Patent Application
20100083638
The present disclosure relates generally to an exhaust system and, more particularly, to an exhaust system having a sulfur removing device.
Power systems that employ combustion engines to produce power also produce exhaust gases that include a complex mixture of air pollutants. Due to increased attention given to the environment, exhaust-emission standards have become more stringent, and the amount and contents of the exhaust emitted to the atmosphere from an engine may be regulated according to the type of engine, size of engine, and/or class of engine. Exhaust-Gas Recirculation (EGR) systems have been used to improve emissions control in order to comply with the regulations. A low pressure EGR system typically includes an exhaust recirculation passageway having one end connected to an exhaust system to receive exhaust from downstream of a particulate filter, a catalyst, or other treatment device, and another end connected with an intake of the engine. Within the recirculation passageway of the EGR system, there is typically a cooling device for reducing the temperature of the recycled exhaust. In this configuration, the EGR system recirculates or recycles a cooled portion of the engine exhaust back into the intake of the engine. The recycled exhaust is then mixed with the intake air, thereby diluting the in-cylinder composition and lowering the combustion temperature. As a result, NOx formation and NOx emission may be reduced.
The pollutants in the exhaust may include, among other things, sulfur oxides (SOx) (i.e., SO2 and SO3), which may oxidize and hydrate to form sulfuric acid (H2SO4) that condenses when cooled, for example, by the cooling device in the EGR passageway. The condensed sulfuric acid may attach to the relatively cool surfaces of the cooling device and downstream portions of the passageway, and cause corrosion of these components. Furthermore, when the sulfuric acid is directed into the engine with the recycled exhaust, the sulfuric acid may also attach to engine components, leading to degradation and decreased life span of the engine components.
In order to help minimize damage to EGR engine components, it may be desirable to remove SOx from engine exhaust before it has an opportunity to condense. One example of removing SOx from engine exhaust is described in U.S. Patent Application Publication No. 2007/0297961 A1 (the '961 patent application). In particular, the '961 patent application discloses a system including an SOx-removing device disposed upstream of EGR components to remove SOx from the exhaust before the exhaust is directed to the EGR components. The SOx-removing devices contain compounds that have a capacity for adsorption or absorption of SOx. The compounds include Magnesium (Mg), Calcium (Ca), Strontium (Sr), Manganese (Mn), Barium (Ba), or Lithium (Li). Due to the high affinity of these compounds for sulfur oxides, the SOx-removing devices are periodically replaced by new SOx-removing devices when the existing SOx-removing devices become saturated.
Although the system disclosed in the '961 patent application may help remove some SOx from the exhaust, thereby helping protect the EGR components from corrosion, the system may be expensive and burdensome to maintain. Specifically, in order to replace the SOx removing devices, the engine may need to be shut down, causing inconvenience and machine downtime loss. In addition, removing the SOx removing devices from the exhaust system and replacing the SOx removing devices may be time consuming, labor intensive, and costly.
The exhaust system of the present disclosure is directed toward improvements in the existing technology.
In one aspect, the present disclosure is directed to an exhaust system for an engine. The exhaust system may include a passageway configured to receive exhaust from the engine and a recirculation circuit. The recirculation circuit is configured to recirculate exhaust from the passageway back into the engine. The exhaust system may also include an SOx removing device disposed within the passageway upstream of the recirculation circuit, and a filter disposed within the passageway to remove particulate matter from the exhaust. The exhaust system may further include a regeneration device configured to substantially simultaneously regenerate the SOx removing device and the filter.
In another aspect, the present disclosure is directed to a method of treating exhaust from an engine. The method may include removing SOx from the exhaust. The method may also include directing SOx-reduced exhaust back into the engine. The method may also include collecting particulate matter from the exhaust. The method may further include heating the exhaust to substantially simultaneously improve an SOx removal capacity and reduce an amount of collected particulate matter.
Engine 20 may include a plurality of cylinders 40 forming combustion chambers for combusting a mixture of air and fuel. Engine 20 may also include an exhaust manifold 45, which may collect exhaust from cylinders 40 and direct the exhaust through exhaust system 30 to the atmosphere. Exhaust system 30 may include a passageway 50 configured to receive exhaust from exhaust manifold 45, and a recirculation circuit 70 configured to recirculate a portion of the exhaust from passageway 50 back into engine 20 by way of an intake manifold 35. Recirculation circuit 70 may include a valve 105 configured to inhibit or allow the exhaust from passageway 50 to flow through recirculation circuit 70. Operation of valve 105 may be regulated by a controller 100. Recirculation circuit 70 may also include one or more cooling devices 75 configured to reduce the temperature of the exhaust flowing therethrough. The exhaust directed back to engine 20 by way of recirculation circuit 70 may be mixed with the air directed into engine 20, thereby diluting the in-cylinder composition and causing a reduction in NOx generation.
