2.2.3 AHP :Control and Instrumentation

2.2.3                 Control and Instrumentation 

                        i)          All instruments like local gauges and switches for pressure/differential pressure (DP)/vacuum/temperature, flow, level; Transmitter for pressure/DP, flow and level, including hopper level, RTDs for temperature measurement, control valves etc. shall be provided as per enclosed tender drawings and as required for safe and efficient operation of the entire plant. 

                        ii)         All required instrumentation cables and junction boxes shall be provided for interconnection of contractor supplied instrument and control device, PLC based control panels and MCC switchgear. 

                        iii)        Control System 

(a)              PLC based control system for the entire ash handling plant 

   (b)        (i)         One (1) no. Main control desk located in the main control room near ash slurry pump house alongwith mimic of entire ash handling plant, push buttons, control & selector switches, lamps, meters & annunciation windows.

                                                            The mimic of the entire ash handling plant alongwith HT/LT switchgears shall be configured on the Operator Work Stations (OWS). 

                                                            One (1) no. processor panel for housing the hot redundant processors. Further, redundant LAN ports shall be provided for integration with Purchaser’s DDCMIS. 

                                                (ii)        Two (2) nos. Bottom ash local control panels with mimic one for each unit for control of various drives in bottom ash area. Necessary push buttons, control/selector switches, lamps, meters, annunciation windows etc. shall be provided.

                                                (iii)       One (1) no. silo control panel with mimic for control of various drives in silo area alongwith necessary push buttons, control/selector switches, lamps, meters & annunciation windows. 

                                                All the above control desk/panels shall include necessary I/O racks.

     (iv)       Remote I/O racks as per system requirement.

     (c)        High & low level switches of ESP Ash hoppers shall be wired to the I/O racks for control, monitoring & annunciation. 

2.2.3.1              Operational Philosophy, Control and Instrumentation 

            a)         Control Panels 

                        Control of various pumps, valves, drives and the system be achieved from the respective control panels to be offered by the Bidder and to be located as  below : 

                        (i)         Main control desk          -           1 no. located in control room near                                                                       Ash Slurry pump house.

                        (ii)        Bottom Ash Local          -           2 nos. (1 for each unit) located in                        control panel                             boiler area at 0.0m.

                        (iii)       Silo Control                   -           1 no. located in Silo area.

                                    panel 

            b)         Basic Control Philosophy

                        Bottom Ash Handling System

                         Bottom ash system shall be manually operated from the local bottom ash control panel of 0.00 m elevation located near the respective Boiler. One no. bottom ash control panel shall be provided for each unit. The operating status of bottom ash handling system equipments of both the units shall be reflected in the mimic diagram of bottom ash handling system mounted in the main control desk in main control room located near ash slurry pump house. 

                        Fly Ash Handling System 

                        Control for each unit fly ash extraction and conveyance plant shall be based on separate programmable logic control (PLC) systems in accordance with PLC specification.     The basic control philosophy is given below : 

                        Fly Ash Extraction 

a)         The main control desk located in main control room near ash slurry pump house common for both the units under the scope of this contract shall also control duct hopper and ESP ash extraction. It will have mimics for indication and control of entire ash handling plant. 

b)         All process control for fly ash extraction of each unit shall be obtained from the main control desk. However, direct local switching of individual drives and actuators shall be possible for maintenance purpose with the necessary basic protection incorporated. “Local/Remote” switching shall disable the relevant remote process control when in “Local” mode. 

c)         The operator will normally pre-set-up the required de-ashing routing and sequence to management instructions. Subject to completion of the necessary permissive and sequence interlocks operator “Start” initiations of the appropriate lines would automatically select and start the service plant for commencement of de-ashing. 

d)         Once started, the systems, will continue in automatic operation as programmed. It shall be possible for the operator to make on-line adjustments to timings, routings, selections etc. with appropriate ‘selection checks’ before “Command” initiation. Also programme interruption shall be possible to effect unscheduled or out of sequence extraction before return to the original programme.

 e)         The emptying of the fly ash collection chute groups to the buffer hoppers or wetting heads will be performed in a pre-determined sequential manner. The command signal for automatic switching over from one group of collection chutes to the next shall be based on the lapse of a set time period. The sequencing of collection chute emptying shall be adjustable, the chute empty signal will be suitably delayed to account for the time required to evacuate the ash remaining below low level probe. 

f)          Manual intervention to permit collection from a collection chute group out of sequence will be provided at the main control desk. This would normally be followed by restarting of the sequence unless further manually directed. Fly ash from ash group of chutes will be pneumatically conveyed to the appropriate intermediate/ surge hopper or storage silo or wetting head. 

       Ash Water System & Bottom Ash Overflow Water System

                         Ash water, seal water pumps, bottom ash overflow water system and associated facilities shall be operated from the main control desk located near ash slurry pump house. The operating status of all ash water, seal water pumps and bottom ash overflow water system shall be reflected in the mimic diagram of ash handling plant mounted on the main control desk. 

Ash Slurry Disposal System 

                        Ash slurry disposal pumps, associated make –up and slurry valves shall be operated from the main control desk located in main control room near ash slurry pump house. The operating status of ash slurry disposal pumps and various valves shall be reflected in the mimic diagram of ash handling plant mounted on the main control desk.

