Note: Descriptions are shown in the official language in which they were submitted.
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BLACK WATER RECYCLE CIRCULATION LOOP USE WITH A GASIFIER
BACKGROUND OF THE INVENTION
The process and advantages of gasifying hydrocarbonaceous material into
synthesis gas
are generally known in the industry. In high temperature gasification
processes, synthesis gas
may be produced from combustible organic fuels, such as coal, residual
petroleum, wood, tar
sand, shale oil, and municipal, agriculture or industrial waste. Prior to the
gasification step, these
combustible organic fuels are commonly mixed with water to form slurry or
emulsion. The solid
combustible organic fuels, in slurry form, are then reacted with a reactive
oxygen-containing gas,
such as air or oxygen, and a moderator such as water or steam in a
gasification reactor to obtain
io synthesis gas.
In the reaction zone of a gasification reactor, the combustible organic fuel
is contacted
with a free-oxygen containing gas, optionally in the presence of a temperature
moderator such as
steam or water. In the reaction zone, the contents will commonly reach
temperatures in the range
of about 1,700 F (930 C) to. about 3,000 F (1650 C), and more typically in
the range of about
2,000 F (1100 C) to about 2,800 F (1540 Q. Pressure will typically be in
the range of about
1 atmosphere (100 KPa) to about 250 atmospheres (25,000 KPa), and more
typically in the range
of about 15 atmospheres (1500 Kpa) to about 150 atmospheres (1500 KPa).
In a typical gasification process, the synthesis gas will substantially
comprise hydrogen,
carbon monoxide, and lessor quantities of impurities, such as water, carbon
dioxide, hydrogen
sulfide, carbonyl sulfide, ammonia, and nitrogen. The synthesis gas is
commonly treated to
remove or significantly reduce the quantity of impurities before being
utilized in downstream
processes.
An example of one such use is integrated gasification combined cycle (IGCC)
power
generation systems. Such systems are used throughout the world to generate
power from the
gasification of a fuel source. In such systems, a raw synthesis gas (or
syngas) syngas stream,
comprising H2, CO, C02, and H2O, is produced by the partial oxidation reaction
of a
hydrocarbonaceous fuel with a free-oxygen containing gas, typically in the
presence of a
temperature moderator such as steam water, in a quench gasification reactor.
The quenching process generates wastewater that must be treated for a wide
range of
contaminates including solids, water soluble compounds and partially water
soluble compounds
often referred to as "black water". Conventional treatment methods for the
treatment of black
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water are expensive and thus most wastewater treatment systems are designed to
store
and treat no more than one day's generation of waste water. Thus any
significant
repair to the waste water treatment system causes the entire gasification
process to be
shut down. For this reason there remains a need for systems that allow the
continued
operation of a gasification system while maintenance is being performed on the
waste
water treatment system.
SUMMARY OF THE INVENTION
The present invention is generally directed to handling the raw syngas
scrubbing wastewaters, or black water, from a quench gasification reactor.
More
particularly, the present invention describes recirculation of the black water
in a
recirculation loop from which at least a portion of the moderator used in the
gasifier
may be taken. The use of a recirculation loop for the black water permits the
operation of the gasifier in situations such as when a source of high pressure
steam is
inadequate. The present invention also permits the service and maintenance of
the
black water treatment system while permitting the continued operation of the
gasifier.
A further aspect of this invention is treating the wastewater from a quench
gasification reactor by recycling the wastewater to a location upstream of the
gasifier.
In this embodiment, the wastewater is recycled back to the gasification stage,
where
the black water and any carbon content is mixed with liquid or pulverized
solid
combustible organic materials to form slurry. The slurry is then fed to the
gasifier
where it is reacted with oxygen and optional additional steam at high
temperatures
and pressures so as to convert any carbon contained in the wastewater, along
with the
combustible organic fuel, into synthesis gas.
According to another aspect, there is provided a process for handling black
water in a storage tank comprising:
a) treating a portion of the black water;
b) recirculating the portion of the black water in a recirculation loop;
c) using a portion of the black water from the recirculation loop in a
gasification unit;
wherein, for a time, the gasification unit is operated independently of the
black
water system by isolating the recirculation loop from the gasification unit.
