Scale problem areas

The development of polythiophenes since the early 1980s has been extensive. Processible conducting polymers are available and monomer derivathation has extended the range of electronic and electrochemical properties associated with such materials. Problem areas include the need for improved conductivity by monomer manipulation, involving more extensive research using stmcture—activity relationships, and improved synthetic methods for monomers and polymers alike, which are needed to bring the attractive properties of polythiophenes to fmition on the commercial scale. 

Matsen (1985) pointed out a number of additional problem areas in scale-up such as consideration of particle size balances which change over time due to reaction, attrition and agglomeration. Erosion of cyclones, slide valves and other components due to abrasive particles are important design considerations for commercial units which may not be resolved in pilot plants. 

Information is lacking on the effectiveness of chlorpyrifos in large-scale (>40 ha) coldwater ecosystems, typical of those found in Alaska or northern-tier states. Accordingly, initiation of longterm studies in these potential problem areas are recommended. As judged by the available literature, three courses of action now seem warranted. 

Control of melanose and scab is a standardized procedure in Florida, using the so-called neutral or insoluble copper materials at low poundage to reduce the scale problem. In both Argentina and Brazil, these diseases are very important—including sweet orange scab, not known in Florida—but generally must be controlled with Bordeaux because of the inability to import the newer materials. In the drier areas, these diseases are not so important. 

Improved measurement methods suitable for observations from airborne platforms, so that the regional-scale impacts of urban emission can be accurately assessed. This is needed because some control options for solving the urban-scale problem have the potential of transferring pollution from one geographic area to others. 

Nanotechnology offers the promise of specific targeting in medicine because its size is on the same scale as cells and proteins it needs to find. Instead of flooding the body with medication, medical applications of nanotechnology zooms in on the problem areas. Nanotechnology seeks to hunt down the bad guys while leaving the peaceful population alone. 

This area is a development in the usage of NDDO models that emphasizes their utility for large-scale problems. Structure-activity relationships (SARs) are widely used in the pharmaceutical industry to understand how the various features of biologically active molecules contribute to their activity. SARs typically take the form of equations, often linear equations, that quantify activity as a function of variables associated with the molecules. The molecular variables could include, for instance, molecular weight, dipole moment, hydrophobic surface area, octanol-water partition coefficient, vapor pressure, various descriptors associated with molecular geometry, etc. For example, Cramer, Famini, and Lowrey (1993) found a strong correlation (r = 0.958) between various computed properties for 44 alkylammonium ions and their ability to act as acetylcholinesterase inhibitors according to the equation... 

This area is a development in the usage of NDDO models that emphasizes their utility for large-scale problems. Structure-activity relationships (SARs) are widely used in the pharmaceutical industry to understand how the various features of biologically active molecules... 

The above example is convenient for illustration because it is relatively small and involves only uni-unimolecular reactions. For large systems with arbitrary reaction stoichiometry, it turns out that the assignment of feasible reactions is an NP-complete computational problem [216], Therefore, application of thermodynamic constraints in genome-scale problems is an area of ongoing research. 

Figure 1 illustrates typical performance of a validated one-dimensional model in the prediction of temperature profiles in a plant-scale tubular hydrogenation reactor. Note that the major problem area is in the relatively low-temperature region near the inlet. The peak temperature is properly located in the tube, but is slightly lower than the actual temperature. With reactions and reactors of this type, the major reaction is over slightly after the peak temperature has been reached, and the remainder of the reactor is described primarily by a cooling curve. The outlet composition of the reactor will be essentially at equilibrium with respect to the principal reaction. 

A few random samples taken from a commercial installation most probably will not provide enough insight to determine that the filter is performing as expected. However, by making use of reasonable variations in the most important parameters, the desired correlations can be developed. Bench-scale tests should be run on representative feed samples taken at the same time test runs are made on the commercial unit. The bench-scale tests can be varied over a much wider range to provide a sound basis for both the location and shape of the appropriate correlation. A comparison of these results with the data taken from the commercial installation provides a good measure for efficiency of the commercial unit and a basis for identifying problem areas on the full-scale unit. 

Production of synthetic crude oil from oil shale has several environmental problem areas. These center on a scarcity of water in the operating area (at least in the U.S.), disposal of spent shales, reclamation of disposal areas, and sulfur gas containment. Even though water is not required for extraction, the water needs are substantial for pretreating shale, condensing the crude and upgraded shale oils, and for the operation of any scrubber-based emission control devices. Thus, while the present water supply is adequate for pilot-scale recovery plants, provision of an adequate water supply for large-scale shale oil producing units is a major concern [73]. 

Small-scale in vitro test systems may now be employed to assess biopharmaceutical properties or the drug s potential behaviour after in vivo administration. For example, drug penetration through monolayers of epithelial cells in tissue culture can be used to examine bioavailability. The drug s metabolism can be studied in vitro using hepatic microsomes and potentially toxic metabolites identified before problems arise in vivo Although not absolute, these tests provide useful indicators of potential problem areas and may eliminate problematical drug candidates early. 

In the ASP pilot test described in this section, the water cut in the test area was already 98% before the ASP flood, and some well water cut reached 100%. Optimization of injection schemes was conducted. In this case, a scaling problem was experienced in the pilot area. For more details, see Wang et al. (1998a). 

Often, a stepwise screening approach enables identification of non-problem areas, problem areas, major sources, etc. This approach may for instance start with providing an overview of expected hot spots and sources to gain a first impression of the scale of the problem. Thereafter, a more focused monitoring can be performed, directed at relevant problem areas and sites. For many substances, screening of levels in water, as well as in biota with limited mobility and in sediment, is the best way to get the optimum information within a given amount of resources. 

In spite of 1000s km in between, model calculations show that the imported part of the deposition from Eastern, Central and ex-Soviet European countries is more effective in Turkey than the self-emitted sulfur dioxide in a general framework. Obviously this may not hold true at some local problem areas within the country, where high emission sources are effective at a smaller scale. ... 

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