Environmental requirements mandate true zero liquid discharge (ZLD) wastewater treatment in various industries, including electricity, manufacturing, refining, mining, pulp and paper, and chemical processing, and Salt Crystallizers. All industrial effluent at a location undergoes conversion to dry solids before recycling or disposal. The factory recycles any usable water collected during the waste treatment process. Frequently, industries use a falling film evaporator, reverse osmosis, or both to preconcentrate large volumes of wastewater.Concentrated wastewater contains 100,000-300,000 mg/l total solids and flows at a rate of 3 to 100 gpm (0.01 to 0.38 m3/minute). A forced circulation crystallizer is then used to decrease the volume to dry solids.
Industries have long utilized crystallization in producing common compounds such as sodium chloride and sodium sulfate. Unlike commodity manufacturing, where only one salt crystallizes, industries often reduce industrial waste to dryness by crystallizing numerous salts. To prevent difficulties like extreme foaming and quick scaling, this sort of mixed salt crystallizer necessitates drastically different design settings. Furthermore, when sizing vapour compressors for mechanical vapour recompression (MVR) cycle, mixed salt solutions have considerably large boiling point increases, necessitating careful consideration to design factors.
Finally, to lower the cost of smaller crystallizer systems, new filtering techniques have been devised. Examining typical functioning crystallizer systems, including steam and MVR cycles, various solids separation devices, and low-flow-rate systems. Even with synthetic waters, the crucial use of testing will be examined.
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Mixed Salt Crystallizers:
Typically, a crystallizer uses a two-pass horizontal or one-pass vertical external heater. Steam heats the solution, sprayed into a vapor body for suppression. This submergence of the tubes prevents boiling. A solids separation equipment, typically a centrifuge or automated pressure filter, extracts crystals from a slipstream.The process employs various energy sources.
The amount of evaporation per pound of steam used is around one pound, which might result in high running expenses. Condensing the created vapor requires using cooling water.
A thermocompressor can be used to reduce the amount of steam required if greater pressure steam is available. The thermocompressor’s suction recycles a part of the vapour that has evaporated in the vapour body. The motive steam is typically between 150 and 200 psig. This arrangement often reduces Steam use by 20% to 30%. Still, a condenser must handle the remaining vapor that the thermocompressor doesn’t return.
Vapour Compression Cycle-
A vapour compressor, powered by electricity or a gas/steam turbine, supplies energy for the crystallizer, elevating water condensation temperature.
Calandria Crystallizer with Salt Basket:
The calandria crystallizer utilizes a compact design for minor flow applications, housing the heater inside the vapor body and Salt Crystallizers. Low-pressure steam powers the calandria crystallizer, either condensing the vapor or releasing it into the environment. A propeller pump in the crystallizer’s lower half absorbs latent heat from condensing steam, aiding liquid rise. The heated liquid (brine) loses its vapour and returns to the propeller suction when it reaches the surface.During crystallizer operation, the salt basket collects solids vertically, and we follow these steps to dewater and discharge the salts:
- Separate the vapour body and the basket (calandria).
- Empty the brine from the salt basket.
- Steam dewatering removes moisture from the solids in the basket.
- Opening the flanged cover discharges the salts. The salt basket efficiently dewaters mixed salts with large crystals like sodium sulphate or sodium chloride. Alternatively, the calandria may be used. crystallizer can be equipped with a pressure filter or centrifuge for more challenging filtering applications.
Mixed salt crystallization saves waste, necessitating design differences from traditional single-salt commodity crystallizers for success.
Alaqua is a crystallizer supplier in the USA along with other processing equipment such as the evaporator, solvent recovery system, distillation equipment and heat exchangers for various industrial purposes. We also provide the system with the necessary size tanks, pumps, and pipework to ensure proper operation. This will allow the customer to have a fully functional system when it has been installed. Alaqua’s scope includes PFD, PID with pump specs, pipe size, control loops, instruments, controls, and GAD with loads.