JP2007119740A - Process for production of carbide product and production apparatus - Google Patents

Abstract

Provided is a technique for industrially producing a carbonized product having a high content of soluble phosphoric acid and a low tar content, using organic waste represented by sewage sludge as a raw material.
An organic waste such as sewage sludge is carbonized at a temperature of 700 ° C. or less by a carbonizer 1 such as a rotary kiln, and an internal pressure connected to a subsequent stage of the carbonizer 1 is −0.5 kPa to +0. It introduce | transduces into the screw conveyance type cylindrical heating apparatus 2 of 5kPa. An inert gas such as water vapor, combustion exhaust gas, or nitrogen is flowed in the direction opposite to the direction in which the carbonized product proceeds, and the carbonized product is heated to 250 to 700 ° C., and the tar content is transferred to the gas side. The obtained carbonized product has a high content of soluble phosphonic acid of about 10% and does not contain any tar content that inhibits the growth of plants.
[Selection] Figure 1

Description

  The present invention relates to a carbonized product manufacturing method and apparatus capable of manufacturing a phosphate fertilizer raw material suitable for plant growth using organic waste such as sewage sludge as a raw material.

  With the spread of sewage treatment facilities, the amount of sewage sludge generated is increasing year by year. Conventionally, incineration was mainly used as a treatment method for sewage sludge, but recently, as shown in Patent Documents 1 and 2, a method of effectively using the combustible component in sludge as a fuel by carbonizing sewage sludge. Has been developed. In addition, paying attention to the fact that sewage sludge and the like contain a large amount of phosphorus, methods for utilizing carbonized products as a raw material for phosphate fertilizer are also being studied.

  The plant fertilizer is required to contain 5% or more of soluble phosphonic acid (citric acid soluble phosphoric acid). For this purpose, it is necessary to set the carbonization temperature of the sludge to a range of 700 ° C. or lower. If carbonized at a temperature higher than this, phosphorus crystallizes, and the amount of kurea-soluble phosphoric acid effective for plant growth decreases. Resulting in. However, if carbonization is performed at a low temperature of 700 ° C. or lower, tar components that inhibit plant growth cannot be sufficiently removed.

On the other hand, carbonization treatment at 700 to 800 ° C. is necessary to obtain a carbide containing no tar content. However, when carbonization is performed in such a temperature range, the tar content can be evaporated and evaporated, but the soluble phosphoric acid is reduced. Therefore, so far, it has been difficult to produce a carbonized product having a high content of soluble phosphoric acid and a low tar content.
JP 2004-256329 A JP 2004-277464 A

  Accordingly, an object of the present invention is to provide a carbonized product production method and apparatus capable of industrially producing a carbonized product having a high content of soluble phosphoric acid and a small amount of tar using organic waste represented by sewage sludge as a raw material. Is to provide.

  In the carbonized product production method of the present invention made to solve the above problems, organic waste is carbonized at a temperature of 700 ° C. or less with a carbonization device, and the internal pressure connected to the subsequent stage of the carbonization device is − It is introduced into a cylindrical heating device of 0.5 kPa to +0.5 kPa, and the carrier gas is allowed to flow in the direction opposite to the direction of carbonization while heating to 250 to 700 ° C. to remove tar content. Is. As the carrier gas, it is preferable to use any one of water vapor, low oxygen gas, and inert gas. Sewage sludge is a typical organic waste, but it may be a mixture of raw materials such as garbage and pruned branches, and organic waste containing phosphorus, such as livestock waste and food factory waste. It may be.

  In addition, the carbonized product manufacturing apparatus of the present invention made to solve the above-mentioned problems has an internal pressure of −0.5 kPa to +0 after the carbonizing apparatus for carbonizing organic waste at a temperature of 700 ° C. or lower. A screw conveying type cylindrical heating device which is maintained at 0.5 kPa and heats the carbonized product to 250 to 700 ° C. is connected to the inside thereof, and the carrier gas is moved to the outlet side of the cylindrical heating device in the traveling direction of the carbonized product. Is provided with a connection port for supplying in the opposite direction. A rotary kiln can be used as the carbonization device, and heat exhaust from the carbonization device or waste heat obtained by burning a combustible gas obtained from the carbonization device can be used as the heat source of the cylindrical heating device. In order to prevent the intrusion of outside air, it is preferable to provide a sealing mechanism that seals the shaft of the conveying screw and prevents the outside air from entering the cylindrical heating device.

