Chlorine gas, as a basic raw material in the chemical industry, is widely used in production processes such as PVC, caustic soda, and disinfection products. However, chlorine gas has strong toxicity and corrosiveness. If not handled properly and leaked, it will seriously threaten personnel safety and the ecological environment. The chlorine absorption tower in chemical enterprises is the core equipment for tail gas treatment, which uses sodium hydroxide (NaOH) solution as the absorption medium to generate harmless products such as sodium chloride and sodium hypochlorite through chemical reactions. The stable control of sodium hydroxide concentration is the key to ensuring absorption efficiency. The Shanghai Xuantian SJT-6000A sodium hydroxide liquid alkali concentration meter, as a specialized online analytical instrument, has become the core guarantee equipment for the safe and stable operation of chlorine absorption towers with its accurate and real-time monitoring capabilities. Here is a detailed introduction:

1、 Working condition background and monitoring core pain points

The working conditions of chlorine gas absorption towers in chemical enterprises have significant particularities: firstly, chlorine gas is highly toxic. The national regulations allow the concentration of chlorine gas in workshop air to be only 1mg/m ³, and the concentration of chlorine gas at the outlet of the absorption tower must be strictly controlled below the emission standard. Once the concentration of sodium hydroxide is insufficient, it will lead to the risk of chlorine gas leakage; Secondly, the absorption system has strong corrosiveness. Even after the reaction between high concentration sodium hydroxide solution and chlorine gas, the mixed solution still has strong corrosiveness characteristics, which requires high corrosion resistance of monitoring equipment; Thirdly, the working conditions fluctuate greatly, and the chlorine gas emissions and intake concentration in chemical production often change with the production load, requiring rapid response to concentration adjustment requirements; Fourthly, traditional manual testing has fatal flaws. The manual sampling titration method not only has a long testing cycle (over 30 minutes) and large errors (± 1% -2%), but also poses a risk of chlorine gas leakage during the sampling process, which cannot meet the real-time monitoring requirements. These pain points determine the necessity of using dedicated online concentration monitoring equipment.

2、 Technical adaptation and core design of concentration meter

In response to the harsh working conditions of chlorine absorption towers, the sodium hydroxide liquid alkali concentration meter needs to have targeted technical design and adaptability: in terms of measurement principle selection, the conductivity method or refractive index method principle is preferred. The conductivity is accurately measured by detecting the linear relationship between the conductivity and concentration of the solution. The built-in temperature sensor automatically compensates for the influence of ambient temperature on the results, and transmits them to the display through a high impedance circuit. After amplification and conversion, the corresponding concentration value is output. The refractive index method is based on the linear relationship between the refractive index and concentration of sodium hydroxide solution, and is not affected by the conductivity and suspended solids of the solution. The measurement accuracy can reach ± 0.2% FS. Both methods support real-time data output with a response time of ≤ 5 seconds, meeting the requirements of rapid adjustment of working conditions. In terms of material and protection design, the sensor probe is made of Jufeng or 316L material, and the instrument has an overall IP68 protection level. The explosion-proof product meets the ExdIICT4 explosion-proof standard and is suitable for the explosion-proof requirements of the chlorine absorption tower area. In terms of system linkage design, the concentration meter supports 4-20mA standard signal and RS4 digital 85 communication protocol, which can be directly connected to the enterprise DCS control system to achieve real-time uploading of concentration data and automatic control linkage.

3、 Core application functions and operating mechanisms

The application of sodium hydroxide liquid alkali concentration meter in chlorine absorption tower forms a complete monitoring and control loop: the instrument is installed by inserting the sensor directly into the circulating alkali liquid tank or spray pipeline of the absorption tower, collecting real-time sodium hydroxide concentration data, and synchronously displaying it on the local display screen and remote monitoring platform; Users can set upper and lower concentration thresholds based on their absorption reaction needs (such as setting the effective absorption concentration range to 8% -15% NaOH). When the concentration falls below the lower threshold, the instrument immediately emits an audible and visual alarm and sends an alkali replenishment signal to the DCS system, triggering the automatic alkali replenishment pump to start and replenish high concentration sodium hydroxide solution; When the concentration exceeds the upper threshold, stop adding alkali to avoid wasting alkali solution and subsequent wastewater treatment pressure.

4、 Practical application value and security guarantee

Strengthen environmental protection and safety defense line: Real time monitoring ensures that the concentration of sodium hydroxide is always within the effective absorption range, avoiding chlorine gas leakage due to insufficient concentration, ensuring that enterprises meet the requirements of regulations such as the Comprehensive Emission Standards for Air Pollutants (GB 16297-1996), and eliminating safety accidents and environmental penalties. After application in a certain chlor alkali enterprise, the concentration at the outlet of the chlorine absorption tower was stably controlled below 0.5mg/m ³, effectively solving the problem of concentration fluctuations in traditional manual control.

Optimize absorption efficiency and cost control: Accurately control the concentration of alkali solution, avoid "over absorption" or "under absorption", and reduce the consumption of sodium hydroxide while ensuring the absorption effect. According to statistics, compared to manual alkali replenishment, the use of concentration meters can reduce alkali loss by 15% -25%.

Enhance system intelligence and operational security: achieve unmanned continuous monitoring, replace manual sampling and testing, avoid operators from coming into contact with toxic and harmful media, and reduce operational risks; Integrate with DCS system to achieve automatic alkali replenishment, reduce manual intervention, and improve the stability and intelligence level of absorption tower operation.

Extend the service life of equipment: A stable concentration of sodium hydroxide can prevent the corrosion of the inner wall, packing, and pipelines of the absorption tower caused by excessive concentration, reduce the frequency of equipment maintenance and replacement costs, and extend the overall service life of the absorption tower by 3-5 years.

5、 Application Summary

In the safe and environmentally friendly operation of chlorine absorption towers in chemical enterprises, the sodium hydroxide liquid alkali concentration meter is not a simple monitoring tool, but an important monitoring equipment that integrates "safety protection, environmental compliance, cost optimization, and intelligent control". Through targeted corrosion-resistant design, precise real-time monitoring, and efficient system linkage, it effectively solves the pain points of concentration control in the chlorine absorption process, providing reliable technical support for the treatment of chlorine gas tail gas in chemical enterprises. With the continuous upgrading of safety and environmental protection requirements in the chemical industry, sodium hydroxide liquid alkali concentration meters will play an increasingly important role in chlorine absorption towers and various acidic gas absorption systems, helping enterprises achieve green, safe, and efficient production.