There is a problem with the recovery system of waste heat from the heating furnace after interlocking – please give some advice!
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The specific process for the waste heat recovery section of my heating furnace is as follows: The flue gas has two routes for discharge, namely direct emission into the chimney or passage through an air preheater before being emitted into the chimney. Each of these routes is equipped with a two-position interlock valve. Under normal conditions, the flue gas flows through the interlock valve, then into the induced draft fan, and subsequently through the air preheater before reaching the chimney. The induced draft fan has an inlet damper but no outlet damper; in such conditions, the interlock valve leading to the chimney remains closed. In case of an emergency, the interlock valve leading directly to the flue opens, while the interlock valve leading to the induced draft fan closes. The problem is that it is difficult to achieve a disturbance-free switchback once interlocking is restored; in other words, how can negative pressure in the furnace be maintained when starting the induced draft fan? I wonder how everyone handles it? Fluctuations will occur whether it is a reset interlock or a direct switching interlock valve, because the interlock valve cannot perform regulation.
It is recommended that a control damper be installed before the two flue gas streams from the waste heat recovery section of the heating furnace are released; the fan should be variable frequency, and both the variable frequency feature and the control damper can be used to achieve negative pressure control. During interlocking, if the fan stops, it should be vented directly. The negative pressure is adjusted via the front adjustment flap. It seems unlikely to achieve disturbance-free operation during interlocking; manually shutting down the fans can still help keep fluctuations to a minimum.