Note: Descriptions are shown in the official language in which they were submitted.
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a MODULAR RADIANT PLATE DRYING APPARATUS
Field of the Invention
This invention relates to an apparatus and method for continuous drying
of sewage sludge, pulp sludge, other industrial sludges, slurries, grains,
cereals,
organic and inorganic fibres and pulps, chemical waste and other materials.
Background of the Invention
Grain and cereal harvest are hampered internationally whenever damp fall
weather prevents crops from naturally drying in the field. Threshing cannot be
completed because there is no large scale viable mechanical process to
satisfactorily and economically dry grains and cereals. As a result, yields
and
product quality seriously deteriorate while farmers wait for favourable sun
and
wind conditions to naturally dry the kernels. And, if these conditions do not
occur, crops can be lost entirely.
Accordingly, there is a long-felt need for means to safely dry these
grains and cereals in a temperature controlled environment in order to
preserve
their commercial value.
Industrial processing of a wide variety of materials produces fine waste
by-products which must be disposed of. Many are slurries of fine organic or
inorganic particles suspended in water, and are referred to in industry as
"sludge". Others are fibrous or chemically contaminated natural and artificial
materials of varying consistency. Rigid and increasingly stringent
environmental
standards and legislation very tightly control disposal of these waste
products.
Sources vary widely and include pulp and paper mills, sewage treatment plants,
large dairy farms, potash mines, coal mines, oil sand plants, chemical plants,
wineries, dry cleaning plants and many other processing operations.
A typical sludge or slurry consists of 20% to 30% organic and/or
inorganic solids and the balance is water. Handling this material is difficult
because of the high water content, but also because it frequently contains
chemicals or heavy materials which are harmful to the environment, or
biologically active components which are dangerous to humans.
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In the past, in order to reduce handling and disposal costs, industry's
focus has been on devising methods to concentrate these waste materials by
reducing the water content. This is accomplished mechanically by using
equipment like belt presses or centrifuges in the processing stream, (common
in the pulp and paper industry) or by constructing expensive and large holding
ponds (common in sewage treatment and mining operations) where the material
is allowed over time to settle and naturally concentrate. These methods
achieve
a maximum concentration of about 40% solids, but do not remove the harmful
chemicals and metals, or sterilize the active biological elements.
Recently, industry has been searching for more effective means to "dry"
industrial waste and at the same time environmental agencies have introduced
legislation forcing mechanical treatment and more secure handling and disposal
of such waste. Several systems have been designed for this purpose. These
systems use indirect heating methods and consist of kilns, furnaces, burners
and
a variety of continuous and batch feed ovens. Typically, the heat energy in
these systems is transferred to the material being processed by blowing hot
air
across the material, or by directing the material over hot heating surfaces.
In
the process, large volumes of air must be used and this air becomes
contaminated by contact with the waste product as a result of picking up small
quantities of fine particles, as well as by capturing volatile gases released
by the
material as it dries. As a result, this "contaminated" air requires processing
before being released into the atmosphere. Such systems tend to be large,
expensive and not portable, and furthermore produce a dried end-product that
has been burned and therefore is of limited use for recycling.
One recent solution to the drying of sewage sludge is found in PCT
application number PCT/CA90/00074 of Schmidt et al, published September 7,
1990. This application describes a proposed mobile method and apparatus for
drying sewage sludge in which the sludge is conveyed on tiered helical
conveyors through a heated chamber and is subjected to radiant heat. The
radiant heat is indicated as being supplied by a plurality of identical burner
chambers disposed side by side. Each of the burner chambers provides an
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equal amount of heat. Air is heated in the burners and blown through the
hollow axles of the auger shafts and through holes in the shafts to mix with
the
sludge. As the sludge dries, it is described as releasing steam which is drawn
off into a condenser where the water and hot vent gases are separated. The
vent gases are recycled through the burner chambers, where harmful gases are
broken down.
At the exit of the heated chamber, it is suggested sewage sludge will
typically have been reduced to a maximum solids content of from 80% to 95%.
