ASTM D7569/D7569M-10(2023)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D7569/D7569M − 10 (Reapproved 2023)
Standard Practice for
Determination of Gas Content of Coal—Direct Desorption
Method
This standard is issued under the fixed designation D7569/D7569M; 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 values stated in each system may not be exact equivalents;
therefore, each system shall be used independently of the other.
1.1 This practice describes methods for the direct determi-
Combining values from the two systems may result in noncon-
nation of the gas content of coal by desorption using samples
formance with the standard.
obtained by drill coring methods from the surface. It sets out
1.6 This standard does not purport to address all of the
guidelines for the equipment construction, sample preparation
safety concerns, if any, associated with its use. It is the
and testing procedure, and method of calculation.
responsibility of the user of this standard to establish appro-
1.2 Indirect methods for the determination of the gas con-
priate safety, health, and environmental practices and deter-
tent of coal (not covered in this practice) are based on either the
mine the applicability of regulatory limitations prior to use.
gas absorption characteristics of coal under a given pressure
1.7 This international standard was developed in accor-
and temperature condition or other empirical data that relate
dance with internationally recognized principles on standard-
the gas content of coal to such other parameters as coal rank,
ization established in the Decision on Principles for the
depth of cover, or gas emission rate.
Development of International Standards, Guides and Recom-
1.3 This practice covers the following two direct methods,
mendations issued by the World Trade Organization Technical
which vary only in the time allowed for the gas to desorb from
Barriers to Trade (TBT) Committee.
the core, or sidewall core, before final crushing:
1.3.1 The slow desorption method in which volumetric
2. Referenced Documents
readings of gas content are taken frequently (for example,
2.1 ASTM Standards:
every 10 min to 15 min) during the first few hours, followed by
D121 Terminology of Coal and Coke
hourly measurements for several hours, and then measure-
D167 Test Method for Apparent and True Specific Gravity
ments on 24-h intervals until no or very little gas is being
and Porosity of Lump Coke
desorbed for an extended period of time.
D1412 Test Method for Equilibrium Moisture of Coal at 96
1.3.2 The fast desorption method in which after initial
to 97 Percent Relative Humidity and 30 °C
desorbed gas measurements to obtain data for lost gas calcu-
D2799 Test Method for Microscopical Determination of the
lations are taken, the canister is opened and the sample is
Maceral Composition of Coal
transferred to the coal crusher. The remaining gas volume is
D3172 Practice for Proximate Analysis of Coal and Coke
measured on a crushed sample.
D3173 Test Method for Moisture in the Analysis Sample of
1.4 This practice is confined to the direct method using core,
Coal and Coke
or sidewall core obtained from drilling. The practice can be
D3174 Test Method for Ash in the Analysis Sample of Coal
applied to drill cuttings samples; however, the use of cuttings
and Coke from Coal
is not recommended because the results may be misleading and
D3176 Practice for Ultimate Analysis of Coal and Coke
are difficult to compare to the results obtained from core
D3180 Practice for Calculating Coal and Coke Analyses
desorption. The interpretation of the results does not fall within
from As-Determined to Different Bases
the scope of the practice.
D3302 Test Method for Total Moisture in Coal
D5192 Practice for Collection of Coal Samples from Core
1.5 Units—The values stated in either SI units or inch-
E1272 Specification for Laboratory Glass Graduated Cylin-
pound units are to be regarded separately as the standard. The
ders
This practice 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. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Dec. 1, 2023. Published December 2023. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
ɛ1
approved in 2010. Last previous edition approved in 2015 as D7569 – 10 (2015) . Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/D7569_D7569-10R23. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7569/D7569M − 10 (2023)
2.2 Australian Standard: 3.1.8 canister, n—container that can be sealed into which a
AS 3980 Guide to the determination of gas content of coal sample is placed to allow desorption to occur.
coal—Direct desorption method
3.1.8.1 Discussion—The reduction in pressure to atmo-
spheric pressure (at surface) causes the sample to release gas
2.3 ISO Standard:
into the canister. By measuring the amount of gas released and
ISO 6706 Plastics laboratory ware—Graduated measuring
the weight of the sample, the gas content can be determined.
cylinders
Gas content is conventionally reported in units of cubic
2.4 DIN Standard:
3 3
centimetres/gram (cm /g), cubic metres/tonne (m /ton), or
DIN 12681 Plastics laboratory ware—Graduated measuring
standard cubic feet/ton (scf/ton). (1)
cylinders
3.1.9 continuous coring, v—refers to continuous coring with
3. Terminology
wireline recovery. (1)
3.1 Definitions:
3.1.10 conventional core, n—“large” diameter core (8.9 cm
3.1.1 For additional definitions of terms used in this
[3.5 in.] diameter or larger) in which the core barrel is
practice, refer to Terminology D121.
recovered to the surface after drilling a fixed interval by pulling
3.1.2 absolute permeability, n—permeability of a rock to a
the drill string. (1)
particular fluid when the rock is 100 % saturated with the
6 3.1.11 core, n—in drilling, a cylindrical section of rock
flowing fluid. (1)
(coal) that is usually 5 cm to 10 cm in diameter taken as part of
3.1.3 absorbed gas, n—gas that is molecularly dissolved
the interval penetrated by a core bit and brought to the surface
within a liquid phase or has penetrated into the lattice structure
for geologic examination, representative sampling, and labo-
of a solid. (1)
ratory analyses. (D121, D5192)
3.1.4 actual lost gas time, n—lost gas time determined from
3.1.12 cuttings, n—in drilling, rock fragments that break
the time at which the sample being recovered reaches a depth
away because of the action of the drill bit and are transported
where the hydrostatic pressure of the drilling fluid column
to the surface by the drilling circulation system (mud or air).
equals the original (immediately before sampling) reservoir
3.1.12.1 Discussion—Cuttings may be screened and col-
pressure in the sample to the time at which the sample is sealed
lected from the circulation medium for lithologic characteriza-
in a desorption canister.
tion or analytical tests. (2)
3.1.4.1 Discussion—Essentially, the actual lost gas time is
3.1.13 delivery tube, n—flexible tube connecting a desorp-
the amount of time between when the core starts its trip to the
tion canister to a volumetric displacement apparatus. (1)
surface and when it is sealed in the canister. (1)
3.1.5 adsorption, n—attachment, through physical or
3.1.14 desorption, n—detachment of adsorbed molecules
chemical bonding, of fluid phase molecules to an interfacial from an interfacial surface (see adsorption). (1)
surface.
