1. Problem Definition
The methanol facility is using Diesel generators for power supply during the plant upsets. Those generators require a lot of maintenance through the whole year. However, government power is available around and can be purchased but with little modification to the connection grid. What is the better option stop using diesel generators and buying power from government or maintain things as they are?
2. Identify the Feasible Alternatives
The alternatives are:
- Do nothing and maintain things as they are.
- Stop using diesel generators and buy power from government.
3. Development of the Outcomes for Alternatives
- Calculate the max annul power requirement from diesel generator.
- Calculate the annual cost of diesel generators maintenance and the diesel cost
- Calculate the annual cost of purchased power along with additional cost for modification.
4. Selection of Criteria
The alternative with higher net present value is selected.
5. Analysis and Comparison of the Alternatives.
In the worst scenario, the plant trips/shuts down 5 day per month which is 60 day/annum.
Then, the total power required per annum is 4320 MWh as the total diesel generators capacity is around 3 MW.
The two alternatives are compared as in the following table at 8.6 %  rate for 5 year. [Negative (-) means cost]
|Comparison Parameter||Diesel Generators||Government Power|
|Annual Operating cost||-450000 $||-15000$|
|Capital Cost||Not applicable||-1000000$|
|Total NPV||-1768680 $||-1058956$|
6. Selection of the Preferred Alternative.
As using government power has higher NPV, it is selected as the preferred alternative.
7. Performance Monitoring and the Post Evaluation of Result.
It is better to keep the diesel generators in good conditions in case we need them in future or something happened in near future which restricts the government power supply. 
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