The sewage sludge is input to the helical conveyors through an open supply
funnel and a helical feeder conveyor.
This design has several problems. Firstly, there is no continuous supply
mechanism. During normal operation, supply of sewage sludge to the helical
conveyors can be disrupted and result in an irregular supply of sewage to the
helical conveyors. Irregular supply could damage components of the dryer since
the extreme heat produced by the burners would not be mitigated by the heat
sink effect of the drying sewage sludge. Burning of the sludge as well as
serious plugging could occur.
Also this prior art dryer has no apparent means to control heat
distribution at machine start up, therefore subjecting all internal components
to
very damaging high heat stress which dramatically affects useful machine
operating life.
Further, this prior art dryer does not distribute flue gases in a manner
that would follow the heat transfer gradient, which declines along the drying
path. That is, as sewage sludge travels through the machine or water is
gradually lost through evaporation which significantly reduces the sludge's
ability to absorb heat, yet this design provides equal heat energy throughout
the
machine, making no provisions for the diminishing heat gradient.
Further, the helical conveyors described in this prior disclosure render
it difficult to move sewage sludge along the conveyor, and the individual
transfer chutes located at the end of each auger flight may be subject to
plugging.
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Summary of the Invention
According to the present invention a universal dryer is provided which
overcomes the above-described specific problems associated with processing
sewage sludge, as well as providing a means to successfully and very
effectively
dry, but more importantly, recycle a wide variety of other materials by
achieving precise drying temperature control. The drying system is housed in
a dryer module that can be affixed to a trailer for portable operation, built
into
a new plant for a permanent installation or added to an existing plant to
upgrade, improve or replace existing drying systems. The invention provides
in its various aspects, a continuous controlled feed into an infrared radiant
heat
dryer module, with a back up reservoir of material to be processed. High
intensity infrared flux is supplied by a radiant plate fire box with a number
of
radiant flame burners which permit zone heat control. Exhaust gases from the
fire box are ducted into variable distribution ducts and supplied to jackets
in
layered horizontal auger banks, described in more detail below, and which
transport the material being processed through the dryer module. A temperature
control system is also provided using water cooling for reducing the
temperature
of the hot flue gases circulated through the auger flight jackets to allow
precise
temperature control in the dryer module to facilitate the processing of
temperature sensitive materials like grains, cereals and recyclable organic
fibres,
pulps and materials. These, together with other features, will be described in
more detail in the remainder of this patent disclosure.
According to an aspect of the invention there is provided:
a dryer module having an input end for receiving wet material containing
solids and an output end for discharging dried solid materials;
one or more auger banks disposed within the dryer module between said
input ends and said output end, each auger bank being made up of a number
of auger flights, each flight including a rotatable spiral auger for
continuously
conveying said material within the auger flight;
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a heat source for providing radiant heat to at least one of said one or
more auger banks so as to heat and thereby dry said material, the heat source
also providing a source of flue gases; and
flue gas distribution means for providing flue gas from the heat source
to at least one of said auger banks for further heating and thereby drying of
said material.
The dryer includes water injection means having an outlet in the flue gas
distribution means upstream of the auger banks. This water injection means
serves to cool the flue gases and the volume of water injected may be
controlled to control the flue gas temperature being supplied to the auger
banks,
therefore providing precise temperature control of the auger banks.
The auger flights are preferably distributed in layered banks inside the
module. The flue gas distribution means is constructed to provide flue gas
volume, and therefore temperature control differentially to the auger banks
and
their flights. The auger banks preferably include a first bank, a second bank
and a third bank, and the flue gases are distributed differentially to the
banks
about 50% to the first bank, about 30% to the second bank and about 20% to
the third bank.
Each auger flight in the lower bank preferably includes an outer tube,
an inner tube disposed within the outer tube to form a jacket between them; a
spiral auger disposed within the inner tube; the jacket having a separate
upper
portion and lower portion; the upper portion being in fluid connection with
the
hot gas distribution means so as to become a radiant as well as convective
heat
exchanger, and the lower portion being isolated from the hot flue gas
distribution means.
