1.Specification of Coal Mill Reject System

 

8.0.0                 Intent of Specification  

                        This specification is intended to cover the following activities and services in respect of all the equipments of Mill Reject System for 2×500 MW units. 

8.1.0                 Scheme of Mill Reject System  

                        Pressurised pneumatic conveying system shall be employed for handling of the mill rejects.  Each mill reject discharge hopper shall be fitted with a positive pressure pneumatic conveying vessel which shall discharge the mill rejects through pipe lines in a storage silo.  Each unit shall be provided with an independent silo having collection capacity of 16 Hours.  The transmitting vessel shall operate on level probe mode with timer back up. 

8.1.1                 Mill Rejects System 

Configuration of the Coal Mills of each boiler unit is with side of the boiler with ten (10) Nos. mills.  Each mill is provided with collection and transportation equipment comprising of one no. Pyrite Hopper with water spray arrangement, plate valves at inlet & outlet and a denseveyor or similar pneumatic bulk conveying equipment / vessel.  Each vessel shall be connected to a storage bunker via conveying pipeline of MS ERW Heavy Duty, welded ends and flanged joints at strategic points & bends of Alloy CI, and a terminal box. The MS ERW pipes inner welding beat is to be removed, if welded joints are used. Bidder shall use bevel edged pipe for welded joints and care should be taken to avoid slag formation in the inside surface of the pipe weld joint. Each stream of eight mills shall be connected to one storage bunker.  The bunker shall be of MS Construction & 3 mm SS Liner on conical portion shall be provided with two hand lever operated bunker discharge gate at its outlet to discharge mill rejects into a truck. 

8.1.2                 Conveying Air System 

3 x 100% capacity compressors, considering 2 units requirements i.e. one compressor meeting one unit requirement and one (1) no. compressor shall act as common standby for both the units.  Screw compressors with drive, housed in fly ash handling compressor house of Ash Handling System shall be provided to supply Compressed Air required for conveying mill rejects.  The compressed air system shall have two air receivers (one for each unit), necessary pipe work and a bag filter on storage bunker in each stream to remove dust from the air before venting into atmosphere.

8.1.3                 Instrument Air System  

For equipment operation, instrument air shall be provided at each stream from plant distribution instrument air/ AHP instrument air pipe network to Pneumatic Cylinder Operated Plate Valves, Denseveyor Panel and Bag Filter.  

8.1.4                 Cooling & Spray Water System 

Cooling water requirements of items such as Water Cooled Top Plate of Dome Valve in Denseveyor Assembly shall be met from the ACW system.  Necessary pipe work for this shall be provided in this system.   

Cooling water requirements of Convey Air Compressor shall be met from ACW circuit.  Necessary pipe work – supply & return shall be provided in this system.    

Spray Water for mill rejects quenching shall be sourced from Service water and sprayed in Pyrite Hopper through solenoid valve operated spray nozzle.  

 8.1.5                 Other Areas 

The pipes in mill bay area shall be supported from mill bay columns wherever possible; pipes from / to compressors shall be taken on pipe rack to mill bay, utilizing pipe rack.  However where such pipe rack / structures shall not be available, Bidder shall provide independent pipe rack.  

 VENDERS 

1 www.dcips.com 

2 www.bsbkgroup.com 

3 www.mcnallybharat.com  

 

1.M/s. Indure Pvt. Ltd.,Indure House, Greater Kailash Part-II,New Delhi – 110048

2. M/s. Macawber Beekay Pvt. Ltd.,Beekay House, L-8 Green Park Extension,New Delhi ,110016. 

Phone : 011-26193396, 26163447 Fax: 011-26192566.

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 www.specahp.wordpress.com

www.specchp.wordpress.com

www.specinstrumentation.wordpress.com

2.Scope of Work – Mill Reject System

Scope of Work

           

                        Bidder’s scope starts from outlet of mills upto mill rejects storage silo including pyrite hoppers, denseveyors / air lock vessels,  dome valves, piping, valves, fittings, transport air compressor, air receiver, storage bunker, and associated structural works, electricals and PLC based control systems.  Necessary grouting for equipment installation is included in the scope.   Scope of Supply and erection shall include followings :

 

8.2.1                 16 sets of Pneumatic cylinder operated Plate /Gate valve at Mill outlet for each unit (one set for each mill of a unit).

 

8.2.2                 For each unit 8 sets of Pyrite Hopper with sizing grid, Flexible joint, Rupture Disc. By pass Chute, over size material chute, water spray nozzle and supporting structure.

