At the current stage, wood pellets, in particular, are the main alternative source of thermal energy in Europe. The volume of pellet consumption for private, municipal and industrial consumers is constantly growing, therefore the range of raw materials from which fuel pellets are produced is also expanding. It is worth paying attention to already classic types of raw materials for the production of pellets, as well as to consider “alternative” types of raw materials for the production of fuel pellets.
Content:
Basic requirements for raw materials for the production of pellets. Wood pellets. Mix pellets. Agricultural pellets. Pellets from alternative raw materials. Basic requirements for raw materials for the production of pellets.
Humidity.
Requirements for the moisture content of raw materials for industrial pellet granulation are from 8 to 15%. In other cases, raw materials require drying, or, conversely, steam treatment to increase humidity.
Ashiness
Ash content of fuel is the percentage of refractory slag residues after burning. In pellets of a high quality class, this indicator is no more than 1% according to the EN Plus A-2 standard and up to 0.5-0.7% according to the EN Plus A-1 standard. The consequences of too high ash content of the fuel are excessive deposits in the combustion chamber and clogging of air ducts. Actually, the ash content of the fuel determines its quality standard. White high-quality pellets have an ash content of no higher than 0.7%. In a gray pellet with bark content, the ash level does not exceed 1%. If this indicator is higher, the pellet is considered industrial.
The level of environmental friendliness of raw materials.
At the moment, in the European Union, the regulations regarding emissions of fuel combustion products into the atmosphere are becoming increasingly strict. Accordingly, raw materials for pellets must contain a minimum amount of such chemicals as nitrogen, chlorine, sulfur, etc.
The size of the raw material fraction.
For granulation, crushed material with a particle size of up to 3 mm is used, that is, thyrso material.
Energy value.
Heat of fuel combustion (calorific value) is a value that characterizes the amount of heat that can be obtained when burning each particular fuel. This is the main consumer value of pellets. A high-quality pellet made from suitable high-energy raw materials has a high calorific value. This parameter is influenced, in particular, by the freshness of the wood. Wood that has undergone rotting or deterioration loses part of its energy potential.
Suitability for granulation.
In the production process, one or another raw material is easier or more difficult to press. It is known that it is difficult to make pellets of sufficient strength and density from weakly granular raw materials so that they do not crumble during packaging or transportation. Granulation of repeatedly crushed and dried raw materials takes place on a press granulator. This device, with the help of a shaft and rollers, pushes the raw material through the holes of the matrix at a temperature of 250-300°C. Under these conditions, the wood secretes a sticky substance – lignin, which contributes to the natural bonding of the granules and preservation of their integrity after cooling.
Wood pellets with a higher lignin content are stronger. Conifers are significantly ahead of hardwoods in terms of this parameter: conifers contain 23-35% lignin, hardwoods – up to 25%. Low lignin content increases the amount of screening after granulation. Secondly, wood species have different hardness. Harder wood is more difficult to press into pellets, creating higher loads on the equipment, especially on the main working nodes – the matrix and press rollers. Softwoods are softer and more malleable, while hardwoods are significantly harder. However, the heat of combustion of hardwood pellets is naturally higher, so a cubic meter of beech or oak pellets will be heavier relative to the same volume of pine pellets, and will certainly give off more heat.
At the same time, as practice shows, manufacturers successfully mix sawdust of different tree species, eliminating the above-mentioned granulation problems. Provided the components are mixed in certain ratios, this method absolutely does not reduce the quality of the final product and allows you to achieve complete compliance of fuel pellets with ENplus A1 or A2 certificates: “Light wood fuel pellets intended for heating private houses.” However, some hardwoods can color the pellet a dark shade, “painting” it in a coffee, gray or brown color. Such a pellet can cause suspicion among consumers, because there is a prejudice against pellets of any other color except light beige, despite for the presence of certificates of confirmation of high quality and calorific value.
Wood pellets.
