The document outlines the design requirements for a flue gas desulfurization (FGD) system, aimed to operate for a minimum of 25 years with specific components to manage flue gas and limestone handling effectively. Key components include wet absorbers, gypsum dewatering systems, and a comprehensive water treatment setup, with provisions for redundancy and operational efficiency. Additionally, it details the chemistry involved in sulfur dioxide removal and the expected operation and maintenance protocols necessary for the systems.

1. GENERAL DESIGN REQUIREMENTS
The FGD plant shall be designed for a service life of minimum twenty five (25) years.
Revised Environmental Limitations

2. GENERAL DESCRIPTION OF WET "LS" FGD SYSTEM
"Flue Gas" System
• For each Unit: hot "Flue Gas" tapped from existing ID-Fans O/L  2x60% FGD booster fans  followed by wet "LS" Absorber.
• Treated "Flue Gas" from Absorber O/L  discharged to atmosphere  via new wet chimney 150 m
• During Unit start-up—Oil Firing or Emergency conditions: FGD is bypassed  untreated "Flue Gas"  to atmosphere via existing Old chimney.
Gas to gas heat exchanger (GGH): GGH in FGD has both merits and demerits.
• Advantage:
a) reducing the temp. of inlet Flue gas to Absorber -- reduces damage potential to scrubber/absorber internals.
b) Reheating of treated Flue gas – prevents stack condensation -- increases buoyancy of Flue Gas exiting the chimney
• Disadvantages:
a) additional space; b) additional pressure drop; c) leakage issues; d) adding to the cost to FGD package.
e) Even with GGH, chimney flue(s) may require additional protection by way of lining or resistive painting.
New wet chimney & suggested height

3. PROCESS CHEMISTRY
SO2 + CaCO3 + ½ H2O Þ® CaSO3 · ½H2O + CO2
Carbon dioxide formed from reaction of limestone with SO2 is released into the flue gas.
Oxidation air is bubbled through slurry to convert CaSO3·½H2O to gypsum (CaSO4·2H2O) following reaction:
CaSO3 · ½H2O + ½O2 + 1.5 H2O Þ® CaSO4 · 2H2O
SO2 collection efficiency and energy consumption of an LSFO system can be improved by adding organic
carboxylic acids to the reaction tank. These additives serve as a buffer to stabilize the pH of the slurry as it absorbs the acidic SO2
This improves absorber performance by increasing solubility of SO2 in the slurry which allows operation at a lower L/G ratio
A number of organic acids -- found to be effective -- acids include adipic, glycolic, maleic, acrylic, & formic acids.
Dibasic acid (DBA), a by-product from the manufacture of adipic acid, is usually selected instead of other acids because of its lower cost (about $460 per ton).
(DBA is a mixture of adipic, glutaric, & succinic acids.) If wastewater treatment is required, organic acids have a biological oxygen demand, which may
require removal in an additional water treatment plant.
LSFO systems -- designed without depending on use of organic acids.
Provision -- sometimes included in designs -- to allow future addition in case SO2 collection efficiency is inadequate.
Disadvantages -- organic acids include a) additional operating cost, b) possible contamination of gypsum by-product, c) increased wastewater treatment cost

4. Liquid-to-gas ratio

6. "LS" Unloading, Crushing & Storage System: 02 Streams
• The "LS" of size (-) 250 mm -- received at power plant
• By Truck -- Unloaded & stored at Storage Yard (covered shed)
• The storage area of RCC with covered -- capacity of 15 days "LS" requirement of the power plant.
• "LS" to  the FGD area -- supplied by trucks / dumpers.
• In the FGD area -- 02 streams of "LS" unloading, feeding, crushing & silo storage facility -- common Power Station
• "LS" from unloading hoppers  fed to 02 sets of conveyor belts via 02 vibrating feeders:
a) 01 each placed under each unloading hopper & b) and then  to 02 "LS" crushers via pent house.
• 100% capacity (per hour) of each stream -- feeding & belt conveyor system -- equal to 6-hrs. requirement of both units
(minimum 60 t/h for 2x500 MW units)
• Each stream -- consist of 01 underground receiving hopper + vibrating feeder + conveyer belt (110 % capacity) with telescopic chutes +
2 x 100% crushers (common for both streams) + bucket elevators + 02 crushed "LS" silos -- storage of 24 hrs. requirement
• In case crushed "LS" of size (-) 25 mm is supplied to the plant, 2x100% -- "LS" crushers and bucket elevators shall not be provided and
"LS" conveyor belts after pent house shall be directly led to crushed "LS" silos.

