Processing of Pulp to Paper and the Role of Steam Boilers in Paper Industry
Paper plays a crucial role in our day-to-day lives. The paper industry in India contributes about 1.6% of the total global paper production with an approximate turnover of 250000 Million. The first-ever machine-made paper was manufactured in India in 1812 when there were only 15 paper mills. Presently, India has approximately 800 paper mills manufacturing paper bags, handmade paper boxes, paper albums, etc., exporting paper products worth 4000 million worldwide. As per a report by the Indian Paper Manufacturers Association (IPMA), the per-capita paper consumption in India is estimated to be 13 kg. The paper industry offers employment to a significant population, and the paper and paper products industry may grow to a market of $ 13.4 billion by 2024.
The Manufacturing Process from Pulp to Paper:
Paper processing includes various operational stages before the paper is deemed ready to be exported to markets. Paper processing mainly requires water, chemicals, energy, and cellulose (extracted from softwood or wood chips). Debarking of the wood logs is essential before forming them into wood chips. The main stages of the paper processing are as follows:
- Pulp formation:
The wood chips are transferred in a high-pressure vessel termed a digester. Over here, the wood chips are cooked and boiled with a chemical solution that is eventually dissolved and formed into a pulp. The pulp is filtered, and if required, bleached before it sending it for further process.
- Beating:
Once the pulp is formed, the process of beating takes place. As the name suggests, the pulp is beat along with adding other filler materials and additives. It impacts the quality of the paper.
- Processing Pulp to Paper:
In this process stage, the pulp is squeezed through a series of rollers by feeding it to automated machines that form it as paper. The beating process is followed, by a press section that consists of pressing the paper between steam-heated cylinders that removes the excess water from the paper.
- Finishing Products:
The resultant paper is rolled in reels that would be moved for further processing depending on the paper product to be manufactured.
Why are Steam Boilers Important in the Paper Industry?
Steam is pivotal in the paper industry for the process of drying the paper, energy requirement, and the cooking of wood chips in the digester. Some of the essential requirements of steam in paper processing are,
Uniform Heating:
The utilization of rolls in paper processing requires it to be heated internally with steam. Therefore, it is essential to maintain an even temperature across the surface of the rolls for uniformity and high-quality products. Steam is an ideal choice as it condenses and distributes heat evenly.
Steam Carries Ample Heat:
Most processing plants require a considerable amount of energy, and the paper industry is no different. One of the optimal ways to carry energy for processing operation is through latent heat in steam. For instance, 150 psig of saturated steam carries around 3.5 times heat content, and the energy is released as soon as the steam comes in contact with the internal surface of the roll.
Precision in Steam Temperature:
As temperature demand increases or the higher grade papers are manufactured, higher pressure and temperature are needed. The plant operators can control the pressure and set the steam temperature inside the roll. The saturated steam maintaining the same temperature at a given pressure allows the operators to control the pressure and steam temperature as required.
Efficient Process Operations:
Steam boilers are highly efficient for generating steam and power for processing purposes. The generated steam is operated in an insulated, closed-loop system. Hence, steam boilers are efficient and reliable for the process industry’s operations.
Challenges in Paper Industry:
Expensive Raw Materials:
The raw material for paper processing mainly includes wood fiber which is high in cost and difficult to procure.
High Power Demand:
Paper mills require a high amount of power to function efficiently. Nowadays, paper processing plants have switched to power generation boilers that aid them in generating both steam and electricity.
Deforestation and Environmental Harm:
The cutting down of trees to acquire wood for process operations results in deforestation. It disturbs the environmental cycle and accelerates the pollution level.
Boilers in Paper and Paper Products Industry:
Steam boilers in the paper industry are used for generating steam and power required in the processing plants. Steam is essential for operations such as heating of chemicals, heating rollers, etc. Because of the paper industry requiring a high amount of steam; it is important to choose efficient and durable steam boilers. Boilers with reciprocating grates are best suited for the effective combustion of fuels like wood chips, wood logs, sawdust, and agro-waste used in paper process plants.