Most often, such granules are called “tyrsopelets”. Raw materials for the production of wood pellets are various types of woodworking waste, which are processed and crushed in the process of pellet production. Such raw materials are:
Shavings, sawdust, obtained during sawing and processing of raw or dried timber; Chips, chips, burrs, balance – the most common wood processing waste; Commercial wood waste, sawn or solid trunks, defective and substandard wood, etc.; Unconditional wooden products: new or recycled. Dry sawdust, shavings, and chips are considered ideal raw materials for obtaining high-quality pellets. They usually do not have bark inclusions, as well as soil, which, when burned, form slag and increase the ash content of the pellet. The quality of raw materials for pellets depends on the type of wood from which it is obtained, the presence of bark, and the characteristics of its storage. The less bark, damage and foreign inclusions that enter the pellets, the lower their ash content, higher calorific value, and therefore, higher quality. The same applies to the processing of the tiller and the balance.
Mix pellets.
According to research company Future Metrics, the consumption of industrial pellets alone will almost double by 2023, amounting to 21.5 million tons against the current 13 million tons. Wood waste has become more and more in demand, not only biofuel producers compete for it, but also chipboard producers and many others. Back in 2010, the European Union adopted a program to expand the base of biological waste that can be used as raw materials for renewable energy.
What is a mix pellet?
Mix-pellets are fuel that is granulated from several components of raw materials, both of wood and other organic origin. Such an “other” component for the production of mix pellets, in particular, can be:
production waste of agricultural crops: legume pods, corn cobs, rice husks, buckwheat husks, sunflower husks and pulp, flax husks, nut shells, berry or fruit pits, fruit brains and skins, bard, spoiled grain, beer grist, etc.; plants: reeds, straw, sugar cane, as well as trees, branches and bushes cut down during landscape works and sanitary cleaning; other natural combustible substances: coal dust, peat, lignin. Such raw materials are quite inexpensive, available and common, they can be well subjected to granulation, however, compared to wood raw materials, they can have a number of disadvantages: excessive content of aggressive chemical compounds, in particular acids, high ash content, excessive moisture and oil content, low melting point of ash, low content of binders, etc. The use of pellets from such homogeneous raw materials in boilers can lead to excessive slag and soot formations, intensive moisture release, chemical corrosion, and the pellet itself can have a fragile structure.
Research and experiments in this direction.
In order to find the optimal composition of raw materials for mix pellets, European researchers conduct experiments on mixing different types of raw materials. On the basis of research, viable “recipes” of mixed pellets from various raw materials have been created and tested, which do not harm the boiler equipment and are almost devoid of harmful substances during combustion. For example, scientists from the Forest Research Institute of Austria created mix-granules from corn cobs, rapeseed and straw with the addition of kaolin, bentonite and coal dust. Such mix-pellets emit a minimum of harmful substances into the atmosphere, when they are burned in the fuel chamber of boilers, slag cakes and significant soot deposits are not formed.
Individual manufacturers combine wood raw materials with 10-15% of coniferous needles or mix sawdust with 20-25% coal dust and 1-3% starch. The calorific value of such pellets due to the raw materials used is about 23 MJ/kg, which makes them a respectable alternative to low-calorie coal and peat, both in terms of calories and fuel cost. For the production of such pellets, wood of any species and quality, in particular dry and burnt wood, is suitable.
The only and main obstacle to the mass distribution of mix-pellets in the countries of the European Union are strict standards for emissions of combustion products into the atmosphere. In the production of mix-pellets, various types of available and relatively cheap additives for binding pellets are often used. If conifers have enough of their own lignin, ordinary starch is usually added to hardwood raw materials, as well as some agro-processing waste. Also used are fish oil, lime, paraffin, vegetable oils, coffee grounds, i.e. everything that has good binding properties, low cost and flammability. Such applications improve the qualitative properties of the pellet, reduce the volume of screening of the base, and increase the calorific value of the fuel.
Agropellets.
Agro-pellets are fuel pellets made from various raw materials of vegetable origin, usually agricultural crops and waste from agricultural processing. One of the most popular and affordable types of pellet raw materials of agrarian origin is the straw of various agricultural crops, in particular grain and rapeseed. In terms of energy potential, this material is slightly inferior to wood, having a calorific value of up to 16 MJ/kg. In addition, straw is a highly renewable source of energy, since burning does not change the balance of nitrogen dioxide in the atmosphere. During ripening, agricultural crops absorb as much carbon dioxide as they can emit during burning.
Similar to straw, the type of raw material is reed. Compared to straw, its calorific value is even slightly higher (up to 19 MJ/kg), and its ash content is about 4%. Such raw materials are quite widespread and very cheap, since they do not require cultivation and processing. Reeds are collected with the help of special harvesters-bundles.
