Eutectic Freeze Crystallization

The Basics The basis of the eutectic freeze crystallization (EFC) process is the existence of the eutectic point. The eutectic point is a characteristic point in the phase diagram of a salt-water mixture. At the eutectic point an equilibrium exists between ice, salt and a solution with a specific concentration. This specific concentration is called the eutectic concentration and the temperature at which this equilibrium is found is the eutectic temperature.

Figure 1. A typical phase diagram for a salt-water system showing the eutectic point. See description in text below.

Figure 1 shows a typical phase diagram for a binary system (salt-water). In the case that an aqueous solution has exactly the eutectic concentration cooling the solution down towards its eutectic temperature will lead to the simultaneous crystallization of both ice and salt. However, in practice it is common that a solution has a salt concentration that is lower or higher than the eutectic concentration. In the former case ice will crystallize first when the temperature is decreased. Due to the formation of ice the salt concentration in the remaining liquid (the mother liquor) increases, which leads to a decrease in freezing point and by continued cooling the ice line is followed till the eutectic point is reached. This is represented by path A in figure 1. When the original salt concentration is higher than the eutectic concentration the opposite happens; first salt is crystallizing till the salt concentration of the mother liquor decreases to the eutectic concentration, from that moment on also ice will be formed. The locations of the eutectic points in a watersalt mixture is dependent on the type of ions in solution and can vary over a broad range (both in temperature as well as concentrations) for different systems.

Eutectic Freeze Crystallization
The Process The concept of eutectic freeze crystallization can be utilized as the working principle for a very efficient separation technology, the EFC-process. In figure 2 a simplified representation of the continuous EFC-process is given. An aqueous waste stream containing dissolved salt(s) is fed to a special EFC crystallizer. In this step ice and salt are crystallizing simultaneously at the eutectic temperature of this specific system. Separation of the produced ice and salt from the crystallizing solution (or mother liquor) is done by utilizing the density difference between the three phases present (i.e. ice, salt and mother liquor). In one particular crystallizer design, called the hybrid crystallizer, this gravitational separation is taking place inside the crystallizer. In the hybrid crystallizer ice is leaving from the top section and a salt slurry is extracted from the bottom section of the crystallizer. Other process designs may utilize a separate three phase settling device to realize the desired level of separation. The liquid in the product slurries is removed by mechanical operations (e.g. belt filtration, centrifuges, etc.) up to the desired level of product dryness. The extracted liquid is recycled back to the EFC process. In some cases, a bleed stream is required to remove trace components from the system, however the volume of this stream is very small compared to the incoming waste stream.

Figure 2. Schematic block scheme of the EFC process. A bleed stream is not necessarily required but can be added for process optimization.

Fields of Application

The range of water streams to which the EFC can be applied is immense. In theory, it can treat any water stream containing dissolved salts and even organics, producing extremely clean water and a high purity product. Examples are:

• Recovery of valuable inorganics from a process or a wastewater stream.

• Reducing the salt content of a wastewater stream to improve water reuse strategies.

• Treatment of reverse osmosis retentates.

• Solution mining of salt deposits.

• Treatment of mine tailings.

The benefits of using the EFC process are in many cases twofold. In the first place the problem of having a wastewater stream (e.g. disposal costs, loss of water, etc.) is solved. Secondly, the user of the EFC process is able to recover (valuable) products from its wastewater. The latter characteristic makes that the EFC process is not only a wastewater treatment technology, it can be seen as a high-quality salt production process as well. The companies and partners which have already shown serious interest in the EFC process are from the following sectors: • Oil & Gas industry

• Waste incineration

• Various chemical industries

• Recycling industry

• Agriculture

• Mining companies

• Research institute

Technologies for Zero Liquid Discharge

Industries generally produce various types of wastewater and the wastewater characteristics and volume are industry and manufacturing process specific. Automotive and General Engineering industries produce difficult to treat waste waters like Waste Metal Working Fluids, Parts Cleaning, Electro Plating, Painting, Surface Pre-treatment, Electrodeposition coating, spray Painting, Die Casting etc. Some of the waste streams contain even toxic pollutants such as Heavy Metals, Cyanide, Phenols etc. which need to be removed to the lowest possible value to protect the environment. The present Pollution control regulatory norms expect the industries to strictly adhere to prescribed discharge norms and, in some cases, insist on zero liquid discharge system to ensure total compliance.

In achieving this, building a functional and effective wastewater treatment system will be essential – not only for meeting corporate sustainability goals but also for the preservation of the ecosystem as well as and in order to stay compliant with the governing laws and regulations. With that in mind, here are the principal considerations you need to take into account when choosing a wastewater treatment system and zero liquid discharge system.

Zero Liquid Discharge : ZLD is both Capex and Opex intensive. There are several project drivers for implementing ZLD in your company such as
a) Pollution control Regulatory requirement
b) Corporate Sustainability and Cleaner production goals
c) Customer requirement for Total compliance to prevent their supply chain disruption Treated water cannot be used for irrigation due to water quality problems
d) Fresh Water scarcity
e) Fresh water cost
f) Fresh water treatment cost
g) Existing Wastewater treatment is inadequate, inconsistent, complex and is expensive and the treated water is not suitable enough to be sent for ZLD system.
h) Volumes is high and hence the Capex and Opex for the system is high
i) No public sewer to discharge
j) Inadequate irrigation (gardening) land to use the treated wastewater
k) All of the above factors

