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Wednesday, 17 August 2022 / Published in Boiler, Steam Boiler

As we are aware, steam boilers play an integral role in the manufacturing and process sector for heating, processing, and sterilizing purposes. Although most process industries aim for high efficiency and production in minimal time, one of the most overlooked factors in the heating process is the dust collection and management that causes severe harm to the operating personnel and the environment. Yet, dust collectors are pivotal in ensuring that the steam boilers are functioning efficiently and safely. Just like any other equipment, industrial dust collectors too require regular maintenance. The dust collector system consists of ductwork, hoods, air-material separators, explosion protection, different airlocks, and exhaust fans and includes cyclone dust collector, baghouse, electrostatic precipitators, wet scrubbers, etc.

A Brief Overview of Dust Collectors:

Multi-cyclone dust collectors have been used along with air preheaters and steam boilers in energy generation and other process industries since the 1950s. Gradually, it has evolved in design and purpose, yet its function remains crucial in many process heating applications. In some cases, dust collectors are installed with air preheaters and steam boiler economizers for the purpose of recycling material and to add another layer of erosion protection. Multi-cyclone dust collectors without moving parts use centrifugal force for separating the particulate from the flue gas as it exits the steam boiler. Dust collectors can remove anywhere from 60% to 99% of the debris from the flue-gas stream.

Components of Dust Collection System:

Dust Collector Hoods:

Dust Collector Hoods are an essential component of a dust collector system that can produce remarkable results with minimum modifications. It is important to examine blown, ripped, or broken filter media, cracked filter assembly, airflow speed to ensure the designed airflow, inaccurate installation, separated bag filter, or a mechanical breakdown of the tube sheet due to abrasion. It must be ensured that it is operating in the right position, if the restricted damper is found by hood for balancing.

Ductwork:

Ductwork is used to extract the dirt and air from the accumulating point of the collector. It must be sized precisely for producing a carrying velocity to keep dust moving.

Explosion Protection Equipment:

An explosion can be caused by a dust collection system preserved incorrectly. A properly designed dust collector managing combustible dust always includes an explosion protection system. The purpose of the explosion protection equipment is to restrain an explosion and reduce hazardous damage.

Air Material Separators:

An air material separator is a mechanical device to divide the conveying air from the material being conveyed.

Rotary Airlock:

A rotary airlock separates the dust collector hopper externally allowing the collected dust to exit the system. Usual types of airlocks include rotary valves, trickle valves, double dump valves, and knife gates.

Rotary valves:

The main objective of a rotary airlock valve is to provide an air seal at the outflow opening of the dust collector hopper. It is installed usually between the hopper flow and a conveyor or release bin.

Trickle valves

Trickle valves, also known as vacuum valves, are used for managing the airlock seal on the dust collector tank and for discharging bulk solid material.

Dust Collector Exhaust Fans:

Dust collection systems require an exhaust fan for stimulating ventilation air from the position of acceleration through the ductwork.

Corrosion and Erosion of Metal in Dust Collector System:

Dust collectors become ineffective due to significant damage caused by erosion or corrosion. Multi-cyclone dust collectors are impacted by abrasion through fly ash, particulate mass, and high-velocity gas flow that causes corrosion from chemical attacks. In severe cases, an ineffective dust collector leads to the failure of vital equipment like tubular air heaters, induced-draft fans, precipitators, or baghouse components. Additionally, a dust collector’s operating efficiency may drop significantly due to changes in velocity and pressure drop when ash or other particles plug a cyclone or tube. An overload of particulates may also plug other equipment in the path of the flue-gas flow.

Therefore, regular inspections allow temporary internal repairs during the inspection process, prolonging the life of the equipment and delaying its replacement.

