U.S. patent application number 12/581966 was filed with the patent office on 2011-04-21 for method of operating a multi-fuel combustion system.
Invention is credited to Vinayak Barve, Jaap van Kampen, Ulrich Worz, Jianfan Wu.
Application Number | 20110091824 12/581966 |
Document ID | / |
Family ID | 43558427 |
Filed Date | 2011-04-21 |
United States Patent
Application |
20110091824 |
Kind Code |
A1 |
Barve; Vinayak ; et
al. |
April 21, 2011 |
METHOD OF OPERATING A MULTI-FUEL COMBUSTION SYSTEM
Abstract
The present invention explains a method of operating a
multi-fuel combustion system. It consist of a first phase and a
second phase, wherein the first phase comprises of providing
ignition to a combustor basket to ignite a first type of fuel,
where the first type of fuel is supplied to the combustor basket
through a first conduit. Also in first phase steam is also supplied
to the first conduit in addition to the first type of fuel and
steam is supplied to the second conduit after the ignition. In the
second phase a second type of fuel is supplied to the combustor
basket after ignition of the first fuel through the second conduit,
while stopping the supply of the first fuel.
Inventors: |
Barve; Vinayak; (Oviedo,
FL) ; Wu; Jianfan; (Orlando, FL) ; Worz;
Ulrich; (Laupheim, DE) ; van Kampen; Jaap;
(Roermond, NL) |
Family ID: |
43558427 |
Appl. No.: |
12/581966 |
Filed: |
October 20, 2009 |
Current U.S.
Class: |
431/6 ; 431/12;
431/278 |
Current CPC
Class: |
F23N 2227/02 20200101;
F02C 7/26 20130101; F23R 3/36 20130101; F23N 2241/20 20200101; F23D
14/20 20130101; F23R 2900/00002 20130101 |
Class at
Publication: |
431/6 ; 431/12;
431/278 |
International
Class: |
F23N 1/00 20060101
F23N001/00; F23C 1/00 20060101 F23C001/00 |
Claims
1. A method of operating a multi-fuel combustion system comprising
a first phase and a second phase, wherein the first phase
comprises: providing ignition to a combustor basket to ignite a
first type of fuel, where the first type of fuel is supplied to the
combustor basket through a first conduit; supplying steam to the
first conduit in addition to the first type of fuel and supplying
steam to the second conduit after the ignition; and wherein the
second phase comprises: supplying a second type of fuel to the
combustor basket after ignition of the first fuel through the
second conduit, while stopping the supply of the first fuel.
2. A method of operating a multi-fuel combustion system according
to claim 1, wherein the steam is provided to the second conduit at
a time earlier than the steam provided to the first conduit.
3. A method of operating a multi-fuel combustion system according
to claim 1, further comprising supplying a medium to the second
conduit during the first phase for stabilizing the combustion
system for any pressure difference between the second conduit and
the combustor basket.
4. A method of operating a multi-fuel combustion system according
to claim 3, further comprising shutting off the supply of the
medium in the second conduit once the steam supply is stabilized in
the first conduit and the second conduit during the first stage of
operation.
5. A method of operating a multi-fuel combustion system according
to claim 1, further comprising supplying a portion of the second
type of fuel to the combustor basket through the first conduit
during the second phase.
6. A method of operating a multi-fuel combustion system according
to claim 5, further comprising continue supplying the steam in the
first conduit from the first phase until the beginning of supplying
the portion of the second type of fuel through the first conduit
during the second phase.
7. A method of operating a multi-fuel combustion system according
to claim 5, wherein the flow of second type of fuel in the second
conduit is regulated based on the portion of the flow of the second
type of fuel in the first conduit during the second stage of
operation.
8. A method of operating a multi-fuel combustion system according
to claim 5, wherein the portion of the second type of fuel supplied
through the first conduit during the second phase is between 1% and
20% of the total mass flow of the second type of fuel supplied
during the operation of the combustion system during the second
phase.
9. A method of operating a multi-fuel combustion system according
to claim 1, wherein the first type of fuel is natural gas.
10. A method of operating a multi-fuel combustion system according
to claim 1, wherein the second type of fuel is syngas.
11. A method of operating a multi-fuel combustion system according
to claim 1, wherein supplying the steam into the first conduit and
the second conduit starts when the combustion system is loaded
between 25% and 40% of its full working capacity.
