A steam boiler is a steam producing heating system. It creates energy by heating water to get steam. It is a heat exchanger that makes steam for outside usage and has a combustion chamber and water container. The several varieties of steam boilers include those that are very small and those that are large for more demanding jobs.
A steam boiler burns fuel to heat water. The combination of heat and water produces steam. There are three forms of heat used to generate steam: radiation, convection, and conduction.
Steam boilers are defined by their construction, portability, tube type, fuel type, and the pressure they produce. When boilers were initially introduced, they were as efficient as modern boilers but were dangerous since there were few control mechanisms. The size, fuel, and dimensions of a boiler change in accordance with the job it is designed to perform and the industry in which it is used. The types of fuel include electricity, wood, natural gas, coal, and fossil fuels. The difference between the fuels is their cost, eco-friendliness, and efficiency. As the demand for electricity and power generation has increased, alternative fuels have been developed, including biomass and refuse or trash.
Hot Water Boilers
Hot water boilers are tanks that transfer heat to water that is circulated for heating purposes. They are made of stainless steel, cast iron, aluminum, and steel and are capable of withstanding increased temperature and pressure.
The types of hot water boilers are defined by their tube systems, which can be fire or water. Fire tube hot water boilers have tubes immersed in water; heat moves through the tubes and heats the water around them. Water tube boilers have water inside the tubes that circulates as the tubes are heated.
Electric Boilers
Electric boilers use electric elements to generate heat; it is a faster and more efficient heating method. It is an eco-friendly, cleaner system since it does not necessitate the burning of a fuel. Electric boilers are longer lasting, require less cleaning, and are maintenance free. The one factor that has to be controlled with electric boilers though is the buildup of scaling in the water reservoir.
Gas Boilers
Gas steam boilers are powered by natural gas or propane and are more efficient than standard boilers. The fuel for a gas boiler is piped into the boiler from an outside source that is connected directly to the boiler. The distribution of heat using a gas steam boiler depends on its configuration. Gas steam boilers can be used for industrial purposes and low pressure applications.
Low Pressure Boilers
Low pressure steam boilers transfer heat at pressures between 10 and 15 psi with a temperature of 300° F (149° C). This type of boiler is used where there is little need for rapid temperature change, where a consistent temperature is required. The popularity of low pressure steam boilers is due to the speed at which they deliver steam; they can do so much faster than high pressure steam boilers.
High Pressure Boilers
High pressure steam boilers create excessive pressure to power equipment and machinery. The force and power of a high pressure steam boiler is produced by a pump that forces the steam at high pressure into the circulation system. To be classified as a high pressure steam boiler, a boiler must be able to produce pressure between 15 psi and 800 psi at temperatures that exceed 250° F (121° C).
For safety and efficiency, high pressure steam boilers are regularly monitored for the pressure they produce and their temperature. The high pressure loads of high pressure steam boilers are classified as batch or continuous, with batch used for short term demand and continuous used for long term demand.
Oil Boilers
Oil steam boilers operate on the same principles as gas boilers; oil is ignited in the combustion chamber instead of gas. The burning oil heats the exchanger that heats the water. Oil steam boilers can reach an efficiency of over 90%. Though they are more expensive than gas steam boilers, they tend to have twice the lifespan of a gas boiler.
One concern with oil boilers is the need for an oil tank inside or outside that has to be refilled regularly to provide a constant supply of fuel.
Water Tube Boilers
Water tube boilers pass water through the tubes of the boiler. Fire created in the combustion chamber burns around the outside of the tubes and heats the tubes, thus heating the water. This boiler design produces high pressure steam by way of the tangential pressure in the tubes, known as hoop stress; it is pressure applied to the circumference of the tubes and is like the stress applied to the bands of a wood barrel as it is filled.
There are different types of water tube boilers that have been used since the development of the first boiler but have gradually changed over the centuries.
La Mont Boilers, Benson Boilers, and Loeffler Boilers
La Mont, Benson, and Loeffler steam boilers use forced circulation and draught fans to produce large quantities of steam at high efficiency. Small diameter, closely spaced tubes have water forced through them by a centrifugal pump. The efficiency of a La Mont, Benson, and Loeffler is due to the economizer that preheats the water using the flue or pipes gases from the combustion chamber.
