CHEN 4470

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Process Safety and Design
CHEN 4470 Process Design Practice Dr. Mario
Richard EdenDepartment of Chemical
EngineeringAuburn University Lecture No. 16
Process Risk Assessment Inherently Safe Process
Design March 6, 2012 Material Developed by Dr.
Jeffrey R. Seay, University of Kentucky - Paducah
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Importance of Process Safety

• The safety record of the chemical process
  industry is the responsibility of all of us in
  the profession.
• Process safety is important for employees, the
  environment, the general public, and its the
  law.
• As process design engineers we are tasked with
  reducing the risk of operating a chemical
  manufacturing process to a level acceptable to
  employees, regulatory authorities, insurance
  underwriters and the community at large.
• Recent chemical plant disasters underscore the
  importance of this point in terms of both human
  and financial losses.

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Recent Incidents
T2 Laboratories Inc Jacksonville, FL December
19, 2007 4 Killed and 13 Wounded in reactor
explosion in manufacture of gasoline
additive. BP America Refinery Texas City, TX
March 23, 2005 15 Killed and 180 Wounded in
isomerization unit explosion and fire. West
Pharmaceutical Services Kinston, NC January 29,
2003 6 Killed and Dozens Wounded in dust cloud
explosion and fire from release of fine plastic
powder.
Source U.S. Chemical Safety Board,
www.chemsafety.gov
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Process Safety Terminology

• Hazard vs. Risk
• HAZARD is a measure of the severity of the
  consequences of a catastrophic failure of a given
  process or system, regardless of the likelihood
  and without considering safeguards.
• RISK is the combination of both the severity of
  the worst case consequence and the likelihood of
  the initiating cause occurring.
• In short, for an EXISTING PROCESS, we have little
  influence on the HAZARD, but through the
  application of safeguards, we can reduce the RISK
  of operating the process.

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Process Hazard Analysis

• Process Hazard Analysis (PHA) is a technique for
  determining the RISK of operating a process or
  unit operation.
• PHAs are required by law for process handling
  threshhold quantities for certain listed Highly
  Hazardous Chemicals (HHC) or flammables.
• Approved techniques for conducting PHAs
• HAZOP (Hazard and Operability)
• What If?
• FMEA (Failure Mode and Effects Analysis)
• In general, a PHA is conducted as a series of
  facilitated, team brainstorming sessions to
  systematically analyze the process.

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Risk Assessment Example

• Consider a low design pressure API storage tank
  filled with cyclohexane.
• Assume that the storage tank is equipped with a
  pad/de-pad vent system to control pressure.

• What hazard scenarios might occur from this
  system?
• What are the consequences of these scenarios?
• What Safeguards might we choose to mitigate the
  risk?

What If? Initiating Cause Consequence Safeguards
1. There is High Pressure in the Cyclohexane Storage Tank? 1.1 Failure of the pressure regulator on nitrogen supply line. 1.1 Potential for pressure in tank to rise due to influx of nitrogen through failed regulator. Potential to exceed design pressure of storage tank. Potential tank leak or rupture leading to spill of a flammable liquid. Potential fire should an ignition source be present. Potential personnel injury should exposure occur. 1. Pressure relief vent (PRV) sized to relieve overpressure due to this scenario. 2. Pressure transmitter with high alarm set to indicate high pressure in Cyclohexane Storage Tank.
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Mitigating Process Risk

• The operating risk is determined by the PHA using
  an appropriate Risk Assessment Methodology.
• This risk is mitigated through the application of
  safeguards that reduce the risk to an acceptable
  level.

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Layer of Protection Analysis

• LOPA is a quantitative technique for reducing
  the RISK of a process.
• The theory of LOPA is based on not putting all
  your eggs in one basket.
• The layers mitigate the process RISK as
  determined by the PHA.
• Each layer reduces the RISK of operating the
  process.

Each layer must be Independent Effective
Reliable Auditable.
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LOPA Example

• Failure of Transfer Pump leading to overfill of
  Process Vessel.
• Potential release of material to the environment
  requiring reporting or remediation.
• Potential personnel injury due to exposure to
  material.
• Severity would be based on properties of the
  material released.

