Generating at High Pressure

Here n is the number of moles and R is the universal gas constant. The temperature term T needs no subscript because the temperature is constant. The motor and pump driving 

For the alternative approach - operation of an electrolyser at high pressure - the energy cost is the Nemst voltage rise, as discussed in Section 2.5. Here it was shown that the voltage rise resulting from an increase in hydrogen pressure only is 

This increase in voltage can be transposed to work and Joules as follows. The extra work done when a charge Q flows through the electrolyser cell is 

We saw in Chapter 2 that the charge produced by one mole of hydrogen is IF, where F is the Faraday constant. Similarly, IF coulombs are needed for each gram mole of hydrogen. The work done in producing n moles of hydrogen at high pressure is thus 

This equation is exactly the same as equation 8.12. The fact that two such different methods of compressing a gas should require the same work is one of those coincidences that makes science, engineering, and thermodynamics so interesting. Of course it is not really a coincidence. The Nemst equation that gave us equation 8.13 was derived using the same thermodynamic laws that gave us equation 8.12. 

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In order to damp almost completely the pulses generated at high pressure in a dual-head, special-drive piston reciprocating pump, the electronic correction circuitry in the Altex Model 100 pump calculates the average back-pressure and then corrects the speed of the pump motor so as to maintain the actual pressure close to the average calculated pressure. The effect of this correction is to speed up the motor momentarily when pumping is switched from one piston to the... 

Recently, in situ studies of catalytic surface chemical reactions at high pressures have been undertaken [46, 47]. These studies employed sum frequency generation (SFG) and STM in order to probe the surfaces as the reactions are occurring under conditions similar to those employed for industrial catalysis (SFG is a laser-based teclmique that is described in section A 1.7.5.5 and section BT22). These studies have shown that the highly stable adsorbate sites that are probed under vacuum conditions are not necessarily tlie same sites that are active in high-pressure catalysis. Instead, less stable sites that are only occupied at high pressures are often responsible for catalysis. Because the active... 

Centrifugal blowers or turbines usually cannot generate enough pressure difference to overcome the added resistance of the recycle pipes. In addition, some components may condense out in the cooler, especially with high-boiling materials or at high pressures. These must be recycled by a liquid pump through an evaporator. This in turn makes them approach a steady-state slowly. ... 

The above discussion holds for dispersion by atmospheric turbulence. In addition, a momentum release of fuel sometimes generates its own turbulence, e.g., when a fuel is released at high pressure in the form of a high-intensity turbulent jet. Fuel mixes rapidly with air within the jet. Large-scale eddy structures near the edges of the jet entrain surrounding air. Compositional homogeneity, in such cases, can be expected only downstream toward the jet s centerline. 

The condensing steam cycle is shown diagrammatically in Figure 15.8. The fuel is tired in a boiler that converts the heat released from combustion to steam at high pressure and temperature. This steam is then expanded through a turbine for generation of electrical power. 

An example is shown in Figure 15.14. By raising steam at high pressure (say, 60 bar-absolute and 540°C) and then expanding this through a turbine to the process steam pressure requirements of 3 bar then useful work can be done by the turbine for generation of electrical power. For this example, each kg/s of steam gives 590 kW of electrical power. 

DEHA breaks down at high pressure. Its survival pressure is probably not in excess of 1,250 psig, but because of its high volatility and rapid reaction rate, it generally provides complete boiler cycle oxygen-control coverage. Some limited ammonia is also generated, and this may be useful for carbon dioxide neutralization. 

Annealing drawn PE hydrostatically at high pressure, generates a wide spectrum of crystal thicknesses varying from the common oriented chain folded to the chain-extended structures — where folds and ties tend to disappear63 —. This range of crystal thicknesses coupled with the chain axis orientation, offers a suitable model in... 

Every gas shows deviations from ideal behavior at high pressure. Figure 11-6 shows PV/nRT for He, F2, CH4, and N2, all of which are gases at room temperature. Notice that PV/nRT for helium increases steadily as pressure increases. Interatomic forces for helium are too small to reduce the ratio below 1, but the finite size of the helium atom generates deviations from ideality that become significant at pressures above 100 atm. 

J. Phys. Chem. B, 106, 5143-5154. Somorjai, G. A. and Rupprechter, G. (1999) Molecular studies of catalytic reactions on crystal surfaces at high pressures and high temperatures by infrared-visible sum frequency generation (SFG) surface vibrational spectroscopy. J. Phys. Chem., 103, 1623-1638. 

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