New Directions for Chemical Engineering (2022) / Chapter Skim
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3 Decarbonization of Energy Systems
3 Decarbonization of Energy Systems
Pages 32-86
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From page 32... ...
The global energy demand today is about 155,000 TWh, 82 percent of which is currently supplied by fossil fuels (32 percent petroleum, 23 percent natural gas, and 27 percent coal) and the rest by nuclear (5 percent)
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From page 33... ...
The chapter is organized from sources to end uses. Opportunities for chemical engineers are explored in energy sources; energy carrier production; energy storage; energy conversion and efficiency; and carbon capture, use, and storage.
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From page 34... ...
A notional average view suggests that in 2040, petroleum and natural gas will continue to play a significant role in the energy mix; coal usage will decrease significantly; energy carriers from nonbiogenic renewables (e.g., solar, wind, hydroelectric power) and biogenic sources (bioenergy)
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From page 35... ...
. Any low-carbon energy transition "bridging" strategy will rely on the greater use of a mix of energy carriers: electrons, hydrogen, and lower-emission liquid fuels (e.g., advanced biofuels, synthetic liquid fuels; Santiesteban and Degnan, 2021)
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From page 36... ...
into biomass. Biogenic sources have been used as energy carriers throughout history -- first soon after their formation as combustion fuels, but much more extensively in modern times as fossil fuels, well after geological chemical reactions have deoxygenated these photosynthetic residues and increased their energy density, forming natural gas, crude oil, and coal.
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From page 37... ...
These factories will produce heat, electrons, energy carriers, and chemicals as part of modular integrated systems designed to capture the largest possible fraction of the solar flux with high quantum efficiencies and convert it into useful forms of chemical energy. Direct photon capture and conversion to electrons as energy carriers.
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From page 38... ...
PSC devices have evolved rapidly in photon capture efficiency, from 4 percent in 2010 to >25 percent in 2019 (Grätzel and Milić, 2019; Figure 3-3)
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From page 39... ...
. Conversion of photons to H2, NH3, or organic fuels as energy carriers.
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From page 40... ...
that couple photovoltaic and electrochemical cells at the device scale to gen erate H2 from H2O, organic energy carriers or H2–CO mixtures from CO2–H2O reactants, or NH3 from N2–H2O mixtures (photoelectrochemical devices)
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From page 41... ...
These PEC devices for the synthesis of solar H2-based fuels, as well as their architectural analogs for artificial photosynthesis strategies for converting CO2–H2O mixtures to CO and organic energy carriers, remain at the proof-of-concept stage (Lewis, 2016)
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From page 42... ...
Systems-based integration, control, and design; reaction-transport formalisms; and knowledge of the catalytic properties of active surfaces and centers will play an enabling role in the design and selection of cost-effective devices for the direct generation of energy carriers from photons in a manner that avoids toxic and scarce elements, as well as containment and sustainability concerns (Montoya et al., 2017)
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From page 43... ...
. These products can be used directly as energy carriers or as precursors to such carriers on heterogeneous catalysts (e.g., H2–CO conversion to liquid transportation fuels via Fischer-Tropsch or methanol synthesis)
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From page 44... ...
. Fossil Fuels Fossil fuels (coal, petroleum, and natural gas)
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From page 45... ...
It can be converted into gas or liquids to produce chemicals and fuels, but is used primarily for direct combustion. As a solid fuel, coal generates more CO2 per unit energy than other fossil fuels -- from approximately 30 percent more than diesel to nearly twice as much as natural gas (EIA, 2021i)
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From page 46... ...
In the United States, natural gas is used primarily for electricity generation (power sector) and for heating (industry, residential, and commercial)
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, 1950–2019. A net increase in natural gas consumption occurred over this time period across all sectors.
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From page 48... ...
