Note: Descriptions are shown in the official language in which they were submitted.
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WO 99/10079 PCT/AU98/00689
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A METHOD AND AN APPARATUS FOR UPGRADING A SOLID MATERIAL
The present invention relates to upgrading a
solid material.
The present invention relates particularly,
although by no means exclusively, to upgrading a solid
material which has low thermal conductivity.
The present invention relates more particularly
to upgrading a solid material by removing water from the
material in a process that includes:
(i) heating the material to an elevated
temperature while the material is being
maintained under high pressures and
thereafter
(ii) cooling the upgraded material to as ambient
temperature.
One particular application of the present
invention is to upgrade carbonaceous material, typically
coal, to increase the BTQ value of the carbonaceous
material.
US patent 5,290,523 to Roppelman discloses a
process for upgrading coal by the simultaneous application
of temperature and pressure.
Koppelman discloses thermal dewatering of coal by
heating coal under conditions including elevated
temperature and pressure to cause physical changes in the
coal that results in water being removed from the coal by a
"sQueeze" reaction.
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8oppelman also discloses maintaining the pressure
sufficiently high during the upgrading process so that the
by-product Water is produced mainly as a liquid rather than
as steam.
Roppelmsn also discloses a range of different
apparatus options for carrying out the upgrading process.
In general terms, the options are based oa
14 heating coal in a pressure vessel which includes an
inverted conical inlet, a cylindrical body, a conical
outlet, and an assembly of vertically or horizontally
disposed heat exchange tubes positioned is the body.
In one proposal the vertically disposed tubes and
the outlet end are packed with coal, and nitrogen is
injected to pre-pressurise the tubes and the outlet end.
The coal is heated by indirect heat exchange with oil that
is supplied as a heat transfer fluid to the cylindrical
body externally of the tubes. Further heating is promoted
by direct heat exchange between the coal and steam that
acts as a working fluid within the packed bed. In
addition, the steam pressurises the tubes and the outlet
end to a required pressure.
The combination of elevated pressure and
temperature conditions is the tubes and the outlet end
evaporates some of the water from the coal and thereafter
condenses some of the water as a liquid. A portion of the
steam generated following the addition of water also
condenses as a liquid in colder regions of the tubes due to
the elevated pressure. Steam Which is not condensed and
which is in excess of the requirements for optimum
pressurisation of the packed bed, must be vented. =n
addition, non-condensable gases teg CO, COs) are evolved
and need to be vested. Periodically, liquid is drained
from the outlet end.
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Finally, after a prescribed residence time, the
vessel is depressurised and the hot upgraded coal is
discharged via the outlet end onto a conveyor which
transports the coal to a wet auger. Water is sprayed onto
the hot upgraded coal as the conveyor transports the coal
to the auger. The coal is cooled further in the auger sad
thereafter is spread out in a thin layer in a stockpile
region and allowed to cool to ambient temperature.
An object of the present invention is to provide
an improved method and apparatus for upgrading coal
compared to that described by Roppelman.
According to a first aspect of the present
invention there is provided a method of upgrading a solid
material which comprises heating the solid material to an
elevated temperature to remove water and thereafter cooling
the upgraded solid material, and Which method is
characterised by:
(i) providing a plurality of vessels
containing packed beds of the solid
material and one or more than one heat
exchange circuit for heating sad cooling
the solid material is the packed beds is
the vessels by heat exchange with a heat
transfer fluid; sad
(ii) controlling the method so that the solid
material fn a first group of the vessels
is at one or more stages of a heating
cycle and the solid material in a second
group of vessels is at one or more stages
of a cooling cycle, sad the controlling
steps) coa~rises selectively connecting
the one or more than one heat exchange
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circuit to the vessels so that the heat
transfer recovers heat from the solid
material undergoing the cooling cycle in
at least one of the vessels in the first
group and transfers the recovered heat to
the solid material undergoing the heating
cycle in at least one of the vessels in
the second group.
