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Air/Gas Blending Calculator

BTU Blending • Wobbe Index • Peak Shaving Analysis

Air-Gas Blending Calculator
Professional tool for calculating mixture properties and heating values for natural gas blending operations. Supports BTU adjustment, interchangeability analysis per AGA standards, and peak shaving planning.
Calculation Mode:

Stream 1 (Primary)

MCF/hr
BTU/cf

Stream 2 (Enriching)

MCF/hr
BTU/cf
Engineering Note

Wobbe Index (WI = BTU/√SG) determines fuel gas interchangeability. Pipeline-quality gas typically requires WI between 1290–1400. Values outside this range may cause combustion issues in end-use equipment.

📐 Core Formulas

BTUblend = Σ(Qi × BTUi) / Σ Qi
Qi = Volumetric flow of stream i
BTUi = Heating value of stream i
WI = BTU / √SG
WI = Wobbe Index (interchangeability)
SG = Specific gravity (rel. to air)
Qair = Qgas × (BTU - 1050) / 1050
Air injection to reduce BTU to pipeline quality

📚 Standards & References

  • AGA Bulletin 36
    Gas Interchangeability (Wobbe Index)
  • ASTM D3588
    Heat Value, Compressibility Factor, Relative Density of Gaseous Fuels
  • GPA 2172
    Heating Value Calculation from Composition
  • ISO 6976
    Natural Gas — Calculation of Calorific Values
📋 Quick Reference: Typical Gas Properties
Gas Type BTU/cf Sp. Gravity Wobbe Index
Pipeline Natural Gas 1,000–1,050 0.58–0.62 1,310–1,390
Propane (C₃H₈) 2,516 1.52 2,041
Butane (C₄H₁₀) 3,262 2.01 2,302
Propane-Air (55/45) 1,384 1.29 1,218

⚠️ Important Considerations

  • Wobbe Index Range: Most equipment requires WI between 1290–1400. Verify equipment tolerances before operation.
  • Perfect Mixing: Calculations assume complete homogeneous mixing. Real-world blending may require static mixers.
  • Peak Shaving: Propane-air (SNG) at ~55/45 is heating-value matched to pipeline gas (≈1384 BTU/cf); its Wobbe (≈1220) is below the typical pipeline minimum, so verify interchangeability against the receiving tariff.
  • Standard Conditions: All values at 60°F, 14.73 psia unless otherwise noted.

Frequently Asked Questions

What does the air/gas blending calculator calculate?

It calculates blended gas properties including heating value, specific gravity, Wobbe Index, and peak shaving requirements per AGA and ASTM standards.

What standards does this blending calculator follow?

The calculator is compliant with AGA Bulletin 36 and ASTM D3588 for gas blending and BTU adjustment.

What is the Wobbe Index used for in gas blending?

The Wobbe Index measures interchangeability of fuel gases, ensuring blended gas will perform correctly in equipment designed for a specific gas type.