Abstract:
Improved methods and systems for power plants with CO2 capture and especially power plants with CO2 capture for enhanced oil recovery (EOR) purposes.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally concerns power plants with CO 2  capture and especially power plants with CO 2  capture for enhanced oil recovery (EOR) purposes. 
       BACKGROUND OF THE INVENTION 
       [0002]    It is known that power plants for the generation of electrical and thermal energy having gas and/or steam turbines driven by fossil fuels may be equipped with systems based on chemical solvent processes (amines, chilled ammonia and others) for the capture of carbon dioxide (CO 2 ) from the flue gas resulting from the combustion of the fossil fuels; the so called “post combustion carbon capture process”. 
         [0003]    It is also known that exhaust gas recirculation can be used in fossil-fired power plants to control the production of gaseous emissions, in particular to enrich the CO 2  content of the exhaust gas, reducing or eliminating the need for costly CO 2  capture. 
         [0004]    It is also known that an alternative technology is the so called “oxyfuel process” based on combustion of fossil fuels in an oxygen-enriched stream instead of the ambient air (which contains approximately 21% by volume of oxygen only). If nitrogen is removed prior to combustion, the flue gas stream would then have less nitrogen and the concentration of CO 2  becomes higher, reducing or eliminating the need for costly CO 2  capture. 
         [0005]    Following any necessary post-treatment, the separated CO 2  can be forwarded into storage or used for enhanced oil recovery or other purposes. 
         [0006]    Further information concerning this technical background can be found in “Developments and innovations in carbon dioxide (CO 2 ) capture and storage technology”; Volume 1; Carbon dioxide (CO 2 ) capture, transport and industrial applications; edited by M. Mercedes Maroto-Valer; Woodhead Publishing Limited, 2010, ISBN 978-1-84569-533-0. 
         [0007]    In the post-combustion CO 2  capture system the whole flue gas flow is processed at low pressure, therefore this system (apparatus, pipelines, etc.) becomes voluminous and expensive. Some vessels can become so large, that the system is not feasible as a one-train solution, therefore several trains working in parallel are required for realization of such a process. 
         [0008]    One issue with the post-combustion CO 2  capture system results from the low CO 2  concentration in the flue gas (3-15% depending on the fuel and combustion system). The efficiency of the chemical solvent process plant depends on the CO 2  concentration in the flue gas, a low CO 2  concentration generally resulting in a low efficiency. 
         [0009]    The oxyfuel-based system has a similar problem, i.e. a large amount of air is required to be treated in the air separation unit for the production of the oxygen that goes into combustion. The system therefore becomes large, possibly requiring a multi-train solution and inefficient. 
         [0010]    Exhaust gas recirculation has the problem that the oxygen lean recirculation gas, when mixed with incoming ambient air results in a oxygen depleted/CO 2  enriched air stream for the power plant that can affect the output, efficiency, stability and operation of the power plant. 
         [0011]    For all of the above reasons, there remains a need in the art for improvements to CO 2  capture from a power plant. 
       SUMMARY OF THE PRESENT INVENTION 
       [0012]    The present invention provides improved techniques for CO 2  capture from a power plant and reuse thereof that is an improvement over the techniques known in the prior art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic drawing showing a fossil fuel power plant with CO 2  capture according to the invention. 
           [0014]      FIG. 2  is a schematic drawing showing a fossil fuel fired combined cycle power plant with CO 2  capture according to the invention. 
           [0015]      FIG. 3  is a schematic drawing showing a fossil fuel fired gas turbine cycle power plant with CO 2  capture according to the invention. 
           [0016]      FIG. 4  is a schematic drawing showing a fossil fuel fired steam cycle power plant with CO 2  capture according to the invention. 
           [0017]      FIG. 5  is a schematic drawing showing a fossil fuel fired combined cycle power plant with CO 2  capture for EOR according to the invention. 
           [0018]      FIG. 6  is a schematic drawing showing a fossil fuel fired combined cycle power plant with CO 2  capture, for providing CO 2 , N 2  and CO 2  /N 2  mixtures for EOR according to the invention. 
           [0019]      FIG. 7  is a schematic drawing showing a fossil fuel fired combined cycle power plant with CO 2  capture for EOR, having a direct contact flue gas cooler according to the invention. 
