Operating a Steam Boiler

In the foregoing sections we have outlined the basic principles of steam generation and the component parts of a steam boiler. Therefore now we may find it convenient and helpful to refer to the earlier portions of this unit to understand the operation of a boiler while reading this section.

i. Feeding Water to the Boiler
For operating a boiler continuous supply of feed water is required. This is to maintain a constant water level in the boiler in relation to generated steam. Water is provided to a boiler by a feed pump. This pump is meant to force water into the boiler. Since the inside pressure of the boiler is high, the water needs pumping to a considerable pressure above that of boiler. Both reciprocating and rotary pumps could be used and generally pumps are installed in duplicate for the safety of boiler operation. Feed water is supplied to the boiler through a special one-way valve. This valve does not allow the back flow of water from the boiler due to higher pressure inside the boiler.

The water supply to a boiler is very important. In most localities the natural water contains impurities like suspended solids or the dissolved chemicals. Suspended matter can usually be handled by proper filtration. The dissolved impurities in water are due to compounds of calcium and magnesium. The water containing such impurities is known as hard water. If this hardness of water is not removed, these impurities result in deposition in the form of scale on the heat exchange surfaces in the boiler. The deposition of scale over the tubes in the boiler reduces the transfer of heat from the hot gases to water and decreases the steam raising efficiency of the boiler. It may also lead to corrosion of tubes and damage to the boiler. To avoid this problem, the feed water to the boiler is treated to remove its hardness. Specialized equipment is used for this treatment of water and it is known as water softening plant. It is advised to install a water softening unit with every boiler to assure a continuous supply of soft water, otherwise the boiler has to blown down and cleaned frequently and regularly.

ii. Air Circulation & Combustion of Fuel

Fans are used to provide adequate and continuous supply of air for combustion of fuel, circulating the hot gases in the boiler and to discharge burnt flue gases into the atmosphere. A small pressure difference is kept between the point of entry of air at furnace and the exit of burnt gases at the chimney. This pressure difference helps in the flow of air throughout the system. This pressure difference is termed as boiler draught. The amount of required draught depends upon the type of fuel and the rate of burning. A high chimney helps in creating the natural draught in the boiler without any fan. A chimney also facilitates the safe discharge of burnt gases to the atmosphere. But the amount of this natural draught is low and is used only in boilers of low capacity. For larger capacity boilers the requirement of combustion air is more and hence a fan is installed at the inlet to the furnace to provide positive pressure. This is called forced drought.

iii. Care and Maintenance

The time that should be taken in raising steam from cold water depends upon the type of boiler and the degree of urgency. In every case steam should be raised as slowly as possible. Similarly rapid cooling of boiler is harmful as it puts excessive strains on the joints. Periodic blow down is necessary with all types of boilers, no matter whether treated or untreated feed water is used. This removes all the solid impurities, if any, present in the boiler. Boiler undoubtedly deteriorates more rapidly when allowed to remain idle than during long periods of normal work. If it is required to remain idle for longer periods most satisfactory method is to remove all doors and covers and thoroughly clean and dry all internal and external surfaces and give a coating of a preservative paint.

Boiler occupies such an important place in dairy plant that much of plant’s successful operation depends upon its unfaltering performance. The life of any steam generating plant is dependent upon the amount of care and attention it receives while under steam and during idle periods. Indian Boiler Act-1923 prescribes that only a Certified Boiler Attendant is authorized to operate a boiler. Yet it is worth while for all the dairy workers to become acquainted with general construction of the boiler, for overall safety and precautions.

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