Method and system for preparing acid from sulfur based on cooling heat recycling

Abstract

The invention discloses a method and a system for preparing acid from sulfur based on cooling heat recovery and utilization, and relates to the field of sulfuric acid production. According to the method for preparing the acid from the sulfur based on the cooling heat recycling, the sulfuric acid is prepared by adopting a two-conversion and two-absorption process, and desalted water is used as a cooling medium in the process; desalted water sequentially flows through a finished product acid cooler, a first drying acid cooler, a low-temperature heat recovery secondary acid cooler, a primary desalted water preheater, a secondary acid absorption cooler and a secondary desalted water preheater and then enters a deaerator; deoxygenated water output from the deaerator is respectively introduced into the first low-temperature waste heat boiler and the second low-temperature waste heat boiler; serial acid returning to the combined cycle acid tank from the low-temperature heat recovery tower sequentially flows through a second low-temperature waste heat boiler, a boiler feed water heater, a first low-temperature waste heat boiler, a second-stage desalted water preheater and a first-stage desalted water preheater and then returns to the combined cycle acid tank; the purposes of improving the waste heat recovery rate of the sulfur acid making device and improving the waste heat recovery quality are achieved.

Description

Technical Field

[0001] The invention relates to the field of sulfuric acid production, and in particular to a method and system for producing sulfuric acid from sulfur based on cooling heat recovery. Background Art

[0002] By 2023, the global sulfuric acid production capacity will be 205 million tons, and China's sulfuric acid production capacity will be 58 million tons. The global sulfuric acid production processes mainly include 3+1 (or 3+2) two-turn two-absorption process, one-turn one-absorption + organic solvent absorption and desorption process. Among them, the two-turn two-absorption process accounts for the absolute majority (accounting for more than 99%, and the 3+1 two-turn two-absorption process accounts for the vast majority), and the one-turn one-absorption + organic solvent absorption and desorption process is a new process developed in recent years, and its industrialization technology is not yet mature.

[0003] The heat generated by each part of the sulfuric acid plant with two-turn two-absorption process is as follows: 52% heat from sulfur incineration, 17% heat from conversion, 28% heat from absorption, and 3% heat from fan compression; the heat recovery situation of the sulfuric acid plant with two-turn two-absorption process with low-temperature heat recovery system is as follows: 66% heat is recovered from by-product medium and high-pressure superheated steam, 25% heat is recovered from low-temperature waste heat, 6% heat is taken away by circulating water, 1% heat is taken away by tail gas and products, and 2% heat is lost due to heat dissipation.

[0004] At present, most domestic sulfuric acid plants recover the byproduct of sulfur incineration heat and conversion heat, 3.82 ~ 6.4MPaG medium-pressure superheated steam, and use low-temperature waste heat recovery technology to recover the flue gas sensible heat, SO3 absorption heat and dilution heat after primary conversion, and produce 0.8 ~ 1.0MPaG (gauge pressure) low-pressure saturated steam. The commonly used process is: the air sensible heat and the condensation heat and dilution heat of the water vapor contained in the air drying process, the sensible heat of the flue gas after secondary conversion in the secondary absorption tower, and the SO3 absorption heat are taken away by the circulating acid at 70 ~ 100 ℃, and the heat is exchanged with the circulating cooling water at 30 ~ 45 ℃ through the acid cooler and finally discharged into the atmosphere through the cooling water tower and wasted. Specifically, the ultra-low temperature waste heat of low-temperature sulfuric acid is taken away by the circulating cooling water through the finished acid cooler, the drying acid cooler, the low-temperature heat recovery secondary acid cooler, and the second absorption acid cooler (this part of the heat is not recovered); the circulating acid or heat exchange with desalted water produces low-temperature hot water below 100 ℃. The acid in the low-temperature waste heat recovery system returns to the dry absorption system. The boiler feed water heater heats the boiler feed water of the low-pressure steam boiler in the low-temperature waste heat recovery system to increase the low-pressure steam output of the low-temperature waste heat recovery system by 0.8~1.0MPaG. The desalted water preheater is used to heat the desalted water entering the deaerator to 85~95℃ to reduce the steam consumption of the low-pressure steam in the deaerator, so that the temperature of the acid in the return dry absorption system is reduced to 95~105℃. At present, the total heat recovery rate of sulfuric acid plants with low-temperature waste heat recovery systems has reached about 91%, and about 6% of the ultra-low temperature waste heat carried away by the circulating water has not been recovered. The circulating water consumption is 20t / t acid (20 tons per ton of acid). Or this part of the ultra-low temperature waste heat is used for by-product hot water, and the use of hot water is limited. Even if the by-product hot water is used for power generation through the organic Rankine cycle, its efficiency is only about 10%. The hot water is used for heating or refrigeration of lithium bromide units. Its scope of use is limited, so the use of ultra-low temperature waste heat by-product hot water has not been widely adopted.

[0005] In general, the heat carried away by tail gas and products (not worth recycling due to low temperature) and heat dissipation loss have no room for further recycling. The heat carried away by circulating cooling water (or hot water recovery) is still recoverable in sulfuric acid plants with low-temperature waste heat recovery systems, accounting for about 6% of the total heat of sulfuric acid plants. How to better utilize this 6% of ultra-low temperature waste heat, which is currently mainly carried away by circulating cooling water or by-product hot water, has become the key to improving the waste heat recovery efficiency and quality of sulfuric acid plants. Summary of the invention

[0006] The object of the present invention is to provide a sulfuric acid production method based on cooling heat recovery, so as to further improve the waste heat recovery rate of the sulfuric acid production device and further improve the waste heat recovery quality.

[0007] The present invention also provides a system for a sulfuric acid production method based on cooling heat recovery.

