Mass input and output

A formal LCA comprises four steps goal definition and scoping, inventory analysis, impact assessment, and interpretation. Figure 2.6 illustrates the process with respect to a material or mass balance, omitting the components of energy balance. Each step is described briefly below [2,93,97,98] as it would be applied to a product or process rather than a service, and with a focus on mass inputs and outputs rather than energy, noise, or other considerations sometimes taken into account in LCA. 

A method for assessing the environmental impacts associated with all stages of a product s life, from raw material extraction right through to disposal (cradle-to-grave). Calculations that assess the greenness of a reaction based solely on mass inputs and outputs. 

This chapter briefly discusses the advantages to be gained from the use of transputers in acquiring and processing data from an instrument like a mass spectrometer, which routinely deals with large-scale input and output at high speed. 

The performance equation of a mixer relates mixer size or mixing time to the input and output of the mixing device. The rate of transfer, r, incorporates the mass transfer coefficient, kL, and interfacial area, a, as calculated above. This rate can be used in conjunction with a material balance to relate concentrations of interest to time or size variables. 

Chemical processes involve a strong interaction between mass and energy. Typically, the overall objective of a plant is to convert and process mass. Energy is used to drive reactions, effect separations and drive pumps and compressors. An overview of the main inputs and outputs of a process is shown in Fig. 1.1. The... 

Figure I. I The mass-energy moliix of die main inputs and outputs of a process (Garrison et al., 1996).

For each unit process, a reference flow may be defined, and the inputs and outputs to the unit process calculated in relation to the reference flow. For instance, the reference flow for mining of iron ore is the mass of iron ore mined per year, and the emissions to the air may be expressed as kg dust per metric ton of ore. 

Identification of the input and output streams used in the overall mass balance equation. 

Input and Output Streams in the Overall Mass Balance... 

The failure to identify the necessary authigenic silicate phases in sufficient quantities in marine sediments has led oceanographers to consider different approaches. The current models for seawater composition emphasize the dominant role played by the balance between the various inputs and outputs from the ocean. Mass balance calculations have become more important than solubility relationships in explaining oceanic chemistry. The difference between the equilibrium and mass balance points of view is not just a matter of mathematical and chemical formalism. In the equilibrium case, one would expect a very constant composition of the ocean and its sediments over geological time. In the other case, historical variations in the rates of input and removal should be reflected by changes in ocean composition and may be preserved in the sedimentary record. Models that emphasize the role of kinetic and material balance considerations are called kinetic models of seawater. This reasoning was pulled together by Broecker (1971) in a paper called "A kinetic model for the chemical composition of sea water."... 

Inputs and outputs assessed in mass balancing are shown in Figure 5.3. The software EATOS was used to calculate all mass balances of processes. Outputs of EATOS are the mass index (equation (5.1), mass of raw material per mass of product output), and the environmental factor (equation (5.2), mass of waste output per mass of product output). EATOS also allows the calculation of cost indices (e.g., reference [15]) (equation (5.3), cost of raw material per mass of product output). 

Figure 5.3 Diagram showing boundaries for Mass Balance (encompassed by black dashed lines) and LCA with processes and flows included. Black arrows and flow names show inputs and outputs of the methods, grey arrows and boxes represent processes analysed to set up mass and energy balances. The process networks for the supply of energy, resources and so on are greatly simplified.

The storage hold-up f/(r) is related to the input and output rates Fu(t) and Fd(0 by the mass conservation equation ... 

It should be clear from Eq. (7) that since mass conservation applies to the flow network as a whole, there can be no net inflow or outflow of material. This requirement is obviously met for an isolated network. However, most applications of practical interest will include external inputs and outputs,... 

I mass balance model at the farm level Calculation of inputs and outputs. 

Thus, by considering the overall mass balance, i.e., looking at the inputs and outputs of the process, one can gain many insights into a process and also identify opportunities for C02 emissions reduction and enhancing feedstock utilization. 

The Level II calculation simulates a situation in which a chemical is continuously discharged into the multimedia environment and achieves a steady-state and equilibrium condition, at which input and output rates are equal. The task is to deduce the rates of loss by reaction and advection and the prevailing concentrations and masses. 

Inputs + Sources = Outputs + Sinks + Accumulations where each of these terms may be a quantity or a rate. Inputs and Outputs are accomplished by crossing the boundary of the reference volume. In case of mass transfer this occurs by bulk flow and diffusion. Sources and Sinks are accretions and depletions of a species without crossing the boundaries. In a mass and energy balance, sinks are the rate of reaction, rdVr, or a rate of enthalpy change, AHrpdC. Accumulation is the time derivative of the content of the species within the reference volume, for example, (<9C/3t)dVr or... 

Chapter 1) that its concentration in the reservoir can be modified only by processes taking place at the boundaries. Species i can be added to or subtracted from the system by solid, liquid or gaseous input and output, not by chemical reaction or radioactive decay inside the reservoir. For the sake of illustration, we will consider a water reservoir, whose properties will be labeled liq . Mass balance requires... 

Generally, a continuous recording of electrically available data - for example, current, cell voltage, electrode potentials, temperatures - is beneficial to supervise the proper procedure of each experiment. Especially in case of a failure this will be a valuable help to find the reason. Today, the best way is to use a data acquisition system in a computer that offers the results directly for further calculations, for example, integration of the consumed current (converted charge). For continuously operated experiments the addition of scales, which acquire the weight of input and output reservoirs, will be advantageous in order to supervise the mass balances continuously. 

Indexing input and output fluxes as /in and Jo, respectively, the mass variation in time dt is given by... 

A certain mass flowmeter (see Section 6.2.3) was tested (calibrated) by comparing the readings given by the instrument G with true (known) values GT of the flow of a gas as measured by the instrument in a 0.15 m ID pipeline. True and measured values are compared in Fig. 6.61 and Table 6.17. Estimate the errors in the flowmeter due to bias and imprecision. Assume that variations in the input and output of the instrument are normally distributed. 

Engineers like to approach process problems with a black box technique. That is, any system or piece of equipment operating under steady-state conditions can be represented by a box with input and output streams consisting of mass flows and/or energy. Figure 3.3 illustrates the concept. 

The following excerpt is accompanied by a simplified flow diagram for the ABCDF (Figure A-l) and mass balance tables of input and output streams (Tables A-l and A-2). The numbered streams in Tables A-l and A-2 correspond to the numbered diamonds in Figure A-l (U.S. Army, 1998). 

---