JP4444798B2 - Fine powder combustion apparatus and fine powder combustion method - Google Patents

Description

  The present invention relates to a pulverized fuel combustion apparatus and a pulverized fuel combustion method in which a solid fuel is finely pulverized and simultaneously dried to obtain a pulverized fuel.

  In response to the increasing demand for energy in recent years, pulverized coal produced by pulverizing and drying coal containing a lot of moisture and volatiles such as lignite instead of high-grade coal such as bituminous coal. In addition, development of a pulverized fuel combustion apparatus using pulverized fuel such as biomass obtained by pulverizing and drying waste wood or the like to form powder is underway.

  As what discloses such a pulverized fuel combustion apparatus, for example, one disclosed in Patent Document 1 is known. In Patent Document 1, for example, as shown in FIGS. 6 and 7, the finely pulverized fuel pulverized and dried by the mill 11 is transferred to the dust collector 12 and collected together with the exhaust gas S1, and then stored in the silo 12 ′. The The pulverized fuel stored in the silo 12 ′ is supplied to the boiler 14 by the conveying airflow S 2 generated by the blower 13. Exhaust gas S3 from the boiler 14 passes through the air heater 15. The air heater 15 absorbs the heat energy of the exhaust gas S3 and applies this heat energy to the airflow S4 generated by the blower 16 and given to the boiler 14 for combustion. The exhaust gas S3 from the boiler 14 whose temperature has been lowered by the air heater 15 is collected by the dust collector 17, desulfurized by the desulfurizer 18, and then discharged from the chimney 19 to the atmosphere. The mill 11 needs to be fed with a drying airflow for drying the pulverized fuel. In Patent Document 1, an example (FIG. 6) in which a part of an airflow S4 ′ generated by heating the airflow S4 with an air heater 15 is sent to the mill 11 as a drying airflow, and the exhaust gas S5 after passing through the dust collector 17 is used for drying. An example of sending air to the mill 11 as an air flow (FIG. 7) is disclosed.

Japanese Examined Patent Publication No. 62-55057 (right column of page 1 to page 2, FIGS. 1 and 2)

  In the configuration of FIG. 6 and FIG. 7, since the raw material is fed into the mill 11 without considering the amount of raw material held in the mill 11, the increase in the amount of raw material held in the mill 11 causes the mill 11 to increase or decrease. There was a problem that the pulverization efficiency fluctuated. The fluctuation in the pulverization efficiency causes variations in the particle size (particle size) of the discharged fine powder fuel. Such variation causes a decrease in combustion efficiency, and is particularly noticeable when wood flour made from wood chips is used as fuel.

  The present invention has been made in view of such problems, and even when wood powder is used as a fuel, the finely powdered fuel is capable of finely pulverizing the wood powder, pulverizing it to a constant particle size, and drying it. An object of the present invention is to provide a combustion apparatus and a pulverized fuel combustion method.

In order to achieve the above object, a pulverized fuel combustion apparatus according to the present invention includes a pulverizing and drying apparatus for pulverizing wood fuel and drying it with a drying airflow to generate wood powder fuel and discharging the fuel together with a first exhaust gas, Based on the measurement value of the supply unit that supplies the wood fuel to the pulverization and drying device, the differential pressure measurement unit that measures the difference between the pressure of the drying airflow and the pressure of the first exhaust gas, and the differential pressure measurement unit A supply control unit that controls the supply amount of the wood fuel per unit time from the supply unit; and the temperature of the drying airflow is adjusted so that the temperature of the first exhaust gas is within a predetermined range. An air flow introduction unit for introducing the air flow for drying into the pulverizing and drying device, and collecting the wood powder fuel conveyed by the first exhaust gas from the pulverizing and drying device, and from the first exhaust gas. Generated excluding the wood powder fuel And a boiler that discharges the third exhaust gas by burning the wood powder fuel as a fuel, and the drying air flow introduction unit includes the second exhaust gas A gas is mixed with the third exhaust gas to generate a mixed gas, and the mixed gas is introduced into the pulverizing and drying apparatus as the drying airflow .

