JPS5870876A - Purifying treatment of desulfurizing waste liquid for coke oven gas - Google Patents

Abstract

PURPOSE:To efficiently perform the titled method with saved energy consumption, by spontaneously oxidizing and burning coke oven gas-desulfurizing waste liquid mainly consisting of NaSCN, Na2S2O3 and Na2SO4, and collecting solid Na2SO4. CONSTITUTION:Coke oven gas-desulfurizing waste liquid contg. NaSCN, Na2S2O3 and Na2SO4 as such or after being concentrated is received in a vessel, and spontaneously oxidized and burnt with a ratio of excess air above 30% at a temperature of 500-800 deg.C to recover gas contg. solid Na2SO4 and SO2. Said method is preferably carried out by using a fluidized roaster 1 where the conc. desulfurizing liquid supplied through a line A to its fluidized bed is fluidized and roasted to form Na2SO4 under the reacting conditions of a roasting temperature of 500-800 deg.C, a ratio of excess air of 30-50% and 50-60cm/sec the velocity of air flowing through the column. Said Na2SO4 is withdrawn through an overflow line B to a hopper 2, while the formed gas is withdrawn through the top part of the column.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating coke oven gas (OOG) desulfurization waste liquid (J mainly containing sodium thiocyanate, sodium thiosulfite, and sodium sulfate) obtained by carbonizing coal; - When using coffer oven gas as fuel, sulfur compounds (mainly hydrogen sulfide) and nitrogen compounds (mainly ammonia) that cause air pollution;
Removal of hydrogen cyanide, etc. is required. Conventionally, methods for removing hydrogen sulfide, hydrogen cyanide, and ammonia have been industrialized using known absorption methods.
Takahax method, Rodax method, Fumax method, etc., which use alkali for removal, are already known.

In the case of the Soda Takahax method in which sodium carbonate is used as the alkali in the above method, hydrogen cyanide is fixed as sodium thiocyanate (Na$gN). Further, hydrogen sulfide reacts with sodium carbonate to form sodium hydrosulfide (NaHJG), which can be fixed as elemental sulfur by using a redox catalyst. In this reaction, the catalyst is regenerated by an oxidation reaction, in which part of the sodium hydrosulfide is oxidized to produce by-products sodium thiosulfite (N* 1% Os ) and sodium sulfate (CNaa Boa ). Sodium thiocyanate, sodium thiosulfite, and
Sodium sulfate does not contribute to desulfurization and decyanization reactions and accumulates in the circulation system, so a portion of the absorption liquid must be constantly removed to remove the by-product circular rings. Several methods have already been commercialized as known techniques for treating the extracted waste liquid mainly containing the above three components. One of these methods is the cyclic combustion decomposition method, in which the waste liquid is co-combusted with auxiliary fuel, the air ratio is α9 or less, and the combustion gas temperature is 700°C or higher and 1100°C or lower. By thermally decomposing the sulfur compound salts and bringing the generated hydrogen sulfide and alkali carbonate into direct contact with water together with the combustion gas, the alkali carbonate is recovered as an aqueous solution and recycled for use, and the hydrogen sulfide is removed from the exhaust gas. get to. The operation of this method requires a large amount of energy such as auxiliary fuel, fuel supply equipment, and air supply equipment, and the generated combustion gas contains a high concentration of hydrogen sulfide. It has disadvantages such as requiring

The purpose of the present invention is to provide an energy-saving treatment method for coke oven gas desulfurization waste liquid mainly containing sodium thiocyanate, sodium thiosulfite, and sodium sulfate. When carrying out the process using a gas containing sodium sulfate and sulfur dioxide gas as the main components, it is possible to form a fluidized bed at +7 um of sulfuric acid and spray the raw material waste directly into the fluidized bed. As for the reaction conditions, the decomposition reaction of sodium thiocyanate starts when the furnace temperature is 500°C or higher, but the highest decomposition rate is shown at 650°C or higher, and when the furnace temperature is 800°C or higher, sodium thiocyanate is formed and sodium thiocyanate is melted. The most preferred temperature range is therefore 650-700°C, which interferes with flow conditions.