3.1.15 desorption data analysis software, n—software used
3.1.5.1 Discussion—The adsorbed phase molecules are se-
for analyzing desorption data. (1)
questered at the interfacial surface in a metastable equilibrium
3.1.16 desorption rate, n—volumetric rate at which gas
state, the stability of which is strongly affected by changes in
desorbs from a sample. (1)
temperature and pressure. (1)
3.1.17 diffusion, n—process whereby particles of liquids or
3.1.6 adsorption isotherm, n—quantitative relationship, at
gases move from a region of higher to lower concentration
constant temperature, describing how the concentration of
independent of the pressure gradient. (1)
adsorbed phase molecules at an interfacial surface varies as a
function of increasing system pressure. (1)
3.1.18 diffusivity, n—ratio of the diffusion coefficient to the
square of a typical diffusion distance. (1)
3.1.7 as-received basis, n—analytical data calculated to the
moisture condition of the sample as it arrived at the laboratory
3.1.19 direct desorption method, n—method for represent-
and before any processing or conditioning.
ing desorption of gas from coal or other materials in which gas
3.1.7.1 Discussion—If the sample has been maintained in a
storage as a result of adsorption is significant.
sealed state so that there has been no gain or loss, the
3.1.19.1 Discussion—It mathematically presumes constant
as-received basis is equivalent to the moisture basis as
temperature diffusion from a sphere initially at uniform gas
sampled. (D3180, D5192, D1412, D3302)
concentration. The solution of the basic equation adopted
suggests that the measured desorbed gas volume is propor-
tional to the square root of time since the start of desorption
Available from Standards Australia Limited, 286 Sussex St., Sydney, NSW,
(time zero). The direct method is the most widely used method
2000, Australia, GPO Box 476, Sydney, NSW, 2001 Australia or via the website:
www.standards.org.au. for estimating lost gas volume. (1)
Available from the International Organization for Standardization (ISO), 1, rue
3.1.20 dry, ash-free basis, n—data calculated to a theoretical
de Varembé, Case Postale 56, CH-1211 Geneva 20, Switzerland or via the website:
http://www.iso.org/. base of no moisture or ash associated with the sample.
Available from Deutsches Institut für Normung e. V., 10772 Berlin or via the
3.1.20.1 Discussion—Numerical values as established by
website: http://www2.din.de.
6 Test Methods D3173 and D3174 are used for converting the
The boldface numbers in parentheses refer to the list of references at the end of
this standard. as-determined data to a moisture- and ash-free basis. (D3180)
D7569/D7569M − 10 (2023)
3.1.21 fast desorption method, n—after initial measure- 3.1.33 manometer, n—see volumetric displacement appara-
ments to obtain the basis for lost gas calculations, the canister tus.
is opened and the sample is transferred to a coal-crushing
3.1.34 measured gas volume, n—measured volume of gas
device that is modified so that the remaining desorbed gas
that is released from a sample into a desorption canister,
volume from the crushed coal sample can be measured.
reported at standard temperature and pressure conditions. (1)
(AS 3980)
3.1.35 mesopores, n—pores in the coal larger than 2 nm and
3.1.22 free gas, n—unabsorbed gas within the pores and
less than 50 nm. (3)
natural fractures. (1)
3.1.36 micropores, n—pores with a width of less than 2 nm.
3.1.23 gas-in-place, n—amount of gas present in a seam or
(3)
an interval of discrete thickness or in multiple seams or
3.1.37 modified direct method, n—modification of the direct
intervals determined from the gas content, bulk density,
method by the U.S. Bureau of Mines according to Diamond
thickness, and drainage area.
and Levine (4) and Diamond and Schatzel (5) to account
3.1.23.1 Discussion—Estimates of gas-in-place usually re-
precisely for changes in the concentration of gaseous species
flect total gas content, which in addition to methane, may
during desorption, with particular applications to situations in
include other gases such as carbon dioxide or nitrogen. (1)
which small amounts of gas are evolved. (1)
3.1.24 gas saturated, adv—state in which the gas content
3.1.38 quick connect fittings, n—pipe fittings designed for
(determined from direct or indirect desorption measurements)
easy and rapid connection and disconnection.
is equal to the gas storage capacity (determined from
isotherms). (1) 3.1.39 raw basis, n—basis for gas content calculation
whereby the gas volume is divided by the actual sample weight
3.1.25 gas storage capacity, n—maximum amount of gas or
regardless of the moisture content or the presence of non-coal
gas mixtures (normalized according to the relevant basis) that
in the canister sample. (1)
can be held by a sample at various reservoir pressures,
reservoir temperature, and a specific moisture (water) content. 3.1.40 residual gas volume, n—volume of the total sorbed
(1) gas that remains in the sample after desorption into a canister
has effectively ceased (after termination of canister desorp-
3.1.26 head space volume, n—void space in a canister
tion).
containing a sample.
3.1.40.1 Discussion—Residual gas volume, as defined and
3.1.26.1 Discussion—Canister desorption measurements are
reported, can be very different for slow desorption and fast
corrected for the effect of expansion or contraction of gases in
desorption methods. Early termination of desorption followed
the canister head space in response to temperature and pressure
by sample crushing will obviously lower desorbed quantities of
fluctuations. (1)
gas and increase the residual values. Maceral composition,
3.1.27 indirect method for the determination of the gas
lithotype composition, and the coal bench being sampled may
content of coal, n—method based on either the gas absorption
all affect permeability on small-scale samples. (1)
characteristics of coal under a given pressure and temperature
3.1.41 sidewall core, n—small diameter core taken down-
condition or other empirical data that relate the gas content of
hole by wireline methods using percussion or mechanical
coal to such other parameters as coal rank, depth of cover, or
methods to drill into the side of the borehole.
gas emission rate.
3.1.41.1 Discussion—The percussion method cores by ex-
3.1.28 in-situ basis, adj—a basis in which gas content is
plosively firing hollow core barrels into a coal seam and then
determined from a plot of gas content versus bulk density
retrieving the coal plug to the surface. The mechanical method
(determined from open-hole high-resolution bulk density log
uses hollow rotary drills to core into the coal seam, pull the
data). (1)
core plugs back into the tool, and then they are retrieved.
