Page 115 - Materials Chemistry, Second Edition

CAT3525_C04.qxd 1/27/2005 11:12 AM Page 86
86 Waste Management Practices: Municipal, Hazardous, and Industrial
EXAMPLE 4.2
A 10 g sample of mixed MSW is combusted in a calorimeter having a heat capacity of 8850 cal/°C.
The temperature increase on combustion is 3.35°C. Calculate the heat value of the sample.

SOLUTION

U C ∆T / M (8850 3.35) / 10.00 2965 cal/g 5278 Btu/lb
V
It should be obvious by now that the heat content of a MSW sample is essentially a function of com-
position; specifically, the percentage of materials having high Btu values such as paper, plastics,
food, and yard wastes will provide the highest heat release. Moisture and inorganics (e.g., ash) will
diminish the heat of combustion in a sample.
Heat values for the individual waste materials can be approximated by using Equation 4.3,
known as the modified Dulong formula:

MJ/kg 337C 1419(H – 0.125O ) 93S 23N (4.3)
2
2
where C, H ,O S, and N are given in percent by weight.
2 2
Using a more direct approach, Khan et al. (1991) estimated the energy content from MSW with
the equation

E 0.051[F 3.6(CP)] 0.352(PLR) (4.4)
where E is the energy content in MJ/kg, F the percent by weight food in the waste, CP the percent
cardboard and paper and PLR the percent plastic and rubber.

EXAMPLE 4.3
Determine the energy content of the MSW sample presented in Example 4.1.

SOLUTION
The chemical formula for the waste mixture given in Example 4.1 was C H O N S
655.3 1028.8 407.7 10.1
Using the Dulong formula

MJ/kg 337C 1419(H – 0.125O ) 93S 23N
2 2
337 (50.4) 1419 (6.6 – 0.125 41.8) 93 (0.21) 23 (0.90)
18,975 MJ/kg

EXAMPLE 4.4
Estimate the energy content using the Khan equation, for MSW having the following properties:

Component Percent by Weight
Paper products 37
Plastics 7
Glass 9
Metals 6
Food waste 24
Textiles 2
Misc. 15
Total 100