7. "LS" Grinding + Slurry Preparation + Storage System
• 02 streams of "LS" slurry preparation system -- common for Power System.
• 100% capacity (per hour) of each stream -- equal to 3 hrs. req. of 02 units (minimum 30 t/h).
• Each stream -- fed "LS" from crushed "LS" Silo & consist of gravimetric feeder + Wet Ball mill (110% capacity) + Hydro-cyclones + "LS" slurry tanks (12 hrs. req.)
• "LS" slurry storage tanks -- shall be interconnected & provided with 2 x 100 % slurry feed pumps for each Absorber unit.
• "LS“: a) Grinding, b) Slurry preparation & c) Storage system, common Unit(s) of Power station.
• Crushed "LS" from 02 Nos. Bulk Storage Silos  supplied to 2x100% Wet Ball Mills via “Gravimetric feeders” -- Wet Grinding of "LS"
• "LS" slurry -- required fineness “Wet Ball Mill”  stored in 02 "LS" slurry tanks of total 24 hr. requirement of Power Station.
• From "LS" slurry tanks  "LS" slurry pumped to individual Absorber by dedicated 2x100% "LS" slurry transfer pumps.
• Adequate Agitators -- provided for each "LS" slurry tank—consistent concentration of absorbent & to prevent settlement of solids.

8. Absorber System
• Each Unit with a separate "LS" Forced Oxidation (LSFO) type—handles 100% of "Flue Gas" flow @ BMCR for specified coal / "Flue Gas".
• "Flue Gas"  enters from Bottom & Comes in intimate contact with spraying "LS" slurry in the Absorber from Top.
• The "Flue Gas" inlet -- designed to ensure “Flue Gas” is well distributed over the entire Absorber cross-section.
• The "LS" slurry shall be sprayed into the Absorber to saturate the gas and remove the SO2 by LS Slurry recirculation Pumps.
• Each spraying level -- served by 01 "LS" slurry recirculation pump.
• The spray type Absorber: a) multiple spray level type or b) single spray level type shall be as per his proven and standard practice.
• Absorber sump / oxidation tank -- designed to give the "LS" enough time for forming “calcium sulphate” & “crystal growth”.
• Absorber sumps: Agitators  agitating the Slurry -- consistent concentration of absorbent – preventing settlement of solids.
• Fresh "LS" slurry: added in sump by "LS" slurry transfer pumps --to compensate calcium carbonate consumed in Absorber tower & sump.
• Min. 02 level Mist Eliminators / separators: provided in vertical / horizontal position @ outlet of Absorber -- to separate "Flue Gas" from absorbent droplets
• A wash water system -- provided -- for cleaning of mist eliminators at regular interval.
• The emptying of the Absorber -- by Gypsum bleed pumps  into Emergency Storage Tank -- purpose of inspection & maintenance.
• Return pumps shall be provided for the refilling of Absorber.

9. Absorber System
• 01 wet "LS" Absorber tower: of Carbon steel + lining / cladding of SS 317 LMN / Alloy 31/ Hastelloy C22/ C 59/ C276 or equivalent high nickel alloys of suitable
thickness.
• Absorber: "LS" spray nozzles + mist eliminators + wash water nozzles + oxidation air grid + headers & nozzles + agitators + inlet/outlet connections for "Flue Gas"
ducting + manholes + ladders + maintenance scaffolding platforms + hand railings etc.
• Each Absorber tower: provided with multiple "LS" slurry spray levels (minimum 4 nos.) or a single spray level
• In Multiple spray level design: each spraying level—provided with 01 individual "LS" slurry recirculation pump. + 01 spray level -- as spare for 100% availability of
FGD
• In Single spray level design: multiple nos. of Identical “Slurry Re-circulation pumps” available with 01 Pump as standby.
• In case of bubbling type: with "Flue Gas" bubbling via "LS" slurry -- gas distribution system to the slurry & 3x50% gas cooling water pumps provided to cool and
saturate the incoming hot "Flue Gas".
• 01 mist eliminator wash water tank + with 2 x 100% mist eliminator wash pumps (if applicable).
• 01 emergency slurry storage tank (common for both units to store slurry content of 01 Absorber).
• The emptying of the Absorber sump shall be done by the gypsum bleed pumps.
• Tank -- suitably lined, + with agitators + 2 x 100% slurry transfer pumps to pump slurry back to Absorber in 8 hour (max).
• Emergency quenching system including dedicated water tank of adequate capacity, 2 x 100% capacity pumps and associated piping to cool the "Flue Gas" inlet to
the Absorber in case of sudden rise in "Flue Gas" temperature.
• Forced oxidation equipment: 2 x 100% blowers/ compressors for each Absorber, complete with all accessories and silencers.
• 02 x100% gypsum bleed pumps for each Absorber taking suction from the Absorber sump.

