Overfire Air Research Articles

Experimental evaluation on co-combustion characteristics of semi-coke and coal under enhanced high-temperature and strong-reducing atmosphere

Co-combustion of coal pyrolysis semi-coke and coal can be a promising approach for large-scale utilization of the high-grade carbon-based product with ultra-low volatiles content. In this paper, experimental evaluation on co-combustion characteristics of semi-coke and coal was conducted with a focus on combustion and NOx formation characteristics using a high-temperature (up to 1873 K) vertical tandem-type drop-tube furnace. A novel technology of enhanced high temperature and strong reducing atmosphere (HT&SRA) was proposed, and the effects of fuel type, blending ratio, blending method were evaluated. More NOx and unburned carbon were produced during combustion of semi-coke than bituminous coal. The combustion characteristics of semi-coke were improved by the addition of more bituminous coal due to interaction. The in-furnace blending method had advantage over out-blending method on the improvement of combustion and NOx reduction. Both NOx formation and unburned carbon first declined and then increased with the delayed injection of bituminous coal. When the stoichiometric ratio in primary zone (SR1) is lower than 1.0, the higher temperature (T1) led to more NOx formation, which was contrary in the oxidizing atmosphere. The parameters of T1 = 1873 K and 0.6 ≤ SR1 ≤ 0.8 were recommended as HT&SRA for the co-combustion. The enhanced HT&SRA was obtained by the approach of increasing oxygen fraction of secondary air (Osa) with the reasonable SR1, and the NOx formation was fortunately further reduced. The parameters of SR1 = 0.8 and Osa = 84% were suggested for the co-combustion. The approach of increasing oxygen faction of over-fire air is an alternative to further improve combustion characteristic due to the acceptable increase of NOx formation. The oxygen fraction of primary air should be limited to 42% to avoid excess NOx formation.

Research and Adjustment of Temperature Deviation on Heating Wall of Front and Rear Wall Opposed Coal-fired Boiler of 1000WM Unit

No.2 boiler is designed by Dongfang boiler group Co., LTD, and is ultra supercritical parameter boiler with variable pressure. In order to alleviate the side wall temperature deviation and to reduce the maximum wall temperature of super-heater, the total air volume alteration test, external secondary air damper alteration test, over-fire air alteration test and the shrinkage adjustment is performed. The test results show that oxygen increase and shrinkage adjustment can improve the deviation of wall temperature and steam temperature. After increasing oxygen, plate super-heater wall temperature deviation reduced by 26 °C, and its outlet steam temperature deviation reduced by 14 °C. After shrinkage adjustment, plate super-heater wall temperature deviation reduced by 34 °C, and the wall temperature difference of final super-heater reduced from 50 °C to 25 °C, the wall temperature of side B plate super-heater reduced by 25 °C.

Optimization of Air Distribution to Reduce NOx Emission and Unburned Carbon for the Retrofit of a 500 MWe Tangential-Firing Coal Boiler

The use of separated overfire air (SOFA) has become a standard technique of air staging for NOx reduction in the coal-fired boiler and can also be applied to existing boilers by retrofit. This study was to optimize the air distribution for the proposed SOFA installation in a 500 MWe tangential-firing boiler that has 20 identical units in Korea. Using computational fluid dynamics (CFD) incorporating advanced coal combustion submodels, the reference case was established in good agreement with the design data, and different flow ratios of burner secondary air, close-coupled OFA (CCOFA), and SOFA were evaluated. Increasing the total OFA ratio effectively suppressed NO formation within the burner zone but had a negative impact on the boiler performance. With moderate air staging, NO reduction became active between the CCOFA and SOFA levels and, therefore, the OFA distribution could be optimized for the overall boiler performance. For total OFA ratios of 25% and 30% with respective burner zone stoichiometric ratios of 0.847 and 0.791, increasing the SOFA ratio to 15% and 20%, respectively, was ideal for decreasing the unburned carbon release and ash slagging as well as NO emission. Too high or low SOFA ratios rapidly increased the unburned carbon because of inefficient mixing between the strong air jets and char particles. Based on these ideal cases, the actual air distribution can be adjusted depending on the coal properties such as the ash slagging propensity.

