Steam Boilers

Steam Boilers (English: boiler ) are devices for producing water vapor, which will be used for heating or driving power. Boilers vary from the popular coal and oil fuels, to electricity, gas, biomass, nuclear and others. Boilers are the most important part of the invention of the steam engine which was the trigger for the birth of the industrial revolution.

A steam boiler must meet the following requirements:

1. In a certain time must be able to produce steam with a certain weight and pressure greater than 1 atmosphere.
2. The steam produced must be as low as possible
3. If further heating is used, then in irregular steam usage, the temperature of the steam should not change much and must be easily regulated
4. At the time of motion where the use of steam changes, the steam pressure should not change much
5. Steam must be able to be formed with the lowest possible amount of fuel
6. The arrangement of the fuel packaging must be such that fuel can be burned without requiring too much cost and energy.

Material

The vessels in a boiler are usually made of steel (steel / alloy steel), or originally from wrought iron. Stainless steel is actually not recommended (by the ASME Boiler Code) for use on wet parts of modern boilers, but it is often used on super heater parts that will not be exposed to liquid boilers. Copper or brass is often used because it is more easy to use. manufacturing for small size boilers. Historically, copper has often been used for fireboxes (mainly for steam locomotives, because of its ease of forming and high heat conductivity; however, at present, high copper prices are an uneconomic choice and cheaper to use substitute materials (such as steel )

For most Victorian steam boilers, only open the highest quality wrought iron, which is assembled using a rivet. The high quality of the sheet and its suitability for high reliability are used in critical applications, such as high pressure boilers. In the 20th century, for practical purposes the move towards the use of steel, which was stronger and cheaper, with welding construction, was faster and less labored.

Cast iron is used for heating vessels for water heating. Although a heater is usually called a “boiler”, because its purpose is to make hot water, not steam, because it is operated at low pressure and avoids actual boiling. The brittleness of cast iron makes it unsuitable for high pressure steam boilers

Applicable regulation

Certification for operators of Steam Boilers and Steam Boilers refers to the following regulations:

1. ASME sect. I, II, and V

2. Steam Law of 1930

3. Steam regulations in 1930

4. Law No.1 of 1970

Inspections are carried out by Steam Workers and Pressure Vessels, through bodies appointed by the Department of Labor. Operators must attend boiler training through a 3rd party appointed by the Department of Labor to organize training and issue certificates.

Boiler Working Principle

Boiler or steam boiler is a machine that functions to convert water into steam. The process of changing water into steam occurs by heating water that is in the pipes by utilizing heat from burning fuel. Combustion is carried out continuously in the combustion chamber by flowing fuel and air from outside.

The steam produced by the boiler is superheat steam with high pressure and temperature. The amount of steam production depends on the surface area of ​​the heat transfer, the flow rate, and the heat of combustion given. Boilers whose construction consists of pipes filled with water are called water tube boilers.

Fig. boiler water tube

In generating units, boilers are also commonly referred to as steam generators (steam generators) given the meaning of the word boilers are only boilers, while in fact from boilers produced high-pressure superheat steam .

In terms of the fuel used, the PLTU can be divided into:

• Coal Power Plant
• PLTU Oil
• Gas power plant
• Nuclear power plant or nuclear power plant

Types of coal power plant can still be distinguished by the combustion process, the power plant by burning pulverized coal ( Pulverized Coal / PC B oiler ) and coal-burning power plants with output ( Circulating Fluidized Bed ).

The difference between a coal power plant and an oil or gas power plant is in the equipment and system for handling and burning fuel as well as handling the ash waste. Coal power plants have more and more complex auxiliary equipment than oil or gas power plants. Gas power plant is the simplest power plant equipment.

Fig. Layout of Pulverized Coal (PC) Coal Boilers

Fig. Circulating Fluidized Boiler (CFB) layout

Judging from the pressure of the boiler combustion chamber, power plants can be divided into:

• PLTU with Pressurized Boiler
• PLTU with Balanced Draft Boiler
• PLTU with Vacuum Boiler

The furnace pressure system is commonly called a draft or static pressure inside the combustion chamber where the fuel combustion process takes place. PLTU with pressurized boiler (positive combustion chamber pressure) is used for burning oil or gas fuel. Positive combustion chamber pressure is caused by air gusts from the Forced Draft Fan (FDF). The exhaust gas exits the combustion chamber into the atmosphere because of the pressure difference.

Fig. Types of pressure ( draft ) boilers

Fig. Balanced Draft Boiler Scheme

PLTU with Balanced Draft Boiler (balanced pressure) is commonly used for burning coal fuel. The combustion chamber pressure is slightly below the atmospheric pressure, usually around -10 mmH ₂ O. This pressure is generated from the regulation of two fans, namely the Induced Draft Fan (IDF) and the Forced Draft Fan (FDF). FDF serves to supply combustion air to the combustion chamber ( furnace ) in the boiler, while the IDF serves to suck gas from the combustion chamber and discharged into the atmosphere through the chimney. Whereas PLTUs with vacuum boilers are no longer being developed, so at this time no one is implementing PLTUs with negative pressure boilers.

