Pellet heating is a heating system in which wood pellets (small pellets from wood chips and sawdust) are combusted. Other pelletized fuels such as straw pellets are used occasionally. Today's central heating system which run on wood pellets as a renewable energy source are comparable in operation and maintenance of oil and gas heating systems.
There are two different operating systems for pellet heating systems, one being single ovens with direct heat release into the living space and the other being central heating systems (pellet central heating systems) including control and feedback control systems.
Pellet stoves or single ovens are generally plants in the power range of max. 6-8 kW and less. They are usually placed directly in the living room. They usually have a small reservoir of pellet fuel which can last for one or more days. Fuel supply and the control of combustion are controlled automatically and the ash removal is done manually. The heat is usually delivered directly into the room. The range of individual pellet stoves is similarly diverse as wood-burning stoves, including versions with viewings window which provide a view of the fire.
Pellet boilers are used as central heating systems for heat requirements (heating load) of more than 3.9 kW (Kilowatt). But pellet central heating systems are not only used in single- or two-family homes (up to 30 kW), but also for larger residential or business units with heat requirements of a few hundred kW. Pellet burner systems run most efficiently at full load and can usually be regulated down to up to 30% of its full capacity. Since the warmup phase of pellet ovens usually takes longer than for oil or gas firing systems, short burning phases have negative effects on the fuel efficiency. In order to improve energy efficiency and reduce harmful emissions, pellet ovens are usually combined with buffer systems like water tanks, for example. [1]
Separate pellet burner, which can be mounted to an existing oil- or wood-fired boiler, are sometimes offered as an inexpensive alternative to a complete heating changeover. But the efficiency of these add-on furnaces is reduced. Usually add-on furnaces are not subsidized by government funds.
Similar to wood chip fuel heating systems also pellet fuel is delivered periodically and automatically from the pellet storage (for central heating systems) or the day tank (for pellet stove) according to need in the combustion chamber. With the heat generated from the heating circuit water is heated in the boiler of the pellet in pellet central heating systems. The heat distribution is the same as in other systems, which use water for heat distribution. Unlike for oil or gas heating systems, pellet heating systems demand the integration of a hot water tank in the heating system in order to reduce heat losses.
The furnace is automatically supplied with combustible material. The control technology of the system regulates the fuel input gradually in order to match the required heat output. Depending on the specific system, the supplied wood pellets are automatically ignited either with hot air blowers, or it uses a permanent ember bed in the combustion chamber.
Wood pellet heating systems work with different techniques of charging and combustion: Today there are specifically developed loading techniques for pellet combustion like drop chute firing, underfeed firing, side-fed firing or the use of a roller grate system. The method of charging and combustion of the pellet fuel is divided into 5 technologies. [2] [3]
For more efficiency and less pollution in the air, modern pellet heating systems control combustion either via a temperature or flame space sensor in combination with an infinitely variable input of combustion air via a suck-blow fan or a lambda probe. The hot flue gases are led into the chimney via a heat exchanger with manual or automatic cleaning of the reheating surfaces.
Pellet systems are available in different power ranges from about 3.9 Kilowatt single ovens between about 4 and 20 kW. Most systems available today have a power control over the fuel and combustion air supply, so that they can be operated at full load and at part load. Currently pellet boilers achieve a combustion efficiency of about 85-95% at full load (nominal thermal output) in thermal power operation.
With few exceptions, the efficiency decreases when the pellets boiler operates at partial load. The technical heating efficiencies described may vary greatly from the actual plant efficiencies, the reason the plant concept plays a major role. The use of a sufficiently large buffer storage is useful.
The wood pellets are stored in bulk in a tank or storage area and supplied to the burner by means of a conveyor system. The storage area must be dry, since the pellets react hygroscopically on clammy walls or high humidity during storage with crumbling.
Compared to oil, wood pellets require about three times the storage volume, though with less technical effort for the space, as pellets, unlike heating oil are not water-polluting substances. For storage, the pellets can be accommodated in a single storage space. The floor should be in the shape of a funnel usually made out of wood. At the end of the funnel is the inlet for the screw conveyor or the extraction pipe. More outlets in the storage room ensure unobstructed operation even in case of problems of one of the extraction points. Alternatives to a storage room are prefabricated tanks made of fabric or sheet steel. [4] Buried underground tanks or free-standing silos can be used, if sufficient space is available in the building. In areas with high humidity it is important to use must tight tank systems to ensure the quality of pellet fuel.
To convey the pellets from the storage facility to the boiler room different systems are in use: Blower or screw systems can be used. The choice depends primarily on the distance from the storage to the boiler room. For distances greater than two meters flexible multi-stage screw conveyors are usually necessary. Blower systems can be used flexibly and feed distances up to 20 m. The discharge from the storage room or container is usually also supported by an inclined tank bottom or a hopper outlet. [5]
A boiler is a closed vessel in which fluid is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central heating, boiler-based power generation, cooking, and sanitation.
A furnace, referred to as a heater or boiler in British English, is an appliance used to generate heat for all or part of a building. Furnaces are mostly used as a major component of a central heating system. Furnaces are permanently installed to provide heat to an interior space through intermediary fluid movement, which may be air, steam, or hot water. Heating appliances that use steam or hot water as the fluid are normally referred to as a residential steam boilers or residential hot water boilers. The most common fuel source for modern furnaces in North America and much of Europe is natural gas; other common fuel sources include LPG, fuel oil, wood and in rare cases coal. In some areas electrical resistance heating is used, especially where the cost of electricity is low or the primary purpose is for air conditioning. Modern high-efficiency furnaces can be up to 98% efficient and operate without a chimney, with a typical gas furnace being about 80% efficient. Waste gas and heat are mechanically ventilated through either metal flue pipes or polyvinyl chloride (PVC) pipes that can be vented through the side or roof of the structure. Fuel efficiency in a gas furnace is measured in AFUE.
