JP2003305303A - Precipitation control method in crystallization tank - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that the temperature and amount of a crystallization mother liquid is affected by fluctuations in the temperature and pressure of steam supplied to a heater in a method for making the particle size of crystals coarse by controlling the precipitation of crystals in a tank, and production quantity and fluctuations in the particle size of crystals are not avoided. <P>SOLUTION: In a method for precipitating crystals by heating a crystal precipitation mother liquid by a heater using steam as a heat source and introducing the heated mother liquid into a crystallization tank, the pressure, temperature and flow rate of steam supplied to the heater are measured and calory is operated from the measured pressure, temperature and flow rate of steam. The calorific difference between the operated calory of steam and precipitation standard calory preset in order to precipitate crystals with a target particle size in the crystallization tank is calculated and the amount of steam supplied to the heater is adjusted on the basis of the calorific difference. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coarsening a crystal grain size by controlling crystal precipitation in a tank.

[0002]

2. Description of the Related Art Conventionally, for example, in a crystallizer for producing an inorganic substance such as ammonium sulfate, urea, ammonium nitrate, and ammonium chloride which precipitates and crystallizes, it is possible to control the grain size to be precipitated in a crystallization tank. It was important to obtain crystal grains with a grain size of high commercial value and with uniform grain size.

As an example, FIG. 1 shows a process for producing ammonium sulfate by reacting an ammonia component in a coke oven gas (hereinafter referred to as COG) generated in a coke oven in an integrated iron-making process with dilute sulfuric acid. The COG containing ammonia flowing in from the lower part of the ammonia saturator 1 rises while coming into countercurrent contact with the ammonium sulfate mother liquor (free sulfuric acid containing) which is the crystal precipitation mother liquor sprayed from the nozzle 2 in the same saturator 1 and rises from the upper part. Derive. At this time, ammonia in the COG is absorbed by the ammonium sulfate mother liquor and flows down to the lower part of the saturator 1. The ammonium sulphate mother liquor that has flowed down returns to the circulation tank 5 through the pipe 4, and when the concentration of ammonium sulfate is a predetermined value, this ammonium sulphate mother liquor is extracted from the circulation tank 5 by the pump 8 through the pipe 9 and the heater 10 and the evaporator 11 , To a crystallizer A comprising a crystallization tank 12.

On the other hand, the ammonium sulphate mother liquor having a low ammonium sulphate concentration is further sent by the pump 6 through the pipe 7 into the saturator 1 again and sprayed from the nozzle 2. The sulfuric acid content in the ammonium sulphate mother liquor that has been reduced by this ammonia absorption is supplied to the circulation tank 5 from the dilute sulfuric acid supply pipe 41. The ammonium sulphate mother liquor sent to the crystallizer A in the above state is further heated by the above-mentioned heater 10, and further, the condenser 11a and the ejector 11b evaporate the water in the evaporator 11 which maintains a vacuum, and the ammonium sulfate supersaturated state. The ammonium sulphate mother liquor is a downward trumpet-shaped downcomer 13 provided by immersing it in the crystallization tank 12.
Flows down to the bottom of the tank 12 and rises in the tank 12.

This supersaturated ammonium sulphate mother liquor is unstable and is deposited and adheres to the growing crystal nuclei which are settling from above while rising in the crystal tank 12 to further grow the crystal and bring it into a supersaturated state. Lost, it flows into the supernatant collection gutter 16 provided below the liquid surface of the crystallization tank 12, and the heater 1 is again supplied by the pump 17.
Sent to 0. The crystal grains grown in this way are extracted from the bottom of the crystal tank 12 in a slurry state by the pump 40 via the pipe 14, and the dehydrator 1 in the dehydration / drying process.
8. After passing through the dryer 19, it becomes ammonium sulfate.

