In some industrial processes such as copper mining, large flows of an aqueous stream containing organic, solid particles, and an aqueous solution (water and dissolved acid and minerals), must be treated. The aqueous stream is treated to remove the organic (principally hydrocarbons) and also to separate out particles. The resulting aqueous solution is used in copper mining, as an electrolyte from which copper, in solution, is removed. It is common to remove the organic by first coalescing microscopic droplets of the organic to provide larger drops that can be more easily further coalesced and floated to the top of a tank.
The initial coalescing of the microscopic droplets (e.g. an average of 0.01 mm) of organic is commonly accomplished by passing the stream through a crushed anthracite bed. The anthracite is oleophillic, which allows its surface to be coated with organic. The organic coats the surface of the small crushed anthracite pieces, until the anthracite is saturated with organic and larger drops (e.g. 1 mm) break off to flow downstream. These drops can be more rapidly coalesced to float to the top of a tank from which they can be removed.
When the stream moves through the anthracite bed, the solid particles gradually clog the input end of the bed, so the flow decreases (for a given pressure drop) and the bed is cleaned by backwashing clean water or other cleaning liquid through it. In one process of backwash, the cleaning liquid, particles and untreated organic are passed to a separate processor that processes small quantities of material, so substantially none of the stream is untreated. During such backwash, the operation is stopped, and the stream is not flowed into the anthracite beds and the treated stream is not flowed to the separator. A system that avoided shut downs during backwash, while avoiding the need for a special separator during backwash, would be of value.