Water is definitely the most important media used to transfer energy from one source to another. Unfortunately the presence of dissolved gases in water could often be an issue because of the severe corrosion problems caused by oxygen and carbon dioxide to steel equipment and circuits. In particular water fed to the steam generators should be free from gases in order to prevent boilers and steam circuits from corrosion.
The thermo-physical deaeration process is by far the most applied technology when a reduction of oxygen to negligible concentrations is required. Dissolved gases are removed by reducing the partial pressure of oxygen and carbon dioxide over the liquid surface by replacing air with steam.
The degassing process is achieved in the deaerating tower where make-up water or oxygen-rich condensate are firstly atomised through “variable-area-spray-nozzles” in contact with the up-flowing steam. Water then falls on a set of special stainless steel packing that increases the contact surface between water and steam. Oxygen and carbon dioxide are stripped by the steam flow and vented through a calibrated orifice or a throttling valve. Deaerated water is collected in the storage tank so as to assure an adequate “Hold-up” time for the boilers downstream.
In order to extend the range of BONO ARTES’ Deaerators to an upper grade, in recent years BONO ARTES’ R&D dept. has performed an accurate study on the geometry of the horizontal degassing tower. On account of this geometry, a larger surface of mass and heat transfer can be implemented compared with a vertical tower while not exceeding the shipping limitations. Several “field” experiences confirmed the dramatic expansion of BONO ARTES’ Deaerators range while reaching and trespassing 1000 tons/hour of deaerated water.
BONO ARTES is therefore able to meet the most demanding requests from its customers in terms of capacities and performance. Furthermore, one aspect that is thrilling BONO ARTES at this moment is the possibility to de-gas water utilising vacuum technology instead of steam, as is usually done in thermophysical deaerators.
Vacuum-based degassers work at the current temperature of the water, while oxygen transfer to the gas phase is enhanced by reducing its partial pressure under vacuum conditions. The major advantage is a substantial saving in energy, since the steam-based system implies that, during the de-gassing operation, water must be first heated-up and later cooled to the operating temperature.
Vacuum Deaerators (VD) are successfully used in all applications where heating of water is not permitted or when heating and cooling would result in wasting large amounts of energy. In particular they find a proper application in the degassing of injection water in the Oil extraction industry. Water is in fact pumped alongside a crude oil reservoir to increase pressure and enhance oil recovery. In such conditions water must be oxygen-free to prevent oxidation and bacteria growth.
Another critical application of VD is in District Heating. VD’s are employed to remove gases from warm water (50 – 60°C) re-filled to the secondary circuits without heating it to boiling conditions. In this way corrosion problems are minimised while warm water is distributed to domestic or industrial users.