Circulating Flue Gas Research Articles

Pilot-tests of the coal-fired power plant indirect coupling with multi-source organic solid waste incineration technology

The production of organic solid waste is increasing as the development of society. However, the investment of waste incineration power plant is very high and the thermal efficiency is very low. At the same time, the load of coal-fired power plant is suppressed due to the carbon neutralization policy. Therefore, using the existed coal-fired power plant to co-process the organic solid waste is a feasible method. In this paper, a coal-fired power plant indirect coupling with waste incineration technology based on flue gas circulation was proposed and studied on a 100 kW pilot-test bench. In this technology, the polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) was reduced by a three stages controlling method, which adopts the blending of multi-source organic wastes, high-temperature decomposition and selective catalytic reduction (SCR) catalyst decomposition, simultaneously. The effects of waste incineration coupling, replacement ratio of coal, and flue gas circulation on the combustion and pollutant emission characteristics of the system were studied. The experimental results indicate that the waste incineration coupling has minor influence on the temperature distribution and the toxicity of fly ash of the coal-fired furnace. The NO, HCl, and PCDD/Fs concentrations of flue gas of coal-fired furnace generally decrease as the replacement ratio of coal increases, while the SO2 concentration increases. With the help of three stages controlling method or the flue gas circulation, the PCDDFs concentration of the flue gas of coal-fired furnace can be much lower than 0.1 TEQ ng/Nm3.

Coupled Oxygen-Enriched Combustion in Cement Industry CO2 Capture System: Process Modeling and Exergy Analysis

The cement industry is regarded as one of the primary producers of world carbon emissions; hence, lowering its carbon emissions is vital for fostering the development of a low-carbon economy. Carbon capture, utilization, and storage (CCUS) technologies play significant roles in sectors dominated by fossil energy. This study aimed to address issues such as high exhaust gas volume, low CO2 concentration, high pollutant content, and difficulty in carbon capture during cement production by combining traditional cement production processes with cryogenic air separation technology and CO2 purification and compression technology. Aspen Plus® was used to create the production model in its entirety, and a sensitivity analysis was conducted on pertinent production parameters. The findings demonstrate that linking the oxygen-enriched combustion process with the cement manufacturing process may decrease the exhaust gas flow by 54.62%, raise the CO2 mass fraction to 94.83%, cut coal usage by 30%, and considerably enhance energy utilization efficiency. An exergy analysis showed that the exergy efficiency of the complete kiln system was risen by 17.56% compared to typical manufacturing procedures. However, the cryogenic air separation system had a relatively low exergy efficiency in the subsidiary subsystems, while the clinker cooling system and flue gas circulation system suffered significant exergy efficiency losses. The rotary kiln system, which is the main source of the exergy losses, also had low exergy efficiency in the traditional production process.

Waste oxy-fuel combustion integrated with supercritical CO2 cycle and high-temperature electrolysis technologies for e-methanol production: A feasibility analysis

The municipal solid waste (MSW) oxy-fuel incineration power plant based on the supercritical carbon dioxide (sCO2) cycle integrated with high-temperature electrolysis technology has been developed with the aim of compensating the energy penalties of air separation unit (ASU), reducing the carbon emission and producing renewable methanol by CO2 hydrogenation process. Results shows that the suitable excess oxygen ratio, flue gas circulation ratio and methanol synthesis temperature are 1.1, 0.74 and 240 °C, respectively. The thermal efficiency of proposed system reaches 74.83%, above the that of traditional MSW incineration power plant. In addition, environmental analysis shows that the carbon retention index (CRI) is 97.76%, and the goal of near zero carbon emission can be achieved. Economic analysis demonstrates that the levelized cost of methanol (LCOM) of proposed system is 728.40 $/t, which is more than double the current market price of methanol. However, with the technological breakthrough and expansion of market scale in the further, e-methanol shows economic competitiveness when the cost of water electrolysis unit is reduced to 40 M$/250 MW and carbon emission credit is higher than 70 $/t. This work is innovative, and provides a high-efficiency and sustainable MSW disposal and energy recovering scheme for e-methanol production.

