Limiting control arrangement for exhaust system operation

A system for maintaining a continuous subatmospheric gas pressure in a gas exhaust system comprising

• a. a canopy for enshrouding a coke oven discharge area, the canopy having portions in communication with the atmosphere,
• b. an exhaust manifold having a plurality of gated inlets,
• c. a duct connected at one end to the interior of the exhaust manifold,
• d. blower means connected to the interior of the duct at a point spaced from the exhaust manifold for applying subatmospheric gas pressure to the interior of the exhaust manifold through the duct,
• e. means for periodically selectively connecting one or more gated inlets to the interior of the canopy to place the interior of the exhaust manifold in gaseous communication with the interior of the canopy to thereby cause a draft to flow through the canopy from the atmosphere, through the exhaust manifold, through the duct and through the blower, there being no opening in the duct nor the exhaust manifold other than the connected gated inlet or inlets,
• f. electric motor means connected to the blower means for driving the blower means,
• g. valve means in the duct for controlling the flow of gases through the duct to the blower means,
• h. control means for actuating valve means (g),
• i. means for continuously measuring the amplitude of the current drawn by the electric motor means and producing a signal proportional to the amplitude of the current drawn by the electric motor means,
• j. means for translating the signal produced by means (i) into a power output for actuating control means (h), and
• k. means associated with the means (j) for varying the power output to actuate means (h) and thereby valve means (g) to control the flow of gases in direct relation to signals corresponding to amplitude of current within a predetermined range of indicated current amplitude and responding to signals indicating an approach to predetermined maximum current amplitude by controlling the flow of gases in inverse relationship to prevent the current from exceeding the predetermined maximum current amplitude.