Page 70 - Environmental Control in Petroleum Engineering

58 Environmental Control in Petroleum Engineering

6% of the total emissions from all sources. About 46% of the NO x
emitted by the petroleum industry was from gas processing activities,
21% from production activities, and 22% from refineries. Crude oil
transport emitted 5.2% of the petroleum industry NO x, onshore drilling
emitted 4.2%, and product transport emitted 0.9% (American Petrol-
eum Institute, 1979).
NO x is formed at high combustion temperatures when molecular
oxygen dissociates into individual oxygen atoms. Atomic oxygen
readily reacts with atmospheric nitrogen to form NO x. Methods to limit
the formation of NO include combustion modifications to lower the
X
flame temperature during combustion and flue gas treatment to remove
any NO x that has formed. However, little can be done during drilling
and production operations to lower NO x emission, other than to
purchase low NO x generating equipment and operate it as recom-
mended by the manufacturer.
Partially burned hydrocarbons are emitted during combustion when
the fuel/air mixture is incorrect. The most common partially-burned
hydrocarbons from internal combustion engines powered by natural gas
are formaldehyde and benzene (Meeks, 1992). About 25 pounds of
formaldehyde and 1.5 pounds of benzene can be generated per million
cubic feet (MMcf) of fuel burned. For fuels containing benzene,
ethylbenzene, toluene, or xylene (BETX), about 3% of those com-
pounds will pass through the engine and be emitted.
Another major source of air pollutants is the operation of heater
treaters, boilers, and steam generators. These types of equipment also
emit NO x and partially burned hydrocarbons like carbon monoxide. If

a sulfur-bearing fuel is used, sulfur oxides, primarily SO 2 and SO 3
(referred to as SO x), can also be emitted. For a crude oil having a
sulfur content of 1.1%, about 7.5 pounds of sulfur will be released
for every barrel of fuel burned. Table 2-10 shows the typical emission
levels of an oil-fired steam generator operating at different levels
(Sarathi, 1991). For reference, a steam generator operating at 50 mil-
lion Btu/hr can inject steam into three to five wells. The data in this
table were adjusted for 365 days of continuous operation.

2.3.2 Emissions from Operations

A number of operations at production facilities emit volatile mate-
rials into the air. Operations that can cause emissions include the use