U.S. patent application number 13/836393 was filed with the patent office on 2014-09-18 for mixture and apparatus for blending non-aqueous slurries.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. The applicant listed for this patent is GENERAL ELECTRIC COMPANY. Invention is credited to Aaron John Avagliano, Thomas Frederick Leininger, Julio Zimbron Nieto, Scott Parent.
Application Number | 20140259882 13/836393 |
Document ID | / |
Family ID | 50238471 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140259882 |
Kind Code |
A1 |
Leininger; Thomas Frederick ;
et al. |
September 18, 2014 |
MIXTURE AND APPARATUS FOR BLENDING NON-AQUEOUS SLURRIES
Abstract
The disclosures described herein provide for a gasification
feedstock which includes a mixture of a solid feedstock with a
liquid feedstock. The solid feedstock includes a heating value of
less than approximately 20 Megajoules/kilogram (MJ/kg), expressed
on a wet basis. The non-aqueous liquid feedstock includes a heating
value of greater than approximately 14 MJ/kg, expressed on a wet
basis. The resulting feedstock is useful as a gasification
fuel.
Inventors: |
Leininger; Thomas Frederick;
(Chino Hills, CA) ; Nieto; Julio Zimbron; (Fort
Collins, CO) ; Parent; Scott; (Houston, TX) ;
Avagliano; Aaron John; (Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GENERAL ELECTRIC COMPANY |
Schenectady |
NY |
US |
|
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
50238471 |
Appl. No.: |
13/836393 |
Filed: |
March 15, 2013 |
Current U.S.
Class: |
44/281 ;
137/561R; 137/565.01 |
Current CPC
Class: |
C10J 3/00 20130101; Y02E
20/18 20130101; Y10T 137/85978 20150401; C10L 1/322 20130101; Y10T
137/8593 20150401; C10J 2300/1653 20130101; C10J 2300/0916
20130101; Y02E 20/16 20130101; Y02E 50/32 20130101; Y02E 50/30
20130101; C10J 2300/0926 20130101; C10J 2300/0906 20130101 |
Class at
Publication: |
44/281 ;
137/565.01; 137/561.R |
International
Class: |
C10L 1/32 20060101
C10L001/32 |
Claims
1. A gasification feedstock, comprising: a mixture comprising a
solid and a non-aqueous liquid, wherein the solid comprises a first
gross heating value less than approximately 20 Megajoules/kilogram
(MJ/kg) expressed on a wet basis, and the non-aqueous liquid
comprising a second gross heating value greater than approximately
14 MJ/kg expressed on a wet basis.
2. The gasification feedstock of claim 1, wherein the solid
comprises a moisture content of between approximately less than 90%
and approximately more than 5%.
3. The gasification feedstock of claim 1, wherein the solid is not
disposed in an aqueous slurry.
4. The gasification feedstock of claim 1, wherein the solid
comprises a biomass solid.
5. The gasification feedstock of claim 1, wherein the solid
comprises at least one of a sub-bituminous coal or lignite
coal.
6. The gasification feedstock of claim 1, wherein the non-aqueous
liquid comprises oil.
7. The gasification feedstock of claim 1, wherein the non-aqueous
liquid comprises vegetable oil, pyrolysis oil, orimulsion,
biodiesel, liquid fossil fuels, petroleum-derived liquids, or a
combination thereof.
8. The gasification feedstock of claim 1, wherein the weight
percent solids contained in the non-aqueous slurry is between
approximately 1 and 60.
9. The gasification feedstock of claim 1, wherein the mixture
comprises a slurry having a viscosity of less than 2 Pascal-seconds
(2,000 Centipoise).
10. A system, comprising: a solid feed supply configured to supply
a solid having a low gross heating value; a liquid feed supply
configured to supply a liquid having a high gross heating value; a
feedstock mixing tank coupled to the solid feed supply and the
liquid feed supply, wherein the feedstock mixing tank is configured
to mix the solid and the liquid to provide a gasification
feedstock.
11. The system of claim 10, comprising a run tank fluidly coupled
downstream of the mixing tank and upstream of a gasifier, wherein
the run tank receives the gasification feedstock from the mixing
tank and provides the gasification feedstock to the gasifier.
12. The system of claim 10, wherein the low gross heating value of
the solid is less than approximately 20 MJ/kg, and the high gross
heating value of the liquid is greater than approximately 14
MJ/kg.
13. The system of claim 10, wherein the solid comprises a biomass
solid or a low rank coal and the liquid comprises a non-aqueous
liquid.
14. The system of claim 13, wherein the solid comprises corn husks,
rice husks, switchgrass, miscanthus, sugar cane bagasse, sorghum
bagasse, wood, wood products, algae, manure, other agricultural
products, municipal solid waste, or a combination thereof, wherein
the liquid comprises vegetable oil, pyrolysis oil, orimulsion,
biodiesel, liquid fossil fuels, petroleum-derived liquids, or a
combination thereof.
15. The system of claim 11, wherein the solid feed supply comprises
a solids grinder and a solids conveyor, the liquid feed supply
comprises a first pump, the system comprises a second pump
configured to recirculate the gasification feedstock around the
mixing tank and to transfer the gasification feedstock to the run
tank, and the system comprises a third pump configured to
recirculate the gasification feedstock around the run tank and to
supply the gasification feedstock to a suction of a slurry charge
pump, wherein the slurry charge pump is configured to transfer
gasification feedstock to the gasifier.
16. The system of claim 10, wherein feedstock mixing tank comprises
a rotatable impeller, a temperature sensor, a viscosity sensor, a
moisture sensor and an internal coil for conducting a heat transfer
fluid.
17. The system of claim 10, comprising a controller configured to
adjust a ratio of the liquid and the solid to achieve a target
gross heating value, a target viscosity, or a combination thereof,
of the gasification feedstock.
18. A system, comprising: a feedstock mixing controller configured
to adjust a ratio of a liquid feedstock and a solid feedstock to
obtain a gasification feedstock, wherein the solid feedstock
comprises a first gross heating value of at least less than
approximately 20 Megajoules/kilogram (MJ/kg) expressed on a wet
basis, and the gasification feedstock has a third gross heating
value of at least greater than 16 MJ/kg expressed on a wet
basis.
19. The system of claim 18, comprising a first pump configured to
transfer the gasification feedstock from a feedstock tank to run
tank, and a second pump configured to transfer the gasification
feedstock from the run tank to a gasifier.
20. The system of claim 18, wherein the controller comprises a
moisture sensor, a viscosity sensor, a temperature sensor and a
gross heating value sensor, wherein the sensors are used to adjust
the ratio of the liquid feedstock and solid feedstock.
Description
BACKGROUND OF THE INVENTION
[0001] The subject matter disclosed herein relates to the
gasification of slurry. More specifically, disclosed embodiments of
the invention relate to the preparation and delivery of feed
slurries to a gasifier.
[0002] Fossil fuels, such as coal or petroleum, may be gasified for
use in the production of electricity, chemicals, synthetic fuels,
or for a variety of other applications. Gasification involves
reacting a carbonaceous fuel with sub stoichiometric amounts of
oxygen at high temperature and pressure to produce syngas, a
gaseous fuel containing primarily carbon monoxide and hydrogen,
which burns much more efficiently and cleaner than the fuel in its
original state.