3.1.29 isotherm (sorption isotherm), n—quantitative
3.1.42 slow desorption method, n—volumetric readings of
relationship, at constant temperature, that describes how the
canister gas content are taken frequently (for example, every
concentration of adsorbed phase molecules at an interfacial
10 min to 15 min) during the first few hours, followed by
surface varies as a function of system pressure. (1)
hourly measurements for several hours, and then measure-
3.1.30 lost gas time, n—time between when the sample gas
ments on 24-h intervals until no or very little gas is being
pressure falls below the reservoir pressure during sample
desorbed for an extended period of time.
recovery (time zero) and the time when the sample is sealed in
3.1.42.1 Discussion—Some coals can desorb in excess of
a desorption canister. (1)
one year and a desorption base line may be established with
3.1.31 lost gas volume, n—volume of gas that is released
measured gas volumes consistently below 10 cm per reading.
from a sample (generally under conditions of decreasing
At this slow desorption rate, no gas is expected to be lost when
temperature and pressure) before it can be placed in a canister
transferring the sample from the desorption canister to the
and measured (between the time when the sample gas pressure
residual gas canister.
falls below the reservoir pressure during sample recovery and
3.1.42.2 Discussion—If the measured gas volume of a
the time when the sample is sealed in a desorption canister). (1)
canister falls at or below 10 cm per reading (where measure-
3.1.32 macropore, n—pores in the coal larger than 50 nm. ment error becomes too great), then that canister may be
(3) elevated to the next time measurement period. This procedure
D7569/D7569M − 10 (2023)
is continued until measured gas volumes are consistently below 4.3 Desorbed gas content (in cubic centimetres) can be
10 cm per reading. (AS 3980, (6)) measured using a volume displacement apparatus by the slow
or fast desorption method, or a combination of the two
3.1.43 sorbed gas, n—coalbed gas retained by adsorption or
methods, depending primarily upon the urgency of having gas
absorption processes or both. (1)
content data. In the slow desorption method, gas measurements
3.1.44 sorption time, n—time required for 63.2 % of the
are continued until measured gas volumes are consistently
total sorbed gas (including residual gas) to be released.
below 10 cm per reading, which for some coals may take more
3.1.44.1 Discussion—It is reported in either hours or days
than a year’s time to desorb to this level. In the fast desorption
(since time zero) depending on the relative rate at which gas is
method, when sufficient measurements are made to obtain data
released from a desorption sample. (1)
for lost gas calculations (usually more than 4 h of frequent
measurements), the canister is opened and the sample is
3.1.45 sorption standard temperature and pressure condi-
transferred to the coal crusher. The remaining gas volume is
tions (STP), n—various standards exist.
measured on a crushed sample. For gas composition or gas
3.1.45.1 Discussion—Historically, the petroleum industry
isotope analyses or both, the gas is sampled during desorption.
almost universally has used Imperial units of 60 °F [15.56 °C
or 288.6 K] as the reference temperature and 14.7 psia [101.3 4.4 All data are entered and maintained on predesigned data
kPa] as the reference pressure. See Ref 7. SI systems have used
forms and spreadsheets. Lost gas, desorbed gas, and residual
0 °C, 20 °C, and 25 °C [32 °F, 68 °F, and 77 °F] most gas contents are added to obtain total gas content that, after
commonly, depending on the data and the area of specialty. The
recalculation on sample weigh basis, yields total gas content
3 3
American Petroleum Institute (API, see Ref 8) has opted for expressed in cm /g, m /ton (SI units) [scf/ton (Imperial units)].
15 °C [59 °F] because it is close to 60 °F [15.56 °C]. The
5. Significance and Use
Society of Petroleum Engineers (Refs 9 and 10) suggests that
the choice between 0 °C and 15 °C [32 °F and 59 °F] is
5.1 Canister desorption is a widely used technique to
arbitrary. Government gas reserve reporting regulations may
measure the gas content of coal. The gas content data when
mandate which system to use, Imperial or SI (metric) (Ref 10).
normalized to volume/weight and multiplied by coal mass is
For coal gas desorption purposes, a standard of 15 °C has been
used to estimate the gas in place in an area around the cored
adopted simply to conform to API standards. It may be
well.
desirable to have a flexible temperature standard for various
6. Apparatus
applications. (1)
6.1 Background—In desorption studies of methane content
3.1.46 time zero, n—time at which a sample falls below the
in coal beds, the goal is to capture quickly the coal sample in
reservoir or desorption pressure during sample recovery.
a pressure-tight container purged of the air-bearing headspace
3.1.46.1 Discussion—Time zero is generally marked when
gas using an inert gas or water to stabilize the sample. Towards
the sample lifts off the bottom of the hole. However, more
this goal, a container (canister) shall be designed and
study of the sample retrieval process is required to determine
constructed/fabricated for core that would be easy to handle,
better the depth that the sample desorption process actually
fill, and close rapidly forming a reliably gastight seal, and
begins. (1)
facilitate rapid desorbing gas measurements. The primary coal
3.1.47 total gas volume, n—sum of lost gas, measured gas,
core desorption equipment consists of desorption canisters
and residual gas volumes (all measured on the same sample
made of sealed aluminum or plastic and a volumetric displace-
volume). (1)
ment apparatus or manometer; these items can be purchased
3.1.48 U.S. Bureau of Mines (USBM) lost gas time, n—lost from suppliers that use custom designs (1, 11) (Fig. 1) or
locally constructed with off-the-shelf materials and parts (12-
gas time determined from time zero, where time zero is defined
as the time when the sample reaches a depth halfway to the 14) (Fig. 2).
surface. (1)
6.2 Materials and Construction of Desorption Canisters—
3.1.49 volumetric displacement apparatus (manometer), Canister materials in widespread use today are aluminum,
plastic-coated aluminum, and plastic, usually polyvinyl chlo-
n—device, maintained at ambient conditions, for measuring the
amount of gas desorbed into a canister. (1) ride (PVC) materials. The use of stainless steel, although
advantageous because of its inert qualities, is not in widespread
use because of the high cost of materials and labor. The use of
4. Summary of Practice
canisters made of unsealed aluminum is not recommended in
4.1 This practice describes standardized guidelines for the
this practice because of the potential for significant reaction
determination of the gas content of coal by desorption using
with coal gases and related formation or drilling fluids after the
samples obtained by drill coring methods.
