Ultra-low Emission Research Articles

Mixture temperature-controlled combustion: A revolutionary concept for ultra-low NOX emission

Mixture Temperature-Controlled (MTC) combustion is a novel concept, offering 50% reduction in NOX emission compared to V-shaped flames without a known compromise. The essence of this concept is the central cold air injection, which is also the atomizing medium of the plain-jet airblast atomizer presently to delay fuel–air mixture ignition. Hence, the flame root is not anchored to the fuel nozzle or burner lip, facilitating distributed combustion through a homogeneous temperature field, ultimately leading to reduced NOX emission. The flame was stable up to an equivalence ratio of 0.57, which was followed by blowout as the lean flammability limit was approached. Lean combustion also means reduced flame propagation speed, being another key feature to keep the flame lifted and facilitating homogeneous mixture formation. It was observed that distributed combustion was easier to achieve under leaner conditions. Unlike flameless combustion or exhaust gas recirculation techniques, such as MILD combustion, the oxidizer can be ambient air, offering robust realization in practical applications. The distributed flame is characterized by low flame luminosity and noise. Its acoustic spectrum contains geometry-related components principally. Hence, it is hypothesized that this concept also has a lower tendency to thermoacoustic instabilities than V-shaped flames.

Research on countermeasures against slurry foaming and poisoning of desulphurization system in coal-fired power plants

With the completion of the ultra-low emission transformation of coal-fired generating units, the boiler flue gas bypass has been completely cancelled. Under extreme operating conditions of the boiler, the flue gas must pass through the desulfurization system. Excessive dust and unburned fuel in the flue gas enter the desulfurization slurry in large quantities, causing slurry bubbles or even overflow, and indirectly leading to a sharp drop in desulfurization efficiency. The emission concentration exceeds the standard. Based on the analysis of previous research results, the reasons for the foaming and overflow of the desulphurization slurry are summarized. Through theoretical analysis of various causes, the countermeasures against foaming and poisoning of desulphurization slurry were proposed and the feasibility of countermeasures was demonstrated through actual cases. It points out the preventive measures for bubble poisoning of limestone-gypsum wet desulfurization slurry, which has important practical guiding significance for the ultra-low SO2 emission of the flue gas of the desulfurization system of coal-fired power plants.

Application Prospect of Energy Cyber-Physical Systems in Operation Optimizing of Wet Flue Gas Desulfurization

Limestone-gypsum WFGD is the most widely used to control SO2 emission of coal-fired power plants in China. Although SO2 and a variety of pollutants can be efficiently removed by WFGD. The WFGD has great potential in controlling SO2 emissions and saving energy and reducing consumption due to the influence of operating conditions of coal-fired power plants after ultra-low emissions. In order to explore and analyse the feasibility of e-CPSs in operation optimizing of WFGD. The concept of e-CPSs is introduced systematically. Then the main building blocks of e-CPSs applied to WFGD are described in detail. The existing problems of WFGD are analysed. The operation optimizing method of WFGD based on e-CPSs is introduced. E-CPSs as a new more efficient and reliable intelligent control system. The prospect and benefit of its application in WFGD of coal-fired power plant are discussed in this paper.

Pilot test of the low temperature SCR technology in cement plant

The low temperature selective catalytic reduction (SCR) was used for deep De-NOx in a cement kiln. The SCR pilot plant with a flue gas of 10000 m3/h was designed and constructed. To meet the emission standard, selective non-catalytic reduction (SNCR) technique was carried out and the concentration NOx in flue gas was ca. 270mg/m3. The De-NOx efficiency of SCR decreased with the increase of space velocity and exceeded 77.7% without the ammonia injection. When space velocity was 2500h-1, the de-NOx efficiency of SCR has been further improved by the addition of ammonia injection. After a long time of test, it suggested that the proposed De-NOx technology scheme could stably and effectively control the NOx emission in flue gas, and could meet the ultra-low emission standard.

