Analysis
of Hazardous Situations in Oil Refinery Plants
by
Askeraliyev T. and Kadyrov O.
Kazakh
National Technical University after K.I.Satpaev
December
18, 2011
Petroleum refineries produce liquefied
petroleum gases (LPG), motor gasoline, jet fuels, kerosene, distillate fuel
oils, residual fuel oils, lubricants, asphalt (bitumen), and other products through
distillation of crude oil or through redistillation, cracking, or reforming of
unfinished petroleum derivatives. There
are three basic types of refineries: topping refineries, hydroskimming
refineries, and upgrading refineries [1].
Process safety in oil refineries depends on
three main factors:
1.
How a unit is designed
2.How
it is constructed
3.How
it is operated
Just as it is almost impossible to build facilities that are infallible
in the hands of improperly trained operators, it is also impossible to safely
operate equipment that is basically faulty in design. Thus, process and design
engineers must provide correctly designed facilities that can be safely
operated by following normal operating procedures. Failure to recognize and
eliminate hazardous situations has resulted in serious injuries to personnel
and costly damage to key facilities.
A significant proportion of serious incidents occur in the
process industry during shutdown or starts-ups. It must be recognized that some failures occurring during routine
operations are sometimes the results of fatigue and stress accumulated in the
equipment by ups and downs.
The hazards encountered most frequently in
shutdowns and startups of units are accidental mixing of air and hydrocarbons,
contacting of water with hot oil, and freezing of residual water in piping and
equipment. Other hazards commonly experienced during turnarounds are corrosive
and poisonous liquids and gases and pyprophoric iron sulfide. Still other
hazards (associated primarily with startups) involve pressure, vacuum, and
thermal and mechanical shock. These can result in fires, explosions,
destructive pressure surges and other damage to the unit, as well as injury to
personnel.
Fires occur when oxygen and fuel vapor or
mists are mixed in flammable proportions and come in contact with a source of
ignition. They may burn out of control or touch off a devastating explosion.
Pressure surges resulting from unplanned mixing of water and hot oil may cause
only minor damage or may wreck equipment. Extensive costly downtime on process
units may result. Fire usually follows if the explosion bursts lines or
vessels. Failure to drain water from equipment or failure to maintain a
sufficient flow of water or steam through a system may permit freezing which
can cause extensive damage. Proper drainage or flow will prevent freeze damage.
The complete plan for a shutdown, turnaround and startup should
include advance preparation at the unit and preparation by other departments
whose operations will be affected (other units, tank farms, pump houses, utilities
and the mechanical department). The shutdown procedure should be in writing,
and it should be followed strictly. Checkoff lists, with blanks for time and
initials, should be used to show the sequence of events to assure safety and
efficiency of operations and continuity of work between shifts. The critical
path (arrow diagram) method has been used effectively in recent years for
planning. In actual practice, separate diagrams are usually made for shutdown,
repair work and startup. In addition to serving as a checkoff list, the
critical path (the chain of interconnected work requiring the longest overall
time for completion) can be determined so that the work can be planned most
efficiently.
The shutdown procedure should include
the following consecutive phases:
1. Cooling and
depressuring
2. Pumping out
3. Removal of
residual hydrocarbons
4. Removal of
corrosive or poisonous materials
5. Disposal of
water
6. Blinding and
opening
7. Removal of
pyrophoric iron sulfide
8. Inspection for
entering
Whenever
practical, emergency equipment should be tested regularly while
the unit is in operation. In addition, all emergency
equipment (e.g., emergency
generator, driver trips, spare pumps and emergency
instrument-air system)
should be tested while the unit is being shut down so
that any malfunction can
be corrected
during the downtime.
Detailed
plans and procedures for re-start should be prepared in advance of the unit
shut-down. Preparation for the startup of a unit should begin with a complete
review of the startup procedure by the supervisors and operators. A detailed
procedure should be set up similar to the shutdown procedure. The arrow diagram
method is ideally suited for both shutdown and startup planning. On startups it
will be necessary to use checklists in combination with the arrow diagram. It is
recommended that the operators record and initial the completion of each step.
There should be a requirement to
follow a Management of Change process for
start-ups after an emergency shut-down, if the normal
start-up procedure
doesn’t cover this situation.
The importance of communications
between shifts and between individuals must be emphasized. Each shift must
clearly understand what has been done on prior shifts and what is expected of it.
Some overlap of supervision between shifts can improve
communications and continuity of work. In some cases management and engineering
staff may be involved in assisting the normal shift team in the startup. In
these cases the ‘chain of command’ and responsibilities of both the normal
shift team and those giving assistance must be clearly defined.
The activities of those on the unit should be
coordinated with the activities of
the pump houses, tank fields, other units, the power
station and the water
pumping station.
The procedure
should include the following consecutive phases:
1. Preliminary
preparations
2. Preparation of
auxiliary equipment and services
3. Elimination of
air
4. Tightness
testing
5. Backing in
fuel gas
6. Elimination of
water
7. Bringing the
unit onstream
The heightened risks present during refinery
process start-ups and shutdowns demand that these systems be highly reliable
and at peak effectiveness. Pre-start-up
safety reviews are an essential tool for identifying and correcting an array of
potentially disastrous refinery conditions and are included in the Process
Safety Management standard.
Virtually every safety system examined
in this study is highly dependent on the presence of highly qualified employees
in sufficient numbers to handle normal, abnormal, and emergency
situations.
As a result of this article I propose
several methods for providing better safety policy for oil refineries. They
are:
1. Establish a Process Safety Team as part of
the Health and Safety Committee at each refinery, including representatives
selected by the local union, to plan, review, monitor, and audit all process
safety activities.
2.
Ensure that process hazard analyses (PHAs) exist for all potentially hazardous
operations and that PHAs are reviewed and revalidated at least every three
years.
3. Develop and implement policies requiring
full safety reviews prior to all process start-ups and scheduled shutdowns.
4.
Provide adequate staffing to ensure safe operation in all potential
operating circumstances including day-to-day operations, start-ups, shutdowns,
abnormal conditions and upsets, and emergencies.
5.
Implement an effective incident and near miss investigation program at each
site that involves workers and their unions in all phases of investigation and
recommendations for improvement.
6. Develop and implement a national set of
standardized process safety metrics and benchmarks to assess leading and
lagging indicators of process safety that can help ensure that sites are able
to identify and correct deficiencies and improve programs, thereby preventing
process safety incidents[2].
Technology headways of modern control systems have also allowed
new innovations to better refinery reliability through advanced diagnostics.
Risks are lessened because of experience, tools and standard procedures.
Specialized companies have completed thousands of migrations from a number of
systems, making “risk-free migration” a reality
References
1. “Available and Emerging Technologies for Reducing
Greenhouse Gas Emissions from Petroleum Refining Industry”, Sector
Policies and Programs Division Office of Air Quality Planning and Standards U.S.
Environmental Protection Agency Research Triangle Park, North Carolina 27711
2. A report on the USW Refinery Survey, October 2007