FUEL SLURRY HEATING SYSTEM AND METHOD
BACKGROUND
[0001] The subject matter disclosed herein relates to the preparation of fuel slurries
used in gasification processes, and more specifically to increasing the concentration of
solids in the fuel slurry.
[0002] Synthesis gas or "syngas" is a mixture of carbon monoxide (CO) and
hydrogen (H ) and other components present in lesser degrees, such as carbon dioxide
(C0 2) that has a number of uses, such as in power generation, steam generation, heat
generation, substitute natural gas (SNG) production, as well as chemical synthesis.
Syngas can be produced using gasification processes, which utilize a solid, liquid,
and/or gaseous carbonaceous fuel source such as coal, coke, oil, and/or biomass, to
react with oxygen (0 2) to produce the syngas within a gasifier. While certain liquid
and gaseous carbonaceous fuels may be provided to the gasifier directly, solid
carbonaceous fuel sources are often provided to the gasifier as a fuel slurry, where the
solid fuel is dispersed within a liquid, such as water. The liquid is used to facilitate
flow of the solid fuel into the gasifier as well as to facilitate dispersal of the solid fuel
within the gasifier, for example to increase gasification efficiency. Unfortunately, the
presence of liquid in the slurry reduces the energy content of syngas produced per unit
weight of feed as compared with other more concentrated fuel sources, such as liquid
or gaseous feeds.
BRIEF DESCRIPTION
[0003] Certain embodiments commensurate in scope with the originally claimed
invention are summarized below. These embodiments are not intended to limit the
scope of the claimed invention, but rather these embodiments are intended only to
provide a brief summary of possible forms of the invention. Indeed, the invention
may encompass a variety of forms that may be similar to or different from the
embodiments set forth below.
[0004] In a first embodiment, a system includes a fuel slurry preparation system
having a slurry tank configured to hold a fuel slurry, the fuel slurry having a solid fuel
and a liquid. The fuel slurry preparation system also includes a heat source and a
controller configured to control the heat source to heat the fuel slurry to decrease a
viscosity of the slurry below a threshold viscosity.
[0005] In a second embodiment, a system includes a controller configured to
control a heat source to heat a fuel slurry having a solid fuel and a liquid. The fuel
slurry is heated to allow a slurry tank to produce the fuel slurry at a solids
concentration that is higher than would be obtained if the fuel slurry were not heated.
[0006] In a third embodiment, a method includes monitoring one or more
parameters of a fuel slurry with a controller, wherein one or more parameters include
a viscosity of the slurry, a solids concentration of the slurry, a temperature of the
slurry, or any combination thereof, and the fuel slurry has a solid fuel and a liquid.
The method also includes maintaining the fuel slurry below a viscosity threshold by
heating the fuel slurry.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] These and other features, aspects, and advantages of the present invention
will become better understood when the following detailed description is read with
reference to the accompanying drawings in which like characters represent like parts
throughout the drawings, wherein:
[0008] FIG. 1 is a process flow diagram illustrating an embodiment of a method
for increasing a solids concentration of a slurry by heating the slurry;
[0009] FIG. 2 is a process flow diagram illustrating an embodiment of a method
for generating a pumpable slurry from an unpumpable slurry by heating the slurry;
[0010] FIG. 3 is a process flow diagram illustrating an embodiment of a method
for increasing a solids concentration of a slurry by heating the slurry and removing a
portion of a liquid from the slurry;
[0011] FIG. 4 is a process flow diagram illustrating an embodiment of a method
for performing a liquid removal step of FIG. 3;
[0012] FIG. 5 is a block diagram illustrating an embodiment of a slurry preparation
system;
[0013] FIG. 6 is a schematic diagram illustrating an embodiment of the slurry
preparation system of FIG. 5 having a heat source configured to allow steam to sparge
the slurry within a slurry preparation tank;
[0014] FIG. 7 is a schematic diagram illustrating another embodiment of the slurry
preparation system of FIG. 5 having a heat exchanger disposed within a slurry
preparation tank to heat the slurry;
[0015] FIG. 8 is a schematic diagram illustrating another embodiment of the slurry
preparation system of FIG. 5 having a steam jacket disposed about a slurry
preparation tank to heat the slurry; and
[0016] FIG. 9 is a schematic diagram illustrating another embodiment of the slurry
preparation system of FIG. 5 having water removal features disposed downstream of a
slurry preparation tank to increase a solids concentration of a heated slurry.
DETAILED DESCRIPTION
[0017] One or more specific embodiments of the present invention will be
described below. In an effort to provide a concise description of these embodiments,
all features of an actual implementation may not be described in the specification. It
should be appreciated that in the development of any such actual implementation, as
in any engineering or design project, numerous implementation-specific decisions
must be made to achieve the developers' specific goals, such as compliance with
system-related and business-related constraints, which may vary from one
implementation to another. Moreover, it should be appreciated that such a
development effort might be complex and time consuming, but would nevertheless be
a routine undertaking of design, fabrication, and manufacture for those of ordinary
skill having the benefit of this disclosure.
[0018] When introducing elements of various embodiments of the present
invention, the articles "a," "an," "the," and "said" are intended to mean that there are
one or more of the elements. The terms "comprising," "including," and "having" are
intended to be inclusive and mean that there may be additional elements other than the
listed elements.
[0019] As noted above, some gasification systems use a slurry of solid fuel and a
liquid (e.g., water) to deliver the solid fuel to a gasifier to produce syngas. The liquid
of the fuel slurry facilitates the flow of the solid fuel to the gasifier, and can also aid
in dispersing the solid fuel within the gasifier to increase gasification efficiency.