The particle size of the product ammonium sulphate thus produced is preferably 10 mesh or more for use as a fertilizer, and when it is extracted from the bottom of the crystallization tank 12, the particle size should be within this range. It is important to always control and adjust the amount of crystals in the crystal tank 12 in the ammonium sulfate manufacturing process and the growth thereof. Therefore, conventionally, the crystal grain size of ammonium sulfate extracted from the bottom of the crystal tank is regularly measured, and a liquid pressure measuring device provided with a plurality of crystal suspension concentration distributions in the height direction in the crystal tank, The liquid pressure was continuously measured, and the amount of vapor to the heater was adjusted from the relationship between the liquid pressure and the concentration to control the amount of crystal evaporation, thereby adjusting the crystal grain size in the tank.

However, conventionally, steam has been generally used as a heat source for the heater. Since this steam used is a steam that has a substantially constant amount of heat and does not fluctuate, a stable supply can be secured only by controlling the flow rate when supplying it to the heater.

[0008]

As described above, in the manufacturing process of ammonium sulfate, the steam used as the heat source to the heater is usually produced by a boiler, and the steam is used, so that there is little fluctuation. It was possible to supply a stable amount of heat to the heater. However, in the integrated steelworks, used exhaust heat is constantly generated from the heat sources used in various factories in the plant, so it is necessary to utilize that heat to make steam in the boiler and reuse that steam for various heat sources. Is being carried out. Therefore, the steam is also used for the heater.

However, the steam, which is generated from various boilers, is not always uniform in temperature, flow rate, pressure, and the like, and large fluctuations may occur depending on the generation timing. For example, an exhaust heat boiler (hereinafter referred to as OG) for recovering heat emitted from the converter.
The steam from (B) is intermittent in the converter operation, and accordingly, the steam generated from the OGB also changes. When this steam is supplied to the heater as it is by controlling the flow rate as it is, the supplied heat amount fluctuates from time to time, and the temperature of the ammonium sulphate mother liquor introduced into the evaporator also fluctuates with the fluctuation of the heat amount.

As described above, in the conventional method, fluctuations in the temperature and pressure of the steam supplied to the heater affect the fluctuations in the temperature and amount of the ammonium sulphate mother liquor, forcing an unstable operation in the production of ammonium sulfate. There was a drawback that the production amount and the particle size variation of ammonium sulfate were unavoidable.

[0011]

The present invention has been made in order to solve the problems in the above-mentioned conventional method, and the gist of the invention lies in the following means. (1) In a method of heating a crystal precipitation mother liquor with a heater using steam as a heat source and introducing the heated crystal precipitation mother liquor into a crystal tank to precipitate a crystal product, the pressure of steam supplied to the heater is The temperature and flow rate are measured, and the calorific value is calculated from the measured steam pressure, temperature and flow rate, and the calculated calorific value of the steam and the preset reference calorific value for precipitating a crystallized product of a target grain size in the crystal tank A method for controlling precipitation in a crystallizing tank, in which the difference in the amount of heat between the heating element and the heating element is calculated, and the amount of steam supplied to the heater is adjusted based on the difference in the amount of heating. (2) The precipitation control method in a crystal tank according to (1), wherein the amount of generated drain is estimated from the temperature of the steam supplied to the heater, and the calorific value of the estimated amount of generated drain is subtracted from the calculated calorific value of steam. (3) The temperature and flow rate of the crystal precipitation mother liquor heated by the heater are measured, the calorific value of the crystal precipitation mother liquor is calculated from the measured temperature and flow rate, and the calculated calorific value and the preset reference calorific value of the crystal precipitation mother liquor are calculated. The method for controlling precipitation in the crystallizing vessel according to (1) or (2), wherein the difference in the amount of heat from the above is calculated and the difference in the amount of heat is added to the amount of heat for precipitation.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, when the temperature, pressure and flow rate of steam supplied to the heater in the manufacturing process of ammonium sulfate fluctuate, an amount of heat corresponding to the amount of ammonium sulphate mother liquor and the temperature is input. The need has arisen. Therefore, in order to ensure stable production, operation and particle size of ammonium sulfate, the present inventors have focused on the effective heat amount supplied to the heater and continuously detected the pressure, temperature, and flow rate of steam flowing into the heater. Then, calculate the effective heat quantity from the measured steam pressure, temperature, and flow rate,
It has been found that the above object can be achieved by adjusting and controlling the steam supplied to the heater based on the calculated effective heat quantity.

