TECHNICAL FIELD
[0001] The present invention relates to a method of and a device for manufacturing solid
fuel using porous coal as a starting material. More particularly, the present invention
relates to a method of and a device for manufacturing solid fuel, characterized by
a stable operation of a drying step in which separated upgraded porous coal is heated
and conveyed to be dried while being supplied with a carrier gas.
BACKGROUND ART
[0002] A conventional method of manufacturing solid fuel using porous coal as a starting
material is for example a method described in Patent Document 1. In the method, porous
coal (material coal) is first crushed at a crushing step, and then mixed with mixture
oil containing heavy oil and solvent oil at a mixing step to obtain material slurry.
After preheating, the material slurry is heated to dehydrate porous coal and impregnate
its pores with mixture oil at an evaporation step, to obtain dehydrated slurry. The
dehydrated slurry is separated into upgraded porous coal and mixture oil at a solid-liquid
separation step and thereafter only the upgraded porous coal is dried at a drying
step. At the drying step, the upgraded porous coal is conveyed and heated within a
heating type rotary dryer so that it is dried by allowing carrier gas to flow. The
dried upgraded porous coal is then cooled and molded to obtain solid fuel. On the
other hand, mixture oil recovered at the solid-liquid separation step and the drying
step is refluxed to the mixing step for reuse. Carrier gas recovered at the drying
step is again refluxed into the dryer for reuse.
[0003] However, the conveyance amount of porous coal may vary due to a variation in the
operation status at each step. For this reason, if the conveyance amount of upgraded
porous coal rapidly increases at the drying step, the amount of evaporated oil may
increase to raise the inner pressure. This may impair the sealing properties (sealability),
with the result that gas may leak out. Ordinarily, although the main component of
carrier gas is nitrogen, carrier gas contains solid in addition to solvent oil and
moisture, so that there may occur increased running cost due to solvent oil loss and
adverse effects on the ambient environment due to scattering of dust and generation
of foreign odor.
[0004] On the other hand, if the conveyance amount of upgraded porous coal rapidly decreases
at the drying step, the amount of evaporated oil may reduce to lower the inner pressure
to a negative pressure. In consequence, the ambient atmosphere enters the inside and
the internal oxygen concentration rises, with the result that the stability of high-temperature
upgraded porous coal may be impaired.
PRIOR ART DOCUMENT
PATENT DOCUMENT
SUMMARY OF THE INVENTION
PROBLEM TO BE SOLVED BY THE INVENTION
[0006] Thus, an object of the present invention is to enable a drying step to be executed
in a stable state regardless of the increase or decrease in the conveyance amount
of porous coal.
MEANS FOR SOLVING PROBLEM
[0007] The present invention provides, as means for solving the problem, a method of manufacturing
solid fuel including:
a mixing step of mixing porous coal with a mixture oil containing solvent oil and
heavy oil, to obtain material slurry;
an evaporation step of heating the material slurry to promote dehydration of porous
coal and impregnating the mixture oil into pores of porous coal, to obtain dehydrated
slurry;
a solid-liquid separation step of separating upgraded porous coal and the mixture
oil from the dehydrated slurry; and
a drying step of drying the upgraded porous coal by heating and conveying it while
supplying carrier gas, wherein
the method includes:
setting a target value of the circulation amount of carrier gas and a target value
of the pressure of carrier gas at the drying step;
calculating control outputs, based on deviations between the target values and measured
values corresponding respectively thereto; and
adjusting the supply amount of carrier gas, based on a smaller value between the control
outputs obtained.
[0008] According to this, the supply amount of carrier gas is adjusted based on a smaller
one between control outputs that are calculated based respectively on the circulation
amount and the pressure of carrier gas, so that carrier gas pressure at the drying
step can be stabilized without significant changes.
[0009] Preferably, the target values are each decided based on the supply amount of upgraded
porous coal to be dried at the drying step and on the amount of oil contained in upgraded
porous coal subjected to the drying step.
[0010] Preferably, the target values are each decided such that the pressure of carrier
gas at the drying step lies within a preset range.
[0011] The present invention provides, as means for solving the problem, a device for manufacturing
solid fuel including:
a mixing vessel that mixes porous coal with a mixture oil containing solvent oil and
heavy oil, to obtain material slurry;
an evaporator that heats the material slurry to promote dehydration of porous coal
and that impregnates the mixture oil into pores of porous coal, to obtain dehydrated
slurry;
a centrifuge that separates upgraded porous coal and the mixture oil from the dehydrated
slurry;
a dryer that dries the upgraded porous coal by heating and conveying it while supplying
carrier gas; and
a control unit that sets a target value of the circulation amount of carrier gas and
a target value of the pressure of carrier gas in the dryer, that calculates control
outputs, based on deviations between the target values and measured values corresponding
respectively thereto, and that adjusts the supply amount of carrier gas, based on
a smaller value between the control outputs obtained.
