Technical Manual - Section 3 (Safety Hazards)

Table III:2-20. SOLVENT DEASPHALTING PROCESS
Feedstock From Process Typical products.....................To
Residual Vacuum tower Treatment Heavy lube oil..........................Treating or lube blending
Atmospheric tower
Asphalt.....................................Storage or shipping
Reduced crude
Deasphalted oil.........................Hydrotreat & catalytic cracker
Propane.....................................Recycle
SAFETY AND HEALTH CONSIDERATIONS
Fire Protection and Prevention
The potential for a fire exists if a product leak or release
contacts a source of ignition such as the process heater.
Condensed steam from the various asphalt and deasphalting
processes will contain trace amounts of hydrocarbons. Any
disruption of the vacuum can result in the entry of
atmospheric air and subsequent fire. In addition, raising the
temperature of the vacuum tower bottom to improve
efficiency can generate methane by thermal cracking. This
can create vapors in asphalt storage tanks that are not
detectable by flash testing but are high enough to be
flammable.
Safety
Deasphalting requires exact temperature and pressure control.
In addition, moisture, excess solvent, or a drop in operating
temperature may cause foaming, which affects the product
temperature control and may create an upset.
Health
Because these are closed processes, exposures are expected
to be minimal during normal operations. Should a spill or
release occur, there is a potential for exposure to residuals
and asphalt. Air blowing can create some polynuclear
aromatics. Condensed steam from the air-blowing asphalt
process may also contain contaminants. The potential for
exposure to hydrogen sulfide and sulfur dioxide exists in the
production of asphalt. Safe work
practices and/or appropriate personal protective equipment
may be needed for exposures to chemicals and other hazards
such as noise and heat, and during process sampling,
inspection, maintenance, and turnaround activities.
HYDROGEN PRODUCTION
High-purity hydrogen (95-99%) is required for
hydro-desulfurization, hydrogenation, hydrocracking, and
petrochemical processes. Hydrogen, produced as a by-product
of refinery processes (principally hydrogen recovery from
catalytic reformer product gases), often is not enough to meet
the total refinery requirements, necessitating the
manufacturing of additional hydrogen or obtaining supply
from external sources.
In steam-methane reforming, desulfurized gases are mixed
with superheated steam (1,100-1,600º F) and reformed in
tubes containing a nickel base catalyst. The reformed gas,
which consists of steam, hydrogen, carbon monoxide, and
carbon dioxide, is cooled and passed through converters
containing an iron catalyst where the carbon monoxide reacts
with steam to form carbon dioxide and more hydrogen. The
carbon dioxide is removed by amine washing. Any remaining
carbon monoxide in the product stream is converted to
methane.
Steam-naphtha reforming is a continuous process for the
production of hydrogen from liquid hydrocarbons and is, in
fact, similar to steam-methane reforming. A variety of
naphthas in the gasoline boiling range may be employed,
including fuel containing up to 35% aromatics. Following
pretreatment to
III:2-46