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=Chemical plant=
{{Image|German Petrochem Plant.jpg|right|353px|[[Petrochemical]] plant in Germany}}
A '''chemical plant''' is an [[industrial process]] [[factory|plant]] that manufactures or otherwise processes [[chemical]]s, usually on a large scale. <s>The general objective of a chemical plant is to create new material wealth via the chemical or biological transformation and or separation of materials.</s>
<ref name="Douglas" >{{cite book | last = Douglas | first = James M. | title = Conceptual Design of Chemical Processes | publisher = McGraw-Hill | year = 1988 | isbn = 0070177627}}</ref> 
Chemical plants use special units, equipment, and technology in the processes.  Other kinds of plants, such as [[polymer]], pharmaceutical, food, and some beverage production facilities, [[power plant]]s, [[Oil refinery|oil refineries]] or other [[Refinery|refineries]], [[natural gas processing]] and biochemical plants, [[water]] and [[wastewater]] treatment, and [[pollution]] control equipment, use many technologies which have similarities to chemical plant technology; for example, the use of fluid systems technology such as [[pump]]s, [[valve]]s, etc.  Many would consider an oil refinery or a pharmaceutical or polymer manufacturer to be effectively a chemical plant.

==Chemical processes==<!-- This section can eventually be linked from [[Unit]] -->

Chemical plants typically use [[chemical process]]es, which are detailed industrial-scale methods, to produce the chemicals.  The same chemical process can be used at more than one chemical plant, with possibly differently scaled capacities at each plant.  Also, a chemical plant at a site may be constructed to utilize more than one chemical process.

A chemical plant commonly has usually large vessels or sections called '''units''' that are interconnected by [[piping]] or other material-moving equipment which can carry '''streams''' of material. Such material streams can include [[fluid]]s ([[gas]] or [[liquid]] carried in piping) or sometimes [[solid]]s or mixtures such as [[Slurry|slurries]]. An overall chemical process is commonly made up of steps called [[unit operation]]s which occur in the individual units.  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'''. In addition to feedstocks for the plant as a whole, an input stream of material to be processed in a particular unit can similarly be considered feed for that unit. Output streams from the plant as a whole are final products and output streams from individual units may be considered intermediate products for their units. However, final products from one plant may be intermediate chemicals used as feedstock in another plant for further processing.  For example, some products from an oil refinery may used as feedstock in petrochemical plants.  

Either the feedstock(s), the product(s), or both may be individual [[Chemical compound|compounds]] or mixtures. It is often not worthwhile separating the components in these mixtures completely based on product requirements and economics.  

===Continuous and batch operation===

Chemical processes may be run in continuous or batch operation. In '''batch''' operation, production occurs in time-sequential steps in batches. A batch of feedstock(s) is fed into a process or unit, then the chemical process takes place, then the product(s) and any other outputs are removed. Such batch production may be repeated over again and again with new batches of feedstock. Batch operation is commonly used in smaller scale plants such as pharmaceutical or specialty chemicals production.  

In '''continuous''' operation, all steps are ongoing continuously in time. During usual continuous operation, the feeding and product removal are ongoing streams of moving material, which together with the process itself, all take place simultaneously and continuously.  Chemical plants or units in continuous operation are usually in a [[steady state]] or approximate steady state. Steady state means that quantities related to the process do not change as time passes during operation. Such constant quantities include stream [[flow rate]]s, heating or cooling rates, [[temperature]]s, [[pressure]]s, and chemical compositions at every point (location). Continuous operation is more efficient in many large scale operations like petroleum refineries. It is possible for some units to operate continuously and others be in batch operation in a chemical plant; for example, see [[Continuous distillation]]<!-- and [[Batch distillation]]-->.  The amount of primary feedstock or product per unit of time which a plant or unit can process is referred to as the '''capacity''' of that plant or unit.  For examples: the capacity of an oil refinery may be given in terms of [[barrel]]s of [[crude oil]] refined per day; alternatively chemical plant capacity may be given in [[ton]]s of product produced per day.  In actual daily operation, a plant (or unit) will operate at a percentage of its full capacity.  

===Location===
[[Petrochemical]] plants (plants using chemicals from petroleum as raw materials) are usually located adjacent to an [[oil refinery]] to [[Optimization (mathematics)|minimize]] [[transport]]ation costs for the feedstocks produced by the refinery.  [[Specialty chemical]] plants are usually much smaller and not as sensitive to location.

