JP7205165B2 - Drying equipment for woody biomass raw materials - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for drying woody biomass raw materials containing water in obtaining woody biomass, and drying equipment used therefor.

In recent years, co-firing of coal and woody biomass (hereinafter sometimes simply referred to as co-firing of biomass) in coal-fired power generation has attracted attention. Wood such as branches, trunks, leaves, and other forest residue left over from felling and building wood, bark and sawdust generated at sawmills, house demolitions, pruned branches of roadside trees, etc. The woody biomass used has so-called carbon-neutral properties, so if it is used as fuel, carbon dioxide emissions can be suppressed, contributing to the prevention of global warming. In particular, under the feed-in tariff (FIT) system for natural energy (renewable energy) introduced in 2012, when calculating power generation efficiency, the energy amount of woody biomass is deducted from the amount of energy input, which serves as a standard. The use of biomass co-firing is also spreading.

When woody biomass is used as fuel, it must be sufficiently dried because the temperature inside the combustion furnace drops if the woody biomass contains a large amount of moisture. In other words, in order to increase the co-firing rate of woody biomass in biomass co-firing, it is important to reduce the moisture content of woody biomass.

Here, as a drying method for obtaining woody biomass, woody biomass raw materials containing moisture are charged into a rotating cylindrical body such as a kiln, hot air is supplied from the outside, and the inside of the rotating cylindrical body is dried by raking blades or the like. There is known a method of drying woody biomass raw materials by stirring them while scraping them up or dropping them (see Patent Document 1, for example). The method of using hot air in this way is advantageous in promoting drying by applying high-temperature air, and has been mainly used in Japan so far.

However, in order to obtain hot air, a boiler or the like is required. In addition, since the temperature of the hot air reaches at least 200 to 300°C, there is a risk that the woody biomass will spontaneously ignite during drying. The danger of ignition must be eliminated by, for example, providing Furthermore, since the high-temperature exhaust gas discharged from the rotating cylinder contains high-concentration moisture, it is necessary to take countermeasures against dew condensation, such as diluting the gas by supplying it separately. Therefore, the method using hot air results in an increase in the size of equipment and an increase in cost.

On the other hand, as a method of using warm air with a relatively low temperature, for example, warm air obtained by heating the air sucked (introduced) from the atmosphere is used in a storage hopper containing a conveyor loaded with woody biomass raw materials. A method is known in which woody biomass raw materials on a conveyor are dried by supplying from the bottom (see Patent Document 2). Since such a method uses hot air of about 50° C., it is possible to reduce the fuel cost compared to the method using hot air. In addition, since low-temperature warm air is used in the first place, the risk of spontaneous ignition of woody biomass can be suppressed (in the method of Patent Document 2, when the temperature in the storage hopper exceeds a predetermined set temperature, Furthermore, the warm air in the storage hopper is dissipated into the atmosphere).

JP 2016-090120 A JP 2016-80217 A

The method of drying woody biomass raw materials using hot air is inferior to the method using hot air in drying efficiency, but it can reduce equipment and costs and reduce the risk of spontaneous combustion.

However, since the air is used to obtain warm air, it is affected by the temperature of the air (hereinafter referred to as air temperature or outside air temperature). In other words, when the temperature drops, the flow rate of the heat medium for obtaining warm air and the amount of fuel required to secure the amount of heat increase accordingly. In addition, in order to keep the drying throughput constant, it is necessary to increase the size of the equipment to cope with low temperatures. This effect is particularly noticeable in places and regions where there is a large temperature difference between summer and winter. will end up owning excessive equipment.

Therefore, the present inventors have made intensive studies on methods for suppressing the influence of air temperature when drying woody biomass raw materials using hot air. It has been found to be effective to use For example, the temperature of groundwater is relatively constant throughout the year with relatively little fluctuation. By obtaining warm air after preheating by heat exchange, the above-described problems can be solved, so the present invention was completed.

Therefore, the object of the present invention is to eliminate the influence of temperature changes due to seasonal factors, to be able to always use equipment, fuel, etc. commensurate with the amount of drying treatment, and to provide a total and efficient woody biomass raw material. To provide a method for drying a woody biomass raw material capable of drying a woody biomass raw material.
Another object of the present invention is to provide a woody biomass raw material drying facility that can use the above method.