12. A method of operating a multi-fuel combustion system according
to claim 1, wherein supplying a second type of fuel through the
second conduit to the combustor basket at the second phase starts
when the combustion system is loaded between 30% and 50% of its
full working capacity.
13. A method of operating a multi-fuel combustion system according
to claim 1, wherein at least one of the first type of fuel and the
second type of fuel is supplied to the combustion system using a
third conduit.
14. A method of operating a multi-fuel combustion system according
to claim 1, wherein the combustion system uses a pre-combustion
CO.sub.2 capture process.
Description
FIELD OF INVENTION
[0001] The present invention lies in the field of combustion
turbines for industrial purposes and more particularly, a method of
operating a combustor system.
BACKGROUND OF INVENTION
[0002] Future energy demand, scarcity of available fuels and
environmental regulations put pressure on power plant producers to
come up with solutions for safe, efficient and clean ways to
generate power. The scarcity of fuels mainly applies to oil and to
a lesser extend to natural gas. With an availability of coal in
abundance, electricity production from coal is mostly done using
steam power plants. A cleaner and more efficient option to generate
power from coals is to use them in an integrated gasification
combine cycle (IGCC). In an IGCC, coals are first gasified to yield
syngas, consisting mainly of CO (carbon monoxide) and H.sub.2
(hydrogen).
[0003] Syngas typically has a significantly lower calorific value
as compared to conventional natural gas fuels. By removing the CO
content from the syngas prior to combusting it, one also has an
effective means for CO.sub.2 (carbon-dioxide) capture. The IGCC
concept with pre-combustion CO.sub.2 capture is one of the most
cost-effective ways to produce electricity and avoid the emission
of CO.sub.2 in the future. The economical potential of the IGCC
plant with CO.sub.2 capture can increase even further when natural
gas prices rise faster than expected or with increased carbon tax
regulation.
[0004] Due to the low calorific value and high hydrogen content,
the combustion of syngas fuels requires the development of adapted
or completely new combustion systems which are able to handle the
wide range of syngas fuels, and produce little emissions and can
handle the high reactivity of the fuels.
[0005] The syngas fuel composition depends on the type of gasifier
used and on whether or not the CO is separated from the fuel.
Besides syngas fuels, the combustion system might run on a second
conventional fuel for backup and start up. The ideal possibility is
to have all the different types of fuels combusted in a stable way
by one combustion system by performing a proper combustion method
to increase the efficiency and compensate for the efficiency loss
due to the gasifier.
SUMMARY OF INVENTION
[0006] In view of the foregoing, an embodiment herein includes a
method of operating a multi-fuel combustion system comprising a
first phase and a second phase, wherein the first phase comprises:
providing ignition to a combustor basket to ignite a first type of
fuel, where the first type of fuel is supplied to the combustor
basket through a first conduit; supplying steam to the first
conduit in addition to the first type of fuel and supplying steam
to the second conduit after the ignition; and wherein the second
phase comprises: supplying a second type of fuel to the combustor
basket after ignition of the first fuel through the second conduit,
while stopping the supply of the first fuel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The present invention is further described hereinafter with
reference to illustrated embodiments shown in the accompanying
drawings, in which:
[0008] FIG. 1 illustrates a longitudinal cross-section of the
multi-fuel combustion system based on an embodiment of the
invention,
[0009] FIG. 2 shows fuel injector holes at the region of nozzle of
the first and the second conduits,
[0010] FIG. 3 shows the side view of the first conduit and the
second conduit along with the fuel injector holes,
[0011] FIG. 4 shows the graphical representation depicting the
first phase of operation of the multi-fuel combustion system based
on an embodiment of the invention, and
[0012] FIG. 5 shows the graphical representation of the second
phase along with the first phase of operation of the multi-fuel
combustion system based on an embodiment of the invention.
DETAILED DESCRIPTION OF INVENTION
[0013] In general terms, a combustion turbine comprises three
sections: a compressor section, a combustor section having a
typical combustor basket and a turbine section. Air drawn into the
compressor section is compressed. The compressed air from the
compressor section flows through the combustor section where the
temperature of the air mass is further increased after combustion
of a fuel. From the combustor section the hot pressurized gas flow
into the turbine section where the energy of the expanding gases is
transformed into rotational motion of a turbine rotor that drives
an electric generator.
