Temperature: 535 �?/DIV>
Flow: 533.71 t/h
Pressure At High Pressure Cylinder Exhust: 2.866 MPa(a)
Pressure At Low Pressure Cylinder Exhust: 9.5 kPa(a)
Heat Rate At Rated Condition: 8526.6 kJ/kW.h
Maximum Flow Of Main Steam: 670t/h
Revolutionary Speed: 3600r/min
Regenerative Cycle System: Seven Grade (Two HP, Four LP, One Deaerator )
The combustion system is positive pressure, cold primary air fans, direct firing and balance draft system.
(1) Cold secondary air system
The function of cold secondary air system is to supply cold air that is going to be heated for the purpose of combustion. The system contains equipment: Two (2) axial forced draft fans at constant speed each with hydraulic blade pitch control system, inlet silencers etc.
The capacity of two 50% fans in parallel operation is designed.
The rotating blades of forced draft fans will automatically regulate the air flow according to the rating variation of the boiler. At the outlet of forced draft fan, there is a damper, which will be shut when the forced draft fan is out of service and will isolate the fan from the boiler system. Steam air heaters for secondary air will be installed at the inlets of each air preheater.
(2) Primary air system
The function of primary air system is to supply the drying agent for coal pulverization system and to blow the coal dust into the furnace of the boiler.
The system contains equipment: two (2) centrifugal air fans at constant speed each with inlet damper control system, inlet silencer etc.
The design capacity of two 50% fans in parallel operation is equipped. Steam air heaters for primary air will be installed at the inlets of each air preheater.
At the inlet of coal mill cold and hot air ducts of primary air, the regulating dampers are installed and automatically regulate the air flow according to the temperature of drying agent. At the inlet of coal mill there are is a slide dampers, to shut down and completely isolate the coal mill from boiler's hot air system, when it is necessary.
(3) Hot secondary Air System
The function of secondary air system is to supply the hot air demanded by combustion of the boiler, when it starts up and normally operates.
The hot air (secondary air) coming from outlets of air heater will be directly blown into the furnace.
(4) Seal Air System
The function of seal air system is to prevent hot air and coal dust escaping from the coal mills and coal feeders into the atmosphere.
Five coal mills are supplied with seal air from seal air fan, and coal feeders are supplied with seal air from the cold primary air, two seal fans (one working and one standby) are provided for the boiler; each fan will be designed to meet the seal air requirements of the coal mills. On the upstream side of the seal fans is fitted a filter to maintain the air clean. The seal air will come from the cold primary air header in front of the boiler. A shut-off valve damper is provided at the inlet of the seal air fan.
(5) Raw Coal Feeding System
The function of raw coal feed system is to receive raw coal with a particle size < 30 mm from a local bunker storage system and to deliver the coal to the coal mills.
The system contains equipment: five (5) raw coal bunkers and five coal feeders of gravimetric, belt type.
The storage of the five bunkers is designed to be enough for not less than 8 hours of operation at B-MCR (worst coal). The bunker is circular type with a hyperbola typed outlet hopper, and the lower section of the hyperbola hoper will be lined with stainless steel plate on the inner side to prevent clogging of the coal.
The coal feeder of gravimetric type will be matched with each coal mill at a rated output.
3.2.2 Pulverization System
The function of pulverization system is to receive raw coal from raw coal feeding system, which will be then dried, pulverized and mixed with the primary air and finally delivered to the burners fitted to the boiler at a controlled quantity.
The "Direct Coal Fired System" proposed for the boiler is designed to consist of five (5) mid-speed bowl mills, which are identical and independent and parallel in operation with four working and one in standby at 100% BMCR coal firing for the design coal, five working at 100% BMCR coal firing for the check coal.
On the body of the coal mills there will be fire fighting interfaces. The medium for fire fighting is steam.
3.2.3 Flue Gas System
The function of flue gas system is to clean the flue gas extracted from the boiler and to balance draught operating condition in the boiler.
The system contains equipment: two (2) electrostatic precipitators (ESP), two (2) induced draft fans and a chimney.
The electrostatic precipitator of outdoor type each has double chambers and five electrical fields to guarantee the emission values of the dust is less than 100 mg/Nm3 at the outlet of the ESP. Two electrostatic precipitators will be provided for each boiler.
The induced draft fans are of axial fan at constant speed each with adjustable stable blades flow control. The two 50% fans in parallel operation are equipped.
The flue gas system is a complex of elements. The combustion products in the system flow from the furnace into the atmosphere, which begin in the boiler furnace and go into the chimney through the super-heaters, economizer, air heaters (at the gas side), electrostatic precipitators and two induced draft fans, FGD system.
3.2.4 Flue Gas DeNOx System
According to the coal and the emission limit ,the flue gas DeNOx system is not needed for the project at this stage.
