THE WOOD PELLET production And Uses

THE WOOD PELLET production And Uses

Contents What are wood pellets? Raw material feedstock
Why wood pellets? Wood pellets production process Pelletizing technologies Advantages and disadvantages of pelletization Wood pellet heating systems Co-firing of wood pellets

Introduction Utilities using wood biomass fuels to improve the environmental profile of energy generation

Introduction Over the last decade there have been two major factors that have been driving the growth of the pellet fuel market. the first is the consistent rise in the cost of fossil fuels and price instability, the second is the increased attention given to the effects of using fossil fuels such as oil and gas on the environment. Other factors that support the case for pellets is that they are a fuel that can be produced locally, from local wood and biomass materials. Local pellet production and distribution can produce an affordable fuel, while creating local jobs and keeping the carbon footprint to a minimum

Biomass Fuel Diversity
Wood or Grass Briquettes Wood Pellets, Wood Chips Logwood

What are wood pellets? Pellet
Wood pellets are a condensed uniformly sized form of biomass energy, making them easier to store and use than many other biomass fuels. Wood pellets are densified wood fuels which have been produced from sawdust, grinding dust, shavings, bark, herbaceous biomass, fruit biomass, or biomass blends and mixtures. etc. Biomass pellets are used for residential heating and for industrial scale combined heat and power production Typical length 5 to 30 mm Moisture 8-12 % Density kg/m3 LHV 17 MJ/kg 4,7 kWh/kg kWh/m3 Cost €/t

What are wood pellets? Compressed biomass Wood Torrefaction
Solid biofuel made by mechanically compressing biomass to mold the solid biofuel into a specific size and shape such as cubes or pressed logs Compressed biomass Sawdust, wastes from sawmilling Normally 6 mm diameter High pressure of the press lignin plasticize forming a natural “glue” Wood Torrefaction Hydrophobic property Tending not to dissolve Store in open air, easy to dry reduce logistics cost Roasting temp ℃

Raw material feedstock
In general, any biomass is suitable as raw material for pelletizing. Currently woody biomass is the predominant raw material for fuel pellet production. Pellets made of hardwood usually have lower qualities, especially with regard to durability. Pelletizing of hardwood is more difficult and requires the adaption of the pelletizing process. Softwood is most commonly used with spruce, fir and pine being the most common woody raw materials. The rising demand for wood, both for the energy related use and as building material, results in increasing competition and price peaks. Consequently, alternative woody raw materials like low quality wood, short rotation coppice (e.g. poplar, willow) as well as non-woody raw materials like agricultural residues (e.g. straw) and energy plants (e.g. miscanthus) are experiencing growing interest.

Raw material feedstock
If wood pellets are produced from short rotation coppice, the high proportion of bark (up to 25% by mass) has to be considered since bark contains higher amounts of ash which could result in operational problems in small household heating systems. The properties of agricultural residues and herbaceous crops are significantly different from those of the woody biomass. The ash content is usually higher, while the ash melting temperatures are generally lower. Higher concentrations of nitrogen, sulfur, potassium and chlorine are often found, leading to the formation of harmful emissions (nitrogen oxides, sulfur dioxide, hydrogen chloride, particulate matter). These substances are involved in corrosion process on metallic surfaces.

Wood Pellets (Industrial)
Wood Pellet Characteristics Property Wood Pellets (Industrial) Bituminous Coal Heat Content (MMBTU/ton) 15.8 – 17.0 16.7 – 26.9 Ash Content (% wt.) 2.0 3.3 – 11.7 Moisture Content (% wt.) < 8.0 (TYP ) 2.2 – 15.9 Sulfur (% wt.) 0.010 – 0.015 0.7 – 4.0 Nitrogen (% wt.) 0.03 1.5 Mercury (% wt.) 0.16 2.21– 6.91 Bulk Density (lb/ft3) 45 43 – 50

Why wood pellets? Similarities to coal make wood pellets an ideal low carbon replacement Wood pellets provide power generators with a “drop in” alternative to coal. Reduces overall carbon footprint of generation by ~80% compared to coal. High energy density and uniform shape enhance transportation and storage economics. Existing conventional generation can be converted.

