Pressure-drop regulator

Bubble-Tube Systems The commonly used bubble-tube system sharply reduces restrictions on the location of the measuring element. In order to ehminate or reduce variations in pressure drop due to the gas flow rate, a constant differential regulator is commonly employed to maintain a constant gas flow rate. Since the flow of gas through the bubble tube prevents entiy of the process liquid into the measuring system, this technique is particularly usefiil with corrosive or viscous liquids, liquids subjec t to freezing, and hquids containing entrained solids. 

Gate valves are used to minimize pressure drop in the open position and to stop the flow of fluid rather than to regulate it. The problem, when the valve is closed, of pressure buildup in the bonnet from cold liquids expanding or chemical action between fluid and bonnet should be solved oy a relief valve or by notching the upstream seat ring. 

When a pulsation frequency coincides with a mechanical or acoustic resonance, severe vibration can result. A common cause for pulsation is the presence of flow control valves or pressure regulators. These often operate with high pressure drops (i.e., high flow velocities), which can result in the generation of severe pulsation. Flashing and cavitation can also contribute. 

To save energy, many HVAC systems employ a mechanism for regulating the flow of outdoor air called an economizer cycle. An economizer cycle takes advantage of milder outdoor conditions to increase the outside air intake and in the process reduces the cooling load on the system. Controlling the rate of flow of outdoor air appears simple, in theory, but often works poorly m practice. The small pressure drop required to control the flow rate of outdoor air is rarely controlled and monitored. Quite often, the damper system used to regulate the airflow is nonfunctional, disconnected from the damper actuators, or casually adjusted by building operators (Institute of Medicine, 2000). 

As the compressed air is used, the pressure drops in the reservoir until the low-pressure set point is reached. At this point, the pressure regulated solenoid valve is deenergized. This causes the hydraulic force to drop off on the low-pressure suction valve, restoring it to the full compression cycle. 

The stripper bottoms contain Cj s, C4 s, and gasoline the debutanizer separates the Cj s and C4 s from the gasoline. In some units, the hot stripper bottoms can be further preheated before entering the debutanizer. In a number of units, the stripper bottoms is sent directly to the debutanizer. The feed enters about midway in the tower. Debutanizer feed is always partially vaporized because the debutanizer operates at a lower pressure than the stripper. A control valve that regulates stripper bottoms level is the means of this pressure drop. As a result of this drop, part of the feed is vaporized across the valve. 

The purpose of the regenerated catalyst slide valve is threefold to regulate the flow of regenerated catalyst to the riser, to maintain pressure head in the standpipe, and to protect the regenerator from a flow reversal. Associated with this control and protection is usually a 1 psi to 8 psi (7 Kp to 55 Kp) pressure drop across the valve. 

If a control valve is included, the pressure drop in the whole system should be increased by 50%. If a valve is to control a flow rate adequately, a major portion of the pressure drop must be across that valve. If it is not, a change in the percentage it. is open will not have much effect on the flow rate, which is what the valve is supposed to regulate. 

Installation of conical reducers immediately downstream of a regulator or control valve will allow a more gradual expansion of hydrogen gas to larger piping, and reduce turbulence and pressure drop during hydrogen gas expansion. 

Several units with a PM collection device located upstream of the SCR have seen increased pressure drop from fine particulates accumulating on the catalyst bed. Soot blowers have been partially successful in this application. When the SCR is applied to a CO boiler with limited pressure drop, the SCR has typically been located upstream of PM removal to avoid this problem. Some refiners have chosen to install a spare SCR reactor to provide redundancy due to pressure drop concerns. Others have used a bypass where local regulations allow. 

C. Large-scale oxidation protocol. The large-scale oxidations reactions were carried out in a 300mL Parr autoclave equipped with an injection port, a thermocouple port, a septa sealed addition port and port connected to the volumetric measurement and gas supply module. The module consists of a forward pressure regulator and a calibrated ballast reservoir. The pressure in the reactor and in the ballast reservoir is monitored constantly and the pressure drop in the ballast reservoir is constantly converted into moles of oxygen uptake recorded vs. the time. 

As the chlorine passes initially into the bottle, the pressure rises rapidly. Shaking greatly increases the rate of absorption, and the pressure drops. The chlorine valve is then regulated so as to maintain the proper pressure with shaking. One hundred millimeters was selected as the approximate pressure, since the rate of chlorination under this pressure is satisfactory. 

Some of the possibilities are illustrated in Figures 17.13 and 17.18. Variations from a single large bed are primarily because of a need for control of temperature by appropriate heat transfer, but also for redistribution of the flow or for control of pressure drop. There are few fixed bed units that do not have some provision for heat transfer. Only when the heat of reaction is small is it possible to regulate the inlet temperature so as to make adiabatic operation feasible butane dehydrogenation, for example, is done this way. 

A. Flow Control without Feedback. Plow can be controlled by means of a needle valve if the pressure drop across the valve is constant. The pressure on the upstream side often can be held constant with a single- or two-stage mechanical diaphragm regulator (Section 10.1. B). If the stream of gas does not experience a variable constriction after the needle valve, the above combination provides a simple and convenient means of providing a steady flow. Often an arrangement such as this is used in conjunction with a rotameter or electronic mass flow meter (Fig. 7.14). 

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