Patent Application
20180340731
The disclosure relates to separations equipment for sequestering pollutants.
Greenhouse gas emissions are among the highest forms of pollution, and are closely monitored. Carbon dioxide (CO2) is the highest source of these greenhouse gas emissions, accounting for 80.9% of all greenhouse gas emissions in the U.S. in 2014, according to the EPA. Efforts are being made to reduce the amount of CO2 emissions. One method is that of carbon capture or sequestration. This is used mainly in industrial processes and power plants, to remove the CO2 before the flue gases are released to the atmosphere.
Flue gas is a product of combustion of wood, coal, natural gas, or other fossil fuels, and is released through a smokestack. Thus, it has a high CO2 concentration. There are many methods in development and in use to decrease the CO2 content of flue gas. It is important to verify that these methods are effective.
In monitoring and regulating CO2 emissions, simulations are often used. For example, the National Institute of Metrology created a Smoke Stack Simulator (SMSS) to study accurate measurement methods for flue gas flow rates. The SMSS was created to model many systems, with the capability to simulate flow fields by generating different swirls. Similarly, the flue gas itself can be simulated. Flue gas is typically composed mainly of carbon dioxide, water vapor, nitrogen, and oxygen. There may also be a small percentage of fly ash or other pollutants. The majority of the flue gas is usually made up of nitrogen—typically, two-thirds or more.
Contacts and carrier fluids may be used, such as:
1,1,3-trimethylcyclopentane, 1,4-pentadiene, 1,5-hexadiene, 1-butene, 1-methyl-1-ethylcyclopentane, 1-pentene, 2,3,3,3-tetrafluoropropene, 2,3-dimethyl-1-butene, 2-chloro-1,1,1,2-tetrafluoroethane, 2-methylpentane, 3-methyl-1,4-pentadiene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-methylpentane, 4-methyl-1-hexene, 4-methyl-1-pentene, 4-methylcyclopentene, 4-methyl-trans-2-pentene, bromochlorodifluoromethane, bromodifluoromethane, bromotrifluoroethylene, chlorotrifluoroethylene, cis 2-hexene, cis-1,3-pentadiene, cis-2-hexene, cis-2-pentene, dichlorodifluoromethane, difluoromethyl trifluoromethyl ether, dimethyl ether, ethyl fluoride, ethyl mercaptan, hexafluoropropylene, isobutane, isobutene, isobutyl mercaptan, isopentane, isoprene, methyl isopropyl ether, methylcyclohexane, methylcyclopentane, methylcyclopropane, n,n-diethylmethylamine, octafluoropropane, pentafluoroethyl trifluorovinyl ether, propane, sec-butyl mercaptan, trans-2-pentene, trifluoromethyl trifluorovinyl ether, vinyl chloride, bromotrifluoromethane, chlorodifluoromethane, dimethyl silane, ketene, methyl silane, perchloryl fluoride, propylene, or vinyl fluoride.
The present disclosure describes systems and methods for recycling separated gases to simulate flue gas. Gases that may be used include an inert gas selected from the list comprising nitrogen, oxygen, air, water, and combinations thereof. A pollutant gas may also be used, selected from the list comprising carbon dioxide, sulfur oxides, nitrogen oxides, fly ash, mercury, arsenic, other pollutants present in flue gas, and combinations thereof. The present disclosure will discuss using only carbon dioxide and nitrogen as an example, however other gases may be used as mentioned above. If other gases are used, there may be obvious variations to the process described in this disclosure. The given example is meant to demonstrate one application of the systems and methods, and is not meant to limit the scope of the invention. Flue gas may be simulated by mixing the desired gases—in this case, carbon dioxide and nitrogen—from a supply source. The concentration of carbon dioxide in this simulated flue gas stream may range from 3% to 30% carbon dioxide. The simulated flue gas stream may be monitored by a pressure transducer. The pressure transducer may allow control over a valve through which the supply nitrogen may be regulated, keeping the simulated flue gas stream at a set pressure. In some preferred embodiments, the set pressure may be constant and positive, and may range from 0.1 psig to 2 psig. In some other embodiments, such as using a compressed simulated flue gas, the set pressure may range from 50 psig to 100 psig. The valve may be a solenoid valve, an actuated ball valve, or a mass flow controller. The supply carbon dioxide may be injected and regulated through a mass flow controller (MFC 1).
The simulated flue gas stream may also be monitored by a flowmeter. The flowmeter may communicate with a blower for the simulated flue gas stream, allowing the blower to operate in such a way to maintain a constant set flow rate for the simulated flue gas stream. The set flow rate may be set by the operator and may be at least 5 SCFM. In some embodiments, the set flow rate may be between 5 SCFM and 100 SCFM.
