Circular furnace boilers

The design of the world first pulverized coal-fired circular furnace boiler for large power units (from 300 to 1200 MW), for burning brown (Kansk-Achinsk field-type) and black (G and D grades of Kuznetsk-type) coal, was developed by a team of co-thinkers directed by Feliks Serant, in the 70s, 80s of the XXth century.

The boiler and its elements design is reserved by means of nine designer’s certificates of the USSR and the Russian patents. According to the governmental resolution, a commercial trial boiler with the capacity of 820 tonnes of steam per hour was designed and manufactured in the 90s for testing and operating the circular furnace design. It was installed in the existing cell of 500 t/h boiler, and has been operated successfully since 1997 in Novo-Irkutskaya CHP (the city of Irkutsk). The boiler tests with burning Kansk-Achinsk (Irsha-Borodinskoye) and Azeyskoye coals (the boiler efficiency factor is 93.5%, NO_x emissions are ≤ 400 mg/nm³, no furnace slagging and convective heating surfaces).

Successful operation for 16 years of Е-820 circular furnace boiler was reviewed and approved by the Scientific and Technical Board of INTER RAO in April, 2015. Based on the trial operation of this boiler, the designs of circular furnace boilers for the 200, 330, 500 and 660 MW units have been elaborated, and demonstrated, that circular furnaces application for the boilers of large power units allows:

• decreasing the boiler height by 30–40%;
• reducing their metal consumption down to 10%;
• ensuring slag-free and high-efficiency combustion of slagging black and brown coals;
• reducing NO_x emissions through process combustion methods to standard values.

The boiler operation results confirm its high reliability and efficiency for burning a wide range of brown coals.

• Gross boiler efficiency factor varies within the range of 92.5-93.5%.
• Reduction of the gas temperature in the flare (down to 1200°С) in the intensive burning zone at the level of burners and at the furnace outlet (down to 980°С).
• At relatively low flare temperatures, the circular furnace provides vortex-like gas movement and stable fuel ignition, without the flare to be in contact actively with internal and external screens, and without separation of particles into a cold hopper.
• Non-uniformity of the flare temperature distribution by the furnace perimeter in the area of the maximum heat release is below 10%, that is 2-3 times lower than in the boilers with a common tangential furnace.
• Compared to the conventional boilers, the octahedral circular furnace has an increased (by 15-20%) heat absorption by the furnace screens due to the convective component in case of the furnace media vortex-like flowing.
• T-shaped boiler circular furnace provides virtually uniform gas distribution between two convective gas ducts.
• The boiler is easily controlled both in steady-state and transient modes.
• The boiler height reduction (by ~30%) and reduction of a boiler cell dimensions allows the costs reduction for main building of the power plant.
• The pressurized heating surfaces weight reduction (by 10%) results in the boiler manufacture and installation cost reduction.
• Decreased flare temperature in the furnace contributes into reduction of Nitrogen Oxides (NO_x) down to 370-450 mg/nm³, which is considerably (1.5-2 times) lower, than in the boilers with conventional furnaces.
• The boiler improved dependability is provided both through no slagging on the heating surfaces, and through the uniformity of the furnace screens heating. Application of the controllable direct-flow burner devices enables changing the jet directions in the circular furnace path because of rearrangement of the secondary air flows, therefore excluding the flare contacts to internal and external screens and providing no-slag furnace operation mode.
• Separate application of main pulverized coal-fired and startup black oil-fired vortex burners in the boiler enables fast boiler startup in a cold air, without black oil dripping into a cold boiler bottom hopper.