Grease Canister Mechanical Seal Flush System
Publication Date: 2014-Apr-03
The IP.com Prior Art Database
This disclosure relates to the development of a grease canister mechanical seal flush system. The system was developed to use grease as a flush fluid for mechanical seal faces in pumps in which the pumped fluid is not suitable for use as a seal flush fluid. It is especially useful in situations where a pump’s location is remote enough such that providing an alternate flush fluid is not practical.
It has long been known that mechanical seals are the weakest link in the operation of a pump. Though many pump designs have mechanical seals, the applications in which twin-screw multiphase pumps often find their best use are in remote applications with viscous, gassy, and particulate-laden streams. Such a twin screw application presented itself, providing an ideal opportunity to develop the grease canister mechanical seal flush system.
The twin-screw multiphase pump has a minimum of 4 mechanical seals. These seals have faces (one stationary and one rotating at pump speed) which have a flatness on the order of 5 Angstroms. The seal faces must be kept cool and lubricated. A liquid stream, called a seal flush, is brought into the seal gland very near where the seal faces are located.
The traditional flush fluid in most pumping services, is the pumped fluid itself, which in the petroleum industry is typically a hydrocarbon stream. In this situation, the flush fluid usually has enough lubricating qualities to keep the seal faces lubricated and cool. With multiphase pumps used in crude production applications, the pumped fluid is a combination of hydrocarbon gas, a hydrocarbon liquid, produced water containing salts and other dissolved solids, and small diameter solid particles. If this fluid is used as the seal flush, the seals will often have a flush varying from nearly all gas to a mixture of gas, liquid, and solids. This stream is not acceptable as a flush fluid and, if used as such, will often quickly result in damage to the seal faces and a leaking seal. Though the result is the same, the cause of a seal leak is different depending on the composition of the flush fluid. With gas being neither a good lubricant nor a good heat transfer medium, the seals, when flushed by gas, are neither lubricated nor cooled as the gas moves across the faces. With solids in the pumped fluid, the solids lodge between the seal faces, score them, and create a leak path. With dissolved solids, the solids precipitate out on the seal faces as the liquid vaporizes in the course of traveling across them. These precipitated solids also either separate the seal faces or score them. The result is that the seal faces either overheat rapidly and are thus destroyed, or the scored or opened seals provide a leak path across the seal faces. In either situation, the seals leak the pumped fluid over the immediate area. This often creates the need for environmental cleanup and may also create the potential f...