JPS6260159B2 - - Google Patents

Description

[Detailed description of the invention]

Several chemical industrial processes are known that discharge aqueous solutions containing ammonium groups NH ₄ ⁺ sulfate groups SO ₄ ^-- and organic substances. A typical example is a process for producing acrylonitrile (hereinafter referred to as AN) using a methacrylic acid methyl ester (hereinafter referred to as MMA) ammoxidation method. All of these produce a large amount of waste liquid per unit of production,
It is undesirable to mix high concentrations of ammonium sulfate and organic matter into this and dispose of it as it is because it will pollute rivers and oceans. Besides,
Ammonium ions other than ammonium sulfate are present in AN waste liquid.
It contains NH ₄ ⁺ and cyanide ions CN ^- , and these treatments must be performed at the same time. In general, incineration is the most reliable and simple method for removing organic matter from wastewater containing a high degree of organic matter. The conditions for incinerating the waste water solution or its concentrate, which is the subject of the present invention, vary depending on the type and size of the furnace, but in normal cases, the incineration temperature is 800°C.
℃ or higher, preferably 900℃ or higher, and maintain the incineration gas under conditions such that 1.5% Vol or more, preferably 3.0% Vol or more of oxygen remains, and the contents in the furnace and the gas are uniform and strong. The organic matter is almost completely combusted by proper mixing. (Hereinafter, all furnace temperatures and residual concentrations refer to those after co-firing in this way.) Before explaining the contents of the present invention in detail, we will explain the thermal decomposition of calcium sulfate CaSO ₄ at high temperatures,
We will explain the behavior of CaSO ₄ , which coexists with organic substances, when it is incinerated at high temperatures. CaSO ₄ decomposes at high temperatures as shown in equation (1) and exhibits a constant decomposition pressure. CaSO ₄ →CaO＋SO ₂ +1/2O ₂ ...(1) The calculated value from the free energy is
When O ₂ →0%, the partial pressure of SO ₂ is approximately 9× at 900℃
10 ^-6 Atm or 9ppm, approximately 100ppm at 1000℃, 1100℃
It increases rapidly to 8500ppm. The present inventors also prepared an aqueous slurry or cake containing CaSO ₄ and 2 to 3 organic substances.
As a result of combustion tests conducted mainly at 900℃ to 1000℃, the amount of CaSO ₄ remaining in the ash was significantly reduced compared to the amount originally present, and the amount of reduction is shown by equation (1). The value far exceeded the decomposition value to SO ₂ . In addition to CaSO ₄ , a considerable amount of CaS remained in the ash. These phenomena are caused by the fact that when organic matter is combusted, the area around CaSO ₄ is temporarily covered with unburned organic matter, creating a reducing atmosphere, which causes equation (2), and the resulting CaS is exposed to CaSO ₄ + (H ₂ , CO )
→CaS+(H ₂ O, CO ₂ ) …(2) CaS+H ₂ O→CaO+H ₂ S …(3) H ₂ S+O ₂ →H ₂ O+SO ₂ …(4) H ₂ O acts to reduce the equation (2). This generates H ₂ S, which mixes with the gas and reacts with the remaining O ₂ to form H 2 S as shown in equation (4).
It is thought that SO ₂ was generated. In fact, experiments have revealed that the greater the amount of organic matter mixed with CaSO ₄ or the lower the ratio value of Ca ⁺⁺ to SO ₄ ^-- , the higher the reaction progress rate of (2), (3), and (4). . Therefore, in order to prevent SO ₂ from being generated in the furnace, SO ₄ ^-- must be removed from the liquid before incineration, or the SO 4 must be thermally decomposed at high temperatures.
Unless conditions are changed to prevent the generation of SO ₂ , the SO ₂ content in incineration waste gas will be enormous, and releasing it into the atmosphere as it is will become a source of pollution. The present invention relates to the treatment of organic matter-containing wastewater solutions containing SO ₄ ^-- , which have such problems, and consists of the following four steps. The first step is to add excess calcium hydroxide Ca(OH) ₂ or calcium oxide CaO to the equivalent amount to neutralize SO ₄ ^-- in the waste liquid, to neutralize the existing SO ₄ ^-- and substantially All calcium sulfate is fixed and precipitated in the liquid as CaSO ₄ , and NH ₄ ⁺ is liberated as NH ₃ . The amount of Ca ⁺⁺ ions added is preferably in the range of 1.5 or more equivalents, preferably 2.0 or more equivalents relative to SO ₄ ^-- . The resulting slurry was filtered with CaSO ₄ 2H ₂ O
It is separated into a cake mainly composed of , and a liquid, which is sent to the next second step. The second step is a liquid concentration step, in which the liquid is heated by direct contact with high-temperature exhaust gas from an incinerator, which will be described later.If necessary, the amount of heating is increased by means such as raising the gas temperature with an auxiliary fuel burner. . Free NH ₃ and other volatile organic substances contained in the liquid are distilled off along with water vapor during concentration. The evaporation residue thus generated is sent to the third step and in an incinerator at an incineration temperature of 800℃ or higher and 1100℃.
