Search

A 300-MW e anthracite and down-fired boiler equipped with swirl burners, which was retrofitted with the previously proposed deep-air-staging combustion technology to reduce particularly high NO x emissions, still suffered from high carbon content in fly ash (despite this content being slightly lower than that before retrofit) on basis of significant NO x reduction. To comprehensively produce a high-burnout and low-NO x setting, a novel combustion technology was proposed in which relative to the axis of the primary air duct, the axes of the inner and outer secondary air ducts of the swirl burner shift away from the furnace center, and this technology is called an eccentric-swirl-secondary-air combustion technology. The coaxial symmetrical arrangements of primary and secondary air ducts for traditional swirl burners are broken. Full-scale industrial measurements under original, deep-air-staging and eccentric-swirl-secondary-air combustion technologies with respect to different loads (i.e., 180, 250, and 300 MW e ) were carried out to compare and analyze the validity of and improvement offered by the eccentric-swirl-secondary-air combustion technology. Under different boiler loads, especially at low and middle loads, compared with original and deep-air-staging combustion technologies, eccentric-swirl-secondary-air combustion technology markedly extends the penetration depth of coal/air flow and recirculation regions below arches. The thermal resistance between primary coal/air flow and high-temperature flue gas at the furnace center is reduced further, and the ignition of pulverized coal is timelier. The heating gradient in the burner outlet zone is maintained throughout, and the flame fullness in the primary combustion zone increases. The above three aspects contribute to pulverized coal burnout. Similar to deep-air-staging combustion technology, a low-oxygen and strong reducing atmosphere was formed in the primary combustion zone to reduce NO x formation due to the introduction of overfire air. Compared with deep-air-staging combustion technology, for the eccentric-swirl-secondary-air combustion technology, the air staged combustion in the furnace is improved further, and pulverized coal combustion in the primary combustion zone is more well distributed, which is beneficial to further reducing NO x emissions. The results of low-NO x and high-efficiency performance show that compared with the original boiler, NO x emissions and carbon content in fly ash for the boiler with the eccentric-swirl-secondary-air combustion technology are significantly reduced by above 42% and 32.5 to 20.7% at loads of 180, 250 and 300 MW e , respectively. [ABSTRACT FROM AUTHOR]

This paper presents experimental research on cold flow, combustion characteristics, and NO x emissions of a swirl burner with air staging. The aim of the research is to investigate the influence of primary air cone length on the swirl burner performance. Cold flow air experiments on a centrally fuel-rich swirl burner with an over-fire air ratio of 25% were performed, and it was observed that when the dimensionless primary-air cone length (i.e., L p / L i , L p and L i respectively denoting the primary-air cone length in the cold-modeling experiments and inner secondary-air cone length) increases from 0 to 0.75, the diameter and length of the recirculation zone reduces from 0.91 d and 1.51 d to 0.68 d and 0.57 d , respectively. An investigation was conducted in a 0.5 MW laboratory furnace in order to optimize the primary-air cone length of a centrally fuel-rich swirl burner. The flame stability, performance of ignition, and burnout are significantly improved by decreasing the primary-air cone length. The NO x emissions measured at the furnace exit with a cone length L p / L i  = 0 decreased by 50.3% compared to those measured with a cone length L p / L i =  1.0. Based on the evaluation of flame stability, performance of the ignition, burnout, and low NO x emissions, the optimum value of primary-air cone length was observed to be L p / L i  = 0. [ABSTRACT FROM AUTHOR]

To burn anthracite and reduce NO x emissions, a new combustion system was applied to a 300 MW e Babcock & Wilcox (B&W) down-fired boiler that included overfire air (OFA) and a decreased flow area of the inner and outer secondary air ducts of the installed swirl burners. Industrial-scale measurements (adjusting OFA ratios from 15.4% to 22.6%) were conducted to evaluate the overall performance of the retrofitted boiler. The experimental results demonstrated that the new combustion system promoted coal/air flow ignition and combustion stability. When the OFA ratio was less than 19.7%, the influence of the burner secondary air ratio on coal/air flow ignition was greater than that of the recirculation region below the arches. The overall combustion level in the primary combustion zone depended on the oxygen content and the recirculation region in the lower furnace instead of the early or late ignition of the coal/air flow. Oxygen and carbon monoxide concentration measurements in the near-sidewall region revealed that the fullness degree of the coal flame varied under different OFA ratios. Considering both environmental and economic effects, 19.7% was chosen as the optimal OFA ratio, thereby achieving a significant NO x reduction of 47% without increasing carbon content in the fly ash. [ABSTRACT FROM AUTHOR]

