Note: Descriptions are shown in the official language in which they were submitted.
CA 02257209 1998-12-04
WO 97/47933 PCT/CA97/00400
- 1 -
A SPOUT-FLUID BED DRYER AND GRANULATOR
FOR THE TREATMENT OF WASTE SLURRIES
TECHNICAL FIELD
The present invention relates to an integrated
drying and incineration system and process wherein refuse
material, such as animal manure, animal excreta,
slaughter-house slurry human waste, industrial sludges or
other related slurry solution is dried by direct contact
1o with hot air in a spout-fluid bed of conical shape packed
with heat exchange particles, and wherein the generated
effluent gases are incinerated in a combustion chamber to
have the volatile organic compounds (VOCs) and odor gases
destroyed.
BACKGROUND ART
Animal manure and other related sewage slurries
from animal farms need to be treated before being
released to the land field to prevent the contamination
of the underground water system and the spreading of
diseases related to bacteria contained in the manure
slurry. There exist two competitive types of processes
for the treatment of manure slurry. The first type of
process treats the slurry biologically in which the waste
solution is digested via aerobic or anaerobic
fermentation, then the treated slurry which has a water
content around 80$ is either applied to the land field,
or further treated to reduce water content to about 10~
and then used as fertilizers. The other type of process
so uses physical operations to treat the slurry in which the
slurry is dried by direct or indirect contact with hot
air or gas stream to evaporate the water, the generated
solids have a moisture content of about 10$ and can be
used as fertilizers. The generated gas-vapor mixture is
ss further treated to remove organic compounds and odor
gases via incineration or wet scrubbing before it is
CA 02257209 1998-12-04
- WO 97/47933 PCT/CA97/00400
_2_
released to the environment. In recent years, the amount
of biologically digested sludge to be spread on the land
field has been greatly limited due to the more strict
regulations on environmental protection. Most of the
s digested slurry thus needs to be treated more thoroughly
to remove naturally undegradable pollutants or to remove
water to such a level that the solids sludge can be used
as substitute fertilizers. As a result, the direct
drying and granulation process becomes economically
~o advantageous over the biological treatment process.
There exist several possible processes for the
drying of animal manure slurry, such as the spray drying
process described by Masters, K. (1972), "Spray drying",
Leonard Hill Books, London; rotary drying process
15 described by Glorioso (1993) in Canadian Patent
1,325,583; traveling grate drying process described by
Bernes and Jensen (1991) in Canadian Patent 2,085,583;
and fluidized bed dryer as described by Huttlin (1991) in
Canadian Patent 2,000,299. To reduce the sludge water
2o content from 90$ to less than 100, extensive evaporation
is involved which requires high heat and mass transfer
rates. Compared to rotary dryers and traveling grant
dryers, a fluidized bed in which slurry is sprayed on the
bed material and evaporation occurs on the surface of
2s particles can provide much larger surface area for the
heat and mass transfer, leading to much higher overall
mass and heat transfer rates. The gas-solids contact can
be further improved in a spout-fluid bed due to the high
internal solids circulation inside the spout-fluid bed
30 (Uemaki, O. and Tsuji, T., "Particle velocity and solids
circulation rate in a jet-spouted bed", Can. J. Chem.
Eng., 70, 925-928, 1992). As a result, spout-fluid bed
dryers can provide a drying efficiency more than 10 times
higher than spray dryers (Masters 1972; Markowski, A. and
3s Kaminski, W., "Hydrodynamic characteristics of jet-
spouted beds", Can. J. Chem. Eng., 61, 377-3811, 1983).
CA 02257209 1998-12-04
- 2a -
With reference to WO 80/01407 there is
disclosed a drying system for drying wet slurry. This
system utilizes a mixing box at a feed end of the mill
to increase the solids contents in the range of 50 to
60 percent. The slurry is heated directly by a burner
at a fixed high temperature. The burner also provides
heat to a heat exchanger where effluent gases are
preheated before being fed to the combustion chamber.
Part of the treated effluent gases are fed to the heat
exchanger for the preheating and part is fed directly
to the mill. The effluent gases are not used to
reduce, in a controlled manner, the temperature of the
hot drying gas.
French Patents FR-A2 496 085 and
FR-A 2 198 112 relate to fluidized bed dryers as
described above with reference to the Canadian patents.
AMENDED SHEET
CA 02257209 1998-12-04
WO 97/47933 PCT/CA97/00400
-3-
SUMMARY OF INVENTION
There exists a need to develop a process to dry
organic waste slurry or other type of industrial waste
s slurry and which is much more efficient than the prior
art and which can destroy generated VOCs and odor gases
at higher levels than previously achieved by the above
referred-to drying processes and wherein the treatment
capacity can be increased and further wherein the
~o effluent gas is incinerated in a combustion chamber which
also provides the hot air for the drying chamber.
