"50T" refers to a rated evaporation capacity of 50 tonnes per hour. The standard parameters for medium-temperature, medium-pressure operation are a pressure of 3.82 MPa and a steam temperature of 450°C. As a water-tube boiler, water flows inside the tubes while flue gas sweeps across the outer tube walls. These boilers are widely used in captive power plants for enterprises and in industries such as chemicals and papermaking, capable of simultaneously generating electricity and supplying process steam.

Core Structure

The steam-water system comprises the steam drum, downcomers, water walls, superheater, economizer, air preheater, and headers. The steam drum facilitates steam-water separation; feedwater enters the drum and is conveyed via downcomers to the lower headers of the water walls. Water walls line the furnace periphery to absorb radiant heat; they serve as the primary evaporative heating surface while protecting the furnace walls. The superheater is located in the flue gas path to heat saturated steam to 450°C and is equipped with a desuperheater for temperature regulation. The economizer utilizes residual flue gas heat to preheat boiler feedwater. The air preheater heats combustion air to enhance combustion efficiency. Headers serve to distribute and collect the working fluid. The combustion system includes the furnace, burners, and flue gas passages. Pulverized coal boilers often employ a tangential firing method; fuel burns within the furnace, and flue gas flows sequentially across heating surfaces before entering dust removal and desulfurization units, finally exiting through the stack.
Auxiliary systems include feedwater, ventilation, steam, blowdown, and water treatment systems, as well as safety accessories. The feedwater flow path runs from the deaerator to the feedwater pump, then through the economizer into the steam drum; deaeration is essential to prevent pipeline corrosion. The ventilation system relies on forced-draft and induced-draft fans to maintain slight negative pressure within the furnace. Blowdown operations are categorized into continuous and intermittent blowdown; continuous blowdown removes high-salinity boiler water from the steam drum, while intermittent blowdown discharges sludge from the lower headers. The water treatment system handles water softening and demineralization and manages in-furnace chemical dosing to control water quality parameters and prevent scaling and corrosion. Safety accessories include safety valves, pressure gauges, water level indicators, water level alarms, over-temperature and over-pressure interlock devices, and explosion-proof doors. **Working Principle**
Feedwater is preheated in the economizer and then fed into the steam drum, from where it flows through downcomers to the lower headers of the water walls. The water walls absorb heat from the furnace to generate a steam-water mixture; this mixture rises back to the steam drum, where steam and water are separated. The separated saturated steam enters the superheater, where it is heated by flue gas to 450°C before being discharged for use. After releasing heat, the flue gas passes sequentially through the heating surfaces in the boiler's tail section and is discharged from the boiler after purification.

Equipment Characteristics

Advantages include high evaporation capacity (suitable for captive power plants), strong pressure-bearing capability due to the water-tube structure, high heat transfer efficiency, flexible steam temperature regulation, and good fuel adaptability (with the potential for retrofitting to use natural gas or biomass). Disadvantages include a complex, bulky overall structure and high construction costs; the startup and shutdown processes are time-consuming and require strict control over temperature and pressure ramps, making frequent cycling unsuitable. Additionally, there are stringent requirements for feedwater quality, a heavy maintenance workload, and a requirement for operators to hold professional certifications.

Operational Control Points

Steam drum water level is the primary control parameter and must be maintained within a normal range of ±50 mm. Excessively high water levels can lead to steam carrying water droplets, which may damage superheater tubes via impact, while excessively low levels risk tube rupture in the water walls due to dry-out. Steam temperature must be stably controlled at 450°C using spray-type desuperheating, with strict prohibition against exceeding this limit. Steam pressure is maintained at 3.82 MPa, as fluctuations can compromise steam turbine safety. The furnace is kept at a slight negative pressure (between -20 and -50 Pa) to prevent flue gas leakage or flame blow-out. Normal flue gas exit temperatures range from 140°C to 160°C; a rise in temperature typically indicates ash accumulation on heating surfaces and a consequent drop in boiler thermal efficiency. Water quality requirements dictate that feedwater dissolved oxygen content must not exceed 15 µg/L, and boiler water pH must be maintained between 9 and 10.5. Common Faults
Tube ruptures caused by wear and corrosion in water wall and economizer piping; tube ruptures due to overheating, oxidation, and wall temperature excursions in superheaters; excessive boiler water salinity triggering foaming and carryover, leading to significant fluctuations in steam drum water levels; ash accumulation and slagging on heating surfaces reducing thermal efficiency; safety valve leakage or premature opening; water level gauge failure; and unstable combustion or flameout posing a risk of furnace implosion or explosion.

Applicable Scenarios

Captive thermal power plants serving large industrial parks in sectors such as chemicals, papermaking, sugar refining, and building materials. A portion of the generated steam drives steam turbine generator sets for electricity production, while the remainder is extracted for use in production processes.

Thermal Efficiency and Qualifications

The designed thermal efficiency for this 50t/h pulverized coal-fired, medium-temperature, medium-pressure water-tube boiler ranges from 88% to 91%; actual efficiency depends on coal quality, ash accumulation, and operation and maintenance conditions. Classified as a Class A special equipment boiler, its manufacturing, installation, and annual inspections require corresponding qualifications. Boiler operators must hold a special equipment operation certificate and comply with the *Safety Technical Regulations for Boilers* (TSG 11).

Applicable Fuels

Primarily pulverized coal; can be retrofitted for natural gas or biomass fuel based on requirements.