However, even if the amount of heat necessary for precipitating ammonium sulfate having a target particle size (10 mesh or more) in the crystallization tank 12 is supplied to the heater 10, the ammonium sulfate having the above target particle size may not be precipitated. It turned out to be. In order to prevent this, the present inventors further conducted experiments and studies, and as a result,
It has been found that this tendency becomes stronger as the steam temperature supplied to the heater 10 becomes lower. And it came to the conclusion that most of the heat was lost due to the generation of drainage in the heater 10.

Therefore, the average temperature of the steam supplied to the heater 10 is used as a reference temperature, and this reference temperature is compared with the supplied steam temperature. Especially, when the supplied steam temperature is lower than the reference temperature, the temperature difference is And based on the temperature difference,
It was found that ammonium sulfate having a target particle size can be stably obtained by increasing the amount of steam supplied to the heater 10.

FIG. 2 is a schematic view of the main part of the control of the supply steam in the present invention. In the present invention, information such as the pressure, temperature, and flow rate of the steam supplied to the heater 10 for heating the steam is measured, and each measured value is input to the controller 25, and the controller 25 causes the crystal tank 12 to operate. The amount of steam commensurate with heating the ammonium sulphate mother liquor to a temperature for depositing ammonium sulfate of 10 mesh or more is calculated, and the amount of steam (total amount of heat) supplied to the heater 10 is determined by the information (signal), and the steam control valve 21 is adjusted, and the adjusted steam is sent to the heater 10.

Further, the controller 25 will be described in detail with reference to FIG. In FIG. 3, reference numeral 26 is a reference calorific value setting device for setting a precipitation reference calorific value for forming an ammonium sulfate mother liquor having a calorific value necessary for precipitation of ammonium sulfate having a target particle size (10 mesh or more) in the crystallization tank 12, and 27 is the reference value. Reference temperature setting device for setting the temperature, 28 is a steam thermometer provided in the steam supply pipe 24 for supplying to the heater 10, 29 is the steam supply pipe 24
Is a steam pressure gauge, and 30 is a steam flow meter provided in the steam supply pipe 24.

Reference numeral 31 is a steam thermometer 28, a steam pressure gauge 29,
Steam temperature, steam pressure measured by each of the steam flow meters 30,
It is a steam calorific value calculation unit that inputs the steam flow rate and calculates the actual calorific value of the steam. Reference numeral 32 is a correction calorific value calculation unit, which is a steam temperature measured by the steam thermometer 28 and a reference temperature setter 27.
Input the reference temperature from to calculate the steam correction coefficient.

When the temperature of the steam supplied to the heater 10 decreases, it becomes drain in the heater 10 and does not work effectively as a heat source for heating the ammonium sulfate mother liquor. Moreover, the amount of this drain increases as the vapor temperature decreases, and the amount of ineffective vapor that does not work effectively as a heat source for heating the ammonium sulfate mother liquor increases. For this reason, the difference between the reference temperature and the actually measured steam temperature and the invalid steam (heat loss) result. Therefore, a table having a relationship with a coefficient for correcting this is input in advance to the correction calorie calculation unit 32, and the steam thermometer is input. The steam temperature measured by 28, the steam temperature measured by the steam thermometer 28, and the reference temperature from the reference temperature setting device 27 are input to find the temperature difference, and the calorific value of the steam is corrected from the temperature difference based on the table. Calculate the coefficient.