The basis of the above-described aspect of the
present invention is recovery of energy from the solid
material being cooled in one group of vessels and
subsequent use of that energy to heat the solid material in
another group of vessels.
In one embodiment of the present invention a
plurality of heat exchange circuits are provided and the
heat exchange circuits selectively connect pairs of the
vessels so that the heat transfer fluid of each heat
20 exchange circuit cools the solid material in one vessel in
each pair and thereafter heats the solid material in the
other vessel in each pair by heat exchange with the solid
material in the pair of vessels.
25 The heat transfer fluid in each heat exchange
circuit heats and cools the solid material in the pairs of
vessels to respective different temperatures is the heating
and cooling cycles, With the result that the solid material
in each vessel is heated or cooled by a series of steps by
sequentially connecting the heat exchange circuits to the
vessel.
hor example, one heat exchange circuit heats
solid material in one vessel from an ambient temperature to
a tea~erature Tl and another heat exchange circuit that is
subsequently connected to that vessel heats the solid
material from the temperature Tl to a higher temperature
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Tz. At the same time, the heat exchange circuits cool the
solid material is another vessel from the maximum
temperature of the heating cycle to a lower temperature.
It is preferred that the contests of the vessel
be at an elevated pressure during the heating and cooling
cycles.
Solid material may be retained is one vessel
during both the heating cycle and the cooling cycle.
Alternatively, solid material may be heated is
one vessel during the heating cycle, transferred hot to
another vessel, sad cooled in accordance with the cooling
cycle is the other vessel.
It is preferred that the heat exchange circuits
heat sad cool the solid material by indirect heat exchange.
The method of the present invention has great
flexibility in terms of the heating and cooling cycles that
can be applied to the solid material while obtaining the
benefit of using heat recovered from the solid material
that is undergoing the cooling cycle to heat the solid
material that is undergoing the heating cycle.
By way of example, the method can be used to
upgrade a solid carbonaceous material, such as coal, by the
combined application of pressure and temperature Which
removes water from the coal in two stages, with:
(i) water being "squeezed" from the coal and
drained as a liquid phase to a lower
section of the vessel in a first, "wet",
stages and
(ii) a substantial part of the remaining water
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in the coal being removed as a vapour phase
in a second, "dry", stage.
The heat transfer fluid may be any suitable fluid
for transferring energy by indirect heat exchange.
By way of example, the heat transfer fluid may be
a fluid, such as oil. that is a single phase in the
operating tea~erature range of the heating and cooling
cycles.
By way of further example, the heat transfer
fluid may be a fluid, such as water, that is in liquid and
gaseous phases is the operating temperature raage of the
heating and cooling cycles and at suitable pressures.
The method may comprise one or more additional
heating stages to complete the heating cycle.
The method may comprise one or more additional
cooling stages to complete the cooling cycle.
The additional heating stages) may be provided
by any suitable means, such as by oxidative heating in the
vessels by supplying as oxygen-containing gas to the
vessels.
The additional cooling stages) may be provided
by any suitable meaas, such as by direct contact of coal
with dry or wet air in the same or other vessel.
~t is preferred that the method further comprises
supplying a working fluid to the vessels to heat and: cool
the solid material by direct heat exchaage With the solid
material and to contribute to pressurising the contents of
the vessels.
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According to the first aspect of the present
invention there is provided an apparatus for upgrading a
solid material which comprises:
(a) a plurality of vessels for containing
packed beds of the solid material under
conditions of elevated tea4yerature and
pressure;
(b) one or more heat exchange circuits far
heating and cooling the solid material is
the packed beds by heat exchange with a
heat transfer fluid;
(c) means for connecting the or each.heat
exchange circuit to the vessels so that is
use the solid material in one group of the
vessels is being heated in accordance With
a predetermined heating cycle by the heat
transfer fluid and the solid material in
another group of the vessels is being
cooled by the heat transfer fluid is
accordance with a predetermined cooling
cycle whereby in use the or each heat
exchange circuit is connected to the
vessels so that each heat exchange circuit
removes heat from the solid material in at
least one vessel and transfers the
recovered heat to the solid material in at
least one other vessel; and
(d) means for selectively changing the
connections between the heat exchange
circuits and the vessels to heat and cool
the solid material in the vessels in
accordance with the heating and cooling
cycles.
