JPH0440055B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for deodorizing exhaust gas produced from organic chemical fertilizers. More specifically, the present invention relates to a method for deodorizing exhaust gas from the granulation and drying process of the fertilizer, in which the exhaust gas is washed with a phosphoric acid solution. Demand for organic chemical fertilizers, that is, fertilizers obtained by wet granulation and drying of so-called chemical fertilizers and natural organic fertilizers, has been increasing in recent years from the viewpoint of labor saving and other rationalization of fertilizer application. However, since the production of organic chemical fertilizers inevitably involves the problem of bad odors, there is a need for technology to deodorize the exhaust gas during production. Among general deodorizing techniques, a wet deodorizing method is usually used for low-concentration complex odors, and acids, alkalis, sodium hypochlorite, glyoxal, and other agents are used as deodorizing agents. However, the exhaust gas from the organic chemical fertilizer factory according to the present invention is large in volume, contains carbon dioxide and various other odorless and odorous components, and it is virtually impossible to completely remove dust.
An industrially possible deodorizing method has not yet been found. As a result of various studies, the present inventors have found that when exhaust gas from an organic chemical fertilizer factory is cleaned with wet phosphoric acid, it is effectively deodorized, and that the phosphoric acid used for deodorization is
The present invention was completed with the knowledge that it can be used without any problem in the production of ammonium phosphate, which is an active ingredient in organic chemical fertilizers. As described later, instead of phosphoric acid,
Even if sulfuric acid, aqueous caustic soda solution, sodium hypochlorite solution, or water is used, the complex odor characteristic of the exhaust gas cannot be removed. On the other hand, according to the method of the present invention, the complex odor is removed and a slight phosphoric acid impurity odor remains instead, but this primary cleaning gas can be cleaned with water or sodium hypochlorite solution. Almost completely removed. As is clear from the above description, an object of the present invention is to provide a method for deodorizing exhaust gas produced in organic chemical fertilizer production. Another object is to provide a deodorizing method that does not require any special treatment method for the used exhaust gas cleaning agent. The present invention has the following main configuration (1) and embodiment configurations (2) to (3). (1) A method for deodorizing exhaust gas from organic chemical fertilizer production, which is characterized by cleaning exhaust gas from the granulation and drying process, which is the final process of organic fertilizer manufacturing, with a phosphoric acid solution. (2) The deodorizing method according to item 1 above, wherein the dust in the exhaust gas is separated and then washed with a phosphoric acid solution. (3) The deodorizing method according to item 1 above, wherein a wet phosphoric acid solution is used as the phosphoric acid solution. The configuration and effects of the present invention will be explained in detail below. The organic compound fertilizer according to the present invention, as mentioned above, includes so-called chemical fertilizers such as ammonium sulfate, ammonium chloride, potassium sulfate, ammonium phosphate, potassium chloride, potassium phosphate, urea,
- Fertilizers produced by chemical reactions, whether organic or inorganic, such as oxo-4-methyl-6-ureidohexahydropyrimidine, isobutylidene diurea, or oxamide, and so-called natural fertilizers, such as rapeseed meal, soybean meal, and cotton. Oil extraction lees such as fruit lees,
A fertilizer made by mixing and granulating fish meal, dried fish, aquatic fertilizers such as fish bacteria, and animal fertilizers such as bone meal. In addition, the granulation and drying process, which is the final process of producing organic chemical fertilizer, is almost the same as the final process of known (composite) chemical fertilizers, in which a predetermined amount of each fertilizer ingredient is mixed and granulated using a granulator. This refers to the process of crushing and drying grains. The exhaust gas from the granulation and drying process (hereinafter referred to as the exhaust gas according to the present invention) mainly consists of air, water vapor, carbon dioxide gas, a small amount of organic compound fertilizer dust, and a trace amount of malodorous components that are treated by the present invention. If this exhaust gas is released into the atmosphere as it is or after the above-mentioned dust has been removed, it will cause foul odor pollution as mentioned above. Although the chemical component of the foul odor cannot be specifically identified, it is thought to be a complex of commonly known low molecular weight amines, mercaptans, and others. The concentration of such malodorous components in the exhaust gas according to the present invention is thought to vary widely depending on the manufacturing conditions of the organic compound fertilizer, but is estimated to be in the range of several ppm to 1000 ppm. The phosphoric acid solution used in the present invention may be a purified product as long as it has a concentration suitable for cleaning exhaust gas according to the present invention (described later) (5 to 35% by weight, preferably 10 to 30% by weight based on ₄ minutes of H ₃ PO). It can be used regardless of whether it is industrial phosphoric acid or not. Generally, the so-called wet phosphoric acid method is easy to use. The cleaning of exhaust gas with a phosphoric acid solution according to the present invention is not limited to a specific liquid-gas contact method, but in order to sufficiently contact a relatively small amount of cleaning liquid with a large amount of the exhaust gas, it is necessary to use a gas-liquid method as described below. A countercurrent contact method is preferred. One aspect of this cleaning method will be explained using figures. The figure is a flow sheet of a deodorizing device used to carry out the method of the present invention. Air taken into the air pump 1 passes through an air pipe a, is heated to, for example, 80°C by a heater 2, and is supplied to a kneader 3 via a heated air pipe b. The organic compound fertilizer that has been pre-loaded into the kneader 3 and humidified is
