Application, Challenges, Factors and Types of Steam Boilers in Chemical Industry
Chemical plays an integral part in the development and advancement of any economy. Various sectors such as oil refining, energy, medicines, military, petrochemical, food processing, etc., depend on the chemical industry. The chemical industry itself depends on efficient steam boilers for its processing. Steam boilers have a crucial impact on the processing operations of chemical plants in terms of quality and productivity. Chemical industries require an ample amount of high-temperature steam for effective operations. Secondly, chemical industries tend to generate a large amount of emissions and waste heat. Therefore, it is essential to check that every requirement is met, before selecting a boiler manufacturer for a chemical plant. Let us have a detailed look over the applications, requirements, and types of steam boilers used in chemical industries.
Application of Boilers in Chemical Industries:
Boilers play a vital role in both the processing operations of chemicals and for the process plant itself. The main functions of a boiler in the chemical plant are,
Heating and Cooling Reactors:
Generally, chemical processing operates in a cyclic mode. Chemical reactors need to be heated at some stages, and at some stages they need to be cooled down. Such fluctuating demand occurs in almost every processing operation starting from raw materials to finished products. Steam plays an important part in accomplishing this requirement. Hot steam is pivotal in increasing the heat in the process that facilitates the chemical reactions with heat.
On the other hand, steam boilers need to be turned off or reduce the steam generation when the process requires cooling of chemical reactors. Hence, it is advisable by leading boiler manufacturers to ensure the resilience of the boilers that can effectively handle the changing demands during chemical processing operations for efficient productivity.
Disinfecting and Sterilizing:
Apart from the heating and cooling of reactors, chemical processing also requires consistent disinfecting and sterilizing of the plant and the equipment used during the operations to ensure the high quality and precision of the chemical components. Steam is essential for complete disinfection and cleaning of the process plants.
Heating and Cooling of Process Plant:
Chemical plants operate for 24 hours, and therefore, it is important to heat and cool it as required for both the operating team and the chemical reactors. It is natural to conclude that since the steam heats and cools the chemical reactors, it is capable of heating and cooling the plants as well
Challenges Faced in a Chemical Industry:
Although steam boilers are indispensable in chemical processes, it faces its share of challenges during process operations. The most common ones are as follows,
Fluctuating Load Demands:
As mentioned earlier, chemical plants require heating and cooling of the system to accomplish the chemical reaction. Therefore, the load and steam demand change rapidly, affecting the operational cycle and efficiency of the steam boiler.
Downtime of the Boiler:
Although chemical plants operate day and night, it does not require steam 24/7 as the processing requires the boiler to be heated and cooled. Boilers in the chemical industry face the issue of heating and cooling with minimal downtime. It is because boilers don’t have to be operating throughout the day, even when steam is not required.
Excess Waste and Emission:
Chemical Industries generate a large amount of waste and harmful emissions, and controlling it is one of the major challenges faced by the chemical sector.
Requirements that need to be fulfilled by Steam Boilers in Chemical Industries:
Considering the challenges stated, it is prudent to choose a boiler manufacturer that ensures that the boilers provided are efficient and meet the criteria of,
Resilience to meet the Fluctuating Needs:
When chemical reactors need heat, a high amount of steam is required. However, when it requires cooling, the temperature needs to drop. Since the chemical industry demands for heating and cooling changes rapidly depending on the stage of operation, a steam boiler must be resilient enough to handle the fluctuating loads and demand of the process plant.
Reduced Greenhouse Emission:
Chemical Industries are monitored to ensure their compliance with the waste emission laws. That is because of its excess release of harmful wastes generated during the process operations. Therefore, a steam boiler must operate at a lower temperature, releasing a reduced amount of CO2 and O2 emissions. Although the harmful emission in chemical industries is inevitable, it can be controlled with efficient boilers.
Easy to Maintain:
The reason that steam boilers do not run to their rated efficiency is the overlooked maintenance of the system. If the boilers are not regularly maintained, it is likely to malfunction and not operate effectively. It is necessary to ensure that the steam boilers are easy to maintain and are regularly serviced.
