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Zero Liquid Discharge (ZLD) & Multi Effect Evaporators (MEE)
Zero Liquid Discharge (ZLD) describes a wastewater treatment that completely eliminates liquid discharge from a system. The goal of any well-designed ZLD system is to minimize the volume of wastewater that requires further treatment, process wastewater in an economically feasible manner, while also producing a clean stream suitable for reuse elsewhere in the facility. The Multi Effect Evaporators (MEE) will be used to increase the concentration of TDS for evaporation.
Why Zero Liquid Discharge (ZLD)?
- Environmental regulation on discharge of specific solutes (salt, toxic elements, nitrate nitrate‐nitrite nitrite etc)
- Water scarcity/water stress growing world‐wide along with still negligible rate of waste water recycling
- Economics: recycled water becomes more affordable as the water supply from conventional sources becomes more expensive;
- Growing social responsibility and education towards awareness of environmental issues
- While ZLD cost is high in most cases, it might be a more economic solution when waste needs to be transported in large volumes over long distances
Conventional Thermal ZLD Technology
- Evaporation usually aims at>90% water recovery
- Crystallization may achieve 100% recovery
- Solids can be further dewatered on a filter‐press for landfill
- Latent heat of Evaporation is partly recovered
- Operational and capital costs are still very high due to high energy consumption (20‐40 kWh/m3 vs. 2‐3 kWh/m3 in desalination), use of chemicals and expensive corrosion‐resistant materials
Multi Effect Evaporators (MEE)
- Multi Effect Evaporators will be used to increase the concentration of TDS for Evaporation.
- The effluent will be sent to balance tank and feed pump will transfer the effluent from balance tank to Two Effect Evaporation system
- The concentration of effluent will increase to 30% TDS by Evaporation Process.
- The concentrated effluent from this system will be taken to Agitated Thin Film Evaporator (AFTD) to recover salt.
Agitated Thin Film Evaporators (AFTD)
In the AFTD will concentrates the effluent from 30% to 85% TDS by evaporation, Outlet Mix Salt coming from the AFTD with 10 - 15% moisture will be collected
Agitated Thin File Evaporators (AFTD)
In the AFTD we will concentrate the effluent from 30% to 85% TDS by Evaporation and outlet mix salt will be coming out from the AFTD with 10 – 15% moisture. The Agitated Thin Evaporators (AFTD) is used for evaporation of Water / Solvents and to make concentrated liquid to dry powder or flakes:
- AFTD is the ideal apparatus for continuous of concentrated material to dry solids. AFTD is consists of Cylindrical vertical body with heating jacket and a rotor inside of the shell which is equipped with rows and pendulum blades all over the length of the dryer. The hinged blades spread the wet feed product in a thin film over the heated wall.
- The turbulence increases as the product passes through the clearance before entering calming zone situated behind the blades as the heat will transfer from jacket to main shell under the smooth agitation water / solvent will evaporate and liquid will convert to slurry to cake or to dry powder of flex.
- The vapors produced rise upward, counter currently to the liquid and pass through Cyclone separator mounted on vapor outlet of AFTD.
- Further these vapor will concentrated in condenser and recovered as condensate, the system will be operated under vacuum for temperature sensitive products and atmospheric condition for normal drying.
Benefits of WTPL MEE System
- All solid and liquid phases from this World Technologies plant design are recoverable
- World Technologies plant design is Mechanical & Biological) with just a few process stages, thus benefiting from relatively low capital costs
- Financial returns are further improved by reducing waste volumes and the associated disposal costs and by savings accrued from recycling of feed and water reuse
- The system is highly automated, with a relatively short operator training time, also reducing operating costs
Multi Effect Evaporators (MEE) Design
Evacuators
Evaporation is a unit operation that separates a liquid from solids by means of heat transfer via vaporization or boiling. The purpose of evaporation is to concentrate a solution of a non volatile solute (i.e., solids) and a solvent (i.e., liquid), which is typically water. Water is removed from a solution by boiling the liquor in an evaporator and withdrawing the vapor. Evaporation occur in three steps:
Multiple Effect Evaporation remains one of the popular methods used for the concentration of aqueous solutions. The multiple-effect configuration combines two or more evaporator bodies to conserve steam, which is condensed in the first-effect heat exchanger only. Water evaporated in the first-effect vapor body is condensed in the second-effect heat exchanger, which provides energy for evaporation in the second-effect vapor body (and so on for additional effects). Vapor from the last effect flows to a condenser.
The last-effect vapor body is maintained at a high vacuum with a steam-jet air ejector or mechanical vacuum pump. The driving force is the pressure drop from the first to the last effect. The number of effects is limited by the total available temperature difference between the plant steam and the cooling water temperature. Process liquors with high boiling point elevations typically operate with fewer effects. A multiple-effect evaporator is divided in to three category on the basis of feed direction:
A multiple-effect evaporator is divided in to three category on the basis of feed direction:
- Forward feed multi effect evaporator
- Backword Feed multi effect evaporator
- Mixed feed multi effect evaporator.
It is also categorised as Raising Film Evaporator, Falling Film Evaporator, Forced Circulation Evaporator and Agitated Thin Film Evaporator
Crystallization
Due to its inherent design features, it is ideal for thermal treatment of solutions and heat sensitive products, where reduced operating temperatures and vacuum operating pressures are desirable. The typical Agitated Thin Film Evaporator consists of a tubular heat transfer area with an external heating jacket and a fast-revolving, inner rotor with flexible or rigid wiper elements. The driving speed is adapted to the product being handled, its particular specifications and task. The feed product is evenly distributed by the rotor and its wipers over the heating surface, forming a thin liquid film of uniform thickness. Highly turbulent swirls are produced at the tip of the rotor blades and wipers with intensive mixing and agitation of the product, as it comes into contact with the heating surface. This assures excellent heat transfer combined with constant renewal of the product film and provides an even heating and short residence time of the product through the heated zone
Some of the applications
- Chemical Processing and Manufacture
- Industrial and Municipal Landfill Mining and Ore Processing
- Oil & Gas Companies
- Power Generation
- Textile Companies
- Pharma Industries
- Food & Breweries
- Automobile Companies
- Chemical Companies
- Metal Platting Companies
- Mixed feed multi effect evaporator.