Bioenergy with Carbon Capture and Storage: Using Natural Resources for Sustainable Development

Bioenergy with Carbon Capture and Storage: Using Natural Resources for Sustainable Development presents the technologies associated with bioenergy and CCS and its applicability as an emissions reduction tool. The book explores existing climate policies and current carbon capture and storage technologies. Sections offer an overview of several routes to use biomass and produce bioenergy through processes with low or even negative CO2 emissions. Associated technology and the results of recent research studies to improve the sustainability of the processes are described, pointing out future trends and needs. This book can be used by bioenergy engineering researchers in industry and academia and by professionals and researchers in carbon capture and storage.

• Presents the most recent technologies in use and future trends in research and policy
• Examines the bioenergy production and biomass processing value chains, including biorefining, negative emission technologies and the use of microalgae
• Includes techno-economic analysis and sustainability assessment of the technologies discussed, as well as an overview of the latest research results

• Language: English
• Publisher: Academic Press
• Release date: Aug 7, 2019
• ISBN: 9780128166000

Book preview

2017;10(6):1389–1426.

Chapter 1

Negative emission technologies

Francisca M. Santos, Ana L. Gonçalves and José C.M. Pires,    LEPABE – Laboratory for Process Engineering, Environment, Biotechnology and Energy, Faculty of Engineering, University of Porto, Porto, Portugal

Abstract

Carbon dioxide (CO2) is an important greenhouse gas (GHG), which concentration in the atmosphere has been rising since the Industrial Revolution due to emissions from anthropogenic activities (mainly burning of fossil fuels). The continuous CO2 emissions may lead to a potentially irreversible climate change (global warming) and ocean acidification. Even if CO2 emissions could be cut to zero today, the environmental impacts would persist in the future due to the long residence time of this GHG. Therefore an international agreement was signed, aiming to limit the increase of the global temperature at 2°C. In this context, CO2 capture from large point sources is gaining the attention of the scientific community as a mitigation option. The pure stream obtained can be transported and stored, avoiding the emission of high amounts of CO2. However, since half of the CO2 emissions come from diffuse sources, capturing CO2 from the atmosphere may be also needed to fulfill the mitigation targets. Despite the higher costs when compared to CO2 capture from large sources, negative emission technologies (NETs) present several advantages: (1) it can capture CO2 emitted from different sources at different locations and time, and (2) the sequestration site can be placed anywhere, avoiding infrastructures’ transportation. NETs can be divided into two routes: (1) direct air capture—using physicochemical processes and (2) indirect air capture—using biological processes. This chapter aims to present an overview of the main NETs, demonstrating their advantages and drawbacks. Currently, there is no single process that can be considered the only solution to achieve the mitigation goals. Research efforts should be made to completely assess the environmental impacts and reduce its costs, possibly through a process integration.

Keywords

Atmospheric CO2; biochar; bioenergy with carbon capture and storage; negative emission technologies; sustainability

1.1 Introduction

Carbon dioxide (CO2), an important greenhouse gas (GHG), has been added to the atmosphere by anthropogenic activities, mainly by the burning of fossil fuels. As a consequence, severe changes in the world’s climate are happening, and different ecosystems are being threatened [1]. Since the pre–Industrial era, the population and economic growth have largely increased the global average atmospheric CO2 concentration. Between 1750 and 2018 the CO2 levels have risen from 280 parts per million (ppm) to, approximately, 408 ppm [2,3]. Global CO2 emissions are about 36 Gt CO2/year [4], where 91% are originated from the combustion of fossil fuels [5]. As a consequence, the ocean has absorbed about 20%–40% of the CO2 emitted to the atmosphere since the Industrial Revolution [6]. This increase has a greater impact on the chemistry of the ocean surface, especially on the levels of hydrogen ion concentrations (H+). The continuous rise in the atmospheric CO2 increases the levels of H+ in the ocean, which leads to its acidification. Surface ocean pH is already 0.1 U lower. At this rate the decrease of ocean pH is expected to be 0.4 U by the end of the century and 0.8 U by 2300 [7,8]. Simultaneously, the carbonate equilibrium is affected, resulting in dramatic impacts on marine life. Reducing ocean pH decreases the amount of carbonate ions available, and it may become more difficult for some species, such as coral reefs and calcareous plankton, to form biogenic calcium carbonate [9]. Thus these species are more vulnerable to dissolution, and their habitats are severely threatened. It is estimated that already 30% was damaged, and approximately 60% may be lost by 2030 [10]. In addition, as a GHG, CO2 can absorb and emit infrared radiation, which affects the global temperature. The planet’s average temperature has risen about 0.9°C since 1880 [11], mainly driven by the increase of CO2 emissions, causing the melt of glaciers and other ice and, consequently, increasing sea levels [12].

