For the production of polyurethanes, two different monomers (polyisocyanates and polyols) are linked together. In this polyaddition, polyether polyol and toluene-2,4-diisocyanate (TDI) are often used. The production can be divided into 3 areas:
- Production of polyether polyol
- Production of toluene-2,4-diisocyanate
- Polyaddition
The TDI is produced by phosgenation from 2,4-toluenediamine (TDA). In the event of an accident, the unused phosgene must be absorbed because it is extremely toxic. Therefore, it is only used in hermetically sealed circuits. The neutralization of the gas to sodium chloride (NaCl) and sodium carbonate (Na2CO3takes place in the scrubber with caustic soda.
Sound velocity measurement with LiquiSonic® 40
Application
In the scrubber, a washing liquid is brought into contact with the gas stream to be cleaned, whereby certain gaseous, liquid, and solid components are absorbed by the liquid. The circulating washing liquid (NaOH) must be kept in the range of maximum absorption. To ensure this, the concentration of NaOH as well as the salts NaCl and Na2CO3 must be monitored.
The LiquiSonic measurement system®enables concentration measurement in 3-component liquids. By recording two physical quantities such as sound velocity and conductivity, two concentrations can be determined simultaneously: the caustic soda as well as the salts NaCl and Na2CO3If the NaOH content is too low, it must be adjusted. If the salt content is too high, it is removed, as it would otherwise crystallize out in the system.
Installation
The LiquiSonic® immersion sensors can be easily installed directly into the pipeline. A common installation site is in the pipes (DN80) from the scrubber to the regeneration tank. The LiquiSonic® Controller 40 is connected with the LiquiSonic® sensor as well as the measurement unit for the second physical quantity. The controller displays the concentration of the caustic soda and the salts in the main menu.
Typical measurement range:
Concentration range NaOH: 5 to 20 m%,
Concentration range Na2CO3/NaCl: 5 to 30 m%
Temperature range: 30 to 60 °C
Customer benefits
The robust sensor construction and the choice of special materials, such as HC2000, ensure long process uptime of the system. LiquiSonic®reduces time-intensive laboratory measurements:
- Time requirement: 1 h per day
By avoiding over- and under-dosing, material costs are saved.
LiquiSonic® ensures precise concentration measurement with permanent data recording. This enables automatic control of the caustic soda in the range of maximum absorption or the maximum efficiency of the scrubber.
