Expanding gas flows

Energy Addition to Expanding Gas Flows. In connection with the analyses of optimal rocket engine cycles, it is of interest to develop generalized solutions for the equations of motion with heat addition. An efficient technique is to write the fraction of reaction completed (c), at any station, as a function of the square of the local Mach number (M2), in the form... 

For expanding gas flow, Vj V, with horizontal pipe, Z2 = Zj. Hence, the differential form of Bernoulli s equation can be expressed as... 

In expanding gas flow, the pressure and density ratio are constant P dp... 

The fluidized-bed system (Fig. 3) uses finely sized coal particles and the bed exhibits Hquid-like characteristics when a gas flows upward through the bed. Gas flowing through the coal produces turbulent lifting and separation of particles and the result is an expanded bed having greater coal surface area to promote the chemical reaction. These systems, however, have only a limited abiUty to handle caking coals (see Fluidization). 

The expander turbine is designed to minimize the erosive effect of the catalyst particles stiU remaining in the flue gas. The design ensures a uniform distribution of the catalyst particles around the 360° aimulus of the flow path, optimizes the gas flow through both the stationary and rotary blades, and uses modem plasma and flame-spray coatings of the rotor and starter blades for further erosion protection (67). 

The expanded version of the van Deem ter equation is used to help understand the relationships between the packing parameters and the gas flow. 

Expander effieieney is related to gas flow, enthalpy drop, and shaft rotating speed. The eombination of these parameters defines impeller blade geometries required to maximize thermal effieieney. Expander... 

Expander performance will shift as plant conditions—such as gas flowrate, gas inlet, and discharge pressure—gas composition, and inlet temperature change. Calculation of expander diermal efficiency from field data is not accurate because expander discharge flow normally consists of two phases, gas and liquid. Efficiency calculations should always be cross-checked with the shaft power produced before any decision on expander performance is made. 

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.

An inerease in ambient air temperature will deerease the available energy for the generator. This assumes that the fresh feed and eoke burn remains eonstant. The expander horsepower does not ehange, but the air blower horsepower inereases with inereased air temperature, eausing the exeess energy to deerease. Steam and water may need to be added to the flue gas flow at various points in the system to eontrol afterburning. In Figure 4-64, the solid eurves are for a normal flow of steam. The dotted eurves are for inereases in the steam rate by 3.05 times, 4.85 times, and 6.05 times the normal flowrate. 

The main flue gas flow was ducted through the expander instead of through the double slide valve. 

At the rated duty point, the differential pressure eontroller is aetive. The inlet eontrol valve and trip valve are eompletely open. The main bypass valve is eompletely elosed and the small bypass valve eontrols the differential pressure. Approximately 96%-98% of the flue gas flows through the expander, with the rest passing through the small bypass valve, orifiee ehamber, and double slide valve to the expander outlet to rejoin the main flue gas flow. 

Under normal operations, the existing differential pressure governor is switehed to manual and the double slide valve is wide open. This valve must be suffieiently opened so that, even in the event of an emergeney expander trip, the entire flue gas flow ean pass through the double slide valve without the regenerator diseharge pressure inereasing to nonpermissible levels. 

In cases where gas flow is about 20% less than rated, the inlet pressure should also decline by 20%. In the Jinan expander, this pressure decrease is about 0.25 MPa. 

As is shown in Fig. 4.3a, the lower pressure cooling is fed by air i/(l at state 7, at a corresponding pressure p-j and a temperature T, and this mixes with air (1 + 4>w) froni the HP exhaust at temperature T,) to produce a temperature Tg as indicated in the diagram. The full turbine gas flow (1 + i/() then expands through a pressure ratio Al to a temperature Tio, and subsequently rejects heat, finishing at Tj = Ta. 

For two step cooling, now with irreversible compression and expansion, Fig. 4.7 shows that the turbine entry temperature is reduced from Ti. to by mixing with the cooling air i/ H taken from the compressor exit, at state 2, pressure p2, temperature T2 (Fig. 4.7a). After expansion to temperature Tg, the turbine gas flow (1 + lp ) is mixed with compressor air at state 7 (mass flow i/h.) at temperature Tg. This gas is then expanded to temperature T g. 

Coupling HPLC to a mass spectrometer is far more complicated than in a GC system because of the large amount of mobile phase solvent expanding into the system (see Table 1 for expansion volumes). Typical mobile phase flow rates for HPLC are 0.5-2 mL min which translates into gas flow rates of 100-3000 mL min . ... 

Now consider the case of steady, compressible flow in a straight pipe. As the gas flows from high pressure to lower pressure it expands and, by continuity, it must accelerate. Consequently, the momentum flow rate increases along the length of the pipe, although the mass flow rate remains constant. 

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