PROCESSING SYSTEM

BACKGROUND

1. Field

[0001] The disclosed subject matter relates to a system and method of managing an amount of energy utilized by a flue gas stream processing system. More particularly, the disclosed subject matter relates to a method of optimizing an amount of energy used in a flue gas processing system that includes oxy- firing boiler combustion and a carbon dioxide capture system.

2. Description of Related Art

[0002] Combustion of fuel, particularly carbonaceous materials such as fossil fuels and waste, results in flue gas streams that contain impurities, such as mercury (Hg), sulfur oxides (SOx) and nitrogen oxides (NOx), and particulates, such as fly ash, which must be removed or reduced prior to releasing the flue gas to the environment. In response to regulations in place in many jurisdictions, numerous processes and apparatus have been developed to remove or reduce the impurities and particulates in the flue gas.

[0003] The typical method of reducing particulates, Hg, NOx, and SOx emissions from steam generating boilers is by the use of flue gas treatment equipment including electrostatic precipitators (ESP), fabric filter bag houses, catalytic systems, or wet and dry scrubbers. Additionally, carbon dioxide capture systems (also referred to as "carbon capture systems") may be employed in a flue gas processing system if carbon dioxide emissions are to be kept at or below a certain level.

[0004] Flue gas treatment equipment, i.e., emission control devices and systems, are large and expensive to purchase and operate, which significantly increases the capital cost of the facility and operating costs. Additionally, flue gas stream treatment equipment typically requires a large amount of space at the plant site.

[0005] One way of reducing the costs of post combustion flue gas stream treatment is to combine various pollutant reduction techniques and equipment into a single operation, often referred to as "multi-pollutant control." However, combined techniques and equipment are not applicable or feasible in every flue gas stream processing system. Accordingly, other processes and/or systems that facilitate the reduction of cost or overall energy use of the flue gas stream processing system are desired. SUMMARY

[0006] According to aspects illustrated herein, there is provided a method for managing an amount of energy utilized by a carbon dioxide capture system, the method comprising: providing a fuel and a feed stream comprising oxygen to a combustion system, the feed stream including a portion of a flue gas stream generated upon combustion of the fuel in the combustion system; subjecting the flue gas stream to a carbon dioxide capture system to remove carbon dioxide therefrom; and adjusting an amount of at least one of an oxygen stream or the portion of the flue gas stream introduced to the feed stream such that the feed stream maintains an oxygen concentration in a range of between 10% to 90% by volume and the carbon dioxide capture system operates at an energy load between 1.4 GJ/ton of carbon dioxide and 3.0 GJ/ton of carbon dioxide, thereby managing an amount of energy utilized by the carbon dioxide capture system.

[0007] According to another aspect illustrated herein, there is provided a method for managing an amount of energy utilized by a carbon dioxide capture system, the method comprising: providing a fuel and a feed stream comprising oxygen to a combustion system, the feed stream including a portion of a flue gas stream generated upon combustion of the fuel in the combustion system; subjecting the flue gas stream to a carbon dioxide capture system to remove carbon dioxide therefrom; and adjusting an amount of the feed stream directed to the combustion system such that the flue gas stream maintains a carbon dioxide concentration in a range of between 10% to 60% by volume and the carbon dioxide capture system operates at an energy load between 1.4 GJ/ton of carbon dioxide and 3.0 GJ/ton of carbon dioxide, thereby managing an amount of energy utilized by the carbon dioxide capture system.

[0008] According to another aspect illustrated herein, there is provided a method for managing an amount of energy utilized by a carbon dioxide capture system, the method comprising: providing a fuel and a feed stream comprising oxygen to a combustion system, the feed stream including a portion of a flue gas stream generated upon combustion of the fuel in the combustion system; subjecting the flue gas stream to a carbon dioxide capture system to remove carbon dioxide therefrom; adjusting an amount of the feed stream directed to the combustion system such that the flue gas stream maintains a carbon dioxide concentration in a range of between 10% to 60% by volume; and adjusting an amount of at least one of an oxygen stream or the portion of the flue gas stream introduced to the feed stream such that the feed stream maintains an oxygen concentration in a range of between 10% to 90% by volume and the carbon dioxide capture system operates at an energy load between 1.4 GJ/ton of carbon dioxide and 3.0 GJ/ton of carbon dioxide, thereby managing an amount of energy utilized by the carbon dioxide capture system, thereby managing an amount of energy utilized by the carbon dioxide capture system.

