WO2008023986A1

WO2008023986A1 - Method for increasing the energy and cost effectiveness of a gas power plant; thermal power plant and a combustor for use in connection with such plants

Info

Publication number: WO2008023986A1
Application number: PCT/NO2007/000198
Authority: WO
Inventors: Arne Lynghjem
Original assignee: Statoil Asa
Priority date: 2006-06-20
Filing date: 2007-06-08
Publication date: 2008-02-28
Also published as: NO20062879L; NO325049B1

Abstract

The invention relates to a method for increasing the energy and cost effectiveness of a gas power plant or thermal power plant, and for energy and cost effective CO2 capturing from flue gas with CO2 enriched content. The plant comprises preferably two gas turbines comprising at least a compressor (13) and a turbine (14) and further comprising a combustor (10), the flue gas from the combustor (10) being expanded, cooled down and passed through a cleaning unit (11) where at least major parts of the CO2 content is removed from the flue gas. Re-circulated flue gas is further used for cooling down the flame tube (40) in the combustor (10), and enriching the CO2 content of the flue gas, the fresh air supplied to the combustor (10) providing a nearly stoichiometric combustion. The invention relates to an improved combustor system resulting in increased energy efficiency and increased output maintained at a highest possible level. The invention also relates to a power plant using the method.

Description

METHOD FOR INCREASING THE ENERGY AND COST EFFECTIVENESS OF A GAS POWER PLANT; THERMAL POWER PLANT AND A COMBUSTOR FOR USE IN CONNECTION WITH SUCH PLANTS

The present invention relates to a method for increasing the energy and cost effectiveness of a gas power plant or thermal power plant and for energy and cost effective CO₂ capturing. The gas power plant or the thermal power plant comprises a gas turbine plant or combined plant with steam or gas turbine cycle, preferably equipped with at least two gas turbine plants with a compressor unit and a turbine unit, and further comprising a combustor with a flame tube working mainly with two separate gas streams, wherein one gas stream comprises air supplied together with the fuel centrally into the flame tube, and where the other gas stream comprises a cooling gas flowing along the exterior of the flame tube, the flue gas from the combustor being expanded and cooled down, passing through a cleaning unit where at least substantial parts of the CO₂ content of the flue gas are removed, prior to venting the cleaned flue gas to the atmosphere-.

The present invention relates further to gas power plant or a thermal power plant, and a combustor designed for such plants . Emission of carbon dioxide (CO₂) has increased substantially the latest decades and represents a global problem. Based on the Kyoto Agreement and the precautionary principle, it is hence a desire to limit the emission of climate gases such as CO₂, in order to counteract changes in climate. One measure is to secure capture of CO₂ in connection with conversion of energy from fossil fuel in a gas power plant and/or thermal power plant. The different elements in the CO₂ value chain include technology for CO₂ capture, transportation of and finally the final stage or exploitation of CO₂, for example for increased oil recovery from oil reservoir (IOR) .

Flue gas cleaning from gas power plants (the so called post combustion type) is to-day used in a medium sized scale. Such flue gas cleaning does also have a potential for cost reductions. The existing technology for flue gas cleaning is based on absorption of carbon subsequent to combustion. A gas power plant of this type is described in open literature, textbooks, and publications. Exhaust gases from a standard combined cycle gas turbine power plant contain ca. 3,5 volume% of CO₂, and the exhaust must be cooled down from about 450-600 ²C to normal operation temperature for amine washing, such temperature being approximately 40-55 ². In an atmospheric absorption tower the CO₂ in the gas is converted to the liquid phase by chemical absorption in the amine liquid. It is imperative to have a large area of contact between the gas and the liquid. Consequently, the tower must be high, having a height of 30 m or more. For a gas power plant of 400 MW the required cross sectional area of the absorption column will be 260-320 m². A standard gas power plant with such type of exhaust gas cleaning has thus an inherent disadvantage that both the investment costs and the operational costs are very high. Further, such type of plants requires very large plant footprint areas.

