Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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1152
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
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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
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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
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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
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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
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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
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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
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(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.
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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;
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(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
100
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
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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;
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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
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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
38
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
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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,
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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
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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.
CA 02315415 2000-08-O1
17
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.
CA 02315415 2000-08-O1
18
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.