 

8.2.3                 16 sets of RF Type Level Probes for Pyrite Hopper High / Permissive for each unit.

 

8.2.4                 8 Nos. of Temperature Switch for Pyrite hopper of each unit.

 

8.2.5                 8 Nos. of Hand Wheel Operated Plate Valve at Pyrite Hopper outlet of each unit.

 

8.2.6                 8 nos. of Hand wheel operated Plate valve at Over size discharge chute of Pyrite Hoppers of each unit.

 

8.2.7                 8 nos. of hand wheel operated Plate valve at By Pass chute of Pyrite Hoppers of each unit.

 

8.2.8                 8 nos. of Denseveyor/Mill reject transporter complete with Dome valve, Outlet bond, Pneumatic Panel for each unit.

 

8.2.9                 1 No. of Terminal Boxes with Up-stand, 1 no. Mill Reject Storage Bunker, 2 nos. Hand Lever Operated Bunker Discharge Gate at Mill Reject Bunker outlet, Bay Filter on Bunker top with associated instruments, RF Type Level Probes for high Level in Bunker and Pressure Relief valve for Bunker for each unit.

 

8.2.10               MS ERW (H) Pipes for Mill rejects conveying and associated Ni-hard bonds, 45^o segments etc.

 

8.2.11               3 nos. of conveying air compressor (screw  type) out of which two (2) working and one standby for two (2) units shall be installed for conveying the mill rejects to bunker 1 no. of Air Receiver with instruments & accessories shall be installed for each unit.

 

8.2.12               1 Lot of Pipe work for conveying Air, Instrument Air, Cooling Water for Dome Valve top plate, Cooling water for Quenching in Pyrite Hopper, Cooling water for air compressor etc. complete with valves, fittings, temperature / pressure gauges, pressure switches and other instruments.  

 

8.2.13               one (1) set of PLC based control & instrumentation system for the unit along with Battery and charger system and UPS for CPUs based MMI system with peripheral devices.   This system shall be envisaged to locate in Main Control room in Ash Handling.

 

8.2.14               one (1) no. of Mimic Panel & mosaic based control desk with window facia annunciation system.

 

8.2.15               Two (2) nos. PC based man-machine interface system consoles i.e. operator with CRT monitor, Key board, Mouse, Printer etc.

 

 

3.System Design

8.3.0                 System Design

 

a)         Denseveyor/ Convey Pipe/ Pyrite Hopper:

 

Design Conveying Rate	:	0.48 tph/mill Continuous basis
Bulk Density of Mill Rejects (volumetric flow and Bunker volume)	:	1.6 t/cu.m
Average conveying velocity	:	3.5 to 6.0 m/sec.
Max. particle size of mill rejects	:	(-) 32 mm
Normal particle size	:	(-) 20 mm

                       

Denseveyor vessel of adequate capacity to convey 480 kg/hr. of generated reject mill shall be provided.

 

b)         Mill Rejects Storage Bunker

 

A mill reject storage bunker of 24 hrs. storage capacity is provided for seven mills of each unit.

 

·                  Reject generation rate per mill    :            0.48 TPH

 

·                  No. of mills per unit                        :      8 Nos. with 7 mill operating                                                                    with worst coal

 

 

·                  Storage capacity                 :      0.48 x 7 x 24 = 80.0 Tonnes

 

            c)         Conveying Air Compressor

 

To cater the compressed air requirements of mill rejects handling system of each Boiler unit, 3 Nos. (2W+1S) air compressors (non-lubricated, reciprocating type) for two (2) units are to be provided for conveying air.   For compressor sizing purpose, 8 mills of one unit and simultaneous operation of 2 Denseveyor shall be assumed (one from each Mill bay/ unit).   Each stream of mills shall be equipped with an Air Receiver of adequate capacity catering to the requirement of conveying air of denseveyor vessel in operation.   Conveying air compressors for mill reject handling system shall be located in the AHP compressor building for Ash Handling Plant.

 

Total Two (2) nos. air receivers for two (2) units shall be provided in the system.   Necessary pipe work for conveying air distribution purpose, comprising of MS ERW (H) pipes, standard fittings and valves shall be provided in the system.   Piping shall be adequately sized as per standard air flow velocities.

 

Based on above, each mill bay vessels would be conveying one after another.   If system of one mill goes out of order or is not in line or in block condition, the system shall shift on to the next mill automatically.

 

d)         Instrument Air

 

instrument air at 5-7 bar (g)required for operation of pneumatic cylinder operated valves, inlet/plate/ dome valve actuator, insert seal of inlet/ plate/ dome valve and for bag filter shall be sourced from plant instrument air system.

