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D291 – Standard Test Method Technical Guide
📐 Test Overview and Scope
ASTM D291/D291M provides robust procedures for determining the bulk density of crushed bituminous coal, essential for optimizing coke oven charging. The standard covers two methods: Procedure A for uncompacted bulk density using a cone apparatus, and Procedure B for compacted bulk density through a dropped‐coal technique. It is applicable only to coal with a top size below 37.5 mm [1.5 in.], excluding powdered coal and storage pile coal. The standard supports both SI and inch‑pound units as independent systems; values from the two systems shall not be combined. Safety compliance is delegated to users, who must adhere to relevant regulations and establish safe practices.
⚙️ Apparatus and Procedures
Procedure A – Cone Procedure: The measuring box and cone are critical. The Standard Method employs a 305 mm cubic box (0.02873 m³ volume) and a cone with a 115 mm chute opening. The Alternate Method uses a 203 mm × 203 mm × 305 mm box (0.01257 m³ volume) and a cone with a 203 mm chute, specifically for coals with total moisture greater than 7 %. Both cones are 610 mm high with a 510 mm inside diameter at the top, and include a slide valve at the bottom for controlled discharge.
Procedure B – Dropped‑Coal Procedure: This method simulates the compaction experienced in coke ovens, providing a bulk density value that more closely reflects actual oven conditions. It involves dropping coal into the measuring box from a standardized height to achieve a compacted state. Accurate water calibration of the measuring box is mandatory for both procedures to maintain the stated volume tolerances.
📊 Key Specifications and Data
| 🟦 Parameter | 📏 Standard Method | 📐 Alternate Method |
|---|---|---|
| Measuring Box | 305 mm × 305 mm × 305 mm [12 in. × 12 in. × 12 in.] | 203 mm × 203 mm × 305 mm [8 in. × 8 in. × 12 in.] |
| Box Volume | 0.02873 m³ ± 0.00008 m³ [1.000 ft³ ± 0.003 ft³] | 0.01257 m³ ± 0.00003 m³ [0.4444 ft³ ± 0.0012 ft³] |
| Chute Opening | 115 mm [4.5 in.] | 203 mm [8.0 in.] |
| Cone Height | 610 mm [24 in.] | |
| Cone Top ID | 510 mm [20 in.] | |
| ⚡ Aspect | 🎯 Procedure A | 🎯 Procedure B |
|---|---|---|
| Density Type | Uncompacted | Compacted |
| Filling Method | Gravity feed through cone | Controlled dropping |
| Primary Use | Standard coke oven charging | Simulated oven conditions |
💡 Tip: For consistent results, verify that the cone’s slide valve operates smoothly without vibration. Any hang‑up or densification during filling can alter the measured bulk density, particularly for moist coals. Water‑calibrate the box regularly to ensure volume remains within the specified tolerances.
❓ Frequently Asked Questions
🔍 Why is moisture content critical in Procedure A?
Coal with total moisture greater than 7 % tends to bridge in a narrow chute. The Alternate Method’s 203 mm opening prevents flow problems and ensures that the measured uncompacted density is representative of the material.
💡 How do I choose between the Standard and Alternate Methods?
Use the Standard Method for coal moisture at or below 7 %. For moisture above 7 %, apply the Alternate Method with its larger chute opening to avoid clogging and achieve proper filling of the box.
⚡ Can this standard be used for powdered coal?
No. ASTM D291/D291M explicitly excludes powdered coal used in boiler plants. It is designed only for crushed coal with a top size less than 37.5 mm destined for coke oven charging.
📌 What is the practical value of Procedure B?
Procedure B delivers a compacted bulk density that closely matches the densities achieved in real coke ovens. This information helps operators charge the correct mass of coal per oven, improving efficiency and coke quality.