Pressure changes, especially negative pressure excursions in boiler furnaces, are the subject of growing concern to designers and manufacturers of large utility type boilers.
Boilers with both induced and forced draft fans may become unbalanced expecially if the forced draft unit becomes tripped and the induced fan unit remains in full operation. The induced draft fan will produce an excessive draft in the furance and create the real likelihood of furnace implosion.
Boiler furnaces are designed larger each year and consequently the draft head requirements increase owing both to the increased size of the units and also to environmental considerations. Therefore protection from the occurrence of a highly unbalanced furance draft is becoming a required safety feature.
A negative pressure excursion of -5 inches Wg. represents an impending danger, if the excursion decreases to furnace design values and lasts for an excessive period of time. A pressure exursion of -5 inches Wg. represents an emergency situation requiring a fan trip for emergency regulation of the draft in the furnace.
While there are systems which are used to control forced draft fans and induced draft fans for creating certain combustion characteristics in the furnace, there is definite need for a system which, in addition to controlling the flow characteristics of the furnace, reduces the possibility of boiler implosion by detecting the aforementioned dangerous and emergency situations.
It is therefore an object of the present invention to provide a system which will prevent, by suitable warning and control, the dangers caused by excessive pressure excursions in a boiler furnace.