Feasibility analysis on the coupling power system of municipal solid waste incinerator and coal-fired unit

In this paper, the coupling capacity matching is related to chlorine content in MSW incinerator, denitrification and desulfurization efficiency of coal-fired boiler. Based on an 850 t/d municipal solid waste (MSW) incinerator and a 1000MW ultra-supercritical coal-fired unit, the effect of the dual-chain coupling of steam and flue gas on the coal-fired unit is studied, including corrosion of heating surface in furnace, dioxin emissions, pollutants emission, and fly ash comprehensive utilization. Through the influence research to the coal-fired boiler, it can be seen that influence on the heating surface is small at high temperature. The flue gas environment of coal-fired boiler can also inhibit the synthesis of dioxin and the flue gas of waste incinerator meet to the ultra-low emission standard of pollutants of coal-fired units and the heavy metals content of fly ash of coal-fired boiler is not hazardous waste. After the coupling, the generation efficiency of MSW incinerator can rise up from 20% to 31.6% and the MSW incinerators operate investment reduced by 40% with significant economic benefits. The coupling mode can be generalized of waste incinerator and coal-fired boiler that obtain feasibility for engineering application.

Correlations between Earthquake Properties and Characteristics of Possible ULF Geomagnetic Precursor over Multiple Earthquakes

In this study, we improved and adapted existing signal processing methods on vast geomagnetic field data to investigate the correlations between various earthquake properties and characteristics of possible geomagnetic precursors. The data from 10 magnetometer stations were utilized to detect precursory ultra-low frequency emission and estimate the source direction for 34 earthquakes occurring between the year 2007–2016 in Southeast Asia, East Asia, and South America regions. As a result, possible precursors of 20 earthquakes were identified (58.82% detection rate). Weak correlations were obtained when all precursors were considered. However, statistically significant and strong linear correlations (r ≥ 0.60, p < 0.05) were found when the precursors from two closely located stations in Japan (Onagawa (ONW) and Tohno (TNO)) were exclusively investigated. For these stations, it was found that the lead time of the precursor is strongly (or very strongly) correlated with the earthquake magnitude, the local seismicity index, and the hypocentral depth. In addition, the error percentage of the estimated direction showed a strong correlation with the hypocentral depth. It is concluded that, when the study area is restricted to a specific location, the earthquake properties are more likely to have correlations with several characteristics of the possible precursors.

SO2 Absorption by Multiple Biomass Ash Types.

As the severity of environmental pollution continues to increase and ultralow emission standards are proposed, biomass power plants must implement additional processes to control SO2 emission. Biomass ash can be utilized as a sorbent for flue gas desulfurization because of its strong alkalinity. In this study, the characteristics of SO2 absorption in simulated flue gas using four types of typical biomass ashes were studied in fixed bed experiments. The results showed that the addition of water, the increase in water vapor, and the lower temperature were beneficial for SO2 absorption. The main components of wheat straw ash are KCl and SiO2, cotton stalk ash is rich in K2O and calcium compounds, poplar bark ash has a considerable content of calcium compounds, and corncob ash contains large amounts of KCl and K2O. Alkali substances, such as oxides or carbonates of potassium and calcium, play a crucial role in SO2 absorption. The SO2 removal effect of corncob ash was the best owing to the abundance of potassium oxides. Meanwhile, wheat straw ash performed worst in SO2 removal due to the small amount of K2O and Ca. The desulfurization products were mainly potassium and calcium sulfate.

Primary Carbonaceous Particle Emission from Four Power Plants with Ultralow Emission in China.