Hereinafter, it is preferably incinerated at a temperature of 900°C or higher and 1000°C or lower. At this time, a large amount of Ca ⁺⁺ and a small amount of SO ₄ ^-- contained in the liquid are converted into ash consisting of a large amount of CaO and a small amount of CaSO ₄ , which is discharged and returned to the first step.
SO ₄ ^-- used as part of the neutralizing agent. On the other hand, in the exhaust gas from the furnace, it remains in the supplied liquid.
Although it contains SO ₂ produced by the decomposition of a portion of SO ₄ ^-- , it passes through the second step and undergoes measures such as effective use of sensible heat, before proceeding to the fourth step. As the temperature of the gas decreases, some of the SO ₂ is oxidized to SO ₃ , which will be collectively referred to as SO _x from now on. The gas is washed with water in a scrubber after adding NH ₃ -containing gas generated in the first step if necessary. As mentioned later, NH ₃ in the gas is
in the gas due to large excess adjustment to SO _x
Most of the SO _x is recovered as an aqueous solution of ammonium salt and returned to the first step. Therefore, the ammonium salt of SO _x from the scrubber ultimately becomes Ca salt and precipitates, which is transferred to a cake in the second step. The gas leaving the fourth step has been sufficiently removed for _SOx , but depending on the nature of the raw solution, it may contain other harmful volatile components in addition to _NH3 , so it will be decomposed appropriately in the next flue gas incineration step. and released harmlessly. An embodiment of the invention will now be described with reference to FIG. This is related to the treatment of waste liquid generated from the AN process. For example, the AN process produces waste liquid with the following composition. Table 1 (NH ₄ ) ₂ SO ₄ 1-15wt% Other NH ₄ ⁺ 0.1-5〃 Cyan CN ^- 0.05-0.8〃 Organic compound 3-15〃 Water 75-90〃 Heat of combustion of organic compound Approximately 6000K cal /Kg The low level raw waste liquid 1 is sent to the mixing tank 3, and at the same time new fine powder calcium hydroxide Ca(OH) ₂ or calcium oxide CaO2 is added to the CaO recovered in the incinerator.
Continuously mixed with ash 16 containing CaSO ₄ . In addition, as shown in the figure, the mixing tank 3 is also supplied with an ammonium salt 23 of SO _x recovered from a water scrubber 22, which will be described later. as a whole balance
Ca ⁺⁺ is approximately twice equivalent to SO ₄ ^-- . A part of the liberated NH ₃ becomes gaseous from the mixing tank 3 and is led to the ammonia pent pipe 20 . Approximately 80% of the total ^SO ₄ injected is calcium sulfate CaSO ₄
This is mixed with other organic calcium compounds to form a slurry, which is sent to the next centrifuge 4.
After removing the cake 32 which is excessively separated and mainly composed of CaSO ₄ , the liquid is sent to one end of the hot air contact type evaporator rotating body 5 . The above corresponds to the first step. Cake 32 can be washed with water to make it virtually free of eluate, so in some regions it is possible to dispose of it as is by burying it in soil, etc.; It is possible and within the range of conventional methods to completely incinerate and render harmless the organic substances contained. However, as mentioned above, the furnace tail gas generated at this time contains a high concentration of SO _x gas, so this is removed by the water scrubber 22 described in the fourth step.
Next, move on to the second step. Combustion gas generated by the method described below is blown into the evaporator rotating body 5 from the same direction as the liquid through the connecting duct 19, thereby heating the liquid and evaporating water. At this time, almost all of the free ammonium NH ₃ and other volatile components contained in the liquid are evaporated together with the water, and the concentrated liquid is discharged from the other end of the evaporator. The hot gas supplied to this evaporator is typically 800°C or higher, and there is a large amount of gas in the concentrate.