canister is closed. In general, all components of the desorption
4.2 Immediately after the coal core sample reaches the canister should be made of material that is, or treated to be,
surface and after the depth of the sample, state of the core, and nonreactive with regard to the coal or the normally low pH
proportion of coal to non-coal material are recorded, the fluids associated with the coal and hydrogen sulfide (H S) or
sample is transferred into a canister and the canister is sealed. other corrosive gases that may evolve during desorption. The
Multiple samples from a coal bed should be collected to obtain canisters should be made leak-proof by using a sealing device
a gas content representative of the whole coal bed. or cap such as a neoprene and plastic plug held in place by a
D7569/D7569M − 10 (2023)
FIG. 1 Progressive Development of Canister and Volumetric Displacement Apparatus Design
(Courtesy of Gas Technology Institute [see Refs 1, 4, and 10])
D7569/D7569M − 10 (2023)
FIG. 2 Custom-Made (A) Volumetric Displacement Apparatus and (B) Canister Constructed from Off-the Shelf Materials
(see Refs 12 and 13)
wing nut or clamp, a threaded PVC plug sealed by an O-ring, 6.3 Equipment for Making Measurements—During
or a coated aluminum cap sealed with a neoprene gasket. One desorption, the closed canister is periodically connected via a
end of the canister should have a permanent cap glued in place hose and quick-connect system to a volumetric displacement
(Fig. 2). To prevent leaks, the removable cap area shall be apparatus (manometer) to measure the desorbed volume of gas.
cleaned of coal particles after the coal sample is placed in the At the time of measurement, the barometric pressure (P) and
canister and before the canister is closed. The use of PVC for ambient temperature (T) in the volumetric displacement appa-
gas desorption canisters was first done in the 1980s by the ratus are recorded. National Institute of Standards and Tech-
USBM (5, 15). nology (NIST) traceable calibrated digital barometers and
D7569/D7569M − 10 (2023)
thermometers are recommended for these P and T measure- estimated at any time during the desorption process after the
ments. If the canister headspace is not filled with water to make initial measurements have been made to obtain the basis for
its volume zero, then it is necessary to measure headspace gas lost gas calculations. Following the slow desorption method,
temperature to correct for expansion or contraction of the residual gas is measured after the samples have completely
headspace gas. This is called the headspace correction. The desorbed. The fast desorption method allows the samples to be
data-entry forms and calculations for making this correction removed from the canisters for residual gas determination soon
are discussed in Refs 1, 13, and 14. after the measurements for lost gas calculations are completed.
It is recommended that the samples be allowed to desorb as
6.4 Materials and Construction of Volumetric Displacement
long as practical considering time and budgetary constraints.
Apparatus (Manometer)—Most desorption systems are de-
To measure residual gas, a crusher is required to pulverize the
signed to work with desorbed gas volume data collected at
coal core to release and measure the remaining gas. The
ambient temperature and atmospheric pressure, and
crusher should be capable of pulverizing the sample to 95 % of
consequently, a manometer is required to make zero-head-
the material passing a 212-µm mesh. Typical representative
pressure measurements. A zero-head measurement is facilitated
coal-mass-to-crusher volume ratios used range from 1:1 to 1:7.
using a sliding reservoir tank, a hand-held reservoir, or a
The ratio should be kept constant. The crusher should allow the
hand-held graduated cylinder (1, 4, 5, 12-16). The recom-
released gas to be bled off and volume measured either during
mended manometer design is based on nested polymethylpen-
or after crushing. See Guide AS 3980. Gas volumes can be
tene plastic graduated cylinders reportedly developed by River
measured using the volumetric displacement apparatus dis-
Gas Corporation (Fig. 2); design and its use are described in
cussed in 6.4.
Barker et al (13) and Barker and Dallegge (14). In this design,
zero-head measurements are made by manually lifting the
6.8 Gas-Sampling Apparatus—Gas-barrier plastics bags and
measuring graduated cylinder until the water levels in the in-line gas sampling tubes are suitable. In-line sampling tubes
reservoir and the measuring graduated cylinder are equal in
placed between the canister and the measuring apparatus
height and, therefore, at zero head. Multiple manometer eliminate the risk of composition change in the measured gas
volumes (50, 100, 250, 500, 1000 cm ) are required to measure
caused by solution in the measuring fluid. Another gas collec-
accurately decreasing gas volumes produced from the canisters tion method by gas displacement of water in glass bottles may
as the desorption process proceeds. also be used to collect desorbed gas directly from the manom-
eter hose. The sample size is determined by the method of gas
6.5 The plastic graduated cylinders used should conform to
analysis. (See Ref 1 and Guide AS 3980.)
at least Class B accuracy requirements set out in Specification
E1272 and ISO 6706. The volume measurement tolerance
6.9 Weighing Device—A scale with accuracy better than
needs to exceed the requirements of DIN 12681. The accuracy
1 % is required to weigh the canisters, coal-filled canisters, and
of graduated cylinders also increases as the volume capacity of
coal- and water-filled canisters.
the graduated cylinder decreases. To maintain adequate
6.10 Potential Problems Encountered—Major problems that
accuracy, it is recommended that the size of the inside
can lead to spurious gas content measurements are: (1) sample
graduated cylinder of the nested pair should be scaled to be
recovery too long; (2) canister leaks; (3) incorrect desorption
about two times the volume of each measurement from the
temperature; (4) excessive pressure buildup in canister; (5)
desorption canister.
reaction of canister materials with coal, gas, or fluids; and (6)
6.6 Materials and Construction of Canister Water Bath—
biogenesis in the canister.
The desorption canisters should be maintained at a constant
6.10.1 Sample Recovery Time—It is critical to minimize the
temperature (either reservoir or drilling mud temperature) for
time required for sample collection, retrieval, and placement
the duration of the desorption process. Mavor et al (Ref 17)
into the canister. If too much time elapses between coal
have shown that estimates of lost gas using desorption mea-
sampling and placing the sample in the canister, much of the
surements made at ambient surface temperatures may be
gas may be lost and an accurate lost gas estimate will not be
significantly less than estimates obtained from canisters main-
possible. To mitigate this problem, try to use a fast core-
tained at higher reservoir temperatures. A constant temperature
retrieval system such as the wireline method. Make all prepa-
can be achieved by submerging the filled canisters into a water
rations for sampling well in advance of the core reaching the
bath heated by submersible electric water heaters or coolers if
surface to minimize the time required to get the samples into
the ambient temperature is higher than the desired desorption
the canister and sealed. For best results, follow the coal-
temperature. Large storage tanks can be purchased from local
sampling techniques described by Luppens e
...

