Pre-boost

Most ethylene plants operate continuously with the expanders operating at or near design conditions. If necessary, due to their unique design characteristics, radial inflow turboexpanders can accommodate a wide range of process conditions without significant losses in thermal or mechanical efficiency. Expanders may be loaded with booster compressors, gear-coupled generators, dynamometers, or other in-plant mechanical equipment such as pumps. In ethylene plants, turboexpanders are typically used in eitlier post-boost or pre-boost applications. 

In pre-boost applications, the turboexpander discharge pressure is considerably lower than the compressor inlet pressure. This situation requires special consideration when designing the turboexpander and auxiliary systems. In pre-boost designs, compressing the gas to a higher pressure produces more refrigeration in the turboexpander. Figure 3-9 shows a cross-section of an expander-compressor unit. 

In developing these eurves, whieh ineidentally follow the trends illustrated in Figures 5-1 through 5-4, it was assumed dial the plant is either a pre-boost or post-boost design with eonventional gas eomposition and proeess eonditions. For unusual plant designs, the expander manufaeturer should be eontaeted. 

The expander-compressor will attain a speed of 5,000-15,000 rpm, depending on the design horsepower of the machine. If the design pressure of the compressor suction is higher than the design pressure of the expander discharge (pre-boost type), increase the speed to approximately 80% of the design speed as rapidly as possible. This... 

Turboexpanders may be used in variable speed (eompressor, blower, or oil brake) or eonstant speed (generator brake) and pre-boost or postboost applieations. In variable speed applieations, the performanee eharaeteristies of turboexpanders, partieularly those driving eom-pressors, are more sensitive to ehanges in normal design eonditions. This examination of turboexpander-eompressors is limited to postboost applieations only. 

In pre-boost applications, an integral booster compressor feeds an expander and the complexity of interactions is different than in postboost applications where the integral booster compressor is downstream from the turboexpander. 

Since the motor s fixed parameters can now be varied to suit a particular load requirement, there is no need to pre-match a motor with the load. Now any motor can be set to achieve the required characteristics to match with the load and its process needs. Full-rated torque (TJ at zero speed (during start) should be able to pick up most of the loads smoothly and softly. Where, however, a higher 7 s, than is necessary, a voltage boost can also be provided during a start to meet this requirement. (See also Section 6.16.1 on soft starting.) The application of phasor (vector) control in the speed control of an a.c. motor is shown in a block diagram in Figure 6.12. 

Thermocompressors are steam jet ejectors used to boost low pressure or waste steam to a higher intermediate pres-... 

Figure 8-6 Flow a Buck Turns into a Boost in Pre-biased Load Conditions... 

The status of chemists in the eyes of executives was boosted by the successes of chemists in fields such as plastics, petrochemicals, and synthetic textiles. The industry s growing demand for trained chemists forged a new relationship with many academic chemistry departments. For example, universities supplied industry with chemists and with basic research to supplement work done in industrial laboratories. In turn, industry provided financial support to chemistry departments. Many of the increasing number of chemistry students in American universities were supported by pre- and post- doctoral fellowships from chemical corporations (Thackray et al., 1985). 

The first of these amplifiers, called the pre-amplifier or pre-amp is usually placed as close to the probe as possible (you will often see it resting by the foot of the magnet). This is so that the weak signal is boosted before being sent down a cable to the spectrometer console. 

Hallermalm K et al. Pre-clinical evaluation of a CEA DNA prime/protein boost vaccination strategy against colorectal cancer. Scand J Immunol 2007 66 43-51. 

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