Steam Boilers Any substance can exist in three primary (or principal) phases, namely solid, liquid and gas,

depending upon its temperature and pressure. However, when the phase of a substance is changing from one phase to other phase, the substance achieves an intermediate condition, known as "secondary phase". At this condition the physical properties of the substance are different compare to those of both the two primary phases, between which phase transformation process takes place. When phase change process occurs from liquid to gas or vice a versa, the substance achieves a secondary phase condition during the process, which is known as "vapour phase or steam".

The exact information about historical event, when human being had started use of water vapour (steam), is not available. However, in 200 B.C., a Greek named Hero designed a simple machine that used steam as a power source. More over, in history of ancient Indian civilization, indication of use of steam in aurvedic medical treatment is available in written forms. Considering industrial fields, historically, use of steam was started in 17th century in Europe. The first use of steam power was in the mining industry. Savery's 'Miner's Friend' was used to pump water out of coal mines and iron mines. Steam engines helped speed up the mining process, as water could be removed from the mines quickly and easily.

Today, steam is widely utilized for following purposes in industrial fields. (1) Steam is utilized for generation of electric power in steam power plants (2) Steam is utilized for generation of mechanical power to run locomotive engines, road rollers,

steamers, pumps, cranes, .., etc. (3) Steam is utilized as a heating medium, to keep warm atmosphere in buildings at the time of

cold climates in certain countries of the world. (4) Steam is used to add moisture to a process while at the same time supplying heat. (5) Steam is utilized as a heating medium in various heating processes in dairy, textile, food

processing, pharmaceutical, and petro-chemical industries. (6) Steam is utilized for cleaning utensils and sterilization of various instruments and vessels in

hospitals and food processing industries. Considering wide range of industrial applications of steam, a question can arise how steam

of required quality and required quantity can be generated from water for different types of industrial applications? STEAM:

Steam is an intermediate phase (secondary phase) between liquid phase and gas phase of a substance. Transition from liquid phase to gas phase is known as vaporization and from gas phase to liquid phase is known as condensation. Vaporization The vaporization of liquid can occur by two ways (1) by evaporation and (2) by boiling. Here we will see the basic difference between these two ways of vaporization. (1) Evaporation: Evaporation means transition of liquid phase into gas phase at any temperature below the saturation temperature. Evaporation of liquid takes place only from free surface of liquid without any visible disturbance within the liquid. Any liquid, open to atmospheric air, tends to evaporate and be diffused into the atmospheric air, irrespective of its temperature. Evaporation is comparatively slow process. Rate of evaporation increases with increase in temperature of liquid, amount of free surface of liquid and decrease in pressure exerted over the liquid. It also depends on amount of moisture contents of surrounding air. (2) Boiling (Ebullition)

Boiling means transition of liquid phase into gas phase at saturation temperature. Vaporization of liquid by boiling occurs throughout the entire body of the liquid as well as at the free surface of the liquid. Vaporization due to boiling is comparatively faster process. Bubbles are formed into the liquid, which travel upto top surface of the liquid due to density difference and collapse at the last during the boiling process. Therefore, visible disturbance (agitation) occurs in the liquid during the boiling process.

In engineering fields, steam of various substance like water, mercury, ammonia, Freon, carbon dioxide, .etc are widely utilized. Among all above mentioned substances, water in its liquid form and vapour form (steam) is widely utilized because of its favorable properties like easy availability, cheapness, non-toxic nature, high specific heat, chemical stability, .etc. 4.2 STEAM BOILERS:

Steam boiler or steam generator is a closed vessel strongly constructed of steel, in which steam is generated from water by the application of heat.

Although the definition is somewhat flexible, it can be said that older steam generators were commonly termed boilers and worked at low to medium pressure (upto 20 bar) but, at pressures above this, it is more usual to speak of a steam generator.

The function of boiler is to transmit heat available from burning of fuel or from other suitable source to water. The primary requirements of boiler are, (1)Water & steam must be very safely contained. (2)Steam must be safely delivered in desired condition as regards its pressure, temperature, & quality at a required rate. (3)Maximum heat from the source should be utilized for economy. (4)It should be rapidly meet the changes in load. (5)Joints should be few & removed from the flame & accessible for inspection. (6)Minimum refractory material should be used.

In initial stage of industrial revolution, in the beginning of 17th century, the design of boiler was very simple as good as kettle. The earliest steam boilers were usually spheres or sections of spheres, heated entirely from the outside. As per example, "Pot boiler" or "Haycock boiler" was a primitive "kettle", where a fire is used to heat a partially-filled water container from below. 18th century Haycock boilers generally produced and stored large volumes of very low-pressure steam, often hardly above that of the atmosphere. These could burn wood or most often, coal and their efficiency was very low.

However, with growth of industrial revolution, importance of steam was realized when two British inventors began to turn steam power into practical devices - Thomas Savery in 1698 and Thomas Newcomen in 1705. James Watt further improved on their inventions, patenting several designs that earned him the title of father of the modern steam engine. The steam engine became in demand energy converter and provided a rapid growth of boilers.

Initially boilers containing horizontal or vertical cylindrical shell had been built and era of cylindrical boilers was started. One of the advantages of the cylindrical boiler is that it has a larger heat transfer surface per unit of working fluid compare to that of spherical shaped boilers. Therefore cylindrical boiler can be built cheaper than the earlier boilers. The pressure

(and thus the temperature) can also be increased with the cylindrical design. The cylindrical boiler was later expanded to contain several passes and eventually formed

the fire tube boiler. Unfortunately fire-tube boilers were limited in capacity and pressure and were also, sometimes, dangerously explosive. Inventive engineers were set to work to develop new boiler types. There was wide scope for improvement as efficiency and safety of fire tube boilers frequently left a lot to be desired.

The water tube boiler was patented in 1867 by the American inventors George Herman Babcock and Stephen Wilcox. The boiler had larger heating surfaces, allowed better water circulation, with reduced risk of explosion. In the water-tube boiler, water flowed through tubes heated externally by combustion gases and steam was collected above in a drum. The large number of tubes and use of cross gas flow increases the heat transfer rate. Boilers of this type could be built with larger heat transfer surface per unit of working fluid than the fire tube boilers. Due to the

higher rate of heat transfer, cooler flue gases could be used. Tubes could be made inexpensively with higher quality. The water-tube boiler became the standard for all large boilers as they allowed for higher pressures. The next step was the emergence of the drum boiler, which introduced a steam drum for separating steam from water. This allowed cheap and reliable joint between the drum and a tube. The drum boiler was also beneficial by providing better control of the water quality by having a mud drum.

The demand for even bigger boiler unit sizes to drive steam turbines required larger furnace volume, which eventually led to the development of the tube walled furnace. In a modern tube walled furnace the inside of the furnace wall is completely covered of heat transferring water tubes, welded together side by side. Since the water tubes are in the furnace the heat is being transferred mainly by radiation from the combustion process.

In order to be able to increase the current unit size and efficiency of boilers, the restriction of natural circulation boilers needed to be overcome. The idea of a once through boiler, were no steam drum would be used and thus no circulation of non-vaporized water would take place, was developed. The once through boiler uses smaller diameter and thinner walled tubes than the natural circulation boiler.