[0003] Known gasification processes overcome the challenge of
feeding solid carbonaceous fuels, such as coal, into a high
pressure gasifier by grinding the coal to a fine powder and mixing
the powder with water to form an aqueous coal slurry that can be
transported into the gasifier using conventional process equipment
such as positive displacement pumps. Slurries which are typically
fed to a gasifier using this method must satisfy at least two
conditions. First, the fuel itself must have a relatively high
gross heating value. Second, the solids content of the aqueous
slurry must be such that the energy content of the solid fuel is
not diluted, as it were, by the presence of excessive amounts of
water.
[0004] The gross heating value is a measure of the amount of
thermal energy a fuel will release when completely reacted with
oxygen via the combustion reaction. It includes the energy released
when all of the water in the products of combustion is condensed
from vapor to liquid. Using a fuel with a relatively high gross
heating value is important for an efficient and economical
gasification process. When a carbonaceous fuel such as coal is
reacted with oxygen in a gasifier, some of the coal is fully
oxidized to carbon dioxide and water via the combustion reaction,
and some of the coal is partially oxidized to carbon monoxide and
hydrogen via several gasification reactions (e.g. reactions of H2O
and CO2 with solid carbon). The combustion reaction is exothermic,
which means it releases thermal energy. The gasification reactions
are endothermic, which means they require thermal energy input in
order to proceed. So, in an operating gasifier, carbonaceous fuel
is simultaneously combusted and gasified. The portion of the fuel
that is combusted supplies the thermal energy that drives the
gasification reactions as well as the energy that heats the
reactants--the fuel, the oxidant and the water--from ambient
temperature to the high temperature at which the reactions proceed
inside the gasifier. If the heating value of a fuel is too low, a
greater portion of the fuel must react via the combustion reaction
in order to supply sufficient thermal energy to heat the reactants
and to drive the gasification reactions. But this degrades the
product syngas composition by shifting more of the gas to carbon
dioxide and water and away from the more desirable carbon monoxide
and hydrogen products. Likewise, if a slurry contains too much
water, more fuel must react via the combustion reaction in order to
provide extra energy to heat the excess water.
[0005] Petroleum coke, anthracite and bituminous coal are examples
of fuels with high gross heating values that can be efficiently
gasified. They also can be made into aqueous slurries with
relatively high solids content, so they represent high quality
gasification fuels. In contrast, lignites and some sub bituminous
coals have lower gross heating values. In addition, many of them
may have high internal moisture content, so they produce aqueous
slurries with lower solids content. Both of these factors make
lignites and sub bituminous coals less desirable feeds for
gasifiers. Like sub bituminous coals and lignites, most biomass has
relatively low gross heating values and produces aqueous slurries
with low solids content. However, biomass is a carbon neutral,
renewable feedstock and low rank coals, such as lignite and sub
bituminous coal, are less expensive than high rank coals, such as
anthracite and bituminous coal. Accordingly, it may be desirable to
develop mixtures, systems, and methods for the gasification of low
gross heating value fuels and of high moisture content fuels,
including biomass and low rank coals.
BRIEF DESCRIPTION OF THE INVENTION
[0006] 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.
[0007] In a first embodiment, a gasification feedstock includes a
mixture of a solid having a gross heating value of less than
approximately 20 Megajoules/kilogram (MJ/kg) and a non-aqueous
liquid having a heating value of greater than approximately 14
MJ/kg expressed on a wet basis.
[0008] In a second embodiment, a system includes a solid feed
supply configured to supply a solid having a low gross heating
value and a liquid feed supply configured to supply a liquid having
a high gross heating value. The system further includes a feedstock
mixing tank coupled to the solid feed supply and the liquid feed
supply, wherein the feedstock mixing tank is configured to mix the
solid and the liquid to provide a gasification feedstock.
[0009] In a third embodiment, a system includes a feedstock mixing
controller configured to adjust a ratio of a liquid feedstock and a
solid feedstock to obtain a gasification feedstock, wherein the
solid feedstock comprises a first gross heating value of at least
less than approximately 20 Megajoules/kilogram (MJ/kg) expressed on
a wet basis, and the gasification feedstock has a third gross
heating value of at least greater than 16 MJ/kg expressed on a wet
basis.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] 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:
[0011] FIG. 1 illustrates a block diagram of an embodiment of an
integrated gasification combined cycle (IGCC) power plant, in
accordance with an embodiment of the present technique;
[0012] FIG. 2 illustrates an a solids-liquids mixing system
depicted in FIG. 1, in accordance with an embodiment of the present
technique;
[0013] FIG. 3 depicts a flow chart of a process for mixing a
non-aqueous slurry, in accordance with an embodiment of the present
technique; and
[0014] FIG. 4 depicts a flow chart continuation of the process of
FIG. 3, in accordance with an embodiment of the present
technique.
DETAILED DESCRIPTION OF THE INVENTION
[0015] 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.
[0016] 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.
[0017] The disclosed embodiments include mixtures, systems and
methods for utilizing, for example, low gross heating value solids
and high moisture content solids (e.g., biomass and high moisture
coals) as gasifier feedstock by adding high gross heating value
non-aqueous liquids (e.g., vegetable oil, pyrolysis oil,
orimulsion, biodiesel, liquid fossil fuels, petroleum-derived
liquids, and the like). The moisture content of the fuel refers to
the presence of water in the fuel and is usually measured as
percentage of water by weight. The gross heating value of a fuel is
a measure of the energy content of the fuel and is often measured
in Megajoules per kilogram (MJ/kg). Low rank coals, for example,
include coals that have low gross heating values, e.g., less than
approximately 20 MJ/kg, as expressed on a wet basis. Examples
include coals such as lignite coals and some sub-bituminous coals.
Some low rank coals may also contain high moisture content, in some
cases of approximately 20% to 40% or more by weight. Table 1 shows
typical composition and gross heating value data for delayed
petroleum coke, a bituminous coal (Illinois #6), two sub bituminous
coals (Wyodak and Montana Rosebud) and a lignite. The moisture
content of the fuels increases from left to right in the table and,
as expected, the gross heating value generally decreases with
increasing moisture content. The bottom four rows in the table show
the range of typical aqueous slurry concentrations that may be more
easily transported into a gasifier by commercially available pumps
as well as the gross heating values of the slurries at the minima
and maxima of those ranges. For delayed coke and Illinois #6 coal,
economic gasifier operation may be achieved using aqueous slurry
concentrations in the mid to upper portions of the slurry
concentration ranges. However, the gross heating values of the sub
bituminous coal and lignite slurries may be too low for economical
gasifier operation at any point within the range aqueous slurry
concentrations, in other words, at aqueous slurry gross heating
values of approximately 16 MJ/kg and below.