[0014] The lower calorific value of the syngas fuels and the
necessity to also operate the burner on a backup fuel like natural
gas, significantly affects the design of the burners. The burner
should be able to handle large fuel mass flows and the fuel
passages consequently need to have a large capacity. A too small
capacity results in a high fuel pressure drop. Due to the large
fuel mass flow involved, a high pressure drop has a much larger
impact on the total efficiency of the engine as compared to a
typical natural gas fired engine.
[0015] FIG. 1 illustrates a cross-sectional view of the multi-fuel
combustion system 10 according to one embodiment of the invention.
A multi-fuel combustion system 10 comprises a combustor basket 12.
The wall 16 of the combustor basket 12 is made of multiple
cylindrical regions 14 arranged to overlap each other at the
transition and extends from an upstream end 20 to a downstream end
22 of the combustor basket. The upstream end 20 of the combustor
basket is close to the region, where the fuel conduits generally
supply the fuels for the combustion and the down stream end is the
region, where the gas after combustion flows out to of the
combustor basket to a turbine section. The combustion system 10 is
designed to combust at least two type of fuels, for example natural
gas and syngas. The types of fuels that could be used are not
restricted to natural gas and syngas and hence the combustion
system 10 could use other fuels for combustion.
[0016] FIG. 1 further shows a first conduit 24 adapted to provide a
first type of fuel, for example natural gas, directly to the
combustor basket 12 and the second conduit 26 is adapted to provide
a second type of fuel, for example syngas directly to the combustor
basket 12. Also there is at last one third conduit 25 adapted to
inject at least one of the first type of fuel and the second type
of fuel through one or multiple openings 18 into the combustor
basket 12. There could be more than one conduit to provide each
type of fuel to the combustor basket based on the design and
requirement. For example, there could be multiple third conduits 25
to supply the fuel through multiple openings 18 in the combustor
basket 12. Also based on the mode of operation of the combustor
basket 12, each of the conduits is adapted to handle a different
fuel. Even the conduits could handle multiple fuels at the same
point of time. The second conduit 26 is positioned to encircle the
first conduit 24 or concentrically arranged for effective delivery
of the fuels. The first conduit 24 is positioned coaxially, and
internally, of a larger diameter second conduit 26. Since the
diameter of the second conduit 26 is greater that the first conduit
24, the said second conduit 26 can handle low calorific value fuels
of larger volumes since large fuel mass flows is needed to achieve
a certain thermal power input.
[0017] The third conduit 25 is adapted to inject at least one of
the first type of fuel and the second type of fuel into a
compressor discharge air that flow through at least one of the
openings 18 associated with at least one of the cylindrical regions
14. The third conduit 25 has a fuel injector nozzle 27 at the end
having 1 to 5 injector holes that are aimed at an angle of 0 to
90.degree. relative to a centerline of the opening 18. The first
conduits 24 and the second conduit 26 under consideration consist
of concentric circles of circular holes at the region of nozzle 28
of the conduits which acts as injectors for the fuels. The nozzle
28 helps to inject the respective fuels directly into the combustor
basket 12 and is positioned at the upstream end 20 of the combustor
basket 12.
[0018] FIG. 2 shows explicitly these two rows of concentric holes
at the region of nozzle 28. Each circle of rows is associated to a
conduit. The inner row of holes 21 corresponds to the first conduit
24 and the outer row of holes 23 corresponds to the second conduit
26. The number of injectors in each conduit can vary, for example
between 8 to 18 holes, but is not restricted to this numbers. A
preferred embodiment having 14 injectors for both conduits is shown
in FIG. 2. The holes can be clocked relative to each other or can
be inline.
[0019] In another preferred embodiment, the holes in the region of
nozzle 28 of the first conduit 24 comprises multiple holes
positioned at, at least two different radial distances from the
center of the nozzle for injecting a fuel flow into a region of
combustion in the combustor basket 12. This nozzle design promotes
a greater amount of fuel flow towards the center of the nozzle,
which cools the nozzle in a cost effective and simple manner. Most
importantly the hole arrangement maintains the aerodynamic
performance of the nozzle.
[0020] FIG. 3 shows the side view of the first conduit and the
second conduit along with the fuel injector holes. The fuel
injector holes 32 in the nozzle region 28 of the first conduit 24
and the second conduit 26 can be positioned radially at an angle X,
between 0-45 degrees relative to a burner axis 34.
