Input-Output Diagrams

Jonathan Verret; Rosie Qiao; Rana A. Barghout

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:

$C_{7} H_{8} + H_{2} C_{6} H_{6} + C H_{4}$

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:

$C_{2} H_{4} + C l_{2} \to C_{2} H_{4} C l_{2} (1)$

$C_{2} H_{4} C l_{2} \to C_{2} H_{3} C l + H C l (2)$

We gather the following information on the process:

Name	Formula	Molecular Weight (g/mol)	Price (USD/tonne)
Ethene	$C_{2} H_{4}$	28.05	733
Chlorine	$C l_{2}$	70.91	240
Dichloroethane	$C_{2} H_{4} C l_{2}$	98.96	300
Hydrogen Chloride	$H C l$	36.46	140
Vinyl Chloride	$C_{2} H_{3} C l$	62.50	750

Assume as well that our production costs are $200 \frac{U S D}{t o n n e}$ of VC produced, and assume our VC production plant costs $50, 000, 000 U S D$ 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:

$V C = 360, 000 t o n n e s / y r * \frac{t o n n e - m o l}{62.50 t o n n e s} = 5, 760 \frac{t o n n e - m o l}{y r}$

$H C l = 5, 760 \frac{t o n n e - m o l}{y r} * 36.46 \frac{t o n n e s}{t o n n e - m o l} = 210, 000 \frac{t o n n e s}{y r}$

Similarly for ethane and chlorine, we get:

$C_{2} H_{4} = 5, 760 \frac{t o n n e - m o l}{y r} * 28.05 \frac{t o n n e s}{t o n n e - m o l} = 162, 000 \frac{t o n n e s}{y r}$

$C l_{2} = 5, 760 \frac{t o n n e - m o l}{y r} * 70.91 \frac{t o n n e s}{t o n n e - m o l} = 408, 000 \frac{t o n n e s}{y r}$

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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