[0008] In order to achieve the above object, the present invention adopts the following technical means: A sulfuric acid production method based on cooling heat recovery and utilization, adopting a two-turn two-absorption process to prepare sulfuric acid, using desalted water as the cooling medium in the process, the desalted water flows through a finished acid cooler, a first drying acid cooler, a low-temperature heat recovery secondary acid cooler, a primary desalted water preheater, a second absorption acid cooler, a secondary desalted water preheater in a countercurrent heat exchange manner, and then enters a deaerator.

[0009] The deoxygenated water output from the deaerator is respectively introduced into the first low-temperature waste heat boiler and the second low-temperature waste heat boiler; 99.4-99.7wt% of the string acid returned to the combined cycle acid tank from the low-temperature heat recovery tower flows through the second low-temperature waste heat boiler, the first low-temperature waste heat boiler, the secondary desalted water preheater and the primary desalted water preheater in sequence and then returns to the combined cycle acid tank.

[0010] Furthermore, the dry circulating acid output from the combined circulating acid tank flows into the first dry acid cooler and the second dry acid cooler respectively, the dry circulating acid output from the first dry acid cooler and the second dry acid cooler are combined and flow into the drying tower, and the second dry acid cooler is cooled by ordinary circulating water.

[0011] Furthermore, the finished acid cooler receives 95-98wt% finished sulfuric acid output from the combined cycle acid tank, the temperature of the desalted water entering the finished acid cooler is 25-30°C, and the temperature of the finished sulfuric acid output from the finished acid cooler is 40°C.

[0012] Furthermore, the first dry acid cooler is used to receive the 95-98wt% dry upper tower acid output from the combined cycle acid tank, and output dry acid at 55-65°C to the drying tower.

[0013] Furthermore, the low temperature heat recovery secondary acid cooler is used to receive 98-98.5wt% of the diabsorption circulating acid directly output from the combined cycle acid tank, and output the diabsorption circulating acid at 60°C to the low temperature heat recovery tower.

[0014] Furthermore, after the acid stream passes through the primary desalted water preheater, the temperature is reduced from 95-100°C to 85°C.

[0015] Furthermore, the secondary absorption acid cooler is used to receive 98-98.5wt% of secondary absorption circulating acid directly output from the combined circulation acid tank, and output secondary absorption circulating acid at 65-82°C to the secondary absorption tower.

[0016] Furthermore, after the acid stream flows through the secondary desalted water preheater, the temperature is reduced from 148-166°C to 95-100°C, and at the same time, the temperature of the desalted water flowing through the secondary desalted water preheater is increased to 115-120°C before entering the deaerator.

[0017] Furthermore, in the first low-temperature waste heat boiler, the temperature of the string acid is reduced from 180~190°C to 148~166°C, the temperature of the deoxygenated water output from the deaerator is 135°C, and the deoxygenated water is evaporated in the first low-temperature waste heat boiler to output low-pressure steam of 0.25~0.4MPaG.

[0018] Furthermore, a boiler feed water heater is connected in series between the first low-temperature waste heat boiler and the second low-temperature waste heat boiler, and the acid stream flows out of the second low-temperature waste heat boiler and enters the first low-temperature waste heat boiler through the boiler feed water heater.

[0019] At the same time, the present invention also provides a system for the sulfuric acid production method based on the above-mentioned cooling heat recovery, comprising a combined circulation acid tank, the dry circulation acid output end of the combined circulation acid tank is respectively connected to a drying tower and a finished acid cooler through a first acid path and a second acid path, the output end of the drying tower is connected to the combined circulation acid tank, and a first dry acid cooler and a second dry acid cooler are connected in parallel on the first acid path; The second absorption circulating acid output end of the combined circulation acid tank is connected to the second absorption tower and the low-temperature heat recovery system through the third acid path and the fourth acid path respectively, the third acid path is connected to the second absorption acid cooler, the acid string end of the low-temperature heat recovery system is connected to the first low-pressure steam by-product system through the fifth acid path, and the acid output end of the first low-pressure steam by-product system is connected to the combined circulation acid tank through the sixth acid path; The first low-pressure steam by-product system comprises a first low-temperature waste heat boiler, a second-stage desalted water preheater and a first-stage desalted water preheater connected in series along the acid path, the first low-temperature waste heat boiler is connected to the fifth acid path, and the first-stage desalted water preheater is connected to the combined cycle acid tank; The cooling pipeline of the whole system is connected in sequence to the finished acid cooler, the first dry acid cooler, the low-temperature heat recovery system, the primary desalted water preheater, the second acid absorption cooler and the secondary desalted water preheater; The water inlet end of the first low-temperature waste heat boiler is connected to the output end of the deaerator.

[0020] Preferably, the low-temperature heat recovery system is used to produce a second low-pressure steam, and the low-temperature heat recovery system includes a low-temperature heat recovery secondary acid cooler, a low-temperature heat recovery tower, a second low-temperature waste heat boiler and a boiler feed water heater which are connected in sequence along the acid path, the acid outlet end of the boiler feed water heater is connected to the acid inlet end of the first low-temperature waste heat boiler, the low-temperature heat recovery secondary acid cooler is connected to the combined cycle acid tank, and the cooling pipeline is connected to the low-temperature heat recovery secondary acid cooler.

[0021] Furthermore, the second dry acid cooler is externally connected with an independent cold water pipe for inputting / outputting circulating water.

[0022] Furthermore, the output end of the deaerator is also connected to the second low-temperature waste heat boiler, and the boiler feed water heater is connected in series between the output end of the deaerator and the second low-temperature waste heat boiler.

[0023] Furthermore, the output end of the deaerator is also connected to the water inlet end of the acid diluter, the acid inlet end of the acid diluter is connected to the acid outlet end of the second low-temperature waste heat boiler, and the output end of the acid diluter is connected to the diluted acid inlet of the low-temperature heat recovery tower.