Why wood pellets? Why wood pellets instead of just burning logs?
Logs only come from trees that in general grow very slowly. Pellets can be made from practically any biomass material including straws, grasses, energy crops etc. pellets burn much more efficiently. pellets produce less ash, less smoke and more heat. pellets have a uniform size, shape, density and moisture content. These consistent qualities make it possible to design highly automated combustion systems such as modern wood pellet stoves and boilers. On a heat-generated basis the cost of wood pellets is very competitive to logs.

Why wood pellets? Modernizing the Bioenergy Heat Production Chain
crop Pellet fuel Stove Boiler Heating Cooking

Wood pellets production process
The manufacturing process for wood pellets involves drying, grinding, and extruding wood fiber under high pressure and temperature into pellets of a specified size. The raw material may consist of sawdust, shavings, and other residues produced from wood products or furniture manufacturing and, increasingly, from chips and whole logs sold and delivered to wood pellet manufactures. Wood fiber naturally contains lignin that serves to bind wood particles together when subjected to high temperature and pressure. Both softwood and hardwood wood species are utilized for making wood pellets. For industrial pellets, bark is typically not utilized because it creates wood pellets with high levels of ash content that has detrimental effects on boilers and greater pollutant emissions when burned. In some pellet manufacturing processes, additional binders are added for durability or to augment the energy density of the pellets.

pellet production process Storing and pretreatment Drying the raw material Pellet storing Pellet cooling

Changes in raw material particle size Before pellet compression in the pellet mill can take place the wood, straw, grass or any other form of biomass must be reduced in size Particles, which are too small or too large, can severally affect pellet quality and increase energy consumption. Changes in raw material moisture content pellets have moisture content below 10%, it burns very efficiently, and produce virtually no smoke during combustion. Pellet production is a high temperature process. The right moisture content will produce the best quality pellets, reduce energy consumption and reduce pellet mill downtime. Changes in raw material composition and the inclusion of binders and lubricants Changing the composition can include adjusting particle size or moisture content. It may also include adding binders and lubricants to help produce higher quality fuel pellets.

Changes in raw material pellet mill feed rate Adjustments on feed rate and maintaining a consistent feed rate can be the key difference to how well the pellet mill operates, even if the raw material is perfectly prepared. Changes in raw material conditioning and steam Conditioning is the pre-treatment of the raw material before it reaches the pellet mill. Conditioning can include specific mixing techniques and the introduction of additional water or steam. Steam can be used to pre-anneal the raw material and start the lignin melting process. Though conditioning can have several benefits in some cases the benefits are negligible and in other cases it is simply not practical to use conditioning.

Changes in pellet mill operating temperatures Temperature is a key requirement in pellet production. Unless a certain temperature is reached in the pellet mill natural lignin will not melt. It is not possible to produce wood pellets without sufficient heat. However, if the temperature is too high this can damage the pellet mill and particular consumables such as the pellet mill die, rollers, bearings and seals. Changes in pellet mill roller and die clearance The roller and die are wearing consumable parts, due to the abrasive nature and pressure of compression. The distance set between the roller and die can impact on how much energy the pellet mill uses, the quality of the pellet, pellet mill productivity and the amount of fines produced. Correctly setting up the die on a pellet mill will also increase the life of the roller and die, and reduce the cost of changing these consumable parts.

Changes in pellet mill die template rotation speed The speeds at which the roller and die turn affect the complex relationships during pellet compression. Some materials require a greater time under compression, and therefore require a slower rotation speed. Also, the speed and torque requirements of the pellet mill change. Changes in pellet mill die design and metal used Many different forms of metal alloy are used to produce pellet mill die templates. Different metal alloys have specific advantages and disadvantages. Using the correct alloy is critical to reduce wear and increase production. The type of metal used also affects the finish of the die holes.

