FI68798B - FOERFARANDE FOER RENING AV SO2-HALTIGA GASER - Google Patents

Description

68798

Method for purifying gases containing SC ^ Förfarande för rening av SC ^ -haltiga gaser

The invention relates to a process for purifying hot SC1-containing roasting and combustion gases from dusty and other impurities for the production of sulfuric acid and pure sulfur dioxide in a three-stage wet gas purification plant. the gas from the step is cooled in the second process step 10 in an orifice wash tower or gas cooler to an even lower temperature, and the water vapor contained in the gas is condensed, - before the gas in the third method step is subjected to wet cleaning.

15 S02 ~ roasting or combustion gases must be thoroughly cooled before being treated with sulfuric acid or pure sulfur dioxide and cleaned of dusty and other impurities. Depending on the amount, particle size distribution and dust resistance, the air dust in the hot gas is first separated mechanically in a cyclone and / or in an electric hot gas cleaning, in an electrostatic precipitator. Dust and other impurities still present in the hot gas, also partly still in the vapor form, such as iron, zinc, lead, arsenic and selenium compounds, mercury and hydrocarbons, as well as gaseous hydrogen chloride, hydrogen fluoride and sulfur trioxide must be completely removed from the gas.

It is known from the relevant literature and from DE patent publications 751,907 to treat gas in a wet gas cleaning plant 30 consisting of three process steps. In the first process step, scrubber towers without fillers or Venturi scrubbers or combined scrubber and cooling towers are used to treat SO2-containing gases, in which the gas is cooled and washed by adiabatic water evaporation to a temperature of about 60-80 ° C. In this case, the impurities present in the steam are largely condensed and enriched in a normally circulating washing liquid, a maximum of 30-50% sulfuric acid, which is continuously removed from the washing liquid circuit and made up with fresh water and / or recovered condensate. Gaseous impurities, such as hydrochloric acid or hydrogen fluoride, are likewise partially separated in the scrubber. The gas is then almost steam-saturated.

10 In the second process step, the gas from the first process step is cooled to reduce the water content. In this case, the gas flows either through the scrubber washing tower with a circulating controlled scrubbing liquid, whereby the heated liquid is recooled in a separate condenser, or through an indirect gas cooler, in which case the condensate obtained is added to the circulating scrubbing liquid again in the first process step. The gas thus treated is finally subjected to an electric wet scrubbing in the third process step in order to completely remove the impurities.

The use of scrubbers prior to electro-wet scrubbing in the third process step not only removes coarse contaminants but also allows the separation of very fine particles below 0.5 microns that agglomerate due to conditions in the scrubber towers, especially the second scrubber tower, after on-line wet scrubbing.

However, all of these methods have the disadvantage that the residence time of the gas flowing through the second scrubber tower for agglomeration of very fine particles is too short to guarantee an economic separation for electro-wet cleaning.

It is therefore an object of the invention to provide a process for the complete wet scrubbing of hot SO2-containing roasting and combustion gases from dusty and other impurities for the production of sulfuric acid or pure sulfur dioxide in the apparatus mentioned above. 3 68798 technically and also in terms of the size of the components of the equipment in an economical manner.

According to the invention, the object is solved in that the nearly water-vapor-saturated gas from the first process step is treated before it passes through the second process step by injecting colder, dilute sulfuric acid or colder water with respect to the saturation temperature.

Injecting or spraying cold, dilute sulfuric acid, or cold water into a near-water vapor-saturated gas causes gas cooling in the trajectory of each individual drop of liquid and, due to the mixing of the uncooled gas, water vapor supersaturation and thus mist formation in the gas. According to the present data, fewer particles larger than 1 [mu] m are disturbed by this operation. In very fine particles below 0.5 ... 1 μm, due to the agglomeration of harmful substances and mist particles and due to the considerably longer residence time up to electro-wet cleaning, a very strong increase in particles is achieved. This results in a very simple and rapid separation of the agglomerated particles, which reduces and simplifies the electrical wet cleaning considerably in a considerable or simple manner, which makes it possible to replace even expensive electrostatic precipitators with simple mechanical wet separators.

