A Guide to Fuel-to-Steam Efficiency in Steam Boilers
Steam Boilers are pivotal for producing steam in process industries for heating, drying, sterilizing, and power generation purposes. Proper combustion is vital for steam production that is ensured by optimal efficiency. Naturally, while selecting a boiler manufacturer, one of the most important factors to consider is the fuel-to-steam efficiency offered by the manufacturer. The knowledge of the fuel-to-steam efficiency of any steam boiler helps with an approximate guess of the operating costs of that boiler that, over time, can be more expensive than the price of the boiler itself. Therefore, the fuel-to-steam efficiency rating of a steam boiler is not something to overlook.
What is Fuel-to-Steam Efficiency in Steam Boilers?
In simple words, the fuel-to-steam efficiency of a boiler is the ratio of BTU (British thermal unit) output divided by BTU input. The input is, in fact, the fuel used for the combustion process in the steam boiler, and the output is the steam generated by the boiler system. Higher fuel-to-steam efficiency leads to more steam generation. In actuality, the higher the efficiency rating results in more value of the money invested in a steam boiler. With the ever-increasing fuel costs, it becomes an attractive prospect for the facilities depending on the industrial steam boilers to maximize its fuel-to-steam efficiency as much as possible as a way to minimize the costs.
Rakhoh Boilers is one of the leading boiler manufacturers in India that provide a range of steam boilers with optimum fuel-to-steam efficiency.
Combustion Efficiency in Steam Boilers:
Steam boiler efficiency is the result of the efficiencies of different components of a boiler system. A steam boiler consists of various subsystems whose efficiency impacts the overall steam boiler efficiency. Two primary efficiencies that eventually determine the boiler efficiency are Combustion efficiency and Thermal efficiency of the boiler system.
The combustion efficiency of the steam boiler indicates the ability of the burner to burn fuel. The two major parameters that decide the burner efficiency are the amount of unburned fuel in the exhaust and excess oxygen levels in the exhaust. As the excess air increases, the unburned fuel quantity in the exhaust decreases. It, therefore, results in reducing the unburned fuel losses but increasing the enthalpy losses. As a result, it is important to strike a balance between enthalpy losses and unburned losses. Combustion efficiency also depends on the fuel that is burned. Combustion efficiency is higher for liquid and gaseous fuels as compared to solid fuels.
How to Improve the Combustion Efficiency in Steam Boilers?
Operating a steam boiler with an optimal amount of excess air reduces the heat loss up the stack and enhances the combustion efficiency. The combustion efficiency indicates how effectively the heat content of a fuel is passed into usable heat. The stack temperature and flue gas oxygen (or carbon dioxide) concentrations are major indicators of combustion efficiency. With complete mixing, a precise amount of air is needed to react entirely with the given quantity of fuel. In actuality, combustion conditions are never ideal, and an additional amount of air is supplied to burn the fuel completely.
The optimal amount of excess air is decided by analyzing the flue gas oxygen or carbon dioxide concentrations. Less excess air causes unburned combustibles (fuel, soot, smoke, and carbon monoxide), while too much causes heat loss because of the increased flue gas flow that reduces the overall boiler fuel-to-steam efficiency.
Fuel-to-Steam Efficiency in Steam Boilers:
Fuel-to-steam efficiency is combustion efficiency minus the percent of heat lost through radiation and convection. Some of the components of combustion, such as fuel specification, stack temperature, excess air, ambient air, and radiation/convection loss contribute to fuel-to-steam efficiency. For example, fuel with higher hydrogen content leads to more water vapor that uses energy while changing phase in the combustion process, causing reduce in efficiencies. Additionally, under similar conditions, the use of fuel oil results in 2.5% to 3% higher efficiency compared to natural gas.
Boiler efficiency is always impacted by the components of combustion. However, unique design characteristics improve the operating efficiency. It includes overall size, heat exchanger design, water circulation, startup time, blowdown, and steam quality.
