Crystallization can provide an efficient and economic alternative process,
designed to produce a pure water stream from dilute multi component waste
streams. The process is generally referred to as Niro Freeze Concentration
(NFC).
The production of pure crystals in the solution is the starting
point. Water is crystallized into ice and the impurities present in the feed,
are concentrated in the remaining liquid. Suspension based crystallization is a
highly selective process that produces extremely pure crystals, due to the
extreme low crystal growth rate. Separation of the pure ice crystals from the
concentrated waste water is completed in a packed-bed wash column. Effectively,
the pure ice crystals are transferred into pure water. The pure water can be
re-used as e.g. process water, cooling water or can be discharged without
additional treatment.
The feasibility of the NFC process has been
successfully assessed on several waste solutions containing a range of organic
and inorganic compounds. The MFC process focuses on the crystallization of
water in the waste solution; the organic and inorganic compounds are simply
concentrated in the remaining liquid.
A commercial application of the
process is the concentration of a waste water stream prior to incineration.
Pure ice crystals in concentrated effluent
Seraya Chemical Singapore Ltd. (SCSL) and Shell Chemicals
Moerdijk B.V. have chosen NFC as the pre-concentration step for their liquid
hazardous waste water, which is subsequently incinerated. Many of the
components in the stream are harmful to standard bio treatment systems.
Incineration was chosen as the preferred method of destruction.
The low
solute concentration, however, reduced the efficiency of the incinerator and
increased the processing costs for this waste stream. In this case, NFC is able
to remove 75% of the water originally in the waste stream at a much lower cost
than direct incineration. Concentrating the waste water will increase capacity
of your downstream incinerator, increase the caloric value of your waste
"fuel", reduce transportation and intermediate hold-up volumes along with the
related hazards and cost.
Pre-concentration with NFC is one possibility
for hazardous waste water treatment. We can quickly provide budget data, based
on available information, for you to examine the MFC concept. Recovery of
certain components has been demonstrated by concentrating a dilute waste stream
to a level where it can be reintroduced into the reaction process. Salts can be
precipitated and removed from the concentrated waste water prior to disposal.