Process Description for Steam Generation (ADNOC LNG Operations)

: 10 : 31 -1.1 PROCESS DESCRIPTION Page 31 -1.1.1 Design Basis 12 31 -1.1.1.1 Introduction 12 31 -1.1.1.2 Process Description of Steam Generation 16 31 -1.1.1.3 Description of System 18 31 -1.1.1.4 Process of Steam Distribution 21 31 -...

: 10 : 31 -1.1 PROCESS DESCRIPTION Page 31 -1.1.1 Design Basis 12 31 -1.1.1.1 Introduction 12 31 -1.1.1.2 Process Description of Steam Generation 16 31 -1.1.1.3 Description of System 18 31 -1.1.1.4 Process of Steam Distribution 21 31 -1.1.2 Equipment D escription 25 31 -1.1.2.1 Boilers 25 31 -1.1.2.2 Forced Draft Fans 37 31 -1.1.2.3 Seal Air Fans 39 31 -1.1.2.4 Deaerators 40 31 -1.1.2.5 Feed Water Pumps 42 31 -1.1.2.6 Waste Heat Boiler Feed Water Pumps 44 31 -1.1.2.7 Chemical Dosing Pumps 45 31 -1.1.2.8 Condens ate Lift Pumps 46 31 -1.1.2.9 Deaerator Make up Pumps 47 31 -1.1.2.10 Spray Water Pumps 47 31 -1.1.2.11 Feed Heaters 47 31 -1.1.2.12 Continuous Blowdown System 48 31 -1.1.2.13 Blowoff System 48 31 -1.1.2.14 Condensate Collection Pump and Receiver 50 31 -1.1.2.15 Distribution Headers and Pressure Reducing Stations 52 31 -1.1.3 Support Services 57 31 -1.1.3.1 Cooling Water System 57 31 -1.1.3.2 Jacket Water 59 31 -1.1.3.3 Instrument Air 60 31 -1.1.3.4 Nitrogen 60 31 -1.1.3.5 Chemical Dosing System 60 31 -1.1.3.6 Electri cal System 62 : 11 : 31 -1.1.4 Instrumentation and Control 63 31 -1.1.4.1 Burner Control and Safeguard System (BMS) 63 31 -1.1.4.2 Boiler Combustion Control system 64 31 -1.1.4.3 Master Pressure Controller (BMC) 65 31 -1.1.4.4 SH Header Pressure Controller 67 31 -1.1.4.5 Fuel Gas Flow Control 68 31 -1.1.4.6 Combustion Air Flow Control 69 31 -1.1.4.7 Lead/Lag Combustion Air/Fuel Gas 71 31 -1.1.4.8 Attemperator Controls 72 31 -1.1.4.9 Three Element Steam Drum Level Control 73 31 -1.1.4.10 Boiler Feed Pump Speed Cont rol 74 31 -1.1.4.11 Automatic Start of Standby Boiler Feed Pump 75 31 -1.1.4.12 Pressure Reducing Stations Controls 76 31 -1.1.4.13 Governor System for Variable Speed Turbines 78 31 -1.1.4.14 Variable Speed Fluid Coupling -FD fan 31 -K-1A 79 31 -1.1.4.15 Automati c Start of Standby Pumps 81 31 -1.1.4.16 Boiler (Burner) Management System (BMS) 83 31 -1.1.4.17 Boiler Control of Electrical System 84 : 12 : 31 -1.1.1 Design Basis 31 -1.1.1.1 Introduction Four in number Foster Wheeler single drum, radiant (SN type) boilers, 31 -F-1, 2, 3 & 4 manufactured by IHI, generate the steam required for LNG Plants Trains 1&2. These boilers are single drum, natural circulation, natural gas fired outdoor installation with water -cooled furnace, superheater, economiser and evaporat or. Each boiler is divided into two sections, the furnace and the heat recovery area. The furnace is the entire front section of the boiler where combustion takes place. The furnace floor, roof, front wall, rear wall and sidewalls are made up of water w all tubes. The front wall contains the nine (9) burners which are arranged in three horizontal rows. The accessories for each boilers includes two forced draught fans, boiler feed water pumps, feed heaters and seal air fans. FLOW CONTROLLER FLUE GAS ANALYSER BLR WATER CONDUCTIVITY ANALYSER BURNERS C3 C2 C1 B3 B1 B2 A3 A2 A1 FLOW INDICATOR GAS AIR FLOW CONTROLLER PRESSURE CONTROLLER STEAM FLOW INDICATOR TEMPERATURE CONTROLLER PRESSURE TRANSMITTER FEED WATER STEAM DRUM LEVEL INDICATOR STACK Simplified Diagram of Boiler : 13 : The Four steam generating units are arranged to operate as two pairs, each with a maximum continuous rating of 360,000 Kg per hour, (360 Tons/hr.) and producing superhea ted steam at a pressure of 62 barg and temperature of 440 0C to drive two steam turbine generators, as well as process Train -1&2 compressors. These boilers also supply steam to two distribution networks, consisting of several pressure levels that serve th e Train 1&2 areas. Summary of design Condition Type IHI -FW single drum radiant type (SN type) Boiler capacity 360,000 Kg/h at M.C.R. 388,000 Kg/h at Peak Rating (2 hours) Design pressure 76.5 barg (78 Kg/cm 2g) Working steam pressure (Superheater ou tlet) 62 barg (63.3 Kg/cm 2g) Working steam temperature (Superheater outlet) 440ºC (at M.C.R.) Feed water temperature (economiser inlet) 149ºC Air temperature 28ºC Firing system Natural gas firing Draught system Forced draught : 14 : Anticipa ted Performance Data (Natural Gas Firing) Description MCR Peak Rating Unit Evaporation 360000 388,000 Kg/h Pressure Economiser inlet 70.5 71.6 barg Superheater outlet 62 62 barg Temperature Economiser inlet 149 149 ºC Final superheater outlet 440 440 ºC Boiler efficiency (Based on lower calorific value of fuel) 84.7 84.2 % Fuel consumption (as fired) 22,600 24,400 Kg/h Air flow (furnace inlet) 392,000 423,000 Kg/h Gas flow (furnace outlet) 414,600 447,400 Kg/h Heating Surface and Furnace Volum e Heating surface Furnace area 854 m 2 Heat recovery area 704 m 2 Superheater 823 m 2 Evaporator 766 m 2 Economiser 2025 m 2 Total 5172 m 2 Furnace volume 1011 m 3 : 15 : Quantity of Water in Boiler Unit Normal water Level condition Full water condi tion Units Drum 10.1 21.6 m 3 Furnace and heat recovery area tubes 43.6 43.6 m 3 Superheater --- 11.0 m 3 Evaporator 10.5 10.5 m 3 Economiser 18.9 18.9 m 3 Total 83.1 105.6 m 3 : 16 : 31 -1.1.1.2 Process Description. Steam is generated in four boilers and supplied at 62.0 barg and 440 0C, as super heated steam. Each boiler is capable of generating 360 tonnes/hr. as maximum continuous rating (MCR), or 388 -tonnes/hr. peak rating which can be maintained for up to 2 hours. The fuel is natural gas and rout ed through knock out drums . This is to remove entrained liquid. The outlets of the knock out drums are routed to a common header, and then to individual boilers. There are nine fuel gas main burners on each boiler and nine pilot fuel gas burners . Elect ronic igniters light these pilot burners. The main fuel gas burners are capable of maintaining boiler MCR with one burner out of service. A burner safe guard system, ensures that start permissive, and sequences are observed during boiler start -up. The co mbustion air for each boiler is supplied by two forced draught fans driven by variable speed steam turbines. Boiler 31 -F-1“A” Fan is provided with a dual drive, steam and motor. No.4 Boiler “A” fan is driven by a motor. This facility permits the start u p of boilers when steam is not available. Air from two forced draught fans is supplied