Eckhoff Explosion Hazards in the Process Industries

1. Auflage 2013
ISBN: 978-0-12-799972-2
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 436 Seiten

Explosions in the process industries injure or kill hundreds, if not thousands, of workers every year. They occur in process plants, refineries, platforms and pipelines all over the world. Millions of dollars are spent repairing damages, replacing equipment and rebuilding facilities in the wake of this destruction. This book explores different types of explosions that can occur in a facility and the necessary steps to guard against them. A clear set of preventative measures, rules and standards combine to make this book a convenient guide to real-world applications. Additional theoretical issues in the use of probabilistic equations and scenarios make this book an absolute necessity for process industry safety.

Rolf K. Eckhoff is Professor Emeritus of Process Safety Technology in the Department of Physics and Technology at University of Bergen, Norway. He is also concurrent professor at Northeastern University, Shen-yang, China, and Scientific Advisor at Oresund Safety Advisors AB, Malmo, Sweden. He is the author of Dust Explosions in the Process Industries, first published in 1991 with an extended version published in 2003. He is also the author and co-author of more than 150 technical and scientific publications and more than 130 research reports. He has advised Industry committees on numerous occasions, lectured to courses, conferences, and seminars in a number of countries in Europe, Bahrain, Isreal, China, India, Australia, Canada, and the US. Dr. Eckhoff earned a Masters in Science in Chemical Engineering from the University of Trondheim, a Master of Philosophy from the University of London, a Doctor Technicae in Dust Explosions from the University of Trondheim, and a Doctor of Science (Eng.) degree from the University of London.

Autoren/Hrsg.

Eckhoff, Rolf K.

Leseproben

Chapter 1

Introduction

1.1 Process Safety—A Persistent Challenge to Educators

Right from the start of the development of the oil and natural gas industry on the Norwegian continental shelf, very high safety standards were established. These standards were a matter of both industry attitude and official national policy. Until the “Piper Alpha” catastrophe, it was felt by some that Norway was overdoing safety issues in its offshore industry. However, after this accident, the imposition of strict safety requirements in this industry has gained wide international acceptance. Moreover, it has also been pointed out that substantial benefits would result if the high standards of safety in the offshore industries could be adapted to industry onshore and to society at large.

However, high safety levels cannot be established once and for all by a single all-out effort. Deterioration results if the high level—once attained—is not actively secured by continuous maintenance and renewal. This applies both to safety technology and to human factors.

Education has a key role in the continuous maintenance and renewal process. This ranges from short practical training courses to in-depth long-term education. Universities and colleges have responded to the challenge by establishing courses of study on a wide range of safety aspects. In the case of process safety, relevant topics include reliability and risk analysis, the physics, chemistry and technology of processes and hazards, and means of accident prevention and mitigation. Much emphasis has been put on methods of reliability and risk analysis, which are indeed very important. However, it is sometimes felt by the process industry itself that education in the “hard” aspects, i.e. the physics, chemistry, and technology of processes and process hazards has been somewhat left behind. This situation presents a special challenge to universities and colleges. Nine years ago my own university established a course of studies in process safety technology, with particular emphasis on the scientific and technological aspects.

In process safety, the prevention of fires and explosions, and the mitigation of their effects, is a central concern. Most often loss of confinement of flammable/explosive substances is the first link in the accidental chain of events. The next step is generation and ignition of flammable clouds, resulting in explosions and fires, which may in turn cause loss of life and limb and damage to the process plant, adjacent process areas, and even more remote building structures. Understanding the processes of accident escalation is an important aspect of process safety technology. Quantitative risk analysis plays an increasing role in the effort to improve offshore process safety. In the offshore oil and gas industries, a highly packed, congested process plant, with compact living quarters as a close neighbor, demands very systematic and thorough analysis of all possible risk factors, including the human elements. A concise and constructive official authority policy constitutes an important basis for ensuring the necessary high level of safety.

The purpose of this book is to provide a source of basic information on the origin, course, prevention, and mitigation of accidental explosions in the process industries. Potential readers/users of the book should include people both from a wide range of process industries, official authorities, engineering companies, and, not least, students in technical colleges and universities.