The 10 steps of pellet production 1. Size reduction: Chippers/Shredders, Hammer Mills 2. Material transportation: Fans, Cyclone Separators and Screw Augers 3. Drying solutions: Rotary/Drum Dryers, Pipe Dryers 4. Mixing solutions: Batch Mixers 5. Conditioning: Water and Steam Addition, Binders 6. Pellet production: Round and Flat Die Pellet Mills 7. Sieving: Removing Fines 8. Cooling: Counter Flow Coolers 9. Pellet transportation: Bucket Elevators 10. Bagging and storage: Bags, Sacks and Silos

Pelletizing technologies
Overview Pelletization is a process which is closely related to the briquetting processes. The main difference is that the dies have smaller diameters (usually up to about 3 cm). A pellet press is composed of a die and generally of two or three rollers. The die is arranged as holes bored in a thick steel disk or ring. Loose milled material is fed into the pelletizing cavity. The rotation of the die and roller pressure forces material through the die holes. The raw material is frictionally heated.

Overview The densified material emerges from the die as strands of uniform section and cut with knives into the desired length. Pellets are cut off when coming out from the die or they can be cut with adjustable knives to a desired length. The density of the pellets depends on the frictional forces which are controlled by the length and the diameter of the apertures in the die, the condition of the die and rollers, the roller adjustment and the raw material properties.

1. Raw materials are fed into pellet cavity 2. Rotation of die and roller pressure forces materials through die, compressing them into pellets 3. Pellets extruded to the outside of the die

Pelletizing Methods There are several different pelletizing methods, which could be broadly categorized into two groups based on roller and die press arrangements as Flat die press and Ring die press. Flat Die Press: Disk matrix press consisting of a die in the form of a plane disk and rollers

Pelletizing Methods Ring die press: Ring matrix press consisting of a die in the form of a ring and inside rollers.

The ring die pellet mill The ring die is positioned vertically The raw material enters the centre of the die and is compressed through the die with a series of compression rollers. Most ring die pellet mills have two compression rollers, however some ring die pellet mills have three maybe four compression rollers. The most common design of ring die pellet mill is where the die is powered and rotating, and the rollers move due to the friction and movement of the die.

Pelletizing Methods Ring die presses are the most popular in the pellet industry. From the basic method it has been several developments. Ring die may rotate or be static, and the power transition becomes either the die or rollers. Inner diameters of the rings vary from about 25 cm up to 100 cm with track surfaces from 500 to 6000 cm². The capacities of the above types of palletizing machines are in the range of few kg/hr to 10 t/hr. Power consumption of the pellet mills ranges from 15–40 kWh/t.

Pelletizing Methods Other Varieties: Punch Press Cog-wheel pelletization principle

Advantages of pelletization
Uniform in size, density and moisture content Less volume Fewer deliveries Consistent size and moisture content Less ash and emissions Pellets are dry and can be stored without degrading Easy to transport, convey and feed using the existing systems High heating value: 18.5 GJ/t Export commodity Domestic heating, animal bedding, power generation, biofuels production

Advantages of pelletization
Using biomass fuels helps mitigate such environmental issues as acid rain and global climate change. The greatest advantage of biomass fuels is that they cost on average percent less than fossil heating fuels and are more stable in pricing. wood pellets: are convenient and easy to use, and can be bulk stored in less space than other biomass fuels have a high energy content, and the technology is highly efficient compared to other biomass fuels are a clean-burning renewable fuel source are produced from such waste materials as forestry residues and sawdust are price stable compared to fossil fuels

Disadvantages of pelletization
Advantages of wood fuel: Flow like a liquid Easier to handle Easier to ignite Disadvantages of wood fuel: Need large storage place Ashes More expensive Pellets stove

Biofuels chips and pellets
1 kg of chips whit moisture 40 % LHW=10,46 MJ/kg is equivalent : 0,28 litre oil (LHWoil =10,19 kWh/ litre) 0,3 m3 CH4 (PCI CH4 =9,5 kWh/Nm3) 1 kg of pellet LHW=16,92 MJ/kg is equivalent : 0,46 litre oil 0,49 m3 of CH4 Confront Chips process simpler and cheaper Chips lower energy density, lower volumetric bulk density, more storage space

