WET owns the know-how for a wide range of technologies applicable to the industrial treatment of process water. The know how is originated by the experience of Dr Marco Rognoni in over 30 years of activity in this field,
The proprietary technologies of WET are grouped as follow:
- Sea Water Desalination (by thermal processes)
- Ion Exchange
- De-oiling, Filtration and others
1. Sea Water Desalination
The thermal processes of desalination are appreciated for the high quality of the distillate and for the availability of the plants, ease in operation and maintenance, as required for the severe duties in the industrial service in Power Plants, Refineries and Petrochemical complexes.
Several thermal processes are available, and the correct choice of the most convenient one should be suited in compliance with the specific requirement of each site, project and performances required.
WET owns references and know-how for each of the thermal processes
1.1 MSF (Multi- Stage-Flash)
MSF is the most popular process of thermal desalination. In spite of the highest investment cost and rather high running costs, this technology is still preferred by many users especially for large size units, owing to the best reliability and easy operation and maintenance
MSF desalination Plant (supply by Sowit) designed by Dr Rognoni
1.2 MED (Multiple-Effect-Distillation)
MED (without thermocompressor) is the thermal process that requires input steam of very low pressure and therefore of the minimum value. Even the exhaust vapour from the turbines output can be used to feed MED plants at the pressure equal or close to the condensation pressure. The rather low thermal efficiency require for quite large plants, with impact on the investment costs and on the lay-out
Small MED plant (supply by SWS) designed by Dr Rognoni
1.3 TVC (Thermal-Vapour-Compression).
The thermocompressor coupled to MED evaporators improves the efficiency of the plant, thus reducing the investment costs and the size of the plant. In this case the feeding steam should be available at the pressure of at least about 3 barg. Nowadays TVC is the process preferred in the majority of industrial projects, owing to the reduced investment costs and the very high quality of the distillate.
TVC Plant (supply by SWS&GB) designed by Dr Rognoni
1.4 MVC (Mechanical-Vapour-Compression)
The mechanical compressor ensures much better efficiency than the thermocompressor, and requires less energy for its operation. Anyway the energy required is electrical, thus having much more value than the equivalent thermal, and therefore causing more expensive running costs. This process is preferred by the users when no steam is available and still the high reliability of thermal desalination is required.
MVC Plant (supply by SWS) designed by Dr Rognoni
1.5 LTF (Low-Temperature-Flash) also named LTTD and sometimes in other ways
LTF is the innovative process developed first by Dr Rognoni with the successful installation at the Power Plant of Piombino (Italy) for the recovery of the waste energy rejected by the turbine condensers. Similar process was implemented in India for the exploitation of the temperature of the surface of the ocean. The flash of any warm water and the condensation of the flashed vapour with cooling water can be the best solution in many industrial application, with limited costs for both the investment and the operation.
WET is experienced in various deaeration process, either thermal or in vacuum. WET technology allows for the maximum degree of de-oxygenation achieved in the mechanical equipment. If required the performance can be completed by the injection of chemicals (oxygen scavenger), and the chemical dosing system may be included in WET scope.
2.1 Thermal Tray Process (also named Spray and Tray)
The “Tray” deaeration process is the most commonly applied for the severe duty required in the production of BFW (Boiler Feed Water). The design of WET has been successfully proven in application to power generation, of capacity from 10 T/h up to nearly 2000 T/h in a single unit, in full compliance with the applicable international codes (ASME, HEI, NACE). The high efficiency of WET design and of the relevant process internals makes the units extremely competitive and successful with the full guarantee of the required performances for the degree of de-oxygenation, water heating, storage capacity, long working life of the equipment, trouble free operation.
Large Deaerator being shipped (supply by SWS)
2.2 Thermal Spray Process
The “Spray” deaerators are not recommended by HEI, but are in some cases accepted by end users as cheap alternative of Tray deaerators applicable in non severe conditions. In this process the deaeration takes place in the spray of the feeding water and is completed in the tank during the storage time. Hence no degasifying tower is necessary, thus cutting the fabrication costs quite remarkably
2.3 Thermal Flash Process
The flash is a very effective deaeration process by nature, with the immediate transfer of any dissolved gas from the liquid phase into the gas phase. Its application is therefore recommended whenever the working conditions are adequate for it
2.4 Vacuum Deaeration Process
The vacuum deaeration is applied when the required duty does not include any heating of the processed water. The stripping of the dissolved gas is therefore draught by the vacuum and driven to the atmosphere by a devoted vacuum system of adequate configuration. This process is typically requested in the oil&gas industry for various applications
- Deaeration of the process water feeding the desalters (small capacity)
- Deaeration of the water to be injected in the oil wells (large capacity)
The working vacuum is typically very deep and the relevant vacuum system is accordingly a crucial issue in the design of the deaeration system. WET is experienced also in the optimization of the vacuum conditions necessary to reduce the dusty of the vacuum system, in compliance with the performances required.
