Q&As about Zero Liquid Discharge (ZLD) evaporation

Q: How do you know if a waste heat source will work for ZLD evaporation?

A: We look at several different criteria including temperature, quality (moisture content), and the amount of heat (kW). From this, we can determine how to best recover the heat and if it makes sense to use the waste heat source for ZLD evaporation. We can recover waste heat from various sources such as dryers, engine jacket water, and engine exhaust.


Q: Can you provide an approximate timeline to develop a ZLD project, from initial conversations to installation and start-up?

A: Once the order is placed, a ZLD System takes 36 to 46 weeks to manufacture. Manufacturing time is mostly a function of the size and materials required. After manufacturing is complete, shipping requires another four to six weeks, then one to two weeks for installation, and another one to two weeks for commissioning. You can expect ZLD projects will require well over a year, from planning through to implementation. This may vary, depending on the amount of time required to finalize the order.


Q: Can these be designed for "lethal service" or hazardous service, which involves evaporation of flammable or toxic material?

A: Yes.


Q: What is the estimated specific energy consumption in kWh/m3 for a mechanical vapour recompression unit?

A: Approximately 65 to 75 kWh/t evaporated, depending on the application. Note that power may vary significantly, depending on the specific requirements of the application.


Q: Do you clean ZLD systems in place? How do you choose the Cleaning-in-Place (CIP) media?

A: Yes, Alfa Laval ZLD systems can undergo Cleaning-in-Place. The CIP media is selected based on the specific application chemistry and type of fouling observed.


Q: What is the maximum concentration that can be achieved using a ZLD AlfaFlash and decanter?

A: The final effluent concentration is based on the specific application chemistry. For sodium chloride-based wastewaters, 85 to 95 wt% total solids (TS) final concentration is achievable.


Q: How do you prevent crystallization fouling when concentrating calcium-rich solutions?

A: The Alfa Laval AlfaFlash ZLD is a plate evaporator working as a forced recirculation flash evaporator that uses high recirculation flow rates and a specialized heat transfer geometry. This generates very high shear stress due to high liquid velocity and turbulence within the evaporator heat exchanger. This maintains a continuous self-cleaning effect that prevents solids from accumulating on the heat transfer surfaces.


Q: Do the ZLD crystallizer systems require “seeding” prior to start-up?

A: No, the Alfa Laval AlfaFlash ZLD does not require 'seeding' prior to start-up.


Q: Can the system operate under vacuum?

A: Yes, the AlfaFlash ZLD typically operates under vacuum. Alfa Laval ZLD systems operate at temperatures between 45°C and 100°C, depending on the design and the specific requirements of the application.


Q: Once I was attempting to model a multi-effect ZLD desalination plant but encountered many issues when converging the heterogeneous evaporation stages due to all the different species. Which software do you prefer? Do you differentiate between speciation at equilibrium, and how is that related to how the solids keep on forming and precipitating?

A: We use the OLI Stream Analyzer to model the evaporator/crystallizer chemistry. With this software, we can conduct a wastewater analysis and model characteristics, such as density, boiling point elevation, and the solubility of various solids. This helps us to design the system for the specific conditions of the application.


Q: What is the range of flow rates that can be treated by a single AlfaFlash ZLD module?

A: AlfaFlash ZLD modules range in size from 1 to 50 m3/h.


Q: Do you have experience in concentrating biological sludge with zero emissions?

A: Yes, we do have a high level of experience in concentrating organic-based waste. Please feel free to contact us if you would like to learn more.


Q: Have you supplied a ZLD system for contaminated rainwater to recover good quality water?

A: We have not yet worked on this specific application but AlfaFlash ZLD could be used here. If the contaminants are in low concentrations, it may be more practical to pre-concentrate the rainwater using reverse osmosis. Alfa Laval can offer integrated systems that incorporate a range of technologies to optimize a specific process for water recovery from contaminated rainwater.