ASTM D4931 Standard Test Method for Gross Moisture in Green Petroleum Coke
8. Procedure
8.1 Preparation Procedure - When the sample contains free moisture, a conditioning step is needed before determining gross moisture. If the sample does not contain free water, go to 8.2.
8.1.1 Distribute the required number of increments of the gross moisture sample in a series of preweighed pans. The sample is spread to a depth of not more than 50 mm (2 in.) or twice the diameter of the largest particle for cokes smaller than 25 mm (1.0 in.).
8.1.2 Weigh each pan with sample as it is filled from the gross sample and record the weights. Place each in an air drying oven that has been adjusted to maintain temperature no more than 15°C (27°F) above ambient to a maximum of 40°C (104°F). Maintain air circulation through oven at a rate of at least one air exchange per minute, but in no case is it to be so high as to blow fine particles from the pans. Gently stir the sample occasionally to ensure uniform drying.
8.1.3 When the coke surfaces appear dry, remove the sample pans from the oven, cool to ambient, weigh, and record mass to the nearest gram. Return the pans with sample to the oven and repeat the drying and weighing at two hour intervals until the weight loss is less than 0.1%/ h.
8.1.4 Allow the sample to reach equilibrium with ambient temperature and humidity before the final air dry weight is recorded. Avoid excess drying. Calculate the air dry moisture loss as shown in Step 9.1.1.
8.1.5 Proceed with sample reduction to at least 25 mm (1 in.) and division into minimum 500 g lots in accordance with the procedures listed in Practice D2013. Use enclosed equipment where possible to minimize moisture change.
8.1.6 The crushed and divided sample, 500 g minimum shall remain in an airtight container with minimum unused volume until starting the determination for Residual Moisture on Prepared Sample.
8.2 Residual Moisture on Prepared Sample (Drying Oven Method):
8.2.1 Determine and record the mass of the drying pan and sample container. Transfer the crushed and weighed sample, including sample container and pan, to an oven maintained at 105 +/- 5°C. Dry sample to a constant weight (see Note 1).
NOTE 1 - Time required to achieve constant weight is estimated to be approximately 1 h per 100 g of sample. However, do not assume 5 h is sufficient to dry a 500 g sample to constant weight.
9. Calculation
9.1 Total Moisture:
9.1.1 Calculate air dry losses (ADL) as follows:
ADL = [(L2 - L1)/G] x 100
where:
ADL = air dry loss, mass %,
L1 = mass of sample after air drying,
L2 = mass of sample before air drying, and
G = mass of gross sample.
9.1.2 Calculate the percent residual moisture, R, as follows when the Air Drying Procedure is used:
R = [(L2 - L1)/G] x 100
where:
R = residual moisture,
L1 = mass of sample after drying,
L2 = mass of sample before drying, and
G = mass of sample.
9.1.3 Calculate the percent total moisture, M, as follows when the Air Drying Procedure has been used:
M = [R(100 - ADL)/100] + ADL
where:
M = total moisture, of sample mass %,
ADL = air dry loss, of sample mass %, and
R = residual moisture.
9.2 Calculate the percent total moisture, M, as follows when the air drying stage is not used:
M = [(WL2 - WL1)/G] x 100
where:
M = total moisture, mass %,
WL1 = mass of sample after drying,
WL2 = mass of sample before drying,
G = mass of sample.
