# 60.641 Definitions.
All terms used in this subpart not defined below are given the meaning in the Act and in subpart A of this part.
*Acid gas* means a gas stream of hydrogen sulfide (H<sub>2</sub>S) and carbon dioxide (CO<sub>2</sub>) that has been separated from sour natural gas by a sweetening unit.
*Natural gas* means a naturally occurring mixture of hydrocarbon and nonhydrocarbon gases found in geologic formations beneath the earth's surface. The principal hydrocarbon constituent is methane.
*Onshore* means all facilities except those that are located in the territorial seas or on the outercontinental shelf.
*Reduced sulfur compounds* means H<sub>2</sub>S, carbonyl sulfide (COS), and carbon disulfide (CS<sub>2</sub>).
*Sulfur production rate* means the rate of liquid sulfur accumulation from the sulfur recovery unit.
*Sulfur recovery unit* means a process device that recovers element sulfur from acid gas.
*Sweetening unit* means a process device that separates the H<sub>2</sub>S and CO<sub>2</sub> contents from the sour natural gas stream.
*Total SO*<sub>2</sub> equivalents means the sum of volumetric or mass concentrations of the sulfur compounds obtained by adding the quantity existing as SO<sub>2</sub> to the quantity of SO<sub>2</sub> that would be obtained if all reduced sulfur compounds were converted to SO<sub>2</sub> (ppmv or kg/dscm (lb/dscf)).
EThe sulfur emission rate expressed as elemental sulfur, kilograms per hour (kg/hr) [pounds per hour (lb/hr)], rounded to one decimal place.
RThe sulfur emission reduction efficiency achieved in percent, carried to one decimal place.
SThe sulfur production rate, kilograms per hour (kg/hr) [pounds per hour (lb/hr)], rounded to one decimal place.
XThe sulfur feed rate from the sweetening unit (i.e., the H<sub>2</sub>S in the acid gas), expressed as sulfur, Mg/D(LT/D), rounded to one decimal place.
YThe sulfur content of the acid gas from the sweetening unit, expressed as mole percent H<sub>2</sub>S (dry basis) rounded to one decimal place.
ZThe minimum required sulfur dioxide (SO<sub>2</sub>) emission reduction efficiency, expressed as percent carried to one decimal place. Z<sub>i</sub> refers to the reduction efficiency required at the initial performance test. Z<sub>c</sub> refers to the reduction efficiency required on a continuous basis after compliance with Z<sub>i</sub> has been demonstrated.
[50 FR 40160, Oct. 1, 1985, as amended at 65 FR 61773, Oct. 17, 2000]