Coal Feed Systems For Boiler And Coal Milling Plant

Coal Feed SystemsFor Boiler and Coal Milling PlantGravimetric and Volumetric Systems Belt and Chain Type Feeders

QStock Equipment Company established in 1929QFirst Gravimetric Coal Feeder (1957) designated as ASME Historic Landmark in 1995QMore Feed System installations than all competitors combined8,000 Feederssupplied worldwideQAustraliaQHong w ZealandQUnited KingdomQColumbiaQIsraelQPakistanQUnited StatesQCosta RicaQItalyQPhilippinesQUkraineQCzech RepublicQJapanQPortugalQVenezuelaQDominican RepublicQKoreaQSouth roven reliability and long life in numerous applicationsQTechnically superior designQComplete bunker to pulverizer system supplyQUnparalleled customer aftermarket supportQWorld wide manufacturing facilitiesQFactory trained and highly experienced field service personnelQISO 9001 Quality CertificationQTotal service from parts supply to turnkey installationsQTest Tower eliminates field R&D

The Composite Gravimetric FeederFor close centred applicationsQThe arrangement andgeometry of thebunker/feeder/mill hasimplications for the design of aGravimetric Feeder, in both newand retrofit applicationsQA typical arrangement isshown, whereby the centre lineof the feed to the mill is insidethe line of the bunker outlet.QAlso note that an emergencydischarge facility is alsorequired. (This tends to be animportant feature, especiallywhere volatile coals are beingused and the residence time ofthe bunker is limited).FROM COAL BUNKEREMERGENCYDISCHARGETOPULVERISERQThe Gravimetric Feeder can be adapted to meet these dimensional constraints by applying the REDLERknowledge of conveying coal with a chain into a STOCK Gravimetric Feeder giving a most suitable andpractical design of feeder to deal with short centreline dimensions from inlet to outlet.QComposite Gravimetric Feeder:To handle up to 70 tonnes/hr of coal.QInstalled in a UK Power Station to replace anexisting volumetric feederQThe Chain Conveyor in the lower part of the Feederreceives fuel from the Weigh Belt Unit and thedischarge can be arranged at any point along theFeeder length. This arrangement suits applicationsfor retrofitting that are being encounteredBunker GatesQCustom designed to suit wide range of bunker sizesQDesigned to close through a standing column of coalQManual or Power operation

Typical Feeder ArrangementsThe Standard Gravimetric Coal FeederQDesigned to withstand 3.5 bar g explosion pressure per NFPA code 85Q2.1 m minimum centres inlet to outletQ610 and 915mm inlet downspout sizesQCapacities over 100 tonnes/hrQWeighing Accuracy /- 0.5%The Compact Gravimetric Coal FeederQ3.5 bar g explosion pressure containmentQ1.22m centres inlet to outletQWeighing Accuracy /- 1.0%QCapacities up to 100 tonnes / hourThe Low Pressure Gravimetric Coal FeederQUsed on Fluid Bed Boiler Boilers to deliver coal and limestoneQSuitable for pressure up to 0.2 bar gVolumetric Belt FeedersQAll the major features of the GravimetricFeeder, without the load cell weighing systemQMinimum 610mm centres of inlet to outletVolumetric Chain FeedersQDesigned to withstand 3.5 bar gexplosion pressure per NFPA code 85QFitted with Redler heavy duty chainQCapacities over 100 tonnes/hr

Why Gravimetric Feeding of Coal?Because of the heterogeneity of coal, gravimetricfeed systems have a number of advantages overvolumetric systems when it comes to achievingoptimized combustion in pulverized coal fired powerplants, with lower emissions. Gravimetric systemsare widely used in the USA, volumetric feederscurrently predominate in Europe, but with thegrowing pressure to reduce emissions this is likely tochange.When firing coal, there is currently no effective wayto measure kilojoule (BTU) flow, so this value mustbe inferred from either volume or weight flow. Thevolume flow measurement will be in error by thevariation in both density and heating value, whereasthe weight flow signal will be in error only to theextent of the variation in heating value. Thegravimetric feeder is vital if an accurate flow rate isto be maintained irrespective of density changes.Maintaining the correct amount ofcoal to the pulverizer is not a simpletask since the coal propertiesconstantly vary due to sizingdifferences and the adverse impactof moisture on heating value, flowcharacteristics, and density.The effects of moisture on coal hasbeen studied for many years withresearch conducted by manyinstitutes, who have published dataillustrating how coal densitydecreases with increasing moisturelevels within the ranges typicallyexperienced at coal fired powerplants. The effects of moisture isalso dependent upon the particlesizing of coal which generallyreflects a lower density level forsmaller sizes.Summary of BenefitsQ Fuel Savings through Improved Boiler EfficiencyThe differences in the amountof coal delivered to thepulverizer and hence theburners by a volumetric andgravimetric feeder areillustrated on this chart.Q Improved Combustion Efficiency/LOIQ Improved Pressure and Superheat ControlQ Less Slagging and PluggageQ Less NOx through Better Control of Excess AirQ Less CorrosionQ Stability and Improved Response ofCombustion ControlsQ Reduced O&M costsQ Improved Coal Mill PerformanceQ SafetyDue to the difficulties in burningcoal, it is necessary for excesscombustion air to be added to thefurnace in order to ensure safe andcomplete burning of the fuel. Thisexcess air is typically 15% to 18%depending upon the volatilecontent of the fuel.Variations in the amount of fueldelivered to the burners due todensity changes and the feedersaccuracy also requires additionalair to avoid loss of carbon andunsafe conditions within thefurnace. This additional air goes upthe stack and represents anefficiency loss for the plant.Gravimetric Feeder PrincipleQThe gravimetric feeder weighs material on a length ofbelt between two fixed rollers using a weighingroller.QBelt speed is determined by a tachometer attachedto the motor shaft. A microprocessor multiplies thespeed and weight signal to arrive at the feederoutput.QThe microprocessor matches the feeder output to thedemanded output by adjusting the feeder motorspeed.

