Modular system for reduction of sulphur oxides in exhaust

An engine exhaust after-treatment system including an exhaust passage including a plurality of legs, with an exhaust control valve being positioned at an inlet of each of the legs that is configured to control an amount of exhaust that enters each leg. A desulfurization treatment component is located within each of the legs. An alkaline reagent tank provides an alkaline reagent to the desulfurization treatment component, and a reagent control valve is disposed between the alkaline reagent tank and the desulfurization treatment component. The reagent control valve is configured to control an amount of alkaline reagent that enters the desulfurization component. A controller may be communication with each of the exhaust control valves and reagent control valves, wherein the controller is configured to control the exhaust control valves independently of the reagent control valves.

FIELD

The present disclosure relates to a modular exhaust after-treatment system for the reduction of sulfur oxides in an engine exhaust.

BACKGROUND

Combustion engines are known to produce emissions that may be harmful to the environment. In an effort to decrease the environmental impact that an engine may have, exhaust after-treatment systems have undergone comprehensive evaluation and development. Various components that assist in treating engine emission include oxidation and reduction catalysts. Dependent on the size of the engine application, the cost of these components can increase greatly. In this regard, larger engine applications such as locomotive, marine, and large horsepower stationary applications can produce substantially more exhaust emissions than, for example, a tractor trailer engine application. The exhaust after-treatment systems, therefore, are generally larger in scale to satisfactorily reduce the harmful emissions produced by these large-scale applications. As the scale of the after-treatment system increases, however, the cost to produce, install, and service such a system increases greatly. It is desirable, therefore, to produce an exhaust after-treatment system that is more conventional in scale, while still being able to reduce the effects of harmful emissions emitted by large engine applications.

SUMMARY

The present disclosure provides an engine exhaust after-treatment system including an exhaust passage including a plurality of legs, with an exhaust control valve being positioned at an inlet of each of the legs. The exhaust control valves are configured to control an amount of exhaust that enter each leg. A first exhaust treatment component located within each of the legs, and a desulfurization treatment component located within each of the legs downstream from the first exhaust treatment component. An alkaline reagent tank provides an alkaline reagent to the desulfurization treatment component, and a reagent control valve is disposed between the alkaline reagent tank and the desulfurization treatment component. The reagent control valve is configured to control an amount of alkaline reagent that enters the desulfurization component. A controller may be communication with each of the exhaust control valves and reagent control valves, wherein the controller is configured to control the exhaust control valves independently of the reagent control valves.

DETAILED DESCRIPTION

FIG. 1schematically illustrates an exhaust system10according to the present disclosure. Exhaust system10can include at least an engine12in communication with a fuel source (not shown) that, once consumed, will produce exhaust gases that are discharged into an exhaust passage14having an exhaust after-treatment system16. Downstream from engine12can be disposed a first exhaust treatment component18, which can be a diesel oxidation catalyst (DOC), a particulate filter (DPF) component, or, as illustrated, a selective catalytic reduction (SCR) component20. Although not required by the present disclosure, exhaust after-treatment system16can further include components such as a thermal enhancement device or burner17to increase a temperature of the exhaust gases passing through exhaust passage14. Increasing the temperature of the exhaust gas is favorable to achieve light-off of the catalyst in the exhaust treatment component18in cold-weather conditions and upon start-up of engine12, as well as initiate regeneration of the exhaust treatment component18when the exhaust treatment component18is a DPF.

To assist in reduction of the emissions produced by engine12, exhaust after-treatment system16can include a dosing module22for periodically dosing an exhaust treatment fluid into the exhaust stream. As illustrated inFIG. 1, dosing module22can be located upstream of exhaust treatment component18, and is operable to inject an exhaust treatment fluid into the exhaust stream. In this regard, dosing module22is in fluid communication with a reagent tank24and a pump26by way of inlet line28to dose an exhaust treatment fluid such as diesel fuel or urea into the exhaust passage14upstream of exhaust treatment component18. Dosing module22can also be in communication with reagent tank24via return line30. Return line30allows for any exhaust treatment fluid not dosed into the exhaust stream to be returned to reagent tank24. Flow of the exhaust treatment fluid through inlet line28, dosing module22, and return line30also assists in cooling dosing module22so that dosing module22does not overheat.

