Some Overall Process Options

As Hendershot (1995) has pointed out, most process options will be inherently safer with respect to one type of hazard, but may be less safe from a different viewpoint. In some cases the overall balance is readily apparent and it is easy to get general agreement on which option offers the safest overall balance. In other cases that balance is less apparent, and more sophisticated tools including qualitative ranking schemes, quantitative risk analysis and formal decision making tools may be needed. 

To adequately determine the overall effect of C02 for each option studied, the C02 balance must incorporate C02 emissions in addition to those emitted from the process itself. For example, each case produces electricity, except for the maximum hydrogen production case (Case 3), and for these cases (Cases 1, 2, and 4) a C02 emissions credit must be taken for displacing electricity from the grid. Because the maximum hydrogen production case (Case 3) requires some grid electricity, the system must be debited (rather than credited) with C02 emissions equivalent to the plant s net electricity requirement. Additionally, for the two options that recover coalbed methane (Case 3 and 4), each of those systems must be credited... 

The method for probe tuning on older spectrometers that are unable to produce the frequency sweep display is to place a directional coupler between the transmitter/receiver and the probe and to apply rf as a series of very rapid pulses. The directional coupler provides some form of display, usually a simple meter, which represents the total power being reflected back from the probe. The aim is to minimise this response by the tuning and matching process so that the maximum power is able to enter the sample. Unfortunately with this process, unlike the method described above, there is no display showing errors in tune and match separately, and there is no indication of the direction in which changes need be made, one simply has an indication of the overall response of the system. This method is clearly the inferior of the two, but may be the only option available. 

There are a number of ways to approach the assessment of the environmental risk that may be associated with a process. Whatever strategy might be chosen, however, some general risk areas should be part of the overall assessment. First, the inherent hazard, fate, and effects of the materials in the process need to be determined and assessed from an environmental perspective. Second, the potential for any process or unit operations releases need to be identified and evaluated. Third, environmental impacts from transportation, storage, and disposal options associated with the materials used in the process need to be identified and evaluated. Finally, the environmental life cycle impacts of producing those materials need to be collected and assessed. 

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