The era following the Second World War brought on rapid economic development and the desire for more efficient power plant operation increased. Improvements in both boiler tube metallurgy and water chemistry technologies in combination with once through boiler technology made a power plant, operating at supercritical water pressure, possible.

Here, we will understand basic terminology related to boiler construction before study of different boilers as per the subject requirement. [A]BASIC TERMINOLOGY FOR BOILERS:

The following terms are commonly used in connection with various types of boilers. (1)Shell:

The boiler shell consists of one more steel plates bent into cylindrical form & riveted or welded together. The ends of shell are closed by means of end plates or heads, which are made flat, convex or concave. The shell together with the closing heads is called the drum. (2)Settings:

The settings form the walls of combustion chamber. It confines the heat to the boiler & forms a passage through which the gases pass. The passages so formed for gases are called flues. The boiler settings provide supports for some types of boilers. (3) Grate:

The grate in a coal or wood fired boiler is the platform in the furnace upon which the fuel is burned. The grate consists of cast iron bars, which are spaced apart so that air for combustion can pass through them. (4)Grate surface: It is the area of the grate on which the fire rests in a coal or wood fired boiler & is usually expressed in square meters. (5)Furnace:

It is also called fire box. It is the space above the grate & below the boiler shell in which the fuel is burnt. (6)Water space & steam space:

The volume of shell that is occupied by the water is termed as water space. The steam space is the entire shell volume less that occupied by water & tubes. (7)Water level: It is the level at which water stands in the boiler drum. (8)Heating surface:

It is the part of the boiler surface that is exposed to the fire & to the hot gases from the fire as hot gases pass from the furnace to the chimney. (9) Mountings:

The equipments or fittings, which are mounted on the boiler for safety & control of the process, are called mountings.

(10)Accessories: The items, which form an integral part of the boiler for economy, are known as accessories.

(11)Blowing off: The mud and other impurities settle in the lower part of the boiler. From time to time they

are removed by the help of a blow off cock or valve. The process of removing impurities from the water is called blowing off. (12)Lagging:

The steam pipes and the shell of a boiler are wrapped with asbestos or magnesia for insulation. This is done to minimize the loss of heat due to radiation. (13)Refractory layer:

The layer of fire bricks or plastic clay, used for lining the combustion chamber is known as refractory layer. This is done so that the walls of the shell/ combustion chamber are not damaged.

[B]CLASSIFICATION OF BOILERS: There are numerous ways in which boiler may be classified. The main basic classifications are as follows. (a)According to tube content (1)Fire tube boiler (2) Water tube boiler (b)According to furnace position (1)Externally fired boiler (2)Internally fired boiler (c)According to circulation of water (1)Natural circulation boiler (2)Forced circulation boiler (d)According to draught system (1)Natural draught boiler (2)Artificial draught boiler (e)According to source of heat (1)Coal fired boiler (2)Oil fired boiler (3)Gas fired boiler (4)Electrically heated boiler (5)Nuclear boiler (6)Waste heat boiler (f)According to axis of drum (1)Horizontal boiler (2) Vertical boiler (g)According to working pressure (1) Low pressure boiler (P

In water tube boiler water is made to pass through the tubes and flue gases surround these tubes. As per examples, Babcock-Wilcox boilers, Sterling boilers, Lamont boilers are water tube boilers.

[C] Comparison between fire tube & water tube boilers Fire tube boilers Water tube boilers (1) In fire tube boiler the product of

combustion or flue gases are made to pass through the tubes and water surrounds these tubes.

(2) The operating pressure range of fire tube boiler is limited to low pressure range up to approximately 25 bar.

(3) Floor space requirement per unit power is higher for fire tube boilers.

(4) Fire tube boiler can not raise steam quickly. (5) Fire tube boiler is less convenient to

transport from one place to another place due to large size of drum.

(6) Fire tube boiler requires less skill for efficient and economic working.

(7)The construction and erection of fire tube boiler is complicated.

(8) Impure & dirty water can also be utilized in fire tube boilers.

(9)The intensity of damage is high in case of bursting of fire tube boiler

(10)Sediment deposition is higher (11)Not suitable for any type of fuel.

(1) In water tube boiler water is made to pass through the tubes and flue gases surround these tubes.

(2) Water tube boiler can operate in low, medium, as well as high pressure range. Modern water tube boilers are capable of generating steam with 300 bar pressure.

(3) Floor space requirement per unit power is less for water tube boilers.

(4) Water tube boiler can raise steam quickly. (5) Water tube boiler is convenient to transport

from one place to another place.

(6) Water tube boiler requires more skill for efficient and economic working.

(7) The construction and erection of water tube boiler is simpler.

(8) Water tube boiler is less suitable for impure & dirty water, because small deposition of scale in water tubes will cause over heating and hence bursting.

(9) The intensity of damage is comparatively lower in case of bursting of water tube boiler.

(10) Sediment deposition is less (11) Suitable for any type of fuel.

[D]VARIOUS TYPES OF BOILER (1)COCHRAN BOILER: (figure 4.4)

Cochran boiler is vertical, stationary, internally fired, multi-tubular, low pressure fire tube boiler with natural circulation and natural draft. It is the modification of a simple vertical boiler where the heating surface has been increased by means of a number of fire tubes. Generally, solid fuels like coal, wood, paddy husk, .., etc can be used as a fuel in Cochran boiler.

Construction:

Construction of Cochran boiler is shown in the figure 4.4.As shown in figure Cochran boiler consists of a vertical cylindrical shell with a hemispherical (dome) shaped top cover, where the space is provided for steam. The fire box (furnace) is made up from single hemispherical shaped steel plate, known as crown. The hemispherical crown is strongest for strength & permits maximum absorption of radiant heat. Hemispherical shape also gives maximum volume of space for given mass of material in the form of plates. The constructions of the grate and the ash pit are created below the furnace as shown in the figure. In the cylindrical shell, above the furnace crown, a fire box and a smoke box are created opposite to each other. A fire hole (short flue) is provided to connect the furnace and fire box. The fire box and the smoke box are connected with the help on number of horizontal straight fire tubes (approximately 100 to 150 depending on space available).

The chimney is provided for the exit of the flue gases to the atmosphere from the smoke box. The fire box and smoke box are provided with inspection doors, which are internally lined with refractory material. Inspection doors of fire box and smoke box are kept exactly at the opposite sides to each other so inspection and cleaning of fire tubes becomes possible. A manhole is provided at the top cover of the shell, a man can enter the boiler for periodic cleaning and maintenance of the boiler. Necessary mountings are provided at appropriate locations in Cochran boiler.

Working: Water level in the drum of

Cochran boiler is kept in such a way that each and every fire tubes is covered with the water. Fuel is fed into the grate through the furnace door and burnt. The combustion of fuel takes place on the grate inside the firebox. The products of combustion flow from firebox through the fire hole into the fire box lined with refractory material. It facilitates the ignition of any unconsumed gases passing through the number of horizontal fire tubes to smoke box, from where the gases pass into the chimney. Steam is formed due to heat transfer from the flue gases and collected in the steam space of the drum, just above the water level. Ash formed during burning is collected in the ash pit provided just below the grate and then it is removed manually.

These boiler range from 1meter dia. x 2meter height x 20

kg/hr evaporation to 3meter dia. x 6meter height x 3000kg/hr evaporation. The total heating surface area is about 10 to 25 times the grate area. The steam pressure is up to 20 bars & efficiency is from 70% to 75%.

