Chemical cleaning uses chemicals to remove various types of scaling, sludges and deposits from equipment and piping. It is commonly used to prevent harm and maintain effectiveness by removing these deposits that form over time from liquids being processed. The document provides examples of different types of chemical cleaning agents like acids for removing mineral deposits and degreasers for removing greasy soils. It discusses how lack of regular chemical cleaning can lead to issues like microbial contamination of fuels. It also explains how chemical cleaning helps systems like district cooling and heat exchangers work more efficiently.