RU1820887C - Process for preparing elementary sulfur - Google Patents

Abstract

The invention relates to the field of inorganic chemistry, in particular to methods for producing sulfur by processing waste industrial gases containing sulfur dioxide. The essence of the method is that in a separate installation, pyrolysis or oxidative cracking of a hydrocarbon (liquid, solid or gaseous) is carried out. Reduced sulfur dioxide with a sulfur dioxide content of 10-20% (the rest: unbound oxygen, nitrogen, carbon dioxide, etc.), which corresponds to the composition of the exhaust gases of metallurgical plants, for preheating, is mixed in a burner consisting of several burners dispersed over the cross section of the reactor with gaseous fuel at a fuel: oxygen ratio close to stoichiometric (fuel supply can be 1-5% higher than the stoichiometric ratio) and set on fire. Hydrocarbon pyrolysis (cracking) products are fed into heated sulfur dioxide. After the gas stream passes through the reactor, it is quenched by cooling to 300-400 ° C at a speed of at least 1000 deg / s. Then, sulfur is recovered by further cooling the gas stream. Gaseous products are sent for catalytic reduction. The sulfur yield is 86%, the process speed increases significantly, 3 s.p. f-ly.

Description

The invention relates to the field of inorganic chemistry, in particular to methods for producing sulfur by processing industrial waste gases containing sulfur dioxide, and can be used, for example, in non-ferrous metallurgy for the treatment of waste gases while producing marketable sulfur.

The aim of the invention is to increase the yield of the target product, reduce the duration of the process, enable the use of liquid and solid hydrocarbons, reduce the content of toxic sulfur compounds in the reduction products.

The goal is achieved by the proposed method for the production of elemental sulfur from gases containing sulfur dioxide, including high-temperature reduction with hydrocarbons with preliminary heating of sulfur dioxide, subsequent cooling of the reduction products, condensation of the resulting sulfur and catalytic reduction

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unreacted sulphurous gases, in which the hydrocarbon is subjected to gyrolysis or oxidative cracking before being fed to the reduction, and the gases containing sulfur dioxide are preheated by burning any hydrocarbon fuel in sulphurous gas due to unbound oxygen or air supplied together with sulphurous gas at a ratio oxygen: fuel close to stoichiometric. - In the case of large volumes of the reactor and supplied gases, the goal is best achieved by the fact that the supply of gases containing sulfur dioxide and unbound oxygen and hydrocarbon fuel for preheating are dispersed over the entire cross section of the reactor.

The following techniques also contribute to the maximum achievement of the goal: 1) preheating of hydrocarbons supplied for the reduction of hydrocarbon pyrolysis or oxidative cracking of hydrocarbons; 2) carrying out reduction in the presence of initiating additives of acetylene, peroxides or unsaturated hydrocarbons; 3) sharp cooling of the gas stream during the recovery process at 300-400 ° C with a cooling rate of at least 1000 deg / s.

In known methods for producing sulfur from gases containing sulfur dioxide, preliminary pyrolysis-Offering of a hydrocarbon prior to its supply to reduction has not yet been used. Preliminary cracking of the hydrocarbon allows, firstly, to reduce the reaction time, and secondly, to reduce the temperature of the process. As was established by experimental studies in the development of the claimed method, the substances directly reducing sulfur dioxide are hydrogen and unsaturated hydrocarbons formed during thermal pyrolysis (cracking) of the hydrocarbon, the speed of the entire reduction process being limited by the pyrolysis process and the reduction of sulfur dioxide by products pyrolysis. ("70-80% H2) proceeds 4-8 times faster than the hydrocarbon itself. A higher process rate during reduction by the proposed method allows to increase the degree of reduction of sulfur dioxide. because in this case, the reduction process manages to go to great depth during the passage of gases through the reactor. The use of products of pyrolysis (cracking), the main component of which is hydrogen, also makes it possible to almost completely avoid unpleasant consequences such as the formation of toxic toxic sulfur compounds CS2 and COS, for the conversion of which into elemental sulfur it is necessary to introduce additional catalytic addition to conventional hydrogen sulfide reduction stage significantly complicating

0 the whole process .. Finally, the introduction of a preliminary pyrolysis or oxidative cracking step allows not only gaseous, but also gaseous, to be used for reducing sulfur dioxide in the same reactor.

5 but also liquid hydrocarbons and even solid

hydrocarbons, for example coal.

using gaseous products of their ter. processing, e.g. coke

gas.

0 Since the preliminary pyrolysis (cracking) of the hydrocarbon fed to the reduction allows lowering its temperature due to the higher speed of the process, less fuel is required for preheating.

In the proposed method, in contrast to the prototype, hydrocarbon fuel for preheating is supplied together with a reduced gas containing sulfur dioxide and unbound oxygen or air at an oxygen: fuel ratio close to stoichiometric.