According to another aspect of this invention there is provided a method
of drying industrial sludges or industrial organic and inorganic slurries
comprising:
storing a volume of wet material adjacent to a dryer module in a holding
tank;
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providing a continuous flow of material from the holding tank to auger
flights disposed within the dryer module;
heating the material by a radiant heat source, the radiant heat surface
being disposed across the length of the dryer module;
moving the material continuously through the dryer module;
drying the material to sufficient dryness to accommodate safe storage or
disposal; and
removing the dried material from the dryer module.
It is preferable during start up, to provide initially greater infrared flux
to a first portion of the top auger bank than to a second portion and
differentially supply hot flue gases to the jackets of the first and second
levels
of auger banks, with more heat going to the upper levels. Distribution of heat
energy improves drying efficiency, therefore reducing fuel costs, but more
importantly, minimizes the thermal stress and unnecessary temperature shock to
key metal components which will occur when there is no material being
processed to act as a heat sink to absorb the heat energy.
For grain drying or drying of other materials, and to prevent over heating
or burning of heat sensitive materials, as well as to permit recycling, the
method may also include selectively cooling the hot flue gases before
distribution into the auger flight jackets so as to permit the finite
temperature
control of each auger bank, and therefore, finite temperature control of all
of
the drying process.
Brief Description of the Drawings
There will now be described a preferred embodiment of the invention,
with reference to the drawings, by way of illustration, in which like numerals
denote like elements and in which:
Figures lA and 1B are together a perspective, partly broken away and
partly in ghost outline of a radiant plate dryer module according to the
invention;
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Figure 2 is a schematic of a delivery system for the radiant plate dryer
module shown in Figures lA and 1B;
Figure 3 is a section through the conical distributor shown in Figure 2;
Figures 4A, 4B and 4C are schematic sections of the radiant plate dryer
module of Figures lA and 1B;
Figures SA and SB together show a schematic section of the radiant
plate dryer module of Figures lA and 1B;
Figures 6A and 6B are sections through auger flights used in the upper
and lower auger beds respectively of the radiant plate dryer module shown in
Figures lA and 1B;
Figure 7 is a schematic showing distribution of the hot flue gases to the
jacketed auger flights;
Figure 8 is a blow up of the flue gas distribution section of the fire box
with the flue gas water spray cooling system identified, and as shown
schematically in Figure 7; and
Figure 9 is a schematic showing the process control of the present
invention.
Detailed Description of the Preferred Embodiment
The preferred embodiment described below concerns a system primarily
in relation to a mobile configuration for industrial and sewage sludge
processing, although the system has utility for fixed or mobile configurations
to
drying many other materials such as grain, cereals, chemical slurries, organic
fibres, dairy waste, mine tailings and other similar waste products. And,
because of its modular design, the system can be built into fixed
installations
like sewage treatment plants, pulp mills, coal mines, potash mines and
industrial
processing plants, either as an add-on to replace old and inefficient existing
equipment, or as a component of the process operation for new facilities. In
such installations, the dryer module of the present invention would form the
base component and material input, material output, condensate cycling,
exhaust
gas cycling, and the control systems would be custom designed to meet specific
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needs to the plant's operation and make the most efficient use of heat
exchange
opportunities.
Referring firstly to Figures lA and 1B, there is shown a dryer module
12 which encloses a drying chamber and which can easily be mounted on a
trailer 14. The dryer module 12 has an input end 16 and an output end 18.
Tiered auger banks 22 are shown in the cutaway view of module 12. A
number of radial flame burners 24 are attached to the upper part of a heater
module 26, to form a fire box heating means. Sludge enters the module at the
input end 16 through the distribution system located there which is more
particularly described below in relation to Figures 2, 3, 4A, 4B and 4C.
