Emerging challenges in design & engineering of new Alumina refinery

Hi Friends,

In earlier posts, we have already discussed the design criteria, process & engineering design calculations and basic requirements for setting up green-field Alumina refinery and methodology for their expansions in phases there after. We have covered all major crucial issues starting from conceptual stage to execution including commissioning procedures of Alumina refinery. In present post, we wish to address the design and engineering challenges in setting up new Alumina refineries in any part of the globe with due consideration of emerging issues being raised all over the World. Major challenges have been briefly described in subsequent paragraphs-

1. Efficient process technology: We can not afford to compromise on efficiency of the plant for judicious utilization of limited natural resources and minimum generation of bauxite residue as waste. Thus we have have to target for all plant efficiency figures better than the best achieved so far in the World. Each process unit should be evaluated in isolation with regard to efficiency irrespective of upward or downward units. The key efficiency parameters like overall alumina recovery at 94% (min.), liquor productivity across precipitators at 92 gpl Al2O3 (min.) and total energy consumption at 8.5 GJ per tonne of alumina (max.) must be kept in mind while designing the new Alumina refinery. Though, it may be little difficult but well achievable target for an efficient Alumina refinery.
2. Rugged design of residue storage pond: Recent failure of earthen dyke of residue storage pond of one of the Alumina refineries in Hungary has created fear psychosis among the people residing in the vicinity of all Alumina refineries in the World. This may be taken as a word of caution by designers and manufacturers of hydrates and alumina. Thus, design of bauxite residue pond to be done with utmost care leaving no chance for any dyke failure as well as percolation of alkaline fluid to nearby natural streams. In addition,   adequate future provisions in the foundation of base must be kept for raising the dyke height at least upto 50 meters from ground level.  
3. Compact design of equipment: Dimension and number of equipment & vessels  are directly proportional to land requirement for installation. Thus bigger capacity equipment & vessels with highest possible H/D ratio should be preferred. All out efforts should be made to maximize the installation of selected process equipment on 1st and 2nd floors of the unit areas wherever possible. During equipment sizing calculations we have to remember that sky is not the limit for designers. These steps will drastically reduce the land requirement for the plant proper. 
4. Optimized plant layout: General layout of the plant plays vital role in operational ease as well as overall space requirement. Thus the general layout and shop layout of the plant should be finalized by working out various permutations and combinations for installation of equipment and facilities to ensure optimum utilization of space within the premises.
5. Zero effluent discharge: As per the recent environmental norms and guidelines, dry residue stacking at more than 50% solids (w/w) and zero effluent discharge outside the premises of plant are essential design parameters for setting up new Alumina refinery. Thus, these issues should be taken up with due care during design and engineering stages of the plant. The residue disposal at higher solid consistency will result in increased pond life as well as faster drying of residue. Similarly, adoption of zero effluent discharge will combat the surface pollution problems and will attribute in reducing the total raw water requirement for the plant.
6. Development of green belt: Under environmental protection measures to prevent threat of global warming, development of green belt in and around the plant is a must in more than 30% of total plant area. This aspect need to be kept in mind and strictly followed while designing the Alumina plant.

These are major emerging challenges in design and engineering of new Alumina refinery. Hope, the topic has been covered in simple words with clarity in expression. The information presented here are purely based on my personal experience in the field. Please put your views / remarks / comments, if any.

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Thanks and regards.

Kunwar Rajendra