The method of purification of gases from sulfur oxides and nitrogen

 

(57) Abstract:

Usage: when cleaning gases from sulfur oxides and nitrogen, flue gas obtained by combustion of solid fuels, as well as in the chemical industry, in particular in the manufacture of sulfuric acid nitrous or combined contact and nitrous method. Essence: gases containing oxides of sulfur and nitrogen, cooled and subjected to absorption impurities sequential contacting of gases with concentrated sulfuric acid, liquid sulfur trioxide at 17-44oC and with concentrated sulfuric acid. After that, the cleaned gases vented into the atmosphere, and absorbent with absorbed nitrogen oxides and sulfur processed in the contact and nitrous process in sulfuric and nitric acid with recirculation of exhaust gases of this process to clean together with source gases. The absorption process is carried out under pressure. 1 C.p. f-crystals, 1 Il.

The invention relates to methods of gas purification from impurities of oxides of sulfur and nitrogen and can be used for cleaning flue gases obtained by combustion of solid fuels, as well as in the chemical industry, in particular in the manufacture of sulfuric acid nitrous or Kumbh tower systems from sulfur oxides and nitrogen by absorbing them with an aqueous solution of hydrogen peroxide [1] . The resultant sulfuric and nitric acid is returned to the process. Moreover, in order to accelerate the absorption and prevent release of nitric oxide in the gas phase in the hydrogen peroxide solution add ammonia. The consumption of hydrogen peroxide is 0.5-1.0 kg per 1 ton of sulfuric acid. The degree of purification from sulfur dioxide ranges from 0.005 vol.%, NOx - 0,01 about. %.

The disadvantage of this method is the need to use hydrogen peroxide is a relatively expensive and chemically unstable product.

There is also known a method of cleaning flue gases from sulfur and nitrogen oxides, including the electrolysis of an aqueous solution containing sodium chloride and a chloride of lead, and the subsequent contacting of the solution after electrolysis with the purified gas [2]. The degree of purification of the gas is sulfur dioxide 86-96%, of nitrogen oxides from 87-92%.

The disadvantage of this method is the relatively low degree of purification.

Closest to the proposed technical essence is a method of purification of waste gases from nitrogen oxides and sulfur by rinsing them with concentrated sulfuric acid [3].

However, this method is suitable for cleaning gases with low sedarah fuels, problematic.

The objective of the proposed invention consists in the exclusion of harmful emissions into the atmosphere, as well as comprehensive cleaning of flue gases obtained by combustion of solid fuels and exhaust gases nitrous or contact-nitrous production of sulphuric acid.

The problem is solved by the method of gas purification from sulfur and nitrogen oxides, including their cooling, absorption of impurities sequential contacting of gases with concentrated sulfuric acid, liquid sulfur trioxide at 17-44oC and with concentrated sulfuric acid, after which the cleaned gases are released into the atmosphere, and absorbent with absorbed nitrogen oxides and sulfur processed in the contact and nitrous process in sulfuric and nitric acid with recirculation of exhaust gases of this process for cleaning together with the flue gases. In order to increase the treatment efficiency of the absorption process is carried out under pressure.

Distinctive features of the invention from the closest analogue is the additional stage gas washing liquid sulfur trioxide at 17-44oC and concentrated sulfuric acid, the flow of the absorbent with absorbed impurities in the contact-NITR the process for joint cleaning flue gases and conducting the cleanup process under pressure.

Along with sulfuric acid products contact-nitrous process is nitric acid and liquid sulfur trioxide in the presence of demand for it as a commodity product. The combination of processes of flue gases of power plants with the processes of production of sulfuric and nitric acids, as well as liquid sulfur trioxide opens the way to creating cost effective and environmentally friendly installations, in which exhaust gas purification consists in the processing of environmentally hazardous compounds into valuable chemical products.

Based on the above proposed solution meets the criterion of "novelty". Analysis of the known technical solutions in the area of study allows to draw a conclusion about the absence of these signs, similar to the distinctive features of the proposed method of gas purification from nitrogen oxides and sulfur, and to accept the proposed solution meets the criterion of "significant differences".

The drawing is a flow diagram of this process consists of two departments: the Department And the contact-nitrous production and separation In gas purification. The Department And includes the contact device 1, the capacitor 2, assortiment 10, the absorbers 11...13, a compressor 14 and an evaporator 15.

Kiln gas, which is produced in the furnace unit (not shown) by burning sulfur, served in the contact device 1 and the catalyst are the oxidation of sulfur dioxide to the trioxide. Get contact gas containing trioxide and sulfur dioxide, is fed to the processing, one part in the condenser 2, and the other in monohydrate absorber 3.

In the condenser 2 by cooling in the temperature range 17...44oC of the gas into contact with liquid sulfur trioxide. Neskondensirovannyh in the condenser 2 gas together with the contact gas from the apparatus 1 serves in the absorber 3. It also directs the gaseous mixture dioxide and sulfur trioxide, which is obtained in the evaporator 15. In absorber 3 sulfur trioxide turn in concentrated sulfuric acid.

