Flange type or Double Flanged Butterfly valves have two flanges - one either end as opposed to lug type which has one flange in the centre. Flange type have a larger face to face than wafer or lugged. These can be used for dead end service.
A Flange butterfly valve is a valve that has flanges on either sides of the valve body that is used to mount the valve to a pipe. They are mostly preferred as to wafer type butterfly valves, because the disc of a flange type valve can turn fully open and fully closed inside the valve body itself. As appose to the wafer type where modifications to a pipe must be made on the inner part for the disc to travel fully open or closed.
picture of how a flange type butterfly valve looks like