Also shown at the input end 16 is a condenser 28 which, together with
its associated ducts, draws steam and waste gases from the module 12.
Uncondensed vent gases from inside the module, discharged from the condenser
28, are recycled to the radial flame burners 24 and consumed in the fire box.
Hot exhaust flue gases, which contain substantial useful energy are directed
to
the auger banks 22 through a flue gas distribution system shown as 32
schematically in Figure 7. The water and gas condensation and circulation
system will be described in more detail in relation to Figures SA, SB, 7 and
8.
The construction of the auger banks 22 will be described in more detail in
relation to Figure 6.
Referring to Figures lA, 1B, 2, 3, 4A, 4B, and 4C there will now be
described the material input and distribution system. A wet product storage
tank 34 for processing sludge or slurries preferably has from 60 to 120m3
storage capacity and is located close by the dryer. A skid mounted mud tank
like those commonly used in oil well drilling may conveniently be used for
mobile operations. For mobile use, the holding tank 34 would be fitted with
plate-coils (not shown) built into the tank's side wall and bottom. These
would be in fluid connection with the condenser 28 to preheat the material to
be processed through lines (not shown) containing heated glycol running from
the condenser 28 to the holding tank 34.
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The holding tank 34 is fitted with one or preferably two progressive
displacement cavity pumps 36. The progressive displacement cavity pumps
are shown in schematic form only since they are preferably MoynoTM cavity
pumps made by Robbins and Myers and are readily available commercially.
In addition to a MoynoTM progressive cavity pump, a true mass flow meter
device may be used to measure input independent of viscosity. The MoynoTM
cavity pumps 36 can pump up to 30% total solids and have a fixed feed
volume relative to RPM ration, thereby enabling precise measurement of the
material being transported. The typical solids content of sludge entering the
dryer will be about 15-30%. The cavity pumps 36 pump from the holding
tank 34 through pipe 38, preferably having a diameter from between 4" to 8",
to a distribution cone 42. The distribution cone 42 is shown in section in
Figure 3. Material in the pipe 38 is divided into numerous (here shown as 10)
equal sized input lines 46. The manner of connection of the input lines 46 to
the upper auger bank 54 is shown in Figures 4A, 4B and 4C. Each input line
46 is connected to the basal portion 48 of a respective auger bank such as
auger bank 54. Each input line 46 is preferably made of a transparent flexible
hose so that the material flowing into any auger bank may be visually
inspected. In this manner, as the spiral auger 52 rotates and sections of the
auger move across the end of the input line 46, material extruded from the
input lines 46 is sheared off and moved along the auger bank 54 by the spiral
auger. Material should preferably be fed at a rate that fills the conveyors to
about 50% volume.
Referring now to Figures SA and SB, the auger banks 22 are layered
and in the preferred embodiment there are three banks, an upper first bank 54,
a middle second bank 56 and a lower third bank 58. The flights of the upper
bank 54 and the materials contained in them are exposed to high intensity
infrared flux from the radiant plate 66 which forms the base of the firebox 64
described in more detail below. The augers in the other two levels are
enclosed. Each auger flight in the banks of augers is formed from a double
shelled tube to form a jacket as will be described in more detail below in
relation to Figures 6A and 6B.
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Material being processed is moved through the dryer module by
rotation of the spiral augers 52, each driven by an individual, variable-speed
electric motor (motors 164, 172 and 178), each of which is readily
commercially available. The spiral auger 52 rotates at speeds from 60 to 5000
revolutions per minute depending on the throughput volume to be dried.
Movement of the material being process is ultimately from the input end 16 to
the output end 18 of the module. The middle auger bank 56 moves the
material in the opposite direction to the other two auger banks. Material is
moved across the module on bank 54, down to bank 56 through box 116 (in
which the material moves by gravity after exiting the augers in bank 54), back
across the module down to bank 58 through box 124, and again across the
module to the output end 18. Dried product is removed from the module by
the discharge auger 62 at the end of the bottom auger bank 58.
