Standby philosophy for equipment in Alumina Refinery

Hi Friends,

We are well aware that specific capital investment for execution of green-field Alumina refinery project varies from 650 to 750 US$ per tonne of alumina production per year depending on various factors like location of plant, availability of infrastructure facilities, topography of land, soil condition, process technology and standby philosophy for equipment and facilities. It is always advisable to be judicious while recommending the standby equipment because installation of any additional equipment boils to added capital expenditure. In present post, standby philosophy for equipment in Alumina refinery shall be addressed in simple words for clarity in understanding. Decision about requirement of standby equipment for any continuous process plant is taken after detailed study of three key factors as described below-

1. Criticality of equipment: Criticality of equipment refers to essential duty requirement for continuous operation without any operating loss time  and downtime of such equipment is directly proportional to production loss because of operational complexity. In Alumina refinery, bauxite grinders, autoclaves, filters, pumps, heat exchangers, precipitators, evaporators, boilers, turbo-generators and calciners are considered as critical equipment where as storage vessels, causticizers etc are non-critical equipment.
2. Availability of equipment: Availability of equipment refers to its reliability with respect to its downtime for maintenance and other preventive measures in view of desired operational efficiency. It is the direct reflection of break down frequency as well as  maintenance management techniques adopted for improved efficiency and reliability. 
3. Required capital investment: Added capital investment has the negative impact on overall profitability of the plant, but can not be ignored at the cost of lower production, safety and environment.

On detailed scrutiny of all these three factors, final call is taken for deciding the percentage standby requirement for any equipment in the plant. Generally, even for critical duty condition equipment, having high availability and requiring high capital investment, are installed with little higher design margin in capacity to take care of normal plant operation without going for standby. However, scaling pron equipment like heat exchangers are provided with 100% standby. The critical process vessels like digesters and precipitators are provided with  10% to 20% as standby. Slurry pumps and liquor pumps in the continuous process circuit are also provided with 50% to 100% standby.

In co-generation plant, schedule outage of steam raising boilers is a must once a year for meeting statutory requirement. Thus standby boilers are installed to take care of normal steam requirement for the plant.

These are the guidelines and there may be difference in opinion, but everybody has the single basic objective - "optimum utilization of equipment for productive purposes aiming to maximizing returns on investment".


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Kunwar Rajendra