Systems & Inventories
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Systems & Inventories
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Inventories: basic principlesThe fundamental idea underlying the calculation of environmental inventories is simple. Any group of industrial operations can be regarded as a system by enclosing them within a system boundary. The region surrounding this system boundary is known as the system environment. This system environment acts as a source of all the materials and fuels inputs to the system and as a sink for all outputs from the system.Diagrammatically this concept can be represented as shown below in Figure 3 where the system is represented by the shaded box.
Figure 3. Schematic diagram of a system showing inputs and outputs. An environmental inventory for this system is therefore simply a list of the quantities of all of the inputs which pass from the system environment, across the system boundary into the system and all of the outputs which pass from the system across the boundary and into the environment. When the inputs are all derived from raw materials in the earth and the final products are all waste materials returned to the earth, the inventory is referred to as a life-cycle inventory. It is important to note that in a true life-cycle system there are no usable products only waste. It is no part of the inventory analysis to make value judgements about the relative significance of the different inputs and outputs; instead the analysis aims to provide the quantitative data upon which judgements can subsequently be made. It will however be clear from the above description of an industrial system that the inputs to the system are the parameters involved in discussing conservation problems while the outputs are the parameters of interest in discussing pollution problems. Top of page Next page |
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