Abstract: A control system for synchronous condensing operation of a hydroelectric turbine-generator wherein the draft tube water level for the turbine is controlled through the use of that generator's power or current consumption. Either parameter may be used in the process. Water impacting the turbine will increase both of these parameters above an optimum minimum value. Either a generator power or current device provides a signal to a control circuit. When the signal from either device exceeds a preset value, the control circuit injects compressed air into the turbine cavity until the signal returns to its optimum value.

Abstract: A simple, efficient and economical process for purifying molybdenum disulfide concentrates by contacting and digesting the molybdenum disulfide feed material with an aqueous acid solution containing a controlled combination of hydrofluoric acid and sulfuric acid in a manner to convert substantially all of the contaminating silica bearing minerals therein to aqueous soluble fluoride and sulfate compounds and any contaminating lead sulfide compounds to lead sulfate compounds, and thereafter washing, neutralizing and drying the purified molybdenum disulfide powder product. In accordance with a preferred practice, when the molybdenum disulfide feed material contains in excess of about 0.1% iron as an indication of pyrite concentration, the concentrate is calcined at an elevated temperature in a nonoxidizing atmosphere prior to the digestion step to effect a conversion of the pyrites to synthetic pyrrhotites, which are softer and less abrasive and are more acid soluble.