Gas Temperature Deviation Research Articles

Numerical and Experimental Study on Nonlinear Phenomena and Thermal Deviation Control in a 1000 MW Tower-Type Boiler

Numerical and experimental studies were conducted to study the nonlinear phenomena of a 1000 MW ultra-supercritical four-corner tangential pulverized coal boiler. In this paper, (1) a 3D model of a furnace with a symmetrical structure was established to analyze the asymmetric flow phenomenon and multi-solution phenomenon of flow for multiple timepoints under the same boundary conditions. (2) The visual experiment verified that the flow in the furnace also behaved asymmetrically. (3) On the basis of correctly predicting the nonlinear law, the “diagonal start up” method and the “sequential start up” method are proposed. (4) An uneven coefficient of velocity distribution M, deviation coefficient of flue gas mass flow rate Eq and gas temperature deviation coefficient ET are proposed to quantitatively analyze the degree to which the actual tangent circle deviates from the ideal tangent circle. The tangent circle under the “sequential start up” method is the closest to the ideal, which can reduce the thermal deviation of the furnace outlet from 67 K under the “simultaneous start up” method to 41 K. In this paper, the initial steady-state flow field in the furnace is established by using the initial value sensitivity of the nonlinear system through different burner-opening methods, so as to reduce the thermal deviation at the furnace outlet and achieve the purpose of accurate control.

Coupled simulation on flue gas and steam deviation of final reheater in a 600 MW tangentially fired boiler with reversed separated overfire air under different loads

Flue gas and steam deviation of the final reheater is an inevitable problem in the tangentially fired boiler due to the remaining gas spinning at the furnace exit. An in-house one-dimensional process simulation code coupled with comprehensive three-dimensional combustion simulation was adopted to accurate investigate the characteristics of the flue gas and steam maldistribution of the final reheater in a 600 MW supercritical tangentially fired boiler. Firstly, the combustion simulation result was validated by the in-house fire-side heat transfer calculation data, then the effect of boiler loads and reversed separated overfire air (SOFA) deflection angles on the gas temperature deviation, velocity deviation and outlet steam temperature of reheater were conducted. The results showed that the deviation of flue gas temperature and velocity increases as the boiler load decreases. The reversed SOFA deflection angle plays a crucial role in improving the gas distribution under low loads, and the deviation of flue gas temperature and velocity is the smallest when the angle is -18? under 100% boiler maximum continuous rating (BMCR), 75% and 50% turbine heat acceptance (THA), but it is the smallest when the angle is -9? under 35% BMCR load. Moreover, the maximum outlet steam temperature difference between parallel heating surfaces of the final reheater increases from 84.68 K to 106.48 K as the boiler load decreases from 100% BMCR to 75% THA, and it is mainly affected by the flue gas temperature deviation rather than the mass flow rate maldistribution when the deflection angle changes from -9? to -18?.

Efficiency improvement technology of front and rear wall hedging boilers based on combustion optimization and balancing heating surface wall temperature

The ”efficiency improvement technology of front and rear wall hedging boilers based on combustion optimization and balancing heating surface wall temperature” is proposed and applied in a 1000MW unit of a power plant, which effectively reduces the large deviation of the heating surface wall temperature, increases the temperature of the main reheated steam, and improves the economy and safety.This paper introduces the principle of ”efficiency improvement technology of front and rear wall hedging boilers based on combustion optimization and balancing heating surface wall temperature”. It takes 1000MW unit as an example to introduce in detail how to use this technology to adjust combustion. The main steam increased by 6 °C, the reheat steam increased by 1.9 °C, the CO decreased from 2000–3000mg/Nm3 before adjustment to about 200 mg/Nm and the wall temperature deviation of the heating surface was significantly reduced. The technology can be widely used in ultra-supercritical once-through boilers with front and rear wall hedging swirl burners to improve the economy and safety of boilers, and has a broad space for promotion. The mutual restriction relationship between environmental performance and environmental protection, while taking into account the potential safety hazards caused by flue gas temperature deviation, establish a more comprehensive and complete combustion model.