There exist known technologies which may provide more cost effective capturing plants by increasing the CO₂ content of the exhaust gases from a gas turbine power plant to about 10 volume% of CO₂. This may be obtained by means of re-circulation of large volumes of exhaust gases. Re-circulation of large volumes of exhaust gases may, however, result in another problem, namely that the oxygen content in the combustor becomes too low for maintaining stable combustion. It is not possible to re-circulate larger volumes of exhaust gases than the volumes corresponding to ca. 6-7 volume% CO₂ without getting problems with insufficient oxygen content for maintaining a stable combustion. The present invention aims at achieving ca. 10 volume% CO₂ in the exhaust gas without encountering problems with insufficient oxygen content, by using an improved combustor arrangement and power plant concept.

Further, it is previously known that more cost effective concepts for CO₂ capture exist. WO 2004/072443 de- scribes for example a capturing plant of similar type for exhaust gases with concentrated CO₂ and higher pressure, but with a completely different combustor arrangement.

Further, it is well known that in order to obtain a lower NO_x emission from gas turbine plants and combustion plants, it is beneficial to re-circulate cooled flue gas back to the combustor.

An object of the invention is to provide basis for a power plant where the emission of climate gases is reduced to a minimum or completely eliminated, by using a standard gas turbine power plant with a standard combustor, partly modified.

Another object is to provide a more energy and cost effective solution, and to reduce, preferably half, both cost of investments and cost of operation, compared to existing technology. It is of particular interest to obtain an energy effective solution where the temperature at the inlet to the turbine unit is kept as high as possible and preferably without deviating from a standard gas turbine power plant . It is also an object to find cost effective solutions for a gas power plant, wherein a new, compact capturing plant for exhaust gas enriched of CO₂ may be used.

According to the invention the objects are achieved by a method and a power plant as described in more detail in the accompanying claims .

According to the invention a more efficient power plant is achieved, where the emission of CO₂ may be reduced by preferably 85-90 %, but where the emissions alterna- tively may be lower, i.e. in the order of 0-90%.

Further, a plant which is more simple to construct and not requiring as large required footprint space compared to the footprint space necessary for the conventional plant for amine washing is obtained, one major reason being that the CO₂ absorption plant necessary in the present invention may be of a much simpler type. An effective exploitation of such a CO₂ solution for cleaning of flue gas requires that the flue gas contains enriched CO₂.

A still further advantage according to the present invention is a substantially reduced need of modifications to a standard combustor, and that the invention may be used in connection with all types of combustors, both external combustors and integrated combustors, including annular type or canned type of combustors. The objects are achieved by a method, a gas power plant or a thermal power plant; and a combustor as defined by the independent claims; Alternative embodiments are defined in the dependent claims .

The following is obtained or is a consequence of the invention:

- The present invention uses an improved combustor system modified for re-circulating flue gas in order to obtain optimal enrichment of CO₂, ca. 10 volume% CO₂ in the flue gas, without causing problem of insufficient oxygen content for maintaining a stable combustion process.

- A cost effective separation of CO₂ may be obtained due to the high concentration of CO₂ in the flue gas .

- All standard types of combustors in conventional gas turbine power plants may be used without having to make any significant modification.

- Combustion may occur at an optimal combustion temperature and surplus of air, thereby meeting the requirement of a sufficiently low emission of NO_x. Preferred embodiments of the invention shall now be described in further details, referring to the accompanying drawings , where :

Figure 1 shows an improved combustor plant according to the invention; Figure 2 shows schematically a diagram of a preferred embodiment of a gas power plant according to the invent- tion,- and