The auger flights of upper auger bank 54 are open and material in the
spiral augers 52 (Figure 6A) is exposed to high intensity infrared flux from
the
radiant plate 66 which forms the base of firebox 64. The radiant plate 66 is
energized by two rows of five radial flame burners 24 located above the
firebox 64. A number of commercial burners of the radial flame design are
available and, therefore, the burners are only shown schematically here. Each
of the radial flame burners 24 should preferably have variable output
settings.
These burners 24 have a characteristically flat flame that spreads out below
the
burners to give even heat to the radiant plate 66 that forms the high infrared
radiant flux base plate for the firebox. While a firebox with ten radial flame
burners has been described, different numbers of burners (for example 9 to 15)
with different arrangements may be used, the object being to provide a
constant, but variable, energy gradient along the radiant plate 66. In one
embodiment, greater heat is provided to a first portion of the radiant plate
such
that a first portion of the auger flights passing thereunder have greater heat
exposure than a second portion of the auger flights. Air for the radial flame
burners is supplied by line 68, and fuel (natural gas, propane, butane,
methane,
diesel fuel, heating oil) by line 70.
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The radiant plate 66 is formed into several plate segments lying
adjacent to each other to form an essentially continuous high infrared flux
energy surface about 30 to 40 centimeters below the burner nozzles. The
radiant plates 66 are separated only by the amount required for the support
mechanism and to accommodate thermal expansion. The support mechanism
may be a cassette system in which the radiant plates are supported in a
framework (element 149 in Figure 9) composed of beams extending in a grid
covering approximately 70% of the upper part of the dryer module 12 running
the length of the dryer module.
Hot flue gas from the firebox 64 is passed through the hot flue gas
distribution ducts 72, 74 and 76 respectively exiting from the firebox 64.
Duct
72 feeds the upper auger bank 53, all as shown at the output end 18 of the
dryer module 12. Preferably, distribution of hot flue gas is about 50% for the
upper bank 54, about 30% for the middle bank 56 and about 20% for the lower
bank 58. It is preferable that the upper bank 54 receive more flue gas heat
energy than the middle bank 56, and that the middle bank 56 receive more flue
gas heat energy than the lower bank 58. For fixed instalations, exhaust gas
exiting the machine could be ducted through other heat exchanges for further
use in other plant processing areas.
Referring now to Figure 6B, there is shown a section through an
auger flight as used in either of the middle or lower auger banks 56, 58. The
flights are formed from an outer tube 92 and an inner tube 94 running the
length of each auger flight. A spiral auger 52 provided within the inner tube
94. The spiral auger is a commercial product and is readily available in
various diameters and pitches from a variety of sources. Specific augers
would be chosen to best transport the material intended to be processed.
The annulus or jacket 96 defined by the outer tube 92 and the inner
tube 94 is divided into an upper portion 98 and a lower portion 102 by baffles
103 on either side of the jacket 96. Several vanes or fins 108, here shown as
five in number, extend radially from the inner tube 94 into the jacket air
space
98. As described immediately below, hot flue gas passes through the upper
section 98, heating vanes 108 which transfer energy by conduction to the inner
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shell 94 which also receives heat directly from the hot flue gas. By this
means, the upper portion of the inner tube becomes very hot, radiating high-
intensity, infrared flux which assists in drying the material being processed
44
in the banks 56, 58. Heat will also pass into the lower portion of the inner
tube 94 by conduction and assist in heating the material from below. The
temperature of the lowest point of the inner tube will be dramatically less
than
the highest point whenever material is present in the auger flight to act as a
heat sink. This heating and drying system, providing a combination of
connective heat around the tube and a radiant heat surface in the upper
portion,
facilitates heat transfer to the material 44 being dried. The low temperatures
in the bottom of the tube 96 prevent the material 44 from burning, and
facilitates the dryer's processing of a variety of temperature-sensitive
products.
