Process engineering is often a synonym for Chemical engineering and focuses on the design, operation and maintenance of chemical and material manufacturing processes. Process engineering and process engineers are found in a vast range of industries, including the Chemical Process Industries(CPI), Mineral process Industries (MPI), Material Process Industries (MatPI), Food Process Industries(FPI), Biotechnological Process Industries (BPI).
Example
Following is an example that illustrates the process engineering part of chemical engineering:
The difference between Chemical engineering and Chemistry can be illustrated by considering the example of producing orange juice. A chemist working in the laboratory investigates and discovers a multitude of pathways to extract the juice of an orange. The simplest mechanism found is to cut the orange in half and squeeze the orange using a manual juicer. A more complicated approach found is to peel and then crush the orange and collect the juice. A company then commissions a chemical engineer to design a plant to manufacture several thousand tons of orange juice per year. The chemical engineer investigates all the available methods of making orange juice and evaluates them according to their economical viability. Even though the manual juicing method is simple, it is not economical to employ thousands of people to manually juice oranges. Thus another, cheaper method is used 9possibly the ‘peel and crush’ technique). The easiest method of manufacture on a laboratory bench will not necessarily be the most economical method for a manufacturing plant.
Overview
Chemical engineers are aiming for the most economical process. This means that the entire production chain must be well planned and controlled for costs. A chemical engineer can both simplify and complicate “showcase” reactions for an economic advantage. Using a higher pressure or temperature makes several reactions easier; ammonia, for example, is simply produced from its component elements in a high-pressure reactor. On the other hand, reactions with a low yield can be recycled continuously, which would be complex, tiring work if done by hand in the laboratory. It is now usual to build 6 or 12-step evaporators to reuse the vaporisation energy for an economic advantage. In contrast, laboratory chemists evaporate samples in a single step, wasting the energy.
The individual processes used by chemical engineers (eg. Distillation or filtration) are called unit operations and consists of chemical reaction, mass-, heat- and momentum-transfer operations. Unit operations are grouped together in various configurations or the purpose of chemical synthesis and/or chemical operation. Some processes are a combination of intertwined transport and separation unit operations.
Three primary physical laws underlying chemical engineering design are Conservation of mass, Conservation of momentum and Conservation of energy. The movement of mass and energy around a chemical process are evaluated using Mass balances and energy balances which apply these laws to whole plants, unit operations or discrete parts of equipment. In doing so, Chemical Engineers use principles of thermodynamics, reaction kinetics and transport phenomena. The task of performing these balances is now aided by process simulators, which are complex software models (such as Aspen Plus, Pro II and Hysys) that can solve mass and energy balances and usually have built-in modules to simulate a variety of common unit operations.
Modern Chemical Engineering
The modern discipline of chemical engineering encompasses much more than just process engineering. Chemical engineers are now engaged in the development and production of diverse range of products, as well as in commodity and specialty chemicals. These products include high performance materials needed for aerospace, automotive, biomedical, electronic, environmental and military applications. Examples include ultra-strong fibers, fabrics, adhesives and composites for vehicles, bio-compatible materials for implants and prosthetics, gels for medical applications, pharmaceuticals, and films with special dielectric, optical or spectroscopic properties for opto-electronic devices. Additionally, chemical engineering is often intertwined with biology and biomedical engineering. Many chemical engineers work on biological projects such as understanding biopolymers (proteins) and mapping the human genome.
What is Process?
“Process is a naturally occurring or designed sequence of changes of properties or attributes of an object or system”.
What is engineering?
“Engineering is the creative application of scientific principles to design or develop structures, machines, apparatus, or manufacturing processes, or works utilizing them singly or in combination, or to construct or operate the same with full cognizance of their design, or to forecast their behavior under specific operating conditions, all as respects an intended function, economics of operation and safety to life and property”.
What is Process Engineering?
“Process Engineering is nothing else but it is the practical and creative application of the chemical engineering knowledge to a certain process so that existing process can be improved and some new design for it can be developed which will be more cost effective and more profitable one”. In other words, process engineering is another name for chemical engineering. Whatever we have studied earlier during the course of chemical engineering, all that knowledge will be combined so that certain design heuristics or as such some thumb rules can be fixed and then according to these thumb rules, existing process can be made much more effective, much more environmental friendly, much more economical and much more improved qualitatively as well as quantitatively. This is what nothing but process engineering.
So in this reference, chemical engineers are sometimes recruited as process engineers in industries. Once we have understood what the process engineering is, then it is now time to know the functions related to process engineering.
Basic functions of Process Engineering:
1.Understanding and Transferring the Licensor’s Know-how:
Licensor is the person who knows everything about the process. So before going to develop a process, the function of process engineering is to know and understand the facts concerned with certain process from licensor of process and transform them in suitable language.
2. Development & Critical Review of P&I (Process & Instrumentation) Diagram:
once the process is understood by all means, then next work is to check or develop P&I diagram for that process. If it is not proper, then that should be reviewed and developed, i.e. here we have to decide, how the process should be sequenced, what should be the sequence of unit operations involved in that process, how should be the linkage or connection between them, what is the instrumental part related to these operation, positioning of valves, fittings, etc.