==Units and fluid systems==
{{Image|FCC.jpg|right|350px|Fluid Catalytic Cracking unit.Note the structural framework around the unit allowing worker access at certain levels.}}
Various kinds of [[unit operation]]s are conducted in various kinds of units. Although some units may operate at ambient temperature or pressure, many units operate at higher or lower temperatures or pressures.  Vessels in chemical plants are often [[Cylinder (geometry)|cylindrical]] with rounded ends, a shape which can be suited to hold either high pressure or [[vacuum]]. [[Chemical reaction]]s can convert certain kinds of [[Chemical compound|compounds]] into other compounds in [[chemical reactor]]s.  Chemical reactors may be stirred tank reactors or [[packed bed]]s that may have solid heterogeneous [[catalyst]]s which stay in the reactors as fluids move through.  Since the surface of solid heterogeneous catalysts may sometimes become poisoned from deposits such as [[Coke (fuel)|coke]], regeneration of catalysts may be necessary.  [[Fluidized bed]]s may also be used in some cases. There can also be units (or subunits) for [[Mixing (process engineering)|mixing]] (including dissolving), [[Separation process|separation]], heating, cooling, or some combination of these.  For example, chemical reactors often have stirring for mixing and heating or cooling going on in them.  When designing plants on a large scale, [[Heat of reaction|heat produced or absorbed by chemical reactions]] should be considered.  Some plants may have units with organism cultures for biochemical processes such as [[Industrial fermentation|fermentation]] or [[enzyme]] production.  

{{Image|Industrial Distillation Columns.jpg|right|250px|Industrial Distillation Columns}}
[[Separation processes]] include [[filtration]], [[settling]] (sedimentation), [[Liquid-liquid extraction|extraction]] or leaching, [[distillation]], [[recrystallization]] or [[Precipitation (chemistry)|precipitation]] (followed by filtration or settling), [[reverse osmosis]], [[drying]], and [[adsorption]].  [[Heat exchanger]]s are often used for heating or cooling, including [[boiling]] or [[condensation]], often in conjunction with other units such as distillation towers.  There may also be storage [[Chemical tank|tanks]] for storing feedstock, intermediate or final products, or waste.  Storage tanks commonly have level indicators to show how full they are.  There may be structures holding or supporting sometimes massive units and their associated equipment.  There are often stairs, ladders, or other steps for personnel to reach points in the units for sampling, inspection, or maintenance.  An area of a plant or facility with numerous storage tanks is sometimes called a ''[[tank farm]]'', especially at an [[oil depot]].  

Fluid systems for carrying liquids and gases include piping and tubing of various diameter sizes, various types of [[valve]]s for controlling or stopping flow, [[pump]]s for moving or pressurizing liquid, and [[compressors]] for pressurizing or moving gases.  Vessels, piping, tubing, and sometimes other equipment at high or very low temperature are commonly covered with [[Thermal insulation|insulation]] called [[lagging]] for personnel safety and to maintain temperature inside.  Fluid systems and units commonly have [[instrumentation]] such as temperature and pressure sensors and [[Flow measurement|flow measuring]] devices at select locations in a plant.  Online [[analyzer]]s for chemical or physical property analysis have become more common.  [[Solvent]]s can sometimes be used to dissolve [[reactant]]s 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.

==Chemical plant design==
[[Image:RefineryFlow.png|thumb|400px|right|Flow diagram for a typical [[oil refinery]]]]
The fundamental aspects of [[design]]ing chemical plants are done by [[chemical engineer]]s.  In plant design, typically less than 1% of ideas for new designs ever become commercialized.  During this solution process, typically, cost studies are used as an initial screening to eliminate unprofitable designs.  If a process appears profitable, then other factors are considered, such as safety, environmental constraints, controllability, etc.<ref name="Douglas" />  The general goal in plant design, is to construct or synthesize “optimum designs” in the neighborhood of the desired constraints.  

