JP2001070995A - Sludge drying method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sanitary final product by efficiently drying sludge without generating a gas emitting a malodor such as ammonia gas or the like. SOLUTION: A sludge drying method comprises a process for cooling air used in the drying of sludge to temp. lower than the temp. of sludge just after drying by 5 deg.C or more to dehumidify the same, a heating process for heating the air cooled in the gooling process to 40 deg.C or higher to obtain drying air and a drying process for bringing this drying air into direct contact with sludge to be dried to dry sludge in such a state that the temp. of the sludge just after drying becomes 20-60 deg.C. The air lowered in temp. and increased in humidity in the drying process is circulated to the cooling process to be used in the drying of sludge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for drying sludge.

[0002]

2. Description of the Related Art The treatment of sludge generated as refuse in municipal sewage or industrial wastewater treatment plants has become an important issue for the parties concerned, and also due to the improvement in living standards and the increase in industrial production. The amount tends to increase significantly more.

[0003] Conventionally, a method of treatment and disposal has been adopted by simply depositing and reclaiming sludge, or by making effective use of sludge in agricultural cultivation to help soil fertilization and improvement. In small sewage treatment plants and wastewater treatment plants, these natural treatment methods are still effective, but in large-scale treatment plants or in densely populated areas, problems have arisen. "Is a particular problem.

[0004] In recent years, as a method for solving the problem of odor, a method of anaerobic or aerobic digestion of sludge has been used.

[0005]

However, the odor cannot be sufficiently eliminated only by anaerobic or aerobic digestion, and unsanitary sludge can be converted into a sanitary final product. It is necessary to dry sludge after anaerobic or aerobic digestion.

Here, when drying sludge, the method of drying by applying heat to the sludge is one of the simplest and frequently used methods.

However, when the sludge is directly heated, if the temperature of the sludge exceeds about 70 ° C., ammonia gas or the like may be generated, which may give off a bad smell more than the smell of the sludge itself.

The present invention has been made in view of the above circumstances, and provides a method for drying sludge which can be dried without generating an odorous gas such as ammonia gas to produce a sanitary final product. Its primary purpose is to provide.

[0009]

According to the present invention, in order to achieve the above object, according to the first aspect, the air used for drying the sludge is cooled and dehumidified to a temperature lower by 5 ° C. than the temperature of the sludge immediately after drying. A cooling step, a heating step of heating the air cooled by the cooling step to 40 ° C. or higher to make drying air, and bringing the drying air into direct contact with the sludge to be dried. A temperature range of 25 ° C. to 60 ° C., a drying step for drying the sludge, and air whose temperature has been reduced and increased in humidity by the drying step;
The present invention provides a method for drying sludge, wherein the sludge is recycled by being sent to the cooling step.

In the present invention, the sludge is dried using dried air without directly heating the sludge, and the temperature of the sludge immediately after drying is 25 ° C. to 60 ° C.
By drying at a low temperature within the range of ° C., sludge can be dried while preventing generation of gas that emits offensive odors such as ammonia, and a sanitary final product can be obtained.

Further, as described in claim 2, in the invention according to claim 1, the sludge obtained by subjecting sludge generated in sewage treatment to anaerobic or aerobic digestion and dewatering the sludge;
It is preferable to use either sludge that has been subjected to anaerobic digestion and dehydration at the time of night soil treatment, sludge that has been mixed with crushed garbage and excreted anaerobic digestion and has been dehydrated, or a mixture of these sludges.

This is because, among the sludges, the above-mentioned sludges generate odorous gas such as ammonia.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method for drying sludge of the present invention comprises the following steps. (1) A cooling step of cooling and dehumidifying air used for drying sludge to 5 ° C. or lower than the temperature of sludge immediately after drying. (2) A heating step of heating the air cooled in the cooling step to 40 ° C. or higher to form drying air. (3) A drying step for bringing the drying air into direct contact with the sludge to be dried and drying the sludge within a range where the temperature of the sludge immediately after drying is 25 ° C to 60 ° C.