However, the amount of syngas produced can be dependent, among other variables,
on the amount of solid fuel within the reactor, and thus typical gasification systems
are limited by the solids concentration of the fuel slurry that can be produced and
pumped at a desired flow rate. Moreover, the viscosity of the slurry in such ambient
conditions can have a detrimental effect on the equipment that produces the fuel
slurry and the equipment that motivates the fuel slurry from a slurry preparation area
to the gasifier. For example, agitators such as impellers within a slurry tank, conduits
such as piping, as well as various pumps, feed injectors, and so forth may erode due to
relatively high viscosity levels of the slurry compared to other fluids.
[0020J While the solids concentration of a slurry may be increased using certain
additives such as fluxants, surfactants, and the like, such approaches may be unable to
mitigate the undesirable effects of high viscosity slurries. Moreover, the solids
concentration increase using such additives is often marginal, and can add cost to
gasification processes. Accordingly, the present disclosure provides a fuel slurry
preparation system that is configured to provide heating to the fuel slurry using steam
or another heated fluid generated within the gasification system or elsewhere in a
gasification plant. In one embodiment, a heat source may be placed in a slurry
preparation tank. The heat source may receive waste steam or other heated fluid such
as hot syngas or heated water from another process within the plant, which provides
beneficial heating to the fuel slurry. The heating may allow for higher concentrations
of solid within the fuel slurry, while maintaining the pumpability of the fuel slurry at a
desired rate. Additionally, in some embodiments, the heating fluid (e.g., steam) may
also be used as a feature for agitation of the fuel slurry in the slurry tank, which can
reduce power requirements by agitation features within the slurry preparation tank.
Indeed, such reductions in viscosity can also prolong the life of fuel slurry preparation
and motivation equipment. Moreover, delivering preheated fuel slurry to the gasifier
may decrease the specific fuel consumption (fuel per unit power) of both 0 and the
solid fuel used in the gasification reaction.
[0021] The embodiments described herein may be performed by a system, such as
a slurry preparation system, that is a stand-alone system or integrated into a
gasification/power production facility. For example, the slurry preparation systems
described herein may be integrated with gasification processes, methanation processes,
or other power or chemical production process that produces an amount of steam that
can be utilized to achieve temperature increases in a fuel slurry. Moreover, certain of
the methods for controlling the slurry heating features described herein may be
performed by a controller, which may be an application-specific or a general-purpose
computer having a memory, a processor, a data-accessing drive, and so on. The
controller may be configured to execute certain routines, for example after accessing
the routines on a machine-readable, non-transitory medium such as an optical disc,
solid state memory, or the like. Alternatively or additionally, the controller may be
connected to a distributed control system and/or a network, and may access the
routines from a remote storage location. The controller may thereafter execute the
routines to facilitate the heating and slurry concentration processes described herein.
Non-limiting examples of embodiments of such control processes are described below
with respect to FIGS. 1-4.
[0022] Keeping in mind that the methods set forth with respect to FIGS. 1-4 may
be performed by any such suitably-configured controller as described above, FIG. 1 is
a process flow diagram illustrating an embodiment of a general method 10 for heating
a fuel slurry. Performing the method 10 allows a solids concentration of the fuel
slurry to be increased while maintaining a viscosity of the fuel slurry below a
predetermined viscosity. In some embodiments, the predetermined viscosity may be a
threshold viscosity at which the viscosity of the fuel slurry transitions from being
pumpable at a desired flow rate to being unpumpable at the desired flow rate by a
suitably-configured fuel slurry pump.
[0023] Method 10 begins by preparation of a fuel slurry. Specifically, a solid fuel
is mixed with a liquid to generate the fuel slurry (block 12). The solid fuel may
include coal, petroleum coke, biomass, or other carbon containing solids items. The
liquid may include any material that remains substantially in the liquid phase during
the slurry preparation processes described herein. The liquid may include an organic
liquid, an aqueous liquid, or mixtures thereof. As an example, the liquid may include
one or more organic solvents, an aqueous solution, an aqueous solution having one or
more surfactants, or mixtures thereof. In one embodiment, the liquid may be water.
The mixing of the solid fuel and the liquid may occur in any suitably configured
mixing vessel, such as a mill, a vessel with agitation features, or the like, as will be
described in further detail below with respect to FIGS. 4-6.
[0024] Once the fuel slurry has been formed, various parameters of the slurry are
monitored (block 14). Additionally, while the step of monitoring the various
parameters is presented as occurring after generating the fuel slurry and prior to other
steps of the method 10, it should be noted that the parameters may be monitored
substantially continuously during the method 10, such that the controller may make
adjustments and any other determinations when suitable. The parameters that may be
monitored include a temperature, pressure, viscosity, solids concentration, or any
combination thereof, of the fuel slurry. Again, as will be discussed below, a
controller may monitor such parameters by substantially continuously or
intermittently monitoring one or more control signals received from transducers
placed within a slurry preparation system.
[0025] Upon initially monitoring the parameters of the slurry, the fuel slurry is
heated (block 16). Generally, the fuel slurry is heated to a desired temperature that
results in a viscosity of the fuel slurry that allows the fuel slurry to be pumpable using
a fuel slurry pump while maximizing the solids concentration of the fuel slurry. The
solids concentration of the fuel slurry is the amount of solid fuel per amount of total
fuel slurry, which may be represented by weight percent, volume percent, moles, or
any similar metric. The temperature to which the fuel slurry is heated may depend on
a number of factors, such as the desired solids concentration, the conditions under
which the fuel slurry will be heated (e.g., open air or in a conduit), and so on.
