A sulfuric acid production method and system based on cooling heat recovery and utilization

Abstract

The present invention discloses a sulfuric acid production method and system based on cooling heat recovery and utilization, which relates to the field of sulfuric acid production. The present invention includes a sulfuric acid production method based on cooling heat recovery and utilization, which uses a two-stage conversion and two-stage absorption process to prepare sulfuric acid, and uses demineralized water as a cooling medium in the process. The demineralized water flows through a finished acid cooler, a first drying acid cooler, a low-temperature heat recovery secondary acid cooler, a primary demineralized water preheater, a second absorption acid cooler, and a secondary demineralized water preheater in sequence and then enters a deaerator; the deaerated water output from the deaerator is respectively introduced into a first low-temperature waste heat boiler and a second low-temperature waste heat boiler; the acid series flowing back to the combined cycle acid tank from the low-temperature heat recovery tower flows through the second low-temperature waste heat boiler, a boiler feed water heater, the first low-temperature waste heat boiler, the secondary demineralized water preheater, and the primary demineralized water preheater in sequence and then returns to the combined cycle acid tank; the purpose of improving the waste heat recovery rate of the sulfuric acid production device and improving the waste heat recovery quality is achieved.

Description

Technical Field

[0001] The present invention relates to the field of sulfuric acid production. Specifically, it is a sulfuric acid production method and system based on the utilization of cooling heat recovery. Background Art

[0002] As of 2023, the production capacity of sulfuric acid production plants worldwide is 205 million tons, and the production capacity of sulfuric acid production plants in China is 58 million tons. The main sulfuric acid production processes worldwide are the 3+1 (or 3+2) double conversion and double absorption process, the single conversion and single absorption + organic solvent absorption and desorption process. Among them, the double conversion and double absorption process accounts for the vast majority (more than 99%, and the 3+1 double conversion and double absorption process accounts for the vast majority), and the single conversion and single 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 in each part of the sulfuric acid production plant with the double conversion and double absorption process is as follows: sulfur combustion heat 52%, conversion heat 17%, absorption heat 28%, and fan compression heat 3%. At present, the heat recovery situation of the sulfuric acid production plant with the double conversion and double absorption process equipped with a low-temperature heat recovery system is as follows: the heat recovered by by-product medium- and high-pressure superheated steam is 66%, the heat recovered from low-temperature waste heat is 25%, the heat carried away by circulating water is 6%, the heat carried away by the tail gas and product is 1%, and the heat loss due to heat dissipation is 2%.

[0004] At present, in domestic sulfuric acid plants, the heat of sulfur burning and conversion heat are basically recovered to by-product medium-pressure superheated steam at 3.82 - 6.4 MPaG, and the low-temperature waste heat recovery technology is applied to recover the sensible heat of the flue gas after the first conversion, the heat of SO3 absorption and dilution heat to by-product low-pressure saturated steam at 0.8 - 1.0 MPaG (gauge pressure). The commonly used process at present is: the sensible heat of air, the condensation heat and dilution heat of the water vapor contained in the air during the air drying process, the sensible heat of the flue gas after the second conversion in the second absorption tower, and the heat of SO3 absorption are taken away by the circulating acid at 70 - 100 °C, and are exchanged with the circulating cooling water at 30 - 45 °C through an acid cooler and finally discharged into the atmosphere through a cooling tower, which is wasted in vain. Specifically, the ultra-low temperature waste heat of the 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 is exchanged with demineralized water to by-product low-temperature hot water below 100 °C. The circulating acid returned from the low-temperature waste heat recovery system to the dry absorption system is heated by the boiler feed water heater and enters the boiler feed water of the low-pressure steam boiler of the low-temperature waste heat recovery system to increase the output of the low-pressure steam at 0.8 - 1.0 MPaG of the low-temperature waste heat recovery system. Then, it is used in the demineralized water preheater to heat the demineralized water entering the deaerator to 85 - 95 °C to reduce the steam consumption of the low-pressure steam in the deaerator, so that the temperature of the circulating acid returned to the dry absorption system is reduced to 95 - 105 °C. At present, the total heat recovery rate of sulfuric acid plants with low-temperature waste heat recovery systems reaches about 91%. The about 6% ultra-low temperature waste heat taken away by the circulating water cannot be recovered, and the circulating water consumption is 20 t / t acid (20 tons per ton of acid). Or this part of the ultra-low temperature waste heat is used to by-product hot water, but the use of hot water is limited. Even if the hot water is used for power generation through an organic Rankine cycle, its efficiency is only about 10%. The hot water is used for heating or refrigeration by a lithium bromide unit, and its application range is limited. Therefore, the use of ultra-low temperature waste heat to by-product hot water has not been widely adopted.

[0005] Generally speaking, there is no further room for recovery and utilization of the heat taken away by the tail gas and the product (which has no recovery value due to low temperature) and the heat dissipation loss. The part of the heat taken away by the circulating cooling water (or hot water recovery) in the sulfuric acid plant with a low-temperature waste heat recovery system still has the potential for recovery, accounting for about 6% of the total heat of sulfuric acid production. How to better utilize the 6% ultra-low temperature waste heat mainly taken away by the 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 purpose of the present invention is to provide a sulfuric acid production method based on the recovery and utilization of cooling heat to further improve the waste heat recovery rate of sulfuric acid plants and further improve the quality of waste heat recovery.

