Headers chlorine header

Unlike in the other two electrolysis processes, the brine is not recirculated and the temperature in the system can be chosen according to optimum conditions and therefore comparatively little titanium is used in a diaphragm cellroom. However, there are some clear candidates. An example is the cell blanket where Permascand has a newly patented design comprising bellows welded to the anode collar. The chlorine header and also the cell top are other components that could be manufactured from... 

A unique feature of the cathode design is the extension of the cathode fingers from the back plate, which allows easy inspection of the cathode surfaces, and the adaptability to use synthetic separators with minor modifications. The anolyte compartment is connected to an independent brine feed tank by flanged connections and chlorine leaves from the top, through the brine feed tank and then to the chlorine header. Each electrolyzer is fitted with a level alarm, which monitors the level of all the cells in the unit. Figure 5.16 is an isometric cutaway of a Glanor V Type 1144 electrolyzer. 

It is possible to run one header for each service to cover both rows of cells. It is common practice to do this for the gases. A frequent variation, included in Fig. 8.1, is to run two separate hydrogen headers (usually carbon steel), which can serve as structural supports for the saddles that hold a single chlorine header (usually FRP). Liquid headers more frequently are installed in pairs. One reason for this is the reduction of leakage currents, which are the topic of Section 8.3.2.2. 

Certain seamless extruded thermoplastics (e.g., CPVC) can be suitable when properly supported but are limited in size. In all but the smaller plants, they are not available in the diameters required for chlorine headers. In the past, rubber-lined piping was used, but its service life was limited and it required more Hanged connections than butt-connected piping. The standard choice for chlorine headers today is still FRP. 

Since condensate forms continuously in a chlorine header, there must be provisions for removing the liquid, and there must be no pockets where the liquid could collect and form a seal. 

In a plant producing liquid chlorine, the compressed gas goes next to the liquefaction system. Rather than impose a pressure drop between the processes, the gas is allowed to flow freely into liquefaction. A valve on the uncondensed gas venting from the liquefaction unit (Section 9.1.7.2) controls the pressure on both systems. When chlorine is sent to another process without liquefaction, it would be possible to withdraw it on downstream pressure control and let the compressor outlet pressure fluctuate. This approach leads to variability in the differential pressure across the compressor recycle valve. Fluctuations in this flow can cause fluctuations in the compressor suction pressure and therefore in the cellroom chlorine header. It is better to control the compressor outlet pressure itself, even at the cost of another pressure control loop at the destination. Section 11.3.2.6 describes instrumentation hardware and the problems of transferring chlorine to more than one destination. 

The water seal is installed somewhere on the low-pressure side of the chlorine process, usually between the cell room and the cooling process of Fig. 9.12. It is in communication with the process by a branch on the main chlorine header, as indicated by Fig. 9.44. The branch line terminates inside the seal vessel, slightly below the surface of a pool of water. When the pressure in the gas line exceeds the difference between the water level and the bottom of the branch line, the seal breaks and gas escapes. A source of brine can be used in place of water consideration of the difference in density then is necessary when setting the height of the seal. 

The seal pot vessel and its components must be chlorine-resistant. Rubber-lined and FRP construction are the most common. The vessel must be able to withstand the small pressure and vacuum which may exist in the process. Since it is connected to the chlorine header, thermal expansion and contraction of the pipe must be considered in placement and support of the seal vessel. 

The seal pipe extends into the vessel from the chlorine header. Water flows into the vessel by condensation in the header and by deliberate addition from an outside source. The height of an overflow pipe, which may be fixed or variable, determines the level of water in the vessel. The difference in elevation between the overflow and the bottom of the seal leg is labeled h. 

Next we consider the slow buildup of vacuum. As water is pulled into the seal pipe from the annulus, there is time for it to be replaced. The overflow level stays the same, and the seal is maintained. The only limitation on the vacuum is the height of the chlorine header. 