The amount of exhaust treatment fluid required to effectively treat the exhaust stream may vary with load, engine speed, exhaust gas temperature, exhaust gas flow, engine fuel injection timing, desired NOxreduction, barometric pressure, relative humidity, EGR rate and engine coolant temperature. A NOxsensor or meter32may be positioned downstream from SCR20. NOxsensor32is operable to output a signal indicative of the exhaust NOxcontent to an engine electronic control unit (ECU)34. All or some of the engine operating parameters may be supplied from ECU34via the engine/vehicle databus to exhaust after-treatment system controller36. The controller36could also be included as part of the ECU34. Exhaust gas temperature, exhaust gas flow and exhaust back pressure and other vehicle operating parameters may be measured by respective sensors, as indicated inFIG. 1.

A second exhaust treatment component38may be positioned downstream from first exhaust treatment component18. Second exhaust treatment component38may be a DOC, DPF, ammonia-slip catalyst, or as illustrated, an desulfurization component. Desulfurization component (hereinafter “scrubber”)38chemically scrubs the exhaust to remove sulfur oxides. An alkaline reagent tank40provides an alkaline reagent such as, for example, sodium hydroxide (NaOH) to scrubber38. The alkaline reagent is fed to scrubber38through feed line42using a pump44. Scrubber28may be vertically oriented such that the alkaline reagent may collect at a bottom of scrubber38. A return line46may return the collected alkaline reagent back to reagent tank40. Alternatively, the collected alkaline reagent may be fed to a waste tank48, where the alkaline reagent may be treated and reused, or disposed of.

If engine12is used on a marine vessel, the alkaline reagent used may be seawater. In such an application, pump44would communicate seawater to desulfurization tank38. The seawater that collects at a bottom of scrubber38may then be fed to waste tank48. Alternatively, the collected seawater may be treated to remove any contaminants and returned to the sea.

FIG. 2illustrates an exemplary scrubber38. Scrubber includes a shell50. Shell50may be cylindrical including a first (bottom) end52and a second (top) end54. Although shell50is illustrated as being cylindrical, shell50may be any other shape known to one skilled in the art. An inlet56may be positioned proximate first end52. Inlet56communicates with exhaust passage14. A flange58may be used to couple inlet56to exhaust passage14. An outlet60may be positioned proximate second end54. As illustrated, outlet60may be aligned with an axis of shell50. It should be understood, however, that outlet60is not required to be aligned with the axis of shell50.

A collection reservoir62may be fixed to first end52. Collection reservoir62is for collecting the alkaline reagent that is sprayed into the exhaust stream. A plurality of nozzle lines64are positioned within shell50. Each nozzle line64includes a plurality of nozzles66. Nozzle lines64, as illustrated, may extend orthogonal to feed passages68. Feed passages68may be coupled to feed lines42at couplings69, which supply feed passages68with alkaline reagent from alkaline reagent tank40. As the engine exhaust comes into contact with the alkaline reagent, the sulfur oxides (SOx) in the exhaust stream undergo reaction with the alkaline reagents to form aqueous or solid reaction by-products such as sulfites and sulfates. These by-products, along with unreacted alkaline reagent, collect in collection reservoir62. As shown inFIG. 2, collection reservoir62includes a connection flange70for connecting to return line46, which either returns the alkaline reagent back to alkaline reagent tank40, or sends the collected reagent to waste tank48. Although not illustrated inFIG. 2, it should be understood that beds of plastic beads may be positioned between first end52and54that, when showered with the alkaline reagent, provide a greater surface area for the alkaline reagent to contact and treat the exhaust as the exhaust passes through scrubber38in comparison to simply passing the exhaust through the misting alkaline reagent emitted from nozzles66.

A mist eliminator72in the form of a fine mesh screen may be located within shell50proximate second end54. As the hot exhaust gases come into contact with the cooler alkaline reagent, a fine mist of droplets may develop. The droplets may contain the sulfur by-products that are desired to be removed from the engine exhaust. As the droplets pass through mist eliminator72, the droplets may adhere to mist eliminator and eventually fall into the collection reservoir. Although mist eliminator72is illustrated and described as being a fine mesh screen, it should be understood that any type of droplet adhesion device may be used. For example, a plurality of blades may be positioned within shell50, without departing from the scope of the present disclosure.