Chips vs. Pellets Parameter Chips Pellets Heat Cost ($/MMBtu) Lower
Higher (about 2X chips) Capital Cost/MMBtu Higher Fuel supply Diversity of suppliers Fewer suppliers Applicability Generally >3MMBTU Generally <3MMBTU Fuel Standards to Ensure Consistency of Fuel No Yes Energy Density (MMBtu/ton) Maintenance Cost Generally higher than pellet system Generally lower than chip system Output efficiency Generally <75% 80-90+% Particulate Emissions Higher than pellets w/out emission controls Lower than chips

Wood pellet heating systems
Pellet stoves Pellet stoves use compressed pellets (made from wood or other biomass) for fuel. Pellet stoves can be categorized into two types based on the pellet delivery systems, top‐fed and bottom‐fed. A top‐fed pellet stove directs pellets into the combustion chamber from the hopper at the top of the stove. Its combustion chamber is more likely to be filled with ash and other debris. A bottom‐fed pellet stove feeds pellets into the combustion chamber from the bottom and automatically pushes the ash into the ash pan. The cleanup of this kind of stove is typically easier because of the larger capacity of the ash pan.

Residential Stoves Residential stoves are used to generate space heating for one or more rooms. A wood stove burns cordwood, and regular tending is required to keep an even temperature as the airflow and fuel supply must be manually handled. A wood stove must be refueled multiple times a day, as well as having the ash pan emptied and the glass panes cleaned daily. A pellet stove burns pellets (i.e., compressed woody or agricultural material). These systems are more automatic as fuel is fed from the storage hopper into the combustion chamber via an auger. A typical pellet stove will generally require the user to top up the storage hopper on a daily basis.

Components of a wood pellet stove

Residential Boilers A pellet boiler (furnace) is a central heating system that takes the place of natural gas or oil boilers. They provide warm water or warm air that is used to heat the entire house. For an indoor wood boiler, water surrounding the combustion chamber absorbs heat. The heated water is then circulated throughout the building, either through a system of pipes for radiant baseboard or radiant floor heating, or through a heat exchanger to allow for forced air heating. Pellet systems have the simplest controls and are closest to the fossil fuelled boilers in terms of maintenance and operation. An advantage to residential boiler systems is that they can also be used to heat water, as well as providing heat for the house.

Pellet systems are fully automatic in fuel feed and offer low costs for both installation and operation. Wood pellet boilers are relatively simple systems that are easily installed and operated. The wood pellets are typically stored in a standard outdoor silo. Pellets are delivered in trucks similar to those that deliver grain. Wood pellet fuel is automatically fed to the boiler via auger systems similar to those used for conveying feed and grain on farms. The pellets are discharged from the silo and conveyed to the boiler using automatically controlled augers set to provide the right amount of fuel based on the building’s demand for heat.

Residential boilers - Outdoor wood boiler An outdoor wood boiler works much the same, except that it is located outside the home, typically 10 – 50 m away. The heated water is delivered to the main building(s) through insulated underground pipes, where a water-to-air or water-to- water heat exchanger sends the heat into the building’s heating system. An advantage to an outdoor system is that no fuels enter the building, eliminating fire hazards, the mess or smoke, and removing the risk of carbon monoxide buildup. The feedstock for outdoor boilers can be pellets, chips or cordwood.

Residential boilers - Outdoor wood boiler

What is the difference between a wood pellet stove and a wood pellet boiler? A wood pellet stove is sized for residential settings. The heating needs of an average-sized home are typically much lower than those of commercial or institutional settings like small schools, municipal buildings, or small businesses. A wood pellet boiler is sized for these larger commercial heating loads. There are also other differences between pellet stoves and boilers in the degree of automation and fuel storage and handling, based on the different needs of residential and commercial users.

