Chemical plant
A chemical plant commonly has usually large vessels or sections called units or lines that are interconnected by piping or other material-moving equipment which can carry streams of material.
Such material streams can include fluids (gas or liquid carried in piping) or sometimes solids or mixtures such as slurries.
A raw material going into a chemical process or plant as input to be converted into a product is commonly called a feedstock, or simply feed.
It is often not worthwhile separating the components in these mixtures completely; specific levels of purity depend on product requirements and process economics.
Batch operation is commonly used in smaller scale plants such as pharmaceutical or specialty chemicals production, for purposes of improved traceability as well as flexibility.
Steady state means that quantities related to the process do not change as time passes during operation.
Vessels in chemical plants are often cylindrical with rounded ends, a shape which can be suited to hold either high pressure or vacuum.
When designing plants on a large scale, heat produced or absorbed by chemical reactions must be considered.
There are often stairs, ladders, or other steps for personnel to reach points in the units for sampling, inspection, or maintenance.
Fluid systems for carrying liquids and gases include piping and tubing of various diameter sizes, various types of valves for controlling or stopping flow, pumps for moving or pressurizing liquid, and compressors for pressurizing or moving gases.
Fluid systems and units commonly have instrumentation such as temperature and pressure sensors and flow measuring devices at select locations in a plant.
Solvents can sometimes be used to dissolve reactants or materials such as solids for extraction or leaching, to provide a suitable medium for certain chemical reactions to run, or so they can otherwise be treated as fluids.
During this solution process, typically, cost studies are used as an initial screening to eliminate unprofitable designs.
The streams and other piping are shown as lines with arrow heads showing usual direction of material flow.
Process flow diagrams may use more detailed symbols and show pumps, compressors, and major valves.
Similarly, sizes for pipes, pumps, compressors, and associated equipment are chosen for the flow capacity they have to handle.
Additional piping lines for non-routine or alternate operating procedures, such as plant or unit startups and shutdowns, may have to be included.
Units and fluid systems in the plant including all vessels, piping, tubing, valves, pumps, compressors, and other equipment must be rated or designed to be able to withstand the entire range of pressures, temperatures, and other conditions which they could possibly encounter, including any appropriate safety factors.
All such units and equipment should also be checked for materials compatibility to ensure they can withstand long-term exposure to the chemicals they will come in contact with.
are exhaustively analyzed in combination through a Hazop or fault tree analysis, to ensure that the plant has no known risk of serious hazard.
Within any constraints the plant is subject to, design parameters are optimized for good economic performance while ensuring the safety and welfare of personnel and the surrounding community.
Large quantities of fluid feedstock or product may enter or leave a plant by pipeline, railroad tank car, or tanker truck.
Routine maintenance can include periodic inspections and replacement of worn catalyst, analyzer reagents, various sensors, or mechanical parts.
Other laws covering chemical safety, hazardous waste, and pollution must be observed, including statutes such as the Resource Conservation and Recovery Act (RCRA) and the Toxic Substances Control Act (TSCA), and regulations such as the Chemical Facility Anti-Terrorism Standards in the United States.
These manufacturing locations often have business clusters of units called chemical plants that share utilities and large scale infrastructure such as power stations, port facilities, road and rail terminals.
In the United Kingdom for example there are four main locations for commodity chemical manufacture: near the River Mersey in Northwest England, on the Humber on the East coast of Yorkshire, in Grangemouth near the Firth of Forth in Scotland and on Teesside as part of the Northeast of England Process Industry Cluster (NEPIC).
Corrosion in chemical process plants is a major issue that consumes billions of dollars yearly.
Electrochemical corrosion of metals is pronounced in chemical process plants due to the presence of acid fumes and other electrolytic interactions.