25

In another embodiment of the invention, it is proposed that the temperature of the dilute sulfuric acid or water is preferably more than 10 ° C lower than the saturation temperature of the gas.

From the point of view of the method, a temperature difference of 15-20 ° C is preferable, so that, for example, when the saturation temperature of the gas is 50-60 ° C, the temperature of the colder liquid injected is 30-45 ° C. In this case, it is crucial that the saturation temperature of the gases above 40 ° C and the determined temperature difference are not decisive for the growth of the particles.

It is further proposed that the concentration of dilute sulfuric acid is at most 20%.

35 4 68798

However, experiments have shown that the optimum concentration of dilute sulfuric acid is 10%.

Another proposal concerns an injected amount of cold, dilute sulfuric acid or cold water of at least 0.1 1 / m gas, preferably 1-3 1 / m gas.

Within the framework of the problem solution according to the invention, it is also proposed that the relative velocity between the injected cold liquid droplets and the gas in the injection inlet range is on average at least 8 m / s.

To achieve this value, the spray pressure required to inject the liquid into the gas by means of a nozzle must be at least 0.5 bar.

3

The minimum liquid volume must be at least 0.1 1 / m gas. However, it is preferable to keep the sprayed liquid volume at 1-3 l / m of gas and to select 2-3 bar as the liquid pressure. As the amount of liquid increases and the spray pressure is higher, the desired effect of the particle growth becomes even greater, so that an increase in the spray pressure itself of more than 20 bar has a very positive effect. In contrast, the optimal value for the amount of liquid is 3 in 4 l / m of gas. When delivering a liquid by means of a mechanical liquid-20 distributor, for example a rotary distributor, its circumferential speed must be at least 8 m / s.

In another embodiment of the invention, it is proposed that the gas from the first process step is further treated with cold air and / or water vapor before injecting cold, dilute sulfuric acid in order to achieve as 100% water vapor impregnation of the gases as possible.

The method according to the invention will be explained in more detail by means of the three preferred embodiments of the wet gas cleaning apparatus shown in the accompanying method diagrams. In the drawings,

Figure 1 shows a process according to the invention, in which cold air and finally cold, dilute sulfuric acid are supplied to the gas cleaning process between the first and second process steps.

Figure 2 shows a method according to the invention, in which steam is used instead of cold air and the addition of cold, dilute sulfuric acid takes place in an empty chamber immediately connected in front of the filler washing tower.

Figure 3 shows a process according to the invention, in which slightly heated, humidified air and water vapor are added to the gas between the first and second process steps before cold, dilute sulfuric acid is added to it in a tank connected in front of the second scrubber tower.

10

According to Figure 1, in the first process step, hot, SC 2 -containing roasting gases of 250-300 ° C enter the upper part of the first empty water tower through the pipe 1. The gases are brought into contact in this tower in a steady stream with hot, dilute sulfuric acid (5-20% ^ SO 2), which is passed without cooling through the tank 8 and the pump 9 into the circulation. The acid is sprayed through the nozzles 10 directly into the hot roasting gases in a steady stream. In this case, a strong adiabatic evaporation of water takes place immediately, followed by cooling of the hot gases, which, when left in the lower part of the first washing tower 2 and left almost cooled to the dew point, leave the tower 3. The gas temperature in this embodiment is 62 ° C, the saturation temperature is 58 ° C. Sulfuric acid containing impurities is taken from the apparatus at 19 as washing acid. After the preparation of this gas, cold, dilute sulfuric acid according to the invention is now sprayed from the washing liquid circuit of the second filler-filled washing tower 4 through the nozzles 12 to the gas pipe 3 connecting the two washing towers 2,4, the injection liquid being available in acid coolers 15 cooled to 38 ° C. In order to completely saturate the gases, moist, cold air is additionally added to the mixture at point 11. In this case, the temperature of the gas drops to 57 ° C and the gas is thus saturated with water vapor.