[0012] Preferably, the control unit decides the target values, each based on the supply
amount of upgraded porous coal to be dried in the dryer and on the amount of oil contained
in upgraded porous coal leaving the dryer.
[0013] Preferably, the control unit decides each of the target values such that the pressure
of carrier gas at a drying step lies within a preset range.
EFFECT OF THE INVENTION
[0014] According to the present invention, the supply amount of carrier gas is adjusted
based on a smaller one between control outputs that are calculated based respectively
on the circulation amount and the pressure of carrier gas. For this reason, the circulation
amount and the pressure of carrier gas can rapidly reach a stable state, thereby contributing
to the stable operability at the drying step.
BRIEF DESCRIPTION OF DRAWINGS
[0015] Fig. 1 is a schematic diagram showing part of an upgraded brown coal manufacturing
device according to an embodiment.
MODE FOR CARRYING OUT THE INVENTION
[0016] An embodiment according to the present invention will now be described with reference
to the accompanying drawing.
[0017] Fig. 1 schematically shows part of an upgraded brown coal manufacturing device (an
example of a solid fuel manufacturing device) according to the embodiment. Although
not shown, the upgraded brown coal manufacturing device executes a mixing step in
a mixing vessel, executes an evaporation step in an evaporator, and executes a solid-liquid
separation step in a decanter centrifuge. The upgraded brown coal manufacturing device
executes a drying step in a dryer 1, to obtain upgraded brown coal.
[0018] In the dryer 1, upgraded porous coal is heated and conveyed to be dried while being
supplied with a carrier gas. Nitrogen (N
2) is used herein as carrier gas to prevent upgraded porous coal from firing. Upgraded
porous coal supplied into the dryer 1 is assumed to contain 30-40 % of oil.
[0019] The dryer 1 used is of an indirect heating type having a heater not shown in which
the temperature of the internal carrier gas is controlled to approximately 200°C.
Upgraded porous coal is conveyed by a screw conveyor within the dryer 1. The screw
conveyor has a tubular rotary shaft whose outer peripheral surface is formed with
a plurality of small-diameter apertures. Carrier gas can newly be supplied via the
rotary shaft into the dryer 1.
[0020] A circulation path 2 is connected to the dryer 1, for recovering carrier gas to again
supply it into the dryer 1. Midway along the circulation path 2 there are arranged,
in the mentioned order from the outlet side of the dryer 1, a dust collector 3, a
spray tower 4, a blower 5, a flow rate detection sensor 6, a first flow rate regulating
valve 7, and a first pressure detection sensor 8. An exhaust pipe 9 is connected to
a piping extending from the spray tower 4 to the blower 5 and is disposed with a second
flow rate regulating valve 10. The pressure in the middle of a piping connecting the
dust collector 3 and the spray tower 4 is detected by a second pressure detection
sensor 11.
[0021] A detection signal from the flow rate detection sensor 6 is input to a flow indication
controller (FIC) 12. A detection signal from the first pressure detection sensor 8
is input to a first pressure indication controller (PIC) 13. The FIC 12 and the PIC
13 calculate control output values from Math. 1 as will be described later. The control
output values calculated by the FIC 12 and the PIC 13 are compared by a low select
circuit (LS circuit) 14 so that the opening of the first flow rate regulating valve
7 is adjusted based on a lower one. In this case, the opening of the first flow rate
regulating value 7 is adjusted so that carrier gas pressure in the circulation path
2 is kept within the predetermined range (e.g., 1-2 kPa. Note that this value varies
depending on the sealing designs and operation conditions for a conveyer, the dryer
1, etc.). A detection signal from the second pressure detection sensor 11 is input
to a second PIC 215. Based on this input signal, the second PIC 15 regulates the opening
of the second flow rate regulating valve 10 in a manner as described later, to thereby
restrain the pressure in the circulation path 2 from rising.
[0022] The dust collector 3 serves to collect upgraded porous coal dust contained in carrier
gas discharged from the dryer 1.
[0023] Upgraded brown coal (UBC) is discharged from the dryer 1 or the dust collector 3.
[0024] The spray tower 4 serves to condense and separate mixture oil from carrier gas passing
through the dust collector 3.