Water Cycle in Boilers

The water cycle is a chain of working fluid cycles. Boilers get a supply of water working fluid and produce steam to flow into the turbine. Water as a working fluid is fed to the boiler using a filling water pump through an economiser and accommodated in a steam drum .

Economiser is a device that is the last water heater before entering the drum. In the economiser water absorbs heat from the exhaust gas that comes out of the superheater before being discharged into the atmosphere through the chimney.

Fig. Economizer type finned tubes ( finned tubes )

The equipment that is passed in the water cycle is the drum boiler, down comer, bottom header, and riser. The water cycle in the steam drum is, water from the drum drops through the down comer pipes to the bottom header . From the underwater header is distributed to the heating pipes ( risers ) are arranged to form the boiler combustion chamber wall. Inside the riser the water undergoes heating and rises to the drum again due to temperature differences.

Heat transfer from fire ( flue gas ) to water in boiler pipes occurs by radiation, convection and conduction. As a result of heating in addition to temperatures rising to boiling also occurs naturally water circulation, ie from the drum down through the down comer to the header down and up again to the drum through the riser pipes . The existence of this circulation is necessary for cooling the heating pipes and accelerate the heat transfer process. The speed of circulation will affect the production of steam and increase in pressure and temperature.

In addition to natural circulation, also known as forced circulation . This type is used for circulating a circulation pump ( circulation pump). Generally circulating pumps have a circulation rate of around 1.7, meaning that the amount of water circulated is 1.7 times the evaporation capacity. Some of the advantages of a forced circulation system include:

• Faster start-up time
• Has a better response in maintaining the flow of water to the heating pipes at start or full load.
• Prevent the possibility of stagnation on the evaporation side

Fig. Water cycle

Classification of Steam Boilers

There are many types of Steam Boilers, and their development can keep up with current technological advancements. Of the many types of kettle need to be grouped into several parts. according to its use, construction and others. Below this grouping will be explained in outline:

Division According to Steam Law

Because the places of use differ, according to the Steam Act article 9, the Steam Boiler is divided into three namely:

1. Fixed Boilers or Land Boilers, namely boilers that are used on land such as factories, power plants and others that have a fixed foundation.
2. Boat Boilers, namely boilers used on ships. Here the equipment for the safety of the boilers usually has a slightly different construction from the other boilers, bearing in mind the condition of ships which are always shaking during sailing.
3. Kettles that can move. that is, the boilers which are not included in the two categories of boilers mentioned above, such as train boilers, boiler stakes and others.

Distribution by Construction

Boilers are made to produce steam by heating the water in it by hot gas from burning fuel. The kettle must work as efficiently as possible _; meaning that it must be able to produce as much steam as possible with the use of minimal fuel. Therefore the boiler construction must be such that the heat from the fuel must be absorbed as much as possible by the boiler water to produce steam. To achieve this, the construction of the boiler is made from the arrangement of pipes that separate water and hot gases that heat the water.

Seen from the position of the boiler pipe is divided into:

1. Horizontal   example: B&W Section
2. Vertical       example: Foster Wheeler
3. Slanted          example: B & W Integral

Judging from the substances flowing in the pipe, the kettle is divided into three groups, namely:

1. Boiler Pipe Api ( Fire Tube Boilers) . In this boiler hot gases flow in the pipe, while the heated water is outside the pipe. Fire pipe boilers are usually used for steam capacities up to 14,000 kg / hr with a pressure of 18 kg / cm2. A fire pipe boiler can use fuel oil, gas or solid fuel in its operation. For economic reasons, most boiler pipes are constructed as “package” boilers (factory assembled) for all fuels.

               For example: – Kettle Schots

                                       – Cochran kettle

2. Boiler Water Pipe (Water Tube Boilers).In this boiler that flows in the pipe is boiler water, while the heating gas is outside the pipe. At present, the development of water pipe boilers is more rapid. In the water pipe boiler, water is fed by the boiler through the pipes into the drum. Circulated water is heated by combustion gases forming a steam pad in the steam area of ​​the drum. This boiler is chosen if the demand for steam and steam pressure is very high as in the case of the boiler for power generation. Modern boilers are designed with a steam capacity of 4,500 – 12,000 tons / hour, with very high pressure. Many water pipe boilers are constructed in packages when using fuel oil and gas. For water pipe boilers that use solid fuel, it is not commonly designed in packages. Water pipe boiler characteristics as follows:
   a. Fored, induced and balanced drafts help to improve combustion efficiency.
   b. Less tolerant of water quality produced from water treatment plants.
   c. Allows for a higher level of heat efficiency

                For example:  – Kettle Babcock and Wilcox

                                        – Foster Wheeler Kettle

                                        – Yarrow kettle

                                        – ISD

                                        – ESD (ESD I, II, III and IV)

3. Boiler Combined Fire Pipes and Water Pipes. In this boiler there are two types of pipes, namely fire pipes and water pipes. Its construction is generally like Kettle Schots. And it seems that the making of this kettle is to correct the deficiencies found in the Kettle Schots, such as poor circulation of water in the kettle.

