Upstream and downstream

When recycling material to the reactor for whatever reason, the pressure drop through the reactor, phase separator (if there is one), and the heat exchangers upstream and downstream of the reactor must be overcome. This means increasing the pressure of any material to be recycled. 

The efficiency of the filter is evaluated in terms of the titer reduction or log reduction value (LRV). The titer reduction is the ratio of the number of microorganisms in the input suspension to the number of organisms in the effluent. Similarly, the LRV is the log Q of this ratio. The ratio of the difference between the numbers of challenge microorganisms recovered upstream and downstream of the test filter to the average total challenge received by the filter... 

Enough space must be available to properly service the flow meter and to install any straight lengths of upstream and downstream pipe recommended by the manufacturer for use with the meter. Close-coupled fittings such as elbows or reducers tend to distort the velocity profile and can cause errors in a manner similar to those introduced by laminar flow. The amount of straight pipe required depends on the flow meter type. For the typical case of an orifice plate, piping requirements are normally Hsted in terms of the P or orifice/pipe bore ratio as shown in Table 1 (1) (see Piping systems). 

The flow velocity is thus proportional to the difference in transit time between the upstream and downstream directions and to the square of the speed of sound in the fluid. Because sonic velocity varies with fluid properties, some designs derive compensation signals from the sum of the transit times which can also be shown to be proportional to C. 

Some drawbacks to the weigh belt are that it is a zero-reference device and thus needs frequent caHbration (re-zeroing). Buildup on the belt and roUers affects accuracy and operation, as does belt tension and dusty or floodable materials. Flexible connections are required to isolate the feeder from upstream and downstream equipment, unless the belt feeder/weigh idler concept is used. 

The proper installation of both orifice plates and Venturi-type flow tubes requires a length of straight pipe upstream and downstream of the sensor, ie, a meter mn. The pressure taps and connections for the differential pressure transmitter should be located so as to prevent the accumulation of vapor when measuring a Hquid and the accumulation of Hquid when measuring a vapor. For example, for a Hquid flow measurement in a horizontal pipe, the taps are located in the horizontal plane so that the differential pressure transmitter is either close-coupled or connected through downward sloping connections to allow any trapped vapor to escape. For a vapor measurement in a horizontal pipe, the taps should be located on the top of the pipe and have upward sloping connections to allow trapped Hquid to drain. 

Many misconceptions exist about cascade control loops and their purpose. For example, many engineers specify a level-flow cascade for every level control situation. However, if the level controller is tightly tuned, the out-flow bounces around as does the level, regardless of whether the level controller output goes direcdy to a valve or to the setpoint of a flow controller. The secondary controller does not, in itself, smooth the outflow. In fact, the flow controller may actually cause control difficulties because it adds another time constant to the primary control loop, makes the proper functioning of the primary control loop dependent on two process variables rather than one, and requites two properly tuned controllers rather than one to function properly. However, as pointed out previously, the flow controller compensates for the effect of the upstream and downstream pressure variations and, in that respect, improves the performance of the primary control loop. Therefore, such a level-flow cascade may often be justified, but not for the smoothing of out-flow. 

Table 18-15 summarizes the several types of commercial centrifuges, their manner of liquid and solids discharge, their unloading speed, and their relative volumetric capacity. When either the liquid or the solids discharge is not continuous, the operation is said to be cycHc. Cyclic or batch centrifuges are often used in continuous processes by providing appropriate upstream and downstream surge capacity. 

The useful parameter for value analysis is the installed cost of the number of centrifuges required to produce the demanded separative effecd (end product) at the specified capacity of the plant. The possible benefits of adjustments in the upstream and downstream components of the plant and the process should be carefully examinee in... 

In the development of new products, optimization of the fermentation medium for titer only often ignores the consequences of the medium properties on subsequent downstream processing steps such as filtration and chromatography. It is imperative, therefore, that there be effective communication and understanding between workers on the upstream and downstream phases of the produc t development if rational trade-offs are to be made to ensure overall optimahty of the process. One example is to make the conscious decision, in collaboration with those responsible for the downstream operations, whether to produce a protein in an unfolded form or in its native folded form the purification of the aggregated unfolded proteins is simpler than that of the native protein, but the refolding process itself to obtain the product in its final form may lack scalabihty. 

