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D3178-89 – Standard Test Method Technical Guide
📐 Scope and Significance
ASTM D3178 – 89 (Reapproved 2002), “Standard Test Methods for Carbon and Hydrogen in the Analysis Sample of Coal and Coke,” provides a unified procedure for determining total carbon and hydrogen. As stated in Section 1.1, both elements are determined in a single operation. The values represent total percentages as analyzed, including carbon from mineral carbonates and hydrogen from free moisture and water of hydration of silicates.
Section 4.1 confirms that these determinations are essential for calculating combustion air requirements and process efficiency. Additionally, they are used in material balances for coal conversion processes (Section 4.2).
| 🟦 Element | 📏 Sources Included (as analyzed) | ⚡ Reporting Note |
|---|---|---|
| Carbon (C) | Organic matter + Mineral carbonates | Optional correction for carbonates per Note 1 |
| Hydrogen (H) | Organic matter + Free moisture + Water of hydration (silicates) | Must be corrected for dry basis reporting (Section 1.2) |
⚙️ Sample Preparation and Procedure
Per Section 3, the determination involves burning a weighed sample in a closed system. The combustion products are fully oxidized, purified, and fixed in an absorption train.
Sample preparation is critical to accuracy. Section 5.1 requires the sample to be pulverized to pass a No. 60 (250-µm) sieve and mixed according to Method D 346 or D 2013. For materials with high mineral content, such as ash or calcined coke, grinding to pass a No. 100 (150-µm) sieve is recommended.
| 🟦 Material | 📐 Recommended Sieve | 🎯 Grinding Standard |
|---|---|---|
| General Coal / Coke | No. 60 (250 µm) | Method D 346 / D 2013 |
| Ash / Pit Ash / Calcined Coke | No. 100 (150 µm) [Beneficial] | Method D 346 / D 2013 |
⚠️ Critical Step: Section 5.2 mandates that the test sample be weighed just prior to analysis. Any change in moisture content directly introduces error into the hydrogen determination.
📊 Key Measured Properties and Corrections
When reporting data on a “dry” basis, Section 1.2 specifies that the hydrogen value must be corrected for the hydrogen present in the free moisture of the sample. Furthermore, Note 1 in the standard states that applications may justify additional corrections, such as compensating for carbon in carbonates or hydrogen from water of hydration in silicates. These rigorous correction methods ensure accurate material balances and combustion calculations.
💡 Calculation Insight: To apply the dry basis correction for hydrogen, you must first determine the moisture content of the sample using Test Method D 3173. This allows for the precise subtraction of hydrogen contributed by free moisture.
❓ Frequently Asked Questions
🔍 Why is ASTM D3178 performed as a combined test for carbon and hydrogen?
These test methods are designed specifically to determine both elements simultaneously in one combustion operation, utilizing a closed system and absorption train for efficiency and accuracy (Section 1.1).
💡 What components contribute to the as-analyzed hydrogen value?
As detailed in Sections 1.1 and 3.1, the hydrogen value includes hydrogen from the organic coal matter, the free moisture in the sample, and the water of hydration of silicates.
⚡ When is a dry basis correction for hydrogen required?
Section 1.2 requires this correction whenever the analytical data is converted and reported on a “dry” basis to remove the effect of sample moisture.
📌 What sample preparation is needed for calcined coke according to D3178?
Section 5.1 indicates that while standard coal must pass a No. 60 sieve, it is beneficial to grind calcined coke and other high-mineral materials to pass a No. 100 (150-µm) sieve.