 

e)         System Operation

 

The pneumatic cylinder operated plate valve at mill outlet (Pyrite Hopper inlet) is normally kept open.   Mill rejects from coal mill drop into the Pyrite Hopper.

 

The High Level Probe in Pyrite Hopper shall pick up when Pyrite Hopper is full.  The pneumatic cylinder operated plate valve at Pyrite Hopper Outlet is normally kept in open position, as it is a maintenance valve.

 

Inlet/ Plate/ Dome valve top plate of Denseveyor shall be provided with continuous cooling water supply to protect the insert seal through cooling water system sourced from ACW circuit.   Level Probe in Pyrite Hopper shall be set to pick up when mill rejects reach a preset level (high level or permissive level) generally kept equal to Vessel volume.  Whenever Level probes pick up, the inlet/ plate/dome valve of Denseveyor shall be actuated to open to allow gravity feed of mill rejects into Denseveyor.   After a preset time lapse, inlet/ plate/ dome valve shall be closed, insert seal is inflated through instrument air supply.   Compressed air from Convey Air line shall be then injected to the Denseveyor to convey mill reject to the storage bunker via pipe work and terminal box.   On completion, the vessel pressure drops down to a preset value and the system is reset for next cycle commencement signaled by the Level Probe in Pyrite Hopper.   As a backup to this, a timer provision shall also be made in control system.  The batch cycling operation and conveying of mill rejects goes on till high level in storage bunker is sensed on which further conveying to bunker is stopped till bunker is evacuated.  The mode of operation shall be same for all mills.   In each stream, vessels are in operation one by one.

 

4.Control System

8.4.0                 Control System

 

a)         Description & Operation of Relay Based System

 

Mill Rejects Handling System for all the two (2) units shall be operated and controlled from Relay based Control desk housed in Ash Handling System Control Room building.  The control desk shall house Alarm Annunciators, Indicators, Indication lamps, start/stop push button, Selector Switches, Relays etc.   It shall also have mimic diagram depicting the entire Mill Reject Handling system for all the mills.

 

b)         Control System for a Typical Denseveyor

 

One no. plate valve is provided between the denseveyor & the pyrite hopper.  This is a maintenance valve & shall generally remain open.

 

One no. Bag Filter alongwith level probe and pressure switch for checking the clogging of bag filter is provided on Bunker.   The Bag Filter is to be switched on by the operator before starting the Denseveyor system.   Mill rejects from the Pyrite hopper shall be conveyed through the Denseveyor to the respective bunkers provided the level of that particular bunker is not high (checked from the level probe of the bunker).   In case of clogging of bag filter, alarm is initiated, the conveying cycle in progress shall be completed, system shall stop and alarm shall be raised.

 

All the conveying systems are identical.  Denseveyor can work in timer as well as in level probe mode.   In probe mode as the Pyrite hopper level picks up or in timer mode after a preset lap of time, the conveying cycle starts.

 

If during conveying, any system observes the line block condition and does not get cleared for next 5 minutes (adjustable), this shall be considered as system not conveying.  Conveying from other Denseveyor systems shall continue.

 

c)         System Operational Philosophy

 

Complete Mill Rejects system shall be operated from a dedicated Relay based Control Desk.   Mimic shall be available on Middle of the control desk for both the units and common facilities.

 

To indicate the alarm conditions, the Annunciation fascia shall be on the top of Control desk.   Whenever a fault is generated, respective flag shall start flashing and alarm shall be raised.  When accept is initiated through push button, sound shall be muted and LED flashing shall be stopped.  The respective window’s LED becomes normal after resetting, provided the fault is cleared.

 

Conveying System operation shall also be controlled through Control Desk.

 

Logic of Operation for Mill Rejects Systems:

 

·                  Operation of all the systems is totally independent of each other.  Conveying cycle for any system could be started/ stopped at any time irrespective of status of any other systems.

 

·                  Complete Mill rejects system shall be operated in auto mode from control desk.

 

·                  One no. Start/Stop selector switch shall be provided on Denseveyor pneumatic panel of each system.  These selector switches are normally kept in start position.   Similarly, one no. Start/Stop selector switch shall also be provided on Control desk.  The system can’t run if it has been stopped from pneumatic panel or control desk.

 

·                  A timer is generated in the system to select only conveying systems (one from each unit/ mill bay) out of 6 (operating 5 mills maximum).   In case of emergency, additional streams shall be force started from control desk.

