An innovative oxy-fired supercritical CO2 power cycle for highly flexible electricity generation

Lead Research Organisation: University of Edinburgh
Department Name: Sch of Engineering

Abstract

The proposed project title is 'An innovative oxy-fired supercritical CO2 power cycle for highly flexible electricity generation.' The power cycle referred to above is also known as the Allam Cycle, and is a novel system which promises to be as efficient as conventional cycles, with the ability to match or improve upon their cost of electricity (Netpower, 2016). The cycle uses an Air Separation Unit (ASU) to isolate the oxygen from the air, resulting in oxy-fuel combustion. The main constituent of the combustion products which drive the turbine generator is carbon dioxide (CO2), the majority of which is then reintroduced to the power cycle. As the rest of the CO2 may be captured and transported for storage, Allam Cycle power production inherently incorporates carbon capture as well as facilitating energy storage, two of the most desirable characteristics of near-future electricity supplies.

Research from the University of Edinburgh introduced the concept of flexible operation of conventional plants with Post Combustion Capture (PCC) using an amine solvent (Lucquiaud et al, 2008; Chalmers et al, 2009). The CO2 absorber is either bypassed or the energy penalty of solvent regeneration and storage is shifted from times of high electricity prices to low electricity prices by employing interim solvent storage. In the same way as amine solvent storage, air separation for oxygen production in the ASU is a very energy intensive step that can be decoupled from the main power generation process, as proposed for oxy-fired coal power generation (IEAGHG, 2012). The decoupling of oxygen production and power generation, which is achievable via the use of liquid oxygen storage, can compensate for the slow start-up time of the ASU, allowing for cheaper electricity generation in times of low production from wind power resources. When power generation from wind is high, the power cycle operates at minimum load to return net zero output to the grid and maintain a substantial CO2 flow to the transport and storage system.

The study will involve the use of gPROMs software to model the power plant, with the incorporation of process optimisation and intensification. Potential improvements to the current design will be evaluated, for example, the use of liquid oxygen storage to compensate for the slow start-up time of the ASU. Integration with the electricity network and the CO2 transport network will also be accounted for to provide a comprehensive first-of-a-kind study applying an advanced operational flexibility concept to Allam Cycle power plants.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509644/1 01/10/2016 30/09/2021
1941221 Studentship EP/N509644/1 01/09/2017 31/08/2019 Charlotte Elizabeth Mitchell
 
Description The Allam Cycle is a novel oxy-combustion gas turbine power cycle with a reported net cycle efficiency of 58-60% LHV and near-zero operating emissions.

An Allam Cycle process model was developed displaying a net cycle thermal efficiency (LHV) of 58.0%, a higher value than previously reported in the literature, due to the inclusion of a bypass stream heat source.

Novel modes of operation of the power plant were modelled to improve plant operational flexibility, including a temporary increase in cycle efficiency to 66.1%, with the use of liquid oxygen storage to shift the energy penalty of oxygen production. This facilitates decoupling oxygen and electricity production and operates as a form of energy storage.

For the first time, a purpose-built Unit Commitment and Economic Dispatch (UCED) model was used to investigate the impact of Allam Cycle plants and of liquid oxygen storage on centralised electricity system costs and grid CO2 intensities, taking the illustrative case of the GB electricity system.

The UCED demonstrated the potential behaviour of Allam Cycle plants in future electricity systems and their impacts on reducing electricity system running costs and on grid CO2 intensity. Adding oxygen storage to these plants was shown to allow surplus renewable energy generation to be stored, thus avoiding wind curtailment.
Exploitation Route Academics can benefit from an improved method for modelling the Allam Cycle power plant, specifically its turbine and heat exchanger system. From the associated research paper, they will now be aware that the addition of liquid oxygen storage to Allam Cycle plants is a promising concept and worthy of further research.

Industrial actors will benefit from an in depth, independant scrutiny of the Allam Cylce technology and also that that the addition of liquid oxygen storage to Allam Cycle plants is a promising concept and potential worthy of industrial development.
Sectors Energy,Environment