3. Ion Exchange
Ion Exchange resins are extensively used in water treatment for the de-ionization service. WET is experienced in each application, and in any necessary pre-treatment too, as may be necessary for the conditioning of the feeding water and the protection of the resins from the pollutants of the water, such as the removal of iron, chlorine and traces of oil.
3.1 Raw Water Demineralization
The typical arrangement consists of Cation resin exchangers, de-carbonating tower, Anion resin exchangers. Finishing mixed beds are added if necessary. The plant may also include the regeneration facilities for the resins and the neutralization system for the effluents. The arrangement is quite usual and the know-how of WET is mainly focused to those details of the plants and to the recommended brand of critical equipment that make the operation stable and reliable, ensuring the longest trouble free working life.
Large Demineralization plant (supply by SWS)
3.2 Polishing of Distillate
The distillate produced by the thermal desalination plant is typically of very high quality. However its use for specifically critical service like make-up to HP boilers, requires for the further polishing by mixed resins beds. In such case, the service is typically heavy duty and the availability of the plant is requested maximum. Hence the quality of the design is essential.
Polisher of desalinated water designed by Dr Rognoni (supply by Sowit)
3.3 Polishing of the Condensate
The recycling condensate of the steam cycle in either power plants or auxiliary boilers require to be continuously polished and the highest quality of the water ensured accordingly. These units are installed inside the steam cycle and the in-line service requires for the total availability, that is ensured by the top quality of the plant design and by the reliability of each component. WET is experienced in the design of the two main types of Condensate Polishing Units (CPU):
- Internal regeneration of the resins:
The saturated resins are separated, regenerated and re-mixed in the same filter where normal operation takes place, after isolating the filter in off-line mode. The regeneration may require from 3 to 5 hours and therefore a spare filter is typically installed to replace the production of the off-line ones. This arrangement is normally preferred for duties that are not extremely severe, because of its limited investment cost and minimum impact on the total lay-out area.
- External regeneration of the resins:
The saturated resins are transferred from the working filters to an external station where the separation and the regeneration takes place This arrangement is preferred for the service to HP power cycles because ensures the shortest time off of each resin filter on line when the saturated resins are to be replaced by regenerated ones. Moreover the regenerants (soda and acid) are used in a separate station without any risk of contamination of the recycling condensate.
External regeneration station of CPU (supply by SWS)
4. De-oiling, Filtration and others
WET is well experienced in any water process that may be necessary as pre-treatment or post-treatment, as ancillary units to the water processing scheme:
Deoiling of the water is often necessary before its re-use or disposal. Many processes are available in WET, to be chosen according to the quantity of oil to be separated and to the degree of allowed residual oil content.
- API separators are adequate to process large flows of highly contaminated water, and the effluents (with reduced oil content) can be treated further if necessary. The design of WET is in compliance with the API publication 421 (1990)
- CPI (Corrugated Plates Interceptors) can ensure better efficiency than API separators in more compact units, still exploiting the difference in density between water and oil. The installed lamellas ensure the laminar flow of the water for the enhanced fast separation of the oil droplets, and allows typically to limit the residual oil below 10 – 25 ppm
- Oil flotators ensure the gravity separation of the oil droplets through the gas adherence to them and the relevant flotation effect. The residual oil can be reduced below 5 ppm. The gas used in oil flotators are typically air (safest arrangement) or natural gas if available (most efficient arrangement, but requiring safety precautions))
- Coalescing media can eliminate the smallest droplets of oil by embedding them into the oily film formed on the surface of oleophilic matters. Nutshell filters and oleophilic resin filters can ensure the residual oil content below 1 ppm
- Activated carbons eliminate any trace of oil through the complete adsorption of it, until the carbons become saturated. When saturated, the carbons must be replaced by regenerated ones and the regeneration costs debited to the de-oiling process. Therefore the activated carbons are recommended only when the inflowing oil content is rather small and the outflowing is requested zero. Very often CPI or oil flotators are installed before the activated carbons, thus ensuring the longest working cycle of the carbons
Small CPI unit designed by M.Rognoni (supply by SWS)
Filtration is quite a common and well known process, and WET is able to calculate the most convenient arrangement in any working condition and according to any specified duty.
