ASTM D1412/D1412M-20

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D1412/D1412M − 19b D1412/D1412M − 20
Standard Test Method for
Equilibrium Moisture of Coal at 96 to 97 Percent Relative
Humidity and 30 °C
This standard is issued under the fixed designation D1412/D1412M; the number immediately following the designation indicates the
year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last
reapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope*
1.1 This test method covers determination of the equilibrium moisture of coal in an atmosphere over a saturated solution of
potassium sulfate at 30 °C.
NOTE 1—For information concerning the experimental work on which this test method is based, see (1-5).
1.2 Units—The values stated in either SI units or non-SI units are to be regarded separately as standard. The values stated in each
system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used
independently of the other, and values from the two systems shall not be combined.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D121 Terminology of Coal and Coke
D388 Classification of Coals by Rank
D2013 Practice for Preparing Coal Samples for Analysis
D2234/D2234M Practice for Collection of a Gross Sample of Coal
D3172 Practice for Proximate Analysis of Coal and Coke
D3173 Test Method for Moisture in the Analysis Sample of Coal and Coke
D3302 Test Method for Total Moisture in Coal
D4239 Test Method for Sulfur in the Analysis Sample of Coal and Coke Using High-Temperature Tube Furnace Combustion
D4596 Practice for Collection of Channel Samples of Coal in a Mine
D5865 Test Method for Gross Calorific Value of Coal and Coke
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
This test method is under the jurisdiction of ASTM Committee D05 on Coal and Coke and is the direct responsibility of Subcommittee D05.21 on Methods of Analysis.
Current edition approved Nov. 1, 2019Sept. 15, 2020. Published November 2019September 2020. Originally approved in 1956. Last previous edition approved in 2019
as D1412/D1412M – 19a.D1412/D1412M – 19b. DOI: 10.1520/D1412_D1412M-19B.10.1520/D1412_D1412M-20.
The boldface numbers in parentheses refer to the list of references at the end of this standard.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D1412/D1412M − 20
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
2.2 ISO Standards:
ISO 5725-4 Accuracy (Trueness and Precision) of Measurement Methods and Results—Part 4: Basic Methods for the
Determination of the Trueness of a Standard Measurement Method
ISO 5725-6 Accuracy (Trueness and Precision) of Measurement Methods and Results—Part 6: Use in Practice of Accuracy
Values
3. Significance and Use
3.1 This test method affords a means of estimating the inherent moisture of either coal that is wet and shows visible surface
moisture or coal that may have lost some moisture. It may be used for estimating the surface, or extraneous moisture of wet coal,
such moisture being the difference between the total moisture as determined by Test Method D3302 and the equilibrium moisture.
3.2 When samples are collected in conformity with Classification D388, the equilibrium moisture is considered to be equal to bed
moisture with the exception of some low rank coals that yield equilibrium moisture values below bed moisture.
3.3 The results obtained by this test method are sensitive to many influences, and therefore, raw (uncorrected) equilibrium
moisture data may be of limited value in and of themselves. When working with low rank coals, the results yielded by this test
method require critical assessments. It is recommended that the procedure outlined in the Appendix X1 be applied, and the results
corrected before use in situations where a more reliable estimation inherent or bed moisture for low rank coals is required. The
Appendix also provides useful quality assurance information which is applicable to coals of all ranks.
4. Apparatus
4.1 Water Bath or Insulated Air Cabinet—The bath or cabinet shall be of sufficient size to accommodate several vacuum-type
desiccators, and shall be provided with a temperature regulator to maintain a uniform temperature of 30.0 °C 6 0.2 °C.
4.2 Moisture Oven—The oven shall be so constructed as to have a uniform temperature in all parts and a minimum of air space.
It may be of the type shown in the Apparatus section of Test Method D3173. Provision shall be made for renewing the air (or, if
desired, dry oxygen-free nitrogen for subbituminous and lignitic coals) in the oven at a rate of two times per minute, with the air
dried as defined in 5.1.
4.3 Mechanical Vacuum Pump.
4.4 Crusher, laboratory, coffee-mill type.
4.5 Sieve, 203 mm [8 in.] diameter, with 2.36 mm [No. 8] openings.
4.6 Shaking Machine.
4.7 Desiccators:
4.7.1 High Vacuum Desiccator—Small vacuum-type desiccator, approximately 160 mm in diameter, when used in conjunction
with a saturated K SO solution provides the necessary humidity for the test conditions (see Fig. 1).