Performance evaluation and thermal analysis of heat pipe flue gas waste heat utilization system

A heat pipe flue gas waste heat utilization system is installed in front of the inlet of the electrostatic precipitator of a boiler to heat the condensate of the steam turbine. In order to understand the performance characteristics of the system, the performance evaluation of flue gas waste heat utilization and transformation is carried out. When the load is 310 MW ∼325 MW, the average flue gas temperature drop of the heat pipe heat exchanger is 26.3 °C. The average flue gas temperature deviation at the outlet of the heat exchanger on the left and right sides of the boiler is 10.9 °C, which reduces the flue gas temperature deviation on both sides by 8.1 °C compared with that before transformation. When the average flow of condensation is 202 t/h, the average temperature rise of condensation is 47.4 °C. Converted to 330 MW load, the flue gas side resistance of heat exchanger is about 151 Pa. By increasing the condensate temperature, the system can reduce the coal consumption of power supply by 1.3 g/(kW h).

Simulation and experimental research on gas temperature deviation on converting to bituminous coals in tangentially lean coal boiler

Simulation and experimental research on gas temperature deviation on converting to bituminous coals in tangentially lean coal boiler

Insights into the causes and controlling strategies of gas temperature deviation in a 660 MW tangentially fired tower-type boiler

• Experiment & simulation on thermal deviation are performed in a tower-type boiler. • Four upper furnace structures are studied to fully reveal the deviation causes. • Properly SOFA horizontal angle of 34–45° is recommended. • SOFA velocity offset with 1.2 of left/right ratio is recommended. • Offsetting SOFA velocity is successfully applied without adverse effects. Gas temperature deviation is a common problem for tangentially fired boilers, affecting the boiler operation safety and the boiler generation efficiency. The gas temperature deviation in the tangentially fired π-type boilers has been well studied. However, the gas temperature deviation in the tangentially fired tower-type boilers has yet to be fully understood. This paper develops insights into the causes and controlling strategies of gas temperature deviation in a 660 MW tangentially fired tower-type boiler with obvious steam temperature deviation by experiment and simulation. Firstly, four upper furnace structures are established to fully reveal the causes of gas temperature deviation. The gas temperature deviation is mainly caused by the flue gas rotation, the heating tubes division, and the suction effect of the induced draft fan. More evident recirculation is observed near the right side than the left side in the platen heater region, resulting in that the flue gas deflects to the left side, and the left side region presents higher temperature. Furthermore, the controlling strategies of gas temperature deviation are studied comprehensively by adjusting SOFA (Separated Over-fire Air) horizontal angle and setting SOFA left–right-side velocity offset. Properly SOFA horizontal angle or enhancing the left-side SOFA velocity may effectively reduce the gas temperature deviation. 34–45° for the SOFA horizontal angle and 1.2 for the SOFA left–right-side velocity ratio are recommended. In the actual operation, offsetting the SOFA left–right-side velocity ( i. e. SOFA air damper opening degree: left side—80% and right side—50%) is successfully applied to reduce the re-heated steam temperature deviation from 18 K to 1 K without bringing adverse effects under the low load. These deep insights may provide useful information to control the steam temperature deviation in the platen heater zone.

Numerical investigation of 700 °C boiler flue gas thermal deviation based on orthogonal experiment

In the present work, computational fluid dynamic (CFD) models have been established to investigate a newly presented flue gas temperature deviation solution on the basis of ANSYS FLUENT16.0 considering a 700 °C tangentially fired pulverized-coal boiler, which confronts with severe flue gas temperature deviation. Orthogonal test method was used to complete the optimization parameters with deflected secondary air swing angle (A), separated over-fire air reverse tangent angle (B), burner upward swing angle (C); and the thermal deviation at the outlet of the furnace as the performance index. The orthogonal test table L9(34) with three levels for each factor was designed. Using the range analysis method and the weight-based matrix analysis method respectively, the significance degree of the influence of different factors and levels on the deviation of the flue gas temperature at the furnace outlet was discussed, the optimal factor and level combination was determined, and the corresponding influence weights were given. It is found (1) Residual swirling flow in the upper furnace causes the flue gas velocity and temperature deviations in crossover pass. (2) The influence degree of various factors on the deviation of the flue gas at the furnace outlet is as follows: separated over-fire air reverse tangent angle > deflected secondary air swing angle > burner upward swing angle, the influence weights of different factors are A = 0.2184, B = 0.5962, C = 0.1560, and the best factor and level combination is A1B3C2. (3) In this test, when the deflection secondary air angle is 0°, separated over-fire air reverse tangent angle is 25°, and the burner upward swing angle is 11°, the flue gas temperature deviation of the furnace outlet section is the minimum, which is 29.297 K, compared with the maximum, the decrease is up to 86.22 K.

