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.
Solution
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:
C2H4+Cl2→C2H4Cl2(1)
C2H4Cl2→C2H3Cl+HCl(2)
We gather the following information on the process:
| Name | Formula | Molecular Weight (g/mol) | Price (USD/tonne) |
|---|---|---|---|
| Ethene | C2H4 | 28.05 | 733 |
| Chlorine | Cl2 | 70.91 | 240 |
| Dichloroethane | C2H4Cl2 | 98.96 | 300 |
| Hydrogen Chloride | HCl | 36.46 | 140 |
| Vinyl Chloride | C2H3Cl | 62.50 | 750 |
Assume as well that our production costs are 200USDtonne of VC produced, and assume our VC production plant costs 50,000,000USD 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.
Solution
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:
VC=360,000tonnes/yr∗tonne−mol62.50tonnes=5,760tonne−molyr
HCl=5,760tonne−molyr∗36.46tonnestonne−mol=210,000tonnesyr
Similarly for ethane and chlorine, we get:
C2H4=5,760tonne−molyr∗28.05tonnestonne−mol=162,000tonnesyr
Cl2=5,760tonne−molyr∗70.91tonnestonne−mol=408,000tonnesyr
From this and the information in the table, we get the following input-output diagram:
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