Rakhoh Boilers have been manufacturing highly efficient and reliable steam boilers for more than 38 years. Rakhoh’s boiler models such as Combo X, Membrane X, and Solid Fuel Bi-Drum are preferred by some of the leading paper mills in India.
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Types and Advantages of Fluidized Bed Combustion in Solid Fuel Boilers
Combustion is a vital and one of the initial processes in the functioning of steam boilers. Various fuels are ignited in solid fuel boilers that require proper combustion to generate steam and avoid greenhouse emissions from unburned fuels. Fluidized bed combustion is a technique that effectively burns the fuels in solid fuel boilers. In the fluidization method, the combustion is performed by mixing fuel and air in a specific proportion. A fluidized bed can be defined as a bed of solid particles, passed through a pressurized fluid (gas or liquid) that causes the solid particles to act as a fluid in certain conditions.
In India, the coal majorly available is of low quality, low calorific value, and high ash content that hinders the conventional grate fuel firing system. Fluidized bed combustion is ideal for burning fuels such as coal, rice husk, bagasse, agro waste, etc. and offers various benefits as compared to traditional firing systems such as flexibility in fuel choice, compact design of solid fuel boiler, combustion efficiency, and reduced emission of pollutants like SOx and NOx.
Working Principle of Fluidized Bed Combustion:
Fluidized Bed Combustion occurs when a gas or air is evenly distributed and passed upwards through a bed of fine solid particles such as sand. Initially, at low velocity, the particles remain undisturbed. As the velocity gradually increases, the particles reach a stage when it is suspended in the air stream, and the bed is fluidized.
Fluidization highly depends on particle size and air velocity. The mean solid velocity increases at a slower rate as compared to gas velocity. The difference between both velocities is termed slip velocity. Maximum slip velocity assures good heat transfer. When sand particles in a fluidized state are heated to the combustion temperature of coal while the coal is administered steadily into the bed, it results in rapid burning of coal and uniform temperature of the bed. The fluidized bed combustion occurs at between 8400C and 9500C. The combustion process requires Time, Turbulence, and Temperature. Particle bed in FBC uses limestone that controls the emission of sulfur dioxide and nitrogen oxide without any pollution control equipment.
Types of Fluidized Bed Combustion in Solid Fuel Boilers:
There are three major types of fluidized bed combustion boilers that are:
Atmospheric Classic Fluidized Bed Combustion (AFBC)/ Bubbling Bed:
In AFBC, the coal is crushed to 1mm to 10 mm, depending on the quality of the coal and the type of fuel fed in the combustion chamber. The atmospheric air acts as fluidization air and combustion air that gets preheated by exhaust flue gas and flows through the bed with a velocity ranging from 1.2 m/sec. to 3.7 m/sec. The amount of fuel reacted depends on the rate at which air passes through the bed.
AFBC solid fuel boilers are generally 0.9 m to 1.5 m deep and consist of in-bed evaporator tubes in the limestone, sand, and fuel bed to extract heat and control the bed temperature. It operates with a determined temperature range of 800oC and 850oC. If the temperature exceeds 950oC, there may be a risk of clinker formation, and if it lowers than 800oC, it may result in loss of combustion efficiency.
Components of AFBC in solid fuel boiler:
- Fuel Feeding System
- Air Distributor
- The in-bed heat transfer surface
- Ash Handling System
Circulating Fluidized Bed Combustion (CFBC):
The CFBC technique performs by administering crushed fuel of 6 mm to 12 mm size and limestone into the combustor. The bottom of the furnace consists of air distribution nozzles that deliver upward flowing air in which the particles are suspended. The fluidizing velocity ranges between 3.7 m/sec. to 9 m/sec. and combustion takes place between 840oC and 900 o C. The CFBC comes without steam generation tubes, but some of them consist of external heat exchangers. The circulation of particles leads to sufficient heat transfer and residence time for the utilization of carbon and limestone.
For larger process plants, CFBC provides greater area, fuel particle, and sorbent residence time for effective combustion and to control SO2. It is more cost-effective than AFBC and an ideal choice for medium to large boiler capacity firing low-grade fuel that requires control on sulfur emission.