In addition to Ca ⁺⁺ , AN waste liquid contains organic components that are easily converted into polymers during concentration, so local overheating tends to cause blockage in the vessel. In order to prevent this, it is desirable that the heat transfer surface where gas and liquid come into contact in the vessel be constantly and vigorously cleaned by a stirring and sliding action. For example, JP-A-52-
A method such as 44448 is an example of such a means. In the figure, 5 is a rotating body, 6 is a partition lattice plate, and 7
is a metallic filling and satisfies the above requirements. In addition, a minute amount of CN ^- and a significant portion of volatile organic matter present in the AN raw waste liquid are transferred to the exhaust gas along with the evaporated water due to the heating and concentration described above. The concentrate obtained in this way is passed through the line 1 from the bottom of the outlet hood 9.
0 is supplied to the incinerator 11. Next, the third step will be explained. The incinerator 11 is of a special rotary furnace type, in which the feed liquid with a high residual moisture content is completely combusted, and the temperature of the charge is desirably kept below 1000° C., as mentioned above. For this purpose, for example, the solid incinerator shown in Application Publication No. 51-47277 is suitable for the purpose of the present invention, and this example will be explained using that type of furnace for convenience. The waste liquid concentrate from the liquid feeding line 10 is transferred to the liquid dispersion pipe 12.
It is dispersed and fed into the furnace in the axial direction. Depending on the heat balance requirements, auxiliary fuel 18 is supplied from an auxiliary burner 17 arranged on the side of the inlet hood 15. In addition, in order to burn combustible materials in the waste liquid in the furnace, it is desirable to have severe airflow turbulence in the space inside the furnace, and the combustion air 14 necessary for this is supplied from the air nozzle group 13 while giving a swirling flow inside the rotary furnace 11. Enter at high speed. The concentrate dispersed inside the body of the rotary furnace 1111 is
At that location, the flame from the auxiliary burner 17 and its own combustion heat cause water evaporation, thermal decomposition of the solid content, and gasification to occur continuously, and finally the combustion occurs in the furnace space with the air from the air nozzle part 13, creating an atmosphere. The temperature is raised and this temperature is used again to gasify the water-evaporated solids. At that time, the charge is uniformly stirred by the rotation of the furnace body, and the high-speed blown gas from the air nozzle group 13 swirls in the furnace.
The atmosphere inside the furnace is uniformly oxidizing and comes in contact with the charge evenly, and the charge is combusted uniformly and completely even at a relatively low temperature of 1000°C or less, as described below. Approximately 20% of the SO ₄ ^-- brought into 3 is brought into the incinerator and burned together with a large amount of organic matter, so some of the decomposition shown in equations (2), (3), and (4) above occurs. expected to be received. The ratio of Ca ⁺⁺ to SO ₄ ^-- is high, about 10 times equivalent, but the ratio of organic matter to SO ₄ ^-- is high, and about 20 to 30% of the amount of SO ₄ ^-- brought in becomes SO ₂ and transfers to combustion gas. do. In this way, the incinerated ash mainly consisting of CaO and a small amount of CaSO ₄ is discharged from the bottom of the outlet hood at the other end, circulates through the transport line 16 to the mixing tank 3, and is reused as a neutralizing agent. In this incinerator, what greatly influences the combustion results is the furnace temperature and the concentration of residual oxygen in the exhaust gas. In order to virtually completely burn the organic matter contained in the raw solution in the furnace, in this case the temperature inside the charge furnace must be 900 to 1000℃ or higher, and the residual oxygen in the gas must be 3.0% vol or more. It is desirable to maintain it under appropriate conditions. For general organic compounds, if the temperature is simply to ensure complete combustion, the higher the temperature is, the more advantageous it is, but when the charging material contains a considerable amount of CaSO ₄ as in the present invention,
In addition to the reactions according to equations (2), (3), and (4), it is necessary to prevent this from decomposing in the furnace and generating SO ₂ as shown in equation (1) above, and the temperature of the charge is preferably 1000. It is necessary to avoid temperatures below 1100°C. As described above, the permissible range of temperature conditions in the combustion zone for waste liquid incineration of the present invention is relatively narrow, so the combustion air and the flame of the auxiliary fuel burner in the furnace are the same as shown in the figure. It is better to use the direction. The high-temperature combustion gas generated in the incinerator in this way contains almost no organic components, but contains some SO _x as described above, but is led to the evaporator 5 via the connecting duct 19 as described above. It is used to evaporate moisture and volatile components such as ammonia in waste liquid. The exhaust gas discharged from the evaporator 5 usually has a temperature lower than 200°C and is processed in the next fourth step. The gas is passed through the ammonia vent pipe 2 by the booster blower 21.