The size of the steam boiler is a major determinant of its overall efficiency. Small boilers with less surface area are relatively more efficient. The heat exchanger produces steam, with some designs being more efficient in transferring heat than others. Steam boilers with forced or controlled water circulation are more efficient. Boiler system that starts up quickly is more efficient as it does not need to be kept on fuel-wasting warm standby, waiting to respond to increased demand.
For efficient and reliable steam boilers and thermal solutions for your process plant, contact Rakhoh Boilers, one of the leading boiler manufacturers in Pune with 38+ years of expertise. We have successfully installed 3000+ boilers in over 26 countries worldwide.
For more details on our products and services, visit www.rakhoh.com
- Published in Steam Boiler
Reducing Steam Pressure | Benefits and Issues
Steam boilers are imperative in the process and manufacturing sector to generate high-quality steam. Plant managers monitor various factors to ensure hassle-free operations. One of such important factors is steam pressure. An oversized steam boiler utilizing saturated steam opt for reducing the steam pressure. Steam pressure is determined by the factors like the maximum safe working pressure of the steam boiler and condensation within the pipe.
What do you mean by Reducing Steam Pressure?
Steam pressure reduction means reducing steam pressure of the boiler through the pressure control included in the steam boiler. Reducing steam pressure impacts the high-pressure part of the boiler. The pressure-reducing valves (PRV) adjust the pressure at lower levels within acceptable limits. Therefore, it can be concluded that reducing steam pressure results in considerable savings in the high-pressure section of the steam boiler.
Why Reduce Steam Pressure?
Listed below are some of the energy losses in steam boiler systems that can be decreased by reducing steam pressure,
- Combustion Loss:
Reducing steam pressure results in lowering the stack temperature that consequently leads to improved combustion efficiency. The ideal method to determine the temperature reduction and savings for a steam boiler is by conducting a combustion test at different pressure and constant load.
- Boiler Blowdown Loss:
Reducing steam pressure leads to a reduction of blowdown loss in a steam boiler. If the energy is recovered through a blowdown heat recovery system, it hinders any chances of further savings through reducing steam pressure. On the other hand, draining of blowdown water and venting of flash steam result in savings from reducing steam pressure.
- High-Pressure Steam Piping Heat Loss:
Heat loss from steam and condensate piping occurs in two stages. Initially, the heat is conducted from the hot steam through the walls and insulation surrounding the pipe to the outer surface. Later, the heat is lost by radiation and convection to the ambient air.
- Steam Leaks from High-Pressure Components like Valves, Piping, and Other Components:
External steam leaks take place in piping, joints, valves, and other components for various reasons. The degree of leakage varies on the maintenance of the steam boiler. It is mainly caused due to corrosion, erosion, water hammer, faulty design, or poor installation. Reducing steam pressure decreases the leakage rate in the high-pressure part of the steam boiler system.
- High-Pressure Steam Trap Leakage:
Poor steam trap maintenance is a major contributor to losses in the steam boiler system. Although reducing steam pressure is not an alternative for regular trap maintenance, it can result in savings of 0.6% of fuel input. Some of the other factors that impact the steam loss that should be considered are,
- Leakage of only a partial opening of the trap orifice, as compared to a “blow through”
- Steam trap flow coefficient
- Condensate passing through the leaking orifice
- Pressurized condensate return line
- The usual reduction of trap inlet pressure when variable process loads are involved
The combination of the factors leads to additional resistance to the flow of steam through the leaking trap orifice. It results in leak calculation for an individual trap to vary between 10% and 100%. Reducing steam pressure eventually reduces the leakage in high-pressure traps.
- Flash Steam Loss through High-Pressure Condensate Receiver Vents:
A large steam boiler includes multiple local condensate receivers that collect hot condensate and pump it back to the boiler plant. Flash steam losses will be decreased directly by reducing the steam pressure in the high-pressure section of the steam boiler.