These and other features of the present invention are more fully set forth in
the
following description of illustrative embodiments of the invention.
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BRIEF DESCRIPTION OF THE DRAWINGS
The description is presented with reference to the accompanying drawings in
which:
FIG. 1 illustrates an embodiment of the invention in schematic form. It
particularly shows the recycle of the black water back to the gasifier.
FIG. 2 illustrates an embodiment of the invention in schematic form. It
particularly shows the recirculation of the black water back within a loop
that can be
isolated from the gasifier.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
The following terms and phrases are used herein and are intended to have the
following meaning:
"Combustible organic fuel" is defined as any combustible organic material
such as coal, residual petroleum, wood, tar sand, shale oil, and municipal,
agriculture
or industrial waste. The scope of this definition is to include any
combustible organic
fuel that can be used in a gasification process to produce synthesis gas.
"Process water" is defined as any water used to make the slurry other than the
wastewater from a hydrocarbon synthesis reactor. The scope of the term
"process
water" is to include any composition of materials in which water is the
predominate
component.
"Slurry" is defined as the combination of solid combustible organic fuel and
water, where the water is process water or wastewater from a hydrocarbon
synthesis
reactor. See US Patents 4,887,383, 4,722,740, 4,477,259, and 4,242,098
describing
some of the multitude of processes known in the art to produce slurry.
"Gasifying" or "gasification" is defined as the process in which various
carbonaceous fuels may be converted to synthesis gas by partial oxidation at
an
elevated reaction temperature and pressure. In the typical gasification
process, the
carbonaceous fuel is contacted with a free-oxygen containing gas, such as air
or
oxygen, optionally in the presence of a temperature moderator such as steam.
In the
reaction zone, the contents will commonly reach temperatures in the range of
about
1,700 F (930 C) to about 3,000 F (1650 C), and more typically in the range
of
about 2,000 F (1100 C) to about 2,800 F (1540 C). Pressure will typically
be in
the range of about 1 atmosphere (100 Kpa) to about 250 atmospheres (25,000
KPa),
and more typically in the range of about 15 atmospheres (1500 Kpa) to about
150
atmospheres (1500 KPa). See US Patent 3,945,942 describing a partial oxidation
burner assembly. See US Patent 5,656,044 describing a method and an apparatus
for
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the gasification of organic materials. See also US Patents 5,435,940,
5,345,756,
4,851,013, and 4,159,238 describing a few of the many gasification processes
known
in the prior art.
"Synthesis gas" (used interchangeably with the term "syngas") is defined as a
gaseous mixture consisting substantially of hydrogen and carbon monoxide, with
lessor quantities of
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impurities present such as water, carbon dioxide, hydrogen sulfide, carbonyl
sulfide, ammonia,
and nitrogen. It is within the scope of this definition to include any
synthesis gas that been
treated to remove or reduce the quantity of any of -the impurities, so long as
the primary
components are hydrogen and carbon monoxide.
In the present invention, carbonaceous fuel is first obtained and prepared for
feeding to a
gasification reactor. Carbonaceous fuel is any solid, liquid, or gaseous
combustible organic
material that can be used as feedstock to a gasification process for produce
synthesis gas
production. The feedstock for a gasification process is usually a
hydrocarbonaceous material,
that is, one or more materials, generally organic, which provide a source of
hydrogen and carbon
io for the gasification reaction. The hydrocarbonaceous material can be in a
gaseous, liquid or solid
state, or in a combination as desired, for example, a solid-liquid composition
in a fluidized state.
The feed preparation step may not be necessary, given the composition and
physical
nature of the feedstock. Generally, solid carbonaceous fuels will need to be
liquefied with oil or
water prior to feeding to the gasifier. Liquid and gaseous carbonaceous fuels
may be suitable for
direct feed to the gasifier, but can be pre-treated for removal of any
impurities that might be
present in the feed.