The air whose temperature has been lowered and humidified by the drying step is sent to the cooling step and circulated.

First, the cooling step (1) will be described. The purpose of the cooling step is that the air used for drying is circulated (described in detail later), so that the air that has been used once for drying and contains a large amount of water is heated to the temperature of the sludge immediately after drying (hereinafter, referred to as the sludge temperature). This is for removing moisture in the air to be circulated (hereinafter referred to as circulating air) by cooling to a temperature not higher than 5 ° C. lower than the product temperature.

Here, the product temperature is the temperature of the sludge immediately after drying when it is dried and discharged in the drying step as described above. The method of the present invention is characterized in that drying is performed so that the product temperature is between 25 ° C. and 60 ° C. so as to prevent generation of malodorous gas such as ammonia gas.

Generally, the amount of air used for drying 1 kg of water is 200 as a standard for drying sludge or the like.
It is preferably less than Nm ^{3, and using} less than 200 Nm ^{3 of} air to dry 1 kg of water is said to be less efficient.

In the method of the present invention, the circulating air is cooled to a temperature lower than the product temperature by 5 ° C. or less, as a result of calculation of the amount of water in a drying apparatus calculation. As a result, air of 200 Nm ³ or less is required to dry 1 kg of water. This is because it was found that the circulating air temperature had to be lower by at least 5 ° C. than the product temperature in order to make the amount sufficient.

The type of sludge to be dried by the method of the present invention is not particularly limited, and may be any type. However, anaerobic or aerobic digestion of sludge generated in sewage treatment and dewatered sludge, anaerobic digestion and dewatered sludge during human waste treatment, or garbage mixed with human waste to mix anaerobic digestion is performed. Preferably, the sludge is applied and dehydrated, or a mixture of these sludges. This is because it is often a problem that the sludge emits an odor due to ammonia gas or the like during drying, and in such a case, performing anaerobic digestion as a pretreatment is one of the causes of the odor. This is because a certain protein or the like can be decomposed. Furthermore, as a pretreatment for drying,
It is preferred that the sludge be roughly dewatered.

In the method of the present invention, the method for cooling the circulating air is not particularly limited, and any cooling method may be used. For example, a heat pump can be used, and circulating air can be cooled using cooling water as a refrigerant.

Next, the heating step (2) will be described.

The heating step is a step for heating the circulating air cooled in the cooling step to 40 ° C. or higher to obtain drying air. Here, the reason why the circulating air is set to 40 ° C. or higher is that in order to satisfy the above-mentioned standard for removing sludge of 1 kg or more using 200 Nm ³ circulating air, which is a general criterion for drying sludge, drying is performed. This is because, from the calorific value calculation in the device calculation, it was obtained that the circulating air had to be heated to 40 ° C. or more.

In the present invention, the method for heating the circulating air is not particularly limited, and any method may be used as long as it can be heated to 40 ° C. or higher. For example, a heat pump that can be used in the cooling step can be used, and a heater or the like can be used.

Next, (3) the drying step will be described.

The drying step is a step of directly contacting the drying air heated to 40 ° C. or more in the heating step with the sludge, and drying the sludge within a temperature range of 25 ° C. to 60 ° C. is there.

Here, the reason for setting the product temperature to be in the range of 25 ° C. to 60 ° C. is to prevent generation of malodorous gas such as ammonia gas from sludge. As described above, one of the purposes of drying sludge is to eliminate the bad smell generated from the sludge, and if gas such as ammonia is generated from the sludge during the drying to achieve this purpose, it means drying. Therefore, the temperature of the sludge was set in the range of 25 to 60 ° C.

The method of drying sludge in the method of the present invention may be any method as long as dry air and sludge are brought into direct contact.

Further, in the present invention, the air whose temperature has been lowered and humidified by the drying step is sent to the cooling step and is circulated for use.

This is because the circulating air contains a malodorous gas such as ammonia and requires a deodorizing treatment or the like to be released to the outside air. This is because sludge can be stably dried without being affected.

