Denitrification Device Research Articles

Electro-nitrification coupled with biological denitrification achieves efficient nitrogen removal from rare earth mine ammonia-nitrate wastewater

Nowadays, ammonia-nitrate wastewater has been posed serious environmental hazards. Electrochemical ammonia oxidation (AOR) technology with environmentally friendly and easy-to-operate features has attracted much attention. In this work, a novel anode catalytic electrode (Ni1Cu1Fe0.5-S/Ti) is prepared by a one-step electrodeposition method for electro-nitrification, and coupled a biological denitrification device for the treatment of real ammonia-nitrate wastewater. The unique three-dimensional layered spherical structure of Ni1Cu1Fe0.5-S/Ti electrode has been verified through physical characterization, and electrochemical tests demonstrated that Ni1Cu1Fe0.5-S/Ti electrode gained an excellent current density of 54.48 mA·cm−2 toward to AOR at 0.65 V vs. Hg/HgO as well as good stability for four times repeated electro-nitrification experiments. The optimal experimental operating conditions were obtained by changing electrode spacing, initial NH4+-N concentration, current density and flow rate. Consequently, 97.7 % total nitrogen (TN) removal efficiency of real wastewater is achieved through electro-nitrification coupled with biological denitrification, providing a new perspective technology for ammonia-nitrate wastewater treatment.

Eulerian investigation of the mechanism of Ultra-low NOx emissions from CFB boilers with finer bed material

Industrial practice has confirmed that decreasing the bed material size substantially diminishes nitrogen oxide (NOx) emissions in coal-fired circulating fluidized bed (CFB) boilers. This reduction allows for compliance with the stringent ultra-low emissions standard (NOx < 50 mg/Nm3@6%O₂, dry) proposed by the Chinese government, all without the need for supplementary denitrification devices. Consequently, it becomes essential to delve into the mechanisms through which particle size, as a gas–solid flow characteristic, directly affects the chemical reaction dynamics within the coal combustion process. Due to the difficulty of field tests, this paper employs the Eulerian-Eulerian numerical method suitable for wide particle size distributions to investigate the impact of bed material particle size on gas–solid flow and NOx concentration. Furthermore, the generalized QC-EMMS drag model is utilized to predict the heterogeneous flow across varying particle size conditions. Industrial test data validated the simulation accuracy, with prediction errors of bed pressure drop, temperature, and NOx emission concentration ranging from 5 % to 8.1 %. The analysis revealed that the particle concentration distribution heterogeneity decreases as the particle size diminishes. The variation trends of NOx with particle size exhibit distinct differences between the lower dense phase region and the upper dilute phase region within the bed. For finer bed material particles, the high NOx concentration generated in the dense phase region experiences a more thorough reduction in the dilute phase region. Through the analysis of material concentration and reaction rate, it is believed that this phenomenon is related to the increased catalytic effect of fine ash particles in the dilute phase region, that is, the reduction in particle size leads to an increase in catalytic specific surface area, enhancing NOx reduction, thus achieving ultra-low emissions at the outlet. These research results provide theoretical support for further development of ultra-low emission coal-fired CFB boilers.

Mixing performance of preheated flue gas entering selective catalytic reactor under low loads

The reduced inlet flue gas temperature of the selective catalytic reduction (SCR) denitrification device is a significant problem during the low-load operation of boilers. In this study, an experimental system for turbulent thermal mixing of high and low-temperature flue gases was built to study the thermal mixing method in bypass flue gas technology and the effect of the temperature difference and flow rate variation of high and low-temperature flue gases at low load on the thermal mixing characteristics. The experiments evaluated the thermal mixing characteristics by measuring the temperature field distribution, calculating the inhomogeneity parameters ζT, and investigate the multi-jet distribution characteristics. The investigation was carried out more accurately by combining the simulation results. The results show that the tube wall jet combined with the bottom jet method provides the highest warming effect and possesses the lowest mixing non-uniformity parameter. At the location which is 1.25 times the hydraulic diameter of the duct away from the jet pipe, the temperature difference between the mainstream and the jet drops from 270 °C to 180 °C, causing ζT to drop from 0.46 to 0.37. Decreasing the jet velocity and increasing the main flow velocity promote a decrease in ζT, indicating that the ratio of jet velocity to main flow velocity and the velocity ratio UJUm are crucial factors affecting the thermal mixing characteristics, which directly affects the heat transfer between hot and cold fluids. The ζT decreases from 0.52 to 0.42 as UJUm changes from 3.58 to 2.15. This study provides a reference for ensuring the safe and stable operation of SCR denitrification system during the low-load operation of coal-fired boilers.