The pulverized fuel combustion method according to the present invention includes a pulverization and drying step of pulverizing wood fuel and drying it with a drying airflow to generate wood powder fuel and transporting it together with the first exhaust gas, the pressure of the drying airflow, A differential pressure measuring step for measuring a difference from the pressure of the first exhaust gas, a supply control step for controlling a supply amount of the wood fuel per unit time based on a measurement result of the differential pressure measuring step, and the first exhaust A temperature adjusting step for adjusting the temperature of the airflow for drying so that the temperature of the gas is within a predetermined range; and collecting the wood powder fuel conveyed by the first exhaust gas, and the first A wood powder fuel collecting step for discharging the second exhaust gas generated by removing the wood powder fuel from the exhaust gas, and a combustion step for discharging the third exhaust gas by burning the wood powder fuel, Dry Airflow, characterized in that said at second those produced exhaust gas and the third exhaust gas and the mixture to the gas mixture.

  According to this invention, even when wood powder is used as fuel, the wood powder can be sufficiently finely pulverized and dried with a constant particle size.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the overall configuration of a pulverized fuel combustion apparatus according to a first embodiment of the present invention. The same elements as those of the conventional pulverized fuel combustion apparatus (FIGS. 6 and 7) are denoted by the same reference numerals, and detailed description thereof is omitted.

In the present embodiment, the exhaust gas having a low oxygen concentration (inert gas having an oxygen concentration of 2 to 5%) discharged from an ECO 14 ′ (Economizer: economizer) provided at the outlet of the boiler 14 in the mill 11 is used. A part S3 ′ of S3 and a part S6 ′ of the exhaust gas S6 discharged from the dust collector 12 are mixed to form a mixed gas S7, and this mixed gas S7 is supplied to the mill 11 via the transport pipe 21 as a drying airflow. It has been introduced. The exhaust gas S3 ′ is exhaust gas after a part of the exhaust gas S3 from the ECO 14 ′ is sent to the cyclone 145 and the dust is separated.
The dust separated by the cyclone 145 can be effectively used as a raw material for cement and granulated sand.

As described above, the exhaust gas S3 ′ has a low oxygen concentration and a temperature of about 350 ° C., while the exhaust gas S6 ′ is about 110 to 130 ° C. The mixing ratio of the exhaust gases S3 ′ and S6 ′ is adjusted so that the temperature of the exhaust gas S1 discharged from the mill 11 is about 90 to 130 ° C., and the oxygen concentration of the mixed gas S7 is about 3 to 10% (preferably Is maintained at about 7%). An oxygen concentration meter may be installed in the exhaust gas S1 line to monitor the oxygen concentration, which is suitable for safety management of the entire process.
As shown in FIG. 1, in this embodiment, a control unit 30 and a temperature sensor 31 are provided, and thereby the temperature of the exhaust gas S1 is controlled. That is, the temperature sensor 31 disposed in the vicinity of the outlet of the exhaust gas S1 of the mill 11 detects the temperature of the exhaust gas S1, and the control unit 30 controls the damper DD at the outlet of the blower 20 based on this detection signal. 'And the supply ratio of the exhaust gases S6' and S3 'from the blower 20 are changed. Instead of controlling the damper DD, the rotational speed of the blower 20 may be controlled. The damper DD may be disposed on the inlet side of the blower 20.
As a result, the temperature of the exhaust gas S1 is maintained at about 90 to 130 ° C., thereby preventing condensation of sulfur components in the mill 11 and the exhaust pipe, and preventing corrosion and clogging of the inside of the mill 11 and the exhaust pipe. However, the wood flour can be dried, for example, to a moisture content of about 1 to 8%, and conveyed by airflow, and can be finely pulverized to such an extent that sufficient combustion efficiency in the boiler 14 can be obtained.

  Here, the particle size and power of pulverization after pulverization when the air flow S7 for drying is sent and when it is not sent (Crushing Examples 1 and 2. Normal temperature air is blown into the mill 11 for drying). Table 1 shows the difference in basic unit (indicating the amount of energy required to obtain a unit weight of wood flour fuel). As wood chips before grinding, construction waste and forest thinning were used.