That is, the present invention is a method for drying a woody biomass raw material by using hot air obtained by heating air introduced from the atmosphere to a temperature below the boiling point of water, wherein the woody biomass raw material is dried,
The heating includes preheating of the introduced air by heat exchange with preheating water having a temperature higher than the outside air temperature, and main heating by heat exchange of the preheated preheated air with a high-temperature heat source. A method for drying a woody biomass raw material, characterized by

Further, the present invention includes an introduced air heating device for heating the introduced air introduced from the atmosphere to a temperature below the boiling point of water to obtain warm air, and a drying device main body for drying the woody biomass raw material using the warm air. A drying facility for woody biomass raw materials having
The introduced air warming device includes a first heat exchanger for preheating the introduced air by exchanging heat between the introduced air and preheating water having a temperature higher than the outside air temperature; A drying facility for woody biomass raw materials, characterized by comprising a second heat exchanger for performing heat exchange between heated air and a heat medium that has absorbed heat from a high-temperature heat source for main heating to obtain warm air. is.

In the present invention, when drying a woody biomass raw material using warm air obtained by heating introduced air introduced from the atmosphere to a temperature below the boiling point of water, the introduced air is preheated with preheating water having a temperature higher than the outside air temperature. After heating, the obtained preheated air is heat-exchanged with a high-temperature heat source having a temperature higher than that of the preheating water, and main heating is performed to obtain warm air. In this way, in order to obtain warm air for drying the woody biomass raw material, the heating of the introduced air introduced from the atmosphere is divided into preheating and main heating, so that the introduced air is directly heat-exchanged with the high-temperature heat source. Energy for obtaining warm air can be reduced compared with the case. In particular, when relatively low-temperature warm air is used as in the present invention, when the temperature of the atmosphere drops, the flow rate of the heat medium such as hot water required to obtain the warm air is affected by the temperature drop. We have to increase the amount of fuel to secure that amount of heat, which means using extra high-temperature heat sources. In the summer when the temperature is high, the specifications are excessive, but by preheating the introduced air using preheating water as in the present invention, the influence of temperature changes due to seasonal factors can be eliminated. These variable costs and fixed costs can be reduced.

In the present invention, preferably, the temperature of the introduced air introduced from the atmosphere and the temperature of the preheating water are compared, and if the temperature of the introduced air is lower than the temperature of the preheating water, heat exchange with the preheating water It is advisable to preheat the incoming air. For example, groundwater has little temperature fluctuation and is relatively constant. It is preferable to preheat the introduced air by heat exchange of . Underground water here also includes hot spring water. This kind of groundwater was mentioned as an example of preheating water, which is advantageous in that it has little temperature fluctuation between day and night and water temperature throughout the year. can do. Thermal wastewater discharged from factories, power plants, waste incineration plants, etc. (hereinafter referred to as "thermal wastewater from factories") is similar to groundwater in that the water temperature is higher than the outside air temperature and the temperature fluctuations are relatively small. In addition to water and tap water, these can be used as preheating water. If the temperature of the introduced air is the same as or higher than the temperature of the preheating water, such as when the temperature of the air is higher than the temperature of the groundwater in the summer, preheating should be bypassed. Therefore, heat exchange between the introduced air and the preheating water should be avoided.

In the present invention, the temperature of the hot air for drying the woody biomass raw material can be set to the boiling point or lower of water, which is about the same as the temperature generally employed in the hot air drying method, preferably 60° C. or higher and 95° C. °C or less. In addition, regarding the main heating for obtaining such hot air, the means is not particularly limited as long as it is heat exchange with a high-temperature heat source that can obtain hot air at the above temperature. The preheated air may be heated by exchanging heat with a heat medium such as hot water or steam that absorbs heat. Also, instead of burning fuel in a boiler or the like, waste heat generated in other facilities may be used.

In utilizing the woody biomass raw material drying method of the present invention, the device to be used is not particularly limited. A drying facility having a heating device and a drying device body for drying the woody biomass raw material using the obtained warm air. A first heat exchanger that preheats the introduced air by exchanging heat with preheating water having a temperature higher than the air temperature, and a high-temperature heat source having a temperature higher than the preheated preheating air and the preheating water. It is preferable to provide a second heat exchanger that performs heat exchange with the heat medium that has absorbed the heat for main heating.