As a result of research on the method of the present invention using a small plant such as a fluidized torrefaction furnace, it was found that this concentrated desulfurization waste liquid has a high viscosity and promotes the growth of sodium sulfate particles forming a fluidized bed, thereby stopping the fluidized state in a relatively short time. However, it is necessary to recycle the produced sodium sulfate with a particle size of 100 to 150μ to the produced sodium sulfate ratio of 25 to 50 x 1 into the roasting furnace, and to increase the in-house flow rate of the roasting air to 50 to 60 ay'8 K for a longer period of time than K. For example, in the case of a stable desulfurization waste liquid produced by the Soda Takahax method, the operation is generally carried out at a concentration of about 2ON in sulfur compound salts and alkali carbonates, which are exothermic substances, and the remaining amount is approximately 8.
0X is water. The calorific value of this 2ON-containing salt is calculated from the content of both sodium thiocyanate salts mentioned above, which has the highest calorific value.For example, if it is treated with 111, -36
It is on the endothermic side of 0-, therefore, it is necessary to evaporate and concentrate the water in the waste liquid.

Regarding the degree of concentration, it is advisable to exchange heat between the oxidation and roasting air and the generated high-temperature exhaust gas in consideration of thermoeconomic efficiency, and the moisture content will vary depending on the heat exchange rate, but the moisture content will be approximately 40 to 60.
It is necessary to concentrate it to about %.

Next, the basic flow of the present invention will be explained using figures.

The desulfurization concentrated waste liquid supplied from the A2 in to the fluidized bed (inside the broken line) of the fluidized roasting furnace No. 1 was heated to a roasting temperature of 500 as the reaction condition.
~800°C, excess air rate 30~SOS.

The oats of B are extracted from the -70- line to the first hopper 2. On the other hand, the generated gas is extracted from the top of the furnace, and the entrained particulate sodium sulfate is removed by the cyclone 3. Afterwards, the generated gas is exchanged with the roasting air sent by the air f lower 6 by the heat exchanger 4, and the desulfurization waste liquid is removed. It is used to reduce the concentration and is discharged from the system. This generated gas can be used as a raw material gas for producing sulfuric acid, containing sulfur dioxide gas (80m) and appropriate residual acidity. On the other hand, the heated roasting air passes through pipe E, and part of it is used for totomizing concentrated waste liquid and sodium sulfate for recycling, and the rest is blown into the furnace from the bottom of the fluidized roasting furnace to form a fluidized bed. do. The particulate sodium sulfate removed from the generated gas by the cyclone 3 is taken out to the second hopper 5, and returned to the roasting furnace through the 25-5ONtl-0 line of the generated sodium sulfate, and the remainder is transferred to the D line and the second hopper. The sodium sulfate extracted from 1-Hotsunozo-2 is combined with the sodium sulfate extracted from O/Safe 0-line and shipped as a product.

Next, using a test roasting furnace with an inner diameter of 30 crIt @ 3 m height and a fluidized bed of 1.5 ㎜, sodium sulfate was formed with air to form a fluidized bed, and a fluidized bed was placed in the fluidized bed. A concentrated desulfurization waste liquid having the composition shown in Table 1 is sprayed.

Next, an example of the reaction conditions is shown in Table 2. Under the above conditions, the waste liquid shown in Table 1 was roasted in an oxidizing stream. 9. Collect the generated gas as shown.

Table 3 Table 4 By constructing and using the present invention as described above,
This method has an extremely large effect as an energy-saving treatment method that can efficiently treat coke oven gas desulfurization waste liquid without using auxiliary fuel.

[Brief explanation of the drawing]

FIG. 1 is a schematic basic flow diagram illustrating the method of the present invention. 1...Fluidized roasting furnace 2...No. + Honnosaw 3...
・Cyclone 4...Heat 3c Hongki 5...Second Hokno" 6 =-Empty f14. Return line D to the furnace: First hot rod extraction line E: Air pipe agent, patent attorney, Masaaki Akizawa, and 2 other people

Claims (1)

[Claims] (1) A method for treating coke oven gas desulfurization waste liquid, which comprises recovering coke oven gas desulfurization waste liquid containing sodium thiocyanate, sodium thiosulfite, and sodium sulfate into seven pits, or recovering concentrated sodium sulfate.