Enhancement of a 300 kWth pilot plant for testing the indirectly heated carbonate looping process for CO2 capture from lime and cement industry

The indirectly heated carbonate looping process (IHCaL) is a promising technology for decarbonizing the lime and cement industry. Advantages of the IHCaL are the synergy with these industries using same solid materials and the avoidance of an air separation unit (ASU), since no technical pure oxygen is necessary in this capture process. Former pilot tests showed the feasibility of the IHCaL for applications in the power plant sector. However, the integration of the IHCaL into cement and lime plants, as well as the usability of spent sorbents as educts in these processes, has not yet been proven in industrially relevant conditions. In this study, the modification of an existing 300 kWth pilot plant for demonstrating the IHCaL process are described, aiming in accelerating the demonstration in an industrially relevant environment for cement and lime industries. A flue gas circulation system and a solid fueling system into the combustor, allowing the heat generation for the calcination with e.g. waste derived fuels, have been designed and installed. Results gained during the operation with the modified reactor configuration, are presented in order to assess the performance of the new components in the framework of the IHCaL configuration. The external combustor was operated while co-firing propane with either dried lignite or waste derived fuels. The carbonator was fluidized with a real flue gas from the external combustor, having CO2 concentrations between 11 and 18 vol-%dry. The results, obtained within more than 200 h of continuous testing with modified reactor configuration, show a good hydrodynamic behavior and adequate reactor performance, while providing a sound basis for further improvement and up scaling of the technology.

Optimization of low-NOx Burner Under the Combined Influence of Multiple Factors

ABSTRACT The influence degree of structural parameters and operating parameters on the low NOx performance of burners was studied by numerical simulation and orthogonal experiment. Excess air coefficient (factor A) and flue gas circulation rate (factor B) were used as operating factors, fuel nozzle diameter (factor C), cyclone blade end deflection angle (factor D), flame-stabilizer inclination angle (factor E), and internal circulation tube diameter (factor F) were used as structural factors, the average temperature (T av), maximum temperature (T max) of the combustion chamber, and NO emission value at the combustion chamber outlet (M NO) were used as indicators. Range analysis and variance analysis were used to analyze the specific influence of the above factors on the indicators. In the studied cases, the most significant factor affecting T av and M NO is the factor B, followed by the factor C. The more significant factor affecting T max is the factor A, followed by the factor C. The coupling of multiple parameters has a significant effect on the distribution of flow field in the combustion chamber. Vortices are produced in all the cases studied. The vortices are basically symmetrical, but the number of vortices varies from 2 to 6. The results show that the burner has good flame stability.

Study on CO–NO Removal Mechanism Based on Sintering Flue Gas Circulation

Study on CO–NO Removal Mechanism Based on Sintering Flue Gas Circulation

Experiment and Numerical Simulation Study of Low-Nitrogen Combustion Technology Inside Small Gas Boiler

Abstract This paper studies different experimental conditions for a 25t/h industrial boiler fueled with nature gas. In the meanwhile, numerical simulation is carried out using the commercial software of fluent. The different excess air coefficients of 1.05, 1.1, 1.15, 1.2, and 1.25 are studied. The different flue gas circulation rates of 5%, 10%, 15%, and 20% are studied compared with that rate of 0. The results show that the maximum temperature of the furnace and NOx emission concentration at the outlet increase first and then decrease with increasing excess air coefficient when flue gas circulation rate is 0, and the peak value of temperature and NOx emission concentration reaches 2071.93 K and 65.21 mg/m3 when excess air coefficient is 1.15, respectively. With increasing flue gas circulation rate, the average temperature of the furnace and the concentration of NOx at the outlet decreased, and the concentration of NOx decreased from 65.21 mg/m3 to 25 mg/m3. The higher the flue gas circulation, the smaller the high-temperature area of the furnace and the lower concentration of O2. However, excessively higher flue gas circulation rate and excess air coefficient can lead to incomplete combustion and lower coefficient. Hence, for optimizing the combustion conditions, the excess air coefficient and the flue gas circulation rate should be within an appropriate range.

Design and optimization of a zero carbon emission system integrated with the utilization of marine engine waste heat and LNG cold energy for LNG-powered ships

Aiming at promoting LNG-powered ships to achieve zero carbon emission, this paper presents an efficient energy utilization system, which can fully recover the marine engine waste heat and LNG cold energy while realizing zero carbon emission. A combination of transcritical CO2 and organic Rankine cycles is adopted to replace the original ship's waste heat generation system. Based on balancing the ship's application constraints and energy efficiency indicators, the existing land air separation system is modified to recycle the products' cold energy and the oxygen-enriched combustion of the main engine is constructed. Then, through a sensible energy gradient design and adjusting the circulating flue gas parameters, the design goals are achieved while meeting the host power. The feasibility of the system's application is assessed through thermodynamic and economic analysis, and the optimal technical parameters are determined after working fluids matching and optimization of sensitive parameters based on the genetic algorithm. The results indicate that the system's CO2 capturing purity, exergy efficiency, net output power and annual net profit are 97.09%, 51.78%, 318.36 kW, US$485,165, respectively, demonstrating significant features such as high effective energy conservation and zero carbon emission.

