Ch 03 Steam Power Plant (DAY-01)

In steam power plants, approximately __________________ kcals of heat per MW per hour has to be disposed of in the condenser.

1.26 × 10^6

Transportation facility is required for ___________________________________________.

bringing heavy machinery for installation and for bringing fuel.

Location of power plant near to coalfield saves ______________________.

transportation charges

Weighing and measuring

📖 weigh bridge 📖 belt scale 📖weigh lorry 📖automatic scale

Uses of water in steam power plant

(i) as working fluid throughout the year, which is repeatedly evaporated and condensed. (ii) For cooling purposes such as in condensers. (iii) As a carrying medium such as disposal of ash and (iv) as a makeup water because some loss in the ckt is possible

The minimum bearing capacity of the land should be_____________________.

1 MN/m^2

CLASSIFICATION OF STEAM POWER PLANT

1. Central stations 2. Industrial power stations or captive power stations

What are the four important circuits in modern steam power plant?

1. Coal and ash circuit 2. Air and gas circuit 3. Feed water and steam flow circuit, and 4. Cooling water circuit

When new units are to be installed, what are the determining factors?

1. Effects of additional units on thermal efficiency of the plant 2. Expected rate of increase of maximum demand over the next few year 3. The room available for the additional unit 4. The suitability of generator to the existing unit regarding temperature, pressure

DESIGN OF INPLANT COAL HANDLING SYSTEM

1. Simple and sound, requiring minimum operations and transportation. 2. No double handling of coal in plant. 3. Handling unit should be centralised to facilitate inspection and maintenance. 4. Electric motors can be used as driver of mechanism. 5. Working parts should be enclosed to avoid abrasion and corrosion. 6. System should be able to supply required quantity of coal as per demand.

The means of working of vee bucket elevators

1. The buckets receive their load by dipping into the coal pocket in the lower end of the system 2. The material elevated in the bucket is discharged either by centrifugal forces at the top or by drawing back the buckets at the discharge end

Central stations

1. The electrical energy available from these stations is meant for general sale. 2. The exhaust steam is NOT discharged to the atmosphere. It is discharged into condenser. 3. In condenser, the pressure is maintained below atmospheric. 4. The plant extracts more energy from per kg of steam and develops the greater amount of power according to the size of turbine.

Industrial power stations or captive stations

1. The electrical energy is available for self use by industry, NOT for sale. 2. The power plant is NON-CONDENSING type 3. A continuous supply of fresh feed water is required.

SITE SELECTION FOR COAL DEAD STORAGE

1. The storage area should be free from standing water. 2. If well drainage is not available artificial drainage should be provided. 3. It should be free from all foreign materials like wood, paper rags, waste oil or material having low ignition temperature. Sealed against wind erosion 4. Handling cost should be minimum. 5. Pile should build up in successive layer and compact. 6. Pile should dressed to prevent entry of rainy water. 7. Alternative drying and wetting should avoided. 8. Conical piling should be avoided.

What are the two purposes served by steam power plant?

1. To produce electricity 2. To produce steam for industrial application in textile, food processing,paper mills,space heating, and other

Importance of bearing capacity for land use

1. To withstand dead load of the plant 2. To withstand forces transmitted to the foundation due to machine operation. 3. To reduce the cost of the foundation of the plant.

Complications from increase in pressure and temperature

1. With increase in pressure, the degree of superheat should be decreased in order to keep the total temperature within limits. 2. Beyond 500°C, there is rapid change in physical properties of the material and the problems become complicated.

Ways to ash disposal

1. can be sold to builders 2. can be used for brick making near the plant site. 3. can be dumped into the disused mines. 4. In case of site located near a river, sea or lake, ash can be dumped into it.

The outputs of units are classified under:

1. economical rating 2. maximum continuous rating

Disadvantages of mechanical handling system

1. needs continuous R/M 2. capital cost is more 3. some of the generated power is consumed and therefore the power output is decreased.

Factors that are considered in selecting a proper fuel handling system

1. plant fuel rate 2. plant location in respect to fuel shipping 3. storage facility

CHOICE OF STEAM CONDITIONS

1. price of coal 2. capital cost of plant 3. time available for erection 4. thermal efficiency obtainable 5. the station 'load factor'

advantages of pipeline coal transportation system

1. simplicity in installation and increased safety in operation. 2. more economical than other mode when dealing with large volume over long distances 3. continuous and remain unaffected by vagaries of climate and weather. 4. high degree of reliability 5. loss due to theft and pilferage is avoided 6. manpower requirement is low.

Mode of transportation of coal

1. transportation by sea or river 2. by rail 3. by ropeways 4. by roads by pipeline

Unloading equipment used when coal is transported by seas

1. unloading bridges 2. self unloading boats 3. coal towers - to unload rail wagons 4. portable conveyors 5. coal accelerators

In a power plant of 400 MW capacity, how many hectares of land is required per year if the ash is dumped to a height of 6.5 meters?

10

The MCR is normally ________________% LESS than maximum capacity of the plant.

10 to 15

In case of direct circulation from the source of water, _____________________ m^3 of water is required per MW per hour for condensing purpose.