The term liquid hydrocarbonaceous fuel as used herein to describe various
suitable
feedstocks is intended to include pumpable liquid hydrocarbon materials and
pumpable liquid
slurries of solid carbonaceous materials, and mixtures thereof. For example,
pumpable aqueous
slurries of solid carbonaceous fuels are suitable feedstocks. In fact,
substantially any combustible
carbon-containing liquid organic material, or slurries thereof may be included
within the
definition of the term "liquid hydrocarbonaceous." For example, there are:
(1) pumpable slurries of solid carbonaceous fuels, such as coal, particulate
carbon,
petroleum coke, concentrated sewer sludge, and mixtures thereof, in a
vaporizable liquid carrier,
such as water, liquid C02, liquid hydrocarbon fuel, and mixtures thereof;
(2) suitable liquid hydrocarbon fuel feedstocks to the gasifier, is intended
to include
various materials, such as liquefied petroleum gas, petroleum distillates
and.residua, gasoline,
naphtha, kerosine, crude petroleum, asphalt, gas oil, residual oil, tar sand
oil and shale oil, coal
derived oil, aromatic hydrocarbons (such as benzene, toluene, xylene
fractions), coal tar, cycle
gas oil from fluid-catalytic-cracking operations, furfural extract of coker
gas oil, and mixtures
thereof;
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(3) also included within the definition of the term liquid hydrocarbonaceous
are oxygenated hydrocarbonaceous organic materials including carbohydrates,
cellulosic materials, aldehydes, organic acids, alcohols, ketones, oxygenated
fuel oil,
waste liquids and by-products from chemical processes containing oxygenated
hydrocarbonaceous organic materials, and mixtures thereof.
Gaseous hydrocarbonaceous fuels that may be burned in the partial oxidation
gasifier alone or along with the liquid hydrocarbonaceous fuel includes
vaporized
liquid natural gas, refinery off-gas, C1-C4 hydrocarbonaceous gases, and waste
carbon-
containing gases from chemical processes.
After the feed preparation step, if used, the carbonaceous fuel is sent to a
gasification reactor, or gasifier. In the gasifier, the carbonaceous fuel is
reacted with a
reactive free oxygen-containing gas. The term free-oxygen containing gas as
used
herein means air, oxygen-enriched air i.e. greater than 21 mole % 02, and
substantially pure oxygen, i.e. greater than about 90% mole oxygen (the
remainder
usually comprising N2 and rare gases). Substantially pure oxygen is preferred,
such
as that that is produced by an air separation unit (ASU). The partial
oxidation of the
hydrocarbonaceous material, is completed, advantageously in the presence of a
temperature control moderator such as steam, in a gasification zone to obtain
hot
synthesis gas, or syngas. Syngas and synthesis gas can and are used
interchangeably
throughout this specification.
The need for a temperature moderator to control the temperature in the
reaction zone of the gas generator depends in general on the carbon-to-
hydrogen
ratios of the feedstock and the oxygen content of the oxidant stream. A
temperature
moderator is commonly used with liquid hydrocarbon fuels with substantially
pure
oxygen. Water or steam is the preferred temperature moderator. Steam may be
introduced as a temperature moderator in admixture with either or both
reactant
streams. Alternatively, the temperature moderator may be introduced into the
reaction zone of the gas generator by way of a separate conduit in the feed
injector.
Other temperature moderators include CO2-rich gas, nitrogen, and recycled
synthesis
gas.
A gasification reactor generally comprises a reaction zone, made up of a
vertical cylindrically shaped steel pressure vessel lined with refractory, and
a quench
drum, such as shown in U.S. Pat. No. 2,809,104. A feed injector, such as shown
in
U.S. Pat. No. 2,928,460 may be used to introduce the feed streams into the
reaction
zone.
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In the reaction zone of a gasifier, the contents will commonly reach
temperatures in the range of about 1,700 F (927 C) to 3,000 F (1649 C),
and more
typically in the range of about 2,000 F (1093 C) to 2,800 F (1538 C).
Pressure
will typically be in the range of about 1 atmospheres (101 kPa) to about 250
atmospheres (25331 kPa), and more typically in the range of about 15
atmospheres
(1520 kPa) to about 150 atmospheres (15,199 kPa), and even more typically in
the
range of about 60 atmospheres (6080 kPa) to about 80 atmospheres (8106 kPa).