(2)Lancashire Boiler:

Lancashire boiler is a horizontal, internally fired, natural circulation fire tube boiler. In this boiler steam is produced at 15 bar, at the rate of 8500 kg per hour. The steam produced in this boiler is used for processing purposes in sugar mills and in chemical industries as the produced at low pressure with low rate of production. Construction:

Lancashire boiler consists of a horizontal cylindrical shell placed on a brick work as shown in the figure. Two large flue tubes of diameter about 0.4 times the diameter of shell are fitted inside the shell which extends over the entire length. In each of these flue tubes two furnace grates are provided at the entrance of flue tube and the space underneath the grate is the ash pit(ash collector).

The arrangement of brick work and shell creates a rear enclosed chamber for each of flue tubes at the rear end of the boiler which in turn is connected to one bottom central channel at the underneath the shell and which in turn is connected to two side channels at the front end. Two side channels are connected at their rear end to a common rear passage which is connected to chimney as shown in the figure. The boiler shell is mounted with necessary mountings like feed valve, steam stop valve, pressure gauge, water level indicator safety valve etc as shown in the figure.

Working: Fill the boiler shell with water to of its volume by the help of feed valve which will submerge both the flue tubes and the remaining space inside the shell is for collection of steam. When the fuel is supplied to the furnace and burnt, the hot gases produced will passes along the flue tubes towards rear enclosed chamber and mean while heat transfer take place from the hot gases to water through the walls of the flue tubes. The hot gas from the rear enclosed chamber is next entered into the bottom central channel and passes towards entrance of the boiler shell. In passing heat transfer takes place from the hot gas to water through bottom portion of the boiler shell which is exposed to bottom central channel. After passing along the bottom central channel, the hot gas divided at the entrance of the boiler shell and enters into the both side channels towards rear exit passage which in turn connected to chimney. In passing through side channels heat transfer take place through side portions of the boiler shell which are exposed to side channels. The steam accumulated in the steam space is collected with the help of steam stop valve. (3) BABCOCK-WILCOX BOILER: Two Americans, George Herman Babcock and Stephen Wilcox, had received patents for the "Babcock & Wilcox Non-Explosive Boiler" and the "Babcock & Wilcox Stationary Steam Engine." in 1867. In that same year they formed Babcock, Wilcox and Company, along with Joseph P. Manton to manufacture the new boiler. Construction:

This is the best known water tube boiler designed by Babcock & Wilcox Co. in 1877 & is made of horizontal shell (steam &water drum). Figure 4.4 shows construction of longitudinal drum type Babcock & Wilcox boiler, which consists of 4 main parts. (1) Shell (2) Nest of water tubes (3) Furnace (4) Superheater.

As shown in the figure the horizontal cylindrical shell is suspended in longitudinal direction with the help of iron girders, which are resting on structure of iron columns. Necessary mountings like feed valve, steam stop valve, pressure gauge, water level indicator, safety valve, etc. are located at appropriate positions on the boiler shell. The front end of the boiler shell is connected to the uptake header by riser pipes & rear end of the boiler shell is connected to down take header by down comer pipes. In between the headers no. of small diameter straight steel tubes are fitted at an angle 5o degree to 15 degree with horizontal to promote the water circulation. The steel tubes are arranged in combustion chamber in zig zag manner so that more surface area of the tube is exposed to hot gas. A hand hole is provided in the header in front of each tube, which allows cleaning & inspection of the tubes. Each hole is covered by threaded or flanged cap. A mud box is connected at the bottom of the down take header with blow off pipe connected to it is to collect contaminants and to remove from the water tubes. The entire boiler, with all the mountings & accessories, is suspended from horizontal iron girders (steel beams) by metallic slings so that each component can expand & contract freely depending on temperature. The brickwork around the boiler is only meant to enclose the furnace & hot gases.

The furnace is provided at the bottom of up take header, which consists of continuous moving chain in between two rollers. The coal is fed at the front end of the chain grate stroke is burnt on the moving grate and residual ash falls at the other end of the grate in to the ash pit.

Superheater, made by joining ends of number of u tubes in horizontal headers, is placed in the combustion chamber underneath the boiler drum. The upper header is connected to anti-priming pipe situated in the steam space inside the boiler drum and allows steam to enter and passes it to superheater and then to steam stop valve by passing through lower header. Two buffels are provided to guide the flow of hot gases, generated by combustion of fuels on the grate. The draught is regulated by a damper, which is provided at the end wall, joining the smoke chamber. Working:

The boiler shell is filled with water through feed valve and a constant water level is maintained up to about 2/3 rd part in the shell. The water from the shell flows through inclined tubes via down take header and then goes back into the in the form of water and steam via uptake header. Obviously the circulation of water is maintained due to density difference created by

temperature difference. Thus a thermo-siphon effect is created, which results in continuous & rapid circulation of water.

The hottest water and steam rise from the tubes to the uptake header and then through riser enter the boiler shell. The steam vapors escape through water to the upper half of the drum. The cold water flows from the drum to the rear header and that completes the water circuit.

When the fuel is supplied to the furnace and burnt, the hot gases produced will rise upwards to the water shell and then downwards due to buffels. During the path of hot gas, the water extracts the heat from the hot gas and converted to steam, then the mixture of steam and hot water raises to up take header and then collects in boiler shell. Finally, hot gases escape to the smoke chamber through the damper and then to chimney. The steam collected in the water drum is next led to the super-heater tubes via anti priming pipe. Since the super- heater tubes are exposed to hot gases, the steam passing through them gets super heated. When steam is raised from cold boiler the superheater should be flooded to avoid its burning. The super heated steam is finally taken out through stop valve and supplied to the engine when needed. DIMENSION & SPECIFICATIONS :

Diameter of the drum 1.22 to 1.83m. Length of the drum 6.096 to 9.144m. Size of the water tubes 7.62 to 10.16cm. Diameter of the superheater tubes 3.84 to 5.71cm. Working pressure 40bar (max.) Steaming capacity 40000kg./hr.(max.) Efficiency 60-80%

Salient Aspects: 1. Draught loss is lower. 2. The replacement of the defective tubes can be made readily. 3. The unit has a capability to quickly cope with high peak loads, which are generally needed at thermal power stations. 4. Inspection can be carried out even when in operation.

[E] BOILER MOUNTINGS AND ACCESSORIES: For attaining proper control of the process of steam generation, maintenance of safety and

efficient operation, the boiler equipped with two categories of components and elements. (1) Boiler Mountings and (2) Boiler Accessories.

(1) BOILER MOUNTINGS: Boiler Mountings are boiler auxiliaries, which are provided for the safety and complete control of process of steam generation. The mounting from an integral part of the boiler and are mounted on the body of the boiler itself. As per the Indian Boiler Regulation (IBR) the following mountings must be provided on the boiler. a) Two Numbers of Water Level Indicator b) Two Numbers of Safety Valve c) Fusible Plug d) Steam Stop Valve e) Feed Check Valve f) Blow off Cock g) Pressure Gauge h) Man Hole and Mud Hole Here, we will study some important mountings in detail. (a)Water level indicator:-

The function of the water level indicator is to indicate constantly and exactly the level of water in the boiler shell. As per IBR, minimum two water level indicators are required to be fitted on a boiler. They are mounted on the front plate of the boiler shell in such a manner that they can be easily visible to the operator. Water level indicator warns the boiler operator if by chance the

water level in the boiler goes below the minimum required level, so that corrective action may be taken in time to avoid any accident.

