Recovering spent liquor is an essential part of the Kraft Process for making paper. The Kraft process enables zero waste and has a minimum environmental impact.  Part of that recovery process is the capture of many commercially important by-products, such as tall oil.  

Captured in the soapy layer of the weak black liquor tank it is drained off and after further refining is used to make many other substances. 

Correctly identifying the soapy layer becomes vitally important to the recovery process. Bass Electronics SE-IR camera can do this with ease by monitoring the heat signature on the outside of the tank.