The role of pulverized coal drying temperature in fly ash carbon content and slagging of a tangentially coal-fired boiler

The purpose of this paper is to investigate the effect of the pulverized coal drying temperature on fly ash carbon content and slagging of a 1000 MW unit coal-fired boiler. The pulverized coal was dried at three selected temperatures of 25 °C, 75 °C and 110 °C, and the moisture and porosity of the pulverized coal particles were measured. Based on the porosity range obtained from the measurement, 3-D steady numerical simulation of combustion in tangentially coal-fired furnace was conducted by use of Fluent Software. It was found, (1) The porosity, specific surface area and pore diameter of pulverized coal particles increase with the increase of pulverized coal drying temperature. (2) The increase in the pulverized coal porosity led to the lower flame center and the lower temperature in over-fired air zone. (3) The fly ash particle capture rate and the fly ash carbon content decreased when the pulverized coal porosity increased. (4) The slagging of water wall presents a downward trend with the growth of the pulverized coal porosity. The slagging problem is well resolved in a power plant after applying the strategy of heating up pulverized coal when burning highly slagging tendency coal.

Numerical Investigation of Over Fire Air (OFA) Effect on Flow Characteristics, NOx Combustion and Emission in a 600 Mw Tangentially Fired Pulverized Coal Boiler

One of the coal-fired air emissions in boilers is NOx, which has a significant impact on the environment and could cause acid rain, ozone formation, visual impairment and health problems in humans. There are several technologies to reduce and control the formation of NOx emissions, which one of these technologies is the use of over-fire air (OFA). In this research will observe the effect of overfire air (OFA) usage and analyze by numerical 3D modeling method using computational fluid dynamics (CFD) in Paiton 9 power plant boiler and analyzed for 5 (five) OFA damper opening variations, i.e 0%, 25%, 50 %, 75% and 100%. This research will analyze several factors that have significant influence on NOx emission formation, that are: the temperature distribution of the boiler during the combustion process, the distribution of nitrogen oxide (NO) and carbon dioxide (CO2), direction of flue gas flow and trajectory of coal particles and residence time indicating the length of time of burning. The results showed that the lower the flame temperature, the smaller the formation of NOx; the smaller the oxygen content in the combustion process, the smaller the formation of NOx; the shorter the residence time of combustion products in the high temperature zone the smaller the formation of NOx, and the smaller the nitrogen content in coal, the smaller the formation of NOx .

Numerical Investigation of Over Fire Air (OFA) Effect on Flow Characteristics, NOx Combustion and Emission in a 600 Mw Tangentially Fired Pulverized Coal Boiler

Numerical Investigation of Over Fire Air (OFA) Effect on Flow Characteristics, NOx Combustion and Emission in a 600 Mw Tangentially Fired Pulverized Coal Boiler

Numerical study on the effect of separated over-fire air ratio on combustion characteristics and NOx emission in a 1000 MW supercritical CO2 boiler

As an advanced power generation system, supercritical CO2 (S-CO2) coal fired power plant has advantages of high electric efficient and compact system layout. In this paper, the coal combustion characteristics and NOx formation in coal-fired S-CO2 boiler has been explored by numerical simulation. The boiler wall temperature distributions were determined according to the 1/8 partial flow strategy for S-CO2 coal-fired power plant. The effect of SOFA ratio on the gas flow field, the gas temperature, the species concentration including NOx distribution was investigated. The results show that the SOFA ratio has a great influence on the coal combustion process and NOx formation. With the increase of SOFA ratio, the O2 concentration decreases in the main coal burning zone, a higher CO concentration can be found. A lower gas temperature zone in the main burning zone and a lower NOx emission near the furnace outlet can also be observed with a higher SOFA ratio. The results presented promote a better understanding of the NOx formation characteristics and would be benefit for the NOx control in coal-fired S-CO2 boiler.

