- Nov 27, 2016
Pretty sure that entire thing was summed up in my first sentence:2 fans in and 2 out will make for excellent airflow; it's referred to as 'balanced draft'. Just because the internal pressure is held near a zero delta to the outside doesn't mean there's no air flow...
Power generating station scenario: petroleum coke fired, top-supported watertube steam generators producing superheated steam which is expanded through steam turbines to generate power. Process control software holds the furnace pressure to -0.5", while twin, steam-turbine driven forced air fans pressurize the unit at the burner deck and a slip stream gets directed to secondary air fans then to ball mills where it mixes with/ carries pulverized coke to the burners. At the exhaust plenum, a single induced-draft fans take suction from the furnace and delivers it to the electrostatic precipitators for ash removal then to the stack. All fans have adjustable inlet vanes to vary airflow.
The furnace is held to a slightly negative pressure so that air infiltration is inward, not outward. Internal restrictions to air flow include a feedwater pre-heater (economizer) and both primary and secondary superheaters (steam must be heated beyond its saturation temperature to prevent condensation on blades as the steam is expanded through turbines. Condensation causes pitting and can lead to deposits on the blades resulting in unbalanced conditions and power loss. Blade washing is a thing.)
This scenario is common to all fired boilers, whether they have just forced air fans or both forced & induced air systems, due to a condition known as 'complete combustion'. Target combustion is a slight excess O2 and zero CO in the exhaust: too much excess O2 and you're wasting fuel by heating too much air and sending it up the stack; too little O2 and the fuel is partially un-burnt and creating CO as a product of incomplete combustion. CO is still capable of being burned, and in large enough % is explosive, and can lead to a 'furnace pressure excursion'. Redundant instrumentation at the stack continuously measures exhaust O2, CO2, CO, NOx, SO2 and particulate matter.
Zero pressure differential does not necessarily indicate zero air flow.
I worked 16 years in this environment; 10 years on the floor and 6 in the control room. 450MW generating station attached to a heavy oil upgrader.
I do not have a background like that, but I do have a background in building computers, speakers, etc and I know from experience what has worked for me and what has not.No it does not, but it also depends a lot on the conditions.
I mean if your turning this switch into a steam turbine, by all means give it a go.
And above all else, like I said to the last person. Try it and report back.