CA2315415A1 - Regeneratable diesel particulate filter assembly - Google Patents
Regeneratable diesel particulate filter assembly Download PDFInfo
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- CA2315415A1 CA2315415A1 CA 2315415 CA2315415A CA2315415A1 CA 2315415 A1 CA2315415 A1 CA 2315415A1 CA 2315415 CA2315415 CA 2315415 CA 2315415 A CA2315415 A CA 2315415A CA 2315415 A1 CA2315415 A1 CA 2315415A1
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- Prior art keywords
- inlet
- forced air
- filter element
- heating means
- dpm
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
- F01N3/021—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
- F01N3/023—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters using means for regenerating the filters, e.g. by burning trapped particles
- F01N3/027—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters using means for regenerating the filters, e.g. by burning trapped particles using electric or magnetic heating means
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
- F01N3/021—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
- F01N3/022—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters characterised by specially adapted filtering structure, e.g. honeycomb, mesh or fibrous
- F01N3/0222—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters characterised by specially adapted filtering structure, e.g. honeycomb, mesh or fibrous the structure being monolithic, e.g. honeycombs
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Processes For Solid Components From Exhaust (AREA)
- Filtering Of Dispersed Particles In Gases (AREA)
Abstract
A method of regenerating in situ a DPM-contaminated diesel particulate filter assembly of an exhaust system connected to a diesel engine, said system comprising (a) a filter shell containing a filter element having an inlet face, an outlet face, and a DPM entrapping-body;
(b) electrical heating means within said shell adjacent said inlet face connectable to an electrical power supply;
(c) inlet temperature measuring means adjacent said inlet face and said heating means;
(d) body temperature measuring means within said body;
(e) means for receiving forced air within said shell and connectable to a forced air supply;
(f) said heating means, said inlet and said body temperature measuring means and said forced air receiving means being connectable to a programmable logic controller (PLC); said method comprising the steps of (i) connecting said heating means, said temperature measuring means and said forced air receiving means to said PLC;
(ii) connecting said heating means to said power supply;
(iii) connecting said forced air receiving means to said air supply;
(iv) heating said electrical heating means by said power supply to a desired temperature controlled by said PLC;
(v) receiving said forced air from said air supply at a desired rate controlled by said PLC to effect heating of said air to a desired temperature by said heating means;
(vi) passing the heated air through said inlet face and filter element to effect combustion of said DPM; and (vii) passing temperature data from said inlet and said body temperature measuring means to said PLC.
The method obviates the need to remove the DPF from a vehicle, particularly a heavy duty underground vehicle, during regeneration.
(b) electrical heating means within said shell adjacent said inlet face connectable to an electrical power supply;
(c) inlet temperature measuring means adjacent said inlet face and said heating means;
(d) body temperature measuring means within said body;
(e) means for receiving forced air within said shell and connectable to a forced air supply;
(f) said heating means, said inlet and said body temperature measuring means and said forced air receiving means being connectable to a programmable logic controller (PLC); said method comprising the steps of (i) connecting said heating means, said temperature measuring means and said forced air receiving means to said PLC;
(ii) connecting said heating means to said power supply;
(iii) connecting said forced air receiving means to said air supply;
(iv) heating said electrical heating means by said power supply to a desired temperature controlled by said PLC;
(v) receiving said forced air from said air supply at a desired rate controlled by said PLC to effect heating of said air to a desired temperature by said heating means;
(vi) passing the heated air through said inlet face and filter element to effect combustion of said DPM; and (vii) passing temperature data from said inlet and said body temperature measuring means to said PLC.
The method obviates the need to remove the DPF from a vehicle, particularly a heavy duty underground vehicle, during regeneration.
Description
REGENERATABI~E DIESEL PARTICULATE FILTER ASSEMBLY
FIELD OF THE INVENTION
This invention relates to a diesel particulate filter assembly, particularly, when part of an exhaust system connected to a diesel engine, and a method by which diesel particulate matter deposited within said filter is readily removed, particularly in situ when still associated with a diesel engine.
B~~CKGROUND TO THE 1NVENTION
The modern diesel engine is a power generating plant that provides excellent I S fuel economy and operating life. The term "diesel engine" in this specification refers to the most common concept of a diesel engine, namely, a compression-ignited (CI) engine that is powered by diesel fuel. It does not include CI
engines designed to use other fiuels, such as compressed natural gas, gasoline or methanol.
The low volatiility of diesel fuel makes the diesel engine type suitable for duties with special safety concerns or enclosed environment applications, such as vehicles for use in underground mines. However, one of the disadvantages of the diesel engine relative to most other internal combustion engines is the high level of diesel particulate matter (DPM) emitted from the diesel engine exhaust.
DPM is the sum of solids and liquids in the exhaust of a diesel powered engine. The solid components of DPM include primarily dry carbon particles (soot), and inorganic sulfates tmd ash from the engine lubrication oil. Soot is formed by a series of chemical traJlsformations during the combustion process in which the hydrogen and carbon ratio decreases to the extent that soot precursor molecules and, subsequently, soot nuclei are formed. The soot particles typically have a bi-nodal distribution of diameters of, approximately, 0.0075 to 0.056 micrometers and 0.056 to 0.75 micrometers. The portion of DPM that is liquid is called the soluble organic fraction (SOF) or volatile organic fraction (VOF) and includes components, such as hydrocarbons, sulfuric acid and water. The accepted measurement procedure for DPM in diesel exhaust requires that the exhaust is diluted, filtered and the mass of particulates measured at 52 °(:. Under these conditions, some of the organic gaseous components ~~re condensed and adsorbed onto the solid particles and become counted as pare: of the total measurement of DPM.
DPM has been identif ed recently as a toxic air contaminant by the California Air Resources Board and is suspected of being a carcinogen for containing carcinogenic polynuclear aromatic hydrocarbons. Thus, it is highly desirable to reduce DPlvI from diesel engine exhaust as much as possible, such as by employing low emissions engines, improvement in fuel quality, regular vehicle maintenance and exhaust after-treatment devices.
Particulate filtration is one exhaust after-treatment approach. There are several types of filters currently used for DPM removal, including particle impaction type filters and wall flow diffusion type falters. There are also several types of filter materials in use, including ceramic fibre, cordierite monolith, sintered metal monolith and sintered mei:al plate.
The wall-flow diesel particulate filter is comprised of a three-dimensional structure, typically cylindrical, having a honeycomb-like plurality of air channels, partitioned by walls having inlet and outlet channel plugs at alternate ends which direct the exhaust gas to pass through the porous walls and reduces the DPM by combustion in the filter.
The deep bed or impaction DPF comprises a pair of concentric cylindrical shell having suitably perforated walls through which exhaust gas exits after entering the shell at an open end of the inner shell and passing through a compacted fibrous filter medium contained in the body of the shell. The DPM is trapped on the fibrous material.
If DPM is assumed to be carbonaceous matter, the simplified chemical reaction of the combustion process can be described as C + OZ ~ COZ. The reaction rate expression for the combustion process of DPM in the filter can be defined as follows:-R c = A e{-E~'cRT»c«
~ a2 ) o wherein:-R(Co2) = reaction rate of DPM (molls) Ao = Frequency factor (constant) (m3/mol) EA = Activation energy for reaction (J/mol) R = universal gas law constant (J/mol*K) T = temperature (K) oc = constant for rE;action (a positive number) Co2 = concentration of oxygen on the DPM particle (mol/m3) From the above reaction rate expression, it can be seen that the rate of reaction can be controlled by adjusting the concentration of oxygen on the DPM
particle.
Increasing the flow of air through the DPF will increase the concentration of oxygen on the DPM particle. It can also be seen that increasing the temperature or lowering the activation energy tihrough the use of a catalyst will also increase the rate of reaction. The reaction is highly exothermic and, therefore, significant risk exists for a "run-away" temperature increasing reaction, which can result in thermal damage to the DPF. Theoretically, the DPF may also operate in a steady state fashion wherein the rate of DPM accumulation on the filter is equal to the rate of DPM
that is combusted. This theoretical point of operation is called the balance point.
A number of exhaust after-treatment methods using DPFs have been employed to treat particulate matter (PM) from diesel engine exhaust.
A first method, herein Method 1, is to install a DPF in the exhaust of a diesel engine of a vehicle or machine which is operated until the DPF has reached its 3 0 maximum capacity of trapped DPM, whereat the DPF is manually removed from the exhaust system and transferred to a location where the DPM is burned off from the DPF. This location can be an oven, kiln or any ofd=board device which blows hot air through the DPF. Typically, the temperature required to burn off the DPM is 550 °C or higher. However, the main problem with this method is that it is a laborious process. For some heavily used vehicles, it could involve several removals of the filter per day.