- Steam Supplied to the Deaerator:
The steam quantity used for the deaerator is decided by the energy required to heat a mixture of hot condensate and cold makeup water to the saturation temperature at the operating pressure of the deaerator. The reduction in the steam leak, steam trap leak, and flash vent loss leads to a reduction in the boiler makeup water rate. It consequently leads to a reduction in the steam supplied to the deaerator.
- The Enthalpy Savings Effect:
The energy supplied to steam loads comes from the latent energy in the steam. Steam utilized at the pressure it is being generated requires less steam to supply the required latent energy at a lower pressure than at a higher pressure. Condensate from reduced steam pressure loses less energy from flash than condensate from high-pressure steam. At lower pressure the steam boiler must supply less energy to the condensate to raise it from the feedwater condition to the saturation point.
- Problems and Limitations with Reducing Steam Pressure:
- Boiler Carryover Steam Boiler
- Boiler Circulation Leading to Tube Overheating
- Boiler Performance at Highest Rated Load and Rated Pressure
- Steam Velocity, Pressure Drop, and Temperature in Piping
- Impact of Steam Pressure Reduction on Flowmeters
- Steam Traps
Rakhoh Boilers are leading boiler manufacturers in Pune, with more than 3000 steam boiler installations in over 26 countries worldwide. We manufacture efficient and reliable steam boilers, waste heat recovery systems, thermic fluid heaters, and boiler accessories and provide the best boiler services to boost the overall efficiency and performance of the steam boiler.
To learn more about our products and services, visit www.rakhoh.com
- Published in Boiler
Condensate Water Treatment and Prevention of Corrosion in Steam Boiler Pipe
Steam boilers are pivotal for generating pressurized steam in the process and manufacturing sector. Steam has various essential properties that make it suitable and economically beneficial for process operations. It is important to perform an appropriate water treatment program as it affects the overall operating costs of steam boilers, particularly for fuel. The steam is generated in the steam boiler by heating water and later transported through pipes for heating, drying, sterilizing, and power generation purposes. However, as the water converts to steam, it leaves behind dissolved solids that concentrate in the boiler water and needs to be removed by blowdown to keep concentrations within the acceptable limits. Therefore, operating the steam boiler system without condensate treatment may lead to hazardous accidents down the line.
What is Condensate?
The steam exits the boiler through piping to transfer heat to a heat exchanger or steam jacket. When the steam condenses in the pipe, it is called condensate, which consists of minimal impurities in it. Therefore, it is essential to capture and return as much condensate water to the boiler as possible as it saves water, but more importantly, it saves fuel. Freshwater needs to be introduced if condensate is not returned to the steam boiler. The water needs to be preheated that burns fuel. Returning most of the condensate results in saving considerable money in energy.
After cooling of steam, it reverts to a liquid known as condensate. Steam traps collect the condensate for return to the deaerator or feedwater tank efficiently. The condensate blends with the fresh makeup water in a deaerator or feedwater tank and converts to feedwater. It is pumped back into the steam boiler when required to cover the water losses that occurred during steam generation and blowdown. The pressure range of the boiler and the use of the steam determine makeup water quality, ranging from raw water, softened water, to high purity de-mineralized water.
On the other hand, there are certain disadvantages with condensate returns. As the condensate is almost entirely pure water, it is one of the most corrosive elements when introduced to steel and starts to cool. Carbon dioxide (CO2) easily dissolves in water once it cools, and at the precise pH, it starts forming carbonic acid, destroying the steel. It is paramount to maintain the pH within acceptable ranges in the pipes. It is necessary to use a dealkalizer for removal of alkalinity from boiler makeup water or a water softener for removal of hardness from boiler water.
Solution for Condensate Water Treatment:
By following a few basic precautionary methods, condensate can be monitored and handled effectively. Here are the primary steps to ensure the condensate return in a steam boiler,
- The system should be checked for leaks and failed steam traps.
- The pipes and condensate receivers should be insulated properly.
