Closed discharge system

Fatigue Failure - The combined discharge header system should be designed in accordance with the same considerations of potential piping fatigue failure as described below for closed discharge systems. 

There are many types of closed discharge systems and they can be very complex. They must be subject to careful, individual analysis of piping. 

Relief Valve. A relief valve is a pressure-relief device actuated by inlet static pressure having a gradual lift generally proportional to the increase in pressure over opening pressure. It may be provided with an enclosed spring housing suitable for closed-discharge system application and is primarily used for liquid service. 

Superimposed Back Pressure - Is the pressure at the outlet of the pressure relief valve while the valve is in a closed position. This type of back pressure comes from other sources in the discharge system it may be constant or variable and it may govern whether a conventional or balanced bellows valve should be used in specific applications. 

Closed Disposal System - This is the discharge piping for a PR valve which releases to a collection system, such as a blowdown drum and flare header. However, a closed system can also be a process vessel or other equipment at a lower pressure. 

Examples of such backup features are given for each utility below. In designs where all pressure rehef valves discharge into a closed collection system, because of environmental restrictions, a total failure of one utility deserves more careful consideration since there are no atmospheric releases which would tend to relieve the load on the closed system. 

Safely Volve Required to Protect Against Closed Block Valve Anywhere in Discharge System. 

Discharge systems—to by provide close control of metal buildup. 

Figure 8-3 Three basic types of cooling water systems. Top the once-through system where the cooling water is used once and then discharged. Middle the open recirculation system where the water is cooled and recycled through a system in which it comes in direct contact with air. Bottom a closed recirculation system where the water is cooled and recycled without coming in direct contact with the atmosphere.

An ideal system would have a balance of the rate of recovered water equal to the reinjected water, in a closed-loop system as shown on Figure 9.7. With a continual recycle system, the pumping would continue until cleanup was achieved. Some regulatory authorities do not allow reinjection of untreated or partially treated water. In that case, fresh makeup water must be continually provided from a nearby source and pumped water must be discharged to a suitable location such as a publicly owned treatment works or surface water body. 

This practice is undesirable because the addition of makeup water often results in the discharge of phossy water, unless an auxiliary tank collects phossy water overflows from the storage tanks, thus ensuring zero discharge. A closed-loop system is then possible if the phossy water from the auxiliary tank is reused as makeup for the main phosphorus tank. 

Is a self-contained, closed-loop system that produces no secondary discharges or air emissions. 

To maintain environmental impact at a minimum, cooling-tower systems must be designed to abate both thermal and chemical pollution in blowdown stream. The latter is accomplished by treating blowdown prior to discharge or reuse. Sedimentation and other methods prepare blowdown streams for discharge to the natural environment. Evaporation or reuse permits a closed cooling system. 

Superimposed backpressure Superimposed backpressures acting on the outlet of an SRV can be either constant or variable. Superimposed backpressure occurs when the valve is closed and pressure already exists at the outlet of the valve. This is due to existing constant and/or variable pressures which exist in the discharge system. 

There are two kinds of discharge systems open and closed. Open systems discharge directly into the atmosphere, whereas closed systems discharge into a manifold or other fluid recuperation device, eventually, along with other SRVs. Both systems can create backpressures, which need to be taken into account at all times when sizing and selecting the correct SRV. 

One of the main concerns in closed systems is the built-up backpressure in the discharge system as this can drastically affect the performance of an SRV. 

Even though the reaction force due to the exhaust jet to atmosphere is significantly greater than the change in momentum component, the API makes no distinction for SRVs discharging into a closed header system compared with discharging through a tail pipe or direct to atmosphere. 

The screw extruder is equipped with a die, and the flow rate of the extruder as well as the pressure rise at a given screw speed are dependent on both, as shown in Fig. 6.16. The screw characteristic line at a given screw speed is a straight line (for isothermal Newtonian fluids). This line crosses the abscissa at open discharge (drag flow rate) value and the ordinate at closed discharge condition. The die characteristic is linearly proportional to the pressure drop across the die. The operating point, that is, the flow rate and pressure value at which the system will operate, is the cross-point between the two characteristic lines, when the pressure rise over the screw equals the pressure drop over the die. 

We recall that at closed discharge conditions fluid particles stay at a fixed axial position. This means that the fluid in the crosshatched incremental volume Ay = nNDHAl does not leave it. Some fluid is dragged over the flight and recycled to the bulk, and since within the volume element the fluid circulates due to the drag of the barrel surface, we can model the system as a well-stirred tank with recycle, as shown in Fig. 9.17. 

Figure 13.15 Changes in thickness and refractive index of TMS plasma coatings with discharge time in a closed reactor system TMS 25 mT, 2 panels of Alclad 7075-T6, DC lOOOV.

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