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D2361-02 – Standard Test Method Technical Guide
Standard Test Method for Chlorine in Coal (D2361-02)
This standard is issued under the fixed designation D 2361; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. It covers the determination of total chlorine content in a coal sample, with all values stated in SI units regarded as the standard.
🧪 Summary of Test Method
ASTM D2361-02 provides two distinct oxidative procedures for the determination of total chlorine in coal specimens. The selection of the method often depends on available laboratory equipment and specific sample characteristics:
- Method A (Combustion Bomb): A weighed coal specimen is burned in a high-pressure oxygen combustion bomb containing a small amount of ammonium carbonate solution. The chlorine released during combustion is quantitatively absorbed in this alkaline reagent.
- Method B (Eschka Method): The weighed specimen is intimately mixed with Eschka mixture (a calcined mixture of sodium carbonate and magnesium oxide) and heated in an oxidizing atmosphere at a specified temperature.
In both methods, the chlorides recovered from the absorbing solution or extracted from the incinerated Eschka mixture are ultimately determined by potentiometric titration to quantify the total chlorine content.
⚠️ Safety Notice: Prior to performing the bomb combustion procedure, carefully review the safety guidelines in Practice E 144 for the Safe Use of Oxygen Combustion Bombs. Specific hazard statements are located in Note 2 and Section 8 of the standard. The combustion bomb must be constructed of materials unaffected by the process and able to withstand a hydrostatic test of 20 MPa (300 psig) without any gas leakage.
⚖️ Apparatus and Material Specifications
The standard mandates precise specifications for instrumentation and consumables to ensure reliable, repeatable results. The chosen wire material and geometry are critical for complete combustion. The standard specifies the following acceptable configurations:
| 🟦 Wire Material | 📏 Length | 📐 Diameter | 🎯 B&S Gauge |
|---|---|---|---|
| Nickel-Chromium (Chromel C) or Iron | 100 mm | 0.16 mm | No. 34 |
| Platinum or Palladium | Per Standard | 0.10 mm | No. 38 |
Balance and Combustion Equipment
Specimens must be weighed using an analytical balance with a sensitivity of 0.1 mg. Open crucibles used for combustion can be constructed of platinum, quartz, or a base-metal alloy. Base-metal crucibles require a preliminary heat treatment in a muffle furnace for 4 hours at 500°C to achieve a stable, constant weight before use (See Note 1).
| ⚡ Key Parameter | 🎯 Specification |
|---|---|
| Balance Sensitivity | 0.1 mg |
| Bomb Hydrostatic Pressure Rating | 20 MPa (300 psig) |
| Crucible Pretreatment (Base-Metal Alloy) | 4 hours at 500°C |
| Laboratory Water Quality | Per Specification D 1193 |
💡 Technical Tip: When preparing base-metal alloy crucibles, a few preliminary firings or heat treating at the specified temperature of 500°C for 4 hours is essential to ensure the weight does not change significantly between subsequent tests, guaranteeing analytical accuracy.
🔬 Significance and Use
The primary purpose of ASTM D2361-02 is to quantitatively measure the total chlorine content of a whole coal sample. This data is highly significant for industrial applications:
- Slagging Evaluation: Chlorine can influence slag formation and behavior in combustion chambers.
- Corrosion Monitoring: Chlorine is a primary contributor to corrosion in high-temperature boiler tubes and other engineering processes associated with coal utilization.
- Total Analysis: Chlorine content is a standard component of the complete ultimate analysis of coal and coke (calculated per Practice D 3180), using samples prepared according to Practice D 2013.
When coal specimens are combusted in strict accordance with this test method, the chlorine is quantitatively retained, providing a representative measurement of the total chlorine in the parent fuel source.
❓ Frequently Asked Questions
🔍 Why is it important to measure chlorine content in coal?
Chlorine levels are crucial for diagnosing slagging problems, predicting corrosion in boilers and scrubbers, and completing a comprehensive total analysis of the coal’s chemical makeup for quality control.
💡 What is the difference between the Combustion Bomb method and the Eschka method?
The Combustion Bomb method (Method A) rapidly oxidizes the sample under pure oxygen pressure, absorbing chlorine in an ammonium carbonate solution. The Eschka method (Method B) involves slow, controlled heating of the coal mixed intimately with Eschka mixture in an oxidizing furnace atmosphere.
⚡ How is the chloride concentration measured after sample preparation?
Both methods rely entirely on potentiometric titration to determine the chloride concentration in the recovered solution. This provides an accurate, quantitative endpoint detection for the analysis.
📌 What primary referenced standards support this test method?
The standard relies on several key ASTM standards including Terminology D 121 (Coal and Coke), Practice D 2013 (Sample Preparation), Practice D 3180 (Calculating Analyses), Practice E 144 (Safe Use of Oxygen Bombs), and Specification D 1193 (Reagent Water).