There are no particular restrictions on the main body of the drying device that dries the woody biomass raw material using the warm air obtained by the introduced air warming device. The woody biomass raw material is loaded on the conveying belt of a conveyer equipped with a ventilation rotary drying device that dries by blowing warm air while drying, or an endless conveying belt having air permeability. A band-type dryer that dries by blowing hot air upward or downward at right angles to the thickness direction of the raw material bed, and a fluidized-bed dryer that dries by vigorously mixing the woody biomass raw material and warm air in the fluidized bed. Among them, a band-type drying apparatus is preferable. In that case, for example, in the introduced air heating device, the first heat exchanger and the second heat exchanger are arranged in this order along the flow of the introduced air introduced from the atmosphere. ), and the warm air obtained by the second heat exchanger is blown in the thickness direction of the raw material layer made of woody biomass raw material loaded on the conveyor belt of the band-type drying device. good. In this way, by blowing hot air from above or below the raw material layer made of woody biomass raw material in the thickness direction, the hot air is blown in parallel with the raw material layer (the warm air is blown in parallel with the moving direction of the conveyor). ), the drying time can be shortened. This also allows the size of the drying equipment to be reduced.

Further, the introduced air heating device of the present invention preferably further comprises a thermometer for measuring the temperature of the introduced air introduced from the atmosphere and a water temperature gauge for measuring the temperature of the preheating water. good. Furthermore, by utilizing these, when the temperature of the introduced air is lower than the temperature of the preheating water, the preheating water is supplied to the first heat exchanger to preheat the introduced air, and the obtained preheating A preheating control mechanism that directs the heated air to the second heat exchanger may be provided at the same time. At that time, considering the efficiency of preheating by these heat exchanges, preheating water is supplied to the first heat exchanger when the difference between the temperature of the preheating water and the temperature of the introduced air exceeds a predetermined value. It is also possible to preheat the introduced air. On the other hand, when the temperature of the introduced air is the same as or higher than the temperature of the preheating water, the supply of the preheating water to the first heat exchanger is cut off to preheat the introduced air. Alternatively, the introduced air may bypass the first heat exchanger and be led directly to the second heat exchanger.

In the present invention, the degree of drying when drying the woody biomass raw material is not particularly limited. However, for example, when used for biomass co-firing, it is common to dry the woody biomass so that the moisture content of the dried woody biomass is about 15 to 35% (wet basis). In addition, it is difficult to specify the moisture content of the woody biomass raw material that is the target of the drying process. Although it varies depending on the type of woody biomass raw material and storage method, it is generally about 40 to 60% (wet basis). It can be said that

According to the present invention, since it is possible to obtain warm air while eliminating the influence of temperature changes, it is possible to use equipment, fuel, etc. that are commensurate with the processing amount of the woody biomass raw material to be dried, resulting in high efficiency. It becomes possible to dry woody biomass raw materials well.

FIG. 1 is a schematic explanatory diagram showing the drying equipment of the present invention. FIG. 2 shows the data of annual transition of temperature in a certain area (Ofunato City) in 2017. FIG. 3 is data showing the amount of circulating hot water when a woody biomass raw material is dried using a conventional drying method. FIG. 4 is data showing the temperature of air after preheating when using the drying method according to the embodiment of the present invention. FIG. 5 is data showing the amount of circulating hot water when a woody biomass raw material is dried using the drying method of the present invention.

Embodiments embodying the present invention will be described below with reference to the attached drawings. In FIG. 1, a case where a band-type drying device is adopted as a drying device main body will be described, but this is an example and the present invention is not limited to the following contents.
FIG. 1 shows an example of a drying facility X used in the method for drying woody biomass raw materials of the present invention. This drying equipment X consists of an introduced air heating device X1 that heats the introduced air introduced from the atmosphere to a temperature below the boiling point of water to obtain warm air, and a band-type device that dries the woody biomass raw material using the warm air. It has a drying device main body X2 and dries the woody biomass raw material 2 conveyed by the conveyor 1 with warm air 8. - 特許庁In this example, the introduced air heating device X1 performs heat exchange between the introduced air 3 introduced from the atmosphere and the groundwater (preheating water) 4 pumped up from the underground, thereby preheating the introduced air 3. Heat exchange is performed between the heat exchanger 5 and the preheated air 6 preheated thereby and the heat medium (hot water in this example) 7 that has absorbed the heat of the high-temperature heat source whose temperature is higher than that of the ground water 4, thereby preheating. and a second heat exchanger 9 for pre-heating the air 6 to obtain warm air 8 having a predetermined temperature.

