Calculator Inputs
Enter the fuel analysis on an as-fired basis. If the percentages do not total 100, the calculator normalizes them.
Example Data Table
This sample shows a typical solid-fuel style case for commissioning checks, stack sizing reviews, and draft system planning.
| Fuel Rate | C | H | S | O | N | Moisture | Ash | Excess Air | Temp | Diameter | Wet Stack Flow |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1200 kg/h | 72% | 6% | 1% | 8% | 1.5% | 10% | 1.5% | 20% | 180°C | 1.2 m | 19,565.50 m³/h |
Formula Used
1) Theoretical oxygen demand
O₂,theory = nC + nH/4 + nS − nO/2
2) Theoretical air
Air,theory = O₂,theory / 0.2095
3) Excess-air method
λ = 1 + (Excess Air / 100)
4) Measured oxygen method
Excess O₂ = x × Stoichiometric Dry Flue / (1 − 4.7619x), where x = measured dry O₂ fraction.
5) Dry flue gas
Dry Flue = CO₂ + SO₂ + N₂ + Excess O₂
6) Wet flue gas
Wet Flue = Dry Flue + H₂O from hydrogen + H₂O from moisture
7) Normal volume
Normal Flow = kmol/h × 22.414 Nm³/kmol
8) Actual volume
Actual Flow = Normal Flow × (Tstack / 273.15) × (101.325 / Pabs), using absolute temperature in kelvin.
9) Velocity
Velocity = Actual Wet Flow / 3600 / Area
10) Oxygen correction
Corrected Dry Flow = Dry Normal Flow × (21 − measured O₂) / (21 − reference O₂)
How to Use This Calculator
- Enter fuel feed rate in kilograms per hour.
- Provide the fuel analysis percentages for carbon, hydrogen, sulfur, oxygen, nitrogen, moisture, and ash.
- Select whether you want to drive the calculation with excess air or measured dry oxygen.
- Enter flue temperature, absolute pressure, and either stack diameter or a known gas passage area.
- Submit the form to show results immediately above the calculator.
- Review dry and wet flow, corrected flow, density, velocity, and composition.
- Use the CSV or PDF buttons to export the calculated summary.
Frequently Asked Questions
1) What is flue gas flow?
It is the exhaust gas rate leaving a combustion source. Designers use it to size stacks, fans, dampers, heat recovery equipment, and test ports.
2) Why show both dry and wet flow?
Dry flow removes water vapor. Wet flow includes water from fuel hydrogen and moisture. Both are useful because different design codes, analyzers, and permits reference different bases.
3) What does normal flow mean?
Normal flow is volume converted to reference conditions. This calculator uses 0°C and 101.325 kPa, which helps compare equipment performance consistently.
4) Why does excess air increase flue gas flow?
More excess air means more nitrogen and unused oxygen pass through the system. That raises gas volume, usually lowers CO₂ concentration, and affects velocity and heat loss.
5) When should I use measured dry oxygen mode?
Use it when a combustion analyzer already gives dry O₂ at the stack. The calculator back-solves the air ratio and updates flow and composition from that field reading.
6) Why is absolute pressure required?
Gas volume depends on pressure. Using absolute pressure gives the correct actual stack flow and density, especially when draft or elevation changes the local gas condition.
7) Is the velocity output enough for final stack design?
No. It is a screening value. Final design should also check code requirements, erosion, noise, particulate carryover, pressure drop, condensation risk, and fan operating limits.
8) What if my fuel analysis does not total 100%?
The calculator normalizes the entered values to 100%. That helps with incomplete lab data, but final project work should still use a verified fuel report.