A second method, herein Method 2, is to use a DPF which contains a catalytic substance, such as for f;xample, platinum, palladium, vanadium oxides, and the like, that is applied or coated onto the filter media. The catalyst lowers the activation energy required for combustion of carbonaceous materials. Without catalytic materials on the filter media, combustion of a DPM on a DPF typically takes place at temperatures exceeding 550 °C, while catalyzed DPF's allow lower operating combustion temperatures. For typical diesel engine applications, the balance point between DPM accumulation on the DPF and DPM combustion rate is 350 °C
to 400 °C. For some heavy duty applications with high exhaust temperatures, a catalyzed DPF can operate effectively for long periods of time. However, this approach is limited to a small number of vehicles that meet a high temperature exhaust criteria.
These are usually certain heavy duty vehicles or stationary engines conducting set tasks. Catalyzed DPFs installed on vehicles which do not meet a high exhaust temperature criteria will usually result in the DPF becoming overloaded or clogged and causing engine malfunction. Many currently manufactured engines produce relatively cold exhaust and, typically, do not meet the above temperature criteria even in heavy duty applications.
A third method, herein Method 3, is to add to the diesel fuel a catalyst such as, for example, an organic compound of cerium, platinum, iron or copper in quantities, typically, of between 10 and 100 parts per million (ppm). This fuel-borne catalyst ultimately combines intimately with the DPM particles and is known to lower the activation energy required for DPM combustion in the exhaust.
This allows DPM that is trapped by a DPF to readily combust at temperatures typically found in diesel engine exhaust. However, much of the fuel-borne catalyst ends up :30 deposited on the DPM. Method 3 can be enhanced by programming the engine control system to periodically provide high exhaust temperature excursions to S
temporarily increase the temperature of the exhaust a.nd enhance DPM
combustion.
This method can also be further enhanced by adding an additional catalyst to the filter media per se as ~describeci in method 2. However, one of the drawbacks to method 3 is that it requires apparatus for the dosing of the fuel-borne catalyst to be installed to the vehicle. This dosing apparatus is relatively technically complex and expensive to retrofit onto existing vehicle, or to incorporate onto the original equipment at the factory. There are also logistic issues involved in re-filling the dosing system. An all:ernative, which involves high capital costs, is to apply the catalyst in bulk to a :fuel supply located at a central fueling depot. A
further problem with method 3 is that the fuel-borne catalyst deposits and remains on the DPM after combustion. of the DPM. Over time, the DPF becomes clogged with spent fuel-borne catalyst and requires cleaning in order to be re-used. In addition, it is believed that up to 10% of the fuel borne catalyst works its way through the filter and ultimately becomes deposited in the ambient air, ground or water. Since these fuel borne catalysts are; metal based, these materials persist in the environment for long periods and concerns exist over safety to human health and environment.
Regulatory approval :For wide-scale use of fuel-borne catalysts may require numerous expensive, long-term studies to prove their safety.
Method 4 uses a two stage system with a catalytic converter installed upstream of the DPF. The converter is specially designed to maximize the conversion of NO (nitrogen oxide) into N02 (nitrogen dioxide) in diesel exhaust.
N02 is known to be a strong oxidizing agent for DPM. In method 4, exhaust gas passes through the catalytic converter and, thereby, raises the level of N02 present in the engine exhaust. The exhaust gas is subsequently next passed through a DPF
to thereby trap the DPl~i on the filter medium. The DPM is then oxidized, primarily through the aid of N02 present in the exhaust. The DPF itself usually contains catalytic materials coated or deposited onto it, as described in Method 2. It is known that the presence of sulfur in the fuel result in sulfur compounds present in the exhaust which will chemically inhibit the ability of the catalytic converter to oxidize NO into N02. 'Therefore, this approach is limited to duties where low sulfur diesel fuel is used. Generally, the sulfur level in the fuel must be below 50 ppm for Method 4 to work well. However, commercially available diesel fuels with sulfur levels below 50 ppm .are currently limited. Formulating diesel fuel with desired sulfur levels is expensive and requires large capital investments on the part of refineries. Another drawback to this method is that it: requires relatively high levels of oxygen in the diesel exhaust and a high ratio of oxides of nitrogen to hydrocarbons in the exhaust in order to function effectively. Therefore, this method is usually restricted to use in only turbo-charged engines. An additional drawback is that this method produces a net increase of N02 exiting the vehicle, compared to a vehicle without this system. NOZ gas is highly toxic to humans, and more toxic than NO precursor. For vehicles operating in enclosed locations with workers in the vicinity, such as a warehouse or underground mine, it is highly undesirable for an emission control system on a vehicle to produce a net increase in N02.
Method 5 is to install an electric heater onto the DPF in order to raise the temperature of the DPF' to a level that is high enough for combustion of the DPM to take place. A compressor to provide air supply is also installed on the vehicle. The heater is operated while; the vehicle is shut off However, a drawback to this method is that the compressor installed on the vehicle must be suffciently durable to maintain a precise flow rate control after being subjected to high shock loads during vehicle operation. The current art does not provide precise control of the combustion airflow rate. Alternatively, the on-board compressor can be removed and combustion air then supplied by operating the engine at idle. A drawback to this approach is that since exhaust gas is passing though the DPM, much of the heat input into the DPF is transferred to the exhaust gas and is quickly lost. This approach requires a high amount of power input into the DPF and this power requirement far exceeds the normal capacity of a vehicle battery. The amount of power required for operation rnay be significant and reduce the efficiency of the engine. Neither of these systems has sufficient control over the combustion airflow to ensure complete rel;eneration and/or protection of the DPF from "run-away"
combustion events.
Method 6 uses a burner system to pre-heat the exhaust gas prior to it entering the DPF. The burner is typically operated on diesel fuel at any engine speed or load. The drawback to this approach is that a high amount of fuel is required to heat the exhaust gas which significantly reduces the fuel efficiency of the vehicle. Installation of a fuel burner system also involves significantly high capital costs.
Method 7 uses multiple DPFs on one vehicle in a parallel arrangement with a system of valves to automatically close flow to one DPF at a time, and allow the closed DPF to be electrically regenerated. A drawback to this approach is that large amounts of power and a bulky system of valves and DPFs are required.
Method 8 uses a number of engine calibration settings to increase exhaust temperature to assist regeneration of a filter. These may include modification of injection timing, throttling of intake airflow, restricting exhaust flow or post injection of fuel to raise; exhaust temperature. The drawback to this method is that it increases fuel consumption and results in higher engine temperatures, leading to special engine cooling requirements and/or higher engine servicing costs.
There is, therefore, a need for a practical, cost-effective, easily manually handleable regeneratab~le DPF assembly that does not suffer from the aforesaid disadvantages and drawbacks.
,~LJMMARY OF THE INVENTION
It is an object of the present invention to provide an improved method of regenerating a DPF whale comprised of an exhaust system still connected to a diesel engine which may be part of a vehicle, particularly an underground mining vehicle.
It is a further object to provide an improved DPF assembly and a diesel engine and vehicle incorporating said DPF assembly to facilitate regeneration of said DPF
while still attached to said diesel engine and said vehicle.
Accordingly, in one aspect t:he invention provides a method of regenerating in situ DPM-contaminated diesel particulate filter assembly of an exhaust system connected to a diesel engine, said system comprising g (a) a filter shell containing a filter element having an inlet face, an outlet face, and a DPM entrapping-body;
(b) electrical heating means within said shell adjacent said inlet face connectable to an electrical power supply;
(c) inlet temperature measuring means adjacent said inlet face and said heating means;
(d) body temperature measuring means within said body;
(e) means fir receiving forced air within said shell and connectable to a forced air supply;
(f) said heating means, said inlet and said body temperature measuring means and said forced air receiving .means being connectable to a programmable logic controller (PLC); said method comprising the steps of (i) connecting said heating means, said temperature measuring means and said forced air receiving means to said PLC;
(ii) connecting said heating means to said power supply;
(iii) connecting said forced air receiving means to said air supply;
(iv) heating said electrical heating means by said power supply to a desired temperature controlled by said :PLC;
(v) receiiving said forced air from said air supply at a desired rate controlled by said PLC to effect heating of said air to a desired temperature by said heating means;
(vi) passing the heated air through said inlet face and filter element to effect combustion of said DPM; and (vii) passing temperature data from said inlet and said body temperature measuring means to said PLC.
In a preferred aspect the invention provides a method as hereinabove defined wherein said filter element is a wall-flow filter element and said body comprises a plurality of axially aligned longitudinal exhaust channels defined by walls formed of a porous material.
In a further pre;ferred aspect said filter element is a deep-bed or impaction filter element wherein aaid body comprises an inner wall defining an inlet gas inner passage having said inlet passage at an end thereof; an outer wall concentric with said inner wall to define therebetween a fibrous material-containing chamber;
and wherein each of said inner and out walls having a plurality of gas permeable apertures.
In a further aspect, the invention provides a method as hereinabove wherein said forced air supply is remote from but operably connectable to said exhaust system.
In a yet further aspect, the invention provides a diesel engine exhaust system connected to a diesel a:ngine and comprising a diesel particulate filter assembly as hereinabove defined.
