JP2006064260A - Drying method and drying equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a drying method and drying equipment capable of stably and properly drying a dried object so that the dried object has prescribed moisture content after drying, even when the moisture content of the dried object before drying is rapidly changed, in the drying method for drying the dried object by feeding hot air to a drier from a hot air generator. <P>SOLUTION: A temperature of exhaust gas at an outlet of a drier is measured, a flow rate of hot air fed to the drier 2 is controlled by adjusting the quantity of exhaust gas returned to a hot air generator 2 so that the measured temperature becomes equal to prescribed target temperature, and further a temperature of hot air at an inlet of the drier 2 is controlled by adjusting the quantity of fuel supplied to the hot air generator 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a drying method and a drying facility for drying an object to be dried such as waste to a predetermined moisture content.

  A process for producing solid waste fuel (RDF) from waste, a process for producing compost from waste, and the like usually include a step of drying waste and the like.

  In this drying process, fuel such as propane, natural gas, kerosene, or heavy oil and combustion air are supplied to a hot-air generator to generate hot air, and the hot air is blown to the waste (to-be-dried) in the dryer for heating. In many cases, the drying equipment is used. At that time, the supplied hot air is discharged as exhaust gas, and a part thereof is returned to the hot air generating furnace through the circulation bypass. The temperature of the hot air generated in the hot air generator is quite high, and if it comes into contact with waste, it may ignite, so it was generated in the hot air generator by returning a part of the exhaust gas to the hot air generator again. This is to reduce the temperature of the hot air to an appropriate temperature. Further, it is possible to minimize the amount of exhaust gas having waste heat to the outside of the system.

  In the drying process as described above, it is important to dry the material to be dried so as to have a predetermined moisture content in order to stably obtain a solid waste fuel of good quality in the subsequent process. However, since the types of objects to be dried are not uniform, it is difficult to make the objects to be dried have a predetermined moisture content only by blowing hot air with a constant air volume at a constant temperature. Accordingly, the following techniques have been proposed as techniques for controlling the moisture content of the material to be dried to a predetermined value in the drying process.

  For example, a technique is disclosed in which the moisture content and weight of a material to be dried before drying are measured and the supply amount of the material to be dried to the dryer is adjusted so that the amount of water evaporated in the dryer is constant. (For example, refer to Patent Document 1).

  In addition, the temperature of the hot air dryer inlet is measured and the amount of exhaust gas returned to the hot air generator is adjusted so that the temperature is constant, and the hot air dryer outlet temperature and the exhaust gas humidity from the dryer are adjusted. And a technique for increasing or decreasing the amount of oil supplied to the hot air generator based on the measurement result is disclosed (for example, see Patent Document 2).

Moreover, the technique of measuring the moisture content of to-be-dried material after drying etc. and controlling the dryer inlet temperature or flow volume of a hot air based on the measurement result is disclosed (for example, refer patent document 3). .
Japanese Patent Laid-Open No. 08-086569 JP 2001-272170 A JP 2002-303489 A

  However, in the technique described in Patent Document 1, the supply amount of the material to be dried to the dryer is adjusted according to the water content of the material to be dried before drying, but the water content of the material to be dried before drying. If the change in temperature is drastic, it is difficult to adjust the moisture content of the dried product by simply adjusting the supply amount of the dried product, and the dried product that is easy to dry is excessively dried before leaving the dryer. In some cases, the object to be ignited or the object to be dried that is difficult to dry leaves the dryer without being dried. In addition, since the amount of material to be dried supplied to the next process varies, the entire operation becomes unstable.

  In the technique described in Patent Document 2, the amount of exhaust gas returned to the hot air generator is adjusted so that the temperature of the hot air at the dryer inlet becomes constant, or the temperature and humidity of the exhaust gas at the dryer outlet are adjusted. The temperature of hot air is controlled by increasing / decreasing the amount of oil supplied to the hot air generator based on this, but when the moisture content of the material to be dried before drying is drastic, the inlet temperature of the hot air dryer is controlled. It is difficult to make the material to be dried after drying only have a predetermined moisture content. As a result, the material to be dried that is easy to dry may be excessively dried before leaving the dryer and catch fire, or the material to be dried that is difficult to dry may leave the dryer without being dried.

  Further, in the technique described in Patent Document 3, the temperature or flow rate of the hot air at the dryer inlet is controlled based on the moisture content of the object to be dried such as after drying. When the moisture content changes drastically, it is difficult to set the material to be dried after drying to a predetermined moisture content only by controlling either the dryer inlet temperature or the flow rate of hot air. Moreover, after measuring the moisture content of the to-be-dried material after drying, control timing will be overdue. As a result, the material to be dried that is easy to dry may be excessively dried before leaving the dryer and catch fire, or the material to be dried that is difficult to dry may leave the dryer without being dried.