It is therefore a feature of the present
invention to provide a spout-fluid bed dryer and a
recuperative type combustion chamber which provide the
~s above need.
According to a further feature of the present
invention there is provided a refuse slurry drying system
employing a spout-fluid bed of conical shape to enhance
mass transfer rate and loading capacity by increasing
2o internal solids circulation.
Another feature of the present invention is to
provide a refuse slurry drying system employing a spout
fluid bed wherein the temperature is maintained at about
120°C to destroy all infectious bacteria contained in the
z5 dried solids.
Another feature of the present invention is to
provide a refuse slurry drying system employing a gas-
fired incinerator wherein the generated VOC vapors and
odor gases are destroyed to prevent air pollution.
so Another feature of the present invention is to
provide a refuse slurry drying system employing a heat
recuperator wherein the high temperature combustion gases
is used to preheat the effluent gases from the drying
chamber to incineration chamber.
35 Another feature of the present invention is to
provide a refuse slurry drying system employing a spout-
CA 02257209 2005-09-13
- 4 -
fluid bed dryer wherein the slurry solution is sprayed
from either the top, the bottom or the side walls into the
bed material by atomizing nozzles, although other
atomizing devices are also workable, to promote intimate
contact between liquid drops, solids particles and drying
gases.
A still further feature of the invention is to
provide an improved method of treating organic or
industrial refuse slurry having fertilizing properties.
Another feature of the present invention is to
provide an optional feeder which can add nutriments to the
drying system to improve the fertilizer quality of the
dried slurry particles.
Another feature of the present invention is to
provide a refuse slurry drying system which produces no
liquid effluent which necessitates further treatment.
According to a broad aspect of the present
invention there is provided a drying system for drying
refuse slurry. The system comprises a spout fluid-bed
dryer housing having a conical section provided in at
least a part thereof with a packing of heat exchange
particles. Means is provided to feed the refuse material
slurry to the packing. Inlet means is provided at a
narrowed end of the conical section to admit a hot drying
gas stream into the housing to heat the packing and to dry
the slurry to produce dried slurry particles and effluent
gases. The dried slurry particles are connected to a
separation means where the dried slurry particles are
separated. The effluent gases are fed to a combustion
chamber for destroying volatile organic compounds and odor
gases from the effluent gases before releasing a regulated
CA 02257209 2005-09-13
- 5 -
amount of the hot treated effluent gases which is now
clean gases and for further heating and drying the hot
drying gas stream to feed said inlet means of the dryer
housing.
According to a still further broad aspect of the
present invention there is provided a method of treating a
refuse slurry to produce dried particles and for
destroying volatile compounds and odor gases contained in
the refuse slurry. The method comprises the steps of:
i) disposing a packing of heat exchange particles in a
conical section a feed port at a narrowed end, ii) heating
said packing to a predetermined temperature range by
passing a hot drying gas stream therethrough from said
narrowed end, iii) feeding a fine spray of a refuse slurry
to said packing, iv) drying said slurry by evaporating its
water content by contact with said heat exchange bodies
and hot drying gas stream, to produce dried slurry
particles and effluent gases, v) connecting said dried
slurry particles to a particle separator for the
extraction of said dried slurry particles, vi) connecting
said effluent gases to a combustion chamber for removing
volatile compounds and odor gases therefrom to produce hot
air and for releasing a regulated amount of hot treated
effluent gases into the atmosphere and to further heat
said air to provide said hot drying gas stream to feed
said narrowed end of said dryer.
BRIEF DESCRIPTION OF DRAWINGS
A preferred embodiment of the present invention
will now be described with reference to the accompanying
drawings in which:
FIG. 1 is a schematic diagram showing the
process of the present invention consisting of a spout-
CA 02257209 1998-12-04
- 5a -
treated gases into the atmosphere and to further provide a
high temperature combustion stream to feed mixing chamber
adjacent an outlet of the combustion chamber. A regulated
flow of another part of the effluent gases is also fed to the
mixing chamber for admixture with the high temperature
combustion stream to reduce the temperature of the gas stream
prior to convecting same to the housing to form the hot drying
gas stream to heat the packing.