But the space for the future flue gas DeNOx equipment is reserved. The pressure loss of the flue gas DeNOx equipment is not considered for the selecting of the ID fan now.
3.3 Fuel Oil System for Boiler
There are three functions, ignition, start-up and burning assistance.
When pulverized coal is used as the fuel for boiler, it is not proper to feed the pulverized coal directly during the start-up of the boiler. The furnace should be preheated to a certain temperature first and the pulverized coal can be fed then.
For pulverized coal fired boiler, the oil is needed to support the burning when the combustion is not stable during low load operation.
For burning -assistant and ignition oil, it is designed based on light fuel oil.
The capacity of the oil system is designed with capacity of 30% of the full needed at BMCR of one boiler.
The capacity of the start-up and burning-assistant system is determined according to the following principles:
Satisfy the requirement of cold start-up and hot start-up as well as burning-assistance at low load.
3.4 Thermal System
3.4.1 Main Steam, Reheat Steam and Bypass System
1) Main Steam System
The main steam pipe is from boiler superheater outlet header with one pipe line and then dual pipe lines to turbine main stop valve inlet. Main steam piping will be constructed of seamless 12Cr1MoVG or ASTM A335-P22 chrome-moly steel.
2) Reheat Steam System
Cold reheat steam pipe is from turbine HP casing exhausts with two lines and then one line to boiler reheater inlet. Hot reheat steam pipe is from boiler reheater outlet with one line and then two lines to turbine IP combine valve. Hot reheat steam piping will be constructed of seamless 10CrMo910 or ASTM A335-P22 chrome-moly steel. Cold reheat steam piping will be constructed of seamless St45.8/III or ASTM A106B carbon steel.
Hydrotest isolation plate valves are installed at boiler superheater outlet, boiler reheater inlet and outlet . Emergency spray desuperheater is installed at boiler reheater inlet.
3) Bypass System
A two stages, cascaded high pressure and low pressure turbine bypass steam system with capacity of 40% BMCR. is located for this unit, it will improve cold, hot start-up condition, reduce start-up time of the unit, protect boiler reheater and maintain boiler operating under lowest steady fire load condition after electric network has emergency and steam turbine shut down, when trouble is solved, the unit will start-up immediately.
3.4.2 Turbine Extraction Steam System
There are seven stages of non-regulating extraction steam for turbine. The first and second extraction steam heat the No.1&No.2 HP heaters, The third extraction steam supplies steam to deaerator and auxiliary steam header, the No.4,5,6 &7 extraction steam to LP heaters separately.
In order to prevent the turbine over speed, pneumatic check valves and motor operated gate valves are installed on the first to the fifth extraction steam pipe line except the six and seven steam line. They should be closed immediately and automatically when turbine loads dump or trips. The heating resource to the deaerator should be changed over to auxiliary steam from the third extraction steam.
The pneumatic check valves should be installed as closer as possible to the turbine.
Clarification: boiler feedwater cycle is based on seven heaters consisting of four LP heaters, one dearator and two HP heaters.
3.4.3 Boiler Feedwater System
The function of the boiler feedwater system is to supply the boiler with required quality and flow of feedwater under all conditions of operation. The feedwater system also supplies cooling water to the attemperator of the superheater, the attemperator of the reheater and the desuperheater of the turbine HP bypass.
The system includes the low pressure feedwater system from deaerator feedwater tank outlet to the boiler feedwater pumps, and high pressure feedwater system from the boiler feed water pump through two H.P heaters, feedwater control valve to the economizer inlet. The equipment, pipes, valves and accessories are included in both low and high pressure boiler feedwater system.
Three 55% capacity boiler feedwater pumps are installed. Two for normal operation, one for standby. The pump is driven by the motor through the hydraulic fluid coupling.
There are two high pressure heaters with a common motor-operating isolation valve bypass in the system to heat the boiler feedwater.
The HP feedwater pipe material is 15NiCuMoNb5 or St45.8/III.
Clarification: It is suggested three 55% capacity boiler feedwater pumps or two 110% capacity boiler feedwater pumps instead of three 60% capacity boiler feedwater pumps. It will be for further discuss.
3.4.4 Condensate System
The condensate system shall remove condensate from the hotwell and deliver it to the deaerator storage tank. In order to enhance the thermal cycle efficiency, to assure safe and reliable operation of the system, the condensate is heated and deaerated.
The system includes two 110% capacity condensate pumps, four low-pressure heaters(No.4, No.5, No.6 and No.7), one gland steam condenser and one deaerator.
Since steam and water loses in thermal cycles, the make up water comes from water treatment plant and then be filled into the condensate system. The make up water is of demineralizer water.
The condenser is of single shell, two passes, divided water boxes, surface type. The hotwell has sufficient capacity to assure enough water supply to the condensate pump. The condenser level is controlled in certain range by both make up water and overflow regulating valves.