A new combustion system has been applied to a 300 MW e down-fired boiler with swirl burners to reduce NO x emissions. The unit provided the introduction of overfire air (OFA) and a decrease in the flow area of the inner and outer secondary air ducts of the swirl burners. Industrial experiments on the retrofitted boiler were performed at different loads. Full-scale measurements of the flue gas temperature distribution in the burner outlet region, the furnace temperature distributions measured by a pyrometer and the local mean gas species concentrations in the region near the sidewall were made at loads of 180, 250, and 300 MW e . The results show that the ignition distance increased with decreasing load, especially as the load decreased from 250 MW e to 180 MW e . At three different loads, the retrofitted coal/air flow could be all ignited in time at a distance in the range of 0.6–1.4 m from the burner outlet. Compared with the original combustion system, the ignition distance of the coal/air flow was significantly reduced at a load of 300 MW e . In addition, at a load of 300 MW e , the temperature of the boiler hopper was much higher than that at loads of 180 MW e and 250 MW e . Compared with the original combustion system, the upper furnace temperature decreased slowly with increasing measurement height at a load of 300 MW e after the retrofit. Measurements of the O 2 and CO concentrations in the region near the sidewall indicate that the fullness degree of the coal flame in the furnace at different loads was different. After the retrofit, the reheat steam temperatures reached the design temperature of 541 °C at loads of 180 MW e and 250 MW e , and the average reheat steam temperatures increased by approximately 13 °C. Compared with the original combustion system, a significant NO x reduction (more than 40%) at different loads was achieved without increasing the levels of unburnt carbon in the fly ash. [ABSTRACT FROM AUTHOR]

To achieve significant reductions in NO x emissions without increasing the levels of unburnt carbon in the fly ash, a new combustion system was applied to a 300-MW e Babcock & Wilcox (B&W) down-fired boiler installed with swirl burners. The unit featured introduced overfire air (OFA) and decreased outlet area of the inner and outer secondary-air ducts of the swirl burners. Full-scale measurements (adjusting the inner secondary-air vane angle to 35°, 45°, and 55°) revealed that the influence of the high-temperature recirculating region under the arch upon the combustion and NO x emission characteristics of the boiler is greater than that of the high-temperature flue gas entrained by the swirl burner itself. The ignition distance of the coal/air flow is reduced by at least 1.8 m compared with that of the original combustion system. For the inner secondary-air vane angle of 35°, the coal/air flow ignites earlier than for the vane angles of 45° and 55°. The measurements of the gas species concentrations in the zone near the sidewall indicates that at inspection port 1, the coal flame of the burners does not spread across the entire furnace cross-section for all three vane angles; however, for the vane angle of 35° the flame is spread across the entire furnace cross-section at inspection port 2. For this optimal (35°) inner secondary-air vane angle, the NO x emissions and carbon content in the fly ash reached levels of 674 mg/m 3 (6% O 2 ), and 11.4%, respectively, achieving a significant NO x reduction of 51.9% without increasing the levels of unburnt carbon in the fly ash. [ABSTRACT FROM AUTHOR]

Abstract: Industrial experiments were performed for a retrofitted 660-MWe full-scale arch-fired boiler. The ignition position of the primary air/fuel mixture flow, furnace temperature and flue gas component after the air heater were measured with different anthracite ratios at loads of 660- and 380-MWe. As the ratio of anthracite increased, the gas temperature decreased in the fuel-burning zones of the C4 and C6 burners, indicating a farther ignition position of the primary fuel/air flow under the arches, the gas temperature of the lower furnace decreased while that of the upper furnace increased, NO x emissions decreased while both the exhaust gas temperature and carbon content in fly ash increased, and the boiler efficiency decreased. At the rated load, an anthracite ratio of 35% was optimal for economical efficiency. At low load, the negative gas pressure fluctuated remarkably, which led to unstable combustion in the furnace. To ensure safe and stable operation of the boiler, a mass ratio of anthracite of 25% is advisable. [Copyright &y& Elsevier]

