WASTE WATER EVAPORATION PLANT. INTRODUCTION.
A chemical company in Spain that produces sulphuric acid, nitric acid and other chemicals approached us to resolve a serious environmental problem that they had
involving the wash water used to clean the tanks where chemicals are stored.
Obviously no wash water could be drained to the river without a previous treatment for eliminating all traces of hazardous chemicals.
SOLUTION
We proposed a solution designed for an unique effect of evaporation and a mechanical vapour re-compression system to reduce the energetic consumption.
Evaporation is performed at 80 ºC, and the vapour obtained is compressed up to a pressure equivalent to 105ºC approximately, thus this vapour is used to provide
the evaporation energy by condensation in the evaporator.
To start the process and only at the beginning of the operation, we included a heating system by electrical resistance used to heat the initial recirculating mass
up to the evaporation temperature.
According to our experience in similar applications, the plant is designed to work in continuous evaporation in recirculation through a buffer tank. The tank has
a decanting bottom to accumulate crystals. There is a product extraction system from the bottom of the tank.
HRS Spiratube can build systems for a capacity of vapour ranked from 200 to 25000 Kg/hr. In this case, we are considering 350 Kg/hr of capacity.
DESIGN CONDITIONS
Our equipment is designed according to the next conditions:
- Product : waste water
- Evaporation capacity : 350 Kg/hr.
- Evaporation temperature : 80ºC
- Heating system : recompressed vapour
Initial heating to get the regimen by electrical resistance.
Continuous working with recirculation.
Continuous unloading of crystals concentrate for crystal separation and liquid return.
Estimate consumptions (for 350 Kg/hr):
- Electricity : 35 Kw
- Compressed air : 5 lt./min. at 5 bar.
The plant has the following elements:
- Buffer tank of recirculation - with 200 liters of useful weight capacity – fitted with upper cyclone chamber for vapour separation, with cleaning ball and access
floodgate.
- Recirculation centrifugal pump at 15 m3/hr.
- Scraped surface evaporator: Unicus®.
- Mechanical vapour re-compression system.
- Initial heating system with electrical resistance.
- Extraction pump for concentrate with crystals.
- Pneumatic actuation valve for cleaning water inlet.
- Pneumatic actuation valve for waste water inlet.
- Pre-heater of water inlet using outlet condensates.
- Level control sensors.
- PT-100 temperature gauge.
- Manometers for vapour and vacuum pressures.
TITANIUM, SANICRO 28 or HASTELLOY-C in heat exchanger tubes. Rest of equipment, accessories and installation in stainless steel.
OPERATION
The evaporator works in a recirculation regime. The evaporator is an UNICUS Dynamic Heat Exchanger to avoid fouling.
The mixture of vapour and saturated water with salt crystals goes to the cyclonic separation chamber, where vapours go out through the top and the waste water goes
down to the decanting hopper.
There is a new liquid entry for recirculation in the evaporator, while the crystals go down to the bottom, where they are picked up by an extraction pump.
The vapour that comes out from the cyclonic separator is picked up by a lobular vapour compressor that compress it to send it to the shell tube of the evaporator,
where it condenses providing the necessary energy to continue the process.
REGULATION AND CONTROL SYSTEM
There is a PCL in the electro-pneumatic panel, with a liquid glass screen and an integrated keyboard for the valves and plant engines control. The regulation and
working instructions are entered through the keyboard. The state of the plant and the sensors is displayed on the screen.
The control program allow to do the injection of the new product in continuous, the evaporation and the unloading of concentrate.
The program also includes a cleaning cycle of the plant.
FLOW DIAGRAM
PLANT DRAWING