Many times [[chemist]]s research chemical reactions or other chemical principles in a [[laboratory]], commonly on a small scale in a "batch-type" experiment.  Chemistry information obtained is then used by chemical engineers, along with expertise of their own, to convert to a chemical process and scale up the batch size or capacity.  Commonly, a small chemical plant called a [[pilot plant]] is built to provide design and operating information before construction of a large plant.  From data and operating experience obtained from the pilot plant, a scaled-up plant can be designed for higher or full capacity.  Sometimes, intermediate capacity [[demonstration plant]]s are built before a final full scale plant.  After the fundamental aspects of a plant design are determined, [[Mechanical engineer|mechanical]] or [[electrical engineer]]s may become involved with mechanical or electrical details, respectively.  [[Structural engineer]]s may become involved in the plant design to ensure the structures can support the [[weight]] of the units, piping, and other equipment.  

{{Image|FCC.png|right|400px|Schematic flow diagram of a fluid catalytic cracking (FCC) unit.  In the overall oil refinery block diagram above, the FCC was just a rectangle.}}
The units, streams, and fluid systems of chemical plants or processes can be represented by [[Block diagram|block flow diagrams]] which are very simplified diagrams, or [[process flow diagram]]s which are somewhat more detailed.  The streams and other piping are shown as lines with arrow heads showing usual direction of material flow.  In block diagrams, units are often simply shown as blocks.  Process flow diagrams may use more detailed symbols and show pumps, compressors, and major valves.  Likely values or ranges of material flow rates for the various streams are determined based on desired plant capacity using material balance calculations.  Energy balances are also done based on [[Heat of reaction|heats of reaction]], [[Heat capacity|heat capacities]], expected temperatures and pressures at various points to calculate amounts of heating and cooling needed in various places and to size heat exchangers.  Chemical plant design can be shown in fuller detail in a [[piping and instrumentation diagram]] (P&ID) which shows all piping, tubing, valves, and instrumentation, typically with special symbols.  Showing a full plant is often complicated in a P&ID, so often only individual units or specific fluid systems are shown in a single P&ID.  

In the plant design, the units are sized for the maximum capacity each may have to handle.  Similarly, sizes for pipes, pumps, compressors, and associated equipment are chosen for the flow capacity they have to handle.  Utility systems such as [[electric power]] and [[water]] supply should also be included in the plant design.  Additional piping lines for non-routine or alternate operating procedures, such as plant or unit startups and shutdowns, may have to be included.  Fluid systems design commonly includes isolation valves around various units or parts of a plant so that a section of a plant could be isolated in case of a problem such as a [[leak]] in a unit.  If pneumatically or hydraulically actuated valves are used, a system of pressurizing lines to the actuators are needed.  Any points where process samples may have to be taken should have sampling lines, valves, and access to them included in the detailed design. If necessary, provisions should be made for reducing high pressure or temperature of a sampling stream, such including a pressure reducing valve or sample cooler.  

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 factor]]s.  All such units and equipment should also be checked for [[compatibility (chemical)|materials compatibility]] to ensure they can withstand long-term exposure to the chemicals they will come in contact with.  Any closed system in a plant which has a means of pressurizing possibly beyond the rating of its equipment, such as heating, exothermic reactions, or certain pumps or compressors, should have an appropriately sized pressure [[relief valve]] included to prevent overpressurization for safety.  Frequently all of these parameters (temperatures, pressures, flow, etc.) are exhaustively analyzed in combination through a ''[[Hazop]]'' or ''[[Fault tree analysis#Fault tree analysis|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 [[Process optimization|optimized]] for good economic performance while ensuring safety and welfare of personnel and the surrounding community.  For flexibility, a plant may be designed to operate in a range around some optimal design parameters in case feedstock or economic conditions change and re-optimization is desirable.  In more modern times, [[computer simulation]]s or other computer calculations have been used to help in chemical plant design or optimization.

==Plant operation==
===Process control===

In [[process control]], information gathered automatically from various sensors or other devices in the plant is used to control various equipment for running the plant, thereby controlling operation of the plant.  Instruments receiving such information signals and sending out control signals to perform this function automatically are process ''[[Controller (control theory)|controllers]]''.  Previously, [[pneumatic]] controls were sometimes used.  [[Electrical]] controls are now common.  A plant often has a [[control room]] with displays of parameters such as key temperatures, pressures, fluid flow rates and levels, operating positions of key valves, pumps and other equipment, etc.  In addition, operators in the control room can control various aspects of the plant operation, often including overriding automatic control.  Process control with a computer represents more modern technology.  Based on possible changing feedstock composition, changing products requirements or economics, or other changes in constraints, operating conditions may be re-optimized to maximize profit.  There are often written procedures to guide plant operators for normal and non-routine operation and for anticipated problems (sometimes called casualty procedures).  