Fire Tube Boilers
In a fire tube steam boiler, the tubes on the boiler are heated, and the water circulates around the tubes. The heat inside the tubes is produced by gases heated by coal or oil, and it is transferred by thermal conduction to the water to create steam. Fire tube steam boilers produce low pressure steam. There are three main types of fire tube steam boilers: Cochran, locomotive, and Lancashire.
A fire tube steam boiler can be fitted with an economizer to enhance its efficiency and heat recovery system.
Shell Boilers
Shell boilers have their heat transfer surfaces enclosed in a shell that is usually made of steel. Several combinations of tube layouts are used; tube layout determines the number of passes heat makes before being discharged. Shell boilers, also known as flue boilers, have a long water tank configuration with fire tubes. The heat from the furnace or combustion chamber passes through these fire tubes to heat the water.
The earliest form of this type of boiler was the Cornish boiler, which consisted of a long cylinder with a single large flue or pipe that contained the heat or fire. It was replaced by the Lancashire steam boiler, which had two flues for the fire.
Shell steam boilers, also known as shell and tube boilers, are the simplest form of boiler that produce steam efficiently and economically.
A steam boiler absorbs heat that is released from combustion. The heat is transferred either by radiation, convection, or conduction. The percentage of heat that is transferred is dependent upon the type of steam, fuel, and transfer surface.
Radiation
Radiation is energy that is transmitted by all elements and bodies. It is the continuous interchange of energy between surfaces using electromagnetic waves. In the case of a steam boiler, the tubes in the boiler absorb radiant heat from the flame produced in the combustion chamber. The heat from radiation heating depends on the rate at which the electromagnetic waves are absorbed.
Convection
Convection is the transfer of heat within a liquid or gas when the liquid or gas is heated. As the liquid or gas is heated, it mixes with the cooler liquid or gas and heats the cooler liquid or gas. In a steam boiler, the convection process occurs when the fluid in the boiler is heated and becomes lighter and less dense. Heavier, cooler fluids or air move in as the lighter heated fluid or gas moves out. The replacement of hot fluids with cold fluids begins the process all over again.
Conduction
Conduction is a physical contact process where heat is transferred from one surface to another by contact. Heat in a metal moves through the metal to heat what it has touched. Conduction in a steam boiler takes place as the outer part of the tubing is heated, and the heat passes through to the inner part and to the cool water in the tube.
A steam boiler heats water much like a teapot, only on a larger and more complex scale. Though not every steam boiler is the same, there are basic elements that are common to all steam boilers: burner, combustion chamber, heat exchanger, expansion tank, steam temperature control, safety relief valve, and low water cutoff.
The designs and types of steam boilers widely vary depending on their construction and purpose.
Burner
The purpose of the burner is to inject fuel and air into the combustion area. The fuels, such as oil, gas, or pulverized coal, have to mix easily with air. Dampers are used to regulate the amount of air that enters the burner. An impeller circulates the air evenly around the burner. Pipes referred to as spuds inject the fuel into the boiler and are ignited by an igniter.
Combustion Chamber
The combustion chamber contains the reaction of the fuel with air and uses it to create the heat to produce steam. To enhance the efficiency of the combustion chamber, it needs to be adequately insulated to avoid loss of heat through radiation. The combustion chamber has tubes containing water and steam that pass through the open box with the burner and controls. Efficient combustion is an essential part of boiler operations. The heat produced in the combustion chamber is absorbed on the surface of the boiler at the top of the combustion chamber.
The heat exchanger allows heat to be exchanged between fluids without allowing the substances to mix. A heat exchanger contains a long coiled pipe that is immersed in the fluid to be heated. Gas or a heated liquid passes through the pipe and heats the water around it. Heat exchangers are made of a variety of materials with stainless steel being the best material since it does not corrode or rust.
Expansion Tank
The expansion tank helps to maintain the pressure in a boiler by providing a place for water to expand, absorb the pressure, and regulate the pressure. The tank has a diaphragm that is divided into two sections with one portion accepting water from the boiler and the other side being controlled by an air valve to alleviate pressure. The air valve pushes against the water in the other section until normal pressure is reached.
Steam Temperature Control
Steam temperature control prevents thermal stress; precise control of steam temperature is important. The control of pressure and temperature is necessary to keep fuel costs down. Steam temperature is normally controlled by spraying water on the first and second stage superheater. This is done using an attemperator or desuperheater.
