A method for inhibiting the scaling of a first effect heat exchanger in the evaporation and concentration process of waste sulfuric acid for titanium dioxide

Abstract

The present application belongs to the field of chemical industry, and particularly relates to a method for inhibiting the scaling of a first effect heat exchanger in the evaporation and concentration process of sulfuric acid method titanium dioxide waste acid. The titanium dioxide waste acid is sent into a multi-effect evaporation and concentration system, and the feature is that only the circulating acid returned from the first effect concentration is sent into the first effect heat exchanger for heating, and the feeding position of fresh titanium dioxide waste acid is set at the rear end of the first effect heat exchanger outlet, so as to avoid the mixing of the circulating acid and the fresh titanium dioxide waste acid and then entering the first effect heat exchanger. The fresh titanium dioxide waste acid is mixed with the circulating acid flowing out of the heat exchanger after being heated, and the mixed acid is sent into an evaporation chamber for evaporation and concentration. The feeding temperature of the fresh titanium dioxide waste acid mixed with the circulating acid is 10-110 DEG C.

Description

Technical Field

[0001] This invention relates to a method for inhibiting scaling on a single-effect heat exchanger during the evaporation and concentration of waste acid from the sulfuric acid process for titanium dioxide production. Background Technology

[0002] The sulfuric acid process is the mainstream method for producing titanium dioxide in my country. Producing one ton of titanium dioxide generates 8-10 tons of waste acid. This waste acid contains approximately 20 wt% sulfuric acid, a large amount of ferrous sulfate, and other metal sulfates such as calcium and magnesium. Direct discharge of this waste acid would cause serious environmental pollution and resource waste.

[0003] Currently, methods for treating waste acid from the sulfuric acid process for titanium dioxide production include neutralization, evaporation and concentration, extraction, and comprehensive utilization. Concentrating and recycling the waste acid is an economical and effective method. However, in actual production operations, severe scaling occurs on the inner walls of the heat exchangers. To ensure normal operation, timely cleaning of the heat exchangers is necessary, leading to frequent start-ups and shutdowns, reducing effective production time, and seriously affecting the recovery and utilization rate of the waste acid.

[0004] The traditional sulfuric acid process for evaporating and concentrating waste acid in titanium dioxide production is as follows: Figure 1 As shown, fresh titanium dioxide waste acid is mixed with concentrated circulating acid, and then sequentially fed into the first-effect heat exchanger and the first-effect flash evaporator. Except for a small portion of the evaporated and concentrated titanium dioxide waste acid entering the second-effect evaporation system, most of the evaporated and concentrated titanium dioxide waste acid is recycled back to the first-effect heat exchanger.

[0005] Our study found that the scale sample from the single-effect heat exchanger contained approximately 70% CaSO4 and 30% TiO(OH)2 (Xu, Bowen et al, https: / / doi.org / 10.1021 / acs.iecr.3c00951). Further investigation revealed that the mixing process and the precipitation of calcium sulfate generated by the mixed acid in the single-effect heat exchanger were the primary causes of scaling. Summary of the Invention

[0006] The purpose of this invention is to provide a method for effectively inhibiting scaling of a single-effect heat exchanger during the evaporation and concentration of waste acid from the sulfuric acid process for titanium dioxide production.

[0007] In existing titanium dioxide waste acid concentration processes, the precipitation of calcium and titanium salts leads to severe scaling on the inner walls of heat exchange tubes. This scaling significantly impairs heat transfer, and frequent start-ups and shutdowns result in substantial economic losses. Furthermore, the hard texture of the scaling makes it prone to damaging the heat exchange tube structure during cleaning. The fundamental cause of scaling in heat exchangers is the precipitation of calcium sulfate caused by the mixing of titanium dioxide waste acid with circulating acid.

[0008] This invention addresses the severe scaling problem on the inner wall of the first-effect heat exchanger during the evaporation and concentration of waste acid in the sulfuric acid process for titanium dioxide production. A solution is found to be... Figure 2 The method shown involves circulating concentrated titanium dioxide waste acid into a single-effect evaporation and concentration system only for heating. The heated circulating acid is then mixed with the titanium dioxide waste acid, avoiding the precipitation of calcium sulfate and scaling on the inner wall of the heat exchanger that occurs during the mixing process in traditional waste acid concentration processes.

