1. New environmental norms: Modalities for adoption of FGD Technologies for NSPCL Projects
Pukhraj Soni & Abhishek Agrawal
NSPCL
(A Joint Venture of NTPC-SAIL)

2. UNITS TO BE INSTALLED FROM 01.01.2017 Dispersion Through Chimney
New Emission Norms Notified by MOEF, GOI on
Old Vs New Environmental Norms
EMISSION PARAMET ERS
OLD NORMS
NEW NORMS (mg/Nm3)
UNITS INSTALLED BEFORE
UNITS INSTALLED AFTER AND UPTO
UNITS TO BE INSTALLED FROM
UNIT SIZE
ALL
< 500 MW
> 500 MW
> 500 MW
SO2
Dispersion Through Chimney
600
200
100
NOx
No Standard
300
SPM
150 mg/Nm3
For >210 MW.
350 mg/Nm3
For <210 MW 50 30
MERCURY NA
0.03

3. New Emission Norms for NSPCL Plants
S. No.
Plant name & Location
Date of installation/ COD
Applicable Norms (mg/Nm3)
SO2
NOx
SPM
MERCURY 1.
Durgapur PP-II (2x60 MW)
U#1: 17-Feb-87
U#2: 23-Mar-88
600
100 NA 2.
Rourkela PP-II (2x60 MW)
U#1:12-Apr-87 3.
Bhilai PP-II (2x30 MW + 1x14 MW)
U#1: 25-Aug-82
U#2: 16-Jun-83
U#3: 08-Nov-85 4.
Bhilai PP-III (2x250 MW)
U#1: 22-Apr-09
U#2: 21-Oct-09
300 50
0.03 5.
Durgapur PP-III (2x20 MW)
Under construction 30 6.
Rourkela PP-II Expansion Project (1x250 MW)

4. Major FGD Technologies at a glance
TECHNOLOGY
REAGENT USED
END PRODUCT
SO2 REMOVAL
I. PRECOMBUSTION OR DURING COMBUSTION TECHNOLOGIES
Direct Furnace Sorbent Injection
Limestone or hydrated lime
Gypsum (CaSO4)
50 % - 60%
Fluidised Bed Combustion Scrubbing
Limestone
90% - 95%
II. POST COMBUSTION TECHNOLOGIES
IIA. WET SCRUBBING
1.Forced Oxidation Wet Limestone FGD (LSFO)
Limestone slurry
95% - 98%
2. Wet Lime FGD System (MEL)
Slaked Lime (Mg enhanced)
CaSO3 / CaSO4, MgSO3
98% - 99%
3. Sea Water Scrubbing
Sea Water
None
90% - 98%
4. Ammonia Scrubbing
Anhydrous Ammonia
Ammonium Sulphate
96% - 99%
IIB. DRY / SEMI DRY SCRUBBING
1. Spray Dryer Absorber (SDA)
Dry Hydrated Lime / Lime Slurry
CaSO3 / CaSO4
85% - 99%
2. Circulating Dry Scrubber (CDS)
Dry Hydrated Lime
>98%

5. IMPLEMENTATION PLAN OF FGD FOR NSPCL PROJECTS
NTPC vide letter Ref: 01/CP/SP/CEA dated informed CEA regarding implementation plan for FGD installation in Coal based thermal units of NTPC.
NTPC has included existing NSPCL Power Projects in the list submitted to CEA i.e X 60 MW Units of Durgapur, 2 X 60 MW Units of Rourkela , 2 X 250 MW Units of Bhilai.
Installation of FGD for Bhilai PP-II is not included in the aforesaid list.
Implementation Plan for above Units as per NTPC commitment to CEA is
For Rourkela Expansion 1 X 250 MW Unit FGD shall be installed in consultation with NTPC.
For Durgapur Expansion 2 X 20 MW Units FGD systems is included in the already awarded EPC Package.

6. Technologies adopted for NSPCL Projects
Technologies adopted for Expansion projects:-
Durgapur PP- III ( 2 x 20 MW ): Dry FGD Circulating Dry Scrubber (CDS)
Rourkela PP-II Expansion ( 1 X 250 MW ): Wet FGD ( Forced Oxidation Wet Limestone FGD LSFO)
Technologies for Existing Units :
Bhilai PP-III Units ( 2 X 250 MW ) : Wet FGD ( Forced Oxidation Wet Limestone FGD LSFO)
NSPCL PP-II Units: Dry FGD - Circulating Dry Scrubber (CDS) or Dry FGD - Spray Dryer Absorber (SDA ) may be used depending upon detailed study.

