JPS5940764B2 - Mixed wet oxidation treatment method for wastewater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention mixes and simultaneously processes the waste liquid discharged from a combustion gas wet desulfurization desulfurization treatment equipment and the waste liquid discharged from a fuel combustion exhaust gas desulfurization treatment equipment to produce by-product ammonium sulfate, The present invention relates to a wastewater treatment method that recovers one or both types of crude nitrogen fertilizer and improves the purity of by-product ammonium sulfate.

Conventionally, fuel gas, such as coke oven gas (hereinafter referred to as COG) generated when coal is carbonized in a coke oven (compartment type), contains H2, CH4, CO, and Qrf(n).

In addition to CO2,0□, N2 components, NH3, H2S, H
C.N.

Contains impure ingredients such as naphthalene and tar.

When using COG as a fuel gas, it is necessary to remove H2S from the gas to below the above-mentioned regulation value due to recent SO□ emission regulations for pollution prevention purposes.

Various methods for removing this H2S have been established in actual scale plants, and a powerful process is, for example, a wet desulfurization/desulfurization method using a liquid containing naphthoquinone derivatives, anthraquinone derivatives, picric acid, and their derivatives. Industrial equipment is being developed to utilize NH3 itself in COG as an effective alkali source.

In all of these, H2S and HCN in COG
(NH4)28203 in the effluent from which it was removed.

It contains NH4SCN, S, (NH4)2SO4, etc. in a dissolved or suspended state (this waste liquid is referred to as liquid A).

On the other hand, it goes without saying that desulfurization is required for combustion exhaust gases from sintering furnaces, boiler heating furnaces, etc., which contain S02.

One of the most effective desulfurization processes is the desulfurization method that uses NH3 as an alkali source, and the ammonia ammonium sulfate method and the ammonia gypsum method are already known depending on the type of by-product.

As the NH3 source, NH3 in COO, recycling of the NH3, liquid ammonia, etc. are used.

(N)T4)2S is contained in the desulfurization wastewater that utilizes this NH3.
O4(NH4)2SO3,NH4H803,(NH4)
Contains 2S203゜NH, SO2NH2, etc.
Furthermore, when applied to sintering furnace exhaust gas, it may also contain NH and CI (these exhaust liquids are referred to as B liquid).

Note that both liquids A and B have high C0D (chemical oxygen demand) values and cannot be discharged into public water bodies unless some treatment is performed.

As a treatment method, various processes have been developed depending on the composition of liquid A or liquid B.

For example, for liquid A, a wet oxidation method at high temperature and pressure has been attempted.

However, it is necessary to dilute the waste liquid in order to avoid excessive heat of oxidation, excessive water evaporation, and crystallization of salts in the wet oxidation system due to excessive substances to be oxidized contained in the waste liquid.

Furthermore, because of problems such as pipe clogging due to sulfur suspended in Liquid A and scaling due to precipitates, it is necessary to dilute Liquid A with a large amount of water for treatment.

For liquid B, the Japan Iron and Steel Institute joint research report "Sintering flue gas desulfurization technology development research/ammonium ammonium sulfate method - October 1970
A treatment method for obtaining ammonium sulfate as a by-product is described in the publication published in 2007, but it requires multiple steps such as an oxidation step, an 8203 decomposition step, and a separation step for the sulfur produced by the 8203 decomposition.

In addition, the B solution generally has a low concentration of oxidizable substances, and when treated alone does not generate much heat in the wet oxidation system, so it is necessary to heat it from the outside.

The following method is generally used to treat the waste liquid (Liquid A) of COG desulfurization and decyanization equipment.

In other words, liquid A contains high concentrations of rhodan salt, thiosulfate,
It contains sulfur, etc., and cannot be treated as activated sludge as it is.

Therefore, by burning this A liquid, S-+SO2, C-+C
A common method is to gasify the gas as O2,N→N2°H-)H20 and fix S02 in this gas as sulfuric acid or gypsum.

On the other hand, the waste liquid (Liquid B) generated from the sintering flue gas desulfurization equipment contains ammonium sulfite, acidic ammonium sulfite, ammonium chloride, ammonium thiosulfate, ammonium sulfaminate, etc. This method fixes the SOx inside as ammonium sulfate or gypsum.