As is apparent from Table 1, when the drying airflow is not sent into the mill 11, the wood powder moisture after pulverization may become larger than the desired 1 to 8%, and the pulverization power unit increases.
On the other hand, when the airflow for drying is fed into the mill 11, the wood powder moisture after pulverization is in the range of 1 to 8% and the pulverization power basic unit can be reduced. Moreover, since the calorific value of wood powder becomes high by supplying the wood powder dried beforehand into the boiler 14, while being able to improve the combustion efficiency of the boiler 14, the usage-amount of fuel is also reduced as a result. Can do. Moreover, when sending the airflow for drying, wood powder with a small particle size can be obtained with small power. Further, the roller surface pressure can be reduced to the same level as when coal is pulverized by a mill.

  Further, since both the exhaust gases S3 ′ and S6 ′ have a low oxygen concentration, the oxygen concentration in the mill 11 can be kept low, thereby preventing ignition of wood powder in the mill 11. In addition, the control unit 30 controls the blower 13 'and the blower 20 so that the total supply amount of the exhaust gases S3' and S6 'is sufficient to discharge the wood powder from the mill 11 and transport it to the dust collector 12. Controls the branch damper DD at the exit.

The ratio of the exhaust gas S6 ′ introduced into the mill 11 to the exhaust gas S6 may be about 50 to 85% by volume, and the remainder is discharged into the atmosphere by the blower 13 ′. This numerical value varies based on the moisture content of the solid fuel supplied to the mill 11.
Further, instead of the dust collector 12 and the silo 12 ', as shown in FIG. 2, fine wood powder and coarse wood powder are classified, and only the classified fine wood powder is transported to the boiler 14 by the transport air current from the blower 13. A cyclone 23 can also be provided. In this case, as in FIG. 1, a part S6 ′ of the exhaust gas S6 from the cyclone 23 is sent to the transport pipe 21 and mixed with the exhaust gas S3 ′. Also in FIG. 2, the ratio of the exhaust gas S6 ′ to the exhaust gas S6 may be about 50 to 85% by volume, and the remainder is supplied to the boiler 14 by the blower 13 ′. In FIG. 2, by introducing the remaining gas into the boiler 14, a dust collector for discharging the cyclone exhaust gas into the atmosphere becomes unnecessary. In the configuration of FIG. 2, when the remaining gas is released to the atmosphere instead of being introduced into the boiler 14, a dust collector may be installed before being released to the atmosphere. In this case, the fine wood powder collected by the dust collector is supplied to the boiler 14 together with the coarse wood powder collected by the cyclone 23, for example, via the introduction pipe of the airflow S2 for conveyance. In such a configuration, since low-temperature exhaust gas is not introduced into the boiler 14, it is possible to prevent a decrease in thermal efficiency of the boiler 14.
The mill 11 is typically a vertical roller mill, but any type can be used as long as the solid fuel can be pulverized, such as a ball mill or a cutter mill.

Further, the pulverized fuel combustion apparatus of this embodiment includes a hopper 41 that stores wood chips as solid fuel, and a supply device 42 that supplies the wood chips from the hopper 41 to the mill 11. Specific examples of the supply device 42 include a table feeder, a circle feeder, and a conveyor.
Further, pressure sensors 43 and 44 for detecting the pressure between the exhaust gas S1 of the mill 11 and the exhaust gas S7 are provided, and a differential pressure Pd that is a difference between the pressures detected by the pressure sensors 43 and 44 is provided. And a control unit 45 for controlling the supply amount Sm of the wood chip per unit time by the supply device 42 based on the calculation result. Specifically, the control unit 45 performs control to reduce the supply amount Sm when the differential pressure Pd is large compared to when the differential pressure Pd is small.