[0009] The above described and other features are exemplified by the following figures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Referring now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike:

[0011] FIG. 1 illustrates a flue gas stream processing system according to one embodiment disclosed herein.

[0012] FIG. 2 illustrates a flue gas stream processing system according to one embodiment disclosed herein.

[0013] FIG. 3 illustrates a flue gas stream processing system according to one embodiment disclosed herein.

DETAILED DESCRIPTION

[0014] FIG.l illustrates a flue gas stream processing system 100 that includes a combustion system 120 in communication with oxygen producing unit 130. The combustion system 120 may be any system configured to combust a fuel 122 to produce a flue gas stream 124. Examples include, but are not limited to pulverized coal (PC) combustion, oxy-firing boilers and circulating fluidized bed combustors (CFB). In FIG.l combustion system 120 is an oxy-firing boiler configured to burn a fuel 122 provided to the combustion system in the presence of a feed stream 132 provided to the combustion system. The flue gas stream 124 is generated upon combustion of the fuel 122 and is produced at an output of the combustion system 120.

[0015] In one embodiment, as shown in FIG. 1, feed stream 132 is a combination of an oxidant stream 134, a fresh air stream 136 and a portion 124a of the flue gas stream, which has been subjected to contaminant removal. In another embodiment, as shown in FIG. 2, the feed stream 132 includes the oxidant stream 134, the fresh air stream 136 and a portion 124b of the flue gas stream 124. In a further embodiment, as shown in FIG. 3, the feed stream includes the oxidant stream 134, the fresh air stream 136 and the portion 124a of the flue gas stream 124 and the portion 124b if the flue gas stream 124. While not illustrated in FIGS. 1- 3, it is contemplated that the feed stream may be the oxidant stream 134, the fresh air stream 136, the portion 124a of the flue gas stream 124, or the portion 124b of the flue gas stream 124. Incorporation of the oxidant stream 134 and the fresh air stream 136 into the feed stream 132 maintains the ratio of oxygen to fuel for proper combustion in the combustion system 120.

[0016] The oxidant stream 134 is generated by the oxygen producing unit 130, which receives an air stream 138. In one embodiment, the oxygen producing unit 130 is an air separation unit (ASU). The ASU may be, for example, an ion transport membrane (ITM), an oxygen transport membrane (OTM), or a cryogenic air separation system, e.g., a rectification column. The oxygen producing unit 130 is not limited in this regard, since the oxygen producing unit may be any equipment capable of producing the oxidant stream 134.

[0017] The oxidant stream 134 generally contains oxygen (0 ₂ ), however, other elements and gases may be present in the oxidant stream as well. In one embodiment, the oxidant stream 134 is at least 90% wt. oxygen. In another embodiment, the oxidant stream 134 is at least 95% wt. oxygen.

[0018] The oxygen producing unit 130 requires a large energy load to process the air stream 138 and generate the oxidant stream 134. However, in many applications, the amount of energy expended on generating oxidant stream 134 is a benefit to the overall flue gas stream processing system 100 since a reduced volume of the flue gas stream 124 is realized as compared to systems not utilizing the oxygen producing unit 130.

[0019] The fresh air stream 136 is not subjected to any processing prior to joining with the oxidant stream 134 and flue gas stream 124a, 124b to form the feed stream 132. Accordingly, the fresh air stream 136 includes a variety of elements and gases, including, but not limited to, oxygen, carbon dioxide, nitrogen, water, and the like. In one embodiment, fresh air stream 136 may be subjected to some processing to remove particulates, if any, therefrom.