Two sets condensate pumps each having 110 percent maximum condensate water flow shall be provided, one for normal operation and one for standby.
To assure minimum flow through the condensate pump to prevent cavitation and through gland steam condenser, the recirculation system is provided from condensate manifold downstream of the gland steam cooler returning to condenser through a regulation station.
In order to heat the condensate, four surface low pressure heaters are employed. whenever any one of them is broken down the bypass valve shall be open prior to shutting off the heaters.
The deaerator is of spraying and tray type in which condensate is deaerated and heated.
The discharge branch with an isolation valve from downstream of No 4 LP heater to discharge pipe of circulation cooling water is designed to discharge dirty condensate during units start up.
3.4.5 Auxiliary Steam System
One auxiliary steam header is designed. Three steam sources are provided as the follows:
(1) Start up boiler during units start up.
(2) No.3 extraction steam during the unit operates normally.
(3) Cold reheat steam during the unit in low load condition.
The system will supply the required steam to the followings in any operation condition.
a. To supply steam for heating to the deaerator during the unit start up ,shut down and turbine trip.
b. To the gland sealing steam system during the turbine start up and shut down.
c. To the cylinder flange heating steam system.
d. To Fuel Oil pipe purging.
3.4.6 Cooling Water Sysytem
A circulating water system in unit type will be adopted to supply cooling water to condenser.
Opened cycle cooling water from circulating water inlet pipe will be pumped to oil coolers and closed cooling water system heat exchanger through electric strainer and opened cycle cooling water pump, and discharged to circulating water outlet pipe. There are two opened cycle cooling water pump, under normal operating condition, one pump working and another standby.
To keep the condenser working smoothly and the condenser tubes cleaning and the degree of condenser vacuum, sponge ball cleaning system will be installed.
Sponge ball cleaning system is very popular and efficient in China power plant, We suggest owner to use this system. If owner insist to use condenser backwash system, we will cooperate with the manufacture.
Periodic blow down flash vessel will be cooled by industry water, the flushing water for turbine hall will comes from circulating water system, the flushing water for boiler house will comes from industry water system.
The closed cycle cooling water system will comprises of two cooling water pumps (one working and one standby), two 100% demineralized water/circulating water heat exchangers (one working and one standby), one expansion water tank. Expansion water tank will located on high position, which can assure system pressure to be stable. The closed cooling water system heat exchanger will be cooled by circulating water. The secondary water source comes from demineralized water.
It is suggested that most of the auxiliary equipments will be cooled by opened cycle cooling water, including generator hydrogen cooler, working oil cooler of electric BFP, lubricated oil cooler of electric BFP etc.
3.5 FGD system
3.5.1 FGD major design principle
The flue gas desulphurization is based on Wet limestone/gypsum.
The principle will be implemented when design the FGD system and choose the equipments, it must be advanced、safety and reliable�?/DIV>
The SO2 concentration into stack is less than 2000mg/Nm3 （standard, dry, 6%O2）when the sulpher content is no more than 3.34% in coal.
One absorber will be set up for each boiler. The capacity of one absorber shall be designed as that it can disposal flue gas in BMCR condition of the boiler.
GGH shall not be supplied for FGD temporarily transitorily. It depends on the environment requirement.
The flue gas pressure drop of the FGD should be overcome by the booster fan.
Two oxidation air blowers shall be supplied for FGD (thereinto one for standby).
One limestone silo shall be supplied which capacity shall be amount for 3 days�?limestone consumption under BMCR operation of 2 boilers.
The gypsum dewatering system shall be equipped for FGD, including two gypsum hydro-cyclones systems, two vacuum belt filters, two vacuum pumps, two vacuum tank s, one cloth water tank and 3 cloth water pumps. The capacity of the capacity vacuum belt filter shall be designed as 100% of the gypsum slurry from the absorber.
Gypsum after dewatering drop into the storage house directly.
Service air for instruments and overhaul of the FGD shall be led from service air header of the power plant compressor house to outside of the FGD island .
3.5.2 FGD process system & main Equipment
A set of flue gas system shall be set for a boiler in FGD Island.
The raw flue gas draws from the main duct at downstream of the ID-fans of boiler. The gas will be cleaned in the absorber on the basis of a wet limestone process and the cleaned flue gas will be discharged via the stack to the atmosphere.
Absorber has various forms. It is very important to choose the form for FGD based on wet limestone-gypsum. The spraying empty tower is widely utilized at the preliminary design stage.
The absorber is designed as the integrated system including spraying bank, nozzles and entire inner components, agitator, mist eliminator, outward steel and heat insulating layer.
The Absorber Circulation system comprises three sets of Absorber Circulation Pumps, pipe, spray groupware ect. The number of Absorber Circulation Pump shall be meeting with the number of spray floor.
