Thermal power plants (TPPs) require flue gas desulphurisation (FGD) systems to comply with the Ministry of Environment, Forest and Climate Change’s SO2 emission norms. With a cumulative installed capacity of 235 GW, TPPs account for 57 per cent of the country’s energy mix and are expected to play a crucial role in balancing the grid as renewable energy capacity increases. It is, therefore, critical for these plants to operate in an environmentally safe manner. While the emission norms were notified in December 2015, the pace of implementation has been slow so far. As of June 2023, only 4 per cent or 9,280 MW of coal and lignite-based projects have commissioned FGD systems. Meanwhile, bids have been awarded for 33 per cent of the privately owned units. At a recent Power Line conference, private gencos shared their views on the technology selection for FGD systems, raw material availability and by-product disposal, as well as issues and challenges faced. Edited excerpts…
Wet FGD systems entered the scene with two 660 units at our Jhajjar power plant, which was commissioned in 2013. Following the 2015 notification, we started trials for the operation of FGD systems on a continuous basis. From 2013 to 2018, we were operating FGD systems intermittently to keep the equipment healthy and reliable.
From 2019 onward, we have been running FGD systems continuously to comply with the 200 mg/Nm3 SOx limit. We were given a predetermined FGD system by our Hong Kong investors who offered FGD along with main package as a caring gesture towards the environment. At the time of plant installation, there were no Central Electricity Authority (CEA)-specific guidelines on SOx limits or any specific guidelines on FGD components. In the past four years of operation, apart from operational challenges, we have been facing a lot of issues with equipment redundancies. The flue canes of our chimneys are cladded with 1.2 mm of titanium over the inner shell. Over time, the titanium sheet got corroded, and we are seeing some leakages happening around the chimney. This chimney is attached at seven locations, with each step connected to another through an expansion bellow. The leakages are prevalent mostly at the bellow area for up to 185 m of length. The flow dynamics of the chimneys were studied by a reputed US-based vendor. After this study, we installed a liquid collection system in one unit, and it is planned for another. As a long-term action plan, borosilicate liner will also be provided in both chimneys to prevent corrosion of internal surfaces.
As far as raw material sourcing is concerned, we visited 50-odd mines in Rajasthan and collected around 75 samples. Based on our internal experimentation and considering the design constraints, we decided to procure high purity limestone (purity 90-92 per cent). Currently, limestone is sourced from Rajasthan. The original design of the FGD system was made for limestone of around 90 per cent purity. When we started trial runs in 2018, we found a lot of issues owing to the stickiness of the residual limestone. Choking of mist eliminator was also one of the major operational issues at that time and led to FGD shutdown in early operation days. We also faced a lot of redundancy issues due to the size of our limestone crusher and wet ball mills. The selected limestone purity is yielding gypsum of over 90 per cent purity.
JPL is fortunate enough to be surrounded by five cement manufacturers. They are the major procurers of our gypsum, with nearly 100 per cent off-take.
Suresh Kumar Narang
Nabha Power is one of the few private developers at an advanced stage of commissioning an FGD system at its power plant. Nabha Power, which is a 2×700 MW plant in Rajpura, Punjab, has been prompt in complying with the notifications for the installation of FGD systems. With regard to raw material availability and by-product disposal, we will procure limestone, which is a key raw material for our FGD systems, from Rajasthan, while we have already floated tenders for the sale of gypsum.
As far as challenges are concerned, obtaining approvals from regulatory bodies has been delayed significantly. The FGD notification was released back in 2015, but the discom were not willing to consider it as a change in law. This has resulted in legal cases and prolonged litigations before the regulatory commissions and the Appellate Tribunal for Electricity (APTEL). We got a favourable order from APTEL three years ago, whereby they affirmed this as a change-in-law event.
Another challenge in FGD installation is the reluctance of financial institutions to fund such a project, primarily owing to a pending case in the Supreme Court on the matter of FGD cost passthrough. Apparently, financial institutions are willing to fund FGD systems after the tariff approval is obtained from the commission. At Nabha Power, the entire investment for the FGD project is being done through the loans availed from the parent company. Therefore, it is important that the government intervenes and issues a directive to the discoms and the regulators to recognise the difficulties faced by the developers in investing so much capex, and expedite the finalisation of FGD tariff. Since the operationalisation of FGD systems incurs extra capex and opex, we have also proposed to the government and the concerned ministries that the environmental compensation cess on coal for projects with FGD systems be waived since the FGD installation will lead to containment of SOx emissions, which fits in with the larger objective of ensuring clean environment.
Another issue with the operation of FGD systems could arise from the flexible operation of power units. Currently, there is not much operating data available regarding the performance of FGD systems during flexible operations. Clearly, with FGD systems, the auxiliary power would increase by more than 1 per cent. If the load comes down to 40 per cent, there is expected to be significant impact on the auxiliary power for FGD systems, and the developer or the operator will need to be compensated for this.
With regard to the impact of FGD installation on merit order despatch, until all plants adhere to the FGD compliance rules, the order of priority will remain unchanged. Therefore, the established order should persist as is till such time as FGD implementation has occurred for all TPPs in the country. We are optimistic that the regulations will be upheld, ensuring that our position in the merit order is maintained. It is worth noting that we are the most efficient plant in Punjab, and our excellence extends beyond the state and across India. Additionally, our power generation costs are the lowest in Punjab, solidifying our place at the forefront of the merit order. Therefore, we will continue to occupy the top spot in the merit order.
Tata Power is among few private developer who have approached to Central Electricity Regulatory Commission (CERC) for in principle approval of feasibility report and to Central Electricity Regulatory Commission for ‘In Principle’ approval for FGD installation.
Tata Power has five coal based thermal generating stations. At Units 5 and 8 of the Trombay Thermal Power Station (TPS), FGD systems were installed way back in the 1984 and 2009 respectively. At the 5×830 MW Mundra TPP, we have already started the construction of seawater waste FGD system and same is under construction. There, we faced challenges pertaining to the technology selection for the type of stack to be used. Later, after discussions and brainstorming, we started the construction of an FGD system at Mundra with in-principle approval from CERC. The construction is currently at an advanced stage, and we will be able to complete it within the stipulated timeline.
In Jojobera, we are installing limestone based FGD System for Unit 2 to 4. In this units, we have selected one absorber for two units. We were also exploring the option of installing single absorber for multiple units but could not do so because of layout limitations.
Objections had been raised by CEA regarding the technology selection for Jojobera’s FGD system. For NTPC’s Dadri Power Plant, the capex for the dry sorbent injection (DSI) system was very low. This was the first DSI project in the country, which could be one of the reasons for the low cost. We also tried to explore DSI system at the Jojobera plant; however, we received bids and lifecycle cost was coming out to be the highest for DSI technology. It took us two to three months to convince the CEA that DSI was not right technology for our units. After a lot of discussion on budgetary considerations and lifecycle analysis, we we convinced CEA that limestone FGD should be selected for Jojobera units.
At the 3×660 MW Prayagraj TPP, wet limestone-based FGD system is selected and is under construction. For our 2×525 MW Maithon TPS, we have selected a limestone-based FGD system, and the project is also under construction stage. We received in principle approval from CERC for Maithon Power Limited, Mundra Thermal Power Plant and Jojobera Unit 2 and 3. We will be submitting the true cost of the FGD projects once they are completed. We expect that the revised tariff will be notified subsequently.