A method for increasing the concentration of alkaline washing waste liquid

Abstract

This invention discloses a method for increasing the concentration of alkaline washing waste liquid. During the continuous entry of hydrogen sulfide waste gas into the reactor, when the low-concentration caustic soda in the solution is consumed, a high-concentration caustic soda solution is injected into the reactor. The injection volume is calculated based on changes in the concentration of the alkaline washing waste liquid and the concentration of hydrogen sulfide waste gas, and is measured using an electromagnetic flowmeter. The concentration is determined by pH detection. The newly added caustic soda continues to react with the incoming hydrogen sulfide to produce sodium sulfide. The sodium sulfide concentration is detected by a concentration meter. The sodium sulfide concentration in the solution continuously increases. When it reaches the concentration required for process control, the addition of caustic soda is stopped. Subsequent excess hydrogen sulfide reacts with sodium sulfide to produce sodium hydrosulfide, achieving the desired sodium hydrosulfide concentration. The sodium hydrosulfide concentration is detected by a sodium hydrosulfide concentration detector or by manual sampling. This invention can increase the concentration of sodium hydrosulfide solution, prevent excess caustic soda from reacting with carbon dioxide in the air to form sodium carbonate, thus avoiding caustic soda waste and saving energy.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen sulfide waste gas treatment, and particularly relates to a method for increasing the concentration of alkaline washing waste liquid. Background Technology

[0002] Currently, caustic soda scrubbing is commonly used to treat hydrogen sulfide-containing waste gas. The concentration of the generated sodium hydrosulfide waste liquid varies with the concentration of hydrogen sulfide in the inlet gas. A low concentration of hydrogen sulfide in the inlet gas results in a low concentration of generated sodium hydrosulfide waste liquid, and vice versa.

[0003] Sodium hydrosulfide waste liquid can be evaporated and crystallized to produce sodium hydrosulfide tablets, which offers considerable economic benefits. Higher concentrations of sodium hydrosulfide waste liquid result in less steam consumption during evaporation and crystallization, thus reducing energy consumption and improving economic efficiency.

[0004] Hydrogen sulfide in the exhaust gas reacts with caustic soda to form sodium sulfide, which then reacts with excess hydrogen sulfide to form sodium hydrosulfide. Therefore, to increase the concentration of sodium hydrosulfide in the solution, the concentration of sodium sulfide must first be increased.

[0005] In existing technologies, the concentration of caustic soda is generally around 25%, and the hydrogen sulfide concentration is 12-15 g / m³ when washing H₂S waste gas with alkali. 3 It can generate a 20-22% sodium hydrosulfide solution when the H2S concentration is below 5 g / m³. 3 At the same time, the concentration of caustic soda should also be reduced. Excessive caustic soda will react with carbon dioxide in the air to form sodium carbonate, wasting caustic soda, and the concentration of sodium hydrosulfide produced will be lower than 8%, or even lower. Summary of the Invention

[0006] To address the deficiencies and shortcomings of the existing technology, this invention provides a method for treating low-concentration hydrogen sulfide waste gas. First, a low-concentration caustic soda solution reacts with low-concentration hydrogen sulfide to produce a low-concentration sodium sulfide solution. After the low-concentration caustic soda solution is consumed, a high-concentration caustic soda solution is added to the resulting low-concentration sodium sulfide solution to continue reacting with the continuously entering low-concentration hydrogen sulfide waste gas, thereby increasing the concentration of the sodium sulfide solution. This not only increases the concentration of the sodium hydrosulfide solution produced in the next step but also prevents excessive caustic soda from reacting with carbon dioxide in the air to form sodium carbonate, thus avoiding caustic soda waste and saving energy.

[0007] The technical solution of this invention is as follows: A method for increasing the concentration of alkaline washing waste liquid. During the continuous entry of hydrogen sulfide waste gas into the reactor, after the low-concentration caustic soda in the solution is consumed, a high-concentration caustic soda solution is pumped into the reactor through a metering pump and pipeline. The pumping amount is calculated based on the concentration of the alkaline washing waste liquid and the concentration of hydrogen sulfide waste gas, and is measured by an electromagnetic flowmeter. The concentration is determined by pH detection. At this time, the newly added caustic soda continues to react with the incoming hydrogen sulfide to generate sodium sulfide. The sodium sulfide concentration is detected by a concentration meter. The sodium sulfide concentration in the solution continuously increases. When it reaches the concentration required for process control, the addition of caustic soda is stopped. The subsequent excess hydrogen sulfide reacts with sodium sulfide to generate sodium hydrosulfide, achieving the required sodium hydrosulfide concentration. The sodium hydrosulfide concentration is detected by a sodium hydrosulfide concentration detector or by manual sampling.

