Dunxi Yu

An experimental research on boiler combustion performance

This paper deals with an experimental study on the influence of coal quality on nitrogen oxide (NOx) formation and unburned carbon in fly ash. Three Chinese coals (lean coals and bituminous coal) have been fired in three tangentially full scale boilers (about 300 MWe power units, 1000 t/h boilers) and in two pilot scale test furnaces (the drop-tube furnace (DTF) and the single burner furnace (SBF)). In furnace NOx emission and unburned carbon in fly ash have been measured synchronously with different combustion condition. Identical trends in NOx emission as a function of coal analysis content and excessive oxygen content have been obtained. NOx emission was found to correlate well with the fuel nitrogen content of the coals. Coal quality characteristic, especially ash content, and operation condition have been studied on the influence of furnace burnout performance.

Emission characteristics and chemical composition of PM10 from two coal fired power plants in China

AbstractBy using low pressure impactor, fly ash was sampled in the entrance and exit of the dust cleaning equipments, such as ESP and venturi scrubber, in a 50 and 100 MW utility boiler. The composition, mass size distribution and microstructure of fly ash were measured. A similar bimodal distribution of PM10 was obtained in the studied boilers. The small and large modes are formed at 0˙1 and 4˙0 μm respectively. Based on the comparison of concentrations of Si and Al in the size segregated ash, it is concluded that the ash with size smaller than 0˙377 μm is formed by the nucleation of vaporised mineral components and growth via coagulation and heterogeneous condensation. The results by microstructure measurements showed that the typical microstructure of submicron and coarse PM is spherical, except for a few irregular particles in shape. The collection efficiency of the dust cleaning equipments had a minimum in particle size range of 0˙01–1 μm.

Ash Formation and Fouling during Combustion of Rice Husk and Its Blends with a High Alkali Xinjiang Coal

Limited data from fluidized bed combustion tests have shown that rice husk, a silicon-rich residual biomass, has the potential to be cofired with coal while not inducing unacceptable ash-related problems. However, there is great concern regarding the behavior of rice husk ash under pulverized fuel combustion conditions, where the temperatures are much higher and expected to facilitate fuel interactions. This work, to the authors’ knowledge, is the first to investigate both ash formation and fouling behavior in rice husk firing and its cofiring with coal at a high temperature relevant to pulverized fuel combustion. A Chinese rice husk and a high alkali Xinjiang coal were selected. Combustion tests of individual fuels and their blends (with the share of rice husk being 10% and 20%, respectively) were performed at 1573 K on a laboratory drop tube furnace. Both bulk ash and fouling deposit samples were collected in each test. Techniques including X-ray diffraction (XRD), scanning electron microscopy with ener...

Central Mode Particulate Matter Control by Enhanced Liquid Formation Under the Condition of Blended Coal Combustion

The detailed process of central mode particulate matter (PM) control under the condition of blended coal combustion was studied. Blended coal combustion and mineral heating experiments were carried out in a drop tube furnace at 1373 and 1573 K. The two parent coals were, respectively, rich in Ca/Fe minerals and aluminosilicates. Calcite and kaolin, as the typical minerals in the two coals, were selected and used in the following mineral heating experiment. PMs and bulk ashes were, respectively, isokinetically collected by a low-pressure impactor (LPI) and fiber filters through a water-cooled N2-quenched sampling probe. The elemental compositions of PM collected on each stage of the LPI were analyzed, and the central mode PM was identified by the mass fraction size distributions of refractory and volatile elements. The bulk ashes collected in mineral heating experiment were further detected by X-ray diffraction (XRD). Through analyzing the PMs and bulk ashes generated in mineral heating experiment at different temperatures, the probable reason for central mode PM restraint with increasing temperature was found. Ca aluminosilicates generated by the interactions between calcite and kaolin lead to liquid formation at high temperature. The existing liquidus compositions decrease fine particle concentration through two possible ways: restraining the fragmentation of mineral particles and promoting the scavenging of existing fine particles. The decrease of fine particles at the same time decreases the inorganic vapor heterogeneous condensed on these particles, and hence, the central mode PM formation is restrained at high temperature. During blended coal combustion, an enhanced liquid formation caused by mineral interactions could control central mode PM formation through decreasing the concentration of fine particles.