Next, an example of an apparatus for carrying out the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram showing an example of a sludge drying apparatus for carrying out the sludge drying method of the present invention. The sludge drying device 1 includes a drying device 2 for actually drying the sludge, a circulation fan 3 for feeding and circulating the dried circulating air to the drying device 2, and a heat pump for producing the dried circulating air. And a general dehumidifying / drying device 4.

A sludge supply hopper 6 for supplying the sludge 5 to the inside of the drying apparatus 2 is provided above the drying apparatus 2. The sludge 5 supplied from the sludge supply hopper 6 is fed by several stages of conveyors 7 installed inside the drying device 2.
Proceed downward in the drying device. The sludge 5 is produced in the heat pump type dehumidifying / drying device 4 and comes into direct contact with the dried circulating air fed from the drying air inlet 8, where the water in the sludge 5 is taken into the dried circulating air. To dry. The dried sludge 5 falls from the lowermost conveyor 7 and is discharged from a sludge discharge port 9 provided at the lower part of the drying device 2.

When the dried circulating air is fed into the drying device 2 through the drying device inlet 8, the dried air deprives the sludge 5 on the conveyor 7 in the drying device 2 of the moisture as described above. Allow to dry. Thereafter, the air is discharged from an air discharge port 10 provided below the drying device 2. In this case, the discharged circulating air is sludge 5
The temperature of the sludge 5 which is dried and discharged from the sludge discharge port 9 at this time is in the range of 25 to 60 ° C. due to the absorption of moisture from the sludge. The low-temperature and high-humidity circulating air passes through the pipe 11 and is sent into the heat pump type dehumidifying / drying device 4.

The inside of the heat pump type dehumidifying and drying apparatus 4 is divided into an air cooling section 12 and an air heating section 13. Piping 1
The circulating air in a low-temperature and high-humidity state passing through 1 is first sent into the air cooling unit 12 in the heat pump type dehumidifying and drying apparatus 4. Here, the circulating air in the low-temperature and high-humidity state is cooled to 5 ° C. or less below the product temperature, and its relative humidity is 10 ° C.
0%, and the moisture in the air is removed.

The refrigerant of the heat pump is supplied to the refrigerant circuit 17
Is circulating. The refrigerant is supplied to the air cooling unit 12 in the heat pump type dehumidifying / drying device 4 through the refrigerant expansion valve 14, and is then pressurized by the refrigerant compressor 15, and partially reheated by the air heating unit 13. And the rest is cooled by the refrigerant heat exchanger 16.

The circulating air from which moisture has been removed in the air cooling section 12 in the heat pump type dehumidifying and drying apparatus 4 is heated to a predetermined temperature in the air heating section 13 to be dried circulating air. It is sent to the drying device 2 again through 18.

The reheating heater 18 is a device for reheating the circulating air heated to a predetermined temperature by the air heating unit 13 in the heat pump type dehumidifying and drying device 4 before sending it to the drying device 2. By using this apparatus, the temperature of the dried circulating air can be further increased, and the sludge can be efficiently dried.

When the sludge is dried by the sludge drying apparatus 1 as described above, the product temperature is 25 to 60 as described above.
° C and does not generate gas such as ammonia.
The object of the present invention can be sufficiently achieved.

The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the claims of the present invention. Within the technical scope of

[0040]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings. (Example 1-1) Example 1-1 was performed using the apparatus shown in FIG.

As shown in FIG.
% Of the circulating air was fed into the drying device 2 from the drying device inlet 8. The sludge 5 is dried in the drying device 2,
The circulating air discharged from the air discharge port 10 provided below the drying device 2 has a temperature of about 32.5 ° C. and a relative humidity of 60%, and is dried at this time and discharged from the sludge discharge port 9. The temperature of the sludge 5 was 25 ° C. 32.5
The circulating air having a temperature of 60 ° C. and a relative humidity of 60% was sent into the air cooling unit 12 in the heat pump type dehumidifying / drying device 4 through the pipe 11 and was cooled to a temperature lower by 5 ° C. than the product temperature, that is, 20 ° C. At this time, the relative humidity of the circulating air was 100%, indicating that the water in the circulating air had been removed.

