• Energy Research

Abstract Carbon dioxide (CO 2 ) and other greenhouse gases from fossil fuel use in many developed and developing countries are expected to be the major source of anthropogenic emissions for the foreseeable future. As a result, the potential to use CO 2 capture and storage (CCS) for significant reductions in CO 2 emissions from the use of coal (and other fossil fuels) at large point sources could become very important in determining the feasibility of climate change mitigation. Large-scale deployment of CCS in the EU from 2020 has been suggested, but this paper illustrates how time is very short if two complete learning cycles are to be achieved before a possible rollout in the early/mid 2020s. It also highlights some key differences between CO 2 capture technologies that suggest that learning can be achieved more quickly with post-combustion capture than with other options. This might allow rollout to be accelerated by perhaps 5 years for post-combustion capture.

This paper discusses considerations for the design of flexibly operated Carbon Capture and Storage (CCS) pipeline networks and is based on the findings of the Flexible CCS Network Development project (FleCCSnet), funded by the UK CCS Research Centre. The project considered the impact of flexibility across the whole CCS chain, as well as studying the interfaces between each element of the system; e.g. at the entry to the pipeline system from the capture plant and at the exit from the pipeline to the storage site. The factors identified are intended to allow CCS network designers to determine the degree of flexibility in the system, allowing them to react effectively to short, medium and long term variations in the availability and flow of CO2 from capture plants and the constraints imposed on the system by CO2 storage sites. The work of the project is reviewed in this paper which explores the flexibility of power plants operating with post combustion capture systems; quantifies the available time to store (line pack) liquid CO2 in the pipeline as a function of pipeline size, the inlet mass flow rate and operating pressure; and explores the influence that uncertainty in storage parameters have on the design of the pipeline. In addition, parameters influencing short and longer term network designs are discussed in terms of varying flow rates. Two workshops contributed to the direction of the project. The first workshop identified and confirmed key questions to be considered in order to understand the most likely impacts of variability in the CO2 sources and variability in CO2 sinks on CO2 transport system design and operation. The second workshop focused on transient issues in the pipeline and storage site. Although the case studies in the work are UK based, this work is applicable to other situations where large and small sources of CO2 feed into a transportation system. The work is expected to inform a broad range of stakeholders and allow network designers to anticipate potential problems associated with the operation of a CCS network. For an effective design of CCS infrastructure, all of the factors that will have a substantial impact on CO2 flow will have to be analysed at an early stage to prevent possible bottle necks in the whole chain.

AbstractPlanning for Carbon Capture and Storage (CCS) infrastructure needs to address the impact of store uncertainties and store flow variability on infrastructure costs and availability. Key geological storage properties (pressure, temperature, depth and permeability) can affect injectivity and lead to variations in CO2 flow, which feed back into the pipeline transportation system. In previous storage models, the interface between the reservoir performance and the transportation infrastructure is unclear and the models are unable to provide details for flow and pressure management within a transportation network in response to changes in the operation of storage sites. Variation in storage demand due to daily and seasonal variations of fossil fuels uses and by extension CO2 flow is also likely to influence transportation infrastructure availability and the capacity to deliver. This work evaluates, at the level of infrastructure planning, the impact of geological uncertainty on CCS pipeline transportation and injection infrastructure. The analysis presented shows how to consider uncertainty in store properties in combination with CO2 flow variability to estimate the likely impact on pipeline infrastructure design. The operational envelope of the storage site infrastructure is estimated by combining the Darcy flow analysis of simple reservoir models with rigorous process simulation of the storage site wells. The proximity of wellhead conditions to the CO2 equilibrium line and the maximum velocities inside the well constrain the operational envelope of the storage site and limit the ability of the storage site infrastructure to handle CO2 flow variation. These factors, which are significantly influenced by variations in subsurface conditions, have also an impact on the design of the offshore pipeline infrastructure, needing to accommodate changes in pressure delivery requirements. Based on the evaluation of examples developed for different offshore transportation scenarios relevant to the United Kingdom, detailed insight on the expected impacts of store properties on pipeline transportation infrastructure design and operation is provided. For instance, it is found that enabling storage site flexibility is simpler in stores with an initial pressure above 20MPa. Given reductions in reservoir permeability, the requirements for pressure delivery are strongly dependent on the store temperature. Although the analysis is performed for specific geological characteristics in the North Sea the evaluation methodology is transferable to other locations and can be used for site screening to identify sites which are more flexible in terms of uncertainty in store performance.