           [0020]      FIG. 8  is a schematic drawing showing a fossil fuel fired combined cycle power plant with CO 2  capture for EOR, having a chilled water direct contact flue gas cooler according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    The present invention provides improved techniques for CO 2  capture from a power plant that is an improvement over the techniques known in the prior art and particularly to CO 2  capture for EOR (Enhanced Oil Recovery) purposes. One goal of the present invention is to create an efficient power plant with CO 2  combustion. 
         [0022]    The process according to the present invention is based on a combination of the exhaust gas recirculation process, oxy-fuel process and post combustion process (chemical solvent process). A portion of the exhaust gas from the power plant is recirculated to the air inlet and mixed with both incoming ambient air and an oxygen rich gas stream. The oxygen content of the mixed stream is adjusted by addition of the oxygen rich stream that may be provided from an air separation unit, or other appropriate source. This mixture results in a CO 2  enriched flue gas from the power plant that is partly recycled to the power plant with the remainder flowing to the chemical solvent process unit, where the CO 2  is separated. This process of flue gas recycle and oxygen enrichment are used to control the parameters of the combustion process for the power plant and to make the CO 2  separation easier. 
         [0023]    The invention will be described in greater detail with reference to the drawing figures, wherein like components are labeled with like reference numerals. In particular,  FIG. 1  is a schematic drawing showing a fossil fuel power plant with CO 2  capture according to the invention. In  FIG. 1 , a power plant  100  is fueled by a fossil fuel source  10  that may be a solid, liquid or gaseous source, in addition to air from an air source  20 , and an oxygen rich gas  32  from an air separation unit (ASU)  30  that is supplied by an air source  34 . The oxygen rich gas  32  is preferably 50% to 100% oxygen. The ASU separates the air supplying the oxygen rich gas  32  to the power plant  100  and releasing a waste stream of nitrogen enriched gas  36 . The power plant  100  emits flue gas  42  that is treated in a flue gas treatment unit  40 . The flue gas treatment unit  40  operates to cool the flue gas  42  and to remove water  44  and various waste  46  while emitting a CO 2  enriched gas stream  48 . Part of the CO 2  enriched gas stream  48  is recycled and mixed with the air from the air source  20  and the oxygen rich gas  32  prior to being fed to the power plant  100 . An optional process of heating part of the flue gas  42  in a heater  43  and then mixing the pre-heated gas with the recycled portion of CO 2  enriched gas stream  48  can be employed. This allows for pre-heating of the feed gas to the power plant  100 . The CO 2  enriched gas stream  48  that is not recycled to the power plant  100  is processed for waste removal in a chemical solvent process unit  50  that emits a waste stream  52  and a CO 2  containing gas  54 . The CO 2  containing gas  54  can then be compressed and dried and sent to storage units  60  from which it can be supplied for end user processes  70 . 
         [0024]      FIG. 2  is a schematic drawing showing a fossil fuel fired combined cycle power plant with CO 2  capture according to the invention. The system shown in  FIG. 2  is the same as that shown in  FIG. 1  with the exception that the power plant  100  has been replace with a combined gas turbine and steam generator plant. In particular, the mixed CO 2  air and oxygen rich gas is delivered to a gas turbine  200  with the flue gas  42  passing through a heat recovery steam generator with rankine cycle  205  prior to the delivery to the flue gas treatment unit  40 . The heat recovery steam generator can optionally be supplied with fossil fuel from the fossil fuel source  10 . Further, optionally the recycle CO 2  stream can be fed directly to the plant  200  without premixing with air or oxygen enriched gas. 
         [0025]      FIG. 3  is a schematic drawing showing a fossil fuel fired gas turbine cycle power plant with CO 2  capture according to the invention. The system shown in  FIG. 3  is the same as that shown in  FIG. 1  with the exception that the power plant  100  is more specifically identified as a gas turbine. In particular, the mixed CO 2  air and oxygen rich gas is delivered to a gas turbine  300  with the flue gas  42  delivered to the flue gas treatment unit  40 . 
         [0026]      FIG. 4  is a schematic drawing showing a fossil fuel fired steam cycle power plant with CO 2  capture according to the invention. The system shown in  FIG. 4  is the same as that shown in  FIG. 1  with the exception that the power plant  100  is more specifically identified as a steam turbine. In particular, the mixed CO 2  air and oxygen rich gas is delivered to a steam turbine  400  with the flue gas  42  delivered to the flue gas treatment unit  40 . 