Features of Circulating Fluidized Bed Combustion System in Solid Fuel Boilers:
- High processing capacity due to high gas velocity
- Low combustion temperature leads to minimal NOX
- Better turndown ratio
- Reduced erosion of the heat transfer surface
- High combustion efficiency
Pressurized Fluid Bed Combustion:
Pressurized Fluid Bed Combustion (PFBC) is mainly used in cogeneration plants and large-scale coal combustion. The gas turbine is driven from the off-gas in fluidized bed combustion. Waste heat from the gas turbine is utilized for preheating the condensate from the steam turbine and used as feed water for generating steam. Combining gas and steam turbines leads to the efficient generation of electricity.
Advantages of Fluidized Bed Combustion in Solid Fuel Boilers:
- Higher Efficiency
- Flexibility in Fuel Choice
- Effective Combustion of Low-Quality Fuels
- Reduced Corrosion and Erosion
- Easy Ash Removal and No Clinker Formation
- Less Requirement of Excess Air
- Quick Startup
- Avoids Soot Blowing
- Highly Reliable
- Quick Response to Load Fluctuations
- Easy Maintenance
- High Efficiency for Power Generation
Rakhoh Boilers has been one of the leading boiler manufacturers since its inception in 1983. We manufacture a wide range of efficient and reliable solid fuel boilers, oil-fired and gas-fired boilers that assure effective combustion of the fuels for optimal productivity and efficiency. We also manufacture high-quality boiler accessories and provide excellent boiler services.
Know more about us at www.rakhoh.com
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Boiler Maintenance | Its Importance and Best Practices for Boiler Efficiency and Longevity
Steam boilers are imperative equipment in almost every process industry, be it pharmaceuticals or chemicals, or food processing. Boilers are undoubtedly a major asset in any industry that serves the facilities for many years. It can be concluded that the quality of the boiler represents the quality of the final product that is processed. It is necessary to ensure that the steam boiler is functioning properly and delivering the optimal outcome. Regular boiler maintenance is of utmost importance to ensure the active functioning and safety of the boiler. Following a maintenance schedule can make a huge difference in accelerating the boiler efficiency and lifecycle and preventing breakdowns and excess cost for the wear and tear of the boilers.
Importance of Boiler Maintenance in Process Industry:
Although boiler maintenance contracts will be an excess cost to the industry, it is worth the outcomes and advantages ensured with such regular programs. One of its primary benefits is the prevention of boiler failure that may result in substantial loss. Some of the significant advantages of boiler maintenance are as follows:
- Higher Safety and Reliability of Boiler and its equipment
- Low Replacement Costs
- Anticipated Downtime for Maintenance
- Saving of Water and Fuel
- Higher Energy Efficiency
- Reduced Emission
Apart from these benefits, there are three crucial reasons to adopt a boiler maintenance program to enhance the overall efficiency and performance of the steam boiler.
Monitoring the Water Quality:
The water quality directly impacts the boiler efficiency. In other words, water containing impurities or oil can result in low-quality steam. It may also cause wet steam and an inadequate operational cycle leading to energy loss and high operating costs. The boiler maintenance program includes the chemical testing of water quality under expert guidance that indicates the quality of water to prevent corrosion, scaling, and other issues. It can affect the efficiency and the lifespan of the boiler.
Proper Boiler Blow Down:
Blowdown is the process of draining the water from the boiler in regular intervals to remove the sludge accumulated at the bottom of the boiler. The dissolved solids in water cause poor water quality that increases corrosion and scaling. Blowdown is essential in a boiler maintenance contract, and it is advisable to seek the measures of performing blow down as per the boiler requirement.
Proper Insulation:
Insulation is essential to ensure efficient and safe boiler operations. The amount of required insulation, the material of the insulation, and the range of insulation depends on the pipe size and its operational temperature. The boiler maintenance program assesses insulation by inspecting the piping, boiler surfaces, and fittings.
Fiberglass, Cellular Glass, Mineral fiber, and Calcium Silicate are the most commonly used insulation materials in steam boilers.
