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, as 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 (Na2CO3) takes place in the gas scrubber with caustic soda.
Sound velocity measurement with LiquiSonic® 40
Application
In the gas 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 within the range of maximum absorption. To ensure this, the concentration of NaOH and the salts NaCl and Na2CO3 must be monitored.
The LiquiSonic measurement system®enables concentration measurement in 3-component liquids. By measuring two physical quantities such as sound velocity and conductivity, two concentrations can be determined simultaneously: the caustic soda and the salts NaCl and Na2CO3. If 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 in the system.
Installation
The LiquiSonic® immersion sensors can be easily installed directly into the pipeline. A common installation location is in the pipelines (DN80) from the gas scrubber to the regeneration tank. The LiquiSonic® Controller 40 is connected to the LiquiSonic® sensor and 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-consuming laboratory measurements:
- Time required: 1 h per day
Avoiding over- and under-dosing leads to savings in material costs.
LiquiSonic® ensures precise concentration measurement with continuous data recording. This enables automatic regulation of the caustic soda in the area of maximum absorption or maximum efficiency of the gas scrubber.