Process optimization and thermodynamic analysis of autothermal coal chemical looping gasification industrial demonstration system

Chemical looping gasification (CLG) is an innovative clean coal conversion technology with industrial application prospects. The technical reliability of coal CLG (CCLG) in an autothermal state remains to be investigated. To clarify the process characteristics of an autothermal CCLG process, a CCLG autothermal operation system was established based on a CLG industrial demonstration unit. Process modeling of the CCLG reactor system and economizer, air preheater, and other heat exchange units was performed, to ensure autothermal operation of the global CCLG process. The optimal operating parameters of the system were established, the optimal heat exchange network was designed, and the source and distribution of thermodynamic irreversibility were clarified. The results showed that the optimal coal feed flow rate, air feed temperature and flue gas circulation temperature were 437.07 kg/h, 550 °C and 450 °C, respectively. The fuel reactor (FR) flue gas circulation was not conducive to system autothermal, resulting in weakened gasification performance. The optimal heat exchange plan allowed the system to operate without an external heat source. The thermodynamic irreversibility mainly originated from the redox process. The system heat efficiency was 81.63 %, the product exergy efficiency was 78.06 %, the total exergy efficiency was 41.10 %, and the total exergy destruction rate was 55.40 %. Additionally, the FR flue gas circulation caused high exergy loss, resulting in reduced system thermodynamic efficiency.

Production of pre-reduced sinter based on sensible heat updraft of sinter

Utilization of pre-reduction burden in the blast furnace ironmaking process is an important measure for realizing low-carbon operation. In this paper, a new process for the production of pre-reduced sinter based on sensible heat updraft of sinter was put forward. The effects of sinter temperature and reducing gas composition in the pre-reduction cooling section on metallization rate and sieve size distribution of pre-reduction sinter were studied. The results showed that the metallization rate and proportion of 10–12.5 mm particle size of pre-reduction sinter increase with the increase of sinter temperature. When the sintering temperature was 950 °C and the reducing gas was the mixture of H 2 and CO, the metallization rate of the pre-reduced sinter was up to 35.5%. When the sintering temperature was lower than 750 °C, the carbon deposition reaction between H 2 and CO reduces the proportion of 10–12.5 mm particle size of the pre-reduced sinter significantly. The metallurgical properties of pre-reduced sinter with different roasting systems under hydrogen-rich smelting in blast furnace were studied. The results showed that compared to the traditional sinter, the reduction degradation index, reducibility index, and softening-melting properties of pre-reduced sinter were improved, and the permeability and maximum differential pressure of the stock column were reduced, which was beneficial to the improvement of blast furnace production efficiency. Based on the comprehensive effects of sinter temperature and reducing gas composition on the metallization rate, sieve size distribution, and metallurgical properties of pre-reduced sinter, the quality of the pre-reduced sinter was better when the sintering temperature was higher than 750 °C and the reducing gas was a mixture of H 2 and CO. In addition, the new process could organically combine sinter sensible heat utilization, flue gas circulation, and denitrification to form a complete technological process, which had a good development prospect. • Production of pre-reduced sinter based on sensible heat of sinter was proposed. • Metallurgical properties of pre-reduction sinter were systematically studied. • The process can organically combine with flue gas circulation and denitrification. • Process route of production of pre-reduced sinter was schematically mapped.

Numerical Research for MILD Burners with Different configurations

ABSTRACT In the experiment or simulation study of Moderate or Intense Low-Oxygen Dilution (MILD) combustion, scholars used different burner structures. In order to evaluate the effects of MILD burner configurations on combustion, five different burners are numerically studied. In addition, the effects of furnace outlet position are also investigated. The results show that the structure of the burner has a great influence on MILD combustion. The burners with high momentum nozzles deviating from the outlet has a more uniform temperature distribution, a lower Damköhler number (Da) and a higher flue gas recirculation rate , so it has a higher MILD combustion performance. When the oxidant inlet is at the center, more fuel inlets disperse the initial momentum of the fuel, which is not conducive to MILD combustion. When the fuel inlet is at the center, the oxidant inlet should be reasonably arranged to avoid hindering the dilution performance of the circulating flue gas. In addition, the outlet position also has a great influence on the flow in the furnace, and a reasonable outlet also has the effect of optimizing the MILD combustion.

