In conclusion, the main objective of this project is to design a process to produce alumina from bauxite. Also it is important to perform the economical study of the project.
In the first part of the project, the process selection (Bayer process) and the conceptual design (mass and energy balances) were done. Then, in the second part, the design of the main equipments of the process was done. After that, the economical study was done. Finally, the HZAOP study was performed for the selected process and its operating conditions.
The project was stated with literature and market survey which was the key to choose the production of 5 Mton/yr to cover the local demand.
In order to achieve those objectives, there were four main possible alternatives that was applied in industry. The Bayer process was selected, because it was the most efficient and economical among the four alternatives after literature review of those processes and discussion to choose the best one.
The design was started with the block flow diagram that shows that main units of the Bayer process. Then, it was modified with the most important units and removing the auxiliaries. After that, the mass and energy balances were done.
Those findings were used to design and size the main equipments of the process.
The process was divided into two lines. Each line has a production rate of 2.5 Mton/yr of alumina.
Then, the digestion unit was design. Two CSTRs with 93 m3 volume are needed for each line. The H/D was 4 for the digester.
The settling tank (clarifier) with 3 m depth and 37.75 m diameter. For each line, one clarifier is needed.
Also, the pre-cooler was designed to prepare the sodium aluminate solution for the precipitation unit (crystallizer). There were 7 heat exchanger in each line with area of 3,651.52 m2 per heat exchanger.
The precipitation unit residence time was calculated to be 13.69 hr as expected for this process. As, a result of that residence time, the size of this unit was huge. There was a need of 22 crystallizers per each line in parallel with 10 m diameter and 30 m height. Those numbers are available in indusial application of the Bayer process.
The rotary kiln volume was calculated to be 270.98 with L/D ratio of 11.6 (35.94 m long and diameter of 3.098 m).
The recycled stream pumps power was calculated to be 1,352.54 kW. There was a need of 4 pumps per one line.
The capital cost of the plant was estimated to be 2.6 billion $. Then cost of manufacturing was estimated to perform the feasibility study. The feasibility study was done as shown in figure 6.1. The payback period of the plant was estimated to be 4.2 years from the start up of the production.
Finally, the HAZOP study was done for the main equipments of the process. The main HAZOP was in the digester that operate at 115ᵒC. Also, the kiln should be operating at 1100ᵒC which resents high risk. The outlet temperature of the pre-cooler should be controlled to avoid the crystallization inside the tubes of the heat exchanger.