A method of treating produced water from heavy oil production to provide
feedwater for the production of high quality steam. A produced water from
heavy oil recovery operations is initially treated by first removing oil
and grease to a desired level, preferably to about twenty parts per
million, or less. The pH is then adjusted, normally downward and by acid
addition, to release at least some carbonate alkalinity as free carbon
dioxide. Preferably, all non-hydroxide alkalinity is removed, or
substantially so, by introducing the feedwater into a decarbonator. In
some cases, the pH may be raised (without, or subsequent to decarbonation,
depending upon water chemistry) preferably by caustic addition, to
maintain silica solubility in the feedwater. Next the feedwater is
introduced into an evaporator, and the feedwater is evaporated to a
pre-selected concentration factor to produce (1) a distillate having a
small amount of residual hardness therein, and (2) a concentrate
containing residual solids (dissolved solids and in some cases, suspended
solids). The distillate is then cooled, and is subsequently introduced
into a hardness removal step, preferably an electrodeionization (EDI)
treatment unit, to remove the residual hardness from the distillate.
Finally, the substantially hardness free treated water stream is sent to
packaged boilers, for production of high quality steam. The hardness
containing stream from EDI is recycled to the evaporator feed, for further
treatment.