These conventional methods are illustrated in FIGS. 1 to 4.

1 and 2 show a method for treating the above-mentioned solution A, and FIGS. 3 and 4 show a method for fixing solution B.

In Fig. 1, liquid A 1 is concentrated in a concentrating facility 2, and this concentrated liquid is fed into a combustion furnace 3 with fuel 4 such as heavy oil and combustion air 5.
The gas containing SOx is injected and combusted to obtain a gas containing SOx, the sensible heat of which is sent to the waste heat boiler 6, the boiler is heated, and the heat of the steam or its pressure can be used for other purposes.

Next, the SOx-containing gas, whose temperature has been lowered through the use of heat from the ship to heat the boiler, enters the gypsum manufacturing facility 7, where it is added and contacted with Ca(OH)2 liquid 8, reacting and generating heat. Gases that do not react with Ca(OH)2 are released into the atmosphere as diffused gas 9, excess moisture becomes waste water 10, gypsum 11 is formed, and SOX is fixed and rendered harmless.

A similar process is carried out in the flow sheet shown in Fig. 2, and the SOx that enters the sulfuric acid production equipment 12 becomes sulfuric acid, and the unreacted gas is released into the atmosphere as diffused gas 9, and the dilute sulfuric acid wastewater 1
SOx is immobilized as a product of 98% sulfuric acid 14, for example.

Figure 3 is a flow sheet of the conventional treatment method for B liquid 15, and this B liquid 15 is used in the ammonium sulfite oxidation equipment 1.
6, NH317, H2SO418 are added, and a catalyst such as NaNO219 is added to react.
, process wastewater 21 is discharged and treated with ammonium sulfate 22 or crude nitrogen fertilizer (e.g. NH4Cl).

(NH4)2SO4 mixture) 23.

FIG. 4 also shows the fixation treatment method of liquid B 15, and shows
OH) 2 liquid 8, NH3 gas 17 and gypsum manufacturing equipment 24
Gypsum is produced therein, lime slag 25 and waste water 26 are discharged, and product by-product gypsum 27 is produced.

Among these conventional methods, the problem or disadvantage of the method shown in Figure 1 is that quicklime, slaked lime, etc. are used as raw materials, so storage tanks, transportation, and crushing of these materials are necessary, and furthermore, these processes generate dust. Since it occurs frequently, countermeasures are required.

Furthermore, it requires gypsum separation and filtration equipment, the process is complicated, gypsum disposal is difficult, and a large amount of sludge is discharged.

Furthermore, when a catalyst containing sodium ions is used to remove H2S in coke oven gas as S, Na
+ is mixed in, and this Na+ damages the refractories in the combustion furnace 3.

Furthermore, since the NH3 in the A liquid is decomposed by combustion, there is a loss of expensive ammonia, and in addition, it is necessary to provide an electrostatic precipitator or the like to remove the SO3 acid mist, making the equipment complicated and expensive.

In the method shown in FIG. 2, the disadvantages of Na+ occur in the same way as in the case of FIG. 1, such as combustion decomposition loss of NH3 in liquid A, and the disposal of dilute sulfuric acid in waste water is also difficult.

It is also necessary to treat the acid mist of sulfuric acid in the diffused gas 9.

In the method shown in Figure 3, the problem is the precipitation of crude sulfur due to the decomposition of (NH4) 2 S 20 s and its treatment.
4) Because excessive H2SO4 is used to decompose 28ρ3,
Neutralization requires a large amount of NH3, which is expensive, and H3O3
It is also necessary to add chemicals such as NaNO2 to decompose NH2, which requires extra cost and effort.

The method shown in FIG. 4 has the same problems in handling the quicklime and slaked lime as in the method shown in FIG. 1, and has the disadvantage that it generates a lot of sludge, which is troublesome to dispose of.

In addition, NH3 may be mixed in the wastewater 26 and must be removed due to water quality regulations, and the pH of the product gypsum may range from 8 to 8.
Since the particle size is small, there is a problem in terms of quality.