to the separated wind boxes (one for each burner). The air flow from the separated windbox is not only rotated but also regulated by the burner registers and is mixed w ith the fuel, and then flows into the furnace. The hot furnace gases give heat to the furnace water walls. The gas flows across the screen at the upper rear of the furnace, and enters the heat recovery area (HRA). In the HRA section, the gas heats the horizontal convection superheater and evaporator, the upper and the lower economiser sections as well as the water walls. At the bottom of the HRA, the gas leaves the boilers and is discharged to atmosphere through the stacks . : 17 : The boilers are op erated in pairs. Each pair of boilers is provided with three feed water pumps, two steam turbine driven and one motor driven. Each pump is capable of supplying 125% of the feed water requirement of one boiler at MCR. Two pumps are normally in operation with the third on automatic standby. Water is introduced into the unit through the economiser. After passing through the lower and upper economiser sections, the water flows through the external unheated pipes to the steam drum. It enters from both ends of the drum and is distributed internally along the drum length through the perforated feed pipes. This water mixes up the water recirculated from the furnace water wall tubes, the HRA side water wall tubes and evaporator, and then flows through, downcom ers and HRA rear water wall tubes to the water wall tubes and the evaporator. The steam generated in the furnace water wall tubes, HRA side water wall tubes and in the evaporator discharges into the steam drum as a steam -water mixture. The steam is separ ated in the drum and then heated in the superheater . The superheater section consists of the primary superheater and the secondary superheater, by the order of flow. The steam then flows out to the headers and the consumers at required pressure and tempe rature . Steam pressures are stepped down to four levels to serve various needs. Three element feed water, fuel combustion and steam temperature controls are provided with auto/manual modes from the TDC 3000 DCS system. : 18 : 31 -1.1.3 Description Of Systems . A) Fuel Gas. The fuel is natural gas and supplied by plant 8 of process Trains 1 & 2 and routed to individual knock out drums 31 -C-9A and 9B, to remove entrained liquid. Also fuel gas connections are provided to boiler fuel gas header downstre am of PV -30 & 31 from Train 1&2 NRU. The outlets of knock out drums are routed to a common header which is connected by an air operated isolation valve 31 -HV -16, which is normally open to maintain system integrity. Pressure control valves are fitted to the outlets of 31 -K-9A and 9B knock out drums (31PV0030 for 9A and 31PV0031 for 9B). Which are designed to maintain 5 barg pressure (at present set at 6 barg). The outlet of each knock out drum is split in to two lines from KO drum . 31 -C-9A side of the header are routed to Boilers 1 and 2 and two lines from 9B side of the header are routed to Boilers 3 and 4. A small stream of fuel gas is tapped from each side of isolation valve 31 -XV -16 and combined to supply the flare pilots. The fuel gas flow is sp lit into two after metering. The main line serving main burners and the other feeding pilot burners. The gas feed to main burners first passes through main fuel trip valve (MFT) 31 -XV -1066. This is a pneumatically operated Open/Shut valve actuated by t he burner control logic system, or a trip signal from the boiler shutdown system. The MFT has a bypass which allows, on load testing of the boiler trip systems. After the MFT the gas passes through fuel control valve 31 -FV -1064, which controls the fuel quantity. 31 -FV -1064 has a small bypass control valve 31 -PV -1095. This is operated during start -up to give fine control of the fuel gas flow. The gas line after fuel control valve 31 -FV -1064 is split into three branches, each branch line serving three main burners, and the main header terminating at an automatic vent valve 31 -XV -1062 which releases the line pressure to atmosphere during start -up purge sequence. The gas to burners is fed through a block and vent valve system. Two valves are linked mech anically and operate simultaneously. On a trip signal from burner logic system, the shutoff valve closes and vent valve opens, on a start up, reverse action takes place. The pilot gas system is also similar except that the fuel control valve is preset r egulating to maintain a constant pressure of fuel gas to pilot burners. : 19 : B) Combustion Air. The boiler combustion air is supplied by two forced draught fans. All the fans are identical, 6 are steam turbine driven. Out of the other two 31 -K-4A has an electric motor drive and 31 -K-1A has two methods of drive, either steam turbine or electric motor. Both the fans discharge air into a common duct through individual isolating dampers. The burners are fed individually through nine ducts rising ver tically from the common duct. For adjustment of airflow each burner is provided with a manual air register and a tertiary air damper. The airflow from each fan is metered, indicated and recorded on TDC in CCB. Fan driver and gear box are forced lubricat ed by shaft driven lube oil pump, backed up by a separate steam driven auxiliary lube oil pump except for 1A and 4A F.D. Fans. Turbine speed is controlled by a Woodward governor, and motor driven unit speed is controlled by a fluid coupling. The fan bear ings are lubricated by ring lubrication provided in the pedestal bearing housing. The Lube oil system is cooled by Sea water. Seal air fan (3 in number for each pair of boilers –2 in service 1 standby) are provided to inject sealing air to the sleeves of p ilot burners and flame detectors, for maintaining integrity of gas -tight furnace walls and to prevent escape of flue gas as well as combustion air for pilot burners. C) Feed Water. Boiler feed water system is a closed loop system, losses due to leaks and dumping of water to waste during start up and shutdown of machine are compensated from demineralised water tanks. Feed for the boiler consists of clean condensate from power turbines (LG1&2), Process Trains 1, 2, & 3, numerous steam traps throughout the LNG Plant. This is collected in condensate storage tanks 31 -D-1A and 1B. Condensate is transferred from condensate tanks to four deaerators 31 -C-1, 2, 3&4 by