special concerns in batch reactions

8/10/2019 Special Concerns in Batch Reactions

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SPECIAL CONCERNS IN BATCH REACTIONSYSTEMS

FPEN 409SAFETY IN FOOD PROCESS

BENJAMIN ADAMTEY

10381550FOOD PROCESS ENGINEERING DEPARTMENT

FACULTY OF ENGINEERING SCIENCES

OCTOBER 21, 2014


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Table of Contents

Introduction ................................................................................ 2

Chemistry ................................................................................... 3

Equipment Configuration and Layout ......................................... 4

Equipments ................................................................................. 5

Instrumentation and Control Systems ........................................ 6Operations and Procedures ........................................................ 6


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Introduction

Process Safety Management is a regulation promulgated by the U.S. Occupational

Safety and Health Administration (OSHA) in February 1992. This promulgation was

motivated by the Bhopal incident which occurred in 1984, where 3,800 people

died and several thousand suffered permanent injured or partial disabilities

because of the release of methyl isocyanate. The objective of processes safety

management is to prevent or minimize the frequency and consequences of

catastrophic releases of toxic, reactive, flammable, or explosive chemicals.

Process safety management requires managers/operators to develop and

implement documented documented procedures to manage changes in the

process chemistry, process equipment and operating procedures through

Management of Change (MOC).

Batch Reaction systems poses unique challenges to process safety

managers since they do not operate under steady state conditions. The sequence

of processing steps (charging, mixing, withdrawal etc.), and frequent start-ups and

shutdowns, increase the possibility of human errors and equipment failures.

Batch reaction plants are often designed for general use rather than being

dedicated to specific processes, thus frequent modification of piping and layout

may occur to meet needs of desired process, resulting in complex management

of change (MOC) issues.

The areas pertaining to this issues, or special concerns unique to batch

reaction systems is presented and reviewed in detail in the following sections


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Chemistry

Understanding the process chemistry of batch reaction systems is verycrucial, as it allows the process operator to foresee, identify, diagnose and

respond to incipient hazardous situations that maybe associated with the

raw materials, chemicals, process and equipments. The operator needs to

understand the hazards or possible hazards that can arise from;

The desired and inadvertent effects of mixing different materials that

could foreseeably occur,

Operating conditions (temperature, pressure, etc.)

Hazards pertaining to the use of process materials,

o Toxicity

o Potential contaminants

o

Physical, thermal, reactivity and chemical stability

o Their interactions with other chemicals, utilities and equipments

Inadvertent reactions between intermediates, products and by-

products,

Energy and mass balances

Reactions between equipments and process,

Cleaning agents

Disposal, shut down and decommissioning of the reactor amongst

others,


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for better optimization and control systems; risk assessment and response;

and ensuring the overall safety of the facility, employees and the immediate

environment. Process safety practices such as pilot scale test before scale up

operations and provision of process safety information pertaining to the

hazards of the process materials also minimizes incidents caused by process

chemistry issues.

The importance of understanding process chemistry does not pertain

only to plant process operation but from the research, design, development

and decommissioning of the plant.

Equipment Configuration and Layout

Batch reaction plants are often designed for general use rather than being

dedicated to specific processes, thus must be designed to accommodate the

frequent modification of piping and equipment layout to meet operational

configuration of desired process. This can only be done through proper

equipment configuration and layout

Proper equipment configuration and layout may primarily seem to ease

access and mapping of a facility but this is secondary, as its main role is to

ensure safety by its layout (safe layout). Adequate spacing between

equipments allows for safe access for operation, maintenance and


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emergency response, it also reduces significantly the risk of electrical fires

and the spread of fires. A safe layout should include proper illumination,

ventilation and drainage systems, fire systems and safety signs. It is also very

necessary to allow room for future expansion to prevent overcrowding of

equipments someday.

A safe layout allows ease of supervision and makes the facility

attractive.

Equipments

Batch reaction plants are often designed to accommodate a variety of

product processes layout, thus their process layout use general purpose

equipments that can be changed rapidly to suit new operations. Theseequipments are usually rearranged to suit the type of process being

performed, causing the inevitable inadvertently usage of an equipment

outside its intended operational envelope.

The aforementioned concern together with accelerated aging of

equipments from the frequent start-ups and shutdowns results in process

conditions that exceeds the safe operating limits of the equipments and lead

to unexpected breakdown of equipments.


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Instrumentation and Control Systems

The general purpose and unsteady state conditions of batch reactionsystems imposes broad demands on the control systems as there is a wide

variety of operating conditions and process layouts, therefore proper

instrumentation and control system has to be selected to provide adequate

control for various possible operational configuration.

Process equipment function changes with different process (e.g. a

vessel maybe used as feed tank, reactor, and crystallizer for different

operational configurations), thus control systems and instrumentation such

control set points, interlocks and meters may be out of phase. This leads to

errors and deviation in the system and instrumentation, making it necessary

for human intervention.

Operations and Procedures

Operators are an integral part of batch reaction systems as theyimplement the procedural safeguards needed for the safe operation of the

process and also serving as the last line of defence during process upset. The

greater number of operations and procedures that operators has to perform


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during a batch reactions presents more opportunities for errors. This risk of

human error (which is largely the cause of incidents) can be reduced by the

proper designing of equipment, procedures, and the work environment and

by proper staffing, training, and implementation of management controls.

special concerns in batch reactions

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