Process system and process method for conversion of sulfur-containing flue gas to sulfuric acid

Abstract

Disclosed is a process system and a process for converting the sulfur-containing flue gas into the sulfuric acid. The process system comprises: a flue gas preheater, which for preheating the sulfur-containing flue gas to 15˜30° C. above its dew point, and the flue gas preheater has a glass tube as a heat exchange tube; a flue gas fan for boosting the pressure of the preheated acid process gas and transporting one part of which to a combustion furnace, and the other part of which to a process gas steam heater; a sulfuric acid steam condenser for condensing SO.sub.3 generated by the combined reactor into sulfuric acid. The device of the present invention can resist the fluctuation of SO.sub.2 concentration in the feed gas, and can realize considerable economic benefits and rational utilization of energy.

Claims

1. A process system for converting sulfur-containing flue gas into sulfuric acid, wherein, the process system comprises: a flue gas preheater for preheating the sulfur-containing flue gas to 15˜30° C. above its dew point, wherein the flue gas preheater has a glass tube as a heat exchange tube; a flue gas fan for boosting the pressure of the preheated acid process gas from the flue gas preheater, and transporting one part of which to a combustion furnace, and the other part of which to a process gas steam heater, wherein the combustion furnace and the process gas steam heater are used for heating the preheated acid process gas to catalytic oxidation temperature of SO.sub.2; the combustion furnace and the process gas steam heater are connected in parallel with a combined reactor, which is used for generating SO.sub.3 by catalytic oxidation of SO.sub.2 in the acid process gas; a sulfuric acid steam condenser for condensing SO.sub.3 generated by the combined reactor into sulfuric acid; the cold end of the sulfuric acid steam condenser is further connected with the flue gas preheater for providing hot air to the flue gas preheater.

2. The process system as defined in claim 1, wherein, the combustion furnace is further provided with a waste heat recycler for converting the heat of high-temperature flue gas in the combustion furnace into saturated steam.

3. The process system as defined in claim 2, wherein, the combined reactor is provided with a first bed, an interstage steam superheater, a second bed and a process gas cooler from top to bottom, and the waste heat recycler and the process gas steam heater are connected with the first bed after being paralleled connected; the outlet of the interstage steam superheater is further connected with the hot end of the process gas steam heater, and superheated steam is used for a heating process of the acid process gas.

4. The process system as defined in claim 3, wherein, the process system further comprises a steam drum, and the steam drum and the waste heat recycler are connected to form a first waste heat collection circuit, the steam drum and the process gas cooler are connected to form a second waste heat collection circuit, and the steam drum is further connected to the interstage steam superheater, so that the saturated steam from the steam drum enters the cold end of the interstage steam superheater to recover heat generated by acid process gas reaction.

5. The process system as defined in claim 1, wherein, the upper part of the sulfuric acid steam condenser is further connected with the combustion furnace through a fan for providing hot air for the combustion furnace.

6. The process system as defined in claim 1, wherein, a top exhaust outlet of the sulfuric acid steam condenser is further connected with an acid mist eliminator and an advance exhaust treatment system in turn.

7. A process for converting sulfur-containing flue gas into sulfuric acid, wherein, the process is carried out in the process system as defined in claim 1, and comprising the following steps: preheating, pressuring and heating, and then subjecting the sulfur-containing flue gas to catalytic oxidation to obtain SO.sub.3, and then condensing; wherein the sulfur-containing flue gas has a concentration of SO.sub.2 higher than or equal to 0.1 mol %, and the catalytic oxidation has a temperature of above 390° C.

8. The process as defined in claim 7, wherein, the sulfur-containing flue gas consisting of: 2% SO.sub.2, 15.5% O.sub.2, 3.6% CO.sub.2, 77.5% N.sub.2, 1.4% H.sub.2O, and the percentage is a molar percentage; the sulfur-containing flue gas that enters the flue gas preheater has a dew point of 120˜150° C.; after passing through the flue gas preheater, preheating the sulfur-containing flue gas to 15˜30° C. above the dew point; boosting the pressure of the acid process gas preheated by the flue gas preheater to 115˜125 kPa by the flue gas fan; carrying out a combustion reaction of the acid process gas, fuel gas and hot air in the combustion furnace, where the acid process gas is heated by ignition to 900˜1200° C.

9. The process as defined in claim 7, wherein, the acid process gas that enters the combined reactor has a temperature of 390˜430° C.; the catalytic oxidation has a reaction order of 2; sending the process gas after catalytic oxidation reaction into the sulfuric acid steam condenser for condensation, cooling obtained product to 10° C. above the dew point of H.sub.2SO.sub.4, then further cooling to 60° C.˜120° C., and collecting obtained H.sub.2SO.sub.4, coalescing and separating, and directly exhausting cooled gas.