  The present invention has been made in view of the above circumstances, and in a drying method in which hot air is sent from a hot air generator to a dryer to dry the material to be dried, the moisture content of the material to be dried before drying is drastic. Even in such a case, an object is to provide a drying method and a drying facility capable of stably and appropriately drying the dried material after drying so as to have a predetermined moisture content.

  In order to solve the above problems, the present invention has the following features.

  [1] A drying method in which hot air is sent from a hot air generator to a dryer to dry the material to be dried, and a part of the exhaust gas from the dryer is returned to the hot air generator, the exhaust gas temperature at the outlet of the dryer A drying method characterized by controlling the moisture content of an object to be dried after drying by adjusting both the amount of exhaust gas to be returned to the hot air generator and the hot air temperature at the dryer inlet.

  [2] When the exhaust gas temperature at the dryer outlet is lower than a predetermined target temperature, the amount of exhaust gas to be returned to the hot air generator is increased, the hot air temperature at the dryer inlet is increased, and the exhaust gas temperature at the dryer outlet is increased. When the temperature is higher than a predetermined target temperature, the amount of exhaust gas returned to the hot air generator is decreased and the hot air temperature at the dryer inlet is lowered.

  [3] A hot air generator for generating hot air, a dryer for drying an object to be dried by the hot air sent from the hot air generator, and an exhaust gas circulation means for returning a part of the exhaust gas from the dryer to the hot air generator. An exhaust gas temperature measuring means for measuring the exhaust gas temperature at the outlet of the dryer, the amount of exhaust gas returned to the hot air generator according to the exhaust gas temperature measured by the exhaust gas temperature measuring means, and the dryer inlet And a moisture content control means for controlling the moisture content of the material to be dried after drying by adjusting the hot air temperature in the drying apparatus.

  [4] When the exhaust gas measurement temperature at the dryer outlet is lower than a predetermined target temperature, the moisture content control means increases the amount of exhaust gas returned to the hot air generator and increases the hot air temperature at the dryer inlet. When the exhaust gas measurement temperature at the dryer outlet is higher than a predetermined target temperature, it is a control means for reducing the amount of exhaust gas returned to the hot air generator and lowering the hot air temperature at the dryer inlet. The drying facility according to [3], which is characterized in that

  In the present invention, the amount of exhaust gas returned to the hot air generator is adjusted so that the exhaust gas measurement temperature becomes a predetermined target temperature, the flow of hot air fed into the dryer is increased and decreased, and the hot air temperature at the dryer inlet is adjusted. Therefore, even when the moisture content of the object to be dried before drying is severe, the object to be dried after drying has a predetermined content as compared with the method of simply adjusting either the hot air flow rate or the hot air temperature. It can be stably and appropriately dried so as to have a moisture content.

  As an embodiment of the present invention, a case where the present invention is applied when producing solid waste fuel (RDF) from waste will be described as an example.

  FIG. 1 is a block diagram showing an embodiment of the present invention. As shown in FIG. 1, the drying facility in this embodiment includes a storage hopper 1 for storing waste before drying, a hot air generator 2 for generating hot air, and a predetermined peripheral speed (20 to 40 m). / Min), a dryer 3 that dries waste by hot air (400 to 550 ° C.) from the hot air generator 2, a dust collector 4 that collects dust from the exhaust gas of the dryer 3, and a dust collector 4 A deodorizing furnace 5 for deodorizing the exhaust gas that has passed through the exhaust gas, a first heat exchanger 6 for exchanging heat between the exhaust gas that has passed through the dust collector 4 and the exhaust gas (about 800 ° C.) from the deodorizing furnace 5, and a first heat exchange A second heat exchanger 7 for exchanging heat between the exhaust gas that has passed through the vessel 6 and room temperature air at normal temperature, an exhaust gas treatment device 8 for detoxifying the exhaust gas that has passed through the second heat exchanger 7, and an exhaust gas treatment The second is the exhaust gas detoxified by the equipment 8 The exhaust gas in the proper temperature without generating white smoke by mixing hall air passing through the exchanger 7 and an exhaust pipe 9 for discharging to the atmosphere.

  Further, a supply fan 11 for supplying combustion air to the hot air generator 2, an oil amount adjusting damper 16 for adjusting the amount of fuel supplied to the hot air generator 2, and the exhaust gas of the dryer 3 are circulated. The circulation fan 12 for returning a part of the exhaust gas to the hot air generator 2, the circulation fan inlet damper 17 provided at the inlet of the circulation fan 12, and the exhaust gas (300 to 400 ° C.) returning to the hot air generator 2 A return damper 18 for adjusting the amount of air, an air supply fan 13 for sending in-field air to the second heat exchanger 7, and an exhaust fan 14 for discharging exhaust gas from the exhaust tube 9 to the atmosphere. Yes.

