Salts Are Plugging Up Your Operations
Salt in the oil refining process can cause serious problems if not removed properly. A refinery in the U.S. had a malfunctioning desalter, leading to extensive damage. The salts started accumulating in stills, exchangers, and heaters, and the resulting fouling required an expensive cleanup.
Desalter and dehydrator vessels are a vital part of emulsion treatment in subsystems. They allow suspended solids, which can damage equipment, to settle out of the liquid. Once the solids have collected in the vessel, they should be removed.
The Choke of Coke
Common salts in oil-associated water are chlorides, calcium, magnesium sulfates, and bicarbonates of sodium. Calcium, strontium sulfates, and magnesium carbonates end up precipitating on the heating surfaces of emulsion treatment equipment. They deposit in pipes, tubes, inside treating vessels, and in fittings. These salts also can produce scales. And when there is a buildup of scales, salt or other fouling material, then coke becomes a problem. When the fouling material causes the skin temperature of the fire tube or other element to hit 600 degrees, coking begins. The coke ends up reducing the heat transfer and may quickly cause the fire tube to malfunction.
Solids Deposits Make the Emulsion Treatment Process Difficult
Salts are rarely present in the crude oil itself, but usually in the water associated with the crude. Salts aren’t the only solid that oil producers need to remove from crude or associated water. Solids in the liquid also can include mud, silt, sand, asphaltenes, paraffin, and more. In smaller amounts, these solids don’t cause many problems. But that story changes when they start building up. These solids may deposit on fire tubes and nearby surfaces, making the fired emulsion treatment vessels difficult to operate.
Keeping Massive Clean-Ups at Bay
Operators can easily clean vessels where damaging solids settle, and should regularly. Operators can install cleaning openings or washout connections so the vessels can be drained and cleaned. If the vessel is large, they should have manways to allow better access. In some cases, steam cleaning and acidizing might be necessary to remove calcium carbonate or other stubborn substances.
Shutting down and draining vessels is also a common cleaning method. When drained, workers can remove sand with rakes, shovels, or a vacuum truck. There also are ways to minimize sand and silt buildup in vessels by using sand pans, automated water jets, and drain systems. Sludge, which builds up at or near the oil and water interface, can be removed through a drain at the interface or by closing the water dump valve and sending it out to another tank for disposal or more processing. Another way operators can remove sludge is to open the water drain valve.
If a refinery has a problem with scaling or coking, decreasing the treatment temperature, using chemical inhibitors, having favorable fluid velocities through equipment, and using spreader plates that are properly designed will minimize the problems. Maintaining smooth and continuous surfaces on internal equipment that’s cleaned regularly also will reduce deposits.
While every piece of machinery in a refinery operation is important for success, systems keeping solids and salts separated from oil and water are vital. If salts and solids aren’t stopped at dehydrator and desalter vessels, they can do serious damage to equipment. When the settling vessels perform properly, operators can easily remove built-up substances and keep them out of the oil.