In a still further aspect, the invention pravides a heavy duty vehicle, particularly of use in underground mining, comprising a diesel engine and exhaust system as hereinabove defined.
Thus, in a still yet further aspect, the invention provides a system for regenerating in situ a :DPM contaminated diesel particulate filter assembly of an exhaust system of a diesel engine in a vehicle, said system comprising in combination said vehicle, said diesel engine and said exhaust system connected to said diesel engine and comprising (a) a filter shell containing a wall-flow filter element having an inlet face, an outlet face, a body comprising a plurality of axially aligned longitudinal exhaust channels defined by walls formed of a porous material;
(b) electrical heating means within said shell adjacent said inlet face;
(c) inlet temperature measuring means adjacent said inlet face and said heating means;
(d) body tennperature measuring means within said body;
(e) means for receiving forced air within said shell;
(f) a programmable logic controller in communication with said heating means, said inlet a.nd said body temperature measuring means and said forced air receiving means (g) an electrical power supply connected to said electrical heating 5 means; ;end (h) a forced air supply connected to said forced air supply means.
In this specification anal claims, the term "in situ" means that the DPF
assembly is still part of the full exhaust system connected to the diesel engine when the DPM is being "burnt-off' during the regeneration operation.
10 It will be understood that the means for receiving, for example, forced air within the shell may be connected directly to or, indirectly, through the forced air supply means to the PI~C. The forced air supply may be permanently located near or adjacent to, and part of, the exhaust system and/or diesel engine, particularly when the latter is part of a vehicle. Most preferably, the forced air supply is remote from, not affixed to, but operably connected to the exhaust system according to the invention. In a most preferred embodiment the forced air supply is an air compressor connectable by an a.ir line, conduit or the like to the means for receiving forced air within the shell.
The main components of the system may be generally described as follows.
Although, generally, any type of DPF filter can be used in association with the present invention, the preferred DPF type is a wall-flow type composed of porous silicon carbide media, preferably coated with a catalyst such as, for example, platinum, palladium, vanadium oxide and the like, for the purpose of reducing the activation energy required for DPM combustion to take effect. Other types of DPF
made of substances, such as cordierite, sintered metal or deep bed filters with fibrous media, may be used.
The electrical heating element is located adjacent the inlet face of the DPF
attached to the DPF housing. Typically, the heating element is located 50 to mm away from the :>urface of the DPF inlet face. The heating element is, preferably, shaped as a flat, circular coil having a coil diameter similar to the diameter of the DPF inlet face. The heating element has a flow-through area of about 25% or greater of the flat coil area so that flow of the exhaust gas into the DPF is not unduly obstructed in normal engine running operation.
Generally, the so-called hardware unit comprises and may, optionally, physically contain the programmable logic controller (PLC); compressed air flow s meter and regulator timers, relays, power supply connectors, compressed air connectors, protection .devices, .and operator control buttons a.nd indicator lights.
The monitoring equipment, generally, comprises thermocouples for measuring engine exhaust gas temperature, post-heater element exhaust gas temperature, DPF temperature and post-DPF exhaust gas temperature.
When compressed air is not available, a blower or compressor may, alternatively and optionally, be built into the hardware unit. Further, a pre-heater of inlet air flow can, optionally, be employed prior to the main heating element.
In a preferred practice of a system and method according to the invention, the operational process parameter values of heating element temperature, air flow rates, and operational time periods are pre-set within the PLC, dependent on the model type, capacity, size and other physical and chemical characteristics of the DPF. These operational parameters are obtained through calibration studies, conducted, preferably, at the factory of DPF manufacture. Thus, the pre-setting of operating parameter values offers virtually automatic running of the regeneration process.
BRIE:E DESCRIPTION OF THE DRAWINGS
In order that the invention may be better understood, a preferred embodiment will now be described by way of example only with reference to the accompanying drawings wherein:
Fig. 1 is a perspective view of a honeycomb wall-flow diesel particulate filter according to the prior art;
Fig. 2 is a diagrammatic cross-section of a wall-flow filter according to the prior;
Fig. 3 represents a diagrammatic sectional view of a PDF assembly according to the inventions connected to an air and electrical power source and programmable logic controller (PLC) undergoing a regeneration process;
Fig. 4 is a sketch of a regenerating assembly according to the invention while mounted on a diesel loader;
Fig. 5 is a graph of controlled flow-rate set points against DPF temperature as fed back to the PLC;
Fig. 6 is a perspective 'view of a deep bed or impaction type embodiment alternative according to the invention DPM; and wherein the same numeral denotes like parts.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Figs. 1 and 2 :.how generally as 10 a cylindrical-shaped honeycomb wall-flow diesel particulate filter element known in the art having an inlet face 11, an outlet face 12, a plurality of axially aligned longitudinal exhaust gas channels 13 defined by walls 14 formed of silicon carbide porous ceramic material. Each of channels 13 is square in cross-section but may be circular or of any other suitable shape. Each of half of the channels at an exhaust gas input end 16 is alternately plugged at one channel end 18 and open at its other end 20. Each of the remaining channels is open at its end 22, adjacent end 18 of each adjacent channel, and closed at its end 24. The physical dimensions of the filter may vary depending on the required space velocities and the configuration of the engine producing the exhaust gas.
In operation, exhaust gas containing particulate material enters wall-flow filter 10 at inlet face 11 into channel ends 22, passes along channel 13 and through ceramic walls 14 as denoted by the arrows in Fig. 2, due to the blockage at ends 24, and out through outlet face 12.
With reference now to Fig. 4, this shows a diesel engine loader shown generally as 30 having a DPF shown generally as 31 mounted thereon and connected to air supply conduit 32, electrical power conduit 34 and a programmable logic controller 36.
With reference now to the regenerating system shown generally as 300 in Fig. 3, DPF 10 as mounted on diesel loader 30 is within an exhaust pipe shell having an inlet 40 and outlet 42. Adjacent inlet face 11 is retained an electric heating coil element 44~ by terminal box 46 which receives electrical power through relay 48 from an electric power source 50 under control of PLC unit 36.
Disposed between filter face 11 and heating element 44 is located a post heater element exhaust gas thermocouple 52. A post DPF exhaust gas thermocouple 54 is retained adjacent outlet face 12 and a DPF thermocouple 56 is retained within the body of filter 10. Each of thermocouples 52, 54 and 56 is in electrical contact with PLC 36.
A combustion air nozzle 58 is located within inlet 40 for providing means for receiving forced air from ai.r hose 32, which has a proportional solenoid valve 62, a flow meter 64 and a pressure regulator 66 to receive compressed air from compressor source 68. Solenoid 62 is under the control of PLC 36.
A butterfly shut-off valve 70 is located within inlet 40.
In operation, a vehicle operator drives diesel engine vehicle 30 normally during the working of his shift, during which DPM accumulates in DPF 10. At the end of the shift, the operator drives vehicle 30 to a maintenance area and shuts off the engine. Before the beginning of the DPF regeneration process, the operator shuts off butterfly valve 70 located within inlet pipe 40 of DPF 10. Air hose 32 is connected to air inlet nozzle 58 on DPF 10. Electric power cable 34 is connected to on-board heating element 44. Thermocouples 52, 54 and 56 are also connected to PLC 36 for monitoring inlet and outlet temperatures and for feedback control.
Alternatively, a single coupling device can be employ ed to provide unified coupling for power supply, air and thermocouples. The operator presses the start button to start PLC hardware unit 36, which, when suitably programmed, automatically controls the regeneration process. After a pre-set desired time period, an indicator light on PLC 36, preferably labeled DONE, comes on to indicate that regeneration is complete. The operator disconnects the power supply, air hose and thermocouples 52, 54 and 56. Before starting vehicle 30, the operator opens butterfly valve 70.
Alternatively, an automatic butterfly valve can be employed which closes at the start of regeneration and opens once regeneration is complete. Vehicle 30 is, thus, ready for the next shift.
S In more detail, once the start button is activated, electrical current to heating element 44 is suppliedl which begins to warm up inlet face 11 of the DPF. This initial warm up period takes place in static air without any flow of inlet air to ensure that hydrocarbon fractions are not stripped away before they can assist in the filter regeneration. The optimum time for this initial warm-up period is about 5 minutes, but varies depending on design parameters of DPF 10 and heater element 44.
Through conduction and radiation of heat from heater element 44, at face 11, a temperature sufficient for DPM combustion to readily take place of about 500 °C, occurs after a 5 minute. period. The SiC (silicon carbide) DPF has a relatively large thermal mass, so even though face 11 of the DPF is hot, the interior of the DPF
initially remains cold and, accordingly, DPM combustion for most of the DPF
does not take place. At the end of the initial warm-up period, air flow to the DPF
is started while electrical current to heating element 44 is maintained. As the flow of air enters face 11, the ;amount of oxygen entering the DPF is increased and the rate of reaction for the combustion process is thereby increased (see aforesaid equation 1). Since the combustion of DPM is exothermic, the reaction itself, also, increases the temperature of the DPF. Thus, the reaction starts at face 11 and spreads deeper into the interior of DPF 10 in the air flow direction until it reaches a point where DPM is combusted tlvroughout the entire DPF. The continuous supply of air into the filter ensures that sufficient oxygen is available for the DPM combustion to take place at a sufficient rage. After a programmed period of time, the current to heating element 44 and the air supply are shut off and regeneration is complete.