Generally, the fuel slurry is heated to a temperature above approximately 40 °C, such
as to between 40 °C and 400 °C. In embodiments in which the fuel slurry is heated in
an open air vessel, the fuel slurry may be heated to a temperature up to about a
temperature at which the liquid will boil, such between 50 and 100% of the
temperature at which the liquid will boil (e.g., approximately 50, 60, 70, 80, 90, 95,
99, or 100% of the boiling point of the liquid). Thus, in embodiments in which the
liquid is water, the fuel slurry may be heated to between about 40 °C and 100 °C, such
as between about 50 °C and 90 °C, or 60 °C and 80 °C. Thus, the fuel slurry may be
heated to approximately 45 °C, 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, 75 °C, 80 °C, 85
°C, 90 °C, 95 °C, or 99 °C. Moreover, it should be noted that the fuel slurry may be
heated to or slightly above (e.g., up to about 15 °C above) 100 °C if the fuel slurry
contains materials that allow boiling point elevation of the water.
[0026] In embodiments in which the slurry is heated in a closed system, such as
within a conduit or other closed fluid-transferring feature, the liquid may be heated
above about 40 °C and up to a temperature below a threshold temperature at which
the fuel slurry may begin to coke (i.e., the coking temperature). Indeed, in some
embodiments, the slurry may be heated to between approximately 10% and 99%, or
20 and 90%, or 30 and 80%, or 40 and 60%, of the coking temperature, such as
approximately 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, or 99 % of the coking
temperature. In embodiments in which the fuel slurry is heated in a closed system and
the liquid is water, the fuel slurry may be heated to between approximately 40 and
300 °C, or 50 and 250 °C, or 60 and 240 °C, or 70 and 230 °C, or 80 and 220 °C, or
90 and 200 °C, such as 50 °C, 60 °C, 70 °C, 80 °C, 90 °C, 100 °C, 125 °C, 150 °C,
175 °C, 200 °C, 225 °C, 250 °C, or 260°C.
[0027] As noted above, the fuel slurry is heated to a desired temperature that
reduces the viscosity of the fuel slurry below a threshold viscosity of the fuel slurry.
Again, the threshold viscosity may be defined as the viscosity at which the fuel slurry
transitions from being pumpable under a given set of conditions to being unpumpable
under the given set of conditions. The given set of conditions may include being able
to be pumped at a given rate by certain types of pumps having certain specifications,
and the pumps are configured to motivate (e.g., pump) the fuel slurry through a slurry
conduit. In some embodiments, the threshold viscosity may depend on these and
other factors, which may be determined experimentally and/or based upon
specifications of a given fuel slurry and pump. As an example, the threshold viscosity
may be between approximately 1 kg n s 1 ( 1 Pascal second (Pa-s)) and 2 kg -s 1,
such as 1.1, 1.2, 1.3, 1.4, 1.5, 1.75, 2 kg-m^-s 1, or higher, depending at least on the
factors above. Indeed, the fuel slurry may be heated to allow a concentration such
that the viscosity of the fuel slurry is between approximately 10% and 99%, or 20 and
90%, or 30 and 80%, or 40 and 60%, of the threshold viscosity. Such higher
concentrations may allow increased syngas output per unit time, decreased liquid
waste, higher plant efficiency, and so forth, compared to configurations where the fuel
slurry is not heated.
[0028] Thus, after heating the fuel slurry, and based upon the considerations
described above, the controller may determine whether the slurry is pumpable based
on the monitored parameters (query 8). In embodiments where the slurry is not able
to be pumped (e.g., is not below a threshold viscosity) at query 18, the method 10 may
cycle back to heating the slurry until a desired pumpability is reached. Decreasing the
viscosity of the fuel slurry in this manner may reduce wear on plant components, may
reduce the required power to pump the fuel slurry, may reduce the size of pumping
equipment, and may increase the maximum solids concentration of a given fuel slurry.
In embodiments where the fuel slurry is pumpable at query 18, the method 10 may
progress to pumping the fuel slurry to a gasifier (block 20). Once the slurry is
provided to the gasifier, at least the solid fuel within the slurry is gasified to produce a
syngas (block 22). As noted above, by heating the fuel slurry, the operation of the
gasification system to produce syngas may be more efficient. For example, the
inventors have calculated that larger amounts of syngas may be produced by gasifying
a heated fuel slurry feed compared to gasifying a non-heated fuel slurry feed.
[0029] The present embodiments, in addition to the general method described
above, also provide approaches to generate a pumpable slurry from an unpumpable
slurry, as depicted by the process flow diagram of FIG. 2. Specifically, the process
flow diagram of FIG. 2 illustrates an embodiment of a method 30 for generating a
pumpable slurry from an unpumpable slurry by applying heat to the unpumpable
slurry.
[0030] As noted with regard to the general method 10 described above, the fuel
slurry may be heated to a temperature that reduces the viscosity of the fuel slurry
below a threshold viscosity of the fuel slurry. Therefore, in the context of the present
embodiment, the method 30 provides for a reduction in the viscosity of the fuel slurry
from a value above the threshold viscosity to a value below the threshold viscosity. In
accordance with certain embodiments, the viscosity of the fuel slurry is dependent on
the solids concentration of the slurry as well as the viscosity of the liquid of the fuel
slurry. Decreasing the viscosity of the liquid of the fuel slurry decreases the viscosity
of the fuel slurry. Indeed, the solids concentration of the fuel slurry may be increased
by adding more solid fuel to the slurry while decreasing the viscosity of the liquid by
adding heat to the slurry. In this way, the solids concentration of the fuel slurry may
be increased while maintaining the viscosity of the fuel slurry at a desired level by
applying heat to reduce the viscosity of the liquid. Therefore, by heating the fuel
slurry, a higher solids concentration may be achieved than the solids concentration
that would be achieved if the fuel slurry were not heated.
