Wet chlorine gas

Dry chlorine has a great affinity for absorbing moisture, and wet chlorine is extremely corrosive, attacking most common materials except HasteUoy C, titanium, and tantalum. These metals are protected from attack by the acids formed by chlorine hydrolysis because of surface oxide films on the metal. Tantalum is the preferred constmction material for service with wet and dry chlorine. Wet chlorine gas is handled under pressure using fiberglass-reinforced plastics. Rubber-lined steel is suitable for wet chlorine gas handling up to 100°C. At low pressures and low temperatures PVC, chlorinated PVC, and reinforced polyester resins are also used. Polytetrafluoroethylene (PTFE), poly(vinyhdene fluoride) (PVDE), and... 

Gaskets in both dry gas and Hquid chlorine systems are made of mbberi2ed compressed asbestos. Eor wet chlorine gas, mbber or synthetic elastomers are acceptable. PTEE is resistant to both wet and dry chlorine gas and to Hquid chlorine up to 200°C. Tantalum, HasteUoy C, PTEE, PVDE, Monel, and nickel are recommended for membranes, mpture disks, and beUows. 

Titanium metal is especially utilised ia environments of wet chlorine gas and bleaching solutions, ie, in the chlor—alkaH industry and the pulp and paper industries, where titanium is used as anodes for chlorine production, chlorine—caustic scmbbers, pulp washers, and CI2, CIO2, and HCIO storage and piping equipment (see Alkali and cm ORiNE products Paper Pulp). 

Fair Good 145 6.3 Excellent resistance to wet chlorine gas and sodium hypochlorite solutions... 

Titanium is the only one of the more common structural metals which is not attacked by wet chlorine gas and it is thus widely used as a heat exchange material for cooling the gas after the electrolysis stage. Preheating of sodium chloride brine is carried out in titanium plate heat exchangers, while titanium butterfly valves, demisters, and precipitators handle the chlorine gas produced in the cell. The most important use of titanium in chlorine production is as anodes in place of graphite in the electrolytic process. This is covered in more detail later. 

The commercial importance of this metal was first recognized in 1950s when its high strength/density ratios were found attractive in aerospace applications. The corrosion resistance in a variety of conditions led to its use in wet chlorine gas coolers for chlor-alkali cells, chlorine and chlorine dioxide bleaching equipment in pulp/paper mills, and reactor interiors for pressure acid leaching of metallic ores. The metal and its alloys were used in seawater power plant condensers, with over 400 million feet installed in application.65,66 The most commonly used alloys and their composition are given in Table 4.48. 

A. Brine. The depleted brine leaving mercury and membrane cells is saturated with chlorine. The same sorts of materials used in wet chlorine gas systems are suitable here. Brine lines generally are smaller than chlorine gas headers, and there is more scope for the use of common thermoplastics. The chlorinated types are frequently chosen. Especially at the temperatures of depleted brine, mechanical properties are also very important, and proper support is essential. The reason for the superiority of CPVC over PVC in this application may have more to do with better physical properties than with improved corrosion resistance. For added strength, these materials are often wrapped with FRP. 

Wet chlorine gas, that is to say gas at low pressure, does not require tongue-and-groove flanges and can be confined by soft PVC and most of the common elastomers. Some polymeric gaskets require steel reinforcement, and some develop protective layers of chlorinated polymer. 

C. Local Measurements. Local measurements of wet chlorine gas pressures below 10 or 15 kPa can be made with U-tube manometers filled with water. Process connections should minimize the collection of condensate in the manometers. A simple but not foolproof technique is to make a connection in the upper half of the header and force the tubing to rise for some distance before descending to the manometer. 

Chlorine Systems. The choice of construction materials for chlorine service depends on equipment design and operating conditions. Figure 14.25 shows the corrosion resistance of various materials to dry chlorine, wet chlorine gas, and chlorine in aqueous solution [27]. 

Hydrogen peroxide Sulfuric acid above 70% Wet chlorine gas Wet sulfur dioxide... 

Alloy C-276 has exceptional corrosion resistance to many process materials, including oxidizing, neutral, and acid chlorides, solvents, chlorine, formic and acetic acids, and acetic anhydride. It also resists highly corrosive agents, such as wet chlorine gas, hypochlorite, and chlorine solutions. 

In electrostatic purification, the wet chlorine gas is passed between wire electrodes in vertical tubes. The electrodes are maintained at a d.c. potential of 50 kV with a current density of 0.2 mA/m. The particles and droplets in the chlorine become charged and collect on the tube walls. The resultant liquid is fed back into the brine system or chemically treated before disposal. 

Wet Chlorine Gas. Wet chlorine gas rapidly attacks most common metallic materials with the exception of tantalum and titanium. To assure a protective oxide layer on the surface of the titanium, sufficient water must be present in the chlorine gas. If the system does not remain sufficiently wet, titanium ignites spontaneously [253]. 

Most organic materials are slowly attacked by wet chlorine gas. Rubber-lined iron is successfully used up to 100 °C. At low pressure and temperature the use of plastic materials like PVC, chlorinated PVC, and reinforced polyester resins is advantageous. Polytetrafluoroethylene (PTFE), polyfvinylidene fluoride) (PVDF), and fluorinated copolymers like tetrafluoroethylene-hexafluoropropylene (FEP) are resistant even at higher temperature. Ceramics have been progressively replaced by plastics. Impregnated graphite is suitable up to 80 C the impregnation should be resistant to wet chlorine. 

Materials for Special Parts. After the ban of asbestos as material for gaskets, substitutes are recommended [254]. In wet chlorine gas, rubber or synthetic elastomers are acceptable. Even at temperatures up to 200 C, PTFE is resistant against wet and dry chlorine gas and liquid chlorine. 

Chlorine gas, chlorine chemicals, and chlorine solutions. Titanium is widely used to handle moist or wet chlorine gas and has earned a reputation for outstanding performance in this service. The strongly oxidizing nature of moist chlorine passivates titanium, resulting in low corrosion rates. The selection of a resistant titanium alloy offers a solution to the possibility of crevice corrosion when wet chlorine surface temperatures exceed 70°C (Table 8.42). Dry chlorine can cause rapid attack of titanium and may even cause ignition if moisture content is sufficiently low. However, as httle as 1% water is generally sufficient for passivation or repassivation after mechanical damage to titanium in chlorine gas under static conditions at room temperature. 

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