Figure 3 shows an alternative further embodiment of a combustor. It should be appreciated that the temperatures and pressures specified below only are meant to be of an indicative nature for the described embodiments and that these values may vary without thereby deviating from the inventive idea. The characteristic feature of the proposed plant shown in Figure 2 is that the combustors 10,10' operate mainly with two separate gas streams, wherein one stream is fed internally to the flame tube 40,40', while the other stream is fed externally of the flame tube 40,40'. The flame tube 40,40' is provided with perforations so that optimal cooling of the flame tube is obtained, and the part stream flowing externally along the flame tube 40,40' gradually is led through the perforations in the flame tube, whereby the part stream may form part of the cooling of the combustion process and combustion products. Thereupon the stream is fed to the turbine unit 14,14' of the gas turbines 12,12' at highest possible temperature, so that the energy effectiveness of and output from the gas turbine process may be kept at as high as possible. It is a major advantage of the proposed plant according to the embodiment shown in Figure 2 that the flue gas, leaving the flame tube 40,40' with as high temperature as for example 1200 ^aC, may flow directly for expansion in a turbine unit designed to withstand such high temperatures. Thereupon, the flue gas is fed via a standard heat recovery steam generator 29,29' to a cooler 47,47'. After the cooler 47, enriched flue gas is fed to the CO₂ capturing plant 11. The flue gas to be fed for the CO₂ capture is not pressurized.

After the cooler 47 ' , flue gas is re-circulated from the second combustor 10' to the compressor unit 13' of the second turbine 12 ' , where flue gas is given a pressure of for example 15 bar and a temperature of 400 ²C, prior to leading the flue gas to the combustors 10,10' for cooling the exterior of the flame tube 40,40'. The re-circulated flue gas is then fed through the holes in the flame tube 40,40' and into the combustion zone where this flue gas cools down the combustion process and mixes with the combustion products, so that these are cooled further down. The result is an increased concentration of CO₂ in the flue gas, so that the CO₂ capturing plant 11 may work at conditions implying advantages both with respect to energy and cost effectiveness. The plant may relatively easy be realized.

Reference is made to Figure 1. In the process shown in Figure 2, a standard combustor 10 is initially used, the modification being necessary with related to the management of the air flow. Standard, more or less conventionally combustors are suitable for use in connection with the invention, since these often are equipped with perforations in the flame tube, allowing cooling air to enter into the combustor, mixing with the combustion products and cooling these further down. The constructive design of a typical standard combustor may be found in open literature, textbooks and publications. It should be appreciated, however, that according to the present invention, the standard combustor is usually used in another way, since the air usually first is fed along the exterior side of the flame tube 40 (between the mantle 27 and the flame tube 40) and then fed into the flame tube 40 at the primary zone and the secondary zone of the combustion process. According to the present invention, however, the method (air management) is different, since the combustor 10 works with mainly two separate gas streams, one stream being fed directly, together with the fuel, centrally internally into the primary zone of the flame tube 40, while the second stream flows along the exterior side of the flame tube 40, cooling said exterior portions prior to entering into the flame tube 40 through the openings 55. The ducts at the primary zone are constructive details which have to be decided upon subsequent to experiments in a combustor test rig at the gas turbine and combustor supplier facilities. Also, at the inlet of the combustion zone there exist valves and distributors which are not shown in the Figure, and which do not part of the invention, but represent known modifications well known for a person skilled in the art.

Even if the Figure shows a plant comprising two combustors, it is possible to use several combustors. Further, it should be appreciated that the combustors are schematically shown, where parts which are obvious for a person skilled in the art are not shown. An example of such omission is amongst other the pressure jacket which necessarily must surround the combustor.

According to the embodiment shown and described the CO₂ capturing plant used may for example be of the amine type. Such type of solution is in use in existing plants. It may, however, be possible to use new types of CO₂ capturing units without deviating from the inventive idea.

