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MINE MACHINERY

COAL HANDLING PLANT

MINE MACHINERYMINE MACHINERYMINE MACHINERYMINE MACHINERYMINE MACHINERYMINE MACHINERYMINE MACHINERY

CONTENT

SL.No. TOPIC PAGE No.

1 Abstract 2

2.

Introduction 2

3 Working of Coal Handling Plant 2

4 Availability of Coal in India 4

5 Transportation of Coal 5

6 CHP Auxiliary And Equipments 5

7 Operational Cycle. 6

8 Measures before Transporting Coal 7

9 Problems in coal handling plant 7

10Dust management in thermal power plant

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ABSTRACT

Many thermal power plants use coal as their fuel.To handle the coal, each power station is equipped with a coal

handling plant. The coal has to be sized, processed, and handled which should be done effectively and efficiently.

While working in the coal handling plant the major factor which reduces staff efficiency is the working environment

i.e., dust etc.. Generally all systems used in power station coal handling plants are wet dust suppression systems.

INTRODUCTION

Coal Handling Plant (CHP) is a plant which handles the coal from its receipt to transporting it to Boiler and store in

Bunkers. It also processes the raw coal to make it suitable for Boiler Opeartion.

Coal Handling Plant (CHP):-

Extent of work: - In brief we can say that receipt of coal from coal mines, weighing of coal, crushing it to required

size and transferring the quanta of coal to various coal mill bunkers. This is the responsibility and duty of the CHP and

its staff.

Receipt of Coal :- 

Normally Thermal Power Station receives the coal by three modes of transportation.

1. By Railway (80-90% of the requirement is fulfilled by this way)

2. By Road ( if required 5-10% of the requirement is fulfilled by this way )

3. By Arial ropeways

General Working of a Coal Handling Plant :-

As mentioned above, coal is brought to power station by either of three means of coal transportation. This coal is first

conveyed to primary crusher with the help of different combination of conveyor belts and its rate of feeding is

controlled by Electro-magnetic vibrating feeders. Conveyor belt before the crusher is provided with hanging magnets

to separate ferrous materials. Stones are picked up manually. In primary crusher, coal is first crushed to 100 mm size.

This coal is again conveyed to secondary/final crusher on belt system. Here vibrating screens are used to feed

crushers, which bypasses coal of size more than 25 mm. In final crushers, coal is further crushed to required 25 mm

size. This sized coal is then send to bunkering belt and with the help of coal trippers. This sized coal is finally fed to

coal bunkers. This cycle is called coal bunkering. In case bunkers are full, then available coal is stored in stock yard

with the help of stacking belts /automatic stacker cum reclaimer. This cycle is called stacking. In emergency when

coal is not available in plant by railways/ropeways, then this stacked coal is diverted to the coal bunkers by

reclaimimg conv. belts. This cycle is called reclaiming. The coal stored in bunkers is further send to coal mill for

pulverization and combustion in boiler furnace.

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GENARAL LAYOUT OF COAL HANDLING PLANT(CHP)

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Availability of Coal In India :-

Mostly E and F grade coal used in India.

Blending Is Done To get Average D Grade.

Grade C.V.

( K Cal / Kg. )

% Ash + Moisture

> 6200 19.57

5601-6200 19.57 - 23.97

4941-5600 23.92 - 28.69

4201-5940 28.69 - 34.05

3361-4200 34.06 - 40.14

2401-3360 40.14 - 47.10

TRANSPORTATION OF COAL:-

Coal is brought to the power station by three modes of transportation :

1.Roadways

2.Railways

3.Ropeways

1. Roadways : Coal is carried in trucks and a truck can carry about 8-10 tons of coal. But due to low capacity, low

unloading rate and time consuming, this mode is not in much use for large thermal power stations.

2. Railways : coal is brought by railway wagons. One rack consists of 58 wagons. Each wagon contains 58 MT of

coal. Locos bring the wagons from the marshalling yard and place them on wagon tippler. These wagons are then

unloaded with the help of wagon tippler. If these wagons are not unloaded in stipulated time period (generally 7 hrs.),

demurrage charges are lavied by railway department.

