Fossil fuel resources of our planet are the product of biological and geologic processes that have occurred over hundreds of million of years. Since the dawn of the industrial age, circa 1750, an estimated 280Gt-C has been combusted and released back into the atmosphere in the form of CO2. In the same period a further ∼150Gt of carbon has been released from soil carbon pools as a result of changes in land use.
Fossil fuels currently satisfy 85% of global energy demand and fuel a similar proportion of global electricity generation. Even if [CO2] is stabilized before 2100, the warming and other climate effects are expected to continue for centuries, due to the long time scales associated with climate processes. It is likely that the full long-term potential of CCS for emissions reduction will be achieved through the application of a broad portfolio of different technical solutions. While the current CCS frontrunners make a direct attack on anthropogenic emissions, reduction of the atmospheric carbon inventory can be achieved by any approach that can limit fluxes.
The carbon inventories in the atmosphere, biosphere, soils and rocks are linked by a complex set of natural and anthropogenic biogeochemical processes.
The earth’s crust, which represents the upper part of the lithosphere, is the final geological carbon sink. Fossil fuels account for between 4000 and 6000Gt-C, or ∼0.05% of the total organic carbon present in sedimentary rocks. These carbon inventories are subject to constant flux as a result of a web of interlinking natural processes. Human activity has introduced new fluxes, and the effect of these has modified some of the natural fluxes.
The future level of anthropogenic CO2 emissions will be dictated by a wide range of demographic, socioeconomic, environmental, and technological factors. The IPCC created a set of such scenarios in the Special Report on Emissions Scenarios (SRES), published in 2000. These scenarios do include technological developments such as advanced power-generation systems and decarbonization of transport fuels, but the implementation of CCS is not considered.
Models used to predict [CO2] for a given emissions scenario can also be run to establish the range of emissions scenarios that would result in stabilization. The ranges of the two sets of scenarios are extremely broad and can give only a very rough indication of the emissions reductions required.
The process of technology development generally goes by the acronym RDD&D—Research, Development, Demonstration, and Deployment. Table 1.3 describes the characteristics of each of these stages. The 20-year time scale required to bring such technologies to the stage of readiness for commercial deployment highlights corporate vision and environmental commitment.
A. Research
Current CCS examples (2010): Amine-facilitated transport membrane for post-combustion CO2 separation from flue gas.
B. Development
Description: Progress along the development road map; applied research focusing on process engineering and system integration; laboratory and pilot-scale demonstration of the process. Additional fundamental research may be spawned as further implementation issues are identified. Refined construction and operating cost estimates and indications of commercial viability.Current CCS examples (2010): Hybrid combustion–gasification chemical looping using calcium compounds
C. Demonstration
Description: Initial industrial-scale implementation, often funded by government and industry partnerships. May involve the integration of existing, proven technologies in a new application. Evaluation and improvement of the design, construction, and operating processes. Budget-level definition of construction and operating costs.
Current CCS examples (2010): Air-separation plant using ion transport membrane to supply oxyfuel combustion
D. Deployment
Description: Progressive commercial implementation, which, in the early stages, may be accelerated by economic incentives in the form of capital grants or premium prices.
Current CCS examples (2010): Transportation of CO2 by pipeline; geological storage for enhanced oil recovery
Between 85–90% of global electrical power is generated from fossil fuel and biomass-powered steam-driven turbines. The thermal efficiency of this type of plant is limited to ∼40–45% by the achievable temperature of the working fluid (steam) Three alternative approaches to CO2 capture from power generation are at various stages of development.
As well as power generation, a number of other industrial processes contribute a significant fraction of the total CO2 emissions from large stationary sources. The most significant of these are "cement production", "integrated steel mills", "oil refineries".
Two main storage options are available: storage in formations containing non- potable water (saline aquifers) or in oil and gas reservoirs. Saline-aquifer storage of 1Mt-CO2 per year has been demonstrated and is continuing at the Statoil Hydro-operated Sleipner field in the North Sea. Long-term storage by direct dissolution into deep waters could be achieved by venting gaseous CO2 or supercritical fluid.
Carbon capture from fossil fuel-burning power-generation plant will be a necessity if CCS is to make a material impact on total anthropogenic emissions. It is also an area where the opportunity exists for a rapid reduction of emissions, since some key technologies have been developed and deployed in other industries.