The water is sucked together with the ammonia vapor from 0 and pushed into the water scrubber 22, and is subjected to an absorption operation in a conventional manner by water withdrawn from the water spray nozzle 24. _NH3
As mentioned above, the concentration of SO _x is in large excess of the neutralization equivalent point compared to the SO x concentration, so the absorption and removal rate of SO _x is extremely high. In the case of waste liquid as in this example, the exhaust gas that has passed through the water scrubber 22 contains not only evaporated water but also excess ammonia and unabsorbed low-boiling organic matter, so it is sent to a gas incinerator 25 to completely oxidize and remove these harmful components. It is then processed and rendered completely harmless.
In this figure, a ceramic heat storage body is used.
An example of a method for heat exchange between intake air and exhaust air is given below.
This is not necessarily a necessary component of the invention.
While passing through the heat storage body 29 from the bottom to the top, the incoming air is heated by the heat it retains, reaching a temperature of approximately 800 to 900°C, and enters the combustion chamber 26, where it is heated to a heating burner supplied with fuel 28. The combustion gases from No. 27 are mixed and reach a temperature of 950-1050°C. Under such temperatures, in order to completely oxidize and decompose the above-mentioned components, the volume of the combustion chamber must be sufficient for the gas residence time of 1 to 2 seconds, and as described in the above-mentioned incinerator, the residual oxygen must be at least 1.5 %vol preferably 3.0%
vol or more is required. The gas that has been incinerated in this way is heated by giving its own heat while passing through the heat storage body 30 from top to bottom, and its temperature drops to around 250 degrees Celsius.
Dissipates into the atmosphere from the chimney 31. After a certain period of time, these heat storage bodies 29 and 30 reach a state where they are either too cooled or too heated depending on their heat capacity, so valves (not shown) are switched to stop the incoming air. It passes through the heat storage body 30 from bottom to top, is heated, and is further heated in the combustion chamber 26, and after incineration is completed, it is heated while passing through the heat storage body 29 from top to bottom, and is cooled from itself to the final Specifically, it is exhausted from the chimney 31. The above is one embodiment of the present invention. The features and effects of the present invention are as follows: (1) CaO or Ca, which is low in cost among alkalis,
When using (OH) ₂ to neutralize and precipitate SO ₄ ^-- , use 1.5 to 2.0 times the amount of the equivalent amount to bring the ratio of Ca ⁺⁺ to SO ₄ ^-- in the precipitation closer to the equivalent amount. . Therefore, overall, the SO ₄ present in the raw waste liquid ^--
can be fixed and removed at an extremely low cost and further calcined to produce ash without the risk of leaching harmful substances. (2) Since most of the SO ₄ ^-- in the stock solution is removed as CaSO ₄ and the remaining solution is incinerated, SO _x is generated less.
Further, the generated SO _x is recovered by washing with water, if necessary, together with free ammonia sufficient to sufficiently neutralize the SO _x generated by the calcination of the CaSO ₄ cake, and finally the CaSO ₄ cake is recovered. Because the waste is fixed and disposed of inside the system, the _{amount of SOx} contained in the exhaust gas from the system is reduced to a minimum. (3) If necessary, the waste gas heat from the incinerator can be used to evaporate the moisture in the raw solution to the maximum extent possible.
In this case, the organic matter and other harmful components contained in the evaporation residue obtained by concentrating the raw wastewater can be led to an incinerator and incinerated using a small amount of auxiliary fuel, which has a large energy saving value. (4) If necessary, all ammonia and other harmful volatile substances contained in the evaporated exhaust gas from the water scrubber will be completely oxidized and incinerated in a gas incinerator, and released as harmless gas. Therefore, together with the calcination of the separated CaSO ₄ cake, 2
No secondary pollution will occur. Example Using acrylonitrile production waste liquid having the following specifications, lime neutralization, concentration, and incineration of the liquid were attempted using the method shown in FIG. Specific gravity 1.05 PH 5.8 Heat of combustion 5300Kcal per 1Kg of organic matter contained
Kg high-level analysis value (NH ₄ ) ₂ SO ₄ 3.3% weight ash 0.3 〃 Light organic matter 1.2 〃 Heavy organic matter 9.2 〃 CN ^- 0.2 〃 Water Residual liquid is directly sent to mixing tank 3, and industrial slaked lime is used as raw lime Neutralization is carried out using 21.5 Kg of Ca(OH) per 1000 Kg of stock solution (1.1 equivalents to SO ₄ ^-- ) for ₂ min. The liquid thus obtained is directly sent to the evaporator without removing the precipitated CaSO ₄ and others, and the liquid is concentrated. The hot gas used as a heating source is sent at a high temperature of approximately 950℃ using waste gas from an incinerator.