2.1 What Is an Explosion?

The concept of explosion is not unambiguous. Various encyclopedias give varying definitions that mainly fall in two categories. The first focuses on the noise or “bang” due to the sudden release of a strong pressure wave or blast wave. The origin of this pressure wave, whether a chemical or mechanical energy release, is of secondary concern. This definition of an explosion is in accordance with the basic meaning of the word (“sudden outburst”). The second category of definitions relevant in the present context is explosions caused by a sudden release of chemical energy. This includes explosions of gases and dusts and solid explosives. The emphasis is then often put on the chemical energy release itself, and explosion is defined accordingly. A possible definition could then be “An explosion is an exothermal chemical process that, when occurring at constant volume, gives rise to a sudden and significant pressure rise.”

In the present book the definition of an explosion will shift pragmatically between the two alternatives, by focusing on either cause or effect, depending upon the context.

3.1 Accidental Explosions—A Real Hazard in the Process Industries

The industries or facilities in which gas, spray/mist, or dust explosions may exist include:

Oil and natural gas industries/activities

• oil and natural gas production installations on and offshore

• oil and gas refineries

• systems for transportation of oil and gas (pipelines, ships, trains, cars etc.)

Petrochemical, chemical, and metallurgical process industries

• petrochemical industries producing chemicals and polymers

• plants producing pharmaceuticals, pesticides, organic pigments etc.

• paint production plants

• pulverized metal production (aluminum, magnesium, silicon, and silicon alloys etc.)

• chemical food and feed production

• production of cellulose, paper etc. from wood

Mechanical processing

• grain and feed storage

• flour mills

• sugar refineries

• mechanical wood refining (hardboard etc.)

Special processes

• production, storage, and handling of explosives, pyrotechnics, and propellants

4.1 Basic Differences in How and Where Explosive Gas, Spray/Mist, and Dust Clouds Are Likely to Be Generated

4.1.1 Similar Ignition and Combustion Properties of the Various Clouds

Explosive gas mixtures and explosive clouds of sprays/mists and dusts, once existing, exhibit very similar ignition and combustion properties, such as

• flammability/explosibility limits

• laminar burning velocities and quenching distances

• the response of the burning velocity to cloud turbulence

• detonation phenomena

• adiabatic constant-volume explosion pressures of similar magnitudes

• well-defined minimum ignition energies, and

• minimum ignition temperatures for given experimental conditions

Recognition of these similarities may have contributed to the development of the idea that the hazards of accidental gas, spray/mist, and dust explosions can be regarded as more or less identical. As discussed in Section 1.4.2, this is a misconception. Also, there is a basic difference in the ranges of hazardous fuel concentrations between dusts, sprays/mists, and gases. For combustible gases and sprays/mists, flame propagation is only possible when the fuel to air mixing ratios lie between the lower and the upper flammability limits. Dust flame propagation, however, is not limited only to the flammable dust concentration range of clouds. The state of settled layers and deposits constitutes an additional singular regime of flame propagation. This is because, contrary to combustible gases and liquids, settled powders/dusts will always have some air trapped in the voids between the particles, which makes it possible for sustained, although often very slow, combustion to propagate throughout the deposit.

4.1.2 Influence of Inertial Forces on the Movement of Dust Particles and Liquid Droplets

Once a combustible gas has been homogeneously mixed with air, the mixture will for most practical purposes stay homogeneous, due to random molecular motion. In clouds of dust particles and liquid droplets, however, the fuel particles are generally so much larger than the molecules of the air (often in the range 1–100 µm), that their movement within the air is controlled by inertial forces, including gravity, rather than by random molecular motion. The role of inertial forces increases systematically with increasing particle or droplet size and increasing density of the particle or droplet material. Turbulence and other convective movement of the air can prolong the time over which the particles will stay in suspension. When liquid droplets in a cloud collide, the droplets may coalesce and form one larger drop, which may require special considerations.

4.1.3 Fundamental Differences between the Ways Explosive Clouds Are Generated

There are fundamental differences in the ways and...