Introduction and Structure - Renewable Energy: Technology, Economics and Environment - page 19

1.4.3 Heat provision technologies
In the following, conversion technologies currently applied for heat generation
from fossil fuel energy are outlined and discussed. First, the techniques and sys-
tems are presented according to the current state of technology. Subsequently,
these techniques are assessed according to economic and environmental parame-
ters.
Economic analysis. The main system elements for plants providing heat using
crude oil or natural gas are, beside the heating boiler with the respective burner,
the fuel storage and supply as well as the domestic hot water provision.
Natural gas-fired heating boilers are usually supplied with the fuel from the
natural gas grid. Besides this option, there is also the possibility of operating heat-
ing gas-fired boilers with producer gas or liquefied gas (e.g. propane). Oil-fired
systems are supplied with fuels by steel or plastic tanks, located underground or
above ground, which are in turn supplied by trucks.
Inside the boiler the liquid or gaseous fuel is oxidised by released heat. A heat
exchanger transfers this heat to an appropriate heat transfer or distributing me-
dium (in most cases water), which transfers the thermal energy to the consumer.
For space heating and domestic hot water supply, today mainly low-
temperature and condensing boilers are applied. Within these systems burners
with and without a fan are used.
− Gas burners equipped with and without fan. Gas burners equipped with a fan
add combustion air to the gaseous fuel before the combustion takes place. Gas
burners without a fan, so-called atmospheric gas burners, run by self-priming
(i.e. combustion air is transferred to the combustion chamber by the thermal
lift). The chimney must thus generate enough flue to overcome all resistances
of the heating system. The gas/air mixture is burnt inside the corresponding
nozzles. Subsequently, heat released due to oxidation is separated from the ex-
haust gas and can subsequently be utilised.
− Oil burners equipped with fan. Oil burners are supposed to atomise or vaporise
the liquid fuel (i.e. the heating oil) as fine as possible, to mingle it intensively
with combustion air added by a fan, and to burn the mixture by producing as
low emissions as possible. For heating purposes mainly pressurised atomising
burners are used. Common oil burners ignite the hydrocarbon molecules inside
the flame and burn them with a yellowish flame (so-called yellow flame burn-
ers). Compared to this within so-called blue burner the oil drops are gasified
prior to the actual combustion inside the burner pipe by recirculation of the hot
fuel gas. This technology is characterised by combustion-related advantages.
− Low-temperature boiler. Depending on the ambient temperature, low-tempera-
ture boilers are operated at variable out-flow temperatures between 75 and
40 °C or lower. Particularly the flue gas and stand-by losses of boilers
equipped with a domestic hot water heating can thereby be considerably re-