Dual-pressure installation

Figure 4-10. Compressor train for dual-pressure installation consisting of an axial flow air compressor with adjustable stator blades and a radial flow nitrous gas compressor and expander. Mass flow air = 139,000 Nm /h, nitrous gases = 122,500 Nm /h Pressure air = 0.82/4.75 bar, nitrous gases = 4.38/10.8 bar Power input total = 16,840 kW Power recovery by expander = 10,950 kW.

Having two degrees of reaction available facilitates the matching of turbocompressors in nitric acid plants, especially in dual-pressure installations, because these two different degrees of reaction may be mixed within the same compressor. 

Figure 15.13 The dual-pressure cycle diagram for a combined-cycle installation...

Pressure measurement for piping and vessels is achieved by the installation of dial indicators or by distributed control systems. The piping and vessels are tapped at the required location and furnished with a 3/4-in threaded or flanged conneaion and a block valve. Tbe dial indicator is screwed into the block ralve if a remote readout system is required, the valve becomes the sensing connection. Like the thermocouple, the dial can be either fixed or swivel-headed to fecilitate readout. A dual local indicator and transmitter s) em needs only one tapping point. Exhibit 14-9 depicts a typical pressure gauge and a dual-pressure system hookup. 

The basis for design overpressure described in this section is related to the ASME Boiler and Pressure Vessel Codes and ANSI B31.3, Code for Petroleum Refinery Piping. Compliance with these codes is a requirement, or is recognized as the equivalent of a requirement in many locations. Where more stringent codes apply, the local requirements must be met. Therefore, local codes must be checked to determine their requirements. For example, some countries do not permit the use of block valves underneath pressure relief valves, unless dual valves with interlocks are installed. Also, in some cases, 20% accumulation under fire exposure conditions is not permitted, and accumulation allowed may be lower than the ASME Codes. In the United States, the ASME Code is mandatory, since it is a requirement under the Occupational Safety and Health... 

The fluid oscillations can be detected by shuttle balls, ultrasonic and piezoelectric detectors. In noisy installations, dual piezoelectric elements provide noise compensation. The various detectors can measure one of the following (1) the oscillating flow across the face of the bluff body, (2) the oscillating pressure difference across the sides of the bluff body, (3) the flow through a passage drilled through the bluff body, (4) the oscillating flow or pressure at the rear of the bluff body, or (5) the presence of free vortices downstream to the bluff body. 

For higher pressure drops, a more erosion-resistant metal is recommended for the slide and seat. Depending upon the particular material employed, the vulnerable parts may be made entirely of this material or merely faced with it. A supported castable wear plate is usually installed on the inside of the body downstream of and opposite the slide. Erosion of slide valves in flue-gas service is usually not a problem if pressure drop does not exceed 6 to 8 p.s.i. (97). A dual-slide valve is normally used in order to maintain center-line flow, and the stack or line downstream of the valve is sized for a maximum velocity of about 100 ft./second to avoid excessive impingement as the gas expands upon leaving the valve restriction. When more than one valve is used in the stack, they should be spaced about 5 line-diameters apart to prevent the discharge from the upstream valve from impinging directly on the internals of the downstream valve. 

The filter beds need to be backwashed periodically as the back pressure increases however, backwashing removes the filter from use. To avoid downtime, often a dual filter bed system is installed. 

Fig. 8.81 Photographs of two high pressure axial screw extruders showing different die changers. (a) Extruder (model 90AD with horizontal mixer/pug sealer and dual hinged mouthpieces (= dies), (b) extruder (model 90AD with hydraulic horizontal die changer dies are not installed in the die holders (courtesy J.C. Steele, Statesville, NC, USA).

Often a boiler has to be designed for dual fuel, e.g., natural gas and heayyipjOL. Sulfur content may also v y. Ilf cH applications it may be justifiable to have the feed water temperature made variable by means of an adjustable feed water heater. Bleed or back pressure steam can be used if available. Thus, optimum use can be made of the installed economizer surface. 

Two modifications of the Berty reactor (19) permitted greater temperature control and more accurate temperature measurements. The first modification involved installation of a 1/8-in. diameter coil in the head of the reactor, through which pressurized air could flow. The air flow through the coil was controlled by a relay switch that was connected to a separate Nanmac temperature controller. The second modification was simply to replace the upper thermocouple by dual chromel-alumel thermocouples (supplied by Thero-Electric) which extended downward into the catalyst bed. One of these thermocouples recorded the bed temperatures as part of a 12-temperature profile, while the other was used to operate the air coil s controller. 

At all reactors but C, there are two complete systems in the 3XX circuit. TWO batteries, two sets of pressure switches, and two latching solenoid mschanisms will allow failure of a single system without the consequence of a "ball drop" A manual pushbutton is located centrally in each control room to trip both systems, thus dropping the balls. Modifications are presently underway at C Reactor to Install a dual system similar to the other reactors. 

When the equipment the PSV is protecting needs to be worked on, the pressure will be bled off the equipment and both upstream and downstream PSV isolation valves will be closed, the piping bled off, and a spade will be installed ahead of the upstream PSV isolation valve. The same procedure applies where there are dual PSVs in parallel. 

For automotive use, an array of thirty-two 5-kWe AFCs were conshucted by Union Carbide and used for propulsion in a General Motors six-passenger van in 1967 [56]. Additionally, a 6-kWe hydrogen/air AFC was installed by K. Kordesch in a lead-acid dual-cell hybrid, and actually ran on public roads for three years with a six-bottle array of compressed hydrogen on the roof [56], using air that was run through a soda hme bed to remove CO2. Modem AFCs now operate at nearly the same conditions as PEFCs, at slightly elevated pressures ( 2 atm) and around 100°C. 

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