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Chapters 7 through 9 have already covered the processes involved in a chlor-alkali plant, along with some of the essentials of their control. This chapter goes into the details of control systems and hardware. The discussion, where differences exist, focuses primarily on the membrane-cell process. The chlorine and hydrogen processes are essentially the same regardless of the type of cell used. Control of absolute and differential pressures is especially important in the gas systems, and so the discussion is divided primarily according to operating pressure level. Membrane cells require extremely pure brine, and some of the operations used are not necessary with the other types of cell. Otherwise, mercury-cell brine systems are for the most part very similar to those in membranecell plants, but they require their own special features and precautions to prevent the escape of mercury into the environment. Diaphragm cells require approximately the same treatment of new brine, but, unlike the situation with the other cells, there is no direct recycle of the anolyte. Therefore, the discussion of brine systems follows the membranecell process, which is the most comprehensive of the three. The caustic systems for the three manufacturing processes are very different and are discussed separately.

This chapter considers the major utility systems in a chlor-alkali plant. These include electricity (Section 12.2), steam and condensate (Section 12.3), the various water systems (Section 12.4), air and nitrogen (Section 12.5), and, for convenient grouping, vacuum (Section 12.6). Finding the best basis for a discussion of utilities in a work such as this is difficult. A comprehensive description is impossible in a reasonable amount of space, and in any case it is undesirable where the emphasis is to be on chlor-alkali technology itself. Our approach is to discuss the individual utilities from the standpoint of a chlor-alkali plant operator while avoiding the complexities of such things as steam boilers.

Commissioning is the activity whereby the installed hardware of a new plant is transformed into an operational facility. Most works on industrial chemical technology ignore the subject/However, it is an extremely important topic, and the successful startup and subsequent operation of a new plant are critically dependent on the approach taken toward its commissioning.

Corrosion is a multibillion dollar worldwide problem. In the United States, corrosion is estimated [] to occur at a rate of 14,000 kg min, costing about $200 billion per year. Incidents from corrosion may force shutdowns of chemical plants, the associated penalties in serious situations being financial loss, loss of human life, and damage to the environment. It is for these reasons that all chemical plants emphasize safety and implement safe operations by training plant personnel. Safety management extends into ensuring proper selection of materials of construction, quality control during manufacturing, fabrication, and construction, and routine maintenance during normal plant operations.

Chlorine is produced not only by the electrolysis of sodium chloride solutions but also from HC1, KC1, and other metal chlorides, by both chemical and electrochemical methods. The amount of chlorine from alternative processes is about 5.9% of the total world production. In the United States, it was about 4.0% of the total in 2002 []. Most of this chlorine was from the electrolysis of KC1 in mercury or membrane cells (Table 15.1) and from HC1. Only small amounts are produced by the electrolysis of other metal chlorides.

Safety considerations are inseparable from the principles of good design and operation and so have been a constant theme in our discussion of the chlor-alkali process. The preceding chapters deal with the practical details of direct protection of personnel in the workplace. They refer frequently to the programs and publications of various organizations with special interest in industrial safety. Other publications [, ] also discuss operating safety and provide guidance in design and operation. In this chapter, we consider safety more generally and also provide more quantitative information on hazard levels. To put those hazards in perspective and show the degree of success the industry has had in coping with them, consider the following []:

Chapter 2 recounts some of the history of chlor-alkali technology and production. While very important industrially, the process is an old one and, as one of the few examples of large-scale electrochemical production, somewhat outside the mainstream of chemical research and development. The industry is part of the commodity chemical business and has often faced difficult economic problems. All this seems a recipe for technological stagnation. However, the past few decades have seen two major developments that have had profound effects on the technology and economics of production. These are the introduction of metal anodes and the partial substitution of membrane technology for the older diaphragm and mercury technologies. The first of these was made possible by the development of durable, low-voltage coatings that could be applied to titanium. Metal anodes offered many advantages over graphite. Furthermore, direct replacement of graphite by metal anodes of essentially the same dimensions was also rather a simple matter. The changeout therefore was rapid. Membrane technology, on the other hand, required extensive changes in the process. Except for the “membrane-bag” cells, which were a compromise approach, these changes included new electrolyzers. This is quite an expensive proposition, and the energy economy of the membrane cell has not in itself justified wholesale conversion. When a producer has the opportunity to expand conversion, new facilities are easier to justify, but the economic state of the industry has, for the most part, been only fair or poor. The conversion to membrane technology has therefore been slow, and only very recently has the membrane process approached the total installed capacities of the other technologies.