Safe and Reliable:
It is important to be assured of the safety and reliability of the boiler system with regular servicing under the guidance of the boiler manufacturer. Also, it is essential to check the safety valves and other equipment are functioning properly for seamless operations in the chemical industry.
Types of Boilers Used in the Chemical Industry:
Although different boiler manufacturers shall suggest different types of boilers for chemical industries, two of the most commonly preferred boilers used are:
Fluidized Bed Combustion Steam Boiler:
Steam Boilers with Fluidized Bed Combustion or FBC are an ideal choice since it has a large capacity of generating steam (approximately 10 to 280 tons per hour) that helps in the hassle-free operation of chemical plants. Secondly, it is effective for the proper combustion of fuels like coal and biomass that result in meeting the high heat demands, saving excess cost and energy.
Waste Heat Recovery Boilers:
As we are aware, chemical industries generate ample amounts of waste heat, the ideal boiler for chemical plants is Waste Heat Recovery Boiler. The system would extract the excess heat and reuses it for other process operations or power generation, thus ensuring optimal use of heat energy and preventing harmful emissions in the environment.
Rakhoh Boilers manufactures highly efficient and reliable steam boilers preferred and trusted by various chemical process plants. Rakhoh’s Optipac and Waste Heat Recovery Boiler is the preferred choice for many chemical plants.
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Electrostatic Precipitators in Steam Boilers | Structure, Working, Types, and Applications
Dust and pollutants are unavoidable and are found in various forms produced from different sources. Dust particles, also termed Particulate Matter (PM) are released in the atmosphere that are varied in size and composition. Particulates with a diameter of more than 2.5 μm are termed coarse particulates, whereas particulates with a diameter less than 2.5 μm. Such particulates are generated from various sources, out of which three main sources are Chemical Reactions, Combustion from Industries, and mechanically generated. Among these, combustion from industries results in particles containing carbon or soot, heavy metals, and ash particles. In most cases, combustion pollutants are fine particulates ranging between 0.1 to 2.5 μm.
What is an Electrostatic Precipitator?
An electrostatic precipitator is pollution control equipment that captures dust particulates released from industrial operations. The objective of electrostatic precipitators is to prevent the release of dust particulates into the atmosphere. It separates the dust particles from the released gases with electrical energy by charging the particles positively or negatively. It leads to it being attracted to the collector plate that contains the opposite charge. These particles are then disposed of as either dry particulates or wet particulates by cleansing them with water. Electrostatic precipitators are the ideal choice as pollution control equipment with an efficiency of up to 99%
Structure of Electrostatic Precipitators:
An electrostatic precipitator mainly consists of 4 components viz. gas distribution plates, discharge electrodes, collection plates or pipes, and rappers. The gas distribution plates are made up of several plates that are pierced with holes to maintain the flow distribution of the gases. The electrodes that are discharged are generally divided into three to four fields. The electrodes discharged are activated with a single transformer-rectifier (T-R) supply that creates ions that later come in contact with particles in the gases and administer electrical charge to it.
The collection surface is either collection plates or pipes that serves as the surface for collecting the particulates. Finally, the rapper removes the collected particulates from the surface.
Working of Electrostatic Precipitators:
The main processes followed in electrostatic precipitators are as follows:
1. Charging:
In most cases, the electrodes for collecting are electrically grounded and connected with the positive end of the high-voltage power supply. The discharged electrodes are released into a flue gas stream and joined to the negative end of the power source. An electric field is created between the discharges and collecting electrodes as the discharge electrodes display an active glow termed corona. When the flue gases are passing through the electric field, the particulates adapts a negative charge
Collecting:
The negatively charged particulates are attracted towards the collecting surface. Resistance is an important factor of particulates. Less resistivity indicates the better capability of charging and getting collected in the Electrostatic precipitators. The particulates remain on the collecting surface because of the forces of the electric field.
2.Cleaning:
Cleaning involves the rapping process, which is performed by striking or vibrating the surface to dispose of the particulates. It is necessary to clean the collecting surface frequently for efficient performance. The disposed particulates with minimum re-entrainment from the collecting surfaces are transferred into hoppers that are, later on, emptied.
