Crystallization
3V Tech designs and supplies tailor-made crystallization plants, which can be arranged as skid-mounted units or suitable systems for on-site installation.Crystallization is the process of formation of solid crystals precipitating from a solution, obtained through a variation of the solubility conditions of the solute in the solvent.
This technique allows to recover or to remove a substance from a solution with a controlled level of purity and yield.
The driving force of the crystallization is the supersaturation of the solute, which can be obtained by evaporation or by cooling. In case of low dependence of the solubility with respect to temperature the evaporation is the optimum choice, while solubility with strong temperature dependence is best suited to cooling crystallizers.
Typical applications- Improving quality and/or stability of the final product
- Solute recovery as crystals from process or waste streams
- Separation of two or more solutes by crystallization of one solute
- Solvent purification from process or waste streams, eliminating precipitating by-products
- Volume reduction for lower transport or disposal cost (ZLD application)
Crystallizer types3V
Tech's crystallization systems, operating under vacuum or at atmospheric condition, optimally use the following technologies:
- Forced circulation evaporative or cooling crystallizers FCC
- Wiped film evaporators TFE
Depending on the application, our crystallizers are fabricated with proper alloy or high quality glass-lined for highly corrosive applications.
General guidelines for crystallization system selection:- Where high capacity is required, usually forced circulation crystallizers FCC, equipped with centrifuge or belt filter for solids separation, are the best suited
- Where the product is difficult to handle due the high viscosity or heavy solids or with high boiling solvents, a technology such as agitated wiped film evaporator TFE is required
Energy saving & plant arrangementTo evaporate 1 kg of solvent, an amount of energy corresponding to the latent heat of the same must be provided, plus sensible heat for pre-heating, heat losses, etc.
In case of water evaporation, a single-effect crystallizer heated by direct steam thus presents a specific consumption of approx. 1,05 to 1,25 kg of steam per kg of evaporated water.
According to the requirements, 3V Tech designs the optimal energetic arrangement of the crystallization plant, in order to minimize capital and operating cost. Some of the options we apply:
- Multiple effect arrangement (ME)
- Thermal vapor recompression (TVR)
- Mechanical vapor recompression (MVR)
- Use of waste heat (e.g. waste steam, hot water, etc.)
- Combination of several techniques
Multiple effect arrangement (ME)- Direct heating by live steam, thermal oil, waste heat
- The
heating medium in any subsequent effect is the vapor generated in the
previous calandria, which condensates at lower pressure. Vapor from the
final effect is condensed by cooling water
- The arrangement can be co-current flow or counter flow or only partially in counter flow, depending on the application
- The
number of effects is limited by thermal product degradation, material
corrosion and boiling point elevation (BPE) of the concentrate solution
- In
case of water evaporation, the specific steam consumption in 3V Tech
systems is typically 1,05 to 1,25 kg of live steam per kg of evaporated
water, divided by the number of effects
Thermal vapor recompression (TVR)- The
heating medium is part of the process vapor, recompressed to a higher
temperature level together with motive steam by means of a steam
ejector, according to the principle of jet pump
- No-recompressed part of process vapor is condensed in a further effect or in a condenser at lower pressure
- The
higher the compression ratio of delivery pressure vs. suction pressure
(e.g. in case of high BPE), the higher will be the specific motive steam
consumption
- The lower the motive ratio of motive steam pressure
vs. suction pressure (e.g. in case of low pressure steam available),
the higher will be the specific motive steam consumption
- Steam ejectors have no moving parts, construction is simple and operation reliable
- Depending upon the operating conditions, the thermal vapor recompressor can act as several additional effects
- In
case of water evaporation with the ejector installed across the first
stage of a ME system, the specific steam consumption in 3V Tech systems
is typically 1,05 to 1,5 kg of live steam per kg of evaporated water,
divided by the (number of effects+1)
Mechanical vapor recompression (MVR)- The
heating medium is the total amount of the process vapor, recompressed
to a higher temperature level by means of a mechanical compressor,
according to the principle of heat pump
- Live steam consumption
is very low, just for start-up and make-up, being electric energy (the
energy input to the plant) used instead of steam
- The boiling
point elevation (BPE) increases the pressure ratio that the compressor
must attain to effect vaporization. The higher the compression ratio of
delivery pressure vs. suction pressure (e.g. in case of high BPE), the
higher will be the specific electric energy consumption
- Due the
complete recompression of the process vapor, another advantage of the
MVR systems is the negligible consumption of cooling water
3V Tech uses the following mechanical compressors, driven by electric motor and frequency converter:- Single stage Centrifugal Fan for
high evaporation flow-rate (1-140 m3/s) and low compression ratio
(≤1,25). Typical energy consumption: 10 to 25 kW per ton evaporated
water
- Roots Volumetric Blower for low evaporation
flow-rate (0,05-5 m3/s) and high compression ratio (≤2,5). Typical
energy consumption: 40 to 80 kW per ton evaporated water
- Double stage Centrifugal Fan for
high evaporation flow-rate (1-140 m3/s) and high compression ratio
(≤2,5). Typical energy consumption: 25 to 50 kW per ton evaporated water