2000 Hook-up Book

Clean Steam

Typical Application Sterile barriers, or block and bleed systems are used extensively in the biotechnology, pharmaceuti cal, food, dairy and beverage industries to prevent contaminat ing organisms from entering the process. A simple example also illustrating steam in place, con densate drainage from a process vessel, is shown in Fig. 59. In this application, the steam trap is directly coupled to the process pipework, which is nor mally of sanitary design. It is quite possible that contamination at the trap, caused by either biological or chemical (corrosion) means, could find its way into the process system, thus resulting in failure of a product batch. Steam traps with corrosion resistant materials of construction and self draining features will reduce this risk, tak ing sanitary standards one step further from the process. Due to piping arrangements, process fluids will often be flushed through the trap. This can often result in plugging if standard industrial designs of trap are used. Specialty steam traps are called for which have the features outlined above plus the ability for rapid removal from the pipeline and quick disassembly for cleaning.

effects of flash steam can be pre vented by using an expansion pot at the end of the manifold and venting through a filtered vent outside the clean room. The vent filter could alternatively be locat ed at a kill tank, if used (Fig. 58). • To prevent the risk of contami nation, the direct connection of “clean” steam and condensate services should be prevented wherever possible. Under no circumstances should the con densate line or manifold lift above the level of the traps. • Where the risk of biological con tamination must be minimized, then care should be taken to select pipeline products which are self draining. This becomes most important in applications where the steam supply is fre quently turned off, and where steam pipeline products are close coupled to sanitary process lines. Under these con ditions, microbial growth will become possible in any pocket of condensate or process fluid retained in the system. However, where the steam supply is guar anteed, then this requirement does not become so stringent. • Never “group trap” i.e. always use a single trap for draining each process line, vessel, etc. Failure to do this will invariably cause back-up of condensate in the system.

• The presence of crevices on pipe and component walls can provide an ideal location for microbial growth. Pipeline com ponents which are likely to become fouled, such as steam traps installed on process sys tems, should be installed so they can be easily taken out of service for thorough cleaning. • A “clean” steam service should not be interconnected to any other service which is not of sanitary design. • Condensate from clean or pure steam systems should not be reused as make up for the clean/pure steam generation plant. • Dead legs of piping which are not open to steam under normal operating conditions should be avoided by proper initial system design and the careful place ment of isolation valves. Any dead leg open to steam must be properly trapped to prevent con densate build up. • The use of OD tubing is becom ing increasingly common for the distribution of clean steam. Table 15 gives capacities in lb/h for dry-saturated steam at vari ous pressures. In order to reduce erosion and noise, it is recommended that designs should be based on flow veloc ities of 100 ft/sec. or less.

SYSTEM DESIGN

Vent Filter (alternatively at kill tank)

Condensate

Condensate

User Equipment

Clean Steam Traps

Clean Steam Trap

Clean Steam Traps

Manifold

Air Break

Air Break

To Process Drain

To Process Drain

Clean Area

Single Trap

Manifold Arrangement

Killer Tank/ Sewer

Figure 57 Steam Trap Discharge Details

Figure 58 Steam Trap Discharge—Clean Room

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