Types of Electrostatic Precipitators:
Electrostatic precipitators are of two types that are, dry electrostatic precipitators and wet electrostatic precipitators. Dry electrostatic precipitators are the most commonly used one among industries that generate hot process particulates ranging from 50 to 450 degrees Celsius. The primary difference between both types of precipitators is the method of cleaning them. The dry electrostatic precipitators are cleaned by the vibration of the collecting surface that releases the collected particulates with the process known as rapping. In wet precipitators, the collector surface is cleaned with water. It is highly used with sticky particulates.
Applications of Electrostatic Precipitators:
One of the most used fuel particulates in this pollution control equipment is coal. Since coal is the highly used fuel for generating steam in the industrial process, it is natural to surmise that electrostatic precipitators are required to dispose of coal particulates. Apart from coal, oil-fired steam boilers as well require precipitators to get rid of the released particulates that are similar to coal.
Steam boilers using wood chips or wood bark as fuel prefer electrostatic precipitators to collect ash from the gases.
Industries that Use Electrostatic Precipitators:
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Although Electrostatic Precipitators are used in various process plants, some of the major industries using them are:
- Iron and Steel
- Copper
- Zinc
- Aluminum
- Stainless Steel
- Dairy
- Sugar
- Palm Oil
- Power Generation
- Distilleries
- Paper and Packaging
- Plywood
- Chemical
- Pharmaceutical
- Textile
- Food
- Refineries and Petrochemical
Rakhoh has always aimed for an advanced and sustainable society by manufacturing world-class quality products and pollution control equipment like Electrostatic Precipitators. It is highly efficient and reliable with minimal maintenance requirements and low operational costs. Electrostatic Precipitators are ideal for disposing of waste pollutants as they cause harm to the environment.
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Air Preheaters in Steam Boilers | Function, Types, Advantages, and Disadvantages
Air Preheaters (APH) are Shell and tube type heat exchangers installed in boilers to heat the air before using it for combustion. The main function of an air preheater is to extract the excess heat from the flue gases in the boiler. As we know, combustion requires air, fuel, and fire to take place. Air preheaters help significantly in feeding the hot air and increasing the combustion efficiency for the operation in steam boilers. For combustion, the fuel fed in boilers is of room temperature that needs heating for ignition, and therefore, hot air is used to enhance the combustion process.
Function of Air Preheater in Boilers:
Air Preheaters, as mentioned, are actually heat exchangers located at the exit of the flue gas duct in the steam boiler. Air preheaters accelerate the overall thermal efficiency of the boiler by regaining the excess heat in the flue gases that might be lost without the preheaters. With an air preheater, the useful heat is recovered and used for preheating in the combustion process. If the exiting heat is 180°C, air preheaters manage to extract the heat of 100°C for combustion in the boiler.
Types of Air Preheaters used in Steam Boilers:
Air preheaters are classified into 2 types namely, Tubular type Air preheater and Regenerative type Air preheater. Let us have a look at both types in detail.
Tubular type air preheater:
A tubular type of air preheater is located at the outlet of flue gas ducting, consisting of bundles of straight tubes. It is found across the outlet ducting and open at both ends at the outside of ducts. The hot gases pass through the internals of ducting from one end. Whereas, the other end of the ducting contains air from forced draft fans. The hot gases and the air is carried to hot air ducting as the air preheater extracts hot air and later transfers it to the furnace for combustion.
Challenges faced in using tubular air preheater:
The structure of tubular air preheaters compels for a separate arrangement in carrying powdered coal. Along with that, hot gases with abrasive dust affects the wear and tear of the tubes leading to their frequent replacement. Lastly, ducting for cold and hot air requires additional space and structure. Therefore, tubular-type air preheaters are not preferred by large-scale process plants or power generating plants.
Regenerative type air preheater:
Regenerative type air preheaters are widely used for large-scale industries and power generation plants due to their compact size and efficiency. The design of regenerative air preheaters enables it to heat primary air that dries and transports fuel and the secondary air used in the furnace for combustion purposes. It is circular in its structure that consistently rotates in the horizontal and vertical axis. This type of air preheater is divided into various sectors, each containing a basket or holder. In most cases, three sectors are found in regenerative air preheaters. The first sector is adjoined with ducting of the hot gas outlet, while the other end is connected with ducting that carries low-temperature gases to the dust collectors.