Practices to Follow for Boiler Maintenance:
Periodic boiler maintenance ensures the smooth functioning of the boiler system. Here are some of the techniques that can be carried for the proper maintenance of steam boilers
Daily Maintenance:
Some basic activities can be performed daily by the operating staff for maintaining the quality of boiler performance. Such practices include:
- Maintaining a Boiler Log/Record to note daily operation activities and metrics like flue gas and operating temperature, water level, consumption of fuel, gas pressure, etc.
- Monitor the water level in the boiler and the steam pressure in the boiler
- Conduct a bottom blowdown
- Conduct a water column blowdown
- Inspect the pressure and temperature of the boiler to determine its capability to handle the load
- Assess the stack temperature to ensure the boiler efficiency
- Monitor pressure level and the downstream pressure
- Check through sight port for any soot accumulation
- Ensure the proper functioning of the other boiler equipment
Weekly Maintenance:
Weekly maintenance of boiler is time-consuming yet important and involves inspection on one day of the week of the following practices:
- Check the burner positioning and the burner shut off
- Conduct an evaporation test to determine the control and burner shut off when the water reaches a low level
- Inspect the functioning of fuel supply valves
- Check the proper functioning of alarms
- Check the motors in the boiler to ensure their proper functioning without excess vibration and noise.
- Check the high-pressure and low-pressure switches
- Conduct a thorough checking of leakages of flue gas, water, steam, and fuel
Monthly Maintenance:
Here are the few things that must be inspected once a month by a technician:
- Check the burner pilot assembly to ensure its positioning and cleaning
- Check the burner diffuser to determine deformation such as cracking or burning
- Inspect air dampers to prevent the accumulation of dirt
- Check the boiler exterior for any indication of any hot spot that can be dangerous
Annual Maintenance:
Annual maintenance is conducted yearly under the guidance of qualified experts that inspects the following:
- Inspection and cleaning of fireside surfaces and chimneys
- Assessment of burner refractory material and manhole gaskets
- Checking of system valves and safety valves
- Inspection of burners and fuel oil levels
- Gauging all operating controls
- Assessment of other boiler equipment
Tips to Ensure General Boiler Maintenance:
- Ensure that boiler, burner, and boiler room are clean
- Avoid closing vents that supply air to the boiler room
- Repair leakages immediately
- Prevent foaming and priming and contact the boiler manufacturer in case of serious issues
Since its inception in 1983, Rakhoh Boilers have achieved an excellent reputation as a world-class boiler manufacturer and boiler service provider. With the expertise and experience of more than 38 years, Rakhoh Boilers are the preferred brand for industrial steam boiler and boiler services such as Annual Maintenance Contract, Energy Audit, Steam Trap Assessment, Boiler Automation, and many more.
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Importance, Types, and Factors to Consider while choosing Steam Trap for Boiler
Steam generation is integral in the process industry and plays an indispensable role in performing processing operations. Steam is ideal for passing through tubes and transferring heat uniformly, as it can hold a substantial amount of energy. Fuels are burned in the furnace that boils the water and generates steam and then carried for the processing, where needed. Although steam is essential, condensate is inevitable in any boiler system. Condensate is the energy released by steam as water that needs to be discharged from the boiler system to ensure efficient processing.
What is a Steam Trap?
Steam traps are automatic valves that hold the steam until it releases energy and condenses into water. The water is eliminated, preventing the loss of efficiency in the steam boiler. Neglecting the removal of condensate may cause water hammer that result in damage to valves, equipment, and tubes in the system.
Importance of Steam Trap:
Steam is generated when the water is vaporized and formed as gas. For vaporization to take place, the water molecules must contain sufficient energy to break the bonds between the molecules. The energy in water molecules that converts the liquid into a gas is known as ‘latent heat.’
The boiler system utilizes latent energy in the steam that is transferred to accomplish process operations. Once the steam loses its latent energy it begins to condensate. Failing to discharge condensate quickly affects the heat transfer and may cause corrosion and water hammer, resultantly reducing the efficiency of the boiler.