2 4
4.7.2 Cooling Desiccator—Cabinet-type desiccator, when used with any of the desiccants (5.2.1 – 5.2.3) allows the dried test
sample to cool to room temperature without substantial regain in mass from adsorption of atmospheric moisture.
4.8 Weighing Bottles, glass, low-form, flat-bottom, cylindrical, 70 mm in diameter, with well-fitting covers.
4.9 Filter Pump, aspirator.
Available from International Organization for Standardization (ISO), ISO Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva,
Switzerland, http://www.iso.org.
D1412/D1412M − 20
FIG. 1 Vacuum-Type Desiccator
4.10 Buchner-Type Funnel, approximately 64 mm [2 ⁄2 in.] in diameter.
5. Reagents
5.1 Drying Atmospheres—The atmosphere used to purge the drying oven is either dry air or dry nitrogen as specified in 5.1.1 or
5.1.2.
5.1.1 Dry Air—Air with a moisture content of 1.9 mg ⁄L or less passed through a drying column containing any of the appropriate
desiccants listed in 5.2.
5.1.2 Dry Nitrogen—Compressed nitrogen gas certified having an oxygen content less than 30 μL/L and passed through a drying
column containing any of the appropriate desiccants listed in 5.2.
5.2 Desiccants—Materials suitable for use in the desiccator may be chosen from the following:
5.2.1 Anhydrous Calcium Sulfate (0.004 mg/L).
5.2.2 Silica Gel.
5.2.3 Magnesium Perchlorate (0.0005 mg/L).
5.2.4 Sulfuric Acid, Concentrated (0.003 mg/L).
5.2.5 The desiccant must be kept fresh enough to assure that the air in the desiccator is dry as defined in 5.1. Values in parentheses
( ) are literature values for the residual amount of moisture in air at equilibrium with these desiccants. (Warning: Sulfuric acid
is corrosive and can cause severe damage to eyes, skin, and clothing. Magnesium perchlorate is a strong oxidant and can react
violently with organic materials.)
5.3 K SO —Crystalline Potassium Sulfate.
2 4
D1412/D1412M − 20
6. Technical Hazards
6.1 In collecting, containing, handling, reducing, and dividing the gross moisture sample, all operations must be done
expeditiously and in a manner that attempts to preserve the original sample moisture integrity.
6.2 If the gross sample is too wet to allow reduction and division, spread sample in a thin layer and expose to the air of the
laboratory. Dry no more than necessary to enable satisfactory reduction and division of sample.
6.3 Take particular care not to overdry low rank coals, especially lignites. Drying will accelerate oxidation and can also result in
shrinkage of pore size and volume which will affect the moisture-holding capacity.
7. Collection of Gross Samples
7.1 Samples shall not be taken from outcrop, weathered, or oxidized coal.
7.1.1 Mine Samples—Take mine samples in accordance with Practice D4596.
7.1.2 Tipple or Shipment Samples—Collect a representative gross sample of coal in accordance with Practice D2234/D2234M. If
only the equilibrium moisture is desired, use the General Purpose Sampling Procedure. If the surface moisture of wet coal is to
be determined, use the procedure for sampling the special total moisture subsample described in Practice D2234/D2234M.
8. Preparation of Laboratory Samples
8.1 Crush the sample to a 2.36 mm [No. 8] sieve size in accordance with Practice D2013; however, it is important to also observe
the technical hazards stated in Section 6 of this test method.
8.1.1 Divide out a 25 g equilibration moisture subsample in accordance with Practice D2013 to be used for testing.
9. Procedure
9.1 Two methods for preparing the sample for equilibration are provided. The wetted procedure has historically been the primary
method. However, mine samples and certain coals that deteriorate when treated with water, particularly low rank coals
(subbituminous C and lignite), may be equilibrated directly without wetting, provided the samples are collected and prepared with
a minimum loss of moisture. Avoid low rank coal samples that have less than their full complement of inherent moisture.