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

[0008] To achieve the above object, the present invention adopts the following technical means:

[0009] A sulfuric acid production method based on cooling heat recovery uses a two-stage conversion and two-stage absorption process to prepare sulfuric acid, and uses demineralized water as the cooling medium in the process. The demineralized water flows through the finished acid cooler, the first drying acid cooler, the low-temperature heat recovery secondary acid cooler, the primary demineralized water preheater, the second absorption acid cooler, and the secondary demineralized water preheater in a countercurrent heat exchange manner and then enters the deaerator.

[0010] The deaerated water output from the deaerator is respectively introduced into the first low-temperature waste heat boiler and the second low-temperature waste heat boiler;

[0011] The 99.4 - 99.7 wt% series acid returned from the low-temperature heat recovery tower to the combined cycle acid tank flows through the second low-temperature waste heat boiler, the first low-temperature waste heat boiler, the secondary demineralized water preheater, and the primary demineralized water preheater in sequence and then returns to the combined cycle acid tank.

[0012] Further, the drying cycle acid output from the combined cycle acid tank respectively flows into the first drying acid cooler and the second drying acid cooler. The drying cycle acid output from the first drying acid cooler and the second drying acid cooler is aggregated and then flows into the drying tower. The second drying acid cooler is cooled by ordinary circulating water.

[0013] Furthermore, the finished acid cooler receives 95 - 98 wt% finished sulfuric acid output from the combined cycle acid tank. The temperature of the demineralized 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.

[0014] Furthermore, the first drying acid cooler is used to receive 95 - 98 wt% drying upper tower acid output from the combined cycle acid tank and output drying acid at 55 - 65 °C to the drying tower.

[0015] Furthermore, the low-temperature heat recovery secondary acid cooler is used to receive 98 - 98.5 wt% second absorption cycle acid directly output from the combined cycle acid tank and output second absorption cycle acid at 60 °C to the low-temperature heat recovery tower.

[0016] Furthermore, after the series acid flows through the primary demineralized water preheater, the temperature is reduced from 95 - 100 °C to 85 °C.

[0017] Furthermore, the second absorption acid cooler is used to receive 98 - 98.5 wt% second absorption cycle acid directly output from the combined cycle acid tank and output second absorption cycle acid at 65 - 82 °C to the second absorption tower.

[0018] Furthermore, after the series acid flows through the secondary demineralized water preheater, its temperature drops from 148 - 166 °C to 95 - 100 °C. Meanwhile, the temperature of the demineralized water flowing through the secondary demineralized water preheater rises to 115 - 120 °C and enters the deaerator.

[0019] Furthermore, in the first low-temperature waste heat boiler, the temperature of the series acid drops from 180 - 190 °C to 148 - 166 °C. The temperature of the deaerated water output from the deaerator is 135 °C, and the deaerated water evaporates in the first low-temperature waste heat boiler to output low-pressure steam of 0.25 - 0.4 MPaG.

[0020] 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. The series acid 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.

[0021] Meanwhile, the present invention also provides a system for a sulfuric acid production method based on the aforementioned cooling heat recovery and utilization, including a combined cycle acid tank. The dry cycle acid output end of the combined cycle 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 cycle acid tank, and a first dry acid cooler and a second dry acid cooler are connected in parallel on the first acid path;

[0022] The double absorption cycle acid output end of the combined cycle acid tank is respectively connected to a double absorption tower and a low-temperature heat recovery system through a third acid path and a fourth acid path. A double absorption acid cooler is connected to the third acid path. The series acid end of the low-temperature heat recovery system is connected to a first low-pressure steam by-product system through a fifth acid path, and the acid output end of the first low-pressure steam by-product system is connected to the combined cycle acid tank through a sixth acid path;

[0023] The first low-pressure steam by-product system includes a first low-temperature waste heat boiler, a secondary demineralized water preheater, and a primary demineralized 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 primary demineralized water preheater is connected to the combined cycle acid tank;

[0024] The cooling pipeline of the entire system is successively connected to the finished acid cooler, the first dry acid cooler, the low-temperature heat recovery system, the primary demineralized water preheater, the double absorption acid cooler, and the secondary demineralized water preheater;

[0025] The water inlet end of the first low-temperature waste heat boiler is connected to the output end of the deaerator.

[0026] Preferably, the low-temperature heat recovery system is used to produce second low-pressure steam. 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 that are connected in series 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.

[0027] Furthermore, an independent cold water pipe is externally connected to the second dry acid cooler for inputting / outputting circulating water.

[0028] 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.

[0029] 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.

[0030] Among them, the demineralized water sequentially passes through the finished product acid cooler, the first dry acid cooler, the low-temperature heat recovery secondary acid cooler, the primary demineralized water preheater, the second absorption acid cooler, and the secondary demineralized water preheater to recover the heat collected for circulating cooling in the whole system, so that the temperature of the demineralized water entering the deaerator is increased to 115 - 120°C, reducing the energy consumption of heating the deaerated water to 135°C during the deaeration process of the deaerator, and reducing the steam consumption of the deaerator by 0.07 - 0.09 t / t acid. In addition, the first low-temperature waste heat boiler utilizes the waste heat in the series acid returned from the low-temperature heat recovery tower to the combined cycle acid tank (the acid temperature is reduced from 180 - 190°C to 148 - 166°C), and the 135°C deaerated water is pressurized by the low-pressure boiler feed water pump and sent into the first low-temperature waste heat boiler to by-product 0.045 - 0.085 t / t acid of 0.25 - 0.4 MpaG low-pressure saturated steam. Thus, the low-value cooling heat is assigned and reused. Moreover, the heat energy recovery rate is increased from 91% to about 95.5 - 97%, and the circulating water consumption of the sulfuric acid production system is reduced from 20 t / t acid to 0 - 5 t / t acid.

