Engineer Chemical Industry key terms

The change in free energy when reactants convert to products under stated conditions. A negative value indicates the reaction is thermodynamically favourable; its magnitude sets the maximum useful work obtainable and the equilibrium position.

A ratio of product to reactant activities at equilibrium, fixed by temperature and pressure. Its value predicts conversion limits and shifts with temperature according to the enthalpy of reaction.

A rule stating that a system at equilibrium shifts to oppose a change in temperature, pressure, or concentration. Engineers use it to choose operating conditions that raise achievable conversion.

The maximum temperature reached when fuel burns completely with no heat loss to surroundings. It bounds combustion temperatures and informs material selection and burner design.

A correction factor relating a real gas's fugacity to its partial pressure. It quantifies departure from ideal-gas behaviour and is essential for accurate phase-equilibrium calculations at high pressure.

A factor correcting concentration to effective concentration in non-ideal liquid mixtures. Values away from one signal strong intermolecular interaction, affecting distillation and extraction design.

A mathematical relation linking pressure, volume, and temperature for a fluid. Cubic and virial forms predict density and phase behaviour for process simulation and equipment sizing.

A computation determining the amounts and compositions of vapour and liquid phases formed when a mixture is brought to a given temperature and pressure. It underpins separator and column design.

The ratio of vapour-liquid distribution coefficients of two components. Values far from one mean easy separation; values near one require many stages or alternative separation methods.

The lowest reflux at which a desired separation remains achievable with an infinite number of stages. Actual columns operate above it, and the ratio guides economic trade-off between stages and energy.

An ideal equilibrium contact stage where leaving streams reach equilibrium. Real trays or packing achieve only a fraction of this performance, expressed as stage or overall efficiency.

The packed-bed height providing separation equal to one theoretical stage. It links laboratory packing data to full-scale column height and depends on flow rates and physical properties.

The vapour velocity at which liquid can no longer drain counter-currently and accumulates in a column. Designers operate below it, typically at 70-85 percent, to avoid capacity loss.

The fraction of unreacted feed returned to a reactor after separation. Raising it improves per-pass conversion but increases separation and pumping costs, so an economic optimum exists.

The volumetric feed rate divided by catalyst volume, expressed per hour. It sets contact time and is a primary scale-up and comparison parameter for catalytic reactors.

Loss of catalytic activity over time through fouling, poisoning, sintering, or leaching. It dictates regeneration schedules, reactor spare capacity, and operating cost.

A dimensionless group comparing intrinsic reaction rate to pore diffusion rate in a porous catalyst. Large values indicate diffusion limitation and reduced effectiveness factor.

The ratio of actual reaction rate in a porous pellet to the rate if the entire interior saw bulk conditions. It quantifies the penalty from internal diffusion resistance.

A description of how long fluid elements spend in a vessel. It reveals bypassing, dead zones, and back-mixing, and supports reactor and sterilizer performance assessment.

An ideal reactor model assuming perfect mixing, so outlet composition equals vessel contents. It gives lower conversion per volume than plug flow for positive-order reactions.

An ideal tubular reactor model with no axial mixing, so concentration varies along the length. It achieves higher conversion than a stirred tank of equal volume for simple kinetics.

A structured team review that applies guide words to process deviations to find hazards and operability problems. It generates actions for design change before construction or modification.

A semi-quantitative method comparing initiating event frequency with independent protection layers to estimate risk. It justifies whether additional safeguards are needed for a scenario.

A discrete reliability target for a safety instrumented function, from SIL 1 to SIL 4. It is assigned from risk assessment and verified through hardware fault tolerance and proof-test intervals.

The minimum fuel concentration in air that supports flame propagation. Below it the mixture is too lean to burn; it defines ventilation and gas-detection alarm thresholds.

Rapid combustion of dispersed combustible particles, producing pressure rise and flame. It requires fuel, oxygen, ignition, and dispersion; inerting and venting are common safeguards.

A risk management principle requiring risks be reduced to as low as reasonably practicable, balancing further control cost against benefit. It underpins tolerability decisions in process safety cases.

A drawing showing process equipment, piping, instruments, and control loops with identification tags. It is the primary reference for hazard studies, commissioning, and maintenance.

A simplified schematic showing major equipment and streams with flow rates and conditions. It communicates process intent without piping detail and supports mass and energy balance reviews.

Systematic matching of hot and cold process streams to reduce external heating and cooling demand. Pinch analysis identifies the minimum utility target and heat exchanger network design.

The closest temperature approach between hot and cold composite curves in a process. It sets the minimum thermodynamic heating and cooling requirement and constrains network design.

A control strategy that uses a process model to predict future behaviour and computes optimal moves over a horizon. It handles constraints and multivariable interaction better than simple loops.

A feedback controller combining proportional, integral, and derivative actions to reduce error. Tuning balances speed of response against oscillation and offset for a given process.

The delay between a control action and the first measurable response of the process. Large dead time limits achievable loop speed and often calls for feedforward or model-based control.

Localized breakdown of a passive film producing deep cavities on metal surfaces. Chloride exposure and stagnant conditions promote it, and it can perforate equipment rapidly.

Crack growth from the combined action of tensile stress and a corrosive environment. It causes sudden brittle failure well below design stress and is mitigated by stress relief and material choice.

Extra metal thickness added to equipment so that expected corrosion does not shorten service life. It is set from material, environment, and inspection interval, and reduces over time.

The sum of discounted future cash flows minus initial investment. A positive value indicates a project earns above the required return and is a standard economic screening criterion.

The time required for cumulative cash inflows to recover the initial investment. It is simple to communicate but ignores cash flows after recovery and the time value of money.

A forecast of funds needed to build a facility, classified by accuracy from screening to definitive. Its class determines contingency and confidence for project approval.