BRIEF DESCRIPTION OF DRAWINGS
A preferred embodiment of the present invention will
now be described with reference to the accompanying drawings
in which:
FIG. 1 is a schematic diagram showing the process of
the present invention consisting of a spout-
CA 02257209 1998-12-04
WO 97/47933 PCT/CA97/00400
-6-
fluid bed dryer, a chamber for combustion, incineration
and heat recuperation, a slurry feed circuit and the
interconnecting pipe lines; and
FIG. 2 is a simplified schematic diagram
s showing the gas and air feed lines connected to the gas
burner.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring now to the drawings and more
~o particularly to Figure 1, there is shown generally at 10,
the spout-fluid bed dryer of the present invention for
producing dried fertilizer from organic refuse material
having fertilizing properties. As can be seen it
consists of a conical shape vertical housing 12 of
circular cross-section, although other cross-sectional
shapes are workable, and defining a circumferential side
wall 12, a conical bottom chamber 11, an open bottom end
13 and a top end 14.
A packing 15 of particles is supported by a
2o perforated distributor 16 in the conical section 11,
although other types of distributors are workable,
permitting the passage of air through the packing and
from the bottom of the housing. A slurry discharge means
in the form of spray nozzles 17, although other spray
2s means are workable, is disposed below the packing 15,
although it can also be mounted at the top or on the side
walls of the housing, and connected to a pressure supply
line 18 whereby to discharge slurry solution to the
packing 15 for the evaporation of water within the
3o housing conical section 11.
A distinct aspect of the design of this drying
chamber is the use of a conical shape chamber 11 which
promotes internal solids circulation and mixing, and thus
prevents particles from sticking together at high slurry
35 loading rates.
CA 02257209 1998-12-04
WO 97/47933 PCTlCA97/00400
Another distinct aspect of the design of this
conical chamber 11 is the division of the chamber into a
lower section 19 and an upper section 29. With a
distributor 16 located at the bottom of the lower section
s 19 and particle packing 15 above the distributor 16, the
spout-fluid bed is operated in a jet-spouting mode which
generates strong internal solids circulation and thus
provide high gas and solids contacting. This enhances
the evaporation of water and, on the other hand, promotes
~o the breakup of formed film layers on the surface of
particles from the deposition of slurry liquid. As a
result, fine particles are generated continuously from
this particle packing 15 and are elutriated by the air-
vapor mixture to the top of the chamber and out of the
chamber to the cyclone separator 20.
When the distributor 16' is located at the
bottom of the upper section 29 of the chamber 11 and
particle packing 15 is above the distributor 16', the bed
is operated in a spout-fluidized bed mode with reduced
2o internal solids circulation rate. As a result, the size
of particles will grow up during the drying process due
to the deposition of layers by layers of fine powders
from the evaporation of slurry films sprayed to the
particle surface. The drying chamber in such a case
z5 serves as both a dryer and a granulator. The generated
large sludge particles may then be discharged
continuously from the side wall of the housing through an
inclined pipe 21 and directed to a receiver 22. The
discharge rate may be controlled by a ball valve 23.
3o In the operation, the hot drying air is
supplied to the bottom of the dryer from a pipe line 28,
which connects a port 13' at the bottom end 13 of the
dryer 10 to the outlet 33' of the mixing chamber 33 which
will be described later. The slurry 65 is supplied to
35 the spray nozzles 17 through a pipe line 18, which is
connected to a slurry pump 61 and a slurry tank 60 with
CA 02257209 1998-12-04
w WO 97/47933 PCT/CA97/00400
_8_
the flow rate of the slurry controlled by a controllable
valve 62 and a modulating controller 63 responsive to the
temperature of the drying chamber 11, and which
temperature is measured by thermocouples 64.
s The sprayed slurry forms a thin film on the
surface of particles within the packing 15 and water
evaporation is realized by both the release of heat from
the heated particles and from the contact with the hot
drying air. The air and vapor mixture and elutriated
~o particles rise up with the air current and leave the
drying chamber from the top port 14, and are directed to
a cyclone 20 wherein entrained dry particles are
separated from the gas stream and collected from the
bottom of the cyclone by a receiver 24. Effluent air and
vapor stream leaves the cyclone from the top port 25 and
are connected to an incinerator chamber 30, which will be
described later with reference to Figure 2, to have the
VOCs and odors destroyed.
A nutriment feed pipe 9 may also be positioned
2o above the packing 15 to introduce into the housing 12
nutriments for admixture to the dried slurry particles to
improve the fertilizing quality of the dried manure
collected by the cyclone separator 20.
The proper evaporation of slurry in the drying
2s chamber 11 is monitored by regulating the feeding rate of
the slurry based on temperature within the particle
layers of the packing 15 and the top freeboard region by
using a series of thermocouples, although it is also
workable to adjust the feeding rate of the drying air.
