2000 Hook-up Book

Steam Tracing

the simple direct acting tempera ture control often provides an economic solution. This will give close control and since it is not necessary to provide either elec tric power or compressed air, the first cost and indeed the running costs are low.

A similar but maintainable type intended for use on instru ment tracer lines, where the physical size of the trap is impor tant as well as its operating characteristics is shown in Fig. 35. Just as the distribution of steam is from a common header, it often is convenient to connect a number of traps to a common condensate header and this sim plifies maintenance. As noted, the discharge should preferably enter the header through swept con nections and the headers be adequately sized as suggested in Table 8 (page 16).

These may be increased where high pressures and traps discharging condensate at near steam temperature are used, or decreased with low pressures and traps discharging cooler con densate. Temperature Control of Tracer Where it is essential to prevent overheating of the product, or where constant viscosity is required for instrumentation, automatic temperature control is frequently used. On many systems, the sim plest way to achieve control is to use a reducing valve on the steam supply to the tracer lines or jacket. This can be adjusted in the light of experience to give the correct steam pressure to pro duce the required product temperature. Clearly this is an approximate way to control product tempera ture and can only be used where the product flow is fairly constant. Where closer control is required,

SYSTEM DESIGN

Figure 35 Maintainable Balanced Pressure Tracer Trap.

Case in Action: Product Steam Tracing with Temperature Control and Overheat Protection

Benefits • The chance of product damage from overheating is min imized and steam consumption is reduced through steam pressure reduction (150 psig to 50 psig) with the pressure regulator. • The product temperature is maintained at a consistent set temperature, maximizing process control under all flow conditions with the temperature regulator. • Product damage from overheating is prevented through use of the high limit safety cutout. The system will shut down completely, should the temperature regulator over shoot its set point. • The tracing system is protected from freezing with the sealed balanced pressure thermostatic steam trap dis charging to drain. Thorough drainage is also facilitated by the vacuum breaker.

During steam tracing project design, it was found that five thousand feet of 2" product piping was to be traced with 150 psig steam. Product temperature was to be main tained at 100°F, with maximum allowable temperature of 150°F and a minimum allowable temperature of 50°F. Of particular concern was the fact that the pipeline would always be full of the product, but flow would be intermittent. Overheating could be a real problem. In addi tion, the tracing system had to be protected from freezing. Solution The 5,000 feet of product piping was divided into 30 sep arate traced sections including: a cast steel temperature regulator, a bronze temperature control valve used as a high limit safety cutout, a sealed balanced pressure ther mostatic steam trap, a vacuum breaker, and pressure regulators supplying steam to all 30 tracing sections. Each section operates effectively at the desired temperature, regardless of flow rate or ambient temperature.

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