Advantages of Regular Maintenance of Dust Collector System:

  • Increased efficiency of dust collector.
  • Longer operating life of the components of the dust collector system.
  • Reduced energy required to operate fans for air leakage.
  • Minimal fan maintenance due to erosion.
  • Lower fuel requirements.
  • Protection of the pollution control equipment.
  • Reduced repair costs for the dust collector system and its components.
  • Increased operating time before replacing the dust collector system.
  • Protection for air heaters, fans, and ducting.
  • Reduced emissions excursions.
  • Conclusion:

    Rakhoh Boilers are one of the leading manufacturers of industrial steam boilers in Pune since 1983. Over 38+ years, Rakhoh has successfully installed more than 3000 boilers in 26 countries worldwide. We also provide excellent boiler services like energy audit, boiler automation, steam trap assessment, annual boiler maintenance, fuel conversion, etc.

    For more details on our products and services, visit www.rakhoh.com

    Tuesday, 16 August 2022 / Published in Boiler, Steam Boiler

    Steam boilers are classified into two types, namely fire tube boilers and water boilers. As the name suggests, fire tube boilers function by flue gases passing through fire tubes immersed in water, whereas water tube boilers operate by water flowing through water tubes placed in a firebox. Steam boilers are an important asset for the process operations in the industries but can be a potential bomb if left overlooked. Boiler explosions can cause tremendous loss and injure the operating personnel. Therefore, boilers include safety equipment to avoid any hazardous mishap. One such equipment is the fusible plug that prevents the exceeding temperature in fire tube boilers resulting in a boiler explosion.

    What is a Fusible Plug?

    A fusible plug is equipment that boosts the safety of the steam boiler and acts as a warning device against overheating. Fusible plugs are found in fire tube boilers and are usually considered the last resort or warning to avert any hazardous failure such as a boiler explosion. Just like safety valves help to protect the boiler system from overpressure, fusible plugs help to safeguard steam boilers from over temperature. Fusible plug is widely acknowledged as the preferred safety equipment for fire tube boilers by many industries due to its simple design, effectiveness, and improvement in safety.

    Design and Material of Fusible Plug:

    Fusible plugs include a fusible alloy made of tin material. The fusible plug itself is made of brass, bronze, or gun material with a threaded plug body that makes it easy to install. It is a hollow gun metal plug screwed at the apex of the firebox. The main metal plug and hollow gun metal plug are separated through an annulus fusible material. A flange protects the material from the fireside. The fusible plug has a high melting point, while the fusible alloy has a low melting point of 232°C (450°F).

    The Role of the Fusible Plug:

    The fusible remains immersed in water with the water in the fire tube boiler at a normal level. As the temperature does not reach the melting point of the fusible alloy, the heat is transferred to the water. As the temperature in the boiler increases, the water level starts decreasing and generates steam. On the other hand, the fusible plug above the firebox gets overheated by the exceeding temperature, and the fusible alloy starts melting. It results in steam and water immediately rushes through the fusible plug to extinguish the fire in the firebox, thus preventing boiler explosion. The fusible plug body is shaped in a way to alert the operating personnel of system pressure vents by a whistling sound. Fusible plugs reduce the possibility of boiler accidents taking place due to low water firing. The low water level in the boiler system leads to overheating of the heat transfer surfaces that can cause catastrophic accidents. It is advisable to replace the fusible plug after two years as they probably get defective after a long period of use.

    Where is the Fusible Plug Installed?

    Fusible plugs in fire tube boilers are located around 1 to 2 inches above the top row of tubes. Usual locations for the fusible plugs include the crown sheet i.e., the apex of the combustion chamber, rear tube sheet, and front tube sheet. The fusible plug location depends on the boiler design.