Portion of the liquid sulfur trioxide and concentrated sulfuric acid is used to maintain the required level of absorbency of fluids in absorption cycles branch of cleaning. With this purpose, liquid sulfur trioxide is served in the irrigation cycle of the absorber 12, and sulfuric acid in the absorber 13. The remaining quantity of the produced liquid sulfur trioxide and sulfuric acid serves traditional tower 4. It lead to the Stripping of oxides of nitrogen from irrigating acid. Part received here sulfuric acid is withdrawn from the process in the form of marketable products, and the remaining amount returned to the General cycle of irrigation tower branch.

Gases from denitrator 4 is directed to the production tower 5, which is irrigated by nitroso received absorbers 8 and 11.

In the final tower is in the process of absorption of sulfur dioxide from the gas phase and its oxidation nitrosol with the formation of sulfuric acid. The process nitrous oxidation of sulfur dioxide is accompanied by release of nitric oxide. Therefore, the gas from the production tower serves on the oxidation of nitric oxide in the tower 6. Here is also served with oxygen.

From the oxidation tower, the gas is sent to the absorber 7, which irrigate nitric acid. In the absorber 7 is the absorption of nitrogen dioxide with water and the formation of nitric acid. The latter forms an azeotrope at a concentration of 68,4%. In order to avoid losses of nitric acid in the gas phase is withdrawn from the absorber 7, the concentration of acid in the cycle of irrigation support below 68,4%, sustaining the water cycle.

Absorption of nitrogen dioxide with water is accompanied by formation and nitric oxide. Therefore, the gas from the absorber 7 meanly exhaust from the boiler unit (not shown) flue gas used in the evaporator 15 and the heat exchanger 9. At the entrance of the evaporator serves liquid sulfur trioxide, saturated with sulfur dioxide, and get a gaseous trioxide and sulfur dioxide. This gas mixture is processed as described above, in the contact-nitrous Department A.

Downstream of the evaporator 15 source gases and recirculated gases contact-nitrous Department initially cooled in the refrigerator 10, and then extract from them the oxides of nitrogen and sulfur by absorption in the apparatus 11...13. The absorption absorbers 11 and 13 are sulfuric acid, and in the absorber 12 is liquid sulfur trioxide.

The temperature of the gases at the outlet of the refrigerator 10, and the temperature regime in the support absorbers in the range 17...44oC. This condition is caused by the following circumstances:

the use of liquid sulfur trioxide exists in the temperature range 17...44oC;

the desire to create conditions ensuring a high degree of purification of flue gases from sulfur oxides and nitrogen.

The low temperature in the apparatus 11...13 promotes the absorption of nitrogen oxides with sulfuric acid and the oxidation of nitric oxide in the volume of these devices. It is known that the reaction rate of oxidation of nitric oxide increases with decreasing temperature, and the reverse speed of the mixture of oxides, nitrogen dioxide and oxygen is negligible. Stay gas absorbers 11... 13 provides the conversion of oxides of nitrogen dioxide.

Another factor affecting removing nitrogen oxides from gases is narodnosti sulfuric acid. The degree of extraction increases with decreasing narodnosti. This fact explains the offer in this way a counter-current flow pattern of the liquid and gas flows between the absorbers Department cleaning. Fresh sulfuric acid concentration of not less than 98% served in the absorber 13, and saturated with nitrogen oxides acid (nitroso) away from absorber 11 in the contact and nitrous Department A.

At the same time this power absorption cycle with fresh acid is favorable and to prevent entrainment of vapor of sulfur trioxide and sulfuric acid with the output of the branch cleaning gases. When the capture of sulfur trioxide from flue gas sulfuric acid, in particular 98.3% of the concentration of water vapor in the absorber 13 are practically absent, and the partial vapor pressure of the acid at 25oC is 0,00025 mm RT.article.

The main quantity of the oxides remove the absorbers 11 and 12. The application of the absorber 13, which serves fresh concentrated sulfuric acid, the process.

The processing gases in the absorber 11 provides simultaneously with the absorption of oxides of nitrogen drying gas before it is fed to the absorption of the sulfur trioxide. This technique eliminates the "dilution" of sulfur trioxide and thereby creates the best conditions for conducting absorption process in the apparatus 12.

Another factor influencing the effectiveness of the processes in the office cleaning is the pressure. Thus, the solubility of sulfur dioxide and nitrogen oxides in the absorbers is proportional to its partial pressure, while the content of the absorbents of sulfur trioxide and sulfuric acid in the gas phase is inversely proportional to the total pressure in the apparatus. Therefore, when increasing the excess pressure in the absorbers 11...13 increases the saturation of the adsorbent of harmful components and reduces the entrainment of absorbents with the gases withdrawn from the process. At the same time increasing the pressure has a positive effect on the oxidation of nitric oxide in the amount of absorbers 11...13, since it is known that the reaction rate increases in direct proportion to the square of the pressure.

