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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 as 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. A computational fluid dynamics model of the bubble flow behaviour in the molten salt reactor has been developed 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. While preparing these results for a journal paper, it was found that the model overestimates the effect of the bubble surface area on the methane conversion compared to experiments, indicating that the present assumption of a surface reaction is invalid. The reaction model is therefore currently being improved. From the experimental side, a setup for salt screening and kinetic studies was built and commissioned, and 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 characterization tests which have also revealed that the produced carbon was mainly amorphous. Key challenges were the chemical aggressiveness (destroying the crucible) and rapid evaporation of the salts. For microwave application, an existing setup was upgraded and adapted for accommodating microwave driven molten salt methane pyrolysis. The focus is on the salts investigated previously using conventional electric heating. Application of microwaves brings other dimensions to salt screening, arising from the nature of salt interaction with microwaves. Salts are usually opaque to microwave radiation at low temperature, making it difficult to melt and heat up to reaction temperature. The focus is on finding creative ways to address this challenge. The microwave driven PyroSalt concept behavior, at molten conditions, will not only depend on the salt catalytic activity towards methane pyrolysis, but largely on the salt interaction with microwave (penetration length and ability to absorb microwave). Multiple approaches are being implemented to address the different molten salt behaviors towards microwave. The different approaches will result in different Pyrosalt reactor designs. Two peer-reviewed papers have been published, showing good economic prospects for the technology. Relative to conventional blue hydrogen production (steam methane reforming with CO2 capture), pyrolysis achieves substantial process simplifications and avoids the need for CO2 transport and storage. The size of the market for the pure carbon product is a key constraint, but results showed that hydrogen from pyrolysis can compete at carbon sales prices of 200-300 €/ton, granting access to large markets in the metallurgical and chemical process industries. 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. Lower-temperature pyrolysis employed as a pre-reforming step to conventional blue hydrogen production was also found to be economically attractive, presenting a promising early market. Ongoing work is exploring lower-temperature pyrolysis for partial decarbonization of natural gas to the level of 20% H2 that can be safely handled by existing natural gas infrastructure. Here, a 500 €/ton sales price of the carbon by-product makes the partially decarbonized natural gas product cheaper than the incoming natural gas. In parallel, detailed energy system modelling work is ongoing to illustrate how pyrolysis can help Norway supply European countries with resistance to CO2 transport and storage with decarbonized natural gas.

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