What is Firewood?
Humans developed the ability to control flames and make them useful. The oldest cooking fuel is wood in the form of logs and branches from trees. Firewood can be classified into either hardwood or softwood. Hardwoods usually have a higher energy content per volume than softwoods, meaning it will take more time for them to ignite, have less heat & require more effort to cut down. However, hardwoods and softwoods have about the same amount of energy content per weight. The moisture content of firewood affects its energy output. The drier the firewood, the less energy it takes to dry it, so there is more energy left for heating/cooking.
How does Firewood Burn?
Firewood can't be lit like it is. It must first turn into wood gas (pyrolysis), which then can be combusted when mixed with a specific amount of oxygen and then ignited. The necessary heat to start the process of combustion is around at least 300° C. External heat is initially provided by a material that lights up (like a match), for example, Once the heat begins to increase, it will create combustible "wood gas." The wood must be dry and seasoned to be able to burn well. If the wood is wet or green, then it will produce a lot of smoke and not much heat.
As the air temperature rises to 100°C, the water in the biomass changes from liquid to gas. The rising air evaporates water from the biomass, leaving dry solid material.
Beyond 300° C, biomass starts to break up and go up in smoke. On a long enough timeline, you'll end up with just the char and some cool gasses. Wood gas is a useful byproduct of extracting fuels from wood and biomass. The vapors contain various carbon compounds that have fuel value and the process of extraction is called carbonization.
The two processes of drying and pyrolysis are both endothermic, meaning that they consume heat instead of creating a useful surplus of heat. The speed of the process depends on the available heat input, the amount of heat required to first dry out the fuel before it can attain a level at which pyrolysis can start, and how much material is being processed: using air-dried fuel (moisture content of 10%-20%) is recommended to shorten the drying time and reduce the required heat input.
Pros and Cons of Cooking with Firewood
You could save a lot of money by cooking with firewood instead of turning on the heater. The only time it might not be worth it is if you've never cooked with firewood before since it can be difficult to do this.
- Wood is a renewable and sustainable resource
- Cooking with wood can be cheaper than using other sources of energy
- The taste of food cooked with wood is better because it absorbs the natural flavors from the wood
- Wood is easy to find in most places and can be collected or bought cheaply
- It can be a fun activity to do in the wintertime when the weather is bad outside.
- Not only does cooking with firewood take longer than using gas or electricity for the same dish, but it can also be a safety issue in some countries.
- Chopping down logs can be difficult and time-consuming. If you're cooking in a high heat setting, it's best to cut the wood smaller so that it can cook faster.
- Most fires go out and it takes longer to get the firewood hot enough by putting in new log after log.
- When you cook with firewood, you need more pots and pans than if you used an electric stove. This takes up more space in your kitchen cabinets and drawers.
Moisture Content of Firewood
To make efficient use of firewood, you need to have a high oxygen level and a high temperature. The Rocket Stove Principle takes these factors into account. One of the best ways to improve efficiency is by reducing moisture content. For example, look at firewood that is damp: it will burn inefficiently and cause a lot of wasted energy. It takes up to 3.21 MJ of energy to evaporate 1 kg of water from an ambient temperature to the 400°C needed for pyrolysis. This includes the heat energy input from the firewood being heated, as steam is also produced during this process. It's important not to use wet fuel and let it dry in the sun as this will save energy. Besides, wet firewood is more difficult to light. In addition, the moisture from the fuel cools the flames, and evaporated steam mixed with combustible gasses extinguishes the fire even further. There are also fewer emissions since there is incomplete combustion.
Global Firewood Production and Consumption
The demand for firewood is growing globally and production is not meeting this demand.
Firewood is a renewable and sustainable source of energy. It is used for cooking and heating, but it can also be used as fuel for power generation.
The use of firewood as an energy source has been declining in recent years due to the adoption of more modern and efficient technologies.
However, there are still many people who rely on firewood as their primary source of cooking or heating fuel.
Global production and consumption have increased by 2% since 2013 to reach 3.2 billion cubic meters per year. This increase in demand has been accompanied by a drastic increase in prices and scarcity, which are likely to continue due to climate change and population growth.
In 2018, the global production and consumption of firewood were estimated to be around 5 billion cubic meters per year. This number is expected to keep increasing in the coming years, mainly due to population growth in developing countries such as India and Indonesia.
The health and environmental impacts of firewood burning for cooking
A fuel's cleanliness depends on how it is processed and used. If fuel is environmentally sound, the public will be much safer. Since many people still use traditional cooking, the burning of firewood continues to have a negative impact on health due to its high emissions such as respiratory and cardiac diseases, lung cancer, and eye irritations. Wood fires have an increased level of particulate matter (PM) inhalation compared to other heating methods. For example, charcoal stoves only expose subjects to PM concentrations of 500μg/m3. The WHO recommends that emission rates of PM2.5 should not exceed 0.23 mg/min in unprotected spaces and 0.65 mg/min in protected spaces. The health impact of such particulate matter will depend on a range of parameters, including the type and age of the fuel used and weather conditions. Fuel moisture, burning rate, ventilation, and cooking behavior.
It's now easier than ever to cut down trees, thanks largely to demand from farmers. But wood energy use is a more important culprit in deforestation. However, concentrated industrial and urban demand for firewood combined with weak regulation and control still contributes to an unprecedented level of global deforestation. Compared to charcoal, producing firewood uses less wood and does not contribute as much to deforestation. This is because in the production of wood fuel there are no conversion losses.
Furthermore, firewood doesn't have a huge market and can be found in many places - especially the fallen branches & trees outside of forests or fallow land. Though there are still many areas of the country where wood harvesting is sadly inefficient, modern practices in manufacturing and energy production are changing things. In these regions, forests may become depleted as quickly as they grow, but in more populous rural towns and villages, firewood is abundant and often harvested carelessly. This would counteract the potential for firewood to be a sustainable resource, and it calls for the establishment of an effective policy framework that promotes sustainable forest production and management, as well as efficient conversion and consumption.