GB/T 211—2007 Method for determination of total moisture in coal
GB/T 211-2007 replaces GB/T 211-1996. This standard outlines the reagents, equipment, operational procedures, calculation methods, and precision for determining the total moisture content in coal. The nitrogen stream drying method (Method A1 and B1) is suitable for all types of coal, while the air stream drying method (Methods A2 and B2) is appropriate for bituminous coal and anthracite. The microwave drying method (Method C) is applicable to bituminous coal and lignite. Method A1 is recognized as the arbitration method.2 Normative references
The following documents are referenced within this standard. For dated references, subsequent amendments or revisions do not apply unless they are explicitly included. Parties involved in agreements based on this standard are encouraged to verify if the latest versions of these documents are available. For undated references, the most recent edition applies.Preparation method of GB 474 coal sample
GB/T 19494.2 Mechanized sampling of coal - Part 2: Preparation of coal samples (GB/T 19494.2-2004, ISO 13909-4:2001, NEQ)
Industrial analysis method for GB/T 212 coal (GB/T 212-2001, eqv ISO 11722:1999, eqv ISO 1171:1997, eqv ISO 562:1998)
3 Method summary
3.1 Method A (two-step method)
3.1.1 Method A1: Drying in a nitrogen stream
A certain amount of coal sample with a particle size of less than 13 mm is dried at a temperature not exceeding 40°C until it reaches a constant mass. It is then crushed to a particle size of less than 3 mm and dried in a nitrogen stream at (105–110)°C until a constant mass is achieved. The total moisture is calculated based on the mass loss from the two-step drying process.3.1.2 Method A2: Drying in an air stream
Similar to Method A1, but the second drying step is performed in an air stream rather than a nitrogen stream.3.2 Method B (one-step method)
3.2.1 Method B1: Drying in a nitrogen stream
A coal sample with a particle size of less than 6 mm is weighed and dried in a nitrogen stream at (105–110)°C until a constant mass is reached. Total moisture is determined based on the mass loss.3.2.2 Method B2: Drying in an air stream
A coal sample with a particle size of less than 13 mm (or 6 mm) is dried in an air stream at (105–110)°C until a constant mass is achieved. Moisture is calculated from the mass loss.3.3 Method C (microwave drying method)
A coal sample with a particle size of less than 6 mm is placed in a microwave oven. The alternating electric field causes water molecules to generate heat, leading to rapid evaporation. Total moisture is calculated based on the mass loss after drying.4 Reagents
4.1 Nitrogen (GB/T8979): Purity 99.9%, oxygen content below 0.01%.
4.2 Anhydrous calcium chloride (HGB3208): Chemically pure, granular.
4.3 Color-changing silica gel (GB/T7822): Available for industrial use.
5 Instruments (for Methods A and B)
5.1 Air drying box: Equipped with automatic temperature control and air circulation, capable of maintaining temperatures between 30–40°C and 105–110°C, with sufficient ventilation.
5.2 Nitrogen drying oven: Features automatic temperature control, maintains 105–110°C, has proper space for weighing bottles, and provides high ventilation.
5.3 Shallow plate: Made of heat-resistant material, can hold up to 500g of coal, with a load per unit area not exceeding 1g/cm².
5.4 Glass weighing bottle: Diameter 70mm, height 35–40mm, with a tight cap.
5.5 Analytical balance: Accuracy to 0.001g.
5.6 Industrial balance: Sensitivity of 0.1g.
5.7 Desiccator: Contains color-changing silica gel or granular anhydrous calcium chloride.
5.8 Flowmeter: Range of 100–1000 mL/min.
5.9 Drying tower: Capacity of 250mL, filled with silica gel or anhydrous calcium chloride.
6 Samples
6.1 Coal sample
A whole moisture coal sample with a particle size less than 13 mm should be at least 3kg, while a sample with a particle size less than 6 mm should be at least 1.25kg.6.2 Sample preparation
6.2.1 Full-moisture coal samples with a particle size less than 13 mm should be prepared according to GB474 or GB/T19494.2.
6.2.2 For samples with a particle size less than 6 mm, the coal should be crushed using a crusher that minimizes moisture loss, and then reduced to at least 1.25kg before being sealed.
6.3 Before measuring total moisture, check the seal of the container. Clean the surface and weigh it to 0.1% accuracy. If the measured mass is less than the labeled mass by no more than 1%, and there's no evidence of moisture loss during transport, the difference should be considered as moisture loss. Apply the correction as described in section 7.3.
6.4 The coal sample should be thoroughly mixed for at least 1 minute before weighing.
7 Determination steps
7.1 Method A (two-step method)
7.1.1 External moisture (Methods A1 and A2, air-dried)
Weigh approximately 500g of coal sample (500±10g) in a pre-dried shallow pan, spread evenly, and dry in an air drying oven at ambient temperature or not higher than 40°C until a constant mass is achieved. Record the mass and calculate external moisture using formula (1).7.1.2 Intrinsic moisture (Method A1, nitrogen drying)
After determining external moisture, crush the sample to less than 3 mm and weigh 10 ± 1 g into a pre-dried weighing bottle. Place it in a nitrogen drying oven preheated to 105–110°C and dry for 1.5 hours for bituminous coal, longer for lignite and anthracite.Wuxi Jinle Automobile Motor Factory , https://www.wxjldj.com