Other methods to control steam temperature are through the use of flue gas circulation, flue gas bypass, or the tilting angle at which the burners fire the furnace. The simplest method for controlling steam temperature is to monitor the temperature of the steam as it exits the boiler and change the position of the spray water valve.
Safety Relief Valve
The pressure relief valve is the most important safety measure for steam boiler use. It ensures that the build up of pressure in a steam boiler will be relieved; this assists in avoiding a catastrophic disaster. The pressure relief valve opens when the pressure reaches a critical level and closes when the pressure returns to normal.
Low Water Cutoff
A low water cutoff turns off the burner or shuts off fuel to a steam boiler when the water level drops below a set point. A dry fired boiler can rupture or suffer significant failure. Low water cutoffs are another safety feature built into a steam boiler to help avoid damage and harm to the boiler. They are a normal part of boiler construction and are installed in steam boilers and hydronic devices to shut down the boiler in the case of the loss of water.
The traditional function of steam boilers is to serve as central heating for homes, offices, businesses, hospitals, and other facilities. Regardless of where they are used, all boilers have the same basic functions and mechanisms that work as a contained heat generating combustion process.
There are a variety of fuels used to generate the heat in a boiler to ignite the burner. The created heat moves through the system using pumps and heat exchangers. In order to specialize the function of a steam boiler, additional control mechanisms are added.
Aquariums
Aquariums use steam boilers to power their operations. The many tanks required to operate an aquarium have to have the water temperature and water conditions carefully regulated to protect the wide varieties of species that are on display. Gas powered steam boilers are used with heat exchangers to regulate fresh and saltwater tanks as well as provide water currents and surges to create ocean like environments.
Food and Beverage
Pasteurization requires products be heated at set temperatures to eliminate pathogens. If the temperature is not precisely controlled, the taste of the final product can be damaged. Brewers and distillers use low pressure steam heat to produce consistent batches at a low cost. Dairy producers use steam boilers for cleaning and sanitization.
Laboratories
Labs on college campuses use exhaust air when experimenting and testing. To replenish the exhausted air, experimenters bring in outside air that can be cold, so they require heating. Since laboratories are large and spacious, an extensive amount of heat is required to heat them. In order to meet the need, universities and colleges use low pressure steam boilers.
Skyscrapers
The heating of multi-story skyscrapers requires a high powered energy production system that is capable of withstanding constant use. The massive size of skyscrapers necessitates the use of multiple boilers to heat them efficiently and effectively. Steam boilers used to heat skyscrapers can weigh up to 165 tons and consume 3000 liters of fuel per hour; this is enough to heat 2000 private residences.
The use of water and steam for skyscrapers is a very practical and effective method for providing heat since it is easy to transport and readily available.
Brewing
Beer is brewed in large kettles, and steam boilers are used to heat and sanitize the kettles. Once the brewing cycle is finished, the kettles have to be completely sanitized and cleaned to ensure the removal of any contaminants. The first consideration in the design of a brewery is the type of boiler that will be used to keep the kettles clean and operating.
The spent grain from the brewing process can be repurposed to serve as fuel for steam boilers. It is an ecologically sound and a cost saving concept.
Power Generation
One of the functions of a steam boiler is to power turbines to produce electricity. A very powerful and large boiler can generate as much as 225,000 pounds of steam per hour at 900 psi. A boiler system of that size can generate 20 megawatts of electricity. With technological upgrades and innovations, steam boilers can be designed to save on energy while producing it.
Lumber Kilns
Low pressure steam boilers are used in the lumber industry for kilns used to dry specialty lumber products. Hardwoods used for making furniture and cedar planks used for cooking require drying in a kiln. A low pressure steam boiler allows producers to perform the drying process safely and effectively to increase the quality of wood products. Since low pressure steam heat is manageable and exceptionally consistent, it is ideal for this type of drying process.
As with all industrial equipment, the production and use of steam boilers are guided by codes, regulations, and standards that have been published by regulating agencies, voluntary organizations, and the United States government. The most widely accepted boiler and pressure codes are published by the American Society of Mechanical Engineers (ASME) in its boiler and pressure vessel code guide.