Upstream and Downstream Units Upstream and downstream units should be notified of the impending test. If the unit test will last over a period of days, analysts should discuss this with the upstream unit to ensure that they are not scheduling activities that could disrupt feed to the unit under study. Analysts should seek the cooperation of the upstream units by requesting as consistent feed as possible. The downstream units shoiild also be notified to ensure that they will be able to absorb the product from the unit under study. For both units, measurements from their instruments will be useflil to confirm those for the unit under study. If this is the case, analysts must work with those operators and supervisors to ensure that the measurements are made. 

Plant Sufficient personnel and supphes will be required for the test. Personnel may include additional operators, sample-gatherers, pipe fitters, and engineers. Upstream and downstream units need notification so that feed and product rates can be maintained. 

AP = Line pressure drop, psi P], P2 = Upstream and downstream pressures in psi ABS S = Specific gravity of vapor relative to water = 0.00150 MP,/T d = Pipe diameter in inches Ui = Upstream velocity, ft/sec f = Friction factor (assume. 005 for approximate work)... 

Example. A trap on a 150 psi steam line has been found to be blowing live steam on the basis of contact pyrometer measurements taken immediately upstream and downstream of the trap. The catalog rating of the trap is 5,000Ib/hr at saturation temperature (°F sub-cooled) at 150 psi. 

TFIIB is arranged in two domains, both of which have the cyclin fold described in Chapter 6. Both domains bind to the TBP-TATA box complex at the C-terminal stirrup and helix of TBP. The phosphate and sugar moities of DNA form extensive non-sequence-specific contacts with TFIIB both upstream and downstream of the middle of the TATA box. 

Isolation Provide for isolation from upstream and downstream operations. Consider provision of automatic and/or remotely operated isolation. Consider isolation for cleaning needs... 

Pressure relief is not required when the heat exchanger, including upstream and downstream piping and equipment, is designed for two-thirds of the high pressure side design pressure (section 3.18.2). 

The 1997 edition of the API RP 521 extends the two-thirds rule to include the upstream and downstream system. At a minimum, the inlet and outlet piping up to and including isolation valves must be designed for the two-thirds rule to be able to block in the exchanger. If the upstream and downstream equipment is not designed for the two-thirds rule, relief devices may be required on both the inlet and outlet piping to protect the piping and adjaeent equipment. 

O There are several unit operations upstream and downstream filtration, such as reaction and thermal drying, are required by the process flow-scheme O There is a risk of environmental hazard from toxic, flammable or volatile cakes... 

Minimize or eliminate in-process inventory of hazardous material, including inventory in the processing equipment as well as in tanks. Elimination of intermediate storage tanks will likely require improvements in the reliability of the upstream and downstream operations. 

Air filter resistance The pressure drop created between the upstream and downstream faces of a filter, increases as the dust burden. 

For a given shell length the number of pas.ses for each coil can be determined. Since the number of passes both upstream and downstream of the choke must be an even integer, actual Tj and T2 may differ slightly from that assumed in the calculation. The actual values of Tj and T2 can be calculated from actual coil lengths L, and L2. 

If the mixing is "perfect," tlie estuary behavior may be approximated by what chemical engineers define as a continuous stirred tank reactor (CSTR) (5). However, accurately estimating the time and spatial beliavior of water quality in estuaries is complicated by the effects of tidal motion as just described. The upstream and downstream currents produce substantial variations of water quality at certain points in the estuary, and tlie calculation of such variation is indeed a complicated problem. How ei er, the following simplifications provide some reiiitirkably useful results in estimating the distribution of estuarine water quality. 

Closed-position indicators on the valves usually satisfy a system check . These show that the valves are nominally in the closed position but do not actually prove that there is no leakage. A proving system can be met by various systems which prove the soundness of the upstream and downstream safety shut-off valves by sequential pressurization, evacuation, mechanical over-travel with limit switches and a normally open vent valve, or other means. 

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