Figure 4.6 shows construction of simple glass tube water level indicator. The unit consists of two horizontal pipes containing arrangements of cock in midway and stuffing box at the ends as shown in the figure. From both the pipes, one is connected to water space and other is connected to steam space of the boiler shell. A strong glass tube is fitted in vertical position by passing its ends through stuffing boxes consists of heat resisting rubber packing to prevent leakage steam and water. The glass tube is generally protected with shield. The flanges are bolted to front end plate of the boiler, the upper flange being fitted to the steam space and the lower to water space in the boiler. There are two cocks namely steam cock and water

cock which communicate the boiler shell spaces to the gauge glass tube. When the handle of the cocks are vertical, they are in operation and the water level in the tube corresponds to water level in the shell. A red mark on the glass tube indicates the safe water level.

Arrangements of free ball are provided in both the horizontal pipes between water/steam cock and stuffing box. In normal position, the balls in both the pipes rest in their groves. At the time of glass tube breakage, initially flows of hot water and steam start from respective broken ends of the glass tube to the atmosphere. Due to these flows, the balls are forced to stick with their valve seats. As a result of this action, flows of hot water and steam stop coming out from the broken ends of the glass tube. After stopping the flows, one can close the water cock and steam cock safely and can replace the broken tube by new one. (b)Safety valve:-

Safety valve is a device which comes into operation when the pressure in the boiler exceeds the limiting pressure. It discharges some of the steam automatically out of the boiler and brings the pressure down to the normal working limit. As per IBR, minimum two water safety valves are required to be fitted on the top surface of the boiler shell.

The safety valve operates by the principle that a valve is pressed against its seat by external force like gravitational force or spring force. When the steam force due to boiler pressure acting under the valve exceeds the external force, the valve gets lifted from its seat and some of the steam rushes out until normal pressure is restored again.

There are four types of safety valves generally used: 1) Dead Weight Safety Valve 2) Lever Safety Valve 3) Spring Loaded Safety Valve 4) High Steam And Low Water Safety Valve

(1)Dead Weight Safety Valve: COPY FIG. 4.6 FME BOOK (R.B.Varia, Atul Prakashan) PAGE 144

Figure 4.7 shows construction of a dead weight safety valve, used for stationary boilers. This valve is the simplest type of valve in which valve is loaded by the direct application of weight above the valve. The valve seat is attached to the top of the vertical steel pipe, which is bolted to the flange provided on the top of the boiler drum. The valve is attached to the weight carrier. Required amount of dead weights are provided on the carrier to keep the valve on its seat under normal working pressure. The dead weights with the valve and the pipe are covered by a cover. When the pressure of steam exceeds the normal pressure, the valves as well as the case (along with the weights) are lifted up from its seat. This enables the steam to escape through the discharge pipe, which carries the steam outside the boiler house.

The lift of the valve is controlled by the studs. The head of the studs projects into the interior of the casing. The centre of gravity of the dead weight safety valve is considerably below the valve which ensures that the load hangs vertically.

The dead weight safety valve is most reliable type of safety valve and has the advantage that it cannot be readily tempered because any added weight must be equal to the total increased pressure of steam on the valve. This type of safety valve is not suitable for boilers like locomotive boilers and marine boilers, where extensive vibrations and movement are present. The second disadvantage of these valves is the heavy load which these valves carry. Due to technological development, boilers of higher working pressure with high steam generation rate became necessary. In this situation heavier dead weight is required for loading dead weight safety valve as the working pressure of the boiler increases and discharge area of the valve also increased with increase in steam generation capacity. Due to these, the size of dead weight safety valve considerably increases. So the dead weight safety valve has limited range of application for low pressure, low steam generation capacity stationary boilers.

(2)Lever Safety Valve:

Figure 4.8 shows construction of lever loaded safety valve. A lever safety valve consists of a valve body with a flange fixed to the steam generator. The valve seat is screwed to the body, and the valve is loaded by means of weighted lever which is pivoted about a fulcrum situated near to the valve. The load is properly adjusted at the other end of the lever. Due to leverage effect the loading weight in lever safety valve is equal to 1/leverage part of the weight necessary for corresponding dead weight safety valve. Thus, there is huge reduction in loading

weight in lever safety valve compare to dead weight safety valve for the same limiting pressure. The pressure limitation experienced by dead safety valve can be removed by use of lever safety valve, but the limitation due to vibration is still present in lever safety valve. So lever safety valve can only be utilized with stationary boilers, where vibrations do not occur.

When the pressure of steam exceeds the safe limit, the upward thrust of steam raises the valve and the lever with its weight. The excess steam escape through the passage created between the valve and valve seat, thus relieving the boiler from excessive pressure. Lever safety valve is located on the top of the boiler shell in steam space. Due to leverage effect the loading weight in lever safety valve is equal to 1/leverage part of the weight necessary for corresponding dead weight safety valve. Thus, there is huge reduction in loading weight in lever safety valve compare to dead weight safety valve for the same limiting pressure. The pressure limitation experienced by dead safety valve can be removed by use of lever safety valve, but the limitation due to vibration is still present in lever safety valve. So lever safety valve can only be utilized with stationary boilers, where vibrations do not occur.

(3)Spring loaded Safety Valve: COPY FIG. 4.8 FME BOOK ( by R.B.Varia , Atul Prakashan) PAGE 145 A spring loaded safety valve was mainly used for locomotives and marine boilers but now a day due to its beneficial characteristics against vibration and adjustable pressure range, they are very common in use with different types of boilers. Spring loaded safety valve is loaded with spring instead of weight. The spring is made of round or square spring steel rod in helical form. The spring may be in tension or compression, as the steam pressure acts along the axis of the spring .In the actual practice, the spring us placed in compression. A Ramsbottom spring loaded safety valve is shown in the figure 4.9. It is usually, fitted to locomotive boilers. It has two separate valves of the same size. There valves have their seating in the upper ends of two hollow valve chest. These valve chests are united by a bridge and a base. The base is bolted to a mounting block on the top of a boiler over the fire box.

The valves are held down by means of a spring and lever. The lever has two pivots. One pivot is joints by a pin to the lever, while the other pivot is forged on the lever. These pivots rest on the centers of the valves. The upper end of the spring is hooked to the arm, while the lower end to the shackle, which is secured to the bridge by a nut. The spring has two safety links, one behind the other, or one on either side of the lever connected by pins at their ends. The lower passes through the shackle while the upper one passes through slot in arm of the lever. The lever has an extension, which projects into the drivers cabin. By pulling or raising the lever, the driver can release the pressure from either valve separately.

(4)High Steam and Low Water Safety Valves: COPY FIG. 4.9 FME BOOK (R.B.Varia, Atul Prakashan) PAGE 146

These valves are placed at the top of Cornish and Lancashire boilers only, where large space is available in the boiler drum.. It is a combination of two valves, one of which is the lever safety valve which blows off steam when the working pressure of the steam exceeds. The second valve operates by blowing off the steam when the water level becomes too low.