In the process shown in Figure 2, a combined cycles gas power plant and an atmospheric CO₂ capturing plant, capturing CO₂ from the flue gas with enriched CO₂, is used. Two integrated gas turbine plants 12,12' are used, the plants being cross connected with part streams to the combustors 10,10', and working in principle with the separate gas streams, wherein one stream is supplied directly together with fuel centrally into the flame tube 40,40', and the other stream is flowing through the jacket 27, before entering through the openings in the flame tube and gradually mixing with the first part stream. The gas supplied to the exterior of the flame tube 40,30' is re- circulated exhaust gas, and is used to cool down the components of the combustor and then mixed with combustion products going to the turbines 14,14' of the gas turbines 12,12', so that practical advantages may be gained with respect to reduced use of expensive high temperature resistant materials. The flue gas is then flowing to a heat recovery steam generator 29,29' wherein the flue gas is cooled down and the flue gas is further directed to a cooler 47,47'. The re-circulated flue gas for the gas turbine plant 12 is directed to a scrubber 56, whereupon the flue gas then is directed to the inlet of the compressor unit 13 ' , where the flue gas is compressed. From the compressor unit 13 ' , the flue gas stream is divided in two streams, one stream leading to the compressor 10 and the other stream leading to the second combustor 10 ' . The re-circulated flue gas is used for cooling the exterior of the flame tube 40,40' and other components of the combustor.

Further, the re-circulated flue gas is fed through the holes in the flame tube and into the combustion zone where it serves as a coolant for the combustion process and is mixed with the combustion products, so that these are cooled further down. The results is that CO₂ concen- tration in the flue gas may be increased to a maximum, since fresh air and fuel is supplied directly and centrally into the interior of the flame tube, producing a nearly stoichiometric combustion process, a small surplus of oxygen may be kept in a controlled manner at a level while at the same time achieving a stable combustion.

According to the embodiment shown in Figure 2 , two different gas turbines producing different output effects are used, for example a difference in output of a ratio 1:3. It should be appreciated, however, that other ratios may be used or similar gas turbines etc. may be used, i.e. with output rations between 1:3 and 1:1 with respect to exploitable output. The other gas turbine parameters, such as for example pressure conditions, should, however, be more or less equal. Since available gas turbines on the market exist as standard models only of a given size and output, the process shown in Figure 2 may be adapted to given gas turbines .

The combined cycle gas turbines 12,12' in the gas power plant may be of a standard type, and the invention will involve a modification of the control system for gas streams to the combustors and the inlet ducts of the com- bustors. The present invention may be adapted in a simple manner to all gas turbine plants, and is not limited to external combustors, «silo type» combustors, but may simply be used for all types of integrated combustors, for example annular combustors or canned shaped combustors. In addition, the interaction of CO₂ capturing plant 11 may be adapted in best possible way for practical implementation and cost effectiveness. The gas turbines 12,12' used, comprise a compressor unit 13,13' and a gas turbine unit 14,14', each of the turbine units driving a generator 16,16'. The compressor unit 13 delivers air through an exit duct 17 to the combustor 10. Typical temperature and pressure of the air delivered by the compressor unit 13 may be 400 ^aC and 15 bar. Flue gas from the combustor 10 is fed through pipe duct 48 to the inlet of the turbine 14. The temperature of the flue gas leaving the combustor 10 may typically be in the order of 1200-1400 ²C, which is a typical inlet temperature for the turbine of conventional gas turbines . From the turbine 14, the flue gas is fed through the heat recovery generator 28 producing steam, delivered to a steam turbine 58 powering a generator 58, and/or possible supplying heat to a industrial plant. The temperature of the flue gas when leaving the cooler 47 may typically be in the order of 100-60 ²C. In the embodiment shown in Figure 2, the pressure is atmospheric at the inlet to the CO₂ capturing plant 11, while the temperature may typically be about 100-60 ²C and the proportion of CO₂ is about 10 volume% . From the CO₂ capturing plant 11 the cleaned flue gas is vented to atmosphere. Captured CO₂ from the CO₂ capturing plant 11 is compressed, condensed, and pumped, for example back to an oil well or to a storage site of any suitable type.

The flue gas from the other turbine 14 has a temperature in the order of 500-600 ²C and is fed from the turbine unit outlet to a heat recovery steam generator 29' and further to a cooler 47 ' , reducing the temperature to approximately 15 ³C. The un-cleaned flue gas is further transferred to the scrubber 56 where water is removed from the flue gas. The flue gas has at this stage a pressure of approximately 1 bar and a temperature of approximately 15 ²C, and is further fed to the inlet of the compressor unit 13 ' of the second gas turbine 12 ' . Here the flue gas is compressed to typically 15 bar and 400 ^SC. The flue gas is then split in two part streams, such that one part stream flows around the combustor 10 and the other part stream is directed to the second combustor 10'.