A. Chlorine Header Pressure Control. As pointed out above, chlorine header pressure control can be one of the most difficult control tasks, because the pressure is being controlled within a few millimeters of water coliunn and the latitude for error is small. Each chlorine production method has its own control range and limits, but the control method is the same. The strategy, as shown in Fig. 11.18, is simple. The control valve should be a fail-closed butterfly type with a conventional disc and a positioner. Preferably, it should be located after the dry demister downstream of the drying columns (Section 9.1.5). In this location, the wetted parts of the valve can be Monel. This strategy... 

FIGURE 11.18. Chlorine header pressure control Gow pressure). 

IB. Chlorine Header Safety Systems. Low-pressure chlorine headers are protected from over- and under-pressures by the use of water-filled seal pots. A typical seal pot relieves at about 50 mm w.c. Some membrane-cell systems operate at pressures too high for effective use of a water seal and must depend upon weighted discs or an automated relieving system. 

Membrane cell room chlorine headers are usually purged with air whenever there is a rectifier shutdown. The purging has two functions, removing chlorine gas from the... 

The whole chlorine processing train can be upset if air enters the system through a vacuum break. If the pressure in the chlorine header is close to the point where the vacuum seal opens, the chlorine compressor should be shut down. This will prevent air from being drawn into the whole chlorine handling system. 

Ensure that hydrogen and chlorine header pressures are under control and that the differential is correct. Small header purge flows will be necessary when the... 

Particularly if liquid nitrogen is available, the use of nitrogen rather than air for chlorine header purging may be considered more secure during power failures. 

Cell room acid addition rate Electrolyzer acid addition rates Caustic export flow rate Cell room outlet caustic temperature Electrolyzer outlet caustic temperatures Chlorine header pressure Hydrogen header pressure Differential pressure between gas headers... 

The industry standard material of construction for chlorine headers is FRP with a resin-rich inner barrier. The main polyesters used in chlorine headers are Hetron 197-3, Hetron 998/35, and Derakane 5ION. Hetron 197-3 has been popular for many years. It is being replaced by 510-N. The 197-3 resin provides the iimer corrosion barrier. The outer layer is 197-3 ATP, which contains antimony to give flame retardant properties. The latter resin is replaced in the new Hetron resin FR 998/35 by a brominated vinylester with superior flame retardant characteristics. 

The chlorine headers popular in Europe are dual laminate headers, which are preferred over FRP for environmental reasons. The dual laminate has an inner ring of less brittle PVC-C of 5-mm thickness for corrosion protection and an outer layer of 10-15 mm thickness of FRP for structural strength, the intermediate layer being 5 mm of resin-rich FRP 5 ION or 197-3. The outer layer contains a flame retardant and is added after the dual laminate is stress relieved. The chlorinated PVC (CPVC)/FRP dual laminate header is fabricated from CPVC tubing up to 60 cm in diameter. The dual laminate headers have a life of 8-10 years vs the 6-12 years of life of FRP, at a comparable cost. 

Titanium chlorine headers are used in Europe and are claimed to reduce the amount of chlorinated organics and other nonvolatile residues in gaseous and liquid chlorine. However, it suffers from crevice corrosion near the welds. The use of titanium headers for pressure operation of membrane cells is discussed in Section 8.4.1.1 A. 

The chlorine header should be maintained at positive pressure to permit detection and correction of any chlorine piping leaks. The hydrc en header is also maintained at a positive pressure to avoid pulling air into the hydrogen, creating a potentially explosive mixture. The brine header pressure should be maintained to give the desired caustic concentration in the cell liquor. Normal practice is to adjust individual brine feed valves so that each cell receives the correct brine flow rate. 

Chlorine gas from each cell circuit should be analyzed for chlorine and hydrogen content at least twice each 8-h shift. Each day a complete analysis of the chlorine header gas should be made. Additions or extensions to list may be dictated by plant operation. 

In order to handle hot chlorine gas from the cells a header system has been developed (Fig. 23.16) whereby stray current dumpers take care of the brine condensates that would otherwise result in damage. 

Chlorine/sulfur dioxide headers in the chlorination (sulfonation) room What if the pressure relief valve sticks open ... 

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