3o The condensation of vapor in the connecting pipe line 26
is prevented by monitoring the temperature within the
cyclone 20 to be higher than the dew point of the mixture
by a thermocouple (not shown).
The combustion and incineration chamber 30
35 shown in Figure 1 is provided with a natural gas burner
31, a heat recuperator 32 and a mixing chamber 33. The
CA 02257209 1998-12-04
WO 97/47933 PCT/CA97/00400
-9-
natural gas, or other fuels, together with the combustion
air, is supplied from a pipe line 40 which will be
described in detail later with reference to Figure 2, to
the burner 31 for the combustion. High temperature
s combustion gases then meets with the effluent gases which
come from the drying chamber 11, compressed by a vapor
fan 38 and fed into the combustion and incineration
chamber 30 before preheated in a tube-shell type heat
exchanger 32. To ensure complete removal of VOCs and
~o odors contained in the effluent gases, the temperature of
the incineration chamber is maintained above 750°C and
the effluent gas stream has a residence time longer than
0.5 second. After passing the incineration chamber, one
stream of the effluent gases goes into the shell side of
15 the heat exchanger 32 to preheat the incoming effluent
gases from the vapor fan 38 before it leaves the system
through vent 34 at a temperature lower than 350°C. A
valve 34' controls the discharge of the treated gases and
balances the system. The vent 34 could be connected to
zo heat exchange devices to extract heat therefrom for other
uses. The other stream of the effluent gases is passed
to a mixing chamber 33 to be mixed with another stream
directly from the exit of the vapor fan 38. With the two
streams well mixed in the mixing chamber, the mixture at
25 a temperature of around 400°C goes to the bottom of the
drying chamber 11 for the drying of the slurry solution
65. To control the temperature of mixture going to the
mixing chamber 33, a controllable valve 35 is installed
in the effluent air line with the flow rate controlled by
3o a modulating controller 36 based on the temperature
inside the mixing chamber 33 measured by a thermocouple
37. As can be seen the blower 38 connects the drying air
flow and effluents in a closed loop from the top of the
housing 12 to the bottom port 13', through the mixing
3s chamber 33.
CA 02257209 1998-12-04
WO 97/47933 PCT/CA97/00400
_70_
The distinct feature of such a combination of
combustion-incineration-recuperation chamber is the
energy saving. The combustion of natural gas in a single
chamber provides energy for the preheating of incoming
s effluent gases, the incineration of effluent gases and
provides moderate temperature gases for the drying
chamber 11. Although only one heat recuperator is
included in this diagram, it is also workable to have
more heat exchangers to further recuperate energy from
~o the down stream venting to the environment.
Figure 2 is a block diagram illustrating a
typical configuration of the gas-air feed circuit 40. As
herein shown a natural gas feed line 41 is connected to a
pressure regulator 42 and feeds a modulating controller
~s 43 connected to a controllable valve 44. Modulating
controller 43 is also connected across the orifice 45 of
an air pressure line 46 fed by a blower 47. The line is
connected to an air valve 48 and also directly to the
orifice 45. An electrovalve 49 is connected upstream of
2o the controlled valve 44 and an adjustable orifice 50.
The controlled valve 44 is controlled by the modulating
controller which senses the amount of air being supplied
in the feed line 51 so that a constant gas-air mixture
may be fed to its outlet 52 which is connected to the
2s feed pipe 40 of the burner 31. This feed circuit is
substantially of standard design.
Although in the present application reference
is made particularly to the treatment of organic refuse
material such as animal manure, it is to the understood
3o that the present invention should not be restricted
thereto. In fact, dried fertilizers produced from
suitable refuse material having fertilizing properties
and to which nutriments may or may not be added is
intended to be covered. For example, slurry from
35 slaughter houses, municipal slurry obtained from water
treatment facility or refuse dumps, human or pulp and
CA 02257209 1998-12-04
- WO 97!47933 PCT/CA97/00400
- 11 -
paper or agricultural or bio-industrial slurries are
examples of organic refuse capable of being treated by
the system and method of this invention.
Other added value properties such as nutriment
s or energy can be produced from organic refuse material
treated by the system and method of this invention.
Moreover other valuable extract can be produced
from other industrial refuse material such as slurries
from contaminated soil, petro-chemical, chemical,
1o mineral, metallurgical, mining, and other industrial
operations are examples of refuse material capable of
being treated by the system and method of this invention.
It is within the ambit of the present invention
to cover any obvious modifications of the preferred
1s embodiment described herein, providing such modifications
fall within the scope of the appended claims.