- The steam should be treated chemically with a condensate treatment.
Among the various types of condensate treatments, amines are commonly used. Amines can be classified into two types i.e., filming and volatile. The volatile amines are entirely soluble and can be fed directly in the steam boiler. It is considered volatile as they flash off and carry the steam into the boiler system. Therefore, it is referred to as short-range, medium-range, and long-range neutralizing amines, depending on the distance it can travel “downpipe.” Neutralizing amines are alkaline that neutralize the acids forming in the condensate by raising the pH. It controls corrosion in condensate by eliminating the effects of carbon dioxide and other acid-forming compounds. Neutralizing amines are used for water treatment in a steam boiler to control condensate return line corrosion. The amines do not have any severe impact on copper or copper alloys under normal conditions, that includes pH between 7.5 to 9.0 and a few ppm of amine continuously added to the boiler water.
On the other hand, filming amines are not entirely soluble, and cannot be fed directly into the steam boiler. For effective results of filming amine, it must be introduced directly into the steam header with specially designed injection quills and pumps used for properly dispersing the filming amine throughout the steam. As the steam condenses, filming amine does not dissolve and instead coats the internal surfaces of the pipe with a microscopic layer of chemicals. The material deposits on the internal of the pipe restrict the liquid from entering it. Consequently, it prevents the condensate from coming in contact with the metal and protects the pipe from acid and oxygen pitting.
It is necessary to examine the amine fed in a steam boiler by,
- The chemical feed pump should only activate during the running of the feedwater pump.
- Slug-feed or minimizing daily feed duration leads to temporary high amine concentrations, impacting copper.
- Treatment chemicals should be introduced directly into the steam boiler with the availability of a separate chemical feed line. It can also be added to the feedwater tank or storage tank of the deaerator.
- Amines should not be fed before a deaerator as it may cause loss of the amine.
Regular maintenance is necessary to ensure the hassle-free operation of the steam boiler. Excess blowdown, scaling, and condensate loss reduce boiler efficiency. Water treatment is crucial for the preventative maintenance program for any steam boiler system. Rakhoh Boilers is a trusted name for over 38+ years for manufacturing steam boilers and boiler accessories of world-class quality. We also provide excellent boiler services like fuel conversion, energy audit, boiler automation, annual boiler maintenance, and steam trap assessment.
For more details on our products and services, visit www.rakhoh.com
- Published in Boiler
Causes and Solutions for Tube Failures in Waterside of Steam Boilers
Steam Boilers are the backbone for processing operations in industries. Plant managers take every measure to ensure the safety of the steam boiler and the operating personnel. One such measure includes maintaining the boiler tubes. Overlooking boiler tubes can lead to hazardous consequences like overheating and boiler failure. Examining the root cause of the boiler tube failures is crucial to reduce the possibility of future boiler issues. An overall assessment is required to examine the cause of boiler tube failure that is usually a cause of other boiler problems. Some of the most common boiler tubes that occur on steam boilers are as follows:
Waterside failure for boiler tube:
- Caustic Attack:
The caustic attack takes place due to excessive deposition on the boiler tube surfaces, leading to reducing the cool water flow in contact with the tube. As a result, it causes local under-deposit boiling and boiler water chemicals concentration. It leads to a caustic condition that corrosively attacks and breaks down protective magnetite if blended with boiler water chemistry with high pH.
It is identified by localized wall loss on the surface of the boiler tube that increases the stress and strain in the tube wall and impacts furnace wall tubes or any inclined tube. Preventing caustic attacks requires avoiding the accumulation of excessive deposits and maintaining boiler water chemistry for preventing the local formation of caustic in areas with chemicals concentrated. In some cases of caustic attack, the top of a sloped tube is related to the steam-water separation that is avoided by using ribbed tubes. Maintaining boiler water chemistry is ensured by appropriate feed water chemistry with phosphate boiler water treatments.