[0008] Preferably, a method for increasing the concentration of alkaline washing waste liquid includes the following specific steps:

[0009] 1) The H2S waste gas is sent into the alkaline scrubbing tower through the alkaline scrubbing fan;

[0010] 2) The high-concentration caustic soda solution is prepared into a low-concentration caustic soda solution and then pumped into the alkali washing tower.

[0011] 3) The circulating spray pump circulates and sprays the low-concentration caustic soda solution in the alkali washing tower, which comes into countercurrent contact with the H2S waste gas, and the reaction first generates Na2S solution;

[0012] 4) By detecting the NaOH concentration online or manually, when the low-concentration caustic soda solution is consumed, the high-concentration caustic soda is directly pumped into the Na2S solution through the concentrated caustic soda transfer pump, so that the incoming H2S waste gas can continue to react with the high-concentration caustic soda to generate Na2S solution.

[0013] 5) When the Na2S solution concentration reaches the required concentration, stop the concentrated alkali delivery pump.

[0014] 6) The H2S waste gas that enters later reacts with the Na2S solution to generate a NaHS solution of the required concentration, thereby increasing the NaHS solution generated by alkaline washing. A small amount of caustic soda reacts with CO2 in the air to generate Na2CO3.

[0015] 7) The generated NaHS solution is pumped to a storage tank and then sent to the NaHS tableting section.

[0016] Preferably, the concentration of H2S waste gas in step 1) is 4.8 g / m³. 3 The waste gas treatment capacity is 45,000 m³. 3 .

[0017] Preferably, in step 2), the high-concentration caustic soda solution has a concentration of 32%, and the low-concentration caustic soda solution has a concentration of 12-15%.

[0018] Preferably, in step 4), the concentrated alkali transfer pump is a metering pump or other transfer pump equipped with a flow meter.

[0019] Preferably, in step 4), the concentration of the Na2S solution reaches the required concentration of 23-25%.

[0020] Preferably, the concentration of the NaHS solution generated in step 6) is 20-22%.

[0021] Preferably, the tablets produced in the NaHS tableting section in step 7) contain a sodium hydrosulfide concentration of 75% or higher.

[0022] This invention uses a low-concentration caustic soda solution to react with a low-concentration hydrogen sulfide waste gas to produce a low-concentration sodium sulfide solution. After the low-concentration caustic soda solution is consumed, a high-concentration caustic soda solution is used to react with the continuously entering low-concentration hydrogen sulfide waste gas in the low-concentration sodium sulfide solution environment to generate sodium sulfide, thereby increasing the concentration of the sodium sulfide solution. This not only increases the concentration of the sodium hydrosulfide solution produced in the next step, but also prevents excessive caustic soda from reacting with carbon dioxide in the air to form sodium carbonate, thus saving energy. Attached Figure Description

[0023] Figure 1 This is a flowchart of the present invention;

[0024] Figure 2 This is a process flow diagram of the present invention;

[0025] In the diagram: 1. Sodium hydrosulfide storage tank; 2. Primary alkali washing tower; 3. Alkali mixing tank; 4. Sodium hydrosulfide transfer pump; 5. Alkali washing fan; 6. Primary alkali washing pump; 7. Concentrated alkali transfer pump; 8. Alkali solution circulation transfer pump; 9. Sodium hydrosulfide flake production section; 10. Hydrogen sulfide-containing waste gas; 11. Alkali washing tail gas; 12. High-concentration sodium hydroxide. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but this is not intended to limit the scope of protection of the present invention.

[0027] Example 1

[0028] like Figure 1 and 2As shown, a method for increasing the concentration of alkaline washing waste liquid involves continuously introducing hydrogen sulfide waste gas into the reactor. After the low-concentration caustic soda in the solution is consumed, a high-concentration caustic soda solution is pumped into the reactor through a metering pump and pipeline. The injection volume is calculated based on the concentration of the alkaline washing waste liquid and the concentration of hydrogen sulfide waste gas, and is measured by an electromagnetic flowmeter. The concentration is determined by pH detection. At this time, the newly added caustic soda continues to react with the incoming hydrogen sulfide to generate sodium sulfide. The sodium sulfide concentration is detected by a concentration meter. The sodium sulfide concentration in the solution continuously increases. When it reaches the concentration required for process control, the addition of caustic soda is stopped. The subsequent excess hydrogen sulfide reacts with sodium sulfide to generate sodium hydrosulfide, achieving the required sodium hydrosulfide concentration. The sodium hydrosulfide concentration is detected by a sodium hydrosulfide concentration detector or by manual sampling.

