L’élimination du COT prend de l’importance dans le secteur de l’énergie
Steam turbines of modern power plants operate at pressure levels higher and higher in order to optimize the yield of electrical energy. The organic compounds that enter the circle of water / steam are introduced into the carboxylic acid and carbon dioxide due to the harsh conditions (temperature, pressure) of the process. This results in an increase in the conductivity of the steam and a decrease in the pH value in the condensate. To ensure proper operation without high conductivity of steam and corrosion problems, should be supplied to the boiler feed water free of minerals and organics.
Limit values for total organic carbon (TOC) have become more stringent over the years for the reasons indicated above. In the past, there was no specification, only the rule * 10.10.10 applied. Since 1999, the TOC was limited to <200 ppb in the VGB / EU and <100 ppb in the US / Electric Power Research Institute. Currently, many projects face limits to <10ppb TOC!
Another important aspect to consider is the raw water source. For environmental reasons, it is increasingly necessary to use surface water sources such as reservoirs, lakes and rivers. Surface waters still contain a number of natural organic compounds such as humic acids, polysaccharides, natural hydrophobic compounds and low molecular weight compounds. While the TOC values of the groundwater is of the order of 1-5 ppm, typical values of surface waters range from 5 to 30 ppm TOC.
A survey in 1999 by DOC-Labor (Dr S. Huber) has evaluated more than 100 power plants (IX) in Europe. It turned out that by using groundwater as feed water, the boiler feed water always meets specifications (absence of fouling of the resin). With the surface of water used as feed water, only 60% of operated facilities meet specifications VGB, 10% meet the specifications EPRI and 30% displayed TOC levels> 200 ppb TOC with the fouling problem of the resin.
The treatment technologies typical surface water such as flocculation combined with mechanical filtration and activated carbon followed by ion exchange can usually reduce the TOC in a range of between 200 and 300 ppb. Unfortunately, ion exchange inadequately removes polysaccharides, hydrophobic compounds and neutral compounds in this stage of pre-treatment, and fouling of the resin occurs when the resins are often faced with high loads of organic materials.
A combination of the ultrafiltration reverse osmosis enables to further reduce the TOC boiler feed water to about 100 ppb. While it is easy enough to remove the POC (particulate organic carbon), parts of the DOC (dissolved organic carbon), especially compounds having a low molecular weight and little or no polarity, can pass through RO membranes ( reverse osmosis).
If TOC values below 100 ppb are required, improved technologies should be applied. One of these technologies is TOC-UV, a treatment using ultraviolet light at a wavelength of about 185 nm. Such UV radiation not only breaks the C-C bonds, but also generates hydroxyl (OH) radicals and other oxidizing compounds that help to break down organic materials to carboxylic acids or carbon dioxide, which are removed by a downstream bed Mixed ion exchange. Special UV lamps low and medium pressures are capable of producing this type of UV light.
Ovivo has a wide range of expertise in power plant projects and in the production of ultrapure water for semiconductor applications, and thus has the expertise needed to meet the growing challenges of supply ultrapure water for high pressure boiler systems. Right now, a project for a large European entrepreneur EPC (engineering, procurement and construction) is ongoing. A processing facility of boiler feed water with a capacity of 5 x 140 m³ / h Net using surface water as a source, will produce demineralized water with a TOC of <10 ppb, using a combination of our submerged ultrafiltration, reverse osmosis, UV-TOC and ion exchange systems.
* (> 10 MΩ · cm = <0.1 S / cm, <10 ppb SiO2, <10 ppb Na)