A best known combination of high steam - low water safety valve is shown in the figure 4.10. It consists of a main valve (known as lever safety valve) which rests on its seat. In the center of the main valve a seat for a hemispherical valve is formed for low water operation. This valve is loaded directly by the dead weights attached to the valve by a long rod. The arrangement of a lever is provided in side the drum as shown in the figure. The lever is attached to its fulcrum. A balance weight is suspended at one end of the lever and a float pad (weight) is suspended to other end of the lever. When the water in the drum is at sufficient high level, the balance weight is balanced by the effective weight of float pad because the float pad remains in its lifted position due to the water level. At that time, the pointer of lever remains untouched to the collar of valve road.

When the water level falls, the float pad comes out of water and the balance weight will move in downward direction. At that time, the pointer of lever touches with the collar of valve road and pushes the valve rod in upward direction. Due to this, hemispherical valve, attached with the

valve rod, is lifted up and the steam escapes with the loud noise, which warns the operator. A drain pipe is provided to carry water, which is deposited in the valve casing. (c)Pressure gauge:- COPY FIG. 4.10 FME BOOK (R.B.Varia, Atul Prakashan) PAGE 146

A pressure gauge is used to measure the pressure of the steam inside the steam boiler. Generally, it is fixed in front of the steam boiler in such a manner that it can be easily and clearly visible to the operator.

Generally, Bourdons tube type pressure gauges are widely utilized. Figure 4.11 shows internal construction of the Bourdons tube type pressure gauge. It consists of an elliptical elastic tube bent into an arc of a circle with closed free end as shown in the figure. This bent up tube is called Bourdons tube. Other end of the tube is fixed and connected to the steam space in the boiler. The closed free end is connected to a sector through a link. The steam, under pressure, flows in the tube. As a result of this increased pressure, the Bourdons tube tends to straighten itself. Since the tube is encased in a circular curve, therefore it tends to become straight because of free end. With the help of a simple pinion and sector arrangement, the elastic deformation of the Bourdons tube rotates the pointer. This pointer moves over a calibrated scale, which directly gives the gauge pressure.

Generally, pressure gauge, which is capable of indicating pressure value double than working pressure of the boiler, should be selected.

(d) Fusible plug:- The function of the fusible plug is to

extinguish the fire or give an indication of alarm in the event of the water level in the boiler shell falling below a certain specified limit. We know that water is transferred into steam by heating in a boiler. Due to this, the level of water in the boiler shell falls down. If the water is not replenished and the steam generation continues then the parts, which have been covered by water may become uncovered and get overheated and subsequently can be melted. To safeguard against this eventuality, we use fusible plug.

The fusible plug is fitted to the crown plate of the furnace over the combustion chamber at the lowest permissible water level. Its object is put off the fire in the furnace of the boiler when the level of water in the boiler

falls to an unsafe limit, and thus avoids the explosion which may take place due to overheating of the furnace plate. Figure 4.12 shows common form of fusible plug. An outer plug, with hexagonal flange to take spanner for fixing or removing, is screwed in the crown plate of the boiler with the help of its external threads. An assembly of two other plugs is screwed into the inner threads of the outer plug. This assembly of two plugs is made up from one hollow plug and one solid conical shaped plug with fusible metal. The hollow plug of this assembly provided with hexagonal flange for screwing the assembly into the inner threads of the outer plug.

In normal condition the fusible plug remains in covered condition by the water. However, when the level of water in the boiler falls to an unsafe limit, the fusible plug becomes uncovered from the water and the fusible metal melts down. As a result of this, the solid plug of the assembly drops in the furnace creating hole in the hollow plug of the assembly. The steam from the drum suddenly rushes into the furnace with a sound like whistle. This sound warns the boiler operator to take necessary action. (e) Steam stop valve:-

The function of the steam stop valve is to shut off or regulate the flow of steam from the boiler to the steam pipe. Some times it is known as junction valve. Usually the junction valve means a regulating valve of larger size and a stop valve refers to a regulating valve of smaller size.

The steam stop valve is mounted on the top of the boiler shell (over the steam space) and is connected to the steam pipe, which carries the steam to the place of application.

Figure 4.13 shows sectional view of steam stop valve. The body of the stop valve is made of cast iron and cast steel. The valve, valve seat and the nut, through which the valve spindle works, are made of brass or gun metal. The spindle passes through a gland and stuffing box. The spindle is

rotated by means of handle wheel. The upper portion of the spindle is screwed and made to pass through a nut in a cross head carried by two pillars. The pillars are screwed in the cover of the body as shown in the figure. The boiler pressure acts under the valve, so that the valve must be closed against the pressure. The valve is generally, fastened to the spindle which lifts it up.

A non-return valve is, sometimes, fitted near the stop valve to prevent the accidental admission of steam from other boilers. This happens when numbers of boilers are connected to the same pipe and when one is empty and under repair.

(f) Feed check valve:-

The feed check valve has the following two functions to perform:- (1) To allow the feed water to pass into the boiler. (2) To prevent the back flow of water from the boiler in the events of the failure of the feed pump.

Figure 4.14 shows sectional view of feed check valve. It is a non-return valve, which permits flow of water from feed pump to boiler shell only and not from boiler shell to feed pump. Its function is to regulate the supply of water, which is pumped into the feed pump. This valve must have its spindle lifted before the pump is started. It is fitted to the shell slightly below the normal water level of the boiler Feed check valve consists of a valve whose lift is controlled by a spindle and wheel. The body of the valve is made of brass casting and of the boiler at a point from which perforated pipe leads the feed water. The pipe distributes the water in the boiler uniformly.

As shown in the figure, the valve is free from the lower end of the spindle. Due to this at the time of supplying the feed water to the boiler, the lift of valve, due to pressure difference between feed pump delivery pressure and boiler pressure, is controlled by position of the spindle. When the feed pump stops, the valve sticks to its valve seat due to difference of boiler pressure and atmospheric pressure (pressure in delivery pipe of the feed pump).

(g)Blow off cock:- The blow of cock serves to drain out the water from the boiler periodically for any one of the following reasons:- (1) To discharge mud, scale and other impurities which settle down at the bottom of the boiler. (2) To empty the boiler for internal cleaning and inspection. (3) To lower the water level rapidly if the level becomes too high.

The blow of cock is fitted at the lowest portion of the water space of the boiler. It may be mounted directly to the boiler shell or through a boiler elbow pipe, which is fitted to the boiler

shell. Figure 4.15 shows sectional view of blow off cock. The blow of cock consists of a conical plug fitted to the body or casing. The casing is packed, with asbestos packing, in grooves round the top and the bottom of the plug. The asbestos packing is made tight and plug bears on the packing. It may be noted that the cocks packed in this way keep the grip better under high pressure and easily operated than unpacked.

The shank of plug passes through a gland and stuffing box in the cover. The position of plug can be changed by handle or spanner as per requirement.

