Chemical Process

By: Poonam Shah | Views: 2259 | Date: 24-Jul-2011

In a "scientific" sense, a chemical process is a method or means of somehow changing one or more chemicals or chemical compounds. Such a chemical process can occur by itself or be caused by somebody.

In a "scientific" sense, a chemical process is a method or means of somehow changing one or more chemicals or chemical compounds. Such a chemical process can occur by itself or be caused by somebody. Such a chemical process commonly involves a chemical reaction of some sort. In an "engineering" sense, a chemical process is a method intended to be used in manufacturing or on an industrial scale (see Industrial process) to change the composition of chemical(s) or material(s), usually using technology similar or related to that used in chemical plants or the chemical industry.
Neither of these definitions is exact in the sense that one can always tell definitively what a chemical process is and what is not; they are practical definitions. There is also significant overlap in these two definition variations. Because of the inexactness of the definition, chemists and other scientists use the term "chemical process" only in a general sense or in the engineering sense. However, in the "process (engineering)" sense, the term "chemical process" is used extensively. The rest of the article will cover the engineering type of chemical process.

Although this type of chemical process may sometimes involve only one step, often multiple steps, referred to as unit operations, are involved. In a plant, each of the unit operations commonly occur in individual vessels or sections of the plant called units. Often, one or more chemical reactions are involved, but other ways of changing chemical (or material) composition may be used, such as mixing or separation processes. The process steps may be sequential in time or sequential in space along a stream of flowing or moving material; see Chemical plant. For a given amount of a feed (input) material or product (output) material, an expected amount of material can be determined at key steps in the process from empirical data and material balance calculations. These amounts can be scaled up or down to suit the desired capacity or operation of a particular chemical plant built for such a process. More than one chemical plant may use the same chemical process, each plant perhaps at differently scaled capacities.

Such chemical processes can be illustrated generally as block flow diagrams or in more detail as process flow diagrams. Block flow diagrams show the units as blocks and the streams flowing between them as connecting lines with arrowheads to show direction of flow.

In addition to chemical plants for producing chemicals, chemical processes with similar technology and equipment are also used in oil refining and other refineries, natural gas processing, polymer and pharmaceutical manufacturing, food processing, and water and wastewater treatment.
Unit processing in chemical engineering

Unit processing is the basic processing in chemical engineering. Together with unit operations it forms the main principle of the varied chemical industries. Each genre of unit processing follows the same chemical law much as each genre of unit operations follows the same physical law.

Chemical engineering unit processing consists of the following important processes:
•    Oxidation
•    Reduction
•    Hydrogenation
•    Dehydrogenation
•    Hydrolysis
•    Hydration reaction
•    Dehydration
•    Halogenation
•    Nitrification
•    Sulfonation
•    Ammoniation
•    Alkaline fusion
•    Alkylation
•    Dealkylation
•    Esterification
•    Polymerization
•    Polycondensation
•    Catalysis

A chemical process is a series of unit operations used to produce a material in large quantities. In the chemical industry, chemical engineers will use the following to define or illustrate a process:

•    Process Flow Diagram (PFD)
•    Piping and instrumentation diagram (P&ID)
•    Simplified process description
•    Detailed process description
•    Project management
•    Process simulation

Process flow diagram
A process flow diagram (PFD) is a diagram commonly used in engineering to indicate the general flow of plant processes and equipment. The PFD displays the relationship between major equipment of a plant facility and does not show minor details such as piping details and designations. Another commonly-used term for a PFD is a flow sheet. Typically, process flow diagrams of a single unit process will include the following:
•    Process piping
•    Major bypass and recirculation lines
•    Major equipment symbols, names and identification numbers
•    Flow directions
•    Control loops that affect operation of the system
•    Interconnection with other systems
•    System ratings and operational values as minimum, normal and maximum flow, temperature and pressure
•    Composition of fluids

Process flow diagrams generally do not include:
•    Pipe classes or piping line numbers
•    Process control instrumentation (sensors and final elements)
•    Minor bypass lines
•    Isolation and shutoff valves
•    Maintenance vents and drains
•    Relief and safety valves
•    Flanges

Process flow diagrams of multiple process units within a large industrial plant will usually contain less detail and may be called block flow diagrams or schematic flow diagrams.

Piping and instrumentation diagram
A piping and instrumentation diagram/drawing (P&ID) is a diagram in the process industry which shows the piping of the process flow together with the installed equipment and instrumentation.

A piping and instrumentation diagram/drawing (P&ID) is defined by the Institute of Instrumentation and Control as follows:

1.    A diagram which shows the interconnection of process equipment and the instrumentation used to control the process. In the process industry, a standard set of symbols is used to prepare drawings of processes. The instrument symbols used in these drawings are generally based on International Society of Automation (ISA) Standard S5. 1.
2.    The primary schematic drawing used for laying out a process control installation.
P&IDs play a significant role in the maintenance and modification of the process that it describes. It is critical to demonstrate the physical sequence of equipment and systems, as well as how these systems connect. During the design stage, the diagram also provides the basis for the development of system control schemes, allowing for further safety and operational investigations, such as the hazard and operability study (HAZOP).

For processing facilities, it is a pictorial representation of
•    Key piping and instrument details
•    Control and shutdown schemes
•    Safety and regulatory requirements
•    Basic start up and operational information

List of P&ID items

•    Instrumentation and designations
•    Mechanical equipment with names and numbers
•    All valves and their identifications
•    Process piping, sizes and identification
•    Miscellanea - vents, drains, special fittings, sampling lines, reducers, increasers and swaggers
•    Permanent start-up and flush lines
•    Flow directions
•    Interconnections references
•    Control inputs and outputs, interlocks
•    Interfaces for class changes
•    Computer control system input
•    Identification of components and subsystems delivered by others

Identification and Reference Designation
The P&ID is used for the identification of measurements within the process. Identification letters for measurements are based on Standard S5. 1 and ISO 14617-6:






Burner, Combustion


User's Choice (usually Conductivity)


User's Choice (usually Density)






User's Choice








Time, Time Schedule




User's Choice


User's Choice (usually Torque)


User's Choice








Speed, Frequency




User's Choice (usually Alarm Output)


Vibration, Mechanical Analysis


Weight, Force


User's Choice (usually on-off valve as XV)


Event, State, Presence


Position, Dimension

For reference designation of any equipment in industrial systems the standard IEC 61346 (Industrial systems, installations and equipment and industrial products — Structuring principles and reference designations) can be applied. For the function Measurement the reference designator B is used, followed by the above listed letter for the measured variable.
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