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FRINATEK-Fri prosj.st. mat.,naturv.,tek

Fundamentals of molten salt pyrolysis for cost-effective production of pure solid carbon and hydrogen from natural gas (PyroSalt)

Alternative title: Grunnleggende om smeltet saltpyrolyse for kostnadseffektiv produksjon av rent karbon og hydrogen fra naturgass

Awarded: NOK 11.3 mill.

This project aims at demonstrating the technical and economic feasibility of a novel PyroSalt concept to sustainably convert natural gas to hydrogen and ultrapure solid carbon. The proposed process uses a molten medium, acting as a heat transfer medium and a catalyst to the methane pyrolysis reaction, enabling high methane conversion at reasonably low temperature and small reactor size, to maximize the process economics. The produced carbon can be easily separated to the melt surface by flotation due to its buoyancy. The computational fluid dynamics model of the bubble flow behaviour in the molten salt reactor, developed earlier in the project, has been validated against lab-scale experimental results. The model is therefore available for the design of the optimized experimental setup and for providing insights in the reactor behaviour. Additionally, the model has been used to evaluate the extent to which the reactor performance can be improved by selecting salts with physical properties (density, viscosity and surface tension) that facilitates the desired hydrodynamic behaviour for high methane conversion (small and slowly rising bubbles). While the results show that some optimization is possible due to the wide range of properties of available salts, the room for improvement is relatively small compared to the importance of other factors that will ultimately determine the selection of the molten salt, such as catalytic activity, rate of evaporation, aggressiveness towards reactor materials and effect on purity of the carbon obtained. From the experimental side, a setup for salt screening and kinetic studies was built and commissioned where methane pyrolysis experiments were completed on several types of salts (chlorides, bromides and iodides). The extent of methane conversion to hydrogen and carbon varied with the highest conversion achieved for MnCl2. The produced carbon had a tendency to float to the surface for most of the salts (except for the CaCl2) implying that its recovery would be feasible during operation. SEM images have revealed existence of impurities from both the salts and the crucible, although with different extents depending on the salt. Those impurities were confirmed by XRD characterisation tests which have also revealed that the produced carbon was mainly amorphous although graphitic-like peaks were found for the case of MnCl2. Interestingly the peaks become sharper as the fraction of MnCl2 was increased in NaCl. However, further thermal treatment of the MnCl2 based samples at 1300 °C haven't shown noticeable change on the sharpness of the peak which means that the analysed samples are unlikely to be graphitic carbon. Key challenges were the chemical aggressiveness (destroying the crucible) and rapid evaporation of the salts. Work started on the techno-economic assessment of the molten salt pyrolysis process via an intern from INP Toulouse, showing good prospects for the technology. Relative to conventional blue hydrogen production (steam methane reforming with CO2 capture), pyrolysis avoids considerable costs related to steam generation, water-gas shift reactions, and CO2 capture, transport, and storage. Aside from technical challenges with the reactor, the key obstacle to the techno-economic success of this technology is the addressable market for the pure carbon product. A preliminary assessment of carbon markets showed that a mature molten salt pyrolysis technology can sell carbon at prices (200-300 ?/ton) that can compete in large markets in the metallurgical and chemical process industries. Access to such large markets makes the pyrolysis technology ideal for producing clean hydrogen from natural gas in countries that face public resistance to CO2 transport and storage. Smaller, higher-priced carbon markets like carbon anodes and graphite (> 400 ?/ton) can ensure profitability of more expensive early plants, helping to drive the technology cost down via learning and scale. In addition, the potential for using molten salt pyrolysis to convert higher hydrocarbons (which crack at much lower temperatures than methane) in natural gas as a pre-treatment step to conventional blue hydrogen production was also investigated. Although it requires CO2 transport and storage, such an approach greatly increases the H2/C output ratio of the plant, alleviating possible constraints from the size of the carbon market, while significantly improving the economics of blue hydrogen. Two journal papers are being submitted summarizing the two technoeconomic assessment studies.

This project aims at demonstrating the technical and economic feasibility of a novel PyroSalt concept to sustainably convert natural gas to hydrogen and ultrapure solid carbon. The proposed process uses a molten salt, acting as a heat transfer medium and a catalyst to the methane pyrolysis reaction, enabling high methane conversion at reasonably low temperature and small reactor size, to maximize the process economics. The produced carbon can be easily separated to the melt surface by flotation due to its buoyancy. The project proposes a holistic approach combining fundamental modelling and experimental studies, as well as market analysis for setting up business cases for industrial use of the produced carbon. A large focus will be on understanding the complex three-phase reactive flow in the molten salt pyrolysis process. Established CFD models, TGA and flow measurement using dynamic pressure will be used to screen and map out the different parameters influencing the process performance. The dynamic pressure probe will be made to carry out measurement under real reactive conditions, making the collection of flow hydrodynamics data under extreme conditions possible. The measured data includes bubble size and frequency to be used for validation of CFD models and as closures for a 1D phenomenological model for simulation of large scale PyroSalt process. Finally, the potential of implementing a microwave system for heat supply to the endothermic pyrolysis reaction will be tested in the project to demonstrate the ability of the PyroSalt process to completely remove CO2 emissions from natural gas based production of pure carbon and hydrogen. If successfully demonstrated, PyroSalt can maximize the eco-environmental value of natural gas and speed up the transition to an energy dominated by hydrogen and renewable energy

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FRINATEK-Fri prosj.st. mat.,naturv.,tek