RU2061652C1 - Method for scrubbing of sulfur roaster gas - Google Patents

Abstract

FIELD: methods for cleaning of roaster gases in production of sulfuric acid, sulfur dioxide, sulfide salts and in similar processes. SUBSTANCE: method for scrubbing of sulfur roaster gas consists in the following. Roaster gas is fed at 200-500 C to the first stage of scrubbing where it is treated with 75% sulfuric acid. Vapor-gas mixture is fed to the second stage of scrubbing into shell-and-tube cooler. Introduced into flow at the inlet of working tubes in distributed form is sulfuric acid with concentration of 50-98%. In so doing, concentration of the acid supplied to the second stage is maintained higher than that at the first stage. Gas- liquid mixture is cooled at the second stage, preferably, down to temperature of 40-100 C. The gas temperature at the outlet of the first stage of scrubbing is preferably maintained within 90-200 C. EFFECT: higher process economical efficiency due to cut down capital investments for equipment and utilization of process heat.

Description

 The invention relates to methods for purifying hot calcining gases in the production of sulfuric acid, sulfur dioxide, sulfite salts, and the like.

The aim of the present invention is to increase the efficiency of the process by reducing capital costs of equipment,
The figure shows a schematic diagram of the implementation of the method, which includes: 1 first washing tower, 2 heat recovery unit, 3 gas refrigerator, 4 wet electrostatic precipitator, 5 drying tower.

 The method is as follows.

Sulfur firing gas with a temperature of 200-500 ^o C at a pressure close to atmospheric, containing 2-20% S0 ₂ and 0.01-1.0 SO ₃ in its composition, is fed into the washing stage 1 in the first washing stage, where the gas interacts with water or acid, having a concentration of up to 75% H ₂ SO ₄ and a temperature of 45-135 ^o C. In this case, the gas is cooled, partially cleaned of impurities and saturated with water vapor.

The gas-vapor mixture after the first washing stage is fed into the second washing stage — into the gas refrigerator 3, which is divided into two zones. In the first zone, an acid with a concentration of 50 to 98.5% H ₂ SO ₄ is introduced into the vapor-gas mixture stream in a distributed form (for example, through nozzles), the concentration of acid supplied to the second stage being maintained above the acid concentration in the first stage. As a result of mixing, part of the water vapor condenses, and the resulting liquid phase heats up.

 In the second zone, the gas-liquid mixture is fed into a surface cooler, for example, in a vertical tube cooler. A cooling agent (e.g. water or air) circulates through the annulus.

When cooling the gas-liquid mixture, further vapor condensation and dilution of the acid with condensate occur, further gas purification occurs as a result of the deposition of aerosols and vapors, and after the second washing stage, the gas and liquid phases are separated. The gas contains H ₂ SO ₄ mist and water vapor.

 In the third stage of purification, which is carried out in the electrostatic precipitator 4, the gas is cleaned from fog.

 In the next stage of purification in the drying tower 5, the gas is dried, that is, water vapor is absorbed from it by treatment with strong sulfuric acid.

 The concentration of acid introduced into the second washing step must be higher than that with which the gas was contacted in the first washing step. In this case, heating of the gas vapor of the liquid mixture occurs, which increases the driving force of the heat transfer process in the second zone of the second washing stage and allows to reduce the required heat transfer surface.

The temperature of the gas-liquid mixture at the outlet of the second washing stage is preferably maintained within the range of 40-100 ^o C.

 Due to this, the driving force of the heat transfer process increases in the refrigerator.

The increase in efficiency by using the heat of the process is achieved by the fact that the gas temperature at the outlet of the first washing stage is maintained within 90-200 ^o C. Under these conditions, the temperature of the refrigerant in the refrigerator of the second washing stage will be at the level of 50-180 ^o C, and the temperature heat can be used in the heat recovery installation 2.

 The invention is illustrated by examples.

 Example 1

Calcined gas obtained from burning sulfur in air containing 11% SO ₂ , 0.2% SO ₃ and 1% H ₂ O with a temperature of 433 ^o C in an amount of 45,000 nm ³ / h enters the first stage of washing, where in a countercurrent scrubber interacts with 50% acid having a temperature of 77 ^o C. The gas temperature after the first stage is 88 ^o C, it contains 17.8% water vapor.