[0029] Example 2

[0030] A method for increasing the concentration of alkali washing waste liquid involves first adjusting a 32% caustic soda solution to approximately 12-15% caustic soda solution, which is then pumped into the alkali washing tower for later use. Waste gas containing H2S at a concentration of 4.8 g / m³, with a flow rate of 45,000 m³, is fed into the alkali washing tower via an alkali washing fan. A circulating spray pump is started, and the 12-15% caustic soda solution circulates and sprays within the alkali washing tower under the action of the circulating pump, coming into countercurrent contact with the H2S waste gas. The reaction first produces Na2S, which then reacts with excess H2S to form NaHS. A trace amount of caustic soda reacts with CO2 in the air to form Na2CO3. After the Na2S generated by the caustic soda reaction is consumed, it reacts with excess H2S before generating NaHS. The pH value of the solution in the alkali washing tower is monitored online or manually. When the pH is around 7, it indicates that the NaOH has been consumed. Then, 32% caustic soda is directly pumped into the Na2S solution in the alkali washing tower via a concentrated alkali transfer pump (metering pump, flow meter). This allows the incoming H2S to continue reacting with the caustic soda to generate Na2S. When the Na2S concentration reaches 23-25%, the concentrated alkali transfer pump is stopped. Subsequently, continuously incoming waste gas containing H2S at a concentration of 4.8 g / m³ reacts with the 23-25% Na2S solution to generate a 20-22% NaHS solution, thus increasing the NaHS solution generated during alkali washing.

[0031] The chemical reaction between the caustic soda solution and hydrogen sulfide waste gas in this invention is as follows: 2NaOH + H2S = Na2S + 2H2O;

[0032] The chemical reaction between sodium sulfide solution and hydrogen sulfide waste gas is as follows: Na2S + H2S = 2NaHS.

[0033] This invention uses a low-concentration caustic soda solution to react with a low-concentration hydrogen sulfide waste gas to produce a low-concentration sodium sulfide solution. After the low-concentration caustic soda solution is consumed, a high-concentration caustic soda solution is used to react with the continuously entering low-concentration hydrogen sulfide waste gas in the low-concentration sodium sulfide solution environment to generate sodium sulfide, thereby increasing the concentration of the sodium sulfide solution. This not only increases the concentration of the sodium hydrosulfide solution produced in the next step, but also prevents excessive caustic soda from reacting with carbon dioxide in the air to form sodium carbonate, thus saving energy.

Claims

1. A method for increasing the concentration of alkaline washing waste liquid, characterized in that: The steps are as follows: 1) The H2S waste gas is sent into the alkaline scrubbing tower through the alkaline scrubbing fan; 2) The high-concentration caustic soda solution is prepared into a low-concentration caustic soda solution and then pumped into the alkali washing tower. 3) The circulating spray pump circulates and sprays the low-concentration caustic soda solution in the alkali washing tower, which comes into countercurrent contact with the H2S waste gas, and the reaction first generates Na2S solution; 4) By detecting the NaOH concentration online or manually, when the low-concentration caustic soda solution is consumed, the high-concentration caustic soda is directly pumped into the Na2S solution through the concentrated caustic soda transfer pump, so that the incoming H2S waste gas can continue to react with the high-concentration caustic soda to generate Na2S solution. 5) When the Na2S solution concentration reaches the required concentration, stop the concentrated alkali delivery pump. 6) The H2S waste gas that enters later reacts with the Na2S solution to generate the required concentration of NaHS solution, thereby increasing the concentration of the NaHS solution generated by alkaline washing. A trace amount of caustic soda reacts with CO2 in the air to generate Na2CO3. 7) The generated NaHS solution is pumped to a storage tank and then sent to the NaHS tableting section; The concentration of H2S waste gas in step 1) is 4.8 g / m³. 3 ; In step 2), the high-concentration caustic soda solution has a concentration of 32%, and the low-concentration caustic soda solution has a concentration of 12-15%. In step 4), the concentrated alkali transfer pump is a metering pump or other transfer pump equipped with a flow meter; In step 4), the concentration of the Na2S solution reaches the required concentration of 23-25%. The concentration of the NaHS solution generated in step 6) is 20-22%; The tablets produced in the NaHS tableting section in step 7) contain a sodium hydrosulfide concentration of 75% or higher.

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