In the second process step, the gases in the second filler washing tower 4 are further washed and cooled countercurrently at 40 ° C. In addition to the gas scrubber, the acid heated by the water condensate flows from the lower part of the scrubber tower to the tank 13, from there it is pumped back by the pump 14 cooled through the suction 15 to the top of the second scrubber tower 4 and distributed through the nozzles 16 to the fillers. The excess liquid flows through the pipes 17 to the collecting tank of the first washing tower 2, the liquid level of which drops due to the continuous water evaporation. If the water vaporization in the first washing tower 2 is greater than the condensation of water-5 in the second washing tower 4, in addition to water 18, water must be added to the washing-liquid circulation. The cooled and electrically filtered gases are passed through gas line 5 to electrostatic precipitators 6. They leave these purified through line 7 for further processing to produce sulfuric acid or pure sulfur dioxide.

Another example of the method according to the invention is shown in the diagram of Figure 2. As in the first embodiment, hot gases at 210 ° C containing not only 10.5% by volume of SO 2 and 3.8% by volume of O 2 and 18% by volume of water vapor are cooled and moistened by hot evaporation of adiabatic water, circulating, dilute sulfuric acid in countercurrent.

Now, the water vapor 20 is blown into the gases exiting the gas pipe 20 from the first scrubber tower for complete impregnation, so that the gases enter the lower part of the second scrubber tower 4 at a saturation temperature of 65-66 ° C. An empty space is connected to the lower part in front of the second washing tower 4, where cold washing liquid is sprayed from the washing-liquid circulation of the second washing tower 4. The amount of this spray liquid is set to 2-3 3 25 l / m gases. The liquid is cooled in a special condenser to a temperature of 21-35 ° C. The further processing of the gases takes place in the same way as in the first example.

In the embodiment illustrated in the third figure 3, the cooling and humidification of the hot roasting gases takes place in a first scrubber tower 2 'filled with filling pieces. The gases then enter the tower from below through the pipeline 1 and are brought into close contact in the filler layer countercurrently with the hot sulfuric acid. This acid leaves the first washing tower at the bottom, enters the tank 35 8 and is pumped back by a pump 9 to the top of the washing tower 2, where it is evenly distributed by means of nozzles 10 to the cross-section of the tower with fillers. In order to achieve complete wetting, 7 68798 air is sucked through the pipe 11 into the discharge tank 22, where sulfur dioxide is removed from part of the washing acid in the washing liquid circuit of the first washing tower, which is added through the pipe 19 to the tank 22. In the exhaust operation, the heated and humidified air enters the gas pipe 3 via the pipe 5 23, to which water vapor or possibly also hot water can finally be introduced via the pipe 20. Only now is the steam-saturated gas treated with cold 3-8% sulfuric acid. In this case, a separate pump 25 maintains a very high liquid pressure of 3.5 bar in the spray-10 nozzles of the cold dilute acid 12. This event takes place in a special empty tank 24 and also in the empty lower part of the second washing tower 4.

Gas further processing, i.e. washing and cooling as well as electrofiltration are carried out in the same way as already shown in both of the above-mentioned embodiments.

Claims (6)

A process for the complete purification of hot SO 2 -containing roasting or combustion gases from dusty and other pollutants for the production of sulfuric acid or pure sulfur dioxide in a three process step comprising hydrogen purification plant, in which the hot raw gas is cooled and almost water vapor in the first process step with circulating, diluted, hot sulfuric acid circulating in a washing device - the gas coming from the first process step is cooled to an even lower temperature in the second process step in a washing tower with filling pieces or in a gas cooler, and the water vapor entering the gas is condensed, - before the gas in the third process step is subjected to electric hydrogen purification, characterized in that it coming from the first process step, is treated in the nearest water-saturated gases before passing through it. second process step by spraying with colder, dilute sulfuric acid or colder relative to the saturation temperature you with colder water. 20 Process according to Claim 1, characterized in that the temperature of the dilute sulfuric acid or water is more than 10 ° C lower than the saturation temperature of the gas. 3. A process according to claim 1 or 2, characterized in that the concentration of the dilute sulfuric acid is not more than 20%. 4. A process according to claims 1-3, characterized in that the injected cold, dilute sulfuric acid amount, respectively. the cold water volume is at least 0.1 l / m gas. 30 Method according to claims 1-4, characterized in that the relative velocity between the injected cold liquid droplets and the gas in the injection area of the injection is on average at least 8 m / s.