Control of the temperature of the air after passing though heating element 44, but before entering thf; DPF face is important. If the temperature of the air is too low, then combustion of the DPM takes place too slowly and complete regeneration of the filter does not occur in the required time period. The temperature of the air is increased by, preferably, decreasing the rate of air flow into the DPF.
Therefore, there is a maximum allowable flow-rate that is achiievable for combustion of the DPF during the specified period. This maximum flow-rate is empirically determined through experimentation.
Feedback control is'. used to adjust the rate of air flow into the DPF.
Feedback 5 control utilizes the temperature of the DPF at a specific location within filter 10, or alternatively and preferably, the temperature of the exhaust at the outlet of the DPF.
If the feedback temperature is too low then the flow-rate of air can be reduced, to result in less transfer of heat away from the DPF and eventually improve rates of reaction as the temperature of the DPF increases. If t:he feedback temperature is too 10 high, for example, over 700 °C, the DPF is in danger of overheating and results in thermal damage to the DPF media. In this case, the flow-rate of air is reduced or temporarily stopped, which reduces the rate of combustion of the DPM (see equation 1). The output result from this feedback data is determined through suitable dependent algorithms, which may or may not be time dependent arrived at 15 after experimental tests used to determine optimum points of operation for air flows and temperatures. A typical relationship of the DPF temperature feedback and controlled as desired air flow-rate set-point is shown in Fig. 5.
With reference now to Fig. 6 which shows, generally, as 78, a deep bed or impaction type DPF comprising a pair of concentric cylindrical shells 80, 82 wherein inner shell 8 2 is within outer shell 80, and which define therebetween a cylindrical cavity 84 I>acked with particulate entrapping fibrous material 86.
Each of shells 80 and 82 has a plurality of apertures 88 longitudinally of shells 80, 82 through which exhaust; gases pass.
Inner shell 82 defines a hollow cylindrical passage 90 and an exhaust gas inlet at one end 92, only. Within passage 90 is a coiled electrical heating element 94 adjacent inner shell 82; which is connected to electrical power trough relay 48, from electric power source 50 under control of PLC unit 36.
Disposed between. inner shell face 96 and heating element 94 is located port heater element exhaust gas thermocouple 52. One or more of post DPF exhaust gas thermocouples 54 are retained within one or more of apertures 88. One or more of body thermocouples SEi are retained within the body of filter 78 longitudinally of its length. Each of thermocouples 52, 54 and 56 is in electrical contact with PLC
36.
A combustion air nozzle is located within inlet 92 for providing means for receiving forced air from air hose 32 as hereinbefore described with reference to Fig. 3. Inlet 92 has a butterfly valve 70.
In operation, regeneration of contaminated impact DPF 78 is similar to that for the wall flow DPF in the set-up with PLC unit 36 and operational process conditions and parameters.
A most preferred utility of the assembly according to the invention is in underground hard-rock mining. The desired vehicles in these applications are typically assigned to specific tasks and operate on a similar duty cycle over a period of several months or longer. These vehicles usually operate in shifts that are, typically, 7 to 12 hours in length with a period of at least 1-2 hours required to switch from one work shift to another. During the period in which the work shift is changed, the vehicle is left stopped with the ignition in the off position.
However, in the present process o~f the invention, at the end of the shift, the PLC
hardware unit with attendant electrical, remote air supply source and thermocouple fittings, is brought to the vehicle and the power supply, thermocouples and compressed air connections made. The flow valve is also turned to the closed position to seal off any air back flow to the remaining components of the exhaust system and engine.
The operator presses a start button to begin the regeneration process under the control of the PLC. The regeneration process is programmed to finish at the same time the next shift is ready to begin work. The new shift operator then unplugs the compressed air, thermocouples, power supply connectors and PLC hardware unit.
The new shift operator also returns the flow valve to vehicle open position to enable the vehicle to begin a new operation.
Thus, the invention as herein defined provides the following advantages for this utility over the aforesaid prior art methods.
Unlike method 1, there is no manual or mechanical heavy lifting required to remove the DPF from the machine on a periodic basis, since the DPF does not have to be taken off the vehicle.
Unlike method 2, the DPF according to the invention can be used on any vehicle, as long as there is an intermittent, say, one to two hour period of vehicle inactivity available for regeneration to be performed provided a power supply is available on site.
Unlike method 3, there are no required fuel-borne catalysts and, therefore, no issues or concerns relating to possible impact on human health and environment from the fuel-borne catalyst entering the air, ground or water.
Unlike method 4, the DPF assembly and associated components do not produce a net increase in NOz. In fact, if this system is used in combination with a filter coating as described in Canadian patent application No. 2,221,118, filed November 15, 1997, in the name of Diesel Controls Limited, is applied to the assembly, a net decrease in N02 will result.
Much less power and energy is required than in method 5 since the regeneration process, according to the invention, operates under low gaseous flow, much less power is required to heat the DPF. Less than 5% of the rated engine power over a period of one to two hours is used. Less power consumption results in lower operating costs. In addition, with programmable logic control feedback of temperature, this system can be optimized to operate on minimum energy requirements. In addition, since an outside source of compressed air is used rather than an on-board system, higher pressure air sources can be used to allow for better control of air flow.
Unlike method 6, the DPF assembly according to the invention does not increase vehicle fuel consumption or require an additional fuel source for the purposes of re-heating the exhaust gas.
Unlike method '7, this system of the invention requires, preferably, only one DPF, to thereby allow for a compact fit into the exhaust system. No expensive automatically actuated exhaust valves are required, or complex exhaust manifold.
Unlike method 8, this system does not increase fuel consumption in order to achieve exhaust temperatures, and does not require any upgrades to the engine cooling system.
Although this disclosure has described and illustrated certain preferred embodiments of the invention, it is to be understood that the invention is not restricted to those particular embodiments. Rather, the invention includes all embodiments which are functional or mechanical equivalents of the specific embodiments and features that have been described and illustrated.
FIELD OF THE INVENTION
This invention relates to a diesel particulate filter assembly, particularly, when part of an exhaust system connected to a diesel engine, and a method by which diesel particulate matter deposited within said filter is readily removed, particularly in situ when still associated with a diesel engine.
B~~CKGROUND TO THE 1NVENTION
The modern diesel engine is a power generating plant that provides excellent I S fuel economy and operating life. The term "diesel engine" in this specification refers to the most common concept of a diesel engine, namely, a compression-ignited (CI) engine that is powered by diesel fuel. It does not include CI
engines designed to use other fiuels, such as compressed natural gas, gasoline or methanol.
The low volatiility of diesel fuel makes the diesel engine type suitable for duties with special safety concerns or enclosed environment applications, such as vehicles for use in underground mines. However, one of the disadvantages of the diesel engine relative to most other internal combustion engines is the high level of diesel particulate matter (DPM) emitted from the diesel engine exhaust.
DPM is the sum of solids and liquids in the exhaust of a diesel powered engine. The solid components of DPM include primarily dry carbon particles (soot), and inorganic sulfates tmd ash from the engine lubrication oil. Soot is formed by a series of chemical traJlsformations during the combustion process in which the hydrogen and carbon ratio decreases to the extent that soot precursor molecules and, subsequently, soot nuclei are formed. The soot particles typically have a bi-nodal distribution of diameters of, approximately, 0.0075 to 0.056 micrometers and 0.056 to 0.75 micrometers. The portion of DPM that is liquid is called the soluble organic fraction (SOF) or volatile organic fraction (VOF) and includes components, such as hydrocarbons, sulfuric acid and water. The accepted measurement procedure for DPM in diesel exhaust requires that the exhaust is diluted, filtered and the mass of particulates measured at 52 °(:. Under these conditions, some of the organic gaseous components ~~re condensed and adsorbed onto the solid particles and become counted as pare: of the total measurement of DPM.
DPM has been identif ed recently as a toxic air contaminant by the California Air Resources Board and is suspected of being a carcinogen for containing carcinogenic polynuclear aromatic hydrocarbons. Thus, it is highly desirable to reduce DPlvI from diesel engine exhaust as much as possible, such as by employing low emissions engines, improvement in fuel quality, regular vehicle maintenance and exhaust after-treatment devices.
Particulate filtration is one exhaust after-treatment approach. There are several types of filters currently used for DPM removal, including particle impaction type filters and wall flow diffusion type falters. There are also several types of filter materials in use, including ceramic fibre, cordierite monolith, sintered metal monolith and sintered mei:al plate.