[0031] Due to the change of meteorological conditions leading to the change of air temperature and the change of the amount of water vapor entering the drying tower, the sensible heat and the increased condensation heat of water vapor entering with the air under high-temperature and high-humidity meteorological conditions lead to an increase in the drying of air. Since the drying acid temperature is usually around 60 - 75 °C, the cost of recovering this part of the cooling heat is too high (causing the problem that the continuously circulating demineralized water rises too fast and too high, resulting in a reduction in heat exchange efficiency). Therefore, a first drying acid cooler is set up to cool part of the drying upper tower acid with demineralized water, and a second drying acid cooler is set up to cool part of the drying upper tower acid with external circulating water, so as to separate part of the heat entering the system under high-humidity and high-temperature meteorological conditions. The temperature of the demineralized water entering the deaerator is controlled at 115 - 120 °C to adjust the acid amount and the circulating cooling water amount of the second drying acid cooler, so that the system is maintained in a controllable optimal operation range. The maximum circulating cooling water amount is 5 t / t acid, and the circulating cooling water amount can be reduced to 0 t / t acid under meteorological conditions with low air humidity.

[0032] Moreover, part of the low-pressure steam with a pressure of 0.25 - 0.4 MpaG by-produced by the whole system is introduced into the deaerator to meet the demand of the deaerator for low-pressure steam. The remaining low-pressure steam can also be injected into the sulfuric acid production system to be converted and produce low-pressure steam with a pressure of 0.8 - 1.0 MpaG. The recovered low-pressure steam with a pressure of 0.25 - 0.4 MpaG is fully comprehensively utilized inside the device. The final result is to displace more low-pressure steam with a pressure of 0.8 - 1.0 MpaG for external supply, increasing the net output (external supply) of low-pressure steam with a pressure of 0.8 - 1.0 MpaG in the sulfuric acid production device by 0.13 - 0.17 t / t acid to achieve the high-value recovery and utilization of ultra-low temperature waste heat.

[0033] Therefore, the sulfuric acid production method based on the recovery and utilization of cooling heat involved in this application has the following beneficial effects:

[0034] The sulfuric acid production system of the present invention increases the heat energy recovery rate of the sulfuric acid production device from 91% to about 95.5 - 97%, enabling the high-value recovery of the cooling heat with the highest recovery difficulty.

[0035] In the sulfuric acid production system with sulfur recovery in this invention, the cooling heat is recovered to increase the temperature of the demineralized water entering the deaerator, thereby reducing the consumption of low-pressure steam and by-producing low-pressure steam of 0.25 - 0.4 MpaG. The by-produced low-pressure steam is used for deaeration (in traditional sulfuric acid plants, there is no low-pressure steam of the 0.25 - 0.4 MpaG grade. Generally, low-pressure steam of 0.8 - 1.0 MpaG is used for thermal deaeration after pressure reduction. This downgraded use of the 0.8 - 1.0 MpaG low-pressure steam causes waste). To meet the demand of the deaerator for low-pressure steam, the remaining low-pressure steam can be injected into the low-temperature waste heat recovery system to be converted into low-pressure steam of 0.8 - 1.0 MpaG for output. A balance is achieved between the increase in the temperature of the demineralized water and the production of low-pressure steam of 0.25 - 0.4 MPaG. The recovered cooling heat realizes a reduction in the internal consumption of low-pressure steam and an increase in output. The ultimate result is an increase in the net output of low-pressure steam of 0.8 - 1.0 MpaG. The net output of low-pressure steam of 0.8 - 1.0 MpaG in the sulfuric acid production system with sulfur recovery is increased to 0.43 - 0.47 t / t of acid, and the net output (for external supply) of low-pressure steam increases by 0.13 - 0.17 t / t of acid. Taking an 800,000-ton sulfuric acid production plant as an example, the annual increased value of the net steam output is 10.4 - 13.6 million yuan (the low-pressure steam of 0.8 - 1.0 MpaG is priced at 100 yuan / ton). The energy is comprehensively utilized in a cascaded manner within the sulfuric acid production plant with sulfur recovery, and the cooling heat is recovered and utilized with high value.