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3. Ropeways : This mode of coal transportation is used where coal mines are located near the power stations. Coal

is brought by hanging buckets/trolleys travelling on track ropes, which are pulled by a haulage rope with a driving

mechanism. The payload of each bucket varies from 1 to 3 tons. Automatic loading and unloading mechanisms are

provided at loading and unloading stations. Rate of unloading varies from 75 to 275 MT/Hr depending on the type of

ropeways used. This type of coal transportation is very economical compared to road or rail transportation and gives

assured supply of coal, being the MSEB property. The only disadvantage of this system is long time for maintenance

works.

Coal Hanndling Plant Auxilaries:-

Major auxiliaries of CHP:-

1. Wagon Tipplers

2. Vibrating Feeders

3. Conveyor Belts

4. Coal Crushers

5. Trippers

6. Electromagnetic Separators

7. Dust extraction systems

8. Gas Extractor

Wagon Tipplers:-These are the giant machines having gear boxes and motor assembly and are used to unload the coal wagons

into coal hoppers in very less time (e.g. 20 wagons/hr. or more).

Vibrating Feeders:-These are electromagnetic vibrating feeders or sometimes in the form of dragging chains which are provided

below the coal hoppers. This equipment is used for controlled removal of coal from coal hoppers.

Conveyor Belts:-These are the synthetic rubber belts which move on metallic rollers called idlers and are used for shifting of

coal from one place to other places.

Coal Crushers:-We receive the coal in the form of odd shaped lumps. These lumps are to be crushed to required size. These

lumps are crushed by coal crushers. 

Trippers:-These are the motorized or manually operated machines and are used for feeding the coal to different coal

bunkers as per their requirement.

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Electromagnetic Separators:-Electromagnets are used for removing of Iron and magnetic impurities from the coal.

Dust Extraction System:-This system is provided in CHP for suppression of coal dust in coal handling plant. 

Gas Extractors:-Gas extractors are provided at the bunker level to remove all types of poisonous and non poisonous gases

from the working area.

Operational Cycles:-1. Normal Bunkering cycle.

2. Stacking cycle.

3. Reclaiming Cycle.

Normal Bunkering Cycle:-Shifting of coal received from coal wagons directly to coal bunkers is normal bunkering cycle.

Stacking Cycle:-When there is no coal requirement at coal bunkers even then CHP has to unload the received coal which is

stacked at open ground called yard. This is stacking cycle. 

Reclaiming Cycle:-when coal wagons are not available the requirement of coal bunkers is fulfilled from the stacked coal this is

reclaiming cycle.

Precautionary Measures before Transporting Coal

Weighing of Coal:-Weighing of coal is carried out at wagon tippler. Weight of loaded wagon is taken; after unloading the coal,

weight of empty wagon is taken the difference of the two will give the weight of the coal (normally 55-60

metric ton of coal come in each wagon).

Payment of Coal:-Payment of coal is made to the coalmines as per the weighing of coal carried out at their premises. However,

if any dispute arises regarding weighing of coal same is to be settled by the committee of both the parties. 

Stone shells:-Sometimes stone shells are received along with coal same has to be removed from the coal before bunkering

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and is done sometimes manually or by different type of machines.

If quantum of stone shells is beyond minimum limit the cost of the coal is recovered from the coal mines

against the quantity of stone shells received from them.

Chemical Analysis of Coal:-Sample of coal is randomly collected from each rake by concerned MSEB (Maharashtra State Electricity

Board) staff and detailed chemical analysis, calculation of calorific value is carried out and is confirmed

whether it is as per agreement with the coal mines or not.

General Problems faced in Coal Handling Plant :

1. Design Problems :-Coal received in power station is having cal. Value much less and ash percentage more than

the rated values recommended by manufacturer. Hence the systems in coal handling plant get overloaded resulting in

low bunkering.

2. Rainy Season Problems : Chute choke ups, Coal yard -Slurry Formation Transfer chutes gets choked up due to

wet or muddy coal. Slurry formed in coal yard may cause problems with electro-magnetic feeders at input points,

frequent choke-ups at transfer chutes etc.

