Page 321 - Wastewater Solids Incineration Systems

282 Wastewater Solids Incineration Systems

To illustrate the concept, the volume of 1 lb-mole of nitrogen at atmospheric pres-
sure (14.696 psia) and a temperature of 60°F is calculated as follows:
Absolute pressure 14.696 psia (144 sq in/sq ft) 2116.2 lbf/sq ft
Absolute temperature 60°F 60 459.67 519.67°R

Rearranging the ideal gas equation:
V n R T/P
V (1 lb-mole) 1545.32 (ft-lbf)/[(lb-mole)°R] 519.67°R/(2116.2 lbf/sq ft)
V 379.5 cu ft

As a second example, the volume of 64 lb of oxygen at atmospheric pressure and
a temperature of 60°F is calculated as follows:
Molecular weight of oxygen 32
64 lb/(32 lb/lb-mole) 2 (lb-mole)
V (2 lb-mole) 1545.32 (ft-lbf)/[(lb-mole)°R] 519.67°R/(2116.2 lbf/sq ft)
V 759.0 cu ft

There are two additional ideal gas laws that are important. These are commonly
referred to as Boyle’s law and Charles’ law. Boyle’s law states that the volume of a
perfect, or ideal gas, varies inversely with the absolute pressure. Written in mathe-
matical terms,
V /P V /P
1 1 2 2
Charles’ law states that the volume of a perfect gas varies directly with the absolute
temperature. Written in mathematical terms,
V T V T
1 1 2 2
When working with an ideal gas undergoing a change in a process, we use the
subscript 1 (V or T ) to denote the beginning and subscript 2 (V or T ) to denote the
1 1 2 2
end of the process. If neither the mass nor gas changes during the process (n and R
remain unchanged), the above equations can be rewritten as follows:
P V /T n R
1 1 1 1 1
P V /T n R
2 2 2 2 2
Because n R n R , P V /T P V /T
1 1 2 2 1 1 1 2 2 2
Thus, another definition of an ideal gas is one that follows Boyle’s and Charles’
laws.