Upstream Devices

Some limitations are associated with UV radiation for disinfection. These include (1) The process performance is highly dependent on the efficacy of upstream devices that remove suspended solids (2) Another key factor is that the UV lamps must be kept clean in order to maintain their peak radiation output (3) A further drawback is associated with the fact that a thin layer of water (< 0.5 cm) must pass within 5 cm of the lamps. 

As in a continuous flow process downstream apparatus is directly linked to upstream devices, the complete production line is interrupted in case of a failure upstream. It will be examined if this failure behavior can be corrected either by the design of several parallel lines or by supplying buffer tanks, additional spare pumps, machines,... 

Reliable and uninterrupted flow of materials from some upstream device (typically a bin or... 

Uniform withdrawal of materials from the outlet of the upstream device, which is particularly important if a mass-flow pattern is desired, such as to control segregation, provide uniform residence time, and minimize caking or spoilage in dead regions... 

Minimal loads acting on the feeder from the upstream device, minimizing the power required to operate the feeder, as well as particle attrition and abrasive wear of the feeder components... 

In false twist texturing (FTT), shown schematically in Figure 7, a device twists yam upstream of its location as the threadline passes across a heater, and the yam untwists downstream from the device and is wound up. If the yam is not heated downstream from the twist device, it has bulk and high elasticity (stretch). If the yam is heated downstream from the twist device, it has bulk, but much less stretch. FTT machines initially used two steps to sequentially draw and texture. Later machines combined those steps to simultaneously draw and texture (92). Initial machines used pin spindles as the false twist device. Texturing speeds were about 150 m/min and slowly increased to about 300 m/min. As POY quaUty and stmctural stabiUty improved, new... 

On upstream side of the primary device On downstream side... 

Nonparenthetical values are zero additional uncertainty. Parenthetical values are 0.5% additional uncertainty. AU. straight lengths are expressed as multiples of the pipe diameter D. They are measured from the upstream face of the primary device. 

The wedge restriction has no critical surface dimensions or sharp edges and tends to retain accuracy despite visible corrosive or erosive wear. It is commonly appHed to high viscosity Hquids, slurries, and hot multiphase mixtures. A similar device is also available using a cone, positioned so that its large diameter is upstream, mounted on the meter centerline. 

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. 

Rupture Disks A rupture disk is a device designed to function by the bursting of a pressure-retaining disk (Fig. 26-15). This assembly consists of a thin, circular membrane usually made of metal, plastic, or graphite that is firmly clamped in a disk holder. When the process reaches the bursting pressure of the disk, the disk ruptures and releases the pressure. Rupture disks can be installed alone or in combination with other types of devices. Once blown, rupture disks do not reseat thus, the entire contents of the upstream process equipment will be vented. Rupture disks are commonly used in series (upstream) with a relief valve to prevent corrosive fluids from contacting the metal parts of the valve. In addition, this combination is a reclosing system. 

Device for adding water to oil Cannot point upstream Can point upstream... 

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. 

Relief Valve - A relief valve is an automatic pressure-relieving device actuated by the static pressure upstream of the valve, and whieh opens in proportion to the increase in pressure over the opening pressure. It is used primarily for liquid service. 

Pressure levels at the flare header depend largely on the type and nature of pressure relieving devices that have been specified to protect upstream equipment, as well as the pressure levels of all equipment connected directly to the flare stack. 

In Chapter 2 we developed models based on analyses of systems that had simple inputs. The right-hand side was either a constant or it was simple function of time. In those systems we did not consider the cause of the mass flow—that was literally external to both the control volume and the problem. The case of the flow was left implicit. The pump or driving device was upstream from the control volume, and all we needed to know were the magnitude of the flow the device caused and its time dependence. Given that information we could replace the right-hand side of the balance equation and integrate to the functional description of the system. 

FIGURE 13.39 Example of a measurir(g- with water removal upstream of the gas-metering device ... 

Primary airflow rate The mass or volume of air entering a supply air terminal device in unit time from an upstream duct or a plenum box. Or the air leaving through an opening and entering a space. 

Each cylinder discharge line should have a relief valve located upstream of the cooler. Like all reciprocating devices, the piston will continue to increase pressure if flow is blocked. The relief valve assures that nothing is overpressured. It must be located upstream of the coolers as icc can form in the coolers, blocking flow. 

As long as pressure, level, and temperature control devices are operating correctly, the safety system is not needed. If the control system malfunctions, then pressure, level, and temperature safety switches sense the problem so the inflow can be shut off. If the control system fails and the safety switches don t work, then relief valves are needed to protect against overpressure. Relief valves are essential because safety switches do fail or can be bypassed for operational reasons. Also, even when safety switches operate correctly, shutdown valves take time to operate, and there may be pressure stored in upstream vessels that can overpressure downstream equipment while the system is shutting down. Relief valves are an essential element in the facility safety system. 

If relief valves discharge to a common header, it is sometimes convenient to install downstream block valves so that the relief valve can be removed for repairs without shutdown of all equipment tied into the common header. Where either upstream or downstream block valve.s are used they should be full bore gate or ball valves with a device that enables them to be locked open and sealed. These are often referred to as... 

The mere fact that voltage, current, or even both, are at low levels does not guarantee a circuit to be intrinsically safe, even though intrinsically safe circuits do utilize relatively low voltage and current levels. Intrinsically safe systems employ electrical barriers to assure that the system remains intrinsically safe. The barriers limit the voltage and current combinations so as not to present an ignition hazard should a malfunction develop. Typically, devices upstream of barriers are not intrinsically safe and are installed in control rooms or other unclassified locations. All devices and wiring on the downstream side of the barriers are intrinsically safe and can be installed in classified areas. 

Velocity flame stoppers have been used for feeding waste fuel gas to furnace burners when the gas can become flammable due to contamination with air. They have also been used for feeding waste or depleted air streams to furnaces when the air streams can become contaminated with flammable gases (Howard 1982). It should be noted that a furnace pressure transient may render this device ineffective and consideration should be given to providing an upstream detonation flame arrester. In this arrangement a demand will only be placed on the detonation flame arrester when the velocity flame stopper fails. Therefore, detonation flame arrester maintenance should be minimal. 

These conditions are similar to flow through orifices, nozzles, and venturi tubes. Flow through nozzles and venturi devices is limited by the critical pressure ratio, r,. = downstream pressure/upstream pressure at sonic conditions (see Figure 2-38C). 

Safety-Relief Valve this is an automatic pressure-relieving device actuated by the static pressure upstream of the valve and characterized by an adjustment to allow reclosure, either a pop or a non-pop action, and a nozzle type entrance and it reseats as pressure drops. It is used on steam, gas, vapor and liquid (with adjustments), and is probably the most general tyqDe of valve in petrochemical and chemical plants (Figures 7-3, 7-3A, and 7-4). Rated capacity is reached at 3% or 10% overpressure, depending upon code and/or process conditions. It is suitable for use either as a safety or a relief valve [1,10]. It opens in proportion to increase in internal pressure. 

Critical pressure will normally be found betw een 53% and 60% of the upstream pressure, P, at time of relief from overpressure, including accumulation pressure in psia. That is, P represents the actual pressure at which the relief device is blowing or relie ing, w hich is normally above the set pressure by the amount of the accumulation pressure, (see Figure 7-7A). 

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