condensate lift pumps 31 -G-8A, B&C. These pumps are identical, except that 8A is driven by a mo tor and 8B & C are driven by steam turbines. Two pumps are in service and the third one is on auto standby during normal full load operation of all four boilers. : 20 : The duty condensate lift pumps discharge into a common header with four branches, each branch feeding a deaerator through a level control valve. Since the presence of dissolved oxygen and carbon dioxide gases cause corrosion, the major part of these dissolved gases are removed in the deaerators. The water is sprayed upward as a fine s pray, and the SU Steam flows downward through a tray stack then flows around the tray compartment to the pre -heating compartment, this scrubbing process separates the major part of dissolved gases from the feed water. This water falls to the storage vesse l with a blanket of steam and maintained at or near the temperature of saturated steam. The incondensable gases and a small amount of steam are discharged through two vents from the pre -heating compartments to the atmosphere. The storage vessel with a ca pacity of 435 tonnes each gravitate into a common header supplying suction for six boiler feed pumps, four waste heat boiler feed pumps and two spray water pumps. DEHA (Di -Ethyl -Hydroxyl -Amine) and ammonia solution is injected to feed water leaving deaera tors for scavenging oxygen. The six boiler feed pumps are identical except that 31 -G-1A/3A are motor driven and 31 -G-1/2/3&4 are variable speed, steam turbine driven. The six stage hydraulically balanced centrifugal types Feed Water Pumps are arranged i n two sets of three pumps each. Feed pump 31 -G-1, 1A& 2 feeds boilers 1&2 and 31 -G-3, 3A & 4 feeds boilers 3&4. Both pump sets discharge headers are linked by cross over header to supply each others. Each set di scharge header has two branches, and each br anch flows through HP feed water heater (31 -E-7, 8, 9 &10), where it is pre heated using SB steam before entering the economizer of the boiler, then through feed regulating flow control valve (31 -FV -1014, 2014, 3014 and 4014). Spray water for attempera tors is provided from the upstream of the feed Regulating valves, through tempe ratures control valves (31 -TV - 1032, 2032, 3032 and 4032). Optisperse HPT -0453 is injected into the steam drum to provide pr otection of the water circuits. Optisperse is the uni que boiler deposits control agent for metals oxide control. R : 21 : 31 -1.1.1.4 Steam Distribution (Refer to drawing No. 31 -1.10.17 ) SH STEAM - Steam from the boilers is supplied to the range at 62 barg pressure and 440 0C temperature. The four boiler s are operated as two pairs. Boilers 1&2 as a pair, supply steam to east lateral header and Boilers 3&4 as a pair supply steam to West lateral header. The lateral headers are interconnected by two crossover lines with appropriate isolation valves. In no rmal practice the range is operated as one unit with interconnecting isolation valves open. The two crossover lines one of 10” with 140 tons/hr. and one 14” with a 360 t/hr. capacity, are installed. A relief valve (31HV5591) on the 10” line with a capaci ty of 100 T/hr. opens to atmosphere at 65.0 barg and reseats at 64 barg. Relief valve is provided with an inching facility, from DCS – point 31HC5591. Two cascade steam distribution systems at five pressure levels are provided to serve the entire LNG. Tr ain 1 & 2 system. All the equipment and controls for these systems are located plant 31 Steam Pressure Reducing Station. A) High Pressure Steam (SH) High pressure, superheated steam at 62 barg and 440ºC from the four Boilers is the starting point for th e distribution networks. This steam is supplied to two cross -connected headers, one from each pair of boilers. Steam from each of these headers is supplied in separate branch headers to a process train, a turbo -alternator, and a 62 to 34.5 barg pressure reducing station. The major users of SH steam are: Process Trains I and II. Feed Gas Compressor : 120 T/hr. each. Propane Compressor : 160 T/hr. each. MCR Compressor : 200 T/hr. each. Booster Compressor : 16 T/hr. each. Utilities LG1 and LG2 : 188 T/h r. each. Export/Import to and from Train – 3 : 340 T/hr. : 22 : B) Medium Pressure Steam (SM) Medium pressure steam at 34.5 barg and 380ºC is primarily supplied from the extraction turbines of LG 1 & 2 . Makeup to this header is supplied from the hi gh pressure system at two 62/34.5 barg pressure reducing stations. Steam from the high pressure headers is metered with FT -5303 and FT -5403 then expanded through throttling control valves PC -5502A and PV -5502B and fed to a single medium pressure header. Temperature is reduced to 380ºC with spray -type desuperheaters that inject boiler feed water, regulated by control valves TV -5305 and TV -5405, into the steam flow to produce the desired outlet temperature. SM.steam is used for turbines driven auxiliaries in Utilities and Process areas as well as Surface condenser Air ejectors such as: Utilities Area : Boiler Feed Water Pumps, F/D Fans, Desuperheater Spray Pumps, Waste Heat Boiler Feed Pumps, Condensate Lift Pumps, LG 1 & 2 Auxiliaries & Air Ejectors, Air c ompressors, Jacket water &Flushing Water Pumps, Demin. Water Pump ,Export/Import Train – 3 utilities. Process Area: H.P&MP.Lean carbonate pumps, DEA pumps, Condensate/Lube oil/Seal oil Pumps of FGC, MCR and C 3 machines, Surface Condenser Air Ejectors and Plant 7 Acid gas & air blowers. C) BFW Heating Steam (SB) Boiler feed water heating steam at 8.6 barg at 185ºC is primarily supplied from the waste heat boilers in the Sulphur plant and exhaust of 35KT -1A Air Compressor Turbine. Makeup to this header is from the medium pressure system at two 34.5/8.6 barg pressure reducing stations. Steam from the medium pressure header is metered with FT -5308 and FT -5408 then expanded through throttling control valves PV -5505A and PV -5505B and fed to the SB steam heade r. Temperature is reduced to 185ºC with spray -type desuperheaters similar to those at the SH/SM pressure reducing stations. Steam from this header is used as the heating medium for the Boiler feed water heaters . SB. steam is also used as the heating med ium in several process reboilers. In the event of one or both sulfur trains out of service, this steam will be supplied from the 34.5/8.6 barg letdown stations. : 23 : D) Low Pressure steam (SL) The exhaust from turbines