                For example: – Kettle Werkspoor

                                        – Howden Kettle – Johnson

Judging from its use, the kettle is divided into:

• Stationary boiler or fixed boiler. Which includes stationary are boilers that are placed on a fixed foundation, such as a boiler for power generation, for industry etc.
• Car boiler ( mobile boiler ), portable boiler / portable boiler. Which includes a car boiler is a kettle mounted on a moving foundation (car), such as a locomotive boiler, a mobile locomotive and a long boiler as well as others which seem to include a marine boiler

Judging from the Location of the Kitchen ( Furnace Position), the kettle is divided into:

1. Boiler with internal combustion ( internally fired steam boiler ). In this case the kitchen is located (burning occurs) on the inside of the kettle. most fire pipes use this system.
2. Boiler with outside burning ( outernally fired steam boiler ). In this case the kitchen is located (burning occurs) on the inside of the kettle. most water pipe boilers use this system

Viewed from the number of aisle ( Boiller Tube), the boiler is divided into:

1.  Boiler with a single tunnel (single tube steam boiler). In the single tube steam boiler, there is only 1 tunnel, the fire tunnel and the water tunnel. Cornish boilers are single fire tube boilers and simple vertical boilers are single water tube boilers.
2. Boiler with double aisle ( multi tube steam boiler ). Multi fire tube boiler for example, Scotch kettle and multi water tube boiler for example boiler B and W etc.

Judging from the Shaft Drum Cover ( Shell), the kettle is divided into:

1. Upright boiler (vertical steam boiler) , such as cocharn boiler, clarkson boiler etc.
2.  Horizontal boiler ( horizontal steam boiler ) , such as kettle cornish, Lancashire, Scotch etc.

Viewed from the shape and location of the pipe, the kettle is divided into:

1. Kettle with straight, bent and curved pipes (stright, bent and sinous tubeler heating surface)
2. Boiler with flat and tilted upright pipes ( horizontal, inclined or vertical tubeler heating surface )

Viewed from the Circulation of Water Kettle ( water circulation), the kettle is divided into:

1. Boiler with natural circulation ( natural circulation steam boiler ). In natural circulation boilers, the circulation of water in a boiler occurs naturally, ie light water rises, while a natural convection flow occurs. Generally boilers operate in a natural flow, such as the lancashire kettle, babcock & wilcox
2. Boiler with forced circulation ( forced circulation steam boiler ). In a forced flow boiler, the peksa flow is obtained from a centrifugal pump driven by an electric motor such as a la-mont boiler, benson boiler, loeffer boiler and velcan boiler.

Kettle Assist

Namely a boiler that produces steam, which is used for auxiliary aircraft, such as pumps, heaters and others. The types of boiler that are usually used as auxiliary boilers, for example:

• La Mont Exh Gas Economicer
• Cochran Composite Boiler
• B & W M – type
• Foster Wheeler D – type.

Large motorboats generally have auxiliary boilers. The benefits of this auxiliary boiler are for heating on ships, such as space heating, kitchens, fuel. and to move auxiliary aircraft.

Kettles of this kind in general in addition to the lid with fuel oil. usually also combined with utilizing the heat from the exhaust gases coming out of the motor

There are several types of systems or systems, including:

1. On a ship there is an auxiliary kettle covered with oil. and a separate kettle with a special exhaust gas for the main motor exhaust. And each of them can form its own steam formation.
2. La Mont system.

The La Mont boiler is widely used to utilize a portion of the exhaust gas heat from the main motor for the formation of steam. This boiler is usually placed on the exhaust gas road from the main motor or in the chimney, thus it is higher than the main motor (See picture).

The function of this boiler is actually only as a place for the circulation of heat, while the place of formation of the steam is in another boiler Thus a circulation pump is needed to drain the water inside the auxiliary boiler (eg Cochran) to the La Mont boiler to finally return to the auxiliary boiler after taking heat. The formation of steam produced by the auxiliary kettle is usually at a pressure of about 7 or the water temperature of the boiler about 170 ° C.

The exhaust gas temperature ranges from 300 – 400 ° C and leaves the La Mont boiler approximately 220 ° C.

The La Mont kettle, which is heated by flue gas, is almost entirely a number of spiral pipes. Each spiral pipe is connected to the intake and exhaust cabinet.

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