(Sep. 27, 2010)
Wax. Hydrates. Asphaltenes. Algal growths. Protein and mineral deposits: Fouling is major industrial problem. Researchers at SINTEF in Norway are testing solutions.
Examples of fouling are many and varied but they have two things in common:
•Solids precipitate out from an industrial flow system, accumulate on permanent surfaces and thus obstruct both flow and heat exchange processes. This results in major remedial costs.
•Fouling problems often arise in connection with the exchange of heat through a dividing wall. The issue is so complex and far-reaching that fouling has rapidly grown into a distinct multidisciplinary field of study involving economics, physics, chemistry and flow mechanics from the micro to the macro scale.
At the Process Technology department at SINTEF Materials and Chemistry, researchers are conducting flow modelling studies in order to investigate both particle transport along pipe walls and the adhesive properties of particles on the walls themselves. It all started with a doctorate degree at the department. In order to come up with solutions, researchers are currently working together with the industry, industrial coating and surface treatment suppliers, and other research institutions.
"Fouling can occur both as a result of crystal growth directly on pipe walls, and also when crystals growing within the fluid flow coagulate to form particles that seek to attach themselves to the walls," says Sverre Gullikstad Johnsen. He is carrying out research into the problem and is involved in several projects.
Projects for the oil industry
SINTEF has many major clients linked to the oil industry, and researchers are working to find solutions that can make the transport of the unprocessed well flow more efficient.
One solution under investigation is the application of a coating on the inside of the pipe wall that reduces precipitation on the wall itself, while at the same time protecting against corrosion and reducing friction by effectively making the pipe wall smoother.
"Experiments have been carried out to compare untreated with coated steel surfaces," says Johnsen. "The challenge is to isolate the various contributory factors in the precipitation process, where we known that both the surface properties and thermal conductivity of the pipe wall, as well as the properties of the oil, will all play a part."
Lime deposits in a hot pipe. (Credit: Image courtesy of SINTEF)
Design tools "in the pipeline"
SINTEF researchers are also working with the Finnish lime industry. This work is part of a larger EU project bringing together research and industry partners from Ireland, Finland and Sweden.
Lime is transported through pipelines as a mud, and problems occur when minerals are precipitated on the pipe walls when the mixture is subjected to heat treatment.
The researchers have developed a mathematical model which they use to study how the particles move against the fluid flow and seek to attach themselves to the pipe walls. Various interactions between the fluid and the particles are built into the model. The aim is to construct a design tool for processing plants that can be utilised in combination with other commercially available flow simulators.
"We will have achieved a great deal if we can demonstrate to the industry when and where fouling will take place," says Sverre Gullikstad Johnsen, who emphasises that his field of study is closely linked with general energy strategies. If we can improve the heat exchangers, their efficiency will increase, and energy consumption will be reduced.