TABLE-US-00001 TABLE 1 Fort Delayed Illinois #6 Wyodak Montana
Union Coke Coal Coal Rosebud Lignite Carbon, wt % 88.69 58.90 47.84
50.07 39.90 Hydrogen, wt % 4.19 5.02 5.15 3.38 2.80 Oxygen, wt %
0.00 13.72 25.34 11.14 11.00 Nitrogen, wt % 2.69 0.94 0.59 0.71
0.60 Sulfur, wt % 4.00 3.13 0.30 0.73 0.90 Ash, wt % 0.43 9.89 4.08
8.19 8.60 Water, wt % 0.00 8.4 16.70 25.77 36.20 Total, wt % 100.00
100.00 100.00 100.00 100.00 GHV wet, MJ/kg 35.4 25.0 19.8 19.9 15.6
Slurry conc. Min, 59 56 51 48 43 wt % solids Slurry conc. Max, 69
66 55 54 49 wt % solids GHV slurry, min, 20.9 15.3 12.2 12.9 10.5
MJ/kg GHV slurry, max, 24.4 18.0 13.1 14.5 12.0 MJ/kg
[0018] Biomass fuels may include a wide range of fuels such as corn
husks, rice husks, switchgrass, miscanthus, sugar cane bagasse,
sorghum bagasse, wood and wood products, algae, manure, other
agricultural products, and municipal solid waste. As with low rank
coals, some biomass may contain considerable amounts of water,
ranging from approximately 5 to 30 weight percent or, even in some
cases, as high as 90 weight percent. Table 2 shows typical
composition and gross heating value data for five typical biomass
fuels. As with the coals in Table 1, moisture content increases
from left to right, with the energy content of the fuels decreasing
with increasing moisture content. In the case of rice waste, the
high ash content makes up for the lower moisture content in the
sense that ash, like moisture, dilutes the energy content of the
organic matter. Also as in Table 1, the bottom four rows in Table 2
show the range of typical aqueous slurry concentrations that may be
more reliably produced and transported into a gasifier by
commercially available pumps as well as the gross heating values of
the slurries at the minima and maxima of those ranges. Because of
the low slurry concentrations for all of the biomass fuels, the
gross heating values of all of the biomass slurries may be too low
for economical gasifier operations.
TABLE-US-00002 TABLE 2 Sugar Untreated Switch- Cane Rice Willow
grass Bagasse Waste Miscanthus Carbon, wt % 43.67 40.71 37.76 36.65
34.09 Hydrogen, wt % 5.34 5.03 4.55 4.62 3.94 Oxygen, wt % 37.79
36.26 33.42 33.64 30.10 Nitrogen, wt % 0.53 0.53 0.30 0.68 0.36
Sulfur, wt % 0.05 0.10 0.05 0.14 0.05 Ash, wt % 1.71 5.27 3.92
16.07 2.56 Water, wt % 10.90 12.10 20.00 8.2 28.90 Total, wt %
100.00 100.00 100.00 100.00 100.00 GHV wet, MJ/kg 17.3 15.8 14.7
14.2 13.5 Slurry conc. Min, 15 15 15 15 15 wt % solids Slurry conc.
Max, 40 40 40 40 40 wt % solids GHV slurry, min, 2.9 2.7 2.8 2.3
2.9 MJ/kg GHV slurry, max, 7.8 7.2 7.4 6.2 7.6 MJ/kg
[0019] As shown in Tables 1 and 2, sub bituminous coal, lignite and
biomass slurries have lower gross heating values and higher water
contents than petroleum coke and bituminous coal slurries. As
explained above, the gasification of feedstocks with low gross
heating values and high water contents may result in inefficient
and uneconomical operation of the gasifier. One way to remove
moisture is to dry the high moisture, low energy materials before
slurrying them with water. However, water removal by drying may
require a high amount of energy, which may negatively impact the
overall energy efficiency of the gasification plant. However, a
more desirable gasification feed may be produced by changing the
slurrying medium from water, which has approximately zero energy
content, to a non-aqueous liquid which can contribute energy
content to the non-aqueous slurry. (Note that the non-aqueous
liquids discussed below are referred to as having high gross
heating value even though, in some cases, they may have gross
heating values that are lower than the solid fuel component of the
slurry. The reason for this is that the gross heating values of the
non-aqueous liquids are being compared with water and not with the
solid fuels. Water has zero energy content and, thus, cannot
contribute any energy content to an aqueous slurry. However, by
virtue of having at least some measurable gross heating value, the
non-aqueous liquids are, by comparison with water, high gross
heating value liquids.)
[0020] By judiciously selecting a desirable non-aqueous liquid
slurrying medium, the non-aqueous slurry may attain a sufficient
energy and moisture combination that enables its use in regular
gasification operations. Additionally, the non-aqueous slurry may
also be more easily transported by a fluid pump instead of a dry
feed system, which may not be as efficient as the fluid pump. Table
3 shows composition and gross heating value data for four example
non-aqueous liquids which may be mixed with low gross heating value
and/or high moisture content solids in order to produce non-aqueous
slurries having sufficient energy content for economical operation
of a gasifier. The first three non-aqueous liquids are oils derived
from the pyrolysis of switchgrass, hardwood and pine. The fourth
liquid is heavy fuel oil, a readily available oil refinery
byproduct.
TABLE-US-00003 TABLE 3 Heavy Switchgrass Hardwood Pine Pyrolysis
Fuel Pyrolysis Oil Pyrolysis Oil Oil Oil Carbon, wt % 41.81 46.00
45.85 85.20 Hydrogen, wt % 4.83 5.05 5.21 11.10 Oxygen, wt % 22.16
28.20 30.95 1.00 Nitrogen, wt % 0.85 0.13 0.17 0.30 Sulfur, wt %
0.08 0.02 0.02 2.30 Ash, wt % 0.07 0.00 0.00 0.00 Water, wt % 30.20
20.60 17.80 0.10 Total, wt % 100.00 100.00 100.00 100.00 GHV wet,
MJ/kg 18.1 18.6 18.7 40.0
[0021] Tables 4A and 4B show some representative results that may
be obtained by mixing two of the non-aqueous liquids from Table 3
with each of the biomass fuels from Table 2 and the sub bituminous
coals and lignite from Table 1. Table 4B is a continuation of table
4A but with additional columns. Just the highest gross heating
value liquid (heavy fuel oil, or HFO) and the lowest gross heating
value liquid (switchgrass pyrolysis oil, or SPO) were chosen for
inclusion in Tables 4A and 4B in order to limit the size of the
tables. It is to be understood, that in other embodiments, other
values may be chosen. The first row of numbers shows the gross
heating value for each of the solid feedstocks expressed on a wet
basis. The second, third and fourth rows of numbers show the gross
heating value for heavy fuel oil, an example solids concentration
of the solids-HFO slurry and the resulting solids-HFO slurry gross
heating value for each one of the solid feedstocks. The fifth,
sixth and seventh rows of numbers show a similar set of data for
switchgrass pyrolysis oil and solids-SPO slurry.
TABLE-US-00004 TABLE 4A Untreated Switch- Sugar Cane Rice Willow
grass Bagasse Waste Solids GHV wet, Btu/lb 17.3 15.8 14.7 14.2 HFO
GHV wet, Btu/lb 40.0 40.0 40.0 40.0 HFO Slurry conc, wt % 50 50 50
50 solids HFO Slurry, Btu/lb 28.6 27.9 27.3 27.1 SPO GHV wet,
Btu/lb 18.1 18.1 18.1 18.1 SPO Slurry conc, wt % 50 50 50 50 solids
SPO Slurry, Btu/lb 17.7 17.0 16.2 16.2
TABLE-US-00005 TABLE 4B Fort Wyodak Montana Union Miscanthus Coal
Rosebud Lignite Solids GHV wet, Btu/lb 13.5 19.8 19.9 15.6 HFO GHV
wet, Btu/lb 40.0 40.0 40.0 40.0 HFO Slurry conc, wt % 50 50 50 50
solids HFO Slurry, Btu/lb 26.8 29.9 29.9 27.8 SPO GHV wet, Btu/lb
18.1 18.1 18.1 18.1 SPO Slurry conc, wt % 46 50 50 50 solids SPO
Slurry, Btu/lb 16.0 19.0 19.0 16.8
[0022] For both sets of examples slurries, a 50 wt % solids slurry
concentration was assumed based on preliminary laboratory results
that suggest that slurry concentrations of at least 50 wt % solids
may be achieved when mixing solid fuels with non-aqueous liquids to
form a slurry. As a consequence of the relatively high slurry
solids concentration, the non-aqueous slurries based on heavy fuel
oil, which has a high gross heating value, all may surpass the
minimum gross heating value target of approximately 16 MJ/kg. But
even the switchgrass pyrolysis oil, which has only 45% of the gross
heating value of the heavy fuel oil, is able to make non-aqueous
slurries with 50 wt % solids that have slurry gross heating values
above the approximately 16 MJ/kg target--with an exception,
miscanthus. For miscanthus, the solids concentration may be
slightly decreased to approximately 46 wt % solids in order to
reach the approximately 16 MJ/kg target. Nevertheless, in most
cases, the use of non-aqueous liquids to produce non-aqueous
slurries results in gasifier feedstocks of sufficient energy
content to allow low gross heating value and/or low moisture
content solids such as biomass, sub bituminous coal and lignite to
be more efficiently and economically gasified. Given the results of
preliminary laboratory results that suggest that non-aqueous
slurries may be produced with solids concentrations as high as 60
wt %, it may be possible to tailor non-aqueous slurries with solids
concentrations ranging from 1 wt % to as much as 60 wt %
solids.