[0024] Among them, the desalted water is successively passed through the finished acid cooler, the first dry acid cooler, the low-temperature heat recovery secondary acid cooler, the first desalted water preheater, the second acid absorption cooler, and the second desalted water preheater to recover the heat collected by the entire system for circulating cooling, so that the temperature of the desalted water entering the deaerator is increased to 115~120℃, and the energy consumption of heating the deoxygenated water to 135℃ during the deoxygenation process of the deaerator is reduced, and the steam consumption of the deaerator is reduced by 0.07~0.09t / t acid. In addition, the waste heat in the acid string returned to the combined cycle acid tank by the first low-temperature waste heat boiler using the low-temperature heat recovery tower (the acid temperature is reduced from 180~190℃ to 148~166℃), and the 135℃ deoxygenated water is pressurized and sent to the first low-temperature waste heat boiler through the low-pressure boiler feed water pump to produce 0.25~0.4MpaG low-pressure saturated steam 0.045~0.085t / t acid. Thus, the low-value cooling heat is assigned and reused. In addition, the heat recovery rate increased from 91% to about 95.5~97%, and the circulating water consumption of the sulfuric acid system was reduced from 20t / t acid to 0~5t / t acid.

[0025] Due to the change of meteorological conditions, the air temperature changes and the amount of water vapor entering the drying tower changes. Under high temperature and high humidity meteorological conditions, the sensible heat and water vapor entering the air increase, resulting in an increase in the condensation heat of air drying. Since the temperature of the drying acid is usually around 60~75℃, the cost of recovering this part of the cooling heat is too high (causing the desalted water that has been circulating to rise too fast and too high, resulting in reduced heat exchange efficiency). Therefore, the first dry acid cooler is set to use desalted water to cool part of the dry upper tower acid, and the second dry acid cooler is set to use external circulating water to cool part of the dry upper tower acid, thereby separating part of the heat entering the system under high humidity and high temperature meteorological conditions. The temperature of the desalted water entering the deaerator is controlled to be 115~120℃ to adjust the acid amount and circulating cooling water amount of the second dry acid cooler, so that the system remains in a controllable optimal operating range. The maximum circulating cooling water amount is 5t / t acid, and the circulating cooling water amount can be reduced to 0t / t acid under meteorological conditions with low air humidity.

[0026] Moreover, part of the 0.25~0.4MpaG low-pressure steam produced as a by-product of the entire system is introduced into the deaerator to meet the demand for low-pressure steam for deoxygenation, and the remaining low-pressure steam can also be injected into the acid-making system, converted and produced into 0.8~1.0MpaG low-pressure steam, and the recovered 0.25~0.4MpaG low-pressure steam is fully utilized within the device. The final result is to displace more 0.8~1.0MpaG low-pressure steam for external supply, so that the net output (external supply) of 0.8~1.0MpaG low-pressure steam of the sulfuric acid-making device increases by 0.13~0.17t / t acid, so as to realize the high-value recovery and utilization of ultra-low temperature waste heat.

[0027] Therefore, the sulfuric acid production method based on cooling heat recovery and utilization involved in this application has the following beneficial effects: The sulfuric acid system of the present invention improves the heat energy recovery rate of the sulfuric acid plant from 91% to about 95.5-97%, so that the cooling heat which is the most difficult to recover can be recovered at a high value.

[0028] The present invention recovers the cooling heat of the sulfuric acid system to increase the temperature of the desalted water entering the deaerator to reduce the consumption of low-pressure steam and produce 0.25-0.4MpaG low-pressure steam as a by-product, and the by-product low-pressure steam is used for deoxygenation (the traditional sulfuric acid device does not have 0.25-0.4MpaG low-pressure steam, and generally uses 0.8-1.0MpaG low-pressure steam after decompression for thermal deoxygenation, and the downgraded use of this part of 0.8-1.0MpaG low-pressure steam causes waste) to meet the demand of the deaerator for low-pressure steam, and the remaining part of the low-pressure steam can be injected into the The waste heat is converted into 0.8~1.0MpaG low-pressure steam output by the low-temperature waste heat recovery system, achieving a balance between the increase in desalted water temperature and the production of 0.25~0.4MPaG low-pressure steam. The recovered cooling heat reduces the internal consumption of low-pressure steam and increases the output. The final result is an increase in the net output of 0.8~1.0MpaG low-pressure steam, and the net output of 0.8~1.0MpaG low-pressure steam in the sulfuric acid system is increased to 0.43~0.47t / t acid, and the net output of low-pressure steam (external supply) increases by 0.13~0.17t / t acid. Taking the 800,000-ton sulfuric acid plant as an example, the annual increase in the net output of steam is worth 10.40~13.60 million yuan (0.8~1.0MPaG low-pressure steam is priced at 100 yuan / ton). The cascade comprehensive utilization of energy is achieved inside the sulfuric acid plant, and the cooling heat is recycled and utilized at a high value.

[0029] Compared with the conventional method of recovering hot water produced by cooling heat of sulfuric acid production system, increasing the temperature of desalted water entering the deaerator to 85-95°C to reduce steam consumption, or using excess hot water for power generation through organic Rankine cycle (the power generation efficiency is only about 10%), or using excess hot water for refrigeration or heating of lithium bromide unit, the use and value of the by-product 0.25-0.4MpaG low-pressure steam are greatly improved in the present invention. By replacing the originally downgraded 0.8-1.0MPaG low-pressure steam used for deoxidation, and injecting the remaining 0.25-0.4MpaG low-pressure steam into the low-temperature waste heat recovery system to be converted into 0.8-1.0MpaG low-pressure steam, the net output of 0.8-1.0MpaG low-pressure steam of sulfuric acid production device is increased, the grade of recovered heat energy is improved, the use of steam is more extensive and the value is higher. For example, the net output of 0.8-1.0MPaG low-pressure steam increased is used for power generation, and the efficiency can reach 62%, which is a qualitative improvement in energy utilization efficiency compared with hot water power generation.