 

·                  Whenever “Conveying System stop” button is pressed from control desk, the running systems of that unit shall complete their current conveying cycles and then stop.

 

                        Pneumatic Panel for Denseveyor and associated plate valves:

 

·                  One no. Pneumatic panel common for each Denseveyor and associated plate valves at Pyrite hopper inlet and outlet shall be provided.

 

·                  This panel shall be mounted on the pyrite hopper support structure.  One Start/ Stop selector switch shall be provided on this panel, which shall be wired up in series through control desk with the Start/ Stop selector switch.

 

·                  The pneumatic panel selector switch shall always be kept in start position to enable the operation of the Denseveyor.  This switch shall be put to stop position only during maintenance.

 

·                  Besides this switch, one push button for Purge operation & another push button for Probe override operation shall also be provided on this panel.

 

·                  Power on indication shall also be provided on the pneumatic panel.

 

·                  Open and close buttons are also provided on pneumatic panel for plate valve at pyrite hopper inlet and outlet for maintenance purpose.

 

·                  Pressure switches, Pressure gauges, solenoid valves etc. are provided inside this panel as per the system requirement.

 

            d)         List of Annunciations

 

In the event of faults listed below, respective indication on annunciation fascia on control desk starts flashing followed by sounding of hooter.  Once the operator presses the ‘Accept’ button provided on the control desk the hooter mutes & the flashing becomes steady.  Upon pressing ‘Reset’ button provided on control desk the colour resumes original provided the fault is cleared.

 

Annunciation Points:

 

i)          Bunker level High

 

ii)         Seal Fail Fault

 

iii)        Convey Air Fail

 

iv)        Line Block

 

v)         Plate Valve at Pyrite hopper inlet and outlet fail to Open

 

vi)        Mill rejects hopper level Hi-Hi

 

vii)       Instrument Air   Fail

 

viii)       Service water Pr. Low

 

ix)        Compressor – 1/2 Fault/ Trip

 

5.Inspection and Testing

Inspection and Testing

 

                        In addition to the requirements indicated under the sub-sections enclosed, the following tests shall be conducted:

           

8.5.1                 Tests at Shop

 

                        Tests for the equipment including compressor and Motors shall be carried out at Manufacturer’s/ Sub-Vendor’s works during & after completion of manufacture of different component parts in accordance with requirement of relevant codes and standards.

 

                        The particulars of the tests and their procedure shall be submitted to the Purchaser for approval, before conducting the tests. Test results shall also be submitted after conducting the tests, for Purchaser approval.

 

                        Where stage inspection is to be carried out for witnessing the dynamic balancing of rotating parts and for witnessing tests as mentioned, the successful Bidder shall submit to the Purchaser at the initiation of the contract, the detailed PERT chart showing the manufacturing programme and indicating the period where Purchaser’s inspection agency are required at the shop for witnessing the tests.

                        All equipment shall be tested at shop with actual operating condition and with actual Job motor. Transportation of motor from motor manufacturer’s shop to the test facility and return to motor manufacturer’s shop is under respective vendor’s scope of work.

 

8.5.2                 Interchangeability

 

                        Components of all equipment of similar type and hang similar design parameters shall be interchangeable with one another.

6.Performance Guarantee

Performance Guarantee

 

                        The equipment to be supplied under this specification shall meet the guaranteed performance specified in enclosed data sheets. The acceptance of the equipment shall be subject to the satisfactory achievement of these parameters during testing and commissioning by the Contractor.

                       

                        If the plant and equipment sets fail to meet the guarantee with respect to the agreed parameters, the Purchaser reserves the right to reject or accept the equipment / plant after assessing the liquidated damages computed as below. If the total power input to the drive motor exceeds the guaranteed figure indicated by the contractor in the “Guarantee Data” Schedule, liquidated damages shall be imposed at the rate as indicated under the head “Liquidated damages” in Conditions of Contract.

 

 

 

 

                        The equipment to be supplied under this specification shall meet the guaranteed performance specified in enclosed data sheets. The acceptance of the equipment shall be subject to the satisfactory achievement of these parameters during testing and commissioning by the Contractor.

                       

                        If the plant and equipment sets fail to meet the guarantee with respect to the agreed parameters, the Purchaser reserves the right to reject or accept the equipment / plant after assessing the liquidated damages computed as below. If the total power input to the drive motor exceeds the guaranteed figure indicated by the contractor in the “Guarantee Data” Schedule, liquidated damages shall be imposed at the rate as indicated under the head “Liquidated damages” in Conditions of Contract.

 

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