GEA Messo AG
EVAPORATION – CRYSTALLIZATION – CHLORALKALI
RECOVERY OF SODIUM SULFATE FROM PROCESS WASTE STREAMS
Scope Design, supply and erection of a turn-key plant for recovering sodium sulfate from a process waste stream. In this particular application a high-quality product is required by the client. The process utilizes various pretreatment and purification steps to reach this goal.
Process description The feed liquor is treated with active carbon in an agitated vessel at first and then pumped through a filter station to obtain a clear, decolourized feed solution. Next the solution is transferred to a flash degassing column where volatile organics (solvents) are stripped off.
Leaving the degasser bottom, the feed passes through two preheaters and is split into two streams, partly enters the salt leg of the first evaporator/crystallizer and the balance enters the melting vessel for Glauber’s salt. Evaporator (1) operates at a high temperature level and produces sodium sulfate anhydrite (SSA), which is discharged as slurry into the melting vessel. This slurry is pumped to a thickener for feeding to centrifuge (1). The washed sodium sulfate crystals enter the fluidized bed dryer/cooler to obtain the final dried product. All the mother liquor streams are fed back to the crystallizer (FC-type, 1).
Simplified typical process flow sheet of the recovery plant.
On the down stream side of the circulation loop the clear mother liquor is drained off in a settling zone. This stream is fed to flash evaporator (FC-type, 2), which operates as a vacuum crystallizer for Glaubers’s salt (GS) at a low temperature level. From the salt leg the crystal slurry is drained by gravity flow directly to centrifuge (2). The separated Glauber’s salt is washed and discharged to the melting vessel. A side stream of clarified mother liquor from the circulation loop of evaporator (2) is mixed with the filtrate of centrifuge (2) and pumped back to the evaporator. To control the level of organics and other impurities in the system a small purge stream is split off.
Characteristics ■ Well proven technology ■ Ability to handle different loads and compositions ■ Excellent heat economy by utilizing vapour from evaporator for the vacuum crystallizer ■ Two stage washing ensures product purity (whiteness) ■ Corrosion and abrasion resistant materials used for high performance and low maintenance costs ■ Numerous references from a variety of feed stocks ■ Plant commissioned in 1984
Technical data (design) FC evaporator/crystallizer for SSA FC flash vacuum crystallizer for GS Waste stream feed rate Na2SO4 concentration Organics concentration Total evaporation rate Purge stream flow rate Na2SO4 production rate Whiteness (organics) Residual moisture Granulometry: d (RRSB)
12’500 kg/h 27 wt % 0.8 - 1.2 wt % 9’200 kg/h 1’000 kg/h 3’300 kg/h 60 - 80% 0.02 wt % 0.2 mm Centrifuging and washing of crystals.
GEA Messo AG, Bürglistrasse 29, CH-8400 Winterthur, Switzerland Telefon +41 52 234 00 00, Telefax +41 52 234 00 99, Email:
[email protected], www.geamesso.com
F7-100406
GEA Messo AG