Efficiency of the Integrated Nitrogen Removal Device to Remove Ammonia in a Hog House

It is crucial to explore new methods to deal with ammonia pollution in hog barns. In this experiment, ammonia gas generated from the decomposition of nitrogenous organic matter, such as feed and manure in hog barns, was studied. Growing environmental parameters monitored included temperature, humidity, and ammonia nitrogen concentration. For 92 days between March and May, ammonia emissions were characterized by monitoring and collecting the ammonia concentration during the selected time. The results showed that the average temperature in the hog house was 18.2 ± 2.7°C, the humidity was 62.7 ± 0.3%, and the average ammonia concentration range was 17.7∼23.1 mg m−3. The collected ammonia-nitrogen-containing wastewater that entered the denitrification device showed 173, 232, 201, and 280 mgNH4-N/L, respectively. An integrated denitrification device with anaerobic ammonia-oxidizing bacteria as a functional strain was used for denitrification treatment. Through the change of ion concentration in the incoming and outgoing water, an 85.5% average denitrification efficiency was calculated according to the denitrification reaction chemical formula. Thus, the results presented here provide data support for the future use of microbial denitrification equipment to treat ammonia in hog houses.

Denitrification devices in urban boilers change mercury isotope fractionation signatures of coal combustion products.

The installation rate of denitrification devices is accelerating in Chinese urban boilers. Previous studies on pulverized coal-fired boilers without denitrification devices showed that combustion products containing mainly oxidized mercury (Hg) preferably enriched lighter Hg isotopes than feed coals. However, the magnitude of this enrichment becomes less pronounced if denitrification devices are installed. The underlying Hg isotope fractionation mechanisms are still unclear. In this study, three types of urban boilers (two pulverized coal-fired boilers, one circulating fluidized bed boiler and one municipal waste incinerator boiler) all installed with denitrification devices were measured for Hg isotope compositions of their feed fuels and corresponding combustion products. We observed little mass independent fractionation but very significant mass dependent fractionation (MDF) between feed fuels and combustion products. The fly ash and desulfurization products both enriched heavier Hg isotopes than feed coals in three coal-fired boilers, and the enrichment of heavy Hg isotopes increased with sequential removal of combustion products in all boilers. Different from previously suggested kinetic MDF for gaseous Hg0(g)→HgII(g) and gaseous HgII(g)→particulate HgII(p) in coal combustion flue gases, we propose an equilibrium MDF for Hg0(g)↔HgII(g) followed by a kinetic MDF for HgII(g)→HgII(p). This equilibrium MDF most likely occurs during Hg0(g) oxidation in denitrification devices, which enriches heavy Hg isotopes in oxidized products (HgII(g) and HgII(p)) that are then sequestrated in fly ash and desulfurization products. The paradigm shift of MDF in boilers with denitrification devices was further verified by parallel Hg isotope measurement in urban atmosphere particulates. Our study clearly demonstrates that modern coal-fired boilers with denitrification devices have a quite different MDF compared to traditional boilers without denitrification devices. This has important implications for estimating isotope signatures of urban boiler Hg emissions, and for isotope tracing of anthropogenic Hg emissions.

