Method for the recovery of sulfur dioxide from gases

 

(57) Abstract:

The invention relates to methods of removing sulfur dioxide from gases. Sulfur dioxide from gases absorb water. The solution after absorption cooled to a temperature of(- 5) - (+5)To separate the precipitation of crystalline and from it produce sulfur dioxide. The solution after separation of the crystalline return to the stage of absorption. The absorption of sulfur dioxide is carried out at a temperature of 0To plus 10C. sulfur Dioxide are separated from the hydrated by heating at a temperature 5 - 45C. From a solution before returning it to the stage of absorption emit sulfur dioxide. The invention allows to reduce the energy consumption of the process. 1 S. and 3 C.p. f-crystals. table 1.

The invention relates to methods for sulfur dioxide, in particular, to methods of its concentration of exhaust gases in the chemical and metallurgical industries.

Known methods of allocation of sulfur dioxide from gas mixtures using aqueous solutions of various inorganic salts and organic compounds, as well as anhydrous organic solvents, based on the chemisorption of sulfur dioxide. The allocation of sulfur dioxide from waste wash liquid is carried out by desorption at protofascist in the process gas mixture. The resulting sulfur dioxide is converted to sulfuric acid or elemental sulfur. Some methods include obtaining an intermediate product liquid sulfur dioxide. (A. L. Cole, F. S., Rosenfeld. Gas cleaning. - M.; Subsoil, 1968, pages 142 - 168).

A disadvantage of the known chemical methods are inevitable loss of reagent due to the formation of by-products of the interaction of washing solutions with gas mixtures containing oxygen. The compounds formed are not involved in the absorption process of sulfur and removed from the process, forming thereby losing the reagent that needs to be filled.

Known reagentless methods of allocation of sulfur dioxide from gas mixtures based on the use as a wash liquid water or salty natural aqueous solutions (e.g., sea water). The absorption process is carried out at the lowest possible temperature and pressure below atmospheric. Waste (degassed) leaching liquid in most cases will not be re-used because of the need of energy consumption for the cooling. The flushing gas mixture enters fresh water.

The disadvantages of such spontania large volumes, that requires a high energy consumption allocations of sulfur dioxide at elevated temperatures and the large consumption of water.

The closest in technical essence and the achieved result is a method for extracting sulphur dioxide, selected as a prototype. 1 SU N682 119, CL C 01 B 17/60. 25.08.79.

The known method includes the following stages: gas cleaning from dust; the absorption of sulfur dioxide from gas water; desorption of sulfur dioxide in the Stripping column while heating the solution to a 15 - 98oC and a pressure below atmospheric; cooling wet sulfur dioxide in the heat exchanger and condensation of the main part of the moisture; drying sulfur dioxide sulfuric acid; the condensation of liquid sulfur dioxide in a heat exchanger by cooling to minus 74 - minus 25oC and a pressure of 27 to 500 mm RT. Art.

A solution of sulfur dioxide supplied to the Stripping column contains about 1.5% SO2. (Patent 682119 the USSR, MKI C 01 B 17/60, B 01 D 53/14. Method for recovering sulfur dioxide from gases. C. A. Peterson (Sweden). - N 2072319/23-26; statements. 15.10.74; publ. 25.08.79, bull. N 31; priority 15.10.73, 7313965-1 (Sweden).-2 C.).

The disadvantage of this method is the low concentration of sulfur dioxide in the feed to the Stripping solution, requiring high energise the plants is the reduction of inputs for production of sulfur dioxide in the process of Stripping solution.

Put the chain is achieved in that in the method of extraction of sulfur dioxide from gases, including the absorption of sulfur dioxide with water according to the invention, the solution after the absorption of sulfur dioxide is cooled to a temperature of minus 5 to plus 5oC, separating the precipitation of crystalline and from it produce sulfur dioxide, and the solution after separation of the crystalline return to the stage of absorption.

The second difference is that the absorption of sulfur dioxide with water are in the temperature range 0 - + 10oC.

The third difference is that sulfur dioxide are separated from the hydrated by heating at a temperature of plus 5 to plus 45oC.

The fourth difference is that from the solution before returning it to the stage of absorption emit sulfur dioxide.