The amount of exhaust treatment fluid required to effectively treat the exhaust stream can also be dependent on the size of the engine12. In this regard, large-scale diesel engines used in locomotives, marine applications, and stationary applications can have exhaust flow rates that exceed the capacity of a single dosing module22, single SCR20, and single scrubber38. Accordingly, although only a single dosing module22and single SCR20are illustrated for treating the engine exhaust, it should be understood that multiple dosing modules22and multiple SCR components20are contemplated by the present disclosure. Similarly, multiple scrubbers38may be used.

FIG. 3schematically illustrates a multi-leg exhaust after-treatment system74. Multi-leg exhaust after-treatment system74is in communication with a large-scale engine12that produces relatively large mass flow rates of exhaust. Large-scale engine12can be an engine used in, for example, locomotive, stationary, and marine applications. Although only a single engine12is illustrated, it should be understood that multi-leg exhaust after-treatment system74can be scaled to receive exhaust from multiple engines12, if desired.

Exhaust produced by engine12enters an exhaust passage76that may include a turbo manifold78. At turbo manifold78, the exhaust can be divided into a plurality of legs80a-80c. It should be understood that although only three legs80a-80care illustrated inFIG. 3, the present disclosure should not be limited thereto. In this regard, multi-leg exhaust treatment system74can include a pair of legs80, or a number of legs80greater than the three illustrated inFIG. 3. Further, although the above description references large-scale engines that produce large amounts of exhaust, the present disclosure is equally applicable to smaller-scale engines used on, for example, passenger vehicles, tractors, and the like.

Each leg80a-80ccan be configured to include a catalyst-coated DPF82, SCR20, and scrubber38. Each leg80a-80ccan include a respective burner (not shown) for increasing a temperature of the exhaust stream to achieve light-off of catalysts in DPF82and SCR20, as well as regenerate DPF82, when necessary. Additionally, each leg80a-80ccan include injectors (not shown) for injecting exhaust treatment fluids such as hydrocarbon and urea treatment fluids at positions upstream of DPF82and SCR20, respectively. Lastly, similar to after-treatment system16, each injector, as well as each burner can be in communication with controller36that is operable to control injection of the exhaust treatment fluids into the exhaust stream, as well as control operation of burner for each leg80a-80c. It should be understood that although each leg80a-80cis illustrated as having a catalyst-coated DPF82, the present disclosure should not be limited thereto. In this regard, scrubber38can also remove particulate matter from the exhaust such that DPF82is not required. In such an instance, DPF82may be replaced in favor of a diesel oxidation catalyst (DOC) or omitted.

The use of multiple legs80a-80callows components such as DPF82, SCR20, and scrubber38to be scaled down, which reduces the overall cost to manufacture exhaust after-treatment system74. In addition, because different numbers of legs80may be used, the after-treatment system74can be specifically tailored to the engine12being used. In other words, after-treatment system74can be modular in design, with each leg80a-80cdefining a sub-after-treatment system75. Each sub-after-treatment system75may include a sub-controller36a-36c, with each sub-controller36a-36ccommunicating with controller36and the other sub-controllers36a-36c. With such a configuration, if one of the sub-controllers36a-36cfails, controller36may continue to operate the sub-after-treatment system75including the defective controller36a-36c. Alternatively, if controller36fails, after-treatment system74may be designed such that the duties of controller36may be divided between sub-controllers36a-36c.

Each sub-after-treatment system75may include exhaust control valves84a-84cfor allowing various legs80a-80cto be closed and opened, as needed. Exhaust control valves84a-84cmay be in communication with controller36such that controller36can open and close exhaust control valves84a-84cin response to various engine operating conditions, and may also be in communication with the particular sub-controller36a-36c, respectively, that is associated with that particular leg80a-80c. For example, if engine12is running at idle or lower loads, only a single leg80bor a pair of legs80aand80cmay be required to adequately treat the engine exhaust. The legs80a-80cnot being used, therefore, may be closed by closing the particular exhaust control valve84a-84cfor that particular leg80a-80c. Moreover, if a component such as DPF82, SCR20, or scrubber38needs to be serviced in a particular leg80a-80c, the exhaust flow can be prevented from entering that particular leg80a-80cby closing the associated exhaust control valve84a-84c.