Paddles 112, each about 1 to 2.5 cm in length, and attached to the
spiral augers 52, stir the material and crush it to assist in exposing fresh,
moist
material to the high intensity infrared flux radiating from the upper portion
of
the inner tube 94 and to connective energy through absorption by contact with
the tube walls 94. The released steam will be superheated from exposure to
the radiant and connective heat inside tube 94 and will reach a temperature of
about 130° C to 150° C. At this temperature, steam will
contribute an
additional drying effect on the material 44. The steam collection system has
been designed to take advantage of the steam's drying capacity by evacuating
it through auger tubes 94 in the middle and lower auger banks 56, 58.
Figure 6A is a section through an auger flight 54f in the upper auger
bank. Auger flight 54f is formed from an outer tube 92A, which is bent to
form curve 90, and an inner tube 94A, that has been cut and welded at seam 94
to form a trough through which the spiral auger rests and the material 44
flows, and an annulus or half jacket through which hot flue gasses flow 90A.
A spiral auger 52 moves the material under power from the electric motor 164
shown in Figure 9. Bridge supports, not shown in Figure 6B, but shown in
Figures 1 B and SA, support the walls of each auger flight by connection to
the
upper portions 90. It will be appreciated that in this patent disclosure where
an auger is exemplified, the other auger flights in the same level have
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essentially the same configuration. Selection of the augers including, for
example, the pitch of blade, diameter of auger, thickness of auger blade and
rotation auger speed would depend upon the material being processed.
Returning now to Figures SA, SB and 7, hot flue gas passes through
the top auger bank 54 by being ducted through the half jacket 90A (Figure 6A)
of each flight in auger bank 54, towards chimney ducts 82 connected to the
jackets. There are 10 auger flights in the upper auger bank 54 connected to a
chimney duct 82 and likewise for the ducts described below. Hot flue gas
supplied to the middle auger bank 56 flows through the upper portion to the
jacket (Figure 6B) of each auger flight towards chimney duct 84. The ducts
82, 84 and 86 lead into the main chimney 88 to which is attached a fan 132 for
evacuating the flue gas within the flue gas distribution and duct system.
The chimney ducts 82, 84 and 86 are provided with flaps 146 that
can be controlled, and preferably electrically actuated, by motors not shown,
so that the hot flue gas flow in each of the ducts 82, 84 and 86, and
consequently within the jackets of the auger flights of each auger bank 54, 56
and 58, can be selected from anywhere between full discharge and closed
position. This is particularly advantageous at start-up since heated flue gas
can be selected for delivery only where there is sludge so as to reduce
thermal
load and shock to dryer components, thus avoiding heating auger flights when
sludge is not present.
The radial flame burners 24 are also preferably independently
operable with a variable output range so that at start-up they will be
operated
sequentially in intervals of about 1 minute. Thermal shock may be reduced by
turning a burner on only when there is, or is about to be, damp material
beneath it. It is believed this will substantially add to the useful operating
life
span of the dryers. The reverse procedure (shot off the burners as the last
material passes underneath the burner) may also be used to reduce heatshock
on dryer shutdown.
Referring now to Figure 8, the inlet portions of tl~e hot flue gas ducts
72, 74 and 76, upstream of the auger banks 54, 56, 58 are provided with water
injection means through nozzles 114. When used as a dryer for grain, or any
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other temperature sensitive material, water can be easily sprayed into ducts
72,
74 and 76 to control the heat delivered to the auger flight jackets. The
nozzles
114 should be placed close to the firebox 63 since the temperature of the flue
gas must be reduced quickly, there being only a short distance between the
firebox exit and auger beds. Preferably there are several nozzles (for
example,
5 to 10) in each duct, each operating at about 20 psi to about 300 psi. Each
nozzle 114 is supplied by a high pressure water pump with a bypass control
(not shown) to keep the water flowing past the nozzle to provide nozzle
cooling except where required. Spray nozzles which will produce a particle
size under 200 microns will be required to assure transformation of water to
steam before entering the auger flight heat exchanger jackets. The water may
be supplied from condensate produced by the condenser 28.