The simultaneous supply of fuel and sulfur dioxide allows the use of unbound oxygen, almost always contained in sulfur dioxide, to oxidize the fuel during preheating and to prevent oxygen from entering the reduction zone, where the presence of even small amounts of oxidizing agent drastically inhibits the reduction process, reducing the yield of the target product.

As was established by research (when developing the inventive method), the presence of stoichiometric hydrocarbon-air mixtures in the gases supplied for combustion for preheating to 20% sulfur dioxide does not move beyond the range of sustainable combustion.

0

Studies have also shown that the stoichiometric ratio of hydrocarbon: oxygen or a very small excess of hydrocarbon (t-5%) with a sulfur dioxide content of at least 20% allows almost completely removing oxygen from sulfur dioxide, without violating stable combustion of the mixture, and obtain the practically calculated adiabatic temperature of the gas stream.

The dispersed supply of hydrocarbon fuel for heating allows the creation of several relatively small areas of stable combustion, while increasing the stability of the recovery unit, reducing the burning time of the hydrocarbon by reducing the length of the flame, and thereby increasing the time allocated to the recovery process (with the same dimensions of the unit), which ultimately increases the yield of the target product. The simultaneous operation of several burner devices eliminates the danger of the formation of an explosive mixture in the reactor upon flame failure in one of them and provides a more uniform heating of the products throughout the reactor cross section.

Preheating the reducing gas, the volume of which can be more than ten percent of the total volume of gases passing through the reactor, allows one to avoid (inevitably otherwise) a temperature drop in the reduction zone of 150-200 °, which would lead to a multiple decrease in speed and. therefore, a decrease in the yield of the target product would require a corresponding increase in the temperature in the combustion zone, which is associated with an increase in the volume of fuel supplied to the reactor and a sharp increase in the rate of wear of the heat-protective coating in the presence of aggressive sulfur compounds

The use of additives initiating the process allows one to increase the speed of the process or to lower the temperature of the process, which is equivalent to an increase in the yield of the target product at the same cost of hydrocarbon fuel. Such additives may include well-known initiators of the decomposition and oxidation of hydrocarbons, such as peroxides or unsaturated hydrocarbons. This is because. As shown by studies in the development of the claimed method, the reduction of sulfur dioxide by hydrocarbons and products of their thermal processing is a radical process with pronounced signs of autocatalysis reaction products.

Our kinetic calculations show that the maximum concentration of elemental sulfur in the course of reduction can exceed the thermodynamically equilibrium value, because part of the already formed sulfur may then be consumed during the process in other, slower radical reactions. In order to realize the possibility of obtaining these concentrations in excess of thermodynamically equilibrium values, i.e. In order to obtain the maximum possible yield of the target product, the gas stream must be quenched by abruptly cooling it to a temperature at which all basic chemical processes in this system cease. In the proposed method, the gas stream is required to be cooled at 300-400 ° C with a cooling rate of at least 1000 deg / s.

The proposed method is carried out as follows.

In a separate installation, pyrolysis or oxidative cracking of a hydrocarbon (liquid, solid or gaseous) is carried out. Reduced sulphurous gas with a sulfur dioxide content of 10-20% (rest: unbound oxygen, nitrogen, carbon dioxide

and others), which corresponds to the composition of the exhaust gases of metallurgical plants, for preheating is mixed in the burner with gaseous fuel with the ratio fuel: oxygen close to

stoichiometric (fuel can be 1-5% more), (the required amount of oxygen is added to the sulfur dioxide before it is fed to the burner), and ignited. The dispersed supply of these gases allows

divide the reactor cross section into a series of independent identical zones of optimal (due to the optimal composition and optimal geometric dimensions) combustion. The sizes and conditions of combustion and reduction of sulfur dioxide in each of these zones are determined only by the amount of reagents entering this zone, and all scale changes with a change in the scale of the process are achieved by a corresponding increase in the number of such zones.

The products of pyrolysis (cracking) of a hydrocarbon are fed into heated sulfur dioxide, which, in the case of large volumes, is best preheated to a temperature

500-1000 ° C. The recovery of sulfur dioxide by the products of pyrolysis (cracking) at the same temperature proceeds 4-8 times faster than in the prototype, or at the same speed as in the prototype, but at a temperature of 50-100 ° C lower. The required temperature of the products in the reactor is maintained due to the stable combustion of fuel in sulfur dioxide.

The recovery process is monitored by spectroscopic methods for absorption in the ultraviolet region on A 2800A (SOz) and A - 2200D (H2S1 and in the infrared region at v 1530 cm (CS2) and v 2070 cm 1 (COS).

After the gas stream has passed through the reactor, the reaction mixture is cooled to condense and liberate sulfur. Gaseous products are sent for catalytic reduction. The sulfur recovery and catalytic reduction stages are carried out according to a known method: ... ..: -; // .v ...:; - ..

The invention is illustrated by the following examples.