driven Auxiliaries primarily s upplies low - pressure steam at 4.2 barg and 201ºC. The principal use for this steam is reboiler heating in the process area. Makeup to this header is from two 8.6 to 4.2 barg pressure reducing stations. Steam from the SB. Steam header is metered with FT -5324 and FT -5424 then expanded through throttling control valves PV -5512A and PV -5512B and fed to the low -pressure header. Temperature is reduced to 201ºC with spray -type desuperheaters. Pneumatically -operated, remote/manual actuated, butterfly valves (3 1HV5328 & 5428) are provided to isolate the Plant 31 SL header from the process Train -1&2 headers. At present these valves are operated by manual hand jack. This Steam is used as general -purpose steam. Heating steam for Process Reboilers. Steaming out of vessels. Fire fighting. Snuffing & purge steam. Export/Import to Train 3 Utility. E) Utility Steam (SU) Utility steam at 1.5 barg and 203ºC is also supplied by the exhaust from turbines driven Auxiliaries. And used for heating and deaerating boiler feed water and as sealing steam at the power turbines. This steam is not exported from the Plant 31 area. Makeup to this header is supplied from the low pressure system at two 4.2/1.5 barg pressure reducing stations. Steam from the low pressure header is me tered with FT -5313 and FT -5413, expanded through throttling control valves PV -5506A and PV -5506B and fed to the utility steam headers. No desuperheating is provided at these letdown stations. Excess steam in this header is vented to atmosphere via a sile ncer through two throttling control valves PV -5503A and PV -5503B. Overpressure protection is provided at the letdown station by relief valves. Normally, the steam system is in balance with no excess steam venting to atmosphere. This Steam is used as dea erator heating steam. : 24 : F) Low Pressure Condensate System Condensate receiver, 31 -C-10, is provided for collecting all the condensate discharged from the steam traps on the utility steam system. This vessel is vented to atmosphere and is equippe d with an overflow line to drain. A motor -driven, centrifugal pump 31 -G-15, is provided to transfer this condensate to the condensate collecting tanks 31 -D-1A&B This pump normally operates intermittently, with the pumping cycle automatically controlled b y high and low level switches on the condensate receiver. : 25 : 31 -1.1.2 Equipment Description 31 -1.1.2.1 Boilers A) Steam Drum (Refer to Drawing No. 31 -1.10.2 ) The steam drum serves as reservoir for the water needed in the steam generating section s and as mixing chamber in which incoming feed water is added to re circulating water from the water walls. The drum contains steam separating equipment, and internal pipings for distribution of feed water and for intermittent/continuous blowdown of the w ater to reduce solids concentration. The steam drum is located at the top of the boiler and extends across full width of the boiler. Feed water enters each end of the drum and is distributed evenly along the full length of the drum by equally spaced hole s in the feed pipe. The water leaves the drum through the down comers and HRA rear water wall tubes. An internal circumferential baffle extending almost the full length of the shell forms as annulus along the bottom half of the steam drum. The steam wat er mixture from water wall risers enters the drum in the space between the circumferential baffle and the drum shell, and then passes through the horizontal steam separators. The first stage separation of steam from water is accomplished here. The horizo ntal separators mounted along each side of the drum separate the steam and water mixture entering the drum through water wall risers. Steam leaves the drum through chevron driers mounted in a row below the dry box at the top of the drum : 26 : As th e mixture follows through the curved counter of the separator, the heavier water particles are expelled out by centrifugal motion, and discharged through the primary or secondary drain into the bottom of the drum. The separated steam flows out of the open ings on both sides of the separators and into the steam spaces. The final separation of moisture in the steam is accomplished as the steam comes into contact with the “W” - shaped chevron elements forming the drier assemblies. Steam enters at a low veloci ty into the driers which makes several abrupt changes of direction of flow. This causes the entrained moisture to adhere to the large surface area of the chevron drier. The water film, then, is drained off to the lower part of the drum through drip tubes by gravity. The separated steam passes through the dry box and leaves the drum through the saturated steam pipes at the top of the drum. Water separated from the steam falls to the water space where it comes together with entering feed water. The water recirculates through the down -comers and HRA rear wall tubes. It is important that the steam is properly dried in the drum because any moisture carried over into the superheater tubes will contain impurities. As the moisture is evaporated in the superhe ater tubes, the impurities may be deposited on the inner surfaces, which will cause localised over heating and failures. Alternatively impurities, in particular, silica, could be carried over and deposited on the turbine blading resulting in reduced turbi ne efficiency and performance . : 27 : B Furnace, Heat Recovery Area and Evaporator Steam is generated in the furnace water wall tubes, the heat recovery area side water wall tubes and evaporator. The water walls are composed of single finned tubes w elded together. The bottom of the furnace is flat, formed by the lower portion of the front water walls. Downcomers or feed tubes from the steam drum carry water to the lower headers of the four furnace walls, evaporator and the HRA side water walls. As the water flows upward in the water walls and evaporator it is heated and steam is generated. From the upper header of the evaporator the steam/water mixture flows into the drum for separation, through riser tubes, at the top of the furnace walls and ris er pipes. The separated water is recirculated through the water wall tubes after mixing with feed water. C Economisers The economiser located at the lower side of evaporator consists of welded tubes arranged in loops and is completely drainable. The ec onomiser inlet and outlet headers are exposed