10. Gypsum: 02 streams of Dewatering, Handling System,
• Each stream: 1x100 % Primary hydro-cyclone + 1x100 % vacuum belt filter + 2x100% vacuum pump with vacuum receiver + 2 x 100% belt wash pumps.
• Absorber bleed slurry from Absorber sump  fed into gypsum dewatering system through 2x100% capacity gypsum bleed pumps.
• Gypsum slurry coming from FGD units  fed into common 2x100% primary hydro cyclones
• Hydro-cyclones (Primary + Secondary): Gypsum is separated into a) Under flow—solid enriched & b) Over flow—reduced solid content.
• Primary Hydro-cyclone Underflow: contains coarser gypsum particle  fed to 2x100% capacity vacuum belt filters.
• Primary Hydro-cyclone Overflow: collected in Reclaim tank (1 hr. capacity)  taken to Secondary Hydro-cyclone.
• Secondary Hydro-cyclone Underflow: collected in Filtrate tank  taken to “Wet ball mill” / gypsum recovery system. (2 x 100% pumps)
• Secondary Hydro-cyclone Overflow: as waste water -- collected in waste water tank (2 hr. capacity of Station. to reduce chloride level).
• Water from vacuum receiver tank(s) -- recycled to Wet ball mill / gypsum recovery system.
• Gypsum from vacuum belt filter  collected in common storage area on ground floor  transportation by trucks.
• Alternatively, gypsum from discharge of vacuum belt filters shall be collected by transfer belts and conveyed to a separate gypsum storage area from
where it shall be further transported by trucks by the purchaser.
• Gypsum storage: 05 days storage capacity of Power Station.
• Gypsum quality: a) Residual moisture <= 10 %, b) chloride < 100 ppm & c) purity >= 90 % (depending upon purity of available "LS").

11. Waste Water Treatment & Disposal System
• The waste water collected -- in waste water tank of FGD -- provided with adequate treatment & then disposed to existing ash handling system
Water Supply for FGD System
• Clarified water / CW blow down water -- for FGD plant
• Water collected in a MS tank with epoxy painting: water req. of FGD met via horizontal pumps provided with adequate redundancy.
Equipment Cooling Water System
• For equipment cooling water requirement of FGD: DM cooling water tapped from DM cooling water piping of both the existing terminal
points.
• The return hot water from FGD terminated at suitable terminal points on hot water sections of DM cooling water piping.

12. Eliminator Wash Water Supply System
i) Clarified water -- for cleaning Mist Eliminators
ii) 1 service water / clarified water storage tank + 2x100% horizontal centrifugal pumps for cleaning
iii) Input water to storage tanks -- supplied from process water tank.
iv) The tanks -- made of Mild steel with complete with inlet/outlet connections, overflow and drain piping connections, level indicator,
manholes, air vents, and ladder etc.
v) The materials of construction of piping, valves and fittings etc. shall be of proven type as per duty involved and shall be subject to
approval of the purchaser during detail engineering.
vi) The pump discharge piping up to the top of the scrubbers shall be of mild steel.