120

Maximum capacity of screw conveyor is ________________________________.

125 tonnes/hour

In case cooling towers are used in condensing circuit, about __________________ m3 of water per MW per hour will be required in addition as make-up water.

2.4

Load carrying capacity of the belt conveyors may vary from ___________ tonnes per hour.

50 to 100

A thermal power plant if 400 MW capacity requires_______________________ tonnes of coal per day.

5000 to 6000

For entirely new stations, present practice favors the use of steam around _____________ bars

60

Average speed of belt conveyors is ..........................................................

60 to 100 meter per minute.

Average speed of screw conveyors

70 to 120 rpm

A generator need NOT operate most economically at full load. For the most economical operation, the present trend is towards economical running at ___________________ percent of the full load.

75 to 85

SITE SELECTION FOR COAL DEAD STORAGE Continued

9. Stoker size coal should be oil treated to prevent absorption of water, O2, and compaction which is not needed. 10. Side of pile should not be steep. 11. Air may circulate freely through pile for proper ventilation to keep temperatures low. 12. Hot surfaces or boiler blow down or hot water or steam pipes and tanks should far from coal storage. 13. Hot bright days are to be avoided. 14. There should be provision for temperature measurement at different points. 15. Fire fighting equipment should be easily available. 16. Solid land, never porous or loose land

Advantages of flight conveyors

All parts are made of steel and iron and has rugged construction, so it can handle hot material. It can transfer coal at high inclination(35°) . It requires small head room Speed and material transfer rate can easily change. Can transfer coal as well ash required little operational care

Means of transfer of coal

Belt conveyors Screw conveyors Vee bucket elevators and conveyors Pivoted bucket conveyors Grab bucket conveyors Flight conveyors (scrapper) Skip hoist Mass flow conveyors Chutes

Components of modern steam power plants

Boiler (air preheater, economiser, superheater), steam turbine, generator, condenser, cooling tower, circulating water pump, boiler feed pump, wagon tippler, crusher house, coal mill, induced draught fans, ash precipitators, forced draught fans, boiler chimney, water treatment plant, control room

Belt Conveyors

Consist of an endless belt of canvas, rubber or balata running over a pair of end drums or pulley and supported by a series of rollers called idlers

Screw Conveyor

Consists of an endless helicoid screw fitted to a shaft. The driving mechanism is connected to one end of the shaft while other end is supported in an enclosed ball bearing. The screw while rotating transfer coal from one end to the other.

The present trends is towards adoption of which type of plant?

High temperature and high pressure plant

Disadvantages of grab bucket conveyor

Initial cost is high Only used when other systems cannot be installed.

Why is ash handling more serious than coal handling?

It comes out in hot condition. It is highly corrosive. Active air pollutants and also hazardous to human health.

Grab bucket conveyor

It consists of a hoist which lifts and transfers the load of a single track or rail from one point to another. It is used with crane or a tower

Flight conveyors

It is used when coal is discharged at different points in bins situated below the conveyor.

Inplant handling

It means a coal handling between the final storage and the firing equipment Or A conveying system to feed coal from any bunker section to ant firing unit or from one bunker section to another bunker section.

What is transfer in coal handling plant?

It means the handling the coal between the unloading point and the final storage point from where it is discharged to firing equipment

Dead Storage

It supplies the coal where there is a shortage of coal in plant due to failure of normal supply of coal. This is long term storage and 10% of annual consumption, so it requires protection against weathering and spontaneous combustion.

Which power plant is generally conservately rated?

Large power plant

If not near the coalfield, what is the next best choice?

Location near to the railway stations

Total installed capacity = maximum demand + sum of capacity of the installed unit applies to which power plant?

Medium power plant

Disadvantages of belt conveyors

Not suitable for greater heights and shorter distances, maximum inclination of transfer is limited(20° to the horizon)

What are the public problems from steam power plant?

Nuisance like smoke, fly ash, and heat discharged from power plant

Underwater Storage benefits

Possibility of slow oxidation and spontaneous combustion can be completely eliminated.

Essential requirements of steam power plant design

Reliability, minimum cost (capital, O/M), minimum loss of energy in transmission, low cost of energy supplied to consumer, reserve capacity to meet future demands, higher efficiency, ability to burn coal with high ash content, reduced water requirements, reduced pollution level,

Vee bucket elevator

Steel V-shaped buckets are rigidly fastened to an endless chain going around sprockets.

What is maximum continuous rating?

The MCR of a generating unit is the maximum load at which it can be run continuously for several hours.

How is coal prepared?

The preparation (sizing) of coal can be achieved by crushers, breakers, sizer, dryers and magnetic separators.

What sorts of truck are more preferable for delivery and unloading?

Trucks with scoop

Skip hoist

Used for high lifts 💔Handling is not continuous Simple and cheap O/M and labor cost low Oldest and cheapest means of elevating and ash handling Favorite among engineers

relation between average output and reduction in capital cost.

When average output increases, the capital requirements decreases.

When is the coal 'prepared'?

