Databased balance

As shown in Fig. 10, an ecological balance sheet must contain definitions of the objective and the framework of the investigation, the databased balance, the impact... 

The main task of a databased balance is to quantify input and output flows over the entire lifecycle of a product. Figure 11 presents a selection of input and output flows of frequent significance. A difference is drawn between coupled and uncoupled material flows ... 

Modular subclassification makes it possible to allocate these material flows, and thus the environmental impacts, to individual process steps, facilitating identification of the polluter or source of contantination. When this basis has been established, and not before, an analysis of weak points and recognition of improvement potentials is possible. In some cases, initial conclusions concerning the defined objective can even be drawn on the basis of the databased balance. 

The impact assessment presents the databased balance in terms of environmental impact so as to derive conclusions concerning the overall impact. The databased balance thus provides the basis for the impact assessment. The aspects under investigation include the potential environmental impacts (e.g., climate change, ozone depletion, acid rain) caused by the input and output flows over the entire lifecycle. 

The steps classification, characterization, and weighting are differentiated within the impact assessment. Classification and characterization constitute the objective part of impact assessment based on principles of natural science. In classification, the materials acting upon the environment are placed in impact categories in accordance with their potential effects. Within the impact categories, the databased balance is applied so as to determine the characteristic impact potential of the material or substance under consideration, which is then assigned to the specific impact category. This step is called characterization. 

In the evaluation, the results of the impact analysis and databased balance are analyzed, leading to conclusions and recommendations. A further aspect is the transparent presentation of the ecological balance sheet results. 

To obtain the core statements, the main contributions of each impact category (which processes and which emissions are dominant in each category ) must be determined. Relevant databased balance information not included under any specific impact category must be integrated in these considerations. The core statements can then be formulated on the basis of the results, since it should have become clear which processes or lifecycle phases are predominant. 

The reaction center has either to be spedfied when inputting a reaction into a database, or it has to be determined automatically. Specification on input is time-consuming but it can benefit from the insight of the human expert, particularly so if the reaction input is done by the primary investigator as is the case in an electronic notebook. Automatic determination of reaction centers is difficult, particularly so when incomplete readion equations are given where the stoichiometry of a reaction is not balanced see Section 3.1). One approach is to try first to complete the stoichiometry of a reaction equation by filling in the missing molecules such as water, N2, etc. and then to start with reaction center determination. A few systems for automatic reaction center specification are available. However, little has been published on this matter and therefore it is not discussed in any detail here. 

The Duns Financial Records Plus (DFR) database provides a balance sheet, income statement, and fourteen of the more widely used business ratios for measuring solvency, efficiency, and profitability. DFR also provides industiy norms and percentages that can be used to compare a toller s financial position to that of their... 

Now you can reconsider the material balance equations by adding those additional factors identified in the previous step. If necessary, estimates of unaccountable losses will have to be calculated. Note that, in the case of a relatively simple manufacturing plant, preparation of a preliminary material-balance system and its refinement (Steps 14 and 15) can usefully be combined. For more-complex P2 assessments, however, two separate steps are likely to be more appropriate. An important rule to remember is that the inputs should ideally equal the outputs - but in practice this will rarely be the case. Some judgment will be required to determine what level of accuracy is acceptable, and we should have an idea as to what the unlikely sources of errors are (e.g., evaporative losses from outside holding ponds may be a materials loss we cannot accurately account for). In the case of high concentrations of hazardous wastes, accurate measurements are needed to develop cost-effective waste-reduction options. It is possible that the material balance for a number of unit operations will need to be repeated. Again, continue to review, refine, and, where necessary, expand your database. The compilation of accurate and comprehensive data is essential for a successful P2 audit and subsequent waste-reduction action plan. Remember - you can t reduce what you don t know is therel... 