Feeder Construction and FeaturesFeeder InletThe feeder inlet is constructed of solid, type 304,stainless steel. A replaceable stainless steellevelling bar shears the coal column, forming auniform profile of coal on the belt necessary foraccurate weighing.Typical Stock FeederAccuracyAccurate fuel delivery ensures stable combustioncontrol and rapid response to changes in boilerload. The STOCK gravimetric feeder is designedto provide uninterrupted fuel delivery with a feedrate accuracy of /-0.5%. Proven accuracy andreliability have been demonstrated over decadesof practical experience.Head PulleyThe pulley is machined flat to within 0.13mm T.I.R.A multiple pin and bushing coupling simplifiespulley removal.Dual Load Cell Weighing SystemDual load cells combine maximum accuracy withreliability. The outputs are checked against eachother prior to transmission to the feed ratecircuitry.Excessive deviation or an unreasonable signalresults in immediate and automatic transfer to avolumetric feed mode without interruption of flowACCUFLEX Feeder BeltACCUFLEX is a mechanically spliced, single-plyfeeder belt that enhances long-term feeder accuracy,has the strength of a two-ply belt, and is easilyinstalled. A molded V-guide maintains propertracking. Molded, notched belt curbs minimize dustspillage.Take –Up PulleyThe pulley body is slotted and contains an internalhelix to provide self-cleaning operation. The pulleyface is also crowned to facilitate belt tracking.Belt Tension/Take –UpBelt tracking and tensioning are accomplished bymeans of a unique take-up assembly consisting oftwo externally operated stainless steel,spring–loaded screws. The take-up screws havehex heads to accommodate a ratchet wrench.Cleanout ConveyerMalleable iron drag chain continuously clean anydust accumulation from bottom of the feeder.Weighted Belt ScraperThe scraper effectively cleans the outside of thebelt.AlarmsAlarms are located downstream from the feederinlet, and at the feeder discharge, to indicate thepresence of coal on the feeder belt and to detect coalpluggage to the mill.Internal Illumination (Optional)Work lights located at each end of the feederprovide excellent illumination of the feeder interior.Light bulbs can easily be changed from outside thefeeder body without disrupting the pressureintegrity of the feeder shell.

Body shellThe 8mm thick carbon steel constructionexceeds NFPA Code 85 Boiler Coderequirements of 50 psi (3.5 bar g) explosionpressure containment. All parts that contactthe active coal flow are fabricated of type 304stainless steel or rubber.Access DoorsLarge access doors are designed for easyentry and convenient feeder maintenance.Each end door is secured with heavy dutyfasteners for rapid entry. Two glass ports arelocated in each end door for viewing belttracking and coal flow.QShell Being MachinedThe Feeder ControllerQThe STOCK 196NT microprocessor system is a refinementof proven electronic controls designed to operate in powerplant environments where harsh conditions and frequentpower disturbance exists.QSpecial circuits, software subroutines and nonvolatilememories for process data are utilised for maximum systemavailability and performance.QThe controls are housed in enclosures rated NEMA 4 orbetter.Two-line vacuum fluorescentdisplay with forty alphanumericcharacters per lineNumbers displayed with a label(Rated) and selectableengineering units (Lbs/hr)LED indicators on MODE keysEnvironmentally sealed membraneswitch keyboardFunctional grouping of keyboardinto five areas-Calibration, Mode,Programming, Operation, andStatusThirty-one embossed function keyswith tactile feedbackLED indicators for system STATUSFeatures:QAn alphanumeric display that clearly communicates text messages to the operator, reducing the useof the operating manualsQHighly integrated electronics which result in fewer components and improved reliabilityQHourly calibration of load cell circuitry is performed automatically and eliminates system drifts due totimeand temperatureQKeyboard designed for simplified operator interface allows direct entry and recall of site-specificparametersQAll operating information and program data stored in non-volatile memory without requiring batterybackupQBuilt-in diagnostics to assist in system troubleshootingQDesigned for long-term accuracy without frequent calibration. Calibration is performed by themicroprocessor and the procedure is fast, accurate, and automatic.

Stock Redler LimitedRedler HouseDudbridge, StroudGloucestershireGL5 3EY EnglandT 44 (0) 1453 763 611F 44 (0) 1453 763 582sales@redler.comPublication No. 29/06Schenck Process GmbHPallaswiesenstraße 10064293 DarmstadtGermanyT 49 61 51-32 10 28F 49 61 51-32 11 72sales@schenckprocess.com

The Compact Gravimetric Coal Feeder Q 3.5 bar g explosion pressure containment Q 1.22m centres inlet to outlet Q Weighing Accuracy /- 1.0% Q Capacities up to 100 tonnes / hour The Low Pressure Gravimetric Coal Feeder Q Used on Fluid Bed Boiler Boilers to deliver coal and limestone Q Suitable for pressure up to 0.2 bar g Typical Feeder Arrangements Volumetric