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.
´1
Designation: D7569/D7569M − 10 (Reapproved 2015) D7569/D7569M − 10 (Reapproved
2023)
Standard Practice for
Determination of Gas Content of Coal—Direct Desorption
Method
This standard is issued under the fixed designation D7569/D7569M; 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.
ε NOTE—Designation was corrected editorially in February 2015.
1. Scope
1.1 This practice describes methods for the direct determination of the gas content of coal by desorption using samples obtained
by drill coring methods from the surface. It sets out guidelines for the equipment construction, sample preparation and testing
procedure, and method of calculation.
1.2 Indirect methods for the determination of the gas content of coal (not covered in this practice) are based on either the gas
absorption characteristics of coal under a given pressure and temperature condition or other empirical data that relate the gas
content of coal to such other parameters as coal rank, depth of cover, or gas emission rate.
1.3 This practice covers the following two direct methods, which vary only in the time allowed for the gas to desorb from the core,
or sidewall core, before final crushing:
1.3.1 The slow desorption method in which volumetric readings of gas content are taken frequently (for example, every 10 to 15
min) 10 min to 15 min) during the first few hours, followed by hourly measurements for several hours, and then measurements
on 24-h intervals until no or very little gas is being desorbed for an extended period of time.
1.3.2 The fast desorption method in which after initial desorbed gas measurements to obtain data for lost gas calculations are
taken, the canister is opened and the sample is transferred to the coal crusher. The remaining gas volume is measured on a crushed
sample.
1.4 This practice is confined to the direct method using core, or sidewall core obtained from drilling. The practice can be applied
to drill cuttings samples; however, the use of cuttings is not recommended because the results may be misleading and are difficult
to compare to the results obtained from core desorption. The interpretation of the results does not fall within the scope of the
practice.
1.5 Units—The values stated in either SI units or inch-pound units are to be regarded separately as the standard. The values stated
in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values
from the two systems may result in nonconformance with the standard.
This practice 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 Feb. 1, 2015Dec. 1, 2023. Published February 2015December 2023. Originally approved in 2010. Last previous edition approved in 2015 as
ɛ1
D7569D7569 – 10 (2015) –10. DOI: 10.1520/D7569_D7569-10R15E01. DOI: 10.1520/D7569_D7569-10R23.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7569/D7569M − 10 (2023)
1.6 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 and healthsafety, health, and environmental practices and determine
the applicability of regulatory limitations prior to use.
1.7 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
D167 Test Method for Apparent and True Specific Gravity and Porosity of Lump Coke
D1412 Test Method for Equilibrium Moisture of Coal at 96 to 97 Percent Relative Humidity and 30 °C
D2799 Test Method for Microscopical Determination of the Maceral Composition of Coal
D3172 Practice for Proximate Analysis of Coal and Coke
D3173 Test Method for Moisture in the Analysis Sample of Coal and Coke
D3174 Test Method for Ash in the Analysis Sample of Coal and Coke from Coal
D3176 Practice for Ultimate Analysis of Coal and Coke
D3180 Practice for Calculating Coal and Coke Analyses from As-Determined to Different Bases
D3302 Test Method for Total Moisture in Coal
D5192 Practice for Collection of Coal Samples from Core
E1272 Specification for Laboratory Glass Graduated Cylinders
2.2 Australian Standard:
AS 3980 Guide to the determination of gas content of coal—Direct desorption method
2.3 ISO Standard:
ISO 6706 Plastics laboratory ware—Graduated measuring cylinders
2.4 DIN Standard:
DIN 12681 Plastics laboratory ware—Graduated measuring cylinders
3. Terminology
3.1 Definitions:
3.1.1 For additional definitions of terms used in this practice, refer to Terminology D121.
3.1.2 absolute permeability, n—permeability of a rock to a particular fluid when the rock is 100 % saturated with the flowing fluid.
(1)
3.1.3 absorbed gas, n—gas that is molecularly dissolved within a liquid phase or has penetrated into the lattice structure of a solid.
(1)
3.1.4 actual lost gas time, n—lost gas time determined from the time at which the sample being recovered reaches a depth where
the hydrostatic pressure of the drilling fluid column equals the original (immediately before sampling) reservoir pressure in the
sample to the time at which the sample is sealed in a desorption canister.
3.1.4.1 Discussion—
Essentially, the actual lost gas time is the amount of time between when the core starts its trip to the surface and when it is sealed
in the canister. (1)
3.1.5 adsorption, n—attachment, through physical or chemical bonding, of fluid phase molecules to an interfacial surface.
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.
Available from Standards Australia Limited, 286 Sussex St., Sydney, NSW, 2000, Australia, GPO Box 476, Sydney, NSW, 2001 Australia or via the website:
www.standards.org.au.
Available from the International Organization for Standardization (ISO), 1, rue de Varembé, Case Postale 56, CH-1211 Geneva 20, Switzerland or via the website:
http://www.iso.org/.
Available from Deutsches Institut für Normung e. V., 10772 Berlin or via the website: http://www2.din.de.
The boldface numbers in parentheses refer to the list of references at the end of this standard.
D7569/D7569M − 10 (2023)
3.1.5.1 Discussion—
The adsorbed phase molecules are sequestered at the interfacial surface in a metastable equilibrium state, the stability of which
is strongly affected by changes in temperature and pressure. (1)
3.1.6 adsorption isotherm, n—quantitative relationship, at constant temperature, describing how the concentration of adsorbed
phase molecules at an interfacial surface varies as a function of increasing system pressure. (1)
3.1.7 as-received basis, n—analytical data calculated to the moisture condition of the sample as it arrived at the laboratory and
before any processing or conditioning.
3.1.7.1 Discussion—
If the sample has been maintained in a sealed state so that there has been no gain or loss, the as-received basis is equivalent to
the moisture basis as sampled. (D3180, D5192, D1412, D3302)
3.1.8 canister, n—container that can be sealed into which a coal sample is placed to allow desorption to occur.