Particulate matters (PMs) were collected in stacks from two types of ultralow emission coal-fired power plants by a heated electrical low-pressure impactor (HT-ELPI+), including ultralow emission pulverized combustion technology boilers (ULPCBs) and ultralow emission circulating fluidized bed boilers (ULCFBs). The characteristics of organic carbon (OC) and elemental carbon (EC) in size-resolved particles were analyzed. The ultralow emission technologies significantly decreased the mass concentrations of the carbonaceous content, and the emission concentrations of OC and EC ranged from 5.64 to 17.9 μg/m3 for ULPCBs and from 0.57 to 1.85 μg/m3 for ULCFBs. However, the number concentration of particles was not significantly decreased in the four ultralow emission power plants. The OC in the particle emission of ULPCBs presents a bimodal size distribution with the particle size, while three successive unimodal distributions were observed in the ULCFB emission. Compared to ULPCBs, much more char-EC and soot-EC condensed in the particles, which were collected from ULCFBs. Furthermore, the char-EC/soot-EC in the particle fractions of ULPCBs characterized by the “V” type with the sequence of PM1.0 > PM2.5–10 > PM1.0–2.5, differing from the PM1.0 > PM1.0–2.5 > PM2.5–10 of ULCFBs. The ratios of OC/EC in the stacks from two types of boilers did not show obvious variations in particle size distributions, and the mean OC/EC was far higher than those for non-ultralow emission power plants. Considering the impact of OC1, OC4, and EC1, the ratio of high-temperature organic carbon (HTOC, defined as OC2 + OC3) and soot-EC was studied. The HTOC/soot-EC increased with the increase of RH in the stack, and the highest HTOC/soot-EC values were obtained from ULPCBs (33.0% (PM1.0), 11.4% (PM1.0–2.5), and 23.9% (PM2.5–10)). Meanwhile, strong correlations (0.69–0.85, p < 0.001) between HTOC and soot-EC were obtained, implying that HTOC and soot-EC probably simultaneously condensed in the purification equipment.

Atmospheric emission inventory of hazardous air pollutants from biomass direct-fired power plants in China: Historical trends, spatial variation characteristics, and future perspectives

The agricultural and forestry biomass direct-fired power generation represents an important technology to promote the low-carbon energy transition and agricultural waste reuse in China. In recent years, emissions of hazardous air pollutants (HAPs) caused by the rapid biomass industrialization have attracted increasing attention. To investigate the characteristics of HAPs emitted from biomass power plants in China, a multiple-year comprehensive emission inventory including NOx, SO2, PM, PM10, PM2.5, and trace elements (As, Cd, Cr, Cu, Hg, Pb, Zn) has been established for the period of 2006–2017. As a result of the emission standard (GB13223-2011), emissions of conventional HAPs have declined since 2014. The results show that national total emissions in 2017 were estimated at 29,516.0 t of NOx, 14,192.1 t of SO2, 4100.7 t of PM, 2353.9 t of PM10, 1630.6 t of PM2.5, 3057.2 kg of As, 1622.8 kg of Cd, 8285.8 kg of Cr, 54,443.4 kg of Cu, 132.9 kg of Hg, 66,325.8 kg of Pb, and 175,587.9 kg of Zn, respectively. The majority of HAPs emissions have been concentrated in eastern, northeastern, and central areas of mainland China. Shandong, Heilongjiang, and Anhui represent the top three provinces with the highest HAPs emissions from 2012 to 2017. Besides, the future emissions in 2025 and 2035 under the ultra-low emission policy are predicted with scenario analysis.

Prospects for the Low Pollutant Emission Control of Circulating Fluidized Bed Combustion Technology

With the pollutant emission standards becoming increasingly stringent and considering the pressure of carbon neutral by 2060, the low pollutant emission potential of circulating fluidized bed (CFB) combustion technology needs to be further exploited, thus to promote the market competitiveness of CFB boilers; this is critical for the clean and efficient utilization of coal as well as for the energy transformation in China. In this article, we summarize the pollutant emission characteristics of CFB combustion, and review the development of major technologies for CFB boiler emission control. Based on the energy development strategies and corresponding policies in China, development suggestions are proposed for reducing pollutant emission of the CFB combustion technology. The most significant approach is to push the limits of original pollutant emission for CFB combustion by re-specifying the fluidization state and through in-furnace combustion adjustment, while the boiler thermal efficiency should be ensured. For the long-term development of coal energy, the new-generation CFB combustion technology with ultra-low emission should be researched and developed while combining with technologies such as supercritical/ultra-supercritical, intelligent operation, carbon capture, utilization, and storage, and energy storage technologies. The existing CFB boilers with small or medium capacity should also be upgraded. Considering the fuel flexibility of CFB combustion, biomass power generation should be promoted to realize low-cost and high-efficiency consumption of low-heat value fuels, urban refuse, industrial wastes, etc. The peak load regulation capacity and low pollutant emission property of the CFB boilers should be promoted to improve operation flexibility and renewable energy consumption. Moreover, the desulphurization ash produced in CFB combustion should be comprehensively utilized, and the N2O emission problem is also significant. The pollutant emission standards and related policies need to be formulated from an overall perspective to guide the healthy development of the energy industry.