When the differential pressure Pd is large, the amount of wood chips being crushed and dried in the mill 11 is increased, and it is expected that the pulverization efficiency is reduced. In such a case, the wood chip may not be sufficiently pulverized, which increases the possibility of variation in the particle size of the wood powder as the pulverized fuel, and the combustion efficiency in the boiler 14 may be deteriorated. is there. For this reason, when the differential pressure Pd increases, the wood chip supply speed to the mill 11 is decreased.
On the other hand, when the differential pressure Pd is small, the amount of wood chips being crushed and dried in the mill 11 is small, and the energy supplied to the mill 11 and the like is not effectively used for pulverization. For this reason, when the differential pressure Pd becomes small, the supply speed of the wood chip to the mill 11 is increased.

As described above, by controlling the supply speed of the solid fuel to the mill 11 based on the differential pressure Pd, it is possible to prevent the particle size of the pulverized fuel discharged from the mill 11 from being varied. 14 can increase the combustion efficiency and can achieve automatic stable operation of the entire combustion apparatus.
In addition, a magnetic separator, a non-ferrous material removing device, etc. are provided at the outlet of the hopper 41 so as to remove magnetic substances such as nails, wires, bolts, etc. and non-ferrous metal foreign substances such as aluminum compounds contained in the wood chip. May be. Further, it is preferable to install a vibrator or an air knocker in the hopper to prevent a so-called cross-linking phenomenon (clogging) and to smoothly supply the wood chips to the mill 11.
Further, the hopper 41 can be provided with an automatic metering device for checking the stock amount of the solid fuel in the hopper 41. By providing the automatic metering device, it is possible to verify the amount of solid fuel supplied to the mill 11 per unit time, which can contribute to further stable operation of the entire combustion device.
Further, when the exit of the hopper 41 has a cone shape, the cone angle is preferably 75 ° or more. Since storing wood chips in the hopper 41 for a long time causes a cross-linking phenomenon (clogging), it is desirable that the residence time in the hopper 41 is short (for example, 2 days or less).
When the moisture content of the wood chip is large, the introduction device to the hopper 41 or the mill 11 can be provided with a heating device. Thereby, the combustion efficiency in the boiler 14 can be further increased, and adhesion and blockage of the wood powder to the inside of the hopper 41 and the inner wall of the introduction pipe can be prevented. The heating device may be either indirect / direct heating. For example, a device in which the hopper 41 is provided with a jacket structure or a half pipe coil and a heating medium such as steam or heat transfer oil is passed.

  In addition, the pulverized fuel combustion apparatus of this embodiment includes a system for supplying pulverized coal to the boiler 14 separately from wood powder. This system includes a hopper 46 that stores pulverized coal generated by pulverizing brown coal or the like with a mill (not shown), and a blower 47 that feeds the pulverized coal to the boiler 14. The ratio of the wood powder and pulverized coal supplied to the boiler 14 can be appropriately changed within the range of 0 to 25% by weight for wood powder and 75% to less than 100% by weight for pulverized coal.

  FIG. 3 illustrates a second embodiment of the present invention. The same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. In the second embodiment, the pulverized coal discharged from the hopper 46 that stores the pulverized coal is mixed with the wood powder and stored in the silo 12 ′ that stores the wood powder. It differs from the first embodiment in that it is fed into the boiler 14 together with the wood powder. Others are the same as in the first embodiment. Instead of mixing wood powder and pulverized coal in the silo 12 ′, it is also possible to adopt a line blend system in which wood powder is blown into a transport pipe that feeds the pulverized coal to the boiler 14 and mixed.

  Next, a third embodiment of the present invention will be described with reference to FIG. In this embodiment, both wood chips and coal are mixed and stored in the hopper 41 at a weight ratio of 1: 9, for example, and this mixture is supplied to the mill 11 by the supply device 42. This is different from the second embodiment. Other points are the same as in the first and second embodiments.

