A turboexpander-generator system employing a housing with a rotatably mounted shaft oriented vertically with a turboexpander associated with the upper end of the housing and shaft, a generator associated with the housing and shaft below the turboexpander and a lubricant pump located at the lower end of the housing and shaft. The lubricant pump controls an actuator valve which controls the variable inlet nozzles to the turboexpander. Thus, a speed control system is achieved through use of the lubricant pump pressure. A seal gas separator is provided with two ports located in the turboexpander exducer at positions of different pressure. High pressure is used to provide a seal between the bearings and the turboexpander. Low pressure is directed to the area of the sump of the pump to enhance continuous lubricant return. A self-priming mechanism causes a reservoir to be charged during pump operation with return of the lubricant to the sump when the pump is off.