Heuristic

In engineering, heuristics are experience based methods that are used to reduce the need for calculations pertaining to equipment size, performance, or operating conditions. Heuristics are fallible and they do not guarantee a correct solution. It is important to understand their limitations when applying them to different equipment and processes. Even though heuristics are limited, they may be of value because they offer time saving approximations in preliminary process design.

Problem solving methods are intrinsic to forensic engineering methods where failures are analysed for the root cause or causes. Only when failures have been investigated with conclusive results can remedial action be taken with confidence.

Examples

Storage Vessels

These heuristics were taken from Turton's "Analysis, Synthesis, and Design of Chemical Processes".^[1]

• Use vertical tanks on legs when the tank is less than 3.8 m³.
• Use horizontal tanks on concrete supports when the tank is between 3.8 and 38 m³,
• Use vertical tanks on concrete pads when the tank is beyond 38 m³,
• Liquids subject to breathing losses may be stored in tanks with floating or expansion roofs for conservation.
• Freeboard is 15% below 1.9 m³ and 10% above 1.9 m³.
• Thirty day capacity often is specified for raw materials and products, but depends on connecting transportation equipment schedules.

Pumps

These heuristics were taken from Turton's "Analysis, Synthesis, and Design of Chemical Processes".^[2]

• Centrifugal pumps: Single Stage: for of 0.057-18.9 m³/min, 152 m maximum head. Multistage: for 0.076-41.6 m³/min, 1675 m maximum head. Efficiency is 45% at 0.378 m³/min, 70% at 1.89 m³/min, 80% at 37.8 m³/min.
• Axial pumps: for 0.076-378 m³/min, 12 m head, 65-85% efficiency.
• Rotary pumps: for 0.00378-18.9 m³/min, 15,200 m head, 50-80% efficiency.
• Reciprocating pumps: for 0.0378-37.8 m³/min, 300 km head maximum. Efficiency is 70% at 7.46 kW, 85% at 37.3 kW, and 90% at 373 kW.

References

1. ^ Turton, Richard, et al. (2003) Analysis, Synthesis, and Design of Chemical Processes, Upper Saddle River, NJ: Prentice Hall. ISBN 0-13-064792-6
2. ^ Turton, Richard, et al. (2003) Analysis, Synthesis, and Design of Chemical Processes, Upper Saddle River, NJ: Prentice Hall. ISBN 0-13-064792-6

External links

• [1]-PDF from AICHE website that shows more heuristics.