Today we show you a new success in water treatment consisting of a turn-key project for a metallic surface treatment company. Our client, an international leader in this sector, has recently open a new facility in Spain. Because of this, it found itself in need of an Integral Water Cycle engineering and supplier in order to adequate raw water to be used withing the new coating processes and treat the effluent generated by those activities to comply with national laws and standards before it could be delivered into the sanitation network.ç
Turn-key project for the metallic surface treatment industry
Basically, the new coating processes for metallic pieces consist of three independent production lines, each of them composed by a different number of pools, disposed one after another.
These three lines are designed to work 16 h/day non-stop, which means they need a high disponibility of water. At the same time, the process generates a contaminated effluent continuously, which it needs to be treated before it goes out the plant towards the sanitation network.
After a high in deep research of all the phenomena carried out within those metallic coating processes, the engineering department of J. Huesa came up with the best technical, environmental, and cost-effective solution.
Raw Water Treatment Plant
The main goal of this whole system consists in reducing the salinity from the raw water by using a reverse osmosis (RO) and ionic exchange resin (DI) in order to be able to use it as “CLASE A” water in the metal surface finishing treatment pools.
As mentioned before, the water quality needs to match the “CLASE A” standard (*). Besides, the water used in the closed loop of the pools where the metallic pieces are fully cleaned need to have a conductivity less than 10 uS/cm² at all time, for this part of the process works 24/7.
(*) Water Classes
We start from a raw water tank which works as a buffer. The water is pre-treated through a 30 m³/h sand filter, which captures the biggest suspended solids, before entering the reverse osmosis system. At the inlet of the osmosis skid, chemical dosage to the filtered water is carried out to avoid free chlorine formation as well as salt deposition over the osmosis membranes. This ensures the membranes do not lose efficiency and ensure their durability.
To remove the smallest colloids from the water, a security cartridge filter of 5 microns is used. Only when water is fully pre-treatment it is pressurized thanks to AISI 316 centrifugal pump and flows into the reverse osmosis pressure vessels.
The reverse osmosis consists of 3+2 two stages in serial arrangement, with polyamide spiral-wound membranes for low pressure applications, mounted inside fibre-reinforced polyester (FRP) vessels. This system offers up to 70-75% of efficiency.
Water from RO is accumulated in a 50 m³ FRP tank. A level transmitter is installed to let the PLC manage the star-stop manoeuvres of the osmosis. A multi-pump pressure group is used to feed osmotized water wherever is needed.
- Re-filling of the metallic surface treatment pools.
- Water for the pulverized nozzles of the metallic pieces pre-cleaning pools.
- Water reposition for the closed loop of the demineralization system.
- Water for resin regenerations of the demineralization system.
Moving on to the next process, a polishing water treatment was implemented to keep low salinity in the water used in the closed loop composed by the metallic pieces full-cleaning pools and their overflow catch basin. This time, J. Huesa decided to implement two ion exchange systems consisting of a cation – anion demineralization, capable of treating 40 m³/h each. Before water flows through the resin, it is filtered by an activated charcoal fixed bed.
Ion exchange phenomena takes place in two different moments:
- While DI is in service, H+ and OH- ions found within the resin are exchanged with the ions to remove from the feed water. This happens until there are not more H+ and OH- ions withing the resin to be exchanged.
- Regeneration cycle: acid and alkaline are dosage to the cationic and anionic resins for these to be fully charged of H+ y OH- ions, respectively.
Usually, the acid and alkaline used during the regeneration are chloridric acid (33% w/w) and caustic soda (50% w/w). The complete regeneration cycles consist in:
- Chemical dosage
- Slow rinse
- Fast rinse
Wastewater from regeneration cycles is accumulated in a 50 m³ buffer tank. The effluent is treated before it flows to the local sanitation network.
The osmosis and demineralization plant includes many instruments (pneumatic actuators, pressure switches and transmitters, flowmeters, conductivity meters…), all managed by a single control cabinet placed in the same osmosis skid. A programmable logic controller (PLC) is included inside that cabinet as well as the human-machine interface (HMI). The I&C department from J. Huesa has designed the control cabinet to be fully integrated in a global SCADA quick and easily.
Inlet-outlets data table
|Average flow to RO||30 m3/h|
|Wastewater outlet||7–9 m³/h|
|Osmotized water outlet||21-23 m³/h|
|Average flow to DI||40 + 40 m3/h|
|Wastewater per regeneration||30 m³|
|Work hours||16 h/día|
|Permeate buffer tank||50 m3|
|Buffer tank for wastewater from regenerations||50 m3|
Wastewater Treatment Plant
The water from the pools needs to be prepared before it reaches the local sanitation network. In order to do that, J. Huesa has designed a chemical-physical water treatment which produces a free-of-solids overflow with a good enough quality to be wasted directly into the closest sanitation network. Solids are separated from the liquid and collected as an inert “cake”, ready to be managed by an accredited company.
Design has been developed considering the nature and complexities of the different effluents. Because of that, to optimize the functioning of this plant, concentrated effluents were accumulated separately in tanks of 25 m³ each, preventing them from mixing. From there, these concentrates are dosage into the treatment system. This process consists of two stages:
- During the first stage, dangerous components from the effluents are neutralized and prepared to be removed from the liquid phase so legal waste parameter of the overflow are achieved.
- Solids precipitation is carried out during the second stage, as well as their decantation and thickening. The “cake” obtained after the filtration is chemically inert and shall be managed by some accredited company.
This plant is configured to treat up to 30 m³/h of effluent.
Knowing that wastewater that cannot be treated this way has to be managed by an accredited company (which means an extra-cost), the plant includes a forced evaporator with 60-70 l/h (≈ 1-1,5 m³/day) of capacity. This makes a high concentrated effluent removing water from the solution, which reduce considerably the extra cost of waste managing. To minimize the energy consumption, the evaporator includes a mechanical vacuum pump and compressor.
Concentrator process flow diagram