The drying process causes steam and other volatile gasses to form
above the material being dried. The steam is collected from auger bank 54
through steam inlet ducts 95, which lead from auger bank 54 between the
individual auger flights into the steam collection chamber 54A, located
between auger banks 54 and 56 as shown on Figures 5 and 6A. From the
chamber 54A, steam is drawn into the steam collection box 124 and processed
through the condenser as described herein. Steam is evacuated from the inner
tube 94 (Figure 6B) of each auger flight in auger banks 56 and 58 (Figure SA)
through the steam collection box 124 into steam ducts 122 and 126 via one-
way valve 127 to the condenser 28. The steam will be contaminated by any
other gasses released by the material being dried. In the condenser 28
(readily
commercially available), the steam is collapsed and condensed out and the
resultant hot water removed through the line 134 and pump 135. The
remaining vent gasses, which may be noxious and odour-containing, are
sucked out of the condenser by a vacuum pump (not shown) and are ducted
back into the burner system through line 118 and fan 132. For fixed
instalations, steam may be drawn off at the condenser for use in other plant
processing functions, or directed through heat exchangers to provide heat
wherever required.
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The dryer module's components, described above, are preferably
made of stainless steel.
Referring now to Figure 9, the present invention contains several
control systems, namely, the control of flue gas temperature; the control of
the
flue gas flow rate; the control of the input material flow rate; the control
of the
burners; and the control of the condenser. The flue gas temperature is
controlled by means of a system including temperature elements 152,
temperature indicators 154 and controllers 156. The elements 152 sense the
temperature of the material in various auger beds 22 and the temperature
indicators 154 read this temperature and pass signals indicative of the
temperatures to controllers 156. Temperature of the material being processed
is preferably kept below 130° C.
If the temperature increases above this range, or any other value
deemed critical to the material being processed, then water may be injected
into the flue ducts 72, 74 and 76 (via nozzles 114) using pumps 158 to reduce
the temperature of the hot flue gasses that are circulated through the auger
flight jackets 90A, 98. If the temperature of the material falls below the
specified value, less water will be injected into the flue ducts 72, 74 and
76.
When flue gas temperatures reach 900° C, or greater, which will occur
during
normal high temperature operations, the flue gas temperature will require
continuous cooling and input of water whenever it is desirable for the
purposes
of recycling, to avoid burning the dried end product. Water is supplied to the
pumps through line 134, which is attached to the condenser 28. The sensors
152 are preferably plate temperature sensors with material being processed
passing over the sensing plate so that the actual temperature of the material
being processed is measured.
Wet material is input to the dryer into the upper auger bed 54
through the progressive displacement cavity pump 36 from holding tank 34
through line 38 and distribution cone 42 which, together, are shown as the
input 138 in Figure
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9. The material level in the first auger bed is measured by level indicator
162,
which like the other level indicators described here is preferably a
commercially
available nuclear radiation level indicator. If the level becomes too high,
the
motor 164 increases the spiral augers' speed to move the material more
quickly.
Similarly, the material level in the box 116 is monitored by high level
indicator
166 and low level indicator 168. Depending on the material level, the speed
of the second auger bank may be changed by motor 172 to increase the speed
of the spiral augers (material too high) or decrease it (material too low).
The
material in the box 124 is monitored by high level indicator 174 and low level
indicator 176, and the speed of the lower auger bank is modified in like
fashion
by motor 178.
Flue gas is controlled through temperature elements 182, temperature
indicators 184 and controllers 186. It is believed that approximate
temperature
equalization of the exhausting flue gases is desirable to achieve the best
thermal
efficiency. The flue gas temperature at the ends of the auger banks (at the
chimney inlet) is sensed by elements 182, and a signal indicative of the
temperature is sent by the temperature indicators 184 to controllers 186. If
the
temperature in an auger bank is too high or too low, then the corresponding
duct 82, 84 or 86 can be closed or opened (respectively) to lower or increase
the flue gas flow rate. The temperature of the material in the box 124 may
also be monitored by temperature element 152, which preferably extends into
the material stream. The temperature signal is sent by the indicator 154 to
controller 186, which can modify the position of all of the flaps 146. If the
material's temperature is too high, then the flaps 146 may be closed somewhat
to reduce the amount of hot flue gas passing through the auger flight jackets
and vice versa.