[0031] Keeping the above viscosity relationships in mind, method 30 begins with
generating an unpumpable slurry (block 32). The unpumpable slurry is generated by
mixing the solid fuel and the liquid in a ratio that produces the fuel slurry at a
viscosity at ambient temperature (e.g., up to about 40 °C) that is above the threshold
viscosity. As an example, in embodiments where the liquid is water, the solid fuel
and the liquid may be provided in a ratio so as to generate a fuel slurry having a solids
concentration of at least 60 weight percent (wt. %), where the weight of the solid fuel
accounts for about 60 percent of the total weight of the slurry. Indeed, in certain
embodiments, the unpumpable slurry may have a solids concentration between
approximately 60 and 70 wt%, or 6 1 and 69 wt%, or 62 and 68 wt%, or 63 and 67
wt%, or 64 and 66 wt %, such as approximately 60 wt%, 6 1 wt%, 62 wt%, 63 wt%,
64 wt%, 65 wt%, 66 wt%, 67 wt%, 68 wt%, 69 wt%, 70 wt%, or higher.
[0032] Upon generating the unpumpable slurry, the method 30 performs the acts
represented by blocks 14-22 as described above with respect to FIG. 1. Generally, the
method 30 proceeds to monitor parameters of the fuel slurry (block 14), such as
viscosity, temperature, solids concentration, and the like. The fuel slurry is then
heated to reduce its viscosity (block 16), such as below a desired threshold viscosity.
The method 30 proceeds to determine whether the slurry is pumpable (query 18). For
example, a controller or similar feature may determine whether the fuel slurry is no
more than approximately 99% of the threshold viscosity, such as between about 10%
and 95%, or 20 and 90%, or 30 and 80%, or 40 and 70%, or 50 and 60%, of the
threshold viscosity. In embodiments where the slurry is pumpable at query 18, the
method proceeds to pumping the fuel slurry to the gasifier (block 20). The fuel slurry
is then gasified (block 22). However, in embodiments where the fuel slurry is not
pumpable (e.g., is at or above 100% of the threshold viscosity) at query 18, the
method may return to the acts represented by block 16.
[0033] Using certain of the approaches described above, it may be desirable to
increase the solids concentration of the fuel slurry by removing water from the slurry,
rather than first generating an unpumpable slurry and heating the slurry to make the
slurry pumpbale. Such an approach may be desirable, for example, in situations
where an unpumpable slurry may be difficult to generate, monitor, and/or process.
FIG. 3 illustrates a process flow diagram of an embodiment of a method 40 for
increasing the solids concentration of the fuel slurry by removing water.
[0034] The method 40 begins by generating a pumpable slurry by mixing the solid
fuel with the liquid (block 42). The fuel slurry may be so generated by mixing the
solid fuel with the liquid in a ratio such that the viscosity of the fuel slurry is below
the threshold viscosity. As an example, in embodiments where the liquid is water, the
initial solids concentration of the fuel slurry may be at or below approximately 60
wt%, such as between approximately 1 wt% and 60 wt %, or 10 and 50 wt%, or 20
and 40 wt%. The fuel slurry having such an initial concentration may be considered a
first fuel slurry.
[0035] The parameters of the first slurry are monitored as described above with
respect to FIG. 1 (block 14), and the first slurry is then heated to a desired temperature
(block 44). The desired temperature may be a modeled temperature based at least
upon the initial solids concentration, the desired final solids concentration, and the
desired final viscosity of the fuel slurry. Again, as noted above, in embodiments
where the fuel slurry is heated in an open-air system, the desired temperature may be
approximately 40 °C and 100 °C, such as between about 50 °C and 90 °C, or 60 °C
and 80 °C. In embodiments where the fuel slurry is heated in a closed system, the
desired temperature may be approximately between 40 and 300 °C, or 50 and 250 °C,
or 60 and 240 °C, or 70 and 230 °C, or 80 and 220 °C, or 90 and 200 °C.
[0036] Once the fuel slurry has been heated to the desired temperature, a portion of
the liquid may be removed from the fuel slurry and/or an additional amount of solid
fuel may be added to the fuel slurry to obtain the desired solids concentration and
viscosity of the fuel slurry (block 46), which may be referred to as a second fuel
slurry. As an example, between approximately 1% and 50% of the total liquid may be
removed, such as between approximately 1 and 50%, or 2 and 50%, or 3 and 40%, or
4 and 30%, or 5 and 20% of the total liquid may be removed. In embodiments where
additional solid fuel is added to the fuel slurry, between approximately 1 and 50%
more solid fuel may be added, such as between approximately 1 and 30%, 5 and 25%,
or 10 and 20% more solid fuel. An embodiment of a method for performing the
liquid removal acts represented by block 46 is discussed in detail below with respect
to FIG. 4. In embodiments where additional fuel slurry is provided (in addition to or
in lieu of liquid removal), the amount of additional solid fuel may be added based on
viscosity measurements, temperature measurements, solids concentration
measurements, or a combination thereof. Once the second fuel slurry has been
generated, the second fuel slurry is pumped to the gasifier (block 20), where at least
the solid fuel is gasified to generate the syngas (block 22).
