How Does a Fuel Handling System Work In a Power Plant
Introduction
Different types of fuels are used in different boilers for steam generation. The waste heat recovery boiler (WHRB) of some process plants and the heat recovery steam generator (HRSG) of the combined cycle power plant do not use fuel. Steam is generated in this case by utilizing the heat of waste gas produced during some processes or other means. Indirectly, fuel is used upstream of the boiler to create this hot gas. Different fuels, such as solid, liquid, and gaseous, are used in boilers.
Handling Of Liquid Fuels
Light diesel oil (LDO), high-speed diesel (HSD), heavy fuel oil (HFO), furnace oil (FO), and low sulfur heavy stock (LSHS) are typically used as fuel in oil-fired Boilers. The handling procedures of different oils are different. The subsequent sections discuss the handling procedures of various liquid fuels.
Handling of LDO and HSD
Small boilers, often package boilers with low generating capacity, use Light Diesel Oil (LDO) or High-Speed Diesel (HSD) as fuel. HSD is also commonly used as a starting fuel in some boilers. The fuel is transported to the boiler site by road tankers and unloaded into storage tanks.
Oil is pumped directly to the boiler from the storage tank through a filter unit and flow meter. A control valve on the return line maintains pipeline pressure, and a relief valve prevents overpressure. In some setups, the fuel is transferred to a day tank for use in the boiler.
A regulating valve controls oil flow to individual burners, while an isolation trip valve shuts off the fuel supply during boiler shutdowns or trips. A bypass valve across the flow meter and filter unit allows maintenance without disrupting operations.
Handling of HFO, FO, and LSHS
Some package boilers and medium-sized boilers rely on HFO (Heavy Fuel Oil), FO (Furnace Oil), and LSHS (Low Sulfur Heavy Stock) as fuel. These oils differ from HSD (High-Speed Diesel) in handling due to their high viscosity. These oils are heated to reduce viscosity and facile pipeline flow.
HFO, FO, and LSHS are typically transported to boiler sites via road or rail by specialized tankers. Storage tanks for these oils are equipped with steam coil jackets to maintain the necessary temperature for pumping. Oil pipelines are heat-traced, with strainers and pumps also heat-traced to prevent heat loss and avoid solidifying oil in any section of the pipeline or equipment. Heat tracing ensures consistent temperature throughout the system, achieved using steam or electrical tracers alongside the oil pipelines. Condensate from the steam tracers and heaters is removed using traps, and the entire pipeline is insulated to retain heat. Draining facilities are provided for maintenance purposes.
Handling of Gaseous Fuel
Gaseous fuels like natural gas, blast furnace gas, and coke oven gas are widely used in boilers due to their efficiency and cleaner combustion properties. Natural gas is often sourced from petroleum wells, while naphtha, a byproduct of petroleum refining, is commonly used in power boilers. These fuels are transported to the boiler site via pipelines, and boilers are typically located near the fuel source to minimize transportation costs and risks.
The gas handling system includes a fuel trip valve and a fuel regulating valve for safety and flow control. An orifice is also installed to measure gas flow. When blast furnace gas contains a significant amount of dust, it is cleaned in a gas cleaning plant before entering the boiler. Wet scrubbing during cleaning adds moisture to the gas, so moisture traps are installed to remove it before the gas is fed into the boiler.
Coke oven gas is usually supplied directly to the boiler through pipelines, but excess gas can be stored in tanks for use during periods of high demand. These systems ensure a steady and reliable fuel supply for efficient boiler operations.
HANDLING OF SOLID FUEL: COAL HANDLING PLANT
Coal is classified into various grades in India depending on the ash content. Based the design
of the boiler, different grade coals are used in different boilers. The coal is handled in a coal
handling plant. At the coal handling plant, the following activities are performed:
• Receiving
• Storage
• Reclaiming
• Preparation or sizing
• Feeding
Coal Transportation and Storage
Coal, mined from coalfields, contains impurities like ash-forming minerals, rocks, and sulfur-bearing materials. After mining, the coal is cleaned and sized in coal beneficiation plants or washeries, often located near coalfields. These facilities use crushers, screens, and jigs to separate impurities based on density differences, providing high-quality coal for the plant.
The processed coal is transported to the plant via rail or road. Rail transport is used for large quantities, with wagons unloaded by wagon tipplers and stored in areas with proper drainage. For medium-sized plants, hydraulic lift trucks transport the coal by road. Coal is weighed at a weighbridge before unloading.
Coal Preparation
Coal from the storage area is transported to the boiler based on demand using equipment like reclaimers, cranes, or payloaders. Before feeding coal into the boiler, it is prepared to meet specific requirements.
The coal is first crushed in a crusher to achieve the desired size suitable for boiler operations. This pulverized coal is passed through a vibrating screen for the proper size. Magnetic separators remove any magnetic impurities from the coal.