There may be a first analyzer placed before the separation unit. This analyzer may monitor the conditions of the simulated flue gas stream, including the concentration of carbon dioxide in the simulated flue gas stream just before entering the separation unit.
The simulated flue gas stream may then enter the separation unit. The separation unit may employ any carbon dioxide (or other pollutant gas) separation process, and may be able to process the entire flow rate of the simulated flue gas stream. For example, in some preferred embodiments, the separation unit may be a Cryogenic Carbon Capture process capable of processing 5 to 100 SCFM of simulated flue gas, using carbon dioxide as the pollutant gas. The separation unit may remove the carbon dioxide from the simulated flue gas stream, forming two outlet streams: a clean gas stream and a purified carbon dioxide stream. The purified carbon dioxide may consist only of carbon dioxide from the simulated flue gas stream. The clean gas stream may consist of all other non-carbon dioxide gases from the simulated flue gas stream, as well as any carbon dioxide that was not removed by the separation unit. In some preferred embodiments, such as one using the Cryogenic Carbon Capture process, the carbon dioxide concentration in the clean gas stream may range from 0.10% to 3%.
Both streams exiting the separation unit may be recycled, but they may pass through other steps before recombining. The clean gas stream may pass through a second analyzer, placed after the separation unit. This analyzer may monitor the concentration of carbon dioxide in the clean gas stream. When compared to the carbon dioxide concentration data from the first analyzer, which is placed in the simulated flue gas stream, the performance of the separation unit may be monitored.
The purified carbon dioxide stream may pass through a mass flow controller (MFC 2). MFC 2 may monitor the flow rate of the purified carbon dioxide stream. This flow rate data may enable feed-forward control on another mass flow controller (MFC 3 (110)) through which excess carbon dioxide may be released. This excess carbon dioxide may be vented, compressed and stored, or returned to the supply from which it came. Similarly, in some embodiments, the excess nitrogen may be vented or stored via a fourth mass flow controller (MFC 4).
In some preferred embodiments, the purified carbon dioxide stream may exit the separation unit at a high pressure. This pressure may be in the range of 70 psig to 150 psig. The pressure of the purified carbon dioxide stream may need to be decreased before continuing in the process, especially if the clean gas stream is at a lower pressure. A pressure regulator may be implemented for this purpose. The purified carbon dioxide stream, after passing through the pressure regulator, may be lowered to a pressure in the range of 30 psig to 50 psig. In some embodiments, the purified carbon dioxide stream may be a liquid, and may need to be vaporized using a heater or a warm process stream before continuing in the process. In these embodiments wherein the purified carbon dioxide stream is a liquid, the excess carbon dioxide flowing through MFC 3 may remain a liquid and be pumped into a bottle.
The purified carbon dioxide stream and the clean gas stream may then combine. The point at which the purified carbon dioxide is injected may be important. It may be located at a point sufficiently downstream of the second analyzer that the recycled and carbon dioxide is not picked up by the second analyzer, and sufficiently upstream of the first analyzer that the gas is well mixed in the simulated flue gas stream before passing through the first analyzer. The carbon dioxide supply may also be injected at this same combination point through MFC 1. The first analyzer may also provide data that allows the controller to regulate each of the mass flow controllers. MFC 1 and MFC 3 may be controlled such that the concentration of carbon dioxide in the simulated flue gas stream is kept at a set value, as measured by the first analyzer.
The combined clean gas, purified carbon dioxide, and supply carbon dioxide form the recycle stream. The supply nitrogen may later injected into this recycle stream through the valve. This valve may be regulated using data from the pressure transducer to maintain the set pressure mentioned above. After the point of nitrogen injection, the simulated flue gas may be reformed and again flows into the separation unit.
A more particular description of the invention briefly described above is made below by reference to specific example. Several examples are depicted in drawings included with this application. An example is presented to illustrate, but not restrict, the invention.