Pellet stoves Pellet stoves have several advantages over appliances that burn natural firewood: Their automatic operation is convenient. One hopper load of fuel can last 24 hours or more. Pellet stoves can produce a steady heat output and some are controlled with a wall thermostat. The fuel is supplied in bags, which store neatly. The fuel is always dry and ready to burn when purchased. Pellet appliances use a special vent that costs less to install than wood stove chimneys. Their smoke emissions are usually lower than those of advanced wood stoves.

Pellet stoves 1 Wood stove = 10 pellet stoves
1 wood stove can emit same PM as 10 pellet stoves. Most pellet stoves put out 1 – 2 grams an hour. Pellet stoves rarely put out any visible smoke and can be vented like a dryer out side of house. Pellet stove: Lab results are often similar to real world emissions, if stove is kept relatively clean. Many certified wood stoves average around 10 grams an hour, if they are operated relatively well.

Pellet stoves Balancing these advantages are some limitations that you may wish to consider: Pellet appliances tend to cost more than firewood burners. Pellet fuel is more expensive than firewood in many areas. Pellet fuel cannot be made by householders so it must be purchased. Pellet stoves need electricity to operate auger motors and fans. The fire produced by a pellet stove does not have the natural appearance of a wood fire.

Co-firing of wood pellets
Wood pellets in utility coal boilers Co-firing is a least cost solution compared to wood chip biomass power plants and is on par with wind energy, typically the most economic of the renewable technologies. Europe has been co-firing pellets successfully with coal since the 1990s Sweden, Denmark, Germany, and Austria are biggest users Co-firing is successful financially in Europe because of carbon legislation and utility cooperation

Wood pellets are well-suited for co-firing with coal Densified, low-moisture, uniform biomass Avoid many challenges of co-firing raw biomass Many characteristics similar to coal Cause fewer harmful emissions than coal, such as mercury and nitrous oxides Lower in ash and result in less boiler corrosion and slagging Carbon neutral

Why use wood pellets for co-firing?
Environmental Benefits Reduction of greenhouse gas emissions, CO2 Reduction of SOx Reduction of NOx Reduction of harmful heavy metals such as mercury and cadmium

Effects on NOx emissions Can reduce NOx through lower N content (depends on biomass) and higher volatiles release in the fuel rich zone of the flame BUT amount of NOx produced does not follow simple additivity Also gives lower flame temperature, reducing thermal NOx But may affect the Selective Catalytic Reduction (SCR) – larger quantities of alkalis such as K, Na, Ca and phosphorus may blind or poison the catalyst, leading to higher Nox emissions and potentially high ammonia slip Can need earlier catalyst change

Effects on SO2 emissions Coal blend principally affecting SO2 emissions are: The total sulphur content (represents maximum amount of sulphur oxides that could be formed) The ash composition (since typically 5-10% of the SO2 is generally captured by alkalis in the coal ash) Biomass generally has much lower contents of sulphur, together with higher concentrations of alkalis in its ash, so SO2 emissions are generally considerably reduced when cofiring Effects on particulates emissions Chemical and physical properties of fly ash particulates from biomass combustion are different from those of coal Can give higher release of trace metals Reduces fly ash loading Can increase overall collection efficiency of ESPs due to larger particulates and ease of agglomeration But may instead reduce collection efficiency, due to high resistivity of fly ash, and increase PM2.5 emissions

Technical Benefits Co-firing fuel – wood pellets vs. Wood chips or ag-residue Consistent fuel specification – provides for high reliability Low moisture content – provides for minimal degradation of boiler performance High heat content – closely matches heat content of coal Low ash content – less ash than coal No agricultural biomass fertilizer residuals – avoid impact on boiler tubes Ease of transport and handling Extensive test runs already performed

Increase Global wood pellet market
Industrial pellets for co-firing, CHP(combined heat & power plant), district heating Northern Europe : Netherlands, Belgium, UK Green electricity policy Residential heating such as pellet stoves and boilers, especially rural areas Italy, Austria, Germany Increase demand in EU stimulate large investments in new pellet plants Canada, U.S., Russia

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THE WOOD PELLET production And Uses

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