Types of Steam Trap in Boilers:
Steam trap performs its primary function of separating steam and condensate, but different types of steam traps use varying mechanisms to discern between steam, air, and condensate. Some of the widely used steam traps are as follows:
1. Inverted Bucket Traps:
As the name suggests, inverted bucket traps consist of an inverted bucket that functions on the principle of buoyancy. The bucket rests at the bottom of the steam trap while the valve is open. The steam and the condensate flow under the bottom of the inverted bucket after moving into the trap. The steam accumulates at the top of the bucket, the bucket inclines upwards and closes the discharge valve. Once the steam is condensate, the condensate fills the bucket that falls and opens the discharge valve that passes the condensate.
2. Ball Float Steam Trap:
A ball float steam trap consists of a ball float connected to a trap discharge valve submerged underwater to avoid steam loss. The condensate enters and accumulates in the float chamber, causing the float to surge upwards. It results in the opening of the discharge valves to pass the condensate. An in-built thermostatic air-vent assists in releasing air to facilitate quick functioning.
Ball float steam traps are extensively used for heating operations during processing because of the continuous discharge of condensate immediately after its formation, high thermal efficiency during both light and heavy loads, and high resistance to water hammer.
3. Thermostatic Steam Traps:
The difference between the temperatures of steam and condensate contributes to the working of thermostatic steam traps. Steam has more temperature than condensate, indicating the port in the thermostatic steam trap to shut when the temperature exceeds its predetermined range and open when it is reduced. The port allows the passing of condensate along with cooler air and CO2.
4. Thermodynamic Steam Traps:
The working of thermodynamic steam traps is based on the thermodynamic principle and depends on the flash steam formed from condensate. Factors such as compact size, single moving part, wide pressure range, and corrosion resistance are the reasons for its wide range of applications.
Factors to Consider while Selecting Steam Trap:
- Air Vent:
During the beginning or ‘start-up’ of a process operation in a boiler system, the heating space is filled with air which, if not replaced, can reduce the heat transfer and accelerate the time required for warm-up, leading to low efficiency. Hence, it is essential to remove air as soon as possible before it blends with the steam. The only way to separate air and steam is through condensing steam. Although it can be accomplished with a steam trap, an air vent is required in large systems. Float traps with in-built air vents are ideal in such situations.
- Discharging of Condensate:
It is necessary to ensure that the trap passes the condensate and captures the steam as the steam leakage would cause a high loss of efficiency. Condensate needs to be released immediately for optimal heat transfer.
- Process Requirements:
Before choosing a steam trap, it is essential to know the operations to be performed in the process plants by considering the factors such as maximum pressure for steam and condensate, operating pressure for steam and condensate, temperature, and flow rate.
- Reliability:
A reliable steam trap of excellent quality ensures that the steam is trapped and distributed for processing effectively. Lack of reliability in the steam trap may cause accumulation of dirt, corrosion, and water hammer.
Rakhoh Boilers is one of the leading boiler companies in India with 38+ years of expertise in manufacturing efficient steam boilers for process industries worldwide. We provide the best boiler services like steam trap assessment, energy audit, boiler automation, annual maintenance contract, etc., to upgrade boiler performance and lifecycle.
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Cogeneration Plants| Types of System, Advantages, and Factors to Consider in Choosing a System
Process industries are opting for Cogeneration plants as the ideal solution for steam and power generation with high efficiency and low cost and to meet the increasing power requirement. Cogeneration, also termed as combined heat and power, can produce two or more forms of energy from a fuel simultaneously. In general terms, it uses excess or recycled heat to generate heat or electricity for the processing units. Cogeneration plants operate with 50% to 70% higher efficiency as compared to single generation plants.
What are Cogeneration Plants?
Cogeneration power plants are the primary source of electricity in many process industries. Compared to the conventional power generating plants, cogeneration plants are highly efficient and cost-saving as the single generation plants are around 35% efficient while the remaining 65% of energy is wasted.