(h)Man hole and mud hole:- Man hole is an opening provided on a

boiler to allow men to enter inside the boiler for inspection and repair. It is generally provided on top or in front of the boiler plate. Mud hole is an opening provided on a boiler to give access for cleaning any sediment deposited in lower part of boiler. It

is placed near lowest part of the boiler shell. The covers of man hole and mud hole are fitted from inside of the boiler shell so they are of

elliptical shape. (2) BOILER ACCESSORIES: Boiler accessories are the appliances which are installed to increase the performance of steam generating process of the boiler (steam generating unit). The important accessories are (1)Superheater (2)Economizer (3) Air Preheater (4)Feed Water Heater (5)Feed Pump.

The heat energy, generated by combustion of fuel, is partly utilized to generate steam of desired quality. When superheated steam is required, steam collected in the steam space is further heated up to desired temperature beyond saturation temperature in the superheater. After generating steam of desired quality, remaining heat energy flows with the flue gases. If this remaining heat energy is recovered from the flue gases for meaningful purpose, then overall efficiency of the steam generator/boiler can be increased considerably. Here, we will study some important boiler accessories in detail. (1) STEAM SUPERHEATER:- Generally saturated steam is utilized for heating and drying purposes in various industries. But in the field power generation, super heated steam is more preferable for steam prime movers due to following reasons. (1)Superheated steam contains more thermal energy compare to saturated steam of same pressure. So the work developed in the steam prime mover by superheated steam is higher than the work developed by saturated steam of same pressure.

(2)Thermal efficiency of power cycle increases by supplying heat at higher average temperature to heat engine. Use of superheated steam reflects as higher thermal efficiency of power cycle. (3) Problems like erosion and corrosion in prime movers can be reduced by use of superheated steam. The steam collected in steam space of boiler drum is generally wet because it is in direct contact with water of boiler drum. For getting dry and saturated steam or superheated steam, the steam should be heated in separate indirect contact type heat exchanger, which is known as superheater. The superheater enables the wet steam to be first dried at the same temperature and

pressure and then raise the temperature above saturation temperature. Heat of flue gasses utilized in super heating the steam and as the superheater is placed in the path of the flue gasses. When superheater is placed near the furnace of the boiler, part of heat received by radiation is higher compare to part of heat received by convection. This type of superheater is generally known as radiant superheater. When superheater is placed in the path of flue gases far beyond from the furnace of the boiler, part of heat received by convection is higher compare to part of heat received by radiation. This type of superheater is generally known as convective superheater.

Wide varieties of superheater designs are familiar from beginning. Figure 4.16 shows Sudgens superheater.

This type of superheater was most familiar for Lancashire boilers, locomotive boilers and Babcock-Wilcox boilers. As shown in figure, it is made from two box type headers of mild steel and number of U shaped solid drawn steel tubes. This superheater is kept generally at back side of the boiler in the flow passage of flue gases. Hot flue gases were diverted over the superheater tubes in a controlled manner with the help of damper. Saturated steam from steam space of drum comes in intake header via connecting pipe and then enters into the U shaped tubes of the superheater. After getting heat from the hot flue gases, steam becomes superheated and comes into the outlet header of the superheater. Supply of superheated steam of desired temperature is available from this outlet header.

Tubes of superheater are filled with feed water and damper is kept closed to prevent overheating in starting condition, when steam is not generated in adequate quantity in the boiler drum. In running condition, the flow of hot gases going to the superheater tubes should be controlled by damper in proportion to the amount of steam passing through the tubes of superheater to prevent overheating of the tubes and to maintain degree of superheat of superheated steam.

(2) ECONOMISER: The flue gases coming out from the chimney of the boiler (steam generator) carries

considerable amount of thermal energy. If this thermal energy is recovered for meaningful purpose, then overall efficiency of the steam generator/boiler can be increased considerably. The economizer is utilized to increase the temperature of feed water with the help of flue gases.

The economizer is an indirect heat exchanger, in which heat is transferred from flue gases to the feed water. The economizer is kept in the path of flue gases between the boiler and the chimney. Exhaust gases from boiler enters the economizer where a part of heat carried by them is

used in heating water flowing through the pipes of economizer. Temperature rise of approximately 5 to 6 C for feed water can be achieved by use of economizer.

The first successful economizer design, patented by Edward Green in 1845, was used to increase the steam-raising efficiency of the boilers of stationary steam engines. Since then it has been known as Green's economizer.

Figure 4.17 shows construction details of Greens economizer. Greens economizer consists of an array of vertical cast iron tubes connected to upper and lower headers. Generally, a safety valve is provided on the top to avoid explosion due to excessive pressure of water developing inside economizer tubes. A blow off cock is provided at suitable location on bottom header to throw out the sediments deposited in feed water. Arrangements of scrappers with warm wheel are provided to clean outer sides of pipes from the deposition of soot carried by the flue gases. Continuous scrapping is always desired so as to maximize heat transfer rate. The most successful feature of Green's economizer is its mechanical scraping arrangement. Economizer also has a bypass provided so that flue gases can be diverted when economizer is out of full or part operation due to failure or cleaning purpose or feed water temperature control.

This economizer is installed in the path of the flue gasses between the boiler and the chimney in such a manner that these flue gases pass from the gaps of these tubes. The raw feed water, coming from feed pump, enters into the tubes of economizer from lower header and then passes through these vertical tubes surrounded by hot gases. Heat transfer takes place between the hot flue gases and the feed water. Part of the heat energy of flue gases is absorbed by the feed water would otherwise be lost into the atmosphere. Thus, with the use of economizer, considerable saving

in input energy (fuel burnt) can be realized with some sort of complicated arrangement and addition in cost. The justified cost of the economizer depends on the total gain in efficiency. Other advantages of using the economizer are as under. Economizer helps in removal of dissolved gases by preheating of water. As a result, tendency of corrosion and pitting reduces to considerable level. Supply of higher temperature feed water reduces thermal strain in boiler parts.

(3)AIR PREHEATER:- The flue gases coming out from the economizer also carries considerable amount of thermal

energy even though some part of energy is absorbed to heat feed water in the economizer. If this thermal energy is recovered for meaningful purpose, then overall efficiency of the steam generator/boiler can be increased considerably. The air preheater is utilized to increase the temperature of air, which is to be utilized to burn the fuel, with the help of flue gases.

The air preheater is kept in the path of flue gases between the economizer and the chimney. Exhaust gases from the economizer enters into the air preheater, where a part of heat carried by them is used in heating atmospheric air going to boiler furnace. Generally, temperature rise of 30 to 35 C of intake air can be possible with the use of air preheater. This rise of temperature results in increment of boiler efficiency by 2%. Use of preheated air for combustion of fuel helps in achieving faster rate of combustion, possibility of burning inferior quality coal/fuel and increased rate of evaporation from boiler etc.

Air preheaters are classified into main two types (1) Recuperative type and (2) Regenerative type.

(1)Recuperative air preheater: An air preheater, in which the heat-transferring metal parts are stationary and form a

separating boundary between the flue gases and atmospheric air, is known as recuperative air preheater. In other words, recuperative air preheater is indirect contact type heat exchanger utilized to heat atmospheric air before entry to the combustion chamber of the boiler. Recuperative air preheater is further classified in two types according to the construction (i) Tubular type air preheater and (ii) Plate type air preheater.

