Most of the sensible heat and the flash steam from the boiler blowdown water can be recycled.   
Blowdown water is high in solids concentration, but comes out at the boiler drum's pressure.  We can recover the flash steam coming out of it by passing through a flash tank and also recover some more sensible heat out of it by passing through a small heat exchanger before draining it to the waste water system.  The flash steam could be sent to the de-aerator directly, since the de-aerator pressure is usually low around 10-psig.  The incoming make-up water from water softener is usually passed to the other side of the heat exchanger to recover the sensible heat.
Pre-engineered blowdown heat recovery equipment packages are available from several vendors.  A Google search would provide most of the vendor details.

Editor's Note: You may find this on-demand webinar that focused on practical and implementable strategies for improving energy efficiency -- including steam systems -- at chemical manufacturing plants useful: Energy Efficiency