THERMAL POWER PLANT AND COAL, ASH PREPARATION AND HANDLING

BY-PROF. AFAQAHMED JAIKTC, NAVI MUMBAI

SUPER CRITICAL POWER STEAMGENERATION

The power plant which operates above the criticalcondition is a ”SUPER CRITICAL POWERPLANT”

Definition of critical ConditionCritical condition is thermodynamic expressiondescribing the state of a substance beyond whichthere is no clear distinction between the liquid andgaseous phase.

SITE SELECTION :-

Availability of Coal – 400 MW NEEDS 6000TONS/DAY Ash Disposal Facility –Major Problem ,Power generation by coal contains 20 – 40 % Ash,Quantity of ash is 1500 – 2000 tons / day400 MW Power Station requires 10 Hectares area/ year of height 6.5 mSpace Requirement Land Required 3 – 4 Acres / MWCost of Land

Nature of Land – Good Bearing capability towithstand Load of Machineries and forcestransmitted. Min bearing capacity of land is 15 BarAvailability of Water –Water required for Condenser, Boiler, Drinking Condensation need 20 to 30 thousand tons / Hrfor 60 MW Boiler need 6 – 10 tons / Hr Transport Facility – Railway Line for coal and machinery transportUK decided to locate the power plant to source notat loadAvailability of Labour Public problem

COAL STORAGE –Purpose -1. Insurance against complete shutdown due to shortage2. Take the advantage of seasonal market. 3. Quarter of annual burn to be stored4. For 200 MW area required 30 acres of height 10m5. Storage of coal is undesirable ( Diff cost )Major Two types of storage1. Dead ( Shortage, Mine strikes, Railway S)2. Live

Scientifically Coal is stored to avoid oxidation in following

1. Stocking in Heaps Ground used for stocking of dry and level Coal is piled at 10 – 20 m Height Coal is compacted in layer to prevent air

circulation Gentle slope is given to pile Temp maintained below 75 Asphalt , Fine coal dust is used to coat the

exterior surface of pile to prevent oxidation

2. Under Water Storage –Slow oxidation and Spontaneous combustion is eliminatedFollowing points should be kept in mind – Free from standing water Artificial Drainage Area should free from foreign particals Handling cost should minimum Piles built up in successive layers Effective Ventilation for coal Temp check Fire Fighting equipments

COAL PREPARATIONConverting unsized coal sized coal.

Following Equipments are used for CoalPreparation

Crushers – 600 Tons / HrSizersDryers – Hot Flue Gases passedMagnetic Separators – Iorn scrap

and metallic particles removed

COAL PREPARATION PLANT

ASH HANDLING SYSTEM

ASH HANDLED 10-20% OF WEIGHT OF

COAL

60,000 TONS / Annum for 200MW

plant in India which covers area of 4

Hectors of height 1.5 m

GENERAL LAYOUT OF ASH HANDLING

MECHANICAL HANDLING SYSTEM

MECHANICAL DUST COLLECTORS1. DRY TYPE2. WET-TYPE

1. GRAVITATIONAL SEPERATORS(Dry)

2. CYLONE SEPARATORHigh velocity gas stream enters intoconical shell, due to whirling motion thedust is collected to sides and fall out.Multi Cyclone dust collectors are alsoused

2. WET TYPE DUST COLLECTORS LOW SULPHUR CONTENT (SO2 ) LOW SULPHUR FUEL IS EXPENSIVE H20 + LIME IS SPREAD ACROSSFINE, SLOW MOVING LIQUID DROPLETSCOLLIED WITH WET DUST PARTICLES.WETTED PARTICLES AGGLOMERATEUNTIL HEAVY ENOUGH TO DROP

ELECTROSTATIC PRECIPITATOR Developed by Dr. Cottel in 1906 Economically used in 1937 It’s generally used to remove fly ash Use of this collector increased rapidlybecause of strict air quality codes30,000 to 60,000 Volts appliedbetween conductors Dust is passed through highly chargedelectrodesThen it is passed through collecting unit

Which consist set of vertical plates.

Alternate plates are positively charged and earthed.High intensity electrostatic field exerts force on +vely charged dust particles and drives them towards grounded plates.

ELECTROSTATIC PRECIPITATOR (GENERAL LAYOUT)

ADVANTAGES1. It removes very small particles like smoke, mist

and flyash (.01 – 1.00u)2. Effective in high dust loaded gas with eff of

99.5%3. Less maintenance4. Ease of operation

DISADVANTAGES1. High voltage and Capital Cost2. Space requirement is more3. Effi affected by velocity exceeded4. Protection is required for plates because of

closeness