Line cleaning

Periodically clean via flushing, blowdown, internal line cleaning devices (e.g., pigs )... 

Nozzles can also be installed on the flame arrester honsing for the injection of hot cleaning solntion for on-line cleaning of polymeric deposits (Dafft 1999). This is especially nseful for very large flame arresters that cannot be easily removed from service. 

In 1994, Nam and King (68) developed a SFE/SFC/GC instrumentation system for the quantitative analysis of organochlorine and organophosphorus pesticide residues in fatty food samples (chicken fat, ground beef and lard). In this way, SFC was used as an on-line clean-up step to remove extracted material. The fraction containing pesticide residues is then diverted and analysed by GC. 

Figure 4-74. Edge-type filter with the external on-line cleaning. Courtesy of AMF Corp., Cuno Div.

As a result, there is a growing trend to off-line clean reverse-pulse filters by using bags with multiple compartments. These sections allow the outlet-gas plenum serving a particular section to be closed off from the clean-gas exhaust, thereby stopping the flow of inlet gas. On the dirty-side of the tube sheet, the isolated section is separated by partitions from the neighboring sections where filtration continues. Sections of the filter are cleaned in rotation as with shaker and reverse-flow filters. 

On-line cleaning—inject walnut hulls into the inlet of the expander weekly. 

For phosphate overlay programs, PAA is generally satisfactory, but where good phosphate control is required or for on-line cleaning of fouled boilers using phosphate-cycle, SS/MA or AA/AMPS should be used. These products also perform in the presence of iron. 

Bonded-phase silica and ion-exchange resins in plastic cartridges and mini-columns are very useful for off-line prepurification of samples, especially those for preparative chromatography, when appropriate pre- or guard columns may not be available for on-line clean-up of a sample. 

The on-line approach shows high efficiency and sensitivity. However, off-line cleaning or replacement requirements of the interface result in limited operational time. On the other hand, problems have been reported with the off-line approach too. The essentially arbitrary collection of fractions (spots) clearly offsets the high resolution of the separation. Other problems may arise from the incomplete deposition of the analyte in the form of drops onto the target, which in turn results in a substantial fraction of the analyte being present in the next deposited drop. 

An automated supercritical fluid extraction and in-line clean-up system has been developed for organochlorine and organophosphate pesticide residues contained in fats (Hopper, 1999). 

S Taguchi, S Yoshida, S Fukushima, S Hori. Rapid determination of tetracycline antibiotics in milk by HPLC using an on-line clean-up system. J Food Hygienic Society Japan 38 259-64, 1997. 

A developing and welcome trend is the promotion of cooling system biocides that owe much of their biocidal properties to effective on-line cleaning abilities rather than just toxicity. This trend is in part a response to increased environmental awareness but also the recognition by many operators of good housekeeping practice and Responsible Care. 

In some circumstances, off-line cleaning or periodic cleanup programs may also be necessary. 

Any proposal for a future chemical inhibitor program needs to employ an alkaline zinc/stabilized phosphate base, similar to that currently used, as required by the customer. However, as noted previously, the inhibitor needs improved deposit control agent (DCA) performance. This is especially important, as a new program would not start with a properly cleaned cooling system (an on-line clean will be recommended, but is likely to have only limited effect). Thus the inhibitor would include better/more polymers. 

---