Tips & Tricks for Chemical Engineers

Heat Loss from Insulated Pipe

Heat loss/gain takes place from a pipe carrying hotter/ colder fluid than ambient temperature. Insulation reduces the heat loss to surroundings. Heat loss depends upon number of factors like insulation thickness, ambient temperature, wind speed etc. This article shows how to calculate heat loss from an insulated pipe and a bare pipe to surroundings.

A 3" Carbon steel pipe is carrying hot oil at 180°C and insulated with 50 mm thick calcium silicate insulation. Insulation is cladded with a sheet with surace emissivity of 0.9. Ambient temperature is 28°C and wind velocity is 3.5 m/s. Calculate surface temperature and heat loss from insulated and bare pipe.

Insulated pipe heat loss example

Continue Reading ...

Pipe Network Analysis

Pipe Network Analysis determine the flow rates and pressure drops in the individual sections of a hydraulic network. Hardy Cross Method is the oldest and probably best known solution method for pipe networks. In this method, each loop correction is determined independently of other loops. Epp and Fowler (1970) developed a more efficient approach by simultaneously computing corrections for all loops. This article illustrates use of Simultaneous Loop Flow Adjustment Algorithm in modelling pipe network analysis in excel spreadsheet.

A water supply distribution system is shown in the figure below. All pipes are cast iron with lengths and diameters as provided in table below. Perform pipe network analysis and calculate water flow in all branches.

Pipe Netowrk Analysis Example 1

Continue Reading ...

Binary Batch Distillation

Batch distillation is widely used in chemical processing industries when high value added, low volume chemicals must be separated. This article shows how to model and solve a multi-stage binary batch distillation problem in excel.

The 50 mol feed comprising 70% mols of A and 30% mols of B is to be distilled in the multi-stage batch distillation with 5 equilibrium stages on top of the reboiler (still pot). Reflux is returned to the column as a saturated liquid with the constant reflux ratio of 1.5. Relative volatility of A is 1.8. It is desired to reduce the mols of A in still to 10%. Determine average distillate composition, final amount of liquid in still pot and total amount of distillate collected.

A material balance is done across the column and following relationship commonly known as Rayleigh Equation is derived.

Continue Reading ...

Linear Programming in Excel

Linear Programming is a widely used mathematical technique designed to help managers and engineers in planning and decision making relative to resource allocation. Linear programming (LP) model essentially consists of 3 components.

  • Decision Variables
  • Objective function
  • Constraints

This article shows how to develop LP model in Excel.

Multipurpose plant is used to manufacture three products A, B and C from raw materials Y and Z. Amount of raw materials required, batch times and profits per batch are shown as below. Determine number of batches to be processed every week for each product to maximize the profit. Plant is operating for 150 hours per week. Raw material available per week is Y : 216 units and Z : 200 units.

Linear Programming example multipurpose plant

Continue Reading ...

Sizing Expansion Tank for Hot Oil System

Expansion tank is provided in hot oil system to accomodate for the increased thermic fluid volume due to thermal expansion. It also helps in removal of moisture and non-condensables during start-up. This article will show how to do sizing of an expansion tank.

Sizing Expansion tank for hot oil system

Continue Reading ...

McCabe Thiele Diagram

This article shows how to draw McCabe Thiele diagram for doing binary distillation analysis in a spreadsheet. A detailed writeup on mccabe thiele method is provided at Distillation Column Design.

Determine total number of stages and feed stage for separation of a binary mixture with relative volatility (α) 2.5, Feed composition (zF) 0.36, Distillate Composition (xD) 0.915, Bottom composition (xB) 0.05 and feed quality (q) 1.5. Reflux ratio to be 1.5 times the minimum reflux ratio (Rm).

Minimum Reflux Ratio (Rm)

Calculate the intersection of q-Line and equilibrium curve.

 y = qx /(q-1) - zF /(q-1)
y = αx / (1+ x (α - 1))

Continue Reading ...