===Workers===

As in any industrial setting, there are a variety of workers working throughout a chemical plant facility, often organized into departments, sections, or other work groups.  Such workers typically include [[engineer]]s, [[plant operator]]s, and maintenance technicians.  Other personnel at the site could include chemists, management/administration and office workers.  Types of engineers involved in operations or maintenance may include chemical process engineers, mechanical engineers for maintaining mechanical equipment, and electrical/computer engineers for electrical or [[computer]] equipment.

===Transport===

Large quantities of fluid feedstock or product may enter or leave a plant by [[Pipeline transport|pipeline]], railroad [[tank car]], or [[tanker truck]].  For example, petroleum commonly comes to a refinery by pipeline.  Pipelines can also carry petrochemical feedstock from a refinery to a nearby petrochemical plant.  [[Natural gas]] is a product which comes all the way from a natural gas processing plant to final consumers by pipeline or tubing.  Large quantities of liquid feedstock are typically pumped into process units.  Smaller quantities of feedstock or product may be shipped to or from a plant in [[Drum (container)|drum]]s.  Use of drums about 55 gallons in capacity is common for [[packaging]] industrial quantities of chemicals.  Smaller batches of feedstock may be added from drums or other containers to process units by workers.

===Maintenance===

In addition to feeding and operating the plant, and packaging or preparing the product for shipping, plant workers are needed for taking samples for routine and troubleshooting analysis and for performing routine and non-routine maintenance.  Routine maintenance can include periodic inspections and replacement of worn catalyst, analyzer reagents, various sensors, or mechanical parts.  Non-routine maintenance can include investigating problems and then fixing them, such as leaks, failure to meet feed or product specifications, mechanical failures of valves, pumps, compressors, sensors, etc.  

{{Image|BP Refinery Fire.jpg|right|350px|Oil refinery fire and explosion damage}}
===Statutory and regulatory compliance===

When working with chemicals, [[safety]] is a concern.  In the [[United States]], the law requires that employers provide workers working with chemicals with access to a [[Material Safety Data Sheet]] (MSDS) for every kind of chemical they work with.  An MSDS for a certain chemical is prepared and provided by the supplier to whomever buys the chemical.  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.  [[Hazmat]] (hazardous materials) teams are trained to deal with chemical leaks or spills.  [[Process Hazard Analysis]] (PHA) is used to assess potential [[hazard]]s in chemical plants.  In 1998, the [[U. S. Chemical Safety and Hazard Investigation Board]] has become operational.

==Plant facilities==

The actual production or process part of a plant may be indoors, outdoors, or a combination of the two.  The actual production section of a facility usually has the appearance of a rather industrial environment.  Hard hats and work shoes are commonly worn.  Floors and stairs are often made of metal grating, and there is practically no decoration.  There may also be [[pollution control]] or [[waste treatment]] facilities or equipment.  Sometimes existing plants may be expanded or modified based on changing economics, feedstock, or product needs.  As in other production facilities, there may be [[shipping]] and receiving, and [[Warehouse|storage facilities]].  In addition, there are usually certain other facilities, typically indoors, to support production at the site.  

Although some simple sample analysis may be able to be done by operations technicians in the plant area, a chemical plant typically has a [[laboratory]] where chemists analyze samples taken from the plant.  Such analysis can include [[chemical analysis]] or determination of physical properties.  Sample analysis can include routine [[quality control]] on feedstock coming into the plant, intermediate and final products to ensure quality [[specification]]s are met.  Non-routine samples may be taken and analyzed for investigating plant process problems also.  A larger [[chemical company]] often has a research laboratory for developing and testing products and processes where there may be pilot plants, but such a laboratory may be located at a site separate from the production plants.  

A plant may also have a workshop or maintenance facility for repairs or keeping maintenance equipment.  There is also typically some office space for engineers, management or administration, and perhaps for receiving visitors.  The decorum there is commonly more typical of an office environment.  

==References==
<references/>

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