coal vibrating feeders

Coal Vibrating Feeders: An Overview

Coal vibrating feeders are essential material handling equipment used extensively in coal-fired power plants, coal preparation plants, coking plants, and other industries involved in bulk coal processing. Their primary function is to reliably and controllably transport raw or sized coal from a storage hopper or bin to downstream equipment such as crushers, screens, conveyors, or mills. By providing a consistent and regulated flow rate, they ensure the efficiency and stability of the entire production line. This article delves into the working principles, key types, selection criteria, and practical applications of these critical industrial components.

Working Principle and Key Types

A coal vibrating feeder operates by generating a linear or elliptical vibratory motion through an exciter (drive unit). This motion is imparted to a trough or pan, causing the coal to hop along the trough's surface in a series of small, rapid movements. This controlled vibration prevents arching and ratholing in the hopper above and ensures a steady, adjustable discharge.

The two most common types are:

• Electromagnetic Vibrating Feeders: Utilize an electromagnetic drive to generate high-frequency, low-amplitude vibrations. They are known for instant control, excellent metering accuracy, and low maintenance due to few moving parts.
• Electromechanical Vibrating Feeders: Employ rotating eccentric weights (vibrator motors) to generate lower-frequency, higher-amplitude vibrations. They are robust, capable of handling heavier loads and larger lump sizes, and are often preferred for high-capacity applications.

The choice between these types depends on specific operational requirements. The following table outlines a direct comparison:

Feature	Electromagnetic Vibrating Feeder	Electromechanical Vibrating Feeder
Drive Mechanism	Electromagnet & spring system	Eccentric weight motors
Vibration Frequency	High (50-60 Hz / 3000-3600 VPM)	Low (15-30 Hz / 900-1800 VPM)
Amplitude	Low (1-3 mm)	High (3-10 mm)
Control Precision	Excellent; instantaneous flow rate adjustment via variable voltage	Good; flow adjusted by varying motor speed or weight position
Capacity & Lump Size	Best for lower capacities & smaller lumps (<300mm typical)	Suited for high capacities & large lumps (>500mm possible)
Maintenance	Generally lower (no bearings in drive)	Requires periodic bearing lubrication/monitoring
Typical Application Precise feeding to crushers, weigh scales, boiler feed systems. Heavy-duty feeding from ROM (Run-of-Mine) hoppers, apron feeder replacement.

Selection Criteria and Industry Application

Selecting the right coal vibrating feeder involves evaluating several factors:

• Material Characteristics: Coal size distribution (including maximum lump size), bulk density (typically ~800-1000 kg/m³ for coal), moisture content, and abrasiveness.
• Flow Requirements: Required feed rate (tons per hour) and the desired range of adjustability.
• Duty Cycle: Continuous or intermittent operation.
• Installation Environment: Factors like dust exposure (requiring sealed designs or dust-tight covers), ambient temperature, and whether the location is classified for explosive atmospheres.

A critical application is ensuring a uniform feed onto belt conveyors or into crushers. An uneven feed can cause belt misalignment, spillage, and crusher choke-feeding or uneven wear. Properly sized feeders mitigate these issues.

Real-World Case Study: Power Plant Boiler Feed System

A 650 MW coal-fired power plant in Eastern Europe faced challenges with inconsistent fuel feed to its pulverizers from its bunkers. The existing gate systems caused erratic flow, leading to fluctuations in boiler efficiency and increased NOx emissions due to imperfect air-fuel ratios.

Solution: Four large electromechanical vibrating feeders were installed beneath the boiler bunkers. These heavy-duty units were designed with abrasion-resistant liners to handle the sharp coal.

Implementation & Result: The feeders provided a smooth, continuous, and fully controllable discharge of coal onto the conveyor belts feeding the pulverizer mills. The control system was integrated with the plant's Distributed Control System (DCS). This allowed for automatic adjustment of feed rates based on real-time boiler demand.
The outcome was a significant stabilization of boiler operation. The plant reported a measurable improvement in combustion efficiency (~1.2% increase), more stable steam parameters, reduced mill blockages,and easier compliance with emission limits due to more consistent combustion conditions.

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Frequently Asked Questions (FAQ)

Q1: How do you prevent dust generation from a coal vibrating feeder?
Dust control is paramount. Common solutions include installing flexible dust skirts at the inlet and discharge points,totally enclosing the feeder pan with gasketed covers,and integrating the feeder into a system with local exhaust ventilation(LEV). For extremely fine or dusty coals,a totally enclosed tubular vibratory feeder may be specified.

Q2: Can vibrating feeders handle wet or sticky coal?
This is a significant challenge.Sticky coal can adhere to the trough,l reducing capacityand eventually cloggingthe unit.Solutions include using feeders with special deck designs(exponential troughs),applying liner materialswith low adhesion properties(e.g.,UHMW polyethyleneor stainless steel),incorporatingheater padsor insulationto prevent moisture condensation,and sometimes using air cannonsor vibrators onthe hopper aboveto assist material flow.

Q3: What arethe main maintenance requirementsfora coal vibrating feeder?
Maintenancevariesby type:

• Electromagnetic: Primarily involves checkingthe integrityof springs,the air gap ofthe electromagnet,and tightening all fasteners(which can loosenfrom vibration).
• Electromechanical: Focuseson themotorsand bearings.Regular lubricationof themotor bearingsas per manufacturer specs is critical.Monthly checksfor bolt tightnessand structural integrityof the troughand support springsare essentialfor both types.Wear linersmust be inspectedandreplaced periodicallybased on abrasion.

Q4: Howis thefeed rate controlled?
For electromagnetic feeders,the feed rateis preciselyand instantly variedby adjustingthe voltageinputto themagnet(viaa variable transformeror solid-state controller),which changesthe amplitudeof vibration.For electromechanical feeders,the amplitude(and thusrate)can be adjustedby changingthe eccentric momenton themotor shafts(manual adjustment)or by usinga Variable Frequency Drive(VFD)tocontrolthemotor speed,a methodthat offersgoodcontrolwhile reducinginrush currenton start-up.

Q5: When wouldyou chooseavibratingfeeder overan apronfeederforcoal?
Vibratingfeedersare generally more economical,havesimpler designs,and requireless maintenanceforapplications involving smallerlump sizes(<500mm)and whereprecise meteringis beneficial.Theyare often usedas an economical alternativeunder stockpile reclaim hoppersor formetered feeding.Apronfeeders,a typeof chain conveyorwith overlapping pans,better suitedforextremely heavy-dutyapplications involvingvery large,direct dumpROMcoalwith massive lumps(>1m),extremely high impactloads,and whereabsolutely positivetractionis requiredregardlessof material conditions(e.g.,directly underacrusher discharge).