[0036] Compared with the traditional sulfuric acid production system with sulfur recovery, which by-produces hot water from the cooling heat to increase the temperature of the demineralized water entering the deaerator to 85 - 95°C to reduce steam consumption, or uses the excess hot water for power generation through an organic Rankine cycle (with a power generation efficiency of only about 10%), or uses the excess hot water for refrigeration or heating by a lithium bromide unit, the use and value of the 0.25 - 0.4 MpaG low-pressure steam by-produced in this invention have been greatly improved. By replacing the originally downgraded 0.8 - 1.0 MpaG low-pressure steam used for deaeration and injecting the remaining 0.25 - 0.4 MpaG low-pressure steam into the low-temperature waste heat recovery system to be converted into 0.8 - 1.0 MpaG low-pressure steam, the net output of 0.8 - 1.0 MpaG low-pressure steam in the sulfuric acid production plant increases, the grade of the recovered heat energy is improved, and the use of steam is more extensive and its value is higher. For example, if the increased net output of 0.8 - 1.0 MpaG low-pressure steam is used for power generation, the efficiency can reach 62%, representing a qualitative improvement in the energy utilization efficiency compared with power generation using hot water.

[0037] The heat energy recovery rate of the sulfuric acid production system of the present invention has been increased from 91% to about 95.5 - 97%. Correspondingly, the circulating water consumption of the sulfuric acid production system (with a low-temperature waste heat recovery system) has been 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 pipelines and the power consumption cost of operation; the total investment and power consumption cost for recovering ultra-low temperature waste heat is 0.6 yuan / t acid. Taking the construction of an 800,000-ton sulfuric acid production plant as an example, 216,000 - 448,000 yuan can be saved annually.

[0038] The present invention does not require major adjustments to the double conversion and double absorption process. Only the heat exchange network and equipment need to be reconstructed, and it is relatively easy to implement for both new installations and the transformation of old installations. The domestic production capacity of the sulfuric acid production system is 58 million tons. Recycling this part of the cooling heat reduces steam consumption and the by-product of low-pressure saturated steam at 0.25 - 0.4 MPaG, with a total increase in net steam output of 7.54 - 9.86 million tons / year, having great value for recycling. Compared with the traditional process, it reduces the investment and power consumption of the circulating water station. Compared with the by-product hot water, the value of the by-product has been greatly improved. The entire process flow is simple and the operating cost is low. Brief Description of the Drawings

[0039] Figure 1 It is a process flow diagram of the recovery process system of the present invention.

[0040] Among them, 1 - finished acid cooler, 2 - first drying acid cooler, 3 - low-temperature heat recovery secondary acid cooler, 4 - primary demineralized water preheater, 5 - second absorption acid cooler, 6 - secondary demineralized 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 drying acid cooler, 13 - drying tower, 14 - second absorption tower, 15 - boiler feed water heater, 16 - first acid path, 17 - second acid path, 18 - drying cycle acid output end, 19 - second absorption cycle acid output end, 20 - third acid path, 21 - fourth acid path, 22 - fifth acid path, 23 - sixth acid path, 24 - cold water pipe, 25 - acid diluter. Detailed Embodiments

[0041] To make the purposes, 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 with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Usually, the components of the embodiments of the present invention described and shown in the accompanying drawings here can be arranged and designed in various different configurations.

[0042] Accordingly, 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 claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0043] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0044] It should be noted that similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0045] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the inventive product is usually placed during use, or the orientation or positional relationship commonly understood by those skilled in the art. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first", "second", etc. are only used for descriptive distinction and cannot be construed as indicating or implying relative importance.

[0046] In the description of the present invention, it should also be noted that unless otherwise clearly specified and defined, the terms "set", "installed", "connected", "connected" 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 directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0047] As Figure 1 shown, a sulfuric acid production system based on cooling heat recovery utilization is used for the preparation of sulfuric acid.

[0048] For the aforementioned sulfuric acid production system based on cooling heat recovery utilization, it includes a combined cycle acid tank 11. The dry cycle acid output end 18 of the combined cycle 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. The output end of the drying tower 13 is connected to the combined cycle acid tank 11. A first drying acid cooler 2 and a second drying acid cooler 12 are connected in parallel on the first acid path 16;

[0049] The second absorption cycle acid output end 19 of the combined cycle acid tank 11 is respectively connected to the second absorption tower 14 and the low-temperature heat recovery system through a third acid path 20 and a fourth acid path 21. A second absorption acid cooler 5 is connected to the third acid path 20. The acid series connection end of the low-temperature heat recovery system is connected to the first low-pressure steam by-product system through a fifth acid path 22. The acid output end of the first low-pressure steam by-product system is connected to the combined cycle acid tank 11 through a sixth acid path 23;

[0050] The first low-pressure steam by-product system includes a first low-temperature waste heat boiler 8, a secondary demineralized water preheater 6, and a primary demineralized water preheater 4 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 primary demineralized water preheater 4 is connected to the combined cycle acid tank 11;

[0051] The cooling pipeline of the whole system is successively connected to the finished acid cooler 1, the first drying acid cooler 2, the low-temperature heat recovery system, the primary demineralized water preheater 4, the second absorption acid cooler 5, and the secondary demineralized water preheater 6;

[0052] The water inlet end of the first low-temperature waste heat boiler 8 is connected to the output end of the deaerator 7.

[0053] Meanwhile, the low-temperature heat recovery system is used to produce 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 connected in series along the acid path. The acid output 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.

[0054] Moreover, an independent cold water pipe 24 is externally connected to the second drying acid cooler 12 for inputting / outputting circulating water.

[0055] 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.