Innovation throughout the entire value chain will be required if natural gas is to continue being a key contributor to the future of the low-carbon energy mix. Areas in which chemical engineers will play a key role include the following: Production - Advances in water-quality management; water recycling for shale or un conventional gas production - Further reduction of methane venting to the atmosphere - Accelerated development of CO2 to replace water as a fracturing agent Processing - Development of low-energy processes for natural gas separation and pu rification Storage and transportation - Methane leakage control - Higher-efficiency compressors and heat exchangers - Smart sensors for pipeline operational efficiency - Materials for intercontinental transport via pipeline versus the current practice, which involves liquefaction and regasification - Low-cost pipeline materials to enable cotransport of natural gas and high concentrations of hydrogen (>20 percent)
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From page 49... ...
In 2020, U.S. crude oil consumption averaged about 18 million barrels per day, with the transportation sector accounting for 66 percent and the industrial sector for 28 percent of this total (EIA, 2021k)
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Thus, they are positioned to play an important role in the oil industry's efforts to minimize its carbon footprint. FIGURE 3-9 Historical crude oil production, 2000–2020, and projected crude oil production, 2020–2050, in the United States.
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As a result of regulations, the oil industry has made good progress in reducing methane emissions; however, more progress is needed. The main source of fugitive methane emissions is well venting, followed by pneumatic devices that use natural gas as the operating fluid, as well as storage and transport venting and leaks.
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From page 52... ...
These challenges remain significant barriers to improving the economic feasibility of at-scale biofuel production. Interest in biofuel production as a potential strategy for offseting GHG emissions and decreasing dependence on fossil resources has seen a resurgence, prompting substantial debate about the long-term viability and utility of biofuels.
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From page 53... ...
The higher oxygen content of biofuels results in a lower energy content relative to fossilbased energy sources. NOTES: AA = acrylic acid; FDCA = furan-2,5-dicarboxylic acid; LAB = linear alkyl benzene; MEG = monoethylene glycol; NG = natural gas; PE = polyethylene; PEF = polyethylene furanoate; PET = polyethylene terephthalate; PP = polypropylene; PTA = purified terephthalic acid.
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From page 54... ...
For example, because on-site lignin combustion is estimated to be the most expensive single unit operation in a biorefinery, as well as a major source of non-GHG emissions, the development of alternative uses for lignin, 40 percent of which can be made of biomass carbon, is a major opportunity for research (Davis et al., 2013; Eberle et al., 2017)
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From page 55... ...
of crude oil and 4.1 trillion cubic meters (3.6 billion tons of oil equivalent) of natural gas (IEA, 2021c,d; EIA, 2021d)
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From page 56... ...
, the source of reducing equivalents, and the cost and sustainability of any type of process in this vein, as discussed earlier in this chapter in the context of photon capture. Overall, biofuels will play a role in reducing GHG emissions associated with transportation fuels.
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From page 57... ...
. Finally, as with all renewable energy sources, challenges exist with respect to the integration of wind energy into chemical production (Centi et al., 2019)
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From page 58... ...
Significant cost reduction is required for this advanced technology to be affordable for industrial heat generation, but with some new concepts based on low-cost natural gas, competitive, cost-effective solutions are not out of reach. Efforts to drive down cost are focused in three areas: New qualified fuels -- TRISO (TRi-structural ISOtropic)
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From page 59... ...
In 2020, about 4,000 TWh of electricity was generated at utility-scale electricity generation facilities in the United States, with about 60 percent of that total being generated from fossil fuels -- coal, natural gas, petroleum, and other gases; about 20 percent from nuclear energy; and about 20 percent from renewable energy sources (EIA, 2021b)
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From page 60... ...
(Specific opportunities in these sectors were discussed earlier in this chapter.) Low-Carbon Liquid Fossil Fuels Liquid hydrocarbons from crude oil have been the preferred energy carrier for the transportation sector because of their high energy density, easy distribution and storage, low cost, and well-established and extensive infrastructure along the value chain.
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From page 61... ...
and "dirty" crude oils in the feedstock mix is maximized. Refineries will require significant reconfiguration not only to satisfy product demand and meet challenges associated with GHG emissions, but also to maintain low production costs for liquid fuels.