Example 1 ... The process of heating and souring of sulfur dioxide is carried out in a single combustion zone. Sulfur gas composition :; .. -. ;. ; / - ::. -:;.:. . :

Substance S02 vaCOa Y20 N2 Vol.% 10 T4.S 2 7 66 close to the composition of the exhaust gases of metallurgical plants used to produce elemental sulfur, simultaneously with natural gas is fed into the burner in a volume ratio of 02: CH4 2, Q-2.1Q and set on fire. A stable flame is observed in a mixture of this composition and the temperature of the products of combustion is reached no higher than 1300 ° C. Щ sulfur dioxide gas heated in such a way at a distance of 15 s from the point of its supply: through an additional hoop at an angle of 70 °, methane thermal pyrolysis products are fed to the stream in an amount stoichiometric to the sulfur dioxide content. Typical composition of methane pyrolysis products: v V; -: -. .: .....: .. / Substance СЫ4 НгСаНг СаЖ CiMg 06.% 22.4 77.2 0.3 ОЛ - The reduction process is monitored by changes in the concentration of sulfur dioxide, measuring the optical absorption on.;.: A : 2800A. During the passage of the mixture through the reactor (1c) at a temperature of the war zone: at the temperature of 1150 ° C, the sulfur dioxide concentration decreases due to its reduction by methine pyrolysis products is 86%. The formation of CS2 and COS in the final reaction products was not observed. Further, the waste gases are sent to catalytic processing.

Example 2. Analogously to example 1, but the reducing agent (methane pyrolysis products) is supplied in an amount exceeding the stoichiometric with respect to sulfur dioxide (exceeding 50%). An excess of the reducing agent leads to the appearance in the reduction products of significant amounts of hydrogen sulfide (80% of the change in the concentration of sulfur dioxide, constituting 86%), observed on R 2200A. The regulation of the quality of the supplied reducing agent can be obtained as follows:

the reduction of HaS and S02 in the reaction mixture, which is optimal for the further catalytic reduction of sulfur-containing gas to elemental sulfur.

Example 3. Analogously to example 1, but 3% acetylene is added to the reducing gases, and a 2-fold increase in the rate of the reduction process is observed (with the same reduction depth of 86%, the reaction time is "0.5 s). The formation of GSa and GOS in the products was not observed. ; Example 4. Analogously to example 1, but the temperature in the recovery zone is reduced by lOO ° G (105p0e), in order to achieve

the recovery depth (86%) was carried out for 5 s.

Example 5, the Process was carried out analogously to example 1, but simultaneously in two single zones of combustion, for which they took

a reactor of a larger (1.5 times) diameter. The results are identical to those obtained in the example.

Claims (4)

1 ;; .. v.:,.-. }: -;.,. ;: ..:, -.-. v ...,; ..: As can be seen from the examples and results of the kinetic studies, the proposed method provides the following advantages, in comparison with the well-known SPROM. ; .. ..:. {- .1) The yield of earrings at the stage of high-temperature reduction increases from 50 up to 06%, which allows, in some cases, avoiding / further; catalytic addition of sulfur dioxide. 2) At c-identical temperature, a higher (4-8 times) speed is achieved The process that will allow for given parameters of the recovery unit (maximum temperature and dimensions of the recovery chamber) to increase the depth of the reaction, i.e. degree of recovery. ;  3) The desired reaction rate, ceteris paribus, is achieved when temperature 50-100 ° lower, which allows to reduce the temperature accordingly process, and consequently, to reduce fuel consumption and increase the service life of the rebuilding unit. 4) Highly toxic sulfur dioxide reduction products such as GS2 and COS are not formed, thereby eliminating the need for their catalytic conversion to sulfur, which greatly simplifies the process, 5) Pre-pyrolysis (cracking) a reducing hydrocarbon allows the use of not only gaseous, but also liquid and solid hydrocarbons in the same reducing aggregates. These advantages will allow the successful use of the proposed method in the metallurgical industry for the purification of exhaust gases with simultaneous production of high-purity commercial sulfur. Formula of the invention 1. A method of producing elemental sulfur from gases containing sulfur dioxide, including pre-heating the source gas, reducing sulfur dioxide at 90-1250 ° C with hydrocarbon to form the target product, isolating the latter from the reaction gases by cooling them, and then catalyzing - processing of residual gases, characterized in that, in order to increase the yield of the product, reduce the duration of the process, provide the possibility of using liquid and solid hydrocarbons, reduce the content of and toxic sulfur compounds in the reduction products, the hydrocarbon is subjected to pyrolysis or oxidative cracking before being fed to the reduction step, and the initial gas is preheated by burning fuel in it in an amount of 100-105% of stoichiometry with respect to oxygen. 2. The method according to claim 1, characterized in that. that the supply of gases and fuel at the preheating stage is carried out dispersed over the entire cross section of the reactor. 3. A method according to claim 1, characterized in that the reduction is carried out in the presence of an initiating additive, in which acetylene is used. 4. The method according to claim 1, characterized in that the gas stream immediately after reduction is cooled to 300-400 ° C at a speed of at least 1000 deg / s.