Computational modeling of flow field in boiler before and after urea injection under different conditions

In order to achieve ultra-low NOx emissions, the effects of total excess air coefficient, air coefficient in main combustion zone, blended-coal combustion, and ammonia-nitrogen molar ratio on a 330 MW coal-fired boiler combustion were studied by numerical simulation. The results show that the velocity field and temperature field in the furnace have synergy, the better the synergy is, the faster the temperature rises, and the more NOx it generates. Compared before and after urea spraying, the NOx concentration decreased with the decrease of the total excess air coefficient, the optimum total excess air coefficient is about 1.15, and the denitrification rate is as high as 76.2%. The smaller the air coefficient in the main combustion zone is, the smaller the NOx concentration is. The optimum air coefficient in the main combustion zone is about 0.92, and the denitrification rate is 85%. After urea injection, the denitrification rate of high volatile coal combustion is higher than that of low volatile coal combustion, and the reasonable blending mode of coal can reduce NOx emissions. The larger the ammonia-nitrogen molar ratio is, the lower the NOx concentration is. When the ammonia-nitrogen molar ratio is greater than 2, the amount of ammonia escape at the flue outlet exceeds the standard. When the ammonia-nitrogen molar ratio is less than 1, the NOx concentration at the flue outlet is greater than that before urea injection. The optimal ammonia-nitrogen molar ratio is about 2.

The impact of London traffic restrictions: Effective but insufficient

Short and long-term exposure to air pollutants has been shown to be strongly associated with mortality and morbidity. This is a particular problem in big cities, largely due to traffic. In response, low emission zones (LEZ) are becoming more common in cities all over the world. London introduced its Toxicity Charge in 2017 and the more restrictive Ultra Low Emission Zone (ULEZ) in 2019. In this paper, we evaluate the effectiveness of these policies on NO2 levels. Our results show that NO2 levels significantly dropped in the roadside stations, especially after the implementation of the ULEZ. Similarly, at the background stations, the Toxicity Charge and the ULEZ had a similar, smaller effect. Furthermore, our results suggest that there was a positive spillover effect associated with both traffic policies, which was, however limited to the area within the North and South Circular Roads. In any case, while these policies have been useful to comply with the recommended limits on NO2 levels, alleviating Londoners’ health problems, they need to be enhanced since some stations still are above those limits.

Developing a Compact Particle Collector by Integrating a Wet Electrostatic Precipitator and an Inertia Mist Eliminator

ABSTRACT Wet electrostatic precipitator (WESP) is a reliable alternative to realize the ultra-low emission of particulate matter from coal-fired power plants. This work proposes to develop a compact particle collector by integrating a WESP and an inertia mist eliminator (IME). The particle collection efficiency and charging characteristics of the WESP were analyzed to determine the potential for compact design. Results show that the WESP was easy to achieve a collection efficiency of 95% for both pin and wire electrodes. Particle charging can still be guaranteed with short WESP length and high voltage, indicating the particle charging was sensitive to electrical parameters. Charges carried by the escaping particles acted as a bridge between the WESP and the IME. The collision enhanced by particle charging can lead to an improvement in overall efficiency and charge loss. The particle charge loss of the particle sized 7.29 μm was 22.6% and 29.4% for the one and two stage IME, which coincided with the efficiency enhancement of WESP. The collection efficiency significantly decreased as the WESP size decreased, but the collection efficiency can be enhanced by the combination with IME. The 6-wire WESP enhanced by one-stage IME can be considered the optimal combination because the WESP size can be shorten by 40% while maintaining a similar efficiency. The research findings are beneficial for the retrofit of air pollution control devices in limited space.

