Pellet fuel
[5][6] 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.
[8] Pellets are extremely dense and can be produced with a low moisture content, below 10%, that allows them to be burned with a very high combustion efficiency.
[11] With the surge in the price of fossil fuels since 2005, the demand for pellet heating has increased in Europe and North America, and a sizable industry is emerging.
[12] In a 2012 report, the Biomass Energy Resource Center says that it expects wood pellet production in North America to double again in the next five years.
[13] Pellets are produced by compressing the wood material which has first passed through a hammer mill to provide a uniform dough-like mass.
The high pressure of the press causes the temperature of the wood to increase greatly, and the lignin plasticizes slightly, forming a natural "glue" that holds the pellet together as it cools.
It suggested the benefits of grass as a feedstock included its short growing time (70 days), and ease of cultivation and processing.
"[15] In 2012, the Department of Agriculture of Nova Scotia announced as a demonstration project conversion of an oil-fired boiler to grass pellets at a research facility.
An environmental impact assessment of exported wood pellets by the Department of Chemical and Mineral Engineering, University of Bologna, Italy and the Clean Energy Research Centre, at the University of British Columbia, published in 2009, concluded that the energy consumed to ship Canadian wood pellets from Vancouver to Stockholm (15,500 km via the Panama Canal), is about 14% of the total energy content of the wood pellets.
(In contrast, the bulk density of a mass of pellets, including trapped air, is only about 0.6-0.7 ton per cubic meter).
[citation needed] Standards used in the United States are different, developed by the Pellet Fuels Institute and, as in Europe, are not mandatory.
[citation needed] Still, many manufacturers comply, as warranties of US-manufactured or imported combustion equipment may not cover damage by pellets non-conformant with regulations.
Pellets may self-heat, ignite and give rise to a deep-seated smoldering fire that is very difficult to extinguish.
The smoldering fire produces toxic carbon monoxide and flammable pyrolysis gases that can lead to silo explosions.
Automatic or auto-pellet boilers include silos for bulk storage of pellets, a fuel delivery system that moves the fuel from the silo to the hopper, a logic controller to regulate temperature across multiple heating zones and an automated ash removal system for long-term automated operations.
High-efficiency wood pellet stoves and boilers have been developed in recent years, typically offering combustion efficiencies of over 85%.
[46] The newest generation of wood pellet boilers can work in condensing mode and therefore achieve 12% higher efficiency values.
[47] Wood pellet boilers have limited control over the rate and presence of combustion compared to liquid or gaseous-fired systems.
[10] Emissions such as NOx, SOx and volatile organic compounds from pellet burning equipment are in general very low in comparison to other forms of combustion heating.
This PM2.5 emissions of older pellet stoves and boilers can be problematic in close quarters, especially in comparison to natural gas (or renewable biogas), though on large installations electrostatic precipitators, cyclonic separators, or baghouse particle filters can control particulates when properly maintained and operated.
[9][50][51][52] Factors in the uncertainty include the wood source, carbon dioxide emissions from production and transport as well as from final combustion, and what time scale is appropriate for the consideration.
[57] Then, scientific papers studying the climate implications of biomass began to appear which refuted the simplistic assumption of its carbon neutrality.
[60] However, the establishment and cultivation of bioenergy crops can displace natural ecosystems, degrade soils, and consume water resources and synthetic fertilisers.
[70] The UK has initiated a grant scheme called the Renewable Heat Incentive (RHI) allowing non-domestic and domestic wood pellet boiler installations to receive payments over a period of between 7 and 20 years.
It is the first such scheme in the world and aims to increase the amount of renewable energy generated in the UK, in line with EU commitments.
[78] Nature's Flame wood pellet processing plant, in Taupo, is due in late 2019 to double its annual production capacity to 85,000 tonnes.
[79] Azwood Energy[80] operates a wood pellet processing plant in Nelson, utilising more than 1.2 million cubic metres of forestry residue each year[81] to provide carbon neutral fuel for domestic use, hospitals, schools and industrial processes, including milk-processing.
