Boiler Flue Gas Research Articles

Combination of Primary Measures on Flue Gas Emissions in Grate-Firing Biofuel Boiler

Increasingly stringent limits for NOx and SO2 emission are forcing the investigation of new reduction methods. This study was conducted to determine the combination of primary measures, i.e., flue gas recirculation (FGR) and excess air effects on sulfur, nitrogen and hydrocarbon emissions, in boiler flue gas. Experimental research was performed using an experimental, small-scale (20 kW) model of an industrial biofuel boiler. During combustion of sunflower seed hulls at different FGR ratios and incomplete combustion regimes, the composition of flue gas (NO, NO2, N2O, HCN, NH3, SO2, SO3, H2S, CO, and CxHy) was compared, allowing an explanation of the determinants of emission concentration changes to be provided. Increasing the flue gas recirculation ratio in the primary air had a positive effect on reducing NOX and CO with certain organic compounds. However, an opposite effect on SO2 was observed. NOX and SO2 concentrations were found to be approximately 500 mg/m3 and 150 mg/m3 under a regular combustion regime. When the FGR ratio of 50% NOX concentration decreased by 110 mg/m3, the SO2 concentration increased by 60 mg/m3. The incomplete combustion regime reduced NOX concentration by 70 mg/m3, whereas SO2 concentration increased by 100 mg/m3. The influence of primary measures presented an unclear relationship to hydrocarbon emissions, with concentrations not exceeding 18 mg/m3.

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.

To calculate heat losses with flue gases of coal-fired boilers

The article is devoted to solving the problem of increasing the efficiency of solid fuel boilers ’ blast control systems. Existing algorithms for calculating losses with outgoing gases, the value of which determines the efficiency of the boiler blow control system, have significant disadvantages due to either high complexity of calculations or insufficient accuracy of the Siegert formula. The authors of the article experimentally confirmed the limitations of practical application of the Siegert formula in the logic of solid fuel boiler blow control systems. To eliminate the identified shortcomings, a new formula for calculating losses with outgoing gases is proposed, which can be used in solid-fuel boiler blast control systems, which has a sufficiently high accuracy and, at the same time, low computational complexity.

Rapid Cycle Temperature Swing Adsorption Process Using Solid Structured Sorbent for CO2 capture from Cement Flue Gas

Concrete is the most widely used man-made material in the world. The production process of cement, a key component of concrete, contributes significantly to CO2 emissions. Every year, over 4 billion tonnes of cement are produced, releasing approximately 7%-8% of global CO2 emissions [1]. Cement flue gas, processes and raw materials, contain around 16% CO2 and 7-10% O2 and NOX /SOX (100-300 ppm), contingent on the fuel type. High amounts of NOX/SOX are a significant challenge for any carbon capture system. The presence of high O2 concentration in the emitted gas stream can chemically degrade typical amines via production of amides or other oxide derivatives. Therefore, it is crucial to conduct preliminary studies at a pilot scale using real cement flue gas conditions to develop a viable technology and accurate techno-economic analysis for large plants (1 million+ tonnes of captured CO2 per year). Svante (formerly Inventys) has a strong patent portfolio on Rapid Cycle Temperature Swing Adsorption (RC-TSA) processes using structured adsorbents, steam-assisted direct regeneration with fast kinetics (< 1.5 mins cycle time) as an alternative to traditional liquid amine technologies. This project utilized scaled up CALF-20 sorbent, one of the first Metal Organic Frameworks (MOFs) used in an industrial CO2 capture project. This MOF is robust with regards to steam, O2 and acidic contaminant gases (such a NOX/SOX) which make it an ideal candidate for the cement CO2 capture application. This article discusses efforts to scale up the CALF-20 MOF sorbent from lab scale to ton scale. A review of CALF-20 performance after 2300 hrs of VeloxoTherm™ capture process results on a boiler flue gas doped with CO2 and Air to simulate Cement kiln flue gas at 0.1 TPD capacity is presented. Also included are results from Phase 1 of the cement project related to NOX/SOX stability tests on CALF-20 sorbent.

