Question

CE2009 3. ally used in combustion control systems to prevent Selectos ations from occurring. FIGURE Q3.1 shows a typical configuration for high and low selectors a rates. The energy de ss how the control system operates in the following pplied mand signal comes from the steam pressure to air and fuel flow three cases i) when the steam pressure is too low (i) when the air flowrate is too low (ii) and when the fuel flowrate is too high. 15 marks) FC FT FT Fuel Air rate flow rate PT) Furnace Steam Water FIGURE Q3.1

Answer 1

i) when the steam pressure is too low:-

'PT' pressure transducer sends signal to 'FC' flow controller of air via the connector and increases the air flow rate.When the air flow rate increases the 'FT' of the air stream send signals to the 'FC' of the fuel flow rate and it also increaeses

On summarizing when the steam pressure is low, the air flow rate and fuel flow rate increases and more heat is generated and more water is converted to steam.

ii) When air flow rate is too low:-

the 'FT' of the air stream send signals to the 'FC' of the fuel flow rate and it decreases the flow rate of the fuel . It limits the incomplete combustion of the fuel due to the unavailability of the required air.

On summarizing when the air flow rate is too low, the flow rate of the fuel also decreases so there will be sufficient air for the complete combustion of the fuel.

iii) When the fuel flow rate is too high:-

the 'FT' of the fuel stream send signals to the 'FC' of the air flow rate and it increases the flow of air. So that there will be sufficient air available for the complete combustion of the fuel incoming.

On summarizing when the fuel flow rate is too high, the flow rate of the air also increases to provide necessary air.