Two Oxidation Air Blowers shall be designed for FGD (therein to one for standby)
Two gypsum slurry discharge pump shall be supplied for absorber, for discharging the slurry to dewatering system.
c)Limestone Slurry Preparation and Supply System
The parciles (<=20mm) meets the requirements will be delivered by the truck to the discharging workshop, through the vibrating feeder, bucket hoister and the scraper belt conveyer to the limestone silo. The limestone delivers to the wet ball mill by the belt conveyor and has been grinded into slurry which will be sent to limestone recirculation tank and then be sent to hydroclone for the separating. Qualified slurry will be delivered to the slurry tank and the unqualified slurry will be returned to the ball mill form the hydroclone to be grinded again . Qualified slurry will be pumped to absorber for the desulphurization.
The limestone slurry preparation will take place in the limestone slurry preparation tank, where the limestone is dosed, mixed together with water and forms a slurry suspension of fine limestone particles. Additionally, the tank serves as a storage capacity.
This system shall include one limestone silo. The capacity of the limestone storage silo shall be amount for 3 days�?limestone consumption under BMCR operation of 2 boilers. The silo shall be applied with two outlets. The clean gas shall have a dust burden of less than 50mg/Nm3.
The silo shall be made of steel，the inner cone of the limestone silo shall be lined bya a kind of macromolecule material preventing from abrasion.
The system comprises one vibrating feeder 、one bucket hoister、one limestone silo 、two belt weigh feeders、two wet ball mills、two limestone slurry pumps & one limestone slurry tank with agitator. Limestone slurry tank, available volume shall be designed as not less than 6 hours�?limestone slurry consumption of boiler under BMCR condition. The Limestone slurry tank shall be made of steel structure.
d) Gypsum dewatering system
The gypsum slurry from 2 absorbers shall be delivered to the hydroclone station for classification. The concentrated slurry will flow automatically to the vacuum belt filters and after the dewatering; the surface water moisture content will not exceed 10%. The dewatered gypsum will be stored in the storage house and waiting for delivery. The overflowed slurry will be sent to the refluence water tank, most of refluence water will be pumped to the absorber for reusing。The else will be pumped to the wastewater cyclone. The overflowed slurry from wastewater cyclone will be sent to wastewater handle system, the downflowed slurry returned to refluence water tank�?/DIV>
In order to control the Cl- content and the quality of the gypsum, the process water shall be used for the scrubbing. The filter water will be collected into the refluence water tank.
The gypsum dewatering system include two gypsum hydro-cyclones systems, two vacuum belt filters, two vacuum pumps, two filtering liquid separation system, one cloth wash water tank and 3 cloth wash water pumps,. The capacity of the vacuum belt filter shall be designed as 100% of the gypsum slurry from 2 absorbers.The gypsum storage house can store about 3 days gypsum production. The scope is the out of the house, and the truck is owned by the owner.
e) Blow down system
The drain engendered at normal operation, facilities overhauling and normal flushing shall be drained to the slurry sump. The drain comes back to the absorber for reusing in the sump of the absorber area and the drain shall be re-used to gypsum dewatering area. Stirring measures shall be taken to avoid slurry sump and emergency slurry tank against deposit.
The emergency tank works as slurry buffer tank, when absorber needs maintenance and must be emptied, the slurry in absorber can be pumped into emergency tank. When the absorber will be run again, the gypsum slurry can be fed to absorber as gypsum crystal.
The capacity of the emergency slurry tank with agitator shall meet the requirement that can contain need discharge slurry minimum during whole internal components in one absorber to be repaired. The slurry in emergency slurry tank shall be discharged to absorber by a pump.
The wet limestone desulphurization process requires a certain amount of supply of process water.
The system comprises one process water tank, two process water pumps, two mist eliminators flush pumps. The usable capacity of process water tank shall be designed as maximal water consumption when FGD plants operate normally an hour. Capacity of the pumps shall be designed as 2x100%（therein to one for standby）for FGD.
By means of pumps, the process water is distributed to several consumers:
In order to bring the compressed oxidation air to a lower temperature level, it is quenched before entering the absorber.
The water loss in the absorber due to the evaporation has to be equalized by addition of process water.
The required solid content of the limestone slurry can be achieved by adding process water.
In the gypsum dewatering process, the vacuum belt filter need a certain amount of process water for washing the cloth of filter.
Other consumers, as for purposes of cleaning, flushing pipes, reduction of dust emission etc.
mist eliminators flush water is used to clean the mist eliminators.
Service air for overhaul and maintenance of the FGD shall be led from service air header of the power plant’s compressor house to outside of the FGD Island, where the air shall be led to each air using point, including pipes and valves.
All places need to be blown by service air shall equipped with platforms and stairs (if necessary), so as to operate easily.