Comparison of Experimental Power Reactor Hot Gas Chamber Geometry for Hot Gas Mixing Optimisation

Experimental Power Reactor (Reaktor Daya Eksperimental/RDE) is BATAN’s proposed demonstration nuclear power reactor based on high temperature gas-cooled reactor (HTGR) design. As such, RDE faces an issue concerning severe temperature deviation in its hot coolant gas channel. Hot gas chamber, thus, is a necessary component to reduce coolant gas temperature deviation into acceptable homogenisation level. A preliminary simulation of hot gas mixing in a different hot gas chamber designs using computational fluid dynamics (CFD) method is performed to study the optimum geometry for homogenising the coolant gas. Of the three designs simulated, the “slope” geometry is found to be performing best in homogenising the RDE hot coolant gas. Pressure drop of each design is also discussed.

Sensitivity analysis of several operational parameters on gas temperature deviation in a tangential firing boiler

In this work, an integrated numerical model combining combustion and fluid heating was established for a 660 MW coal-fired boiler. To validate the accuracy of the developed model, related experiment was also conducted, and shows that the relative errors (REs) of several predicted parameters on both flue-gas side and water-steam side of the boiler are less than 7 %, which meets the requirement of analysis. The results indicate that the effect of SOFA tilt angle on gas temperature deviation (GTD) is greatest, and that of SOFA’s proportion follows; while GTD presents a smallest sensitivity to the concentration of O2. This is because O2 concentration mainly affects the average value of the gas temperature, but barely changes its distribution. By contrast, altering SOFA’s tilt angle and its proportion directly varies the shape, location, and area of the high-temperature and low-temperature regions at the entrance profile of the horizontal crossover pass, so these two factors play a more important role in the variation of GTD.

Investigation on the operating characteristics of a 350 MWe supercritical CFB boiler with a polygonal furnace

A 350 MWe supercritical circulating fluidized bed (CFB) boiler with an optimized cyclone separator arrangement and an innovative polygonal furnace was successfully demonstrated. The boiler exhibited excellent uniformity in terms of bed material fluidization, bed temperature distribution, flue gas temperature distribution, and circulating ash temperature distribution. The standard deviation of the cross-sectional bed temperatures in the lower part of the furnace ranged between 12 and 20 °C under four different boiler loads. The bed temperature distribution on the rear wall was more uniform than that on the front wall. The flue gas temperature uniformity among three cyclone separator entrances was better than that among their exits. The flue gas temperature deviation between the middle cyclone separator entrance and exit was higher than that of the other two cyclone separators. The optimized cyclone separator arrangement improved the circulating ash temperature uniformity, and the circulating ash temperature deviation among three loop seals was 12–25 °C. During a continuous 168-hour trial operation, the average emission concentrations of NOx and SO2 were 17.1 mg/m3 and 22.1 mg/m3 (at 6% O2), respectively, which were lower than the Chinese ultra-low emission limits.

Effect of FGR position on the characteristics of combustion, emission and flue gas temperature deviation in a 1000 MW tower-type double-reheat boiler with deep-air-staging

