Accumulator tank - A large, well insulated hot water tank.
Accumulators are plumbed in to take heat directly from the boiler,
they then have a secondary heating coil to take heat for heat and
hot water to the rest of the system. This has the effect of
decoupling heat demand from heat production, allowing the boiler to
operate at best efficiency and to accept interruptions to the heat
supply. It also allows some lee-way in the specification of the
boiler, as the accumulator is able to smooth some of the peaks and
troughs in demand.
Archimedes screw (auger) - rotating spiral of metal
inside a tube used in boiler feed mechanisms for woodchips or
pellets, and in automated ash extraction mechanisms.
Ash - The non-combustible, mineral content of
biomass. During combustion bottom ash is the ash that is left
behind in, or under the grate or combustion region, or at the
bottom of a gasifier. Fly ash consists of very small particles of
ash that are carried out of the system along with the flue gases.
Both types of ash can potentially be spread on the land as a soil
conditioner, to help return the mineral content to the soil,
however owing to the potentially very high concentration of
minerals it is important that this is done with caution. In
particular, if there is the potential presence of heavy metals or
arsenic in ash as a result of accumulation from soil or air, or
from wood treatment, it must be checked before the ash is used in
this way. Alternatively, ash may be used in the manufacture of
construction blocks and cement. Ash that melts or fuses is known as
slag or clinker.
Auger (Archimedes screw) - rotating spiral of metal
inside a tube used in boiler feed mechanisms for woodchips or
pellets, and in automated ash extraction mechanisms.
Biodiesel - diesel made from biomass, such as
oilseed rape.
Bioenergy - a term used to describe
energy produced from biomass. Sometimes describes potential energy
within biomass.
Bioethanol - ethanol made from biomass.
Biofuel - term generally used to
encompass liquid fuel made from biomass, such as biodiesel or
bioethanol.
Biomass - potential fuel energy in the
form of biological material such as timber, miscanthus, dung or
straw.
Boiler - device for extracting heat energy from
fuel to provide hot water or steam.
Brash - Low density forestry material consisting of
tops of trees and small branches. Also referred to as
'lop and top'
Briquette - larger diameter
cylindrical section of compressed dried sawdust used as fuel in a
similar way to logs.
Bulk density - the weight per unit volume for a
solid materials.
Calorific value - the amount of heat produced by
the complete combustion of a unit weight of fuel, often expressed
in megawatt hours per cubic metre.
Chipper - machine, mobile or static,
used for the production of woodchips.
Chipping - the process of making small
fragments of timber (usually to a specified size) by passing larger
logs or pieces of timber through a chipper.
Chips - (shortened form of woodchips)
small fragments of timber sliced from a larger log or piece of
timber by a chipper, usually to a specified size.
Combined heat and power (CHP) - a term used to
describe systems that derive and utilise both thermal and
electricity energy from a given fuel source.
Combustion - the process of converting
fuel into heat energy.
District heating scheme - system by
which heat is distributed via underground pipe-work from a single
centralised boiler to a number of individual users, usually
domestic dwellings.
Energy crop - typically a crop of
trees, woody plants or grasses grown for the purpose of providing
biomass for energy.
Energy density - The
amount of energy stored per unit volume (volume energy density) or
mass (mass energy density) of a fuel. A high energy density
generally makes storage and transport of a fuel more convenient.
Fossil fuels typically have higher energy density than solid or wet
biomass fuels, though converted liquid biofuels and biogas are
similar to those of their fossil counterparts.
ESCO - Energy supply
company. Sells heat to the customer instead of a boiler and/or
fuel. May install, own and maintain the boiler, or may sub-contract
some or all of that. Heat used by the customer is metered, usually
as hot water flow rate and temperature difference between outflow
and return. Fully responsible for ensuring continuous operation and
suitable quality fuel supply. Particularly well suited to district,
site or large or multiple building heating systems.
Flue - a chimney-like tube for the
venting of gases and vapour from the boiler after combustion.
Fossil fuels - fossilised fuel such as
coal, mineral oil and natural gas. When burnt fossil fuel releases
carbon into the atmosphere that has been trapped beneath the
earth's surface for millions of years. Thus fossil fuel use can
contribute to an increase in current atmospheric greenhouse gases
and lead to global warming.
Gas turbine - device for turning
thermal energy from gasified biomass into electrical energy.
Gasification - conversion of solid
material such as woodchip into a gas for use as a fuel.
Heat exchanger - device, within a
boiler or water tank, to transfer heat from one system to
another.
Hopper - fuel storage container
usually adjacent to a boiler house.
Kilowatt - a unit of energy equal to
1000 watts.
Kilowatt hour (Kwh) - the basic unit
of energy equal to 1 kilowatt or 1,000 watts of power used for one
hour. A single bar electrical fire would typically use about 1
kilowatt hour (kwh) of electricity if operated for 1 hour.
Logs - section for a tree or branch
cut/split to a specified length for use in a wood burning stove or
automated log boiler.
Megawatt - unit of energy
equal to one million watts, or one thousand kilowatts.
Megawatt hour (Mwh) - measure of
energy production or consumption equal to one million watts
produced or consumed for one hour (equal to 1000 kilowatt
hours).
Miscanthus - a grass often planted as
an energy crop.
Moisture content (mc%) - the
percentage by weight of water in a material.
Moisture content - The proportion of
water in a sample of biomass, defined as the weight of water as a
percentage of the weight of biomass. This can be defined on either
a wet basis, as a percentage of the total (wet) weight of the
sample, or a dry basis, as a percentage of the oven dry weight of
biomass. Wet basis is usually used for fuel purposes.
Oven dry tonne (odt) - 1 tonne of
material (woodfuel) at 0% moisture content.
Pellets - small diameter cylindrical
section of compressed sawdust formed by passing dry sawdust under
high pressure through a dye. Usually between 6-8mm in diameter and
10 to 30mm in length.
Pyrolysis - the chemical decomposition
of woodchips by the action of heat to produce a liquid fuel.
Pyrolysis oil - Bio-oil produced by
fast pyrolysis of biomass. A dark brown, mobile liquid containing
much of the energy content of the original biomass, with a heating
value about half that of conventional fuel oil. Can be burned
directly, either alone or co-fired with other fuels, gasified or
otherwise upgraded. Conversion of raw biomass to pyrolysis oil
represents a considerable increase in
energy density and it can thus represent a more efficient form
in which to transport it.
Silo - fuel storage container usually
adjacent to a boiler house, can be below ground.
Solid fuel - fuel in solid form,
typically wood or coal, often used in stoves, open fires and some
boilers.
Steam turbine - device for converting
thermal energy from steam into electrical energy.
Stove - device for use indoors to
provide room heat, usually from solid fuel.
Watt - a unit of energy defined as one
joule transferred or dissipated in one second.
Wood chips - small fragments of timber
sliced from a larger log or piece of timber by a chipper, usually
to a specified size.