The second sector is joined to the outlet of Forced Draft Fan on one side, and on the other side, to the ducting that carries hot air to the furnace for combustion. The third sector is connected with the primary fan outlet on one end, while the other end is connected with ducting to absorb hot air for heating purposes in the steam boiler. The air from the primary fan heated with regeneration air preheaters are used as hot air for the removal of moisture content from fuels like coal and as primary air for combustion
Challenges faced in using Regenerative type air preheaters:
The baskets or holders in regenerative air preheaters have ample space between them to facilitate easy passing of gases and more surface area for extracting excess hot air. However, flue gases contain dust particles, ash content, or corrosive gases depending on the fuels used for combustion. For example, Indian coal contains a high level of ash, silica, and sulphur that leads to maintenance issues of the baskets. Eventually, it needs to be replaced frequently to ensure the effective functioning of the air preheater. In some cases, unburnt fuels left deposited in air preheaters may cause fire during operations or, in extreme scenarios, an explosion inside it.
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Advantages of Air Preheater:
- Absorption of maximum waste heat from flue gases
- Air preheaters increase the efficiency of the steam boiler by 2% to 3%
- Low payback time
- Enhanced stability by using hot air
- Proper combustion of poor quality fuels
- High heat transfer rate and low heat transfer area requirement
- Reduced unburnt fuel particles result in high combustion efficiency
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Disadvantages of Air Preheater:
- Air preheaters in the path of flue gas increase the flue gas pressure drop, thereby increasing the use of Induced Draft Fan.
- Due to corrosion in the heat transfer surface caused by the reduced flue gas temperature, Air preheaters are not able to shutdown the units.
Rakhoh Boilers started their journey in 1983 as a steam boiler manufacturer in Pune. With more than 3000 installations globally, Rakhoh is presently one of the leading manufacturers of boilers in India and worldwide by delivering high-quality industrial steam boilers and boiler accessories that are manufactured with world-class precision to increase efficiency and productivity of process industries.
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Blowdown in Boilers | Types, sources, advantages, disadvantages, and calculation.
Steam boilers are one of the most important devices required for the seamless operation in any processing plant and industry. Therefore, it is an essential factor for the boiler manufacturers that the boilers are well-maintained for their smooth running and long-lasting performance. Blowdown is a vital step to avoid suspended solids and sludge in the boiler and to generate high-quality steam.
What is Blow Down?
When the boiler is operating, the feedwater contains a high level of Total Dissolved Solids (TDS) along with other dissolved and undissolved solids. These dissolved solids are unable to evaporate once the steam is generated, which results in their settling on the bottom of the boiler shell. It leads to an interruption in the transfer of heat between flue gases and water, eventually resulting in the overheating of the boiler tubes or shell. These undissolved solids may also cause corrosion, scaling, and carryover of solids along with the steam.
Types of Blowdown in Boilers:
As per the design and capacity of the steam boiler and the characteristics of the boiler water, blowdown can be conducted in two ways:
Continuous Blowdown:
Continuous blowdown means when the blowdown is conducted automatically and constantly to maintain the suspended and dissolved solids at their required limit. Continuous blowdown assists in separating a larger amount of dissolved solids through only a slight loss of heat and water from the steam boiler. Moreover, with continuous blowdown, the heat of the water is further used to preheat the feed water with the help of a heat exchanger. In continuous blowdown, the quality of the boiler water is monitored constantly and the blowdown takes place as soon as the TDS level exceeds the optimal limit.
Manual Blowdown:
Manual blowdown is the blowdown conducted manually by operating staff at regular intervals. Manual blowdown helps to separate the sediments and the suspended solids from the steam boiler by opening the valves frequently to conduct blowdowns. In manual blowdown, only a slight opening of the valve is preferred to ensure minimal heat loss. It eventually results in high pressure and heat loss in the steam boiler.