Available data sets for flow boiling critical heat flux (CHF) of water in small-diameter tubes are shown in Table 6.9. There are 13 collected data sets in all. Only taking data for tube diameters less than 6.22 mm, and then eliminating duplicate data and those not meeting the heat balance calculation, the collected database included a total of 3,837 data points (2,539 points for saturated CHF, and 1,298 points for subcooled CHF), covering a wide range of parameters, such as outlet pressures from 0.101 to 19.0 MPa, mass fluxes from 5.33 to 1.34 x lO kg/m s, critical heat fluxes from 0.094 to 276 MW/m, hydraulic diameters of channels from 0.330 to 6.22 mm, length-to-diameter ratios from 1.00 to 975, inlet qualities from —2.35 to 0, and outlet thermal equilibrium qualities from -1.75 to 1.00. 

Does the thermodynamic dataset contain the species and minerals likely to be important in the study A set of thermodynamic data, especially one intended to span a range of temperatures, is by necessity a balance between completeness and accuracy. The modeler is responsible for assuring that the database includes the predominant species and important minerals in the problem of interest. 

A flexible method for modeling redox disequilibrium is to divide the reaction database into two parts. The first part contains reactions between the basis species (e.g., Table 6.1) and a number of redox species, which represent the basis species in alternative oxidation states. For example, redox species Fe+++ forms a redox pair with basis species Fe++, and HS- forms a redox pair with SO4. These coupling reactions are balanced in terms of an electron donor or acceptor, such as 02(aq). Table 7.1 shows coupling reactions from the llnl database. 

The second part of the database contains reactions for the various secondary species, minerals, and gases. These reactions are balanced in terms of the basis and redox species, avoiding (to the extent practical) electron transfer. Species and minerals containing ferric iron, for example, are balanced in terms of the redox species Fe+++,... 

To be useful in modeling electrolyte sorption, a theory needs to describe hydrolysis and the mineral surface, account for electrical charge there, and provide for mass balance on the sorbing sites. In addition, an internally consistent and sufficiently broad database of sorption reactions should accompany the theory. Of the approaches available, a class known as surface complexation models (e.g., Adamson, 1976 Stumm, 1992) reflect such an ideal most closely. This class includes the double layer model (also known as the diffuse layer model) and the triple layer model (e.g., Westall and Hohl, 1980 Sverjensky, 1993). 

Two methods of balancing reactions are of interest. We can balance reactions in terms of the stoichiometries of the species considered. In this case, the existing basis B is a list of elements and, if charged species are involved, the electron e. Alternatively, we may use a dataset of balanced reactions, such as the llnl database. Basis B, in this case, is the one used in the database to write reactions. We will consider each possibility in turn. 

A reaction dataset, such as the LLNL database, provides an alternative method for balancing reactions. Such a database contains reactions to form a number of aqueous species, minerals, and gases, together with the corresponding equilibrium constants. Reactions are written in terms of a generic basis set B, which probably does not correspond to set B, our choice of species to appear in the reaction. 

To further illustrate how the basis-swapping algorithm can be used to balance reactions, we consider several ways to represent the dissolution reaction of pyrite, FeS2. Using the program RXN, we retrieve the reaction for pyrite as written in the llnl database... 

Equations similar to 12.3-10 to -15 may be written in terms of internal energy, U, with Cv, the heat capacity at constant volume, replacing CP. For liquid-phase reactions, the difference between the two treatments is small. Since most single-phase reactions carried out in a BR involve liquids, we continue to write the energy balance in terms of H, but, if required, it can be written in terms of U. In the latter case, it is usually necessary to calculate AU from AH and Cv from CP, since AH and CP are the quantities listed in a database. Furthermore, regardless of which treatment is used, it may be necessary to take into account the dependence of AH (or AU) and CP (or C,) on T ... 

In addition, chemical data for 661 ground-water and 627 surface-water samples were obtained from the USGS National Water Information System database. Only subsets of all available data that included analyses for major cations, anions, and pH, and had cation-anion charge balances within 20% were utilized. 

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