3.1.8.1 Discussion—
The reduction in pressure to atmospheric pressure (at surface) causes the sample to release gas into the canister. By measuring the
amount of gas released and the weight of the sample, the gas content can be determined. Gas content is conventionally reported
3 3
in units of cubic centimetres/gram (cm /g), cubic metres/tonne (m /ton), or standard cubic feet/ton (scf/ton). (1)
3.1.9 continuous coring, v—refers to continuous coring with wireline recovery. (1)
3.1.10 conventional core, n—“large” diameter core (8.9 cm [3.5 in.] diameter or larger) in which the core barrel is recovered to
the surface after drilling a fixed interval by pulling the drill string. (1)
3.1.11 core, n—in drilling, a cylindrical section of rock (coal) that is usually 5 to 10 cm 5 cm to 10 cm in diameter taken as part
of the interval penetrated by a core bit and brought to the surface for geologic examination, representative sampling, and laboratory
analyses. (D121, D5192)
3.1.12 cuttings, n—in drilling, rock fragments that break away because of the action of the drill bit and are transported to the
surface by the drilling circulation system (mud or air).
3.1.12.1 Discussion—
Cuttings may be screened and collected from the circulation medium for lithologic characterization or analytical tests. (2)
3.1.13 delivery tube, n—flexible tube connecting a desorption canister to a volumetric displacement apparatus. (1)
3.1.14 desorption, n—detachment of adsorbed molecules from an interfacial surface (see adsorption). (1)
3.1.15 desorption data analysis software, n—software used for analyzing desorption data. (1)
3.1.16 desorption rate, n—volumetric rate at which gas desorbs from a sample. (1)
3.1.17 diffusion, n—process whereby particles of liquids or gases move from a region of higher to lower concentration independent
of the pressure gradient. (1)
3.1.18 diffusivity, n—ratio of the diffusion coefficient to the square of a typical diffusion distance. (1)
3.1.19 direct desorption method, n—method for representing desorption of gas from coal or other materials in which gas storage
as a result of adsorption is significant.
3.1.19.1 Discussion—
It mathematically presumes constant temperature diffusion from a sphere initially at uniform gas concentration. The solution of
the basic equation adopted suggests that the measured desorbed gas volume is proportional to the square root of time since the start
of desorption (time zero). The direct method is the most widely used method for estimating lost gas volume. (1)
3.1.20 dry, ash-free basis, n—data calculated to a theoretical base of no moisture or ash associated with the sample.
D7569/D7569M − 10 (2023)
3.1.20.1 Discussion—
Numerical values as established by Test Methods D3173 and D3174 are used for converting the as-determined data to a moisture-
and ash-free basis. (D3180)
3.1.21 fast desorption method, n—after initial measurements to obtain the basis for lost gas calculations, the canister is opened
and the sample is transferred to a coal-crushing device that is modified so that the remaining desorbed gas volume from the crushed
coal sample can be measured.
(AS 3980)
3.1.22 free gas, n—unabsorbed gas within the pores and natural fractures. (1)
3.1.23 gas-in-place, n—amount of gas present in a seam or an interval of discrete thickness or in multiple seams or intervals
determined from the gas content, bulk density, thickness, and drainage area.
3.1.23.1 Discussion—
Estimates of gas-in-place usually reflect total gas content, which in addition to methane, may include other gases such as carbon
dioxide or nitrogen. (1)
3.1.24 gas saturated, adv—state in which the gas content (determined from direct or indirect desorption measurements) is equal
to the gas storage capacity (determined from isotherms). (1)
3.1.25 gas storage capacity, n—maximum amount of gas or gas mixtures (normalized according to the relevant basis) that can be
held by a sample at various reservoir pressures, reservoir temperature, and a specific moisture (water) content. (1)
3.1.26 head space volume, n—void space in a canister containing a sample.
3.1.26.1 Discussion—
Canister desorption measurements are corrected for the effect of expansion or contraction of gases in the canister head space in
response to temperature and pressure fluctuations. (1)
3.1.27 indirect method for the determination of the gas content of coal, n—method based on either the gas absorption
characteristics of coal under a given pressure and temperature condition or other empirical data that relate the gas content of coal
to such other parameters as coal rank, depth of cover, or gas emission rate.
3.1.28 in-situ basis, adj—a basis in which gas content is determined from a plot of gas content versus bulk density (determined
from open-hole high-resolution bulk density log data). (1)
3.1.29 isotherm (sorption isotherm), n—quantitative relationship, at constant temperature, that describes how the concentration of
adsorbed phase molecules at an interfacial surface varies as a function of system pressure. (1)
3.1.30 lost gas time, n—time between when the sample gas pressure falls below the reservoir pressure during sample recovery
(time zero) and the time when the sample is sealed in a desorption canister. (1)
3.1.31 lost gas volume, n—volume of gas that is released from a sample (generally under conditions of decreasing temperature
and pressure) before it can be placed in a canister and measured (between the time when the sample gas pressure falls below the
reservoir pressure during sample recovery and the time when the sample is sealed in a desorption canister). (1)
3.1.32 macropore, n—pores in the coal larger than 50 nm. (3)
3.1.33 manometer, n—see volumetric displacement apparatus.
3.1.34 measured gas volume, n—measured volume of gas that is released from a sample into a desorption canister, reported at
standard temperature and pressure conditions. (1)
3.1.35 mesopores, n—pores in the coal larger than 2 nm and less than 50 nm. (3)
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3.1.36 micropores, n—pores with a width of less than 2 nm. (3)
3.1.37 modified direct method, n—modification of the direct method by the U.S. Bureau of Mines according to Diamond and
Levine (4) and Diamond and Schatzel (5) to account precisely for changes in the concentration of gaseous species during
desorption, with particular applications to situations in which small amounts of gas are evolved. (1)
3.1.38 quick connect fittings, n—pipe fittings designed for easy and rapid connection and disconnection.
3.1.39 raw basis, n—basis for gas content calculation whereby the gas volume is divided by the actual sample weight regardless
of the moisture content or the presence of non-coal in the canister sample. (1)
3.1.40 residual gas volume, n—volume of the total sorbed gas that remains in the sample after desorption into a canister has
effectively ceased (after termination of canister desorption).