9.1.1 Wetted Procedure—Place the 25 g sub-split equilibration sample coal into a 250 mL Erlenmeyer flask and add approximately
100 mL of recently boiled, cooled, distilled water (Note 2). Shake the flask mechanically for 30 min, and then place it in the
constant-temperature bath for 3 h at 30 °C. At the end of the wetting period, remove the excess water from the coal by filtering
on a Büchner-type funnel approximately 64 mm [2 ⁄2 in.] in diameter, using suction supplied by a water filter pump. Use a
minimum amount of water to transfer the coal to the filter. After transfer of the coal, close the funnel with a rubber stopper fitted
with a glass tube through which air saturated with water vapor is passed to prevent drying of the coal (Note 2). Cease filtration
as soon as the wet sheen on particle surfaces begins to dull or coal particles first begin to disaggregate (particles stop clinging
together). Thoroughly mix the wet coal in the funnel with a spoon and place about 5.0 g in a uniform layer in a weighing bottle
of known mass. Proceed to 9.2.
NOTE 2—Over drying the sample during the filtration process to remove excess moisture can result in anomalously low equilibrium moisture values.
Conversely, stopping the filtration prematurely may leave the sample too wet. In the latter case, the sample may not reach equilibrium in the desiccator
within the prescribed equilibration period.
9.1.2 Unwetted Procedure—The use of the unwetted procedure for coal samples that have sustained partial drying is not
recommended due to the hysteresis effect (Note 3). Place about 5.0 g of the crushed gross sample coal in a uniform layer in a
weighing bottle of known mass. Proceed to 9.2.
NOTE 3—Moisture desorption and adsorption curves for coal are not entirely reversible. The difference between the original and readsorbed moisture
Allardice, D. J., and Evans, D. G., "Moisture in coal," in C. Karr, Jr. (Ed.), Analytical Methods for Coal and Coal Products, Vol 1, Academic Press, New York, 1978,
pp. 247–262.
D1412/D1412M − 20
at the maximum relative vapor pressure is due to a failure to close the hysteresis loop, and is often termed the “hysteresis effect.” The effect increases
with decreasing coal rank and is believed to be a result of shrinkage due to drying that reduces the coal pore volume, which, in turn, decreases moisture
holding capacity. Because of this effect, coal samples subjected to partial drying below their full complement of inherent moisture, or samples of low
rank coals (which have large pore sizes)sizes), may yield anomalously low equilibrium moisture values.
9.2 Place the uncovered weighing bottle in the small vacuum-type desiccator containing a saturated solution of K SO for
2 4
maintaining the relative humidity of 96 % to 97 %. An excess of crystalline K SO shall extend above the solution level. Evacuate
2 4
the desiccator to an absolute pressure equivalent to about 4 kPa [30 mm Hg] by means of a mechanical vacuum pump and then
totally immerse in a constant-temperature water bath or place in an insulated air cabinet maintained at 30 °C 6 0.2 °C for 48 h
for all coals higher in rank than subbituminous C. Subbituminous C and lignite coal will require 72 h to reach equilibrium for
practical purposes.
9.3 After equilibration of the coal, restore the pressure in the desiccator to atmospheric, with the desiccator still in the bath, by
slowly admitting dry air or nitrogen for a period of not less than 15 min. Admit the gas to the inlet tube of the desiccator after
passing it through a train consisting first of a bubbler containing H SO (sp gr 1.84), then a capillary tube with one end drawn out
2 4
to a tip having a suitable bore for regulating the rate of gas flow, and finally a coiled copper tube placed in the constant-temperature
bath. Using nitrogen obviates the need for the bubbler containing concentrated H SO . Remove the desiccator from the bath and
2 4
open immediately. Quickly close the weighing bottle and weigh to the nearest 0.1 mg. Uncover the weighing bottle, place it in the
moisture oven preheated to 105 °C, through which passes a current of dry air or nitrogen per 5.1, and heat for 1 ⁄2 h. Then remove
the weighing bottle from the oven, cool for 30 min, over one of the desiccants specified in 5.2, in a desiccator, and weigh.
10. Calculation
10.1 Calculate the percent equilibrium moisture in the analysis sample as expressed in Eq 1:
EQM 5 100 B 2 C ⁄ B 2 A (1)
~ ! ~ !
where:
EQM = equilibrium moisture, %,
A = mass of weighing bottle, g,
B = mass of weighing bottle and wet coal, g,
C = mass of weighing bottle and dried coal, g, and
100 = conversion factor from g/g to %.