Furthermore, since NH3 is generated when double decomposition occurs in the gypsum production facility 24, a recovery facility is required.

Further, there are drawbacks such as the need to use sulfuric acid for pH adjustment, which requires additional costs.

In view of the shortcomings of these conventional methods, the present inventors have studied and researched methods for improving these shortcomings, and have arrived at the present invention, which they provide herein.

The present invention not only adjusts the calorific value by mixing and simultaneously processing liquids A and B, which are different from each other, but also compensates for the defects of each other and eliminates all impurity components in one step without the need for additional dilution water. This provides a wet oxidation method at high temperature and pressure in which ammonium sulfate, sulfuric acid, and ammonium chloride are obtained as solutes through decomposition oxidation or modification.

The present invention mixes both waste liquids discharged from a desulfurization desulfurization equipment that uses ammonia in gas such as coke oven gas as an alkali source and an ammonia method desulfurization equipment for combustion exhaust gas containing sulfur dioxide gas, This is a mixed wet oxidation treatment method for wastewater in which ammonium sulfate or crude nitrogen fertilizer is recovered through wet oxidation.

In addition, in the above treatment method Q, the mother liquor is extracted from the recovery system after mixing both of the waste liquids, and the waste liquid is concentrated and impurities that have not yet reached a saturated state are removed to improve the purity of the recovered ammonium sulfate. This is a mixed wet oxidation treatment method.

In this way, the present invention can produce ammonium sulfate or ammonium sulfate or It can be advantageously recovered as nitrogen fertilizer such as ammonium chloride.

In general, COG desulfurization wastewater has a high concentration of dissolved salts, so when wet oxidizing only this wastewater, wet oxidation is performed after adding the minimum amount of water necessary to prevent salt precipitation, but the present invention Now, instead of this dilution water, the flue gas desulfurization liquid from the sintering flue gas can be used, which is economical because no new make-up water is required, and because it is concentrated again in the wet oxidizer system, the ammonium sulfate recovery process can be improved. Since the concentration step can be omitted, the cost of concentration can be greatly reduced.

Furthermore, in the present invention, since both the liquid A and liquid B are mixed and treated, the facility area required for separate treatment can be approximately 1/2, and the amount of operational work can be halved.

In the present invention, both wastewaters are used simultaneously, and there is no need to add special chemicals or raw materials to remove impurities.Moreover, oxygen in the air is used to oxidize ammonium sulfite in the B wastewater to ammonium sulfate. Part of the NH4Cl, NH4SCN, and HO802NH2 (sulfamic acid) in the B wastewater is extracted from the system to avoid violating by-product ammonium sulfate standards, and a part of this extracted liquid is mixed with the COG desulfurization wastewater and oxidized at high temperature and pressure. By doing so, it has become possible to advantageously process NH, SCN, and sulfamic acid to improve the purity of nitrogenous fertilizers such as recovered ammonium sulfate.

In addition, in the present invention, wastewater containing NH4Cl can be wet-oxidized at high temperature and high pressure and recovered as a crude nitrogen fertilizer consisting of a mixed fertilizer of ammonium chloride (ammonium chloride) and ammonium sulfate, but if necessary, only NH3 can be recovered or treated with activated sludge. It is also free not to collect it as fertilizer.

More than 60% of water in the mixed wastewater of the present invention is brought into contact with COG in an ammonium sulfate saturator and used to humidify the COG, and this increased humidity is condensed in a gas cooler installed after the ammonium sulfate saturator. Since wastewater can be treated, there is no need to install a special water evaporation device, and there are significant advantages in equipment construction and operation.

. In this way, the present invention utilizes NH3 in the waste liquid,
Since the waste liquid containing H2S and S02 can be effectively oxidized in air at the required liquid ratio and recovered to ammonium sulfate, etc., it can be effectively used in other similar processes that produce waste liquid.

Next, the present invention will be further explained with reference to examples.