[0025] The blower 5 serves to form a carrier gas flow from the circulation path 2 to the
dryer 1.
[0026] Actions of the upgraded brown coal device having the above configuration will then
be described.
[0027] Upgraded brown coal (an example of solid fuel) is obtained through a mixing step,
an evaporation step, a solid-liquid separation step, and a drying step.
[0028] At the mixing step, porous coal is mixed with mixture oil containing solvent oil
and heavy oil to obtain material slurry.
[0029] At the evaporation step, the material slurry obtained at the mixing step is heated
to promote the dehydration of porous coal. At the same time, the mixture oil is impregnated
into pores of porous coal to obtain dehydrated slurry.
[0030] At the solid-liquid separation step, upgraded porous coal and the mixture oil are
separated from the dehydrated slurry by the decanter centrifuge.
[0031] At the drying step, the upgraded porous coal obtained at the solid-liquid separation
step is heated and conveyed to be dried while being supplied with carrier gas within
the dryer 1, to obtain upgraded brown coal.
[0032] The drying step featuring the present invention will hereinbelow be described in
detail.
[0033] At the drying step, a target value of the carrier gas circulation amount and a target
value of the carrier gas pressure at the inlet of the dryer 1 are set based on the
supply amount of porous coal supplied into the dryer 1 and on the oil amount contained
in the porous coal at the outlet side of the decanter centrifuge. In this case, the
target value of the carrier gas circulation amount and the pressure target value are
set such that the carrier gas pressure in the dryer 1 lies within a previously set
pressure range (set pressure range) with respect to the supply amount of porous coal
and the amount of oil contained therein. These target values to be set may be found
in advance by experiment, etc.
[0034] A control output value is then calculated from Math. 1, based on the set target value
of the carrier gas circulation amount and on a measured value of the carrier gas flow
rate detected by the flow rate detection sensor 6 (hereinafter, this control output
value is referred to as first control output value). Similarly, a control output value
is calculated from Math. 1, based on the set target value of the carrier gas pressure
and on a measured value of the carrier gas pressure detected by the first pressure
detection sensor 8 (hereinafter, this control output value is referred to as second
control output value).
MV: control output
e(t): control deviation (target value SV-detected value PV)
PB: proportional band (%)
Ti: integral time (min.) control deviation regulating parameters
Td: derivative time (min.)
[0035] Subsequently, by a low select control, the calculated control output values are compared
so that the opening of the first flow rate regulating valve 7 is adjusted in accordance
with a smaller value.
[0036] When the flow rate and the pressure of carrier gas flowing through the circulation
path 2 are stable, the control output value is calculated based on a flow rate detected
by the flow rate detection sensor 6 and on the target value so that the opening of
the first flow rate regulating valve 7 is adjusted.
[0037] If the amount of oil evaporating therein increases as a result of a temporary sudden
increase in the amount of upgraded porous coal conveyed into the dryer 1, the flow
rate of carrier gas detected by the flow rate detection sensor 6 does not vary so
much, but the pressure detected by the first pressure detection sensor 8 rises. In
consequence, the second control output value calculated from Math. 1 becomes smaller
than the first control output value. Thus, the opening of the first flow rate regulating
valve 7 is adjusted based on the second control output value. This suppresses the
flow rate of carrier gas refluxed into the dryer 1 so that the pressure in the dryer
1 can stably be kept within a desired range.
[0038] At this time, a control output value is calculated from Math. 1, based on a pressure
detected by the second pressure detection sensor 11 and on the previously set target
value. The opening of the second flow rate regulating valve 10 is then adjusted based
on the calculated control output value. This suppresses an excessive pressure rise
attributable to carrier gas within the circulation path 2. Discharged carrier gas
is directed to an off-gas treatment device not shown. Carrier gas delivered to the
off-gas treatment device is properly supplied into the dryer 1 for reuse.
[0039] If the amount of oil occurring therein decreases as a result of a temporary sudden
decrease in the amount of upgraded porous coal conveyed into the dryer 1, the internal
pressure in the dryer 1 and the circulation path 2 lowers. Then, both the flow rate
detected by the flow rate detection sensor 5 and the pressure detected by the first
pressure detection sensor 8 become lower. As a result, the first control output value
and the second control output value calculated from Math. 1 both become larger. Ordinarily,
the change in the flow rate detected by the flow rate detection sensor 6 is not so
large, and the first control output value becomes smaller than the second control
output value. For this reason, the first control output value is selected by the low
select control so that the opening of the first flow rate regulating valve 7 is adjusted
based on this first control output value. In some cases, the second control output
value may be smaller than the first control output value. In this case, the opening
of the first flow rate regulating valve 7 is adjusted based on the second control
output value.
