. However, the separated CO2 must be somehow used to avoid its emission to the atmosphere [14]. Carbon capture and storage (CCS) technologies are ready to be implemented at industrial level, but they still face the storage problem [15]. For this reason, carbon capture and utilisation (CCU) technologies [16], [17], which treat CO2 as raw material rather than a waste are thriving. Examples of CCU technologies are mineral carbonation, biofuels production, polymers production or enhance oil recovery [18]. The conversion of CO2 from biogas to value-added products is an ambitious strategy aimed to be the flagship of the aforementioned bio-based policies [19].
During the last decade, biogas industry not only has attracted the research attention but has also seen a surge in Europe. The number of biogas production plants in Europe has increased by 185%, from 6227 in 2009 to 17,783 in 2017 [20]. Thus, the current installed electric capacity from biogas is 10532 MW [20]. Such development has been unequal among European countries, leading to different biogas production in each country. Fig. 2 reveals the distribution of biogas plants among the European countries. The biogas production leader is Germany with a share of 61.71% of total biogas plants, well ahead the rest of the European countries. The electricity production from biogas in Germany reached 14% of the electricity generation (32.15 TWhe) from renewable energy sources in 2018, while 16.7 TWht were used to produce heat [21]. The main reason for the German leadership is a strong public support scheme from 2009 to present. Governmental incentives for biogas production in Germany have suffered variations during this decade, and are currently focused on improving the profitability of small plants. In 2018, feed-in tariffs for biogas production plants ranged from 10 to 14 cents/kWh for small-medium capacities. Moreover, biogas production plants can benefit from low-interest bank loans (4%) [22].
The second major productor of biogas in Europe is Italy. The Italian biogas market experienced a big expansion from 2008 to 2012 (from 510 to 1264), when 280 €/MWh where offered for biogas plants of up to 1 MW [21]. In 2013, a drastical change in the policy support for biogas production shifted the positive tendency [23]. Similar cases were observed in some countries such as Spain after the suppresion of subsidies for renewable energy production in 2012 [24]. In France, the development of biogas production was slower than that in Germany and Italy because of the lower incentives from the French government. From 2014, the baseline tariff for plants up to 150 kW is 13.37c/kWh while this value decrease to 11.19 for plants of up to 2 MW [25].
On the other hand, biomethane production from biogas have also been the focus of some incentives policies for renewable energy production. Even though research on biogas upgrading has intensified in the past years, Europe still reveals a poor outlook for biogas upgrading to biomethane. Indeed, only 540 plants out of the 17,783 total biogas plants are set to produce biomethane. The main reason is the prevalence of subsidies for biogas production over biomethane production. Fig. 3 reveals the distribution of these 540 biomethane plants by country [20]. As shown, 98.33% of the biomethane production plants are centralized in 10 countries. As is the case for biogas production, Germany is the leader in terms of total number of biomethane plants, followed in this case by United Kingdom and Sweeden. In Germany, the support scheme for biomethane production has followed similar trends to biogas production historically. Indeed, from 2014 to present, small scale biogas upgrading plants are not profitable [21]. A curious case is presented in the United Kingdom, where the stablishment of ‘Renewable Obligations’ in 2015 boosted the biomethane production for fuel transport. The ‘Renewable Transport Fuel Obligation’ (RTFO) forces fossil fuel suppliers to produce a set percentage of road fuels from renewable sources [26]. Surprisingly, Italy and Spain are two countries with relatively high biogas production but almost zero biomethane production. Recently, the Italian government has proposed new incentives to boost the presence of biomethane production plants in the Italian market. The new scheme proposes a feed-in premia of 61 €/MWh to biomethane production plants [21]. To the best of the authors’ knowledge, the Spanish government has no plans for supporting biomethane production.
The analysis carried out in the previous section reveals that biomethane production has not been part of the European bets till now. The reasons are purely economic. Shifting the current situation requires novel alternatives to make biomethane production more appealing both in terms of technical and economical aspects. The synergy between biogas upgrading and CO2 utilisation may be the key to unlock the potential of biomethane production in Europe [27]. To date, the alternatives presented for this end are power to gas [28], [29], power to liquid [30], syngas production [31], [32] and mineral carbonation [33], [34]. Nonetheless, the current market demands chemicals that cannot be produced with the mentioned process. Therefore, exploring new paths for synergizing CCU and biogas upgrading is an ongoing task that must be accomplished in the upcoming years.
In this work, we propose a new path which may help to bridge the CCU-biogas upgrading gap. Under these premises, the goal of our study is to propose a novel process to combine biogas upgrading and urea production. Urea is selected because of its potential as CCU ending product and its extensive applications in the fertilizers industry. In fact, more than 90% of world industrial production of urea is destined for use as a nitrogen-release fertilizer [35]. Considering that biogas is often produced in rural areas where fertilezers are vital, harmonizing urea production and biogas upgrading in an integrated process may bring excellent opportunities to maximize the resources of rural communities. The novelty of this work lies indeed on the integration and economic analysis of the entire process from biogas upgrading to biomethane & urea production. In this direction, our work deals with the techno-economic evaluation in terms of profitability of the integrated process. The scope of our work covers the profitability analysis in four different countries with different biogas/biomethane production policies. These countries, selected in agreement with Section 1.2, are: Spain, with great potential for biogas production but null biomethane production; Italy, where the recent policies support the production of biomethane; the United Kingdom, where the RTFO law is genuine; and Germany, which is the leader in biogas production in Europe. Our results could contribute to shed light on the future EU green policies roadmap to achieve the urgent transition towards sustainable societies.
Section snippets
Process description and main assumptions
The proposed biogas to biomethane & urea process (represented schematically in Fig. 4) consists in three stages, which are: biogas pre-cleaning, where minor impurities such as H2S and siloxanes are removed; biogas upgrading, in which biogas is upgraded to biomethane; and urea production, where the CO2 separated from biogas is transformed into bio-urea. As previously reported in literature, four biogas plant sizes were studied: small scale (100 and 250 m3/h), medium scale (500 m3/h), and large
Baseline results
Fig. 5 and Table 2 present the economic output from the baseline scenarios in each country. As showcased in Fig. 5, NPV value is only positive in Italy under the recent policy scheme for biomethane production and only for medium/large plants (Fig. 5(B)). Small plants might reach profitability if urea production is avoided, however, CO2 would be emitted to the atmosphere and GHG emissions would not be reduced. The measure taken by the Italian government proves a worthy path to transform our
Conclusions
This work presents a novel alternative to synergize biogas upgrading and CO2 utilization through urea production. The green path proposed was techno-economically analysed in terms of profitability for four countries (Spain, Italy, Germany and the United Kingdom), with different circumstances for biogas/biomethane production. Our results showcase that under the current scenario, only medium (500 m3/h) to large (1000 m3/h) biomethane & urea co-production plants in Italy would be profitable.
CRediT authorship contribution statement
Francisco M. Baena-Moreno: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Resources, Writing - original draft, Writing - review & editing. D. Sebastia-Saez: Investigation, Methodology, Visualization, Writing - review & editing. Qiang Wang: Investigation, Methodology, Resources, Supervision, Validation, Visualization. T.R. Reina: Conceptualization, Formal analysis, Funding acquisition, Project administration, Resources, Software, Supervision, Validation, Writing -
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work was supported by University of Seville through V PPIT-US. This work was also partially funded by the CO2Chem UK through the EPSRC grant (No. EP/R512904/1) and the Royal Society Research Grant (No. RSGR1180353).
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