[0023] In the production of such non-aqueous slurries, certain
mixing and delivery embodiments may include a mixing tank, a run
tank, a set of pumps, interconnecting piping and control valves, a
series of sensors associated with the tanks, pumps, piping and
control valves, and a controller. Controller embodiments may manage
the supply of solids and liquids into a mixing tank to achieve an
approximate ratio of solid to liquid, the mixing of the solids and
the liquids into a non-aqueous slurry, the delivery of the
non-aqueous slurry into the run tank, which provides storage
capacity within the system, and the pressurization and delivery of
the non-aqueous slurry into a gasifier. The non-aqueous slurry
embodiments may be produced by mixing low gross heating value
solids and high gross heating value liquids at a ratio that may be
derived from the energy content of the solids, the energy content
of the non-aqueous liquids, and the moisture content of the solids,
as discussed in more detail below. After the slurry is mixed, it
may be delivered into a gasifier for use, for example, in a power
generation system.
[0024] With the foregoing in mind and turning now to FIG. 1, the
figure is a diagram of an embodiment of an integrated gasification
combined cycle (IGCC) system 10 that may be powered by syngas.
Components of the IGCC system 10 may include a feedstock mixing
system 12 which may be used to produce a fuel for the IGCC system
10. The feedstock mixing system 12 may mix low gross heating value
or high moisture content solid feedstock supplied by the solid
supply 14 and high gross heating value non-aqueous liquid feedstock
supplied by the liquid supply 15 into a non-aqueous slurry fuel as
explained in more detail below in relation to FIG. 2. As mentioned
above, the solid supply 14 may include biomass fuel. Biomass fuels
may include a wide range of fuels such as, but not limited to, corn
husks, rice husks, switchgrass, miscanthus, sugar cane bagasse,
sorghum bagasse, wood, wood products, algae, manure, other
agricultural products, and municipal solid waste. Indeed, biomass
fuels may vary in moisture content from approximately less than 1%
moisture content to approximately 90% moisture content expressed on
a wet basis. Similar numbers may be derived for dry basis. Biomass
fuels may also vary in heating value, ranging from approximately 5
MJ/kg to upwards of approximately 20 MJ/kg.
[0025] The non-aqueous slurry may be pumped to a gasifier 16 from
the feedstock mixing system 12 by using pump 18. Pump 18 may
include any class of pump designed for handling non-aqueous
slurries including, but not limited to, positive displacement pumps
and progressive cavity pumps. The gasifier 16 may convert the
non-aqueous slurry into syngas, a combination consisting primarily
of carbon monoxide and hydrogen, but also containing carbon dioxide
and water with lesser amounts of methane, nitrogen, argon, hydrogen
sulfide, carbonyl sulfide and ammonia, plus trace components that
depend on the composition of the non-aqueous slurry feed. This
conversion may be accomplished by reacting the non-aqueous slurry
with a controlled amount of steam or liquid water and an oxidant,
such as oxygen, air or oxygen-enriched air, at elevated pressures
(e.g., from approximately 400 psi-1250 psi) and temperatures (e.g.,
approximately 2200.degree. F.-2700.degree. F.), depending on the
type of gasifier 16 utilized. At the high temperatures prevailing
inside the gasifier, essentially all of the non-aqueous slurry may
be converted to syngas. However, depending upon gasifier operating
conditions, such as the ratio of oxygen in the oxidant to carbon in
the slurry, some unconverted slurry may remain in the form of soot,
or char, which may contain some carbon along with some of the ash
material present in the feedstock. The amount of carbon exiting the
gasifier in the form of soot or char may vary from 0 to 10 weight
percent of the carbon in the feed slurry depending upon the
operation conditions of the gasifier. The remainder of the ash
material present in the feedstock may exit the gasifier in the form
of slag 20.
[0026] As a result of the reactions that occur inside the gasifier
16, a resultant gas may be manufactured by the gasifier 16. The
resultant gas may include approximately 60 to 90 volume percent of
carbon monoxide and hydrogen, as well as CO2, H2O, CH.sub.4, N2,
Ar, H2S, COS, NH.sub.3, trace amounts of other compounds that
depend on the composition of the feedstock and unconverted
feedstock in the form of soot or char. This resultant gas may be
termed "untreated syngas." The gasifier 16 may also generate
byproduct solids, such as slag 20, which may be a wet ash material.
As described in greater detail below, a gas treatment unit 22 may
be utilized to treat the untreated syngas. The gas treatment unit
22 may scrub the untreated syngas to remove the soot or char, the
NH.sub.3 and the sulfur compounds from the untreated syngas, which
may include separation of sulfur 28 in a sulfur processor 30 by,
for example, an acid gas removal process in the sulfur processor
30. Furthermore, the gas treatment unit 22 may separate salts 24
from the untreated syngas via a water treatment unit 26, which may
utilize water purification techniques to generate usable salts 24
from the untreated syngas. Subsequently, a treated syngas may be
generated from the gas treatment unit 22.
[0027] The IGCC system 10 may further include an air separation
unit (ASU) 40. The ASU 40 may separate air 19 into component gases
using, for example, distillation techniques. The ASU 40 may
separate oxygen from the air supplied to it from an air compressor
42 and may transfer the separated oxygen to the gasifier 16.
Additionally, the ASU 40 may direct separated nitrogen to a diluent
gaseous nitrogen (DGAN) compressor 44. The DGAN compressor 44 may
compress the nitrogen received from the ASU 40 at least to pressure
levels equal to those in the combustor 36, for use in enhancing
combustion of the syngas. Thus, once the DGAN compressor 44 has
adequately compressed the nitrogen to an adequate level, the DGAN
compressor 44 may direct the compressed nitrogen to the combustor
36 of the gas turbine engine 38.
[0028] As described above, the compressed nitrogen may be
transferred from the DGAN compressor 44 to the combustor 36 of the
gas turbine engine 38. The gas turbine engine 38 may include a
turbine 46, a drive shaft 48, and a compressor 50, as well as the
combustor 36. The combustor 36 may receive fuel, such as the
syngas, which may be injected under pressure via fuel nozzles. This
fuel may be mixed with compressed air from a compressor 50 as well
as compressed nitrogen from the DGAN compressor 44 and combusted
within the combustor 36. This combustion may create hot pressurized
exhaust gases.