It is known that when cooled concentrated aqueous solutions of sulfur dioxide, a solid crystalline phase (gas hydrate) having a composition of SO2nH2O, where n = 6-7 (B. C. Nekrasov. Fundamentals of General chemistry. M; Chemistry, 1973 , I. 1, page 329). The proportion of sulphur dioxide in the crystalline, as can be seen from its composition, is 33 - 37%. For the decomposition product of such a composition operation selection dioxide is ATM.

A gas mixture containing 30 to 50% of the sulfur dioxide treated water or aqueous solution at a temperature below 10oC. Processing is carried out in countercurrent mode, when the source gas mixture contacts a saturated solution, and the exhaust gas is in contact with fresh water (solution) supplied to the operation of absorption. When a sufficient concentration of sulfur dioxide in the solution of the solution volume is allocated a solid crystalline phase at the stage of processing of the gas mixture. At the end of processing of the gas mixture and further lowering the temperature of a saturated solution below 10oC increases the number and proportion of sulfur dioxide emitted in the form of crystalline.

A solid crystalline phase is separated from the solution and heated to highlight gaseous sulfur dioxide.

The liquid phase washing liquid, which represents a weakly saturated solution of sulfur dioxide, processed by one of the following options: perform the Stripping of obtaining sulfur dioxide and degassed water (solution), which after cooling is re-used for absorption of sulfur dioxide; use without degassing for absorption of sulfur dioxide source gas when the variations that an increasing proportion of sulfur dioxide, released from solution in the form of hydrated and reduced energy costs for heating and cooling of the wash liquid.

The method is illustrated by the following example. A gas mixture containing 31.5% of sulfur dioxide selected from the conditions of flow of metallurgical processes, sequentially passed through two installed in thermostat hermetic bubble reactor with a volume of 1 liter with a false bottom, ensuring the dispersion of the gas mixture at the stage of absorption and separation of the solution from the precipitate. The flow rate of the gas mixture is 0.03 m3/h, the temperature of the water in the reactor is supported in the interval plus 3 plus 4oC. After 30 min of purging the solution is saturated, the flow of the gas mixture stop and lower the temperature in the reactor to 0oC. the Solution from the first to the direction of gas flow reactor is filtered through the false bottom when the supply of the source gas mixture into the reactor, the reactor is sealed and placed in a thermostat with temperature plus 15oC. the Reactor with sludge containing 117 g of product absorption, combined with dehydration, condensation and collection of sulfur dioxide, comprising leaching vessel with sulfuric acid, the cooler - condenser and vessel for liquid sulfur dioxide. Selection DIAC is Bernice liquid sulfur dioxide minus 35oC. the Solution from the first reactor in the amount of 954 g in a sealed reactor is placed in a thermostat with temperature plus 45oC and emit sulfur dioxide in the parameters collection system, similar to that described previously, the total amount of sulfur dioxide, obtained by carrying out the method according to example 65,

This temperature range the absorption of selected due to the fact that at temperatures below zero degrees possible ice formation on the items of equipment, when water temperature is above 10oC reduced concentration of sulfur dioxide in solution and the amount of the formed hydrated.

The allocation of sulfur dioxide from crystalline at temperatures below + 5oC does not occur. At temperatures above + 45oC dramatically increase energy costs for heating, drying and cooling.

A partial refund of the solution after separation of the crystalline allows you to allocate a greater amount of sulfur dioxide in the form of hydrated and thereby decrease the energy consumption for heating, drying and cooling solutions and gaseous mixtures.

Thus, the allocation of the absorbed sulfur dioxide in the form of hydrated reduces energy is

1. Method for the recovery of sulfur dioxide from gases, including the absorption of sulfur dioxide with water, wherein the solution after absorption cooled to a temperature (-5) - (+5)oC, separating the precipitation of crystalline and from it produce sulfur dioxide, and the solution after separation of the crystalline return to the stage of absorption.

2. The method according to p. 1, characterized in that the absorption of sulfur dioxide is carried out at a temperature of 0 to 10oC.

3. The method according to p. 1, characterized in that the sulfur dioxide are separated from the hydrated by heating at a temperature 5 - 45oC.

4. The method according to p. 1, characterized in that from the solution before returning it to the stage of absorption emit sulfur dioxide.

 

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