Process Equipment and Plant Design Vocabulary

Vocabulary practice cards covering process equipment design, heat exchangers, distillation, and plant safety based on industry lecture notes.

Chemical Pipeline Color Coding (Fresh Water)

Pipelines carrying fresh water in chemical industries are colored sea green.

Modulus of Rigidity

The ratio of shear stress to shear strain.

25 Percent Cut Segmental Baffle

A baffle where the height is $75\%$ of the I.D. of the shell.

Petroleum Fuel Storage Limit (Underground)

Liquid/petroleum fuel storage tanks are built underground when storage capacity is less than $45$ kilolitres.

Lug Support

A type of vessel support provided usually for vessels of much smaller height than skirt supported vessels; it is the same as bracket support.

Valve Tray Advantage

Possesses the highest turn down ratio (highest to lowest vapour flow rates) and provides the maximum flexible operating range.

Sieve Tray Pitch

Holes are arranged in a triangular pitch of $2.5$ to $5$ times the hole diameter.

Elastic Limit

The stress developed in a material without any permanent set.

Tube Pitch

The shortest centre to centre distance between adjacent tubes in a shell and tube heat exchanger.

Overall Distillation Column Efficiency ($\eta$)

Defined by the equation $\eta = 17 - 61.1 \log(\mu)$ for $\mu = 0.07 - 1.4\,cp$ and relative volatility $< 4$.

Tube Side Pressure Drop (1-2 vs 1-1 Exchanger)

In a 1-2 heat exchanger at turbulent flow, the pressure drop is about $4$ times that in a 1-1 heat exchanger of the same size and flow rate.

LMTD Correction Factor ($F_T$) Design Limit

It is not desirable to design a heat exchanger for an $F_T$ value of less than $0.80$.

Schedule Number Equality

Two iron pipes of the same nominal diameter but different schedule numbers will have the same outside diameter.

Factor of Safety

The ratio of the ultimate stress to the working stress.

Bag Filter Operating Pressure Drop

The range is typically between $50 - 150\,mm$ water gauge.

Hemispherical Head

The end shape of a cylindrical vessel that can withstand the highest pressure for a given thickness.

Optimum Inside Pipe Diameter (Laminar Flow)

Determined by the formula $D_{i, opt} = 3.9 Q^{0.45} \cdot \rho^{0.23}$.

Stuffing Box

An accessory used for the prevention of fluid leakage around moving parts.

HETP (Height Equivalent to a Theoretical Plate)

The height of packing that will give the same separation as one theoretical plate in gas-liquid mass transfer operations.

Allowable Vapour Velocity

The factor used to set the diameter of a distillation column.

Ponchon Savarit Method

A more accurate analytical method than McCabe-Thiele that accounts for enthalpy changes and facilitates direct calculation of heat loads.

Bracket Supports

Supports most suitable for thick walled vertical vessels.

Liquid Redistributors

In packed towers (saddle packing), these are positioned every $5 - 8$ times the column diameter or $6\,metres$, whichever is less.

Feed Line Slope (Distillation)

Represented by the expression $\frac{-q}{1-q}$.

Circumferential (Hoop) Stress (Thin Cylinder)

Induced stress calculated as $\frac{pd}{2t}$, which is twice the longitudinal stress.

Overall Tray Efficiency

The ratio of the number of ideal trays required to the number of real trays required.

Corrosion Allowance Threshold

Generally, no corrosion allowance is required if the wall thickness is more than $30\,mm$.

Floating Head Heat Exchangers

Used for cases where the temperature difference between the shell and the tubes is more than ($> 50^{\circ}C$).

Absorption Factor

Defined as $\frac{S_2}{S_1}$ where $S_1$ is the slope of the equilibrium curve and $S_2$ is the slope of the operating line.

Unwin's Formula

Relates rivet hole diameter ($d, mm$) and plate thickness ($t, mm$) as $d = 6 \sqrt{t}$.

Baffle Spacing (Heat Exchanger)

The centre to centre distance between two consecutive baffles, usually ranging between $D/5$ (or minimum $2"$) to $D$ (shell diameter).

Horton Sphere

A spherical vessel used for storage of gases and volatile liquids at moderate pressures ($1$ to $10\,kg/cm^2$).

Standard Bubble Cap Pitch

Bubble caps are located on trays with a pitch of $1.3$ to $2$ times the outside diameter of the caps.

Young's Modulus of Elasticity

Material property shared with Stress in terms of units.

Multiple Effect Evaporation Economy

Increasing the number of effects in evaporation increases the steam economy but does not affect the total capacity.

Peclet Number ($Pe$)

A value of $Pe = \infty$ represents plug flow, while $Pe = 0$ represents complete back mixing.

Poisson's Ratio

The ratio of unit lateral strain to the unit axial elongation within the elastic limit; for structural steel, it is taken as $0.3$.

Joint Efficiency ($J$)

For a seamless pipe, the value of $J$ is taken as $1$.

Sounders-Brown Equation

Equation used for the calculation of the diameter of a bubble cap or sieve tray distillation column.

Weep Holes

Holes in distillation plates (usually $1/4"$ to $5/8"\,dia$) that facilitate draining liquid when the unit is not in operation.