The wall-flow diesel particulate filter is comprised of a three-dimensional structure, typically cylindrical, having a honeycomb-like plurality of air channels, partitioned by walls having inlet and outlet channel plugs at alternate ends which direct the exhaust gas to pass through the porous walls and reduces the DPM by combustion in the filter.
The deep bed or impaction DPF comprises a pair of concentric cylindrical shell having suitably perforated walls through which exhaust gas exits after entering the shell at an open end of the inner shell and passing through a compacted fibrous filter medium contained in the body of the shell. The DPM is trapped on the fibrous material.
If DPM is assumed to be carbonaceous matter, the simplified chemical reaction of the combustion process can be described as C + OZ ~ COZ. The reaction rate expression for the combustion process of DPM in the filter can be defined as follows:-R c = A e{-E~'cRT»c«
~ a2 ) o wherein:-R(Co2) = reaction rate of DPM (molls) Ao = Frequency factor (constant) (m3/mol) EA = Activation energy for reaction (J/mol) R = universal gas law constant (J/mol*K) T = temperature (K) oc = constant for rE;action (a positive number) Co2 = concentration of oxygen on the DPM particle (mol/m3) From the above reaction rate expression, it can be seen that the rate of reaction can be controlled by adjusting the concentration of oxygen on the DPM
particle.
Increasing the flow of air through the DPF will increase the concentration of oxygen on the DPM particle. It can also be seen that increasing the temperature or lowering the activation energy tihrough the use of a catalyst will also increase the rate of reaction. The reaction is highly exothermic and, therefore, significant risk exists for a "run-away" temperature increasing reaction, which can result in thermal damage to the DPF. Theoretically, the DPF may also operate in a steady state fashion wherein the rate of DPM accumulation on the filter is equal to the rate of DPM
that is combusted. This theoretical point of operation is called the balance point.
A number of exhaust after-treatment methods using DPFs have been employed to treat particulate matter (PM) from diesel engine exhaust.
A first method, herein Method 1, is to install a DPF in the exhaust of a diesel engine of a vehicle or machine which is operated until the DPF has reached its 3 0 maximum capacity of trapped DPM, whereat the DPF is manually removed from the exhaust system and transferred to a location where the DPM is burned off from the DPF. This location can be an oven, kiln or any ofd=board device which blows hot air through the DPF. Typically, the temperature required to burn off the DPM is 550 °C or higher. However, the main problem with this method is that it is a laborious process. For some heavily used vehicles, it could involve several removals of the filter per day.
A second method, herein Method 2, is to use a DPF which contains a catalytic substance, such as for f;xample, platinum, palladium, vanadium oxides, and the like, that is applied or coated onto the filter media. The catalyst lowers the activation energy required for combustion of carbonaceous materials. Without catalytic materials on the filter media, combustion of a DPM on a DPF typically takes place at temperatures exceeding 550 °C, while catalyzed DPF's allow lower operating combustion temperatures. For typical diesel engine applications, the balance point between DPM accumulation on the DPF and DPM combustion rate is 350 °C
to 400 °C. For some heavy duty applications with high exhaust temperatures, a catalyzed DPF can operate effectively for long periods of time. However, this approach is limited to a small number of vehicles that meet a high temperature exhaust criteria.
These are usually certain heavy duty vehicles or stationary engines conducting set tasks. Catalyzed DPFs installed on vehicles which do not meet a high exhaust temperature criteria will usually result in the DPF becoming overloaded or clogged and causing engine malfunction. Many currently manufactured engines produce relatively cold exhaust and, typically, do not meet the above temperature criteria even in heavy duty applications.
A third method, herein Method 3, is to add to the diesel fuel a catalyst such as, for example, an organic compound of cerium, platinum, iron or copper in quantities, typically, of between 10 and 100 parts per million (ppm). This fuel-borne catalyst ultimately combines intimately with the DPM particles and is known to lower the activation energy required for DPM combustion in the exhaust.
This allows DPM that is trapped by a DPF to readily combust at temperatures typically found in diesel engine exhaust. However, much of the fuel-borne catalyst ends up :30 deposited on the DPM. Method 3 can be enhanced by programming the engine control system to periodically provide high exhaust temperature excursions to S
temporarily increase the temperature of the exhaust a.nd enhance DPM
combustion.
This method can also be further enhanced by adding an additional catalyst to the filter media per se as ~describeci in method 2. However, one of the drawbacks to method 3 is that it requires apparatus for the dosing of the fuel-borne catalyst to be installed to the vehicle. This dosing apparatus is relatively technically complex and expensive to retrofit onto existing vehicle, or to incorporate onto the original equipment at the factory. There are also logistic issues involved in re-filling the dosing system. An all:ernative, which involves high capital costs, is to apply the catalyst in bulk to a :fuel supply located at a central fueling depot. A
further problem with method 3 is that the fuel-borne catalyst deposits and remains on the DPM after combustion. of the DPM. Over time, the DPF becomes clogged with spent fuel-borne catalyst and requires cleaning in order to be re-used. In addition, it is believed that up to 10% of the fuel borne catalyst works its way through the filter and ultimately becomes deposited in the ambient air, ground or water. Since these fuel borne catalysts are; metal based, these materials persist in the environment for long periods and concerns exist over safety to human health and environment.
Regulatory approval :For wide-scale use of fuel-borne catalysts may require numerous expensive, long-term studies to prove their safety.
Method 4 uses a two stage system with a catalytic converter installed upstream of the DPF. The converter is specially designed to maximize the conversion of NO (nitrogen oxide) into N02 (nitrogen dioxide) in diesel exhaust.
N02 is known to be a strong oxidizing agent for DPM. In method 4, exhaust gas passes through the catalytic converter and, thereby, raises the level of N02 present in the engine exhaust. The exhaust gas is subsequently next passed through a DPF
to thereby trap the DPl~i on the filter medium. The DPM is then oxidized, primarily through the aid of N02 present in the exhaust. The DPF itself usually contains catalytic materials coated or deposited onto it, as described in Method 2. It is known that the presence of sulfur in the fuel result in sulfur compounds present in the exhaust which will chemically inhibit the ability of the catalytic converter to oxidize NO into N02. 'Therefore, this approach is limited to duties where low sulfur diesel fuel is used. Generally, the sulfur level in the fuel must be below 50 ppm for Method 4 to work well. However, commercially available diesel fuels with sulfur levels below 50 ppm .are currently limited. Formulating diesel fuel with desired sulfur levels is expensive and requires large capital investments on the part of refineries. Another drawback to this method is that it: requires relatively high levels of oxygen in the diesel exhaust and a high ratio of oxides of nitrogen to hydrocarbons in the exhaust in order to function effectively. Therefore, this method is usually restricted to use in only turbo-charged engines. An additional drawback is that this method produces a net increase of N02 exiting the vehicle, compared to a vehicle without this system. NOZ gas is highly toxic to humans, and more toxic than NO precursor. For vehicles operating in enclosed locations with workers in the vicinity, such as a warehouse or underground mine, it is highly undesirable for an emission control system on a vehicle to produce a net increase in N02.
Method 5 is to install an electric heater onto the DPF in order to raise the temperature of the DPF' to a level that is high enough for combustion of the DPM to take place. A compressor to provide air supply is also installed on the vehicle. The heater is operated while; the vehicle is shut off However, a drawback to this method is that the compressor installed on the vehicle must be suffciently durable to maintain a precise flow rate control after being subjected to high shock loads during vehicle operation. The current art does not provide precise control of the combustion airflow rate. Alternatively, the on-board compressor can be removed and combustion air then supplied by operating the engine at idle. A drawback to this approach is that since exhaust gas is passing though the DPM, much of the heat input into the DPF is transferred to the exhaust gas and is quickly lost. This approach requires a high amount of power input into the DPF and this power requirement far exceeds the normal capacity of a vehicle battery. The amount of power required for operation rnay be significant and reduce the efficiency of the engine. Neither of these systems has sufficient control over the combustion airflow to ensure complete rel;eneration and/or protection of the DPF from "run-away"
combustion events.
Method 6 uses a burner system to pre-heat the exhaust gas prior to it entering the DPF. The burner is typically operated on diesel fuel at any engine speed or load. The drawback to this approach is that a high amount of fuel is required to heat the exhaust gas which significantly reduces the fuel efficiency of the vehicle. Installation of a fuel burner system also involves significantly high capital costs.
Method 7 uses multiple DPFs on one vehicle in a parallel arrangement with a system of valves to automatically close flow to one DPF at a time, and allow the closed DPF to be electrically regenerated. A drawback to this approach is that large amounts of power and a bulky system of valves and DPFs are required.
Method 8 uses a number of engine calibration settings to increase exhaust temperature to assist regeneration of a filter. These may include modification of injection timing, throttling of intake airflow, restricting exhaust flow or post injection of fuel to raise; exhaust temperature. The drawback to this method is that it increases fuel consumption and results in higher engine temperatures, leading to special engine cooling requirements and/or higher engine servicing costs.
