How the DDT Descaling Decoking Process Works
The DDT process begins after the completion of "steaming out" residual feedstock in the assigned heater. Then, Pigg® launchers are installed to 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.
Safe and Environmentally Sound Coke & Scale Removal
Employing a closed loop, self contained hydraulic system, the DDT process is safe and environmentally friendly. During the cleaning operation, the adjustable metal appendages on a Pigg® clean and remove coke deposits. Controlled amounts of water flow around the Pigg and past the cleaning appendage, flushing loose coke deposits ahead of the advancing Pigg® and into a collection tank.
The key variables that can be controlled during a cleaning include:
Pigg diameterNumber of appendagesAppendage metallurgySurface textureHeightAppendage typeAs an example, changing the appendage height affects the rate at which coke deposits are removed and determines the amount of water that flows around the Pigg® body. In turn, water flow velocity around the Pigg® body controls removal of just-broken-coke in a manner that avoids the possibility of Pigg® blockage.
Precision Pigg Control and Cleaning
A series of valves controls the direction of Pigg® travel. Since the fouling of heater tubes is not uniform throughout a furnace, DDT operators can 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.
Our bi-directional Pigg® control method is a DDT patented process.