Study on SO3 emission test of typical ultra-low emission coal-fired units in western region of Inner Mongolia

To study the effect of types of boilers, pollutant treatment facilities and coal quality on SO3, emission concentration of SO3 was tested by controlled condensation method for seven typical ultra-low emissions coal-fired units in western region of Inner Mongolia. The test results showed that the SO3 emission concentration of all units ranged from 0.36 mg/m3 to 2.04 mg/m3, much lower than 5 mg/m3, so there was no need to add SO3 removal facilities. For the units burning the coal of same sulfur content, which adopt LLTESP and WESP has the lower SO3 emission concentration. The SO3 emission concentration can also be controlled at a lower value when SNCR and double-tower double-cycle WFGD technology are adopted in the unit burning medium-high sulfur coal.

Estimating the effectiveness of vehicle emission regulations for reducing NOx from light-duty vehicles in Korea using on-road measurements

The South Korean government has reinforced emission regulations for newly manufactured vehicles to reduce air pollution from automobiles. The government has applied different emission regulations depending on the fuel, following the regulations set for gasoline vehicles in California, USA, and those set for diesel vehicles in the European Union (EU). In this study, the on-road NOx emissions of 109 light-duty vehicles in South Korea were measured on roads in Seoul and the surrounding metropolitan area using a portable emissions measurement system (PEMS). The results were then analyzed to evaluate the effectiveness of the emission regulations introduced in Korea for NOx reduction. The average on-road NOx emissions for the Euro 5 and Euro 6b diesel vehicles were approximately five times higher than the laboratory emission limits set by the EU regulation. The NOx emissions also showed significant variation depending on the driving parameters, such as the driving dynamics and the ambient temperature. From the Euro 6d-TEMP regulation in which the real driving emissions-light duty vehicles (RDE-LDV) regulatory package was implemented, the average on-road NOx emissions from the diesel vehicles were controlled within the laboratory emission limits, but were still higher than those of the gasoline vehicles. Despite the absence of the RDE-LDV regulations, the average on-road NOx emissions of the gasoline vehicles that had ultra-low emission vehicle (ULEV) and super ultra-low emission vehicle (SULEV) standard certifications were controlled within the laboratory emission limits set by the FTP-75, regardless of the various driving parameters. The results of this study show that it is necessary to include a wide range of driving conditions in emission certification test procedures, such as RDE-LDV, and enhance the regulatory measures that enable manufacturers to maintain the effectiveness of emission control systems.

Emission characteristics of condensable particulate matter and sulfur trioxide from coal-fired power plants

Non-criteria air pollutants, namely, sulfur trioxide (SO3) and condensable particulate matter (CPM), are attracted more attention due to the non-negligible emission. In this work, the migration and emission characteristics of SO3 and CPM were investigated in two typical coal-fired power plants using the isopropanol absorption method and the dry impinger method, respectively. One of the power plants was equipped with two-stage wet flue gas desulfurization (WFGD) and the other one was self-generation power plant using Zhundong coal equipped with one-stage WFGD. The mass concentrations of SO3 and CPM were measured at the inlet and outlet of the air pollution control devices. To further understand the removal characteristics, the chemical compositions in organic and inorganic fractions of CPM were analyzed. Based on the measurement data, the emission factors of CPM and SO3 were calculated. The final emissions of SO3 range from 2.16 to 2.29 mg•Nm−3 and the emission factor is 0.024–0.040 kg/(t of coal). The stack emissions of filterable particulate matter all meet the ultra-low emission standard and are less than 5 mg•Nm−3. However, CPM emissions all exceed 10 mg•Nm−3 and account for more than 85% in total particulate matter. CPM concentrations are notable and the emissions should not be ignored. In both power plants, WFGD and wet electrostatic precipitator can reduce the emission of organic fraction in CPM; while one-stage WFGD has negative effect on the mitigation of inorganic fraction in CPM with the concentrations of water-soluble ions NH4+, SO42- and Cl− increasing by 41.37%, 52.22% and 91.73%, respectively.