According to the present invention, carbonization is performed in a screw conveyance type cylindrical heating device provided in a subsequent stage while increasing the content of soluble phosphoric acid by carbonizing organic waste at a temperature of 700 ° C. or lower. While heating at 250 to 700 ° C., the carrier gas is caused to flow in the direction opposite to the direction in which the carbonized product proceeds, and the tar content is removed along with the carrier gas flow. As a result, there is no risk of plant growth inhibition due to tar content, and a carbonized product having a high content of soluble phosphonic acid can be stably produced. This carbonized product can be used not only as a raw material for the soluble phosphate fertilizer, but also to obtain a carbonized product free from an unpleasant tar odor, and is effective for uses other than the raw material for the phosphate fertilizer.

  In this type of device, where flammable gas and combustible carbonized products are produced inside the device, the internal pressure of the cylindrical heating device should be much higher than atmospheric pressure in order to prevent explosions due to the suction of outside air. It is normal. However, in the present invention, since the internal pressure of the cylindrical heating apparatus is set to a pressure in the vicinity of atmospheric pressure of −0.5 kPa to +0.5 kPa as a gauge pressure, the reattachment of tar to the carbonized product is suppressed, and the tar content is reduced. Removal is performed efficiently.

  Further, in the present invention, since the shaft of the conveying screw is sealed to provide a sealing mechanism for preventing the outside air from entering the cylindrical heating device, it is safe even under the above-described pressure, and particularly with the carrier gas. If the same kind of gas is supplied to the seal portion, it is safer.

Hereinafter, preferred embodiments of the present invention will be described in detail.
FIG. 1 is a view showing an example of a device configuration used in the present invention, in which a carbonizing device 1 and a cylindrical heating device 2 are connected by a vertical tube 3. The carbonization apparatus 1 is an externally heated rotary kiln, and a heating jacket 4 is provided on the outer periphery of the furnace body. By supplying hot air generated in a hot air furnace (not shown) to the jacket 4, the internal temperature Is maintained at 700 ° C. or lower, more preferably 500 to 550 ° C. Of course, the inside of the carbonization apparatus 1 is maintained in a low oxygen atmosphere.

  Organic waste such as sewage sludge is charged into the carbonization apparatus 1 from the charging hopper 5 and carbonized at a relatively low temperature of 700 ° C. or lower. The organic matter contained in the organic waste is thermally decomposed in a low oxygen atmosphere, and is combusted by volatilizing combustible dry distillation gas and moisture. The generated dry distillation gas and water vapor are extracted from the rear end portion of the carbonization device 1 and are discharged from the chimney 7 after dust removal, cleaning, secondary combustion of the dry distillation gas, and the like are performed by the exhaust gas treatment device 6. Of course, it is also possible to recover the dry distillation gas as fuel gas without causing secondary combustion.

  As described above, since the organic waste is carbonized at a relatively low temperature of 700 ° C. or lower, the carbonized product that has reached the rear end of the carbonization apparatus 1 contains abundantly soluble phosphoric acid, but also contains tar content. In the present embodiment, the carbonized product falls to the inlet of the cylindrical heating device 2 through the vertical pipe 3 provided at the lower end of the rear end of the carbonizing device 1.

The cylindrical heating device 2 is provided with a conveying screw 9 installed inside an elongated cylindrical main body 8, and the conveying screw 9 is rotated by a motor 10 to send the carbonized product to the outlet side while stirring. The length of the cylindrical main body 8 is about 1 to 10 m, and the inner diameter is about 100 to 2000 mm. Moreover, the rotational speed of the screw 9 for conveyance shall be about 1-20min < ^-1 >, and carbonized goods are transferred at the speed of 5-30 cm per minute. On the outer periphery of the cylindrical main body 8 is installed a heating means 11 such as a heater or a burner, or a heating exhaust of the carbonizing device 1 or a device using waste heat obtained by burning a combustible gas obtained from the carbonizing device 1. The inside is heated to 250 to 700 ° C. If this temperature is less than 250 ° C., the tar content cannot be sufficiently removed, and if it exceeds 700 ° C., soluble phosphoric acid decreases.

  From the outlet-side connection port 12, the carrier gas flows from the outlet side toward the inlet side. As the carrier gas, any one of water vapor, low oxygen gas, and inert gas can be used. The low oxygen gas is, for example, combustion exhaust gas, and the inert gas is, for example, nitrogen. The flow rate is 0.1 to 1000 L / min. Since water vapor has excellent heat transfer properties for transferring heat to the carbonized product, the tar content can be efficiently volatilized and scattered in a short time.