The band-type drying device main body X2 in the drying equipment X includes a conveyor chamber 10 in which a conveyor 1 is accommodated and the woody biomass raw material 2 is dried. It has a two-story structure with a heat exchanger room 11 in which the heat exchanger 5 and the second heat exchanger 9 are accommodated. are partitioned by a metal floor material 12 having air permeability such as grating. In the conveyor room 10 on the first floor, an exhaust duct 14 having a plurality of suction ports 13 is provided on the floor surface on the lower side of the conveyor 1, and an exhaust blower 15 is connected to the exhaust duct 14 outside the room. there is On the other hand, a plurality of outside air intakes (not shown) are provided above the side wall (ceiling side) of the heat exchanger room 11 on the second floor. Air is introduced from the side wall of the chamber 11, and the introduced air 3 taken into the heat exchanger room 11 passes through the air-permeable floor material 12, is supplied to the conveyor room 10 on the first floor, and is finally exhausted. The air is exhausted to the outside through the duct 14 .

Meanwhile, in the heat exchanger room 11 on the second floor, the first heat exchanger 5 and the second heat exchanger 9 are sequentially arranged along the flow of the introduced air 3. Hot air 8 is supplied to the chamber 10 . Moreover, since the suction port 13 leading to the exhaust duct 14 is provided on the floor surface below the conveyor 1, the hot air 8 is blown from above the raw material layer 2a composed of the woody biomass raw material 2 on the conveyor 1, It exits below the raw material layer 2a. That is, the conveyor 1 has an endless permeable conveying belt attached to belt rollers. During this time, hot air 8 is blown in the thickness direction of the raw material layer 2a to dry it. A raw material input port (not shown) is provided in the conveyor room 10 on the first floor, and the woody biomass raw material 2 containing moisture is supplied to the conveyor 1 . Further, on the downstream side of the conveyor 1 opposite to the raw material inlet, the dried woody biomass 16 from which moisture has been removed is recovered.

The first heat exchanger 5 is supplied with groundwater 4 pumped up from underground by a pump 17, and treated as waste water after heat exchange with the introduced air 3 introduced from the atmosphere. Hot water 7 obtained by a boiler 18 as a high-temperature heat source is supplied to the second heat exchanger 9 . The hot water 7 circulates between the boiler 18 and the second heat exchanger 9, and after heat exchange with the preheated preheated air 6, the heat is absorbed again by the boiler 18 and used.

The drying equipment X also includes a thermometer 19 for measuring the temperature of the air 3 introduced from the atmosphere in the heat exchanger room 11 on the second floor, and a water temperature gauge for measuring the temperature of the groundwater 4 pumped from the underground by the pump 17. 20. Therefore, considering the efficiency for obtaining warm air 8 by the preheating control mechanism using these, the temperature T1 of the introduced air 3 is lower than the temperature T2 of the groundwater 4 (T2>T1), or When the difference between the temperature T2 of the groundwater 4 and the temperature T1 of the introduced air 3 exceeds the set temperature X (T2-T1>X), the shutoff valve 21 provided in the pipe connected to the first heat exchanger 5 may be opened to supply groundwater 4 to the first heat exchanger 5 . That is, when the temperature T1 of the introduced air 3 is equal to or higher than the temperature T2 of the groundwater 4 (T1≧T2), or the difference between the temperature T2 of the groundwater 4 and the temperature T1 of the air 3 is equal to or lower than the set temperature X (X≧ During T2-T1), the shut-off valve 21 may be closed so that the groundwater 4 may not be supplied to the first heat exchanger 5 and may be bypassed by returning to the drain side.

Figure 2 shows data on the yearly changes in temperature in Ofunato City in 2017. It can be seen that the temperature fluctuates greatly depending on the season, from over 30°C in the summer to -5°C or less in the winter. .
Here, assuming a case where 7.5 ton-wet/hr of woody biomass raw material with a moisture content of 50% is dried to a moisture content of 25%, the drying apparatus X shown in FIG. Using the temperature data of FIG. 2 as the temperature of the air 3 introduced from the atmosphere, the woody biomass raw material was dried while heat-exchanging the air 3 with the second heat exchanger 9 to obtain warm air 8. FIG. 3 shows the result of calculation of the circulating water volume of the hot water 7 at that time. At this time, the temperature of the hot water 7 supplied to the second heat exchanger 9 was set to 80°C on the inlet side, and the temperature of the hot water 7 on the outlet side was set to 60°C, so that the warm air 8 of 72°C was obtained. .

As described above, according to the results of FIG. 3, which corresponds to the comparative example of the present invention, the amount of circulating hot water 7 supplied to the second heat exchanger 9 is about 150 tons/hr in winter, and 160 tons/hr at the maximum. /hr. In addition, the maximum amount of fuel required for combustion in the boiler 18 at this time is about 2.7 ton-wet/hr in winter. On the other hand, the amount of circulating hot water 7 in summer is about 80 to 90 ton/hr, and the fuel for the boiler 18 is about 1.3 to 1.5 ton-wet/hr. That is, when hot air 8 is obtained from air 3 introduced from the atmosphere, the amount of circulating hot water 7 supplied to the heat exchanger varies greatly from 80 to 160 tons/hr depending on the season.