10. The process as defined in claim 7, wherein, the obtained H.sub.2SO.sub.4 has a concentration of 93%˜98%, and the percentage is a mass percentage.

11. A process for converting sulfur-containing flue gas into sulfuric acid, wherein, the process is carried out in the process system as defined in claim 2, and comprising the following steps: preheating, pressuring and heating, and then subjecting the sulfur-containing flue gas to catalytic oxidation to obtain SO.sub.3, and then condensing; wherein the sulfur-containing flue gas has a concentration of SO.sub.2 higher than or equal to 0.1 mol %, and the catalytic oxidation has a temperature of above 390° C.

12. A process for converting sulfur-containing flue gas into sulfuric acid, wherein, the process is carried out in the process system as defined in claim 3, and comprising the following steps: preheating, pressuring and heating, and then subjecting the sulfur-containing flue gas to catalytic oxidation to obtain SO.sub.3, and then condensing; wherein the sulfur-containing flue gas has a concentration of SO.sub.2 higher than or equal to 0.1 mol %, and the catalytic oxidation has a temperature of above 390° C.

13. A process for converting sulfur-containing flue gas into sulfuric acid, wherein, the process is carried out in the process system as defined in claim 4, and comprising the following steps: preheating, pressuring and heating, and then subjecting the sulfur-containing flue gas to catalytic oxidation to obtain SO.sub.3, and then condensing; wherein the sulfur-containing flue gas has a concentration of SO.sub.2 higher than or equal to 0.1 mol %, and the catalytic oxidation has a temperature of above 390° C.

14. A process for converting sulfur-containing flue gas into sulfuric acid, wherein, the process is carried out in the process system as defined in claim 5, and comprising the following steps: preheating, pressuring and heating, and then subjecting the sulfur-containing flue gas to catalytic oxidation to obtain SO.sub.3, and then condensing; wherein the sulfur-containing flue gas has a concentration of SO.sub.2 higher than or equal to 0.1 mol %, and the catalytic oxidation has a temperature of above 390° C.

15. A process for converting sulfur-containing flue gas into sulfuric acid, wherein, the process is carried out in the process system as defined in claim 6, and comprising the following steps: preheating, pressuring and heating, and then subjecting the sulfur-containing flue gas to catalytic oxidation to obtain SO.sub.3, and then condensing; wherein the sulfur-containing flue gas has a concentration of SO.sub.2 higher than or equal to 0.1 mol %, and the catalytic oxidation has a temperature of above 390° C.

16. The process as defined in claim 8, wherein, the sulfur-containing flue gas that enters the flue gas preheater has a dew point of 120˜150° C.; after passing through the flue gas preheater, preheating the sulfur-containing flue gas to 140˜170° C.

17. The process as defined in claim 9, wherein, the further cooling has a temperature of 105° C.˜120° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flowchart of the process system for converting sulfur-containing flue gas into sulfuric acid in Example 1

(2) FIG. 2 is a flowchart of the process system for converting sulfur-containing flue gas into sulfuric acid in comparative Example 1.

(3) In FIG. 1 and FIG. 2, marks are illustrated as follows:

(4) flue gas preheater 1

(5) flue gas fan 201

(6) fan 202

(7) combustion furnace 3

(8) waste heat recycler 301

(9) process gas steam heater 4

(10) combined reactor 5

(11) the first bed 501

(12) interstage steam superheater 502

(13) the second bed 503

(14) process gas cooler 504

(15) sulfuric acid steam condenser 6

(16) acid mist eliminator 7

(17) exhaust scrubbing tower 8

(18) circulating cooler 801

(19) circulating pump 802

(20) steam drum 9

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(21) The present invention is further illustrated by the following examples, but the scope of the present invention is not limited therein. The experimental methods for which specific conditions are not indicated in the following examples shall be selected in accordance with the conventional methods and conditions or the commodity specifications.

EXAMPLE 1

(22) The flue gas consists of 2% SO.sub.2, 15.5% O.sub.2, 3.6% CO.sub.2, 77.5% N.sub.2 and 1.4% H.sub.2O, and the percentage is a molar percentage.