The whole process test and analysis of flue gas SO3 in coal-fired power plant under variable load conditions

Under the current situation of ultra-low emission, it is of great significance to study the formation and removal of SO3 in various equipments of coal-fired power plants. At present, most researches on SO3 in coal-fired power plant focus on the influence of single equipment on flue gas SO3 under a certain load condition. In this research, a 300MW generating unit is tested under variable load conditions to explore the variation law of SO3 in various equipments under variable load conditions. The results show that SO3 is mainly generated in the boiler furnace and SCR denitrification device, and the total removal rate of SO3 is 84.6%. However, the removal efficiency of SO3 in electrostatic precipitators and the wet desulfurization systems shows great differences. Under full load condition, the removal rate of SO3 is 46.8% - 69.8%. When the load changes, the SO3 removal rate changes with the change of load, and the ESP is affected by the load most. The SO3 content in the ash increases from 11.267mg/g under 50% load to 14.763mg/g under 100% load, and such changes are mainly determined by flue gas temperature and flue gas flow.

Causes and Countermeasures for Decrease in Denitration Efficiency and Excessive Ammonia Escape in SCR System of Coal-fired Power Plants

The good operation of the SCR flue gas denitration system in coal-fired power plants is of great significance to the environment. This paper introduces the denitrification efficiency drop and the ammonia escape exceeding standard in the operation process of a coal-fired power plant denitrification device. According to the actual situation of the plant equipment and the field investigation results, the problem is analyzed in depth, and the test measures for the optimization of ammonia injection are proposed. Through experiments, reducing the NOx concentration distribution of the outlet is to improve the denitration efficiency of the SCR system, at the same time reduce the ammonia escape rate of the denitration outlet, and ensure the safety, continuity and economical stable operation of the unit equipment.

An iron-carbon-activated carbon and zeolite composite filter, anaerobic-aerobic integrated denitrification device for nitrogen removal in low C/N ratio sewage.

In this study, we use an anaerobic-aerobic integrated denitrification (Fe/C-ZACID) device with an iron-carbon-activated carbon and zeolite composite filter to remove nitrogen from simulated low carbon-nitrogen ratio (C/N) sewage. The impacts of dissolved oxygen (DO) level, hydraulic retention time (HRT), C/N and nitrate recirculation ratio on denitrification performance were studied. The results show that when HRT was 6 h, DO was 3 ± 0.1 mg/L, influent C/N was 3, and nitrate recirculation ratio was 100%, and removal rates of 95% for ammonia and 85% for total nitrogen (TN) were achieved. A beaker comparison test demonstrated that this synergistic denitrification system included heterotrophic denitrification, physicochemical denitrification, iron autotrophic denitrification and hydrogen autotrophic denitrification, etc. The Fe/C-ZACID device has a high-efficiency nitrogen removal effect for low C/N ratio sewage and strong shock resistance, which provides technical support and a theoretical basis for advanced denitrification of rural domestic sewage.

Establishment of Pollutant Component Spectrum of Atmospheric Emission Sources in Typical Petrochemical Enterprises in Hainan Province

On the basis of investigating the production process of petrochemical enterprises, The components of non-methane volatile organic compounds (NMVOCs) of each emission link in two typical petrochemical enterprises in Hainan Province using adsorption tube adsorption-thermal desorption/gas chromatography were measured and studied. The sampling analysis was conducted on the wastewater treatment and organic waste gas collection device, isomerization device, product refining deodorization device, desulfurization and denitrification device, as well as the unorganized (ambient) air around the factory. Based on this, the NMVOCs component emission inventory and ozone formation potential were studied. The results show that the emission mass concentration of NMVOCs from the above-mentioned petrochemical enterprises in Hainan Province was rather high, at 33-627.9 mg/m3. A total of 21 types of NMVOCs were quantified, of which acetaldehyde, methanol and acetone were the three dominant substances. In addition, as major categories of photochemical pollutants in petrochemical enterprises, aromatic hydrocarbons and olefins were mainly shown as xylene, propylene and butane.

