Energy balance calculations

The first law of thermodynamics is the basis for material- and energy-balance calculations. Because there is no significant transformation of mass to energy in most manufacturing operations, for a material balance the first law can be reduced to the simplified form ... 

Performs preliminary design of MliA, DliA, and MDEA plants through mass and energy balance calculations for all major equipment involved. 

In energy balance calculations, which we will handle later on, we use Eq. (4.94). 

Thus the total mass flows tn= m, + m,) differ in different cases. Water vapor flow th, is obtained by multiplying the dry air mass flow by the corresponding humidity x (Eq. 4.93). As a basic quantity in humid air mass and energy balance calculations, we use dry air mass flow m and the effect of humidity on the energy balance is noted in the enthalpy h, (Eq. 4.87). 

Doremus, R. II. (1994). Glass Science. New York Wiley. Fine, II. A., and Geiger, G. II. (1993). Handbook on Material and Energy Balance Calculations in Metallurgical Processes. Warrendale, PA TMS. 

More detailed accounts of the principles and applications of energy balances are given in the texts covering material and energy balance calculations which are cited at the end of Chapter 2. 

Energy balance calculations are best solved using spreadsheets or by writing a short computer program. A suitable program is listed in Table 3.2 and its use described below. The use of a spreadsheet is illustrated in Example 3.14b. 

Component enthalpies are readily available on a per mass basis from data such as JANAF (4). Product enthalpy usually includes the heat of formation in published tables. A typical energy balance calculation is the determination of the cell exit temperature knowing the reactant composition, the temperatures, H2 and O2 utilization, the expected power produced, and a percent heat loss. The exit constituents are calculated from the fuel cell reactions as illustrated in Example 10-3, Section 10. 

This category was used to provide chemical and physical data for nitric acid. The references also contain extensive details of chemical equilibria appropriate to the process, and several formulae used in the mass and energy balance calculations. 

From mass balance and energy balance calculations, the raw material and energy costs are... 

The software system, to meet the needs of the 1980 s, has wide flexibility and capabilities. For processes such as coal gasification or coal liquefaction, it can be used to perform steady state material and energy balances, calculate sizes of equipment, and carry out economic evaluations. Its flexibility can allow for the handling of coal or other solids in streams and equipment, and its capabilities allow for the simulation of many different types of process equipment and the calculations of physical properties under widely different conditions. Included in this is the ability to analyze conventional chemical and petroleum processes. Another valuable feature 1s a good preliminary cost estimation capability that permits the comparison of alternative processes on an economically consistent basis at an early stage of development. 

To illustrate this point, one may consider the detailed mass and energy balance calculations that are an integral part of fluidization gasification modeling. For example, Weil and his co-workers, at the Institute of Gas Technology (1 ), are... 

In professionally drawn flowcharts, special sj mbols are used to denote different types of process units such as distillation columns and heat exchangers. We will not generally use these symbols in this text, since our main purpose is to show you how to perfonn material and energy balance calculations. Simple boxes are perfectly adequate to represent process units on the flowcharts you draw for these calculations. 

Most process systems are conveniently analyzed using one of the two forms of the energy balance equation presented in Sections 7.3 and 7.4. To perform energy balance calculations on other types of processes, such as seraibatch processes or continuous processes that are being started up or shut down, the full transient energy balance equation is required, This equation is discussed in an introductory fashion in Chapter 11. A more thorough treatment of the full equation is deferred to thermodynamics courses and texts. 

Equation 7.4-15 states that the net rate at which energy is transferred to a system as heat and/or shaft work (Q- W,) equals the difference between the rates at which the quantity (enthalpy + kinetic energy potential energy) is transported into and out of the system (A// + AE + A p). We will use this equation as the starting point for most energy balance calculations on open systems at steady state. 

The value of U for a pure substance in a given state (temperature, pressure, and phase) is the sum of the kinetic and potential energies of the individual molecular, atomic, and subatomic particles in a unit amount of the substance. It is impossible to determine the true value ofU for a substance, and hence also impossible to determine the true value ofH = (/ + PV. However, we can measure the change in i/ or // corresponding to a specified change of state, which is all we ever need to know for energy balance calculations,... 

At this point, you can perform energy balance calculations only for systems in which A / (closed system) or AH (open system) can be neglected and for nonreactive systems involving species for which tables of f/ or H are available. Energy balance procedures for other types of systems are presented in Chapters 8 and 9. 

Define the dry-bulb temperature, wet-bulb temperature, and humid volume of humid air. Given values of any two of the variables plotted on the psychrometric chart (dry-buib and wet-bulb temperatures, absolute and relative humidity, dew point, humid volume), determine the remaining variable values and the specific enthalpy of the humid air. Use the psychrometric chart to carry out material and energy balance calculations on a heating, cooling, humidification, or dehumidification process involving air and water at 1 atm. 

Use the heat of solution data in Table B.IO and solution heat capacity data to (a) calculate the enthalpy of a hydrochloric acid, sulfuric acid, or sodium hydroxide solution of a known composition (solute mole fraction) relative to the pure solute and water at 25 C (b) calculate the required rate of heat transfer to or from a process in which an aqueous solution of HCl, H2SO4, or NaOH is formed, diluted, or combined with another solution of the same species and (c) calculate the final temperature if an aqueous solution of HCl, H2SO4, or NaOH is formed, diluted, or combined with another solution of the same species adiabatically. Perform material and energy balance calculations for a process that involves solutions for which enthalpy-concentration charts are available. 

Here is the procedure to follow for the energy balance calculation. 

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