(23) As shown in FIG. 1, the active components of the catalyst for converting SO.sub.2 into SO.sub.3 is mostly V.sub.2O.sub.5. The sulfur-containing flue gas needs to reach a certain reaction temperature before entering the catalyst. The flue gas in the front section is preheated, and the heat of the flue gas preheating first comes from the heat generated by the condensation of sulfuric acid, and the heat generated by the waste pot and the heat released from each reaction bed can be used subsequently. See drawing for the detailed process.

(24) After front end cooling and dedusting, temperature reduction and purification, the low concentration of smelting sulfur-containing flue gas (hereinafter referred to acid process gas) enters the cold end inlet of the flue gas preheater 1, an the acid process gas is preheated to 165° C. The hot end of the flue gas preheater 1 is the hot air from the cold end outlet of the sulfuric acid steam condenser 6. The acid process gas preheated by the flue gas preheater 1 is then boosted to 118 kPa by the flue gas fan 201.

(25) The acid process gas with boosted pressure is divided into two streams using a split flow, and then enters the combustion furnace 3 and the process gas steam heater 4 respectively for heating. One stream of the acid process gas, the fuel gas and the hot air enter the combustion furnace 3 for combustion and heating to 1050° C., then enter into the pipe side of the waste heat recycler 301 for cooling and heat recovery. The waste heat recycler 301 uses a shell and tube heat exchanger, and all the heat exchange pipes are immersed in boiler feed water. 5.6 MPag medium pressure saturated steam is generated outside the heat exchange tube; the other stream of the acid process gas enters the process gas steam heater 4 for heating. The hot end of the process gas steam heater 4 uses superheated steam from the outlet of the interstage steam superheater 502 of the combined reactor 5 to heat the acid process gas. The acid process gas heated by the waste heat recycler 301 and by the process gas steam heater 4 are mixed and sent to the inlet of the first bed 501 of the combined reactor 5 after reaching the best reaction temperature of 420° C.

(26) The acid process gas mixed from the waste heat recycler 301 and the process gas steam heater 4 enters the inlet of the first bed 501 of the combined reactor 5. Under the action of catalyst, SO.sub.2 is converted into SO.sub.3. This reaction process is a strong exothermic reaction, so the temperature of the acid process is increased after leaving the first bed 501 of the combined reactor 5. The acid process gas from the outlet of the first bed 501 of the combined reactor 5 enters the shell side of the interstage steam superheater 502 for cooling and heat recovery. The saturated steam from the medium pressure steam drum 9 enters the cold end of the interstage steam superheater 502 to recover the heat generated by the acid process gas reaction. The superheated steam after the heating of the interstage steam superheater 502 is divided into two streams: one stream of steam is sent out of the boundary area as the final steam product; The other stream of steam is sent to the process gas steam heater 4 as a heat source to heat up the acid process gas, which condenses itself into saturated and condensate water and is sent out of the boundary area.

(27) The acid process gas cooled by the interstage steam superheater 502 to recover heat enters the inlet of the second bed 503 of the combined reactor 5. SO.sub.2 in the acid process gas is further converted. After reaction i the second bed 503 of the combined reactor 5, the acid process gas enters the process gas cooler 504 for cooling. The cold end of the process gas cooler 504 uses the circulating boiler feed water from the steam drum 9. The circulating boiler feed water exchanges heat with the acid process gas, then vaporizes and returns to steam drum 9 for flash evaporation to produce 5.6 MPag medium pressure saturated steam.

(28) The acid process gas from the process gas cooler 504 is sent to the sulfuric acid steam condenser 6 for condensing into acid, and the product is cooled to 10° C. above the dew point of H.sub.2SO.sub.4, and then further cooled to 110° C. H.sub.2SO.sub.4 products are collected, and the gas obtained after cooling is coalesced and separated, and then directly exhausted. In this process, the gaseous SO.sub.3 is combined with water to form sulfuric acid and condensed to form 98% concentrated sulfuric acid. The upper part of the sulfuric acid steam condenser 6 is further connected with the combustion furnace 3 through a fan 202 for supplying hot air for the combustion furnace 3.

(29) The uncondensed acid process gas containing a small amount of SO.sub.2 and a small amount of sulfuric acid is sent to the acid mist eliminator, and the exhaust after removing tiny droplets by the acid mist eliminator enters the advanced exhaust treatment system (e.g, an exhaust scrubbing tower 8, in which an external circulation loop formed by a circulating cooler 801 and a circulating pump 802 is arranged). The advanced exhaust gas treatment system can adopt a variety of mature wet flue gas desulfurization processes, such as ammonia desulfurization, calcium desulfurization, double alkali desulfurization and other new forms of desulfurization.