[0030] The heat energy recovery rate of the sulfuric acid system of the present invention is increased from 91% to about 95.5-97%, and the circulating water consumption of the corresponding sulfuric acid system (with a low-temperature waste heat recovery system) is reduced from 20 t / t acid to 0-5 t / t acid, which can save a total of 0.87-1.16 yuan / t acid for the circulating water station, circulating water pipeline and operating power consumption costs; the investment increased by recovering ultra-low temperature waste heat and the operating power consumption costs are 0.6 yuan / t acid in total. Taking the construction of an 800,000-ton sulfuric acid plant as an example, 216,000-448,000 yuan can be saved annually.

[0031] The present invention does not require major adjustments to the two-turn and two-absorption process, but only requires reconstruction of the heat exchange network and equipment, and is relatively easy to implement for both new and old installations. The domestic sulfuric acid system has a production capacity of 58 million tons. Recycling this part of cooling heat to reduce steam consumption and by-product 0.25~0.4MPaG low-pressure saturated steam increases the net steam output by 7.54~9.86 million tons / year, which has great recycling value. Compared with traditional processes, it reduces the investment and power consumption of circulating water stations, and the value of by-products is greatly improved compared with by-product hot water. The entire process is simple and the operating cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a flow chart of the recovery process system of the present invention.

[0033] Among them, 1-finished acid cooler, 2-first dry acid cooler, 3-low-temperature heat recovery secondary acid cooler, 4-first desalted water preheater, 5-second absorption acid cooler, 6-second desalted water preheater, 7-deaerator, 8-first low-temperature waste heat boiler, 9-second low-temperature waste heat boiler, 10-low-temperature heat recovery tower, 11-combined cycle acid tank, 12-second dry acid cooler, 13-drying tower, 14-second absorption tower, 15-boiler feed water heater, 16-first acid line, 17-second acid line, 18-dry cycle acid output end, 19-second absorption cycle acid output end, 20-third acid line, 21-fourth acid line, 22-fifth acid line, 23-sixth acid line, 24-cold water pipe, 25-acid diluter. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0035] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0037] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0038] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the product of the invention is usually placed when in use, or the positions or positional relationships commonly understood by those skilled in the art, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0039] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0040] like Figure 1 As shown, sulfuric acid is prepared by a sulfuric acid production system based on cooling heat recovery.

[0041] For the aforementioned sulfuric acid system based on cooling heat recovery, it includes a combined circulation acid tank 11, a dry circulation acid output end 18 of the combined circulation acid tank 11 is connected to a drying tower 13 and a finished acid cooler 1 through a first acid path 16 and a second acid path 17, respectively, the output end of the drying tower 13 is connected to the combined circulation acid tank 11, and a first dry acid cooler 2 and a second dry acid cooler 12 are connected in parallel on the first acid path 16; The second absorption circulating acid output end 19 of the combined circulation acid tank 11 is respectively connected to the second absorption tower 14 and the low-temperature heat recovery system through the third acid path 20 and the fourth acid path 21, the third acid path 20 is connected to the second absorption acid cooler 5, the acid string end of the low-temperature heat recovery system is connected to the first low-pressure steam by-product system through the fifth acid path 22, and the acid output end of the first low-pressure steam by-product system is connected to the combined circulation acid tank 11 through the sixth acid path 23; The first low-pressure steam by-product system comprises a first low-temperature waste heat boiler 8, a second-stage desalted water preheater 6 and a first-stage desalted water preheater 4 which are connected in series along the acid path, the first low-temperature waste heat boiler 8 is connected to the fifth acid path 22, and the first-stage desalted water preheater 4 is connected to the combined cycle acid tank 11; The cooling pipeline of the whole system is connected in sequence to the finished acid cooler 1, the first dry acid cooler 2, the low-temperature heat recovery system, the primary desalted water preheater 4, the second acid absorption cooler 5 and the secondary desalted water preheater 6; The water inlet end of the first low-temperature waste heat boiler 8 is connected to the output end of the deaerator 7 .

[0042] At the same time, the low-temperature heat recovery system is used to produce a second low-pressure steam. The low-temperature heat recovery system includes a low-temperature heat recovery secondary acid cooler 3, a low-temperature heat recovery tower 10, a second low-temperature waste heat boiler 9 and a boiler feed water heater 15 which are connected in sequence along the acid path. The acid outlet end of the boiler feed water heater 15 is connected to the acid inlet end of the first low-temperature waste heat boiler 8, the low-temperature heat recovery secondary acid cooler 3 is connected to the combined cycle acid tank 11, and the cooling pipeline is connected to the low-temperature heat recovery secondary acid cooler 3.

[0043] In addition, the second dry acid cooler 12 is externally connected with an independent cold water pipe 24 for inputting / outputting circulating water.

[0044] Furthermore, the output end of the deaerator 7 is also connected to the second low-temperature waste heat boiler 9 , and the boiler feed water heater 15 is connected in series between the output end of the deaerator 7 and the second low-temperature waste heat boiler 9 .

[0045] Moreover, the output end of the deaerator 7 is also connected to the water inlet end of the acid diluter 25, the acid inlet end of the acid diluter 25 is connected to the acid outlet end of the second low-temperature waste heat boiler 9, and the output end of the acid diluter 25 is connected to the diluted acid inlet of the low-temperature heat recovery tower 10. Example 1

[0046] The sulfuric acid system of the present invention uses desalted water to pass through a cooling pipeline, sequentially through a finished acid cooler 1, a first drying acid cooler 2, a low-temperature heat recovery secondary acid cooler 3, a primary desalted water preheater 4, a second acid absorption cooler 5, and a secondary desalted water preheater 6 to recover the ultra-low temperature waste heat of low-temperature sulfuric acid to increase the temperature of the desalted water entering the deaerator 7 to reduce the consumption of low-pressure steam. In addition, part of the waste heat of the acid returned to the combined cycle acid tank by the low-temperature waste heat recovery system is produced through the first low-temperature waste heat boiler 8 to produce low-pressure steam.

