Mechanical power can be produced in a system in which heat at an elevated temperature from a heat source is introduced into the system and then rejected into a heat sink at a lower temperature. Thermal power recovery systems under normal operation typically utilize a volatile working fluid which is pumped in a liquid state under substantial pressure through a heat exchanger where heat from the heat source raises the temperature of the working fluid and substantially increases the volume of the working fluid. One common way to increase the volume of the working fluid is through vaporization. Once vaporized, the working fluid still under pressure is expanded after introduction into an expansion engine where the gas expansion may be utilized to produce mechanical power. The exhaust vapor leaving the expansion engine will then flow at a reduced pressure into a condenser where the heat is rejected to the heat sink and the vapor is condensed and returned to the pump where the process is once again repeated. Since the working fluid may be in a liquid state at one phase of circulation in the system while in a gaseous state at another phase of the system, the term "fluid" is used herein to designate a flowable medium, either gas or liquid.
In a commercial thermal power recovery system, a turbine is often used for the expansion engine. A turbine rotor can be supported on a rotating shaft, requiring a shaft seal to isolate and retain the working fluid within the turbine. Beyond the seal, conventionally, there are lubricated bearings such that the shaft seal also serves to keep the working fluid and the lubricant separate. Such sealing systems are normally not perfect. The working fluid may be contaminated with lubricant or sealing fluid, especially due to possible misoperation and the like. Besides the sealing system, the working fluid may also be contaminated from other possible sources, such as from deposits in newly installed equipment or from equipment repair. Commercial processes often have different means for dealing with the contamination of the working fluid, and in fact, some processes actually utilize the lubricating oil in the start-up of their processes.
During start-up of a thermal power recovery system, the working fluid is usually pumped through a heater in which only a limited portion of the working fluid is vaporized because the equipment has not yet warmed up to its normal operating temperature. The portion of the working fluid which is not vaporized is returned to a reservoir from which it is once again pumped to the heater. The vaporized portion of the working fluid passes through the recirculation system and may in fact generate a limited amount of power. As the equipment becomes warmer and the temperature is raised higher, the vapor pressure increases and less and less liquid is left unvaporized to be returned to the reservoir while more and more vapor is passed through the recirculation system until full-power is reached. Under normal operation, the time typically required to safely warm up such a system is usually on the order of one half hour.
It is known that shaft lubrication oil and the working fluid may be combined together during start up. An example of one such application is found in U.S. Pat. No. 3,797,248 to Wetzel et al. Such a thermal power recovery system will employ additional special equipment in order to separate the working fluid and the lubricating fluid before the system is run at full scale. In the Wetzel et al. patent, after the fluids are mixed during start-up, a distillation step and a gravity or screen separator are utilized to remove the lubricant from the working fluid.
Other thermal power recovery systems keep the working fluid and the lubricating fluid completely separated. In a prior patent of mine, U.S. Pat. No. 4,005,580, a seal system is disclosed wherein the working fluid is sealed from escape along the shaft. In another patent, U.S. Pat. No. 3,831,381, a lubricating and sealing system for a rotary shaft utilized in a power plant is described. The disclosure of both of these patents are hereby specifically incorporated by reference.