Relative compression efficiency

Atm. pres. = 14.7 psia = 0 Figure 30.1 Example of relative compression efficiency. 

I like to calculate the relative compression efficiency because I do not have to know the flow of process gas. I do not have to know the driver horsepower output, the steam to the turbine, the fuel gas to the gas turbine, or the speed of the compressor. I do not have to know Z (the gas compressibility factor) or K (the ratio of the specific heats). The things I do have to know—the suction and discharge temperature and pressure—I can check with my own hands and my own tools. 

Caution If the inlet side T1 for any cylinder end is hotter than the main gas inlet header pipe, then there is zero gas flow through this cylinder end. Then both the adiabatic and relative compression efficiencies are also zero. 

If individual thermowells are not available, one can still use the above technique to determine the relative compression efficiency of individual cylinder ends. A contact thermocouple may be used to measure the surface temperature of the compressor discharge valve. It is the relative temperature rise of the compressed gas that is of interest. 

It is worth repeating that the relatively low efficiency for the appKTP crystal is due to the fact that Je (KTP) < Je (KNb03). Performing the same assessment with lithium niobate (LiNbOs) should yield up to four times the efficiency, because dg/f (LiNbOs) = 17.6 pmV. Unfortunately, insufficient power was available to measure the duration of the blue pulses from the bulk appKTP crystal. However, our calculations show that the generated blue pulses would be characterized by an uncompensated duration of 370 fs. These pulses could be compressed to around 270 fs in order to access higher peak powers. 

Figure 3. Pressure dependence of the relative light efficiency for uniaxial compression along [1-10] (1) and [110] (2) directions.

The alternative preferred today is the candle filter shown in figure 5.4. The physical process is one of impingement but because the glass fibre is only one-hundredth of the diameter of the crimped stainless steel wire, the compressed glass fibre candle filters are able to remove the fine mist. They have proved to be relatively cheap, efficient and reliable. Their main disadvantage is pressure drop which can be up to 0.1 bar. For a 2000 tonne per day plant, the extra power consumption is around one megawatt. 

This system suffers from relatively low efficiency due to the relatively large amount of power consumed by the air compressor. To increase the efficiency of the system, water (steam) can replace the role of compressed air. Much less energy is required to raise water pressure than to compress air to the same pressure. The system is illustrated in Fig. 5.58. The system with a bottom cycle based on an open steam turbine cycle has better performances than the one based on an air turbine due to the reduced compression and better conduction of heat in the heat recovery steam generator (HRSG). 

Keywords compressibility, primary-, secondary- and enhanced oil-recovery, drive mechanisms (solution gas-, gas cap-, water-drive), secondary gas cap, first production date, build-up period, plateau period, production decline, water cut, Darcy s law, recovery factor, sweep efficiency, by-passing of oil, residual oil, relative permeability, production forecasts, offtake rate, coning, cusping, horizontal wells, reservoir simulation, material balance, rate dependent processes, pre-drilling. 

Seawater Distillation. The principal thermal processes used to recover drinking water from seawater include multistage flash distillation, multi-effect distillation, and vapor compression distillation. In these processes, seawater is heated, and the relatively pure distillate is collected. Scale deposits, usually calcium carbonate, magnesium hydroxide, or calcium sulfate, lessen efficiency of these units. Dispersants such as poly(maleic acid) (39,40) inhibit scale formation, or at least modify it to form an easily removed powder, thus maintaining cleaner, more efficient heat-transfer surfaces. 

Hydrogen onboard storage systems for vehicles are bulkier, heavier, and costlier than those for liquid fuels or compressed natural gas, but are less bulky and less hca than presently envisaged electric batteries. Even with these constraints, it appears that hydrogen could be stored at acceptable cost, weight, and volume for vehicle applications. This is true because hydrogen can be used so efficiently that relatively little fuel is needed onboard to travel a long distance. 

It may be noted that energy will be required for compressing the air to the injection pressure which must exceed the upstream pressure in the pipeline. The conditions under which power-saving is achieved have been examined by DZIUB1NSKI(25j. who has shown that the relative efficiency of the liquid pump and the air compressor are critically important factors. 

Figure 16.33 shows a schematic of a simple gas turbine. The machine is essentially a rotary compressor mounted on the same shaft as a turbine. Air enters the compressor where it is compressed before entering a combustion chamber. Here the combustion of fuel increases its temperature. The mixture of air and combustion gases is expanded in the turbine. The input of energy to the combustion chamber allows enough power to be developed in the turbine to both drive the compressor and provide useful power. The performance of the machine is specified in terms of the power output, airflow rate through the machine, efficiency of conversion of heat to power and the temperature of the exhaust. Gas turbines are normally used only for relatively large-scale applications, and will be dealt with in more detail in Chapter 23. 

A fuel cell system for automobile application is shown in Figure 1.5 [41]. At the rated power, the PEMFC stack operates at 2.5 atm. and 80°C to yield an overall system efficiency of 50% (based on lower heating value of hydrogen). Compressed hydrogen and air are humidified to 90% relative humidity at the stack temperature using process water and heat from the stack coolant. A lower system pressure is at part load and is determined by the operating map of the compressor-expander module. Process water is recovered from spent air in an inertial separator just downstream of the stack in a condenser and a demister at the turbine exhaust. 

---