The first thing you should know is that biomass is nothing more than organic matter of plant or animal origin, this includes organic waste and waste, which is liable to be used to produce energy.
The reason is because plants transform the radiant energy of the Sun into chemical energy through photosynthesis and part of this energy is stored in the form of organic matter, which we can take advantage of.
Currently, the following definition of biomass is accepted:
"Biomass is considered to be a group of renewable energy products and raw materials that originate from organic matter formed by biological means".
It is for this reason that the concept of fossil fuels and the organic materials derived from them, such as plastics and most synthetic products, is out of place in the definition of biomass.
Although these fuels and derived organic materials had a biological origin, their formation took place in times past.
Biomass is therefore a renewable energy of solar origin through the photosynthesis of plants.
In addition, according to 2003 / 30 / CE Directive biomass is:
"Biodegradable fraction of waste products and residues from agriculture, forestry and related industries, as well as the biodegradable fraction of industrial and municipal waste."
From what we realize is that in a general way, any definition of biomass encompasses 2 terms mainly; renewable and organic.
Biomass as an energy source
Since ancient times, man has used biomass as a source of energy to carry out his daily tasks.
Since the use of fossil fuels began to gain strength, biomass was forgotten on a lower plane, where its contribution to primary energy production was negligible.
Today, thanks to various factors, biomass has had a resurgence as an energy source.
The factors that have been responsible for reviving biomass as an energy source are:
- The rising price of oil.
- Increased agricultural production.
- Need to seek alternative uses to agricultural production.
- Climate change.
- Possibility of using scientific and technical knowledge to optimize the energy production process.
- Favorable economic framework for the development of plants that use biomass as fuel, thanks to the production subsidies received by power generating plants with this source.
- Regulatory difficulty to develop other types of projects, leaving biomass as the most reasonable alternative to make an economic investment profitable.
Types of biomass
The biomass destined for the production of energy is obtained from the remains of forest exploitation, from the industries of the first and second transformation of wood, from the organic fraction of urban solid waste, from waste from livestock operations, from agricultural and forestry products, energy crops, those destined exclusively to their exploitation to obtain biomass.
Overall, biomass is obtained from any organic product susceptible to energy use, although these are the main ones.
Natural biomass
Natural biomass is that produced in natural ecosystems. The intensive exploitation of this resource is not compatible with the protection of the environment, even though it is one of the main energy sources in underdeveloped countries.
This natural biomass is created without any human intervention to modify or enhance it.
It is fundamentally about forest residues:
- Derivatives of cleaning forests and plantation remains
- Firewood and branches
- conifers
- Leafy
Residual biomass
The residual biomass is what generated in human activities that use organic matter. Its elimination in many cases is a problem. This type of biomass has associated advantages in its use:
- Reduces pollution and fire risks.
- Reduce landfill space.
- Production costs can be low.
- Transportation costs can be low.
- Avoid CO2 emissions.
- Generate jobs.
- Contributes to rural development.
The residual biomass is in turn divided into a series of categories mentioned below.
Agricultural surplus
Agricultural surpluses that are not used for human consumption are considered suitable for use as biomass for energy purposes.
This use of agricultural products used in the human food chain has caused an unjustified bad name of the use of biomass for energy purposes, as this use has been accused of an increase in the cost of certain agricultural products that are the basis of food in many third world and developing countries.
These agricultural surpluses can be used both as fuel in electricity generation plants and transformed into biofuels.
Energy crops
The energy crops mentioned above are specific crops exclusively dedicated to energy production.
Unlike traditional agricultural crops, their main characteristics are their high biomass productivity and high rusticity, expressed in characteristics such as resistance to drought, disease, vigor, early growth, regrowth capacity and adaptation to marginal lands.
Energy crops can include traditional crops (cereals, sugar cane, oilseeds) and non-conventional ones (cynara, pataca, sweet sorghum) that are being the subject of numerous studies to determine their cultivation needs.
Biomass transformation processes
As seen above, the great variety that exists of materials that is included within the concept of biomass allows in turn to establish a variety of possible transformation processes of this biomass into energy.
For this reason, biomass can be transformed into different forms of energy by applying various conversion processes, these types of energy are:
Heat and steam
It is possible to generate heat and steam by burning biomass or biogas.
Heat can be the main product for heating and cooking applications, or it can be a by-product of electricity generation in plants that cogenerate electricity and steam.
Gaseous fuel
The biogas produced in anaerobic digestion or gasification processes can be used in internal combustion engines for electricity generation, for heating and conditioning in the domestic, commercial and institutional sectors and in modified vehicles.
Biofuels
The production of biofuels such as ethanol and biodiesel (you can take a look at the article How to make homemade biodiesel) has the potential to replace significant amounts of fossil fuels in many transportation applications.
The extensive use of ethanol in Brazil has shown, for more than 20 years, that biofuels are technically feasible on a large scale.
In the United States and Europe their production is increasing and they are being marketed mixed with petroleum derivatives.
For example, the mixture called E20, made up of 20% ethanol and 80% petroleum, is applicable in most ignition engines.
Currently, this type of fuel receives some type of grant or state aid, but, in the future, with the increase in energy crops and economies of scale, the reduction of costs can make their production competitive.
Electricity
The electricity generated from biomass can be marketed as "green energy", since it does not contribute to the greenhouse effect because it is free of carbon dioxide (CO2) emissions.
This type of energy can offer new options to the market, since its cost structure will allow users to support higher levels of investment in efficient technologies, which will increase the bioenergy industry.
Co-generation (heat and electricity)
Co-generation refers to the simultaneous production of steam and electricity, that can be applied to many industrial processes that require both forms of energy.
