2x58 MW Coal Fired Power Plant at Mauritius The coal-fired power plant produces electricity by the burning of coal and air in a Circulating Fluidized Bed Combustion Boiler (CFBC), where it heats water to produce high pressure and high temperature steam. The steam flows through steam turbine which spins an electrical generator to produce electricity. The exhaust steam from the turbine is cooled in an air cooled condenser, condensed back into water, and returned through regenerative heaters to the steam generator to start the process over. Following is the flow processes Coal is transported form coal jetty using an external pipe conveyor to crusher house. 1. Coal is conveyed through coal conveyor from crushed stock pile to coal bunkers. 2. This crushed coal is then fed to the CFBC boiler where it rapidly ignites. 3. Water required for steam generation and other uses is generated in an water treatment plant which uses the water discharged from the Motagne Jacquot sewage treatment plant of Mauritius. 4. Demineralized Water of required purity (from demineralised plant) flows vertically up the tube-lined walls of the boiler, where it turns into steam, 5. The steam is piped to the steam turbine where it rotates the blades of the turbine and is coupled on the same shaft to a three-phase electrical generator which generates electricity at an intermediate level voltage (11 kv). 6. The exiting steam from the steam turbine is condensed in an air cooled condenser. 7. The condensed steam goes to the regenerative cycle through two low pressure heaters, deaerator, boiler feed pumps and high pressure heaters back to the boiler. 8. The generator transformer steps up the electricity generated in the Generator to a voltage (66 kv) suitable for transmission and sent out onto the three-phase transmission system through a gas insulated switchyard (GIS). 9. Exhaust gas (flue gas) from the boiler is drawn by the induced draft fan through a bag filter and is then vented out into the atmosphere through the chimney. 10. The fly ash obtained after burning the coal is transported through trucks and bottom ash also in trucks into the ash pond. Please refer Enclosed Process Flow Diagram (Annexure-1 to Attachment-4) and Schematic Block Diagrams (Annexure-2 to Attachment-4) depicting the process. Page 1 of 6
DESCRIPTION OF THE NEW TECHNOLOGY PROPOSED 1. The main pieces of equipment forming part of the Facility and their expected characteristics are: 1.1. Steam Generator 1.1.1 There are two boilers manufactured by Bharat Heavy Electricals Ltd, India (BHEL). Each boiler shall be of natural circulation, single drum, outdoor type, designed for firing coal as the principal fuel. The complete furnace section is of water cooled weld wall type, arranged as a gas and pressure tight envelope. Details of the operating parameters of each boiler at 100% Boiler Maximum Continuous Rating ( BMCR ) condition are as follows: (a) Superheater ( SH ) Steam flow: 239 t/h (b) Superheated Steam Pressure at Main Steam Stop Valve MSSV: 106 kg/sq. cm (g) (103.9 bara) (c) Superheated Steam Temperature at SH outlet: 540 deg C (+/- 5 deg. C) (d) Feed water Temperature at economizer inlet: 237 deg C (e) Stability at Lowest Load: minimum 30 % of BMCR THE SALIENT DESIGN FEATURES OF THE BOILER ARE AS FOLLOWS: - Balanced draft furnace at furnace outlet - High Efficiency Cyclones - Natural circulation - Front Bunker arrangement - Suitable for dry ash handling system for furnace bottom, Economizer - Air heaters and Bag/Fabric filters hoppers - Variable Frequency Drive controlled Drag Link Feeders. - Horizontal Tubular Air preheater - Radial Forced Draft /Secondary Air fans with silencer - Radial Primary Air fans with silencer - Radial Induced Draft fans with hydraulic coupling drives. Page 2 of 6
- Light Diesel Oil pumping unit with firing capacity of 30% Boiler Maximum Continuous Rating. 1.1.2 The long residence time along in combination with temperature allow both the decomposition of limestone and the subsequent capture of sulphur and formation of gypsum which results reduction of SO 2 : 200 mg / Nm3 at Chimney outlet. Staged combustion, at controlled low temperatures (900 Deg. C), effectively suppresses NOx formation which results in reduction of NO x : 200 mg / Nm3 at Chimney outlet. Fabric Filter shall be designed to meet the Particulate Matter: <30 mg/nm3 with all compartments in service at Chimney outlet. To measure the above parameters necessary analyzers shall be provided. SO 2, NO x and PM shall be maintained in-line with EIA Licence conditions. 1.1.3 Noise Level Noise level inside the plant shall be maintained at 85 db @ 1.0 mtr which in-turn meets the noise level requirement of 70dB at plant boundary. The two boilers use a common Reinforced Cement Concrete ( RCC ) chimney with twin steel flue. Each boiler has its own flue or sleeve within the chimney. The height of the chimney is approx. 110 m. 1.1.4 Codes and Regulations for boiler All the pressure parts of the main boiler sections of this proposal will be designed in accordance with the current applicable ASME Standards. For the main boiler pressure part section, the materials used shall be in accordance with ASME Materials and ASME published stress values. For the non-pressure parts, internationally acceptable codes and standards shall be used. All materials used for non-pressure parts will conform to ASME or Indian Standards or equivalent International Standards. Page 3 of 6