When the coal delivered is in the form of big lumps and it is not of proper size.

What percentage of total OPERATING cost is incurred in fuel purchasing and handling?

almost 50 to 60 percent

SELECTION OF SITE FOR STEAM POWER PLANT

availability of raw material, nature of land, cost of land, availability of water, transport facilities, ash disposal facilities, availability of labor, size of plant, load center, public problems, future extensions

How can the capacity of steam power plant be determined?

by studying the load duration curve and anticipated future demands.

In case the coal is brought by railway wagons, ships or boats, the unloading may be done by ................................................................................

car shakes, rotary car dumpers, cranes, grab buckets and coal accelerators.

The consumption of steam per kWh _______________ with increase in pressure.

decreases up to a certain value and then increases

The buckets of vee elevators are _________________________ on the chains.

equally spaced

The choice of the site should allow for economical extensions consistent with _________________________________________.

estimated growth of load

If NOT being located near to the coalfields, what are the things of concerns?

failure of transportation systems, strikes, building large storage facilities near to the plants

Mechanical handling is preferred to manual handling because

higher reliability, less labor required, economical for medium and large plant, easy and smooth operations, easily started, economically adjusted as per the need, minimum labor is put to work in unhealthy condition, losses in transportation is minimized.

What problems do the large storage facility brings to a power plant?

increased investments, increased spaces, losses in storage, additional staff requirements

The expenses involved in electric transmission from small plants are relatively severe because

it is impractical to use high voltage transmission system

The belt conveyors can be used in _______________________________ power plants.

medium and large

REQUIREMENTS OF GOOD TRANSPORTATION SYSTEM

minimum maintenance, reliable, simple and sound, require minimum number of operatives, minimum wearing, deliver required quantity at the destination during peak hours.

The type of coal unloading equipment used depends upon types of ______________________________________________________________________.

out-plant handling mode like trucks, rails, or ship.

With increase in pressure, the efficiency obeys which law?

the 'law of diminishing returns'

With increase in temperature, the efficiency obeys which law?

the 'straight line law'

Transportation of coal by truck is usually used in case where ____________________________________________________________________________________.

the coalfield is NOT located far from the plant.

A large plants in the heart of the city and near the load center is NOT economical because _________________________________________________.

the cost of land is high.

Storage of coal gives protection against ___________________________________.

the interruption of coal supplies when there is delay in transportation if coal or due to strikes in coal mines.

The minimum capacity of the plant must be equal to at least ___________________________________.

the peal load

If the coal is delivered by the truck, the need of unloading equipment is eliminated as ________________________________________________________________________.

the truck may dump the coal to the outdoor storage

In small load plant, it may be economical to install how many units of equipment, each of which are capable of supplying the maximum demand independently?

two

Fuel system is designed according to _______________________________________.

type and nature of fuel

Consent from town planning department must be sought if the plant is to be located in ___________________ area.

urban

Advantages of belt conveyors

very suitable for mass transport over large distance, smooth and clean operation, low R/M cost, minimum power consumption, rate of transfer can be varied easily

TYPES OF COAL STORAGE

✨Dead Storage ✨Live Storage

STEPS INVOLVED IN COAL HANDLING

🍪Coal delivery 🍪Unloading, 🍪Preparation 🍪Transfer 🍪Storage (Outdoor, indoor covered) 🍪In-Plant handling 🍪Weighing and measuring 🍪Furnace firing i.e. Feeding the coal into furnace

Disadvantages of flight conveyors

💔High wear and tear, so short life. 💔High maintenance required. 💔Speed is limited up to 300 m/min due to abrasive action of material. 💔High power consumption per unit of material transfer due to dragging action.

Storage of coal is undesirable, because it costs more as there is

💔risk of spontaneous combustion, 💔 weathering, 💔possibility of loss and deterioration during storage, 💔interest on capital cost of coal lying dormant, 💔 cost of protecting the stored coal from deterioration and so on.

Live storage

📖It supplies coal to plant for day to day usage. 📖Capacity of live storage is less than that of dead storage. 📖Usually stored in vertical cylindrical bunkers or coal bins or silo, from where coal is transferred to boiler grate. 📖Bunkers are normally diamond-shaped cross- section storage area, made up of steel or reinforced concrete.

MEANS OF COAL STORAGE - Storage in Coal Heaps It is required to :

📖Keep coal at low temperature (>70ºC) 📖Prevention of air circulation from bottom of coal piles. 📖Proper drainage of rainy water to prevent weathering - drainage should not be rapid to prevent washing away of coal. Hence, ground used for stocking should be dry and leveled for proper drainage and concrete-floored to prevent flow of air from bottom. 📖Coal is piled at a height of about 10 to 12 m and compacted in layers of 15 to 30 cm. 📖In dead storage, coal pile is sealed by asphalt, fine coal dust, bituminous coating or other coating material.

PURPOSE OF DEAD STORAGE OF COAL

📖To prevent shutdown of power plant in case of failure of normal supplies of coal due to coal strike, failure of the transport system etc. 📖Storage permits choice of the date of purchase allowing management to take advantage of seasonal market conditions.