  FIG. 5 illustrates a fourth embodiment of the present invention. In the above embodiment, as the drying airflow, a part S3 ′ of the low-oxygen concentration exhaust gas S3 exhausted from the ECO 14 ′ of the boiler 14 and a part S6 ′ of the exhaust gas S6 exhausted from the dust collector 12 The mixed gas S7 was introduced into the mill 11 via the blower 13 ', the branch damper DD at the outlet of the blower 20 and the transport pipe 21. In contrast to this, in the fourth embodiment, the transport pipe 21, the blower 20, and the like are not provided, but instead, a hot air generating furnace 22 that combusts fuel and generates an exhaust gas S8 having a low oxygen concentration is provided. An exhaust gas S9 generated by mixing the gas S8 with the exhaust gas S6 'is introduced into the mill 11 as a drying airflow. The hot air generating furnace 22 is configured to be able to adjust the temperature of the exhaust gas S8 to be generated, and the control unit 30 performs the adjustment based on a detection signal from the temperature sensor 31. The control unit 30 controls the hot air generating furnace 22 so that the temperature of the exhaust gas S1 from the mill 11 is about 90 to 130 ° C. Thereby, dew condensation of sulfur components at the outlet of the mill 11 can be prevented, and corrosion and clogging of the inside of the mill 11 and the exhaust pipe can be prevented.

In the pulverized fuel combustion apparatus of the above embodiment, the SO _x emission concentration, the NO _x emission concentration, the dust emission concentration when the co-firing rate of the wood powder to the pulverized coal is changed stepwise from 0 to 10% by weight, And the change of boiler efficiency was measured. The boiler used was a water tube type, with steam volume, steam pressure, and steam temperature of 160 tons / hour, 124 kg / cm ² G, and 505 ° C., respectively. The SO _x discharge concentration was measured according to JIS K 0103 (precipitation titration method), the NO _x discharge concentration was measured according to JIS K 0104 (phenol disulfonic acid absorptiometry), and the dust discharge concentration was measured according to JIS Z 8808 (circular filtration method). The results are shown in Table 2. Even when the wood powder mixed firing rate increased, the SO _x emission concentration and NO _x emission concentration decreased and the dust emission concentration was comparable compared to the case of pulverized coal combustion, that is, the wood powder mixed firing rate 0%. Thus, it has been demonstrated by the present invention that co-firing of woody biomass can be achieved on a commercial equipment scale. The amount of ash at the time of wood powder co-firing was also small compared to pulverized charcoal firing, that is, wood powder co-firing rate of 0% by weight.

The embodiment of the invention has been described above, but the present invention is not limited to this, and various design changes can be made without departing from the spirit of the present invention. For example, in the above embodiment, an example in which wood powder and pulverized coal are co-fired has been shown, but it is also possible to use biomass other than wood powder.
Further, as the drying airflow, not the gas from the ECO 14 ′ and the hot air generator 22, but an exhaust gas from another combustion device, for example, a preheater exhaust gas such as a cement kiln may be used. In this case, in order to remove dust and the like in the exhaust gas, it is preferable to pass a dust collector or a cyclone.

1 shows an overall configuration of a pulverized fuel combustion apparatus according to a first embodiment of the present invention. The modification of 1st Embodiment is shown. The whole structure of the pulverized fuel combustion apparatus which concerns on the 2nd Embodiment of this invention is shown. The whole structure of the pulverized fuel combustion apparatus which concerns on the 3rd Embodiment of this invention is shown. The whole structure of the pulverized fuel combustion apparatus which concerns on the 4th Embodiment of this invention is shown. The whole structure of the pulverized fuel combustion apparatus which concerns on a prior art is shown. The whole structure of the pulverized fuel combustion apparatus which concerns on a prior art is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Mill, 12 ... Dust collector, 12 '... Silo, 13, 13' ... Blower, 14 ... Boiler, 14 '... ECO, 145 ... Cyclone, 15 ... Air heater , 16 ... Blower, 17 ... Dust collector, 18 ... Desulfurization device, 19 ... Chimney, 20 ... Blower, 21 ... Conveying pipe, 22 ... Hot air generator, 23 ...・ Cyclone, 30 ... Control unit, 31 ... Temperature sensor, 41,46 ... Hopper, 42 ... Supply device, 47 ... Blower, 43,44 ... Pressure sensor, 45 ... -Control unit.