See
US Patent 3,945,942 describing a partial oxidation feed injector assembly. See
US
Patent 5,656,044 describing a method and an apparatus for the gasification of
organic
materials. See also US Patents 5,435,940, 4,851,013, and 4,159,238 describing
a few
of the many gasification processes known in the prior art.
The hot gasification process product synthesis gas, or syngas, comprises
carbon monoxide and hydrogen. Other materials often found in the synthesis gas
include hydrogen sulfide, carbon dioxide, ammonia, cyanides, and particulates
in the
form of carbon and trace metals. The extent of the contaminants in the feed is
determined by the type of feed and the particular gasification process
utilized as well
as the operating conditions.
The hot raw effluent syngas stream leaving the refractory lined reaction zone
of the partial oxidation gas generator at substantially the same temperature
and
pressure as in the reaction zone, less ordinary drop in the lines is directly
introduced
into a pool of water contained in the bottom of a quench drum or tank such as
the one
described in coassigned U.S. Pat. No. 2,896,927. The quench drum is located
below
the reaction zone of the gas generator, and the stream of raw syngas which it
receives
carries with it substantially all of the ash and/or slag and the particulate
carbon soot
leaving the reaction zone of the gas generator. The turbulent condition in the
quench
drum, caused by large volumes of gases bubbling up through the water helps the
water to scrub much of the solids from the effluent gas. Large quantities of
steam are
generated within the quench vessel and saturate the gas stream. The stream of
raw
gas is cooled in the quench drum and leaves at a temperature in the range of
about
350 F to 600 F (about 175 C to 315 C), such as about 450 F to 550 F (about 230
C
to 290 C), and a pressure in the range of about 500 to 2500 psia, such as
about 1000
psia. Thus a significant amount of waste water contaminated with solids,
particulate
carbon soot and other water soluble and insoluble materials is generated by
the
quench process being carried out in the quench drum.
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In order to prevent the plugging of downstream catalyst beds and/or the
contaminating of liquid-solvent absorbents that may be used in subsequent gas
purification steps, the cooled and partially cleaned syngas stream leaving the
quench
drum is further cleaned by contact with hot scrubbing water in another gas
cleaning
zone. This gas cleaning zone may include a conventional orifice such as shown
and
described in coassigned U.S. Pat. No. 3,524,630 and conventional venturi
scrubbers
and sprays, along with a gas scrubbing chamber such as shown and described in
coassigned U.S. Pat. No. 3,232,727. In the gas scrubbing chamber, the stream
of raw
syngas is scrubbed with scrubbing water comprising hot return condensate and
make-
up water as described herein. For example, in one embodiment the gas stream
leaving
the quench tank associated with the gasifier is scrubbed and intimately
contacted with
scrubbing water e.g. in a venturi scrubber. However, the use of a venturi
scrubber in
the gas cleaning zone is optional. The syngas passes into and up through a
pool of gas
scrubbing water contained in the bottom of a gas scrubbing chamber. The
scrubbed
gas is then passed up through a packed section or trays in the upper portion
of the
scrubbing chamber where it is contacted by condensate i.e. scrubbing water
flowing in
a downward direction.
The syngas can optionally be subjected to further cooling and cleaning
operations involving a scrubbing technique wherein the syngas is introduced
into a
scrubber and contacted with a water spray which further cools the syngas and
removes particulates and ionic constituents from the synthesis gas. The
initially
cooled gas is then treated to desulfurize the gas prior to utilization of the
synthesis
gas.
Syngas can be utilized as a fuel gas for power generation or for the synthesis
of hydrocarbons in a Fischer-Tropsch operation or for use as a feedstock gas
to many
other different chemical process. One of ordinary skill in the art should
appreciate
and understand the value and use of syngas in the petrochemical industry.