[0020] As shown in FIG. 1, the feed stream 132 and the flue gas stream 124 may proceed through an air preheater (APH) 126, which facilitates an increase of temperature of the feed stream by transferring heat from the flue gas stream.

[0021] In one embodiment, the flue gas stream 124 includes contaminants such as, but not limited to, sulfur oxides (SOx), mercury (Hg), carbon dioxide (C0 ₂ ), particulates, nitrous oxide (N ₂ 0), and to a lesser extent, nitrogen oxides (NOx). The concentration of NOx present in flue gas stream 124 is dependent upon several factors, including, but not limited to, the nitrogen content of the fuel 122, and the concentration of nitrogen provided to the combustion system 120 via feed stream 132. As the percentage of oxygen present in feed stream 132 increases, the percentage of nitrogen in the feed stream provided to the combustion system decreases, thereby decreasing the percentage of NOx present in the flue gas stream 124.

[0022] Downstream of the combustion system 120 is a contaminant control system

140 (also referred to as an air quality control system or "AQCS"). In one embodiment, as shown in FIG. 1, the contaminant control system 140 includes an electrostatic precipitator (ESP) 142 and a flue gas desulfurization (FGD) system 144. It is contemplated that the contaminant control system 140 may include more or less devices than what is shown in FIG. 1. For instance, in one embodiment, the contaminant control system 140 includes only a flue gas desulfurization system 144. The flue gas desulfurization system 144 may either be a dry flue gas desulfurization (DFGD) system or a wet flue gas desulfurization (WFGD) system. While not shown in FIG. 1 , it is contemplated that different and/or additional devices may be included in the contaminant control system 140, including, but not limited to, a selective catalytic reduction (SCR) system, a bag house, a venturi-type scrubber, and the like.

[0023] The flue gas stream 124 generated by the combustion system 120 is subjected to the contaminant control system 140. In one embodiment, the flue gas stream 124 is subjected to the flue gas desulfurization system 144, which facilitates the removal of SOx from the flue gas stream.

[0024] After proceeding through the contaminant control system 140, a treated flue gas stream 124' is subjected to a carbon dioxide capture system 150 to remove carbon dioxide from the flue gas stream. The carbon dioxide capture system 150 may be any system capable of removing carbon dioxide from the flue gas stream 124' to produce a carbon dioxide stream 151 and a reduced carbon dioxide flue gas stream 152. Examples of the carbon dioxide capture system 150 include, but are not limited to systems referred to as "advanced amine" systems, "chilled ammonia" systems such as is disclosed in International Patent Application Publication No. WO2006/022885, as well as other solvent absorption processes (e.g., carbonates/bicarbonates), molecular sieves, membrane separation processes, gas processing units, and the like.

[0025] Still referring to FIG. 1, at least a portion 124a of the treated flue gas stream

124' may be directed to form the feed stream 132 after the flue gas stream exits the combustion system 120. The portion of the flue gas stream 124a directed to the feed stream 132 is drawn from a location A within the flue gas stream processing system 100. As shown in FIG. 1, location A is positioned downstream of the flue gas desulfurization system 144. In another embodiment, as shown in FIG. 2, a portion 124b of the flue gas stream 124 is drawn from a location B within the flue gas stream processing system 100, which is positioned upstream of the desulfurization system. In yet a further embodiment, as shown in FIG. 3, a portion 124a of the flue gas stream 124a is drawn from the treated flue gas stream 124' at location A and a portion 124b of the flue gas stream is drawn from the flue gas stream 124 at a location B.

[0026] While FIGS. 1-3 illustrate at least two different locations A and B, the system

100 is not limited in this regard as the flue gas stream may be drawn from another point within the system, e.g., between the ESP 142 and the flue gas desulfurization system 144. Locations A and B may depend on the fuel 122 combusted in the combustion system 120. For example, the flue gas stream 124 may be recycled to the combustion system prior to going through the flue gas desulfurization system 144 if the fuel 122 has a low concentration of SOx.