Thermodynamic analysis of coal-fired power plant based on the feedwater heater drainage-air preheating system

As coal-fired power plants are the main source of coal consumption, their energy generation efficiency needs to be improved urgently. One of the main reasons for irreversible energy loss in coal-fired power plants is the mismatched energy levels. To reduce the irreversible energy loss and improve the generation efficiency, the thermodynamic system of the coal-fired power plant needs to be optimized. In this work, a mathematical model of thermodynamic system has been established based on balance principles of mass and energy, which has been validated by design values of a 600 MW coal-fired power plant. Meanwhile, a novel air preheating system based on the feedwater heater drainage has been proposed, to utilize energy from the steam turbine extraction and boiler flue gas. Compared with the conventional schemes, the power supply efficiency of this optimized scheme improved by 1.7%, the coal consumption reduced by 13.1 g/kWh, and the generation cost reduced by 1.85 $/MWh. This work provides an accurate mathematical model for the thermodynamic system of a thermal power plant and an effective optimization method for improving the generation efficiency of a coal-fired power plant.

Analysis of optimal humidification temperature for a flue gas thermoelectric generation system with gas humidification

Using thermoelectric generator to recover the condensation latent heat of flue gas for power generation can not only improve the utilization efficiency of fuel but also recover the moisture in the flue gas, making the exhaust cleaner. Based on the heat transfer characteristics of flue gas condensation, a flue gas thermoelectric generation system with gas humidification is constructed, and the mathematical model is established in this paper. By comparing the power generation performance of dry and wet flue gas, it is found that the output power of wet flue gas can reach 2.24 times of dry flue gas, and the moisture recovery rate of flue gas can reach 65.7%. Through gas humidification, the output power of the system can be significantly improved. In addition, the existence of an optimum humidification temperature is found to minimize optimum module area and maximize power output. The mechanism that gives rise to the optimum humidification temperature is discussed, and the condition for the optimal humidification temperature is pointed out. A thermal resistance model of the thermoelectric generator is employed to deduce the relationship between the optimum humidification temperature and initial parameters of the system. It is found that the variation of flue gas and vapor parameters can make the optimal humidification temperature higher than 150 °C. The moisture content of flue gas, heat transfer coefficient of flue gas, and cooling water temperature are the main factors affecting the optimal humidification temperature. The research results have a certain guiding significance for the deep utilization of wet flue gas and clean operation of boilers.

3D CFD simulation of a 250 MWel oxy-fuel boiler with evaluation of heat radiation calculation

The oxy-fuel process is a promising technology for capturing carbon dioxide from power plants. The fuel, in this case coal, is burned with pure oxygen instead of air in the oxy-fuel process. Since combustion with pure oxygen results in very high temperatures, flue gas must be recirculated and returned to the combustion chamber to lower and control the combustion temperature. This in turn leads to significantly higher concentrations of carbon dioxide and water vapor in the flue gas of the power plant boiler compared to the regular air-fired process, which result in increased radiant heat transfer to the evaporator tubes along the combustion chamber walls. Efficient models are available that can be applied to the numerical simulation of combustion chambers. A widely used model is the Weighted Sum of Gray Gases Model (WSGGM).In this work, the combustion chamber of an oxy-fuel power plant on a demonstration scale with an electrical output of 250 MWel was simulated to compare the results of different gas and particle radiation models. The gas radiation was modelled with the different WSGG model formulations. In addition, the influence of particle radiation was investigated. Therefore the emissivity of the particles were correlated to experimental data. The results corresponds in all cases with the output design of the power plant. The combustion exit temperature is slightly over-predicted for all models and particle properties. It has shown that the particle radiation has a strong influence on the heat wall flux in the burner region where the particle load is high.

Grate-Firing Boilers Grate Movement Impact onto NOx, SO2 Emissions

Measurements of pollutant concentrations in the flue gases of a biofuel boiler show that pollutants concentrations fluctuate by 10-100% and more at short time intervals. Large fluctuations in concentrations hinder the effective application of pollution reduction measures. During the research, flue gas composition measurements were performed in 4 MW, 8 MW industrial biofuel boilers and 20 kW experimental model. The results of the research showed that the change of CO, NO, NO2, SO2, H2S, O2 and particulate matter concentrations is related to the periodicity of the boiler grate movement. During the movement of the grate, the surface of the fuel bed is mechanically disrupted. The different composition of the fuel layers is mixed and this affects the changes in the concentration of combustion products. The clarity of the concentration fluctuations depends on the emissions, the type of fuel and the combustion parameters.