  The carbonized product is heated to 250 to 700 ° C. while slowly moving inside the cylindrical heating device 2 over a period of about 15 to 120 minutes, and is discharged from the outlet side of the cylindrical heating device 2. In addition, the tar content is volatilized and removed with the carrier gas flowing in the direction opposite to the traveling direction of the carbonized product. The reason why the carrier gas was allowed to flow in the direction opposite to that of the carbonized product is to prevent the tar that has moved to the carrier gas side from reattaching to the carbonized product. The carbonized product from which the tar content has been removed in this manner is discharged from the outlet side of the cylindrical heating device 2, and the carrier gas containing the tar content of the carbonized device 1 through the vertical pipe 3 on the inlet side of the cylindrical heating device 2. It enters the rear end and is extracted together with the dry distillation gas.

  In this type of apparatus, the internal pressure of the cylindrical heating device 2 is generally set to be considerably higher than the atmospheric pressure in order to prevent an explosion due to outside air suction. However, in the present invention, as described above, the internal pressure of the cylindrical heating device 2 is set to a pressure in the vicinity of atmospheric pressure of −0.5 kPa to +0.5 kPa as a gauge pressure. By setting it as such a slight negative pressure-a minute positive pressure, volatilization of the tar part from a carbonized product is not suppressed, but removal of a tar part is performed efficiently as shown to the data of the Example mentioned later.

  Thus, in order to prevent the suction of outside air and maintain the inside of the cylindrical heating device 2 at −0.5 kPa to +0.5 kPa, the shaft 9 a of the conveying screw 9 and the cylindrical main body 8 of the cylindrical heating device 2. It is preferable to provide a sealing mechanism 15 that seals between the two. As shown in FIG. 2, the seal mechanism 15 mainly includes a ring-shaped packing 15a that seals the shaft 9a of the conveying screw, a main body member 15b that holds the packing 15a, and a gas supply pipe 15d. ing.

  Two packings 15 a are attached in close contact with the outer surface of the shaft 9 a at a certain interval in the axial direction of the shaft 9 a of the conveying screw 9. The main body member 15b is disposed adjacent to the cylindrical main body 8, restricts the movement of the two packings 15a in the axial direction of the shaft 9a of the conveying screw 9, surrounds the outer periphery of the packing 15a, and seals the packing 15a. Holding. A gap 15 c is formed between the two packings 15 a over the entire circumference of the shaft 9 a of the conveying screw 9. A gas supply pipe 15d for supplying gas is connected to the gap 15c.

  Carrier gas is supplied to the gas supply pipe 15d, and the entire periphery of the portion exposed to the gap 15c of the shaft 9a is purged with the carrier gas, thereby reliably preventing outside air from entering the cylindrical heating device 2. is doing. Therefore, even if the internal pressure of the cylindrical main body 8 is a slight negative pressure, there is no risk that the cylindrical main body 8 is mixed with air and contacts with the hot dry distillation gas to cause an explosion. Even when the internal pressure of the cylindrical body 8 is set to a slight positive pressure, it is preferable to provide the sealing mechanism 15 as described above.

  As described above, according to the present invention, it is possible to industrially produce a carbonized product having a high content of soluble phosphoric acid and a low tar content using organic waste as a raw material. Examples are shown below.

  A sludge sample of dried sludge (water content 10%) was produced by pre-drying sewage dewatered sludge (water content 74%) discharged from a belt press dehydrator in a sewage treatment plant at 500 to 550 ° C. This was supplied to the carbonization apparatus described in the embodiment, and the carbonization temperature was changed to 500 ° C., 550 ° C., and 600 ° C. for processing. This temperature was the same for both the carbonizing device 1 and the cylindrical heating device 2, and the internal pressure was 0 kPa (atmospheric pressure). The cylindrical heating device 2 used had an inner diameter of 500 mm and a length of 4 m, and water vapor and nitrogen gas were flowed in the opposite direction as the carbonized product as the carrier gas. The residence time in the carbonization apparatus 1 is 60 minutes, and the residence time in the cylindrical heating apparatus 2 is 20 minutes.

  About the obtained carbonized product, the content rate and tar content of soluble phosphoric acid were measured. The tar content is measured based on the “Simple method for measuring tar content in sewage sludge carbide” prepared and published by Nippon Fertilizer Co., Ltd. This was carried out by measuring the absorbance at 200 to 800 nm with a total. Although the evaluation is indicated by a numerical value from 0 to 5, the plant fertilizer is required to be 0.5 or less. The results are shown in Table 1. For comparison, Table 1 also shows data when the cylindrical heating device is not used.

