This calculator converts a measured effective mass delivered per screw revolution and entered screw speed into average mass-flow units. It does not derive conveyor capacity from geometry or predict firebox distribution or combustion.
Jones Mechanical Stoker Interactive Calculator
Explore average mass feed from screw rpm and an installation-specific effective pounds-per-revolution calibration.
Equation Used
- Steady average screw speed and constant effective mass delivered per revolution.
- qrev is measured at the calculator's chosen delivery boundary and representative of the current material and fill state.
- No transient startup, bridging, variable bulk density, geometry, fill efficiency, slip, leakage, elevator loss, crushing, jamming, torque/power, wear, jet trajectory, combustion, boiler demand, emissions or safety model.
Effective coal per revolution must be measured under representative material, fill and operating conditions. It already absorbs fill, slip and downstream delivery effects only to the extent captured by that measurement.
Calibrated average feed
A screw rotates N times per minute. If representative measurement shows that qrev pounds cross the chosen delivery boundary per revolution, average feed is 60Nqrev pounds per hour.
The simplified section follows the hopper, screw conveyor and underfeed retort arrangement in J. E. Jones’s 1908 patent, figures 2 and 3. The illustration shows that feed subsystem; it does not include the complete furnace, air supply or clinker-removal drives. Fuel trajectories and combustion are not calculated. Playback shows one screw revolution per cycle, slowed eightfold for visibility.
Use as a calibration conversion
The calculation can convert a measured mass-per-revolution calibration to common rate units and explore proportional speed changes within a validated operating range. It cannot design or rate a stoker or screw conveyor.
Rate and unit conversions
Feed in lb/h is 60Nqrev. Divide by 2,000 for short ton/h or by 60 for lb/min. Multiply lb/h by 0.45359237/3600 for kg/s.
A mass-flow conversion does not establish a furnace’s firing capacity or required feed rate.
Worked example
At 90 rpm and measured effective delivery 2.2222 lb/rev, average feed is 12,000 lb/h, or 6.0 short ton/h, 200 lb/min and about 1.512 kg/s. This follows directly from the entered calibration and is not a capacity guarantee.
Limits of the feed calculation
Actual delivery can change with material density, particle size, fill and screw operating conditions. A measured mass-per-revolution value is useful only where it remains representative. The conversion does not calculate screw torque, jamming, fuel distribution or the heat demand and combustion of the furnace.
Frequently asked questions
Is qrev a geometric screw displacement?
No. It is the effective mass delivered per revolution measured at the chosen boundary.
Does the result predict fuel distribution in the retort?
No. The model does not calculate how material leaves the screw or spreads through the fuel bed.
Can the result set a maximum operating rpm?
No. Mechanical and combustion limits are not included.
References & Further Reading
- Wikipedia contributors. Mechanical stoker. Wikipedia
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
