Ashing is a test to deduce the amount of ash forming material present in a petroleum product so as to decide its use in certain applications. Ash-forming materials are considered to be undesirable impurities or contaminants.
In the ash analysis of petroleum products, ash content represents the incombustible component remaining after a sample of the furnace oil is completely burned. The ash content of petroleum products is generally low. It is defined as the inorganic residue that remains after combustion of the oil in air at specific high temperature. Ash typically ranges from 0.1 to 0.2% in oil. Some of the ash forming constituents occur naturally in crude oil; others are present as a result of refining or contamination during storage or distribution. Knowledge of the amount of ash-forming material present in a product can provide information as to whether or not the product is suitable application.
In the ash analysis of coal and other solid fuels, the amount of sulfur retained in the ash during the ashing process is not constant, but rather is dependent upon the conditions of ashing as well as the other inorganic constituents in the ash that may form sulfates during the ashing procedure. As such, different ashing procedures may yield different ash contents.