The boiler manufacturers in India and across the world provide the required accessories and valves as per the blowdown operation viz. continuous blowdown or manual blowdown.
Sources of Blowdown in a Steam Boiler:
There are two sources of blowdown found in a steam boiler– bottom blowdown and surface blowdown.
Bottom Blowdown:
Sediments are found in the bottom of the fire tube boilers and inside the mud drum in a water tube boiler. With bottom blowdown, sediments or sludge are separated in regular intervals. It makes sure that it does not contaminate the heat transfer surfaces that result in boiler vessel failure or boiler tube failure. Bottom blowdown occurs by manually opening the concerned valve or valves for a determined period to allow the sludge to exit from the steam boiler. Boiler manufacturers suggest that the bottom blowdown should ideally occur once a day or once in an operational cycle.
Surface Blowdown:
Surface blowdown aids in separating the suspended solids in the boiler water surface. Surface blowdown highly depends on the quality of the water used in the boiler. Therefore, if the water requires a high amount of chemical treatments and contains a higher level of impurities, then it increases the need for surface blowdown.
Boiler manufacturers advise that during blowdown, water needs to be released when its TDS level increases, followed by feeding fresh water in the steam boiler, which leads to the loss of usable heat that is drained out. It results in a reduction in the water temperature and an increase in fuel usage. In this way, blowdown affects the steam fuel ratio of a steam boiler.
Despite that, blowdown has its fair share of advantages and disadvantages.
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Advantages of Blowdown:
- With the blowdown, the TDS can be kept to an optimal level.
- Blowdown prevents corrosion by removing the impurities that encourage its formation in a steam boiler.
- It prevents carryover of impurities from steam thereby, facilitating the generation of pure steam.
- It prevents scaling in the boiler tubes as well as in the internal surface
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Disadvantages of Blowdown:
- Neglecting the proper scheduling for blowdown may result in an escalation in heat and pressure losses.
- Eventual reduction in boiler efficiency due to high heat and pressure loss
- Manual blowdown requires additional hours to perform the operation
The formula for calculating boiler blowdown and blowdown percentage:
Boiler manufacturers generally use the following formula to determine boiler blowdown rate and its percentage.
Calculating boiler blowdown rate,
qBD = qS fc / (bc – fc)
Where,
qBD: Blowdown rate in kg/h
qS: Steam Consumption in kg/h
fc: Total Dissolved Solids in feedwater in ppm
bc: Maximum limit of Total Dissolved Solids in boiler water in ppm
Calculating boiler blowdown percentage,
Percent or % of Blowdown = Quantity blowdown water/Quantity feed water X 100
Rakhoh is one of the leading boiler manufacturers in India. With our dedicated team of experts, we have been manufacturing and successfully installing highly efficient boilers for various industries for more than 38 years. We strive to consistently provide advanced steam boilers and excellent boiler-related services to our clients.
Explore our steam boilers and our services on http://www.rakhoh.com
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Combustion Efficiency | Heat Output, Heat Losses, and Types of Burners Used in Combustion
Efficiency is an undeniably important factor while choosing a boiler manufacturer. Many other components contribute to the overall efficiency of the boiler. One of them is the combustion efficiency of a system. It is a well-known fact that the efficiency rated by the boiler manufacturer is more than the actual boiler efficiency. However, combustion efficiency plays a major part in the overall efficiency and can be calculated to ensure optimal and proper combustion in process operations. Combustion efficiency depends on various factors such as the amount of air, heat losses, burners used, etc.
What is Combustion Efficiency?
Combustion efficiency is measured and calculated in percentage to determine the capability of the steam boiler in the burning of fuels. Naturally, every industry aims to achieve 100% combustion efficiency by the complete burning of fuels by the system. But, such a feat is impossible to achieve, and the maximum combustion efficiency found in most cases is between 90% and 95%
Combustion efficiency depends on three major factors:
- The stack gas net temperature
- Percent of carbon dioxide (CO2) and oxygen in volume after the combustion
- The chemical properties of the fuel
Heat Output by Fuel:
The calorific value is further classified, into two terms i.e. Gross Calorific Value and Net Calorific Value
1. Gross Calorific Value:
Gross Calorific Value is the net total energy in the fuel. Most of the commonly used fuel consists of hydrogen that, after burning with oxygen, produces water that passes as steam. Since the flue gases are not condensing in nature, the amount of heat in steam boilers is reduced than actually available. The gross calorific value determines the amount of energy utilized in evaporating the water.