    Faults and Inspection of Fusible Plugs:

  • The fusible plug body is impacted by corrosion in fire tube boilers. As a result, the lifecycle of the fusible plugs starts declining. Therefore, it is recommended to record the washout before refilling it. Usually, the lifespan of the fusible alloy is 2 to 3 washouts periods, and that of the fusible plug is 4 to 6 washout periods.
  • The fusible alloy may get affected by corrosion, depending on the water level in the boiler. The lead and body interface ensures corrosion, particularly if the tinning has been used in plug manufacturing.
  • In a fire tube boiler, the soot from the combustion may accumulate on the fusible plug that forms an insulating barrier. During such occurrences, the operations of fusible plugs are hindered. Therefore, it is important to remove the soot from the heating surface during maintenance.
  • Fusible plugs need to be inspected regularly for leakages. The plug must not be tightened while the boiler is in operation if leakage is detected. If required, plugs can be checked when the boiler is cool and can be removed, inspected, cleaned, and refitted after partially draining the water in the boiler.
  • Conclusion:

    Rakhoh Boilers are one of the globally leading boiler manufacturers for more than 38 years. We have provided efficient and reliable water tube boilers, fire tube boilers, waste heat recovery systems, thermic fluid heaters, and boiler accessories for over 20 process industries worldwide. With proficiency in thermal solutions, we offer the best boiler services like energy audit, steam trap assessment, boiler automation, annual boiler maintenance, etc., that enhances the productivity and lifespan of the boiler.

    To know more about our products and services, visit www.rakhoh.com

    Saturday, 13 August 2022 / Published in Boiler, Steam Boiler

    Steam Boilers are of paramount importance in the process and manufacturing industries. However, merely the excellence of the boiler manufacturer does not assure the boiler’s safety. The boiler system also requires precision in handling and operations to prevent hazardous consequences. Although plant managers take every precaution to ensure the safety of the plant and the personnel, some boiler issues are inevitable and require immediate action. Despite the usage of steam boilers in industries from the mid-1800s, process plants continue to face common issues with their operation.

      Some of the most common boiler issues include:

    • Low water conditions
    • Improper techniques of blowdown
    • Improper warm-up
    • Poor water treatment
    • Training of operating team
    • Neglect of preventive maintenance
    • Proper documentation
    • Overlooking outdated equipment
    • Manual factor

    Low Water Conditions in Steam Boilers:

    Facing low water in a boiler system is a hazardous situation but can be easily prevented with proper maintenance and precautions. The low water level in a steam boiler occurs when the water reaches below the base safe, that is the working level recommended by the boiler manufacturer. With the low water level, the tubes remain exposed and no longer cooled by the boiler water. It leads to the rapid increase of the metal temperature, resulting in reducing the metal’s strength and causing rupture as the metal’s strength decreases.

    The likelihood of severe or even catastrophic damage to a steam boiler due to low water conditions is easy to understand, considering that the temperature of the furnace exceeds 1,800 oF., yet, the steel strength drops significantly at temperatures above 800 oF. The only factor that enables a boiler system to withstand the furnace temperatures is water in or around (depending on whether the boiler is a fire tube or a water tube design) the pressure parts at all times when a fire is present. Therefore, low water conditions can melt the steel pressure parts.

    Generally, industrial steam boilers are natural circulation boilers that do not use pumps for circulating water through the pressure vessel. The units depend on the varying density between hot and cold water for providing circulation. As the water eliminates heat from the pressure parts, the water temperature increases and rises to the steam chamber. As a result, sufficient heat is transferred, generating steam. Cold feed water replaces the rising water, causing natural circulation.

    Because of the crucial need for water, advanced boiler systems are equipped with automatic low water trip switches. However, some outdated boilers do not include these relatively inexpensive devices. If the boiler does not have low-water trips, it is necessary to promptly initiate its installation to prevent any accidents and expensive repairs in the process plant. The resultant repairs can range from re-tubing to unit destruction if the overheating is neglected. In the situation of low water, the low water trips will trip the burner or fuel flow for solid fuel boilers and shut down the forced draft fan. It leads to shutting down the heat input.

    The trips need to be installed at a water level to prevent damage. Low-water trips are installed at 6” lower than the acceptable operating level. The control of the boiler water level is challenging, and even the best-tuned control systems cannot ensure complete prevention of a low-water condition. The water level in a pressure vessel is, in fact, an unstable compressible mixture of water and steam bubbles that can shrink and swell with pressure changes and will ultimately shrink momentarily when more cold feedwater is introduced.