Reference numeral 33 denotes an adjusting calorific value calculating unit, which is a precipitation calorific value calculating unit 31 for the precipitation reference calorific value set in the standard calorific value setting unit 26.
Actual calorific value of the steam calculated in step 3, corrected calorific value calculation unit 32
Input the calorific value correction coefficient calculated in step 1, calculate the required calorific value from the precipitation reference calorific value and calorific value correction coefficient, calculate the calorific value difference between the calorific value and the actual calorific value, and calculate the adjusted calorific value so that this calorific value difference disappears. . Reference numeral 34 is a steam control valve adjustment instructing unit, which adjusts the amount of heat from the adjusting heat amount calculation unit 33, and the steam thermometer 2
The valve control unit 35 that inputs the steam temperature measured in 8 and the steam pressure measured by the steam pressure gauge 29, calculates the opening adjustment amount of the steam control valve 21, and adjusts the opening of the steam control valve 21.
The opening adjustment instruction is given to.

Then, the valve control unit 35 adjusts the steam control valve 21 in accordance with the adjustment instruction of the steam control valve adjustment instruction unit 34. The calorific value correction coefficient set in the corrected calorific value calculation unit 32 can be arbitrarily set. This is because the amount of steam that causes heat loss varies depending on the season, that is, the outside air temperature, and therefore it is necessary to periodically measure the particle size of ammonium sulfate that precipitates in the crystal tank 12 and adjust the calorific value correction coefficient. is there.

When the temperature and flow rate of the ammonium sulfate mother liquor flowing into the heater 10 change, a thermometer 15 and a flow meter 20 are provided on the inlet side of the heater 10 to measure the temperature and flow rate of the ammonium sulfate mother liquor. To do. Then, the measured temperature of the ammonium sulfate mother liquor,
The flow rate is input to the ammonium sulphate mother liquor calorific value calculation unit 22, the calorific value of the ammonium sulphate mother liquor is calculated, and output to the fluctuating calorific value calculation unit 23. This fluctuating heat quantity calculation unit 23 calculates the difference between the preset reference heat quantity and the inputted ammonium sulfate mother liquor heat quantity as the fluctuating heat quantity,
It outputs to the adjustment calorie calculation part 33.

When the input fluctuating calorific value is positive, that is, when the calorific value of the ammonium sulphate mother liquor is higher than the reference calorific value, the adjusted calorific value calculating section 33 corresponds to the standard calorific value setting unit 2 for the higher calorific value.
The amount of steam supplied to the heater 10 is reduced by subtracting from the reference heat amount input from 6. On the contrary to the above, the fluctuating heat quantity input to the adjusting heat quantity calculating unit 33 is negative, that is,
When the calorific value of the ammonium sulfate mother liquor is lower than the standard calorific value, the low calorific value is added to the standard calorific value input from the standard calorific value setting device 26 to increase the steam amount supplied to the heater 10.

If the crystallization of ammonium sulfate in the crystallization tank 12 fluctuates due to any factor even if the amount of vapor is adjusted, it is preferable to adjust the amount of ammonium sulfate mother liquor supplied to the evaporator 11. An adjustment control valve 3 is also provided in the ammonium sulfate mother liquor line so that the supply amount of ammonium sulfate mother liquor can be adjusted. Although not shown, the ammonium sulphate mother liquor is equipped with an ammonium sulphate mother liquor tank on the upstream side, and in the case where the crystallization of the ammonium sulphate mother liquor in the above-mentioned crystallization tank is delayed, an operation to reduce the amount of ammonium sulphate mother liquor supply is performed.
At that time, the ammonium sulphate mother liquor is temporarily stored in the ammonium sulphate mother liquor tank and placed as a buffer in terms of equipment according to the operating conditions. Although the case of producing ammonium sulfate has been described above, the present invention is not limited to this, and the same reason can be applied to the case of producing the above-mentioned urea, ammonium nitrate, ammonium chloride or the like.