A barbecue grill or barbeque grill is a device that cooks food by applying heat from below. There are several varieties of grills, with most falling into one of three categories: gas-fueled, charcoal, or electric. There is debate over which method yields superior results.
Water heating is a heat transfer process that uses an energy source to heat water above its initial temperature. Typical domestic uses of hot water include cooking, cleaning, bathing, and space heating. In industry, hot water and water heated to steam have many uses.
A stove or range is a device that generates heat inside or on top of the device, for local heating or cooking. Stoves can be powered with many fuels, such as electricity, natural gas, gasoline, wood, and coal.
Wood fuel is a fuel such as firewood, charcoal, chips, sheets, pellets, and sawdust. The particular form used depends upon factors such as source, quantity, quality and application. In many areas, wood is the most easily available form of fuel, requiring no tools in the case of picking up dead wood, or few tools, although as in any industry, specialized tools, such as skidders and hydraulic wood splitters, have been developed to mechanize production. Sawmill waste and construction industry by-products also include various forms of lumber tailings.
A central heating system provides warmth to a number of spaces within a building from one main source of heat. It is a component of heating, ventilation, and air conditioning systems, which can both cool and warm interior spaces.
In a steam engine, the firebox is the area where the fuel is burned, producing heat to boil the water in the boiler. Most are somewhat box-shaped, hence the name. The hot gases generated in the firebox are pulled through a rack of tubes running through the boiler.
Pellet fuels are a type of solid fuel made from compressed organic material. Pellets can be made from any one of five general categories of biomass: industrial waste and co-products, food waste, agricultural residues, energy crops, and untreated lumber. Wood pellets are the most common type of pellet fuel and are generally made from compacted sawdust and related industrial wastes from the milling of lumber, manufacture of wood products and furniture, and construction. Other industrial waste sources include empty fruit bunches, palm kernel shells, coconut shells, and tree tops and branches discarded during logging operations. So-called "black pellets" are made of biomass, refined to resemble hard coal and were developed to be used in existing coal-fired power plants. Pellets are categorized by their heating value, moisture and ash content, and dimensions. They can be used as fuels for power generation, commercial or residential heating, and cooking.
A pellet stove is a stove that burns compressed wood or biomass pellets to create a source of heat for residential and sometimes industrial spaces. By steadily feeding fuel from a storage container (hopper) into a burn pot area, it produces a constant flame that requires little to no physical adjustments. Today's central heating systems operated with wood pellets as a renewable energy source can reach an efficiency factor of more than 90%.
Renewable heat is an application of renewable energy referring to the generation of heat from renewable sources; for example, feeding radiators with water warmed by focused solar radiation rather than by a fossil fuel boiler. Renewable heat technologies include renewable biofuels, solar heating, geothermal heating, heat pumps and heat exchangers. Insulation is almost always an important factor in how renewable heating is implemented.
A steam generator is a type of boiler used to produce steam for climate control and potable water heating in railroad passenger cars. The output of a railroad steam generator is low pressure, saturated steam that is passed through a system of pipes and conduits throughout the length of the train.
Forced-air gas heating systems are used in central air heating/cooling systems for houses. Sometimes the system is referred to as "forced hot air".
An oil burner is a heating device which burns #1, #2 and #6 heating oils, diesel fuel or other similar fuels. In the United States, ultra low sulfur #2 diesel is the common fuel used. It is dyed red to show that it is road-tax exempt. In most markets of the United States, heating oil is the same specification of fuel as on-road un-dyed diesel.
Jetstream furnaces, were an advanced design of wood-fired water heaters conceived by Dr. Richard Hill of the University of Maine in Orono, Maine, USA. The design heated a house to prove the theory, then, with government funding, became a commercial product.
Biomass heating systems generate heat from biomass. The systems may use direct combustion, gasification, combined heat and power (CHP), anaerobic digestion or aerobic digestion to produce heat. Biomass heating may be fully automated or semi-automated they may be pellet-fired, or they may be combined heat and power systems.
A wood-burning stove is a heating or cooking appliance capable of burning wood fuel, often called solid fuel, and wood-derived biomass fuel, such as sawdust bricks. Generally the appliance consists of a solid metal closed firebox, often lined by fire brick, and one or more air controls. The first wood-burning stove was patented in Strasbourg in 1557. This was two centuries before the Industrial Revolution, so iron was still prohibitively expensive. The first wood-burning stoves were high-end consumer items and only gradually became used widely.
A multi-fuel stove is similar to a wood-burning stove in appearance and design. Multifuel refers to the capability of the stove to burn wood and also coal, wood pellets, or peat. Stoves that have a grate for the fire to burn on and a removable ash pan are generally considered multi-fuel stoves. If the fire simply burns on a bed of ash, it is a wood-only fuelled appliance, and cannot be used for coal or peat.
A coal burner is a mechanical device that burns pulverized coal into a flame in a controlled manner. Coal burners are mainly composed of the pulverized coal machine, the host of combustion machine control system, ignition system, the crater and others.
A pellet boiler is a heating system that burns wood pellets. Pellet boilers are used in central heating systems for heat requirements from 3.9 kW (kilowatt) to 1 MW (megawatt) or more. Pellet central heating systems are used in single family homes, and in larger residential, commercial, or institutional applications. Pellet boiler systems run most efficiently at full load and can usually be regulated down to 30% of full load. Since the warm up phase of pellet boilers usually takes longer than for oil or gas firing systems, short burning phases have negative effects on the fuel efficiency. In order to improve energy efficiency and reduce harmful emissions, pellet boilers are usually combined with buffer systems, such as insulated water tanks.
