What are the calorific values of different biomass fuels LHV-HHV for energy applications?
The Lower Heating Value (LHV) and Higher Heating Value (HHV) are measures of the energy content of a fuel, but they differ in how they account for the water vapor produced during combustion. Here’s the difference:
1. Higher Heating Value (HHV):
- Definition: The total amount of heat released when a fuel is completely combusted, including the heat recovered from the condensation of water vapor in the combustion products.
- Involves: Assumes that the water vapor produced during combustion is condensed back into liquid, releasing its latent heat of vaporization.
- Measurement: Includes all the heat available from fuel combustion, making it a larger value than LHV.
- Application: Useful for applications where heat recovery systems (like condensers) are used to capture the latent heat of water vapor.
2. Lower Heating Value (LHV):
- Definition: The amount of heat released when a fuel is completely combusted, excluding the heat contained in water vapor (assuming it remains in vapor form and is not condensed).
- Involves: Does not include the latent heat of vaporization of water vapor produced during combustion.
- Measurement: Represents the energy actually available for practical use in most systems, as water vapor is typically not condensed in conventional engines or boilers.
- Application: Commonly used for comparing fuels in real-world applications like internal combustion engines and gas turbines.
Key Differences:
| Aspect | HHV | LHV |
| Water Vapor | Includes latent heat of water | Excludes latent heat of water |
| Energy Value | Higher | Lower |
| Use Case | Systems with heat recovery | Conventional systems without heat recovery |
| Relevance | Theoretical maximum energy | Practical, usable energy |
Formula Relationship:
LHV=HHV−(m⋅ΔHvaporization) Where mmm is the mass of water produced and ΔHvaporization is the latent heat of vaporization.
Practical Implication:
- For fuels like natural gas or biomass, the difference between HHV and LHV can be significant, especially if the fuel has a high hydrogen content (which produces more water during combustion).
- LHV is typically used in real-world efficiency calculations, while HHV is used for theoretical comparisons.
Biomass Calorific Values in both MJ/kg and kcal/kg, showing the Lower Heating Value (LHV) and Higher Heating Value (HHV) for different biomass types:
| Biomass | LHV (MJ/kg) | HHV (MJ/kg) | LHV (kcal/kg) | HHV (kcal/kg) |
| Bagasse | 17.7 | 19.4 | 4230 | 4637 |
| Bamboo | 19.0 | 19.8 | 4541 | 4732 |
| Birch | 18.7 | 20.1 | 4469 | 4804 |
| Cherry | 17.9 | 19.1 | 4278 | 4565 |
| Coconut | 16.6 | 17.8 | 3967 | 4254 |
| Cypress (Saru) | 21.5 | 23.0 | 5139 | 5497 (Highest) |
| Douglas Fir | 19.7 | 21.0 | 4708 | 5019 |
| Elm | 19.0 | 20.5 | 4541 | 4900 |
| Eucalyptus | 18.3 | 19.6 | 4374 | 4684 |
| Hemp | 16.5 | 17.6 | 3944 | 4206 |
| Larch | 18.7 | 20.1 | 4469 | 4804 |
| Maple | 18.7 | 20.0 | 4469 | 4780 |
| Miscanthus | 17.8 | 19.1 | 4254 | 4565 |
| Oak | 17.4 | 18.8 | 4159 | 4493 |
| Pine | 19.5 | 20.8 | 4661 | 4971 |
| Poplar | 19.4 | 20.8 | 4637 | 4971 |
| Rice Husk | 14.2 | 15.4 | 3394 | 3681 |
| Spruce | 18.5 | 19.8 | 4422 | 4732 |
| Switchgrass | 16.8 | 19.1 | 4015 | 4565 |
| Teak | 18.9 | 20.2 | 4517 | 4828 |
| Willow | 17.3 | 18.6 | 4135 | 4445 |
Observations:
- Cypress has the highest LHV (21.5 MJ/kg) and HHV (23.0 MJ/kg), making it a highly efficient biomass fuel.
- Rice Husk has the lowest calorific values (LHV: 14.2 MJ/kg, HHV: 15.4 MJ/kg), reflecting its lower energy density.
- Woody Biomass (e.g., Birch, Douglas Fir, Teak) generally exhibits higher calorific values compared to Herbaceous Biomass (e.g., Miscanthus, Switchgrass).
- Moisture Content Impact: The difference between LHV and HHV is more pronounced for biomass with higher inherent moisture (e.g., Rice Husk, Coconut).
This comparison helps in evaluating biomass fuels for specific energy applications such as heating, power generation, or pellet production.
