Oxygen water treatment

Oxygen Scavenger Corrosion Inhibitor Figure 10.23 Injection water treatment scheme... 

Several methods have been developed to estimate the oxygen demand in waste water treatment systems. Commonly used laboratory methods are biochemical oxygen demand (BOD), chemical oxygen demand (COD), total oxygen demand (TOD), total organic carbon (TOC), and theoretical oxygen demand (ThOD). 

Two main operational variables that differentiate the flotation of finely dispersed coUoids and precipitates in water treatment from the flotation of minerals is the need for quiescent pulp conditions (low turbulence) and the need for very fine bubble sizes in the former. This is accompHshed by the use of electroflotation and dissolved air flotation instead of mechanically generated bubbles which is common in mineral flotation practice. Electroflotation is a technique where fine gas bubbles (hydrogen and oxygen) are generated in the pulp by the appHcation of electricity to electrodes. These very fine bubbles are more suited to the flotation of very fine particles encountered in water treatment. Its industrial usage is not widespread. Dissolved air flotation is similar to vacuum flotation. Air-saturated slurries are subjected to vacuum for the generation of bubbles. The process finds limited appHcation in water treatment and in paper pulp effluent purification. The need to mn it batchwise renders it less versatile. 

Oxygen scavengers other than hydrazine are also used, especially catalyzed sodium sulfite, which reacts rapidly with oxygen even at room temperatures to form sodium sulfate. Catalyzed hydrazine formulations are now commercially available that react with oxygen at ambient temperatures at rates comparable to catalyzed sulfite (189). At elevated temperatures, the reaction rates are all similar. Table 14 Hsts the standard hydrazine solution products offered by Olin Corp. for sale to the water-treatment market. Other concentrations are available and other companies offer similar products. 

Oxygen is used to treat municipal wastewater and wastewater from the pulp and paper industry (see Aeration, water treatment Wastes, industrial Water). Many of these water appHcations can use VSA-produced oxygen (advantage /). Demonstration and development programs are in place that use oxygen to oxidize sludge from municipal waste and bum hazardous wastes and used tires (advantages 1—4). 

Water Treatment. Sodium sulfite is an agent in the reduction of chlorine or oxygen in water. Dissolved oxygen in boiler water tends to enhance pitting and other types of corrosion. In boilers operated at below 4.82 MPa (700 psi), a residual concentration of 30 ppm of sodium sulfite is generally effective. Catalytic amounts of cobalt are often added to accelerate the reaction of oxygen with sulfite (321,322) (see Water, industrial water treatment). 

Environment Internal Oxygen External Cooling water at 95°F (35°C), phosphate and zinc water treatment... 

Selected physical properties of oxygen are included in Table 9.24. It is a colourless, odourless and tasteless gas which is essential for life and considered to be non-toxic at atmospheric pressure. It is somewhat soluble in water and is slightly heavier than air. Important uses are in the steel and glass industries, oxyacetylene welding, as a chemical intermediate, waste-water treatment, fuel cells, underwater operations and medical applications. 

For some applications, notably feed-water treatment for high-pressure boilers, removal of oxygen is essential. For most industrial purposes, however, de-aeration is not applicable, since the water used is in continuous contact with air, from which it would rapidly take up more oxygen. Attention must therefore be given to creating conditions under which oxygen will stifle rather than stimulate corrosion. 

The explicit aims of boiler and feed-water treatment are to minimise corrosion, deposit formation, and carryover of boiler water solutes in steam. Corrosion control is sought primarily by adjustment of the pH and dissolved oxygen concentrations. Thus, the cathodic half-cell reactions of the two common corrosion processes are hindered. The pH is brought to a compromise value, usually just above 9 (at 25°C), so that the tendency for metal dissolution is at a practical minimum for both steel and copper alloys. Similarly, by the removal of dissolved oxygen, by a combination of mechanical and chemical means, the scope for the reduction of oxygen to hydroxyl is severely constrained. 

In addition to the reactions of luciferin shown in Fig. 7.2.3, Trainor (1979) made an interesting discovery that arylsulfatase from Pattela vulgata (Sigma) converts luciferin into a violet compound (treatment conditions pH 5.05, 37°C, 4 hr). The compound showed absorption peaks at 344 nm and 560 nm (Fig. 7.2.7), and the peaks shifted reversibly to 347 nm and 547 nm in acid, and to 364 nm and 720 nm in an alkaline solution. The violet compound was also obtained from the pink compound by treatment with arylsulfatase, or from luciferin by heating in 50% trifluoroacetic acid at 100°C for 1 hr, followed by an addition of oxygenated water. These results, together with the... 

Electrode boilers produce hot water or steam (generally saturated steam) by conducting current through the BW. The water provides resistance, which causes heat to be generated when electrical current flows from one electrode to another. As a consequence, the electrical conductivity of the water is a primary factor in the satisfactory operation of these boilers. Other aspects of water treatment control (such as alkalinity levels, oxygen content, and foam control) and maintenance also must be considered if optimum efficiency is to be obtained. 

Water treatment monitoring and control is often a knife-edge operation and must be tailored to the overall operation of the boiler because waterside and gas-side problems usually are interlinked. Consequently (and as with other types of WT boiler), not only should the utility boiler FW be essentially free of dissolved oxygen to prevent waterside pitting corrosion of the economizer and other boiler components, but also the temperature must be high enough to prevent dewpoint condensation and subsequent acid attack on the gas side of the economizer tubes. 

In all space heating boiler systems there is a tendency to keep water treatment programs as simple as possible. Ideally, chemical inhibitors should be added in proportion to MU demands, metered water consumption, oxygen content, or other preemptive measurement. More typically, the standard process is to periodically (weekly to monthly) analyze the BW for a few basic control parameters, including measuring the multimetal corrosion inhibitor reserve, and then to merely top-up the inhibitor when the reserve is below the minimum specification. Chemical treatment often is added directly to the BW by hand-pump via a hose cock (bib cock) connection. 

For all types of boilers, from the most simple HW heaters to immense power generating plants, one of the most fundamental objectives of any water treatment program is (as stressed several times) to minimize boiler section waterside corrosion, especially those common types of corrosion involving oxygen. The actions taken to achieve this objective are generally the same, irrespective of boiler size or design. These actions include ... 

---