In employing the syngas generation and cleaning procedure described above,
the amount of solid particles in the scrubbed syngas stream is reduced to very
low
level such as less than about 3 parts per million (ppm), and preferably less
than about
1 ppm. However, this also generates a considerable amount of waste water that
is
contaminated with solids, hydrocarbons and other various materials and often
is
referred to as "black water". Due to clean water regulations, such water must
be
treated prior to release. Conventional treatment methods such as
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clarification, bioreactor treatment, filtration, centrifugation, chemical
treatment and other such
techniques significantly add to the cost of operation. In addition, many
plants only have the
capacity to store one day or less of this waste water before the gasification
reactor must be shut
down. Thus anything but minor maintenance on the waste water treatment system
causes the
entire system to be shut down.
The present invention resolves the above problems by using a recycle loop in
which the
black water is passed though a recycle loop. It is further contemplated that
at least a portion of
the moderator water can be drawn from the recycle loop of the black water. In
such
embodiments the use of the black water as a source of moderator can
substantially reduce the
io gasifier's requirements for high pressure steam as a moderator.
Turning now to FIG. 1 illustrated is one exemplary embodiment of the present
invention
in schematic form. A quench gasification reactor 2 with a quench drum 3
produces synthesis gas
4 by the partial oxidation a hydrocarbon source 6 in the presence of an oxygen
rich feed stream 8
and a moderator 10. The synthesis gas is quenched in the quench drum 3 and the
slag generated
is by the gasification reaction is collected and handled by a slag handling
system (not shown). As
quench water becomes contaminated with fine carbon solids, and other fine
particulate materials
suspended in the water, water soluble compounds and the like, it is removed
from the gasifier
and sent to the black water storage tank 12. As black water accumulates, it is
sent to
conventional water treatment facilities that may include clarification, bio-
reactor treatment,
20 filtration, centrifugation, chemical treatment and other conventional
treatment processes for
black water. In order to prevent the settling out of the suspended solids, the
black water is
passed through a recirculation loop. The recirculation loop is composed of a
recycle black water
pump 14 which pumps the black water through a manual block valve 16 to either
a recirculation
valve 18 or a auto block valve 20. The recirculation loop for the black water
is completed by
25 opening the recirculation valve 18 and allowing of the black water to
return to the black water
tank 12. The black water returning to the gasifier can be used as the liquid
portion of the
hydrocarbon slurry feed or it may be used as an additional source of
moderator. In such an
embodiment the black water is used as a source of moderator and the quality
and quantity
demands on the primary source of moderators (in this case high pressure steam)
is significantly
3o reduced. Thus, the gasifier can continue operations when the primary source
of moderator (in
this case high pressure steam) is incapacitated. It should also be appreciated
that the gasifier can
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be started up on the black water if there is careful control over the timing
of the auto block valve
such that the amount of black water moderator is appropriate. In other
situations, the amount of
black water that can be recirculated back to the gasifier will be limited and
thus an alternate
source of fresh feed water 22 may be included upstream of the autoblock valve.
If volume of the
black water and steam is not sufficient or incapacitated, it is possible to
start and run the gasifier
using the alternate feed water source.
One of ordinary skill in the art should appreciate that the configuration
illustrated in FIG.
1 is capable of operating in a manner that allows the recirculation of the
black water to prevent
the settling out of any suspended particles. It should also be appreciated
that it is possible to
io pressurize the black water handling system by recirculating the black water
in a closed loop
system prior to the start-up of the gasifier. Thus one is able to bring the
gasifier on-line under
more stable conditions than is the current practice.
As shown in FIG. 1, maintenance is possible on the recycle black water pump so
long as
the steam source is sufficient to maintain the operation of the gasifier. This
is possible because
is the scheme provides for double isolation of the recycle black water pump.
This is in contrast
with the present state of the art which requires that the gasifier be shut
down.
FIG. 2 illustrates another exemplary embodiment of the invention in schematic
form. It
particular, FIG. 2 shows the recirculation of the black water back within a
loop that can be
isolated from the gasifier. It should be noted that items having the same
functional role have
20 been given the same reference number in FIG. 2 as they were given in FIG.
1.
