Patent Application
20130259780
The present disclosure is generally directed to apparatus and methods for reducing solvent emissions from a carbon capture process used in power generation. In particular, a control process is disclosed that provides a novel method for reducing solvent emissions in a post-combustion solvent-based carbon capture process. More particularly, the disclosure provides a new and useful technique for processing a flue gas for solvent emission reduction.
A number of power generation stations combust fossil fuels such as coal and natural gas to produce electricity. The heat energy of combustion is converted into mechanical energy and then into electricity. Combustion emissions, commonly referred to as a flue gas, are released into the atmosphere. Such combustion emissions may comprise nitrogen oxides (“NOx”) and carbon dioxide (“CO2”), as well as traces of other pollutants and particulate matter. Electricity generation using carbon-based fuels is responsible for a large fraction of the NOx and CO2 emissions worldwide.
A technology for reducing CO2 emissions from fossil fuel used in power generation is carbon capture and storage (“CCS”). Carbon dioxide emissions are controlled and captured at the point of generation, stored and transported for sequestration, and thereby prevented from being released into the atmosphere. Unfortunately, CCS consumes a high percentage of the power generated at the particular source.
Known solvent-based CO2 capture technologies for reducing CO2 emissions from a coal-fired or natural gas-fired boiler flue gas carry an inventory of a solvent circulating through a loop. A CO2 absorber provides for the chemical absorption of gaseous CO2 into the solvent from a mixed-stream flue gas. The CO2 absorber is operated under certain conditions including ranges of temperature and pressure, turbulence, and inter-phase mixing. Subsequently, a CO2-rich solvent stream is conditioned appropriately and is conveyed to a regenerator thereby establishing an environment conducive to CO2 removal.
As a result of vapor pressure, equilibrium and possible degradation, an aqueous solvent releases gaseous by products including its original components in the final top stage of the absorber. Typically, a solvent effluent stream from the absorber final top stage is captured in a two-stage water wash system. The solvent effluent stream typically comprises derivatives of the solvent itself and the respective byproducts that form due to its reaction with CO2. The water wash is employed to capture the solvent vapor by absorption in a separate water loop. Optionally, the solvent-rich water is steam-stripped in an additional stripper. Accordingly, the solvent is recovered and recycled for subsequent use in the CO2 absorber. The described method for solvent recovery and recycle can be operationally cumbersome and can intensely increase the capital expense and the operating expense of a power plant.
According to aspects illustrated herein, there is provided a method and system for controlling solvent emissions from a carbon capture unit that includes providing a CO2 absorber, an acid wash, and a water wash. A flue gas effluent stream from a combustion unit is passed through the CO2 absorber and in counter-current to the solvent passing through an upper section of the CO2 absorber to a lower section of the CO2 absorber. Subsequently, a gas-phase effluent stream from the CO2 absorber is passed through the acid wash and the water wash to reduce an emission of solvent within a gas-phase effluent stream from the acid wash and a gas-phase effluent stream from the water wash. Gas-phase analyzers detect the solvent level or concentration in the gas-phase effluent stream from the acid wash and the water wash, and a pH sensor monitors the pH of the acid wash. A control logic unit receives and processes a first, second, and third signal from the gas-phase analyzers and the pH sensor, respectively, and passes a stream of acid wash and acid to the acid wash, a stream of water wash to the water wash, via respective first, second, and third control valves. The above described and other features are exemplified by the following figures and detailed description.
Referring now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike:
As depicted in
Although the use of a CAP is shown and described, other post-combustion CCS processes are considered within the scope of this disclosure such as, for example, an Amine Process or an Advanced Amine Process. In these processes, the flue gas stream is treated with an aqueous amine solution which reacts with CO2. Subsequently raising the temperature of the CO2-rich amine solution promotes the release of CO2 and provides for the recycling of the amine solution for reuse.
The block diagram depicted in
A means for detecting constituent concentrations in a gas, such as for example Gas-phase analyzers, detects the concentration of the solvent in the gas effluent stream from the CO2 absorber and passes the detected concentration (“data”) to a control logic unit, such as for example a programmable logic controller, and the appropriate amounts of acid wash and water wash are discharged into the respective sections of the wash unit based on the data. The acid wash of the first section (61) controls solvent emissions from the CO2 absorber (58) when acid reacts with the rising solvent in effluent stream (60). A gas-phase analyzer (13) detects the concentration of solvent in effluent stream (60) and passes the data to a control logic unit (15). Based upon a signal received from control logic unit (15), a sufficient amount of an acid wash (11) is released via a first control valve (17) and passed to the first section (61). The amount of acid wash is dependent upon the concentration of solvent detected by the gas-phase analyzer (13) and the processing of the data by control logic unit (15). The pH of the acid wash (11) is measured by a pH sensor (29) that passes the data to a control logic unit (15). Based upon a signal received from control logic unit (15), an acid (19) can be released via a second control valve (21) and added to the acid wash (11) to control the acid concentration of the acid wash.
The water wash second section (62) controls the final emissions from the CO2 absorber (58) that will be passed to the stack or one or more other CCS process units. A gas-phase analyzer (23) detects the concentration of solvent in the effluent stream (60) and passes the data to the control logic unit (15). Based upon a signal received from control logic unit (15), a sufficient amount of a water wash (25) is released via a third control valve (27) and passed to the second section (62). The amount of water wash is dependent upon the concentration of solvent detected by the gas-phase analyzer (23) and the processing of the data by control logic unit (15).
In one embodiment of the process disclosed herein: (i) the first control valve (17) is operated in accordance with a signal received from the control logic unit (15) that is based upon the data recorded by the gas-phase analyzer (13); (ii) the second control valve (21) is operated in accordance with a signal received from the control logic unit (15) that is based upon the data recorded by the pH sensor (29); and (iii) the third control valve (27) is operated in accordance with a signal received from the control logic unit (15) that is based upon the data recorded by the gas-phase analyzer (23). While the respective control valves have been shown and described as being operated in accordance with a signal received from the control logic unit (15) that is based upon the data recorded by a respective measurement device, alternative embodiments of the disclosed process may comprise operating one or more of the control valves in accordance with a signal received from the control logic unit (15) that is based upon the data recorded from a plurality of the measurement devices or based upon a result of a programmable logic code sequence. In addition, while a gas-phase analyzer has been shown and described as means for detecting constituent concentration in a gas, the present disclosure is not limited in this regard as other types of methods such as, but not limited to, gas chromatography and quantitative chemical analysis may be substituted without departing from the broader aspects of the present disclosure.
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.
