Innovative In Situ CO2 Capture Technology for Solid Fuel Gasification (ISCC)

Final Report Summary - ISCC (Innovative In Situ CO2 Capture Technology for Solid Fuel Gasification)

The ISCC project aimed to develop a new process for upgrading high moisture low rank brown coals yielding three valuable products:
- a fuel gas consisting of mainly hydrogen to be used in power generation;
- a purge gas stream containing > 95 % CO2, ready for transportation to storage (CO2 capture > 90 %) or chemical fixation;
- a pre-calcined feed for a cement kiln consisting of CaO, coal ash and required additional minerals.

The ISCC technology is based on the lime enhanced gasification (LEGS) reaction. The LEGS reaction combines steam gasification of low rank, high moisture brown coal, with the high temperature removal of CO2 by using high temperature efficient sorbent materials (e.g. lime). The combination of the gasification and the in situ CO2 capture shifts the reaction towards H2 production in the gas stream. The CO2 laden sorbent material must be regenerated in an additional regeneration step before being recycled back into the gasifier. The high number of carbonation-calcination cycles experienced by the sorbent particle places high demands on the necessity for a robust, mechanically and chemically stable sorbent.

The project was structured into six work packages (WPs), as follows:

- WP1: Definition of feed characteristics and process requirements
Due to the strongly exothermic CO2 absorption during steam reforming a slightly exothermic gasification reaction can be adjusted leading to minimised energetic losses and a simple reactor design. In addition to the main reactions steam reforming, water gas shift reaction and CO2 absorption must be taken into account in a detailed examination. Furthermore, the removal of sulphur by CaO must be investigated in more detail.

Beside the hydrogen rich gas a solid product consisting of limestone, CaO, char, ash, gypsum and CaS is produced during the LEGS reaction. The solid product has to be separated from the gas and must be processed in a further process unit. This process can be described as a modified lime kiln with high temperature input and simultaneous CaS oxidation.

- WP2: Basic investigations CO2 absorbent properties and mechanical performance
Natural limestones have been the main focus of investigation, because they are the cheapest and most widely available materials for the purpose of the ISCC process. Test have been carried out in a range of laboratory installations and devices in the different institutions, including different termogravimetric equipment, small fixed and fluidised beds reactors both at atmospheric and high pressure. Electron microscopy and mercury porosimetry have been the techniques employed to follow the textural changes in the sorbent as reaction progresses.

- WP3: Regeneration process development
The first task of WP3 started with a screening of heat transfer methods showing the borders of technically and economically feasibility. Based on that, some of the initial ideas for the regeneration process had to be rejected and the experimental work was concentrated on the remaining options. During the ongoing ISCC process development the parameter frame conditions of gasification and regeneration became more clarified. Operating at elevated pressure helps in the gasifier to increase conversion rate and CO2 absorption, but it is disadvantageous for the regeneration step. One of the project aims was to produce a concentrated CO2 stream (> 95 %) in the regenerator. Equilibrium calculations showed that along with high pressure and pure CO2 atmosphere very high regeneration temperatures were required. Under that challenging process conditions (up to 1 000 degrees Celsius and above) little experience was available which had to be generated in experimental work mainly at ZSW and VTT. In task 3.3 IVE evaluated the remaining regeneration options concerning their performance in an integrated ISCC concept.

On the one hand the activities in WP3 (screening, experimental, evaluation) showed the upper limitation of regeneration process conditions. On the other hand, this knowledge is available to develop and evaluate first applicable solutions for the regenerator even for a pressurised ISCC system up to 20 bar. Further process evaluation can be found in WP5.

- WP4: Pilot scale experiments of gasification and regeneration process
The major objective of this WP was to test the feasibility of the pressurised gasification and calcination process. The feasibility of the process has been demonstrated. The semi-batch tests showed good and promising results and the deactivation of the sorbents was corresponding to the TGA results which confirmed the design rules used in the following work packages. The future works should concentrate on testing the coupled process in an interconnected fluidized bed system. In a first step, atmospheric testing is suggested before a pressurized plant with its huge investment requirements is planned.

- WP5: Process design and technical assessment
The objectives of WP5, according to the work programme, were the following:
- determine the plant design with all required components;
- simulation of the overall process and evaluation of the efficiency;
- comparison with alternative processes for very low emission power generation from coal;
- design of a semi-technical plant to demonstrate the technical feasibility of the process and industrial plant design.

By the end of the project, the original goals of the WP have been achieved.

- WP6: Socio-economic assessment
The technical, economic and environmental performance of six IGCC plant designs, including four ISCC plant concepts with CO2 capture and two conventional shell type IGCC plants, one with and one without CO2 capture, fuelled by lignite coal were studied through ECLIPSE simulations. ECLIPSE mass and energy (M&E) simulation results were validated with NTUA results from WP5.2 and 5.4. The main aims and objectives of the techno-economic study were to evaluate the impacts of new ISCC CO2 concepts on the plant output, efficiency, CO2 capture efficiency, environmental emissions, investment costs, cost of electricity and CO2 mitigation costs including sensitivity studies.

The ISCC process is a new technology in support of European Union policy objectives. These include reduction of greenhouse gas emissions, a safe and cost effective energy supply, and decreased dependency on energy imports. Europe has large, economically available reserves of brown coal for which the ISCC process is designed. After a basic description of cement production process, the specific problems of using purge as a raw material substitute like influence of sulfur from brown coal and re-carbonation of CaO by kiln exhaust gas are made evident.

The non-questionable advantage of LEGS is the ability of direct coal conversion to one valuable product - hydrogen with a separate stream of sequestration ready carbon dioxide as the second major product from the plant. The high sulphur content, low quality coal up to the wasted coal residues could be gasified in the process. This makes the LEGS to be an attractive offer for the potential utilisation of coal fines produced in large amounts by long wall mining techniques. Contrary to the classic IGCC techniques, low quality fuels with high sulphur content could be processed in the LEGS system without any extra modification of the future plant.

Final Report Summary - ISCC (Innovative In Situ CO2 Capture Technology for Solid Fuel Gasification)

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