Turning now to FIG. 2, a quench gasification reactor 2 produces synthesis gas
4 by the
partial oxidation a hydrocarbon source 6 in the presence of an oxygen rich
feed stream 8 and a
moderator 10. The synthesis gas is quenched in the quench drum 3 and the slag
generated by the
gasification reaction is collected and handled by a slag handling system (not
shown). As quench
25 water becomes contaminated with fine carbon solids, and other fine
particulate materials
suspended in the water, water soluble compounds and the like, it is removed
from the gasifier
and sent to the black water storage tank 12. As black water accumulates, it is
sent to
conventional water treatment facilities that may include clarification, bio-
reactor treatment,
filtration, centrifugation, chemical treatment and other conventional
treatment processes for
3o black water. In order to prevent the settling out of the suspended solids,
the black water is
passed through a recirculation loop. The recirculation loop is composed of a
recycle black water
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pump 14 which pumps the black water through a first manual block valve 16 to
either a
recirculation valve 18 or a second manual block valve 24. The recirculation
loop for the black
water is completed by opening the recirculation valve 18 and allowing at least
a portion of the
black water to return to the black water tank 12. Thus one can open the first
manual block valve
16, close the second manual block valve 24 and open the recirculation valve 18
and establish a
closed loop recirculation of the black water.
When desired, the second manual block valve can be opened thus permitting the
circulation of black water to the gasifier, via the auto block valve 20. The
black water returning
to the gasifier can be used as the liquid portion of the hydrocarbon slurry
feed or it may be used
io as an additional source of moderator. In such an embodiment the black water
is used as a source
of moderator and the quality and quantity demands on the primary source of
moderators (in this
case high pressure steam) will be significantly reduced. Thus, the gasifier
can continue
operations when the primary source of moderator (in this case high pressure
steam) is
incapacitated. It should also be appreciated that the gasifier can be started
up on the black water
if there is careful control over the timing of the auto block valve such that
the amount of black
water moderator is appropriate. One of skill in the art should also note that
the gasifier can be
operated independently of the black water system. That is to say the alternate
feed water source
can be used to provide the moderator water needed by the gasifier. This can be
beneficial during
the start up or shut down of the gasifier, or when maintenance on the black
water handling
system is needed. For example, as shown in Fig. 2, the recycle black water
pump can be isolated
from the gasifier by double isolation which would allow maintenance on the
black water pump
whie the gasifier is still running. It should be noted that the amount of
black water that can be
recirculated back to the gasifier may be limited and thus can be balanced with
the alternate
source of fresh feed water 22.
One of skill in the art should appreciate that the ability to isolate the
black water
circulation system is important for both maintenance purposes and operation of
the gasifier. As
noted above, because the black water recirculation system can be isolated,
maintenance on the
system can be conducted without having to shut down the gasifier. The only
practical limit to
such operation is the ability to store and /or treat any generated black
water. The above
illustrative embodiment also permits the start up of the gasifier on an
alternate feed water source
and then bring on-line the black water under pressure. This is possible
because of the ability to
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recirculate and thus pressurize the black water recirculation loop. Another
advantage of the
present invention is that it permits the continuous recirculation of the black
water in a closed
loop system. This prevents the settling out of any suspended solids in the
black water during
time in which recycle of the black water to the gasifier is not desired. For
example, when the
gasifier is not running.
It should also be appreciated that as shown in the above embodiments of the
present
invention, wastewater from a gasification reactor can be recirculated in a
recycle loop such that
at least a portion of the waste water can be sent to a gasification reactor
and thus used as a
moderator. By doing so, many process and economic advantages may be realized.
First, and
io perhaps most importantly, the wastewater can be disposed of with no adverse
environmental
affects. The large capital and operating costs associated with traditional
water treatment
facilities may be drastically reduced, if not eliminated. In addition the on-
site requirements for
high pressure steam as the source of moderator can be substantially reduced
and the reliability of
gasifier operations may be enhanced.
While the devices, compositions and methods of this invention have been
described in
terms of preferred embodiments, it will be apparent to those of skill in the
art that variations may
be applied to the process described herein without departing from the concept
and scope of the
invention. All such similar substitutes and modifications apparent to those
skilled in the art are
deemed to be within the scope and concept of the invention.
