HEAT EXCHANGER AND MIXER

Designing Heat Exchanger and a Mixer for the Synthesis of Zeolites from Fly Ash

Designing Heat Exchanger and a Mixer for the Synthesis of Zeolites from Fly Ash

Unit 1: Designing Heat Exchanger for the Synthesis of Zeolites from Fly Ash

The design is based on a shell and tube heat exchanger that is used to cool down fly ash flowing from a calcinations column at a rate of 16973.48 kg/hour from 800 to 100 degree C.

Thermal design of shell-and-tube heat exchangers (STHEs) is done by sophisticated computer software. However, a good understanding of the underlying principles of exchanger design is needed to use this software effectively.

It is essential for the designer to have a good working knowledge of the mechanical features of STHEs and how they influence thermal design. The principal components of an STHE are:

• shell;

• shell cover;

• tubes;

• channel;

• channel cover;

• tubesheet;

• baffles; and

• nozzles.

Other components include tie-rods and spacers, pass partition plates, impingement plate, longitudinal baffle, sealing strips, supports, and foundation. The Standards of the Tubular Exchanger Manufacturers Association (TEMA) (1) describe these various components in detail. An STHE is divided into three parts: the front head, the shell, and the rear head. Figure 1 illustrates the TEMA nomenclature for the various construction possibilities. Exchangers are described by the letter codes for the three sections — for example, a BFL exchanger has a bonnet cover, a two-pass shell with a longitudinal baffle, and a fixed-tubesheet rear head.

A fixed-tube sheet heat exchanger (Figure 2) has straight tubes that are secured at both ends to tube sheets welded to the shell. The construction may have removable channel covers (e.g., AEL), bonnet-type channel covers (e.g., BEM), or integral tube sheets (e.g., NEN).

The principal advantage of the fixed tube sheet construction is its low cost because of its simple construction. In fact, the fixed tube sheet is the least expensive construction type, as long as no expansion joint is required. Other advantages are that the tubes can be cleaned mechanically after removal of the channel cover or bonnet, and that leakage of the shell side fluid is minimized since there are no flanged joints. A disadvantage of this design is that since the bundle is fixed to the shell and cannot be removed, the outsides of the tubes cannot be cleaned mechanically. Thus, its application is limited to clean services on the shell side. However, if a satisfactory chemical cleaning program can be employed, fixed-tube sheet construction may be selected for fouling services on the shell side. In the event of a large differential temperature between the tubes and the shell, the tube sheets will be unable to absorb the differential stress, thereby making it necessary to incorporate an expansion joint. This takes away the advantage of low cost to a significant extent.

Service of single-phase (both shellside and tubeside) is used such as the cooling or heating of a liquid or gas. The following nomenclature is usually used:

Heat exchanger: both sides singlephase and process streams (that ...