The second stage of washing is carried out in a vertical tubular refrigerator with an upper hollow zone. Acid (98% H ₂ S0 ₄ , 55 ^° C) is introduced into this zone in an amount of 0.127 L per 1 nm _{3 of} gas. The temperature of the gas-liquid mixture at the inlet to the pipes is 145 ^° C. Cooling water enters the refrigerator at 25 ^{° C.} , leaves at 38 ^° C.

At the outlet of the tube bundle of the refrigerator, the temperature of the gas-liquid mixture is 46 ^o C, the concentration of the liquid phase is 56% H ₂ S0 ₄ , the residual water vapor content in the gas is 2.7%. 6093 Mcal / h are discharged in the refrigerator.

 The following examples relate to various types of raw materials.

 Example 2

The gas is obtained by roasting copper ore using oxygen and air. At the entrance to the washing compartment, the gas has a temperature of 381 ^o C and contains 21.5% SO ₂ , 0.3% SO ₃ and 1% H ₂ O. Other significant parameters are given in the table.

 Example 3

The gas from the pyrite firing contains 14.9% SO ₂ , 0.2% SO ₃ and 2% H ₂ O. Other process parameters are given in the table.

 Example 4

The gas obtained by roasting zinc ore using oxygen and air at the inlet to the washing compartment has a composition of 11% SO ₂ , 0.2% SO ₃ and 1% H ₂ O. Other process parameters are given in the table.

 Example 5

In the production of sulfuric acid from pyrites with a capacity of 360 thousand tons. For 6 years, the firing gas containing 11% SO ₂ , 0.1% S0 ₃ and 3.6% H2O, enters the washing unit at a temperature of 350 ^° C. The volumetric flow rate of dry gas at the inlet is 93700 nm ₄ / h.

In the first washing stage, the process is conducted in such a way that thermodynamic equilibrium at the outlet of the washer is not achieved. Irrigating acid has a temperature of 95 ^o C, and the gas leaves at a temperature of 160 ^o C.

The second stage of washing is carried out in a vertical shell-and-tube refrigerator. A refrigerant is passed through the annulus of the refrigerator, which is superheated water at a pressure of 2.5 atm (1.5 atm). The water temperature at the inlet is 70 ^{o C.} , at the outlet 120 ^o C.

 8500 M cal / h of heat is removed in the refrigerator, which is transferred by water to the heat recovery unit.

The heat used is 189 M cal per one ton of Н ₂ SO ₄ in production (of which heat of mixing is about 20%).

 The table shows the indicators of the gas flushing process specifically for each of the five above examples. In the first column, indicators are given for the prototype method, for which the method described in the source [1] is accepted where the gases obtained by calcining zinc ore are washed in a known manner.

 Thus, the examples 1,2,3,4 confirm the achievement of the purpose of the invention according to claims 1 and 2, and example 5 according to claim 1 and 3.

The method improves the efficiency of the process by reducing the capital cost of the heat exchange surface. According to the prototype method, the heat transfer surface is 2220 m ₂ , and according to this method, with the same production capacity, 583 1970 m ₂ . TTT1

Claims (3)

1. The method of wet purification of firing gas, comprising washing it with sulfuric acid in at least 2 stages using an acid in the first stage with a concentration of up to 75% H ₂ SO ₄ while cooling the resulting gas-liquid mixture in the second stage through a wall, characterized in that , in order to increase the efficiency of the process by reducing the capital cost of equipment, in the second stage of washing, sulfuric acid is used with a concentration of 50-98.5%, and the concentration of acid supplied to the second stage is maintained higher than ation acid in the first step. 2. The method according to p. 1, characterized in that the cooling of the gas-liquid mixture in the second stage is carried out to a temperature of 40 100 ^o C. 3. The method according to p. 1, characterized in that the gas temperature at the outlet of the first washing stage is maintained within the range of 90-200 ^o C.

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