Investigation of Slagging Characteristics on Middle and low temperature heat transfers by Burning High Sodium and Iron coal

ABSTRACT

The severe slagging problems during Zhundong coal combustion caused by the high alkali attracted broad attention. To obtain the characteristics and the formation of the deposits at lower gas temperature when the boiler was burning high sodium and iron content Zhundong coal, the slags were sampled in a 260 t/h medium temperature separation circulation fluidized bed boiler and analyzed by X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD). The slagging status at the same temperature range of a 350 MW ∏ type boiler was used to compare and the results indicated that when the Na₂O and Fe₂O₃ content in coal ash was higher, the serious slagging would occur in reducing atmosphere at lower gas temperature area (539°C–876°C). Almost all of the slag presented maroon. Even the gas temperature only was 539°C, the thickness of the slag was 5.61 mm. Nearly all of the sodium and iron content in slag samples in MTS-CFBB exceeded 5% and greater than 10% in part of the collected slag. The Fe species played a key role in the slagging process in reducing atmosphere for the Fe presented Fe²⁺ based compounds with lower melting points, which reacted with the other elements to form the lower temperature eutectics adhered to depositing surface, and then promoted the slagging process.

KEYWORDS:

• Zhundong coal
• slagging characteristics
• sodium
• iron
• lower gas temperature

Highlights

• The impact of Fe on slagging in combustion was studied at lower temperature area.

• The high iron content and the reducing atmosphere promoted the slagging process.

• The properties and reasons of depositing at lower gas temperature were analyzed.

Additional information

Funding

This study was supported by the National Natural Science Foundation of China [Nos. 51966017 and 51606163], the Foundation of State Key Laboratory of Coal Combustion [FSKLCCA1602], and the Xinjiang university doctoral fund (2018).