  Further, a cutting device 21 for cutting out a predetermined amount of waste from the storage hopper 1, a supply conveyor 22 for supplying the waste cut by the cutting device 21 to the dryer 3, and drying by the dryer 3 And a discharge conveyor 23 for discharging the waste generated from the dryer 3.

  Then, a weigh scale 31 for measuring the weight of the waste on the supply conveyor 22 and a cutting device so that the amount of waste supplied to the dryer 3 becomes a predetermined amount based on the measurement result of the weigh scale 31 21, an inlet thermometer 33 that measures hot air temperature at the inlet of the dryer 3, an outlet thermometer 34 that measures exhaust gas temperature at the outlet of the dryer 3, and an outlet thermometer 34 Based on the measurement result, the amount of exhaust gas that is returned to the hot air generator 2 by adjusting the opening of the return damper 18 so that the exhaust gas temperature at the outlet of the dryer 3 becomes a predetermined target temperature (here 130 ° C.). The exhaust gas temperature control device 35 that controls the amount of fuel supplied to the hot air generator 2 by adjusting the opening of the oil amount adjusting damper 16 and the pressure gauge 36 that measures the internal pressure of the dryer 3 And based on the measurement result of the pressure gauge 36, Circulation fan so that the internal pressure of the dryer 3 is set to a predetermined negative pressure state (-100 to -50 Pa) and the wind speed inside the dryer 3 is set to a predetermined speed (1.5 to 2.5 m / s). An internal pressure control device 37 for adjusting the opening degree of the inlet damper 17 and the rotational speed of the circulation fan 12 and a moisture meter 38 for checking the moisture content of the waste discharged from the dryer 3 are provided. .

  A procedure for drying the waste to have a predetermined moisture content (here, 5%) using the drying equipment configured as described above will be described below.

  Waste that has been cut out from the storage hopper 1 by the cut-out control device 32 is supplied to the dryer 3 by the supply conveyor 22. The waste supplied to the dryer 3 is dried by hot air of 400 to 550 ° C. sent from the hot air generator 2 and taken out by the discharge conveyor 23.

  On the other hand, the exhaust gas from the dryer 3 is sent to the first heat exchanger 6 via the dust collector 4, and after exchanging heat with the exhaust gas from the deodorizing furnace 5, some hot air is generated via the return damper 18. The remainder is returned to the machine 2, and the remainder is discharged from the exhaust tube 9 to the atmosphere via the deodorizing furnace 5, the first heat exchanger 6, the second heat exchanger 7, and the exhaust gas treatment device 8.

  At that time, the internal pressure control device 37 sets the internal pressure of the dryer 3 to a predetermined negative pressure state (−100 to −50 Pa) based on the measurement result of the pressure gauge 36, and the wind speed inside the dryer 3 is increased. The opening degree of the circulation fan inlet damper 17 and the rotation speed of the circulation fan 12 are adjusted so that a predetermined speed (1.5 to 2.5 m / s) is obtained.

  Then, the exhaust gas temperature control device 35 adjusts the opening degree of the return damper 18 based on the measurement result of the outlet thermometer 34 so that the exhaust gas temperature at the outlet of the dryer 3 becomes a predetermined target temperature (130 ° C.). Then, the amount of exhaust gas returned to the hot air generator 2 is controlled, and the amount of fuel supplied to the hot air generator 2 is controlled by adjusting the opening of the oil amount adjusting damper 16. Thereby, the flow rate and temperature of the hot air sent to the dryer 3 are controlled simultaneously.

  The detailed control method at that time is shown below.

  First, FIG. 2 is obtained by temperature calculation. In the above-described drying facility, the horizontal axis represents the amount of evaporation generated when the waste having different moisture content before drying is dried to a predetermined moisture content (5%). In addition, the amount of exhaust gas to be returned to the hot air generator 2 (circulated exhaust gas) required when the exhaust gas temperature at the outlet of the dryer 3 at that time (dryer outlet exhaust gas temperature) is set to a predetermined temperature (130 ° C.). Amount) and hot air temperature at the inlet of the dryer 3 (dryer inlet hot air temperature) on the vertical axis. Thus, it is understood that when the waste having a high moisture content before drying and a large evaporation amount is dried, it is necessary to raise both the circulating exhaust gas amount and the dryer inlet hot air temperature.

  Next, in FIG. 3, the hot air temperature at the inlet of the dryer in FIG. 2 is plotted on the vertical axis, the amount of circulating exhaust gas is plotted on the horizontal axis, and the opening of the return damper 18 for obtaining the amount of circulating exhaust gas is plotted along the horizontal axis. Show things.