A plurality of exhaust treatment devices may be disposed within passageway 50 upstream of recirculation circuit 70. The exhaust treatment devices may include, for example, an SOx removing device 55 configured to remove SOx from the exhaust, a filter 60 configured to remove particulate matter from the exhaust, and a regeneration device 65 configured to substantially simultaneously regenerate SOx removing device 55 and filter 60. SOx removing device 55 may be an SOx adsorbing or absorbing device. Filter 60 may also be referred to as a particulate filter, which may include a filtration substrate (not shown) to collect particulate matter from the exhaust and thus reduce an amount of particulate matter within the exhaust. Regeneration device 65 may be any suitable heating device, such as a fuel-fired burner or electric grid.
Among the various exhaust treatment devices within passageway 50, at least SOx removing device 55 may be disposed upstream of recirculation circuit 70. In some embodiments, each of SOx removing device 55, filter 60, and regeneration device 65 may be disposed upstream of recirculation circuit 70, as shown in
SOx removing device 55 may include a housing 80 having an inlet 85 and an outlet 90 for directing the exhaust through SOx removing device 55. SOx removing device 55 may contain an SOx removing material capable of adsorbing or absorbing SOx from the exhaust. The SOx removing material may be coated, e.g., washcoated, on a substrate 95 disposed within housing 80 of SOx removing device 55. Substrate 95 may be any suitable substrate known in the art. The SOx removing material may include any suitable base metal, such as Iron (Fe), Copper (Cu), Aluminum (Al), etc., or may include a combination of those base metals. When the exhaust passes through SOx removing device 55, the exhaust may come into contact with the SOx removing material and SOx within the exhaust may react with the SOx removing material to form sulfur compounds, such as Fe2(SO4)3 (iron-sulfate), CuSO4 (copper-sulfate), Al2(SO4)3 (aluminum-sulfate), etc., depending on the base metal content of the SOx removing material. As a result, SOx may be removed from the exhaust and stored as sulfates. Stable sulfates are stored on catalyst sites, reducing the number of active sites over time. Thus, after a period of time in service, the removal capacity of SOx removing device 55 may be significantly reduced.
Filter 60 and SOx removing device 55 may be regenerated by regeneration device 65. That is, regeneration device 65 may heat the exhaust passing through filter 60 to burn away the particulate matter collected therein. This burning away of the particulate matter may start, for example, at about 500° C., and may become more effective as the temperature is increased, for example, to at about 600° C. or higher. The regeneration of filter 60 may be completed within a time frame of, for example, 5-20 minutes, while power system 10 is operating normally. It is to be understood that, when heating filter 60, regeneration device 65 may increase the temperature of the exhaust flowing through SOx removing device 55 and filter 60 gradually, for example, from 500° C. to 650° C. in about 5-20 minutes. The SOx removing material may be properly selected such that the stable sulfates may also be decomposed during regeneration of filter 60. The SOx removing material may be further selected such that the decomposition of the sulfur compounds may be substantially complete within the same regeneration time frame of filter 60, e.g., within about 5-20 minutes, and within the same temperature range, e.g., 500° C. to 650° C. In this way, SOx removing device 55 and filter 60 both may be regenerated substantially simultaneously.
The regeneration process of SOx removing device 55 and filter 60 may be controlled by controller 100 configured to be in communication with regeneration device 65. Controller 100 may regulate the operation of regeneration device 65 to increase the exhaust temperature to a particular level within a particular time frame, and for a particular duration.
In some embodiments, SOx removing device 55 and filter 60 may be integrated as a single treatment device 60′, as shown in
The disclosed exhaust system may be utilized in any power system application, where exhaust is produced from combustion of a sulfur-containing fuel. Particularly, the disclosed exhaust system may be used to protect exhaust components from corrosion caused by sulfuric acid formed from SOx contained within the combustion byproducts. SOx removing device 55 may remove SOx from the exhaust before the exhaust is recirculated back into the engine, thereby reducing the formation of sulfuric acid within recirculation circuit 70 when the exhaust is cooled.