Example 1 In a titanium shaking autoclave with an internal volume of 0.81, equal amounts of a mixed solution of wet desulfurization waste from flue gas and wet desulfurization desulfurization waste from coal carbonization gas (compositions shown in Table 1) were placed. After preparing a predetermined amount and filling it with the necessary air, the temperature was raised to 260° C. while shaking, and then reacted for 1 hour.

Immediately after the reaction, the contents were cooled and the contents were taken out and analyzed. The results are shown in Table 1.

Example 2 A mixture of equal amounts of wet desulfurization liquid of flue gas, wet desulfurization liquid of coal carbonization gas, and wet desulfurization desulfurization liquid of coal carbonization gas was placed at the bottom of a titanium rigid cylindrical reactor with an internal volume of 100 mm. (
A predetermined amount of high-pressure air (the composition of which is shown in Table 2) is continuously pumped through the preheater, and at the same time a predetermined amount of high-pressure air from an air compressor ship is mixed with the waste liquid at the pump outlet.

At the top outlet of the reactor, the temperature was set at 260°C and the pressure cuff was set at 5 kg/d, and the residence time of the liquid in the reactor was adjusted to 1 hour.

After cooling, the gas-liquid mixture leaving the reactor undergoes gas-liquid separation.
The results of analysis of the continuously taken out treatment liquid are shown in Table 2.

Example 3 The treatment was carried out according to the flow sheet shown in FIG.

H2S and HCN contained in the gas of C0G28 are COG
In the desulfurization equipment 29, ammonia in the gas is reacted and removed as an alkali source.

In order to carry out this desulfurization operation smoothly and maintain a high removal rate, it is necessary to extract the desulfurization waste liquid 30 (liquid A), which has degraded reactivity due to the reaction, out of the system of the desulfurization equipment 29. .

On the other hand, the sintering gas 31 generated from the sintering factory contains a large amount of SOx, which is removed by the flue gas desulfurization equipment 32 and released into the atmosphere as clean gas 33.

The operation of this desulfurization equipment 32 uses NH3 in the C0G 34 as an alkali source, and the ammonia absorption tower 35
3 is added as an ammonia-containing liquid 36 to a flue gas desulfurization equipment 32 for sintering gas, where it reacts with SOx, and the reacted absorption liquid 37 is sent back to the ammonia absorption tower 35.

The above circulation operation is repeated to increase the concentration of the ammonia-containing liquid 36 whose main components are ammonium sulfite and ammonium sulfate, and in order to increase the concentration up to the concentration at which ammonium sulfate crystals precipitate, a part of this circulating liquid is used for flue gas desulfurization. Drainage liquid 38 (
It is extracted from the above system as liquid B).

Since the C0G 39 that has passed through the ammonia absorption tower 35 contains residual ammonia, it is completely absorbed and removed in the subsequent saturator 40, and then cooled to near room temperature in the cooler 41 and introduced into the subsequent equipment as purified COG gas 42. .

The desulfurization waste liquid 30 discharged from the COG desulfurization equipment 29 contains NH4SCN.

(NH4)2S203. (NH4)2S04. NH4O
Consists of H etc.

In addition, the components of the flue gas desulfurization liquid 38 discharged from the ammonia absorption tower 35 are (NH4) 2 S 04 -(NH4)
2S03. NH4H8O3, (NH4)2S203°N
It consists of H4Cl, NH45O3NH2, etc.

This desulfurization waste liquid 30 and flue gas desulfurization waste liquid 38 are sent to the stock solution tank 43 and mixed.

The liquid mixture in the raw liquid tank 43 is led to a wet oxidizer 44 where it undergoes an oxidation reaction with oxygen in the air under high temperature and high pressure, converting the components in each waste liquid into (NH4)2SO4 and H2SO4.

The treated liquid 45 from this wet oxidizer 44 is led to a circulation tank 46 attached to the saturator 40, used as a sulfuric acid source, and CO
NH3 in G39 is reacted with saturator 40 to form ammonium sulfate.

The exhaust gas from the wet oxidizer 44 enters the scrubber 47 and the liquid phase 48 is recovered into the raw solution tank 43, and the scrubber 47's scrubbing air 49 is harmless and is therefore released into the atmosphere.