to the flue gas stream. Water enters the boiler through the economiser inlet header and flows upward, counter to flue gas flow, through the economiser tubes. Heated water from the economiser outlet flows dire ctly to steam drum externally through unheated feed pipes. The economiser tubes are supported by lugs attached to the furnace rear wall and HRA rear wall. : 28 : D) Superheaters The steam generated in the furnace HRA water walls and evaporator leaves the drum as dry saturated steam. The steam flows down through the saturated steam pipes to the primary superheater inlet header. It is then superheated in the following sections 1. Primary Superheater The primary superheater consists of elements in t he middle part of the heat recovery area between the primary superheater inlet and outlet headers Each element consists of two completely drainable tubes, bent in horizontal loops, supported by lugs attached to the furnace rear wall and HRA rear wall. Th e primary superheater inlet header is exposed to the combustion gas stream. Steam from the primary superheater inlet header enters into the primary superheater and flows upward through the looped tubes, counter to the flow of combustion gases. From the o utlet header, the steam flows through transfer pipes, containing spray -type steam temperature control headers, to the secondary superheater inlet header. 2. Secondary Superheater The secondary superheater is located at the HRA inlet above the primary sup erheater section. Each element consists of four completely drainable tube banks in horizontal loops, supported by lugs attached to the furnace rear wall and HRA rear wall. Steam leaving the spray -type temperature control pipes enters the end of the secon dary superheater inlet header, flows through the secondary superheater and leaves the Boiler through the outlet header to the main NRV and Boiler outlet MOV. : 29 : E) Valves In general, valves are designed and manufactured as described as below. Val ves have welded or flanged joints to pipes and fitted with outside screw spindles. The valve spindle is rotated in clockwise direction to close the valve viewed from the outer end of the spindle. Generally, two valves in series are provided for operation al drains, the upstream isolating valve being of the parallel slide type and lockable in the open position, the down stream or operating valve is of the globe type. F) Casing, Gas Flues, Air Ducts and Stacks The draft system of this boiler is of the forc ed type. The furnace construction is, designed to ensure the pressure tightness of furnace. Water wall tubes composed of single finned tubes from the mono -wall construction is an all welded pressure tight enclosure. The parts where the superheater tubes penetrate through the HRA rear wall tubes are kept pressure -tight by wall box welded to the outside of HRA rear wall tubes. Backstay structural members are installed horizontally around the wall with vertical spacing of 2400 or 2600 or 3200 mm. The prima ry function of the backstays is to prevent the deflection of the wall tubes due to the internal pressure of the boiler. The backstay system is also utilized to keep furnace and heat recovery area wall tubes in alignment and to resist such a force affecting this alignment as external wind and internal pressure. Buffers are attached to the main backstays , transfers the load to the structural steel frame. : 30 : The final outer wall covering of the boiler is made of steel plate of 1.2 mm or 2.3 mm thickn ess. (used only on the roof). All gas flues and air ducts are designed to withstand internal and external pressures. The ducts generally are rectangular in shape and are sized to obtain reasonable gas or air velocity. The ducts are properly stiffened an d reinforced with angles for the outside and tubular bracings for the inside. The gas flues and air ducts are of the all -welded construction of steel plates of 4.5 mm. Expansion joints are provided where necessary to absorb the thermal expansion of gas flues and air ducts. Dampers and manholes are provided where necessary. A steel stack with a height of 34,700 mm is installed for each unit. The flue gas is discharged to the atmosphere from the top of this stack. : 31 : G Burners and Air Registers 1. Main Burner The multi -spud gas burner assembly consist of a gas inlet connection, a gas ring and six (6) equally spaced gas spuds installed in the annulus of the intersleeve. The tip of each 2 inch gas gun spud tube contains a total of Fourteen (14) h oles of 5.6 millimeter dia. drilled through the nozzle plate. Specification Type : IHI -FW multi -spud type. Number required : 9 sets (per 1 boiler). Locating position : Front wall. Max. capacity (per 1 burner) : 3400 Kg/h. Max. gas pressure at bur ner inlet : 1.96 barg.(2 kg/cm2 g). Fuel : Natural gas. 2. Pilot Burner Fuel gas/air pipe, spark rods and the flame detection rod are mounted on each fire tube. The fuel gas/air pipe has a gas nozzle at the pipe inlet, where the fuel gas velocity increases. The combustion air is induced in the pipe by fuel gas flow and mixed with the fuel gas, and the mixed combustible gas is discharged at the top of the pipe. Two spark rods are installed, one for positive pole and the other negative which is gro unded and is used in common to that for the flame detection rod. The flame detector for pilot burner makes use of the rectifying function of the flame, creating a small flow of electricity. : 32 : Specification Type : Electric ignition system gas bu rner with flame detecting device. Number required : 9 sets (per 1 boiler). Max. gas capacity : 10 Nm 3/h. Fuel : Natural gas. Max. gas pressure at burner inlet : 1000 mm H 2O. Maximum combustion air pressure at burner inlet : 30~100 mm H 2O. Ign ition system : Sparking. Electric power source : AC 110 V, 50 Hz. Output voltage of ignition transformer : 6,000 V. 3. Air Registers Air register assembly consists of air register vanes, burner throat ring and air register control drive unit. Air register vanes opening can be changed by the hand operated drive unit. These vanes are provided to give rotation to the combustion air, and proper mixture of fuel and air, but never control the combustion air flow. The windbox is of divided type, a nd the correct air distribution between burners is achieved by manual setting of dampers fixed to the separated windbox inlet during commissioning. : 33 : H) Control Panels The following