Application of Fork Liquid Level Switch in Pharmaceutical Extraction

There are many methods for separation and purification. The common one at present is liquid-liquid extraction. We know that a compound has different solubility in two incompatible solvents. We can use extraction method to transfer a compound from one solvent to another. Through repeated multiple extractions, most of compounds can be extracted. Let´s take the production process of polyoxymethylene as an example. In this process, the aqueous solution of paraformaldehyde is as an intermediate reaction product. Benzene can be used as an extractive agent to separate paraformaldehyde from water because its affinity to paraformaldehyde is greater than water, its gravity density is less than that of water, and it is easier to be separated from water. During the extraction process, when separation layer is formed, the upper layer is the mixture of paraformaldehyde and benzene, the lower layer is the mixture of water and other sediments. At this moment, level measurement for two different solvents in the separation tower is needed. The liquid level is controlled through high/low alarm to ensure efficient and smooth operation of the entire production process.

Flammable, explosive, poisonous, harmful and corrosive solvents are often used in the extraction process in pharmaceutical industry. And the process temperature is usually high. Therefore, technical requirements for a fork liquid level switch used for level measurement in the separation and purification process are focused on wetted material, explosion-proof characteristics and high temperature resistance.

1) Wetted material： Due to corrosive nature of the solvent, fork body should be with high corrosion resistance. From weak to strong by the corrosive resistance, material of the fork body can be selected from carbon steel, 304ss, 316ss, 316L, stainless steel lined with PTFE, and Hastelloy etc.

2) Explosion-proof characteristics：There are many types of explosion protection. The common types are flameproof enclosure and intrinsic safety explosion protection. Flameproof enclosure explosion protection is to keep the flammable and explosive hazards from entering the interior of the instrument. It is a passive protection. Intrinsic safety explosion protection is to use energy-limited design in electric circuit, which means the instrument is safer to operate even if there are flammable and explosive hazards in the environment because the instrument does not have the possibility to actively ignite the flammable and explosive hazards in the environment. It is relatively safer.

3) High temperature resistance：High temperature resistance refers to the temperature of the measured material, not the environment temperature as one commonly thought. Required material temperature for different process can be ranged from minus tens to hundreds of degrees. Metal's thermal conductivity is usually very high, and the temperature resistance of electronic components is usually up to 85ºC. Therefore, the high temperature resistance determines the service time of the level switch. High-temperature working condition in the extraction process requires high temperature resistance of the liquid level switch.

Higher technical requirements on the level switch are necessary because of special working conditions in pharmaceutical extraction process. Last year， a pharmaceutical company in Inner Mongolia purchased dozens of Jiwei Ring-11 Fork Liquid Level Switches with intrinsic safety explosion protection after careful comparison of many level switch products in the market. Jiwei Ring-11 Fork Liquid Level Switch was selected by the customer for liquid level measurement and control in pharmaceutical extraction process is because of its following advantages: 

4) Based on detecting changes of vibration frequency, the measurable medium density can be as low as 0.5g/cm³，more accurate and higher reliability.