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From page 62... ...
Develop a hydrogen infrastructure for distribution and storage at scale to sat isfy demand. Globally, 96 percent of hydrogen is produced from fossil sources (48 percent natural gas, 30 percent liquid hydrocarbons, and 18 percent coal)
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From page 63... ...
Methane pyrolysis, or methane splitting of natural gas using renewable electricity to produce hydrogen and black carbon, is currently in the commercial demonstration scale.8 Many other routes to low-carbon hydrogen, such as thermochemical water splitting, direct photocatalysis, and biological production from microorganisms, are in various stages of R&D. It is generally accepted that hydrogen from fossil fuels without CCUS will remain the main source of hydrogen production.
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From page 64... ...
. Synthetic Fuels Synthetic fuels are produced by converting hydrogen and a carbon source into compounds that can be used as energy carriers, such as methane; methanol; ethanol; and such higher-carbon-number products as gasoline, diesel, and aviation fuel.
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From page 65... ...
Because many of these are mature technologies, chemical engineers have limited potential to impact some modes of energy storage, especially those involving mechanical energy, such as pumped hydropower and compressed gas storage. For energy carriers that involve electrons or chemical bonds, however, chemical engineers can play a critical role in the development and deployment of scalable and economical energy storage.
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From page 66... ...
The energy density and ease of transporting these carriers relative to gases or electrons give them strong intrinsic advantages. Chemical engineering played a central role in what might be termed the hydrocarbon economy of the 20th century, and the discipline will also be central to the deployment of more sustainable and environmentally benign liquid energy carriers in the 21st century.
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From page 67... ...
Tackling this challenge will require structural shifts in the transportation of people and freight, much larger gains in energy efficiency, major advances in technology, effective government policies, significant levels of investment in infrastructure for low-carbon energy carriers, and the manufacture of low-carbon and zero-emission vehicles. No single energy carrier can, in the foreseeable future, satisfy the requirements across all segments of the transportation sector (EPA, 2021a)
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From page 68... ...
The lithium-air battery has faced battery life and energy efficiency challenges. The lithiumsulfur battery has shown more promise than the lithium-air, but it, too, has been limited by life and volume concerns because of its low energy density.
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PEM fuel cells are used in FCEVs because they offer higher power density, lower overall weight, and lower total volume compared with other fuel cell types (NRC, 2015)
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From page 70... ...
A better alternative is to design sintering-resistant catalysts or replace platinum with lower-cost metals. Increasing efficiency -- PEM fuel cells for on-road FCEVs have a peak power efficiency of up to 60 percent in terms of converting the available fuel energy of hydrogen into electrical energy, well below the theoretical maximum effi ciency of approximately 80 percent.
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From page 71... ...
. In the Sustainable Development Scenario projections, the use of fossil fuels in industry would be reduced by more than 60 percent by
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From page 72... ...
) in the International Energy Agency's Sustainable Development Scenario, 2019–2070.
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From page 73... ...
Key technologies needed to decarbonize the steel industry include improvements in energy efficiency; a switch to low-carbon fuels; use of green hydrogen instead of natural gas in direct reduction of iron (DRI) ; production of iron by electrolysis of iron ore using only renewable electrical energy; postcombustion CCUS (such as top-gas recycling in BFs)
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From page 74... ...
; and CCUS. Chemical engineers can contribute to the RD&D necessary to achieve these technological advances, including the following examples: Achieve viability for natural gas crackers and improve catalyst production; improve the efficiency of olefin production via catalytic cracking of naphtha or via methanol; and address environmental issues for used catalysts, includ ing regeneration and catalyst selectivity and lifetime.
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From page 75... ...
global greenhouse gas (GHG) emissions versus production volumes for the top 18 large-volume chemicals in 2010.
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From page 76... ...