panels are provided: 1. TDC 3000 Main panel (CCB Steam) The TD C main panel contains all the normal, automatic, DCS controls for combustion and feed water control. There is no provision for remote burner start from TDC panel. This has to be done from local panel. There is provision for remote “Emergency Stop” which shuts down all burners by closing the MFT valve. This is located on the steam panel and is a hard wired push button switch. Individual burner shutdown to match load reductions etc. Indications associated with these points are to show which burners are i n operation (“ ON ”) and which are shutdown (“ OFF ”). Should any burner trip -out at the boiler front the same indication will flash until “acknowledged”. Also audible alarm system is incorporated in TDC system. If the main burners are taken out of service from the main panel or burners are tripped due to a protection trip, the pilots will remain in operation. This will also happen if the main burners are taken out from the “Burner Control Panels” but the pilots can be switched off from the “Burner Control Panels” by their own switches. : 34 : 2. Boiler Purge Panel One for each boiler , located on the lowest firing floor (“A” level )adjacent to the “Burner Control Panel”. It contains the indication lamps for purge permissives and purge switch. Pur ge Permissive Indications: - (All white lamps ) Air flow : Normal. Registers : Open. Main B & V valves : Closed. Pilot B & V valves : Closed. MFT Valve : Closed. PFT Valve : Closed. Drum levels : Normal. Fuel gas pressures : Normal. Furnace pressu re : Normal. Vent valves : - (All white lamps) Pilot supply line vent valve : Open. Pilot supply line vent valve : Closed. Main supply line vent valve : Open. Main supply line vent valve : Closed. Furnace purge permissive : (White Lamp). Furnace Pur ge Completed : (White Lamp). : 35 : Switches These are all momentary control with spring return to central neutral position. Furnace purge : Start. Pilot supply line vent valve : Open/Close. Main supply line vent : Open/Close. 3. Burner operation panels Three per boiler, one to each firing floor and located approximately opposite the central burner. Burner operation panel – three for each boiler and located on each firing floor. On these panels are located the following lights: a) For each pilo t (3). Pilot burner off (green). Pilot burner available (white). Pilot burner on (red). b) For each main burner (3 each). Main burner off (green). Main burner available (white). Main burner on (red). And the burner ON/OFF switches, one each for of three pilots and associated burners. : 36 : 4. Boiler trip indication panel . This panel is located on the “A” level East side. It contains the indication lamps for the following boiler trips. a) 31 -XL -B1 -0-00 : Loss of combustion airflow “A". b) 31 -XL-B1 -0-01 : Loss of combustion air flow “B". c) 31 -XL -B1 -0-02 : Low fuel gas pressure. d) 31 -XL -B1 -0-03 : High fuel gas pressure. e) Spare. f) 31 -XL -B1 -0-04 : Low level drum water (right). g) 31 -XL -B1 -0-05 : Low level drum water (left). h) 31 -XL -B1 -0-33 : High furnace pressure. i) Spare. j) HS -B1 -0-31 : Lamp test button. : 37 : 31 -1.1.2.2 Forced Draft Fans Combustion air is supplied to each boiler by two forced draft fans: Boiler No. FD Fans Nos. 31 -F-1 : 31 -K-1A and 1B. 31 -F-2 : 31 -K-2A a nd 2B. 31 -F-3 : 31 -K-3A and 3B. 31 -F-4 : 31 -K-4A and 4B. These fans are identical, variable speed, turbine driven units except that 31 -K-1A is provided with dual -drive (turbine and motor) and 31 -K-4A is motor driven to permit startup of a first boiler when no steam is available. During normal full load operation both fans are on line for each boiler. The air stream from each fan discharge flows into a common, horizontal duct across the front of the boiler. Nine vertical ducts lead to each burner asse mbly. A manual air register and a tertiary air damper are provided at each burner assembly for adjustment of airflow. Specification a) Fan Type : Double -entry centrifugal with variable speed control. Quantity : 2 sets for one boiler. Capacity : 4,860 m 3/min at 48ºC. Static pressure : -6.4 mbr at suction. 77.5 mbr at delivery. Air temp. at fan inlet : 48ºC. Speed of fan : 1,450 rpm. Manufacturer : EBARA MFG. Co., Ltd. (Japan). : 38 : b) Turbine for F. D. Fan Type : Single curtis impulse tur bine. Quantity : 2 sets for one boiler. Steam condition : Inlet pressure : 33.5 barg. temperature : 375ºC. Exh. Pressure : 1.5 barg. Temperature : 210ºC. Speed : 5485/1450 rpm. Power : 950 KW. Steam rate : 13.4 Kg/KW.hr. Steam consumption : 12700 Kg/hr. Manufacturer : EBARA MFG. Co., Ltd. (Japan). c) Motor for F.D. Fan Type : Squirrel cage induction type, water proof Totally enclosed, closed air circuit and water cooled . Rating : Continuous. Out put : 990 KW. Pole N. : 4. Synchron ous speed : 1,500 rpm. Electricity : 3,300 V, 50 Hz, 3 phase. Insulation : ‘B’. Space heater : With (240 V, 560 W). Direction : Counter -clockwise viewed from coupling side. Manufacturer : GEC Machines Ltd. (U. K.). : 39 : 31 -1.1.2.3 Seal Air Fans In order to maintain the integrity of the gas -tight furnace walls and prevent the escape of flue gases, sealing air is injected into the sleeves of the pilot burners and flame detectors, at the furnace peep holes, and also provides combustion air for the pilot burners. Fan No. Boiler No. 31 -K-8 : 31 -F-1 31 -K-9 : 31 -F-2 31 -K-10 : 31 -F-3 31 -K-11 : 31 -F-4 31 -KT -19 : 31 -F-1 & 2 31 -KT -20 : 31 -F-3 & 4 This machines 31 -K-8, 9, 10 and 11 are single suction overhung type turbo blower and driven by a mo tor through coupling. 