3.1.40.1 Discussion—
Residual gas volume, as defined and reported, can be very different for slow desorption and fast desorption methods. Early
termination of desorption followed by sample crushing will obviously lower desorbed quantities of gas and increase the residual
values. Maceral composition, lithotype composition, and the coal bench being sampled may all affect permeability on small-scale
samples. (1)
3.1.41 sidewall core, n—small diameter core taken downhole by wireline methods using percussion or mechanical methods to drill
into the side of the borehole.
3.1.41.1 Discussion—
The percussion method cores by explosively firing hollow core barrels into a coal seam and then retrieving the coal plug to the
surface. The mechanical method uses hollow rotary drills to core into the coal seam, pull the core plugs back into the tool, and
then they are retrieved.
3.1.42 slow desorption method, n—volumetric readings of canister gas content are taken frequently (for example, every 10 to 15
min) 10 min to 15 min) during the first few hours, followed by hourly measurements for several hours, and then measurements
on 24-h intervals until no or very little gas is being desorbed for an extended period of time.
3.1.42.1 Discussion—
Some coals can desorb in excess of one year and a desorption base line may be established with measured gas volumes consistently
below 10 cm per reading. At this slow desorption rate, no gas is expected to be lost when transferring the sample from the
desorption canister to the residual gas canister.
3.1.42.2 Discussion—
If the measured gas volume of a canister falls at or below 10 cm per reading (where measurement error becomes too great), then
that canister may be elevated to the next time measurement period. This procedure is continued until measured gas volumes are
consistently below 10 cm per reading. (AS 3980, (6))
3.1.43 sorbed gas, n—coalbed gas retained by adsorption or absorption processes or both. (1)
3.1.44 sorption time, n—time required for 63.2 % of the total sorbed gas (including residual gas) to be released.
3.1.44.1 Discussion—
It is reported in either hours or days (since time zero) depending on the relative rate at which gas is released from a desorption
sample. (1)
3.1.45 sorption standard temperature and pressure conditions (STP), n—various standards exist.
3.1.45.1 Discussion—
Historically, the petroleum industry almost universally has used Imperial units of 60°F [15.56°C or 288.6K]60 °F [15.56 °C or
288.6 K] as the reference temperature and 14.7 psia [101.3 kPa] as the reference pressure. See Ref 7. SI systems have used 0, 20,
and 25°C [32, 68, and 77°F]0 °C, 20 °C, and 25 °C [32 °F, 68 °F, and 77 °F] most commonly, depending on the data and the area
of specialty. The American Petroleum Institute (API, see Ref 8) has opted for 15°C [59°F]15 °C [59 °F] because it is close to 60°F
[15.56°C].60 °F [15.56 °C]. The Society of Petroleum Engineers (Refs 9 and 10) suggests that the choice between 0 and 15°C [32
and 59°F]0 °C and 15 °C [32 °F and 59 °F] is arbitrary. Government gas reserve reporting regulations may mandate which system
to use, Imperial or SI (metric) (Ref 10). For coal gas desorption purposes, a standard of 15°C15 °C has been adopted simply to
conform to API standards. It may be desirable to have a flexible temperature standard for various applications. (1)
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3.1.46 time zero, n—time at which a sample falls below the reservoir or desorption pressure during sample recovery.
3.1.46.1 Discussion—
Time zero is generally marked when the sample lifts off the bottom of the hole. However, more study of the sample retrieval
process is required to determine better the depth that the sample desorption process actually begins. (1)
3.1.47 total gas volume, n—sum of lost gas, measured gas, and residual gas volumes (all measured on the same sample volume).
(1)
3.1.48 U.S. Bureau of Mines (USBM) lost gas time, n—lost gas time determined from time zero, where time zero is defined as the
time when the sample reaches a depth halfway to the surface. (1)
3.1.49 volumetric displacement apparatus (manometer), n—device, maintained at ambient conditions, for measuring the amount
of gas desorbed into a canister. (1)
4. Summary of Practice
4.1 This practice describes standardized guidelines for the determination of the gas content of coal by desorption using samples
obtained by drill coring methods.
4.2 Immediately after the coal core sample reaches the surface and after the depth of the sample, state of the core, and proportion
of coal to non-coal material are recorded, the sample is transferred into a canister and the canister is sealed. Multiple samples from
a coal bed should be collected to obtain a gas content representative of the whole coal bed.
4.3 Desorbed gas content (in cubic centimetres) can be measured using a volume displacement apparatus by the slow or fast
desorption method, or a combination of the two methods, depending primarily upon the urgency of having gas content data. In the
slow desorption method, gas measurements are continued until measured gas volumes are consistently below 10 cm per reading,
which for some coals may take more than a year’s time to desorb to this level. In the fast desorption method, when sufficient
measurements are made to obtain data for lost gas calculations (usually more than 4 h of frequent measurements), the canister is
opened and the sample is transferred to the coal crusher. The remaining gas volume is measured on a crushed sample. For gas
composition or gas isotope analyses or both, the gas is sampled during desorption.
4.4 All data are entered and maintained on predesigned data forms and spreadsheets. Lost gas, desorbed gas, and residual gas
contents are added to obtain total gas content that, after recalculation on sample weigh basis, yields total gas content expressed
3 3
in cm /g, m /ton (SI units) [scf/ton (Imperial units)].
5. Significance and Use
5.1 Canister desorption is a widely used technique to measure the gas content of coal. The gas content data when normalized to
volume/weight and multiplied by coal mass is used to estimate the gas in place in an area around the cored well.
6. Apparatus
6.1 Background—In desorption studies of methane content in coal beds, the goal is to capture quickly the coal sample in a
pressure-tight container purged of the air-bearing headspace gas using an inert gas or water to stabilize the sample. Towards this
goal, a container (canister) shall be designed and constructed/fabricated for core that would be easy to handle, fill, and close rapidly
forming a reliably gastight seal, and facilitate rapid desorbing gas measurements. The primary coal core desorption equipment
consists of desorption canisters made of sealed aluminum or plastic and a volumetric displacement apparatus or manometer; these
items can be purchased from suppliers that use custom designs (1, 11) (Fig. 1) or locally constructed with off-the-shelf materials
and parts (12-14) (Fig. 2).
