Flow surging

A major cause of pulsing in flare systems is flow surging in the water seal drum. One of several reasons why it is important to eliminate pulsing is to reduce flare noise. Combustion flare noise has been shown to increase as the steam rate increases. Since the amount of steam required to suppress smoke in a flare is set by the flaring rate, flow surges will require a higher steam rate than for a steady flow. 

Flow surges in the seal drum are likely generated by the cyclic formation of large bubbles as the flare gas is discharged into the drum. These pulsations can be virtually eliminated by the use of a horizontal sparger ineorporating many small diameter holes arranged specifically to allow the open area to increase as flow increases. These holes must be spaced sufficiently far apart to avoid interference between bubbles. 

If a demister pad is not used, the value of u, obtained from equation 10.10 should be multiplied by a factor of 0.15 to provide a margin of safety and to allow for flow surges. 

Spalding, M.A., Powers, J.R., Wagner, P.A., and Hyun, K. S., Flow Surging in Single-Screw, Plasticating Extruders, SPEANTEC Tech. Papers, 46, 254 (2000)... 

Improper solids-conveying temperatures for the barrel Flow surging and low specific rates 12.7.4... 

Figure 10.10 Filtered and unfiltered discharge pressure data. The unfiltered data were collected using a portable data acquisition system while the filtered data was the pressure that was observed by plant personnel. The plant personnel believed that they had a very stable process even though this extruder was flow surging. The transducer was positioned in the transfer line and the extruder was operating at a screw speed of 60 rpm...

The standard array of diagnostic equipment is required for the troubleshooting of a process that is flow surging. These tools include screw measuring devices, pyrometers, and devices to calibrate sensors in the process. These devices are discussed in Chapter 10. Often it is very difficult to Impossible to determine a cause and effect relationship from process displays that are attached to typical extrusion... 

Flow surging can occur if the temperature of the screw becomes too high in the solids-conveying section. In general, the temperature of the screw in this section needs to be less than the Tg for amorphous resins or less than the melting temperature for semicrystalline resins. Small-diameter screws will typically operate at feed... 

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