Cogeneration plants or Combined Heat and Power (CHP) generate two forms of energy, mainly mechanical and thermal from a single fuel source. Mechanical energy is mainly used for producing electricity and functions such as motor, pump, fan, or compressor. On the other hand, thermal energy is utilized for direct applications by generating steam, hot air, or hot water for the processing operations in industries. The basic components for a cogeneration system are as follows:
Turbine/Prime Movers: Prime Movers or Turbines converts fuel into mechanical and thermal energy
Electrical Generator: The function of an electrical generator is to convert mechanical energy into electrical energy
Heat Recovery System: Heat recovery systems effectively harness the heat from the turbines.
Heat Exchanger: The heat exchanger assures that the heat captured is distributed for the processing
Types of Cogeneration Plants:
Cogeneration plants are mainly classified as steam turbines, gas turbines, and reciprocating engine cogeneration systems.
Steam Turbine Cogeneration System:
Steam turbine cogeneration system is a full-condensing steam turbine installed in industries that generates power from the waste heat from process operations. The benefit of using steam turbines is that it works with a wide range of fuels like coal, natural gas, fuel oil, and biomass. Its efficiency for electricity demand ranges between more than one MW to around a hundred MW. The backpressure and the extraction are two widely used steam turbines.
Gas Turbine Cogeneration System:
Gas turbine cogeneration system is capable of producing complete or partial energy requirements of the process industry through the high-temperature exhaust stack released. Apart from natural gas, it functions effectively with fuels like light fuel oil or diesel. The average range of gas turbines is between a fraction of MW to 100 MW. Gas turbines require less start-up time but low heat to power conversion efficiency. Supplementing the natural gas with additional fuels to the exhaust gas increases the heat output at high temperatures. In case of excess power requirement, gas turbines are combined with a steam turbine system that can generate more power with the steam released from the exhaust gas from the gas turbine.
Reciprocating Engine Cogeneration System:
Reciprocating engine cogeneration systems, also termed Internal Combustion (I.C) engines, have high power generation efficiency. These systems are mainly preferred by small sites having a higher requirement of electricity than thermal energy i.e., low-pressure steam or hot water. It works with fuel like diesel, heavy fuel oil, and natural gas. Such systems are ideal for infrequent operation and have less investment cost but high maintenance. The heat recovery in the reciprocating engine cogeneration system is through exhaust gas at high temperature and engine jacket cooling system at low temperature.
Classification of Cogeneration Plants:
Cogeneration Plants are classified by energy utilization and the operating method. It is broadly classified as a topping cycle and bottoming cycle cogeneration system.
Topping Cycle Cogeneration System:
The topping cycle cogeneration system generates power while the thermal energy is produced as a by-product of the operation. It is a preferred and majorly used system in various industries.
Bottoming Cycle Cogeneration System:
Bottoming cycle cogeneration systems generate thermal energy, and the excess heat from the process is later used for generating power. The bottoming cycle is less used than the topping cycle. It is primarily used in industries such as cement, steel, gas, and petrochemicals.
Advantages of Cogeneration Plants:
Some of the noteworthy benefits of cogeneration plants are,
- Higher Efficiency
- Reduced Fuel and Transportation Requirement
- Low Cost of Fuel
- Reduced Emission
- Less Energy Waste
- Higher Power Generation
Factors to Consider While Choosing Cogeneration Plants:
While selecting a cogeneration system, it is important to ensure that it meets the industry’s requirements. Some of the crucial parameters to consider are:
- Heat-to-Power Ratio
- Thermal Energy Quality
- Load Patterns
- Grid Dependent System and Independent System
- Retrofit and New Installation
- Availability of Fuels
- Reliability of System
- Compliance with Environmental Regulation
Conclusion:
Rakhoh Boilers, with their expertise and knowledge of more than 38 years in thermal solutions, understands the demands and requirements of their process industry clients and strives to deliver them with highly efficient boilers of world-class quality. Rakhoh’s Solid Fuel Bi-Drum and Bi-Drum/D Type/Power X models are highly preferred as cogeneration systems in many industries such as
- Sugar
- Petrochemical
- Refineries
- Tea
- Milk Dairy
- Distilleries
- Paper and Packaging
- Textile
- Rice
- Food Processing
- Chemicals
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