[0037] FIG. 4 illustrates a process flow diagram of an embodiment of the method
46 for generating the second fuel slurry when it is desirable to remove liquid from the
fuel slurry to obtain a particular solids concentration. The method 46 begins by
removing a portion of liquid from the first fuel slurry (block 48). The amount of
liquid removed from the first fuel slurry may depend at least partially on the initial
solids concentration and the desired final solids concentration, the temperature of the
initial fuel slurry, as well as the threshold viscosity for the fuel slurry. The removal of
the liquid may be performed by liquid vaporization, for example to generate steam, or
by performing a separation of a portion of the liquid from the solid fuel based on size,
density, or other property. As an example, the liquid may be separated from the solid
fuel using a filter and a valve, a cyclone, a membrane, an absorbent material, or a
combination of such features or similar features.
[0038] Once the portion of the liquid has been removed, the controller may
determine whether the fuel slurry has a solids concentration above a desired minimum
solids concentration (query 50). In embodiments where the fuel slurry does not have
a sufficient solids concentration, the method 46 may cycle back to the acts represented
by block 48, and another portion of liquid may be removed. In embodiments where
the solids concentration of the fuel slurry is above a desired minimum, the method 46
progresses to determine whether the viscosity of the fuel slurry is below the threshold
viscosity (query 52). In embodiments where the viscosity of the fuel slurry is above
the threshold viscosity (e.g., if more liquid was removed in block 48 than is suitable),
the method 46 then proceeds to determine whether the fuel slurry has reached a
temperature threshold (query 54), which may be at least partially determined by the
considerations described above with respect to FIG. 1. In embodiments where the
fuel slurry is below the temperature threshold, the fuel slurry is heated (block 56).
The method then returns to query 52. In embodiments where the slurry is at or above
the temperature threshold, additional liquid is added to the fuel slurry (block 58). The
method then returns to query 50. Returning to query 52, in embodiments where the
viscosity of the fuel slurry is below the threshold viscosity, the method 46 progresses
to the acts represented by block 20 of FIG. 3 (block 60).
[0039] The methods described above, as previously mentioned, may be performed
by a suitably-configured controller operatively connected to various slurry preparation
features. The slurry preparation features may be a part of a gasification system,
integrated into the gasification system, or may otherwise be a standalone portion of a
gasification system. FIG. 5 illustrates a block diagram of an embodiment of a system
70 that uses slurry heating features and/or solid fuel addition features to beneficially
increase the solids concentration of a fuel slurry. The system 70 includes a feedstock
preparation unit 72 that receives a solid fuel 74 and prepares the solid fuel 74 for
mixing with a liquid 76. As an example, the feedstock preparation unit 72 may
include a grinder, a mill, or any similar vessel that is capable of producing smaller
particles from large particles of the solid fuel 74. As illustrated, the liquid 76 is
introduced to the solid fuel 74 downstream of the feedstock preparation unit 72.
However, in other embodiments, the liquid 76 may be introduced directly into the
feedstock preparation unit 72.
[0040] A slurry preparation unit 78 configured to receive the solid fuel 74 and the
liquid 76 is disposed downstream from the feedstock preparation unit 72. The slurry
preparation unit 78 may be a vessel having one or more agitation features such as a
grinder, an impeller, a sonication unit, or the like. The slurry preparation unit 78, in a
general sense, mixes the solid fuel 74 and the liquid 76 to generate a fuel slurry. In
accordance with the disclosed embodiments, the slurry preparation unit 78 is
connected to or otherwise disposed upstream of a slurry heating unit 80 and a fuel
addition unit 83. The slurry heating unit 80 is configured to provide a source of heat
(e.g., steam or other heated fluid) to the fuel slurry to increase the temperature of the
fuel slurry so as to allow a solids concentration of the fuel slurry to be increased. In
embodiments using heated water or steam as the heat source, the slurry heating unit
80 may provide a recycle or make-up steam flow 8 1 (e.g., water and/or steam) as a
source of the liquid 76. The flow 8 1 also may be used to preheat the liquid 76
upstream of the slurry preparation unit 76. In certain embodiments, the slurry heating
unit 80 may be partially or completely contained within the slurry preparation unit 78.
[0041] Additional solid fuel 74 may be added to a fuel slurry stream 82 containing
the solid fuel 74 and the liquid 76, after being prepared by the slurry preparation unit
78 and the slurry heating unit 80. In the illustrated embodiment, the system 70 also
includes the fuel addition unit 83, which is configured to provide additional solid fuel
74 to the stream 82, in addition to or in lieu of liquids removal, to increase the solids
concentration of the stream 82. The additional fuel, as noted above with respect to
FIG. 3, may be added based on viscosity, pumpability, flow velocity, concentration,
or similar measurements. After the stream 82 has been adjusted to a desired
concentration range, the system directs the stream 82 to a gasifier 84. The gasifier 84
is configured to subject the fuel slurry stream 82 to gasification conditions. As a
result of being subjected these conditions, the solid fuel within the fuel slurry stream
82 reacts with oxygen (0 2) and water (H20 ) to generate syngas 86. In a general sense,
the amount of syngas 86 that is produced is limited by, among other things, the size of
the gasifier 84 as well as the amount of solid fuel 74 that enters the gasifier 84.
