A kilogram per minute (abbr. K/min) was a unit of measure for mass flow rate, specifically kilograms across a threshold per minute.
According to Doctor Farallon's initial projections for the Tyran particle fountain mining technology was a lift rate, from the surface of Tyrus VIIA to the Tyrus VIIA station in orbit, to be 500 kilograms per minute, however, at the time the project fell under review by Starfleet its lift capacity was far below this, a mere 23.4 K/min. (TNG: "The Quality of Life")