Note: Descriptions are shown in the official language in which they were submitted.
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1 CASE 4525
"MONITOR~NG COAL EXTRACTION"
This invention concerns the monitoring of coal extraction, and
more particularly concerns the monitoring of the condition of
hydrogen donor solvents used in coal extraction.
In the liquid solvent extraction of coal, including bituminous
coals and lignites, we have found that the highest yields of
extracted coal substance are obtained using hydrogen donor
solvents. Such a solvent is a high boiling partially hydrogenated
aromatic oil which transfers hydrogen from itself to hydrocarbon
radicals formed by thermal cleavage of molecules of coal substance,
ehus stabilising the resulting moieties against recombination or
polymerisation. The solvent itself becomes more aromatic in
character, and less effective as a solvent, during the extraction
process, and requires re-activation or replenishment by
hydrogenation. However, it has proved difficult to monitor the
amount of donatable hydrogen ln process solvents in continuous coal
extraction plants, not least because such process solvents are not
single compounds but are complex mixtures of a large number of
compounds. Methods of characterisation of process solven~6 which
have been proposed, such as adsorption chromatography, ~MR
spectro copy, gas chromatography and mass spectrometry are not only
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very time consuming, thus making them unsuitable for proce6s
control, but can be m~sleading or open to alternative
interpretation. It i~ therefore an aim of the present
invention to provide a method of monitoring the conditlon of
hydrogen donor solvents ~hich is sufficiently quick to be relevant
in process control and also is applicable to the extraction of
lignites as well as bituminous coals.
The pre~ent invent~on provide~ a method of monito~ing the
condition of a hydrogen donor solvent in a coal extraction process,
comprising sampling the solvent, diluting the solvent with a pre-
determined amount of an aromatic liquid diluent compatible with the~olvent, effecting a test extraction of the coal with the diluted
solvent under standard condltions, and determining the extraction
yield. The extraction yield i6 conveniently expressed in terms of
the total yield of liquid and gas on a dry minersl matter free
(DMMF) basis. The liquld yield may be readily determined using a
known method based on quinoline insolubility (e.g. "Fuel",
1978,57, 147) and the gas yield tetermined by collecting and
analysing the gas evolved during digestion.
Tests have shown that there is a sub6tantially linear
relationship between the yield a~ determined in the method of the
invention and the sctual amount of donor hydrogen present. It is
thus posslble and, we believe, useful, to perform a number of
cal~bration tests with the particular coal and solvent and to
create a "~olvent di6solving index for the assessment of process
~olvents. Accordingly, the method of the invent~on enables the
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amount of tonatable hydrogen, or the position of the solvent on a
"solvent dissolving index , to be monitored. The dilution of the
solveDt ln the test enables a prediction of a fall-off of
performance to be made and enabling counter measures to be taken
before a significant 1088 of yield is experienced with the
~ndiluted solvent. The method of the invention requlres only
relatively simple equipment of the bomb type and may be carried out
in a few hours under favourable conditions.
The invention also provides a method of controlling a liquid
solvent extraction of coal process comprising the monitoring of the
condition of a hydrogen donor solvent u~ed ~n the process accord~ng
to the $nvention, and applying corrective measures when necessary
to restore the conditlon of the solvent to a predetermined
acceptable range of donatable hydrogen content.
In lntegrated coal solvent extraction plants utili6ing liquid
hydrogen donor solvent, there has to be provision for the
regeneration of the process solvent, and mere recycle of a cut from
the straight product is not sufficient. The solvent cut may be
hydrogenated, or as is more likely, the appropriate cut may be
taken after the hydrogenation or hydrocracklng of all the liquid
product. It i6 posslble that a hydrogenated recycle solvent
contains more donatable hydrogen than is necessary to achieve
maximum yield; the method of the invention enables this condition
also to be monitored (unllke any straightforward test based on
extraction yield) and permits optimisation of the amount of
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hydrogenated product recycle.
The aromatic diluen~ u6ed in the present invention is
preferably a polynuclear ~romatic, which may be substituted by
alkyl groups, and may be a 6ingle compound or a ~tandard mixture of
compounds. The preferred diluent i8 naphthalene, although
compoundæ such as anthracene or phenanthrene and mi~tures thereof
may be used or any compound which i6 not reactive in the extraction
process .
The standard conditions for the test extraction need not
exactly replicate those of the main extraction process, but are
preferably 6imilar to the nominal conditions of the main extraction
process. The conditions of the main extraction process may be
difficult to reproduce in test apparatus or the main process may be
operated under non-constant conditions.
The invention will now be described by way of example only.
EXAMPLE
The coal being extracted on a continuous pilot plant was a
lignite crushed to 80% less than 75um and vacuum dried to a
moisture content less than 5~. A hydrogenated anthracene oil
solvent which had been rigorously characterised by NMR spectroscopy
was used, and calibration extrsctions with the solvent blended with
naphthalene in concentrations from 0 to 100% were carried out using
a 40% coal in ~olvent slurry. The test extractions were carried out
by loading accurately weighed amounts of coal, solvent and
naphthalene into a stirred bomb reactor, which was immersed in a
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fluldised sand bath of 4300. After 67 ml~utes, the reactor was
removed from the sand bath and water quenched. The gas evolved was
collected and its volume measured. The li~uld product was
thoroughly removed from the bomb, weighed and the qulnoline
insolubles measured by a stsndard method. The total yields were
determined and calculated on a DMMF basis.
The sample of hydrogenated anthracene oil had previously been
e6tabli~hed to have a donatable hydrogen concentration of 2.lX.
Even in the absence of donatable hydrogen, le using 100%
naphthalene a6 solvent, approximately 45% of the coal was
extracted. To achieve the maximum obtainable extraction yield of
95%, a minimum of 1.4% donatable hydrogen was requlred. A
calibration chart was prepared, giving a "solvent di~solving index"
value (SDI) of 0 to an extraction yield of 45%, equivalent to 0%
donatable hydrogen, and an SDI of 20 to an extraction yield of 9~%,
corresponding to 1.4X donatable hydrogen. Thls chart is reproduced
in the accompanying Figure.
For the assessment of process solvents, the solvent~as diluted
with it6 own weight of naphthalene. Hence, the SDI for the
hydrogenated anthracene oll was 15, and solvent6 having higher as
well as lo~er concentrations of donatable hydrogen find a place on
the SDI scale. The ~cale accurately predicted that process
fiolvents having an SDI of 10 or above were capable of obtalning
excellent extraction yields of the lignite, and solvents having an
SDI below 10 showed dlminlshlng ylelds.
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The sensitivity of the SDI test is dependent upon the
precislon of mea6urement of the yield of quinolineinsolubles, but
dupllcatlon could be expected to give values of quinoline
lnsolubles within +1%. For a high mlneral matter lignite, this ~s
equivalent to + 3% on the measurement of extraction yield and +1.5
on the SDI value.
The above Example was repeated using, instead of lignite, a
British high volatile bituminous coal. A different SDI calibration
i6 u6ed, but accurate predictions were achleved of the extraction
capability of test solvents.