[0056] In addition, the output end of the deaerator 7 is also connected to the water inlet end of an acid diluter 25. The acid inlet end of the acid diluter 25 is connected to the acid output end of the second low-temperature waste heat boiler 9. 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

[0057] For the sulfuric acid production system applying the present invention, demineralized water passes through the cooling pipeline and sequentially passes through the finished acid cooler 1, the first drying acid cooler 2, the low-temperature heat recovery secondary acid cooler 3, the primary demineralized water preheater 4, the second absorption acid cooler 5, and the secondary demineralized water preheater 6 to recover the ultra-low-temperature waste heat of the low-temperature sulfuric acid and increase the temperature of the demineralized water entering the deaerator 7 so as to reduce the consumption of low-pressure steam. In addition, part of the waste heat returned to the combined cycle acid tank for acid cross-filling by the low-temperature waste heat recovery system is utilized to generate low-pressure steam by the first low-temperature waste heat boiler 8.

[0058] The scale of the sulfuric acid production plant is 800,000 tons / year, the sulfuric acid output is 100 t / h, the atmospheric temperature is 25 °C, the relative humidity is 75%, the water vapor brought into the sulfuric acid production plant by air is 4,030 Kg / h, and according to the device water balance calculation, the concentration of the finished sulfuric acid is 98%.

[0059] Specifically: The 98 wt% finished sulfuric acid is cooled by demineralized water in the finished acid cooler 1. The temperature of the finished sulfuric acid is reduced from 69 °C to 40 °C, and the temperature of the demineralized water is increased from 25 °C to 31 °C.

[0060] The 98 wt% dried upper tower acid is cooled by demineralized water in the first drying acid cooler 2. The temperature of the drying acid is reduced from 69 °C to 65 °C, and the temperature of the demineralized water is increased from 31 °C to 44 °C.

[0061] The 98 wt% low-temperature waste heat recovery secondary upper tower acid is cooled by demineralized water in the low-temperature heat recovery secondary acid cooler 3. The acid temperature is reduced from 97 °C to 60 °C, and the temperature of the demineralized water is increased from 44 °C to 58 °C.

[0062] The 99.6 wt% acid cross-filling returned from the low-temperature heat recovery tower 10 to the combined cycle acid tank 11 is cooled by demineralized water in the primary demineralized water preheater 4. The temperature of the acid cross-filling 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 demineralized water is increased from 58 °C to 65 °C.

[0063] The 98 wt% sulfuric acid in the second absorption upper tower is cooled by demineralized water in the second absorption acid cooler 5. The temperature of the sulfuric acid in the second absorption upper tower is reduced from 97 °C to 82 °C, and the temperature of the demineralized water is increased from 65 °C to 82 °C.

[0064] The 99.6 wt% acid cross-filling returned from the low-temperature heat recovery tower 10 to the combined cycle acid tank 11 is cooled by demineralized water in the secondary demineralized water preheater 6. The temperature of the acid cross-filling returned from the low-temperature heat recovery tower 10 to the combined cycle acid tank 11 is reduced from 157 °C to 98 °C, and the temperature of the demineralized water is increased from 82 °C to 115 °C.

[0065] The boiler feed water at 135°C is sent to the first low-temperature waste heat boiler 8 for heat exchange with the acid series flow returning from the low-temperature heat recovery tower 10 to the combined cycle acid tank 11. The temperature of the acid series flow returning from the low-temperature heat recovery tower 10 to the combined cycle acid tank 11 is reduced from 187°C to 157°C, and 6.6 t / h of low-pressure saturated steam at 0.3 MpaG and 144°C is by-produced. The circulating water consumption of the sulfuric acid production unit (with a low-temperature waste heat recovery system) is reduced from 20 t / t acid to 0 t / t acid (Δt = 8°C), and the thermal energy recovery rate of the sulfuric acid production unit is increased from 91% to about 97%.

[0066] 6.4 t / h of the 0.3 MpaG low-pressure steam by-produced in the present invention is introduced into the deaerator 7 to meet the deaeration requirement, and the 0.3 MpaG low-pressure steam recovered in the present invention is comprehensively utilized inside the unit. Example 2

[0067] The scale of the sulfuric acid production unit is 800,000 tons / year, the sulfuric acid output is 100 t / h, the atmospheric temperature is 33°C, and the relative humidity is 88%. The water vapor brought into the sulfuric acid production unit by air is 7,667 Kg / h, and the concentration of the finished sulfuric acid is 95% according to the unit water balance. Due to the high air temperature and high humidity, the sensible heat of the air and the latent heat of the water vapor brought into the sulfuric acid production unit system increase. According to the system heat balance, part of the heat of the dry acid needs to be taken away by the circulating cooling water to achieve the balance of the demineralized water heated by the ultra-low temperature waste heat and the by-produced 0.25 MpaG low-pressure steam inside the unit.

[0068] The demineralized water is passed through the cooling pipeline and sequentially through the finished acid cooler 1, the first dry acid cooler 2, the low-temperature heat recovery secondary acid cooler 3, the primary demineralized water preheater 4, the second absorption acid cooler 5, and the secondary demineralized water preheater 6 to recover the ultra-low temperature waste heat of the low-temperature sulfuric acid and increase the temperature of the demineralized water entering the deaerator 7 to reduce the consumption of low-pressure steam. In addition, part of the waste heat of the acid series flow returned from the low-temperature waste heat recovery system to the drying and absorption system is utilized to by-produce low-pressure steam through the first low-temperature waste heat boiler 8. The circulating cooling water is passed through the second dry acid cooler 12 to take away part of the waste heat of the dry circulating acid entering the sulfuric acid production system.