In order to reduce the atmospheric CO2 concentration, several nations recognize the urgent need to commit to a low-carbon economy [13,14]. In 2015 countries adopted an international agreement to combat climate change under the United Nations Framework Convention on Climate Change (21st Conference of the Parties—COP21). The Paris Agreement aims to avoid the increase in global average temperatures in 2 °C and to make efforts to limit this increase to 1.5 °C above preindustrial levels. In order to limit warming the total amount of CO2 emitted needs to be finite, and it includes the utilization of both preventive and remediation strategies [15]. Preventive measures are related with (1) improving energy efficiency, (2) increasing the use of low-carbon fuels, (3) promoting the use of renewable energy sources, and (4) using geoengineering approaches [for example, afforestation and reforestation (AR), which increase the natural carbon sink]. Remediation methods are linked to carbon capture and storage (CCS) techniques [16,17]. The anthropogenic sources of CO2 can be divided into two categories: large stationary sources (such as power plants and industrial activities) and dispersed sources (mainly from transportation). While CCS can reduce CO2 emissions from large sources (around 85%–90%), the aim of reducing anthropogenic CO2 emissions close to zero requires CO2 capture from diffuse emissions as well (e.g., cars, trucks, airplanes) [18,19]. Since the capture from diffuse sources may be technically impossible, due to its large number, CO2 can be captured from the atmosphere using negative emission technologies (NETs), which offset these emissions. Capturing CO2 from the atmosphere may be more expensive than capturing from stationary points, but this supplementary approach presents some advantages: (1) CO2 capture is sector independent, in other words, it can capture CO2 emissions from both diffuse and point sources; (2) transportation infrastructures may be avoided since the CO2 capture unit can be placed anywhere; (3) the separation process is less affected by the presence of other pollutants (e.g., nitrogen oxides, sulfur oxides) since their atmospheric concentration is much lower when compared to flue gases [17,18,20]. Nevertheless, the NETs’ feasibility to meet the required scenarios is still questioned. Technical and social barriers, such as the absence of political actions, public understanding and acceptability of these technologies, or the side effects that NETs could have, are conditioning the scale-up of the technology [21,22]. NETs encompass several techniques, and it can be divided into two routes: (1) direct air capture through physicochemical processes [absorption, adsorption, ocean alkalinity enhancement (OAE), and soil mineralization] and (2) indirect air capture through biological processes [afforestation, ocean fertilization, algal culture, bioenergy with CCS (BECCS), and biochar]. This chapter aims to present an overview of the main NETs, also presenting the advantages and drawbacks of each technology.

1.2 Direct air capture

The concept of capturing CO2 from air is not new. It was previously applied as a life-support system in submarines and spacecraft, but it was mentioned for the first time for climate change mitigation purposes in 1999 by Lackner et al. [23]. Since half of the CO2 emissions come from diffuse sources, its capture from the atmosphere is essential to comply with the targets of limiting the warming within 1.5 °C–2 °C. However, this technology presents challenges regarding the high energy demands associated to the low CO2 concentration on ambient air (approximately 350 times lower than a typical coal-based flue gas [17]). Large air volumes need to pass through the absorbers to collect significant amounts of CO2. Therefore capture technologies that use heat, cool, or pressurized air cannot be applied in air capture due to their economical unfeasibility [23,24]. The atmospheric CO2 can be captured from the following methodologies: (1) absorption, (2) adsorption, (3) OAE, and (4) soil mineralization.

