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Total Air Required:0 kg/hr
Total Mass Flow Rate:0 kg/hr
Actual Volumetric Flow Rate (Am³/hr):0 m³/hr
Normal Volumetric Flow Rate (Nm³/hr):0 Nm³/hr
Understanding Flue Gas Flow Rate Calculation
Calculating the flue gas flow rate is a critical engineering task in the design and operation of industrial boilers, furnaces, and combustion engines. It refers to the measurement of the volume or mass of exhaust gases produced during the combustion process and released through the stack or chimney.
Accurate flow rate calculation helps engineers size pollution control equipment (such as electrostatic precipitators or scrubbers), design stack dimensions to ensure proper dispersion of pollutants, and monitor the energy efficiency of the combustion system.
The Core Variables
Fuel Consumption Rate: The amount of fuel (coal, oil, natural gas, biomass) burned over a specific period, typically measured in kilograms per hour (kg/hr).
Stoichiometric Air-to-Fuel Ratio: The theoretical mass of air required to completely burn one unit mass of fuel. This varies by fuel type (e.g., Natural Gas is approx 17.2, Diesel/Oil approx 14.4, Coal approx 11.5).
Excess Air: In real-world applications, perfect mixing is impossible, so extra air is supplied to ensure complete combustion. This is expressed as a percentage over the stoichiometric requirement.
Flue Gas Temperature: The temperature of the exhaust gas affects its density and volumetric flow. Higher temperatures result in expanded gas volumes.
Calculation Methodology
This calculator uses a mass balance approach combined with the Ideal Gas Law to estimate flow rates. The logic follows these steps:
1. Mass Balance: By law of conservation of mass, the mass of the flue gas leaving the stack is approximately equal to the mass of the fuel entering plus the mass of the air entering.
Total Mass Flow = Mass of Fuel + (Mass of Air × (1 + Excess Air % / 100))
2. Density Correction: Once the mass flow is determined, the volumetric flow is calculated by adjusting for the density of the gas at the operating temperature. Hotter gases are less dense, resulting in a higher Actual Cubic Meters per Hour (Am³/hr).
3. Normalization: The flow is often converted to "Normal" conditions (Nm³/hr) at standard temperature (usually 0°C or 273.15 K) and pressure to allow for standardized comparisons regardless of operating temperature.
Why is Excess Air Important?
While excess air ensures complete combustion and reduces the formation of carbon monoxide and soot, too much excess air reduces thermal efficiency. The extra air must be heated up to the flue gas temperature, which carries useful heat energy out of the stack rather than transferring it to the process. Calculating the flow rate helps optimize this balance.
function calculateFlueGas() {
// Get input values
var fuelConsumption = document.getElementById('fuelConsumption').value;
var stoicRatio = document.getElementById('stoicRatio').value;
var excessAir = document.getElementById('excessAir').value;
var flueTemp = document.getElementById('flueTemp').value;
var errorMsg = document.getElementById('errorMsg');
var resultsDiv = document.getElementById('results');
// Reset display
errorMsg.style.display = 'none';
resultsDiv.style.display = 'none';
// Parse values
var fuel = parseFloat(fuelConsumption);
var ratio = parseFloat(stoicRatio);
var excess = parseFloat(excessAir);
var tempC = parseFloat(flueTemp);
// Validation
if (isNaN(fuel) || isNaN(ratio) || isNaN(excess) || isNaN(tempC) || fuel <= 0 || ratio <= 0 || excess < 0) {
errorMsg.style.display = 'block';
return;
}
// Calculation Logic
// 1. Calculate Mass of Air Required (Stoichiometric + Excess)
// Formula: Air Mass = Fuel * Ratio * (1 + Excess/100)
var airMass = fuel * ratio * (1 + (excess / 100));
// 2. Calculate Total Mass Flow of Flue Gas (Conservation of Mass)
// Formula: Mass Flue = Fuel + Air Mass
var totalMassFlow = fuel + airMass;
// 3. Determine Density of Flue Gas
// Assumption: Flue gas density approximates Air density at given Temp
// Standard Air Density at 0°C (273.15K) is approx 1.293 kg/m³
var standardDensity = 1.293;
var tempK = tempC + 273.15;
var standardTempK = 273.15;
// Density at actual temperature = Standard Density * (Std Temp / Actual Temp)
var actualDensity = standardDensity * (standardTempK / tempK);
// 4. Calculate Actual Volumetric Flow (Am³/hr)
var actualVolFlow = totalMassFlow / actualDensity;
// 5. Calculate Normal Volumetric Flow (Nm³/hr) – referenced to 0°C
// Norm Flow = Actual Flow * (Actual Temp K / Std Temp K) * (Pressure correction assumed negligible/constant)
// Or simpler: Mass Flow / Standard Density
var normalVolFlow = totalMassFlow / standardDensity;
// Display Results
document.getElementById('resAirReq').innerText = airMass.toLocaleString(undefined, {maximumFractionDigits: 1}) + " kg/hr";
document.getElementById('resMassFlow').innerText = totalMassFlow.toLocaleString(undefined, {maximumFractionDigits: 1}) + " kg/hr";
document.getElementById('resVolFlow').innerText = actualVolFlow.toLocaleString(undefined, {maximumFractionDigits: 1}) + " m³/hr";
document.getElementById('resNormFlow').innerText = normalVolFlow.toLocaleString(undefined, {maximumFractionDigits: 1}) + " Nm³/hr";
resultsDiv.style.display = 'block';
}