Typical construction of tubular type recuperative air preheaters are shown in the figure 4.18. Figure 4.18 (copy figure 4.15 page no 150 FME (Gujarati medium))

(b)Regenerative Air Preheater

The regenerative air preheater consists of a heat conducting element, which is exposed alternatively to hot gases and cold air. This element absorbs heat from the hot gases and gives it up to the cold air coming from forced draft fan, when it is exposed to above mentioned mediums. This element is made up from metallic mesh or matrix having high heat capacity. Regenerative air preheaters are of two types (i) stationary regenerative air preheater and (ii) rotary regenerative air preheater.

Typical construction of stationary and rotary regenerative air preheaters are shown in the figure 4.19.

(4) FEED WATER HEATER:- Generally, feed water heaters are utilized in the field of power generation. In steam power plants, part of steam is withdrawn or extracted at some intermediate stages of steam turbine during the process of expansion. The extracted steam is known as bleed steam. These bleed steam is utilized for regenerative heating of feed water. Feed water heater is a heat exchanger which is utilized for heating feed water with the help of the bleed steam from turbine. Feed water heaters are classified into two types (1)Direct contact type. and (2)Indirect contact type( surface type).

Direct contact type feed water heater is known as open feed-water heater. Extracted steam is allowed to mix with the feed-water in this type of feed water heater. This kind of heater will normally require a feed pump at both the feed inlet and outlet since the pressure in the heater is between the boiler pressure and the Surface Condenser pressure.

Indirect contact type feed water heater is known as closed feed water heater. It is typically shell and tube type (surface) heat exchanger. Feed-water passes throughout the tubes of feed water heater and is heated by turbine extraction steam. It does not require separate pumps before and after the heater to boost the feed-water to the pressure of the extracted steam as with an open heater. (5) :- Feed pumps are used to supply feed water to the steam generator at required rate and pressure. Generally, pressure of feed water is kept 20% higher then steam pressure. Feed pumps are of three types i.e. centrifugal pump, reciprocating pump and injectors.

For small capacity, low pressure steam generator generally reciprocating pumps are utilized as feed pump and for high capacity, high pressure steam generators generally multistage centrifugal pumps are utilized as feed pumps. Generally, steam ejector type feed pump is utilized in locomotive boilers. [F] DIFFERENCE BETWEEN BOILER MOUNTINGS AND ACCESSORIES:

BOILER MOUNTINGS BOILER ACCESSORIES (1)Boiler Mountings are the auxiliaries provided for the safety and complete control of process of steam generation.

(2)The mounting from an integral part of the boiler and are mounted on the body of the boiler itself. (3)As integral part of boiler, the cost of each mounting is included in the basic cost of the boiler. (4)Boiler mountings are compulsory as per Boiler Act. (5)As per the Indian Boiler Regulation (IBR) the following mountings must be provided on the boiler. (a) Two Numbers of Water Level Indicator (b) Two Numbers of Safety Valve (c) Fusible Plug (d) Steam Stop Valve (e) Feed Check Valve (f) Blow off Cock (g) Pressure Gauge (h) Man Hole and Mud Hole

(1)Boiler accessories are the appliances installed to increase the performance of steam generating process of the boiler (steam generating unit).

(2)The accessories are not integral parts of the boiler so they are mounted at suitable places in the boiler system as per their function.

(3)As extra part of boiler system, the cost of each accessory is not included in the basic cost of the boiler. (4)Boiler accessories are not compulsory as per Boiler Act. (5)The important accessories are

(a) Superheater (b) Economizer (c) Air Preheater (d) Feed Water Heater (e) Feed Pump

[G]LOCATION AND FUNCTION OF BOILER MOUNTINGS AND ACCESSORIES:

BOILER MOUNTINGS ITEM LOCATION FUNCTION

Water level indicator On the front plate of the boiler shell in such a manner that they can be easily visible to the operator. Its water tube is joined to water space of the boiler shell and its steam tube is joined to the steam space of the boiler shell.

To indicate constantly and exactly the level of water in the boiler shell.

Safety valve On the top surface of the boiler shell in such a manner that its inlet is connected to steam space of the boiler shell.

Safety valve enables the surplus steam to escape from the boiler shell to bring the steam pressure in safe limit when the pressure in the boiler exceeds the limiting pressure.

Pressure gauge It is fixed in front of the steam boiler in such a manner that it can be easily and clearly visible to the operator.

To measure the pressure of generated steam in the boiler.

Fusible plug The fusible plug is fitted to the crown plate of the furnace over the

To extinguish the fire or give an indication of alarm in the event of

combustion chamber at the lowest permissible water level.

falling the water level below a certain safe limit in the boiler shell.

Steam stop valve The steam stop valve is mounted on the top of the boiler shell (over the steam space).

To shut off or regulate the flow of steam from the boiler to the steam pipe.

feed check valve Fitted to the boiler shell slightly below the normal water level of the boiler

(1) To allow the feed water to pass into the boiler. (2) To prevent the back flow of water from the boiler in the events of the non working condition and failure of the feed pump.

blow of cock The blow of cock is fitted at the lowest portion of the water space of the boiler. It may be mounted directly to the boiler shell or through a boiler elbow pipe, which is fitted to the boiler shell.

To discharge mud, scale and other impurities, which settle down at the bottom of the boiler. (1) To empty the boiler for internal cleaning and inspection. (2) To lower the water level rapidly if the level becomes too high.

Man hole On top or in front of the boiler plate

To allow men to enter inside the boiler for inspection and repair.

Mud hole Near lowest part of the boiler shell. To give access for cleaning any sediment deposited in lower part of boiler.

BOILER ACCESSORIES ITEM LOCATION FUNCTION

Superheater Superheater is placed in the path of the flue gasses.

For getting dry and saturated steam or superheated steam from the boiler.

Economizer The economizer is kept in the path of flue gases (generally after superheater) between the boiler and the chimney.

To increase the temperature of feed water with the help of flue gases.

Air preheater The air preheater is kept in the path of flue gases between the economizer and the chimney.

To increase the temperature of air for combustion of fuel, with the help of flue gases.

Feed water heater At suitable stage, between condenser and feed pump.

For heating feed water with the help of the bleed steam from turbine.

Feed pumps In the pipe line of feed water before feed check valve.

To increase the pressure of feed water higher then steam pressure.

[H]Applications of boiler: Steam is utilized for different purposes since long time. Pressure, quality and quantity of steam differ according to purpose of utilization. Boiler is essential equipment to generate steam of desired quality and desired pressure at desired rate from water. As per example, wet steam of low to moderate pressure is required for heating purpose but super heated steam of high pressure is required for power generation. In the beginning of industrial revolution, the use of steam is limited to medium for energy transfer, ie, for power generation only. Due to development in technology, the use of steam is not limited up to medium for heating medium or energy transfer. Steam is now used in a number of areas. Most of the industries use steam. In fact, there are very few industries that don't use steam at all. Depending upon requirement, different types of boiler are utilized for

generation of steam. Here, different fields, using steam for different purposes, are listed below. All these fields require boiler for generation of steam as per requirement.

(1) Steam is utilized for generation of electric power in steam power plants (2) Steam is utilized for generation of mechanical power to run locomotive engines, road rollers,

steamers, pumps, cranes, .., etc. (3) Steam can also be used as a direct motive force to move liquid and gas streams in piping.

Steam jet ejectors are used to pull vacuum on process equipment, continuous removal of air from surface condensers, turbines.