31 -K-19 & 20 are steam driven and normally standby. The regulation of air quantity and pressure is regulated by hand operated dampers situated at the outlet ports. Method power transmission : Direct coupled. Inlet port : mm. Outl et port : 166 + mm. Air volume : 20 m 3/min. Static pressure : 670 mm H 2O at 40ºC. Temperature : 10~48 ºC. Handling gas : Air. Revolutions : 2,900 rpm. Bearing : N. T. N # 6310. Coupling : -CL -100. Electric motor : 7.5 K. W. 2P. Electric source : 415 v 50 Hg. Discharge arrangement : Clockwise up blast. Damper : Outlet. Use : Seal air fan. Quantity : 4 sets motor and 2 steam driven. Steam driven standby fans. : 40 : 31 -1.1.2.4 Deaerators Function The presence of dissolved gases, oxygen and carbon dioxide in the wa ter, causes accelerated corrosion, especially at elevated temperatures such as are encountered in boilers and heat exchangers. It is the primary function of the deaerating heater to prevent this corrosion by removing the dissolved gases from all sources o f water supply to the heat exchangers and the boilers. Principles of Heating and Deaerators Complete heating of boiler feed water is accomplished by direct contact between the water and the steam. As in all heat transfer phenomena, contact surface and t he time of contact are important and are provided by sprays and atomization. To remove non -condensable gases from solution in the water the temperature must be raised to the boiling point. The solubility of a gas depends upon the temperature of the water and the partial pressure of the gas in contact with it. Obviously, when the temperature of the water is actually at the boiling point for the pressure, the solubility of the gas is zero. Merely rendering gases insoluble by heating to the boiling point a lone does not eliminate molecules and bubbles of gas in the mass of water. In order to escape from the mass of the water, gas molecules must diffuse through the surface film surrounding the particle of water. Thorough atomization by the incoming steam an d maintenance of a pure steam atmosphere by venting, causes rapid diffusion and elimination of this gas. Principles of Operation (Refer to Drawing No. 31 -1.10.6 ) The Cochrane Horizontal Jet Tray Deaerator consists of the following essential parts: 1. Deaer ator Shell. 2. Spray Distributors. 3. Down comer and Water Seals. 4. Deaerating Trays. 5. Storage vessel. : 41 : Water enters the pre -heating compartment through a perforated distributor. The water is sprayed upward in a finely divided state into an atmosphere of steam where the water is heated to practically steam temperature. The spraying and heating brings about the separation of a major portion of the dissolved gases from the water. The sprayed and heated water then falls to the bottom of the pre -heating c ompartment from which it flows through a down comer to the water seal above the trays. The heated and partially deaerated water passes from the water seal to the deaerating trays. The water seal prevents bypassing of steam from the tray compartment into the pre -heating compartment and ensures against non -condensable gases entering the tray compartment from the pre -heating compartment. The water seal distributes the water evenly over the entire cross sectional area of the deaerating trays. The water casc ades downward in thin sheets through the tray stacks. The water is continuously subjected to the scrubbing action of the concurrently flowing steam. The arrangement of trays is such that a complete re -distribution of water is accomplished at each layer o f trays. Final deaeration is accomplished in the tray section. The heated and deaerated water flows from the bottom of the tray section to the storage section where it is blanketed by steam and maintained at or near the temperature of saturated steam at the operating pressure. The steam is introduced to the deaerator through a connection in the shell and discharged into the space above the trays in the tray section. The steam flows downward through the tray stack. Since the water entering the tray comp artment is heated and the bulk of non -condensable gases were removed in the preheating compartment, practically no condensation of steam occurs in the tray compartment. Therefore, the entire volume of steam is employed in the scrubbing action, removing th e final traces of oxygen and other non -condensable gases. The steam, leaving the bottom of the tray stack, flows outside the tray compartment to the pre -heating compartment where the major portion of the steam is condensed in heating the water. A very sl ight amount of steam and the non -condensable gases are discharged through the vent from the preheating compartment to the atmosphere. : 42 : 31 -1.1.2.5 Feed Water Pumps There are six boiler feed water pumps for the four boilers. They are: 31 -G-1A 31 -G-3A 31 -G-1 31 -G-2 31 -G-3 31 -G-4 The pump has six stage and is hydraulically balanced centrifugal type. The “F. I.” range of multi -stage, barrel casing, diffuser type centrifugal pumps has been developed to meet high -pressure duties at medium temp eratures. They are specifically designed to satisfy the requirements of boiler feed applications. Specification Manufacturer : Matter & Platt Ltd. Turbine : 2 DYRPG. Serial Number : N-2579. Rated Power : 1850 HP 1380 KW Rated speed : 3000 r/min. Speed range : 2100/3150 r/min. Over Speed trip setting : 3465/3528 r/min. Steam pressure : 34.4 barg. Steam temperature : 371ºC. Steam consumption : 20 tonnes/hr. Exhaust pressure : 4.27 barg. Oil pressure (Pressure lubricated turbines) : 0.6/1.0 ba rg. Number of hand valves : Two (2). Motor driven. Steam driven. : 43 : The boiler feed pumps are identical six stage, hydraulically balanced centrifugal units; four of which are driven by variable speed turbines, and two by constant speed electric motors. They are arranged in two sets of three. Each set consisting of two turbine -driven and one motor -driven Pump, supplying one pair of boilers. Pumps 31 -G-1, 2 &1A supplies to boilers 31 -F-1&2 and 31 -G-3, 3A&4 supplies to boilers 31 -F-3 &4. During normal full load operation tw o pumps of each set are on line with the third on automatic standby. Instrumentation is provided to permit any combination of two on line with the third on standby. Each pump and driver is provided with a forced -feed lubrication system from a shaft -drive n pump backed up by an auxiliary oil pump, driven by a turbine or a motor, according to the pump driver. Turbine speed control is accomplished with a Woodward governor, which contains its own oil supply and pump ( Refer to Drawing Nos. 31 -1.10.13&14 ). Each pump set discharges into a common header with two branches. Each branch flows through a feed heater (31 -E-7, 8, 9 & 10), and passes through a flow control valve (FV -1014), 2014, 3014, and 4014) before entering the economiser section of the boilers. A sl ipstream from Feed Water header of each boiler is taken (just ahead of the control valve manifold) to the boiler attemperator, through control valve (TV -1032, 2032, 3032 and 4032). Water discharge from each pump passes through a check valve to a common pu mp balance header for each set of pump and through restriction orifices to the associated pair of