[0040] At this time, similar to the above, a control output value is calculated from Math.
1, based on a pressure detected by the second pressure detection sensor 11 and on
the previously set target value. The opening of the second flow rate regulating valve
10 is then adjusted based on the calculated control output value. In this case, since
the detected pressure lowers to a large extent, the second flow rate regulating valve
is fully closed, not permitting carrier gas to be discharged to the exterior.
[0041] In this manner, if the amount of upgraded porous coal conveyed into the dryer 1 temporarily
increases or decreases, the opening of the first flow rate regulating valve 7 is adjusted
correspondingly. In this case, by the low select control, a smaller value is used
between the first control output value and the second control output value. Accordingly,
it is possible to stabilize the pressure of carrier gas in the dryer 1, without a
sudden change in the opening of the first flow rate regulating valve 7.
[0042] The present invention is not limited to the above configuration described in the
embodiment, but may variously be modified.
[0043] For example, although the opening of the first flow rate regulating valve 7 is adjusted
by a proportional integral derivative (PID) controller in the embodiment, it may be
adjusted by another feedback control.
[0044] Although in the embodiment, a detection signal from the flow rate detection sensor
6 is processed by the FIC 12, a detection signal from the first pressure detection
sensor 8 is processed by the first PIC 13, and a detection signal from the second
pressure detection sensor 11 is processed by the second PIC 15, the configuration
may be, for example, such that these are controlled together by a single control unit
(microcomputer) or such that the FIC 12 and the first PIC 13 are controlled by a single
control unit (microcomputer).
EXPLANATIONS OF LETTERS OR NUMERALS
[0045]
- 1
- dryer
- 2
- circulation path
- 3
- dust collector
- 4
- spray tower
- 5
- blower
- 6
- flow rate detection sensor
- 7
- first flow rate regulating valve
- 8
- first pressure detection sensor
- 9
- exhaust pipe
- 10
- second flow rate regulating valve
- 11
- second pressure detection sensor
- 12
- FIC
- 13
- first PIC
- 14
- LS circuit
- 15
- second PIC
1. A method of manufacturing solid fuel comprising:
a mixing step of mixing porous coal with a mixture oil containing solvent oil and
heavy oil, to obtain material slurry;
an evaporation step of heating the material slurry to promote dehydration of porous
coal and impregnating the mixture oil into pores of porous coal, to obtain dehydrated
slurry;
a solid-liquid separation step of separating upgraded porous coal and the mixture
oil from the dehydrated slurry; and
a drying step of drying the upgraded porous coal by heating and conveying it while
supplying carrier gas, wherein
the method comprises:
setting a target value of the circulation amount of carrier gas and a target value
of the pressure of carrier gas at the drying step;
calculating control outputs, based on deviations between the target values and measured
values corresponding respectively thereto; and
adjusting the supply amount of carrier gas, based on a smaller value between the control
outputs obtained.
2. The method of manufacturing solid fuel according to claim 1, wherein
the target values are each decided based on the supply amount of upgraded porous coal
to be dried at the drying step and on the amount of oil contained in upgraded porous
coal subjected to the drying step.
3. The method of manufacturing solid fuel according to claim 2, wherein
the target values are each decided such that the pressure of carrier gas at the drying
step lies within a preset range.
4. A device for manufacturing solid fuel comprising:
a mixing vessel that mixes porous coal with a mixture oil containing solvent oil and
heavy oil, to obtain material slurry;
an evaporator that heats the material slurry to promote dehydration of porous coal
and that impregnates the mixture oil into pores of porous coal, to obtain dehydrated
slurry;
a centrifuge that separates upgraded porous coal and the mixture oil from the dehydrated
slurry;
a dryer that dries the upgraded porous coal by heating and conveying it while supplying
carrier gas; and
a control unit that sets a target value of the circulation amount of carrier gas and
a target value of the pressure of carrier gas in the dryer, that calculates control
outputs, based on deviations between the target values and measured values corresponding
respectively thereto, and that adjusts the supply amount of carrier gas, based on
a smaller value between the control outputs obtained.
5. The device for manufacturing solid fuel according to claim 4, wherein
the control unit decides the target values, each based on the supply amount of upgraded
porous coal to be dried in the dryer and on the amount of oil contained in upgraded
porous coal leaving the dryer.
6. The device for manufacturing solid fuel according to claim 5, wherein
the control unit decides each of the target values such that the pressure of carrier
gas at a drying step lies within a preset range.