AbstractRisks associated with technology, market and regulatory uncertainties for First-Of-A-Kind fossil power generation with CCS can be mitigated through innovative engineering approaches that will allow solvent developments occurring during the early stage of the deployment of post-combustion CO2 capture to be subsequently incorporated into the next generation of CCS plants. Power plants capable of improving their economic performance will benefit financially from being able to upgrade their solvent technology. One of the most important requirements for upgradeability is for the base power plant to be able to operate with any level of steam extraction and also with any level of electricity output up to the maximum rating without capture. This requirement will also confer operational flexibility and so is likely to be implemented in practice on new plants or on any integrated CCS retrofit project.

AbstractResultsfor ignition behaviour of pulverised biomass fuels in a 20 litre (L) spherical combustion chamber are presented and discussed. Four types of biomass currently used in UK utility pulverised fuel boilers have been tested for ignition behaviour in air, so at 21%v/v O2, and also, to assess relative performance under oxy-fuel combustion conditions, in a 21%v/v O2, balance carbon dioxide (CO2) balance mixture (21Oxy) and a 25%v/v O2 mixture (25Oxy) respectively. Peak pressures (Pmax) during constant volume ignition and combustion with 2500J and 5000J igniters were measured and recorded. The pressure ratios (P/R), defined as the ratio of the maximum pressure (Pmax) to the pressure at the start of ignition (P0) for each test are reported. A P/R above a threshold of 2.5 is taken as an indication of positive ignition. All four biomass types ignited nearly as readily in 25Oxy as in air at a range of fuel concentrations. Ignition was much less readily achieved in 21Oxy for all fuel concentrations and peak pressures were also generally lower. Results were more erratic with 2500J igniters compared to 5000J igniters, suggesting a relatively stronger ignition source is required with these biomass samples than with pulverised coals previously tested; this is tentatively attributed to larger particle sizes and higher moisture contents. Implications for pulverised fuel oxy-fuel combustion applications are: 1) a primary recycle (PR) stream with 21%v/v O2 would give improved pulverised fuel (PF) milling safety when compared to air firing but reduced ignitability in the burners; 2) a 25%v/v O2 primary stream would approach air behaviour in mills and burners. These preliminary results suggest that approximately 25%v/v O2 may give air-like performance in oxy-fuel pulverised coal plants using oxy-biomass.

AbstractWhilst carbon capture and storage (CCS) technologies are now in the demonstration phase, they are still characterised by a range of technical, economic, policy, social and legal uncertainties. This paper presents the results of an interdisciplinary research project funded by the UK Energy Research Centre (UKERC). The aim of the project was to analyse the main uncertainties facing potential investors in CCS and policy makers wishing to support these technologies through demonstration to commercial deployment. The paper presents a framework for the analysis of these uncertainties, and applies this framework to nine analogue case studies of CCS. These case studies have focused on historical developments in technologies and/or policy frameworks where one or more of these uncertainties has been prominent – and have, in most cases, been partly resolved. The paper also shows applies the insights from these historical case studies to develop three potential pathways for CCS deployment in the UK over the period to 2030. Finally, the paper concludes with some implications for CCS policies and strategies.

AbstractOxyfuel combustion technology is one of several Carbon Abatement Technologies (CATs) currently being developed. The technology offers a means of generating carbon dioxide rich flue gas requiring minimal treatment prior to sequestration or beneficial application. The oxyfuel process is based on excluding the inert components (mainly nitrogen) of air from the combustion process. In oxyfuel combustion, nitrogen is largely absent from the flue gas, since the fuel is combusted with a mixture of nearly pure oxygen (∼95% O2-separated from air in an air separation unit (ASU)) and CO2 rich recycled flue gas. It is recognised as a leading Carbon Capture technology for new and retrofit power plant.Previous studies undertaken by Doosan Power Systems, Air Products, University of Edinburgh and others have shown that there is significant scope to optimise overall plant efficiency, both at the design stage and during normal operation. Therefore the current work seeks to realise these benefits through the adoption of optimised designs and the development of appropriate control and dynamic optimisation strategies.Recycling flue gas in the Oxyfuel process gives rise to a number of operational and control features not seen in conventional air-fired power plant systems. Comprehensive dynamic models of the Oxyfuel process systems and associated controls are being developed as part of the TSB collaborative project “Optimisation of Oxyfuel PF Power Plant for Transient Behaviour” to study these aspects. The Oxyfuel specific models are coupled to a whole cycle, non-linear, dynamic model of the boiler and turbine systems allowing development of control schemes, which can meet the full range of operational requirements and capabilities of the Oxyfuel plant.Early results from the model suggest that operation in Oxyfuel mode may provide an opportunity to improve plant flexibility and both primary and secondary response, a capability which is of increasing importance as the mix of conventional, nuclear and renewable generation changes.