Technology of desorption of dissolved oxygen from water by boiler exhaust gases

A new technology of water degassing based on the use of boiler flue gases as a desorbing agent is described. In the process of burning gaseous fuel, almost all oxygen is consumed, which ensures its absence in the composition of exhaust gases. This makes it possible to use the flue gases of a gas-tight boiler as a desorbent in the process of water deaeration and to avoid using steam. The increasing concentration of carbon dioxide in deaerated water is proposed to be reduced by metering an alkaline agent. The article presents the results of evaluating the mass transfer efficiency of water degassing by the proposed method, as well as the results of calculating the theoretically required specific flow rate of exhaust gases for deaeration.

Neural network system for monitoring indicators of harmful emissions of a ship's steam boiler

he issues of reducing the content of nitrogen and sulfur oxides in the flue gases of steam boilers using the proposed neural network system for monitoring the content of harmful emissions in flue gases are considered.

Application Research on deep recovery and utilization technology of flue gas waste heat of coal water slurry boiler

Coal water slurry boiler has attracted great attention in the field of urban heat system because of its efficient and clean coal combustion. The coal water slurry contains 35% moisture, which makes the waste heat recovery potential of flue gas greater. After the combustion of coal water slurry, the 100°Cunsaturated flue gas becomes 50°C saturated wet flue gas after Wet Desulfurization Process. The Direct Contact Thermal Storage System and Heat Pump technology are used to realize the deep recovery of low-temperature flue gas. The technology has been successfully applied in the 6×70MW coal water slurry boiler of La Shan Heat Source Company. After 120 days of operation, 393000 GJ of flue gas waste heat is recovered, about 23000 tons of coal water slurry is replaced, and 84000 tons of flue gas condensate is recovered. It has good economic and social utility. It is an effective way to recover and utilize waste heat from flue gas of coal-fired boiler, and has a broad application prospect.

PERFORMANCE ENHANCEMENT FOR ROTARY AIR PREHEATER OF A THERMAL POWER PLANT

The corrosion phenomenon is considered the main problems for air preheater in thermal power plant. The boiler flue gas contamination leads to decrease the air preheater performance and increases the maintenance cost, which causes the degradation of the cold end heating elements and thus leads to decrease the heat recovery rate. In this study, an experimental investigation was done for the transient thermal behavior and the pressure drop of the standard regenerative air preheater (Pmatrix) model, evaluating the performance factor, then modifying the air preheater (P+CG) model by changing the plates at the cold end last basket to the coarse gravel media. Since the gravel media have low thermal conductivity and predicted to give a high pressure drop, a new technique was done for the modified air preheater to compensate the low heat transfer rates and reduce the pressure drop in the gravel media by inserting bypass tubes at ratios (i and s), Which, the (i) model represents the inner aperture of tubes for the hot baskets facing to the inner aperture of tubes for the cold basket. While (s) model the insertion the tubes of the hot baskets as a staggered distribution with the tubes for the cold basket. The experimental investigation was carried out for the Reynolds number based on the test duct hydraulic diameter at a range of 24500.

Waste heat recovery from coal-fired boiler flue gas: Performance optimization of a new open absorption heat pump

After wet desulfurization, coal-fired flue gas contains enormous amounts of water and waste heat that can be recovered for energy savings. Compared with the conventional condensation method, the application of an open absorption heat pump (OAHP) has greater potential for latent heat recovery. However, the performance of an OAHP is greatly affected by the heat consumption during solution regeneration. In response to this problem, this study proposes an OAHP system combined with flash evaporation for coal-fired flue gas. Two optimized systems based on the two-stage regeneration open absorption heat pump (TROAHP) and part regeneration open absorption heat pump (PROAHP) systems are proposed. The thermodynamic models of these three systems are established, and the parameters influencing the coefficient of performance (COP), water and thermal recovery efficiencies are evaluated. Compared with the original OAHP system in heating, the OAHP system combined with flash evaporation achieves an improvement in the COP of 0.5% to 2.2%. For the optimized TROAHP and PROAHP, the maximum COPs increase by 4.2% and 17.3%, respectively. The exergy analysis also indicates better exergy efficiencies of the optimized systems than the original one and shows the greatest exergy destruction parts are the regenerator and the condenser.

