Calorific value of waste
Calorific value (CV) of waste - "Waste to Energy"
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:
| 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.