- Acid Attack:
The acid attack occurs due to poor process control of boiler chemical cleanings or inadequate cleaning of residual acid. The tube metal surfaces result in an irregular pitted appearance on the boiler tube and affect water wall tubes.
It is prevented by maintaining water chemistry, proper controls for boiler chemical cleanings, and assessing the chemical hideout.
- Hydrogen Damage:
Hydrogen damage in the steam boiler is the result of excessive deposition on boiler tube surfaces and boiler water with less pH excursion. Inappropriate water chemistry from condenser leaks with saltwater cooling medium leads to acidic contaminants that are concentrated in the deposit and causes under-deposit corrosion releasing atomic hydrogen that passes to the tube wall metal and reacts with carbon in the steel. It causes intergranular separation.
Hydrogen damage is detected by intergranular micro-cracking, ductility loss, and boiler tube material embrittlement. It leads to brittle catastrophic rupture. It usually takes place in regions of high heat flux and can be prevented by maintaining water chemistry and avoiding scaling on the waterside of the boiler tube.
- Oxygen Pitting:
Oxygen pitting occurs by the excess oxygen in boiler water that takes place during operation due to in-leakage of air at pumps or failure in boiler water treatment. It also occurs during extended out-of-service periods of steam boilers. Aggressive localized boiler tube corrosion and loss in tube walls are signs of oxygen pitting.
Proper layup procedures during steam boiler outages, enhanced oxygen control during steam boiler startups, and operations can prevent oxygen pitting.
- Stress Corrosion Cracking:
Stress corrosion cracking occurs due to the combination of high-tensile stresses and the presence of corrosive fluid. It results from cracks that propagate from the boiler tube. The corrosive fluid results from the carryover into the superheater from the steam drum.
Stress corrosion cracking is identified by a thick wall, brittle-type crack at locations of higher external stresses. Stress corrosion cracks are usually related to various secondary cracks branched with the main ruptured area. The ideal solution for stress corrosion cracking includes preventing water carryover control and flush after cleaning.
- Waterside Corrosion Fatigue:
Waterside corrosion fatigue occurs due to thermal fatigue and corrosion. Corrosion fatigue depends on steam boiler design, water chemistry, boiler water oxygen, and steam boiler operation, leading to the breakdown of the protective layer on the surface of the boiler tube that prevents the boiler tube from corrosion.
Waterside corrosion fatigue can be detected by wide transgranular cracks taking place adjacent to external attachments. It is prevented by minimizing the operational cycles, constraints on tubes, and reducing dissolved oxygen on start-up.
It is imperative to ensure regular maintenance of the steam boiler for optimal efficiency and productivity with hassle-free operations. Rakhoh Boilers are one of the renowned names as manufacturers of boilers in India with 38+ years of expertise in boiler manufacturing and thermal solutions. We manufacture a range of efficient and reliable industrial steam boilers, waste heat recovery boilers, thermic fluid heaters, and boiler accessories. We provide excellent boiler services like annual boiler maintenance, steam trap assessment, energy audit, boiler automation, fuel conversion, etc.
We are proudly catering to over 20 process industries in 26 countries worldwide.
Know more about our products and services by visiting www.rakhoh.com
- Published in Boiler
An Overview on Steam Boiler Failure and Breakdown
A steam boiler is essential for the proper functioning of the manufacturing and process industries. Process plant managers must ensure that the steam boiler is free from any catalyst that may cause boiler breakdown or boiler failure. However, various factors can negatively impact the performance of the steam boiler. Neglecting regular inspections and maintenance can lead to severe consequences like boiler breakdown or boiler explosion, resulting in a loss in process plant and injuries to the operating personnel. Therefore, it is vital to adhere to strict safety guidelines for steam boiler operation and use safety gear and equipment while handling.
Here are some of the common signs that indicate steam boiler failure:
Odor: Steam boiler failure can lead to the emission of strange odor/smell from the steam boiler.
Noises: Steam boiler making loud, unusual noises is a sign of the failure of the boiler system.
