Water degasification

FIGURE 2.8 Central ultrapure water degasification system. 

FIGURE 2.13 (See color insert following page 588.) Boiler water degasification system using membrane contactors. 

Weisler Fred Sodaro, Rick (Hoechst Celanese Corp.). Degasification of Water Using Novel Membrane Technology. Ultrapure Water, Tall Oaks Publishing Inc., USA, September 1996. 

In the case of a feed TDS ranging from 1.5 to 2 kg/m3, the energy consumption is of the order of 1.6-2.6 kWh/m3 of treated water. In the circumstances, there is no need to remove organic matter, colloids, and Si02 from raw water, while treated water is just chlorinated for disinfection. On the contrary, degasification and alkaline injection for pH adjustment are used with RO systems. Also, caustic neutralization is needed before RO retentate is discharged to the environment. 

Wiesler EE and Sodaro RA, Degasification of water using novel membrane technology, Ultrapure Water 1996, 35, 53. 

Peterson PA, Runkle CJ, Sengupta A, and Wiesler EE, Shell-less hollow fiber membrane fluid contactor, US Patent 6,149,817, 20(30. Sengupta A, Runkle CJ, Vido TR, and Kitteringham BA, Economy of scale Large membrane modules for degasification and purification, International Water Conference, Pittsburgh, PA, October 2003. 

The equilibrium of sulfide in water, the percentages of H2S, HS, and species, is dependent on the pH. Figure 1 shows the distribution of each species at various pH. At a pH of approx 5.7, the sulfide species in water would be near 100% H2S and at approx pH 7, 50% of the sulfide species in water would be H2S and the other 50% would be HS species. The H2S species are volatile as a result, the aeration process effectively removes it from the water. Therefore, the removal efficiency of sulfide depends on pH. As the pH increases, aeration becomes less effective because there are fewer sulfides in the form of H2S, which is readily removed by aeration. This process is utilized by both municipalities and chemical industries. In water treatment, the process is called degasification, and is effectively used to remove both H2S and carbon dioxide from well water and product water from the reverse osmosis process. 

Air stripping requires packed towers for maximum operational efficiency [13]. Water is pumped to the top of a tower packed with media as shown in Figure 2.6. The water is evenly distributed across the media. As it flows down under gravity it forms a film layer on the packing surfaces. Air is blown upwards from the bottom contacting the large surface areas. The blown air enhances the removal of the volatile species by mass transfer. Degasification is... 

Figure 2.12 Membrane contactors (MC) system for degasification. Typical operating conditions water flow rate 55 mVh at 25°C feed and outlet O2 concentration is 5 ppm and <10ppb MC 25 cm diameter X 70 cm long 3 series x 2 parallel array vacuum 700 mm Hg N2 sweep-flow rate...

In (partially) open steam networks, the demineralised make-up water is usually mixed with the returning condensate and has to be degassed before it can enter the steam boiler. This degasification is usually done thermally using process steam from the steam boiler. 

Fig. 114. Degasification apparatus for water samples containing radon (schematic) 1) = Glass tube 2) = Rubber blower (or diaphragm pump) 3) = Flexible tubing 4) = Drying tube (with CaC12) 3) = Lead for chamber...

The pyrolytic conversion of coal into coke, gas and aromatic liquid products is the oldest and, in quantitative terms, most important coal-refining process. In the absence of air, carbonization processes are considered to occur in stages up to 150 °C, carbon dioxide, water and volatile C2 to C4 hydrocarbons are evolved. At pyrolysis temperatures above 180 °C the volatile components also contain aromatics. At temperatures in excess of 350 °C, rapid degasification occurs, which continues to around 550 °C, leading to semi-coke. The rate of degasification approximately follows a reaction of the 1st order, which can be explained by the rupture of the bonds of the macromolecules in the coal. In the secondary degasification of the semi-coke (600 to 800 °C) hydrogen and methane are the main products. 

Various methods of on-line reactor surveillance have been used, including neutron noise monitoring in boiling water reactors (BWRs) to detect internals vibration, and pressure noise surveillance at TMI-2 to monitor primary loop degasification. On-line surveillance data has been used in the assessment of loose thermal shields. 

The fission product noble gas isotopes Xe and Xe are the predominant radionuclides in the primary coolant of a pressurized water reactor when failed fuel rods are present in the reactor core, in particular when the coolant degasification system is not in operation. Appearance of additional defective fuel rods in the reactor core results in a prompt response of the activity concentrations of the xenon isotopes in the coolant. For this reason, periodic analyses at comparatively short time intervals are required in order to initiate countermeasures in time, e. g. starting operation of the degasification system, whenever necessary. 

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