Page 329 - Chemical engineering design

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CHEMICAL ENGINEERING
7.10.1. Glass
Borosilicate glass (known by several trade names, including Pyrex) is used for chemical
plant as it is stronger than the soda glass used for general purposes; it is more resistant
to thermal shock and chemical attack.
Glass equipment is available from several specialist manufacturers. Pipes and fittings
are produced in a range of sizes, up to 0.5 m. Special equipment, such as heat exchangers,
is available and, together with the larger sizes of pipe, is used to construct distillation and
absorption columns. Teflon gaskets are normally used for jointing glass equipment and pipe.
Where failure of the glass could cause injury, pipes and equipment should be protected
by external shielding or wrapping with plastic tape.
Glass linings, also known as glass enamel, have been used on steel and iron vessels
for many years. Borosilicate glass is used, and the thickness of the lining is about 1 mm.
The techniques used for glass lining, and the precautions to be taken in the design and
fabrication of vessels to ensure a satisfactory lining, are discussed by Landels and Stout
(1970). Borosilicate glass is resistant to acids, salts and organic chemicals. It is attacked
by the caustic alkalies and fluorine.

7.10.2. Stoneware
Chemical stoneware is similar to the domestic variety, but of higher quality; stronger and
with a better glaze. It is available in a variety of shapes for pipe runs and columns. As
for glass, it is resistant to most chemicals, except alkalies and fluorine. The composition
and properties of chemical stoneware are discussed by Holdridge (1961). Stoneware and
porcelain shapes are used for packing absorption and distillation columns (see Chapter 11).

7.10.3. Acid-resistant bricks and tiles

High-quality bricks and tiles are used for lining vessels, ditches and to cover floors. The
linings are usually backed with a corrosion-resistant membrane of rubber or plastic, placed
behind the titles, and special acid-resistant cements are used for the joints. Brick and tile
linings are covered in a book by Falcke and Lorentz (1985).

7.10.4. Refractory materials (refractories)
Refractory bricks and cements are needed for equipment operating at high temperatures;
such as, fired heaters, high-temperature reactors and boilers.
The refractory bricks in common use are composed of mixtures of silica (SiO 2 )and
alumina (Al 2 O 3 ). The quality of the bricks is largely determined by the relative amounts
of these materials and the firing temperature. Mixtures of silica and alumina form a
Ž
eutectic (94.5 per cent SiO 2 , 1545 C) and for a high refractoriness under load (the ability
to resist distortion at high temperature) the composition must be well removed from
the eutectic composition. The highest quality refractory bricks, for use in load-bearing
structures at high temperatures, contain high proportions of silica or alumina. “Silica
bricks”, containing greater than 98 per cent SiO 2 , are used for general furnace construction.
High alumina bricks, 60 per cent Al 2 O 3 , are used for special furnaces where resistance
to attack by alkalies is important; such as lime and cement kilns. Fire bricks, typical