The systems and methods disclosed herein relate to simulating flue gas and separating gases in the flue gas stream, then recycling the gases to again simulate the flue gas. These methods may be used to test the effectiveness of a separation unit. For example, carbon dioxide and nitrogen may be combined at a desired concentration to simulate a flue gas. This simulated flue gas may be regulated and analyzed, and then sent through a separation unit. The separated streams which may be formed—one of clean gas comprised mostly of nitrogen and one of purified carbon dioxide—may also be analyzed to monitor the effectiveness of the separation unit and the measurement devices. The step of determining, via the processor, that a measured reading of a parameter of the separations processor is suboptimal may refer to determining via input from a sensor that a parameter, such as temperature of a section of the system performing the process, pressure level at a section of the system performing the process, flow rate at a conduit of the system, pollutant concentration, or some other parameter is at a suboptimal level. Such parameter may be any parameter for which data is stored by the master controller, which may be a computer system. In some embodiments a suboptimal level is determined when the measured reading of the parameter falls out of an acceptable range known by one skilled in the art and the overall output of the separation process is affected negatively. Referring to cleaning of flue gas, optimal conditions may be defined as a ratio of a certain amount of pollutant in the flue gas to a certain amount that is precipitated and removed from the flue gas. Suboptimal conditions may be when the ratio drops to less than 10% of the ratio under optimal conditions; however, depending on the settings of the apparatus, the optimal conditions may be adjusted. For example, in some setting it may be desired to remove 99% of the pollutant by precipitation; in other settings, it may be desired to remove greater than 80% of the pollutant by precipitation. Returning to a substantially optimal range may refer to returning within 5% or greater of the ratio of the optimal conditions; for example, if the optimal ratio is 90%, and the ratio drops to 79%, then that may be considered as a suboptimal condition; then if the ratio returns to between 85% and 100% inclusive, then that may be considered as returning to an optimal condition, which may also mean returning or exceeding an optimal condition threshold.
Processor (700), which may be connected wirelessly or wirelessly to controllers, sensors, and other components of the system, may be any computing processor from a server or master controller adapted for monitoring of equipment.
The clean gas stream (204) passes through a second analyzer (104), which may also monitor the carbon dioxide concentration. When comparing the carbon dioxide concentration in the clean gas stream (204), as measured by the second analyzer (104), to the carbon dioxide concentration in the simulated flue gas stream (200), as measured by the first analyzer (102), the effectiveness of the separation unit (100) may be monitored. The difference in amount of carbon dioxide between the two streams is equal to the amount of carbon dioxide removed from the flue gas stream. After passing through the second analyzer (104), the clean gas stream (204) is then recycled with the purified carbon dioxide stream (202).
In some preferred embodiments, before recombining with the clean gas stream (204), the purified carbon dioxide stream (202) may pass through a second mass flow controller (MFC 2) (108). In some embodiments, MFC 2 (108) may be replaced by a flowmeter. MFC 2 (108) monitors the flow rate of the purified carbon dioxide stream (202). A PID controller may use data from MFC 2 (108) to enable feed-forward control over MFC 1 (106), meaning data from MFC 2 (108) is fed forward to the PID to control the output of MFC 1 (106), rather than using data from the first analyzer (102). If the flow rate through MFC 2 (108) increases, the flow rate through MFC 1 (106) decreases accordingly to maintain a set constant concentration as monitored by the first analyzer (102). If a process upset occurs and more carbon dioxide is released into the system than is necessary to maintain the set concentration, the flow rate through MFC 2 (108) will be high enough that the PID will output a negative value for the flow rate through MFC 1 (106). In this case, there is excess carbon dioxide in the system that may need to be released through a third mass flow controller (MFC 3 (110)). If the output for MFC 1 (106) is negative, the PID controller will use the absolute value of the negative output as the output for MFC 3 (110). There may be no supply carbon dioxide (122) flowing through MFC 1 (106), and excess carbon dioxide being released from the purified carbon dioxide stream (202) through MFC 3 (110). The following table gives an example of the feed-forward control mechanism.
In some other embodiments, the PID controller may use data from the first analyzer (102) to control the output through MFC 1 (106) and MFC 3 (110), keeping the concentration of carbon dioxide constant at the set point as monitored by the first analyzer (102). This may render MFC 2 (108) unnecessary. However, MFC 2 may still be used to enable the mass balance described below.
When excess carbon dioxide may be released through MFC 3 (110), the released gas may be vented to the atmosphere, compressed and stored, or returned to the carbon dioxide supply.
When the purified carbon dioxide stream (202) and the clean gas stream (204) combine, the supply carbon dioxide (122) may also be injected via MFC 1 (106). Data from the first analyzer (102) and the second analyzer (104) may be used by the operator or controller, along with data from MFC 1 (106), MFC 2 (108) and MFC 3 (110), to close a mass balance on carbon dioxide around this combination point (107). In some preferred embodiments, an indicator on an HMI may perform the calculations. The mass balance calculation may be used to ensure that all measuring instruments used in the process are calibrated and operating correctly. The calculation is to verify that the mass of the carbon dioxide entering the combination point (107) is equal to the mass of the carbon dioxide leaving the combination point (107). An example calculation uses the following equation:
Where FT is equal to the flow rate as measured by the flowmeter (116), x1 is equal to the mass fraction of carbon dioxide in the simulated flue gas stream (200) as measured by the first analyzer (102), x2 is the mass fraction of carbon dioxide in the clean gas stream (204) as measured by the second analyzer (104), MFC1 is the flow rate of the supply carbon dioxide stream (400) through MFC 1 (106), MFC2 is the flow rate of the purified carbon dioxide stream (202) through MFC 2 (108), and MFC3 is the flow rate of the excess carbon dioxide through MFC 3 (110). If the mass balance is incorrect, the HMI may signal an error, and the operator may choose to recalibrate the instruments.