The mixing by the kneading machine and the heating by the hot water jacket 3' generate a foul odor, which is diluted by the heated air supplied from pipe b and becomes foul-smelling exhaust gas (Note: The part marked ←A→ in the diagram is the foul-smelling device). ).
The foul-smelling gas leaving the kneader 3 passes through the pipe c to the first
Enter the bottom of absorption tower 4. The column used in the Examples and Comparative Examples described later had an inner diameter of 25 cm ψ and a height of 35 cm in the packing section, and the packing section was filled with magnetic rings measuring 8 mm ψ x 8 mm h. An absorption liquid tank 5 with a jacket 5' provided at the bottom of the absorption tower contains a predetermined amount of absorption liquid, and the absorption liquid is fed to the top of the tower through an absorption liquid pump 6 and piping f, and the inside of the tower is Pass and circulate. The operating conditions of the first absorption tower are not limited, but 10 to 200 ml of absorption liquid is allowed to pass through 1Nl of malodorous gas.
Preferably 20 to 100 ml is allowed to flow down. The foul-smelling gas is
Since it is waste gas from the granulation drying process, the temperature is e.g.
~100℃, which is considerably higher than normal temperature. On the other hand, the temperature of the absorption liquid in the first absorption tower does not necessarily have to match, but it is possible to absorb the heat of the malodorous gas and
The temperature will be something like 30-70℃. In the method of the invention, the aforementioned phosphoric acid solution is used as an absorption liquid in the first column. The foul-smelling gas from which most of the odor characteristic of organic chemical fertilizers has been removed in the tower is supplied to the bottom of the second absorption tower 7 via pipe d. The shape and dimensions of this column are the same as those of the absorption column 1, and the washing liquid is fed to the top of the column 7 and circulated through the absorption liquid tank 8, the washing liquid pump 9, and the piping g. In the second absorption column, an auxiliary absorbent such as water or a dilute solution of sodium hypochlorite (note, concentration 100-1000 ppm) is used in place of the phosphoric acid in the first column. Removes phosphoric acid impurity odor from exhaust gas. The gas/liquid ratio is almost the same as in the case of the first column, and the treatment temperature is not limited, but the temperature of the exhaust gas exiting the first column is 30 to 70°C, and the gas temperature at the exit of the second column is 25 to 55°C. That's about it. The temperature of the circulating absorption liquid, initially at room temperature, rises to about 25-50°C.
The exhaust gas treated in the tower is discharged from pipe e. The part ←B→ in the diagram described above is the odor removal device. In an industrial-scale device, it is desirable to remove the dust in the exhaust gas from the malodor generating device A above using a known dust separator, cyclone, etc., and then supply it to the first absorption tower. This is because when the dust comes into contact with the phosphoric acid liquid, which is the absorption liquid in the first column, the odor removal ability of the phosphoric acid liquid is greatly reduced (see Example 3 below). Whether or not the deodorizing power of the phosphoric acid solution and the second column absorption liquid is maintained can be determined by sampling the exhaust gas at each stage from S1, S2, and S3 over time during operation of the device shown in the figure. Part or all of the absorbing liquid is replaced intermittently or continuously before the force drops significantly. The substituted used phosphoric acid and absorption liquid can be used without any problem in the production of organic chemical fertilizers by neutralizing them with ammonia and/or magnesium hydroxide, and no foul odor will be generated during the neutralization. (Note, see Reference Examples 1 and 2 below). The deodorizing power of organic compound fertilizer exhaust gas with phosphoric acid solution varies depending on the type of phosphoric acid solution, concentration, cleaning conditions, proportion of natural organic fertilizer in organic compound fertilizer, and granulation drying conditions, but on a dry basis. 30 to produce 1000g of organic fertilizer containing 30% by weight of natural organic content.
% phosphoric acid solution 10-500ml, preferably 50-200ml is required. Therefore, if it is an organic chemical fertilizer that contains P ₂ O ₅ as a chemical fertilizer component, the P ₂ O ₅
By neutralizing and mixing part or all of the above-mentioned absorption-treated phosphoric acid solution, the treatment of the "absorption-treated phosphoric acid solution" can be considered separately in a place other than organic fertilizer production. There will be no need. The present invention will be explained below with reference to Examples and Comparative Examples. Example 1, Comparative Examples 1 to 4 Using the apparatus shown in the figure, humidified organic chemical fertilizer was placed in a kneader 3, and heated air was sent to the kneader via an air pump 1 and a heater 2 to generate malodorous gas. While the malodorous gas was sequentially passed through the first column 4 and the second column 7, it was washed with a predetermined cleaning agent (absorbing liquid), respectively, to obtain a post-exhaust gas. During this time, the degree of odor of the malodorous gas, primary cleaning gas, and exhaust gas was evaluated by a sensory test on the following four levels. Degree of odor A: Slight odor B: Weak odor C: Strong odor D: Bad odor The material charged in kneader 3 is organic compound fertilizer 500
1:1 of oil cake and fish bacteria as a natural organic fertilizer
The mixture contains 30% by weight (weight ratio) and is further humidified by adding 150g of water. While mixing, pass this mixture through a jacket of warm water for 80 minutes.
heated to ℃. During this time, the heated air mentioned above was
The malodorous gas generated was sent to the bottom of the first column 4. foul-smelling gas, 1
Samples of the next cleaning gas and exhaust gas were collected from sampling ports S1, S2, and S3. The cleaning test continued for 2 hours after the onset of odor, and
The degree of odor of gases S2 and S3 was evaluated every 30 minutes. Each column was circulated with a pump at a rate of 150/min with a given absorption liquid (note: 200 ml each in tank 5 or 6). The table below shows the type of absorbent and the degree of deodorization.