Numerical investigation of combustion optimization in a tangential firing boiler considering steam tube overheating

A comprehensive numerical study of the combustion optimization of a 660-MW tangentially fired boiler under the constraint of steam tube overheating is presented. To obtain the chemical products and the heat flux at the heating surfaces, a three-dimensional (3D) combustion model was established using computational fluid dynamics (CFD) software. In addition, a 1D + 1D thermal hydraulic model was developed using MATLAB to describe the heating process inside the tubes. Detailed mapping methods were also provided to connect the mesh systems in CFD and MATLAB. As a result, the tube wall temperature can be calculated by considering the coupled heat transfer on the gas and steam sides. The simulation results reveal that under full load conditions, the upward tilting of the separated over-fire air (SOFA) burners can reduce the formation of CO and NOx, which helps achieve higher boiler efficiency. However, when the SOFA tilt angle increases from +20° to +30°, 0.16% of the outer surfaces of the final re-heater would exceed the allowable temperature of the TP347H material; additionally, the improvement in the boiler efficiency and decrease in NOx formation are much less. Thus, considering the unit’s safe operation, the optimal SOFA tilt angle for combustion optimization should be +20°.

Numerical Investigation on Co-firing Characteristics of Semi-Coke and Lean Coal in a 600 MW Supercritical Wall-Fired Boiler

Semi-coke is one of the principal by-products of coal pyrolysis and gasification, which features the disadvantages of ignition difficulty, low burnout rate, and high nitrogen oxides (NOx) emission during combustion process. Co-firing semi-coke with coal is a potential approach to achieve clean and efficient utilization of such low-volatile fuel. In this paper, the co-firing performance of semi-coke and lean coal in a 600 MW supercritical wall-fired boiler was numerically investigated which has been seldom done previously. The influences of semi-coke blending ratio, injection position of semi-coke, excess air ratio in the main combustion zone, the co-firing method, and over fire air (OFA) arrangement on the combustion efficiency and NOx generation characteristics of the utility boiler were extensively analyzed. The simulation results indicated that as the blending ratio of semi-coke increased, the NOx emission at furnace outlet decreased. The blending methods (in-furnace versus out-furnace) had certain impacts on the NOx emission and carbon content in fly ash, while the in-furnace blending method showed more flexibility in co-firing adjustment. The injection of semi-coke from the upper burners could significantly abate NOx emission at the furnace outlet, but also brought about the rise of carbon content in fly ash and the increase of outlet temperature. Compared with the condition that semi-coke and lean coal were injected from different burners, the burnout ratio of the blend premixed outside the furnace was higher at the same blending ratio of semi-coke. With the excess air ratio in the main combustion zone increased, NOx concentration at the furnace outlet was increased. The excess air ratio of 0.75 in the main combustion zone was recommended for co-firing 45% semi-coke with lean coal. The operational performance of the boiler co-firing semi-coke was greatly affected by the arrangement of OFA as well. The amount of NOx generated from the supercritical wall-fired boiler could be reduced with an increase of the OFA height.

Development of Subair Technique for Combustibility Enhancement and NOx Reduction in a Pulverized Coal-Fired Boiler.

In this work, subair injection was proposed to improve the combustibility and NOx emission in a 500 MW tangentially fired coal boiler. The location of injection ports was determined based on the coal particle trajectory and its effect was investigated numerically. The flow rate of subair was set to 0, 5, and 10% of the total combustion air. The secondary air flow rate was decreased appropriately to ensure that the total quantity of combustion air remained constant. The over-fire air was not adjusted to retain the effect of an air-staged combustion. The simulation results showed that the subair improved the combustibility of coal particles originating from burners A and B in the lower part of the furnace. Particles from other burners were not affected significantly. In addition, this method achieved reduction of NOx by 6.3 and 13.2% when the subair accounted for 5 and 10% of the combustion air, respectively. This reduction was attributed to the decrease in the peak temperature as a result of a wider combustion region. The proposed subair technique improved the coal combustibility and reduced the NOx emissions successfully in the furnace.

