4 Input-Output Diagrams

Learning Objectives

By the end of this section, you should be able to:

Create input-output diagrams

Input-Output Diagrams

These diagrams are considered to be the simplest of process flow sheets. In input-output diagrams, the entire process is represented by 1 block only. They usually only reference the main process streams in and out of a process.

Example: Ammonia Production Input-output Diagram

Consider an ammonia production process where 3 main streams of raw materials enter the process:

  • 700 tons/day of methane
  • 1590 tons/day of water
  • 1650 tons/day of nitrogen

The process produces 2 main product streams:

  • 2000 tons/day of ammonia
  • 1940 tons/day of carbon dioxide

We can put together the following input-output diagram for this process:


Exercise: Benzene Production Input-output Diagram

Consider a process where toluene is fed into a process at 1000 kg/hr and hydrogen is fed at 82 kg/hr. The following reaction takes place in the process:

[latex]C_{7}H_{8} + H_{2} ➡ C_{6}H_{6} + CH_{4}[/latex]

The reaction achieves 75% conversion and the products of the process are separated into 2 streams. The first product stream is benzene, exiting at 821 kg/hr. The second product stream is a mixed gas stream (including the unreacted reactants and by-products) exiting at 261 kg/hr. Draw an input-output diagram for this process.


Exercise: Production of Vinyl Chloride

Our client wants to produce 360,000 tonnes/yr (800 million lbs/yr) of vinyl chloride monomer. We decide to use the following reaction pathway, which contains two reaction steps as follows:

[latex]C_{2}H_{4} + Cl_{2} → C_{2}H_{4}Cl_{2} (1)[/latex]

[latex]C_{2}H_{4}Cl_{2} → C_{2}H_{3}Cl + HCl (2)[/latex]

We gather the following information on the process:

Name Formula Molecular Weight (g/mol) Price (USD/tonne)
Ethene [latex]C_{2}H_{4}[/latex] 28.05 733
Chlorine [latex]Cl_{2}[/latex] 70.91 240
Dichloroethane [latex]C_{2}H_{4}Cl_{2}[/latex] 98.96 300
Hydrogen Chloride [latex]HCl[/latex] 36.46 140
Vinyl Chloride [latex]C_{2}H_{3}Cl[/latex] 62.50 750

Assume as well that our production costs are [latex]200\frac{USD}{tonne}[/latex] of VC produced, and assume our VC production plant costs [latex]50,000,000 USD[/latex] to build. Note these values usually depend on the size of the plant, location, and other factors.

Create an input-output diagram of the process.


We know that one of the product streams will be 360,000 tonnes/yr of vinyl chloride. Hydrogen chloride is produced in a 1:1 molar ratio with vinyl chloride:

[latex]VC = 360,000 tonnes/yr*\frac{tonne-mol}{62.50 tonnes} = 5,760\frac{tonne-mol}{yr}[/latex]

[latex]HCl = 5,760\frac{tonne-mol}{yr}*36.46\frac{tonnes}{tonne-mol}=210,000\frac{tonnes}{yr}[/latex]

Similarly for ethane and chlorine, we get:

[latex]C_{2}H_{4} = 5,760\frac{tonne-mol}{yr}*28.05\frac{tonnes}{tonne-mol}=162,000\frac{tonnes}{yr}[/latex]

[latex]Cl_{2} = 5,760\frac{tonne-mol}{yr}*70.91\frac{tonnes}{tonne-mol}=408,000\frac{tonnes}{yr}[/latex]

From this and the information in the table, we get the following input-output diagram:



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Foundations of Chemical and Biological Engineering I Copyright © 2020 by Jonathan Verrett is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License, except where otherwise noted.

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