[0069] Specifically: The 95 wt% finished sulfuric acid is cooled by the demineralized water in the finished acid cooler 1, and the temperature of the finished sulfuric acid is reduced from 65°C to 40°C, while the temperature of the demineralized water is increased from 30°C to 36°C.

[0070] The 95 wt% dry upper tower acid is cooled by the demineralized water in the first dry acid cooler 2, and the temperature of the dry acid is reduced from 65°C to 55°C, while the temperature of the demineralized water is increased from 36°C to 52°C.

[0071] The 98.5 wt% low-temperature heat recovery secondary upper tower acid is cooled by the demineralized water in the low-temperature heat recovery secondary acid cooler 3, and the acid temperature is reduced from 98°C to 60°C, while the temperature of the demineralized water is increased from 52°C to 66°C.

[0072] The 99.4 wt% acid stream returned from the low-temperature heat recovery tower 10 to the combined cycle acid tank 11 is cooled by demineralized water using a primary demineralized water preheater 4. The temperature of the acid stream returned from the low-temperature heat recovery tower 10 to the dry gas absorption system decreases from 98 °C to 85 °C, and the temperature of the demineralized water increases from 66 °C to 73 °C.

[0073] The 98.5 wt% sulfuric acid in the upper second absorption tower is cooled by demineralized water using a second absorption acid cooler 5. The temperature of the sulfuric acid in the upper second absorption tower decreases from 98 °C to 82 °C, and the temperature of the demineralized water increases from 73 °C to 91 °C.

[0074] The 99.4 wt% acid stream returned from the low-temperature heat recovery tower 10 to the combined cycle acid tank 11 is cooled by demineralized water using a secondary demineralized water preheater 6. The temperature of the acid stream returned from the low-temperature heat recovery tower 10 to the combined cycle acid tank 11 decreases from 150 °C to 98 °C, and the temperature of the demineralized water increases from 91 °C to 120 °C.

[0075] The 135 °C boiler feed water is sent to the first low-temperature waste heat boiler 8 for heat exchange with the acid stream returned from the low-temperature waste heat recovery system to the dry gas absorption system. The temperature of the acid stream returned from the low-temperature waste heat recovery system to the dry gas absorption system decreases from 187 °C to 150 °C, and 8 t / h of low-pressure saturated steam at 0.25 MpaG and 139 °C is by-produced. The circulating water consumption of the sulfuric acid production system (with a low-temperature waste heat recovery system) is reduced from 20 t / t acid to 4.6 t / t acid (Δt = 8 °C), and the thermal energy recovery rate of the sulfuric acid production system reaches about 95.6%.

[0076] Part of the 95 wt% acid in the upper drying tower is cooled by additional external circulating cooling water using a second drying acid cooler 12. The temperature of the drying acid decreases from 65 °C to 55 °C, the temperature of the circulating water increases from 33 °C to 41 °C, and the circulating cooling water consumption is 460 t / h.

[0077] 4.5 t / h of the 0.25 MpaG low-pressure steam by-produced in the present invention is introduced into the deaerator 7 to meet the deaeration requirement, and the remaining 3.5 t / h of low-pressure steam is injected into the low-temperature heat recovery tower 10 for conversion and an additional 3.5 t / h of low-pressure steam (0.8 - 1.0 MpaG) is produced through the second low-temperature waste heat boiler 9. All the 0.25 MpaG low-pressure steam recovered in the present invention is comprehensively utilized within the device. In this embodiment, due to the high atmospheric temperature and high humidity, the sensible heat of the air and the latent heat of the water vapor brought into the sulfuric acid plant by the air increase, and the heat brought into the system increases. Although the net output of steam increases, the total heat recovery rate slightly decreases. Example 3

[0078] The scale of the sulfuric acid production unit is 800,000 tons per year, the sulfuric acid output is 100 t / h, the atmospheric temperature is 30 °C, the relative humidity is 75%, the water vapor brought into the sulfuric acid production unit by air is 5450 Kg / h. According to the device water balance calculation, the process makeup water of the device is 0 Kg / h, and the concentration of the finished acid is 97%.

[0079] The demineralized water is passed through the cooling pipeline and successively through the finished acid cooler 1, the first drying acid cooler 2, the low-temperature heat recovery secondary acid cooler 3, the primary demineralized water preheater 4, the second absorption acid cooler 5, and the secondary demineralized water preheater 6 to recover the ultra-low temperature waste heat of the low-temperature sulfuric acid and increase the temperature of the demineralized water entering the deaerator 7 to reduce the consumption of low-pressure steam. In addition, part of the waste heat returned to the dry absorption system for acid series connection in the low-temperature waste heat recovery system is used to generate low-pressure steam through the first low-temperature waste heat boiler 8. The circulating cooling water is passed through the second drying acid cooler 12 to take away part of the waste heat of the drying circulating acid entering the sulfuric acid production system.

[0080] Specifically: The 97 wt% finished sulfuric acid is cooled by demineralized water in the finished acid cooler 1. The temperature of the finished sulfuric acid is reduced from 71 °C to 40 °C, and the temperature of the demineralized water is increased from 30 °C to 37 °C.