The circulating air from which water has been removed in the air cooling section 12 in the heat pump type dehumidifying and drying apparatus 4 is heated to 33 ° C. and a relative humidity of 45.8% in the air heating section 13 to become dry air. Then, it was sent again to the drying device 2 through the reheating heater 18.

By using the reheat heater 18, the dried circulating air could be kept at 43 ° C. and a relative humidity of 27%, and the sludge could be dried efficiently.

When the sludge is dried by the sludge drying apparatus 1 as described above, the product temperature is 25 ° C. as described above, and no gas such as ammonia is generated, and the object of the present invention is sufficiently achieved. Was achieved.

When the sludge is dried using the method and apparatus as described above, the amount of air required for drying 1 kg of water is 200 Nm ^3, which is a general drying standard (1 k of water).
(an air amount of 200 Nm ³ per g) was used. (Example 1-2) Further, Example 1-2 of the method of the present invention.
Will be described with reference to FIG. In Example 1-2, the same apparatus as in Example 1-1 was used while changing the temperature conditions.

In Example 1-2, 73 ° C. and relative humidity
8% of dry air was fed into the drying device 2 from the drying device inlet 8 to dry the sludge 5 and discharged from the air outlet 10 provided below the drying device 2. In this case, the discharged circulating air had a temperature of about 37 ° C. and a relative humidity of 60%, and the temperature of the sludge 5 dried at this time and discharged from the sludge discharge port 9 was 30 ° C. The circulating air at 37 ° C. and a relative humidity of 60% was sent through the pipe 11 into the heat pump type dehumidifying and drying apparatus 4.

Next, the circulating air enters the air cooling unit 12 in the heat pump type dehumidifying / drying apparatus 4, where it is heated at 15 ° C.
That is, it was cooled to a temperature lower by 5 ° C. than the product temperature. Fifteen
When cooled down to ℃, the relative humidity of the circulating air is 100%
It was found that the moisture in the air had been removed.

The circulating air from which moisture has been removed in the air cooling section 12 in the heat pump type dehumidifying and drying apparatus 4 is heated to 33 ° C. and a relative humidity of 34% in the air heating section 13 to become dry air. According to 18, 7
It was heated to 3 ° C. and a relative humidity of 4.8%, and was fed into the drying device 2 again.

When the sludge is dried under the above conditions, the final product temperature is 30 ° C. as described above, and no gas such as ammonia is generated. Was achieved.

When the sludge is dried by the method described above, the amount of air required to dry 1 kg of water is 58 N
m ³ , which indicates that the drying efficiency is much better than a general drying standard (using an air amount of 200 Nm ³ per kg of water). (Comparative Example) Next, a comparative example will be described with reference to FIG.

The comparative example shown in FIG.
Except for the fact that the air heating unit 13 is not provided, the temperature and the humidity at the time of discharging the air heating unit 13 are 33 ° C. and the relative humidity as in Example 1-2. The circulating air of 34% was directly sent into the drying device 2 without being reheated.

The circulating air discharged from the air discharge port is 25
° C and a relative humidity of 60%, and the temperature of the sludge dried and discharged from the sludge discharge port 9, that is, the product temperature was 19.6 ° C.

The circulating air having a temperature of about 25 ° C. and a relative humidity of 60% was cooled and dehumidified to 15 ° C. and a relative humidity of 100%, which is lower than the product temperature by about 5 ° C. or less. At this time, the required air amount was 632 Nm ³ per 1 kg of water, and it was found that the drying efficiency was very poor.

As is clear from the comparison between Example 1-2 and Comparative Example, it was found that it is preferable from the viewpoint of drying efficiency that a reheating heater is installed and the temperature of the dry air is increased to 40 ° C. or higher.