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The heat exchange circuit may be of any suitable
conf iguratioa.
=t is preferred that the heat exchange circuit
comprises:
(i) heat exchange assemblies located in the
vessels; and
(ii) means for circulating heat transfer fluid
through the heat exchange assemblies of the
vessels and between the heat exchange
assemblies of the vessels.
It is preferred particularly that the heat
exchange assembly of each vessel comprises:
(i) an assembly of heat exchange plates having
oae or more passageways for heat transfer
fluid positioned in the vessel;
(ii) an inlet for supplying the heat transfer
fluid to the passageway(s); and
(iii) an outlet for discharging the heat transfer
fluid from the passageways(s).
It is preferred that the plates have minimal
thermal mass.
It is preferred that the means for selectively
changiag the coanectioas between the heat exchange circuit
and the vessels includes a suitable control means.
According to a secoad aspect of the preseat
invention there is provided a method of upgrading a solid
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material which comprises:
(i) charging the solid material into a vessel
and forming a packed bad of the solid
material in the vessel;
(ii) heating sad pressurising the solid material
to remove water from the solid material, the
heating step comprising heating the solid
material by indirect heat exchange with a
heat transfer fluid;
(iii)cooling the solid material at the elevated
pressure; and
(iv) discharging the cooled upgraded solid
material.
The basis of the above-described second aspect of
the present invention is a multi-function vessel which
receives a charge of the solid material and thereafter
retains the solid material in a packed bed through the
heating and cooling cycles.
One considerable advantage of the above-described
method and apparatus of the present invention is that the
use of multi-function vessels minimises materials handling
of hot solid material compared to that required by
lcoppe loran .
Another advantage is that the mufti-function
vessel minimises the cycle time associated with emptying,
filling, pressure-up and pressure-down, compared to that
required by Roppelman.
It is preferred that the heating step further
comprises heating the solid material by direct heat
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exchange with a working fluid.
The energy recovery first aspect of the present
invention may be carried out With or without using the
multi-function vessel of the second aspect of the present
invention.
Similarly, the multi-function vessel of the
second aspect of the present invention may be used with or
without the energy recovery first aspect of the present
invention.
In one embodiment of the first aspect of the
present invention, 5 vessels A, 8, C, D, E contain packed
beds of coal at elevated pressure and are at different
stages of heating and cooling cycles of a method to upgrade
the coal by removing water from the coal. The heating
cycle of the method comprises:
(i) transferring heat to the coal sad allowing
water in the coal to be removed as a liquid
phase is a first "wet" stage of the method;
sad
(ii) transferring heat to the coal to boil at
least a part of the remaining water in the
coal as a vapour phase in a second "dry"
stage of the method and thereafter heating
the coal to a final product temperature.
The coal in each packed bed is heated and
thereafter cooled by indirect heat exchange with heat
transfer fluids that are pumped through heat exchange
circuits that are sequentially connected to pairs of the
vessels. The heat exchange circuit for each pair of
vessels includes as assembly of heat exchange plates having
one or more passageways for heat transfer fluid in each
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vessel and a means for circulating the heat transfer fluid
through the heat exchange assemblies in the pair of
vessels. This arrangement of a pair of vessels and heat
exchange circuit is shown in Figure 1. In the figure the
vessel 3a contains a packed bed of coal that is in a
heating cycle and the vessel 3b contains a packed bed of
coal that is in a cooling cycle. The heat exchange plates
in the vessels are identified by the numeral 5. The heat
transfer circulation means includes the lines and pump
which are identified by the numerals 7, 9.