[0027] The portion 124a, 124b of the flue gas stream directed to form the feed stream

132 may be directed by any mechanism having the capability of doing so, including, but not limited to, pipes, conduits, valves, and the like, as are known in the art.

[0028] After the portion 124a, 124b of the flue gas stream is combined with either the fresh air stream 136, the oxidant stream 134, or both, to form the feed stream 132, the feed stream is then provided to the combustion system 120.

[0029] The amount of the portion 124a, 124b of the flue gas stream present in the feed stream 132 is adjusted such that the feed stream maintains an oxygen concentration in a range between about 10% to about 90% by volume. In another embodiment, the amount of the portion 124a, 124b of the flue gas stream present in the feed stream 132 is adjusted such that the feed stream maintains an oxygen concentration in a range between about 40% to about 60% by volume.

[0030] Maintenance of the oxygen concentration in the feed stream 132 in a range between about 10% to about 90% by volume allows the carbon dioxide capture system 150 to operate at an energy load below about 3.0 gigajoule per ton of carbon dioxide (GJ/ton). In one example, the energy load is between 1.4 gigajoule per ton of carbon dioxide (GJ/ton of carbon dioxide) and 3.0 GJ/ton of carbon dioxide while in another example the energy load is between 1.4 GJ/ton of carbon dioxide and 2.5 GJ/ton of carbon dioxide.

[0031] In another embodiment, maintenance of the oxygen concentration in the feed stream in a range between about 40% to about 60% by volume allows the carbon dioxide capture system 150 to operate at an energy load below about 3.0 GJ/ton of carbon dioxide. In one example, the energy load is between about 1.4 GJ/ton of carbon dioxide and about 3.0 GJ/ton of carbon dioxide while in another example the energy load is between 1.4 GJ/ton of carbon dioxide and 2.5 GJ/ton of carbon dioxide.

[0032] In a further embodiment, maintenance of the oxygen concentration in the feed stream in a range between about 40% and about 60% by volume allows the carbon dioxide capture system 150 to operate at an energy load between about 2.1 to about 2.9 GJ/ton of carbon dioxide.

[0033] As shown in FIG. 1, adjustment of the amount of the portion 124a of the flue gas stream directed to the feed stream 132 may be done by a valve 200 positioned by location A and operated by a controller 210. The controller 210 may be programmed with instructions concerning the opening and closing of the valve 200, or may receive feedback from other measurements done in the system 100 (not shown).

[0034] As shown in FIG. 2, adjustment of the amount of the portion 124b of the flue gas stream directed to the feed stream 132 may be done by a valve 212 positioned by location B and operated by a controller 214. The controller 214 may be programmed with instructions concerning the opening and closing of the valve 212, or may receive feedback from other measurements done in the system 100 (not shown).

[0035] In another embodiment, as shown in FIG. 3, adjustment of the amount of the portion 124a, 124b of the flue gas stream directed to the feed stream 132 may be done by both of the valves 200 and 212, which are coupled to a controller 220. The controller 220 may be programmed with instructions concerning the opening and closing of the valves 200 and 212 or may receive feedback from other measurements done in the system 100 (not shown).

[0036] In another embodiment, an amount of the feed stream 132 provided to the combustion system 120 is adjusted such that the flue gas stream 124 is mixed with the feed stream to maintain a carbon dioxide concentration in a range of between 10% to 60% by volume. In another embodiment, an amount of the feed stream 132 provided to the combustion system 120 is adjusted such that the flue gas stream 124 is mixed with the feed stream to maintain a carbon dioxide concentration in a range of between 12% to 46% by volume. In a further embodiment an amount of the feed stream 132 provided to the combustion system 120 is adjusted such that the flue gas stream 124 is mixed with the feed stream to maintain a carbon dioxide concentration in a range of between 30% to 50% by volume. [0037] When the carbon dioxide range present in the flue gas stream is between 10% to 60% by volume, the carbon dioxide capture system 150 operates at an energy load below about 3.0 GJ/ton of carbon dioxide, without the load of the oxygen producing unit 120 and 2.3 to 6.6 GJ/ton of carbon dioxide with the load of the oxygen producing unit. In one example, without the load of the oxygen producing unit 120, the energy load is between 1.4 GJ/ton of carbon dioxide and 3.0 GJ/ton of carbon dioxide while in another example, the energy load is between 1.4 GJ/ton of carbon dioxide and 2.5 GJ/ton of carbon dioxide