The temperature of radiant heat plate 66 is controlled as follows.
Temperature elements 202 detect the heat and signals indicating plate
temperature are sent by the indicators 204 (connected to the sensors as shown)
to the controllers 206. The fire box temperature may be modified by
controlling the radial flame burner output settings to produce the desired
plate
._ _ 17- ~ ~p $ ~ 31 1
temperature. Burner management systems are commercially available and the
feedback loops will not be further described here. Each radiant plate is
sensored. While one plate has been shown for each burner in Figure 9, there
may be different numbers of plates for each burner.
The condenser 28 is commercially supplied and several commercial
control systems are also available. Therefore, specific details will not be
provided here except for the following operation summary. Glycol is stored in
overflow tank 212 and pumped through the condenser 28. A heat sink 214,
preferably air cooled, cools the glycol. The glycol, as previously described,
is
also circulated through line 218 from the condenser 28 to the storage tank 34
in the input system shown at 138. For fixed installations, the glycol could be
circulated to capture excess heat, eliminating the air cooler, through other
plant
heat exchanges deemed useful for the specific processing operation. The
condenser 28 is fluidly attached to the dryer module 12 through line 126.
Pressure inside the condenser 28 is monitored by pressure transmitter 222
which
in turn is connected to controller 226. Controller 226 controls valve 228 by
regulating the glycol flow through the condenser which in turn regulates the
rate
of steam condensation. By controlling the glycol flow rate through the
condenser 28, and hence the rate of steam collapse, the amount of suction
generated by the condenser and therefore the rate of steam withdrawal out of
the dryer module 12, may be controlled. The pressure in the dryer module 12
should always be maintained slightly negative.
The temperature control of the glycol leaving the heat sink 214 is
monitored with sensor 232 connected to indicator 234 and controller 236.
Controller 236 controls the cooling effect of the air cooler (i.e. heat sink
214)
to maintain a prescribed glycol temperature measured by sensor 232. A relief
valve (not shown) should be provided in the condenser 28 to release accidental
excess negative or positive pressure.
The moisture evaporation rate may be monitored from knowing the input
moisture content (determined for example using a hand held device) and
measuring the rate of water draining from the condenser through flow meter 238
~~8231 1
_lg_
on line 134. Calibrating this measurement with the feeder input control 138
provides a means to self regulate the end product's moisture content.
The dryer module thus described for mobile processing could be mounted
on a conventional trailer 14 with wheels and front supports 13 (one shown).
The storage or holding tank 34 is preferably skid mounted, and the dryer is
preferably supplied in operation with a mobile control station, for example a
converted motor home. In fixed installations, remote control operation by
plant
staff would be facilitated by integrating the dryer module's control system
with
the plant's control system to accommodate full system operation and monitoring
from a remote computer console in the plant's control room. During mobile
processing, sludge would be pumped from a lagoon into the holding tank 34,
which would hold about a 12 hour supply. In a fixed installation, material
input feed into the dryer module would be custom designed. Dried sludge
would be discharged by the spiral auger to discharge 62 to a commercially
available storage bin {not shown) that will need to be emptied at a frequency
that depends on its volume. Power supply (150 kilowatts of 220 volt three
phase power) may be from the local power grid or from a standard diesel
generator. The radial flame burners described may use as a fuel supply heating
oil, natural gas, methane, butane, propane and diesel, although natural gas is
preferred. A fuel tank will of course be required where there is no continuous
supply of fuel.
A person skilled in the art could make immaterial modifications to the
invention described and claimed herein without departing from the essence of
the invention.