Referring to
After being conditioned by the exhaust treatment devices of exhaust system 30, SOx in the exhaust may have been reduced. A portion of the SOx-reduced exhaust may be directly discharged to the atmosphere, another portion of the SOx-reduced exhaust may be directed back into engine 20 through recirculation circuit 70. Valve 105, the operation of which may be regulated by controller 100, may open to allow the exhaust to flow through recirculation circuit 70, or close to inhibit exhaust flow therethrough. When flowing through recirculation circuit 70, the exhaust may be cooled by cooling device 75. If the exhaust contains SOx, sulfuric acid may form and attach to surfaces of cooling device 75, recirculation circuit 70, and engine 20.
SOx removing device 55 may significantly reduce the SOx content from the exhaust before the exhaust is directed back to engine 20 through recirculation circuit 70, thereby reducing the formation of sulfuric acid within recirculation circuit 70 and engine 20. As SOx is removed from the exhaust and stored in SOx removing device 55 as sulfates, stable sulfates may attach to surfaces of substrate 95 and reduce its SOx removal capacity. Particulate matter, when removed from the exhaust by the filter substrate of filter 60, may accumulate in filter 60 and block the exhaust flow, resulting in increased backpressure of exhaust system 30 that adversely affects engine performance. Therefore, after a period of time in service, one or both of the SOx removing device 55 and filter 60 may become saturated.
The particulate matter stored within filter 60 may be burned away and the sulfur compounds within SOx removing device 55 may be decomposed when heated. Therefore, both SOx removing device 55 and filter 60 may be regenerated substantially simultaneously using regeneration device 65. Regeneration device 65 may produce heat to increase the temperature of the passing exhaust flow. When the heated exhaust passes through SOx removing device 55 and filter 60, the exhaust may increase the temperatures of both SOx removing device 55 and filter 60. In one example, the temperature of the exhaust is increased from about 500° C. to about 650° C., and maintained at about 650° C. for about 15 minutes during a regeneration event.
Regeneration device 65 may be controlled by controller 100 so that the temperature of the exhaust is increased in a predetermined manner. For example, the temperature may be increased at a constant rate, such as an increase of about 10° C. every minute, or at a variable rate, such as an increase from about 500° C. to 600° C. in about 5 minutes, and from about 600° C. to 650° C. in about 10 minutes. Controller 100 may also regulate regeneration device 65 such that the temperature may stay at a value for a period of time, for example, at about 600° C. for 2 minutes. The regeneration event may last for a predetermined duration of time, for example, about 5-20 minutes. After the predetermined duration of time has elapsed, the regeneration event may be terminated, for example, by shutting down regeneration device 65. Alternatively, the regeneration event may be terminated based on the results of the regeneration event. For example, sensors, virtual sensors, or indicators may be associated with SOx removing device 55 and/or filter 60, which may indicate a progress of the regeneration event. Once the regeneration event has been adequately completed, for example, about 90% or more of the particulate matter in filter 60 has been burned away, or about 90% or more of the sulfur compounds in SOx removing device 55 have been decomposed, as indicated by the sensors, controller 100 may shut down regeneration device 65. The particulate matter may continue to burn and the sulfur compounds may continue to decompose due to residual heat even after regeneration device 65 is shut down. The regeneration event may be performed on a regular basis, for example, once every 8-10 hours of service time of power system 10.
During the regeneration event, the decomposed sulfur compounds may release SOx back into the exhaust. Therefore, before starting the regeneration of filter 60 and SOx removing device 55, controller 100 may close valve 105 such that recirculation circuit 70 is inhibited from recirculating the exhaust when SOx removing device 55 and filter 60 are being regenerated. The SOx released during the regeneration event may be discharged to the atmosphere directly from exhaust system 30. After the regeneration event has been terminated and regeneration device 65 has been shut down by controller 100, controller 100 may re-open valve 105 to allow exhaust to flow through recirculation circuit 70.
By utilizing the disclosed SOx removing device, SOx in the exhaust may be significantly reduced, thereby protecting components of recirculation circuit 70 and engine 20 from corrosion due to sulfuric acid formed by SOx. By regenerating SOx removing device 55 and filter 60 substantially simultaneously without shutting power system 10 down, time for servicing SOx removing device 55 and filter 60 may be reduced. Furthermore, regenerating SOx removing device 55 instead of periodically replacing it can also reduce maintenance time and cost.
It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed exhaust system. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed embodiments herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims.