Figure 3 shows in principle an alternative embodiment of a combustor 10 and an alternative method of re- circulating the flue gas through and around the flame tube 40. Also this combustor 10 works in principle with two separate gas steams, where one stream of fresh air is supplied directly together with fuel centrally into the primary zone internally in the flame tube 40. The other gas stream is supplied to the exterior of the flame tube 40, flowing in an opposite direction through the annual space between the flame tube 40 and the jacket 27, in order to obtain optimal cooling of the flame tube 40 and the other components of the components, whereupon the stream flows into the flame tube 40 through the openings 55. This solution is based on the same principle as for the combustor shown and described in connection with Figure 1. The combustor according to Figure 3 is particularly adapted to a practical embodiment of a standard gas turbine type, based on counter stream heat exchange, and which also provides advantages in order to secure an optimal temperature difference in the heat exchanger.

The present invention is not limited to a CO₂ capturing plant working at atmospheric pressure, since it is feasible to install a pressurized CO₂ capturing plant in the system downstream of the combustor 10 in the pipe line

48 or integrated in the turbine 14, and still being able to obtain the advantage residing in that the CO₂ portion in the flue gas represents approximately 10 volume%. The temperature at the inlet of the CO₂ capturing plant must, however, be reduced to 100-50 ^aC by using expensive gas- gas heat exchangers, for example as described in WO 2004/072443. Hence, a more cost effective and energy effective CO₂ capturing plant 11 may be obtained, while the heat exchanging plant will more expensive.

According to the invention, cooling of the flame tube 40,40' may be based either on counter flow or parallel flow cooling, without deviating from the inventive idea.

Claims

C l a i m s

1. Method for increasing energy and cost effectiveness of a gas power plant or a thermal power plant, and for energy and cost effective CO₂ capturing, said gas power plant or thermal power plant comprises gas turbine plants or combined plants with steam and gas turbine cycles, comprising preferably at least two gas turbine plants with a compressor unit (13,13') and a turbine unit (14,14') and further comprising combustor (10) with a flame tube (40), where said combustor (10) works with mainly two separate gas streams where one gas stream comprises air supplied together with fuel centrally internally in the flame tube, and where the second gas stream comprises a cooling gas which flows along the exterior of the flame tube, the flue gas from said combustor (10) is expanded and cooled down, passing through a cleaning unit (11) where at least substantial portions of CO₂ content of the flue gas is removed, prior to being vented to the atmosphere, c h a r a c t e r i z e d i n t h a t a second combustor (10') is used, the flue gas from said second combustor (10'), in un-cleaned, cooled and pressurized condition, being fed to at least one of the combustors (10,10'), flowing along the exterior of said at least one flame tube for cooling said flame tube (40,40'), whereupon said re-circulated, more or less un-cleaned flue gas is directed into said flame tube through holes in said flame tube in order to cool the combustion process and mix with the combustion products.

2. Method according to claim 1, wherein both flame tubes (40,40') are cooled by flue gas delivered from the first combustor (10), the flue gas being cooled, for example down to approximately 15 ²C prior to and then compressed to approximately 400 ³C prior to flowing along the exterior of said flame tubes (40,40').

3. Method according to claim 1 or 2 , wherein the re- circulated flue gas is directed through holes (55) in said flame tube (40,40') along the entire length of the flame tube.

4. Method according to one of the claims 1-3, wherein the air stream from the compressor unit (13) is directed directly together with fuel into the primary zone in the combustor (10,10'), in order to provide as close to a stoichiometric combustion and where the combustion process is cooled down by means of re-circulated flue gas.