7. DRY FGD SYSTEM – CIRCULATING DRY SCRUBBER (CDS)
LIME HYDRATED AT SITE i.e. (Ca(OH)2) IS THE SCRUBBING AGENT - INTRODUCED AS A DRY FREE FLOWING POWDER
THE PROCESS INVOLVES EVAPORATIVE COOLING AND RECIRCULATION OF UNREACTED REAGENT – IMPROVES LIME UTILIZATION
90% OF THE SOLIDS (CONTAINING UNREACTED LIME) DISCHARGED FROM ESP or FF ARE RECYCLED TO THE CDS BY GRAVITY USING AIR SLIDES – FRESH HYDRATED LIME ALSO IS FED IN THE ABSORBER BY ROTARY FEEDERS.
EXTREMELY LONG SOLIDS RETENTION TIME ALLOWS HIGH ABSORPTION OF GASEOUS POLLUTANTS AND IMPROVES LIME UTILISATION
BY PRECISE CONTROL OF PROCESS PARAMETERS (GAS DISTRIBUTION, REAGENT FLOW RATE, ETC.) ENSURES FREE FLOWING DRY BY PRODUCT ( CaSO3 / CaSO4)

8. SUITABLE FOR HIGH SULFUR FUELS WITH 98%+ SO2 REMOVAL
DRY FGD SYSTEM – CIRCULATING DRY SCRUBBER (CDS) – CONTD.
SUITABLE FOR HIGH SULFUR FUELS WITH 98%+ SO2 REMOVAL
ABSORBER, DOWNSTREAM DUCTS / COMPONENTS, CHIMNEY ARE CARBON STEEL CONSTRUCTION. NO CORROSION RESISTANT LINING IS REQUIRED.
WATER REQUIREMENT IS LOW.
NO WASTE WATER TREATMENT REQUIRED
ELEVATED ESP / BAGHOUSE

9. DRY FGD – Scheme for Dry Scrubber

10. The reactions occurring during lime scrubbing are :
CDS CHEMICAL EQUATION
The equipment and the processes are similar to those in limestone scrubbing Lime Scrubbing offers better utilization of the reagent. The operation is more flexible. The major disadvantage is the high cost of lime compared to limestone.
The reactions occurring during lime scrubbing are :
Hydrated Lime: Ca(OH)2 (s) + SO2 (g) → CaSO3 (s) + H2O(l)
CaSO3 (s)+ ½O2 (g) → CaSO4 (s)

11. POSSIBLE UTILISATION OF DRY FGD BYPRODUCT
Utilisation in agriculture- Fertiliser
Utilization as Backfilling (combination with fly ash) in road construction
Utilization for Underground mining Filling
Landfill for Low Lying Areas

12. WET FGD SYSTEMS - CHARACTERISTICS
Wet FGD accounts for about 80% of all FGD installation.
Among Wet FGD Systems, Limestone Forced Oxidation (LSFO) most commonly used technology.
ADVANTAGES of WET FGD SYSTEMS
DISADVANTAGES of WET FGD SYSTEMS
Coal Sulphur range from 0.2% to 8%
High Water Consumption
Inlet SO2 ranges from 200 – 6500 ppm
High Auxiliary Power Consumption
SO2 Removal efficiencies up to 99%
Requires Waste Water Treatment
Mature Technology
Alloys or coatings required for corrosion protection
One tower per boiler ( no spare tower required upto 1100 MW capacity boiler.
Wet Stack required
Gypsum / Ammonium Sulphate saleable / marketable by – product
Sulfites formed in Wet lime System are difficult to be disposed off. Conversion into Sulfates also possible.