The ammonium sulfate solution is circulated between the saturator 40 and the circulation tank 46 to saturate the ammonium sulfate solution to the ammonium sulfate precipitate concentration in the ammonium sulfate solution, and the saturated solution 50 is guided to the centrifuge 51.

After the crystalline ammonium sulfate 52 is separated by a centrifuge 51, the tear fluid 53 is returned to the circulation tank 46.

A part of the tear fluid 54 of this R fluid 53 is extracted from the system, and the furnace fluid 5
Crystal separation of NH4Cl contained in 4 is performed.

For this purpose, tear fluid 54 is led to an evaporator 55 and concentrated to a crystallization concentration, and the concentrated liquid 56 is led to a centrifuge 51 to separate crude nitrogen fertilizer 58, which is a mixture of ammonium chloride and ammonium sulfate.

The filtrate 59 from the centrifugal separator 57 is led to a wastewater treatment facility 60 for treating activated sludge, etc., and is rendered harmless and discharged as wastewater 61.

The compositions of the liquids in each of these steps are shown in Table 3.

The N content in the ammonium sulfate shown in Table 3 above exceeds the fertilizer standard, and the impurities H3O3NH2 and SCN are well below the fertilizer standard's permissible value, so the product is of excellent quality and has no problems.
Similarly, crude nitrogen fertilizer has no problems with its ingredients and is an excellent fertilizer.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are flow sheets showing a method for treating desulfurization waste liquid (Liquid A) discharged from a conventional COG exhaust gas detoxification treatment facility. FIG. 3 and FIG. 4 are flow sheets showing a method for treating desulfurization waste liquid (liquid B) discharged from a conventional treatment facility for detoxifying exhaust gas from a sintering furnace in a steel mill or the like. FIG. 5 is a flow sheet showing one embodiment of the method of the present invention. 1...Liquid A, 2...Concentration equipment, 3...
... Combustion furnace, 4 ... Fuel, 5 ...
Combustion air, 6... Waste heat boiler, 7...
・Gypsum production equipment, 8...Ca(OH) 2 liquid, 9
... Diffusion gas, 10 ... Drainage, 11.
...Gypsum, 12...Sulfuric acid manufacturing equipment, 13
・・・・・・Dilute sulfuric acid wastewater, 14・・・98%H2
SO4,15...Liquid B, 16...Ammonium sulfite oxidation equipment, 17...NH3,1
8...H2SO4,1-9...NaN
O2, 20...crude sulfur, 21...process wastewater, 22...ammonium sulfate, 23...crude nitrogen fertilizer, 24...gypsum Manufacturing equipment, 25...
...Lime slag, 26...Drainage, 27...
By-product gypsum, 28...COG, 29...
Desulfurization equipment, 30... Desulfurization waste liquid, 31...
・Sintering gas, 32...Exhaust gas desulfurization equipment, 33...
...Clean gas, 34...C0G1.35.
... Ammonia absorption tower, 36 ... Ammonia-containing liquid, 40 ... Saturator, 41 ...
・Cooler, 42...Refined COG, 43...
... Raw solution tank, 44 ... Wet oxidizer, 46.
...Circulation tank, 49...Sale price, 50...
... Ammonium sulfate saturated solution, 51 , 57 ... Centrifuge, 52 ... Crystalline ammonium sulfate, 53 ... Filtrate, 58 ... Crude nitrogen fertilizer , 60...
Wastewater treatment equipment, 61...Drainage.

Claims (1)

[Claims] 1. Mixing of both waste liquids discharged from a desulfurization/desulfurization equipment that uses ammonia in gas such as coke oven gas as an alkali source and an ammonia method desulfurization equipment for combustion exhaust gas containing sulfur dioxide gas. A mixed wet oxidation treatment method for wastewater, characterized by performing wet oxidation at high temperature and high pressure to recover ammonium sulfate or crude nitrogen fertilizer. 2. In the method for treating wastewater according to claim 1, the mother liquor is extracted from the recovery system after mixing both wastewaters,
A mixed wet oxidation treatment method for wastewater, which is characterized by improving the purity of recovered ammonium sulfate by removing impurities that are concentrated and do not reach a saturated state.