Calorific value of waste

Calorific value (CV) of waste

The CV of the waste depends on the composition of the waste. Waste with a lot of PVC has a higher calorific value then waste with less PVC and more paper. To estimate the calorific value of the waste mix you have, you can make an average on your composition.

For example : How to calculate the average calorific value of a waste mix?

We have a waste mix consisting out of 3 fractions, 
Hazardous waste represents 20% of the mass amount and has a calorific value of 12 MJ/kg.
Medical waste represents 50% of the mass amount and has a calorific value of 19 MJ/kg.
Plastics - PVC waste represents 30% of the mass amount and has a calorific value of 35 MJ/kg.

Questions : What is the average calorific value of the waste mix ?

Calculation:

Calculation of calorific value of waste
Material - fraction CV (MJ/kg) %amount %CV representing in waste mix
Hazardous waste 12 20% 2,4 (= 12 x 0,2)
Medical Waste 19 50% 9,5 (= 19 x 0,5)
Plastics - PVC 35 30% 10,5 (=35 x 0,3)
------------------------- ---------------- ------------- -------------------------------------------
    Total : 22,4 (= 2,4 + 9,5 + 10,5) MJ/kg

Conclusion: the waste mix has an average calorific value of 22,4 MJ/kg.

CV examples of waste:

Here we give some approximate numbers about the calorific value of materials.

 Type of material CV (MJ / kg)  CV (kCal / kg)
 Medical waste

19 - 24

4540 - 5735

 Industrial & hazardous waste

22 - 40

5257 - 9558

 Domestic waste (without recycling)

7 - 16

1673 - 3823

 Domestic waste (afther recycling)

10 - 14

2389 - 3345

 PVC

41

9797

 Dry wood

14,4

3441

 Paper

13,5

3226

 Braun carbon

7 - 12

1673 - 2867

 Petrol (benzine)

45 - 47

10573 - 11231

 Coal

15 - 27

3584 - 6452

 Diesel

46

10992

 Ethanol

30

7168

A material can burn without supporting fuel when it has a calorific value of min. 14,4 MJ/kg, this is approximatly dry wood. To know the overall calorific value of the waste, you need to measure the calorific value or estimate by analizing the composition. 

If there is no chemical reaction by mixing the different materials together, a weighted average of the different calorific values are a good approximate value for the CV of the waste mix.

If the amount of waste is known, and the calorific value of the waste is known, it is possible to design the size of the incinerator and flue gas treatement system.