Experimental study on a new enhanced in-situ denitrification device for upgrading domestic wastewater treatment plants

Experimental study on a new enhanced in-situ denitrification device for upgrading domestic wastewater treatment plants

Reason Analysis and Countermeasures of Coal-Fired Power Plant Denitrification Ammonia Injection Valve Blockage

This paper introduces the technological process and operation mode of denitrification and ammonia supply in coal-fired power plants. The Selective Catalytic Reduction (SCR) flue gas denitrification technology of coal-fired power plant is a great significant to environmental protection, which denitrification efficiency is up to 90%. A coal-fired power plant SCR boiler flue gas denitrification device of ammonia controlling valves often block in the winter, and need stopping the device to carry out manual cleaning, that seriously affecting the normal operation of the SCR system and NOx emissions standards. Through the mothed of analyzing of the physical scale components of liquid ammonia quality, environmental temperature, equipment, material, jam, we had found the causes of the problem. Ammonia injection valves plug is mainly made of carbon steel rusting and ammonia supplying of inner tube in oily volatile mixed cause. According to the actual situation of the equipment in the power plant, the operation mode of liquid ammonia evaporator was adjusted, the denitrification ammonia suppling pipeline was purged, the structure of ammonia injection regulating valve was reformed, and the stainless steel-pipeline was replaced. The retrofitting reason of ammonia injection regulating valves and their structure are introduced in detail, which is the key to solve the problem.

Nitrifying–denitrifying filters and UV-C disinfection reactor: a combined system for wastewater treatment

ABSTRACTBiological treatment systems use the natural processes of ubiquitous organisms to remove pollutants and improve the water quality before discharge to the environment. In this paper, the nitrification/denitrification reactor allowed a reduction in organic load, but offered a weak efficiency in nitrate reduction. However, the additions of the activated sludge in the reactor improve this efficiency. A decrease of values from 13.3 to 8 mg/l was noted. Nevertheless, sludge inoculation led to a net increase of the number of pathogenic bacteria. For this reason, a UV-C pilot reactor was installed at the exit of the biological nitrification–denitrification device. Thus, a fluence of 50 mJ.cm-2 was sufficient to achieve values of 20 MPN/100 ml for fecal coliform and 6 MPN/100 ml for fecal streptococci, conforms to Tunisian Standards of Rejection. On the other hand, the DGGE approach has allowed a direct assessment of the bacterial community changes upon the treated wastewater.

Nitrogen Oxides Emissions from Thermal Power Plants in China: Current Status and Future Predictions

Increasing emissions of nitrogen oxides (NOx) over the Chinese mainland have been of great concern due to their adverse impacts on regional air quality and public health. To explore and obtain the temporal and spatial characteristics of NOx emissions from thermal power plants in China, a unit-based method is developed. The method assesses NOx emissions based on detailed information on unit capacity, boiler and burner patterns, feed fuel types, emission control technologies, and geographical locations. The national total NOx emissions in 2010 are estimated at 7801.6 kt, of which 5495.8 kt is released from coal-fired power plant units of considerable size between 300 and 1000 MW. The top provincial emitter is Shandong where plants are densely concentrated. The average NOx-intensity is estimated at 2.28 g/kWh, markedly higher than that of developed countries, mainly owing to the inadequate application of high-efficiency denitrification devices such as selective catalytic reduction (SCR). Future NOx emissions are predicted by applying scenario analysis, indicating that a reduction of about 40% by the year 2020 can be achieved compared with emissions in 2010. These results suggest that NOx emissions from Chinese thermal power plants could be substantially mitigated within 10 years if reasonable control measures were implemented effectively.

Technical Evaluation of the Selection of Flue Gas Purifying Device of Power Plant

The paper introduced several ash separator, desulfurization devices and denitrification devices which were widespread used in thermal power plant in recent years and respectively compared the technicality efficiency of them. It comes to the conclusion that: in the choice of ash separators, bag filter which has more merits than ESP, it has the advantages of reliable operation, simple maintenance, adapting to change in different coal and higher efficiency. In the choice of desulfurization technology, wet limestone-gypsum desulfurization technology is the most mature, which has stable operation and wide adaptability. Therefore, the thermal power plant prefer to it. In the choice of denitrification devices, SCR with low NH3 escape rate and easy to maintain, so it has become the mature and mainstream technology at home and abroad.

The efficiency upgrading of denitrification device using rotating meshed plates reactor focusing the effect of diffusion layer

The efficiency upgrading of denitrification device using rotating meshed plates reactor focusing the effect of diffusion layer