China's COVID-19 lockdown challenges the ultralow emission policy

China's COVID-19 lockdown closed many of its air pollution sources and created an unprecedented clean-air scenario. However, air pollution remained significant, arousing questions about its causes and reawakening debate over the country's ultralow emission (ULE) policy. Here, we analyze the characteristics and causes of China's air pollution during this period to assess ULE's effectiveness. We find that the concentrations of fine particles (PM2.5, PM10), NO2, and CO in Wuhan decreased significantly during the lockdown. However, O3 and SO2 concentrations increased, though to different extents. The ULE policy promoted emission reductions, but emissions from coal-fired industries (e.g., thermal power and steel) remained the fundamental source of air pollution and appeared to have been underestimated in previous researches. In contrast, emissions from construction and transportation and the ULE's effectiveness may have been overestimated. The characteristics of air pollution in southern and northern cities support these conclusions. Therefore, it is necessary to strengthen the adjustment of China's energy and industrial structures, and identify more suitable mitigation measures for each region's characteristics. It is also necessary to strengthen the synergistic governance of pollutants and promote emission reduction technologies.

Influence Study of Ammonia-Nitrogen Molar Ratio on SNCR Denitrification

The influences of different ammonia-nitrogen molar ratios (Normalized Stoichiometric Ratio, NSR) on the NOx emission concentration, ammonia escaping amount, and selective non-catalytic reduction (SNCR) denitrification efficiency were measured through a field test. The results show that with the increase of NSR, the NOx emission concentration changes little, the ammonia escaping amount is gradually increased, and the SNCR denitrification efficiency is basically kept stable after increasing firstly. In full consideration of the ultralow emission limit and reducing agent consumption, it is believed that 2.01 is the optimal NSR value under the test load.

China's retrofitting measures in coal-fired power plants bring significant mercury-related health benefits

Summary China has implemented retrofitting measures in coal-fired power plants (CFPPs) to reduce air pollution through small unit shutdown, the installation of air pollution control devices (APCDs), and power generation efficiency improvement. The reductions in highly toxic Hg emissions and their related health impacts by these measures remain poorly understood. Here, we evaluated the health benefits of reduced Hg emissions via retrofitting measures during China's 12th Five-Year Plan (2011–2015) by combining plant-level Hg emission inventories with the China Hg Risk-Source-Tracking Model. We found that the measures reduced Hg emissions by 23.5 tons (approximately 1/5 of that from CFPPs in 2010), preventing 30,484.77 total points of intelligence quotient decrement and 114 deaths between 2011 and 2015. These benefits were dominated by CFPP shutdowns and APCD installations, and nearly 50% of provincial health benefits were attributable to Hg reductions in other regions. We suggest that Hg control strategies should consider various factors, such as CFPP location, population density, and trade-offs between reductions in total Hg and in Hg2+.

Study on energy-saving operation technology of environmental protection facilities of ultra-low emission coal-fired unit

The operation optimization of low nitrogen combustion, denitrification and desulfurization facility of a 335 MW coal-fired unit met ultra-low requirements has been conducted in order to lower energy and material consumption. The operation mode of low nitrogen combustion with consideration of boiler efficiency and furnace exit nitrogen oxides concentration is determined. The boiler efficiency is 0.4% higher and the power supply coal consumption is reduced by 1.4 g/(kW h). The furnace exit nitrogen oxides concentration is reduced by 16 mg/m3. The SCR outlet nitrogen oxides concentration distribution uniformity is improved by ammonia spraying optimization, and the response speed and control quality of denitrification automatic control is improved by control logic optimization, therefore the liquid ammonia consumption is decreased by 0.13 kg/(104 kW h). The combination methods of absorber slurry pumps have been improved and the total mean running current of the pumps is lowered 33 amperes. The effect of limestone slurry feed automatic control is improved. The limestone slurry flow is reduced by 18.7 kg/(104 kW h).