[0042] As noted above, because the solid fuel 74 is provided to the gasifier 84 as a
part of the fuel slurry stream 82, it may be desirable to maximize the amount of solid
fuel 74 contained within the fuel slurry stream 82. The amount of solid fuel 74
contained within the fuel slurry stream 82 may be considered to be a solids
concentration of the fuel slurry 82. Again, the solids concentration of the fuel slurry
82 may be advantageously increased by heating the solid fuel 74 and the liquid 76
with the slurry heating unit 80. An embodiment of a slurry preparation and heating
system 90 is diagrammatically illustrated in FIG. 6. The system 90 includes a mill 92
having an inlet 93 for receiving the solid fuel 74 and prepares the solid fuel 74 for
slurrying. As an example, the mill 92 may be a ball mill, a grinding mill, or any
similar feature or combination of features for reducing the particle size of the solid
fuel 74. In some embodiments, by reducing the particle size, the solid fuel 74 may be
more easily dispersed within the liquid 76, which, in the illustrated embodiment, is
water. In addition to receiving the solid fuel 74, the mill 92 is also configured to
receive other additives 94, such as fluxants, catalysts, and so on. A water supply 96
feeds water into the mill 92 via conduit 98. The mill 92 further includes an outlet 100
for discharging a mixture of the solid fuel 74, the liquid 76, and the additive 94 into a
mill discharge tank 102.
[0043] The system 90 also includes a controller 104 that is communicatively
connected to a first transducer 106 configured to generate signals representative of an
amount of solids within the mill 92, a temperature of the solids within the mill 92, and
the like. The controller 104 is also communicatively connected to a second transducer
108 configured to generate signals representative of an amount of solids exiting the
mill 92, a temperature of the material exiting the mill 92, a viscosity of the material
exiting the mill 92, and the like. The controller 104 is also operatively connected to
an actuator 110 of a flow control valve 112 disposed along the conduit 98. The
controller 104 is configured to adjust a flow rate of the water through the conduit 98
by adjusting the position of the flow control valve 112 via the actuator 110. The
controller 104 sends signals to the actuator 110 to perform such adjustments in
response to received signals from the first and/or second transducers 106, 108 that
indicate measured parameters outside of a desired range.
[0044] In addition to the features described above for grinding and, to a certain
extent, mixing the solid fuel 74 with other slurry components, the system 90 also
includes features for slurrying the solid fuel 74 as well as heating the resulting fuel
slurry. The system 90 includes a transfer pump 114 for motivating a pre-mix of solid
fuel 74 and other slurry components to a mixing vessel 116 (e.g., a slurry tank). The
mixing vessel 116 includes one or more features configured to agitate and suspend the
solid fuel 74 within the water to produce a fuel slurry. In the illustrated embodiment,
the mixing vessel 116 includes an impeller 118 having blades for mixing and agitating
the solid fuel 74 within the water.
[0045] The mixing vessel 116 also includes a heat source configured to provide
heat to the fuel slurry while the fuel slurry is in the vessel 116. Specifically, in the
illustrated embodiment, the heat source is a perforated applicator 120 (e.g., a manifold,
grid, or tube) having a plurality of orifices for allowing a heated fluid (e.g., steam)
122 to escape the perforated applicator 120 to heat the fuel slurry, depicted generally
as arrows. Advantageously, as the steam 122 escapes the perforated applicator 120 to
directly heat the fuel slurry, the steam 122 provides additional agitation to the fuel
slurry by sparging. The perforated applicator 120 receives the steam 122 from a
steam source 124 by way of a conduit 126.
[0046] The controller 104 is coupled to various features disposed on and/or within
the mixing vessel 116 and the conduit 126 to enable heating of the fuel slurry to a
desired temperature. For example, the controller 104 may be configured to adjust the
heat transfer to the fuel slurry by the perforated applicator 120 (or other heat source)
to adjust the solids concentration and viscosity of the fuel slurry between upper and
lower thresholds. The controller 104 is coupled to a third transducer 128 disposed on
and/or within the mixing vessel 116, which enables monitoring of the temperature,
solids concentration, and/or viscosity of the fuel slurry as it is generated and heated in
the mixing vessel 116. Additionally, the controller 104 is coupled to a fourth
transducer 130 that enables the controller 104 to monitor a temperature of the steam
122 as it flows through the conduit 126. The controller 104 is operatively coupled to
an actuator 132 of a flow control valve 134 disposed along the conduit 126 to enable
the controller 104 to adjust a flow rate of the steam 122 through the conduit 126.
Adjusting the flow rate of the steam 122 adjusts the amount of steam 122 that escapes
the perforated applicator 120, and therefore adjusts the rate at which the fuel slurry is
heated. Thus, the controller 104 is capable of providing more or less heat to the fuel
slurry in response to monitored temperatures and/or solids concentrations of the fuel
slurry within the mixing vessel 116.
[0047] After the fuel slurry has been prepared and heated as described above, at
least a portion of the fuel slurry is discharged to a slurry pump 136. The slurry pump
136 is configured to motivate the generated fuel slurry at a desired flow rate. Indeed,
as noted above, the desired solids concentration of the fuel slurry may depend at least
on the specifications of the slurry pump 136 and the capability of the slurry pump 136
to motivate the fuel slurry at the desired flow rate. Therefore, the controller 104 is
connected to a fifth transducer 138 that may generate and send signals representative
of a flow rate and/or viscosity of a fuel slurry 140 that is sent to a gasifier.
Accordingly, the monitored parameters of the fuel slurry 140 that is sent to the
gasifier may also be a factor for determining a desired temperature and/or solids
concentration of the fuel slurry.
[0048] While the embodiment illustrated in FIG. 6 depicts the system 90 as
including the perforated applicator 1 0 for providing direct contact between the steam
1 2 and the fuel slurry to heat the fuel slurry, it may be desirable, alternatively or
additionally, to have a feature for providing indirect heating to the fuel slurry.