The codes most pertinent to boilers were published in 2013 and are organized into different sections:
Section I Power Boilers This applies to high pressure boilers.
Section II Materials Covers all acceptable metals for boiler use.
Section IV Heating Boilers This applies to low pressure boilers.
Section V Nondestructive Examination This section covers the inspection and certification of boilers and pressure producing equipment.
Section VI Covers Boiler Care and Operation
Section VII Guidelines for the Care of Power Producing boilers
Section VIII Guidelines for Pressure Vessels of which there are three types:
Fired and unfired pressure vessels operating in excess of 15 psig
Rules for the design of pressure vessels
Rules for high-pressure vessels.
Section IX Welding and Brazing Qualifications
The ASME has other codes and standards for boiler systems; these include the B31 series of piping and the CSD series of controls and safety equipment.
The main concern for OSHA is worker safety. Steam boilers have been identified as potentially dangerous and unsafe devices that can only be operated by trained, experienced, and authorized workers. OSHA requires frequent and regular inspection of boilers to check for leakage, proper combustion, and operational safety devices and gauges.
Older steam boilers that have been insulated with asbestos coatings, wraps, or lagging should be inspected for leaks, damage, flaking, or deterioration. Any damaged materials should be removed and replaced.
The ABMA was founded in 1888 and is the longest operating trade association in the United States. The original purpose of the association was to deal with the many safety issues that were prevalent at the turn of the century. Due to the ABMA, several safety measures have been implemented for steam boilers, and they have advanced their use into the 21st Century.
The mission of the modern ABMA is to lead and unite the boiler industry by providing education, awareness, and a commitment to solving steam boiler issues and problems. The ABMA represents manufacturers in all facets of the industry from heavy duty steam boilers for power plants to those for the utility sector. Any device that produces steam and hot water is covered by the ABMA.
A steam boiler is a steam producing heating system; it produces energy by heating water to create steam.
A steam boiler burns fuel to heat water. The combination of heat and water produces steam.
Steam boilers are defined by their construction, portability, types of tubes, types of fuel, and the pressure they produce.
A steam boiler absorbs heat that is released from combustion. The three ways that the heat is transferred are radiation, convection, and conduction.
The designs and types of steam boilers widely vary depending on their construction and purpose.
Steam heating is one of the oldest forms of heating for commercial and residential buildings. While it might not be as energy-efficient as other, newer hydronics systems, it’s often more energy efficient than using a forced-air furnace to heat your building. Unlike forced-air systems, steam systems send humidified air throughout the building, which prevents your building’s air from drying out during winter. Also, if your business is in a building built before 1950, it may be more cost-effective to maintain your steam system than to install a new one. If you want to keep your current steam heating system design, here is how you can keep it running efficiently.
Perform Regular Preventive Maintenance
Performing preventive maintenance on your boiler system not only will keep your heating system clean and working well, it will keep everyone and everything in your building safer. If not monitored closely, steam boilers can explode, injuring or killing people in the building. These explosions also can cause massive amounts of property damage. Employing a service company like Legacy Mechanical to perform preventive maintenance on your steam system can ensure your safety and save you a lot of repair time and money in the long run. Here are five preventive maintenance steps you can take when you choose a professional to maintain your steam heating system:
Perform regular boiler cleanings: These cleanings remove buildup and residue from the boiler, which should be cleaned at least once a year.
Perform a boiler blowdown: This procedure removes scale buildup including potassium, calcium, chlorides, and sulfates. Removing scale buildup reduces the chances of boiler failure and increase your boiler’s heat transfer efficiency.
Check and maintain water quality: Performing this step is extremely important. The water in your boiler should be free of organic matter and dissolved materials. By checking your boiler’s water quality, you are making sure your system works properly and safely.
Insulate your steam system: Make sure your pipes and fittings are properly insulated. If they are uninsulated and remain that way, this can lead to unnecessary heat loss.
Maintain a daily boiler inspection checklist and accurate inspection logs: Keeping accurate maintenance logs will help you stay aware of what’s going on with your boiler so your building stays properly heated and safe for everyone in it.
Maintain Boiler Controls
Along with maintaining the boiler itself, you should have the boiler control system maintained. The controls should be tested regularly by a professional to ensure they perform properly. This allows the technician to detect and repair small problems before they become big ones.
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