Gas compression duty

Results of process calculations of all cases are summarized in Table 16. The major variations on the thermal and C-efficiencies were lower values in Case DPOM-3 resulting mainly from a lower CH3OH selectivity. There was a small reduction in the heat-transfer duty in Case DPOM-2 due to lower recycle flow. In Case DPOM-3, higher CO, selectivity resulted in a 23% increase in O2 consumption, a 35% increase in steam generation, and a large increase in energy required for gas (mainly O2) compression. All of them contributed to substantial increases in both the heat-transfer and the gas compression duties. 

The final energy input is power for the three gas-compression duties synthesis gas compression, synthesis loop circulation, and ammonia refrigeration. The power required for these duties depends, for example, on synthesis pressure and on converter design. Refrigeration power is strongly dependent on ambient temperature. However, typical figures for a modern 1000 ton per day low-pressure... 

The large, heavy-duty, integral engine-compressor has long been the workhorse of the gas compression industry. The in-line or V-shaped power cylinder, horizontal compressor cylinder configuration is lamitiar. 

The Clow Model GMZ check valves installed in the OP-III process gas compression system were not appropriately designed and manufactured for the heavy-duty service they were subject to in OP-III. This resulted in the valves being susceptible to shaft flow-out during normal use. 

Most gas-fired, heavy-duty gas turbines installed as of 1996 operate at gas pressures between 1.2 and 1.7 MPa (180—250 psig). However, aero derivative gas turbines and newer heavy-duty units can have such high air-inlet compression ratios as to require booster compressors to raise gas inlet pressures, in some cases as high as 5.2 MPa (750 psig). 

FIGURE 16.42 Measured emissions of (a) particles (PM) and (b) NO, from more than 300 buses and heavy-duty trucks running on compressed natural gas (CNG), two diesel fuels, or alcohol fuels (E93, E95, and M100). The bars are the means and the boxes encompass the 95% confidence intervals. E93 = 93% ethanol, 5% methanol, 2% K-l kerosene E95 = 95% ethanol, 5% gasoline M100 = 100% methanol (adapted from Wang et al., 1997). 

Polytropic efficiencies are obtained from measurements of power consumption of test equipment. They are essentially independent of the nature of the gas. As the data of Figure 7.27 indicate, however, they are somewhat dependent on the suction volumetric rate, particularly at low values, and on the compression ratio. Polytropic efficiencies of some large centrifugal compressors are listed in Table 7.6. These data are used in Example 7.9 in the selection of a machine for a specified duty. 

The use of natural gas as a vehicle fuel has been known for many years -however, basically as compressed natural gas (CNG). The volume of natural gas consumed by transportation vehicles is projected to rise from 5300 TJ in 1996 to around 620 000 TJ in 2015. Expectedly 50% of this gas is going to be consumed by the heavy-duty trucks [16], It is further assumed that targeting of a fleet of vehicles with high fuel demand would make LNG utilisation more economical. This may also be required in order to justify the incremental cost of the vehicles and the infrastructure. 

The second stage of compression uses a centrifugal compressor with a gas expander drive. It has a duty of approximately 3400 brake horsepower. Using Ref. CE9 (Figure 13.50, p.561), the estimated cost is US 55 0 000 (1979). The final Australian cost is adjusted to be As951 000. 

The synthesis loop boiler on the exit of the converter is also a very important piece of equipment. In some modern plants not equipped with an auxiliary boiler it supplies nearly half of the total steam generation. It may generate as much as 1.5 t of steam per tonne of ammonia, equivalent to about 90% of the reaction heat. Fire-tube versions have been also used, including Babcock-Borsig s thin-tubesheet design. But compared to the secondary reformer service, where the gas pressure is lower than the steam pressure, the conditions and stress patterns are different. In the synthesis loop boiler the opposite is the case, with the result that the tubes are subjected to longitudinal compression instead of being under tension. Several failures in this application have been reported [993], and there was some discussion of whether this type of boiler is the best solution for the synthesis loop waste-heat duty. 

There is interest in compressed natural gas (CNG), which is largely methane, as a clean fuel for passenger and heavy-duty vehicles. However, relative cost and ease of distribution and availability are additional factors to be considered in order for its use to become widespread. In contrast to U.S. legislation, in Europe methane is not excluded from the hydrocarbon emission measurement, and so it would appear that the European requirements... 

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