PESIT BANGALORE SOUTH CAMPUS

Hosur road, 1km before Electronic City, Bengaluru -100 DEPARTMENT OF MECHANICAL ENGINEERING

SCHEME AND SOLUTION Subject & Code : Energy Engineering & 10ME53 Section : ‘A’/’B ’/C

Name of faculty : Yogendra/Siva Murali Mohan Reddy A/pradeep

NOTE: Answer any FIVE full questions 1.a) Explain with a neat sketch the working principle of Spreader stoker.

(7)

This type of stoker can be used for boiler capacities from 70000 kg to 140000 kg of

steam/hour. Spreader stoker can burn any type of fuel.

b) What are the advantages and disadvantages of Travelling grate stoker.

SOL:- Advantages of Travelling grate stoker

Simple in construction.

Initial cost is low.

Maintenance charges low.

Self-cleaning stoker.

Gives high release rates per unit volume of the furnace.

Heat release rates can be controlled just by controlling the speed of chain.

Disadvantages:

Preheated air temperatures are limited to 180ºC maximum.

The clinker troubles are very common.

There is always some loss of coal in the form of fine particles through riddlings.

Ignition arches are required (to suit specific furnace conditions).

This cannot be used for high capacity boilers (200 tonnes/hr or more). (3)

2.a)

Explain with a neat sketch the working principle of central pulverised coal feeding system. (7)

(3)

Sol:- Central Pulverised Coal Feeding System

B.E/5th Semester PESIT-BSC Internal Document

1 — PFS; 2 — Dust lead;3 — Hopper for coal dust;4 — Bunker for solid fuel;5 — Apron Feeder; 6 —

Economizer;7 — Cyclone;8 — Smoke exhauster;9 — Blow fan;10 — Blow fan of PFS;

11 — Device Ash;12 — Distribution plate;13 — Boiler;14 — Pressure transmitter;15 — Converter

dilution; 16 — Coolant loop.

Pulverized coal bunker for the explosion is made in private. With the help of a screw feeder,

which is rotated by drive motors, coal dust gets into the mixing chamber with the primary air and

then through pyleprovod circular cross section with a flow rate of more than 25 m / s (to avoid dust

deposits) is sent to the burner.

When turned off by locking screw feeder chute, feed coal mixture. At times, certain b) algorithm of PFS, control slide gate is realized by one-turn electric machinery

What are the advantages and disadvantages of central pulverised coal feeding system. Advantages:

1. No spillage and rehandling. 2. High flexibility 3. There is no chance of ash freezing or sticking in the storage bin and material can

be discharged freely by gravity. 4. The dustless operation is possible as the materials are handled totally in an

enclosed conduit. 5. The cost of plant per tonne of ash discharged is less in comparison to other

systems. Disadvantages:

B.E/5th Semester PESIT-BSC Internal Document

1. There is a large amount of wear in the pipe work necessitating high maintenance

charges.

2. More noisy than other systems.

3. (10)

The ash carrying capacity of this system varies from 25 to 15 tonnes per hour. Advantages:

1. No spillage and rehandling. 2. High flexibility 3. There is no chance of ash freezing or sticking in the storage bin and material can be

discharged freely by gravity. 4. The dustless operation is possible as the materials are handled totally in an enclosed

conduit. 5. The cost of plant per tonne of ash discharged is less in comparison to other systems. Disadvantages: 1. There is a large amount of wear in the pipe work necessitating high maintenance charges. More noisy than other systems

4. With a neat sketch explain any two types of pulverized coal burners SOL:- Pulverised fuel burners may be classified as follows:

1. Long flame burners 2. Turbulent burners 3. Tangential burners

LONG FLAME BURNERS: These are also

called U-flame or streamlined burners

Furnaces for low volatile coal are equipped

with such burners to give a long flame path

for slower burning particles.

TANGENTIAL BURNERS (10) The parts of the burner are well-protected

by furnace wall tubes.

The operation of these burners is very simple.

High heat release with complete and effective

utilisation of furnace volume is possible.

The completeness of combustion is

exceptionally good and a maximum degree of

turbulence exists throughout the furnace.

Liquid, gaseous and pulverised fuels can be

readily burned either separately or in

combination.

B.E/5th Semester PESIT-BSC Internal Document

(7) 5. a) Explain with a neat sketch the working principle of Benson

Boiler. Sol:- Benson Boiler

This boiler has a unique characteristic of absence of steam separating drum. The entire process of heating, steam generation and superheating is done in a single continuous tube.

Economiser The feed water by means of the feed pump is circulated through the economiser tubes. Hot flue gases pass over the economiser tubes and the feed water is preheated. Radiant evaporator The feed water from the economiser flows into the radiant evaporator with radiant parallel tube sections. The radiant evaporator receives heat from the burning fuel through radiation process and majority of water is converted into steam in it. Convection Evaporator The remaining water is evaporated in the convection evaporator, absorbing the heat from the hot gases by convection. Thus the saturated high pressure steam at a pressure of 210 kg/sq.cm is produced. Convection superheater The saturated steam is now passed through the convection superheater where the saturated steam os superheated to 650’C. The radiant evaporator, the convection evaporater and the convection superheater are all arranged in the path of the flue gases. Steam outlet The superheated steam is supplied to the steam turbine through the steam outlet. Capacity Capacity of benson boiler is about 150 tonnnes/hr at a pressure of 210 kgf/sq.cm. and at a temperature of 650’C. (Efficiency may be improved by running the boiler at a pressure slightly lower than the critical pressure).

b) What are the advantages of super critical boilers. Sol:-

Mass flux reduction from 2,000 to 1,000 kg/m²s with a similar flow

characteristic to that of drum boilers Cost-effective fabrication and assembly Low BENSON minimum load and simple start-up system

Reduced slagging and erosion on furnace wall due to parallel gas flow (3)

Reduced evaporator pressure drop

(5) B.E/5th Semester PESIT-BSC Internal Document

6).

Ma=10.795kg/kg of fuel Air required for complete combustion =9.275kg/kg of coal (10)

7) Draught in mm of water

(10)

=15.61 mm of water Draught head in meters of hot gases= 24.59 m

8)

Pid =5.84kW Pfd =3.95 kW (10)

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B.E/5th Semester