Process intensified miniature ammonia plant using advanced catalyst technology

Christophe Pochari, Pochari Technologies

Distributed ammonia production, high-technological readiness fertilizer electrification for high irradiance photovoltaic geographies

The ammonia industry is in need of disruption. Highly consolidated industries such as chemical production are notably resistant to change and unwilling to alter their business models. Consumers often suffer as players will price-gouge the buyers with little bargaining power. Ammonia is a prime example, there is no substitute for anhydrous, thus farmers are at the mercy of large producers generating high returns. Large producers have monopolized the market and charge far above what the price of natural gas would predict. For example, as of April 2021, the price of anhydrous is $710/ton, while the price of natural gas is only $2.5/thousand-cubic feet, or $0.13/kg. The price of producing hydrogen from natural gas is only $1-1.5/kg, so the price of ammonia should only be $213/ton, with a reasonable estimate for plant CAPEX of $1500/TPY amortized over 15 years yielding less than $100/ton. The conclusion is ammonia shouldn’t be over $300 ton at today’s rock-bottom natural gas prices, yet ammonia prices continue to rise. Secondly, carbon-emissions are a concern but of which cannot be a nuisance to already cost-sensitive farmers, so the only way to reduce carbon emissions from ammonia is by producing it for a lower price than the current large-scale production methods. Thankfully, rapidly falling solar and electrolyzer costs have largely solved this problem for us. With production from water and air, distributed production becomes feasible, over-turning the current business model away from centralized production.

Modern photovoltaic systems wholesaling on Chinese marketplaces such as Alibaba sell for as little as $0.18/watt from RISEN ENERGY CO., LTD for monocrystalline architecture.
Degradation rates are typically around 15% for 20 years, or around 0.8% per anum. That means a 1 kW system will produce 84% of its original power output after two decades.
Panel type: 275-280/330-335W Multi-Module
Price per watt (USD): 0.28 High, 0.175 Low, 0.185 Average.
The average price for 350-watt panels is 18.5 cents per watt.
The second major cost input is the DC/AC converter. Using data from Alibaba, numerous products were sampled. The most cost-competitive DC/AC rectifiers were ones used for solar-powered well water pumps. 7.5 kW units were priced around $250, yielding a price per kilowatt of $34. In our case, we only need a DC-DC converter, stepping down the voltage from the panel peak of around 35 to 12 for the electrolyzer. DC/DC converters are roughly the same price as DC/AC inverters.

The Levelized Cost of Energy (LCOE) is determined by the irradiance available much more so than it is by slight differences in the panel module costs. A solar array in Scotland (880 kWh/kWp/yr) won’t be nearly as cheap as one in Chile (2300 kWh/kWp/yr), or in Los Vegas (1900 kWh/kWp/yr).

With the availability of low-cost photovoltaic energy without the need for balancing grid requirements, the need for storage is eliminated, this opens up the possibility of producing ultra-low cost hydrogen below the price of methane reforming. Hydrogen on its own is virtually useless, it has virtually no application as a fuel, thus we are forced to turn to ammonia. Until ammonia begins its use as a low-emission fuel in the near future, the fertilizer market is the biggest opportunity for disruption. Rather than purchasing overpriced ammonia for major producers who charge high margins, farmers can produce it themselves at cost, savings considerable sums of money and paying for the capital expenditure of the plant in a short time.

Contrary to popular belief among experts on catalytic synthesis, ammonia synthesis is actually very easy to scale down to levels permitting distributed production. In 1909, Haber originally produced 90 grams per hour using an osmium catalyst with a miniature plant. Using photovoltaic energy, farmers in regions with high annual irradiance can cover all of their fertilizer needs as well as covering their farm equipment propulsion using low emission ammonia fuel. Using autonomous production, payback times can reach less than 3 years depending on annual irradiance. Small scale ammonia plants suffer from lower efficiency due only to high heat transfer since the reactor vessel has a high surface to volume ratio. Using rock-wool insulation designed for high temperatures, with a thermal conductivity of 0.04 W/m-K, heat loss can be minimized and brought down to industrial-scale levels. For a 10 kg/hr reactor, 7 kWh of heat is released, the heat flux for a reactor this size would approximate 2 watts with 7” of rock-wool insulation. Over 90% of the compression energy needed can thus be met by the excess heat produced during the formation of the ammonia molecule.