  As shown in this data, according to the present invention, a carbonized product having a high concentration of soluble phosphoric acid and containing no tar content could be obtained. However, the conventional method using only the carbonization apparatus cannot satisfy the standard of tar content of 0.5 or less required as a plant fertilizer. Further, in the case of water vapor, it was confirmed that the tar removal time can be processed in a short time of about 1/3 as compared with the case of nitrogen gas.

  FIG. 3 shows a graph of the relationship between the carbonization temperature and the soluble phosphoric acid concentration. As is apparent from the graph of FIG. 3, a carbonized product having the most concentrated soluble phosphoric acid concentration at a carbonization temperature of 500 ° C. to 700 ° C. can be obtained.

  Next, the result of the simple measurement of tar content when the temperature conditions and the furnace pressure of the carbonization furnace and the cylindrical heating apparatus are changed will be shown.

  From the results of RUN1 and RUN2 in Table 1, when the heating temperature of the cylindrical heating device is 150 ° C. and 200 ° C., the removal of tar contained in the carbonized product is insufficient, and the heating temperature of the cylindrical heating device When the temperature is 280 ° C., the tar content contained in the carbonized product is sufficiently removed. For this reason, the heating temperature of a cylindrical heating apparatus shall be 250 degreeC or more.

  From the results of RUN5 and RUN6 in Table 1, when the inside of the carbonizing device and the cylindrical heating device is a positive pressure exceeding the range of the present invention, the tar content extracted with ethanol is large, and the tar content contained in the carbonized product The remaining amount of is large. This is because the organic waste put into the carbonization device generates dry distillation gas after the water evaporates, but when the pressure in the carbonization device or the cylindrical heating device is high, the organic waste This is because the tar content in the dry distillation gas adheres and solidifies on the carbonized surface. Therefore, by setting the internal pressure of the carbonization device or the cylindrical heating device within the range of the present invention as shown by RUN3 and RUN4, a carbonized product from which tar content has been sufficiently removed can be obtained.

It is an apparatus block diagram which shows embodiment of this invention. It is detail drawing of a sealing mechanism. The graph which shows the relationship between carbonization temperature and a soluble phosphoric acid concentration is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Carbonization apparatus 2 Cylindrical heating apparatus 3 Vertical pipe 4 Jacket 5 Input hopper 6 Exhaust gas processing apparatus 7 Chimney 8 Cylindrical main body 9 Transfer screw 9a Shaft 10 Motor 11 Heating means 12 Outlet side connection port 15 Seal mechanism 15a Packing 15b Main body Member 15c Air gap 15d Gas supply pipe

Claims (7)

  The organic waste is carbonized by a carbonization device at a temperature of 700 ° C. or lower, and introduced into a cylindrical heating device having an internal pressure of −0.5 kPa to +0.5 kPa connected to the subsequent stage of the carbonization device, and 250 to 700 A method for producing a carbonized product, characterized in that a tar gas is removed by flowing a carrier gas in a direction opposite to the direction of travel of the carbonized product while heating to ° C.   The method for producing a carbonized product according to claim 1, wherein any one of water vapor, low oxygen gas, and inert gas is used as the carrier gas.   The carbonized product according to claim 1 or 2, wherein the organic waste is mainly sewage sludge, or a mixture of biomass raw materials such as garbage and pruned branches with sewage sludge. Method.   Screw transport for maintaining the internal pressure at -0.5 kPa to +0.5 kPa and heating the carbonized product to 250-700 ° C in the subsequent stage of the carbonization device for carbonizing organic waste at a temperature of 700 ° C or lower Of a carbonized product characterized in that a connecting port for supplying a carrier gas in a direction opposite to the direction of travel of the carbonized product is provided on the outlet side of the cylindrical heating device. apparatus.   The carbonization apparatus according to claim 4, wherein the carbonization apparatus is a rotary kiln.   The apparatus for producing a carbonized product according to claim 4, wherein the heat source of the cylindrical heating device uses heating exhaust of the carbonization device or waste heat obtained by burning a combustible gas obtained from the carbonization device. .   The carbonized product manufacturing apparatus according to claim 4, wherein a sealing mechanism is provided for sealing the shaft of the conveying screw to prevent outside air from entering the cylindrical heating device.

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