(4) Many large commercial and industrial facilities, especially in colder climates, use low pressure saturated steam as the predominant heat source for indoor seasonal heating. HVAC coils, often combined with steam humidifiers, are the equipment used for conditioning the air for indoor comfort, preservation of books and records, and infection control.

(5) Steam is used to add moisture to a process while at the same time supplying heat in food processing industries, textile industries, in paper industries,.

(6) Steam is utilized as a heating medium in various heating processes in dairy, pharmaceutical, and petro-chemical industries.

(7) Steam is utilized for cleaning utensils and sterilization of various instruments and vessels in hospitals and food processing industries.

(8) Steam is used to clean a wide range of surfaces. One such example from industry is the use of steam in soot blowers.

(9) Steam atomization is a process where steam is used to mechanically separate a fluid. In some burners, for example, steam is injected into the fuel in order to maximize combustion efficiency and minimize the production of hydrocarbons (soot),

(10) Steam is utilized for cooking food, shrinking-wrapping meat, exploding corn to make cornflakes by direct injection or jacket heating.

(11) Steam is utilized for keeping chocolate soft, so it can be pumped and molded. (12) Steam is utilized for depressing the caps on food jars and for making bubble wrap (13) Steam is utilized for peeling potatoes by the injecting high pressure steam into a vessel full of

potatoes. Then it is quickly depressurised, drawing the skins off. (14) Steam is utilized for making instant coffee, milk or cocoa powder. (15) Steam is utilized for making rubber items of different forms and shapes. (16) Steam is utilized for repairing underground pipes (steam is used to expand and seal a foam

which has been pumped into the pipe. This forms a new lining for the pipe and seals any cracks).

(17) Steam is utilized for drying glue (heating both glue and materials to dry on a roll). (18) Steam is utilized heating swimming pools. (19) Steam is utilized for molding tires, making carpets, making card board, block board,

corrugating cardboard, ensuring a high quality paint finish on cars [I] INDIAN BOILER ACT: Boiler is one type of pressure vessel. According to energy content, each and every pressure vessel is capable to act as a bomb, if not properly maintained or not properly operated. Due to pressurized condition of high temperature steam and feed water as well as combustion of fuel, extremely higher care should be taken in selection, erection, operation, maintenance and inspection of boilers. Safety precautions at each and every stage should not be ignored.

(As general rule, history should teach us lessons. Immediately after an accident occurs we become safety conscious and even write new policies and procedures. However, as time passes we tend to forget. Often we revert back to our old ways simply because we have been doing it that way for years. As a result, when an accident happens, it is too late to care.)

After invention of successful steam engine by Jams Watt, use of steam in various industries became common. In the Mid-Nineteenth Century, during the initial stage of industrial revolution, steam was in great demand to provide the power necessary to operate manufacturing equipment. During this period, there was no one standard in existence to guide individuals in the construction of boilers. Consequently, boilers of all types and sizes were being constructed. Many designs resulted in terrible explosions. During beginning of nineteenth century, accidents were occurring at the rate of one every four days. Only the most spectacular explosions received front-page status in newspapers. Boiler explosions peeked around 1905.

The development of a standard for construction of boilers and the adoption of these requirements into law was become need of those days. After careful study of those accidents, people had thought for appropriate laws and then many countries had formulated laws for safe working of boilers. Those laws were become famous as boiler acts. Initially in UK, the British Government set up a British Boiler Regulation which specified that a Government Inspector would be responsible and would have to certify all steam boiler as suitable from a safety and engineering point of view. With the development of better materials, safer control systems, advanced manufacturing techniques etc., it became meaningless to have a government inspection for each and every unit. So government has moved on to either self compliance to specified standards, or at most a type approval system. However, the IBR still specifies a unit approval, and every item used in an IBR steam system has to be manufactured, installed, tested, operated and maintained under the watchful eye of local inspector. As time past, many amendments were taken place in this original boiler acts same as in other laws.

In our country, India, same story was occurred for boiler act. In the year 1863, a very serious boiler explosion occurred in Calcutta which caused the loss of several lives. As a result of this explosion, the necessity of inspection of boilers was widely recognized and a bill was introduced in the Bengal Council to provide for the inspection of steam boilers. In the year 1864, the Bengal Act VI of 1864 was passed which provided for the inspection of steam boilers and prime movers in the town and suburbs of Calcutta. This is the beginning of boiler legislation in India.

Following the Bengal Act of 1864, each of the other provinces framed legislation. At that time there were seven different Acts and seven different sets of rules and regulations. Those Acts and rules & regulations were inconsistent with one another. As the differences in the Acts and rules and regulations among the various provinces in India gave rise to many difficulties, the Central Government appointed a committee called "The Boiler Law Committee" in 1920 general legislation for boilers in India. The Boiler Law Committee had formed standards for material, design, construction and operation of boilers and prepared a draft Act. The Boiler Laws Committee also prepared a uniform set of technical regulations and a model set of administrative rules. According to these standards and draft act Indian Government had passed boiler act in 1924. This law is known as Indian Boiler Act-1924

The Committee prepared a draft Act on the lines of which, the basic All-India Act was passed in 1923. The Boiler Laws Committee had not only prepared a uniform set of technical regulations and a model set of administrative rules but also made a sharp difference between the regulations and the rules. The regulations referred entirely to technical matters where as the rules referred to questions concerning the administration of the Act. Indian Boiler act, 1924 provides for the safety of life and property of persons from the danger of explosion of boilers. The current version of these regulations is known as the Indian Boiler Regulations, 1950 with amendments up to 22nd February, 2005.

Each consumer using the boiler, which comes under the IBR Act, has to do registration of his boiler with the Chief Inspector of Boilers. At the time of registration, inspection and required tests are carried out by Boiler Inspector. After satisfying required criteria, the Chief Inspector of Boilers gives certificate in the prescribed form authorizing the user of the boiler for a period not exceeding

twelve months at a pressure not exceeding such maximum pressure as he thinks fit in accordance with the rules and regulations. After getting certificate, the consumer can use the boiler by strictly following each and every provision of the Indian Boiler Act. Some of the provisions of Indian boiler act are explained below for primary knowledge.

(1) No one can utilize boiler without registration with Chief Inspector of Boilers. (2) Maximum steam pressure of a boiler is finalized after inspection of the boiler by Boiler

Inspector. Boiler Inspector gives certificate for use of boilers for specific duration (generally one year) and finalized maximum steam pressure after doing inspection of the boiler as per standard procedure and finding satisfactory condition of the boiler for utilization. In any circumstances, no one can operate boiler at a pressure higher than pressure mentioned into the certificate.

(3) Every newly registered boiler and every other boiler of which the working pressure has been altered shall, before the issue of an original or renewal certificate for such boiler, be tested under steam to the satisfaction of the Inspector.

(4) In the case of accident, the owner or person in charge of boiler should submit report of the accident to Boiler Inspector within 24 hours of the accident indicating complete details for type and possible causes of accident and losses.

(5) Central boiler board, which is under control of government, is empowered to look after rules and regulations, registration, inspection, suggestion of maximum steam pressure, observe safety precautions related to boiler maintenance.

(6) Any owner of a boiler who, in any case in which a certificate is required for the uses of the boiler under this Act, uses the boiler without any such certificate or at a higher pressure than allowed , shall be punishable with fine as per law.