Location, processing efficiency

Gas-to-liquids plants are generally located close to natural gas fields, as the transport costs for liquid fuels are less than those for gaseous fuels. The production of GTL is considered to be an alternative to liquefied natural gas (LNG), specifically when focusing on the end-product vehicle fuel and not the long distance transport of energy. In 1993, a first large-scale GTL plant was erected by Shell in Bintulu, Sarawak in Malaysia, based on Fischer-Tropsch synthesis. The plant s total thermal process efficiency is about 63% (Shell, 1995) (see Table 7.11) a second plant is under construction in Qatar, with production expected to begin in 2010. 

Assess whether finite rate mixing affects the choice of NH3 injection location or the estimated process efficiency for the MSW incinerator application of the previous problem. Use an estimated mixing time (90%) of 300 ms. 

Over the past 50 years, the petrochemical industry has evolved into a sophisticated system for processing and distributing hydrocarbons. There has also been a huge investment in the infrastructure to support this particular source of carbon skeletons. Two major aspects that must be considered for the future processing efficiency of renewable resources are separations/conversions, and geographical location. 

For example. Figure 10 illustrates an IGCC flowsheet with CO2 removal by a commercially available acid gas solvent process [4]. Traditional engineering design approaches suggest several possible locations for a membrane separator in the IGCC flowsheet Each locatimi requires a membrane with unique materials and mechanical design each locatimi would result in a different impact on the overall process efficiency. 

As the product is processed in one unit after another, its flow may become more variable. Thus the terminal stage of refinement encounters flow variations imposed by all the other units in the plant. Control systems on the individual units can do little to smooth these variations in flow, but they should be able to deliver material of consistent quality. Flow variations can only be absorbed by surge vessels which are suitably located and efficiently used. 

A measurement of particle moisture content will normally be taken at the exit of the dryer. This allows the process operators to make such adjustments as may be needed to maintain moisture within the desired range. Various instmments are used, none of which are entirely satisfactory, and periodic hand samples are used in some mills. Considering the importance of moisture sensing and control at the dryers, it is unfortunate that a truly efficient, consistent, and accurate sensing system is not yet available to the industry. The primary reasons for the difficulty of measuring moisture at the dryer exit are the extreme and adverse conditions of heat, dust, and moisture present at this location. 

Absorber oil units offer the advantage that Hquids can be removed at the expense of only a small (34—69 kPa (4.9—10.0 psi)) pressure loss in the absorption column. If the feed gas is available at pipeline pressure, then Httle if any recompression is required to introduce the processed natural gas into the transmission system. However, the absorption and subsequent absorber-oil regeneration process tends to be complex, favoring the simpler, more efficient expander plants. Separations using soHd desiccants are energy-intensive because of the bed regeneration requirements. This process option is generally considered only in special situations such as hydrocarbon dew point control in remote locations. 

Cleaners are most efficient on relatively large particles, 80—300 pm in diameter (see Fig. 1). Flat toner ink particles can fragment during processing, therefore it is probably best to locate mechanical cleaners early in the sequence of office paper deinking unit operations (40). 

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