    Some of the common causes of low water levels in the steam boiler are:

    • Failure of feedwater pump
    • Failure of control valve
    • Water loss to the deaerator or make-up water system
    • Failure of drum level controller
    • The drum level controller is left in the manual position
    • Plant air pressure loss to control the valve actuator
    • Lifting of safety valve
    • Large, sudden change in steam load

    Impact of Low Water Levels On Steam Boilers:

    Some of the commonly found damage caused by low water levels are:

    • Loose tubes
    • Cracked tubes
    • Melted metal
    • Leaking water

    One of the most hazardous results of low water takes place when the water is added to the boiler, but the system has already passed the point of no return where the boiler vessel is significantly overheated. It causes the water to immediately turn into steam, resulting in extreme pressure being created, and the boiler potentially exploding. It is one of the most dangerous consequences in a process plant with any boiler system and should be prevented at all costs.

    Prevention from Low Water Level:

    Steam boilers should be fitted with low water cut-offs (LWCO) for detecting the low water condition and shut down the boiler to prevent the impact of low water levels. Additionally, controls need to monitor the water level and take appropriate action such as sounding the alarm, shutting down the burners, and the feedback supply. It is also crucial to provide an external indication of the water level.

    A low level of boiler water is checked through the sight glass. It is the only visual available to check the steam boiler’s water level.
    Some boiler systems use floating bulbs with the LWCO shutting down the boiler if the bulb hits the cutoff level. With a float system, the device must be regularly blown down to prevent buildup.
    Some LWCO systems utilize a probe that enters directly into the water and shuts down the boiler again if the water gets below the permissible water level.

    Conclusion:

    Rakhoh Boilers is a trusted boiler manufacturer in Pune since 1983. With 39+ years of experience and expertise in thermal solutions, we deliver highly efficient and reliable industrial steam boilers, waste heat recovery systems, thermic fluid heaters, and boiler accessories to over 20 process industries in 27 countries worldwide. We provide excellent boiler services to boost the efficiency and productivity of the boilers.

    Visit www.rakhoh.com for more details on our products and services

    Friday, 12 August 2022 / Published in Boiler

    Combustion in industrial boilers and fluid heaters generates a significant amount of NOX. To fulfill the required ambient air quality standards, especially those for ozone, low-cost ultralow NOx burners are needed for these applications. It is a fact that emissions regulations have continued the downward trend that has been witnessed in the last decade. Present regulations in many countries are focused on single-digit NOX levels of 9 ppm. With our years of experience and knowledge, Rakhoh boilers have delivered innovative technologies designed to reduce nitrogen oxide (NOx) emissions for new or existing coal, oil, and gas-fired boilers.

    Reduced NOx in Industrial Boilers:

    In the case of industrial boilers, along with reducing NOx, it is equally important to achieve minimal greenhouse gas emissions while ensuring the highest thermal efficiency. Multiple advanced choices are available to assure both low emissions and high efficiency. It includes design and operational practices involving excess air, flue-gas temperature, low flue-gas recirculation, and selective catalytic reduction (SCR) technologies.

    Usually, an industrial boiler system consumes the equivalent of its initial capital expenditure in fuel usage within its first year, depending on the continuous operation. Considering that factor, increases in a boiler’s efficiency with merely a few percentage points can lead to substantial cost savings. We have listed below six methods to increase a boiler’s efficiency while reducing NOX.

    Tips to Reduce NOX in a Boiler System:

    Reduction of stack gas temperature to increase efficiency:

    One of the ways to immediately increase the boiler efficiency is by reducing the flue-gas temperature, or the temperature of the combustion gases that exits the stack of the boiler system. Boiler flue gas consists of useful amounts of energy that can be captured by using an economizer. Once stored in the economizer, the heat from the flue gas can be used through heat transfer to preheat the feedwater entering the boiler. In usual cases, a decrease of flue-gas temperature by 40°F (4°C) leads to an increase in efficiency by 1 percent.