[0047] The scale of the sulfuric acid plant is 800,000 tons / year, the sulfuric acid output is 100t / h, the atmospheric temperature is 25℃, the relative humidity is 75%, and the water vapor brought into the sulfuric acid plant by the air is 4030Kg / h. According to the water balance calculation of the plant, the concentration of the finished sulfuric acid is 98%.

[0048] Specifically: 98wt% finished sulfuric acid is cooled with desalted water through finished acid cooler 1, the temperature of finished sulfuric acid is reduced from 69°C to 40°C, and the temperature of desalted water is increased from 25°C to 31°C.

[0049] 98 wt% of the dry upper acid is cooled with desalted water through the first dry acid cooler 2, the temperature of the dry acid is reduced from 69°C to 65°C, and the temperature of the desalted water is increased from 31°C to 44°C.

[0050] 98wt% of the low-temperature waste heat recovery secondary upper tower acid is cooled by desalted water through the low-temperature heat recovery secondary acid cooler 3, the acid temperature is reduced from 97°C to 60°C, and the desalted water temperature is increased from 44°C to 58°C.

[0051] The 99.6wt% string acid returned from the low-temperature heat recovery tower 10 to the combined cycle acid tank 11 is cooled by using desalted water in the primary desalted water preheater 4, and the temperature of the string acid returned from the low-temperature heat recovery tower 10 to the dry absorption system is reduced from 98°C to 85°C, and the temperature of the desalted water is increased from 58°C to 65°C.

[0052] The 98wt% sulfuric acid in the second absorption tower is cooled by the second absorption acid cooler 5 using desalted water, the temperature of the sulfuric acid in the second absorption tower is reduced from 97°C to 82°C, and the temperature of the desalted water is increased from 65°C to 82°C.

[0053] The 99.6wt% string acid returned from the low-temperature heat recovery tower 10 to the combined circulation acid tank 11 is cooled using desalted water through the secondary desalted water preheater 6, and the temperature of the string acid returned from the low-temperature heat recovery tower 10 to the combined circulation acid tank 11 is reduced from 157°C to 98°C, and the temperature of the desalted water is increased from 82°C to 115°C.

[0054] The 135℃ boiler feed water is sent to the first low-temperature waste heat boiler 8 to exchange heat with the acid stream returned from the low-temperature heat recovery tower 10 to the combined circulation acid tank 11. The temperature of the acid stream returned from the low-temperature heat recovery tower 10 to the combined circulation acid tank 11 is reduced from 187℃ to 157℃, and 0.3MpaG and 144℃ low-pressure saturated steam are produced as a by-product, which is 6.6t / h. The circulating water consumption of the sulfuric acid plant (with low-temperature waste heat recovery system) is reduced from 20t / t acid to 0t / t acid (Δt=8℃), and the heat recovery rate of the sulfuric acid plant is increased from 91% to about 97%.

[0055] 6.4 t / h of the 0.3 MpaG low-pressure steam produced as a byproduct of the present invention is introduced into the deaerator 7 to meet the deoxygenation requirement, and the 0.3 MpaG low-pressure steam recovered by the present invention is comprehensively utilized inside the device. Example 2

[0056] The scale of sulfuric acid plant is 800,000 tons / year, sulfuric acid output is 100t / h, atmospheric temperature is 33℃, relative humidity is 88%, water vapor brought into the sulfuric acid plant by air is 7667Kg / h, and the concentration of finished sulfuric acid is 95% according to the water balance of the plant. Due to the high air temperature and humidity, the sensible heat of air and latent heat of water vapor brought into the sulfuric acid plant system increase. According to the heat balance of the system, part of the heat of the dry acid is taken away by circulating cooling water to achieve the balance of desalted water heated by ultra-low temperature waste heat inside the plant and the by-product 0.25MPaG low-pressure steam.

[0057] The ultra-low temperature waste heat of low-temperature sulfuric acid is recovered by using desalted water through a cooling pipeline, in turn, through a finished acid cooler 1, a first dry acid cooler 2, a low-temperature heat recovery secondary acid cooler 3, a first desalted water preheater 4, a second acid absorption cooler 5, and a second desalted water preheater 6 to increase the temperature of the desalted water entering the deaerator 7 to reduce the consumption of low-pressure steam. In addition, part of the waste heat of the acid returned to the dry absorption system by the low-temperature waste heat recovery system is produced through the first low-temperature waste heat boiler 8 as a by-product of low-pressure steam. Circulating cooling water is used to take away part of the waste heat of the dry circulating acid entering the acid production system through the second dry acid cooler 12.

[0058] Specifically: 95wt% finished sulfuric acid is cooled with desalted water through finished acid cooler 1, the temperature of finished sulfuric acid is reduced from 65°C to 40°C, and the temperature of desalted water is increased from 30°C to 36°C.

[0059] 95 wt% of the dry upper acid is cooled with desalted water through the first dry acid cooler 2, the temperature of the dry acid is reduced from 65°C to 55°C, and the temperature of the desalted water is increased from 36°C to 52°C.

[0060] 98.5wt% of the low-temperature waste heat recovery secondary upper tower acid is cooled by desalted water through the low-temperature heat recovery secondary acid cooler 3, the acid temperature is reduced from 98°C to 60°C, and the desalted water temperature is increased from 52°C to 66°C.

[0061] The 99.4 wt% string acid returned from the low-temperature heat recovery tower 10 to the combined cycle acid tank 11 is cooled by using desalted water in the primary desalted water preheater 4, and the temperature of the string acid returned from the low-temperature heat recovery tower 10 to the dry absorption system is reduced from 98°C to 85°C, and the temperature of the desalted water is increased from 66°C to 73°C.