13. WET FGD SYSTEM CHEMISTRY
Limestone slurry is sprayed on the incoming flue gas. The sulfur dioxide gets absorbed The limestone and the sulfur dioxide react as follows :
Limestone: CaCO3 (s) + SO2 (g) → CaSO3 (s) + CO2 (g)
CaSO3 (s)+ ½O2 (g) + 2H2O(l) → CaSO4·2(H2O)(s)
(Gypsum)

14. TYPICAL WET FGD (LSFO) SYSTEM

15. GGH ENTAILS ADDITIONAL AUXILIARY POWER CONSUMPTION
GAS TO GAS HEATER (GGH) – SOME IMPORTANT CONSIDERATIONS
GGH ENTAILS ADDITIONAL AUXILIARY POWER CONSUMPTION
GGH REQUIRES CONSIDERABLE SPACE FOR INSTALLATION
PRONE TO LEAKAGE FROM UNTREATED GAS SIDE TO TREATED GAS SIDE
GGH ENTAILS HIGH O&M COST DUE TO CHOKING PROBLEM REQUIRING FREQUENT BASKET CLEANING
WET FGD SYSTEMS WITHOUT GGH ARE BEING PREFERRED NOW A DAYS. HOWEVER, WITHOUT GGH CLEAN GAS TEMPERATURE WOULD BE ABOUT 50 – 600C. AT OUTLET OF ABSORBER INSTEAD OF 90 – 950C WITH GGH.
LOW TEMPERATURE CLEAN GAS MAKES SYSTEMS DOWNSTREAM OF ABSORBER PRONE TO ACID CORROSION.
TO AVOID / MINIMISE CORROSION, SUITABLY DESIGNED WET STACK / CHIMNEY WITH LINERS WOULD BE REQUIRED. SUITABLE ACID RESISTANT MATERIAL / LINER FOR THE CLEAN GAS DUCT FROM ABSORBER TO GGH AND TO CHIMNEY ALSO WOULD BE REQUIRED. COMMON CHIMNEY LINERS BEING CONSIDERED ARE BOROSILICATE GLASS, FLAKE GLASS REINFORCED VINYL ESTER, FRP ETC.

16. Conventional Chimney Flue Liner for Retrofit Cases

17. Chimney Flue Liner

18. Conventional Chimney Flue Liner for New Projects

19. Chimney Liner for FGD Systems at NSPCL
For Rourkela PP-II Expansion, due to the operational problems associated with the GGH, we have envisaged the FGD system at Rourkela without GGH.
But due to reduced temperature and increased moisture content of the Flue gases, the Chimney is to be considered as a Wet Stack and appropriate liner has to be provided to avoid the corrosion of the Flue Can.
Various Liners are available in the market and choice has to be made based on technical requirement and cost effectiveness.
Rourkela PP-II Expansion- Titanium cladded Flue Can
Bhilai PP-III- Flue Can cladded with Borosilicate blocks/ C-276/ Ti
For existing PP-II Plants decision on liner shall be taken after detailed study

20. ISSUES & CHALLENGES
NSPCL plants are very old and captive in nature.
FGD retrofit …. Difficult in many of the older stations due to space constraint due to already executed and ongoing R&M.
Technology suppliers are mostly situated abroad and costly.Indigenous manufacturing capacity needs to be developed / ramped up fast due to huge demand of FGD systems.
Large water requirement (about 0.25 m3/hr/MW of Water) for Wet FGD . Increased Aux. Power Consumption with FGD operation (by %).

21. ISSUES & CHALLENGES (Contd.)
Lime stone supply and gypsum off take chain needs to be augmented.
Disposal of Gypsum in environmentally friendly manner.
Time Limit Constraint: Limited time period specified for implementation of FGD for new & old plants. Little progress made in last two year.
Financing & Regulatory Problems:Financing for investment required, impact of investment on cost of generation and Tariff approval remains one of the main concerns.

22. CONCLUSION AND ACTION PLAN
High Capital and operation cost for the proposed system may impact the cost effectiveness of the generated Power.
Rock bottom tariff for Solar Power will pose a big challenge for thermal power.
NSPCL has mostly smaller capacity captive units and non compliance of the new Environment norms may risk the entire Business of NSPCL.
Timely implementation of FGD system to meet the Environmental Norms for
“Safe , Reliable, Efficient and Environment friendly operation of existing and upcoming NSPCL Power Plants”

23. MECON LIMITED
A House of Engineering Excellence

24. WET FGD ABSORBER ABSORBER IMPORTANT FEATURES MATERIAL OF CONSTRUCTION
PH MAINTAINED INSIDE THE ABSORBER IS 5-6
317 LMN STEEL or Equiv. / CARBON STEEL WITH RUBBER / FRP LINING
CARBON STEEL WITH HIGH CORROSION RESISTANT AND ACID RESISTANT CERAMIC LINING
RCC CONSTRUCTION WITH HIGH CORROSION RESISTANT AND ACID RESISTANT CERAMIC LINING