Renewable Energy Sources for the mCCHP-SE-RES Systems - Design for Micro-Combined Cooling, Heating and Power Systems - page 109

burner ignition and extinguishing are safe, by correlating these operations with
the functions of the control loops of the system they belong to;

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ignition and flame monitoring and protection during operation;

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protection against reaching minimum fuel pressure at which burner operation is
no longer safe;

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protection against air supply cut off;

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protection against power supply interruption.

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Combustion ignition is usually achieved by means of ignition devices, mobile or

ame both at
starting and after the burner was activated, operating continuously in parallel with the
main

fixed, also called igniters such as a pilot burner used to ignite the main

flame, thus providing stability. Igniters operate with gas fuels (natural gas, liq-

ue ed petroleum gas as propane and butane) or liquid fuels (diesel and light fuel oil).

Ignition of pilot burners can be performed nonelectrically or by electrical sparking.
Normal operation of combustion systems should comply with the material and
energy balances (steady operation). During the operation, fuel intake and its param-
eters, along with the parameters of both air and

flue gas are closely controlled. For this

purpose, on the fuel side, the fuel ow rate, pressure, and temperature are measured,

when appropriate. On the flue gas side, pressure, temperature downstream the com-

bustion chamber till the chimney inlet are measured, and the chemical composition is
analyzed, both to control combustion and to watch the pollutant emissions.
Under optimum operation conditions of combustion system, the following fac-
tors are important: thermal output, plant safety, and reduced pollutant emissions. In
abnormal circumstances, such as when the temperature of the combustion chamber
metal exceeds the upper limit, the boiler control system should focus on it as being
the most important thing, sacri

cing the other two factors.
In most cases, the combustion system operates at variable parameters as a result
of heat consumer s request. In the transitional modes, the energy and material

balance is no longer met, and therefore variations of the combustion gas parameters
are reported. This leads to the need to provide an automatic control system able to
provide optimal combustion conditions, i.e., to maintain a proper ratio between fuel
and air

'

uence the combustion process
(primary air- secondary air distribution, the pressure in the combustion chamber).
The automatic control system of the combustion plant must achieve the fol-
lowing functions:

flow rate, and the other factors that in

maintain the optimum flow rate ratio combustion air - fuel;

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￿ ensure the development of a heat flow inside the combustion chamber as

required by the consumer;

￿ maintain the pressure in furnace to a fixed value, slightly less than the atmo-

spheric pressure to avoid gas leakage.

The three functions are achieved by means of the burner fuel supply system
equipped with the necessary regulating devices, with the fan that supplies air to the
furnace and/or the fan drawing the flue gas from the furnace, fitted with its own
regulating devices.