Chapter 4
The Roles and Responsibilities of Chemical Engineers
4.1 Introduction
Many chemical engineers design and operate large-scale and complex chemical production facilities supplying diverse chemical products to society. In performing these functions, a chemical engineer will likely assume a number of roles during a career. The engineer may become involved in raw materials extraction, intermediate materials processing, or production of pure chemical substances; in each activity, the minimization and management of waste streams will have important economic and environmental consequences. Chemical engineers are involved in the production of bulk and specialty chemicals, petrochemicals, integrated circuits, pulp and paper, consumer products, minerals, and pharmaceuticals. Chemical engineers also find employment in research, consulting organizations, and educational institutions. The engineer may perform functions such as process and production engineering, process design, process control, technical sales and marketing, community relations, and management.
As engineers assume such diverse roles, it is increasingly important that they be aware of their responsibilities to the general public, colleagues and employers, the environment, and also to their profession. One of the central roles of chemical engineers is to design and operate chemical processes yielding chemical products that meet customer specifications and that are profitable. Another important role is to maintain safe conditions for operating personnel and for residents in the immediate vicinity of a production facility. Finally, chemical process designs need to be protective of the environment and of human health. Environmental issues must be considered not only within the context of chemical production but also during other stages of a chemical’s life cycle, such as transportation, use by customers, recycling activities, and ultimate disposal.
This chapter introduces approaches to designing safe chemical processes (Section 4.2). The point of briefly introducing this important topic is to demonstrate that the evolution of the methods used to design safe processes mirrors the evolution of methods described in this text, which are used to design processes that minimize environmental impacts. Section 4.3 reviews, in slightly more detail, the types of procedures that will be used in designing processes that minimize environmental impacts, and the responsibilities of chemical engineers to reduce pollution generation within chemical processes. Section 4.4 briefly notes some of the other professional responsibilities of chemical engineers, i.e., issues dealing with engineering ethics.
4.2 Responibilities For Chemical Process Safety
A major objective for chemical process design is the inclusion of safeguards that minimize the number and severity of accidental releases of toxic chemicals and the incidence of fires and explosions. A number of chemical plant accidents have occurred in the relatively recent past illustrating the importance of integrating safety into process designs. These accidents resulted in loss of life, permanent disability, and the destruction of chemical plant, process equipment and neighboring residences. The most famous accidents occurred in Flixborough, England (1974) and Bhopal, India (1984).
Flixborough
The Flixborough Works of Nypro Limited was designed to produce 70,000 tons per year of caprolactam, a raw material for the production of nylon. The process used cyclohexane as a raw material and oxidized it to cyclohexanol in the presence of air within a series of six catalytic reactors. Under process conditions, cyclohexane vaporizes immediately upon depressurization, forming a cloud of flammable cyclohexane vapor mixed with air. Reactor 5 was found to have a small crack in the stainless steel structure and was removed. The number 4 reactor was connected to the last reactor in the series using a 20” pipe, even though the reactors are normally connected using 28” pipe. The temporary section of piping was not properly supported and it ruptured upon pressurization, releasing an estimated 30 tons of cyclohexane in a large cloud. An unknown ignition source caused the cloud to explode, leveling the entire plant facility. A total of 28 people died, another 36 were injured, and damage extended to nearby homes, shops, and factories. The resulting fire in the plant burned for over 10 days. The accident could have been prevented by following proper safety design and operating procedures, including reducing the inventory of flammable liquids on site.
Bhopal
Bhopal is located in a central state of India and on December 3, 1984, an accidental release of methyl isocyanate (MIC) occurred, killing 2,000 nearby residents and injuring over 20,000. The plant, which was partially owned by Union Carbide and partially owned by local investors, manufactured pesticides. One of the intermediates was MIC. MIC is a liquid at ambient conditions, it boils at 39.1 C, its vapor is heavier than air, and it is very toxic even at low concentrations. The maximum allowable exposure concentration of MIC for workers during an eight-hour period is only 0.02 parts per million (ppm). Death at large dose is due to respira-tory damage. MIC reacts with water exothermically, but slowly, and the heat released can cause MIC to boil if cooling is not provided. On the day of the accident, the unit using MIC was not operating due to a labor dispute. The storage tank holding the MIC was contaminated with water from an unknown source. A reaction between MIC and water occurred in the tank causing the temperature to rise above the boiling point of MIC. The vapors generated escaped the pressure relief valve on the tank and were diverted into a scrubber and flare system designed to control MIC releases. Unfortunately, the release control system was not operating on this day and an estimated 25 tons of MIC vapor was released into the surrounding community with catastrophic effects. The accident could have been prevented by any number of steps, including the use of proper safety review procedures, by redesigning the process to accommodate a lower inventory of MIC, or by using alternative reaction chemistries that eliminate MIC.