[0029] The combustor 36 may direct the exhaust gases towards an
exhaust outlet of the turbine 46. As the exhaust gases from the
combustor 36 pass through the turbine 46, the exhaust gases may
force turbine blades in the turbine 46 to rotate the drive shaft 48
along an axis of the gas turbine engine 38. As illustrated, the
drive shaft 48 may be connected to various components of the gas
turbine engine 38, including the compressor 50.
[0030] The compressor 50 may include blades coupled to the drive
shaft 48. Thus, rotation of turbine blades in the turbine 46 may
cause the drive shaft 48 connecting the turbine 46 to the
compressor 50 to rotate blades within the compressor 50. The
rotation of blades in the compressor 50 causes the compressor 50 to
compress air received via an air intake in the compressor 50. The
compressed air may then be fed to the combustor 36 and mixed with
fuel and compressed nitrogen to allow for higher efficiency
combustion. The drive shaft 48 may also be connected to a load 52,
which may be a stationary load, such as an electrical generator,
for producing electrical power in a power plant. Indeed, the load
52 may be any suitable device that is powered by the rotational
output of the gas turbine engine 38.
[0031] The IGCC system 10 also may include a steam turbine engine
54 and a heat recovery steam generation (HRSG) system 56. The steam
turbine engine 54 may drive a second load 58, such as an electrical
generator for generating electrical power. However, both the first
and second loads, 52 and 58, may be other types of loads capable of
being driven by the gas turbine engine 38 and the steam turbine
engine 54, respectively. In addition, although the gas turbine
engine 38 and the steam turbine engine 54 may drive separate loads,
52 and 58, as shown in the illustrated embodiment, the gas turbine
engine 38 and the steam turbine engine 54 may also be utilized in
tandem to drive a single load via a single shaft. The specific
configuration of the steam turbine engine 54, as well as the gas
turbine engine 38, may be implementation-specific and may include
any combination of sections.
[0032] Heated exhaust gas from the gas turbine engine 38 may be
directed into the HRSG 56 and used to heat water and produce steam
used to power the steam turbine engine 54. Exhaust from the steam
turbine engine 54 may be directed into a condenser 60. The
condenser 60 may utilize a cooling tower 62 to exchange heated
water for chilled water. In particular, the cooling tower 62 may
provide cool water to the condenser 60 to aid in condensing the
steam directed into the condenser 60 from the steam turbine engine
54. Condensate from the condenser 60 may, in turn, be directed into
the HRSG 56. Again, exhaust from the gas turbine engine 38 may also
be directed into the HRSG 56 to heat the water from the condenser
60 and produce steam.
[0033] As such, in combined cycle systems such as the IGCC system
10, hot exhaust may flow from the gas turbine engine 38 to the HRSG
56, where it may be used to generate high-pressure,
high-temperature steam. The steam produced by the HRSG 56 may then
be passed through the steam turbine engine 54 for power generation.
In addition, the produced steam may also be supplied to any other
processes where steam may be used, such as to the gasifier 16. The
gas turbine engine 38 generation cycle is often referred to as the
"topping cycle," whereas the steam turbine engine 54 generation
cycle is often referred to as the "bottoming cycle." By combining
these two cycles as illustrated in FIG. 1, the IGCC system 10 may
lead to greater overall efficiencies in the plant. In particular,
exhaust heat from the topping cycle may be captured and used to
generate steam for use in the bottoming cycle.
[0034] Turning to FIG. 2, the figure illustrates an embodiment of
the feedstock mixing system 12 shown previously in FIG. 1. In the
illustrated embodiment, the mixing system 12 may include a mixing
tank 64 that may be used to mix batches of the non-aqueous slurry,
e.g., mixtures of the low gross heating value solid feedstock
(e.g., biomass or low rank coal) and the high gross heating value
non-aqueous liquid feedstock (e.g., vegetable oil, pyrolysis oil,
orimulsion, biodiesel, liquid fossil fuels, petroleum-derived
liquids) and a run tank 65 that may be used to continuously supply
non-aqueous slurry via recirculation pump 81 and charge pump 18 to
gasifier 16 in FIG. 1 during operations. The low gross heating
value solids are delivered into a grinder 66 by the solid supply
14. The grinder 66 may be controlled by controller 68, for example,
to resize or to reshape the solids by crushing, shearing, chopping,
milling, shredding, or pulverizing the solids in order to generate
a particulate solid feedstock having a desired particle size
distribution. The resized or reshaped solids may have a particle
size distribution where at least 99% of the particles are smaller
than 5 mm in diameter. Alternatively, the solids may have a
particle size distribution where at least 98-100% of the particles
are smaller than 1.5 mm, at least 95-100% of the particles are
smaller than 0.42 mm and at least 25-35% of the particles are
smaller than 0.044 mm. As discussed below, the disclosed
embodiments do not use solid feedstock alone or mix the solid
feedstock with water to generate an aqueous slurry. A low gross
heating value, non-mixed solid fuel or water-based slurry fuel may
not have enough energy content to convert efficiently to syngas in
a gasifier. Moreover, a high moisture solid fuel or water-based
slurry fuel may require additional energy to preheat and vaporize
the excess moisture in the fuel once inside the gasifier. This
extra energy requirement for low gross heating value and low
moisture content fuels results in gasifier yields of carbon
monoxide and hydrogen that may be too low to be economical.
Accordingly, the feedstock mixing system 12 may employ the high
gross heating value non-aqueous liquid to add to the low gross
heating value solid feedstock in order to produce a non-aqueous
slurry fuel with sufficient energy content to support efficient
gasification. The resulting non-aqueous slurry fuel may have a
lower moisture percentage than that of the low gross heating value
solid feedstock, may have a higher energy content than that of the
low gross heating value solid feedstock, may be transportable by
using appropriately designed slurry pumps, and may be used as
feedstock for a gasifier, such as the gasifier 16 show in FIG. 1
above.
[0035] The non-aqueous slurry may be produced by the feedstock
mixing system 12 which may be controlled by the controller 68. The
high gross heating value non-aqueous liquid feedstock may be added
first to the mixing tank by a pump 70 in order to establish an
initial level or weight of liquid to which the solids may
subsequently be added. Controller 68 may employ one or more sensors
78 to determine when the initial level or weight target has been
achieved. Controller 68 may then energize motor 74 to begin
rotation of mixer 76. The design of mixer 76, may have one or more
sets of mixing blades connected to the same shaft at different
elevations along the length of the shaft. The number of blade sets,
the number of blades in each set and the size and shape of each
blade may chosen so that rotation of mixer 76 by motor 74 more
thoroughly stirs the contents of mixing tank 64, establishes
vertical recirculation patterns within the stirred contents which
aid in the mixing of the solids and the non-aqueous liquid and
minimizes the settling and/or accumulation of solids in the bottom
or along the vertical sidewall of mixing tank 64. Mixing tank 64
may also be configured with one or more vertical baffles (not
shown) extending radially inwards from the vertical sidewall of
mixing tank 64. After the controller 68 has started mixer 76, the
controller 68 may also close block valve 73, open block valve 71
and start pump 80 in order to establish a recirculating flow of
non-aqueous liquid around tank 64 via the pathway that includes the
discharge of pump 80 and valve 71. The recirculation flow may turn
over the contents of tank 64 in approximately 1 hour, in 30
minutes, in 15 minutes or in 5 minutes in order to assist mixer 76
with the stirring of the tank contents and with the prevention of
solids settling once solids are added to the tank. Once the initial
liquid level or weight has been established and the mixer 76 and
the pump 80 started, solid feedstock processed by the grinder 66
may then be conveyed into the mixing tank by using a solid
feedstock conveyor 77. As the solids enter the stirred and
recirculating pool of liquid within mixing tank 64, they may become
thoroughly mixed with the liquid by action of the mixer 76 and the
recirculation flow maintained by pump 80. In one embodiment, the
controller 68 may employ the solids conveyor 77, pump 70 and one or
more sensors 78 to control the volume and/or the weight of each of
the solid feedstock and the non-aqueous liquid feedstock to add to
the mixing tank 64 in order to achieve an initial approximate
solids-to-liquid ratio. In this embodiment, the controller 68 may
then employ one or more additional sensors 78 to measure one or
more properties of the initial mixture such as moisture content,
gross heating value, viscosity, density and so forth, and then use
the results to derive an actual as-mixed solid-to-liquid ratio. The
ratio may be derived by the controller 68 based on several
variables, including the gross heating value of the solid
feedstock, the moisture content of the solid feedstock, the
viscosity of the mixture, the temperature of the mixture, the
density of the mixture, the heating value of the non-aqueous
liquid, and so forth. In another embodiment, the variables that may
be used for the determination of the solid-to-liquid ratio may be
entered into the controller manually, for example, from the results
of lab tests done on grab samples obtained from the mixing tank or
from the recirculation line. For example, results from off-line
analyses for moisture content, gross heating value, viscosity,
weight percent solids, density and so forth, may be entered into
the controller 68 manually, for example, by typing the values into
a keyboard. In yet another embodiment, the ratio of solid to liquid
fuel may be entered directly in the controller 68, for example by
typing the ratio into a keyboard.