Study on NOx removal from simulated flue gas by an electrobiofilm reactor: EDTA-ferrous regeneration and biological kinetics mechanism

The regeneration of EDTA-FeII is a key step in electrobiofilm reduction-integrated systems for NOx removal from industrial boiler flue gas. The current and carbon sources are proposed to be the two crucial electron donors for EDTA-FeII regeneration. These parameters strongly influence the reactivity of EDTA-FeII-generated products in the system. Therefore, their effects on EDTA-FeII-NO and EDTA-FeIII reduction and the EDTA-FeII generation mechanism were studied. The results showed that the electrobiofilm method has obvious advantages over biological or electrochemical methods used alone for EDTA-FeII regeneration. Under the optimal conditions at a current of 22.9A m-3 net cathode chamber, the rate of EDTA-FeII regeneration reached 98.35%. The glucose concentration is the primary factor influencing the reduction of both EDTA-FeII-NO and EDTA-FeIII, while the current significantly promotes both processes. Comparison of the Km values of the two substrates indicated that microbial activity was crucial to the reduction of EDTA-FeII-NO, but the biological reduction of EDTA-FeIII had a competitive influence on EDTA-FeII-NO reduction, which limited the abundance and effectiveness of the bacteria responsible for EDTA-FeII-NO reduction in the electrobiofilm system.

Novel metal mesh filter using water-based regeneration for small-scale biomass boilers

Particulate matter emissions are a key issue of modern biomass boilers. A novel gas cleaning method using a metal mesh filter combined with water-based cleaning was developed and tested. The filter was tested batch-wise. Flue gas of a commercial 50-kW boiler was filtered until a pressure drop of 2000 Pa was reached. Afterwards, the filter was regenerated. The initial prototype used ultrasound in order to remove the filter cake from the filter candles. Regeneration was complete and, even after boiler malfunctions producing tar, the filter cake could still be removed. Given the good results, a second cleaning mode, flushing the filter candles with water, was tested. The results were as good as with ultrasonic cleaning. Peak mass collection efficiency was very high with 98 ± 2% (burning wood pellets). However, directly after cleaning, the first layer of filter cake has to be developed. In this initial phase, collection efficiency is low. Service time until maximum pressure drop was reached depended on the gas velocity. Using pellets as fuel, at a gas velocity of 66.6 m/h, 12-h service time was reached and 4.1 g dust was collected per square meter filter surface, while at 33.3 m/h, service time increased to 55 h and collected dust to 13.9 g/m2. Using low-quality wood chips, the raw gas dust loading was much higher but also the maximum loading of the filter was higher with 13.3 to 28.9 g dust separated per square meter. Still, the service time decreased to 3.4 respective 38 h. Peak collection efficiency increased to 99.5 ± 0.8%. The overall collection efficiency including the buildup of the filter cake depends on the gas velocity and fuel. It ranges from 74 ± 4 to 91 ± 1%. The feasibility of the filter concept could be proven, and further development towards a commercial application is in progress. Metal mesh filters with countercurrent cleaning showed a high potential given their simple and robust design, as well as high collection efficiency.

Thermal oxidation of carbon monoxide in air using various self-prepared catalysts

Carbon monoxide (CO) is a very toxic pollutant emitted from wood fired boiler, which is widely used in small and medium enterprises in Vietnam. The treatment of CO containing flue gas faces many difficulties due to the inert property of CO and cannot be removed by traditional adsorption and absorption methods and one of the effective CO treatments is catalytic oxidation. Therefore, we aimed to prepare various catalysts on different carriers for treatment of CO in flue gas, including γ-Al2O3-based metal oxides (Co3O4/Al2O3, Cr2O3/Al2O3, and CuO/Al2O3), CuO–MnOx/OMS-2, and CuO-MnOx/zeolite. The CO removal tests were conducted in a continuous fixed bed reactor in laboratory scale with temperature range of 50 – 550 oC. The characteristics of catalytic materials were then determined by various methods such as Brunauer-Emmett-Teller measurement, X-ray diffraction, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. Results showed that CuO-MnOx/OMS-2 was the best catalyst with high removal efficiency of 98.41% at reactor temperature of 250 oC while gas outlet temperature of &lt; 50 oC, proving the suitability of this material for practical treatment of CO in flue gas. The reaction follows Mars-Van-Krevelen mechanism with the presence of Cu2+-O2--Mn4+ ↔ Cu+-o-Mn3+ + O2 redox in the structure of the material. Moreover, the effect of environmental factors such as flow rate, inlet CO concentration, and catalysts amount on the CO removal efficiency were investigated and noted for designing and operation purposes. Concentration of outlet CO met well QCVN 19: 2009/BTNMT - National technical regulation on industrial emissions for dust and inorganic substances. Therefore, CuO-MnOx/OMS-2 catalyst material could be a potential catalyst for treatment of CO in flue gas of boiler.