Effects of blending crude Jatropha oil and heavy fuel oil on the soot behavior of a steam atomizing burner

The aim of this study is to investigate the detailed soot formation characteristics of crude Jatropha oil (CJO) and heavy fuel oil (HFO) blends (lower heating value (LHV) basis: 50%/50%) in a 550 kW-class combustion test furnace equipped with an industry-scale steam atomizing burner using optical measurement systems. In the present study, time-resolved flame images through the high-speed photography, flame radiation intensity through Hottel & Broughton (H&B) two-color method, instantaneous soot volume fraction and the velocity field around the fuel nozzle through laser induced incandescence (LII) and particle image velocimetry (PIV), and the soot absorbance through the dust analyzer were obtained. The results of this study show that soot volume fraction around the fuel nozzle became lower with blending CJO in HFO, thereby the flame radiation intensity decreasing. This seems to be caused by fewer polycyclic aromatic hydrocarbons (PAHs) in the CJO. By the exhaust gas recirculation (EGR), a larger soot volume fraction around the fuel nozzle and a lower soot volume fraction in the downstream region were obtained, which are probably due to a decrease in oxygen concentration slowing the soot oxidation rate around the fuel nozzle and the increase in oxygen concentration behind overfire air holes, respectively.

Effects of OFA Ratio on Coal Combustion and NOx Generation of a 600-MW Downfired Boiler after Changing Air Distribution around Fuel-Rich Flow

AbstractBoth experimentation and numerical simulations were conducted to study the effects of the overfire air (OFA) ratio on the coal combustion and NOx generation characteristics of a 600-MW down...

Combustion optimization and NOx reduction of a 600 MWe down-fired boiler by rearrangement of swirl burner and introduction of separated over-fire air

In this paper, a 600 MWe Babcock & Wilcox boiler is selected as the research object. Numerical simulation and field experiments have been applied to this study under original and new combustion systems. The new approach mainly involves changing the operation mode of swirl burner, rearranging secondary air, and employing separated over-fire air. Numerical results showed that NOx emissions and the unburned combustible in flue dust decrease with the arrangement of the swirl burner changing from co-rotating mode to counter-rotating one. Consequently, counter-rotating mode of adjacent burners was chosen as the optimized arrangement. The introduction of separated over-fire air resulted in a remarkably reduction of the NOx emissions, which reduced from 1085 mg/m3 to 547 mg/m3. With increase of the distance between separated over-fire air and arch from 0.5 m to 3.0 m, NOx emissions changed slightly and the unburned combustible in flue dust were not greatly affected. When the distance continued increase to 6.0 m, NOx generation was suppressed and boiler efficiency declined. Considering the economic efficiency and NOx emissions reduction, the optimal sofa position is 3.0 m above the arch. In situ measurement results are consistent with the modelling predictions This work provides a feasible and economic approach for Babcock & Wilcox down-fired boilers to achieve high efficiency and low pollutant emissions.

Application of overfire air technology on an example of a steam boiler PK-39 of the Aksu TPP (Kazakhstan)

When burning any fossil fuels, one of the most harmful combustion products are nitrogen oxides NOx, which damage both the environment and human health in particular. Reduction of NOx emissions from fuel combustion at TPPs plays an important role in reducing the total level of nitrogen oxides NOx emitted into the atmosphere. One way to reduce the concentration of nitrogen oxides NOx is the stepwise combustion of the pulverized coal mixture, in particular the «Overfire Air» technology. The essence of this method is that the main volume of air is fed into the pulverized burners, and the rest of the air is further along the height of the torch through special nozzles. Structurally, the method of stepwise combustion of fuel can be carried out in boilers with a two-tier arrangement of burners along the height of the combustion chamber. In this case, practically no significant reconstruction of the boiler is required, which is associated with additional costs. In the present work, computational experiments on the use of modern overfire air technology (OFA) in the combustion chamber of the PK-39 boiler of the Aksu TPP were carried out and the fields of the main characteristics of heat and mass transfer, as well as the influence of the mass flow of the oxidant through the OFA injectors on the combustion process were obtained.