Accordingly, FIG. 7 is a diagrammatical representation of a system 150 having a heat
exchanger 152 disposed within the mixing vessel 116. The heat exchanger 152 may
include any shape, size, or other configuration suitable for receiving a feed of steam
through the conduit 126. In certain embodiments, the heat exchanger 152 may be
configured to maximize a surface area of the heat exchanger 152 that is exposed to
both the steam and the fuel slurry. For example, the heat exchanger 152 may be a coil
that is disposed proximate the impeller 118 for providing an indirect heating source to
the fuel slurry. After the steam begins to cool within the heat exchanger 152, or in a
substantially continuous fashion, the cooled steam (and/or condensed water) may be
provided to a pump 154 or another similar feature for sending a recycle stream 156 to
the water supply 96 (e.g., a water tank or other boiler feedwater source).
[0049] In other embodiments, it may be desirable to heat the fuel slurry while the
fuel slurry is in the mixing vessel 116 without interfering with (or extending into the
path of) mixing of the fuel slurry by the impeller 118. For example, such features
may be desirable to avoid erosion of conduits (e.g., piping), heat exchangers, tubing,
and so forth. Therefore, FIG. 8 is a diagrammatical illustration of a system 160
having a jacketed mixing vessel 162. The jacketed mixing vessel 162 includes an
interior portion 164 where the fuel slurry is generated and agitated, as well as an
external portion defining a heating jacket 166, which is an annular structure
surrounding the interior portion 164 where the fuel slurry is produced.
[0050] The heating jacket 166 is generally configured to receive the steam 122
from the steam supply 124, and enables an interior surface 168 of the interior portion
166 to heat the fuel slurry within the mixing vessel 162. The steam 122 enters the
heating jacket 166 at an inlet area 170, and may progress to other areas 172 of the
jacket 166. The steam 122, after undergoing heat transfer to the surface 168, may
condense and be removed via conduit 178. A stream of condensate 180 is then
directed to a condensate pump 182, which motivates (e.g., pumps) the stream 180 as a
recycle stream 184 to the water supply 96.
[0051] As discussed above with respect to the method 40 of FIG. 3, it may be
desirable to initially generate a pumpable slurry (i.e., before heating), and remove the
liquid of the fuel slurry or add additional fuel to the fuel slurry during and/or after
heating. FIG. 9 illustrates an embodiment of a system 190 having a general heating
unit 192, which may include any one or a combination of the embodiments of a heat
source discussed above with respect to FIGS. 6-8, as well as a heat exchanger/liquid
removal unit 194 for increasing a solids concentration of a generated fuel slurry. In
embodiments where the heating unit 192 is used to heat the slurry in the mixing vessel
116, steam or other heated fluid (e.g., oil, hot syngas) is provided via a conduit 193.
The flow rate of the steam to the heating unit 192 is controlled by the controller 104,
which sends control signals to an actuator 195 of a flow control valve 197 to adjust
the position of the valve 197.
[0052] After the fuel slurry is initially formed, and, in some embodiments, heated
in the mixing vessel 116, the generated slurry is pumped by the slurry pump 136
through a conduit 196. As noted above, the controller 104 may monitor one or more
parameters of the generated fuel slurry using the fifth transducer 138. Indeed, the
solids concentration of the generated fuel slurry in conduit 196 may be lower than is
desired. Accordingly, the generated fuel slurry is provided to the heat
exchanger/liquid removal unit 194, where the fuel slurry is further heated and a
portion of the water of the fuel slurry is removed. In removing a portion of the water,
the solids concentration of the fuel slurry is increased.
[0053] The controller 104 may then monitor various parameters of the fuel slurry
at the heat exchanger/liquid removal unit 194 using a sixth transducer 198. For
example, the sixth transducer 198 may generate signals representative of a viscosity
of the fuel slurry, the solids concentration of the fuel slurry, the temperature of the
fuel slurry, the flow rate of the fuel slurry, or any combination thereof, of the fuel
slurry. Indeed, the sixth transducer 198 may generate signals representative of any
measurement that may represent, directly or indirectly, a solids concentration and/or
pumpability of the fuel slurry. In response to receiving these signals, the controller
104 may adjust the amount of steam (or other heated fluid such as oil or syngas)
provided to the heat exchanger/liquid removal unit 194. Moreover, the heat
exchanger/liquid removal unit 194 may include various features that allow water to be
removed, such as a vaporization chamber, a gas-liquid interface region for stripping
the liquid with a stream of gas, or the like, that is heated by the heat exchanger portion
of the heat exchanger/liquid removal unit 194. In embodiments in which a portion of
the water is removed, the water, along with any steam condensate, is sent along a
conduit 200 to the water supply 96 as recycle. In certain embodiments, as noted
above with respect to FIGS. 3 and 5, it may be desirable to provide additional solid
fuel 74 to the slurry after being heated. Indeed, in addition to, or in lieu of removing
water from the fuel slurry to increase the solids concentration of the same, the
controller may direct a fuel supply unit 201 to provide additional solid fuel 74 to the
fuel slurry at an area of the system 190 downstream from the mixing vessel 116. The
fuel supply unit 201 may be a hopper or any such feature capable of providing a solid
feed to the fuel slurry. Again, the additional solid fuel 74 may be added based on
viscosity, pumpability, flow velocity, concentration, or similar measurements of the
fuel slurry. For example, these or similar measurements may be made by the sixth
transducer 198, and signals representative of these measurements are provided to the
controller 104, which is capable of directly or indirectly determining the solids
concentration and/or the pumpability of the fuel slurry. The controller 104, as a
function of these determinations, sends control signals to the fuel supply unit 201 to
provide a certain amount of additional solid fuel 74 to the fuel slurry.
