The issue of calorific value before and after material drying

The issue of changes in calorific value of materials before and after drying is indeed very interesting. First, we need to figure out how to calculate the changes in the mass and calorific value of the material before and after drying. 1. **Initial conditions**: The initial calorific value of the material is 1,000 kcal/kg. 2. **Condition after drying**: After drying, the material weighs 0.4 kilograms, and the calorific value per kilogram has increased to 3,500 kilocalories. The issue of an energy yield of 140% you mentioned actually refers to the increase in the total heat of the material after drying compared to its initial heat content, which seems to violate the law of conservation of energy. But in fact, this method of calculation may overlook some key information: - **The basis for calculating calorific value**: The calorific value generally refers to the energy released per unit mass of a material. The drying process primarily removes moisture from the material, rather than its energy content; therefore, it is normal for the calorific value per unit mass (such as per kilogram) to increase. - **Total mass and total heat of the material**: Before drying, it is assumed that the total mass of the material is X kilograms; after drying, this mass decreases to 0.4 kilograms. Since only water is removed, the energy content should remain unchanged in theory, unless there is additional energy input or output. **Key point**: If the total heat content of the material is calculated as initial mass × 1000 kcal/kg, and this value is compared to the value after drying: 0.4 kg × 3500 kcal/kg, the results should be equal or show a slight loss (taking into account that there may be some energy loss during actual operations). This means that if the total heat after drying exceeds the initial total heat, it could be a measurement or calculation error, or there may be additional energy input during the drying process. In general, without any additional energy input, the total heat content of the dried material should theoretically not exceed its initial total heat content. Therefore, it is recommended to re-examine the measurement methods for mass and calorific value to ensure the accuracy of the data. .

This post was last edited by Pure.Earth on 2024-6-7 10:13. Thanks for the replies. 1. To supplement the previous question: For ease of calculation, assume that before drying there is 1 kg of material with a moisture content of 66% and a low calorific value of 1000 Kcal/kg, while after drying there is 0.4 kg of material with a moisture content of 14% and a low calorific value of 3500 Kcal/kg. The testing process should not present any problems. In this case, the energy content of the material changes from 1 kg × 1000 Kcal/kg = 1000 Kcal to 0.4 kg × 3500 Kcal/kg = 1400 Kcal, which seems illogical. 2. Looking at the definition of calorific value again: The calorific value, also known as calorie value or heat content, refers to the amount of heat released when a unit mass (or volume) of fuel is completely burned. During the fuel combustion process, an oxidation reaction takes place that releases heat; the water present in the fuel does not participate in this reaction. Moreover, the evaporation process absorbs heat as well. Therefore, the total calorific value is equal to the heat released by the organic compounds in the fuel, minus the heat absorbed during the evaporation of the water. Therefore, the calorific value is closely related to the moisture content of the material. For the same material at the same mass, the higher the moisture content, the lower the absolute dry content; and with a lower absolute dry content, a greater amount of heat is required to remove the moisture, resulting in a lower total calorific value. 3. Returning to the drying issue, 1 kg of material reduces to 0.4 kg after drying; what is removed is water, while the anhydrous portion remains unchanged, meaning its calorific value does not change. Assuming perfect conservation in both cases, the former value needs to be reduced by the higher heat of vaporization of water, whereas the reduction for the latter is minimal. In this light, it makes sense that the latter has a higher calorific value, right? I’m not sure if this understanding is correct; I hope we can continue to discuss it. :handshake

This situation is normal. Because after drying, a large amount of moisture is removed from the material, which increases the relative calorific value of the remaining material. The actual increase in heat is not due to the creation of energy, but rather to the removal of water, which increases the calorific value per unit mass. Therefore, although the total mass of the material decreases after drying, its calorific value per kilogram increases, resulting in a higher total heat value when calculated. This does not violate the law of conservation of energy. .

Removing moisture increases the calorific value. It is because moisture reduces the calorific value.

4th floor is correct. Let 1 kg of wet material be considered. When measuring the lower heating value of this wet material, the heat absorbed due to water evaporation is denoted as Qw. The formula for calculating the lower heating value of the wet material is then (0.4 kg * 3500 – Qw) / 1 kg = 1000. The heat absorbed by moisture, Qw, can be determined to be 400.

The drying process consumes heat + wet material = dry material

The drying process consumes heat; wet material + heat = dry material – the wet material, after going through the drying process and having heat consumed, becomes dry material

The calorific value has increased; I calculated it! I calculated it using the software below: http://www.fishsting.com/xxjh/soft/wnghfs.html