[0024]

EXAMPLES Examples of the present invention will be described below together with conventional examples. The ammonium sulfate manufacturing equipment used in the examples is conventional, and the equipment is 1) ammonium sulfate manufacturing capacity: 9 t / h. 2) Capacity of crystal tank: height 10m, body diameter 6mφ, capacity 2
00 m ³ . 3) Standard ammonium sulfate mother liquor: temperature 52 ° C., supersaturation degree (ammonium sulfate production amount / circulating ammonium sulfate mother liquor volume) 2.0 to 2.5 / m ³ , circulating ammonium sulfate mother liquor volume 3600 to 4500 Nm ³ / h. Is. Table 1
The operating conditions and the operating results are shown in. Both the present invention example and the conventional example are values during a period of 20 days of operation.

[0025]

[Table 1]

Regarding the density of ammonium sulphate in the crystallizing tank, the variation was large in the conventional example, but the variation was small in the example of the present invention. As a result, the ratio of ammonium sulfate as the product particle size to the total ammonium sulfate was 10 mesh or more. Fluctuation of
It is possible to obtain a uniform production amount, and the effect of the present invention is clearly shown.

[0027]

As described above, according to the present invention, by improving the appropriate control system so that the steam supplied to the heater is supplied based on the effective heat quantity, the steam quantity can be reduced without any labor. It is possible to constantly maintain the optimum state, to suppress the variation of the crystal grain size in the crystal tank, and to avoid various operational inconveniences caused by the fluctuation of the steam, which enables stable operation. As a result, the particle size of the manufactured product can be maintained at a stable particle size. It is also possible to fully automate the fluctuation control of the steam supply amount to the heater, which has a beneficial effect in industry.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an outline of a manufacturing process of ammonium sulfate.

FIG. 2 is a diagram schematically showing a control system for supply steam and ammonium sulfate mother liquor in the present invention.

FIG. 3 is a diagram showing details of a signal system in a controller.

[Explanation of symbols]

1 Ammonia saturator 2 nozzles 3 control valve 5 circulation tanks 10 heater 11 evaporation cans 12 Crystal tank 15 Thermometer 18 dehydrator 20 Flowmeter 21 Control valve 22 Ammonium sulfate mother liquor calorific value calculation unit 23 Varying calorific value calculation unit 24 Steam supply pipe 25 controller 26 Reference calorie setting device 27 Reference temperature setting device 28 Steam thermometer 29 Steam pressure gauge 30 Steam flow meter 31 Steam calorific value calculation unit 32 Corrected calorie calculation unit 33 Controlled calorie calculator 34 Steam control valve adjustment command section 35 valve controller 40 pumps 41 Dilute sulfuric acid supply pipe A crystallizer

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) B01D 9/02 B01D 9/02 625D C01C 1/24 C01C 1/24 B

Claims (3)

[Claims] 1. A method of heating a crystal precipitation mother liquor with a heater using steam as a heat source and introducing the heated crystal precipitation mother liquor into a crystal tank to precipitate a crystal, The pressure, temperature and flow rate are measured, and the calorific value is calculated from the measured vapor pressure, temperature and flow rate, and the calculated calorific value of steam and the preset deposition for precipitating a crystallized product of a target grain size in the crystallizing tank. A method for controlling precipitation in a crystallizing vessel, which comprises obtaining a difference in calorific value from a reference calorific value and adjusting the amount of steam supplied to the heater based on the calorific value difference. 2. The crystal tank according to claim 1, wherein a drain generation amount is estimated from a temperature of steam supplied to the heater, and a heat amount of the estimated generated drain amount is subtracted from the calculated steam heat amount. In-house precipitation control method. 3. The temperature and flow rate of the crystal precipitation mother liquor heated by the heater are measured, the calorific value of the crystal precipitation mother liquor is calculated from the measured temperature and flow rate, and the calculated calorific value and the preset crystal precipitation mother liquor are calculated. The deposition control method in a crystallizing tank according to claim 1 or 2, wherein a difference in calorific value from a reference calorific value is obtained and the calorific value difference is added to the precipitation standard calorific value.