The manufacture of the equipment will be done as per ASME. The shop inspection and all NDE tests will be carried out as per ASME. 1.2 Steam Turbine and Alternators 1.2.1 Steam Turbine Two numbers regenerative, condensing Steam Turbine shall be driving the Alternator. Technical Specification of the Steam Turbine is as follows: (a) Type of steam turbine : regenerative condensing Steam Turbine (b) Inlet Steam Pressure and Temperature: 106 ata & 535 Deg.C (c) Exhaust Steam Pressure : 0.11 ata at 27 Deg.C (Ambient Temperature) (d) Vacuum steam extraction. : Steam Ejector Steam Turbines shall meet the specifications and heat rates as set out in Annexure 1 of this Appendix 4A 1.2.2 Alternators Two alternators manufactured by Bharat Heavy Electricals Ltd. Each includes a multi-stage regenerative steam turbine and a 11kV alternator, running at 3000 rpm with a name plate rating of 72.5 MVA for each unit. Technical Specification of the Alternators are as follows: Type : CACW Rated Power : 58 MW Rated Voltage : 11 kv Power Factor : 0.80 (lag.) Rated Frequency : 50Hz Number of Phase : 3- phase Mode of Excitation : Brushless Excitation The design of turbine & alternator shall be in accordance to DIN and IEC 60045. Page 4 of 6
2. TECHNICAL DESCRIPTION OF FABRIC FILTER 2.1. FILTER CHAMBER: The Fabric Filter selected for the given gas parameters will have four chambers in total, arranged as per the enclosed sketch. The raw gas coming through the inlet duct manifold enters the raw gas chambers of the Fabric Filters and clean gas leaves the Fabric Filter through outlet duct manifold. The gas is distributed among all chambers simultaneously. The chambers are made up of mild steel material. Each compartment comprises of three segments viz. clean gas chamber, raw gas chamber and hopper. The general arrangement sketch is enclosed herewith. 2.2. TUBE SHEET: Each chamber is partitioned into raw gas chamber and clean gas chamber by providing a horizontal plate, known as tube sheet. The tube sheet has got a number of circular holes in the longitudinal and transverse direction with constant pitch. The tube sheet is of mild steel and supports the cages & bags. 2.3. FILTER BAGS & CAGES: The bags are made out of suitable bag material. The bags will be of cylindrical shape, with nominal diameter of 150 mm and length of 7000 mm. The bags are hung vertically from the tube sheet. In order to ensure verticality and retain the cylindrical shape of the bag, the cage fabricated from carbon steel wires is inserted inside the bag. The snap rings provided at the bag top hold the bag in place in the tube sheet, providing a gas tight seal between the raw gas and clean gas sections of the system. 2.4. HOPPER: There will be four hoppers - one below each raw gas chamber. The hoppers are fabricated from 5 mm thick carbon steel. The bottom portion of the hopper walls is provided with heating chamber along with tubular type electrical heaters. One number of ash level indicators is envisaged in each hopper to indicate the high level of ash in the hopper. The bottom of hopper will be provided with a square flange of 400 x 400mm opening for connection to dust disposal system. 2.5. DAMPERS: At inlet and outlet opening provided in the duct manifolds for each chamber, there will be two dampers with pneumatic actuator to isolate the chamber in case of need. 2.6. PULSING SYSTEM: The pulsing system consists of a set of blow pipes for each compartment, one air distributor for each compartment, solenoid operated diaprahgm type pulse valve for each blow pipe, compressed air line from storage vessels. The storage vessel is connected to the air distributors through mild steel pipelines. One blowpipe feeds Page 5 of 6
pulse cleaning air to all the bags arranged in one row, at a time. The air from the air distributor is allowed to the blowpipe through the pulsing valve, which is opened for a short duration automatically at a preset internal of time. 2.7. Fabric filter by-pass is provided during oil firing (initial cold start) to prevent possible damage to fabric filter. 2.8. PLC: The Programmable Logic Controller (PLC) supplied for the Fabric Filter will take care of the operation of pulse valves during pulse cleaning and control of Motor Control Centre (MCC) feeders while MCC feeders selected in auto. The PLC has provision to connect to Distributed Control System (DCS) through communication to know the status of applicable Fabric Filter parameters. 3.0 Air cooled Condenser (ACC) The ACC unit is designed in multiple modules. Each module consists of a number of finned tube bundles. The bundles are arranged in A-Frame shape. Each module is served by one axial flow fan driven by an electrical motor via a gearbox. The mechanical equipment is located underneath the tube bundles, delivering cooling air in forced draft mode. The steam from the turbine exhaust flows through the duct, riser/s to the manifold at top of the tube bundles. The steam enters the primary modules first. The uncondensed steam enters the secondary modules from the bottom header, operating in reflex mode. The non-condensable are removed at the top of the secondary modules. The condensate is drained from the bottom headers through condensate drain lines to the Condensate Storage Receiver (CSR). The condensate is pumped back to the deaerator by condensate extraction pumps. Semi-Automatic Fin cleaning system is provided to maintain the heat transfer efficiency. The Wind wall is provided to arrest cross winds & avoid recirculation. Page 6 of 6