[0062] The 98.5wt% sulfuric acid in the second absorption tower is cooled by using desalted water through the second absorption acid cooler 5, the temperature of the sulfuric acid in the second absorption tower is reduced from 98°C to 82°C, and the temperature of the desalted water is increased from 73°C to 91°C.

[0063] The 99.4wt% string acid returned from the low-temperature heat recovery tower 10 to the combined circulation acid tank 11 is cooled using desalted water through the secondary desalted water preheater 6, and the temperature of the string acid returned from the low-temperature heat recovery tower 10 to the combined circulation acid tank 11 is reduced from 150°C to 98°C, and the temperature of the desalted water is increased from 91°C to 120°C.

[0064] The 135℃ boiler feed water is sent to the first low-temperature waste heat boiler 8 for heat exchange with the acid returned from the low-temperature waste heat recovery system to the dry absorption system. The temperature of the acid returned from the low-temperature waste heat recovery system to the dry absorption system is reduced from 187℃ to 150℃, and 0.25MpaG, 139℃ low-pressure saturated steam 8t / h is produced as a by-product. The circulating water consumption of the sulfuric acid system (with low-temperature waste heat recovery system) is reduced from 20t / t acid to 4.6t / t acid (Δt=8℃), and the heat energy recovery rate of the sulfuric acid system reaches about 95.6%.

[0065] Part of 95wt% of the dried upper tower acid is cooled by external additional circulating cooling water through the second dry acid cooler 12, the dry acid temperature is reduced from 65°C to 55°C, the circulating water temperature is increased from 33°C to 41°C, and the circulating cooling water consumption is 460t / h.

[0066] 4.5t / h of the 0.25MpaG low-pressure steam produced as a byproduct of the present invention is introduced into the deaerator 7 to meet the deoxygenation requirements, and the remaining 3.5t / h of low-pressure steam is injected into the low-temperature heat recovery tower 10 for conversion and outputs 3.5t / h of low-pressure steam (0.8-1.0MpaG) more through the second low-temperature waste heat boiler 9. The 0.25MpaG low-pressure steam recovered by the present invention is fully utilized in the device. In this embodiment, due to the high atmospheric temperature and high humidity, the sensible heat of air and the latent heat of water vapor brought into the sulfuric acid device by air increase, and the heat brought into the system increases. Although the net output of steam increases, the overall heat recovery rate is slightly reduced. Example 3

[0067] The scale of the sulfuric acid plant is 800,000 tons / year, the sulfuric acid output is 100t / h, the atmospheric temperature is 30℃, the relative humidity is 75%, and the water vapor brought into the sulfuric acid plant by the air is 5450Kg / h. According to the water balance calculation of the plant, the process water replenishment of the plant is 0Kg / h, and the concentration of the finished acid is 97%.

[0068] The ultra-low temperature waste heat of low-temperature sulfuric acid is recovered by using desalted water through a cooling pipeline, in turn, through a finished acid cooler 1, a first dry acid cooler 2, a low-temperature heat recovery secondary acid cooler 3, a first desalted water preheater 4, a second acid absorption cooler 5, and a second desalted water preheater 6 to increase the temperature of the desalted water entering the deaerator 7 to reduce the consumption of low-pressure steam. In addition, part of the waste heat of the acid returned to the dry absorption system by the low-temperature waste heat recovery system is produced through the first low-temperature waste heat boiler 8 as a by-product of low-pressure steam. Circulating cooling water is used to take away part of the waste heat of the dry circulating acid entering the acid production system through the second dry acid cooler 12.

[0069] Specifically: 97wt% finished sulfuric acid is cooled with desalted water through finished acid cooler 1, the temperature of finished sulfuric acid is reduced from 71°C to 40°C, and the temperature of desalted water is increased from 30°C to 37°C.

[0070] 97 wt% of the dry upper acid is cooled with desalted water through the first dry acid cooler 2, the temperature of the dry acid is reduced from 71°C to 65°C, and the temperature of the desalted water is increased from 37°C to 54°C.

[0071] 98.5wt% of the low-temperature waste heat recovery secondary upper tower acid is cooled by desalted water through the low-temperature heat recovery secondary acid cooler 3, the acid temperature is reduced from 103°C to 60°C, and the desalted water temperature is increased from 54°C to 70°C.

[0072] The 99.5wt% string acid returned from the low-temperature heat recovery tower 10 to the combined cycle acid tank 11 is cooled by using desalted water in the primary desalted water preheater 4. The temperature of the string acid returned from the low-temperature heat recovery tower 10 to the dry absorption system is reduced from 98°C to 85°C, and the temperature of the desalted water is increased from 70°C to 77°C.

[0073] The 98.5wt% sulfuric acid in the second absorption upper tower is cooled by using desalted water through the second absorption acid cooler 5, the temperature of the sulfuric acid in the second absorption upper tower is reduced from 103°C to 82°C, and the temperature of the desalted water is increased from 77°C to 92°C.

[0074] The 99.5wt% string acid returned from the low-temperature heat recovery tower 10 to the combined circulation acid tank 11 is cooled using desalted water through the secondary desalted water preheater 6, and the temperature of the string acid returned from the low-temperature heat recovery tower 10 to the combined circulation acid tank 11 is reduced from 149°C to 98°C, and the temperature of the desalted water is increased from 92°C to 120°C.

[0075] The 135℃ boiler feed water is sent to the first low-temperature waste heat boiler 8 for heat exchange with the acid returned from the low-temperature waste heat recovery system to the dry absorption system. The temperature of the acid returned from the low-temperature waste heat recovery system to the dry absorption system is reduced from 187℃ to 149℃, and 0.25MpaG and 139℃ low-pressure saturated steam are produced as a by-product of 8.5t / h. The circulating water consumption of the sulfuric acid system (with low-temperature waste heat recovery system) is reduced from 20t / t acid to 0.8t / t acid (Δt=8℃), and the heat recovery rate of the sulfuric acid system reaches about 96.8%.