3. Other Misc. Problems: • Snapping of belts /ropes : Conv. belts and ropeway ropes get damaged or broken

because of jerks and overloading problems due to various reasons. Repairing and replacement of these belts and ropes

require more time for maint.

• Derailment of coal wagons : De-railment of wagons result in obstacle in unloading of balance wagons in line.

This results in lower bunkering and may attract demurrage charges from railway department.

• Oversized coal/Muddy Coal : Oversized / muddy coal may cause damage to the belt system, frequent choke-ups

of transfer chutes and damages to the crusher rings.

DUST MANAGEMENT AT COAL HANDLING PLANT OF A THERMAL

POWER PLANT :-

INTRODUCTION :-Coal fire thermal power plants are keys to power production in the country. They play vital role in power

generation and distribution, and constitute 64.75% of total power production in India. Since coal is the basic raw

material used in such power plant, so they are equipped with a large coal handling plant (CHP) where coal

transported from coal mines are stored and processed before sending to boiler and steam generation section. A

CHP may also be called a "coal handling and preparation plant" (CHPP). At this plant, major ergonomic concern

is of dust particles which become airborne while coal storage and processing. CHP require very large area for coal

storage and processing, therefore large scale dust generation occurs at such plant. People working here become

victim of Pneumoconiosis which is an occupational lung disease and a restrictive lung disease caused by the

inhalation of dust. Thus ergonomic design of CHP is necessary for betterment of workers and authority concern.

Since CHP require large amount of water for dust suppression, therefore innovative methods have to be design

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in order to minimize use of water. Since many thermal power plant in India facing acute shortage of

water, therefore efficient method of dust suppression and prevention is highly recommended which uses least

amount of water. The following paper discusses design of a dust collector which discharges dust in concentrated

form in order to reduce water consumption. Apart from Dust Collector, typical nozzle design is also proposed

which utilizes elegant diverging water spray for dust prevention minimizing water wastage. Dust suppression plays

vital role in improving performance of workers and their health, hence ergonomic design of CHP is very important

issue discussed at industry level, especially at Thermal Power Plant.

Layout of a Typical Coal Fired Thermal Power Plant

The above diagram typically outline a coal fire thermal power plant where coal transported from coal

mines through coal vessels called wagon Tripler is unloaded and coal silo is formed. As clearly outline the

major region of dust generation while performing above operations results in large scale airborne particles

which must be suppressed. We clearly define the region for which ergonomic design should be proposed. The

dust particles emanating from coal are typically is of size 1 to 100 microns. A typical NTPC plant requires

4.4 cubic meters per megawatt per hour.

DESIGN PROPOSALS FOR DUST CONTROL AT FIVE DIFFERENT STAGES OF A

TYPICAL CHP OF A THERMAL POWER PLANT :-

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Design proposals for preventing and suppressing dust at CHP using efficient methods. The above

figure clearly depicts the design proposal for preventing and suppressing dust at CHP using efficient

methods and implementing cutting edge technology. The given design proposal targets five different

stages where dust generation is quite large.

STAGE 1

At this stage, coal transported from coal mines is brought at CHP using Wagon Tripler and unloaded to

reclaimer. Large amount of dust is generated and in order to prevent dust, moisture addition is most efficient

technique as water is very powerful binding solvent. Directly adding moisture to coal prevents dust from

becoming airborne. Here diverging nozzles are used for moisture addition. Diverging nozzle will allow optimum

proportionate of water to be added with coal. Since it is necessary to know exactly what amount of water to be

added as too much water will cause mud and make coal heavier, on the other hand, too little water will be

ineffective in dust control.

STAGE 2 Here (reclaimer stage) coal is unloaded from wagon Tripler to be reclaimed. The area where reclaiming is

done is quite large and hence water addition will be futile. Also wind play devastating role in increasing dust. Thus

wind is the major factor.So wind speed i s c o n t r o l l e d in order to prevent dust to become airborne.

windshield net or windbreak forest is provided in order to reduce dust generation.