Effect of low-nitrogen combustion system with flue gas circulation technology on the performance of NOx emission in waste-to-energy power plant

NOx as a major gaseous contaminant, reducing NOx emissions has become a pressing concerns. At present, the SNCR process is preferred for waste-to-energy power plants. In this paper, a method of low-nitrogen combustion system with flue gas circulation combined with SNCR was proposed to reduce NOx emissions. A portion of the hot flue gas at the tail of the furnace is extracted as circulation flue gas, and the circulation flue gas is sprayed into the SNCR as tertiary air. The experimental research was conducted in a 500 t/d waste-to-energy power plant. Firstly, the air distribution of the incinerator with the low-nitrogen combustion system is discussed, the circulation flue gas can completely replace the secondary air to reach the boiler rated evaporating capacity and reduce NOx emissions. Next, the supply position of the tertiary air was studied, and the supply position worked best in the upper of SNCR. Finally, the usage of the low-nitrogen combustion system can reduce urea consumption by around 35%. The circulation flue gas extracted in the incinerator contains a small amount of particulate matter. It is a problem to be considered for further industrial application.

Nonferrous metal flue gas purification based on high-temperature electrostatic precipitation

The removal of fly ash from nonferrous metals industry at high temperatures in electrostatic precipitators (ESPs) has attracted wide attention in reducing the industrial pollution. In this study, the removal characteristics of copper smelting (ash A) and nickel smelting fly ash (ash B) under regular and circulating flue gas conditions were investigated through a high-temperature wire-plate ESP. The two kinds of ash have various resistivity ranges at different temperatures, resulting in better removal of ash B than ash A at relatively low temperatures, whereas the opposite result was obtained at 573 K and 673 K. Besides, under the circulating flue gas condition, the number percentage of large particles was decreased while small particles ascended as the increase of the residence time. After sufficient residence time, the particle mass concentration would reach a stable value under 10 mg/m3. Furthermore, the removal characteristics of the two ash under the barbed electrode (DE2) compared with the round rod electrode (DE1) was also conducted. Results indicated DE2 owned a higher removal efficiency for both ash at high temperature no matter under which condition. Combining the electrode optimization by DE2 and the action of circulating flue gas, the ultimate collection efficiency of ash A and ash B could reach 95.65 % and 95.12 % at 673 K.

Catalytic NO Reduction by CO over Ca–Fe Oxides in the Presence of O2 with Sintering Flue Gas Circulation

Flue gas circulation is an important method to reduce NOx emission in the iron ore sintering process. In flue gas circulation, NOx is eliminated mainly through the reduction reaction with C or CO, ...

Experimental Study of NO x Formation in a High-Steam Atmosphere During a Pressurized Oxygen-Fuel Combustion Process.

Pressurized oxy-fuel combustion is considered to be one of the most promising carbon capture technologies due to its low energy consumption and high carbon capture rate. Part of the combustion-supporting environment is composed of circulating flue gas, so the concentration of steam in the carrier gas is higher than that of conventional combustion. However, as an important factor in this technology, steam has not been mentioned in the vast majority of studies. In this study, combustion experiments simulating wet flue gas recycling were performed in a pressurized tube furnace to analyze the effects of the steam ratio (0–40%), oxygen concentration (21–50%), and pressure (0.1–0.6 MPa) on the formation of NOx. The results show that increased system pressure significantly inhibits NO emissions during the oxy-fuel combustion process. Meanwhile, the increase of the injected steam concentration enriches the various radical pool compositions in the carrier gas, inhibiting the formation of NO and N2O. In contrast, the increase of the combustion temperature promotes and inhibits the formation of NO and N2O, respectively, during oxy-fuel pressurized combustion. Moreover, elevated oxygen concentration enhances the oxidation of the carrier gas, leading to an increase in NO emissions.

Effects of oxygen concentration and inlet velocity on pulverized coal MILD combustion

The inlet velocity is an important parameter in the Moderate or Intense Low-Oxygen Dilution (MILD) combustion. Different inlet velocities not only change the flow of the flue gas, but also affect the dilution effect of the circulating flue gas and the temperature distribution of the furnace. In coal MILD-oxy combustion, different oxygen concentrations change the amount of flue gas and inlet velocity when the excess oxygen coefficient is fixed. Therefore, the change of inlet velocity is worthy of attention in MILD-oxy combustion. In this work, the MILD combustion characteristics with different inlet velocities at different oxygen concentrations are discussed by changing the burner diameter. The results show that increasing the inlet velocity suppresses the temperature peaks in both MILD-air and MILD-oxy combustion. When the inlet velocity is fixed, the flame temperature is increased with the O2 concentration. The facilitation of char gasification reaction with increasing oxygen concentration is also partly due to the increase of temperature and char gasification is also partially affected by the O2 concentration. In terms of heat transfer, the inlet velocity has a large effect on convective heat transfer.