Flue gas recirculation (FGR), which is widely adopted to control the steam temperature of ultra-supercritical (USC) double-reheat boiler, significantly affects the temperature distribution, NOx generation, and flue gas temperature deviation in furnace. This study presents a numerical study on the combustion process in a 1000 MW tower-type double-reheat boiler with deep-air-staging. The effect of FGR injection position on the temperature distribution, NOx emission, and gas temperature deviation was studied and discussed under 100% boiler maximum continuous rating (BMCR), 75% turbine heat acceptance (THA), and 50% THA loads. The numerical model was validated by the in-house thermal calculation code and design parameters provided by the boiler manufacturer. The results show that, under the same load, when recirculating flue gas (RFG) is injected into the furnace from the nozzle blow the burner, the burner zone temperature is lower but the NO generation is higher than the case in which RFG is injected from the nozzle above the burner. Compared to the former, NOx emission of the latter reduced by 12.3%, 31.2%, and 33.8% under 100% BMCR, 75% THA, and 50% THA load, respectively. Both the inlet flue gas temperature and the heat flux of the primary superheater decrease when RFG was introduced from the nozzle above the burner. The case in which RFG is injected from the nozzle above the burner was found to be an applicable and effective method to control the NO generation and regulate the steam temperature of the double-reheat boiler.

Causes and mitigation of gas temperature deviation in tangentially fired tower-type boilers

Gas temperature deviation is a common problem for tangentially fired boilers due to the residual swirling at the furnace exit. It can induce overheating or even explosion of superheaters and/or reheaters tubes. Tower design of tangentially fired boilers is expected to abate the deviation. However, large gas temperature deviation still exists in tower-type boilers. In this study, a numerical method that is validated by experimental data and designed value is used to investigate the gas temperature deviation in a 1000 MWe tangentially coal-fired tower-type boiler, from which the two main causes of the deviation are identified and a new method to mitigate the deviation is proposed. First, the traction of the induced draft fans skews the flue gas flow towards the rear wall, on which the furnace exit is located. Such gas flow skewness becomes aggravated along with the furnace height. Second, the dense panel heaters obstruct the gas flow, which further aggravates the gas flow skewness. Both in combination result in a highly non-uniform gas flow in the panel heaters zone and thus a large gas temperature deviation. In the 1000 MWe tower-type boiler under investigation, the gas temperature deviation between the left side and the right side on the entrance cross-section of the final superheater reaches 120 K. A new method, i.e., adding an arch nose under the furnace exit, is proposed to mitigate the deviation, in which the height of the arch nose is a decisive factor and needs to be carefully determined. A too low arch nose cannot eliminate the skewness of flue gas towards the rear wall while a too high arch nose skews the flue gas towards the front wall. The new mitigation method has been proven effective.

A compatible configuration strategy for burner streams in a 200 MWe tangentially fired oxy-fuel combustion boiler

The configurations of burner streams under oxy-fuel combustion are highly affected by its increased initial oxygen level. In this study, an air combustion and oxy-fuel combustion compatible configuration strategy for burner streams is proposed for a 200 MWe tangentially fired boiler, by aid of numerical simulation. Firstly, to achieve a momentum of primary and secondary streams that is similar to that of air combustion, the tertiary stream is switched-off in oxy-fuel combustion. In addition, the opposing tangential primary stream technology is suggested to reduce the gas temperature deviation in the upper furnace, which affects the quality of the steam and the safe operation of the boiler. For the present study, the appropriate opposing tangential angle is 5°–7° relative to the original primary stream design, and the ratio of opposing tangential momentum flow moment should be controlled at the low limit of 0.8 to decrease gas temperature deviation. To achieve a supported flame by the secondary stream, the momentum of the bottom secondary stream in oxy-fuel combustion should not be less than that in air combustion. The study illustrates for the first time that, the key design features of tangentially fired burners under oxy-fuel combustion. Although there are significant changes in the oxidant volume, oxidant composition, and chemical reaction under oxy-fuel combustion conditions, the design criteria of oxy-fuel tangentially fired boiler, in terms of momentum of the primary stream, momentum of the bottom secondary stream, and momentum ratio and momentum flow moment ratio of the secondary stream to primary stream, are consistent with those under air combustion.