STAGE 3

Reclaimer piles up the coal at a large storage area and forms a stacker or coal pile. While doing this, large

amount of dust is generated. Also coal stacker is a constant source of airborne dust particles. Therefore it is

necessary to suppress dust generation. At this stage surface compaction method is used to suppress dust using 6-

12% water solution of very good binding substance which binds the coal dust and prevent it from becoming

airborne. Moisture addition is done at this stage using well designed spray which allows controlled flow of solution

over coal pile in order to properly suppress dust without affecting the quality of coal.

STAGE 4

This stage is major area of concern because dust particle size is as low as 1-10 microns. Therefore this stage

requires a suitable, innovative and efficient technique of dust suppression. Since moisture addition is futile

exercise, therefore we develop wet dust collector which can reduce dust concentration as low as 1% in the

concerned area. Dust collector is very elegant device which discharges dust in concentrated form reducing water

consumption. Even for suppressing 1mm thick dust layer, we require large amount of water, but dust collector

with minimum use of water, suppresses large amount of dust. The following section discusses design of wet

centrifugal dust collector with automatic discharg for suppressing dust at this stage. Here processed coal is

transferred from coal stack through conveyor to relay section, hence large amount of dust is generated which can be

suppressed using dust collector.

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STAGE 5

Last stage is unloading of coal from relay section and transfer to the boiler section. At this stage, usual method of

moisture addition is sufficient since small amount of dust generates which can easily be suppress using proper

amount of moisture addition. At this stage also, diverging nozzles of optimum diameter are used for proper water

spray.

DESIGN OF A WET CENTRIFUGAL DUST COLLECTOR :-

Centrifugal collectors use cyclonic action to separate dust particles from the gas stream. In a typical cyclone, the

dust gas stream enters at an angle and is spun rapidly. The centrifugal force created by the circular flow throws

the dust particles toward the wall of the cyclone. After striking the wall, these particles fall into a hopper

located underneath.

The most common types of centrifugal or inertial collectors in use today are:

1) Single-cyclone separators

2) Cyclone Multiple-separators

3) Secondary Air Flow Separators

A typical wet centrifugal dust collector uses scrubbing effect of water to suppress dust. Water is very good binding

substance for dust and therefore it is used as scrubbing element. This device applies the principle of film

formation over the dust layer and confines dust particles leaving fresh air to escape.. The power rating of motor

varies as per requirement. This device uses the principle of dynamic precipitation technique in which very high

suction pressure suck the dusty air and allow to centrifuge through it. Centrifugal action separates dust from

fresh air and fresh air is allowed to escape from other end of dust collector.

The dust collector has a small tank full of water which has two valves. These two springs loaded valves are

operated to allow passage of concentrated dust and automatic filling of fresh water using sensors. These

sensors sense the concentration level of dust in the container and when it goes beyond 90%, it opens the

discharge valve. This remains open until total discharge of concentrated dust occurs from the tank. At the same

time, it opens inlet valve to allow fresh water to fill up.

The dust collector uses automatic discharge technique and hence save time for manual operations for

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discharging and refilling. Also discharge is recycled in order to have minimum water wastage. This centrifugal dust

collector is very efficient and requires minimum amount of water since it discharges dust in concentrated

form. Taking a typical case of a NTPC plant which uses 4.4 cubic meter per megawatt per hour, assuming power

production of 1000MW, total water consumption will be 4400 million cubic meter water. This is huge amount of

water which is utilized at such plant. But with the above mentioned techniques, if implemented properly can save

large amount of water and hence reduce chances of acute water shortage.

RESULTS AND DISCUSSION :-A wet centrifugal dust collector with automatic discharge can reduce airborne dust particles and minimize water

wastage. Also other methods of dust collection reduce dust and water wastage as discussed earlier. This has great

impact not only at workplace but also in environment. Proper implementation of dust suppression and prevention

methods reduces health hazards of workers, employees and people residing nearby. Since current situation demands

eco- friendly methods of dust suppression without much water wastage, above mentioned ergonomic designs are

noteworthy.

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PRESENTED BY

ROHIT KUMAR :- 111MN0521

JITEN KUMAR PAL :- 111MN0522

M. SHIVA SAI :- 111MN0523

N.SHASHANK :- 111MN0524

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