13. • Adequate nos. LS slurry recirculation pumps + min. 1 standby pump
• 2 x100% Gypsum bleed pumps -- supply of gypsum slurry  to Gypsum dewatering system,
• 2 x 100% make up slurry pumps -- for each absorber
• 2x100% emergency slurry transfers pumps (if required)
• 2 x 100% slurry Recirculation pumps for each mill. Other pumps required as per system requirement shall also be included.
• The pumps -- horizontal type -- designed for continuous operation -- single stage centrifugal
• Slurry pumps -- with design margin of min. 10% in the rated flow & min. 10% in the rated head calculated at duty point of the pump.
• Slurry pumps -- provided with motorized suction and discharge valves.
• In addition -- flushing water lines with MOVs -- provided for each pump for automatic flushing of the pump after shut down.
• The pump casing should be radially split to allow easy removal of impeller.
• Pump wear parts -- in contact with slurry -- provided with replaceable rubber/elastomer liners suitable for the fluid handled.
• Material & thickness of liners -- ensure a min. service 2 years service life before replacement.
• All the wear parts of the pump shall be guaranteed for a minimum wear life of not less than 14000 hrs.
Slurry Pumps

14. Terminal Points
• Flue Gas inlet  to FGD plant: tapped from common outlet duct of existing I.D. Fans
• Treated Flue Gas  FGD Exit: connected to new wet chimney with provision for bypass of raw flue gas to the existing chimney.
• Water for LS slurry: CW blow down water (clarified water) to be tapped from a terminal point suitable to Power Station.
• Clarified Water for cleaning Mist Eliminators, sealing of LS slurry pumps: a terminal point suitable to Power Station.
• Water for Fire Hydrant: a terminal point suitable to Power Station
• Overflow / Drain connections & drain channels of various equipment in areas of FGD: collected in a sump – for recycling in the system
• DM cooling water for equipment cooling: tapped from and returned to suitable terminal points suitable to Power Station
• Service water for various plant areas: tapped from a terminal point suitable to Power Station
• Potable water for various plant areas: tapped from a terminal point suitable to Power Station
• Service air for Equipment Cleaning: tapped from a terminal point suitable to Power Station
• Power supply for FGD: Requisite number of 6.6 kV feeders shall be provided a terminal point suitable to Power Station
• C&I hardwired signal exchange with existing plant: To be connected with Main Plant DCS

15. • 2X100 % Air Blowers -- supply oxidation air in Absorber Sump Tank for oxidizing CaSO3 to GYPSUM--calcium sulphate (CaSO4).
• Minimum redundancy of 10% on oxidation air nozzles/ spargers shall be provided.
• Air supply hdrs. – of FRP or Carbon Steel with min. 10 mm natural rubber lining) corrosions & erosion resistant inner & outer sides (Silicon Carbide coat on metal/FRP exposed to slurry).
• Oxidation Air blowers -- centrifugal/rotary/ +ve displacement type + base frame with shock absorbers, intake filter with hood, silencers, safety valves and check valves etc.
• The blowers -- sturdy construction with various components made of suitable corrosion resistant material.
• Air blowers -- supply at least 2.5 times the stoichiometric air req. for spray tower process & at least 4.0 times the stoichiometric air req. for Bubbling Type process, with 10 % margin
• Air blower -- compact & simple in design requiring minimum number of spare parts.
• Blower -- designed for continuous operation + of water-cooled/air cooled type.
• Rotor blades -- made of chrome steel / equivalent & shall move freely and smoothly in the rotor slots.
• The shaft -- hot rolled steel or equivalent accurately ground, polished and keyed to the rotor & shall run in precision heavy duty roller bearings.
• Lubrication system -- designed such that visual checking of lubricant level is possible.
• The blower -- provided with water jackets for cooling the bearings and the casing and prevent excessive heating of parts.
• The casing -- grey cast iron conforming to IS:210 grade 25 designed for the duty specified.
• One cleanable, dry, air intake filter cum silencer to prevent dust and other atmospheric impurities from entering the blower shall be provided for each blower.
• The silencer -- reduce the noise level to 85 decibels at a distance of 1 meter from the blower.
• The filter area -- at least twice that of the inlet pipe area -- filter shall be suitable for removing dust particles down to 5 microns size.
Oxidation Air blowers

16. • The minimum number of tanks to be provided shall be as mentioned below
• 2 x 100% (one for each unit) LS slurry storage tanks.
• 1 no. (common to both units) emergency slurry tank
• 2 (one for each unit) emergency quenching water storage tank
• 2 (one for each mill) slurry recirculation tank for wet ball mills
• 1 no. (common to both units) reclaim water tank
• 1 no. (common to both units) filtrate tank
• 2 no. (common to both units) waste water tanks
Other Tanks

26. BALL MILLS