Condensate polishing is a proven method of producing high purity, which can be economically returned to an ultra-pure state by simple polishing rather than using fresh make up process water.
The design of condensate polishing system will be influenced by:
I. Steam cycles,
II. Site conditions,
III. Space considerations,
IV. Cooling water availability and temperature,
Material of construction used in condensers,
- Ancillary equipment’s
Lastly by engineering requirements by the Client
The most widely used design, all proposed by KASRAVAND are:
- Pre coat filter demineralizer’s o, using powdered ion exchange resins for simultaneous removal of dissolved and suspended solids;
- High rate bead type cationic units followed by high rate bead type mixed bed demineralizers;
- High rate mixed bed alone or in combination with pre coat filter demineralizers.
Condensate polishing systems for the super critical boilers typically feature external regeneration. Once the service cycle has finished, the resin is transferred from the service vessels for regeneration, and transferred back once regeneration is complete. This arrangement ensures that no regeneration chemicals can enter the condensate system or the boilers.
Condensate polishing systems for other applications typically feature in-situ regeneration using conventional equipment.
Two type of condensate will be produced in plants:
Hot Condensate: This is condensate produced from steam reboilers / heat exchangers. Process Condensate shall be generated at MP and LP levels and these shall be routed separately to the respective vessels in the Condensate Recovery System composed by several sections, each one located and dedicated to different Process Units areas.
Recovered condensate shall be then routed and treated in the Condensate Polishing Unit (CPU).
The possibility of oil contamination in this type of condensate depends on the reciprocal, process and steam sides, operating pressures at the exchangers. In case the process side operating pressure is lower than the steam side one, the possibility of condensate contamination with the process fluid is minimal and the condensate produced from such a source can be deemed ‘clean condensate’; on the contrary, in case the process side operating pressure is higher than the one on the steam side, the possibility of contamination of condensate with process organic fluid always exists and the condensate produced from such a source is deemed ‘suspect condensate’.
The “suspect” and the “clean” hot condensates will be collected and respectively routed to the CPU or recycled to the Boiler Feed Water preparation: this will allow the continuous treating of the “suspect” stream and the direct feed of the hot “clean” stream to the Deaerator, minimizing losses in case of partial dumping: it is to be noted that, in case of dissolved solids contamination, part of this last condensate, normally “clean”, may be routed to the Mixed Beds Polishing installation, which will be properly sized for this additional stream.
For the “suspect” hot condensate a Total Organic Carbon (TOC) monitoring system shall be provided at the outlet of each of the Condensate recovery systems Stations (CRS), in order to allow dumping of contaminated condensate upstream the common collecting header: nevertheless, a leakage of oil into the recovered condensate stream is deemed not avoidable.
Considering that nearly no oil content is allowed for the water feeding the Steam Generation Boilers, a de-oiling treatment (through oleophilic resins) shall be provided, before recycling the recovered suspect condensate to the Deaerator for the preparation of Boiler Feed Water.
An additional kind of contamination of the condensate is due to possible dissolved solids content.
Therefore, in order to assure the required quality of the Boiler Feed Water and of the produced steam, feeding the turbines, a Polishing Treatment on Mixed Beds Filters preceded by an “organics safety guard” through Activated Carbon shall be also provided.
Cold Condensate: Due to the nature of the cold condensate no dissolved solids are normally present in this stream; nevertheless as the condensing pressure is lower than the cooling water pressure, steam condensate produced at the surface condenser of a condensing type steam turbine is suspect in quality. Due to the above considerations, and in order to optimize the CPU configuration, the Cold Condensate shall be routed to the Polished Condensate Tank, after a dedicated separated Polishing treatment on Mixed Beds Filters, with the provision to dump it in case of high conductivity. Cold condensate is therefore collected and kept separated from the hot suspect and clean condensate.
In case of heavy contamination (as TDS content), due to the short response time of a typical Conductivity Analyser, any increase of conductivity will be promptly revealed, so that an effective dump of the contaminated stream can be done quite near to the contamination source, well before sending it to the Deaerator.
PROCESS CONDENSATE DE-OILING
The De-oiling section shall be composed of a first section of treatment parallel lines in operation, based on Oleophilic resins filters technology, and a further finishing treatment by an Activated Carbon Filters (ACF) guard station, just upstream the MB polishing unit.
For proper operation of the Condensate polishing unit, it is important that the recovered hot Condensate fed to this unit for treatment, is properly cooled downstream the treatment on Oleophilic Resin beds, before routing it to the ion exchanging Resin beds.
To this purpose, a Plate Heat Exchanger (Hot untreated Condensate/polished Condensate), followed by a trim Cooler (untreated Condensate/Sea water), will be provided to cool down to the proper temperature, the incoming Condensate, before routing it to the storage Tanks and further treatment.
CONDENSATE STORAGE & PUMPING
Storage Tanks for storing unpolished process Condensate shall be provided. These Tanks shall have not less than 8 hours storage capacity each, based on the total max process Condensate fed to treatment from the Recovery Unit.
Separated oil collection facility will be provided at this storage.
PROCESS CONDENSATE hc-ADSORBING
Activated Carbon Filters (ACF) will be provided, as a safe guard for the downstream MB Resins, and designed to treat steam condensate from the upstream storage at the design flowrate, so to reduce any organic compounds, possibly present in recovered Condensate stream.
Polished Condensate shall be used for the backwashing of ACF Resin Filters.
MIXED BED POLISHERS
The recovered de-oiled process Condensate from the ACF, will be routed to the Mixed Bed ion exchanging resins for further polishing treatment. .
The Cation exchange resin will be regenerated by H2SO4 solution; the anion exchange resin will be regenerated by NaOH solution.