High-temperature trips

The results were not serious. The pumps supplied water to cool the hot gases leaving an incinerator when the water flow stopped, a high-temperature trip shut down the burner. The incinerator was nev/, was still undergoing tests, and the job had not been done before. The water was recycled, and ash in it probably caused the choke [40]. 

Two furnaces were each fitted with a temperature recorder controller and high-temperature trip. The two recorders were side by side on the instrument panel in the control room, with the recorder for A furnace on the left (Figure 3-2). 

Positive pumps are normally fitted with relief valves. These are not usually fitted to centrifugal pumps unless the process material is likely to explode if it gets too hot. As an alternative to a relief valve, such pumps may be fitted with a high-temperature trip. This isolates the power supply. Or a kick-back, a small-diameter line (or a line with a restrietion orifice plate) leading from the delivery line baek to the suction vessel, may be used. The line or orifice plate is sized so that it will pass just enough liquid to prevent the pump from overheating. Small-diameter tines are better than restriction orifice plates as they are less easily removed. 

Tests should be like real life. For example, a high-temperature trip failed to work despite regular testing. It was removed from its case before testing so the test did not disclose that the pointer rubbed against the case. This prevented it from indicating a high temperature. 

Do not reset this high-temperature trip above the manufacturer s specifications, without prior consultation with the equipment manufacturer. Ladies and gentlemen, you can imagine how I became so smart on this subject. 

This incident could have been prevented by a routine check of the high-temperature trip. A straightforward procedure to do this is ... 

Do not reset this high-temperature trip above the manufacturer s specifications without prior consultation with the equipment manufacturer. 

Trips shut down systems that are already in operation. For example, a high temperature trip on a furnace will shut off all the burners when temperatures get too high. Trips can be activated either automatically or by operator action. 

Calculate single channel failure rates for the high temperature trip example. 

Diagram 1 shows a high temperature trip on a reactor. 

Three temperature transmitters are provided, each of which transmits to a trip amplifier device that acts as a high temperature trip device. 

Diagram 1 Reactor with high temperature trip using 2oo3 sensor architecture. 

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