It was used to evaporate raw waste liquid. During this time, the solids content of the liquid increases from about 15% to around 46%, and most of the ammonia content is dissipated to the gas side together with volatile organic substances. The exhaust gas temperature when leaving such a direct contact type evaporator is about 150℃, and the concentrated slurry is 90 to 95℃.
It is maintained at a certain level. The evaporated water, ammonia and other volatile components contained in the exhaust gas, along with the ammonia gas from the mixing tank, are led to the gas incinerator via a water scrubber, where they are completely oxidized and decomposed at a furnace temperature of 1100°C, becoming harmless and being released into the atmosphere. Dissipated. On the other hand, the concentrated slurry is directly led to a rotary furnace where it is incinerated at a maximum charge temperature of 950°C with an excess air content in the range of 20-30%. At this time, heavy oil is used as auxiliary fuel at an average cost of 180,000~ per 1000 kg of raw solution.
Requires 200,000Kcal (high) equivalent amount. The obtained cake, which is mainly composed of CaSO ₄ , reaches a level where almost no remaining organic substances or CN ^- are observed after washing with water, but the analytical values continue to be as shown in the following table. This could be reduced as shown in the following table by processing in a rotary kiln type calcination furnace at 900°C for 1 hour.

[Table] The air sent to the incinerator is sent with an excess rate of 20% to 30%, and the organic _substances in the raw solution are completely burned. It was possible to recycle and reuse it. Thus, the SO _x concentration in the exhaust gas generated from the incinerator is about 200 ppm (by volume), and the SO _x generated from the CaSO ₄ calcining kiln is high at about 2000 ppm, but the SO _x concentration after leaving the water scrubber can be lowered to below 50 ppm. can.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing an embodiment of the present invention, and the numbers in the figure are as follows. 1... Raw wastewater, 2... Slaked lime, 3... Mixing tank, 4... Centrifugal separator, 5... Evaporated product rotating body, 6... Partition grid, 7... Filler, 8... Inlet hood, 9... Outlet hood, 10... Sending Liquid line, 11... Incinerator rotating body,
12...Dispersion pipe, 13...Air nozzle group, 14...Combustion air, 15...Inlet hood, 16...Transportation line,
17... Auxiliary burner, 18... Auxiliary fuel, 19... Connection duct, 20... Ammonia bend pipe, 21... Boost blower, 22... Water scrubber, 23... Recovery liquid line, 24... Water nozzle, 25... Gas incinerator, 2
6... Combustion chamber, 27... Heating burner, 28... Fuel, 2
9, 30... Heat storage body, 31... Chimney.

Claims (1)

[Claims] 1. When treating wastewater solutions containing ammonium groups, sulfate groups, and organic compounds, add calcium hydroxide or calcium oxide in excess of the equivalent amount to neutralize the sulfate groups, and convert most of the sulfate ions in the solution into calcium sulfate. A first step in which the ammonium groups are fixed and precipitated and separated, and the ammonium groups are liberated as ammonia, and the liquid obtained in the first step is brought into contact with the high temperature exhaust gas from the third step and concentrated while vaporizing volatile substances such as ammonia together with water vapor. The second step is to distill off the substances, and the resulting evaporation residue is sent to an incinerator and incinerated in an oxidizing atmosphere at an appropriate temperature of 800°C or more and 1100°C or less to remove ash mainly composed of calcium oxide. The obtained product is returned to the first step and used as part of the neutralizing agent for the sulfate group, and the third step is produced by decomposition of a part of the sulfate group in the third step.
The incineration exhaust gas containing SO _x is passed through the second step, and the gas containing ammonia generated in the first step is added as necessary, and then washed with water using a scrubber to temporarily absorb SO _x as ammonium salt. A method for treating a wastewater solution containing an ammonium group, a sulfuric acid group, and an organic compound, comprising a fourth step of returning the wastewater to the first step to precipitate and remove it as a calcium salt.