Chemical Plant

Lore & Background

Chemical plants use chemical processes, which are detailed industrial-scale methods, to transform feedstock chemicals into products. The same chemical process can be used at more than one chemical plant, with possibly differently scaled capacities at each plant. A chemical plant commonly has 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. An overall chemical process is commonly made up of steps called unit operations 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. Output streams from the plant as a whole are final products. Either the feedstock(s), the product(s), or both may be individual compounds or mixtures. It is often not worthwhile separating the components in these mixtures completely; specific levels of purity depend on product requirements and process economics.

In Their Own Story

The engineer adjusted the pressure valve on the pipe feeding the Chemical Plant. Steam hissed from a nearby joint, but the conveyor belt kept moving, carrying fresh stacks of plastic bars toward the assembler line. Night had fallen over the factory floor, illuminated only by the glow of burning oil and the rhythmic clatter of machinery. It was here, amidst the smell of sulfur and ozone, that the true scale of their colonization effort became visible.

Reader's Guide

Chemical processes may be run in continuous or batch operation. In batch operation, production occurs in time-sequential steps in discrete batches. A batch of feedstock(s) is fed (or charged) 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. 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 rates, heating or cooling rates, temperatures, pressures, and chemical compositions at any given point (location). 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. In actual daily operation, a plant (or unit) will operate at a percentage of its full capacity. Engineers typically assume 90% operating time for plants which work primarily with fluids, and 80% uptime for plants which primarily work with solids.

Did You Know?

• Chemical plants use chemical processes, which are detailed industrial-scale methods, to transform feedstock chemicals into products.
• The same chemical process can be used at more than one chemical plant, with possibly differently scaled capacities at each plant.
• A chemical plant commonly has large vessels or sections called units or lines that are interconnected by piping or other material-moving equipment.
• Chemical processes may be run in continuous or batch operation.
• Engineers typically assume 90% operating time for plants which work primarily with fluids, and 80% uptime for plants which primarily work with solids.