Bitumen froth treatment is a process used in the Athabasca oil sands (AOS) bitumen recovery operations to remove fine inorganics—water and mineral particles—from bitumen froth, by diluting the bitumen with a light hydrocarbon solvent—either naphthenic or paraffinic—to reduce the viscosity of the froth and to remove contaminants that were not removed in previous water-based gravity recovery phases. Bitumen with a high viscosity or with too many contaminants, is not suitable for transporting through pipelines or refining. The original and conventional naphthenic froth treatment (NFT) uses a naphtha solvent with the addition of chemicals. Paraffinic Solvent Froth Treatment (PSFT), which was first used commercially in the Albian Sands in the early 2000s, results in a cleaner bitumen with lower levels of contaminates, such as water and mineral solids. Following froth treatments, bitumen can be further upgraded using "heat to produce synthetic crude oil by means of a coker unit."
Background
Oil sand consists of a matrix of solid mineral material—quartz sand and clays, water, and the hydrocarbon, bitumen, which is the heaviest form of petroleum. According to the United Nations Institute for Training and Research, bitumen's normal viscosity is greater than 10 mPa·s and its density is greater than 1000 kg/m3. Oil sands, before processing, comprise fine particles of silt and clay, that are 44 microns or less, and coarse particles of sand and rock, that are larger than 44 microns. Each grain of quartz sand, which is extremely abrasive and has an angular shapes, is "completely enveloped within bitumen". Each sand grain is surrounded by a thin film of water and bitumen covers the aqueous layer and the angular sand grain. The bitumen-and water-covered grains of quartz sand stick to one another. When untreated, the highly abrasive oil sands would damage pipelines, trucks, and all the equipment used in mining and operations. As well, the viscosity of bitumen changes with heat and cold. It is like molasses when warm, and will freeze when cold. Bitumen as a hydrocarbon, is considered to be a valuable energy resource. The more bitumen in an oil sands deposit, the more valuable it is. If a deposit contains less than 6% of bitumen it is not worth mining. The oil sands deposit has to have at least 18% of bitumen has to be economically viable.
Bitumen production in 2004 included six inter-related and integrated processes or units—mining, utilities, extraction, froth treatment, water management, oil sands tailings ponds, and upgrading, according to a 2004 article in the Canadian Journal of Chemical Engineering (CJCE). The frothing treatment is part of an integrated process.
Due to its high viscosity, heavy oil is much more challenging to produce and transport. Viscosity—the "internal resistance to the flow of fluid", is a physical property of crude oil—and an important parameter in the development and design of ultimate oil recovery and effective fluid flow pipelines. Viscosity is one of the pressure–volume–temperature (PVT) properties that is estimated during the different stages of oil exploration, production, recovery, and transportation.
In bitumen, asphaltenes, which are often defined as the fraction which cannot be dissolved in n-heptane, impact negatively in oils sands operations—they "impart high viscosity to crude oils" and can cause a "myriad of production problems." Asphaltenes are molecular substances found in crude oil along with saturates—saturated hydrocarbons such as alkanes, aromatic hydrocarbons, and resins, known as (SARA).
The first stage of the extraction process, used by oil sands operators in commercial operations, is a modified Clark hot water extraction (CHWE) process which was developed by Karl Adolf Clark's (1888–1966) in the 1920s. According to a 2017 Oil Sands Magazine article, after bitumen froth has been separated using the first stage of the bitumen recovery process—water-based gravity separation—the solution contains on average "60% bitumen, 30% water and 10% fine solids." The gravity separation vessel—the Primary Separation Cell (PSC), Primary Separation Vessel (PSV) or the SepCell—recovers 90% of the bitumen. During this process bitumen froth is produced. The froth is highly aerated—full of air bubble—and requires deaeration before it can be pumped to a Froth Storage Tank.
The second stage is the froth treatment. The quality of bitumen froth prior to the frothing treatment—a solvent-based gravity separation treatment—is "too low to be processed by an upgrader or refinery." The water-based gravity separation alone cannot remove the remaining contaminants, which are 10 to 15% solids and up to 40% water.