In Central America, for example, this process is very common in the sugar industry, where it is possible to take advantage of the process waste, mainly bagasse.
Due to the high reliability of available bagasse, traditionally, co-generation is performed quite efficiently. However, in recent years there has been a trend to improve the process to generate more electricity and sell the surplus to the electricity grid.
The processes that can be followed to carry out this transformation can be divided into physical, physicochemical, thermochemical and biological.
Combustion in biomass plants
Simply put, combustion is a fairly rapid chemical reaction, whereby combines oxygen from the air (what is the oxidizer) with the different oxidizing elements of the fuel thus originating a release of heat.
For this reason, for this chemical process to occur, these 4 circumstances must occur:
- There must be a sufficient amount of fuel, ie biomass.
- It must make a sufficient amount of combustion air, which contains the oxygen necessary to oxidize or react with the fuel.
- The temperature must be high enough for the reaction to occur and be sustained. If the temperature does not exceed a certain value, called the ignition temperature, oxidizer and fuel do not react.
- There must be a combustion initiator, usually a pre-existing flame. This means that other elements normally participate in the ignition of the combustion system, even other fuels.
Biomass pretreatment
The biomass, before proceeding to its combustion in the boiler, must be subjected to a previous preparation process, which facilitate the reaction process between fuel and oxidizer.
This process facilitates combustion since it fundamentally adjusts the granulometry and degree of humidity.
The set of processes or previous treatments have three fundamental objectives:
- Homogenize the input of biomass into the boiler, so that the boiler receives a constant flow of energy of a similar value.
- Decrease its granulometry to increase its specific surface area.
In fact, the smaller the grain size, the greater the surface area so that the fuel and the oxidizer can react, thus accelerating the reaction and reducing the amount of biomass that does not react (unburned) - Decrease humidity that it contains, preventing part of the heat released in combustion from being used as heat of vaporization of the water, reducing the temperature of the fumes.
All this must also be done with the lowest possible energy consumption, since all the energy consumed in these processes, unless it is residual energy or energy that can be used at no cost, will mean a decrease in the net energy generated by the plant.
The biomass boiler
The boiler is definitely the main equipment of a biomass combustion thermoelectric plant.
In it, the process of transforming the chemical energy contained in the biomass into thermal energy is carried out, which will later be transformed into mechanical energy.
The boiler, in addition to being the main equipment, is also the main concern of the technicians who are in charge of the operation of a plant.
It is without a doubt the equipment that can cause the most potential problems, causes the most downtime, and requires the most stringent maintenance.
The reasons why the boiler is problematic equipment are as follows:
- It is an emerging technology, not sufficiently developed. Faced with the great experience accumulated in other combustion processes that release a large amount of thermal energy from the oxidation of a solid fuel, such as coal plants, biomass combustion faces a series of new problems that have not yet been addressed. have been resolved completely satisfactorily.
- The high potassium and chlorine content of the biomass causes scale and corrosion in various parts of the boiler.
- Combustion is not totally stable, presenting significant variations in pressure and temperature.
- There is great difficulty in fully automating the control of the boiler, due to the variability of the conditions in which the biomass can occur at the entrance.
- The profitability of the plants, even with the premiums for electricity production offered by Spanish legislation, is very tight, which requires saving on all components, including the boiler. Therefore, the best materials or the best techniques are not used, due to the increase in cost they entail.
Just one Proper selection of the type of boiler can lead to a success in the achievement of a biomass electricity generation projectAt the same time, an inappropriate choice will make it extremely difficult for an investment in this type of plant, which represents between 1 and 3 million euros per MW of installed electrical power, to be profitable.
Biomass thermoelectric plants
A biomass thermoelectric plant is a power generation plant that takes advantage of the chemical energy contained in a certain amount of biomass and that is released as thermal energy through a combustion process.
In the first place, a biomass energy recovery plant must have a biomass pretreatment system, the main purposes of which are to reduce the humidity it contains, the adaptation of the size and the uniformity of the biomass, in order to standardize the conditions. entry into the boiler and achieve the highest efficiency of the combustion system.
Once the thermal energy is released in an appropriate furnace, the gases released in combustion, composed of CO2 and H2O mostly together with other solid and gaseous substances, exchange their heat in a boiler through which water circulates, and which is normally converted into steam at a certain pressure and temperature.
The biomass combustion gases pass through the boiler, yielding their energy to the water / steam in different stages: water walls, superheater, vaporizer beam, economizer and air preheaters.
The steam under pressure formed in the boiler is then transported to a turbine, where it expands, producing a new energy transformation by which the potential energy contained in the steam under pressure is converted first in kinetic energy, and then in rotational mechanical energy.
Legislative framework for biomass thermoelectric plants in Spain
Electricity generation in Spain corresponds to private investors, although it is an activity strongly regulated by the state.
Different laws and decrees regulate this activity, and it is essential for any technician who works in biomass power plants to know this legal framework.
The different activities related to electrical energy are subject to a certain state intervention, given the importance of these activities.
Traditionally, the character of Public Service has been used, with the State responsible for the generation, transport, distribution and commercialization of electrical energy.
Today it is no longer a Public Service, since these activities are fully liberalized.
Public intervention is currently maintained as they are activities subject to strong regulation. It will be interesting to study in the first place how are the different norms that can affect the activities related to the generation, transport and sale of electrical energy.
Biomass for domestic use
Although I have focused more on obtaining energy for electricity, the use of biomass to generate heat for the use of heating has also been mentioned and better still, at a domestic level with boilers and stoves dedicated exclusively to it.
If you want more information you can read my colleague Germán's article Everything you need to know about pellet stoves
In this way, there will be no one to stop you on the issue of biomass and who knows, perhaps you dare to install one of these stoves in your home.