The vessels and the heat exchange circuits may be
any suitable type of pressure vessel, such as described in
U.S. Patent No. 6,249,989 issued June 26, 2001 FOR "Method
and Apparatus for Heat Transfer", U.S. Patent No. 6,266,894
issued July 31, 2011 entitled "Liquid/Gas/Solid Separation"
and U.S. Patent No. 6,185,841 issued February 13, 2001
entitled "Enhanced Heat Transfer".
The heating and cooling of the coal in the
vessels is further promoted by supplying a working fluid to
the packed beds in the vessels. The working fluid:
(i) heats and cools the coal by direct heat
exchange between the coal and the working
fluid and between the working fluid and the
heat transfer fluid in the heat exchange
circuits; and
(ii) contributes to pressurising the contents of
the vessels.
Working fluid circulation circuits are identified
by the numeral 11 in Figure 1.
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The connections of the heat exchange circuits to
the vessels are selected so that the heat transfer fluid
recovers heat from one vessel that contains coal undergoing
the cooling cycle and thereafter transfers heat to another
vessel that contains coal undergoing the heating cycle.
One exaa~le of a sequence of connections of a
single heat exchange circuit to pairs of the vessels A, B,
C, D, E is illustrated is Figure 2. This is an example of
20 a single stage energy recovery cycle.
Figure 2 illustrates that, while vessel A
contains a packed bed of coal at the final required product
temperature of 371°C and vessel D contains a packed bed of
coal at an ambient temperature of 25°C, the connection of a
heat exchange circuit to vessels A and D results in:
(i) cooling the coal in vessel A from 371°C to
230°C~ and
(ii) heating the coal in vessel D from 25°C to
185°C by virtue of indirect heat exchange
with the recovered heat from vessel A.
The above-described heat transfer connection of
the packed beds of vessels A and H results in the beds
approaching a common approach temperature - Which is
determined by relative heat capacity and any heat losses.
Figure 2 also illustrates that subsequently
providing additional cooling arid heating to vessels A and
D, respectively results in:
(i) further cooling of the coal in vessel A from
230° to the ambient temperature: and
(ii) further heating of the coal in vessel A to
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the final required product temperature of
371°C .
The additional cooling and heating may be
provided by a chiller and a boiler or any other suitable
mesas.
=t can readily be appreciated from the above
discussion and Figure 2 that selectively connecting the
heat exchange circuit that heated and cooled the coal in
vessels A sad D to other pairs of the vessels A, H, C, D, E
in accordance with the sequence shown in the table that
forms part of Figure 2 and selectively providing external
heating and cooling of the vessels as described for vessels
A and D results in similar heating and cooling of the coal
in the vessels.
Many modifications may be made to the above-
described method and apparatus for upgrading a solid
material without departing from the spirit and.scope of the
present invention.
By way of example, the first aspect of the
present invention is not restricted to the single stage
energy recovery cycle with 5 reactors described in relation
to Figure 1. Hy way of example, the first aspect extends
to a 2 stage energy recovery cycle with additional heating
and cooling in 3 vessels. With this arrangement, the
heating and cooling stages are arranged countercurrent in
time and there are 2 approach temperatures, typically 240°C
and 150°C. More specifically, the 2 stage energy recovery
cycle is as follows. A hot vessel A which has just
completed a heating cycle is connected to a colder vessel B
and transfers heat which heats vessel 8 in the second stage
of heating. When the higher of the two approach
tea~eratures is reached, vessel A is connected to a cold
vessel C sad transfers heat which heats vessel C in the
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first stage of heating. Finally, when the lower. approach
temperature is reached, vessel A is connected to a chiller
to complete cooling of the coal in the vessel and deliver
cold final coal. Vessel B, which has been heated in the
second stage of heating to the higher approach temperature
is connected to a steam supply circuit to complete the
heating cycle of the coal in the vessel. It can readily be
appreciated that this sequence of heating and cooling the
vessels With fresh packed beds of coal can be repeated.
*rB