[0036] Once the initial as-mixed solids-to-liquid ratio has been
determined, the controller 68 may compare the actual, as-mixed
solids-to-liquid ratio with a target solids-to-liquid ratio in
order to determine the size of the deviation, if any, from the
target ratio. Depending upon the magnitude of the deviation, for
example 2%, 1%, 0.5% or 0.1%, the controller may calculate an
additional amount of solids and/or an additional amount of liquid
to be added to the slurry in order to reach the target ratio after
which the controller may add the calculated amount of additional
solids via conveyor 77 or additional non-aqueous liquid via pump
70. In one embodiment, this procedure of calculating a deviation
from a target solids-to-liquid ratio followed by making an
appropriate adjustment, either by adding more solids or more
liquid, may occur one time. In another embodiment, this "calculate
deviation-make adjustment procedure" may occur "N" number of times,
where "N" is an integer entered into controller 68, for example, by
typing into a keyboard. In yet another embodiment, the "calculate
deviation-make adjustment procedure" may occur as many times as
needed to reduce the magnitude of the deviation to a predetermined
level, for example to 2%, 1%, 0.5% or 0.1%.
[0037] Once the target solid-to-liquid ratio has been achieved in
mix tank 64, the controller 68 may open block valve 73 and close
block valve 71 to transfer the completed batch of slurry from
mixing tank 64 to run tank 65 via pump 80. Once the transfer is
complete, the above procedure may be repeated in order to make
another batch of slurry. Run tank 65 may be the same size as mixing
tank 64, or it may be larger, and in limited cases, smaller. In
either case, the rate at which batches of slurry can be mixed and
adjusted to a target solids-to-liquid ratio may be greater than the
maximum rate at which slurry can be withdrawn from run tank 65 and
fed to the gasifier 16 via slurry charge pump 18. This ability of
system 12 to produce a non-aqueous slurry mixture faster than the
mixture is fed to the gasifier ensures that run tank 65 will rarely
or ever run dry and the gasifier 16 will rarely or ever be deprived
of slurry during operation. Run tank 65 is equipped with a motor 75
and a mixer 79 which are similar in design and function to the
motor 74 and mixer 76 in mixing tank 64. Controller 68 may start
motor 75 as soon as an initial batch of slurry has been transferred
into run tank 65 in order to maintain the transferred slurry in a
thoroughly mixed state. Thereafter, controller 68 may continue
operation of mixer 79 as long as there is any slurry within run
tank 65. One or more level or weight sensors 72 may provide
controller 68 with the required information about the level or
weight of slurry within run tank 65 at operational times. If run
tank 65 is full, as determined, for example, by one of the level or
weight sensors 72, the controller 68 may close block valve 73 and
open block valve 71 to prevent any more slurry from being
transferred from mixing tank 64 to run tank 65. In addition,
controller 68 may also direct solids conveyor 77 and liquid pump 70
to at least temporarily cease delivering more solids and more
liquid, respectively, into mixing tank 64 in order to at least
temporarily halt production of more slurry until such time as
additional slurry is needed to maintain sufficient level or weight
in run tank 65.
[0038] Run tank 65 is also equipped with a slurry recirculation
pump 81 which recirculates slurry around run tank 65 in order to
assist mixer 79 in maintaining the slurry in a thoroughly mixed
state. The configuration of the recirculation line, e.g. pipe
diameter and control valves (not shown), from the discharge of pump
81 back to the top of run tank 65 as well as the configuration of
the slurry charge pump 18 suction line, e.g. pipe diameter and
control valves (not shown), may be such that the flow rate in the
recirculation line may be approximately 5 to 10 times larger than
the flow rate of slurry to charge pump 18. This may ensure that the
suction of charge pump 18 is always or almost always filled with an
adequate supply of slurry. Once run tank 65 has been filled with a
supply of slurry sufficient to start the gasifier 16, charge pump
18 may be started in order to deliver the non-aqueous slurry for
use in the gasifier 16 as described above with respect to FIG. 1.
Charge pump 18 may be any type of pump that is suitable for pumping
slurries to high pressure such as a positive displacement pump, a
progressing cavity pump or the like.
[0039] In the embodiment described above, solid or semi-solid
material and at least one non-aqueous liquid are mixed in order to
produce the desired non-aqueous slurry. However, in another
embodiment, any number of solid and liquid fuels may be added for
mixing, for example, switchgrass, cornhusks, pyrolysis oil, and
fuel oil. In yet another embodiment, the non-aqueous liquid may be
solid or highly viscous at room temperature. For such cases, mixing
tank 64 may be fitted with a control valve and a heat transfer coil
67 through which flows a heat transfer fluid from a heat transfer
fluid source (HTFS) to a heat transfer fluid return (HTFR). The
heat transfer fluid may include, but not be limited to, hot water,
low pressure steam, high pressure steam and hot heat transfer oil.
Likewise, run tank 65 may be fitted with a control valve and heat
transfer coil 69 having a similar design and function. In such
cases, the non-aqueous liquid would be delivered to mixing tank 64
via pump 70 from a heated source of non-aqueous liquid. Both mixing
tank 65 and run tank 65 would be insulated, and the heat transfer
coils 67 and 69 would be designed to maintain a desired temperature
in the mixing tank 64 and the run tank 65 sufficient to ensure that
the viscosity of the non-aqueous liquid and the viscosity of the
non-aqueous slurry were within a range of values that could be
handled by pumps 80, 81 and 18. Using one or more temperature
sensors 78 in mixing tank 64 and its recirculation line and one or
more temperature sensors 72 in run tank 65 and its recirculation
line, controller 68 may adjust the amount of heating provided by
coil 67 and/or by coil 69 to maintain the temperature and, thus,
the viscosity of the contents of each tank at the desired
level.
[0040] Turning to FIG. 3, the figure depicts the first half of a
flowchart of an embodiment of a process 82 (e.g., control logic)
that may be used, for example, by the controller 68 shown in FIG.