There is, therefore, a need for a practical, cost-effective, easily manually handleable regeneratab~le DPF assembly that does not suffer from the aforesaid disadvantages and drawbacks.
,~LJMMARY OF THE INVENTION
It is an object of the present invention to provide an improved method of regenerating a DPF whale comprised of an exhaust system still connected to a diesel engine which may be part of a vehicle, particularly an underground mining vehicle.
It is a further object to provide an improved DPF assembly and a diesel engine and vehicle incorporating said DPF assembly to facilitate regeneration of said DPF
while still attached to said diesel engine and said vehicle.
Accordingly, in one aspect t:he invention provides a method of regenerating in situ DPM-contaminated diesel particulate filter assembly of an exhaust system connected to a diesel engine, said system comprising g (a) a filter shell containing a filter element having an inlet face, an outlet face, and a DPM entrapping-body;
(b) electrical heating means within said shell adjacent said inlet face connectable to an electrical power supply;
(c) inlet temperature measuring means adjacent said inlet face and said heating means;
(d) body temperature measuring means within said body;
(e) means fir receiving forced air within said shell and connectable to a forced air supply;
(f) said heating means, said inlet and said body temperature measuring means and said forced air receiving .means being connectable to a programmable logic controller (PLC); said method comprising the steps of (i) connecting said heating means, said temperature measuring means and said forced air receiving means to said PLC;
(ii) connecting said heating means to said power supply;
(iii) connecting said forced air receiving means to said air supply;
(iv) heating said electrical heating means by said power supply to a desired temperature controlled by said :PLC;
(v) receiiving said forced air from said air supply at a desired rate controlled by said PLC to effect heating of said air to a desired temperature by said heating means;
(vi) passing the heated air through said inlet face and filter element to effect combustion of said DPM; and (vii) passing temperature data from said inlet and said body temperature measuring means to said PLC.
In a preferred aspect the invention provides a method as hereinabove defined wherein said filter element is a wall-flow filter element and said body comprises a plurality of axially aligned longitudinal exhaust channels defined by walls formed of a porous material.
In a further pre;ferred aspect said filter element is a deep-bed or impaction filter element wherein aaid body comprises an inner wall defining an inlet gas inner passage having said inlet passage at an end thereof; an outer wall concentric with said inner wall to define therebetween a fibrous material-containing chamber;
and wherein each of said inner and out walls having a plurality of gas permeable apertures.
In a further aspect, the invention provides a method as hereinabove wherein said forced air supply is remote from but operably connectable to said exhaust system.
In a yet further aspect, the invention provides a diesel engine exhaust system connected to a diesel a:ngine and comprising a diesel particulate filter assembly as hereinabove defined.
In a still further aspect, the invention pravides a heavy duty vehicle, particularly of use in underground mining, comprising a diesel engine and exhaust system as hereinabove defined.
Thus, in a still yet further aspect, the invention provides a system for regenerating in situ a :DPM contaminated diesel particulate filter assembly of an exhaust system of a diesel engine in a vehicle, said system comprising in combination said vehicle, said diesel engine and said exhaust system connected to said diesel engine and comprising (a) a filter shell containing a wall-flow filter element having an inlet face, an outlet face, a body comprising a plurality of axially aligned longitudinal exhaust channels defined by walls formed of a porous material;
(b) electrical heating means within said shell adjacent said inlet face;
(c) inlet temperature measuring means adjacent said inlet face and said heating means;
(d) body tennperature measuring means within said body;
(e) means for receiving forced air within said shell;
(f) a programmable logic controller in communication with said heating means, said inlet a.nd said body temperature measuring means and said forced air receiving means (g) an electrical power supply connected to said electrical heating 5 means; ;end (h) a forced air supply connected to said forced air supply means.
In this specification anal claims, the term "in situ" means that the DPF
assembly is still part of the full exhaust system connected to the diesel engine when the DPM is being "burnt-off' during the regeneration operation.
10 It will be understood that the means for receiving, for example, forced air within the shell may be connected directly to or, indirectly, through the forced air supply means to the PI~C. The forced air supply may be permanently located near or adjacent to, and part of, the exhaust system and/or diesel engine, particularly when the latter is part of a vehicle. Most preferably, the forced air supply is remote from, not affixed to, but operably connected to the exhaust system according to the invention. In a most preferred embodiment the forced air supply is an air compressor connectable by an a.ir line, conduit or the like to the means for receiving forced air within the shell.
The main components of the system may be generally described as follows.
Although, generally, any type of DPF filter can be used in association with the present invention, the preferred DPF type is a wall-flow type composed of porous silicon carbide media, preferably coated with a catalyst such as, for example, platinum, palladium, vanadium oxide and the like, for the purpose of reducing the activation energy required for DPM combustion to take effect. Other types of DPF
made of substances, such as cordierite, sintered metal or deep bed filters with fibrous media, may be used.
The electrical heating element is located adjacent the inlet face of the DPF
attached to the DPF housing. Typically, the heating element is located 50 to mm away from the :>urface of the DPF inlet face. The heating element is, preferably, shaped as a flat, circular coil having a coil diameter similar to the diameter of the DPF inlet face. The heating element has a flow-through area of about 25% or greater of the flat coil area so that flow of the exhaust gas into the DPF is not unduly obstructed in normal engine running operation.
Generally, the so-called hardware unit comprises and may, optionally, physically contain the programmable logic controller (PLC); compressed air flow s meter and regulator timers, relays, power supply connectors, compressed air connectors, protection .devices, .and operator control buttons a.nd indicator lights.
The monitoring equipment, generally, comprises thermocouples for measuring engine exhaust gas temperature, post-heater element exhaust gas temperature, DPF temperature and post-DPF exhaust gas temperature.
When compressed air is not available, a blower or compressor may, alternatively and optionally, be built into the hardware unit. Further, a pre-heater of inlet air flow can, optionally, be employed prior to the main heating element.
In a preferred practice of a system and method according to the invention, the operational process parameter values of heating element temperature, air flow rates, and operational time periods are pre-set within the PLC, dependent on the model type, capacity, size and other physical and chemical characteristics of the DPF. These operational parameters are obtained through calibration studies, conducted, preferably, at the factory of DPF manufacture. Thus, the pre-setting of operating parameter values offers virtually automatic running of the regeneration process.
BRIE:E DESCRIPTION OF THE DRAWINGS
In order that the invention may be better understood, a preferred embodiment will now be described by way of example only with reference to the accompanying drawings wherein:
Fig. 1 is a perspective view of a honeycomb wall-flow diesel particulate filter according to the prior art;
Fig. 2 is a diagrammatic cross-section of a wall-flow filter according to the prior;
Fig. 3 represents a diagrammatic sectional view of a PDF assembly according to the inventions connected to an air and electrical power source and programmable logic controller (PLC) undergoing a regeneration process;
Fig. 4 is a sketch of a regenerating assembly according to the invention while mounted on a diesel loader;
Fig. 5 is a graph of controlled flow-rate set points against DPF temperature as fed back to the PLC;
Fig. 6 is a perspective 'view of a deep bed or impaction type embodiment alternative according to the invention DPM; and wherein the same numeral denotes like parts.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Figs. 1 and 2 :.how generally as 10 a cylindrical-shaped honeycomb wall-flow diesel particulate filter element known in the art having an inlet face 11, an outlet face 12, a plurality of axially aligned longitudinal exhaust gas channels 13 defined by walls 14 formed of silicon carbide porous ceramic material. Each of channels 13 is square in cross-section but may be circular or of any other suitable shape. Each of half of the channels at an exhaust gas input end 16 is alternately plugged at one channel end 18 and open at its other end 20. Each of the remaining channels is open at its end 22, adjacent end 18 of each adjacent channel, and closed at its end 24. The physical dimensions of the filter may vary depending on the required space velocities and the configuration of the engine producing the exhaust gas.
In operation, exhaust gas containing particulate material enters wall-flow filter 10 at inlet face 11 into channel ends 22, passes along channel 13 and through ceramic walls 14 as denoted by the arrows in Fig. 2, due to the blockage at ends 24, and out through outlet face 12.
With reference now to Fig. 4, this shows a diesel engine loader shown generally as 30 having a DPF shown generally as 31 mounted thereon and connected to air supply conduit 32, electrical power conduit 34 and a programmable logic controller 36.
With reference now to the regenerating system shown generally as 300 in Fig. 3, DPF 10 as mounted on diesel loader 30 is within an exhaust pipe shell having an inlet 40 and outlet 42. Adjacent inlet face 11 is retained an electric heating coil element 44~ by terminal box 46 which receives electrical power through relay 48 from an electric power source 50 under control of PLC unit 36.
Disposed between filter face 11 and heating element 44 is located a post heater element exhaust gas thermocouple 52. A post DPF exhaust gas thermocouple 54 is retained adjacent outlet face 12 and a DPF thermocouple 56 is retained within the body of filter 10. Each of thermocouples 52, 54 and 56 is in electrical contact with PLC 36.
