JP7802759B2 - Organic sludge treatment device and treatment method - Google Patents

Description

The present invention relates to a treatment device and treatment method for organic sludge such as sewage sludge, and to a device that effectively utilizes organic sludge as fuel, etc.

As it is becoming increasingly difficult to bury organic sludge, such as sewage sludge discharged from sewage treatment plants, on land, various methods have been proposed for effectively utilizing it as fuel. For example, Patent Document 1 discloses a technology in which organic sludge, such as sewage sludge, is converted into fuel by directly feeding it in the form of a water-containing slurry into the kiln end or calciner of a cement manufacturing facility.

Patent Document 2 discloses a technique for mixing sewage sludge with quicklime, dehydrating the sewage sludge, and then feeding the resulting solids into a cement kiln to produce cement together with other cement raw materials. Patent Documents 3 and 4 also disclose techniques for drying sewage sludge using quicklime from preheater bottom raw materials and quicklime from bypass dust.

However, in the method described in Patent Document 1, organic sludge is fed in the form of a wet slurry into the cement kiln at the area where the cement raw materials undergo decarbonation (from the kiln end to the inlet of the lowest cyclone), which results in a large amount of heat being required to evaporate the sludge water, and the location and time at which the water evaporates are not constant, resulting in fluctuations in the amount of exhaust gas and a sudden drop in the firing temperature, which reduces cement production efficiency.

Furthermore, if drying is performed using the heat generated by the reaction of quicklime, as in Patent Document 2, quicklime is expensive and the drying process requires a long time because the heat generated after the quicklime is hydrated is used for drying.

As in Patent Documents 3 and 4, drying using the heat of hydration of quicklime in cement raw materials is less expensive than using commercially available quicklime, but when used as a cement raw material, it must be dehydrated again, and the heat loss is significant, being 1.5 to 2 times the theoretical value required for the dehydration reaction.

Therefore, in Patent Document 5, the applicant proposed a method for treating organic sludge, in which preheated raw material is separated from preheater cyclones (excluding the lowest cyclone) of a cement calciner, organic sludge is mixed with the separated preheated raw material, the sensible heat of the preheated raw material is used to dry the organic sludge, and the dried organic sludge is supplied to the calciner of the cement calciner or to a duct between the end of the cement kiln and the calciner.

According to the invention described in Patent Document 5, organic sludge is dried using the sensible heat of the preheated raw material, and the dried sludge is then supplied together with the preheated raw material to a calciner or a duct between the end of a cement kiln and the calciner. This allows the dried sludge to be effectively used as a fuel alternative, and its heat source can efficiently contribute to the decarbonation of cement raw materials in the calciner, etc., making it possible to process organic sludge while minimizing equipment costs and decreases in cement production efficiency and clinker production volume.

Japanese Patent No. 3933194 Japanese Patent No. 2803855 Japanese Patent No. 4106449 Japanese Patent Application Publication No. 2015-66477 International Publication No. WO2019/193938 Pamphlet

However, in the invention described in Patent Document 5 above, the dried sludge dried using the sensible heat of the preheated raw material has a temperature of around 100°C and emits an odor, so it cannot be returned to the cement raw material system. Instead, it is returned to the calciner together with the preheated raw material or to the duct between the end of the cement kiln and the calciner, resulting in heat loss.

In addition, when using preheated raw material collected from the chute of the third cyclone from the top of the preheater cyclone, the temperature of the preheated raw material is relatively low at around 650°C, which means that the amount collected is large and processing costs increase.

Furthermore, since the material was separated using a screw conveyor installed in the center of the preheater cyclone's raw material chute, the amount separated fluctuated, making it difficult to maintain stable operation.

The present invention was made in consideration of the problems with the above-mentioned conventional technology, and aims to treat organic sludge with little heat loss, small amounts of separation, and while maintaining stable operation.

To achieve the above-mentioned objectives, the present invention is an organic sludge treatment device characterized by comprising a separation device that separates preheated raw material from the calciner of a cement calciner; a mixer that mixes organic sludge with the preheated raw material separated by the separation device and dries the organic sludge using the sensible heat of the preheated raw material; and a supply device that supplies the mixture discharged from the mixer to the raw material supply system of the cement calciner.

According to the present invention, a mixture of dried organic sludge and separated preheated raw material is returned to the raw material supply system of the cement firing equipment, thereby reducing the heat loss that occurs when a conventional mixture is returned to the duct between the end of the cement kiln and the calciner. Furthermore, since the organic sludge is dried using high-temperature preheated raw material at approximately 800°C separated from the calciner, the amount of preheated raw material used can also be reduced.

In the above-mentioned organic sludge treatment device, the separation device is a screw conveyor with the upper half of the casing removed, and the longitudinal opening edge of the casing can be extended along the wall surface of the raw material flow section of the calciner, thereby preventing pulsation in the separation volume and maintaining stable operation.