2, to mix solid fuel with liquid fuel so as to produce a fuel
slurry. At block 84, several suitable parameters may be provided to
the control logic 82 including liquid fuel data 86 (e.g. elemental
composition, ash content, moisture content and viscosity as a
function of temperature), solid fuel data 88 (e.g. elemental
composition, ash content and moisture content), the minimum
acceptable gross heating value of the mixed fuel slurry 90, the
maximum acceptable gross heating value of the mixed fuel slurry 92,
the maximum acceptable mixed fuel slurry viscosity 94, the mixed
fuel slurry temperature target 96 and the maximum number of mixture
adjustment iterations 98 that will be allowed by the control logic
during the production of a single batch of mixed fuel slurry. These
parameters may be provided to the control logic at block 84 by, for
example, typing values into a keyboard or they may be provided by
another controller or computer via a suitable connection, such as
an Internet connection, an Ethernet cable or a wireless connection.
Certain other parameters used by the control logic 82 to perform
its intended function may already be programmed into the control
logic 82. Examples include, but are not limited to, system
geometrical parameters such as the volumes of the mixing tank 64
and the run tank 65, the tare weights of the mixing tank 64 and the
run tank 65, the locations of the high and low fill levels for both
the mixing tank 64 and the run tank 65, the speed settings of pumps
80, 81 and 18, the speed settings of mixers 76 and 79 and so forth.
In addition, the control logic may contain code for calculating the
gross heating value of the liquid fuel, the solid fuel and the
solid-liquid fuel slurry mixture from the elemental compositions of
the liquid and solid fuel feedstocks. For example, the Dulong
formula (Equation 1) enables the gross heating value (GHV) in
MJ/kg, dry basis, to be calculated from the mass fractions of
carbon (C), hydrogen (H), oxygen (O) and sulfur (S) in the fuel,
where all mass fractions are expressed on a dry basis.
GHV=33.86C+144.4(H--O/8)+9.428S (Equation 1)
Other GHV equations may also be used, some having been derived
especially for calculating the gross heating value of biomass or
for other types of fuels. The gross heating value of a fuel
expressed on a wet basis can be calculated from the gross heating
value of the fuel expressed on a dry basis using Equation 2, in
which M is the mass fraction of moisture (water) in the wet
fuel.
GHV.sub.wet=GHV.sub.dry(1-M) (Equation 2)
[0041] In addition to the above input data and GHV equations,
control logic 82 may also contain code which, using the principals
of mass balance, allows control logic 82 to calculate initial
estimates of the quantities of liquid fuel and solid fuel that must
be added to mixing tank 64 in order to produce the desired quantity
of final mixed slurry with a gross heating value that falls within
the range of acceptable values defined by the minimum GHV 90 and
the maximum GHV 92. Once estimates for the initial quantities of
liquid fuel and solid fuel have been calculated by control logic
82, an initial mass of liquid fuel may be added (block 100) to, for
example, a mixing tank. Once the liquid fuel has been added, a
mixer and a recirculation pump may be started (block 102) to
provide a well stirred liquid into which the initial mass of solid
fuel may then be added (block 104). Once the initial masses of
solid fuel and liquid fuel have been added, the process 82 may
continue via the connector 105 labeled A at the bottom of FIG. 3 to
the connector 105 labeled A at the top of FIG. 4. Continuing
process 82, the solid and liquid fuels may be mixed and
recirculated (block 106). Mixing and recirculation may occur for a
preset period of time that may have been programmed or otherwise
entered into the control logic 82. The preset time may be
determined empirically by making a trial batch of slurry either in
the plant or in an analytical laboratory.
[0042] FIG. 4 depicts an embodiment of a continuation of the
process 82 shown in FIG. 3. Once mixing and recirculation has
proceeded for the preset period of time, the process 82 may then
test the slurry (i.e., liquid-solid mixture) at decision point 108
to determine the slurry's gross heating value. It is to be
understood that slurry may be collected for testing of the gross
heating value at different physical locations within, for example,
the mixing tank 64 (e.g., bottom of the tank, top of the tank, left
wall of the tank, right wall of the tank) or along the
recirculation line. Each location sample may be tested and the
results of the tests may be averaged in order to arrive at a
heating value representative of the slurry.
[0043] In an alternative embodiment, the gross heating value of the
slurry may be measured online by a sensor located, for example, on
the recirculation line or at one or more points in the mixing tank.
If, after mixing the initial masses of liquid and solid fuels, the
slurry has a measured gross heating value that falls within the
range of values defined by the minimum and maximum desired values
(90 and 92 respectively), the process 82 moves on to the check
slurry viscosity decision point 116. However, if the slurry does
not have a gross heating value that falls between the minimum 90
and maximum 92 acceptable values, then the process 82 may adjust
the slurry, for example, by adding liquid fuel (block 110) or by
adding solid fuel (block 112). Liquid fuel may be added (block 110)
if the slurry gross heating value testing or sensing determines
that the slurry has too low of a gross heating value. Solid fuel
may be added (block 112) if the slurry gross heating value testing
or sensing determines that the slurry has too high of a gross
heating value. After the addition of the fuel, the process 82 may
again mix and recirculate (block 106) the slurry for a preset
period of time followed by a repeat determination of the slurry's
gross heating value at decision point 108. Each time that the
process 82 proceeds from the mix and recirculate step 106 to the
check slurry GHV decision point 108, a loop counter is checked and
incremented (decision point 114) within the control logic 82 in
order to keep track of the number of times through the loop, i.e.
the number of slurry GHV adjustment iterations. The control logic
82 allows the process to continue to cycle through the slurry GHV
adjustment loop until either the measured gross heating value of
the slurry falls between the minimum 90 and maximum 92 acceptable
values or the number of cycles, i.e. the number of iterations,
equals or exceeds the maximum allowable iterations, N, that was
input at block 98.
[0044] The loop counter (decision point 114) limits the number of
slurry adjustment iterations that may be made by the control logic
82 in order to prevent the system from becoming stuck in an endless
loop. When the checked number of iterations at decision point 114
equals or exceeds the maximum allowable iterations, N, the control
process 82 skips to decision point 116 to check the slurry
viscosity. However, it should be appreciated that, because the
control program 82 has an updated GHV measurement following each
slurry GHV adjustment iteration, each iteration represents a
refinement of the previous set of fuel addition and mixing steps.
Thus, it may be expected that the number of iterations required to
produce a fuel slurry with a GHV falling within the acceptable
range will be limited to no more than one or two or three
iterations. The value for N can be determined empirically in the
plant for a given set of liquid and solid feedstocks and adjusted
as needed (block 98). For example, the minimum gross heating value
may be approximately 1%, 2%, 3%, 4%, 5% below the target GHV.
Alternatively, the minimum GHV may be about 2% or 0.5% or 0.1%
below the target GHV. Likewise, the maximum gross heating value may
be approximately 1%, 2%, 3%, 4%, 5% above the target GHV.
Alternatively, the maximum GHV may be about 2% or 0.5% or 0.1%
above the target GHV. It should also be appreciated that, the
description of a preset mixing and recirculation time (blocks 102
and 106) does not mean that mixing and/or recirculation are stopped
at the end of the specified time period. Instead, mixing and
circulation may continue at all times that liquid is present in the
mixing tank 64. The preset mixing and recirculation time merely
refers to time that must elapse before the control logic 82
proceeds from step 102 to step 104 or from step 106 to step 114. In
fact, for both the mixing tank 64 and run tank 65 in FIG. 2, mixing
and recirculation may occur whenever any liquid is in either one of
the tanks.