Sunflower husks and pulp are one of the most promising materials for the production of agricultural pellets in Ukraine. The ash content of sunflower pellets is about 3%, and the calorific value is identical to brown coal – up to 21 MJ/kg due to the oil content. Ash after burning sunflower agricultural pellets is a valuable and useful fertilizer.
Buckwheat husks, cereal and rice bran are also successfully used for the production of agropellets. As in the case of mixed pellets, strict environmental regulations are a significant obstacle to the mass distribution of agro-pellets in the countries of the European Union.
Pellets from alternative raw materials.
Ukraine has large deposits of fuel peat, which is suitable for granulation. Peat pellets and briquettes are made using the same technology as wood pellets. The calorific value of peat is quite high – up to 21 MJ/kg, but the ash content of such pellets is up to 5% due to the high sand content. However, such fuel can be successfully used in industrial and communal boiler houses, due to the low cost of raw materials, its availability and industrial volumes. In Northern Europe, peat is recognized as a partially renewable raw material and its use in the energy sector is encouraged by state authorities.
Granulation of waste paper is a fairly new, but promising industry, as this type of raw material does not require expensive drying facilities. Pellets made of paper and cardboard are capable of producing a large amount of heat and have a small percentage of ash. In some countries, granulation of old banknotes has been established.
In recent years, quite exotic types of fuel raw materials, such as chicken droppings, animal manure, hydrolyzed lignin, etc., have been increasingly used for the production of fuel pellets.
The expansion of the raw material base for the production of fuel pellets provides an opportunity to benefit from the utilization of a huge amount of biological waste, as well as to solve environmental problems related to their storage, processing and disposal. The transition from carbon to ecologically clean fuel reduces the amount of emissions of harmful substances into the air, which in recent decades has become a very urgent and priority issue of global environmental security.
In addition, this is related to the general problem of depletion of traditional extractive energy resources and their gradual replacement by renewable and alternative sources of energy, where the use of this type of fuel in the world is becoming more popular every year both among private users and in industry, as evidenced by the general dynamics increase in the production and sale of solid fuel boilers.
Wood and sunflower husk pellets for boilers
At the current stage, wood pellets, in particular, are the main alternative source of thermal energy in Europe. The volume of pellet consumption for private, municipal and industrial consumers is constantly growing, therefore the range of raw materials from which fuel pellets are produced is also expanding. It is worth paying attention to already classic types of raw materials for the production of pellets, as well as to consider “alternative” types of raw materials for the production of fuel pellets.
Content:
Basic requirements for raw materials for the production of pellets.
Wood pellets.
Mix pellets.
Agricultural pellets.
Pellets from alternative raw materials.
Basic requirements for raw materials for the production of pellets.
Humidity.
Requirements for the moisture content of raw materials for industrial pellet granulation are from 8 to 15%. In other cases, raw materials require drying, or, conversely, steam treatment to increase humidity.
Ashiness
Ash content of fuel is the percentage of refractory slag residues after burning. In pellets of a high quality class, this indicator is no more than 1% according to the EN Plus A-2 standard and up to 0.5-0.7% according to the EN Plus A-1 standard. The consequences of too high ash content of the fuel are excessive deposits in the combustion chamber and clogging of air ducts. Actually, the ash content of the fuel determines its quality standard. White high-quality pellets have an ash content of no higher than 0.7%. In a gray pellet with bark content, the ash level does not exceed 1%. If this indicator is higher, the pellet is considered industrial.
The level of environmental friendliness of raw materials.
At the moment, in the European Union, the regulations regarding emissions of fuel combustion products into the atmosphere are becoming increasingly strict. Accordingly, raw materials for pellets must contain a minimum amount of such chemicals as nitrogen, chlorine, sulfur, etc.
The size of the raw material fraction.
For granulation, crushed material with a particle size of up to 3 mm is used, that is, thyrso material.
Energy value.
Heat of fuel combustion (calorific value) is a value that characterizes the amount of heat that can be obtained when burning each particular fuel. This is the main consumer value of pellets. A high-quality pellet made from suitable high-energy raw materials has a high calorific value. This parameter is influenced, in particular, by the freshness of the wood. Wood that has undergone rotting or deterioration loses part of its energy potential.
Suitability for granulation.