[0081] The 97 wt% drying up-tower acid is cooled by demineralized water in the first drying acid cooler 2. The temperature of the drying acid is reduced from 71 °C to 65 °C, and the temperature of the demineralized water is increased from 37 °C to 54 °C.

[0082] The 98.5 wt% low-temperature heat recovery secondary up-tower acid is cooled by demineralized water in the low-temperature heat recovery secondary acid cooler 3. The acid temperature is reduced from 103 °C to 60 °C, and the temperature of the demineralized water is increased from 54 °C to 70 °C.

[0083] The 99.5 wt% acid series connection returned from the low-temperature heat recovery tower 10 to the combined circulation acid tank 11 is cooled by demineralized water in the primary demineralized water preheater 4. The temperature of the acid series connection 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 demineralized water is increased from 70 °C to 77 °C.

[0084] The 98.5 wt% sulfuric acid in the second absorption up-tower is cooled by demineralized water in the second absorption acid cooler 5. The temperature of the sulfuric acid in the second absorption up-tower is reduced from 103 °C to 82 °C, and the temperature of the demineralized water is increased from 77 °C to 92 °C.

[0085] The 99.5 wt% acid series connection returned from the low-temperature heat recovery tower 10 to the combined circulation acid tank 11 is cooled by demineralized water in the secondary demineralized water preheater 6. The temperature of the acid series connection returned from the low-temperature heat recovery tower 10 to the combined circulation acid tank 11 is reduced from 149 to 98 °C, and the temperature of the demineralized water is increased from 92 °C to 120 °C.

[0086] The boiler feed water at 135°C is sent to the first low-temperature waste heat boiler 8 for heat exchange with the acid cross-flow returned from the low-temperature waste heat recovery system to the dry absorption system. The temperature of the acid cross-flow returned from the low-temperature waste heat recovery system to the dry absorption system drops from 187°C to 149°C, and 8.5 t / h of low-pressure saturated steam at 0.25 MpaG and 139°C is by-produced. The circulating water consumption of the sulfuric acid production system (with a low-temperature waste heat recovery system) decreases from 20 t / t acid to 0.8 t / t acid (Δt = 8°C), and the thermal energy recovery rate of the sulfuric acid production system reaches about 96.8%.

[0087] Part of the dry upper tower acid with 97 wt% is cooled by the second dry acid cooler 12 using external additional circulating cooling water. The dry acid temperature drops from 71°C to 65°C, the circulating water temperature rises from 33°C to 41°C, and the circulating cooling water consumption is 80 t / h.

[0088] 4.5 t / h of the 0.25 MpaG low-pressure steam by-produced in the present invention is introduced into the deaerator 7 to meet the deaeration requirement, and the remaining 4 t / h of low-pressure steam is injected into the low-temperature heat recovery tower 10 for conversion and 4 t / h of low-pressure steam (0.8 - 1.0 MpaG) is produced more through the second low-temperature waste heat boiler 9. All the 0.25 MpaG low-pressure steam recovered in the present invention is comprehensively utilized within the device. Example 4

[0089] The scale of the sulfuric acid production plant is 800,000 tons / year, the sulfuric acid output is 100 t / h, the atmospheric temperature is 18°C, the relative humidity is 70%, the water vapor brought into the sulfuric acid production system by air is 2430 Kg / h. According to the device water balance calculation, the process make-up water of the device is 2030 Kg / h, and the concentration of the finished acid is 98%.

[0090] Desalted water is passed through the cooling pipeline and successively 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 absorption acid cooler 5, and the secondary desalted water preheater 6 to recover the ultra-low temperature waste heat of the low-temperature sulfuric acid and increase the temperature of the desalted water entering the deaerator 7 to reduce the consumption of low-pressure steam. Additionally, part of the waste heat of the acid cross-flow returned from the low-temperature waste heat recovery system to the dry absorption system is utilized to by-produce low-pressure steam through the first low-temperature waste heat boiler 8.

[0091] Specifically: The 98 wt% finished sulfuric acid is cooled by the finished acid cooler 1 using desalted water. The temperature of the finished sulfuric acid drops from 62°C to 40°C, and the temperature of the desalted water rises from 25°C to 30°C.

[0092] The 98.5 wt% dry upper tower acid is cooled by the first dry acid cooler 2 using desalted water. The dry acid temperature drops from 62°C to 60°C, and the temperature of the desalted water rises from 30°C to 35°C.

[0093] 98.5 wt% of the acid from the upper tower of the low-temperature heat recovery secondary stage is cooled by desalted water using 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.

[0094] 99.7 wt% of the acid flowing back from the low-temperature heat recovery tower 10 to the combined cycle acid tank 11 is cooled by desalted water using the primary desalted water preheater 4. The temperature of the acid flowing back from the low-temperature heat recovery tower 10 to the dry absorption system is reduced from 98 °C to 85 °C, and the desalted water temperature is increased from 50 °C to 57 °C.

[0095] 98.5 wt% of the sulfuric acid from the upper tower of the second absorption is cooled by desalted water using the second absorption acid cooler 5. The temperature of the sulfuric acid from the upper tower of the second absorption is reduced from 101 °C to 65 °C, and the desalted water temperature is increased from 57 °C to 82 °C.