On the other hand, using the drying equipment X shown in FIG. 1, the above woody biomass raw material was dried by the method according to the present invention, and the results are as follows. Here, the temperature of the groundwater 4 pumped up from the ground is assumed to be the same as the average temperature of Ofunato City in 2017, 11.6° C., as shown in FIG. Also, in the first heat exchanger 5, it is assumed that the heat exchange between the air 3 introduced from the atmosphere and the groundwater 4 is in an ideal state (both the heat exchange performance and the amount of groundwater are infinite). ), the preheated air 6 after preheating matches the water temperature of the groundwater 4 (preheated to 11.6° C.). However, the heat exchange between the introduced air 3 and the groundwater 4 is performed when the temperature T1 of the introduced air 3 is lower than the temperature T2 of the groundwater 4, and when the temperature T1 of the introduced air 3 is equal to or higher than the temperature T2 of the groundwater 4. No heat exchange was performed. Others are the same as in the previous comparative example, and calculations are made on the same assumptions as in the comparative example.

FIG. 4 shows the temperature of the preheated air 6 after being heat-exchanged in the first heat exchanger 5 . FIG. 5 shows results corresponding to the examples of the present invention, which are calculation results of the circulating water volume of the hot water 7 when the woody biomass raw material was dried as described in the comparative example. there is As can be seen from FIG. 5, seasonal variations in the amount of circulating hot water 7 supplied to the second heat exchanger 9 are suppressed compared to the case of the comparative example (FIG. 3). That is, the amount of circulating water in winter is about 120 tons/hr, and it can be lowered to about 125 tons/hr at maximum. Also, the fuel required for combustion in the boiler 18 can be suppressed to a maximum of about 2.0 ton-wet/hr in winter.

That is, according to the present invention, when hot air for drying the woody biomass raw material is obtained, the flow rate of the heat medium used for the main heating and the fuel required to secure the heat amount can be reduced. Since it is possible to suppress the influence of , the size of the drying equipment can be reduced to match the throughput.

X: Drying equipment, X1: Introduced air heating device, X2: Drying device main body, 1: Conveyor, 2: Woody biomass raw material, 2a: Raw material layer, 3: Introduced air, 4: Underground water, 5: First heat exchange device, 6: preheated air, 7: hot water, 8: hot air, 9: second heat exchanger, 10: conveyor chamber, 11: heat exchanger chamber, 12: floor material, 13: suction port, 14: Exhaust duct, 15: Exhaust blower, 16: Woody biomass (after drying), 17: Pump, 18: Boiler, 19: Thermometer, 20: Water temperature gauge, 21: Shutoff valve.

Claims (2)

Drying of woody biomass raw materials, comprising an introduced air heating device for heating air introduced from the atmosphere to a temperature below the boiling point of water to obtain warm air, and a drying device main body for drying the woody biomass raw materials using the warm air. equipment,
The introduced air warming device includes a first heat exchanger for preheating the introduced air by exchanging heat between the introduced air and preheating water having a temperature higher than the outside air temperature; A second heat exchanger for main heating by exchanging heat between heated air and a heat medium that has absorbed heat from a high-temperature heat source, a thermometer for measuring the temperature of the introduced air, and the temperature of the preheating water. and a water temperature gauge that measures
When the temperature of the introduced air is lower than the temperature of the preheating water, the preheating water is supplied to the first heat exchanger to preheat the introduced air, and the obtained preheated air is transferred to the first heat exchanger. 2, and when the temperature of the introduced air is the same as or higher than the temperature of the preheating water, cut off the supply of the preheating water to the first heat exchanger. Then, the introduced air is passed through the first heat exchanger and guided to the second heat exchanger without being preheated, or the introduced air is bypassed the first heat exchanger. A drying facility for woody biomass raw materials, characterized by comprising a preheating control mechanism that directly leads to the second heat exchanger to obtain warm air. The drying apparatus main body is a band-type drying apparatus having a conveyor provided with an endless air-permeable conveying belt, and the thickness direction of the raw material layer made of the woody biomass raw material loaded on the conveying belt 2. Drying equipment for woody biomass material according to claim 1 , characterized in that the warm air obtained by said introduced air heating device is passed through for drying.

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