Leaks: Steam boiler failure causes leakages of water or other fluids.
Thermostat: Consistent adjusting of the thermostat is a sign of steam boiler failure.
High Bills: A tremendous increase in the heating bills, as compared to previous months indicates a boiler failure issue.
Hazards of Using Faulty Steam Boilers:
Faulty boilers on the verge of failure or breakdown result in hazardous consequences that severely impact the operating personnel. Carbon monoxide, also known as the silent killer, can be fatal if overlooked. The odor of spent gas and fumes are signs of the danger of steam boiler failure. In such situations, it is advisable to contact the steam boiler manufacturer. It is also important to look for any visible soot or spillage marks and take immediate action on them.
Another hazard in using a faulty boiler is combustion turning into a yellow flame, rather than the usual blue one. It is caused due to an excessive amount of carbon monoxide in the steam boiler that spills the harmful, fatal gas in the boiler room. In such cases, it is prudent to contact the boiler manufacturer immediately for guidance, and it is suggested to turn off the steam boiler promptly until help arrives.
How to Maximize the Lifespan of a Steam Boiler?
Lifecycle cost is one of the important factors to consider while selecting a steam boiler for an industry. Although the efficiency of the boiler system is crucial, it is not the only factor that ensures the optimal lifespan of the steam boiler. Generally, an industrial boiler system functions effectively for 20 to 30 years. However, various factors impact the performance of the steam boiler.
- Selecting a Modular Steam Boiler:
Nowadays, boiler manufacturers provide efficient and sustainable steam boilers through advanced research in thermal engineering. Such a steam boiler system generates the precise amount of steam needed to meet the industrial demands. Additionally, process plants can rotate modular boiler systems with the lead boiler. During low demand, process facilities need to operate only one boiler, known as the lead boiler.
- Proper Boiler Water Treatment:
Improper and insufficient boiler water treatment causes hard scale build-up that damages the steam boiler system over time and significantly reduces the lifespan of the steam boiler. In severe cases, it can lead to critical failures or even hazardous threats to the safety of the process plant and operating personnel.
- Automated Monitoring and Control:
Advanced monitoring and control components optimize the system efficiency and maximize the steam boiler longevity. Rakhoh Boilers provides the best services in boiler automation that monitor the steam boiler in real-time, detecting the issues before major issues, and suggestions to prevent boiler issues.
- Regular Boiler Maintenance and Inspection:
The most effective way to maximize the lifespan of the steam boiler is to schedule regular maintenance and inspection of the steam boiler to prevent any mishaps that may occur due to negligence in maintenance and handling of the steam boiler.
Signs for Replacing Steam Boiler System:
Although steam boiler failure or breakdown requires immediate attention, it may cost a fortune to the processing facilities. However, after two to three decades of operation, steam boilers need to be replaced for enhanced performance and higher efficiency. Some of the factors that determine the replacement of steam boilers are:
Safety problems are usually detected in scheduled safety inspections as the inspectors assess the condition of the pressure vessel and the safety devices in a steam boiler. Additionally, boiler operation should be monitored closely and the following factors must be considered,
High stack temperatures
Irregular stopping/starting of steam boiler
Poor combustion tuning
Poor boiler water treatment
Steam boiler inefficiencies along with fuel cost are major factors to consider boiler replacement. In some cases, the repair costs are higher, that replacement seems to be a better economic decision.
Lastly, plant steam requirements change over time. Therefore, an oversized boiler operating in its low range is usually less efficient than a unit sized for the load.
Rakhoh Boilers has been a leading boiler manufacturer for 38+ years, providing efficient and reliable industrial steam boilers, waste heat recovery boilers, thermic fluid heaters, boiler accessories, and boiler services to over 20 process industries in 26 countries worldwide. Our services include annual boiler maintenance, steam trap assessment, energy audit, boiler automation, fuel conversion, and much more.
For more details, visit our website www.rakhoh.com
- Published in Boiler