[0021] Coming back to FIG. 1, the circumferential wall 16 of the
combustor basket 12 comprises multiple openings 18. At least two of
the cylindrical regions 14a and 14b nearer to the upstream end 20
of the combustor basket 12 further comprise multiple openings 18
distributed along the circumference of the respective cylindrical
regions. This multiple openings 18 allow a compressor discharge air
from a compressor stage to flow towards a region of combustion in
the combustor basket. At the same time, at least one of the
cylindrical region near to the downstream end 22 of the combustor
basket 10 may also comprise plurality of openings 18 distributed
along the circumference of the cylindrical region to allow the
compressor discharge air to flow towards a region of combustion in
the combustor basket 12. The combustion system 10 further comprises
a cover plate 29 coupled to the combustor basket 12 and the first,
second and third conduits. This enables the combustor basket and
the conduits to be attached to a casing. The multi-fuel combustion
system 10 further comprises a flow conditioner 45 positioned to
encircle the combustor basket 12 and having a conical section 46
and a cylindrical section 47 having plurality of holes 48 adapted
to allow the compressor discharge air to flow towards a region of
combustion in the combustor basket 12. The flow conditioner 45 is
used to achieve the pressure drop required for cooling and to
provide a uniform air flow towards the region of combustion in the
combustor basket 12. Holes 48 in both the cylindrical section 47
and the conical section 46 are used as flow passage for air. The
multi-fuel combustion system 1 of FIG. 1 further comprises an exit
cone 35 at the downstream end 22 of the combustor basket 12 having
multiple slots 37 aligned to the plurality of openings 18
associated with at least one of the cylindrical regions 14. This
exit cone 35 is intended to improve the mixing between the hot
combustion gasses and the cold air flow coming out of a spring-clip
passage 39. The improved mixing between these flows lead to better
CO emissions. The exit cone slots 37 aligned with the scoops 18
prevent overheating of the exit cone 35.
[0022] The method of operating the multi-fuel combustion system 10
is now described. The operation could be divided into two main
phases a first phase and a second phase. FIG. 4 shows a graph 40
depicting the first phase of operation of the multi-fuel combustion
system based on an embodiment of the invention. The X-axis
represents the load of the combustion system in percentage, where 0
represents the idle stage and 100 represent the full load. Y-axis
represents the fuel flow through the nozzle of the conduits.
[0023] During the first phase an ignition is provided to a
combustor basket 12 by an ignition coil to ignite a first type of
fuel, for example natural gas supplied to the through the first
conduit 24. The line 41 represents the flow of a first fuel type
through the first conduit 24. Natural gas, could be used as a first
type of fuel during the start up of this first stage. At this point
there might not be any need for any purging of the second conduit
26.
[0024] The method further involves supplying a medium, for example
an inert gas, nitrogen or steam or seal air to the second conduit
26 during the first phase for stabilizing the combustion system 10
for any pressure difference in the combustor basket 12. In a
typical industrial arrangement the combustion system comprises a
plurality of combustor baskets, and while in operation there could
be pressure differences that could be built up between these
combustor baskets. The supply of the medium also takes care of this
pressure difference in the combustor basket due to this type of
arrangement. Line 42 in the graph 40 represents the supply of the
medium. The method also involves supplying steam to the first
conduit 24 in addition to the first type of fuel and supplying
steam to the second conduit 26 after the ignition. Line 43
represents the steam supply through the first conduit 24 and line
44 represents the steam supply through the second conduit 26. Hence
in the first conduit 24, the steam gets mixed with the first type
of fuel. Steam is provided to the second conduit 26 at a time
earlier than the steam provided to the first conduit 24. The
medium, for example the seal gas can be taken from the combustion
system 10, by making use of the pressure differences that exist in
the system. About 25% of the steam is injected through the first
conduit 24 and the rest through the second conduit 26. Overall
steam mass flow injection rate increases to a maximum at base load
when using the first type of fuel. The steam ratio between the
first conduit 24 and the second conduit 26 could change between
10/90% and 40/60%. Line 45 in the graph 40 represents the combined
total steam flow in both the conduits. Generally, supplying the
steam into the first conduit and the second conduit starts when the
combustion system is loaded between 25% and 40% of its full working
capacity. This can also vary based on the condition of operation or
based on the design or requirement. Meantime the supply of the
medium in the second conduit 26 is shut off once the steam supply
is stabilized in the first conduit 24 and the second conduit 26
during the first stage of operation.