Numerical investigation of air-staged combustion emphasizing char gasification and gas temperature deviation in a large-scale, tangentially fired pulverized-coal boiler

A refined char gasification model, successfully validated in a pilot-scale 20kW down-fired furnace, is now applied to a numerical investigation of the characteristics of the flow, temperature, and species distribution under various air-staged levels of combustion in a 600MWe tangentially fired (T-fired) pulverized-coal (PC) boiler. The simulation results with char gasification show that the CO concentration profile in both the primary combustion zone and the reduction zone is much higher than the corresponding case without the gasification model for deep (burnout air rate, fS=0.42), middle (fS=0.30), and shallow (fS=0.17) air-staged cases. Moreover, this result is in accordance with the tests from an industrial pulverized-coal-fired furnace. It can be concluded that the char gasification mechanism should be considered in the numerical simulation of large-scale air-staged T-fired PC boilers. On the basis of a reasonable prediction of combustion characteristics, the gas temperature deviation in the crossover pass was also depicted under conditions of various air-staged levels. The result of the thermal load curve of the final super-heater panels clearly presents a saddle-type distribution for the existing two peak values. These inherent deviations originate from the residual swirling flow at the furnace exit. More specifically, parameters of swirling momentum intensity (δ) in the furnace and heat flow intensity (Ψ) at the entry of the final super-heater were employed to identify the temperature deviation in degrees.

Influence of vertical burner tilt angle on the gas temperature deviation in a 700 MW low NOx tangentially fired pulverised-coal boiler

In the present paper, computational fluid dynamic modelings were established to research a newly presented re-heat steam temperature deviation solution on the basis of FLUENT 6.3.26 considering a 700MWe tangentially fired pulverised-coal boiler, which confronted with severe flue gas and re-heat steam temperature deviation. The model was solidly validated by grid independence test and comparison with the experimental data obtained from a series of on-site measurements. Upon reliable validation, the model was further used to investigate the forming mechanism of re-heat steam temperature deviation as well as the influence of burner tilt angle on it. The conclusions mainly include (1) Residual swirling flow in the upper furnace caused the flue gas velocity and temperature deviations in crossover pass. For a typical anticlockwise tangential firing system, the flue gas velocity and temperature were lower in left part of crossover pass. The deviation of flue gas further generated the convective heat transfer imbalance of final re-heater, therefore, the temperature deviation of re-heat steam was severe. (2) Tilting the burner upward can effectively reduce the intensity of residual flow as well as the flue gas deviation degree. The +11° tilt angle of burner was relatively optimum considering the flue gas deviation and final re-heater overheating potential. Specifically, the intensity of residual swirl flow dropped 44% with burner tilting upward for +11°. Practical operation of boiler demonstrated that the reheat steam temperature deviation was reduced from 22°C to 10°C in this case. (3) When the tilt angle of additional air (AA) was bias set, the flow field of upper furnace was changed. Consequently, the residual swirl flow intensity and the flue gas deviation were reduced considerably. On-site measurements indicated that the combination of tilting burner upward for +11° and setting the bias of AA tilt angle for 10° can further reduce the re-heat steam temperature deviation to 4°C.

Study of Cold-State Aerodynamic Field Test on the Outlet of 2150t/h Supercritical Once-Through Boiler

The new unit putting into production is the supercritical boiler with a level of or above 600 MW, and most of them take the corner tangential combustion technology. The Long-term operation practice shows that there is gas temperature deviation on all the horizontal flues of boilers, which usually leads to the overheating tube burst of the high-temperature superheater and reheater, thus threats the safe and economic operation of power station. Towards the gas temperature deviation phenomenon that exists commonly in tangentially fired boiler, this paper went on the pertinent cold-state aerodynamic field test on the tangentially fired boilers in one new power plant and studied the airflow velocity at the furnace outlet in eight vertical levels by changing the SOFA horizontally rotating angle. The experiment showed that changing the baffles opening and horizontally rotating angle of SOFA air door could adjust airflow quite well and make it uniform, furthermore, the airflow can reach a basic balance at the biggest anti-tangential angle. This paper has some reference value towards improving the gas temperature deviation problem of tangentially fired boilers.