2. Net Calorific Value:
Net calorific value is used in calculating the efficiency of the boiler. Net calorific value is calculated by excluding the energy that gets released in steam from the gross calorific value. In other words,
Net Calorific Value = Gross Calorific Value – Energy Released in Steam
Amount of Air Required for Optimal Combustion:
For proper and complete combustion, a certain amount of excess air is required. However, it is not an easy task to achieve optimal combustion due to the given reasons,
The burner in the furnace may not always operate as required, and the mixing of carbon, oxygen, and hydrogen is not always precise
Sometimes, the oxygen blends with nitrogen and forms nitrogen oxide (NOX)
Precision in the amount of air is important to ensure proper combustion. Failing which might result in,
Incomplete combustion and unburned fuels with carryover and smoke due to less than required air
Cooling of furnace and carryover of useful heat due to excessive heat
1. Heat Losses:
Although the air amount is important, it is not the only factor to ensure the complete combustion in the steam boilers. Heat loss, too, is an essential component that decides combustion efficiency. Let us have a look at the various sources of heat losses.
2. Flue Gases Heat Losses:
Heat loss by flue gases is one of the major losses affecting boiler efficiency. The contributor to the flue gas heat loss is the flue gas temperature that exits the furnace. Simply put, as the temperature of the flue gases increases, the efficiency of the boiler decreases. However, if the flue gas temperature is less than optimal or ‘dew point,’ it may lead to corrosion in the steam boilers.
3. Radiation Losses:
Poor installation or insulation of the steam boilers results in radiation loss. Even a well-insulated boiler loses about 0.3% to 0.5% of its energy. Although it may not seem like a great loss, it is noteworthy that the loss is excluded from the overall efficiency rating ensured by the boiler manufacturer. Radiation loss tends to remain constant even in case of the boiler not being operational.
Burners in Combustion:
Burner Turndown:
Turndown is imperative in burners. In general terms, burner turndown is a ratio calculated by the maximum ignition rate divided by the minimum controllable ignition rate. Burner turndown rate provides important results for efficient and complete combustion, controlling emission that affects the economic decisions of the process plant.
Types of Burners:
Some of the majorly used burners for the combustion process are:
1. Oil Burners:
One of the important factors of liquid fuels is viscosity. In other words, liquid fuels of high temperatures flow easily. It is interesting to note that due to changing temperature, the viscosity of the fuels affects the size of the oil particles formed at nozzles. Effective combustion of oil fuels requires a high area-to-volume ratio. Boiler manufacturers suggest that the ideal particle size is between 20 to 40 μm for effective combustion. Less than 20 μm travel quickly without burning properly, and more than 40 μm might get carried without complete combustion.
2. Gas Burners:
With gas fuels, one has to ensure atomization and proper blending of gas and air to achieve optimal combustion. Gas burners are classified as low-pressure burners and high-pressure burners in which low-pressure burners operate between 2.5 to 10 mbar and the high-pressure burners operate between 12 to 175 mbar.
3. Rotary Cup Burners:
In a rotary cup burner, the fuel is transported through a central tube and released inside a rotating cone. With fuel rotating in the cup, it gets thinner and gets released as a spray. The turndown ratio is higher due to atomization by the rotary cup.
4. Pressure Jet Burners:
Pressure jet burners use pressure to tear droplets from the oil stream and propel it for combustion requiring simple and spill-back nozzles. However, the nozzles chock frequently due to sticky and dirty fuels.
Rakhoh Boilers are a leading name as boiler manufacturers in India and overseas. With more than 38 years of expertise in thermal solutions, Rakhoh manufactures a wide range of highly efficient and reliable industrial steam boilers that ensure effective and complete combustion with different types of fuels.
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