A combustion air nozzle 58 is located within inlet 40 for providing means for receiving forced air from ai.r hose 32, which has a proportional solenoid valve 62, a flow meter 64 and a pressure regulator 66 to receive compressed air from compressor source 68. Solenoid 62 is under the control of PLC 36.
A butterfly shut-off valve 70 is located within inlet 40.
In operation, a vehicle operator drives diesel engine vehicle 30 normally during the working of his shift, during which DPM accumulates in DPF 10. At the end of the shift, the operator drives vehicle 30 to a maintenance area and shuts off the engine. Before the beginning of the DPF regeneration process, the operator shuts off butterfly valve 70 located within inlet pipe 40 of DPF 10. Air hose 32 is connected to air inlet nozzle 58 on DPF 10. Electric power cable 34 is connected to on-board heating element 44. Thermocouples 52, 54 and 56 are also connected to PLC 36 for monitoring inlet and outlet temperatures and for feedback control.
Alternatively, a single coupling device can be employ ed to provide unified coupling for power supply, air and thermocouples. The operator presses the start button to start PLC hardware unit 36, which, when suitably programmed, automatically controls the regeneration process. After a pre-set desired time period, an indicator light on PLC 36, preferably labeled DONE, comes on to indicate that regeneration is complete. The operator disconnects the power supply, air hose and thermocouples 52, 54 and 56. Before starting vehicle 30, the operator opens butterfly valve 70.
Alternatively, an automatic butterfly valve can be employed which closes at the start of regeneration and opens once regeneration is complete. Vehicle 30 is, thus, ready for the next shift.
S In more detail, once the start button is activated, electrical current to heating element 44 is suppliedl which begins to warm up inlet face 11 of the DPF. This initial warm up period takes place in static air without any flow of inlet air to ensure that hydrocarbon fractions are not stripped away before they can assist in the filter regeneration. The optimum time for this initial warm-up period is about 5 minutes, but varies depending on design parameters of DPF 10 and heater element 44.
Through conduction and radiation of heat from heater element 44, at face 11, a temperature sufficient for DPM combustion to readily take place of about 500 °C, occurs after a 5 minute. period. The SiC (silicon carbide) DPF has a relatively large thermal mass, so even though face 11 of the DPF is hot, the interior of the DPF
initially remains cold and, accordingly, DPM combustion for most of the DPF
does not take place. At the end of the initial warm-up period, air flow to the DPF
is started while electrical current to heating element 44 is maintained. As the flow of air enters face 11, the ;amount of oxygen entering the DPF is increased and the rate of reaction for the combustion process is thereby increased (see aforesaid equation 1). Since the combustion of DPM is exothermic, the reaction itself, also, increases the temperature of the DPF. Thus, the reaction starts at face 11 and spreads deeper into the interior of DPF 10 in the air flow direction until it reaches a point where DPM is combusted tlvroughout the entire DPF. The continuous supply of air into the filter ensures that sufficient oxygen is available for the DPM combustion to take place at a sufficient rage. After a programmed period of time, the current to heating element 44 and the air supply are shut off and regeneration is complete.
Control of the temperature of the air after passing though heating element 44, but before entering thf; DPF face is important. If the temperature of the air is too low, then combustion of the DPM takes place too slowly and complete regeneration of the filter does not occur in the required time period. The temperature of the air is increased by, preferably, decreasing the rate of air flow into the DPF.
Therefore, there is a maximum allowable flow-rate that is achiievable for combustion of the DPF during the specified period. This maximum flow-rate is empirically determined through experimentation.
Feedback control is'. used to adjust the rate of air flow into the DPF.
Feedback 5 control utilizes the temperature of the DPF at a specific location within filter 10, or alternatively and preferably, the temperature of the exhaust at the outlet of the DPF.
If the feedback temperature is too low then the flow-rate of air can be reduced, to result in less transfer of heat away from the DPF and eventually improve rates of reaction as the temperature of the DPF increases. If t:he feedback temperature is too 10 high, for example, over 700 °C, the DPF is in danger of overheating and results in thermal damage to the DPF media. In this case, the flow-rate of air is reduced or temporarily stopped, which reduces the rate of combustion of the DPM (see equation 1). The output result from this feedback data is determined through suitable dependent algorithms, which may or may not be time dependent arrived at 15 after experimental tests used to determine optimum points of operation for air flows and temperatures. A typical relationship of the DPF temperature feedback and controlled as desired air flow-rate set-point is shown in Fig. 5.
With reference now to Fig. 6 which shows, generally, as 78, a deep bed or impaction type DPF comprising a pair of concentric cylindrical shells 80, 82 wherein inner shell 8 2 is within outer shell 80, and which define therebetween a cylindrical cavity 84 I>acked with particulate entrapping fibrous material 86.
Each of shells 80 and 82 has a plurality of apertures 88 longitudinally of shells 80, 82 through which exhaust; gases pass.
Inner shell 82 defines a hollow cylindrical passage 90 and an exhaust gas inlet at one end 92, only. Within passage 90 is a coiled electrical heating element 94 adjacent inner shell 82; which is connected to electrical power trough relay 48, from electric power source 50 under control of PLC unit 36.
Disposed between. inner shell face 96 and heating element 94 is located port heater element exhaust gas thermocouple 52. One or more of post DPF exhaust gas thermocouples 54 are retained within one or more of apertures 88. One or more of body thermocouples SEi are retained within the body of filter 78 longitudinally of its length. Each of thermocouples 52, 54 and 56 is in electrical contact with PLC
36.
A combustion air nozzle is located within inlet 92 for providing means for receiving forced air from air hose 32 as hereinbefore described with reference to Fig. 3. Inlet 92 has a butterfly valve 70.
In operation, regeneration of contaminated impact DPF 78 is similar to that for the wall flow DPF in the set-up with PLC unit 36 and operational process conditions and parameters.
A most preferred utility of the assembly according to the invention is in underground hard-rock mining. The desired vehicles in these applications are typically assigned to specific tasks and operate on a similar duty cycle over a period of several months or longer. These vehicles usually operate in shifts that are, typically, 7 to 12 hours in length with a period of at least 1-2 hours required to switch from one work shift to another. During the period in which the work shift is changed, the vehicle is left stopped with the ignition in the off position.
However, in the present process o~f the invention, at the end of the shift, the PLC
hardware unit with attendant electrical, remote air supply source and thermocouple fittings, is brought to the vehicle and the power supply, thermocouples and compressed air connections made. The flow valve is also turned to the closed position to seal off any air back flow to the remaining components of the exhaust system and engine.
The operator presses a start button to begin the regeneration process under the control of the PLC. The regeneration process is programmed to finish at the same time the next shift is ready to begin work. The new shift operator then unplugs the compressed air, thermocouples, power supply connectors and PLC hardware unit.
The new shift operator also returns the flow valve to vehicle open position to enable the vehicle to begin a new operation.
Thus, the invention as herein defined provides the following advantages for this utility over the aforesaid prior art methods.
Unlike method 1, there is no manual or mechanical heavy lifting required to remove the DPF from the machine on a periodic basis, since the DPF does not have to be taken off the vehicle.
Unlike method 2, the DPF according to the invention can be used on any vehicle, as long as there is an intermittent, say, one to two hour period of vehicle inactivity available for regeneration to be performed provided a power supply is available on site.
Unlike method 3, there are no required fuel-borne catalysts and, therefore, no issues or concerns relating to possible impact on human health and environment from the fuel-borne catalyst entering the air, ground or water.
Unlike method 4, the DPF assembly and associated components do not produce a net increase in NOz. In fact, if this system is used in combination with a filter coating as described in Canadian patent application No. 2,221,118, filed November 15, 1997, in the name of Diesel Controls Limited, is applied to the assembly, a net decrease in N02 will result.
Much less power and energy is required than in method 5 since the regeneration process, according to the invention, operates under low gaseous flow, much less power is required to heat the DPF. Less than 5% of the rated engine power over a period of one to two hours is used. Less power consumption results in lower operating costs. In addition, with programmable logic control feedback of temperature, this system can be optimized to operate on minimum energy requirements. In addition, since an outside source of compressed air is used rather than an on-board system, higher pressure air sources can be used to allow for better control of air flow.
Unlike method 6, the DPF assembly according to the invention does not increase vehicle fuel consumption or require an additional fuel source for the purposes of re-heating the exhaust gas.
Unlike method '7, this system of the invention requires, preferably, only one DPF, to thereby allow for a compact fit into the exhaust system. No expensive automatically actuated exhaust valves are required, or complex exhaust manifold.
Unlike method 8, this system does not increase fuel consumption in order to achieve exhaust temperatures, and does not require any upgrades to the engine cooling system.
Although this disclosure has described and illustrated certain preferred embodiments of the invention, it is to be understood that the invention is not restricted to those particular embodiments. Rather, the invention includes all embodiments which are functional or mechanical equivalents of the specific embodiments and features that have been described and illustrated.