3. Equipment Selection and Specification:
Once we develop P&I diagram, then the task remains is of selecting the particular equipments for selected process. Once we understood that what process we are going to carry out then according to it we have to select perfect equipment which is matching the process requirement. e.g. If process involve the separation of components of liquid mixture, then distillation column is required. So for designing a distillation column, specifications like height of column, the number of plates required, diameter of column, heating arrangement etc. should be mentioned. If fluids are to be heated or cooled or heat is to be transferred between fluids, then proper heat exchanger (HE) is required. So for designing HE, first we have to specify the type of HE such as shell & tube HE, plate & frame HE, 1-2 pass HE or any other. If it is shell & tube HE, then we have to size shell and tube, decide which will be shell side fluid and which one will be tube side fluid, where the vents to be provided, flow should be co current or counter current, what should be heating or cooling medium; all these specifications we have to make available for designing shell & tube HE. Likewise we have to select proper equipment and its all specifications should be mentioned.
4. Inputs to other Engineering Disciplines:
Once everything is decided, then we have to concern with other engineering disciplines like civil, mechanical, electrical etc. Detail knowledge about the process should be provided to these various disciplines as well as basic knowledge of all these disciplines should be obtained by process engineer so that best process configuration can be developed. e.g. when we are using equipments like HE, Distillation column or any other equipment where it is required to supply the power for various purposes, then in order to have an idea about energy loads, process engineer has to concern with the electrical department; for designing the base supports/foundations to various equipments, process engineer has to consult with civil engineering department.
This concludes the basic functions of process Engineer.
Duties of Process Engineer
Once the process has been finalized, then process engineer has to carry out various activities as below:
Calculate Mass & energy balance:Apply the principles of Stoichiometry to the equipments and process streams involved in the process and carry out M&E balance.
Gathering the data on Properties of fluids:While doing it, different properties like transport properties of fluid, thermodynamic properties, flash point, dielectric constant, electrical and thermal conductivity, toxicity, auto ignition temperature of fluid, solidifying temperature of fluid, corrosive nature, abrasive nature, fouling properties, etc. should be taken into consideration. Once PE will be aware about these properties, it becomes easy to design the process and equipments suitable to these properties.
Establishing Design Basis:While designing the plant or process, PE should think about emergency shut down requirement, future provision for expansion, site data, utility conditions, voltage fluctuations, corrosion allowance, ambient conditions etc.
Preparing P&I diagram and strategy for control and instrumentation:Process and instrumentation diagram should be accurately prepared considering scale up, position of each part (like valves, vents, orifice or venturi meters etc.), sloping to pipes etc. Decide types of instruments, their operating ranges/accuracy, control valves etc.
Preparing Equipment specifications:Decide which equipments are needed, their availability in the market, new modifications in equipments, all such things to be surveyed with the help of magazines available for equipment data or from vendors who supply these equipments.
Deciding the requirement for Interlock Shutdown arrangement:In case of emergency, if it is required to shut down the whole plant immediately, all equipments should be interlocked so that whole plant can be shut down at a time.
Deciding Piping Requirements:Decide about types of valves, special duty pipes, routes pf pipes, stresses inside the pipes, power requirement, operating cost etc. Slopes to the pipes should be provided if they are being used for fast operations (like fast cooling, fast heating) and to avoid unnecessary mixing of the fluids.
Deciding Civil Requirements:Find out what is the civil work related to process, like designing supports, building construction, designing storage facilities etc.
Deciding Electrical Requirements:Take care that all drives should be connected to emergency power supply and sequence of starting the process should be fixed; consider the plant diversity factors like range of load, variable speed drives 9for making drives to work at required load or available load).
Acquiring Knowledge about Codes and Standards:
PE should have basic understanding of the codes and standards like, HE codes(TEMA), material codes (ISI/ASTM), standard composition of materials, standard properties like hardness, thickness etc. All the materials to be used in process should be according to these codes and standards. PE should have good understanding of safety codes and environmental rules and regulations.
Knowledge about Statutory Requirements:
Statutory requirements are nothing but the knowledge about, at a particular time or in a particular situation, where and to whom should be contacted for resolving a certain problem; PE should have an idea about it.
Safety study: PE has to carry out safety analysis like, HAZOP study, quantitative risk analysis study, classification of hazardous areas as per the hazardous properties of fluids in that area like, flammability, auto ignition temperature, flash point, etc.
Preparation of Operating Manuals
Commissioning
Interaction with other engineering disciplines
Interaction with other external agencies like, vendors, suppliers, equipment manufacturers, market analysers, financers etc.
These are the various activities that PE has to carry out before developing the actual process at site.
In brief, process engineer should have the following skills:
Good understanding of chemical engineering principles
Approach to other engineering disciplines
Basic knowledge of all other process related things
Awareness of codes, standards & statutory requirements