[0045] Once the process 82 has produced a mixed fuel slurry with a
gross heating value within the acceptable range of values, or once
the number of iterations has reached the maximum allowable number
N, the process may then test the slurry at decision point 116 to
determine the slurry's viscosity to ensure that the slurry can be
handled by downstream processing equipment. As mentioned above, it
is to be understood that slurry may be collected for testing of the
viscosity at different physical locations within, for example, the
mixing tank 64 (e.g., bottom of the tank, top of the tank, left
wall of the tank, right wall of the tank) or along the
recirculation line. Each location sample may be tested and the
results of the various tests may be averaged in order to arrive at
a viscosity representative of the slurry. In an alternative
embodiment, the viscosity of the slurry may be measured on line by
a sensor located on the recirculation line or at one or more points
in the mixing tank. If the slurry's viscosity is below the maximum
desired slurry viscosity (block 94), the control process 82 moves
on to the check moisture content at decision point 120. However, if
the slurry viscosity is above the maximum desired slurry viscosity,
the control logic 82 calculates an appropriate amount of additional
liquid fuel to add to the mix in order to reduce the slurry
viscosity, loops back to add this additional amount of liquid fuel
(block 110) and then once again mixes and recirculates for a preset
period of time (block 106).
[0046] Once the preset mixing and recirculation time has been
computed for the viscosity adjustment, the controller 82
automatically returns to decision point 116 to recheck the slurry
viscosity. It does this because, when it checked the viscosity the
first time, the controller 82 also set the number of iterations to
the maximum number, N, in order to disable the GHV adjustment loop
by bypassing it. Thus, at this point in the process, the control
logic 82 will only check and adjust viscosity. This is done
because, while it is beneficial to get the GHV of the slurry within
the desired range, it may be more beneficial that the slurry
viscosity not exceed the maximum allowable value in order to avoid
problems (e.g. plugging or high pressure drop or low flow rates)
with slurry that may be too thick (viscosity too high) for the
downstream equipment (e.g. pumps, piping or gasifier feed injector)
to handle. Thus, the control logic 82 may ensure that the maximum
allowable viscosity is not exceeded at the expense of possibly
adding too much liquid fuel, which may raise the slurry gross
heating value above the desired target range by a small amount. The
maximum allowable slurry viscosity may be approximately 2
Pascal-seconds (2000 Centipoise). Alternatively, the maximum
allowable slurry viscosity may be approximately 1 Pascal-seconds
(1000 Centipoise) or 0.7 Pascal-seconds (700 Centipoise).
[0047] It should also be noted that the system 82 may adjust the
temperature (and, thus, the viscosity) of the contents of the
mixing tank 64 (block 118), for example, by adjusting the flow rate
of heat transfer fluid through the internal heating coil 67.
Adjusting the temperature in mixing tank 64 may impact the
viscosity of the liquid fuel and the viscosity of the slurry.
Increasing the temperature in the tank may decrease the viscosity;
decreasing the temperature in the tank may increase the viscosity.
Using the data on liquid fuel viscosity as a function of
temperature that was entered at block 86, the system 82 may adjust
the temperature (and, thus, the viscosity) during the mixing and
recirculation that occurs after the initial mass of liquid fuel has
been added to tank 64 (block 100) and/or during the mixing and
recirculation that occurs during the GHV and/or viscosity
adjustment steps (block 106). By using the ability to increase the
temperature of the tank 64 contents, the system 82 may decrease the
viscosity to an acceptable level while minimizing or eliminating
the need to add additional liquid fuel.
[0048] Once the system 82 has generated a slurry mixture with a
gross heating value that falls within the desired range and has
adjusted the viscosity, if needed, to ensure that the slurry is not
too thick, the system may test the slurry for moisture content, M
(block 120). As with the GHV and the viscosity, it is to be
understood that slurry may be collected for testing of the moisture
content at different physical locations within, for example, the
mixing tank 64 (e.g., bottom of the tank, top of the tank, left
wall of the tank, right wall of the tank) or along the
recirculation line. Each location sample may be tested and the
results of the various tests may be averaged in order to arrive at
a viscosity representative of the slurry. In an alternative
embodiment, the moisture content of the slurry may be measured on
line by a sensor located on the recirculation line or at one or
more points in the mixing tank. The moisture content of the slurry
may be something that needs to be known for gasifier operation but
not necessarily something that may need to be manipulated by the
control logic 82 in the slurry mixing system 12. Typically, a
certain amount of water may be fed to the gasifier during gasifier
operations in order to help control gasifier operating temperature,
e.g., to help keep it from going too high. Water also may provide
some of the oxygen that partially oxidizes the fuel during
gasification, thereby reducing the gaseous oxygen feedstock
requirement. However, water may be fed to the gasifier
independently of the slurry mixing and feed system via a separate
conduit connected to the gasifier feed injector; so there may be an
independent means of controlling the amount of water that is fed to
a gasifier. Therefore, in practical operation of the present
techniques, the slurry that is prepared by mixing system 12 may be
prepared with a moisture content that exactly matches the needs of
the gasifier during operation. In that case, no additional water
may need to be fed to the gasifier. Alternatively, the slurry may
be prepared with a moisture content that is lower than that which
may be needed by the gasifier during operation. In that case,
additional water may be added to the gasifier using the independent
water feeding system connected to the gasifier feed injector.
However, for control purposes, the gasifier control system always
needs to know the moisture content of the slurry so that the
independent water feed system may be controlled, if needed.
Therefore, control logic 82 measures the slurry moisture content,
M, at decision point 120 and outputs the value M to the gasifier
control system.
[0049] Once the control logic 82 has completed the preparation of a
mixed fuel slurry with desired gross heating value and viscosity
and has checked the moisture content, the control logic 82 checks
the level in the run tank 65 (decision point 124) to see if it may
be low enough to receive a full batch of recently mixed slurry from
the mixing tank 64 without overflowing. If the level in run tank 65
is less than full, which may be defined as having a level low
enough to accept the entire volume of slurry in mixing tank 64
without overflowing, control logic 82 may transfer the entire batch
of recently mixed slurry from the mixing tank 64 to the run tank 65
via pump 80 by closing valve 71 and opening valve 73. Once the
transfer is complete, control logic may turn off pump 80, close
valve 73 and reopen valve 71, returning the system to its original
condition. The system may then be ready to being making another
batch of mixed fuel slurry according to process 82. However, if at
decision point 124 the control logic 82 determines that the run
tank 65 is still full, which is defined as having a level high
enough that the transfer of a full batch of recently mixed fuel
slurry would cause run tank 65 to overflow, the control logic 82
just waits at step 124 and continues to check the run tank level
until the condition changes and the level in the run tank drops to
the point where a new batch can be transferred, as described above.
As noted above, the slurry mixing system 12 is capable of
continuously supplying mixed fuel slurry to a gasifier 16 because
the mixing tank 64 and its associated equipment and the control
logic 82 are able to produce batches of freshly mixed slurry at a
rate that exceeds the rate at which slurry is withdrawn from run
tank 65 to feed gasifier 16. Thus, once filled, run tank 65 always
remains full for the duration of operation of gasifier 16.
[0050] Technical effects of the invention include the gasification
of low heating value solids such as biomass and low rank coals, the
gasification of high moisture content solids such as low rank coals
and lignites, the production and use of a non-aqueous slurry that
is transportable through pumps, and the capability to mix a
non-aqueous slurry so as to control the slurry's heating value and
viscosity. The disclosed embodiments also allow for the use in
regular gasification operations of certain solid fuels, including
certain biomass fuels and low rank coals, which were traditionally
not used as gasification fuels.
[0051] 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 languages of the claims.
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