[0076] Part of 97wt% of the dried upper tower acid is cooled by external additional circulating cooling water through the second dry acid cooler 12, the dry acid temperature is reduced from 71°C to 65°C, the circulating water temperature is increased from 33°C to 41°C, and the circulating cooling water consumption is 80t / h.

[0077] 4.5 t / h of the 0.25 MpaG low-pressure steam produced as a by-product of the present invention is introduced into the deaerator 7 to meet the deoxygenation demand, and the remaining 4 t / h of low-pressure steam is injected into the low-temperature heat recovery tower 10 for conversion and produces an additional 4 t / h of low-pressure steam (0.8-1.0 MpaG) through the second low-temperature waste heat boiler 9. The 0.25 MpaG low-pressure steam recovered by the present invention is fully and comprehensively utilized inside the device. Example 4

[0078] The sulfuric acid plant has an annual capacity of 800,000 tons and a sulfuric acid output of 100t / h. The atmospheric temperature is 18°C ​​and the relative humidity is 70%. The water vapor brought into the sulfuric acid system by the air is 2430Kg / h. According to the water balance calculation of the plant, the process water makeup of the plant is 2030Kg / h, and the finished acid concentration is 98%.

[0079] The desalted water is used to pass through the cooling pipeline in sequence through the finished acid cooler 1, the first dry acid cooler 2, the low-temperature heat recovery secondary acid cooler 3, the primary desalted water preheater 4, the second acid absorption cooler 5, and the secondary desalted water preheater 6 to recover the ultra-low temperature waste heat of the low-temperature sulfuric acid to increase the temperature of the desalted water entering the deaerator 7 to reduce the consumption of low-pressure steam. In addition, part of the waste heat of the acid returned to the dry absorption system by the low-temperature waste heat recovery system is produced through the first low-temperature waste heat boiler 8 as a by-product of low-pressure steam.

[0080] Specifically: 98wt% finished sulfuric acid is cooled with desalted water through finished acid cooler 1, the temperature of finished sulfuric acid is reduced from 62°C to 40°C, and the temperature of desalted water is increased from 25°C to 30°C.

[0081] 98.5 wt% of the dry upper acid is cooled with desalted water through the first dry acid cooler 2, the temperature of the dry acid is reduced from 62°C to 60°C, and the temperature of the desalted water is increased from 30°C to 35°C.

[0082] 98.5wt% of the low temperature heat recovery secondary upper tower acid is cooled by desalted water through the low temperature heat recovery secondary acid cooler 3, the acid temperature is reduced from 101°C to 60°C, and the desalted water temperature is increased from 35°C to 50°C.

[0083] The 99.7 wt% string acid returned from the low-temperature heat recovery tower 10 to the combined cycle acid tank 11 is cooled by using desalted water in the primary desalted water preheater 4, and the temperature of the string acid returned from the low-temperature heat recovery tower 10 to the dry absorption system is reduced from 98°C to 85°C, and the temperature of the desalted water is increased from 50°C to 57°C.

[0084] The 98.5wt% sulfuric acid in the second absorption upper tower is cooled by using desalted water through the second absorption acid cooler 5, the temperature of the sulfuric acid in the second absorption upper tower is reduced from 101°C to 65°C, and the temperature of the desalted water is increased from 57°C to 82°C.

[0085] The 99.7 wt% string acid returned from the low-temperature heat recovery tower 10 to the combined cycle acid tank 11 is cooled using desalted water through the secondary desalted water preheater 6, and the temperature of the string acid returned from the low-temperature heat recovery tower 10 to the combined cycle acid tank 11 is reduced from 166°C to 98°C, and the temperature of the desalted water is increased from 82°C to 120°C.

[0086] The 135℃ boiler feed water is sent to the first low-temperature waste heat boiler 8 to exchange heat with the acid stream returned from the low-temperature heat recovery tower 10 to the combined circulation acid tank 11. The temperature of the acid stream returned from the low-temperature heat recovery tower 10 to the combined circulation acid tank 11 is reduced from 187℃ to 166℃, and 0.4MpaG and 152℃ low-pressure saturated steam are produced as a by-product, 4.7t / h. The circulating water consumption of the sulfuric acid system (with low-temperature waste heat recovery system) is reduced from 20t / t acid to 0t / t acid (Δt=8℃), and the heat recovery rate of the sulfuric acid unit reaches about 97%.

[0087] 4.5 t / h of 0.4 MpaG low-pressure steam produced as a by-product of the present invention is introduced into the deaerator 7 to meet the deoxygenation demand. The 0.4 MpaG low-pressure steam recovered by the present invention is basically fully utilized in the device.

[0088] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A sulfuric acid production method based on cooling heat recovery, using a two-turn two-absorption process to prepare sulfuric acid, characterized in that: Desalted water is used as a cooling medium in the process, and the desalted water flows sequentially through a finished acid cooler (1), a first drying acid cooler (2), a low-temperature heat recovery secondary acid cooler (3), a primary desalted water preheater (4), a secondary acid absorption cooler (5), and a secondary desalted water preheater (6) in a countercurrent heat exchange manner before entering a deaerator (7); The deoxygenated water output from the deaerator (7) is respectively introduced into the first low-temperature waste heat boiler (8) and the second low-temperature waste heat boiler (9); 99.4-99.7 wt% of the string acid returned from the low-temperature heat recovery tower (10) to the combined cycle acid tank (11) flows through the second low-temperature waste heat boiler (9), the first low-temperature waste heat boiler (8), the secondary desalted water preheater (6) and the primary desalted water preheater (4) in sequence before returning to the combined cycle acid tank (11).