The sludge dried by the above-mentioned drying method was used without any problem as a fertilizer. (Example 2) Next, the results of tests as to whether or not the generation of ammonia gas or the like when drying sludge can be prevented by the method of the present invention are shown below.

FIG. 4 is a flow chart for the above test (hereinafter referred to as a peeping test). As can be seen from FIG. 4, the structure is basically the same as that of the sludge drying apparatus 1 shown in FIGS. 1 and 2, but for testing purposes, it is simplified, and the drying air is circulated. Not to be. The sludge is dried, and the air discharged from the drying section is directly sent into the gas collection bottle 21 immersed in the thermostat 20, and then into the water in the gas collection bottle 21.

Here, if ammonia gas is generated when the sludge is dried, the generated ammonia gas should be discharged from the drying section together with the drying air and dissolved into the water in the gas collection bottle 21. is there. That is, by measuring the ammonium ion (NH ₄ ⁺ ) dissolved in the water in the collection bottle 21, it is possible to determine whether or not ammonia gas is generated when the sludge is dried.

Table 1 shows the results of the above peeping test.

[0059]

[Table 1]

Table 1 shows that a large amount of ammonia was generated when the sludge temperature was 75 ° C., but almost no ammonia was generated at 45 ° C. in this way,
In the present invention, since the sludge is dried with relatively low-temperature dry air, the sludge can be dried in a temperature range of 25 ° C. to 60 ° C., thereby preventing generation of ammonia gas. is there.

[0061]

According to the above-mentioned method, that is, the sludge is dried at a temperature of 25 ° C. to 60 ° C. by using air dried under a predetermined condition without directly heating the sludge, so that the odor of ammonia or the like is reduced. The generation of gas can be prevented and the sludge can be efficiently dried, so that the sludge can be made a sanitary final product.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of an apparatus for drying sludge of the present invention and drying conditions in Example (1-1).

FIG. 2 shows an example (1-
It is explanatory drawing which shows the drying condition of 2).

FIG. 3 is an explanatory diagram showing drying conditions of a comparative example.

FIG. 4 is a flow chart for a peeping test of ammonia gas.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Sludge drying apparatus, 2 ... Drying apparatus, 3 ... Circulation fan, 4 ... Heat pump type dehumidifying and drying apparatus, 5 ... Sludge, 6 ... Sludge supply hopper, 7 ... Conveyor, 8 ... Dry air inlet, 9 ... Sludge discharge Outlet, 10: Air outlet, 11: Piping, 12: Air cooling unit, 13: Air heating unit, 14: Refrigerant expansion valve, 15: Refrigerant compressor, 16: Refrigerant heat exchanger, 17: Refrigerant circulation circuit, 18 ... reheating heater, 20 ... constant temperature bath, 21 ... gas collection bottle.

Continued on the front page F term (reference) 3L113 AA02 AA07 AB03 AC01 AC16 AC21 AC22 AC25 AC35 AC45 AC48 AC49 AC51 AC63 AC79 AC87 AC90 BA37 CA04 CA08 CA09 DA02 4D059 AA03 AA07 AA23 BA01 BA11 BA21 BD01 BD21 BD40 BE00 BJ00 CA01 CB04 CB

Claims (2)

[Claims] 1. A cooling step of cooling and dehumidifying air used for drying sludge to 5 ° C. or lower than the temperature of sludge immediately after drying, and heating the air cooled in the cooling step to 40 ° C. or more. A heating step of drying air; and a step of directly contacting the drying air with the sludge to be dried, and drying the sludge within a range where the temperature of the sludge immediately after drying is 25 ° C to 60 ° C. A drying step, comprising: circulating and using the air whose temperature has been reduced and humidified by the drying step to the cooling step. 2. The sludge obtained by subjecting sludge generated by sewage treatment to anaerobic or aerobic digestion and dewatering sludge, sludge subjected to anaerobic digestion and dehydration during human waste treatment, or garbage crushed into human waste. The sludge drying method according to claim 1, wherein the sludge is mixed with anaerobic digestion and dehydrated, or a mixture of these sludges.