[Table] As is clear from the table, if an effective absorbent is used in the first column, water washing is sufficient for the second column. sulfuric acid,
Cleaning with caustic soda or sodium hypochlorite cannot remove the complex odor characteristic of natural organic fertilizers. Example 2 The same procedure was carried out except that the humidified organic compound fertilizer in the kneader 3 was replaced after 2 hours. As a result, it was found that the deodorizing ability of the phosphoric acid absorption liquid could be maintained up to two batches of the organic compound fertilizer. Reference Example 1 Phosphoric acid whose bad odor absorption capacity reached its limit in Example 2
100ml was taken and ammonia water was added to neutralize it to pH 7.0. The neutralized product was then heated to 80°C, a small amount of air was blown into it, and the odor in the exhaust gas was evaluated in the same manner as in Example 1. This odor was a phosphoric acid impurity odor and the odor level was B. Reference Example 2 Phosphoric acid whose bad odor absorption capacity reached its limit in Example 2
100 ml was taken, and equivalent amounts of aqueous ammonia and magnesium hydroxide were added and reacted to produce magnesium ammonium phosphate. Thereafter, an air blowing test was conducted in the same manner as in Reference Example 1, and the degree and content of the odor were the same as in Reference Example 1. The results of Reference Examples 1 and 2 show that even if phosphoric acid, whose malodor absorption capacity has reached its limit, is used as a raw material for chemical fertilizers, the malodor of natural organic fertilizers will not be regenerated. Example 3 Instead of the wet method phosphoric acid solution used in Example 1, organic chemical fertilizers with a phosphoric acid content of 0.2, 1, and 5% by weight (note, the one used in Example 1) were mixed and dispersed or dissolved. Exhaust gas deodorization was carried out in the same manner except that the same method was used. As a result, even in the case of addition of 0.2% by weight, the deodorizing effect clearly decreased. This result indicates that the exhaust gas from the granulation and drying process of organic chemical fertilizer should be treated after removing dust from the exhaust gas before the deodorizing treatment according to the present invention. Example 4 The same procedure was carried out as in Example 1, except that the air supplied in Example 1 was replaced with exhaust gas from the chemical fertilizer granulation and drying process (note: no natural organic fertilizer was included). There was no change in the deodorizing power of the phosphoric acid solution. This result shows that the deodorizing power of the phosphoric acid solution is not reduced by the exhaust gas from the chemical fertilizer granulation process.

[Brief explanation of drawings]

The figure shows a flow sheet of a deodorizing device used in the method of the invention. In the figure, 1... Air pump, 6, 9... Cleaning liquid pump, 2... Heater, 3... Kneader, 5, 8
...Tank, 4...Washing 1st tower, 7...Washing 2nd
Tower, S1, S2, S3...Gas sampling ports.

Claims (1)

[Claims] 1. An organic chemical compound characterized in that the exhaust gas from the granulation drying step, which is the final step in the production of organic compound fertilizer, is washed with a phosphoric acid solution and then subsequently washed with water or an aqueous sodium hypochlorite solution. Deodorizing method for fertilizer manufacturing exhaust gas. 2. The deodorizing method according to claim 1, wherein the dust in the exhaust gas is separated and then washed with a phosphoric acid solution. 3. The deodorizing method according to claim 1, wherein a wet phosphoric acid solution is used as the phosphoric acid solution.