As noted above, alkaline reagent tank40is in communication with scrubbers38by way of feed lines42. Each scrubber38may be in communication with waste tank48by return lines46. Return lines46are preferably gravity-assisted, but a pump (not shown) may be in communication with each return line46to feed waste tank48. To prevent the unnecessary feeding of the alkaline reagent to scrubbers38when a particular leg80a-80cis not in use, feed lines40may include valves86a-86ctherein at each scrubber38. Valves86a-86cmay be controlled by controller36or sub-controllers36a-36csuch that if controller36or sub-controllers36a-36ccloses a particular exhaust control valve84a-84cfor a leg80a-80c, controller36or sub-controller36a-36cmay also close the valve86a-86cassociated with the scrubber38in the closed leg80a-80c. In this manner, no alkaline reagent is permitted to be fed to the scrubber38not being used so that no fresh alkaline reagent is improperly drained to waste tank48. It should also be understood that a reagent purification apparatus may be positioned upstream from waste tank48that can purify used alkaline reagent and return the purified alkaline reagent to alkaline reagent tank40, with any waste material being passed to waste tank48, as is known in the art.

In another aspect of the present disclosure, valves86a-86cmay be controlled independently from exhaust control valves84a-84c. That is, although the engine exhaust may be free to pass through scrubber38, the feeding of alkaline reagent thereto may be prevented by closing the valve86a-86cassociated with that scrubber38. Such a scenario may be desired in marine applications were desulfurization is not required when the vessel is far enough out to sea that no emission regulations are in effect or reduced. In this regard, if the vessel is travelling in a region where desulfurization is not required, controller36or sub-controller36a-36cmay instruct valves86a-86cto close. Then, although the exhaust may be free to flow through scrubber38, no alkaline reagent may be sprayed into the exhaust stream to remove SOx.

After the exhaust passes through scrubbers38, the exhaust may travel into an outlet manifold88. If scrubbers38are vertically oriented, outlet manifold may be vertically oriented as well. Alternatively, if scrubbers38are horizontally oriented, outlet manifold88may horizontally oriented as well.FIG. 4illustrates an exemplary horizontal scrubber90that may be used in accordance with the present disclosure. Scrubber90includes a horizontally oriented housing92including an inlet93and an outlet95. Housing92is illustrated as being parallelepiped having first, second, third, and fourth side panels94,96,98, and100, but may be cylindrical as well without departing from the scope of the present disclosure.

A plurality of feed passages102each including a plurality of nozzles104inject alkaline reagent into housing92. Feed passages102receive the alkaline reagent from feed lines42(not shown). Similar to scrubber38, valves106may be located between feed lines42(not shown) and feed passages102. In the illustrated embodiment, a plurality of valves106may be used for each scrubber90. Valves106may be controlled by controller36or sub-controllers36a-36csuch that if controller36or sub-controller36a-36ccloses a particular exhaust control valve84a-84cfor a leg80a-80c, controller36or sub-controller36a-36cmay also close the valves106associated with the scrubber90in the closed leg80a-80c. In this manner, no alkaline reagent is permitted to be fed to the scrubber90that is not being used so that no fresh alkaline reagent is improperly drained to waste tank48. A plurality of collection reservoirs108may be positioned at an underside (i.e, panel96) of housing92. Collection reservoirs108collect the alkaline reagent injected into housing92. A plurality of return lines (not shown) may feed the used alkaline reagent to waste tank48(not shown).

Valves106may be controlled independently from exhaust control valves84a-84c. That is, although the engine exhaust may be free to pass through scrubber90, the feeding of alkaline reagent thereto may be prevented by closing the valve106associated with that scrubber90. Then, although the exhaust may be free to flow through scrubber90, no alkaline reagent may be sprayed into the exhaust stream to remove SOx.

A mist eliminator110may be positioned downstream from nozzles104. Mist eliminator110includes a plurality of blades112that allow mist droplets of the alkaline reagent to adhere thereto and eventually fall into one of collection reservoirs108. Although mist eliminator110is illustrated and described as including blades112, it should be understood that any type of droplet adhesion device may be used. For example, mist eliminator110may be a fine mesh screen like mist eliminator72described in conjunction with scrubber38. After passing through mist eliminator110, the engine exhaust is free to enter outlet manifold88and exit after-treatment system74.