Once prepared, the coal is weighed using a weigh feeder and stored in a storage bin or hopper. This processed coal is then ready for use in the boiler, ensuring efficient combustion and optimal performance.
Conveyor Belt System
The conveyor belt system is crucial for transporting coal from storage areas to the boiler. It comprises an endless rubberized belt running between pulleys, supported by idlers and equipped with tensioning mechanisms. These components are mounted on a sturdy steel structure.
Key Components of a Conveyor System
Conveyor Belt
The system’s core is the conveyor belt, made of nylon or steel cords bound with rubber. It is strong enough to handle driving tension and material loads.
Pulleys
- Drive Pulley: Provides motion to the belt and connects to a motor.
- Head Pulley: Positioned at the discharge end.
- Snub Pulley: Increases belt contact with the drive pulley to prevent slipping.
- Take-up Pulley: Maintains belt tension using a gravity-based mechanism.
Idlers
- Troughing Idlers: Support and shape the belt into a trough to carry materials efficiently.
- Return Idlers: Guide the empty belt back to the tail pulley.
- Impact Idlers: Using rubber-covered rollers, protect the belt from material impact at loading points.
- Self-aligning Idlers: Automatically adjust the belt’s alignment to keep it centered.
- Guide Rollers: Prevent lateral movement of the belt but don’t fix alignment issues
Safety and Protection Systems for Belt Conveyors
Coal handling plants require safety systems to detect abnormalities and protect personnel and equipment. Key features include:
- Pull Cord Switch
Installed along the conveyor at intervals of 20–25 meters. Stops the belt in emergencies when the wire rope is pulled. It must be manually reset after activation. - Belt Sway Switch
Detects belt misalignment and stops the conveyor or generates warnings. Automatically resets when the belt realigns. - Hold Back Device
Prevents reverse movement of inclined conveyors. Includes ratchet-pawl or clutch systems (roller or sprag types). - Underspeed/Zero Speed Detector
Detects reduced or zero speed in the tail-end pulley. Stops the conveyor during belt slippage or breakage. - Belt Damage Detector
It uses electromagnetic sensors to detect belt health. Stops the system when a damaged belt section is identified. - Magnetic Separator
Suspended above the conveyor to remove ferrous materials.Prevents damage to downstream equipment. Self-cleaning types automatically remove collected materials. - Metal Detector
Detects both ferrous and non-ferrous metals missed by magnetic separators.Stops the conveyor to remove detected metals manually.
Bucket Elevator
A bucket elevator is used for vertical material transport. It consists of buckets attached to an endless loop of a belt or chain. The belt or chain moves continuously around pulleys or sprockets powered by a motor and gearbox. Buckets are loaded at the bottom, and material is discharged at the top.
Key Components
- Buckets
- Moving belt or chain
- Pulley or sprocket
- Motor with speed reduction gearbox
- Adjustable tensioner and casing
- Loading and discharge chutes
- Types of Bucket Elevators
- Belt Bucket Elevators: Use a belt as the lifting element.
- Chain Bucket Elevators: Use a single or double chain.
- Discharge Methods
- Centrifugal Discharge: High-speed, widely used in power plants.
- Continuous Discharge: Low clearance between buckets, steady material flow.
Coal Feeder
A coal feeder is equipment a coal handling plant uses to control or regulate the coal flow rate from a bin or hopper. It is used with conveyors, crushers, and vibrating screens. Many types of coal feeders are used in power plants.
Coal Crusher
Coal obtained from coal mines is not sized as per the boiler requirement. Bigger-size
coal cannot be used in a boiler. So, it is required to size the coal properly before feeding it
into the boiler. Reduction of coal size is done at the crusher. Sometimes, it is necessary to reduce
the size of coal lumps before final crushing. For this, a combination of primary and secondary
crushers are used. Different types of coal crushers are used in coal handling plant
Coal Pulverisation and Other Solid Fuels
Coal for pulverized coal-fired boilers is fed to pulverizers, classified as:
- Individual System: Each burner has its pulverizer.
- Closed Drying: Uses hot primary air for drying and carrying coal to burners.
- Open Drying: Uses flue gas for drying; coal dust is stored in bins for burner use.
- Central System: One pulverizer serves multiple burners with central storage for coal dust.
Other Solid Fuels
Biomass Fuels
Common examples include wood chips, sawdust, rice husk, and bagasse. Biomass is transported and stored as loose material or briquettes. Bagasse, a sugarcane byproduct, is widely used in sugar plants for power generation and is stored for off-season use.
Municipal Solid Waste (MSW)
MSW includes household and light industrial waste. After removing non-combustibles, it is sorted, sized, and fed into boilers. Storage areas are maintained under negative pressure to control odors.
These alternative fuels are increasingly used for sustainable energy generation.
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