(30) The heat exchange network in this example is relatively complex, but self-heat balance can be completely realized, with less fuel gas consumption. The acid process gas adopts a shunt measure, and the fuel gas and its own by-product steam are respectively used to heat the acid process gas to the optimal reaction temperature of the SO.sub.2 catalyst, which can resist the fluctuation of the sulfur-containing flue gas SO.sub.2, and stabilize the operation of the device.

COMPARATIVE EXAMPLE 1

(31) The flue gas consists of 1% SO.sub.2, 16.12% O.sub.2, 3.3% CO.sub.2, 78.07% N.sub.2, 1.2% H.sub.2O, and other 0.31%, and the percentage is a molar percentage.

(32) As shown in FIG. 2, the active components of the catalyst for converting SO.sub.2 into SO.sub.3 is mostly V.sub.2O.sub.5. The sulfur-containing flue gas needs to reach a certain reaction temperature before entering the catalyst. The process gas in the front section is heated by burning fuel gas and hot air, and the heat of combustion can further be recovered by the waste heat recycler 301. See drawing for the detailed process.

(33) After front end cooling and dedusting, temperature reduction and purification, and concentration, the low concentration of smelting sulfur-containing flue gas (hereinafter referred to acid process gas) and the hot air and the fuel gas from the combustion fan 202 enter the combustion furnace 3 for combustion with a combustion temperature of 1025° C., and then enter the pipe side of the waste heat recycler 301 for cooling and heat recovery. The waste heat recycler 301 uses a shell and tube heat exchanger, and all the heat exchange pipes are infiltrated into boiler feed water. 5.6 MPag of medium pressure saturated steam is generated outside the heat exchange tube. The acid process gas is sent to the inlet of the first bed 501 of the combined reactor 5 when the acid process temperature after heat recovery by the waste heat recycler 301 reached the optimal reaction temperature of 423° C.

(34) The acid process gas from the waste heat recycler 301 enters the inlet of the first bed 501 of the combined reactor 5, and under the action of catalyst, SO.sub.2 is converted into SO.sub.3. This reaction process is a strong exothermic reaction, so the temperature of the acid process gas is increased after leaving the first bed 501 of the combined reactor 5. The acid process gas from the outlet of the first bed 501 of the combined reactor 5 enters the shell side of the interstage steam superheater 502 for cooling and heat recovery. The saturated steam from the medium pressure steam drum 9 enters the cold end of the interstage steam superheater 502 to recover the heat generated by the acid process gas reaction. The superheated steam heated by the interstage steam superheater 502 is sent out of the boundary area as a steam product.

(35) The acid process gas cooled by the interstage steam superheater 502 to recover heat enters the inlet of the second bed 503 of the combined reactor 5. SO.sub.2 in the acid process gas is further converted. After reaction in the second bed 503 of the combined reactor 5, the acid process gas enters the process gas cooler 504 for cooling. The cold end of the process gas cooler 504 uses the circulating boiler feed water from the steam drum 9. The circulating boiler feed water exchanges heat with the acid process gas, then vaporizes and returns to the steam drum 9 for flash evaporation to produce 5.6 MPag of medium pressure saturated steam.

(36) The acid process gas from the process gas cooler 504 is sent to the sulfuric acid steam condenser 6 for condensing to acid. In this process, the gaseous SO.sub.3 is combined with water to form sulfuric acid and condensed to form 98% concentrated sulfuric acid.

(37) The uncondensed acid process gas containing a small amount of SO.sub.2 and a small amount of sulfuric acid is sent to the acid mist eliminator, and the exhaust after removing tiny droplets by the acid mist eliminator enters the advanced exhaust treatment system (e.g., an exhaust scrubbing tower 8, in which an external loop formed by a circulating cooler 801 and a circulating pump 802 is arranged). The advanced exhaust gas treatment system can adopt a variety of mature wet flue gas desulfurization processes, such as ammonia desulfurization, calcium desulfurization, double alkali desulfurization and other new forms of desulfurization.

(38) The heat exchange network in the comparative example is simple, but it will consume more fuel gas to supplement heat, and correspondingly, the combustion furnace 3 and the waste heat recycler 301 are larger in size.

(39) According to the above analysis, the low concentration of smelting sulfur-containing flue gas and flue gas containing SO.sub.2 in various chemical devices are purified and then enter the described process system and device to solve the problem that current low concentration of flue gas anti-fluctuation has poor ability and cannot meet the existing relevant standards for emission of SO.sub.2-containing flue gas, and simultaneously produce sulfuric acid products and high grade superheated steam. The present invention not only solves the problems in environmental protection, but also produces certain economic benefits.