Boiler Basics

Welcome to Boiler Basics. The purpose of this course is to introduce you to a basic boiler system and the varied uses for the steam it produces. The two major types of boilers and their classifications will be covered. Lastly, we will discuss the factors affecting steam production and introduce some fundamental equations used in operating the system at top performance.

WATER:

Water is unique, because it can absorb more heat than any other common inorganic material. As steam, it can carry large quantities of energy, making it an ideal material for use in numerous industrial processes. These properties have been known and utilized for over one hundred years.

STEAM

Steam is used to turn massive steam turbines for generating electrical power. It is also utilized in many processes, such as refining oil and paper manufacturing. It provides energy for hospitals and office buildings and for the textile, food, and aerospace manufacturing industries.

LEARNING OBJECTIVES

        understand the various uses of steam in industry today

         describe the types and classifications of boilers that are used in today's industry

        describe the various types of fuel and heat sources used to operate boilers,

        identify the components that comprise a boiler system

        and learn basic mathematical relationships which describe cycles of concentration, mass  

               balance, blowdown, and makeup.

The term "boiler system" is a phrase which encompasses a multitude of components, piping systems, and control systems used in the production of steam.

The boiler, at the heart of the system, is where the steam is generated. The steam is then delivered to be utilized in a variety of ways. This is known as the process part of the system. Once the steam is used, it condenses to water and is returned to the boiler. Some steam and condensate is lost and is replaced by fresh make-up water. Roll your cursor over the various parts f the boiler system to see their names.

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Although somewhat complex in construction, the boiler itself is quite basic in principle. It is the component which heats water to produce steam. The heat produced by the burning of a fuel then circulates around or through metal tubes. The tubes then transfer the heat to the water, causing it to boil. Steam collects at the top of the steam drum where it exits the boiler for its intended use.

The support system provides water to the boiler to replace the steam that is being used. Once the steam is used, it is condensed and collected in a condensate receiver. The condensate is pumped to a deaerator and may be processed through a condensate polisher or filter enroute to the deaerator.

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If water is lost from the system, it must be replaced. This replacement water is known as make-up. Make-up water is treated to remove impurities and pumped to the deaerator. Then it goes to the boiler to maintain constant volume.

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Finally, the feedwater system supplies the necessary pressure to allow the feedwater needs to overcome this pressure to get the water into the boiler. The feedwater can also undergo some form of preheating prior to entering the boiler.

BOILER TYPES

This section will discuss the types of boilers generally found in use in today's industry and how they are classified.

Classification of boilers is based on several characteristics, which are use, pressure, materials of construction, size, tube contents, heat source, and circulation.

Boilers are normally classified by the particular service they perform such as building heating, steam for plant processes, electrical power generation or recovering available heat from process waste sources. Additionally, they are either classified as package or field erected boilers. Package boilers are usually small and can be shipped by rail car. Field-erected boilers are usually quite large and are assembled and built at the plant site.

Boilers operate over a wide range of pressures based on need. Lower pressure boilers are typically found in applications such as building heating and some industrial processes. Higher pressure boilers are typically found in power generation and industrial applications.

Boilers are normally constructed of steel plates and steel tubes joined together by welding and rolling. Gray iron castings, held together by tie-rods or bolts, may be used infrequently for low-pressure heating boilers.

Size is another important aspect of boilers. Boilers are rated in square feet of heating surface available, and the amount of heat input per hour they can tolerate is measured in BTUs. Residential boilers may have heating surfaces ranging from a few to hundreds of square feet. Industrial boilers may have heating surfaces ranging from hundreds to thousands of square feet.

Tube content describes how water and heat are separated inside the boiler. There are water tube and fire tube boilers. In water tube boilers, water flows through the inside of the tubes and hot gases are on the outside. In fire tube boilers, water surrounds the tubes and the hot gases pass through the tubes.

The heat to warm the water and generate steam may be derived from the following sources: combustion of solid, liquid, or gaseous fuels; hot waste gases from other chemical reactions; electrical energy; and nuclear energy. If the heat source is the direct result of the burning of fuel in the furnace contained in the unit, it is known as a fired boiler. In an unfired boiler, there is no direct burning of fuel. Waste heat is used to generate steam.

Finally, boilers are classified by circulation. They can be natural circulation, positive or forced circulation, or once-through type boilers. In a natural circulation boiler, differences in water density due to temperature in different areas of the boiler cause the water to circulate naturally. In positive or forced circulation boilers and in once-through boilers, water is moved through the tubes by pumps.

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As discussed earlier, there are two major types of boilers based on tube content: Water tube units and fire tube units.

A water tube boiler consists of one or more steam drums, one or more mud drums, and tubes. The tubes are where the water is heated and the steam is generated. The steam drum is used to collect steam and the mud drum is used to store water.

Water tube boilers are available in a variety of designs and sizes ranging from package boilers that are manufactured and delivered as a complete unit, to large field erected boilers that are manufactured in modules and assembled on site.

When the amount of steam required for a process is greater than the amount available from the smaller package boilers, larger boilers must be built on-site. These field-erected boilers are generally required for the large demands of steam production required by utilities and many types of pulp and paper production, petrochemical, chemical, refinery, and other types of industrial manufacturing facilities. They are also used in systems where low heat value fuel is used, such as refinery CO boilers.

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