In the production process, one or another raw material is easier or more difficult to press. It is known that it is difficult to make pellets of sufficient strength and density from weakly granular raw materials so that they do not crumble during packaging or transportation. Granulation of repeatedly crushed and dried raw materials takes place on a press granulator. This device, with the help of a shaft and rollers, pushes the raw material through the holes of the matrix at a temperature of 250-300°C. Under these conditions, the wood secretes a sticky substance – lignin, which contributes to the natural bonding of the granules and preservation of their integrity after cooling.
Wood pellets with a higher lignin content are stronger. Conifers are significantly ahead of hardwoods in terms of this parameter: conifers contain 23-35% lignin, hardwoods – up to 25%. Low lignin content increases the amount of screening after granulation. Secondly, wood species have different hardness. Harder wood is more difficult to press into pellets, creating higher loads on the equipment, especially on the main working nodes – the matrix and press rollers. Softwoods are softer and more malleable, while hardwoods are significantly harder. However, the heat of combustion of hardwood pellets is naturally higher, so a cubic meter of beech or oak pellets will be heavier relative to the same volume of pine pellets, and will certainly give off more heat.
At the same time, as practice shows, manufacturers successfully mix sawdust of different tree species, eliminating the above-mentioned granulation problems. Provided the components are mixed in certain ratios, this method absolutely does not reduce the quality of the final product and allows you to achieve complete compliance of fuel pellets with ENplus A1 or A2 certificates: “Light wood fuel pellets intended for heating private houses.” However, some hardwoods can color the pellet a dark shade, “painting” it in a coffee, gray or brown color. Such a pellet can cause suspicion among consumers, because there is a prejudice against pellets of any other color except light beige, despite for the presence of certificates of confirmation of high quality and calorific value.
Wood pellets.
Most often, such granules are called “tyrsopelets”. Raw materials for the production of wood pellets are various types of woodworking waste, which are processed and crushed in the process of pellet production. Such raw materials are:
Shavings, sawdust, obtained during sawing and processing of raw or dried timber;
Chips, chips, burrs, balance – the most common wood processing waste;
Commercial wood waste, sawn or solid trunks, defective and substandard wood, etc.;
Unconditional wooden products: new or recycled.
Dry sawdust, shavings, and chips are considered ideal raw materials for obtaining high-quality pellets. They usually do not have bark inclusions, as well as soil, which, when burned, form slag and increase the ash content of the pellet. The quality of raw materials for pellets depends on the type of wood from which it is obtained, the presence of bark, and the characteristics of its storage. The less bark, damage and foreign inclusions that enter the pellets, the lower their ash content, higher calorific value, and therefore, higher quality. The same applies to the processing of the tiller and the balance.
Mix pellets.
According to research company Future Metrics, the consumption of industrial pellets alone will almost double by 2023, amounting to 21.5 million tons against the current 13 million tons. Wood waste has become more and more in demand, not only biofuel producers compete for it, but also chipboard producers and many others. Back in 2010, the European Union adopted a program to expand the base of biological waste that can be used as raw materials for renewable energy.
What is a mix pellet?
Mix-pellets are fuel that is granulated from several components of raw materials, both of wood and other organic origin. Such an “other” component for the production of mix pellets, in particular, can be:
production waste of agricultural crops: legume pods, corn cobs, rice husks, buckwheat husks, sunflower husks and pulp, flax husks, nut shells, berry or fruit pits, fruit brains and skins, bard, spoiled grain, beer grist, etc.;
plants: reeds, straw, sugar cane, as well as trees, branches and bushes cut down during landscape works and sanitary cleaning;
other natural combustible substances: coal dust, peat, lignin.
Such raw materials are quite inexpensive, available and common, they can be well subjected to granulation, however, compared to wood raw materials, they can have a number of disadvantages: excessive content of aggressive chemical compounds, in particular acids, high ash content, excessive moisture and oil content, low melting point of ash, low content of binders, etc. The use of pellets from such homogeneous raw materials in boilers can lead to excessive slag and soot formations, intensive moisture release, chemical corrosion, and the pellet itself can have a fragile structure.
Research and experiments in this direction.