In incidents such as this, loss of life and injuries are tragic, and economic consequences are severe. Engineers have a special role to play in preventing such incidents. Part of an engineer’s professional responsibility is to design processes and products that are as safe as possible. Traditionally, this has meant identifying hazards, evaluating their severity and then applying several layers of protection as a means of mitigating the risk of an accident. Figure 4.2-1 shows the layer of protection concept and includes examples of layers that might be found in a typical chemical plant. This approach can be very effective and has resulted in significant improvement of the safety performance of chemical processes. However, the layer of protection approach has disadvantages that place limitations on its effectiveness: (1) the layers are expensive to build and maintain, and (2) the hazard remains and there is always a finite risk that an accident will happen despite the layers of protection.
Inherently safer design is a fundamentally different approach to chemical process safety. Instead of working with existing hazards in a chemical process and adding layers of protection, the engineer is challenged to reconsider the design and eliminate or reduce the source of the hazard within the process. Approaches to the design of inherently safer processes have been grouped into the four categories listed below. This list contains a short checklist of questions related to inherently safer processes. A more extensive checklist can be found in the Center for Chemical Process Safety (CCPS) publications (CCPS, 1993a; Crowl, 1996).
Minimize | Use smaller quantities of hazardous substances. |
• Have all in-process inventories of hazardous materials in storage tanks been minimized? |
Figure 4.2-1 Typical layers of protection for a chemical plant (CCPS 1993b, Crowl 1996). SIS is safety interlock system and ESD is emergency shutdown.
• Are all of the proposed in-process storage tanks really needed?
• Can other types of unit operations or equipment reduce material inventories (for example, continuous in-line mixers in place of mixing vessels)?
Substitute | Use a less hazardous material in place of a more hazardous substance. |
• Is it possible to completely eliminate hazardous raw materials, process intermediates, or byproducts by using an alternative process or chemistry?
• Is it possible to substitute less hazardous raw materials or to substitute noncombustible for flammable solvents?
Moderate | Use less hazardous conditions or facilities which minimize the impacts of a release of a hazardous material or energy. |
• Can the supply pressure of raw materials be limited to less than the working pressure of the vessels they are delivered to?
• Can reaction conditions (temperature, pressure) be made less severe by using a catalyst, or by using a better catalyst?
Simplify | Design facilities which eliminate unnecessary complexity and make operating errors less likely, and which are forgiving of errors that are made. |
•Can equipment be sufficiently designed to totally contain the maximum pressure generated, even if the “worst credible event” occurs?
Textbooks (Crowl and Louvar, 1990), case studies, and other materials (Crowl, 1996) document procedures for improving the safety of chemical processes and that material is not duplicated in this text. Instead, the focus in this text is the prevention of chronic (slow, continuous) as opposed to acute (fast, rare and intermittent) releases, and the role that chemical process and product design can play in minimizing these releases. As these tools for minimizing environmental impacts are described in this text, however, it is useful to recognize analogies between chemical process safety and the design of processes that minimize environmental impacts. As noted in this section, traditional approaches to chemical process safety rely on designing layers of protection around process hazards. Similarly, traditional approaches to environmental management have focused on designing processes to treat wastes. A new generation of inherently safer processes relies on designs that reduce hazards, rather than providing protection from hazards. Similarly, new generations of processes that minimize environmental impact do not rely on treating wastes, but instead are designed so that they do not generate wastes.
4.3 Responsibilities For Environmental Protection
When the method for managing environmental performance is to treat wastes, the process is designed, wastes are generated, and treatment technologies are deployed. The design method for meeting environmental objectives is sequential. In contrast, if the primary design, rather than the design of peripheral waste treatment units, is to be modified to meet environmental objectives, a key question to answer is “At what stage in the design should environmental considerations be considered?”
