The by-product gases of BF and LD are burnt before releasing to the atmosphere through Chimneys (known as Flare Stacks). This consists of three chimney heads for releasing the main gas, each having 4 ignitors (along with pilot flame burners) at the top of Chimney. The pilot flame is used for igniting these gases which are positioned at the topmost point of these flare stacks. A detection system (based on the temperature of flame) is used to detect, if the pilot flame is glowing. It becomes difficult to detect the presence or absence of the flame for various reasons.
The igniter system consisting of an igniter i.e. the spark plug, electrode & insulators assembly at the top to ignite the pilot burner fired by Coke Oven Gas (COG).This ignition system uses high voltage transformer located at the bottom of Chimney for Blast Furnace Gas ((BFG) and located at the top of the chimney for LD Gas (LDG). This igniter fails to generate enough spark at the spark tip because of internal insulation failure/low insulation, as it is affected by heat and ambient condition (dust & moisture).
At the start of Blast Furnace & LD Gas the CV values of the gas are lean and at times pilot Gas COG is also lean after shutdown. The CO gas used for Pilot flame also carries impurities and chokes up the Pilot line after a certain time of operation.
If loss of pilot flame is not immediately detected, it can eventually lead to loss of the main flame which is needed for flaring the by-product BF gas. Since BF gas has significant CO concentration, this cannot be released to the atmosphere without flaring which otherwise will be a potential safety threat for people working near the stack and to nearby operating units of the Steel Plant. This situation leads to unsafe condition and may force shutdown of Blast Furnace.
The solution should provide a reliable ignition system and flame detection system for the operation of the flare system with zero maintenance at the top and all controllable features at the bottom of Chimney. Note: The main gas which has to be ignited by the Pilot burner also has varying CV value in the beginning and the flow volume also changes as per the operating condition of process.
Successful implementation would comprise of,