Claims (7)

A pulverizing and drying device for pulverizing wood fuel and drying it with an air flow for drying to generate wood powder fuel and discharging it together with the first exhaust gas;
A supply unit for supplying the wood fuel to the crushing and drying device;
A differential pressure measuring unit for measuring a difference between the pressure of the drying airflow and the pressure of the first exhaust gas;
A supply control unit that controls a supply amount of the wood fuel per unit time from the supply unit based on a measurement value of the differential pressure measurement unit;
A drying air flow introduction section for adjusting the temperature of the drying air flow so that the temperature of the first exhaust gas is within a predetermined range and introducing the drying air flow into the pulverization drying device ;
The wood powder fuel that collects the wood powder fuel transported by the first exhaust gas from the pulverization and drying device and discharges the second exhaust gas generated by removing the wood powder fuel from the first exhaust gas. A collection section;
A boiler for discharging the third exhaust gas by burning the wood powder fuel as a fuel;
With
The drying airflow introduction unit mixes the second exhaust gas and the third exhaust gas to generate a mixed gas, and introduces the mixed gas into the pulverization drying apparatus as the drying airflow. A pulverized fuel combustion apparatus. The pulverized fuel combustion apparatus according to claim 1 , further comprising a wood powder fuel storage section that stores the wood powder fuel collected by the wood powder fuel collection section.   The pulverized fuel combustion apparatus according to claim 1 or 2, wherein the supply unit that supplies the wood fuel to the pulverization / drying apparatus includes a heating device for heating the supply unit. A pulverizing and drying device for pulverizing wood fuel and drying it with an air flow for drying to generate wood powder fuel and discharging it together with the first exhaust gas;
A supply unit for supplying the wood fuel to the crushing and drying device;
A differential pressure measuring unit for measuring a difference between the pressure of the drying airflow and the pressure of the first exhaust gas;
A supply control unit that controls a supply amount of the wood fuel per unit time from the supply unit based on a measurement value of the differential pressure measurement unit;
A drying air flow introduction section for adjusting the temperature of the drying air flow so that the temperature of the first exhaust gas is within a predetermined range and introducing the drying air flow into the pulverization drying device;
With
Before bellflower supply unit, pulverized fuel combustion apparatus, characterized in that it comprises a heating device for heating the supply unit. The wood powder fuel that collects the wood powder fuel transported by the first exhaust gas from the pulverization and drying device and discharges the second exhaust gas generated by removing the wood powder fuel from the first exhaust gas. A collection section;
  A boiler for discharging the third exhaust gas by burning the wood powder fuel as a fuel;
A hot air generating furnace for generating a fourth exhaust gas,
  The drying air flow introduction unit mixes the second exhaust gas and the fourth exhaust gas to generate a mixed gas, and introduces the mixed gas into the pulverization drying apparatus as the drying air flow.
The pulverized fuel combustion apparatus according to claim 4. A pulverizing and drying step of pulverizing the wood fuel and drying it with an air flow for drying to produce a wood powder fuel and transporting it together with the first exhaust gas;
A differential pressure measuring step of measuring a difference between the pressure of the drying airflow and the pressure of the first exhaust gas;
A supply control step of controlling the supply amount of the wood fuel per unit time based on the measurement result of the differential pressure measurement step;
A temperature adjustment step of adjusting the temperature of the drying airflow so that the temperature of the first exhaust gas is a temperature within a predetermined range;
A step of collecting the wood powder fuel transported by the first exhaust gas and discharging a second exhaust gas generated by removing the wood powder fuel from the first exhaust gas;
A combustion step of burning the wood powder fuel and discharging a third exhaust gas;
With
The pulverized fuel combustion method , wherein the drying airflow is a mixture gas produced by mixing the second exhaust gas and the third exhaust gas . The pulverized fuel combustion method according to claim 6 , wherein the drying airflow is an inert gas having an oxygen concentration of 3 to 10%.

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