Deciding on the right treatment ZLD system

Implementing the Wastewater treatment, Zero Liquid Discharge and Reuse system requires careful consideration to many aspects such as
a) The type and characteristics of waste streams
b) Flow and Volume of waste streams
c) Centralised or decentralised waste treatment approach – Many individual streams sometimes cannot be combined together and treated since the nature of pollutants present in the waste water will require specialised independent treatment approach. Stream segregation and decentralised approach is recommended in such cases.
d) Eliminating the waste source – is it more cost effective to eliminate waste or to manage it after it has been generated?
e) Minimising the wastewater volume – adopting better water management practice, better more efficient water treatment technologies, adopting closed loop recycling, better process control etc.
f) Upgrading the existing system to more efficient modern wastewater treatment based on Best Available Disruptive Technologies

What to keep in mind when installing a new treatment system

There are numerous considerations to note when looking for and installing a new wastewater treatment system, of which the capacity and the location of the system itself will be essential. Moreover, the quality of the effluent has to meet the safety standards issued by the regulatory bodies in your area. Finding the best wastewater treatment system and zero liquid discharge system for your company’s needs can be tricky, and the decision will depend on a myriad of factors. You will need to take into account the type and size of the manufacturing processes, waste water characteristics and the number of wastewater-generating units, daily wastewater volumes, and peak and off-season volumes as well. You want to install an efficient system that will save precious resources and help preserve the environment.

The wastewater produced by your company must meet the environmental standards of its location in order to ensure that your business is not harming the environment. Should the effluent fall below standard levels, there could be business-crippling ramifications including show cause notices, fines, closure, bad publicity, Poor public perceptions, expansion, customer confidence (possibility of supply chain interruption as many Indian and Overseas customers look for Total environmental compliance and ) etc. Given the fact that environmental protection is of the utmost importance for the survival of the hotel, you will need to follow strict environmental protection regulations. Depending on your location, you might even have to obtain a permit to discharge treated wastewater. The good thing is that abiding by the environmental protection rules will help your business thrive and expand in the long run, as you will be able to attract more confidence and create a brand that is respected by the public!

Few questions to ask yourselves to ascertain the ZLD project driver and implementation!

1. What are my project drivers?
2. How do I meet the project drivers?
3. Have I consulted all the stake holders in your organisation including Corporate, projects, Production, R&D, quality assurance, quality control, Maintenance, EHS, sales, Marketing, Business development etc?
4. Do I have adequate financial resources?
5. What is the project implementation time-line? Do I have adequate time to implement it? If not what alternatives do I Have?
6. Do I have adequate and skilled manpower resources? Are my people having adequate domain knowledge to support a sound decision-making process? Have I formed a project implementation team and do they have adequate domain knowledge? Do they need training and skill development?
7. Can the existing water treatment and wastewater system be replaced or upgraded with better more efficient technology to improve process control, reduce secondary waste, energy, chemical, maintenance, labour, sludge disposal costs?
8. Since the treated water is to be used as feed to ZLD system what impact it will have on the selection of ZLD process technology, Size, Complexity, Capex and Opex?
9. Have I identified the process in which the final treated water will be reused? Can I reuse it in single process or in multiple processes? If reuse in multiple processes are to be met do I have all the necessary information? Have I consulted the production department?
10. What is the quality of treated water that I need to meet to reuse in identified Target reuse application?
11. Have I identified all the water quality, quantity attributes? Can I meet all the Physio-chemical water quality attributes to be met including colour, odour, organic, inorganic, gaseous, water temperature, microbial aspects to name a few?
12. Have I done a Risk assessment to determine what can go wrong and how to factor in this risk factors to reduce or eliminate the risks?
13. Does the selected system meet a) process safety b) Equipment safety c) Operator and facility safety?
14. Do I have adequate land /space available to install / upgrade the existing system ? 15. Do I have necessary infrastructure, Utilities available to meet the ZLD project requirement?
16. Is my current practices and controls adequate or do I have to improve to eliminate or minimise the waste generation?
17. If my current practices inadequate can I improve? How and in which areas? Is their scope for waste minimisation (Volume reduction)? 18. Is my existing treatment system technology simple, effective, consistent, flexible and meets the treatment goals?
19. Do I have a Real Time IIoT enabled water quality monitoring system in place to measure critical water quality attributes, Set control and alert parameters , do trending, data logging, Generate alerts, generate automatic reports, communicate with various stake holders?
20. What constraints do I have? have I identified all the constrains? Finance, Manpower, land, time, Utilities, external and internal factors etc?
21. Do I need an internal consultant or external consultant? Can I get help from within the organisation but from other manufacturing facilities located elsewhere? Can I gain experience from them?
22. Can the selected technology meet all the desired water quality attributes consistently? Is it proven technology? Is it installed elsewhere? Do I need a feasibility, treatability and pilot study? Have I evaluated all the available technology options? Have I screened the technologies and narrowed down to one or two technologies? Do I need to go for a pilot system for onsite site trials?
23. Is the technology available indigenously or to be sourced from overseas? Is the vendor has adequate experience and domain knowledge in meeting the requirement? Can they provide necessary after sales service and provide adequate technical and troubleshooting support if required?
24. There are many unknown unknown things that may come up during as well as post project implementation and one should be prepared to address the same.

There are many such questions that will need a critical review and to be addressed if the ZLD project to be completed successfully! Failure to carefully address the above seriously will decide the fate of the project – A good Asset or Liability? An Apple or a Lemon in your hand!

Contact us today for the Right advice and solution because “ The right advice is half the battle won”