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Solar Steam Reforming of Methane Rich Gas for Synthesis Gas Production (SOLREF)

Final Report Summary - SOLREF (Solar Steam Reforming of Methane Rich Gas for Synthesis Gas Production)

The solar reforming process which is carried out in the SOLREF project enhances the calorific value of CH4 by 25%, contributed by the solar energy. The synthesis gas produced (CO+H2) can either be used to generate electricity, to provide hydrogen as an energy vector or to produce Fischer Tropsch synthetic fuels. Solar reforming of CH4 was tested in a 400 kW scale. a result of this project was that essential modifications are required to advance this unique solar technology to the prototype stage in the 1 MW range.

In the beginning a design study for a prototype to be operated at a natural gas well in southern Italy was planned. Due to a change in the consortium this was changed to cover more possible locations in the whole Mediterranean region. The major innovative modification of SOLREF is a new catalytic system for higher operating temperatures which allows a broad range of feed compositions and means to avoid the carbon deposition in the reformer reactor.
In addition an advanced solar reformer was developed including basic mechanical and process improvements, like a new front flange, innovative insulation and replacement of the nitrogen purge streams. These modifications were tested and validated under real solar conditions at the Weizmann Institute of Science in Israel. Besides, biogas, landfill gas and contaminated natural gas (CH4 with a high content of CO2) can be processed and upgraded, using the SOLREF technology. With this feedstock, reduction of CO2 emission is significantly enhanced.

The work in SOLREF was carried out in five work packages (WPs). The following aims were tackled.

- investigate various catalyst systems;
- determine the kinetics of the final selected catalyst;
- simulate mass and heat transport and reaction in porous absorber;
- simulation of the transport and reaction in the porous absorber;
- preparation of the solar reformer-scale catalyst-coated segments.

Using a wide variety of experimental analysis methods, an appropriate catalyst was selected and coated onto a 3D-foam absorber material. Its thermal durability was partially assessed by experimental methods as a function of temperature. N2 physisorption (BET), CO adsorption (COMA), transmission electron microscopy (TEM) and x-ray diffraction (XRD) were used to characterise the catalysts.

Moreover computational models were used to develop a silicon carbide 3D foam as a carrier for the catalyst with excellent thermal properties for this task. Models for the simulation of the heat and mass transfer based on computer tomography generated 3D foams were developed by ETH and are available.

- develop an advanced 400 kW solar reformer;
- perform thermodynamic and thermo-chemical analyses to support the system design phase.

Based on the boundary conditions at the Weizmann Institute of Science (WIS), the layout of the absorber was realised. The shape of the absorber was chosen in a way that the angular averaged solar flux density is between 470 kW/m2 and 700 kW/m2 on the centre disc and the rings of the main absorber section. To bring SOLREF technology forward to market introduction, a certification process for the pressurised metal components (vessel and flange) was carried out in the Netherlands organised by HyGear and DLR. The final detailed construction is based on the certified vessel and flange.

In parallel a thermo-chemical analysis and a system model of the existing test plant at WIS were realised. a steady state system model for the WIS test plant was implemented and tested. The model can be used to predict the results of changes in the system layout.

For investigating the transient behaviour of the solar reforming plant, a dynamic model of the existing test plant was developed. This model is focusing on the transient behaviour of the solar chemical receiver. This model allows studying the transient behaviour of the reactor during solar operation. It is a tool for implementing reactor controls, optimising start-up and shut-down routines and assessing the influence of design changes on reactor dynamics to substitute the purge gas (N2) feed.

A pressure swing adsorption system was developed and installed. H2 can now also be used as purge gas feed to reduce cost.

- operate the reformer with gas mixtures which represent the variety of possible feedstock on the solar tower at WIS, Israel, producing partly-solar hydrogen;
- evaluate new operation strategies.

The receiver is fully functional and was installed on the solar tower at the Weizmann Institute of Sciences. A test campaign was carried out demonstrating the feasibility of the SOLREF technology. The storage vessel was used for the test with an amount of 2.2 tons liquefied petroleum gas (LPG) (for generating the steam and preparation of the methane). a battery of 16 cylinders with CO2 with a pressure of 50 bars and a total weight of 400 Kg, a battery of 42 cylinders with H2 with a pressure of 200 bars and total volume of 420 Nm3 and a battery of 24 cylinders with N2 with a pressure of 200 bars and total volume of 240 Nm3 were used to run the test campaign. The catalyst in the pre-reformer was activated. All system checks were performed positively. Minor adjustments were carried out to guarantee a fast start-up from standby status to the hot tests.

- pre-design of a 1 MWth prototype plant in southern Italy;
- conceptual layout of a commercial 50 MWth reforming plant.

Two different cases, 1 MW and 50 MW solar tower concepts, were analysed. For each case two types of reformer were investigated and two possible solutions were analysed. The first solution consists in the reformer integrated type. The second solution is the separated reformer type. The integrated reformer type allows a more compact construction, since the solar receiver has the catalyst on the internal surfaces that permit the reforming process. The separated reformer type allows a wider range of working temperature and a smaller and more compact solar receiver.

Assessments on the solar sub components were performed. For the top solutions results for the small 1 MW prototype and the 50 MW commercial plant are obtained based on cost and optical optimisations. Due to the cost-benefits analysis, the tower top solution with the integrated reformer type was chosen.

- assess on potential markets including cost estimation and environmental, socioeconomic, and institutional impacts.

In order to analyse the markets for a renewable energy technology such as the solar reforming process of methane or LPG, well founded information on demand and resources, technologies and applications is essential. In a detailed analysis carried out by the systems analysis department of DLR showed the possibilities for the application of the technology with a focus of the Middle East and Northern African (MENA) region.

The SOLREF technology has efficiency benefits compared to other technologies for renewable fuel especially hydrogen production, since it allows the production of hydrogen and storage of the produced CO2 in the same location using only solar energy. Therefore its carbon footprint is much smaller compared to its competitors based on fossil resources. It becomes even smaller if renewable carbon sources are used like biogas. Based on these results it could be shown that SOLREF is a feasible technology as well for the generation of a partly renewable fuel for the MENA region as for the fuel supply for Europe.

The communication actions were related to:
- presentation of research results;
- interaction with other European projects;
- introduction of the technology into the market;
- planned actions beyond the project (e.g. realisation and the construction of a 1 MWth prototype plant);
- continuation of the operation of the SOLREF reactor at CSIRO, Newcastle, Australia.

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