Capturing CO₂ using coal gasification

Fundamentals of gasification

• Scientific investigation of the material changes in gasification processes (material models) with the goal of improving understanding and then using this as a basis to optimise the gasification process
• Modelling/simulation of reactive multi-phase flows (process models) with the goal of improving reactor zones and geometries
• Establishment of databanks as the basis for material and process modelling/simulation
• Investigation of interactions between the gas phase, slag, deposits and equipment materials during heating and cooling processes with the goal of improving the temperature-dependent process control
• Modelling/simulation of the dynamic behaviour of gasifiers with the goal of optimally coordinating the process control of the individual plant components

 

IGCC power plant concepts and components

• Flexible and efficient gasification / cooling of raw gas
• Increasing the cold gas efficiency to over 85% using quench conversion, partial conversion and heat coupling inside the gasifier
• Improving robustness by avoiding slagging, soiling and corrosion
• New flexible fuel supply systems
• Entrained-flow gasification: Making high-temperature heat useful without reducing availability (e.g. partial quench)
• Fluidised bed gasification: Flexible operation with various fuels and an extension of the range of fuels
• Complete gasification, e.g. by integrating fixed-bed gasification for post-oxidation of carbon-containing residues
• Reducing the CH₄ and CO content of raw gas
• Low-emission combustion of hydrogen-rich gases in highly efficient gas turbines
• Optimisation of the overall IGCC concept, i.e. integration of air separation unit, CO conversion and CO₂ capture in particular
• Dynamic modelling of the overall process
• Optimisation of operation control during start-up and shut-down processes and during load changes
• Study of partial-load capability
• IIGCC, CTG and CTL, and combinations of these processes (polygeneration)

 

Developments in combined power plants for the period after 2020

• High-temperature IGCC processes with CO₂ capture
• Gas purification processes that work at high temperatures and are ideally dry
• High-temperature H₂ membranes for conversion reactions
• High-temperature CO₂ capture with chemical sorbents that can be regenerated
• Hybrid power plant (IGCC + fuel cell)
• High-temperature fuel cell (SOFC) with integrated CO₂ capture

The combined power plant technology with integrated coal gasification is important because it offers certain promising advantages for CO₂ capture. One advantage is that other products alongside electricity and heat are produced by the power plant. These include synthetic fuels and raw materials for the chemicals industry. In this way, the power plant sector will be able to offer alternatives that reduce dependency on oil in the future. Another advantage is that the gasification unit and the combined power plant can be built in separate construction phases and at separate locations. The initial challenge is to develop robust, efficient and cost-effective technology on a commercial scale.

 

Alongside their great potential for efficiencies of over 50%, coal-fired power plants based on IGCC technology also offer the advantage that CO₂ can be captured in an effective manner. Even with CO₂ capture, relatively high efficiencies of over 40% and a high degree of fuel flexibility can be achieved with very low overall emissions. The power plant can also be run without CO₂ capture.

 

A range of different gasification processes have now been implemented from an engineering viewpoint. These can be classified as fixed-bed, fluidised-bed and entrained-flow gasification depending on the type of gas-solid contact that takes place. Pressure gasification processes are used on a large technical scale for coal gasification. Technical-grade oxygen or mixtures of steam and oxygen are used as the gasification agent here. The processes are classified depending on the process temperature into those with dry ash removal (conventional fixed-bed and fluidised-bed processes with temperatures below 1300 °C) and those with liquid slag removal (entrained-flow and slag-bath processes with temperatures above 1300 °C). The actual temperature limit is ultimately defined by the melting behaviour of the ash, which depends on the fuel.

 

A commercial breakthrough for IGCC power plants has been hindered by insufficient competitiveness, reliability and availability up to now. The high investment costs, which are over 20% above those for conventional coal-fired power plants, cannot yet be compensated by the efficiency and availability values of a maximum of 45% and 80%, respectively, for plants already in operation. The integration of CO₂ capture technology leads to additional costs and to losses in efficiency of 6-10%. This increases the financial and engineering risks associated with this technology.