1.2.1 Absorption

Absorption is a process where the gas (ambient air) captured enters in contact with a physical or chemical solvent in an absorption column. The solvent has specific characteristics that only absorb CO2 and let the other gases pass , depending on the initial operation parameters.

Ionic liquids (ILs) have emerged as a possible alternative to the chemical and physical absorbents. ILs are composed exclusively by ions, which remain liquid at room temperature. Their favorable solvent properties (e.g., high thermal stability, insignificant volatility, tuneable capacity, and high CO2 solubility) make them feasible candidates for absorption process [33]. Due to the thermal stability, ILs can absorb CO2 presenting lower regeneration energy requirements. One constraint of IL is the increase of viscosity with the absorption of CO2, which can create some issues regarding solvent pumping and mass transfer kinetics [34]. Another limitation of IL is the high costs compared to organic solvents. So, for an industrial scale, it is necessary to improve their recovery, product isolation and reuse efficiency as well as evaluate the environmental impacts [35]. Ma et al. [36] evaluated the energy consumption of CO2 absorption using IL and a conventional MEA process. The IL selected was the 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl) ([bmim][Tf2N]). The feed composition was 12.5% CO2, 5% H2O, and 78% N2. The results showed that the IL performed better than the MEA. IL consumed more electricity than MEA, but the thermal energy was substantially lower, which led to global savings on energy consumption of 30.0%. The total cost was also lower for IL (29.9%). The energy consumption for CO2 storage was analyzed, where MEA based had a better performance. For the entire CO2 capture and storage the IL-based process was more economical than MEA-based process.

1.2.2 Adsorption

In the adsorption process, air is fed to a bed of a solid adsorbent, which fixes CO2 selectively until the equilibrium is reached. Desorption or regeneration is an important feature for an industrial application of the adsorption process. To reduce the CO2 recovery cost, adsorbents must be regenerable, allowing their reuse for a large number of cycles [18]. CO2 desorption is usually performed by swinging the pressure (PSA) or temperature (TSA). In PSA the adsorption process occurs at high pressures and the swing for low pressures (generally atmospheric pressure) for the desorption process. In TSA, CO2 is desorbed from the solid absorbent by raising the system temperature using hot air or steam injection [19]. PSA has a simpler operation, low power consumption, and fast regeneration. However, the presence of water may lower the CO2 recovery. TSA has longer regeneration times than PSA but presents higher CO2 purity and recovery, avoiding the energy requirements to pressurize CO2.

Although CO2 capture by adsorption is only commercialized for high concentrations, for atmospheric CO2 capture, this process has several advantages over the absorption process, such as (1) the low regeneration energy requirements, (2) the smaller environmental concern of the solid waste compared with the liquid waste, (3) resistance to corrosion, and (4) the broader range of operational temperatures [37]. The selection of the adsorbents should take into account the specific surface area, the selectivity, and the regeneration ability. Typical adsorbents are zeolites and activated carbon [19]. However, the atmospheric pressure and the water content in the air affect the adsorption capacities, making these adsorbents not appropriated for air capture [18]. Amine-functionalized solids have higher selectivity at low concentrations, stability, and tolerance to moisture, due to the chemical character of the sorbent–adsorbate interaction [25]. In fact, humid environments can improve the adsorption efficiency. Amine-functionalized adsorbents have some disadvantages: (1) at high temperatures, the amine adsorbents degrade; and (2) TSA is required for desorption (due to the chemical bonding), which can reduce the adsorption capacity [38]. Wurzbacher et al. [39] evaluated the adsorption/desorption process to capture CO2 from air using an amine-functionalized sorbent. Desorption process was performed using a combined temperature-vacuum swing to avoid the compression requirements during adsorption and the adsorbent degradation during desorption. The sorbent CO2 capture capacity was determined under different operational conditions (10–150 mbar, 74–90°C, and 0%–80% relative humidity). A desorption capacity of 0.30 mmol/g (at 10 mbar and 90°C) was achieved, producing a stream with a CO2 purity of 95.8%. In addition, the adsorption process was enhanced under humid