deaerators (31 -C-1, 2 and 31 - C-3, 4). A recirculation device located in the check valve of each pump bypasses a slipstream of water through a pressure -reduci ng device to a common pump leak -off header of each pump set. Two branch lines from this header discharges to each of the associated deaerators through flow orifices. These orifices are sized to pass the required minimum flow for each pump as specified by the manufacturer. An underground suction header with branch lines to each of the six boiler feed pumps, supplied from the condensate storage tanks, is provided in the event of failures in the normal feed water systems. The use of this alternate system s hould be restricted, however, to boiler startups and low load operations, and only if required. It will be necessary, also, to closely monitor feed water treatment during such operation. : 44 : 31 -1.1.2.6 Waste Heat Boiler Feed Water Pumps The waste heat boiler feed water pumps takes suction from the boiler feed water suction header. These Pumps are identical centrifugal units; two of which are driven by constant speed turbines, the other two are by electric motors. These pumps are arranged in sets of two. Each set consisting of a turbine -driven and a motor -driven unit. Each set supplies feed water to the sulphur plants (Plant 7) in Train 1/2 . During normal operation one pump of each set is on line with the other on automatic standby. Pumps 31 -G-16A &B discharge into a common header that supplies Plant 7 sulphur plant on Process Train 1. Pumps 31 -G-17A&B supply Plant 7 process Train 2 through a separate header. The minimum flow requirement is ensured by continuous bypassing of a slipstream back to the deaerators. This connection is taken from the discharge of the pump,(upstream of the check valve) and through a restriction orifice into a common header for each pump set. The orifices are sized to pass the specified minimum flow. Two branch lines f rom the minimum flow headers lead to each of the associated deaerators. Specification 31 -G-16A/17A : Motor driven. 31 -G-16B/17B : Steam driven. Manufacturer : Ingersoll -Rand, New York, U.S.A. Suction Pressure : 1.8 barg. Discharge Pressure : 18.3 bar g. Lubrication : Ring lubrication with oil sump and cups. Capacity : 78.5 m 3/hr. Motor : 415V. Speed : 2950 rpm. : 45 : 31 -1.1.2.7 Chemical Dosing Pumps The feed water must be free of dissolved corrosive gases and the pH of the water must be maint ained to prevent the attack of gases on metal surfaces. DEHA (Di -Ethyl -Hydroxyl -Amine) and Ammonia solution for oxygen scavenging is fed to the water leaving deaerators. There are four pumps for these purposes: Pumps Mixing Tanks 31 -G-11A 31 -D-5A 31 -G-11B “ 31 -G-11C 31 -D-5B 31 -G-11D “ Optisperse HTP -0453 is liquid formulations based on the advanced, p atented HTP -2 polymer technology. HTP -2 is the most effective boiler deposit control agent for (iron/copper) oxides yet developed. It's effective at Boilers pressure up to (105 Kg/cm2). Optisperse HTP series products incorporate metallic tracer in order to monitor the appropriate boiler water concentr ation. Optisperse technology , when metallic oxides do enter the boiler, the HTP -2 polymer is highly effective in dispersing them. HTP -2 present in Optisperse HTP series products inhibits deposition through crystal structure and surface charge changes. Synthetic Polymers will a dsorb onto the metal particles, control their growth, al ter surface charge and inhibit deposition on heat transfer surface. The result is that solids are easily removed from the boiler water by blowdown. Optisperse HTP series products , should be used as part of a phosphate, co - coordinated phosphate/PH based p rogram in order to effectively control boiler deposition and prevent losses associated with tube failures. Optisperse HTP series products are particularly effective in high pur ity/high pressure systems, where iron is the dominant contaminant, but products are also effective in low -pressure systems, where hardness is also present. R : 46 : Pumps are: Tanks: Boiler 1: 31 -G-0061A/B 31 -D-0013A Boiler 2: 31 -G-0062 A/B " Boiler 3: 31 -G-0063A/B 31 -D-0013B Boiler 4: 31 -G-0064A/B " Descript ion The HASKEL International, Controlled Volume Pump is a Diaphragm type, positive displacement pumps designed to deliver accurately measured liquid volumes against a positive differential pressure (or head) between pump suction and discharge 99.9 % maximum and rated at 89.9 %. The pump delivers a controlled volume of liquid with each discharge stroke. Pump flow rate is adjusted by changing plunger stroking speed and/or length. Capacity adjustment can be made manually or Automatic Via PLC, which amounte d at OS 1. Principles of Operation DURAMETER Haskel International, (EVA) Pumps consist of two basic m echanisms; the drive system and the liquid end. The drive mechanism is unique and operates on a patented polar crank principle. Essentially, a crank driv en by a worm gear reduction system rotates on a plane whose slope is variable. The EVA pumps flow rate can be adjusted from 100% rated capacity to 10% of flow rate accurately. Turning stroke control knob varies flow. The pump is providing max flow when ind icator is showing 100%. When the pump has an Electronic Flow Control the indicator is on the Actuator Neck. 31 -1.1.2.8 Condensate Lift Pumps Cold condensate is transferred from the storage tanks to four deaerators 31 - C-1,2,3&4 by condensate lift pumps, 3 1-G-8A, B & C. These pumps are identical units except for the drivers; 31 -G-8B and 8C are turbine -driven while 31 -G-8A is motor -driven. During normal full load operation two pumps will be required while the third is on automatic standby. Instrumentation is arranged so that any combination can be used on line. The deaerator condensate lift pumps discharge into a common header with four branches, each feeding a deaerator, and a fifth branch to transfer a slipstream of condensate to the demineralisers in t he event contamination is detected in the condensate storage tanks. Flow to each deaerator passes through a level control valve. These valves are provided with lock -up devices to hold the valve in existing position in the event of instrument air failure. Capacity : 885 T/hr. Discharge pressure : 5.25 barg. R : 47 : 31 -1.1.2.9 Deaerator Make up Pumps The makeup water requirement is transferred from the demineralised water tanks 31 -D-2A &B to the deae