[0009] The technical solution of this invention is:

[0010] A method for inhibiting scaling on a single-effect heat exchanger during the evaporation and concentration of waste acid from the sulfuric acid process for titanium dioxide production, specifically comprising:

[0011] (1) Only the concentrated titanium dioxide waste acid is passed into the first-effect heat exchanger, and the temperature after heating in the first-effect heat exchanger is 105~115 ℃;

[0012] (2) The feed point for fresh titanium dioxide waste acid is set after the first-effect heater. The heated circulating titanium dioxide waste acid is mixed with the fresh titanium dioxide waste acid and then enters the evaporation chamber. Part of the titanium dioxide waste acid after evaporation and concentration is recycled back to the first-effect heat exchanger;

[0013] (3) The feed temperature of the fresh titanium dioxide waste acid mixed with the circulating acid is 10~110 ℃;

[0014] (4) The flow ratio of fresh titanium dioxide waste acid to recycled titanium dioxide waste acid is 1:50~1:300.

[0015] Preferably, the recycled concentrated titanium dioxide waste acid is heated to 105~110 °C in a single-effect heat exchanger.

[0016] Preferably, the feed temperature of the fresh titanium dioxide waste acid mixed with the circulating acid is 40~100 ℃.

[0017] Preferably, the flow ratio of fresh titanium dioxide waste acid to recycled titanium dioxide waste acid is 1:120 to 1:280. Attached Figure Description

[0018] Figure 1 This is a simplified flow chart of the traditional sulfuric acid process for evaporating and concentrating waste acid in titanium dioxide production.

[0019] Figure 2 This is a simplified flow chart of the sulfuric acid process for evaporating and concentrating waste acid in titanium dioxide production according to the present invention. Detailed Implementation

[0020] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention and provide specific implementation methods and operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0021] Example 1

[0022] Titanium dioxide waste acid with a sulfuric acid concentration of 23% was fed into a single-effect evaporation system. Circulating acid was then passed through a single-effect heat exchanger for heating. The heated circulating acid was mixed with the titanium dioxide waste acid at a ratio of 1:170. The mixture flowed into the evaporator at a temperature of 106 °C. After single-effect concentration, the sulfuric acid concentration in the system was 37%. The scaling cycle in the single-effect heat exchanger was extended from approximately 9 days to approximately 100 days, ensuring smooth production.

[0023] Example 2

[0024] Titanium dioxide waste acid with a sulfuric acid concentration of 25% was fed into a single-effect evaporation system. Circulating acid was then passed through a single-effect heat exchanger for heating. The heated circulating acid was mixed with the titanium dioxide waste acid at a ratio of 1:180. The mixture flowed into the evaporator at a temperature of 105 °C. After single-effect concentration, the sulfuric acid concentration in the system was 35%. The scaling cycle in the single-effect heat exchanger was extended from approximately 9 days to approximately 120 days, ensuring smooth production.

[0025] Example 3

[0026] Titanium dioxide waste acid with a sulfuric acid concentration of 20% was fed into a single-effect evaporation system. Circulating acid was then passed through a single-effect heat exchanger for heating. The heated circulating acid was mixed with the titanium dioxide waste acid at a ratio of 1:160. The mixture flowed into the evaporator at a temperature of 110 °C. After single-effect concentration, the sulfuric acid concentration in the system was 38%. The scaling cycle in the single-effect heat exchanger was extended from approximately 9 days to approximately 90 days, ensuring smooth production.

[0027] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. The above are merely specific implementation examples of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for inhibiting scaling on a single-effect heat exchanger during the evaporation and concentration of titanium dioxide waste acid, characterized in that: Only the circulating concentrated titanium dioxide waste acid is allowed to enter the first-effect heat exchanger, while the feed point for fresh titanium dioxide waste acid is set after the first-effect heat exchanger. The heated circulating titanium dioxide waste acid is mixed with the fresh titanium dioxide waste acid and then enters the evaporation chamber. Part of the concentrated titanium dioxide waste acid is recycled back to the first-effect heat exchanger.

2. The method for inhibiting scaling of a single-effect heat exchanger during the evaporation and concentration of titanium dioxide waste acid according to claim 1, characterized in that: The circulating acid is directly fed into the first-effect heat exchanger and heated to 105~115 ℃ at the heat exchanger outlet.

3. The method according to claim 1, characterized in that, The feed temperature of the fresh titanium dioxide waste acid mixed with the circulating acid is 10~110 ℃.

4. The method according to claim 1, characterized in that, The flow ratio of fresh titanium dioxide waste acid to recycled titanium dioxide waste acid is 1:50~1:300.

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