Complying with emission norms is one of the key priorities for power generation companies. While they are opting for flue gas desulphurisation (FGD) systems to meet SOx norms, for NOx norms, they are using combustion modification as the preferred solution. The Central Electricity Authority (CEA) has prepared a detailed phasing plan for FGD upgrades across 440 units aggregating 166 GW of capacity by 2022. However, the progress in FGD installations has been sluggish so far.
In the public gencos space (state and central sectors), as of July 2020, FGD systems have been commissioned across only two 210 MW units each at NTPC Limited’s Dadri thermal power plant (TPP). Meanwhile, as per the CEA, bids have been awarded for 36.8 GW, representing around 34 per cent of the planned capacity. Notice inviting tenders (NITs) have been issued for 96 GW (74 per cent of the planned capacity). Overall, public gencos have made better progress in the issuing of tenders and awarding of bids, as against private gencos, which have issued tenders for 70 per cent of the planned capacity and awarded bids for 18 per cent.
A look at the progress in the installation of emission control systems by public gencos and their future plans…
So far, NTPC Limited has commissioned FGDs at two units of its Dadri project (2×210 MW). It has opted for dry sorbent injection (DSI) technology for the units. The total thermal capacity for award of FGD for NTPC exceeds 62 GW. Of this, FGD tenders for more than 59 GW have already been awarded while FGD systems for around 2 GW of capacity are under implementation. The timeline for the commissioning of the FGD systems is 24-36 months. The genco is mostly opting for wet FGD solutions across its power plants. The technology is primarily based on location, plant load factor, sulphur content and saleability of byproduct (gypsum). It is primarily opting for borosilicate lining in the FGD chimneys; however, for some plants including Patratu and Telangana TPP, titanium lining has been selected. Besides, NTPC is providing consultancy services to state gencos in Uttar Pradesh, Punjab and Haryana as well as its joint venture companies.
With regard to the de-NOx initiatives, NTPC has done pilots to assess the efficacy of various NOx reduction technologies and methods. According to its trials, it has been found that the NOx reduction achievable from combustion modification is around 750 mg per Nm3 to 450 mg per Nm3. For SNCR technology, NOx reduction is in the range of 20 per cent to 30 per cent only. Further, it was found that while a reduction of around 80 per cent is achievable in NOx, it is not consistent due to the part-load operation of power plants. Hence, the issue of review and relaxation of the existing NOx emission norms is currently under review with the Ministry of Environment, Forest and Climate Change (MoEFCC), to modify the current limit of 100 mg per Nm3 for NOx. As per NTPC’s de-NOx action plan, combustion modification has already been implemented at five units of 2,480 MW capacity. Combustion modification contracts have been awarded or are under execution at 42 units with 18,080 MW of capacity. Further, de-NOx contracts for three units totalling 1,000 MW are currently under tendering.
Damodar Valley Corporation
The genco has awarded FDG systems for its 500 MW and 600 MW units, and these are currently under implementation. While one of the FGD systems is expected to be commissioned by October 2021, the second is likely to come up by January 2022. The resources for the projects have been mobilised; however, work at the sites has suffered because of the Covid pandemic. Meanwhile, for 250 MW and 210 MW power plants, the award of FGD systems is currently at the NIT stage. The tender opening dates for these were extended due to the pandemic. The genco is deploying wet FGD technology for de-SOx. In order to save costs, for old power units, the genco is setting up a combined FGD system, which would comprise a common chimney and a common control room. Damodar Valley Corporation (DVC) is setting up combined FGD systems for its units at the Mejia power plant. Notably, the Mejia power plant has already tied up with a cement plant in the vicinity for utilising the gypsum generated from its FGD system. Overall, the genco has planned a shutdown time of 30-35 days for the interconnection of the FGD system to the thermal power unit, along with the implementation of the de-NOx schedule at the unit. It is expecting a shutdown cost of Rs 25 million per day for a 500 MW pithead unit.
Key concerns and challenges
A major concern facing the industry in the implementation of air quality control systems is the technological limitation in implementing de-NOx systems. Space constraints for setting up FGD systems in existing projects are also a challenge. Another challenge has been the high capex involved, of around Rs 4 million–Rs 9 million per MW, for installing FGD systems. This, in turn, leads to higher tariffs as the generation cost increases by 25-30 paise, affecting consumers. The availability of quality limestone, which is a necessary raw material for FGD systems, is another challenge. There are concerns with regard to its transportation as well, given that new railway and road infrastructure has to be created. Further, the disposal of quality gypsum is a concern, as a readily available market is not available for the byproduct. Although the cement industry uses gypsum, its utilisation is only 5 per cent, that is, 20 million tonnes, out of a total production of 400 million tonnes of gypsum at TPPs.
To conclude, the 2022 deadline is highly challenging for gencos, which were required to begin FGD construction by 2019. The FGD implementation schedules are likely to take a further hit due to the Covid-19 pandemic leading to supply chain disruptions. Besides this, TPPs are facing a liquidity crunch owing to the demand slowdown.