6.2 Materials and Construction of Desorption Canisters—Canister materials in widespread use today are aluminum, plastic-coated
aluminum, and plastic, usually polyvinyl chloride (PVC) materials. The use of stainless steel, although advantageous because of
its inert qualities, is not in widespread use because of the high cost of materials and labor. The use of canisters made of unsealed
aluminum is not recommended in this practice because of the potential for significant reaction with coal gases and related
formation or drilling fluids after the canister is closed. In general, all components of the desorption canister should be made of
D7569/D7569M − 10 (2023)
FIG. 1 Progressive Development of Canister and Volumetric Displacement Apparatus Design
(Courtesy of Gas Technology Institute [see Refs 1, 4, and 10])
D7569/D7569M − 10 (2023)
FIG. 2 Custom-Made (A) Volumetric Displacement Apparatus and (B) Canister Constructed from Off-the Shelf Materials
(see Refs 12 and 13)
material that is, or treated to be, nonreactive with regard to the coal or the normally low pH fluids associated with the coal and
hydrogen sulfide (H S) or other corrosive gases that may evolve during desorption. The canisters should be made leak-proof by
using a sealing device or cap such as a neoprene and plastic plug held in place by a wing nut or clamp, a threaded PVC plug sealed
by an O-ring, or a coated aluminum cap sealed with a neoprene gasket. One end of the canister should have a permanent cap glued
in place (Fig. 2). To prevent leaks, the removable cap area shall be cleaned of coal particles after the coal sample is placed in the
canister and before the canister is closed. The use of PVC for gas desorption canisters was first done in the 1980s by the USBM
(5, 15).
D7569/D7569M − 10 (2023)
6.3 Equipment for Making Measurements—During desorption, the closed canister is periodically connected via a hose and
quick-connect system to a volumetric displacement apparatus (manometer) to measure the desorbed volume of gas. At the time
of measurement, the barometric pressure (P) and ambient temperature (T) in the volumetric displacement apparatus are recorded.
National Institute of Standards and Technology (NIST) traceable calibrated digital barometers and thermometers are recommended
for these P and T measurements. If the canister headspace is not filled with water to make its volume zero, then it is necessary
to measure headspace gas temperature to correct for expansion or contraction of the headspace gas. This is called the headspace
correction. The data-entry forms and calculations for making this correction are discussed in Refs 1,13, and 14.
6.4 Materials and Construction of Volumetric Displacement Apparatus (Manometer)—Most desorption systems are designed to
work with desorbed gas volume data collected at ambient temperature and atmospheric pressure, and consequently, a manometer
is required to make zero-head-pressure measurements. A zero-head measurement is facilitated using a sliding reservoir tank, a
hand-held reservoir, or a hand-held graduated cylinder (1, 4, 5, 12-16). The recommended manometer design is based on nested
polymethylpentene plastic graduated cylinders reportedly developed by River Gas Corporation (Fig. 2); design and its use are
described in Barker et al (13) and Barker and Dallegge (14). In this design, zero-head measurements are made by manually lifting
the measuring graduated cylinder until the water levels in the reservoir and the measuring graduated cylinder are equal in height
and, therefore, at zero head. Multiple manometer volumes (50, 100, 250, 500, 1000 cm ) are required to measure accurately
decreasing gas volumes produced from the canisters as the desorption process proceeds.
6.5 The plastic graduated cylinders used should conform to at least Class B accuracy requirements set out in Specification E1272
and ISO 6706. The volume measurement tolerance needs to exceed the requirements of DIN 12681. The accuracy of graduated
cylinders also increases as the volume capacity of the graduated cylinder decreases. To maintain adequate accuracy, it is
recommended that the size of the inside graduated cylinder of the nested pair should be scaled to be about two times the volume
of each measurement from the desorption canister.
6.6 Materials and Construction of Canister Water Bath—The desorption canisters should be maintained at a constant temperature
(either reservoir or drilling mud temperature) for the duration of the desorption process. Mavor et al (Ref 17) have shown that
estimates of lost gas using desorption measurements made at ambient surface temperatures may be significantly less than estimates
obtained from canisters maintained at higher reservoir temperatures. A constant temperature can be achieved by submerging the
filled canisters into a water bath heated by submersible electric water heaters or coolers if the ambient temperature is higher than
the desired desorption temperature. Large storage tanks can be purchased from local hardware stores and are adequate for
low-temperature desorption jobs; however, heat-resistant tanks are required for higher desorption temperatures. Check the heat
tolerance of the tanks before use. Submersible electric water heaters and coolers are available from most scientific supply dealers.
“Dry” heaters for individual canisters can also be used to maintain a constant canister desorption temperature.
6.7 Materials and Construction of Residual Gas Measurement Equipment—Residual gas content of the coal can be estimated at
any time during the desorption process after the initial measurements have been made to obtain the basis for lost gas calculations.
Following the slow desorption method, residual gas is measured after the samples have completely desorbed. The fast desorption
method allows the samples to be removed from the canisters for residual gas determination soon after the measurements for lost
gas calculations are completed. It is recommended that the samples be allowed to desorb as long as practical considering time and
budgetary constraints. To measure residual gas, a crusher is required to pulverize the coal core to release and measure the remaining
gas. The crusher should be capable of pulverizing the sample to 95 % of the material passing a 212-μm mesh. Typical
representative coal-mass-to-crusher volume ratios used range from 1:1 to 1:7. The ratio should be kept constant. The crusher should
allow the released gas to be bled off and volume measured either during or after crushing. See Guide AS 3980. Gas volumes can
be measured using the volumetric displacement apparatus discussed in 6.4.
6.8 Gas-Sampling Apparatus—Gas-barrier plastics bags and in-line gas sampling tubes are suitable. In-line sampling tubes placed
between the canister and the measuring apparatus eliminate the risk of composition change in the measured gas caused by solution
in the measuring fluid. Another gas collection method by gas displacement of water in glass bottles may also be used to collect
desorbed gas directly from the manometer hose. The sample size is determined by the method of gas analysis. (See Ref 1 and Guide
AS 3980.)
6.9 Weighing Device—A scale with accuracy better than 1 % is required to weigh the canisters, coal-filled canisters, and coal- and
water-filled canisters.
6.10 Potential Problems Encountered—Major problems that can lead to spurious gas content measurements are: (1) sample
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