[0054] In some embodiments, the heat exchanger/liquid removal unit 194 may
allow the steam that is used for heating to also be used as make-up liquid for the fuel
slurry. For example, in situations where it may be desirable to add liquid back to the
fuel slurry, such as when the viscosity of the fuel slurry is above the threshold value,
the heat exchanger/liquid removal unit 194 may recycle at least a portion of the steam
back to the fuel slurry. In embodiments where the fuel slurry does not flow through
the heat exchanger/liquid removal unit 194 in a substantially continuous fashion, the
heat exchanger/liquid removal unit 194 may also include pumping features. After the
fuel slurry has the desired specifications (e.g., solids concentration, temperature), it is
provided to the gasifier as fuel slurry feed 202.
[0055] This written description uses examples to disclose the invention, including
the best mode, and also to enable any person skilled in the art to practice the invention,
including making and using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the claims, and may
include other examples that occur to those skilled in the art. Such other examples are
intended to be within the scope of the claims if they have structural elements that do
not differ from the literal language of the claims, or if they include equivalent
structural elements with insubstantial differences from the literal language of the
claims.
CLAIMS:
1. A system, comprising:
a fuel slurry preparation system, comprising:
a vessel configured to hold a fuel slurry comprising a solid fuel and a
liquid;
a heat source; and
a controller configured to control the heat source to heat the fuel slurry
to decrease a viscosity of the slurry below a threshold viscosity.
2. The system of claim 1, wherein the heat source is disposed along an
output flow path external to the vessel.
3. The system of claim 1, wherein the heat source is configured to heat
the fuel slurry in the vessel.
4. The system of claim 3, wherein the heat source comprises a steam
sparging applicator configured to output a flow of steam into the vessel to directly
contact the fuel slurry in the vessel.
5. The system of claim 3, wherein the heat source comprises a heat
exchanger disposed in the vessel.
6. The system of claim 3, wherein the heat source comprises a heating
jacket configured to at least partially surround the vessel.
7. The system of claim 1, comprising a slurry pump configured to receive
the fuel slurry from the vessel, and the threshold viscosity is at a transition between a
pumpable viscosity and an unpumpable viscosity of the fuel slurry by the slurry pump.
8. The system of claim 1, wherein the controller is configured to control
the heat source to adjust heat transfer to the fuel slurry to adjust a solids concentration
and a viscosity of the fuel slurry between upper and lower thresholds.
9. The system of claim 8, comprising a liquid removal unit disposed
downstream from the vessel and configured to remove an amount of liquid from the
fuel slurry to adjust at least one of a viscosity or a solids concentration of the fuel
slurry, wherein the controller is configured to control the amount of liquid removed
from the fuel slurry by the liquid removal unit.
10. The system of claim 9, wherein the controller is configured to monitor
the viscosity or a solids concentration of the fuel slurry, and to adjust the heat source,
the liquid removal unit, or a combination, in response to a change in at least one of the
viscosity or the solids concentration.
11. The system of claim 10, comprising a fuel supply unit configured to
provide an additional amount of solid fuel to the fuel slurry downstream of the vessel
to adjust at least one of a viscosity or a solids concentration of the fuel slurry, wherein
the controller is configured to control the additional amount of solid fuel provided to
the fuel slurry by the fuel supply unit in response to a monitored viscosity or solids
concentration of the fuel slurry.
12. A system, comprising:
a controller configured to control a heat source to adjust heat transfer
to a fuel slurry comprising a solid fuel and a liquid, wherein the controller is
configured to adjust the heat transfer to reduce a viscosity below an upper viscosity
threshold or increase a solids concentration above a lower concentration threshold.
13. The system of claim 12, wherein the controller is configured to adjust
the heat transfer to adjust the viscosity between the upper viscosity threshold and a
lower viscosity threshold.
14. The system of claim 12, where in the controller is configured to adjust
the heat transfer to adjust the solids concentration between the lower concentration
threshold and an upper concentration threshold.
15. The system of claim 12, wherein the controller is configured to
monitor the viscosity or the solids concentration of the fuel slurry, and the controller
is configured to adjust heat transfer to the fuel slurry by the heat source in response to
a change in the viscosity or the solids concentration.
16. The system of claim 12, wherein the system comprises the heat source,
the heat source comprises a steam flow path, and the controller is configured to
control a steam flow through the steam flow path to control the heat transfer to the
fuel slurry.
17. The system of claim 12, wherein the system comprises a gasifier
configured to receive the fuel slurry at the viscosity below the upper viscosity
threshold and the solids concentration above the lower concentration threshold.
18. A method, comprising:
monitoring one or more parameters of a fuel slurry with a controller, wherein
the one or more parameters comprise a viscosity of the fuel slurry, a solids
concentration of the fuel slurry, a temperature of the fuel slurry, or any combination
thereof, and the fuel slurry comprises a solid fuel and a liquid; and
maintaining the fuel slurry below an upper viscosity threshold by heating the
fuel slurry, wherein the upper viscosity threshold is at a transition between a
pumpable viscosity and an unpumpable viscosity of the fuel slurry by a slurry pump
configured to pump the fuel slurry.
19. The method of claim 18, comprising removing a portion of the liquid
from the fuel slurry to increase the solids concentration of the fuel slurry after heating
the fuel slurry.
20. The method of claim 18, comprising adding additional fuel to the fuel
slurry to increase the solids concentration of the fuel slurry after heating the fuel
slurry.