2. The method for producing sulfuric acid with sulfur based on cooling heat recovery according to claim 1, characterized in that: The dry circulating acid output from the combined circulating acid tank (11) flows into the first dry acid cooler (2) and the second dry acid cooler (12) respectively. The dry circulating acid output from the first dry acid cooler (2) and the second dry acid cooler (12) is combined and then flows into a drying tower (13). The second dry acid cooler (12) is cooled by ordinary circulating water.

3. The method for producing sulfuric acid with sulfur based on cooling heat recovery according to claim 1, characterized in that: The finished acid cooler (1) receives 95-98 wt% finished sulfuric acid output from the combined cycle acid tank (11), the temperature of the desalted water entering the finished acid cooler (1) is 25-30° C., and the temperature of the finished sulfuric acid output from the finished acid cooler (1) is 40° C.; The first dry acid cooler (2) is used to receive the 95-98 wt% dry upper tower acid output from the combined cycle acid tank (11), and output the dry acid at 55-65° C. to the drying tower (13); The low-temperature heat recovery secondary acid cooler (3) is used to receive 98-98.5 wt% of the secondary absorption circulating acid directly output from the combined circulation acid tank (11), and output the secondary absorption circulating acid at 60° C. to the low-temperature heat recovery tower (10); After the acid stream passes through the primary desalted water preheater (4), the temperature is reduced from 95-100°C to 85°C; The secondary absorption acid cooler (5) is used to receive 98-98.5 wt% of secondary absorption circulating acid directly output from the combined circulation acid tank (11), and output secondary absorption circulating acid at 65-82° C. to the secondary absorption tower (14); After the acid stream flows through the secondary desalted water preheater (6), the temperature is reduced from 148-166°C to 95-100°C. At the same time, the temperature of the desalted water flowing through the secondary desalted water preheater (6) is increased to 115-120°C before entering the deaerator (7).

4. The method for producing sulfuric acid with sulfur based on cooling heat recovery according to claim 1, characterized in that: In the first low-temperature waste heat boiler (8), the temperature of the string acid is reduced from 180-190° C. to 148-166° C., the temperature of the deoxygenated water output from the deaerator (7) is 135° C., and the deoxygenated water is evaporated in the first low-temperature waste heat boiler (8) to output low-pressure steam of 0.25-0.4 MPaG.

5. The method for producing sulfuric acid with sulfur based on cooling heat recovery according to claim 1, characterized in that: A boiler feed water heater (15) is also connected in series between the first low-temperature waste heat boiler (8) and the second low-temperature waste heat boiler (9); the acid stream flows out of the second low-temperature waste heat boiler (9) and enters the first low-temperature waste heat boiler (8) through the boiler feed water heater (15).

6. A system for the sulfuric acid production method using cooling heat recovery according to any one of claims 1 to 5, characterized in that: The invention comprises a combined circulation acid tank (11), wherein a dry circulation acid output end (18) of the combined circulation acid tank (11) is respectively connected to a drying tower (13) and a finished acid cooler (1) through a first acid path (16) and a second acid path (17), wherein the output end of the drying tower (13) is connected to the combined circulation acid tank (11), and a first dry acid cooler (2) and a second dry acid cooler (12) are connected in parallel to the first acid path (16); The secondary absorption circulating acid output end (19) of the combined circulation acid tank (11) is connected to the secondary absorption tower (14) and the low-temperature heat recovery system respectively through the third acid path (20) and the fourth acid path (21); the third acid path (20) is connected to the secondary absorption acid cooler (5); the acid connection end of the low-temperature heat recovery system is connected to the first low-pressure steam by-product system through the fifth acid path (22); and the acid output end of the first low-pressure steam by-product system is connected to the combined circulation acid tank (11) through the sixth acid path (23); The first low-pressure steam by-product system comprises a first low-temperature waste heat boiler (8), a second-stage desalted water preheater (6) and a first-stage desalted water preheater (4) which are sequentially connected in series along the acid path, the first low-temperature waste heat boiler (8) being connected to the fifth acid path (22), and the first-stage desalted water preheater (4) being connected to the combined cycle acid tank (11); The cooling pipeline of the entire system is connected in sequence to the finished acid cooler (1), the first dry acid cooler (2), the low-temperature heat recovery system, the first desalted water preheater (4), the second acid absorption cooler (5) and the second desalted water preheater (6); The water inlet end of the first low-temperature waste heat boiler (8) is in communication with the output end of the deaerator (7).

7. The system of the sulfuric acid production method based on cooling heat recovery according to claim 6 is characterized in that: The low-temperature heat recovery system is used to produce a second low-pressure steam, and the low-temperature heat recovery system comprises a low-temperature heat recovery secondary acid cooler (3), a low-temperature heat recovery tower (10), a second low-temperature waste heat boiler (9) and a boiler feed water heater (15) which are sequentially connected along the acid path, the acid outlet end of the boiler feed water heater (15) is connected to the acid inlet end of the first low-temperature waste heat boiler (8), the low-temperature heat recovery secondary acid cooler (3) is connected to the combined cycle acid tank (11), and the cooling pipeline is connected to the low-temperature heat recovery secondary acid cooler (3); The output end of the deaerator (7) is also connected to the second low-temperature waste heat boiler (9), and the boiler feed water heater (15) is connected in series between the output end of the deaerator (7) and the second low-temperature waste heat boiler (9); The output end of the deaerator (7) is also connected to the water inlet end of the acid diluter (25), the acid inlet end of the acid diluter (25) is connected to the acid outlet end of the second low-temperature waste heat boiler (9), and the output end of the acid diluter (25) is connected to the diluted acid inlet of the low-temperature heat recovery tower (10).

8. The system of the sulfuric acid production method based on cooling heat recovery according to claim 6 is characterized in that: The second dry acid cooler (12) is externally connected to an independent cold water pipe (24) for inputting / outputting circulating water.

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