How to accurately calculate heat load when selecting industrial gas burners？

When selecting an industrial gas burner, accurately calculating the thermal load is the core step to ensure efficient, safe, and economical system operation. Below is a systematic and rigorous calculation method and practical guide for you.

Step 1: Clarify Core Concepts

Thermal Load: Refers to the heat energy the burner needs to release per unit of time, typically expressed in kilowatts (kW), megawatts (MW), or kilocalories per hour (kcal/h). It is the fundamental basis for selection.
Rated Thermal Load vs. Actual Operating Thermal Load: Selection should be based on the actual required maximum thermal load, considering a reasonable safety factor.

Step 2: Gather Key Baseline Data

Accurate calculation relies on the following reliable data:

Process Requirements
- Type of medium to be heated (air, water, oil, metal, reactor, etc.).
- Required temperature increase of the medium (ΔT, unit: °C). Example: Heating air from 20°C to 300°C.
- Mass flow rate or volumetric flow rate of the medium (units: kg/h or m³/h).
- Peak heat demand and average heat demand of the process.
Fuel Properties
- Type of gas (natural gas, LPG, coke oven gas, hydrogen, etc.).
- Lower Heating Value (LHV, or Net Calorific Value) of the gas, in kJ/m³ or kcal/m³. This is a key parameter! This data should be provided by the supplier or local gas company.
- Gas supply pressure and pressure fluctuation range.
System Efficiency and Heat Losses
- Overall System Efficiency: Not just the burner's combustion efficiency, but the percentage of heat effectively used for the process. Must consider:
  - Heat loss through insulation of the furnace/heat exchanger.
  - Exhaust gas heat loss (heat carried away by flue gases).
  - Incomplete combustion loss (usually minimal, >99.9% for modern burners).
- Empirical Estimate: A well-designed industrial furnace system may have an overall efficiency between 50% and 85%, depending on furnace type, temperature, and insulation.

Step 3: Select Calculation Formula and Perform Calculation

Method 1: Calculation Based on Process Medium Requirements (Most Fundamental and Recommended Method)

This is the most accurate physical method, based directly on the law of energy conservation.

General Formula:

Q = \frac{m \times c_{p} \times Δ T}{η}

Or for gases (volumetric flow):

Q = \frac{V \times ρ \times c_{p} \times Δ T}{η}

Where:

$Q$ : Required thermal load of the burner (kW or kcal/h) — the final value to obtain.
$m$ : Mass flow rate of the heated medium (kg/h).
$V$ : Volumetric flow rate of the heated medium (m³/h, note whether under standard or operating conditions).
$ρ$ : Density of the medium at average temperature (kg/m³).
$c_{p}$ : Specific heat capacity at constant pressure of the medium at average temperature (kJ/(kg·°C) or kcal/(kg·°C)).
$Δ T$ : Required temperature increase of the medium (°C).
$η$ : Overall thermal efficiency from the burner to the process medium (expressed as a decimal, e.g., 0.75 for 75%).

Calculation Example:
Heating 10,000 m³/h of air from 20°C to 300°C, with estimated overall furnace system efficiency of 70%. The volumetric specific heat capacity of air at average temperature is approximately 1.05 kJ/(m³·°C) (Note: This is an approximate value for volumetric heat capacity, simplifying calculation by considering density changes).

Q = \frac{10000 \times 1.05 \times (300 - 20)}{0.70} \approx \frac{10000 \times 1.05 \times 280}{0.70} \approx 4, 200, 000 kJ/h

Unit Conversion: 1 kW = 3600 kJ/h

Q \approx \frac{4, 200, 000}{3600} \approx 1167 kW

This is the theoretical thermal load the burner needs to provide.

Method 2: Calculation via Furnace Heat Balance (Suitable for Heating Furnaces, Heat Treatment Furnaces, etc.)

A more comprehensive method considering all heat income and expenditure.

Heat Income Items: Primarily heat release from fuel combustion (i.e., $Q$ ).
Heat Expenditure Items:
1. Effective heat (heat absorbed by the workpiece).
2. Heat loss through furnace wall insulation.
3. Heat loss carried away by exhaust gases.
4. Other losses (radiation from doors, gaps, etc.).
Setting Income = Expenditure allows solving for the required $Q$ . This method is more complex but more precise, often used in detailed design.

Step 4: Determine Burner Model Specifications

Rated Thermal Load Selection:
- Use the calculated thermal load $Q$ as the minimum rated value.
- Typically, select a rated value 10%~20% higher than the calculated value as a design margin (safety/regulation margin). That is:
  $Q_{burner rated} = (1.1 \sim 1.2) \times Q_{calculated}$
- Important: The burner's turndown ratio (e.g., 1:5, 1:10) must meet the process's minimum load requirement. The rated load should not be oversized, otherwise it may lead to flameout or low efficiency at low loads.
Gas Consumption Calculation:
- Used to check pipeline sizing and supply capacity.
$Gas Consumption (m³/h) = \frac{Q_{burner rated} (kW) \times 3600}{Gas Lower Heating Value (kJ/m³) \times Combustion Efficiency}$
- Combustion efficiency (>99%) is close to 1 and can be simplified.
Matching Other Key Parameters:
- Furnace Back Pressure & Burner Pressure Drop: The burner must operate stably against the furnace pressure.
- Air/Gas Pressure & Ratio Control Method: Ensure on-site gas supply conditions are met.
- Flame Size and Shape: Must match the furnace or combustion chamber dimensions to avoid flame impingement on walls.
- Emission Requirements: Whether low-nitrogen oxide (NOx) design is needed.
- Control Method: Compatibility with existing DCS/PLC systems.

Step 5: Verification and Consultation

Cross-Verification: If possible, use different methods (e.g., medium heat absorption, analogy with similar equipment, heat balance) to cross-verify calculation results.
Review Historical Data: Operating data from similar or old equipment is an excellent reference.
Professional Consultation:
- Submit your calculation process, baseline data, and preliminary selection results to at least 2-3 reputable burner manufacturers.
- They possess extensive engineering databases and experience coefficients, can review your calculations, and recommend the most suitable models from their product lines.
- They will comprehensively consider combustion stability, regulation performance, lifespan, and cost.

Summary: Accurate Calculation Checklist

Confirmed the process's peak mass/volumetric flow rate and maximum temperature rise.
Obtained the accurate Lower Heating Value (LHV) of the gas.
Reasonably estimated the overall system thermal efficiency (η), considering major heat losses.
Performed the core calculation using the energy conservation formula.
Added a reasonable 10-20% design margin to the calculated result.
Verified the burner's turndown ratio can meet the minimum load requirement.
Incorporated non-thermal load parameters like furnace pressure, flame size, and control into the selection considerations.
Most Important Step: Have engaged in in-depth technical communication with professional manufacturers regarding all the above information.

Final Reminder: Thermal load calculation is a combination of science and experience. When data is uncertain, it's preferable to be slightly conservative (choose a slightly larger model), but this must be coupled with a burner featuring a wide turndown ratio to ensure performance at low loads, avoiding frequent on-off cycling and efficiency degradation caused by "overpowered" operation. Collaboration with experienced engineers and manufacturers is the best guarantee for successful selection.