ULTRA-LOW COST ALKALINE ELECTROLYZERS USING COMMERCIAL-OFF THE SHELF (COTS) COST REDUCTION METHODOLOGY

Posted on  by christophepochari

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180 C at 38% wt KOH at 4 MPa Oxygen

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150 C at 38% wt KOH at 4 MPa Oxygen

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120 C at 38% wt KOH at 4 MPa Oxygen

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Typical alkaline electrolyzer degradation rate. The degradation rate varies from as little as 0.25% per year to nearly 3%. This number is almost directly a function of the electrocatalyst deactivation due to corrosion.

Dramatically reducing the cost of alkaline water electrolyzers using high surface area mesh electrodes, commercial off the shelf components and non-Zirfon diaphragm separators

Christophe Pochari, Pochari Technologies, Bodega Bay California

Alkaline electrolyzer technology is ripe for dramatic cost reduction. Current alkaline electrolyzer technology is excessively expensive beyond what material costs would predict, mainly due to very small production volumes, a noncompetitive market with a small number of big players, and relatively little use of COTS (commercial off the shelf) methodology of cost reduction.

Pochari Technologies’s researchers have thus applied this methodology to finally bring to market affordable hydrogen generators fabricated from readily available high-quality components, raw materials, and equipment procured on Alibaba.com ready to be assembled as kits to reduce labor costs.

An alkaline cell is a relatively simple system, consisting of four major components. The electrode (a woven wire mesh), a gasket (made of cheap synthetic rubbers, EPDM etc), and a material for fabricating the diaphragm membrane for separating and oxygen and hydrogen while permitting sufficient ionic conductivity (usually composites of potassium titanate (K2TiO3) fibers and polytetrafluoroethylene (PTFE) (as felt and as woven), polyphenylene sulfide coated with zirconium oxide, (Zirfon), or polysulfone, and asbestos coated with polysulfone. “Separators should be constructed from materials chemically resistant to the alkaline electrolyte composition. Many polymers are suitable for constructing separators, such as Teflon® and polypropylene”. “A commercially available polyethersulfone ultrafiltration membrane (marketed as Pall Corporation, Supor®-200) with a pore size of 0.2 um and a thickness of 140 um was employed as the separator between the electrodes”. Nylon monofilament mesh with a size of over 600 mesh/inch, or a pore size of 5 micron can also be used. Polyethersulfone is ideal due to small more size, retaining high H2/O2 selectivity at elevated pressures. It can handle temperatures up to 130 C. If polyethersulfone is not satisfactory (excessive degredation rate if temperature is above 50 C), Zirfon-clones are available to purchase on B2B marketplaces https://b2b.baidu.com for $30/m2 from Shenzhen Maibri Technology Co., Ltd.

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The fourth component are the “end plates” which consist of heavy-duty metallic or composite flat sheets which house a series of rods tightly pressing the stacks to maintaining sufficient pressure within the stack sandwich. For higher pressure systems, such as up to 30 bar, the endplates encounter significant force.

Unlike batteries, noble mineral intensity in alkaline technology is relatively small, with nickel mesh loading of under 500 grams/m2 of active electrode surface area needed to achieve anode life of 5 or more years assuming a corrosion rate of below 0.25 MPY. With current densities of 500 miliamp/cm2 at 1.7-2 volts being achievable at 25-30% KOH concentration, power densities of nearly 10 kW/m2 is realizable. This means a one megawatt electrolyzer at an efficiency of 75% (45 kWh/kg-H2 LHV) would use 118 square meters of active electrode surface area. Assuming a surface/density ratio of a standard 80×80 mesh, 400 grams of nickel is used per square meter of total exposed area of the mesh wires. Thus, a total of 2.25 kg of nickel is needed to produce 1 kg of hydrogen per hour. For a 1 megawatt cell, the nickel would cost only $1000 assuming $20/kg.

