The storage of nearly five lakh metric tons of coal at Dr. Narla Tatarao Thermal Power Station (NTTPS) for more than two-and-a-half months due to the temporary closure of seven units (six units of 210-MW capacity and one 500-MW unit) has resulted in a steady fall in the Gross Calorific Value (GCV) of the fuel.
If the storage continues for a longer duration, the GCV will deteriorate further and the specific coal consumption will go up. Ultimately, the variable cost will rise by about 47 paisa per unit.
In order to avoid this situation, permission should be given to resume generation at the units, NTTPS Chief Engineer (Operations and Maintenance) requested the AP-Genco management through a letter, a copy of which is available with The Hindu.
The CE stated that approximately 6,35,120 metric tons of coal was procured over a period of time and stored at the stock yard by the end of April. The steep fall in demand from bulk consumers because of the lockdown-necessitated hand-tripping (keeping on reserve stand - by) of seven units.
The 500-MW unit was synchronised to the grid in May and the other six units remain on standby.
If all the units were in service, around 30,000 metric tons of coal would have been consumed on a daily basis. Storage of coal for long durations causes it's GCV to drop due to oxidation and internal spontaneous combustion.
As the carbon and hydrogen content decreases, the ignition temperature (of coal) increases so does the activation energy. The AP-Genco should, therefore, allow taking six units into service at the earliest if the variable cost is to be kept under check, the CE appealed.