5. Method according to one of the claims 1-4, wherein the pressure of the flue gas is increased after expansion and cooling, and where this pressurized flue gas is re- circulated back to the combustor (40,40'), optimally enriched of CO₂ before the CO₂ membrane plant (11), to the annular space of the combustor (10,10') between the flame tube (40,40') and the jacket (27,27').

6. Method according to one of the claims 1-5, wherein the flue gas from the gas turbine (s) passes through a heat recovering steam generator (29,29') producing steam, the steam powering one or more steam turbines (58) .

7. Method according to one of the claims 1-6, wherein a first and second cross connected gas turbine plant

(12,12') are used, having combustor(s) (10,10'), the gas cooling the exterior of the flame tube (40) , and then being mixed with combustion products and flowing to the turbine unit (14,14'), and that the flue gas produced in the flame tube (40') is fed to the turbine unit (14') in the other gas turbine (12'), whereupon the flue gas further is fed to a heat recovery steam generator (29') where the flue gas is cooled down and then directed via a water cooler (47') to the inlet of the compressor unit

(13') of the other gas turbine (12') wherein the flue gas is compressed and split in two flue gas streams.

8. Thermal power plant comprising at least one gas turbine plant or a combined cycle gas turbine plant, comprising at least two gas turbine plants (12,12'), comprising a compressor unit (13,13'), a turbine unit (14,14') and preferably also at least one steam turbine (58), said thermal power plant further comprising a combustor (10) equipped with a flame tube (40) and a surrounding mantle (27) forming an annulus , a cooler (47), a plant (11) for capturing CO₂ from the flue gas from the combustor (10) and one or more heat recovery steam generator (29,29'), and corresponding pipe line system between the various units in the gas turbine plant, the CO₂ being removed from the flue gas from the combustor (10) before venting to the atmosphere, c h a r a c t e r i z e d i n that the thermal power plant further comprises a second combustor (10') equipped with a flame tube (4O')and a surrounding mantle (27), the thermal power plant being configured in such way that the flue gas from the second combustor (10'), subsequent to being cooled, is used to cool down the flame tube (40,40') in the at least one combustors (40,40'), preferably both combustors (40,40'), and that the flame tube (40,40') is equipped with a number of openings for supply of re- circulated, un-cleaned flue gas into the flame tube (40) through the openings in the flame tube in order to cool down the combustion process and to be mixed with the combustion products.

9. Power plant according to claim 8, wherein the re- circulated flue gas is compressed and wherein CO₂ is concentrated up to a level which is within the operating conditions of the combustor (10,10').

10. Power plant according to claim 8 or 9 , wherein re- circulated flue gas is supplied to the mantle (27) in the region of the exit from the combustor (10) , and that the flue gas flows towards the primary zone of the combustor, so that optimal cooling of the flame tube is obtained.

11. Power plant according to one of the claims 8-10, wherein the turbine plant comprises two cross connected gas turbine plants (12,12') where both gas turbine plants (12,12') are run on un-cleaned flue gas from the combustors (10,10'), air being supplied to the combustors (10,10') from the compressor unit (13) of the first turbine plant (13).

12. Combustor intended to be used in a thermal or gas power plant, comprising at least two gas turbine plants or a combined cycle gas turbine plant, where said combustor (10,10') comprises a flame tube (40,40') and a surrounding mantle (27), forming an annulus surrounding the flame tube (40,40') , c h a r a c t e r i z e d i n t h a t the flame tube (40,40') is equipped with a plurality of openings, at least arranged in the region of the primary combustion zone of the combustors (10,10'), so that the cooling gas is made to flow through the mantle (27,27') in the same direction as the combustion products and so that the re- circulated flue gas contributes to cooling of the combustion process, mixing with the combustion products, and the fresh air being supplied directly together with fuel centrally into the flame tube (40,40') in order to provide a nearly stoichiometric combustion.

13. Combustor according to claim 12, wherein the inlet for the cooling flue gas is arranged in the region of the outlet of combustion products, so that the cooling flue gas flows through the mantle (27,27') in opposite direction of the combustion products.