A schematic of the DDT Process is shown below. The process begins after the completion of "steaming out" of the residue feedstock in the assigned heater. Pigg launchers are then installed on both the inlet and outlet pipes of the assigned fired heater. These launchers provide the connection points for the pressurized waterlines and permit the loading and unloading of the appropriate Pigg. Pressurized water, supplied from a pumping unit, pushes a flexible Pigg through the fouled heater tubes.
The DDT Process employs a closed loop, self contained hydraulic system, making it a very safe and environmentally friendly system. During the cleaning operation, the protruding metal appendages on a Pigg will clean and remove the coke deposits. A controlled amount of water flows around the Pigg and past the cleaning appendage, thereby flushing the loose coke deposits ahead of the advancing Pigg and into a collection tank.
The key variables that can be controlled during a cleaning run are as follows: Pigg diameter; number of appendages; and, appendage metallurgy, surface texture, and height. For example, changing the appendage height will affect the rate at which coke deposits are removed and will also determine the amount of water that flows around the Pigg body. In turn, the water flow velocity around the Pigg body controls the removal of just-broken-coke in a manner that avoids the possibility of Pigg blockage.
A series of valves controls the direction the Pigg travels. Since the fouling of heater tubes is not uniform throughout a furnace, our Operators have the ability to direct the Pigg over only the most fouled sections. This precision control of cleaning also permits the decoking of furnace tubes with variable pipe diameters and prevents the unnecessary repeated-cleaning of less contaminated pipe sections, thereby reducing pipe abrasion.
The Bi-Directional Pigg Control Method is a DDT patented process.