Limiting differential pressure

Control Systems. Control systems are used to regulate the addition of Hquid waste feed, auxiHary fuel, and combustion air flows to the incinerator furnace. In addition, scmbber operation is automated to help ensure meeting emission limits. Flows are measured using differential pressure... 

A pressure limiting controller, in the event of excessively high absolute pressure in the regenerator, disables the differential pressure controller and limits the pressure to a preset maximum value. 

The pressure limiting eontroller prevents the absolute diseharge pressure from the regenerator from exeeeding an upper threshold. The aetion signal from this eontroller overrides the aetion of the differential pressure eontroller. 

If the system differential pressure requirements are low, sometimes a fan can be used. A fan is limited to a maximum of about 65 inches of water (just over 2psi) in vacuum service or 77 inches of water in pressure service (just under 3psi). To estimate fan horsepower use the equations found in Chapter 6 in the section entitled Horsepower Calculation. In lieu of manufacturer s data use an adiabatic efficiency of 50% for initial work. 

Even though 15 psi is possible from a blower, most positive-pressure systems are limited to 10-12psi differential pressure because of limits of the rotary air lock feeder valves (deflections in shaft and bearings and increased blowback air). 

Rupture discs are also used below relief valves to protect them from corrosion due to ves.sel fluids. The rupture disc bursts first and the relief valve immediately opens. The relief valve reseals, limiting flow when the pressure declines. When this configuration is used, it is necessary to monitor the pressure in the space between the rupture disk and the relief valve, either with a pressure indicator or a high pressure switch. Othei-wise, if a pinhole leak develops in the rupture disk, the pressure would equalize on both sides, and the rupture disk would not rupture at its set pressure because it works on differential pressure. 

As the positive displacement motor is lowered and weight is placed on the motor and thus the bit, the motor speed continues but the differential pressure increases, resulting in an increase in torque and horsepower. As more weight is added to the positive displacement motor and bit, the torque and horsepower will continue to increase with increasing differentiated pressure (i.e., standpipe pressure). The amount of torque and power can be determined by the pressure change at the standpipe at the surface between the unloaded condition and the loaded condition. If too much weight is placed on the motor, the differential pressure limit for the motor will be reached and there will be leakage or a mechanical failure in the motor. 

Figure 4-205. Positive displacement motor, 6y4-in. outside diameter, 5 6 lobe profile, 400 gal/min, differential pressure limit 580 psi. (Courtesy Smith International, Inc.)...

This can be a real problem for baghouses that rely on automatic timers to control cleaning frequency. The use of a timing function to control cleaning frequency is not recommended unless the dust load is known to be consistent. A better approach is to use differential-pressure gages to physically measure the pressure drop across the filter media to trigger the cleaning process based on preset limits. 

Catalyst circulation can also be limited by mechanical problems with the slide/plug valves. They may have limited travel or will not open fully. This is indicated by the lack of response when an adjustment is made. The differential pressure and the flow will not change. Troubleshooting the valves is a function of the valve design and the vendor will supply troubleshooting information,... 

You are to specify an orifice meter for measuring the flow rate of a 35° API distillate (SG = 0.85) flowing in a 2in. sch 160 pipe at 70°F. The maximum flow rate expected is 2000 gal/hr and the available instrumentation for the differential pressure measurement has a limit of 2 psi. What size orifice should be installed ... 

Pressure nozzles are somewhat inflexible since large ranges of flowrate require excessive variations in differential pressure. For example, for an atomiser operating satisfactorily at 275 kN/m2, a pressure differential of 17.25 MN/m2 is required to increase the flowrate to ten times its initial value. These limitations, inherent in all pressure-type nozzles, have been overcome in swirl spray nozzles by the development of spill, duplex, multi-orifice, and variable port atomisers, in which ratios of maximum to minimum outputs in excess of 50 can be easily achieved(34). 

A differential pressure sensor monitors the pressure drop across the reactor, giving also an indication of the coke formation. The outside shell of the reactor is thermally insulated to limit heat loss. 

CA 68,61112 (1968) [The authors report on their mathematical analysis of the expl decompn of mixts of H azide with w. From kinetic data and IR spectra of the decompn products a series of reactions were developed to describe the initiation, growth, and completion of the decompn (deton) process. From these reactions the authors derived a series of differential equations based on the variation of the energy of activation with time. They found that the limiting partial pressure of H azide ign is dependent upon the partial pressure of the diluent (w)l... 

C, activity coeff. y°°-differential pressure transducer, Wright et al. 1992) 12300 (20°C, limiting activity coeff. y by equilibrium air stripping-GC, Hovorka Dohnal 1997)... 

The maximum operating temperature is 195°F (90°C). The maximum feed pressure is only limited by the mechanical design pressure of the flanges on the pressure vessel. The maximum differential pressure across the membrane... 

Experiments to measure pressure drop and flooding limits were performed in a set-up accommodating monoliths with diameters of 43 mm (Fig. 8.16), while the length of the monoliths varied up to total length of 1 meter. The liquid was distributed by a nozzle the gas was introduced in countercurrent mode via mass flow controllers in the system. At the outlet of the monolith, a special device was mounted (Fig. 8.17), which improved draining of the monolith. The pressure drop along the column was measured using differential pressure transmitters. All experiments were performed at room temperature and atmospheric pressure. 

---