And, for example, when the amount of circulating exhaust gas when drying waste with a standard moisture content before drying is 530 m ³ / min (return damper opening 50%) and the dryer hot air temperature is 475 ° C. If the exhaust gas temperature at the outlet of the dryer is lower than 130 ° C., it means that the waste water content before drying is higher than the standard. Therefore, based on FIG. 3, for example, the return damper opening degree is set to 60%. By increasing the amount of exhaust gas to 565 m ³ / min and increasing the amount of fuel oil supplied to the hot air generator 2 while measuring with the inlet thermometer 33 so that the hot air temperature at the inlet of the hot air generator is 485 ° C. Control the exhaust gas temperature at the outlet of the dryer to 130 ° C. On the contrary, if the exhaust gas temperature at the outlet of the dryer is higher than 130 ° C., it means that the waste water content before drying is lower than the standard waste. Therefore, based on FIG. 3, for example, the return damper opening is set to 40%. The amount of fuel supplied to the hot air generator 2 is reduced while the circulating exhaust gas amount is reduced to 495 m ³ / min and the temperature at the inlet of the dryer is measured at the inlet thermometer 33 so that the temperature is 465 ° C. The exhaust gas temperature at the outlet of the dryer is controlled to 130 ° C. As a result, the supplied waste is appropriately dried, and the waste dried to a predetermined moisture content (5%) is taken out from the dryer 3.

  As described above, in this embodiment, the amount of exhaust gas returned to the hot air generator 2 is adjusted based on the temperature calculation result obtained in advance so that the exhaust gas temperature at the outlet of the dryer becomes a predetermined target temperature. In addition to controlling the flow rate of hot air sent to the dryer 3 and adjusting the amount of fuel oil supplied to the hot air generator 2 to control the hot air temperature at the inlet of the dryer 3, disposal before drying Even when the moisture content of the product changes drastically, the waste after drying is stably and appropriately dried so as to have a predetermined moisture content, compared to the method of controlling either the hot air flow rate or the hot air temperature. be able to.

It is a block diagram which shows one Embodiment of this invention. It is a figure which shows the relationship between the amount of evaporation in one Embodiment of this invention, the amount of circulating exhaust gas, and hot air temperature. It is a figure which shows the relationship between the return damper opening degree and circulating exhaust gas amount, and hot air temperature in one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Storage hopper 2 Hot air generator 3 Dryer 4 Dust collector 5 Deodorizing furnace 6 1st heat exchanger 7 2nd heat exchanger 8 Exhaust gas processing equipment 9 Exhaust pipe 11 Supply fan 12 Circulation fan 13 Air supply fan 14 Exhaust fan 16 Oil quantity Adjustment damper 17 Circulating fan inlet damper 18 Return damper 21 Cutting device 22 Supply conveyor 23 Discharge conveyor 31 Weighing scale 32 Cutting control device 33 Inlet thermometer 34 Outlet thermometer 35 Exhaust gas temperature control device 36 Pressure gauge 37 Internal pressure control device 38 Moisture meter

Claims (4)

  A drying method in which hot air is sent from a hot air generator to a dryer to dry the object to be dried, and a part of the exhaust gas from the dryer is returned to the hot air generator, depending on the exhaust gas temperature at the outlet of the dryer A drying method characterized by controlling the moisture content of the dried material after drying by adjusting both the amount of exhaust gas returned to the hot air generator and the hot air temperature at the dryer inlet.   When the exhaust gas temperature at the dryer outlet is lower than the predetermined target temperature, the amount of exhaust gas to be returned to the hot air generator is increased and the hot air temperature at the dryer inlet is increased so that the exhaust gas temperature at the dryer outlet is predetermined. 2. The drying method according to claim 1, wherein when the temperature is higher than the target temperature, the amount of exhaust gas returned to the hot air generator is reduced and the hot air temperature at the dryer inlet is lowered.   Drying provided with a hot air generator for generating hot air, a dryer for drying an object to be dried by the hot air sent from the hot air generator, and an exhaust gas circulation means for returning a part of the exhaust gas from the dryer to the hot air generator Exhaust gas temperature measuring means for measuring the exhaust gas temperature at the outlet of the dryer, and the amount of exhaust gas returned to the hot air generator and hot air at the inlet of the dryer according to the exhaust gas temperature measured by the exhaust gas temperature measuring means A drying facility comprising: a moisture content control means for controlling the moisture content of the material to be dried after drying by adjusting the temperature together.   When the exhaust gas measurement temperature at the dryer outlet is lower than a predetermined target temperature, the moisture content control means increases the amount of exhaust gas to be returned to the hot air generator and increases the hot air temperature at the dryer inlet. When the exhaust gas measurement temperature at the outlet is higher than a predetermined target temperature, the control means is configured to reduce the amount of exhaust gas returned to the hot air generator and lower the hot air temperature at the dryer inlet. The drying facility according to claim 3.

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