The combination point (107) of the purified carbon dioxide stream (202) and supply carbon dioxide stream (400) with the clean gas stream (204) may be located carefully. The combination point (107) may be sufficiently upstream of the first analyzer (102) that the gases are well mixed before passing through the first analyzer (102), and sufficiently downstream of the second analyzer (104) that the purified carbon dioxide and the injected supply carbon dioxide (122) are not picked up by the second analyzer (104).
The stream leaving the combination point (107) is a mixture of the purified carbon dioxide stream (202), the clean gas stream (204), and the supply carbon dioxide stream (400); and may be referred to as the recycled gas stream (404). In some preferred embodiments, the supply nitrogen (120) may then be injected into the recycled gas stream (404) through the solenoid valve (114). The stream that may leave this injection point is the simulated flue gas stream (200), which may then continue through the process toward the separation unit (100). The pressure transducer (118) may be placed after this injection point, and on the suction side of the blower (112). The PID controller may use data from the pressure transducer (118) to control the output of the solenoid valve (114), and keep the simulated flue gas stream (200) at a constant set pressure. In some preferred embodiments, this pressure may be in the range of 0.1 psig to 2 psig. In some other embodiments, such as using a compressed simulated flue gas stream, this pressure may range from 50 psig to 100 psig. The pressure-regulated simulated flue gas stream (200) may then pass through the blower (112) and recycle through the process.
System 301 may be identical to system 101 from the injection point of the supply nitrogen (120) until the separation unit (100). In system 301, the clean gas stream (204) may emerge from the separation unit (100) and pass through the second analyzer (104), just as in system 101. The clean gas stream (204) may also branch off and pass through a fourth mass flow controller (MFC 4) (300). The PID controller may receive data from the pressure transducer (118) and use this data to control MFC 4 (300). MFC 4 (300) may be closed except for when an error occurs and the pressure is too high. In this case, excess clean gas may be released through MFC 4 (300). This released excess clean gas may be vented to the atmosphere or compressed and stored. Clean gas that is not released through MFC 4 (300) may continue to the combination point (107) where the clean gas stream (204), the purified carbon dioxide stream (202), and the injected supply carbon dioxide stream (400) combine.
In system 301, the purified carbon dioxide stream (202) may emerge from the separation unit (100) at a high pressure. This pressure may be around 150 psig. The pressure of the purified carbon dioxide stream (202) may then need to be reduced before recycling through the process. The purified carbon dioxide stream (202) may pass through a pressure regulator (302), which may lower the pressure to approximately 30-50 psig. The purified carbon dioxide stream (202) may then pass through MFC 2 (108), which may further reduce the pressure to the range of the set pressure maintained by the pressure transducer (118) and the solenoid valve (114). After passing through MFC 2 (108), the purified carbon dioxide stream (202) may then proceed to the combination point (107). If there is excess carbon dioxide, as determined by the same methods as system 101, it also may need to be released through MFC 3 (110). There may be a compressor (not shown in
Step 604 is measuring and controlling initial concentrations and flow rates. This may be done using equipment and methods depicted in
Step 606 is passing the simulated flue gas through a separation unit (100) to separate the pollutant gas from the inert gas. The simulated flue gas stream (200) is the only inlet into the separation unit (100). The two outlet streams from the separation unit (100) are a clean gas stream (204), consisting of the inert gas and any pollutant gas that was not removed by the separation process; and a purified pollutant stream, which contains all the pollutant gas that was removed from the simulated flue gas stream (200) during the separation process. For example, if the simulated flue gas stream (200) consisted of only nitrogen and carbon dioxide, then the purified pollutant stream would consist only of carbon dioxide, and the clean gas stream (204) would consist of mostly nitrogen with a small amount of carbon dioxide.
Step 608 is measuring the concentration of pollutant gas in the clean gas stream (204). This may aid in controlling the concentration of the simulated flue gas stream (200), or in monitoring the effectiveness of the separation unit (100). Step 610 involves measuring the flow rate of the purified pollutant gas stream. This may also aid in controlling the concentration of the simulated flue gas stream (200), and may also be used in a mass balance to check the performance of the measurement instruments, as described in system 101.
Step 612 is combining and recycling the separated streams. Once the clean gas stream (204) and the purified pollutant stream have both been measured, they may again combine to form a recycled gas stream (404). Step 614 is injecting clean gas and pollutant gas into the recycled gas stream (404) as needed to maintain the desired concentrations and flow rates as measured in step 604. Once the clean gas and pollutant gas have been injected into the recycled gas stream (404), the simulated gas stream is again formed and may then continue through the process, starting at step 604.