    Using Flue-Gas Recirculation for Lowering NOX Emissions:

    Flue-gas recirculation (FGR) commonly is used to control thermal NOX. It is accomplished by lowering the burner flame temperature and staging the combustion of air and fuel. The step usually reintroduces 15% to 30% and in some cases as high as 45% of the flue gases into the mixing process leads to decreased production of thermal NOX.

    However, operating with high FGR needs a significant increase in fan horsepower. Consequently, it results in reduced efficiency due to the rise in the volumetric flow and pressure drop of the combustion air and flue gas through the unit. During this process, the stability of the burner and response is compromised, causing high O2 concentrations. Undoubtedly, there are limitations on the amount of FGR that can be introduced based on the burner design.

    Monitoring Excess-Air Levels for Optimal Performance:

    Managing excess air levels or the amount of excess combustion air required to burn a given amount of fuel is important to improve efficiency. Increasing additional air provides process benefits. It includes improved air, flame stabilization, fuel distribution, and low CO levels. On the other hand, too much excess air can cause reduced efficiency. It is due to increased fan horsepower consumption and high heat loss up the stack. A burner operating with minimum excess air, at 3 percent O2, is ideal for optimum burner and efficiency enhancements.

    Selective Catalytic Reduction for Low NOX Emission:

    Ultra-low NOX emissions can be accomplished by utilizing selective catalytic reduction (SCR) technology. This method is post-combustion and involves using a single reactor unit with a catalyst and a reducing-agent delivery system. The unit passes the combustion gases through an injection system to add the reducing agent to the combustion gases, thoroughly mix, and then catalytically reduce them to eliminate the NOX. The process lets the reaction of NOX (NO or NO2) and NH3 (ammonia) chemically convert to resultant products of nitrogen and water vapor.

    The usual performance of such units will see NOX levels reduced from 30 ppm to below 5 ppm or up to 95% reduction. SCR systems can also perform efficiently across a flue-gas temperature range of 325 to 1000°F (163 to 538°C) for industrial boilers, gas turbines, and fired refinery equipment. Particularly for boiler applications, SCR can reduce fan requirements by eliminating or significantly reducing the need for flue-gas recirculation. The savings in an electrical load along with a more stable burner during load swings over time could provide the payback when deciding on what equipment to purchase.

    Combining Economizers and SCR Systems for Low Emissions:

    The advantages of low emissions and high efficiency can be achieved when an SCR system is combined with an economizer and standard burner. The first phase of the SCR system utilizes a catalyst and a reagent to convert NOX to nitrogen and water. The next phase is gained with the finned-tube economizer, capturing waste heat and sending it back into the boiler feedwater or makeup water. The process can lead to significant reductions in operating costs. Its operational benefits are flame stability, higher turndown, and faster response to load swings.

    Monitoring Emissions and Efficiency Performance:

    Process plant owners nowadays keep tabs regarding emissions, efficiency, and carbon footprint. Additionally, such information is often a requirement for reporting purposes.
    Most analyzers used in the package boiler market measure O2 and stack temperature, providing calculated CO2 value and corresponding efficiency. To measure NOX emissions, a secondary analyzer is usually required. Continuous emissions-monitoring systems (CEMS) are also used for reporting both NOX and CO, but they are generally large and complicated systems.

    Conclusion:
    Rakhoh Boilers is one of the trusted boiler manufacturers in Pune since 1983. With 39+ years of experience and expertise in thermal solutions, we deliver highly efficient and reliable industrial steam boilers, waste heat recovery systems, thermic fluid heaters, and boiler accessories to over 20 process industries in 27 countries worldwide. We provide excellent boiler services to boost the efficiency and productivity of the boilers.

    Visit www.rakhoh.com for more details on our products and services

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