Designs for new processes and retrofitting of existing procedures are multistep procedures (Seider et al., 1999). The first step is the definition of a primitive problem, such as identifying the chemical to be produced and the annual quantity.
Table 4.3-1 CMA Pollution Prevention Code of Management Practices (Now the American Chemistry Council)
This Code is designed to achieve ongoing reductions in the amount of all contaminants and pollutants released to the air, water, and land from member company facilities. The Code is also designed to achieve ongoing reductions in the amount of wastes generated at facilities. These reductions are intended to help relieve the burden on industry and society of managing such wastes in future years.
Management Practices
Each member company shall have a pollution prevention program that shall include:
1. A clear commitment by senior management through policy, communications, and resources, to ongoing reductions at each of the company’s facilities, in releases to the air, water, and land and in the generation of wastes.
2. A quantitative inventory at each facility of wastes generated and releases to the air, water, and land, measured or estimated at the point of generation or release. (Chapter 8)
3. Evaluation, sufficient to assist in establishing reduction priorities, of the potential impact of releases on the environment and the health and safety of employees and the public. (Chapters 1, 2, 5, 8, and 11)
4. Education of, and dialogue with, employees and members of the public about the inventory, impact evaluation, and risks to the community.
5. Establishment of priorities, goals and plans for waste and release reduction, taking into account both community concerns and the potential health, safety, and environmental impacts as deter-mined under items 3 and 4.
6. Ongoing reduction of wastes and releases, giving preference first to source reduction, second to recycle/reuse, and third to treatment. These techniques may be used separately or in combination with one another. (Chapters 7, 9, and 10)
7. Measurement of progress at each facility in reducing the generation of wastes and in reducing releases to the air, water, and land, by updating the quantitative inventory at least annually. (Chapter 8)
8. Ongoing dialogue with employees and members of the public regarding waste and release information, progress in achieving reductions, and future plans. This dialogue should be at a personal, face-to-face level, where possible, and should emphasize listening to others and discussing their concerns and ideas.
9. Inclusion of waste and release prevention objectives in research and in design of new or modified facilities, processes, and products.
10. An ongoing program for promotion and support of waste and release reduction by others, which may, for example, include:
a. Sharing of technical information and experience with customers and suppliers;
b. Support of efforts to develop improved waste and release reduction techniques;
c. Assisting in establishment of regional air monitoring networks;
d. Participation in efforts to develop consensus approaches to the evaluation of environmental, health, and safety impacts of releases;
e. Providing educational workshops and training materials;
f. Assisting local governments and others in establishment of waste reduction programs benefiting the general public.
11. Periodic evaluation of waste management practices associated with operations and equipment at each member company facility, taking into account community concerns and health, safety, and environmental impacts and implementation of ongoing improvements.
12. Implementation of a process for selecting, retaining, and reviewing contractors and toll manufacturers taking into account sound waste management practices that protect the environment and the health and safety of employees and the public.
13. Implementation of engineering and operating controls at each member company facility to improve prevention of and early detection of releases that may contaminate groundwater.
14. Implementation of an ongoing program for addressing past operating and waste management practices and for working with others to resolve identified problems at each active or inactive facility owned by a member company taking into account community concerns and health, safety, and environmental impacts.
This is followed by a process creation step that includes choosing reaction chemistry, the use of design heuristics to identify process equipment and operating conditions, development of a base case flowsheet, and process simulation. The third step is a more detailed process synthesis of separation trains and a heat/power integration analysis. What follows is a detailed design and simulation of the flowsheet, profitability analysis, and optimization. The final steps include a plantwide controllability assessment, startup assessment, and reliability and safety analysis. In Part II of this text, systematic methods are presented for incorporating environmental considerations into all of these steps of chemical process design.
As part of their professional responsibilities, engineers should, through their designs, continuously improve the environmental performance of chemical processes. Recently the Chemical Manufacturers Association (CMA, now the American Chemistry Council) has adopted the Pollution Prevention Code of Management Practice, which outlines tangible steps along a path to continuous reductions in the amounts of all contaminants released to air, water, and soil. Table 4.3-1 shows the set of management practices and specific chapters in this textbook that will aid engineers and other decision makers in achieving pollution prevention objectives. These practices demonstrate a clear commitment by senior management, a path to quantify waste generation and prioritize waste reduction, a preference for source reduction and reuse/recycle rather than pollution control, and a plan to measure and report on progress in achieving reduction goals.