Steam temperature is the fundamental determinant of thermal efficiency in a steam cycle. The development of materials capable of operating at ever-higher temperatures is the main focus of RD&D work aiming to achieve higher efficiencies. The progressive development of steels for more advanced steam conditions is illustrated in Figure 3.19.
The elimination of carbon from power plant emissions therefore requires either: Decarbonation of the fuel prior to combustion (pre-combustion capture) or. Separation of CO2 from the products of combustion (post-combustion capture) Reengineering the combustion process to produce CO2 as a pure combustion product, obviating the need for its separation (oxyfueling or oxyfuel combustion).
The Advanced Zero Emission Power Plant (AZEP) concept was originally proposed by Norsk Hydro in 2002. The AZEP concept is a Brayton-cycle gas turbine in which oxyfueled combustion of natural gas is achieved in a mixed conducting medium (MCM) membrane reactor. The ZEC concept integrates a number of advanced technologies including coal gasification and steam methane reforming for hydrogen production.
The capture of CO2 from post-combustion flue gas is complicated by the low partial pressure ofCO2 and the presence of various contaminants in the gas stream. The key requirements for sorption processes to achieve capital and energy efficiency are therefore: High loading of CO 2 per unit volume of sorbent, coupled with low sorbent cost.
The injection of CO2 into permeable rock formations is the only method of carbon storage that has been applied on a commercial scale to date. The key oil and gas industry concepts and technologies that are important for geological storage of captured CO2 are introduced. The most significant problem faced by the geologist is how to characterize sedimentary rock formation for CO2 storage.
Amine-based systems have ongoing development programs aimed at improving the effectiveness and market competitiveness of their proprietary processes. Dry sorbent-based process R&D is developing a process that uses a dry, regenerable, sodium carbonate-based sorbent that captures CO2 in a carbonation reactor.
In contrast to absorption, in which the absorbed component (the sorbate) enters into the bulk of the solvent, adsorbed atoms or molecules (known as adparticles) remain on the surface of the sorbent. Gas separation or purification based on adsorption has a history of industrial application as long as that for absorption-based technologies.
Membranes have a number of potential applications in carbon capture. A membrane acts as a filter, separating one specific component (the permeate) from a mixture of gases in a feed stream. This “filtration” process can involve a variety of different physical and chemical processes, depending on the membrane design and materials.
Distillation has been applied as a technique for separating a mixture of liquids since the second millennium bc. Modern industrial distillation methods were first developed in the 1800s. Distillation techniques are relevant to CCS in two areas: oxygen production by cryogenic air separation for oxyfuel combustion, and the separation of CO2 from natural gas either to treat gas to sales specification.
The aim of the carbon capture methods described in the previous chapters is to produce a pure or near-pure CO2 stream that can then be stored using one or other of the approaches described in Part II. In contrast, approaches based on the processes of mineral carbonation seek to store carbon in the form of products that are chemically stable and relatively benign.
As described in Chapter 2, the world’s oceans contain an estimated 39,000Gt-C. Options that have been investigated to store carbon by increasing the oceanic inventory are described. These include biological (fertilization), chemical (reduction of ocean acidity), and physical methods (CO2 dissolution, supercritical CO2 pools in the deep ocean).
Carbon storage in terrestrial ecosystems can be achieved by increasing the flux of CO2 from the atmospheric into long-lived terrestrial carbon pools, either in or de- rived from plant biomass. Terrestrial ecosystems also respond to local, regional, and global climate variability and change on a variety of time scales and through a multitude of feedback loops. Carbon storage options therefore have a potential role to buy time while other technologies are being brought to readiness for large-scale deployment.
While CO2 is used in a wide range of industrial processes, very few applications result in a reduction of CO2 emissions since products such as urea and methanol have a very short lifetime. Of those applications that do reduce emissions, few have the potential to grow to a scale that would materially affect global emissions. The production of precipitated calcium carbonate by the carbonation of various alkaline wastes and the enhanced use of CO2 in the cement industry are considered.
CO2 transportation in pipelines is possible in the vapor phase. All existing pipelines are designed to operate above the CO2 critical pressure (Pc = 7.38MPa) This has the advantage of smaller pipelines and lower pressure drops for a given mass flow rate. The pressure drop due to friction per unit length of pipeline depends on the diameter and internal roughness of the pipeline.
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