Cheap ammonia crackers for automotive, heavy duty mobility, and energy storage using using nickel catalysts

Industrial scale catalysts have been processed intensified by reducing particle size, increasing Ni loading, and increasing specific surface. “Employing the catalyst in powder form instead of in granulated or pellet form significantly reduces the temperature at which an efficient decomposition of ammonia into hydrogen and nitrogen can be effected”. The main reason why the industrial-scale annealing (forming gas) crackers have higher decomposition temperature is due to large catalyst pellet size, usually 20 mm. While typical industrial ammonia cracking catalysts from China (Liaoning Haitai Technology), have Ni loadings of 14%, with GHSVs of 1-3000 with conversion of 99+% at 800-1000 C, some literature pulled up from mining Google patents citing physical testing indicate variants of standard nickel catalysts with higher Ni loading with similar densities (1.1-1.2 kg/liter) can achieve GHSVs of 5000 at lower temperatures (<650 C) and retain high conversion (99.95%). Such a system would equate to a techno-economic power density of 3.85 kg cat/kg-H2/hr, yielding a net of 0.96 kg nickel/kg-H2 at a nickel price of $20/kg, equating to $20kg-hr capacity, leaving little incentive to use noble or exotic alloys. The rest of the cost is found in the metal components, of which around 7 kg of stainless steel is needed for a 1 kg reformer, costing about $140. Aluminum oxide support is virtually insignificant, costing only $1/kg. Pochari Technologies’ goal is to make ammonia crackers cheaper than standard automotive catalyst converters, this appears a tenable goal as catalyst converters require palladium and platinum, albite in smaller quantities. The reformer is approximately the size as a large muffler, which will be fitted near exhaust manifold of the engine, to minimize conductive heat losses through the exhaust. Beyond economics, the power density is already more than satisfactory, with the volume of the catalyst occupying less than 3.2 liters for a reformer capacity of 1 kg-H2-hr, most of the volume is occupied by insulation, the combustion zone (the inner-third portion of the cylinder), and miscellaneous piping, flow regulators, etc.

While the theoretical energy consumption is 3.75 kWh/kg-H2, the minimum energy consumption is somewhere in the order of 4.2-4.8 kWh/kg, but in reality, it is usually higher. This number can be easily ascertained by taking the specific heat capacity of the catalyst mass (mostly aluminum oxide), the active component (nickel 500 kJ-kg/K), the metallic components (500 kJ/kg-K for SS304) that comprise the reactor vessel, catalyst tubes, containment cylinder etc, and finally, the temperature required to raise 5.5 kg of gaseous anhydrous ammonia (2175 kJ/kg-K) to 800 degrees Celsius, which is exactly 2.65 kWh, plus any heat loss. We also need to take into account the higher capacity of the released hydrogen. As the ammonia progressively breaks down, hydrogen is released, this hydrogen has a certain residence time since for complete decomposition, the reformate gas will reside until no appreciable quantities ammonia is present, this in effect means the reformer is also heating hydrogen gas, not just ammonia, so we need add the heat absorption of the hydrogen, which is another 3.17 kWh (14,300 kJ/kg-K). This takes the total to 7.84 kWh/kg-NH3, very close to numbers found on industrial reformers. Heat loss through conduction is minimal, using 40mms of rock-wool insulation wrapped around a 100mm reactor vessel, we can reduce heat transfer for a 3 liter reformer to around 60 watts. The net total amounts to 7.9 kWh/kg NH3, or 23% of the LHV of hydrogen. Nearly 100% of this energy can be supplied by exhaust gases for H2-ICE systems, while for fuel cells, no such heat is available.

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