4.4 Further Reading in Engineering Ethics
Process safety and environmental protection are not the only responsibilities of professional engineers. Engineers also have responsibilities to clients, to colleagues, and to the profession. The American Institute of Chemical Engineers has assembled a Code of Ethics that highlights the main issues in the area of professional conduct. This code can be found at AIChE website (http://www.aiche.org/membership/ethics.htm). Case studies in engineering ethics are available in the journal Chemical Engineering (March 2, 1987). Nine ethical dilemmas pertinent to chemical engineers are presented and reader responses are reported in a subsequent issue (Sept. 28, 1987 issue). Some of the responses dealt with putting health, safety, and environmental issues ahead of profits; placing self-respect as professionals above loyalty to companies; working within organizations versus whistleblowing to promote ethical behavior; and taking career risks in order to get a company to do the right thing. Further discussion of engineering ethics is provided by Mitcham and Shannon Duval (2000).
References
CCPS, Center for Chemical Process Safety, Guidelines for Engineering Design of Process
Safety, New York, NY, American Institute of Chemical Engineers, 1993a.
CCPS, Center for Chemical Process Safety, Guidelines for Safe Automation of Chemical
Processes, New York, NY, American Institute of Chemical Engineers, 1993b.
CMA, Pollution Prevention Codes of Management Practices, Chemical Manufacturers Association (renamed American Chemistry Council), http://www.cmahq.com/.
Crowl, D.A. and Louvar, J.F., Chemical Process Safety: Fundamentals with Applications,
Prentice Hall PTR, Englewood Cliffs, NJ, 1990.
Crowl, D.A. ed., Inherently Safer Chemical Processes: A Life Cycle Approach, Center for
Chemical Process Safety, American Institute of Chemical Engineers, 1996 Mitcham, C. and Shannon Duval, R., Engineering Ethics, Prentice Hall, Upper Saddle River, NJ (2000).
Seider, W.D., Seader, J.D., and Lewin, D.R., Process Design Principles: Synthesis, Analysis, and Evaluation, John Wiley & Sons, New York, 1999.
Problems
1. Compare and contrast the Inherently Safer Design concepts presented in this chapter with the Pollution Prevention concepts from Chapter 3. Note in particular that design methods for improving process safety are focused on preventing catastrophic releases, while pollution prevention design methods are primarily concerned with reducing chronic emissions.
2. What chemical properties will be most important in evaluating the potential for catastrophic releases? What chemical properties would be most important in developing methods to prevent chronic releases? Draw upon the material presented in this chapter and in Chapter 1.
3. You are the chemical engineer responsible for all new processes for your facility. Your facility operates processes that extract valuable natural products from various botanicals. Presently, the extraction process uses hot water to extract the requisite material, followed by concentration, crystallization, separation, drying and packaging.
You have been asked to evaluate a new process for a different botanical yielding a new “natural” product. That process could use the same unit operations as the present process. The new process would however, use either n-hexane or USP grade ethanol (anhydrous) as the extractant. There are no storage tanks on your site for use as a solvent storage tank. The extraction, with either solvent, is done by recirculating the solvent throught a packed bed of botanical operating at 40 C. N-hexane performs the extraction in half the time (12 hrs) when compared to ethanol.
You have been requested to analyze the proposed process (each solvent) and define its impact (regulatory, permit, safety) on this facility. The product from this new process will be new and is not on the TSCA inventory. Solvent recovery is available on-site. The only cooling media available on-site is a source of 85 F water operating in a closed cycle.
The questions that need to be addressed are:
• What are the physical properties, including toxicological data on the proposed solvents?
• Are utilities available to support the process?
• What are the local, state and federal permits issues?
• Is annual reporting required?
• Is there any additional medical monitoring required?
• Are there other unit operations you could use to do the same thing?
(a) What is your recommendation? Justify with a careful analysis.
(b) If the plant may have to shut down if it does not get a new process, eliminating your job, could this impact your decision?
(c) If your facility cannot (or will not) implement the process, it has been suggested that the process could be done in an overseas facility in Asia or other locations (other states) in the US. What is you recommendation? Justify.