High-pressure streams, energy

In plants such as oil refineries that have many streams at high temperatures or high pressures, their energy can be utilized to generate steam or to recover power. The two cases of Example 1.4... 

Turbines can be used to recover energy from high-pressure liquid streams. However, they are not used when the high-pressure stream is a saturated liquid. Why Illustrate by determining the downstream state for isentropic expansion of saturated liquid water at 5 bar to a final pressure of 1 bar. 

Turbines (Expanders) High-velocity streams from nozzles impinging on blades attached to a rotating shaft form a turbine (or expander) through which vapor or gas flows in a steady-state expansion process which converts internal energy of a high-pressure stream into shaft work. The motive force may be provided by steam (turbine) or by a high-pressure gas (expander). 

The jet pump relies on the same hydraulic power being delivered sub-surface as to the hydraulic reciprocating pump, but there the similarity ends. The high-pressure power fluid is accelerated through a nozzle, after whioh it is mixed with the well stream. The velocity of the well stream is thereby increased and this acquired kinetic energy is converted to pressure in an expander. The pressure is then sufficient to deliver the fluids to surface. The jet pump has no moving parts and can be made very compact. 

The hquid-phase processes are more energy efficient than the vapor-phase processes, however, they iacur costiy high pressure equipment investment and also produce waste streams containing used catalyst (213). Both methods produce substantial quantities of by-products which cause refining difficulties. The by-products consist primarily of mesitylene [108-67-8] phorone [504-20-17, and the foUowiag xyUtone isomers (215) ... 

Cog enera.tion in a. Steam System. The value of energy in a process stream can always be estimated from the theoretical work potential, ie, the deterrnination of how much power can be obtained by miming an ideal cycle between the actual temperature and the rejection temperature. However, in a steam system a more tangible approach is possible, because steam at high pressure can be let down through a turbine for power. The shaft work developed by the turbine is sometimes referred to as by-product power, and the process is referred to as cogeneration. 

Two-fluid (see Fig. 14-87h). Gas impinges coaxially and supplies energy for breakup. High velocities can he achieved at lower pressures because the gas is the high-velocity stream. Liquid-flow passages can he large, and hence plugging can he minimized. Because gas is also accelerated, efficiency is inherently lower than pressure nozzles. 

When a large flow of gas is reduced from a high pressure to some lower pressure, or a high-temperature process stream (waste heat) is available at moderate pressures, turboexpanders should be considered to recover the energy (see Figure 7-22). The turbine can drive a compressor... 

Wet scrubbers rely on a liquid spray to remove dust particles from a gas stream. They are primarily used to remove gaseous emissions, with particulate control a secondary function. The major types are venturi scrubbers, jet (fume) scrubbers, and spray towers or chambers. Venturi scrubbers consume large quantities of scrubbing liquid (such as water) and electric power and incur high pressure drops. Jet or fume scrubbers rely on the kinetic energy of the liquid stream. The typical removal efficiency of a jet or fume scrubber (for particles 10 g. or less) is lower than that of a venturi scrubber. Spray towers can handle larger gas flows with minimal pressure drop and are therefore often used as precoolers. Because wet scrubbers may contribute to corrosion, removal of water from the effluent gas of the scrubbers may be necessary. 

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