For a lower corrosion rate of 1 um/yr, a total mass loss of 7% per year will occur with a surface/mass ratio of 140 grams/m2-exposed area, the nickel requirement is only $350 or 17.5 kg for one megawatt! Although this number is achievable, higher corrosion rates will likely be encountered. To insure sufficient electrode reserve, a nickel loading of around 400-500 grams/m2 is chosen. Pure nickel experiences an excessively high corrosion rate when it it “active”, it becomes “passive” when a sufficient concentration of iron (NiFe2O4), or silicate is found in the oxide layer. For Incoloy alloy 800 with 30% Ni, 20% Cr and 50% Fe experiences a corrosion rate of 1 um/yr at 120 C in 38% KOH, pure nickel is over 200 um. “The “active” corrosion of nickel corresponds to the intrinsic behavior of this metal in oxygenated caustic solutions; the oxide layer is predominantly constituted of NiO at 180°C and of Ni(OH) 2 at 120°C. The nickel corrosion is inhibited when the oxide layer contains a sufficient amount of iron or silicon is present”. The results drawn from this study indicates the ideal alloy contains around 34% Ni, 21% Cr, and 45% Fe. The cost breakdown for the three elements are $18/kg, $9/kg and $0.2/kg, giving an average of $8.1/kg. For a passive corrosion rate of 1 um/yr, a 10% annual material loss corresponds to a electrode mesh loading of 90-100 grams/m2, or $0.11/kW. That is 11 cents per kW! This does not include mesh weaving costs. A 600 mesh weaving machine costs $13,000. The conclusion is meshing costs are very minimal, less than a few cents per square meter.

The modeling of our cells is based a 6.8 kW/m2 electrode area.

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For the diaphragm separators using a 200 um thick sheet of polyethersulfone (PES), around 20 grams is used per kilowatt, at a typical cost of PES of $25/kg assuming density of 1.37 g/cm2, the cost would be around $0.50/kilowatt assuming an electrode power density of 6.8 kW/m2 (400 miliamps at 1.7 volts). Since Pochari Technologies’ always adheres to COTS methodology, the expensive and specialized Zirfon membrane is dispensed with in favor of a more ubiquitous material, this saves considerable cost and eases manufacturability as the need to purchase a specialized hard to access material is eliminated.

Gasket costs are virtually negligible, with only 4.8 grams of rubber needed per kilowatt, EPDM rubber price are typically in the range of $2-4/kg.

For 30% NaOH at 117 C, a corrosion rate of 0.0063 millimeter per year (0.248 MPY) is observed for an optimal nickel concentration of 80%. This means 55 grams of Ni is lost for one square meter, if we choose 10% per year as an acceptable weight loss, we return to 550 grams per square meter as the most realistic target nickel loading, with much lower loading achievable with reduced corrosion rates. A lower concentration of KOH/NaOH and lower operating temperature can be utilized as a trade-off between corrosion and power density.

The total selling price of these units cost including labor and installation is $30/kW. In 2006, GE estimated alkaline electrolyzers could be produced for $100/kW, clearly, must lower prices are possible today. At an efficiency of 6.5 MMW (47.5 kWh/kg-H2), the price is $1430/kg-hour.

After the cell stack costs, which we demonstrated can be made very minimal with COTS design philosophy, the second major cost contributor is the power supply. For a DC 12 volt power supply, $50 is a typical price of 1000 watt DC power module. This, in compendium, alkaline stack costs are effectively miniscule, and the cost structure is dominated by the power supplies and unique requirements of low voltage direct current high amperage power.

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Assuming the solar installation already provides DC, an additional dedicated power supply is redundant, all that is needed is a DC-DC step down converter. If the electrolyzes runs off an AC power supply, the buyer must add the cost of the DC power supply.

WORLD’S ONLY MINIATURE AMMONIA PLANTS FOR FERTILIZER AUTONOMY

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

 

 

 

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Christophe Pochari, Pochari Technologies

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

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: 30L

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