Sustainable Technologies, Systems & Policies - العدد الحالي

The paper gives a general introduction and overview of Carbon Capture and Storage (CCS) with an emphasis on the capture of CO 2 and other greenhouse gases from the waste gas streams of power plants and industrial processes. This stage accounts for about 80% of the overall cost of the CCS process so is the area where efficiency and cost improvements will have the greatest future impact. The major drivers for continuing to use fossil fuels for most of this century are first considered and the need to implement CCS as one of many measures to mitigate carbon emissions. Current targets will require a commercial CCS capacity to remove about 10Gte CO 2 pa by 2050. The overall features of CCS processes are described – capture, compression and transport, sub-surface storage – covering the main capture options and the three main types of storage site (deep saline aquifers, depleted oil and gas reservoirs and unmineable coal seams). The current status of large-scale CCS demonstration projects is reviewed. The main classes of carbon capture technologies are then described, both those currently capable of large-scale deployment and those in development for the future. Finally the main challenges facing CCS, to make it a globally-deployed commercially viable technology, are summarised and suggestions made for future developments in the clean recovery and use of fossil fuels which combine CCS with sub-surface processing.

Fossil fuel-based power generation technologies with and without CO 2 capture offer a number of alternatives, which involve different fuel production and supply, power generation and capture routes with varied energy consumption rates and subsequent environmental impacts. The holistic perspective offered by Life Cycle Assessment (LCA) can help decision makers to quantify the trade-offs inherent in any change to the fuel supply and power production systems and ensure that a reduction in greenhouse gas (GHG) emissions does not result in increases in other environmental impacts. Beside energy and non-energy related GHG releases, LCA also tracks various other environmental emissions, such as solid wastes, toxic substances and common air pollutants, as well as the consumption of resources, such as water, minerals and land use. In this respect, the dynamic LCA model developed at Imperial College incorporates fossil fuel production, transportation, power generation, CO 2 capture, CO 2 conditioning, pipeline transportation and CO 2 injection and storage, and quantifies the environmental impacts at the highest level of detail, allowing for the assessment of technical and geographical differences between the alternative technologies considered. The life cycle inventory (LCI) databases that were developed, model the inputs and outputs of the processes at component or unit process level, rather than “gate-to-gate” level, and therefore generate reliable LCI data in a consistent and transparent manner, with a clearly arranged and flexible structure for long-term strategic energy system planning and decision-making.

The presentation discussed the principles of the LCA models developed and the newly extended models for the natural gas-fired power generation, with alternative CO 2 capture systems. Additionally, the natural gas supply chain LCA models, including offshore platform gas production, gas pipeline transportation, gas processing, liquefied natural gas (LNG) processes, LNG shipping and LNG receiving terminal developed are used to estimate the life cycle GHG emissions for an idealised case study of natural gas production in Qatar, LNG transportation to a UK natural gas terminal and use in a power plant. The scenario considers a conventional and three alternative CO 2 capture systems, transport and injection of the CO 2 offshore in the Irish Sea.

Combustion modes in gas turbines are evolving in order to meet requirements related to lower emissions and greater thermodynamic efficiency. Such demands can be contradictory and the additional complication of fuel flexibility comes to the fore with potential new fuel stream opportunities arising. The latter may include hydrogen and carbon monoxide rich streams as well as blends with significant amounts of carbon dioxide arising from certain types of syngas (e.g. bio-derived). The matter is further complicated by the impact of combustion stability related issues that arise in the context of the ubiquitous transition to lean pre-vapourised premixed (LPP) combustion for power generation applications. Post-combustion carbon capture is generally considered the leading candidate in the context of LPP based technologies. Significant capture related issues arise in terms of parasitic losses associated with CO 2 separation and transportation technologies (e.g. compression). The former is typically the major contributor and the relatively low concentration of CO 2 in flue gases, combined with excess oxygen resulting from LPP based operation, does impact separation technologies. It hence appears natural to consider the operating mode of the gas turbine and the impact of the fuel composition on the flue gas characteristics alongside the development of efficient and novel separation technologies.

Large improvements in separations technology will require novel materials with enhanced properties and performance. The fundamental interlinks for success in merging synthesis and process incorporation are the structure, relevant physical/chemical properties, and performance of new materials. Specific materials with these interlinks are room-temperature ionic liquids (RTILs) and their polymers and composites. As a chemical platform, RTILs have an enormous range of structural variation that can provide the ability to “tune” their properties and morphology for a given application. Introduction of chemical specificity into the structure of RTIL-based materials is an additional key component. Membrane separation is the focus as a process for implementation. There have not been new materials successfully developed for this process in thirty years. For CO 2 capture, the target improvement in productivity is two orders of magnitude or more compared to commercial materials currently available.

The ability to rationally design materials for specific applications and synthesize materials to these exact specifications at the molecular level makes it possible to make a huge impact in carbon dioxide capture applications. Recently, advanced porous materials, in particular metal-organic frameworks (MOFs) and porous polymer networks (PPNs) have shown tremendous potential for this and related applications because they have high adsorption selectivities and record breaking gas uptake capacities. By appending chemical functional groups to the surface of these materials it is possible to tune gas molecule specific interactions. The results presented herein are a summary of the fundamentals of synthesizing several MOF and PPN series through applying structure property relationships.

The literature concerning the application of CCS to industry is reviewed. Costs are presented for different sectors including “high purity” (processes which inherently produce a high concentration of CO 2), cement, iron and steel, refinery and biomass. The application of CCS to industry is a field which has had much less attention than its application to the electricity production sector. Costs range from less than $ 2011 10/t CO 2 up to above $ 2011 100/t CO 2. In the words of a synthesis report from the United Nations Industrial Development Organisation (UNIDO) “This area has so far not been the focus of discussions and therefore much attention needs to be paid to the application of CCS to industrial sources if the full potential of CCS is to be unlocked”.

Absent an economic or social cataclysm, there is no plausible way to meet what will be the world’s unavoidable energy demands without utilizing its vast supply of fossil fuels. One important technology being contemplated to mitigate the negative impact of anthropogenic carbon dioxide loading of the atmosphere is Carbon Capture and Storage (CCS). CCS will play a vital role in least-cost efforts to limit global warming.¹ To achieve future least-cost solutions, second generation or ‘2.0’ carbon capture materials are being developed with government support to improve efficiencies over the current applied solution that is “a very expensive proposition”² for the installed energy generation base. One 2.0 material, Metal Organic Frameworks (MOFs), is “capable of increasing (carbon dioxide) selectivity, improving energy efficiency, and reducing the costs of separation processes”³ in CCS. Such materials can address CCS utilization outcomes in addition to lowering the carbon capture cost. To support further 2.0 carbon capture material development while CCS faces economic challenges, framergy™is leveraging alternative usages for MOFs and other 2.0 materials developed for carbon capture.

In this contribution, we present an overview of the contribution made by the shipping sector to global CO 2 emissions. We review the currently proposed technology options for mitigating these emissions, and propose a new option for the control of greenhouse gas emissions from shipping.