Claims (23)
1 A method of regenerating in situ a DPM-contaminated diesel particulate filter assembly of an exhaust system connected to a diesel engine, said system comprising (a) a filter shell containing a filter element having an inlet face, an outlet face, and a DPM entrapping-body;
(b) electrical heating means within said shell adjacent said inlet face connectable to an electrical power supply;
(c) inlet temperature; measuring means adjacent said inlet face and said heating means;
(d) body temperature measuring means within said body;
(e) means fir receiving forced air within said shell and connectable to a forced air supply;
(f) said heating means, said inlet and said body temperature measuring means and said forced air receiving means being connectable to a programmable logic controller (PLC); said method comprising the steps of (g) connecting said heating means, said temperature measuring means and said forced air receiving means to said PLC;
i. connecting said heating means to said power supply;
ii. connecting said forced air receiving means to said air supply;
iii. heating said electrical heating means by said power supply to a, desired temperature controlled by said PLC;
iv. receiving said forced air from said air supply at a desired rate controlled by said PLC to effect heating of said air to a desired temperature by said heating means;
v. passing the heated air through said inlet face and filter element to effect combustion of said DPM; and vi, passing temperature data from said inlet and said body temperature measuring means to said PLC.
(b) electrical heating means within said shell adjacent said inlet face connectable to an electrical power supply;
(c) inlet temperature; measuring means adjacent said inlet face and said heating means;
(d) body temperature measuring means within said body;
(e) means fir receiving forced air within said shell and connectable to a forced air supply;
(f) said heating means, said inlet and said body temperature measuring means and said forced air receiving means being connectable to a programmable logic controller (PLC); said method comprising the steps of (g) connecting said heating means, said temperature measuring means and said forced air receiving means to said PLC;
i. connecting said heating means to said power supply;
ii. connecting said forced air receiving means to said air supply;
iii. heating said electrical heating means by said power supply to a, desired temperature controlled by said PLC;
iv. receiving said forced air from said air supply at a desired rate controlled by said PLC to effect heating of said air to a desired temperature by said heating means;
v. passing the heated air through said inlet face and filter element to effect combustion of said DPM; and vi, passing temperature data from said inlet and said body temperature measuring means to said PLC.
2. A method as defined in claim 1 wherein said filter element is a wall-flow filter element and said body comprises a plurality of axially aligned longitudinal exhaust channels defined by walls formed of a porous material.
3. A method as defined in claim 1 wherein said filter element is a deep-bed or impaction filter element wherein said body comprises an inner wall defining an inlet gas inner passage having said inlet passage at an end thereof; an outer wall concentric with said inner wall to define therebetween a fibrous material-containing chamber; and wherein each of said inner and out walls having a plurality of gas permeable apertures.
4. A method ass defined in claim 1 wherein said forced air supply is remote from but operably connectable to said exhaust system.
5. A method as defined in claim 2 wherein said porous material is selected from the group consisting of a ceramic, cordierite, silicon carbide and a metal.
6. A method as defined in claim 5 wherein said porous material is a silicon carbide coated with a catalyst to minimize activation energy of combustion of particulate carbonaceous matter.
7. A diesel particulate filter assembly comprising (a) a filter shell containing a filter element having an inlet face, an outlet face, and a DPM entrapping-body;
(b) electrical heating means within said shell adjacent said inlet face connectable to an electrical power supply;
(c) inlet temperature measuring means adjacent said inlet face and said heating means;
(d) body temperature measuring means within said body;
(e) means fir receiving forced air within said shell and connectable to a forced air supply;
said heating means, said inlet and said body temperature measuring means a,nd said forced air receiving means being connectable to a programmable logic controller.
(b) electrical heating means within said shell adjacent said inlet face connectable to an electrical power supply;
(c) inlet temperature measuring means adjacent said inlet face and said heating means;
(d) body temperature measuring means within said body;
(e) means fir receiving forced air within said shell and connectable to a forced air supply;
said heating means, said inlet and said body temperature measuring means a,nd said forced air receiving means being connectable to a programmable logic controller.
8. A filter assembly as defined in claim 7 wherein said filter element is a wall-flow filter element and said body comprises a plurality of axially aligned longitudinal exhaust channels defined by walls formed of a porous material.
9. A filter assembly as defined in claim 7 wherein said filter element is a deep-bed or impaction filter element wherein said body comprises an inner wall defining an inlet gas inner passage having said inlet passage at an end thereof; an outer wall concentric with said inner wall to define therebetween a fibrous material-containing chamber; and wherein each of said inner and out walls having a plurality of gas permeable apertures.
10. A diesel engine exhaust system connected to a diesel engine said system comprising a diesel particulate filter assembly as defined in any one of claims 7-9.
11. A heavy duty vehicle comprising a diesel engine and exhaust system as defined in claim 10.
12. A vehicle as defined in claim 11 of use in underground mining.
13. An assembly as defined in any one of claims 7-12 wherein said forced air supply its remote from but operably connectable to said exhaust system.
14. An assembly as defined in any one of claims 7, 8, and 10-12 wherein said porous material is selected from a ceramic, cordierite, silicon carbide and a metal.
15. An assembly as defined in claim 11 wherein said porous material is silicon carbide coated with a catalyst to minimize activation energy of combustion of particulate carbonaceous matter.
16. A system for regenerating in situ a DPM contaminated diesel particulate filter assembly of an exhaust system of a diesel engine in a vehicle, said system comprising in combination, said vehicle, said diesel engine and said exhaust system connected to said diesel engine and comprising (a) a filter shell containing a filter element having an inlet face, an outlet face, and a DPM entrapping-body;
(b) electrical heating means within said shell adjacent said inlet face;
(c) inlet temperature measuring means adjacent said inlet face and said heating means;
(d) body temperature measuring means within said body;
(e) means for receiving forced air within said shell;
(f) a programmable logic controller in communication with said heating means, said inlet and said body temperature measuring means and said forced air receiving means;
(g) an electrical power supply connected to said electrical heating means; and (h) a forced air supply connected to said forced air means.
(b) electrical heating means within said shell adjacent said inlet face;
(c) inlet temperature measuring means adjacent said inlet face and said heating means;
(d) body temperature measuring means within said body;
(e) means for receiving forced air within said shell;
(f) a programmable logic controller in communication with said heating means, said inlet and said body temperature measuring means and said forced air receiving means;
(g) an electrical power supply connected to said electrical heating means; and (h) a forced air supply connected to said forced air means.
17. A system as defined in claim 16 said filter element is a wall-flow filter element and said body comprises a plurality of axially aligned longitudinal exhaust channels defined by walls formed of a porous material.
18. A system as defined in claim 16 wherein said filter element is a deep-bed or impaction filter element wherein said body comprises an inner wall defining an inlet gas inner passage having said inlet passage at an end thereof; an outer wall concentric with said inner wall to define therebetween a fibrous material-containing chamber; and wherein each of said inner and outer walls having a plurality of gas permeable apertures.
19. A system as defined in claim 16 wherein said forced air supply is remote from but operably connectable to said exhaust system.
20. A system as defined in claim 17 wherein said porous material is selected from a ceramic, cordierite, silicon carbide or metallic material
21. A system as defined in claim 20 wherein said porous material is silicon carbide coated with a catalyst to minimize activation energy of combustion of particulate carbonaceous matter.
22. A system as defined :in any one of claims 16-21 wherein said PLC is pre-set with operating process parameter control data comprising heating
23 element operating temperatures, air flow rates, and process periods of time.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2315415 CA2315415A1 (en) | 2000-08-01 | 2000-08-01 | Regeneratable diesel particulate filter assembly |
| AU38788/01A AU3878801A (en) | 2000-08-01 | 2001-04-23 | Regeneratable diesel particulate filter assembly |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2315415 CA2315415A1 (en) | 2000-08-01 | 2000-08-01 | Regeneratable diesel particulate filter assembly |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2315415A1 true CA2315415A1 (en) | 2002-02-01 |
Family
ID=4166854
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2315415 Abandoned CA2315415A1 (en) | 2000-08-01 | 2000-08-01 | Regeneratable diesel particulate filter assembly |
Country Status (2)
| Country | Link |
|---|---|
| AU (1) | AU3878801A (en) |
| CA (1) | CA2315415A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8029592B2 (en) | 2007-06-15 | 2011-10-04 | Fram Group Ip Llc | Diesel particulate filter assembly |
-
2000
- 2000-08-01 CA CA 2315415 patent/CA2315415A1/en not_active Abandoned
-
2001
- 2001-04-23 AU AU38788/01A patent/AU3878801A/en not_active Abandoned
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8029592B2 (en) | 2007-06-15 | 2011-10-04 | Fram Group Ip Llc | Diesel particulate filter assembly |
Also Published As
| Publication number | Publication date |
|---|---|
| AU3878801A (en) | 2002-02-07 |
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| EEER | Examination request | ||
| FZDE | Dead |