The required excess pressure in the absorbers 11...13 supported by the compressor 14.

Example 1. In the evaporator 15 of the branch cleaning B from the boiler agrega and nitrogen oxides 3,6 kg On the other inlet of the evaporator 15 from absorber 12 serves 43,32 kg of liquid sulfur trioxide containing 13,32 kg of sulphur dioxide. From the evaporator 15, the gas mixture of sulfur dioxide with a temperature of 110oC served in the absorber 3 pin-nitrous separation and flue gases, the temperature of which is reduced to 307oC - in the heat exchanger 9. To another input of the heat exchanger 9 of the absorber 11 is supplied 55,38 kg of sulfuric acid containing sulfur dioxide 4,06 kg and nitrogen oxides 1,32 kg From the output of the heat exchanger is heated to 70oC acid is sent to production tower 5, and the flue gases with the exhaust from the contact-nitrous branch of the gas fed into the refrigerator 10. This gas is recycled to the scrubbing temperature 40oC, contains sulphur dioxide 0,98 kg and nitrogen oxides 0.5 kg

In the refrigerator 10, the gas mixture is cooled to 25oC and with a compressor 14 serves on flushing absorbers 11...13. The pressure in these devices support naturally. In the absorber 11 serves 98% sulfuric acid from the absorber 13 in the amount of 45,17 kg, containing nitrogen oxides 0.11 kg and sulphur dioxide 0,06 kg This acid absorbs from a mixture of gases, water vapor 5 kg, nitrogen oxides 3,95 kg and sulphur dioxide 1,26 kg due to the heat of dilution of sulfuric acid the temperature of the gases at the IDA nitrogen 0.15 kg, served on the contacts in the absorber 12 with liquid sulfur trioxide, which in the amount of 30 kg at a temperature of 25oC is supplied from the capacitor 2 branches Century it absorbs sulfur trioxide from the gas to be purified sulphur dioxide 13,32 kg, after which the absorbent is fed to the input of the heat exchanger 9. In turn, 319,35 kg of gas with the remnants of nitrogen oxides 0.15 kg and sulphur dioxide 0.2 kg is sent to the absorber 13 for contacting with fresh 98% sulfuric acid fed from the absorber 3 pin-nitrous branch A. In the absorber 13 are gas purification from harmful components. From the Department of cleanup deduce 319,18 kg gas that contains sulfur dioxide 0.14 kg and nitrogen oxides 0,04 kg

The degree of purification of the mixture of flue gas and recirculated flue gas is sulfur dioxide 99,053%, nitrogen oxides 99,024%.

Example 2. The process of cleaning gas absorbers 11...13 are under pressure of 7.3 MPa. In office cleaning serves smoke and recirculated gases with the same initial parameters as in the previous example.

At the inlet of the evaporator 15 from the absorber 12 is supplied to 43.5 kg of liquid sulfur trioxide containing 13.5 kg of sulphur dioxide, and in the heat exchanger 9 of the absorber 11 - 55,36 kg of sulfuric acid, steriade is dependent on the 25oC under pressure fed into the absorber 11 wash 98% sulfuric acid coming from the absorber 13 in number 45,1 kg and containing nitrogen oxides 0,09 kg and sulphur dioxide 0,01 kg This acid absorbs from a source gas mixture of water 5 kg, nitrogen oxides 4 kg and sulphur dioxide 1,26 kg Next 332,62 kg gas containing 13.5 kg of sulfur dioxide and 0.1 kg of oxides of nitrogen, is fed into the absorber 12 for contacting with 30 kg of liquid sulfur trioxide. The latter absorbs from the purified gas 13.5 kg of sulphur dioxide. In turn, 319,12 kg of gas with the remnants of nitrogen oxides 0.1 kg and sulphur dioxide 0.02 kg is sent to the absorber 13 in contact with 45 kg of fresh 98% sulfuric acid. In this apparatus douchemat gas from harmful components and take in the atmosphere 319,02 kg gas that contains sulfur dioxide 0.01 kg and nitrogen oxides 0,01 kg

The degree of purification of the mixture of flue gas and recirculated flue gas is sulfur dioxide 99,932%, nitrogen oxides 99,756%.

Literature.

1. USSR author's certificate N 245012, class B 01D 53/14, 1969.

2. USSR author's certificate N 1183157, class B 01D 53/14, 1985.

3. Amelin, A., Technology of sulfuric acid. M., 1983, S. 263, 264.

1. The method of purification of gases from sulfur oxides and nitrogen by factious with liquid sulfur trioxide at 17 44oWith, and then with concentrated sulfuric acid, after which the cleaned gases are withdrawn from the process, the absorbent with absorbed sulfur oxides and nitrogen processed into sulfuric and nitric acid with a contact-nitrous process with recirculation of exhaust gases for cleaning.

2. The method according to p. 1, characterized in that the absorption of gases are under pressure.

 

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