    Silo Area :

                        One (1) no. silo control panel shall be provided for controlling the unloading of ash from two (2) silos. Operating status of various equipments shall be reflected in the mimic diagram of the ash handling plant mounted on the main control desk.

                        The above is only a general description of operational philosophy. The Bidder shall include in his proposal a detailed description of the control system as offered by him and as required for safe operation of the plant, complete with bill of materials, schematic diagrams, description of function of different components, component ratings etc.

2.2.3.2              Protective Interlock Arrangement for Ash Handling System

                        To ensure safe operation of the equipment connected with handing system of bottom ash and fly ash, the following minimum protective features and safety interlocks shall be included in Bidder’s scope of supply. 

i)          It shall not be possible to start the Bottom Ash overflow water pump and ash slurry disposal pump unless the following conditions are satisfied:

                                     a)         Pre-set gland seal water pressure is available.

                                     b)         One stage of pumps shall start only if other stage/stages in the upstream side of this stage is running. (Applicable to series pumping only). 

                                    c)         Suction valve is open 

                                    d)         Main Ash slurry sump and BA overflow water tank level is at or above the preset safe operating level. 

                                    e)         In case of series pumping the sequence of starting of each series of slurry disposal pumps shall be suction valve first, 1st stage pump (closest to suction valve) next, followed by 2nd stage pumps so on and finally discharge valve. This shall be achieved by sequence start control switches. 

                                    f)          By using a suitable device, the interlock requiring the last stage is tripped when discharge valve is closed is to be suitably by passed during a normal starting. However, the pump shall automatically trip if the discharge valve fails to open within a preset time after starting of the last stage pump. 

ii)         The BA overflow water pump and ash slurry disposal pumps shall trip in the event of the following emergency conditions. 

                                    a)         Seal water pressure falls below a preset value (for any stage of pumping). 

                                    b)         Main Ash slurry sump and BA overflow water tank level falls at or below preset danger (low) level. 

                                    c)         If for any reasons one pump stage in a series tank, the other stages of the series shall also trip. (Applicable to series pumping).

                                     d)         Suction/discharge valve is closed.

 iii)        The discharge valve of BA overflow water pumps, ash slurry disposal pumps shall close as soon as the slurry pump/last pump stage in the series has tripped. Discharge valve will open after running of Ash slurry pump stream. 

iv)        a)         It shall not be possible to start the clinker grinder motor unless the preset gland water pressure for the grinder is available and preset water pressure is available at jet pump. 

            b)         In the event of gland seal water pressure falling below preset value, the running grinder motor shall trip and the corresponding hopper gate closed. 

            c)         In the event of an overload on the grinder, the grinder motor shall trip. In such a case, subject to availability of preset gland seal water pressure, the ginder motor shall reverse in short impulses to remove materials jammed in the grinder. After pre-determined cycles, in case jamming is not cleared, the grinder motor shall trip.

             d)         It shall not be possible to open the hopper discharge gate unless clinker is started and running. 

v)         Protective interlocks on fly ash handling system :

             a)         Evacuation initiation and status monitoring check shall include:

                         -           Air pressure/vacuum and flows

                         -           Valves status

                         -           Surge/buffer hoppers/storage silos levels/ESP hopper ash &             Blow Tank/ash transporter  Level

 vi)        Protective Interlock Arrangement for Ash Water Pumps

             It shall be possible to keep any one Ash Water Pumps as standby. Ash Water Pump shall be arranged to start automatically when any one of the working Ash Water pumps trips of Ash Water Line Header pressure falls below pre-set value.

vii)       Level Detection Equipment for Combined Ash Slurry Sump, Ash Water Sumps, Drain Sumps and Settling Tanks of BA overflow water system.

            The Bidder shall furnish the following equipment for the detection of Level is sumps:

a)         High Level & Low Alarms

            Necessary Sump level switches shall be furnished for providing annunciations in Control Panels. The electric switch assembly of the above level switches shall be located outside water space. Horns and other accessories shall be provided for local alarms.

b)         Low Level Switch for Tripping of Pumps

            Low level switches shall be provided for tripping the slurry pumps, for extreme low level (danger level) of sumps.

c)         Level Indicators

            Level indication device complete with local arrow scale type level indicator shall be provided for all sumps.

d)         Tank/Sump Make-up Water Valve

            The Bidder shall supply adequate size valves for installation in the make-up water line to ash slurry sumps/tanks. These valves shall be complete with device for operation form main control panels. The valves shall be ON-OFF type.

viii)       Seal Water Pump Control

a)         It shall be possible to start the seal water pumps only if preset suction pressure is available.

b)         The seal water pump shall trip in the event of suction pressure dropping below preset value.

c)         During normal operation, any one of the two seal water pumps shall be working. On seal water discharge pressure falling below a preset value, the standby pumps shall be automatically switched on subject to availability of preset suction pressure. Starting of this standby pump shall be annunciated in the main control panel. It should also be possible, by means of selector switch provided in the main control panel, to keep any one of the pumps as normally working and other as standby.

ix)        Sump Drainage Pump Controls

            Either of the two (2) sump pumps provided in Ash Supply pump house, BA pumphouse & silo area shall be automatically switched on if the level in the sump rises above a preset level. The second pump shall automatically start if the first pump fails to start when level is high or if the level continues to rise.

                                    The operating pump shall trip in case the sump level goes below a preset level.

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