7/31/2019 Roaster Bed Fusion After Power Failure

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ROASTER BED FUSION AFTER POWER FAILURE

Brief description of the incident.

Roaster Plant was in normal operation and all the parameters of furnace were normal.

At around 1100 hours, there was complete blackout due to power failure & the whole plant stopped

automatically. Immediately, within in 10 minutes DG set was started to meet emergency powerrequirement for Roasters bed fluidization and at 1120 hours another DG was started as per load

requirement. Since there is a 30 minutes time interlock in restarting of roaster air blower, as per normal

operating procedure, therefore, clearance for fluidization was given at 1145 hours by electricaldepartment.

However, the roaster fluidization could be started only at 1206 hours with controlled air flow but it could

not be revived. Air lancing from feed hole started for reviving the bed. Two bulkers with about 60 mtcalcine charged inside the furnace for filling the gaps, which developed in roaster bed during fluidization

process. With consistent effort till 2000 hour, the R3 bed could not be revived.

Based on the roaster bed parameters, it was decided to cool down and empty out the roaster furnace bed.In parallel, few other jobs were also planned and decided to complete before restart of the roaster.

Fact finding

At the time of power failure following were the parameters.

Feed rate 40.37 mt/hour

Water injection 4401 ltr/hourBed pressure 2145 mm wc.

Bed temps. From 896 to 912 deg C

Furnace outlet temp 847 deg C

Blend consumption pattern for last one week is mentioned below.Quantity wise Ratio

Date Mine1 Mine2 Mine3 Imported Total Mine1 Mine2 Mine3 Imported

7.10.2011 698 125 0 30 853 0.82 0.15 0.00 0.04

8.10.2011 422 200 184 0 806 0.52 0.25 0.23 0.00

9.10.2011 433 150 238 0 821 0.53 0.18 0.29 0.00

10.10.2011 230 116 115 0 461 0.50 0.25 0.25 0.00

11.10.2011 476 80 240 0 796 0.60 0.10 0.30 0.00

12.10.2011 764 100 0 0 864 0.88 0.12 0.00 0.00

13.10.2011 656 90 0 0 746 0.88 0.12 0.00 0.00

14.10.2011 467 30 0 0 497 0.94 0.06 0.00 0.00

Agglomerated Calcine samples from furnace were analyzed at our Laboratory. Results are given below:

ISM SiO2 Pb H2S/S

Sample 1 8.4% 5.56 % 2.0% 0.1

Sample 2 6.1% 4.3% 1.8% 0.1%Sample 3 5.73% 3.86 % 1.62 % 0.1%

7/31/2019 Roaster Bed Fusion After Power Failure

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Reasons for incident:

The sequence of events and available analysis of agglomerated Calcine from bed, it is evident that high

content of SiO2 and Lead in the concentrate is responsible for this mishap. High level of SiO2 in Mine1

& Mine2 concentrate is always a concern for fluidized bed Roasters.

Recommendations:

1. Regular analysis of bed Calcine for Silica & Lead percentage, whenever using concentrates fromvarious sources having higher percentage of these impurities. Accordingly change in blend ration

based on XRF analysis till silica & lead come down below 3% & 2%.

2. Change is practice of fluidization sequence of existing Roasters in case of power failure i.e. Firstbigger roaster shall be fluidized, followed by smaller ones.

3. Review of existing fluidization practice of roaster bed after sudden stoppage of plant based on the

values of silica and lead in the concentrate.4. At least four days concentrate stock to be available in Blend yard.

5. Installation of XRF instrument in lab for quicker analysis of Lead & Silica. By XRF, the analysis

could be completed in 5 minutes against 8 hours in classical method of analysis.