[0096] 99.7 wt% of the acid flowing back from the low-temperature heat recovery tower 10 to the combined cycle acid tank 11 is cooled by desalted water using the secondary desalted water preheater 6. The temperature of the acid flowing back from the low-temperature heat recovery tower 10 to the combined cycle acid tank 11 is reduced from 166 to 98 °C, and the desalted water temperature is increased from 82 °C to 120 °C.

[0097] The 135 °C boiler feed water is sent to the first low-temperature waste heat boiler 8 for heat exchange with the acid flowing back from the low-temperature heat recovery tower 10 to the combined cycle acid tank 11. The temperature of the acid flowing back from the low-temperature heat recovery tower 10 to the combined cycle acid tank 11 is reduced from 187 °C to 166 °C, and 4.7 t / h of low-pressure saturated steam at 0.4 MpaG and 152 °C is by-produced. The circulating water consumption of the sulfuric acid production system (with low-temperature waste heat recovery system) is reduced from 20 t / t acid to 0 t / t acid (Δt = 8 °C), and the thermal energy recovery rate of the sulfuric acid production plant reaches about 97%.

[0098] 4.5 t / h of the 0.4 MpaG low-pressure steam by-produced in the present invention is introduced into the deaerator 7 to meet the deaeration requirements. The 0.4 MpaG low-pressure steam recovered in the present invention is basically fully utilized within the device.

[0099] Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A sulfuric acid production method based on cooling heat recovery and utilization, which uses a double conversion and double absorption process to prepare sulfuric acid, characterized in that, Desalted water is used as the cooling medium in the process. The desalted water flows through the finished acid cooler (1), the first drying acid cooler (2), the low-temperature heat recovery secondary acid cooler (3), the primary desalted water preheater (4), the second absorption acid cooler (5), and the secondary desalted water preheater (6) in turn by means of countercurrent heat exchange, and then enters the deaerator (7); The deaerated 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); The 99.4 - 99.7wt% series 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 turn, and then returns to the combined cycle acid tank (11); The finished acid cooler (1) receives 95 - 98wt% 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 drying acid cooler (2) is used to receive 95 - 98wt% drying upper tower acid output from the combined cycle acid tank (11), and outputs drying acid at 55 - 65°C to the drying tower (13); The low-temperature heat recovery secondary acid cooler (3) is used to receive 98 - 98.5wt% second absorption cycle acid directly output from the combined cycle acid tank (11), and outputs second absorption cycle acid at 60°C to the low-temperature heat recovery tower (10); After the series acid flows through the primary desalted water preheater (4), the temperature drops from 95 - 100°C to 85°C; The second absorption acid cooler (5) is used to receive 98 - 98.5wt% second absorption cycle acid directly output from the combined cycle acid tank (11), and outputs second absorption cycle acid at 65 - 82°C to the second absorption tower (14); After the series acid flows through the secondary desalted water preheater (6), the temperature drops 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) rises to 115 - 120°C and enters the deaerator (7); In the first low-temperature waste heat boiler (8), the temperature of the series acid drops from 180 - 190°C to 148 - 166°C. The temperature of the deaerated water output from the deaerator (7) is 135°C. The deaerated water evaporates in the first low-temperature waste heat boiler (8) to output low-pressure steam of 0.25 - 0.4MPaG.

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

3. A sulfuric acid production method based on cooling heat recovery and utilization 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), and 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).

4. A system for the sulfuric acid production method using cooling heat recovery according to any one of claims 1 to 3, characterized in that, It includes a combined cycle acid tank (11). The dry cycle acid output end (18) of the combined cycle 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). The output end of the drying tower (13) is connected to the combined cycle acid tank (11). A first dry acid cooler (2) and a second dry acid cooler (12) are connected in parallel on the first acid path (16); The double absorption cycle acid output end (19) of the combined cycle acid tank (11) is respectively connected to a double absorption tower (14) and a low-temperature heat recovery system through a third acid path (20) and a fourth acid path (21). A double absorption acid cooler (5) is connected to the third acid path (20). The acid stream end of the low-temperature heat recovery system is connected to a first low-pressure steam by-product system through a fifth acid path (22), and the acid output end of the first low-pressure steam by-product system is connected to the combined cycle acid tank (11) through a sixth acid path (23); The first low-pressure steam by-product system includes a first low-temperature waste heat boiler (8), a secondary demineralized water preheater (6), and a primary demineralized water preheater (4) 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 primary demineralized water preheater (4) is connected to the combined cycle acid tank (11); The cooling pipelines of the whole system are sequentially connected to the finished acid cooler (1), the first dry acid cooler (2), the low-temperature heat recovery system, the primary demineralized water preheater (4), the double absorption acid cooler (5), and the secondary demineralized water preheater (6); The water inlet end of the first low-temperature waste heat boiler (8) is connected to the output end of a deaerator (7).

5. The system of a sulfuric acid production method based on cooling heat recovery according to claim 4, characterized in that, The low-temperature heat recovery system is used to produce 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) connected in sequence along the acid path. The acid output 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). The output end of the acid diluter (25) is connected to the diluted acid inlet of the low-temperature heat recovery tower (10).

6. The system of a sulfuric acid production method based on cooling heat recovery utilization according to claim 4, characterized in that, An independent cold water pipe (24) is externally connected to the second dry acid cooler (12) for inputting / outputting circulating water.

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