LSTM-based soft sensor design for oxygen content of flue gas in coal-fired power plant

To address problems of high cost, complicated process and low accuracy of oxygen content measurement in flue gas of coal-fired power plant, a method based on long short-term memory (LSTM) network is proposed in this paper to replace oxygen sensor to estimate oxygen content in flue gas of boilers. Specifically, first, the LSTM model was built with the Keras deep learning framework, and the accuracy of the model was further improved by selecting appropriate super-parameters through experiments. Secondly, the flue gas oxygen content, as the leading variable, was combined with the mechanism and boiler process primary auxiliary variables. Based on the actual production data collected from a coal-fired power plant in Yulin, China, the data sets were preprocessed. Moreover, a selection model of auxiliary variables based on grey relational analysis is proposed to construct a new data set and divide the training set and testing set. Finally, this model is compared with the traditional soft-sensing modelling methods (i.e. the methods based on support vector machine and BP neural network). The RMSE of LSTM model is 4.51% lower than that of GA-SVM model and 3.55% lower than that of PSO-BP model. The conclusion shows that the oxygen content model based on LSTM has better generalization and has certain industrial value.

Research on removal of NOX, SO2 and PM from flue gas of coal-fired boilers and engineering application

Removal of NOX and SO2 from flue gas by Ozone (O3) oxidation and NaOH absorption was carried out in practical engineering. The effects of the liquid to gas ratio (L/G), the molar ratio of O3 dosage and initial content of NOX (O3/NOX), pH and NaOH concentrations on the removal efficiencies of NOx and SO2 were investigated. In addition, the influences of O3/NOX and voltage on the removal of PM were analyzed. The results show that the NOX removal efficiency increases with the increasing of O3/NOX (0∼2.0), solution pH (4∼7) and L/G (2∼8), while is slightly affected by NaOH concentration (0.05∼1%). The SO2 removal efficiency increases with the increase of L/G from 2 to 8 L/Nm3, but is hardly changed by O3/NOX (0∼2.0), NaOH concentration (0.05∼1%) and solution pH (4∼10). It was found that the outlet concentration of PM (CPM) decreased with the rise of voltage ranging from 0 to 40 kV, however, slightly increases with the increment of O3/NOX at a range from 1.6 to 2.0. The optimal operating conditions can be established when taking running costs and rigorous ultra-low emission standards into consideration. Under the optimal conditions, the removal efficiencies of NOX and SO2 reached more than 75% and 98% respectively, and CPM could be also controlled within 5 mg/Nm3.

Comparison of methods for evaluating particle charges in the electrostatic precipitation of fly-ash from small-scale solid fuel combustion

Small-scale heating units with solid fuels combustion cause a global atmospheric pollution by fine particles. Electrostatic precipitation is suggested as a method of controlling fine particle emissions. The correctness of modelling for precipitation efficiency is defined by the accuracy of the evaluation of particle charges. This work focuses on reviewing the existing particle charging theories in terms of their suitability for practical engineering for the electrostatic precipitation of fly ash particles from the flue gases of small-scale boilers. Charging calculation methods were rated as a function of the particle sizes, external discharge electric field strength, and ion density-time product and compared to published experimental data. Two particle charge rating methods were identified to be suitable for the electrostatic precipitation of such particles.

Key issues and innovative double-tangential circular boiler configurations for the 1000 MW coal-fired supercritical carbon dioxide power plant

When supercritical carbon dioxide (S–CO2) Brayton cycle is introduced into conventional coal-fired power plant, there exists the problems in S–CO2 boiler configurations due to the working medium physical properties’ change. This paper is taking a typical 1000 MW single reheat double-tangential circular boiler as example and investigations focus on the key issues of S–CO2 power plant with traditional boiler configuration from the thermodynamic system, combustion and heat transfer in the furnace, flow and heat transfer in tube. The results show that the studied traditional boiler configuration does not adapt for the 1000 MW S–CO2 coal-fired single reheat power plant for the mismatch heat duty. The effects of boiler size and flue gas recirculation ratio on the heat duty distribution and boiler performance are analyzed. Decreasing the boiler heat duty singly will have a negative impact on boiler performance. The newly developed “partial expansion at the upper zone + double furnace + symmetry flow mode” boiler configurations for the S–CO2 Brayton cycle are presented in order to coordinate the heat duty distribution and boiler performance. The overall net efficiency of the innovative 1000 MW single reheat S–CO2 power plant is up to 48.26%, higher ∼4% than the same-grade traditional steam power plant.