Zero Liquid Discharge (ZLD)

With the respect and promise to the environment, every type of industrial plant should comply with the current regulations of each sector, respecting the treatment of effluent and industrial water.

Introduction

With the respect and promise to the environment, every type of industrial plant should comply with the current regulations of each sector, respecting the treatment of effluent and industrial water.

Specifically, when regarding water treatment discharge parameters such as: conductivity, COD (Chemical Oxygen Demand), etc. Treatments can take into account: osmosis or nanofiltration, physical chemistry, biologicals, etc. A common method which allows for the combination of the aforementioned methods is evaporation. Evaporation consists of the distilling of water (light product) with the heavier compounds that it come with. Since water evaporation is quite costly from an energetic standpoint, multiple effect evaporation or mechanical steam recompression is normally used.

When using multiple effect technology, the steam or vapor generated within the equipment is driven directly to the next (piece of equipment / tank), therefore only a single evaporator has direct intake from the steam boiler, the rest use the vapor created within the equipment. In the mechanical vapor recompression technology, the steam created is driven towards a steam compressor, where it is compressed and it is then reintroduced in the evaporation installation.

Zean Engineering has extensive experience with both technologies regarding zero discharge, with the objective of reducing the discharge while minimizing energy costs. With the ability to work with dissolved solids and/or suspended solids, high organic matter content, temperature sensitive products, etc.

 

Description:

The installation is comprised of two or more evaporating equipment, each fitted with separator tanks, vacuum condenser, process pumps, vacuum, interconnecting piping, instrumentation, automation and control.

Plants can be provisioned in stainless steel 316L or corrosion resistant steels: Duplex 2205, 2507, Hastelloy, etc.

The commissioning can be done, depending on the size, in modular SKID plants to ease the assembly at the client’s installation. Furthermore, FAT tests can be carried out so that the client can verify both the equipment and assembly prior to shipment / delivery.

Zero discharge plant characteristics:

Production: from 100 lt/hr to 15.000 lt/hr.

Workload can be adapted based on necessities and requirements such as: falling film evaporators of the forced circulation type, the number of effects chosen depending on investment cost and energy yield, pressure or operating vacuum, etc.

As an energy source the following can be used: hot water, saturated steam, thermal oil. Our technical department at Zean can study the project and recommend what values should be used to maximize performance.

The advantages of ZLD technology:

  • Proven technology capable of working with solids and viscous products.
  • The materials used to construct it allow for corrosive dilutions (high inorganic salt concentrations).
  • Low energy cost: for example, for 1 Kg/hr of evaporated water 0.58 Kg/hr of steam is needed in the case of double effect. See attached table:
  • Modular SKID constructed plants facilitate destination assembly, especially if the final destination point is within explosive atmosphere classified areas.
CONSUMPTION TO EVAPORATE 1 KG OF WATER KG OF STEAM
SIMPLE EFFECT 1,1
DOUBLE EFFECT 0,58
TRIPLE EFFECT 0,4
QUADRUPLE EFFECT 0,3
QUINTUPLE EFFECT 0,27