11. Report
11.1 Report the equilibrium or bed moisture to the nearest 0.1 % as the percentage loss in mass of the equilibrated coal.
12. Precision and Bias
12.1 The precision of this test method is based on an interlaboratory study of ASTM D1412/D1412M, conducted in 2011. A total
of 14 laboratories participated in this study, testing nine coal samples (three each of bituminous, subbituminous, and lignite ranks)
and using either air or nitrogen as the drying atmosphere. Each of the total 796 “test results” reported represents an individual
determination and all participants were asked to report duplicate test results. Except for those analyses with fewer than six
laboratories reporting for a sample, ASTM Practices E691 and E177 were followed for the design and analysis of the data; the
details are given in ASTM Research Report No. D05-1049.
12.1.1 The precision of this test method for the determination of Equilibrium Moisture in Coal is expressed as best-fit regression
trendlines in Eq 2 and Eq 3.
r 5 0.035 3EQM1 0.216 (2)
R 5 0.057 3EQM1 0.398 (3)
Selvig, W.A., and Ode, W. H., Determination of Moisture-Holding Capacity (Bed Moisture) of Coal or Classification by Rank: US Bureau of Mines, RI-4968, 1953, p.
10.
Supporting data have been filed at ASTM International Headquarters and may be obtained by requesting Research Report RR:D05-1049. Contact ASTM Customer
Service at service@astm.org.
D1412/D1412M − 20
where:
r = Repeatability Limit, %,
R = Reproducibility Limit, %, and
EQM = Equilibrium Moisture, %.
12.1.2 Repeatability Limit (r)—The value below which the absolute difference between two test results of separate and consecutive
test determinations, carried out on the same sample, in the same laboratory, by the same operator, using the same apparatus on
samples taken at random from a single quantity of homogeneous material, may be expected to occur with a probability of
approximately 95 %.
12.1.3 Reproducibility Limit (R)—The value below which the absolute difference between two test results carried out in different
laboratories, using samples taken at random from a single quantity of material that is as homogeneous as possible, may be expected
to occur with a probability of approximately 95 %.
12.2 Bias—Certified standards or absolute methods are not available for this test; therefore, bias of results cannot be determined.
13. Keywords
13.1 bed moisture; coal; equilibrium moisture; extraneous moisture; surface moisture
APPENDIXES
(Nonmandatory Information)
X1. PRACTICE FOR COMPARING THE RELATIONSHIP BETWEEN INHERENT AND
EQUILIBRIUM MOISTURE
X1.1 The purpose of the equilibrium moisture test is to provide an estimate of the inherent (bed) moisture. However, evidence has
shown that equilibrium moisture results on many low rank coals, including most lignite coal, are often lower than inherent
moisture. The procedure described in this appendix can be used where there is a question about the applicability of the equilibrium
moisture result as an estimator of inherent moisture. The method is straightforward and has proven effective in many situations
for examining this moisture relationship.
X1.2 Special coal samples, collected at their inherent moisture level, are analyzed for both total (inherent) and equilibrium
moisture. The results are then compared to see if differences exist between the two moisture parameters, and the end user(s) can
then determine whether such differences have any practical significance. This procedure does not directly yield inherent moisture
values for an entire coal seam or mine, because the samples are not necessarily representative of the full seam as would be the
case for face channel samples (Practice D4596). Nevertheless, the procedure does provide a tool for evaluating the relationship
between inherent and equilibrium moisture for a given area. See (6).
X1.3 The most critical step in evaluating this relationship is the collection of samples containing their full complement of inherent
moisture. Occasionally, it may be difficult to obtain a channel sample that contains no surface moisture. Also, obtaining a channel
sample from thick coal seams, such as those in the Western United States, is generally impractical, especially from a safety
standpoint. However, the collection of fresh, unfractured pieces of coal from freshly-exposed seam faces or blasted coal piles
without visible surface moisture is usually feasible. Such samples are considered to contain only inherent moisture (Terminology
D121, Classification D388).
NOTE X1.1—The collection of coal at its inherent moisture levels requires some degree of judgement, and t
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