[0025] FIG. 5 shows a graph 50 representing a second phase along
with the first phase of operation of the multi-fuel combustion
system based on an embodiment of the invention. In the second phase
of operation, a second type of fuel for example syngas is supplied
to the combustor basket 12 through the second conduit 26, while
stopping the supply of the first fuel. If there is a pre-combustion
CO.sub.2 capture employed in the design, then the second type of
fuel supplied could be a H2 fuel. Line 51 in the graph 50, shows
the supply of second type of fuel through the second conduit 26.
The supply of the second type of fuel through the second conduit 26
to the combustor basket 12 could starts when the combustion system
is loaded generally between 30% and 50% of its full working
capacity.
[0026] The method further comprises supplying a portion of the
second type of fuel to the combustor basket 12 through the first
conduit 24 during the second phase. Line 52, in the graph 50
represent the supply of the portion of the second type of fuel to
the through the first conduit 24. This increases the syngas flow
area and reduces the fuel supply pressure demand and the portion of
the second type of fuel also acts as purging medium for the first
conduit 24. If first conduit is not used for supplying of the
portion of the second type of fuel, a medium like for example
steam, nitrogen or air could be used as a purging medium. Between
40% and 70% load, this purging is done. 100% of the second type of
fuel may be supplied through the second conduit 26 at lower loads.
Above 70% load, the first conduit 24 is generally used for
supplying the second type of fuel. The portion of the second type
of fuel supplied through the first conduit during the second phase
is between 0% and 20%, but preferably between 1% and 20% of the
total mass flow of the second type of fuel supplied during the
operation of the combustion system during the second phase. The
steam is continuously supplied in the first conduit 24 from the
first phase until the beginning of supplying the portion of the
second type of fuel through the first conduit 24 during the second
phase. Here steam also acts as a purging medium.
[0027] Also the third conduit 25 may also be used to supply any one
of the first or second type of fuel for enabling an effective and
more complete combustion by introducing the said fuels through the
openings 18 if required. This further helps in reducing NOx
emissions. The syngas, which is the second type of fuel is diluted
for NOx control. The dilution amount varies over the load
range.
[0028] It is noted that by the end of the first stage and the onset
of the second stage the first fuel type is stopped and the
combustor system 10 is provided with a second type of fuel. There
is a fuel transfer occurring in the combustor system 10. To do
this, the level of the syngas, which is the second type of fuel
through the second conduit 26 is brought up from the minimum and
gradually increased while reducing the supply of natural gas, which
is the first fuel type through the first conduit 24. Steam will be
supplied through the first conduit 24 for keeping the pressure drop
in the first conduit 24 constant and for maintaining NOx targets.
The syngas is diluted if the lower heat value (LHV) of the fuel at
the second conduit 26, is higher than the require LHV. Once the
natural gas flow reaches to a minimum, the natural gas flow is shut
off, and steam is continued to be used as purging medium or else
purged with N2. When the load level is higher than 70%, then up to
20% of the syngas can be directed to the first conduit 24 and the
purging medium in the first conduit can be shut down.
[0029] In a pre-combustion CO.sub.2 capture employed design, when
the CO.sub.2 sequestration process starts, the syngas operation
automatically changes to H.sub.2 operation. When the CO.sub.2
sequestration process stops, the H.sub.2 operation automatically
changes to syngas operation. The dilution levels are monitored and
controlled to meet NOx emission target. The Syngas/H.sub.2
operation could be brought again back to natural gas operation if
required by reducing the syngas/H.sub.2 in the second conduit 26
when the load level is larger than 70%, and by starting the supply
of natural gas in the first conduit 24 to compensate for the
pressure difference. Steam injection in the first conduit 24 is
used to maintain pressure drop and control NOx. Steam injection in
second conduit 26 is used to replace syngas. Once the syngas in the
second conduit 26 reaches the allowable minimum, then syngas is
shut down.
[0030] Although the invention has been described with reference to
specific embodiments, this description is not meant to be construed
in a limiting sense. Various modifications of the disclosed
embodiments, as well as alternate embodiments of the invention,
will become apparent to persons skilled in the art upon reference
to the description of the invention. It is therefore contemplated
that such modifications can be made without departing from the
embodiments of the present invention as defined.
* * * * *