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Inherently Safe Process Design

• Inherent safety is a concept based on eliminating
  the causes and/or reducing the consequences of
  potential process upsets.
• Inherently Safe Process Design is a technique
  applied during the conceptual phase of process
  design.
• Inherently Safe Process Design targets the
  HAZARD, rather than reducing the RISK after the
  fact.
• This technique is based on making inherently
  safer design choices at a point in the process
  development where the engineer has the most
  influence on the final design.

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Inherently Safe Process Design

• Definitions
• Inherently safe process design can be grouped
  into 5 categories
• Each of these inherently safer design choices is
  applied in the conceptual phase of development.

Category
Example
1
Intensification
Continuous reactor vs. batch reactor
2
Substitution
Change of feedstock
3
Attenuation
Alternate technology
4
Limitation of effects
Minimization of storage volume
5
Simplification
Gravity flow vs. pumping
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Inherently Safe Process Design

• Azeotropic Distillation vs. Pervaporation

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Inherently Safe Process Design

• Traditional Process
• Sample Risk Assessment using What If? Methodology
• Consider what types of safeguards would be
  required to mitigate the Process Risk due to
  these scenarios.

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Inherently Safe Process Design

• Azeotropic Distillation vs. Pervaporation

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Inherently Safe Process Design

• Inherently Safer Process
• When considering the potential upset scenarios
  for the process, the benefits of the inherently
  safer process become clear.

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Inherently Safe Process Design

• Inherently Safer Process (Contd)
• Based on this risk comparison, it is clear that
  multiple independent protection layers would be
  required to mitigate the operating risk of the
  traditional process.
• This risk can be reduced by designing an
  inherently safer, ie, less hazardous process.
• Although a complete economic analysis would be
  required, this example has illustrated that the
  need for independent protection layers is reduced
  in the inherently safer process design.

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Summary 12

• Conclusions
• Clearly, process safety is a critical component
  of process design. In industry, no process is
  put into service without a comprehensive risk
  assessment.
• It is important to realize that the management of
  operating risk is the key focus of process
  safety. As design engineers, we have
  responsibility for and the most influence on the
  overall hazard of a process.

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Summary 22

• References
• R. Sanders, Chemical Process Safety Learning
  from Case Histories, 3rd Edition, Elsevier, Inc,
  2005.
• D. Nelson, Managing Chemical Safety, Government
  Institutes, 2003.
• Environmental Protection Agency, Process Hazard
  Analysis, 40 CFR 68.67, 2005.
• Occupational Safety and Health Administration,
  Process Safety Management of Highly Hazardous
  Chemicals, 29 CFR 1910.119, 2005.
• Center for Chemical Process Safety, Layer of
  Protection Analysis Simplified Process Risk
  Assessment, AIChE, 2001.
• T. Kletz, Process Plants A Handbook for
  Inherently Safety Design, Taylor and Francis,
  1998.
• Center for Chemical Process Safety, Guidelines
  for Engineering Design for Process Safety, AIChE,
  1993.
• Seay, J. and M. Eden, Incorporating Risk
  Assessment and Inherently Safer Design Practices
  into Chemical Engineering Education, Journal of
  Chemical Engineering Education, 42(3), pp.
  141-146, 2008.

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Other Business

• Next Lecture March 20
• Role of design engineer in technology development
• Bob Kline, Eastman Chemical
• Control strategy development
• Jennifer Kline, Eastman Chemical
• Progress Report 2
• Friday March 9?
• Remember to turn in the team evaluation forms
• Next Lecture March 22
• Integration of design and control part I
• SSLW 322-340

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Other Business

• Zoë Elizabeth Kline
• Born Thursday, March 1, 1003 AM
• 8 lb, 13 oz 21 inches

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Other Business

• Individual Team Assignments
• Should be assigned this week
• Choose one from the project description or
• Email me two sentences describing what you would
  like to investigate and I will respond with the
  official problem statement.