The first IGCC demonstration projects were carried out back in the 1970s and 1980s and had electrical efficiencies of up to 36% and power ratings of up to 160 MW. Among these was a project in Germany which saw the construction of the first IGCC power plant in the world in Lünen in 1972. Another system had already been built in 1964 in Schwarze Pumpe. This system, which is still being operated today in partially overhauled and extended form, is mainly used for methanol synthesis. The gas and steam part of the plant generates 75 MW of electrical power and raises process steam for the seven fixed-bed gasifiers, the slag-bath gasifier and the two entrained-flow gasifiers.

A large-scale plant for lignite gasification has been designed by Rheinbraun (KOBRA), but after completion of a comprehensive R&D programme it was not built. The raw gas was to be produced in a high-temperature Winkler (HTW) gasifier. The process had previously been successfully tested in a pilot plant (1978–1985) and in two demonstration plants (1986–1997 and 1989–1992).

Among the IGCC power plants currently in operation are those in Buggenum in the Netherlands, Wabash River und Tampa in the USA, Puertollano in Spain, and Vresova the Czech Republic.  These plants have been in service since the mid-1990s and are also referred to as second-generation IGCC power plants. Most of these plants are based on the entrained-flow process. The Vresova plant is currently the only lignite-fired IGCC power plant. Since 2008, a Siemens entrained-flow gasifier has also been in service alongside Lurgi dry ash fixed-bed gasifiers. The electrical efficiencies of the plants lie between 40 and 45%, and the maximum availability achieved is 80%.

HotVeGas - Fundamental investigations on the development of future high-temperature gasification and gas purification processes for IGCC power plants with CO₂ capture and on the production of synthetic fuels
Organisations carrying out research: Technische Universität München - Institute for Energy Systems
Technische Universität Bergakademie Freiberg - Faculty of Mechanical, Process and Energy Engineering - Department of Energy Process Engineering and Chemical Engineering
Project numbers: 0327773A, 0327773B

Thermochemical modelling
Organisation carrying out research: Forschungszentrum Jülich GmbH, Institut für Werkstoffe und Verfahren der Energietechnik (IEK)
Project number: 0327773C

Thermochemical and thermophysical databases
Organisation carrying out research: GTT Gesellschaft für Technische Thermochemie und -physik mit beschränkter Haftung
Project number: 0327773D

 

TEIMAB - Entrained-flow gasification reactor with partial quench and heat recovery system
Organisation carrying out research: Siemens AG - Power Generation
Project number: 0327797A

Thermodynamic modelling of ash and slag
Organisation carrying out research: Technische Universität Bergakademie Freiberg - Faculty of Mechanical, Process and Energy Engineering - Department of Energy Process Engineering and Chemical Engineering
Project number: 0327797B

Entrained-flow gasification reactor with partial quench and steam generator based on heat recovery, CFD calculations for gasifier
Organisation carrying out research: Universität Duisburg-Essen - Chair of Environmental Process Engineering and Plant Design
Project number: 0327797C

 

Development of special measurement and analysis technology, measurements in the test plant, and modelling of the various process stages with CFD calculations
Organisation carrying out research: German Aerospace Center  (DLR) - Standort Stuttgart - Institute of Combustion Technology (EN-VT)
Project number: 0327797D

 

CO₂ reduction using innovative gasifier design - COORVED (development of innovative large-scale gasifier designs for the production of combustion gas and synthesis gas from lower-quality coal for use in IGCC power plants)
Organisation carrying out research: Technische Universität Bergakademie Freiberg - Faculty of Mechanical, Process and Energy Engineering - Department of Energy Process Engineering and Chemical Engineering
Project number: 0327865

 

Coal gasification using polygeneration
Organisation carrying out research: Technische Universität Bergakademie Freiberg - Faculty of Mechanical, Process and Energy Engineering - Department of Energy Process Engineering and Chemical Engineering
Project number: 0327768A