Cell room ventilation

When hydrogen recovery is unsafe or otherwise impractical it is vented into the cell room or tank house. The light weight and high diffusion rate of hydrogen and good cell room ventilation have made this an accepted practice. 

The purification of the cell room ventilation air would require the removal of very low mercury concentrations from very large volumes of air. This would not be effective. Therefore, this concentration is kept very low by means of good housekeeping [20]. 

Mercury vaporization losses to the cell room air can amount to 1-5 g/tonne chlorine [30]. Therefore, ventilation is important to ensure safe working conditions, which require that the mercury vapor concentration be kept below 0.05 mg/m. This is achieved by tight cell construction, localized hoods and venting of critical cell areas, and cell room ventilation rates of six to eight air changes per hour (e.g., [31]). Mercury cell chloralkali plants in moderate climates are able to operate their cells outside, which avoids these ventilating problems, but does not control potential emissions. 

Air Emissions. In an early study of methods for plantwide mercury control, Hine and coworkers [101] recognized at the outset that control of emissions in the cell room ventilating air would be the most difficult task. This situation is due to the diversity of possible sources and the difficulty of treatment of the air. The use of gravity ventilation in cell rooms (Section 8.2.3) noakes such treatment impracticable. Likewise, it is not... 

The significant emission of oxygen and hydrogen bubbles, upon bursting the electrolyte surface, ejects acidic aerosol droplets into the cell room environment. This mist is reduced by the addition of surfactants and adequate cell house ventilation improves the working conditions. 

Fig. 4 Mercury cell room (cross section, schematic), (a) Basement floor (b) floor drains (c) cell supports with insulators (d) supply pipes (e) cells (f) decomposers (g) service walkways (h) crane (i) ridge ventilator (j) ventilation air supply ...

Significant modifications to the electrolytic zinc plant operated by Big River Zinc Corporation were made at the end of the 1990 s resulting in increased oqtacity and improved efficiencies. A new cell room, with the innovative use of acid-resistant concrete cells and a modem ventilation system, was installed to raise the capacity fiom 80,000 tonne/y to 106,000 tonne/y of finished zinc. Improvements to the leaching section include the conversion from a single to a two-step process, with associated equipment changes, to improve the quality of the residues produced. Another key change is the constmction of a facility to allow the use of zinc oxides fk>m secondary sources as a feed to the plant. This paper describes these improvements and the current operations. 

The natural inclination to refer to an electrolyzer installation as a cell room reflects the fact that most cells are located inside buildings. There are advantages to locating cells outdoors, however. Besides the obviously lower cost, these include greater opportunities for emergency escape from the area, the dissipation of minor releases of gas, and the cooler temperatures that result from unconfined ventilation. Outdoor construction makes it easier to limit ceiling concentrations of chlorine vapor and to reduce worker heat stress [2]. 

The operating temperature of some electrolyzers is close to 100°C, and buswork temperatures are similar. The total amount of heat generated in a cell room by convection and radiation therefore is quite large. Besides the high temperatures of process fluids and equipment, the thermal hazards in the cell area may include prolonged exposure of personnel to high ambient temperatures. Summertime cell room temperatures in hot climates can reach 50°C. This fact is a major consideration in the decision to place a cell room outdoors. When the cells are placed in a building, the heat is removed by ventilation. 

Cell rooms usually are not electrically classified. The possible release of hydrogen would be the reason for such classification, but it is present at very low pressure and dissipates rapidly and over very short distances. Proper ventilation, as discussed in Section 8.2.3, is necessary to this rapid dissipation. Hydrogen concentrations may be higher near the roof of the cell building. Many designs therefore eliminate electrical contacts at high levels and include extra protection in lighting fixtures. 

J.H. Nichols, Ventilation in Mercuiy Cell Rooms, 8th Chlorine Institute Plant Operations Seminar, New York, NY (1963). 

Surface mercuiy usually is in the metallic form. Simple washing of the surface can be very effective. High-pressure water can remove mercury quickly splash containment is necessary. Steel and rubber-lined pipework can be retorted or cleaned with HCI/CI2 or NaOH/H2C>2. These solutions oxidize the metal to the soluble Hg +. Heavily contaminated steel will sweat mercury. Lott [19] points out that broken concrete from a cell room floor also can sweat mercury if allowed to stand overnight. Components should be stored with this in mind. Liquid droplets can be collected. The storage area should be ventilated because of evaporation of the mercury. Buswork and copper fabrications are protected by surface films and usually are not seriously contaminated with mercury. Surface washing is good practice before recycle. Copper braid or flexible strips can be more heavily contaminated and require treatment in a mercury distillation oven. 

At high pressure experiments the reactor should be installed in a pressure cell. All check valves before it, and the filter with the flow controller after it, can be kept in the vented operating room. As a minimum, the bypass valve and the flow controller must be accessible to the operator. This can be done by extended valve stems that reach through the protecting wall. Both the operating room and the pressure cell should be well ventilated and equipped by CO alarm instruments. 

A special room, or suite of rooms, should be kept for the transfer and growth of cells infected with virus. This room should be adequately ventilated under positive pressure and should contain an elbow operated wash hand basin. 

There are more examples for the application of these requirements If a study involves analytical procedures, the facility has to have an adequate power supply with adequate provisions for the case of power failures or breakdowns. The same provisions have to be taken for the air-conditioning system of the animal rooms. It is self-evident that the IT system of a test facility will have to be protected against this kind of event, too. Furthermore, an adequate ventilation system will be needed in order to protect test systems, equipment and technicians from noxious or corrosive gases and volatile solvents. In the area of in vitro test systems, a surveillance system for the facilities (i.e. the containers) used to store cell lines in a deep-frozen stage will have to assure that the level of liquid nitrogen does not fall below the critical minimal level. Many more examples could be cited and the appropriateness of the facility and its construction can be followed down to the small table on which the balance to be used in the study is placed Does this table have sturdy legs and a special. 

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