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Evaporators
The evaporator & crystalliser includes 19 tanks and 15 heat exchangers of different sizes
some 100 different lines of piping of various diameters . The system includes a pre-heater , degasser , evaporator and crystallisation sections , together with a final condenser . In order to meet the challenging specification , including the highly corrosive nature of the sodium chloride-rich brine , which is produced by the client ’ s reverse osmosis system , the HRS system incorporates a number of non-standard features . Firstly , the heat exchangers have been constructed from titanium , rather than HRS ’ s standard construction materials of AISI 304 and AISI 316L stainless steel . Secondly , rather than using a traditional five-effect forced recirculation evaporator , this system uses a five-stage multistage flash evaporator comprising the following elements :
• Preheater
• De-gasser
• Main recirculating pump
• Five sequential heat exchanger sections
• Five sequential flash tanks
• Final condenser
The benefits of this flash evaporator over forced recirculation are that in only requires a single recirculation pump , instead of one pump for each effect , and that the pump is installed at the lowest temperature level in the loop , meaning less risk of cavitation and fewer issues with corrosion – a important consideration given the nature of the brine being handled . Finally , this design means that a lower overall recirculation rate is required , meaning less energy is required for the pumping process , improving overall process energy efficiency . Once the brine has passed through the five-stage evaporator , the now concentrated brine is sent to a crystalliser unit , which removes the last of the distillate
Because of the highly corrosive nature of the sodium chloriderich brine the heat exchangers have been constructed from titanium rather than stainless steel
and produces 700 kg per hour of humid crystals ( at approximately 70 % dry matter ). The crystalliser unit itself comprises a two-stage flash evaporator with :
• Main recirculating pump
• Two sequential heat exchanger sections
• Flash tank without crystal separation
• Flash tank with crystal separation
• Final condenser ( the system actually uses the same condenser as the evaporator section described above )
Once the crystals have been formed , the crystal ‘ slurry ’ is transferred to the client ’ s mechanical separator , where the humid crystals are extracted and any remaining saturated brine solution is returned to the crystalliser . As a result of this final crystallisation stage , no liquid from this process or waste stream will be discharged from the client ’ s site , making this a true ZLD effluent treatment solution .
Production , installation and commissioning From winning the order in early 2022 , it has taken 15 months for the multi-disciplinary HRS team , lead by Technical Sales Engineer Tomas Stiebe , to design the evaporator and crystalliser and construct it at the manufacturing hub in Murcia . The unit is currently undergoing final checks and testing and will then be partial dismantled for delivery to the client . It is expected to be delivered to site in May and will then be commissioned by HRS engineering staff later in the year . Once fully operational it will process nine tonnes of brine effluent per hour , producing 700 kg of humid crystals and returning all distillate water to the existing client processes . This system is the largest evaporator produced by HRS to date and builds on previous ZLD systems that the company has delivered to clients in Europe and further afield .
About HRS Heat Exchangers
Located in the UK , HRS Heat Exchangers is part of the EIL Group ( Exchanger Industries Limited ) which operates at the forefront of thermal technology . HRS offers innovative heat transfer solutions worldwide across a diverse range of industries . With more than 40 years ’ experience in the waste treatment and environmental sectors , specialising in the design and manufacture of an extensive range of turnkey systems and components , incorporating our corrugated tubular and scraped surface heat exchanger technology , HRS products are compliant with global design and industry standards . www . heat-exchanger-world . com Heat Exchanger World May 2023
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