- The most common filtration media is the sand, that is available in several controlled meshes and in several qualities of composition (silica and quartz). WET is experienced in optimizing the bed composition and the filter sizing, in the arrangement either vertical or horizontal.
Horizontal sand filters in parallel (supply by SWS)
- In the case of traces of oily matters in the water, the sand should be protected from sticky contamination by a bed of anthracite (dual media or multimedia filters). The anthracite is disposed when saturated. WET is experienced in recommending the proper sizing and the way of adding anthracite, either as power during the progress of the filtration or as additional bed overlayed on the sand.
- Micro-cartridges filtration is recommended when the size of the solid particles to be filtrated should not exceed a limited number of microns (typically fro 2 to 10). WET owns the valuable know-how of backwashing the cartridges with air pulses, thus reducing the backwash time and the backwash water consumption by over 90% to a negligible extent. This process is typically used in severe services like the treatment of the condensate in Power Plants. The elimination of the iron content (micro-filtration of the flocs) in some cases allows to recycle the condensate even without any polishing treatment, with negligible water consumption for backwashing
Cartridges microfiltration with backwash by air pulses (supply by SWS)
Dr Rognoni invented a novel filtration system (patent owned by SWS in J.V with delta Engg.) in which the sand is replaced by poplypropylene floating particles. Filtration therefore takes place from bottom to top and the backwash from top to bottom, such to be boosted by gravity. In this way a number of advantages are ensured including the dramatical reduction of the waste effluents and the reduced backwash time. The reduced backwash time (from 30 min to only 5 min) may even allow not to install any spare filter and ensure the continuity of the flow with a rather small buffer tank.
FIF pilot plant being shop tested
4.3 Potabilization of desalinated water
The desalinated water may require for the specific potabilization treatment, mostly consisting in the reminaralization (addition of potabilising salts). Various remineralisation technologies are available in WET,
- Dosing of CaCl2 and NaHCO3 solutions, in stoichiometric ratio
- Addition of Caustic Ca(OH)2 and CO2
- Acidification with CO2 and filtration through CaCO3 bed
The recovery of CO2 from the vent of the thermal desalination plants is often the most convenient source of carbon dioxide for the remineralisation process
4.4 Chemical conditioning
WET designs and optimizes the chemical dosing system for various chemicals, such as oxygen scavenger, hypochlorite, antiscalant, antifoam, BFW additives.
Chlorination is the most common biocide treatment for various types of water, including potabilised. The chlorination may be carried out according to several technologies, such as:
- Injection of hypochlorite, either as solution or solid prills
- Injection of chlorine gas, typically stored in pressure tanks
- Generation of hypochlorite from sea water by electrochlorination.
Continuous dosage and shock dosing are specified according to the biocide required effectiveness
De-chlorination is necessary as pre-treatment for some water processes, such as demineralization by ion exchange resins. The strong oxidation capacity of chlorine is destructive for the resins material and for other fabrication materials of water treatment plants. De-chlorination is carried out according to two main technologies:
- Dosing of scavenging compounds. The most typical is sodium bisulphite.
- Filtration through a bed of activated carbons. The activated carbons convert chlorine into chlorides, that can be processed downstream like any natural salinity content..
4.7 Iron removal
Among other services, iron removal units are often recommended for the pre-treatment of the water to be demineralised in ion exchange filters. The presence of iron traces may cause the fast aging of the resins, and therefore the previous iron removal may become necessary. The oxygenation of the water at controlled pH condition, separates the iron in the form of flocs tat can be filtrated and disposed
4.8 pH adjustment
The controlled dosage of either acid or caustic corrects the pH as necessary to attain either neutralization or the requested pH value. The dosage optimization may be crucial in the case of buffered solutions, and the applicable materials and equipment correctly selected
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