. Key technologies for decarbonization of petroleum refining include fuel switching, electrification, biomass hydrothermal liquefaction and biocrude oil, synthetic fuel synthesis, reduction or elimination of flaring, selective membranes, advanced control and improved monitoring, CCUS, catalytic cracking, progressive distillation, self-heat recuperation, and biodesulfurization.
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From page 77... ...
Although some decarbonization technologies are commercially available, further RD&D is needed in such areas as shifting from steam and fossil fuels to electric and solar heating technologies; demonstrating and certifying alternative processing technologies to reduce GHG emissions while maintaining product safety and quality, and reducing degradation in the supply chain; using waste to produce bioenergy; and adopting fuel switching and expanded implementation of energy efficiency. Cross-Cutting Approaches for Decarbonization of the Industrial Sector To achieve the net-zero emissions goal for industry, five broadly applicable decarbonization pillars require vigorous pursuit in parallel over the next decades: demand reduction, energy efficiency, fuel switching and electrification, transformative technologies in sectors, and abatement.
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From page 78... ...
Although significant opportunities exist for improving energy efficiency in commercial and residential settings, the highly dispersed nature of this sector creates challenges not shared by the industrial subsectors discussed in the previous section, which have large, fixed facilities. A recent National Academies report on decarbonization identifies key strategies that employ existing technologies, including electrification of energy use and dramatically increased use of electric heat pumps for heating and hot water (NASEM, 2021a)
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From page 79... ...
Opportunities include the development of passive materials, such as paints for roofs that reflect the solar spectrum more effectively and, as a result, reduce the cooling load required for buildings (Li et al., 2021a) ; and active materials, such as "smart glass," which adapts to external sunlight to reduce the net energy demands in buildings (Alias et al., 2019)
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From page 80... ...
. Of these priorities, chemical engineers could contribute in the following areas: Capture -- designing high-performance solvents and developing environmen tally friendly solvent processes, designing sorbent materials and integrated processes, developing membranes and related processes, and producing hy drogen from fossil fuels with CO2 capture.
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From page 81... ...
; 6 = bioenergy with carbon capture and storage; 7 = enhanced weathering; 8 = forestry techniques; 9 = soil carbon sequestration techniques; and 10 = biochar. SOURCE: Hepburn et al.
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From page 82... ...
Challenges and opportunities for chemical engineers in this area include control of carbonation reactions, process design, accelerated carbonation and crystal growth, green synthesis routes for alkaline reactants, structure property relationships, analytical and characterization tools, and construction methodologies. Chemical Conversion of CO2 Urea, polycarbonate, ethylene and propylene carbonates, salicylic acid, and polyether carbonate are currently produced from CO2 at commercial scales; however, the CO2 used is not derived from carbon capture processes.
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From page 83... ...
Biological Conversion of CO2 Biological conversion of CO2 holds great promise because some microorganisms have a natural ability to capture and covert CO2. Photosynthetic pathways to CO2 utilization include approaches using algae (products include biofuels, dietary protein and food additives, and commodity and specialized chemicals)
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From page 84... ...
While natural gas is a cleaner bridge fuel compared with other fossil fuels, innovations are still needed throughout the value chain. Chemical engineers can enable advances that will minimize or replace water use as a fracturing agent, improve storage and transportation, and better integrate natural gas with renewable energy sources.
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From page 85... ...
For intermittent energy sources, chemical engineers can contribute to the development of advanced materials that can increase the viability of wind and marine energy. Chemical engineering research will also be critical to advancing low-carbon fuels; improving petroleum refining; advancing clean hydrogen production; and developing improved synthetic fuels for sectors, such as aviation, that are difficult to decarbonize.
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From page 86... ...
86 New Directions for Chemical Engineering systems; and developing cost-effective and secure carbon capture, use, and storage methods. Recommendation 3-2: Researchers in academic and government laboratories and industry practitioners should form interdisciplinary, cross-sector collaborations focused on pilot- and demonstration-scale projects and modeling and analysis for lowcarbon energy technologies.
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