The organic sludge treatment device can be equipped with an introduction device that introduces exhaust gas containing dust, odor, and water vapor from the mixer into the gas outlet of the lowest cyclone of the cement calciner, allowing the odorous gas generated by sludge drying to be effectively utilized for denitrification of the cement kiln exhaust gas while being treated. Furthermore, while returning the exhaust gas to the calciner or cement kiln results in heat loss during calcination, the present invention returns the exhaust gas to the gas outlet of the lowest cyclone (exhaust gas after calcination is completed), minimizing heat loss.

The temperature of the mixture at the outlet of the mixing device can be set to 100°C or higher, which allows the organic sludge to be dried to a moisture content of 5% by mass or less, which does not produce an odor, and prevents problems caused by condensation of moisture during transportation.

The present invention also provides a method for treating organic sludge, which comprises mixing the organic sludge with preheated raw material collected from the calciner of a cement calciner, drying the organic sludge using the sensible heat of the preheated raw material, and supplying the mixture to the raw material supply system of the cement calciner.

According to the present invention, a mixture of dried organic sludge and separated preheated raw material is returned to the raw material supply system of the cement firing equipment, thereby reducing the heat loss that occurs when a conventional mixture is returned to the duct between the end of the cement kiln and the calciner. Furthermore, since the organic sludge is dried using high-temperature preheated raw material at approximately 800°C separated from the calciner, the amount of preheated raw material used can also be reduced.

In the above-mentioned organic sludge treatment method, exhaust gas containing dust, odor, and water vapor generated when the organic sludge is mixed with the preheated raw material can be introduced into the gas outlet of the lowest cyclone of the cement firing device, and the ammonia components contained in the odorous gas generated by drying the sludge can be effectively utilized for denitrification of the cement kiln exhaust gas while being treated.

The mixing ratio of the organic sludge to the separated preheated raw material can be set to organic sludge (solids excluding moisture): separated preheated raw material = 1:3 to 1:4, which allows for stable evaporation of moisture in a short period of time. Furthermore, by diluting the combustible components of the organic sludge with the separated preheated raw material, which is non-combustible, the risk of dust explosions can be reduced, and the handling of highly viscous organic sludge can be improved.

As described above, according to the present invention, organic sludge can be treated with little heat loss and small amounts of separation, while maintaining stable operation.

1 is a schematic diagram showing an embodiment of an organic sludge treatment apparatus according to the present invention. 2 is a schematic cross-sectional view showing an example of installation of a fractionation device in the organic sludge treatment device shown in FIG. 1. FIG.

Next, the form for implementing the present invention will be described in detail with reference to the drawings.

Figure 1 shows a cement calcination apparatus equipped with an organic sludge treatment device according to the present invention. In addition to typical cement calcination apparatus components such as a cement kiln 2, a calciner 3, and a preheater 4, this cement calcination apparatus 1 also includes a fractionator 5 that fractionates a portion of the preheated raw material R1 descending through the calciner 3, and a mixer 8 that dries the organic sludge S while mixing the fractionated preheated raw material R2 with the organic sludge S supplied from the organic sludge supply device 6. The preheater 4 has four or five cyclones, but Figure 1 does not show the equipment above the three-stage cyclones 4C1 and 4C2. Organic sludge S refers to sewage sludge, paper sludge, building pit sludge, food sludge, etc.

The fraction collection device 5 can be, for example, a screw conveyor with the upper half of the casing 5a (the upper half of a cylindrical casing) removed and the top open. As shown in Figure 2, the fraction collection device 5 has the longitudinal opening edge 5b of the casing 5a that passes through the calciner 3 extending along the wall surface 3a of the flow section of the preheated raw material R1 in the calciner 3. Because the preheated raw material R1 flowing along the wall surface 3a is smoothly introduced into the fraction collection device 5, stable operation can be maintained without pulsation in the amount of fraction collection. It should be noted that fraction collection devices with configurations other than those described above can also be used.

As shown in Figure 1, the mixer 8 is a pug mill or similar device with multiple blades 8b attached to a horizontal shaft 8a. Rotating the horizontal shaft 8a also rotates the blades 8b, and the mixer simultaneously mixes, dries, and transports the organic sludge S and the separated preheated raw material R2. This mixer 8 is not limited to the above-described type, and other types of devices capable of drying the organic sludge S using the sensible heat of the separated preheated raw material R2 can also be used.

Although not shown in the figure, the mixing device 8 is provided with an introduction device that introduces exhaust gas G containing dust, odor, and water vapor from the mixing device 8 into the gas outlet of the lowest cyclone (lowest cyclone 4A2 in the illustrated example).

Next, the organic sludge treatment method according to the present invention using the cement firing apparatus 1 having the above-described configuration will be explained with reference to Figure 1.

When the cement firing apparatus 1 is operating, organic sludge S is supplied to the mixer 8 via the organic sludge supply device 6, and a portion of the preheated raw material R1 descending through the calciner 3 is separated by the separation device 5, and the separated preheated raw material R2 is introduced into the mixer 8 to dry the organic sludge S.

The amount of preheated raw material R2 dispensed can be instantly adjusted by changing the rotation speed of the screw conveyor of the dispenser 5. Even if the supply amount of organic sludge S changes, the amount of preheated raw material R2 dispensed can be instantly adjusted to accommodate the change, enabling stable processing.