The Effects of Coke Parameters and Circulating Flue Gas Characteristics on NOx Emission during Flue Gas Recirculation Sintering Process

The new process of flue gas recirculation, which reduces coke consumption and reducing NOx emissions, is now extensively used. Compared with traditional sintering, the characteristics of circulating flue gas and coke parameters significantly affect the combustion atmosphere and coke combustion efficiency. Based on the actual complex process of sintering machine, this study proposes a relatively comprehensive one-dimensional, unsteady mathematical model for flue gas recirculation research. The model encompasses NOx pollutant generation and reduction, as well as SO2 generation and adsorption. We focus on the effects of cyclic flue gas characteristics on the sintering-bed temperature and NOx emissions, which are rarely studied, and provide a theoretical basis for NOx emission reduction. Simulation results show that during sintering, the fuel NOx is reduced by 50% and 10% when passing through the surface of coke particles and CO, respectively. During flue gas recirculation sintering, the increase in circulating gas O2 content, temperature, and supply-gas volume cause increased combustion efficiency of coke, reducing atmosphere, and NOx content in the circulating area; the temperature of the material layer also increases significantly and the sintering endpoint advances. During cyclic sintering, the small coke size and increased coke content increase the char-N release rate while promoting sufficient contact of NOx with the coke surface. Consequently, the NOx reduction rate increases. Compared with the conventional sintering, the designed flue gas recirculation condition saves 3.75% of coke consumption, i.e., for 1.2 kg of solid fuel per ton of sinter, the amount of flue gas treatment is reduced by 21.64% and NOx emissions is reduced by 23.59%. Moreover, without changing the existing sintering equipment, sintering capacity increases by about 5.56%.

Influence of the operating parameters and nozzle characteristics on flat double-P radiant tube performance

In this paper, based on the structural characteristics of the double-P radiation tube, a novel type of flat double-P radiant tube was designed to improve the heating uniformity of the radiator tube and the heating efficiency of the workpiece. A new three-dimensional computational fluid dynamics modeling of the flat double-P radiant tube was conducted to discuss the heat transfer and combustion phenomenon. The influences of air and gas flow rate, air oxygen content, air consumption coefficient and air preheating temperature on flue gas circulation, surface temperature distribution and radiation power of the flat double-P radiant tube were analyzed and discussed, respectively. The amount of circulating flue gas, ratio of circulating flue gas, surface temperature non-uniformity coefficient, surface temperature distribution and radiation power of the flat double-P radiant tube with different sizes and positions of the burner nozzle characteristics were also studied in depth. The results showed that the fuel speed should be control between 40 m/s and 60 m/s. When the distance between the air nozzle and the fuel nozzle was 50 mm, or the position of the nozzles was 0 mm, the temperature non-uniformity coefficient was the lowest, which were both 0.058.

Performance analysis of a novel W-type radiant tube

In this study, based on the structural characteristics of the traditional W-type radiation tube, a novel W-type radiant tube (N-WRT) with a flue gas circulation structure was developed to improve the heating uniformity of the radiator tube and the heating efficiency of the workpiece. New three-dimensional computational fluid dynamics modeling of the N-WRT was conducted to assess the heat transfer and combustion phenomena. In addition, the effects of nozzle diameter, nozzle location, and circulating tube diameter (all of which affect the main performance of the N-WRT) on the gas flow, temperature distribution, and nitrogen oxide (NOx) emission were analyzed and discussed in detail. Moreover, the amount of heat transfer, ratio of circulating flue gas, surface temperature distribution, thermal efficiency, and NOx concentration of the N-WRT based on different nozzle characteristics were compared. The results showed that the circulation ratio of flue gas increased from 0.47 at D60 mm to 2.2 at D28 mm. The NOx emission decreased most significantly from 100 ppm at D60 mm to 40 ppm at D50 mm. When the circulating tube diameter changed from 180 to 120 mm, the gas velocity at the junction decreased by 12%.

Effects of Temperature and Circulating Flue Gas Components on Combustion and NO<i><sub>x</sub></i> Emissions Characteristics of Four Types Quasi-particles in Iron Ore Sintering Process

Effects of Temperature and Circulating Flue Gas Components on Combustion and NO<i><sub>x</sub></i> Emissions Characteristics of Four Types Quasi-particles in Iron Ore Sintering Process