Emerson Process Management IM-106-910Xi instruction manual Stoichiometer, Programmable, Reference

Instruction Manual

IM-106-910Xi, Original Issue November 2010

Xi Advanced Electronics

Stoichiometer	Process upsets can sometimes cause a combustion process to go into
	sub-stoichiometric or reducing conditions. The oxygen readings from one or
	more probes may decline all the way to zero. The stoichiometer cell will
	measure the amount of oxygen deficiency during these reducing conditions.
	The trends in your DCS can be set up for a lower range limit of -1 or -2%
	oxygen to depict the level of oxygen deficiency.
	The operator can see if his control recovery actions are having the desired
	effect. These types of events do not occur frequently, but knowing the
	parameters of the situation prevents over-correcting while coming out of the
	reducing condition.The stoichiometer feature requires purchasing the acid
	resistant stoichiometer cell and the stoichiometer feature inside the Xi.
	NOTE
	Make sure the DCS is configured for the same range as the Xi. For instance:
	-1% O2 to 10% O2.
Programmable	The zirconium oxide sensing technology has historically measured process
Reference	oxygen by using ambient or instrument air as a reference (20.95% oxygen).
	The sensor develops most of its signal at the low oxygen levels typically found
	in combustion flue gasses (2-4% oxygen), and is most accurate at these
	levels. When measuring near 20.95% O2, the sensor develops only a few
	millivolts of signal, and accuracy degrades.
	The programmable reference feature permits the user to use a bottled
	reference gas of low oxygen value (0.4% oxygen recommended). When
	measuring at or near 21% oxygen, a strong negative oxygen signal results,
	with much improved accuracy. A bottle of reference gas typically lasts about a
	month at the low flows required. Typical applications would be:
	Flue gas recirculation - controlling the mixing of flue gasses into the burner
	windbox prior ahead of the burner to reduce NOx emissions.
	Moisture monitoring - measuring the amount of moisture coming off of
	industrial dryers by noting the dilution effect water vapor has on the normal
	20.95% ambient drying air. (Non-combustion drying processes only.)
	Enriched oxygen concentration - pure oxygen is sometimes mixed in with
	the combustion air to increase heat at the flame. This is used in steel and
	other metals reduction processes and in some catalyst regenerators.

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