It is preferable to adjust the mixing ratio of organic sludge S and separated preheated raw material R2 in the mixer 8 to organic sludge S (solids excluding moisture): separated preheated raw material R2 = 1:3 to 1:4. This allows for stable evaporation of moisture in a short period of time. Furthermore, diluting the combustible content of organic sludge S with the non-combustible preheated raw material R2 reduces the risk of dust explosions and improves the handleability of highly viscous organic sludge.

In the mixer 8, the organic sludge S and preheated raw material R2 are conveyed while being mixed and stirred, preferably for 1 to 5 minutes, and the organic sludge S is heated and dried using the sensible heat of the separated preheated raw material R2. The remaining preheated raw material R1 is decarbonated in the usual way in the calciner 3 and the lowest cyclones 4A1 and 4A2, and then burned in the cement kiln 2 to produce cement clinker.

Table 1 shows the relationship between the moisture content (mass%) and odor of the mixture M of organic sludge S and preheated raw material R2 dried as described above.

Moisture content was measured in accordance with JIS Z 7302-3 "Refuse-derived fuel - Part 3: Moisture content test method." Specifically, the sample was heated and dried at 107±2°C for 1 hour, and the difference in mass before and after drying was taken as the mass percentage of the sample.

On the other hand, the odor intensity was measured by the following procedure.
(1) 100 g of sample is sealed in a 1 L plastic container.
(2) Allow to stand for 1 hour in a constant temperature environment of 30°C.
(3) Using a flex pump, collect the gas from the plastic container containing the sample into a 3 L gas bag.
(4) The odor intensity of the gas collected from the gas bag is measured using an odor sensor (Neo Sigma, manufactured by Calmor Corporation).

The odor intensity that humans can tolerate as unpleasant, based on the odor sensor readings, is 600 or less. From Table 1, the moisture content at which an odor intensity of 600 is reached is 5% by mass. To keep the moisture content of mixture M at 5% by mass or less, the temperature of mixture M at the outlet of mixing device 8 is set to 100°C or higher. This allows the organic sludge (mixture M) to be dried to a moisture content that does not produce an odor, and also improves handling during transport.

Because mixture M has been dried to a moisture content of 5% by mass or less, which does not produce an odor, it can be returned to the raw material supply system of the cement burning device 1, i.e., from the raw material storage area to the raw material supply device to the preheater 4. This reduces the heat loss that would occur if mixture M were previously returned to a duct or the like between the end of the cement kiln 2 and the calciner 3 by approximately 50 kJ/kg-cli. Furthermore, because the organic sludge is dried using high-temperature preheated raw material at approximately 800°C taken from the calciner, the amount of preheated raw material used can also be reduced.

Meanwhile, exhaust gas G containing dust, odor, and water vapor from the mixer 8 is returned to the gas outlet of the lowest cyclone 4A2 of the cement burning apparatus 1, where odorous gases produced by drying the organic sludge S are effectively utilized for denitrification of the cement kiln exhaust gas. Furthermore, while returning exhaust gas G to the calciner 3 or cement kiln 2 results in a heat loss during calcination, in the present invention, heat loss is minimized by returning it to the gas outlet of the lowest cyclone 4A2 (exhaust gas after calcination is completed).
1 Cement burning device 2 Cement kiln 3 Calciner 4 Preheater 5 Separation device 6 Organic sludge supply device 8 Mixing device G Exhaust gas M Mixture R1, R2 Preheated raw material S Organic sludge

Claims (7)

a sampling device that samples preheated raw materials from a calciner of the cement burning device;
a mixer that mixes the organic sludge with the preheated raw material separated by the separation device and dries the organic sludge using the sensible heat of the preheated raw material;
a supply device for returning the mixture discharged from the mixer from the raw material storage area to the raw material supply device for the preheater; 2. The organic sludge treatment apparatus according to claim 1, wherein the separation device is a screw conveyor with the upper half of the casing removed, and the longitudinal opening edge of the casing extends along the wall surface of the raw material flow section of the calciner. 3. The organic sludge treatment apparatus according to claim 1, further comprising an introducing device that introduces the exhaust gas containing dust, odor, and water vapor from the mixing device into a gas outlet of the lowest cyclone of the cement burning apparatus. 4. The organic sludge treatment apparatus according to claim 1, wherein the temperature of the mixture at the outlet of the mixer is set to 100° C. or higher. A method for treating organic sludge, comprising mixing organic sludge with preheated raw material taken from a calciner of a cement calciner, drying the organic sludge using the sensible heat of the preheated raw material, and returning the mixture from a raw material storage area to a raw material supply device for a preheater. 6. The method for treating organic sludge according to claim 5, wherein exhaust gas containing dust, odor, and water vapor generated when the organic sludge and the preheated raw material are mixed is introduced into a gas outlet of a lowermost cyclone of the cement burning apparatus. 7. The method for treating organic sludge according to claim 5 or 6, wherein the mixing ratio of the organic sludge to the separated preheated raw material is organic sludge (solid content excluding water): separated preheated raw material = 1:3 to 1:4.