Field Tests Elimination of the Gas Temperature Deviation in Large Scale, Advanced Low NOx, Tangentially Fired Pulverized Coal Boiler

The developments of coal tangentially fired technology are concisely reviewed and technical details of reducing NOx emissions combined with alleviating the gas temperature deviation are discussed for a newly designed combustion system in pulverized coal boiler.Field tests are carried out to alleviate the steam temperature deviation in the crossover pass of a 660 MW boilers,major attention was paid to the coordination of the rotational momentum required for the residual swirl elimination with the air staged flow necessary for reducing NOx emissions by the changes in yaw angles of separated over-fire air.The effects of nozzle tilt angle for reheater steam temperature regulation,pressure difference of furnace with wind box,flow-rates and yaw angles of over-fire air,are quantitatively investigated on steam temperature deviation in division platen superheaters in the upper furnace,it shows that the gas temperature deviation are eliminated in tangentially fired pulverized coal boiler by field combustion optimization,and keeping low NOx emissions of 449.0 mg / m3and higher combustion efficiency in the meantime.Suggestions of putting steam temperature deviation into automatic control are proposed in large scale,advanced low NOx,tangentially fired pulverized coal boiler.

Numerical Simulation of a 600 MW Utility Boiler with Different Tangential Arrangements of Burners

Corner tangentially fired boilers (CTFBs), in which the burners are tangentially arranged at the corners, have been widely used in the modern thermal power plants in China. However, because of the variation in coal and inherent characteristics of the corner tangentially fired furnace, slagging and high-temperature corrosion on the surfaces of water walls and large temperature deviation at the furnace outlet are often detected during operation. In comparison to CTFBs, wall tangentially fired boilers (WTFBs), including wall-center tangentially fired boilers (WCTFBs) and wall-off-center tangentially fired boilers (WOTFBs), in which the burners are tangentially arranged on the walls and pulverized coal burns stably, are believed to be able to solve the above-mentioned problems. The commercially available software package Fluent is used to simulate the performances of different tangential arrangements of burners, including CTFB, WCTFB, and WOTFB, in the flow and combustion characteristics of pulverized coal in a 600 MW utility boiler. The results show that, in contrast to the CTFB, the high- speed airflow erosion does not happen to the wall tangential burners. In the WCTFB, the high-temperature flame center is lowered, benefiting the burnout of coal particles, the decrease of the carbon content in fly ash, and the reduction of energy loss. In addition, combustion of coal in a local reducing atmosphere is avoided, which reduces the possibility of slagging and high- temperature corrosion. Because of the entrainment effects, uneven wall heating is eased. The flue gas temperature deviation and overheating at the furnace outlet are restrained, benefitted from the symmetric distributions of velocity and temperature. The WCTFB is concluded as the best tangential burner arrangement among the three arrangements studied in this work.

Numerical and experimental investigations on the gas temperature deviation in a large scale, advanced low NOx, tangentially fired pulverized coal boiler

This paper describes the numerical and experimental investigations of the gas temperature deviation in the crossover pass of a large scale, advanced low NOx, tangentially fired pulverized coal boiler. Major attention was paid to the region of the final super-heater where the tube ruptures occasionally had been occurred due to the tube overheating. Computational Fluid Dynamics (CFD) simulation and measurements of gas temperature just in front of the final super-heater showed the gas temperature distribution was biased to the left, lower region of that heater. It was found that this deviation is originated from the residual swirl flow in the upper furnace. To alleviate the gas temperature deviation, the changes in yaw angles of over-fire air have been suggested and the field tests carried out to identify their effects on that deviation. The test showed it is quite effective method to reduce that deviation.

Experimental and numerical study on the flow fields in upper furnace for large scale tangentially fired boilers

Experimental and numerical study on the aerodynamic field has been carried out in a tangentially fired boiler model of a 600 MW unit, with emphasis on the flow fields in upper furnace and the gas velocity nonuniformity in horizontal flue gas pass. The results show that there exists residual swirl intensity of nearly 20% at the entry of the plate zone in upper furnace for large scale tangentially fired boilers. And the flow fields are obviously different in the left and right sides of upper furnace and the gas velocity deviation is large in horizontal flue gas pass. Moreover, some new furnace arch structures and arrangements of division platen superheaters are proposed to effectively alleviate gas velocity deviation in horizontal flue gas pass for large scale tangentially fired boilers. The numerical results agree well with the experimental ones, which can give a good insight into the flow characteristics in upper furnace and a clear explanation on the forming mechanism of flue gas velocity and temperature deviation for large scale tangentially fired boilers.