Calculations

How to Calculate Milling Throughput, Particle Size Yield, and Drying Energy in Graphite Anode Processing

Work through the five formulas that govern graphite and anode material processing, from mill power to furnace heat balance, with real units and worked examples for each input.

Graphite anode processing lives or dies on five numbers: milling throughput in kg/h, particle size yield as a mass fraction, slurry solids balance, drying energy in kWh per batch, and calcination heat load in kW. A 10,000 tonne per year anode line that misjudges any one of these by 10 percent either starves its coaters or pays for oversized furnaces. This guide works each formula with real units and shows where every input comes from, whether that is a drive power meter, a laser diffraction report, or a moisture balance. Pricing and benchmark targets live in the companion cost and KPI guides; here we only do the math.

Milling throughput is mill power divided by specific grinding energy: throughput (kg/h) = P (kW) / E (kWh/kg). Spheroidizing natural flake graphite in an air classifier mill typically demands 0.8 to 1.5 kWh/kg, while jet milling synthetic graphite to a 5 µm D50 can exceed 2.5 kWh/kg. A 200 kW mill at 1.2 kWh/kg delivers 167 kg/h; drop specific energy to 1.0 kWh/kg through sharper classifier tuning and the same mill yields 200 kg/h. Read P from the drive power meter minus idle draw, about 15 to 25 kW on a mill that size, and confirm mass flow on the discharge loadcell. The Milling Throughput calculator handles the unit bookkeeping.

Particle size yield is the mass fraction of milled product landing inside the specification window: yield = mass in spec / feed mass × 100. For a 16 µm D50 anode grade with a 10 to 25 µm acceptance window, run the laser diffraction PSD, integrate the volume distribution between the limits, and multiply by feed mass. Example: 1,000 kg of feed produces 620 kg inside the window, 290 kg of fines below 10 µm, and 90 kg of overs, so yield is 62 percent. Fines are not waste; they resell as conductive additive feed. Enter the PSD limits and batch masses into the Particle Size Yield calculator to track drift shift by shift.

Slurry math starts with solids fraction: solids % = dry mass / (dry mass + liquid mass) × 100. A standard anode slurry runs 45 to 50 percent solids with a 96:2:2 split of graphite, SBR binder, and CMC thickener by dry weight. To coat 100,000 m² at a 10 mg/cm² dry loading, you need 100 g/m² × 100,000 m² = 10,000 kg of dry solids, which at 48 percent solids means 20,833 kg of mixed slurry. Binder demand is 2 percent of dry mass, so 200 kg of SBR on a dry basis. The Coating Solids Usage, Slurry Yield, and Binder Consumption calculators chain these three results from one set of inputs.

Drying energy follows Q = m_water × (cp × ΔT + h_fg), where cp of water is 4.18 kJ/kg·K and latent heat h_fg is 2,257 kJ/kg at atmospheric pressure. Coating 1,000 kg of that 48 percent slurry deposits 480 kg of solids and evaporates 520 kg of water. Heating from 25 to 100 °C takes 520 × 4.18 × 75 = 163,020 kJ; evaporation adds 520 × 2,257 = 1,173,640 kJ, so theoretical demand is 1.34 GJ, or 371 kWh. Real convection ovens run 40 to 60 percent thermal efficiency, so budget 620 to 930 kWh. The Drying Energy Cost calculator converts that load straight into your gas or electric tariff.

Calcination load is a sensible heat balance: Q (kW) = mass flow (kg/s) × cp (kJ/kg·K) × ΔT (K). Graphite cp averages roughly 0.71 kJ/kg·K near room temperature and climbs past 1.6 kJ/kg·K above 1,000 °C, so use a mean value near 1.1 for wide temperature spans. Heating 500 kg/h from 25 to 1,150 °C at cp 1.1 gives 500/3600 × 1.1 × 1,125 = 172 kW before losses; add 30 to 50 percent for shell and offgas losses on a rotary unit. Full graphitization at 2,800 to 3,000 °C is a different regime, consuming 10 to 14 kWh per kg. Size the furnace with the Calcination Load calculator, then verify against nameplate.

These calculations chain together: milling throughput sets classifier feed, particle size yield sets net output, slurry solids set coating demand, and water content sets drying load. Close the loop with a mass balance; feed in should equal product plus fines plus baghouse catch plus moisture loss within 2 percent, or one of your inputs is wrong. Two supporting checks matter. Run the Dust Collection Load calculator to confirm the baghouse handles the airflow the mill circuit generates, typically 1.0 to 1.5 m³/min per kg/h of milled graphite. Run the Moisture Control Cost calculator when a spec calls for under 200 ppm final moisture, because the last drying decade often consumes as much energy as the first.

Published 2026-07-02.