• 1. A novel fine ash entrained-flow gasification process is proposed; • 2. Co-gasification could meet the liquid slag discharging requirement of gasifier; • 3. Syngas Concentrations were greatly affected by the carbon content of fine ash. Fine ash from gasification is produced in huge quantities, and has the carbon content of around 20–––40%. The treatment of fine ash is urgently needed to be resolved. However, large-scale industrial utilization of fine ash has not yet been realized. The ash content of fine ash is 60––70%. The calorific value of fine ash is usually lower than that of coal. The adiabatic combustion temperature of fine ash gasifier is lower than that of pulverized coal gasifier, and the outlet temperature is also lower. This paper pointed out the reason why the outlet temperature of the entrained-flow gasifier was low when fine ash produced by Ende gasifier was used as the gasification feedstock. A novel process of using the entrained-flow gasifier to utilize the carbon in fine ash was proposed. Fine ash in raw syngas was captured by a bag dust collector, mixed with pulverized coal, and transported to the entrained-flow gasifier. The gasification parameters of the process were obtained. When fine ash was used alone as feedstock, it was difficult to reach the required temperature for the discharge of liquid slag. When fine ash and coal were co-gasified, the outlet temperatures were 1461 and 1529 ℃, which could meet the gasifier's safe operational requirements for smooth discharge of liquid slag. The syngas concentrations were greatly affected by the carbon content of fine ash. The results of the current work provide a useful reference for industrial design and application of fine ash in atmospheric entrained-flow gasifier. [ABSTRACT FROM AUTHOR]

Abstract: Industrial experiments were performed for a retrofitted 660MWe full-scale down-fired boiler. Measurements of ignition of the primary air/fuel mixture flow, the gas temperature distribution of the furnace and the gas components in the furnace were conducted at loads of 660, 550 and 330MWe. With decreasing load, the gas temperature decreases and the ignition position of the primary coal/air flow becomes farther along the axis of the fuel-rich pipe in the burner region under the arches. The furnace temperature also decreases with decreasing load, as does the difference between the temperatures in the burning region and the lower position of the burnout region. With decreasing load, the exhaust gas temperature decreases from 129.8°C to 114.3°C, while NO x emissions decrease from 2448 to 1610mg/m3. All three loads result in low carbon content in fly ash and great boiler thermal efficiency higher than 92%. Compared with the case of 660MWe before retrofit, the exhaust gas temperature decreased from 136 to 129.8°C, the carbon content in the fly ash decreased from 9.55% to 2.43% and the boiler efficiency increased from 84.54% to 93.66%. [Copyright &y& Elsevier]

Abstract: We measured various operational parameters of a 200-MWe, wall-fired, lignite utility boiler under different loads. The parameters measured were gas temperature, gas species concentration, char burnout, component release rates (C, H and N), furnace temperature, heat flux, and boiler efficiency. Cold air experiments of a single burner were conducted in the laboratory. A double swirl flow pulverized-coal burner has two ring recirculation zones that start in the secondary air region of the burner. With increasing secondary air flow, the air flow axial velocity increases, the maximum values for the radial velocity, tangential velocity, and turbulence intensity all increase, and there are slight increases in the air flow swirl intensity and the recirculation zone size. With increasing load gas, the temperature and CO concentration in the central region of burner decrease, while O2 concentration, NO x concentration, char burnout, and component release rates of C, H, and N increase. Pulverized-coal ignites farther into the burner, in the secondary air region. Gas temperature, O2 concentration, NO x concentration, char burnout and component release rates of C, H, and N all increase. Furthermore, CO concentration varies slightly and pulverized-coal ignites closer. In the side wall region, gas temperature, O2 concentration, and NO x concentration all increase, but CO concentration varies only slightly. In the bottom row burner region the furnace temperature and heat flux increase appreciably, but the increase become more obvious in the middle and top row burner regions and in the burnout region. Compared with a 120-MWe load, the mean NO x emission at the air preheater exits for 190-MWe load increases from 589.5mg/m3 (O2 =6%) to 794.6mg/m3 (O2 =6%), and the boiler efficiency increases from 90.73% to 92.45%. [Copyright &y& Elsevier]