[0038] If the carbon dioxide capture system 150 utilizes amine, when the carbon dioxide range present in the flue gas stream is between 10% to 60% by volume, there may be a reduction of amine thermal degradation, chemical degradation, and/or formation of heat stable salts.

[0039] In one embodiment, when about 90% of carbon dioxide is removed from the flue gas stream in the carbon capture system 150, the carbon capture system has an energy load in the range between about 1.5 GJ/ton and 3.0 GJ/ton without the load of the oxygen producing unit 120, and an energy load in the range between about 2.3 GJ/ton to about 3.3 GJ/ton with the load of the oxygen producing unit.

[0040] As shown in FIGS. 1-3, the amount of the feed stream 132 provided to the combustion system 120 may be adjusted by a valve 230 coupled to a controller 240. The controller 240 may be programmed with instructions concerning the opening and closing of the valve 230, or may receive feedback from other measurements done in the system 100 (not shown).

[0041] It is contemplated the amount of the portion 124a, 124b of the flue gas stream in the feed stream 132 may be adjusted without adjusting the amount of the feed stream directed to the combustion system 120. However, it is also contemplated that the amount of the portion 124a, 124b of the flue gas stream in the feed stream 132 may be adjusted without adjusting the amount of the feed stream directed to the combustion system 120.

[0042] The foregoing is exemplified in the following Example.

EXAMPLES

[0043] The relationship between the concentration of oxygen delivered from an oxygen producing unit and the concentration of carbon (C0 ₂ ) is shown by conducting simulations of different flue gas conditions by enrichment of feed air with various mass flow fractions (concentration) of oxygen in oxidant streams from an oxygen producing unit. [0044] Table 1 includes the results of five (5) simulations of systems having an air separation unit (ASU) as the oxygen producing unit and the flue gas stream is recycled to the combustion system after it has proceeded through a contaminant control system (referred to as air quality control systems or "AQCS" on Table 1). In the simulations, the contaminant control system includes an ESP and an FGD system. The concentration of oxygen in the oxidant stream from the ASU to the combustion system is different in each simulation shown in Table 1.

[0045] Table 1 illustrates the relationship between the concentration of oxygen and

C0 ₂ in the simulations.

Table 1 : Partial Oxygen Firing Simulations on Flue Gas

[0046] As shown in Table 1, as the concentration of oxygen from the ASU increases, the concentration of C0 ₂ present in the flue gas stream exiting the combustion system increases. As noted in Table 1, the concentration of C0 ₂ in the flue gas stream is measured at the outlet of the contaminant control system

[0047] The impact of the increased C0 ₂ concentration within a recycled flue gas stream is illustrated in Table 2. Table 2 includes the results of four (4) simulations of a system that recycles a flue gas stream to a combustion system after the flue gas stream proceeds through the contaminant control system. As shown in Table 2, the concentration of C0 ₂ in the recycled flue gas stream varies between the simulations. Table 2: Load Requirements in Systems Employing a Flue Gas Recycle

[0048] As shown in Table 2, as the concentration of the C0 ₂ present in the recycled flue gas stream increases, the load (GJ/ton) of the carbon capture system decreases. The decrease in the carbon capture system load in turn decreases the total load used by the ASU and the carbon capture system.

[0049] Unless otherwise specified, all ranges disclosed herein are inclusive and combinable at the end points and all intermediate points therein. The terms "first," "second," and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The terms "a" and "an" herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. All numerals modified by "about" are inclusive of the precise numeric value unless otherwise specified.

[0050] While the invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.