For an ammonia reactor vessel of 3 meters in diameter, 100mm of insulation was used. This translates into a negligible heat flux of 0.22 kwh/m3 reactor volume heat flux for the typical large-scale plant. For a 1 kg/ht NH3 plant, the heat flux is 1.1 kwh/m3 with 14” of rock-wool insulation at 0.04 Wm-K.

An ammonia plant is in reality a quite simple device, ammonia reactors were once a technically challenging endeavor as high-temperature nickel alloys were not yet available. The reactor consists of a vessel that encompasses the catalyst tubes, within these tubes is a pebble-sized granular Iron catalyst. A small mesh is placed at the ends of the catalyst tubes to prevent unwanted migration of the catalyst pellets. The catalyst is relatively inexpensive and lasts 5-10 years. The particular catalyst used is the HTA110-1-H Pre-reduced ammonia synthesis catalyst by Liaoning Haitai Sci-Tech Development Co., Ltd. The composition of the catalyst is the standard for modern NH3 synthesis, consisting of alpha-Fe, supported on Al2O3, with CaO and K2O promoters. The particular catalyst is rated for up to 32 MPa pressures and 530 C operating temperatures. These ammonia synthesis catalysts are highly productive, with 1 kg of catalyst producing 0.37 kg of NH3 per hour. Thus, at current prices ($15/kg for bulk-purchases), the catalyst cost of a 80 TPY plant is only $1250!

One of the biggest challenges in producing a viable small-scale ammonia plant is purifying the oxygen. A maximum oxygen concentration of 40 ppm is allowed to minimize temporary catalyst poisoning, a concentration of 99.999% is ideal. Using carbon molecular sieves, a yield of 90 Nm3-N2/ton can be achieved. For 3 Nm3/hr, 60 kg of molecular sieve is needed assuming an output density of 50 Nm3-N2/ton. The final concentration of oxygen would be 10 parts per million. The price of the carbon molecular sieve is $8-10/kg.

The second challenge is syngas compression. On large plants, centrifugal compressors dominate. At high flow rates, boundary layer and tips losses are minimal, but when these compressors are scaled-down, these losses increase making reciprocating compressors more attractive. Pochari Technologies uses a novel low-speed hydraulic compressor using ultra-low friction technology. Since the plant is relatively small, the footprint of the compressor is not a large concern, therefore we have oversized the compressor to enable it to operate at a lower speed, enabling low friction. While the compressor is oil-lubricated, a large absorbent module is utilized to capture the bulk of the unwanted oil residues that escape the piston ring.

Financial viability, specifications and rough cost breakdown for 77 TPY NH3 plant:

Solar array: 300 kWp $0.18/watt monocrystalline photovoltaic panels at 2030 kWh/kWp (Lancaster, CA): $54,000

DC-DC step up converter: $50/kw: $3,500

Douglas fir solar frame structure: $6000 (pre-Covid lumber prices)

Osmosis water distillation: 2 kWh/m3 15 LPH $100 ($1,500 for 500 LPH)

70 kW 8 MMW 38 kwh/kg 2 m2/kw $125/kw 15,200 kg/yr Dry cell HHO generator with pure nickel foil electrodes: $16,800

Sized for 75% kWp capacity at peak, can increase power density by 25% during peak hours, equaling 168 kW, oversized by 140% to eliminate the need for battery storage. 

Compression energy: 4 kWh heat energy per kg of hydrogen, insufficient to cover 3.5 kWh/kg compression

300 kg carbon-molecular sieve: $2,700

88 kg Fe2O3/K2O/CaO catalyst-hr 2700 kg/m3. $1250

Low-speed 350 bar 70 Nm3/hr oil-lubricated reciprocating compressor (12,000 hr MTBO): $7,000

Reactor materials, Inconel tubing, insulation, valves, fittings, flowmeters, and miscellaneous items: $5,000

Reactor volume: 37L

Total: $95,950

Pay-off time: 2.49 years

Total gross revenue @$500/ton: $38,500

Net revenue: $35,500

1st year return on capital (ROI): 36.99%

Annual maintenance cost, primarily compressor maintenance, principally compressor piston ring replacement: $3000