In order to find the optimal composition of raw materials for mix pellets, European researchers conduct experiments on mixing different types of raw materials. On the basis of research, viable “recipes” of mixed pellets from various raw materials have been created and tested, which do not harm the boiler equipment and are almost devoid of harmful substances during combustion. For example, scientists from the Forest Research Institute of Austria created mix-granules from corn cobs, rapeseed and straw with the addition of kaolin, bentonite and coal dust. Such mix-pellets emit a minimum of harmful substances into the atmosphere, when they are burned in the fuel chamber of boilers, slag cakes and significant soot deposits are not formed.
Individual manufacturers combine wood raw materials with 10-15% of coniferous needles or mix sawdust with 20-25% coal dust and 1-3% starch. The calorific value of such pellets due to the raw materials used is about 23 MJ/kg, which makes them a respectable alternative to low-calorie coal and peat, both in terms of calories and fuel cost. For the production of such pellets, wood of any species and quality, in particular dry and burnt wood, is suitable.
The only and main obstacle to the mass distribution of mix-pellets in the countries of the European Union are strict standards for emissions of combustion products into the atmosphere. In the production of mix-pellets, various types of available and relatively cheap additives for binding pellets are often used. If conifers have enough of their own lignin, ordinary starch is usually added to hardwood raw materials, as well as some agro-processing waste. Also used are fish oil, lime, paraffin, vegetable oils, coffee grounds, i.e. everything that has good binding properties, low cost and flammability. Such applications improve the qualitative properties of the pellet, reduce the volume of screening of the base, and increase the calorific value of the fuel.
Agropellets.
Agro-pellets are fuel pellets made from various raw materials of vegetable origin, usually agricultural crops and waste from agricultural processing. One of the most popular and affordable types of pellet raw materials of agrarian origin is the straw of various agricultural crops, in particular grain and rapeseed. In terms of energy potential, this material is slightly inferior to wood, having a calorific value of up to 16 MJ/kg. In addition, straw is a highly renewable source of energy, since burning does not change the balance of nitrogen dioxide in the atmosphere. During ripening, agricultural crops absorb as much carbon dioxide as they can emit during burning.
Similar to straw, the type of raw material is reed. Compared to straw, its calorific value is even slightly higher (up to 19 MJ/kg), and its ash content is about 4%. Such raw materials are quite widespread and very cheap, since they do not require cultivation and processing. Reeds are collected with the help of special harvesters-bundles.
Sunflower husks and pulp are one of the most promising materials for the production of agricultural pellets in Ukraine. The ash content of sunflower pellets is about 3%, and the calorific value is identical to brown coal – up to 21 MJ/kg due to the oil content. Ash after burning sunflower agricultural pellets is a valuable and useful fertilizer.
Buckwheat husks, cereal and rice bran are also successfully used for the production of agropellets. As in the case of mixed pellets, strict environmental regulations are a significant obstacle to the mass distribution of agro-pellets in the countries of the European Union.
Pellets from alternative raw materials.
Ukraine has large deposits of fuel peat, which is suitable for granulation. Peat pellets and briquettes are made using the same technology as wood pellets. The calorific value of peat is quite high – up to 21 MJ/kg, but the ash content of such pellets is up to 5% due to the high sand content. However, such fuel can be successfully used in industrial and communal boiler houses, due to the low cost of raw materials, its availability and industrial volumes. In Northern Europe, peat is recognized as a partially renewable raw material and its use in the energy sector is encouraged by state authorities.
Granulation of waste paper is a fairly new, but promising industry, as this type of raw material does not require expensive drying facilities. Pellets made of paper and cardboard are capable of producing a large amount of heat and have a small percentage of ash. In some countries, granulation of old banknotes has been established.
In recent years, quite exotic types of fuel raw materials, such as chicken droppings, animal manure, hydrolyzed lignin, etc., have been increasingly used for the production of fuel pellets.
The expansion of the raw material base for the production of fuel pellets provides an opportunity to benefit from the utilization of a huge amount of biological waste, as well as to solve environmental problems related to their storage, processing and disposal. The transition from carbon to ecologically clean fuel reduces the amount of emissions of harmful substances into the air, which in recent decades has become a very urgent and priority issue of global environmental security.
In addition, this is related to the general problem of depletion of traditional extractive energy resources and their gradual replacement by renewable and alternative sources of energy, where the use of this type of fuel in the world is becoming more popular every year both among private users and in industry, as evidenced by the general dynamics increase in the production and sale of solid fuel boilers.