         [0027]      FIG. 5  is a schematic drawing showing a fossil fuel fired combined cycle power plant with CO 2  capture for EOR according to the invention. The system shown in  FIG. 5  is the same as that shown in  FIG. 2  with the exception that the end user is specifically identified as an EOR. In particular, CO 2    62  can be delivered from storage unit  60  to an EOR user  72 . Alternatively, the nitrogen rich gas  36  from the ASU  30  can be delivered to and EOR user  74 . In a further alternative, CO 2    62  from the storage unit  60  can be mixed with the nitrogen rich gas  36  from the ASU  30  and delivered as a mixture to an EOR user  76 . 
         [0028]      FIG. 6  is a schematic drawing showing a fossil fuel fired combined cycle power plant with CO 2  capture, for providing CO 2 , N 2  and CO 2 /N 2  mixtures for EOR according to the invention. The system shown in  FIG. 6  is the same as that shown in  FIG. 5  with the exception that the CO 2 /N 2  gas mixture is derived in a different manner. In particular, part of the recycle CO 2  stream can be treated in oxygen removal unit  600  to remove oxygen and provide a N 2  enriched stream  602  that is then mixed with the CO 2  containing gas  54  to form a CO 2 /N 2  gas mixture that is delivered to storage unit  60  and delivery to EOR user  76 . The oxygen removal unit  600  can be any suitable unit, such as a catalytic de-oxo unit with CH 4  or H 2  from an external source or from reforming of natural gas, or a conventional burner with CH 4  or H 2 . 
         [0029]      FIG. 7  is a schematic drawing showing a fossil fuel fired combined cycle power plant with CO 2  capture for EOR, having a direct contact flue gas cooler according to the invention. The system shown in  FIG. 7  is the same as that shown in  FIG. 5  with the exception that the flue gas treatment unit has been replaced with a more specific water coolant treatment unit and the chemical solvent process has been more specifically identified as an amine wash plant. In particular, the flue gas  42  is treated in water coolant treatment unit  700  to remove water  44  and waste  46  prior to being recycled or further treated in amine wash plant  750 . In this system the ASU  30  can be a cryogenic ASU. 
         [0030]      FIG. 8  is a schematic drawing showing a fossil fuel fired combined cycle power plant with CO 2  capture for EOR, having a chilled water direct contact flue gas cooler according to the invention. The system shown in  FIG. 8  is the same as that shown in  FIG. 7  with the exception that the water coolant treatment unit is specifically identified as a chilled water direct contact flue gas cooler. In particular, the flue gas  42  is treated in chilled water direct contact flue gas cooler  800  to remove water  44  and waste  46  prior to being recycled or further treated in amine wash plant  750 . This system may also employ a cryogenic ASU. 
         [0031]    The invention offers several advantages. By using oxygen enriched air from an ASU as part of the recycle feed to the power plant, the CO 2  concentration in the recycle gas is greater than a feed stream because there is less nitrogen in the feed. This makes the power plant more efficient. In addition, since less nitrogen is entering the system, there is a greater concentration of CO 2  in the flue gas. This makes the chemical solvent treatment process more efficient and increases the efficiency of the whole power plant system. In addition, only a fraction of the air required needs to be separated in the air separation unit when operating according to the invention. Therefore the irreversibility caused by the air separation is reduced. The air separation plant can be more compact in the invention because of the reduced air flow requirement and the size of the absorption plant is also reduced because of the lower nitrogen concentration in the flue gas. It is therefore possible for the system of the invention to be used in either a single-train- or double-train solution, which allows for simpler control methodology. 
         [0032]    By using the invention, the mixed gas provided to the power plant is oxygen enriched and therefore the output, efficiency, stability and operation of the power plant is enhanced. Further, the system of the invention can advantageously be used for retrofitting of existing power plants, because only minor changes are required to the power plant input. 
         [0033]    It is anticipated that other embodiments and variations of the present invention will become readily apparent to the skilled artisan in the light of the foregoing description, and it is intended that such embodiments and variations likewise be included within the scope of the invention as set out in the appended claims.