Effects of secondary air distribution in primary combustion zone on combustion and NOx emissions of a large-scale down-fired boiler with air staging

A new air-staged and low-NOx emission combustion technology has been applied to a 300 MWe anthracite- and down-fired boiler with swirl burners. To achieve the optimum air distribution in the primary combustion zone and further reduce NOx emissions, full-scale industrial experiments varying the ratios between burner secondary air ratio (Rbsa) and staged air ratio (Rsa) (i.e., Rbsa/Rsa ratios of 42.9/17.8, 47.1/13.5 and 51.5/9.3), on the premise that the overfire air (OFA) ratio was approximately 20%, were performed to evaluate the overall performance of retrofitted boiler. The improved ignition of coal/air flow was at a distance of 0.8–1.4 m to the burner outlet with increased Rbsa/Rsa ratio. Compared with the boiler before retrofit, under Rbsa/Rsa ratios of 47.1/13.5 and 51.5/9.3, the flue gas temperature in the primary combustion zone of the retrofitted boiler increased slightly. Oxygen and carbon monoxide concentrations in the near-sidewall region revealed the furnace flame fullness varied under different Rbsa/Rsa ratios. With increased the air staged level in the lower furnace, NOx emissions decreased continually and the carbon content in fly ash did not necessarily increased. Under the optimum Rbsa/Rsa ratio of 47.1/13.5, the NOx reduction efficiency was approximately 46% with increasing boiler thermal efficiency slightly.

Studying the Aerodynamics of the TPP-210A Boiler Furnace When It Is Shifted to Operate with Dry-Ash Removal and Vortex Fuel Combustion

To reduce the amount of nitrogen oxide emissions and achieve more reliable operation of the TPP-210A boiler, a process arrangement for firing Grade TR Kuznetsk coal that involves using straight-flow burners and shifting the boiler from slag-tap to dry-ash removal is developed. Owing to a large burner downward slope angle and special arrangement of burners and nozzles, four large vertical vortices rotating in opposite directions are produced in the furnace lower part, as a result of which the combustion products dwell for a longer period of time in the burning zone and more complete fuel combustion is achieved. For verifying the operability and efficiency of the proposed combustion arrangement, investigations on a boiler furnace physical model were carried out using a technique for visualizing fuel jets and secondary and tertiary overfire air jets. The fuel jet temperature boundaries in the course of jet propagation in the furnace model are also determined. The study results have shown that staged fuel combustion will be set up with using the proposed arrangement of burners and nozzles. In addition, large vertical vortices produced in the furnace lower part will help to achieve more efficient use of the dry bottom hopper heating surfaces, due to which lower coal combustion product temperature in the furnace upper part and smaller content of combustible products in fly ash will be obtained. Owing to low values of air excess factor at the pulverized coal burner outlet and gradual admission of air into the vortex zone through a few nozzles with intense inner recirculation of combustion products to the jet initial section, staged combustion of pulverized coal and low nitrogen oxide emissions will be secured. Owing to expansion of fuel jets, a rapid growth of mass in the fuel jet is achieved, which is obtained both due to ejection of the jet itself and due to forced admission of hot fuel gases from other jets. Investigations carried out on the physical model have confirmed that the proposed combustion arrangement features high efficiency and that a low content of nitrogen oxides in flue gases is obtained.

Use of wood dust fly ash from an industrial pulverized fuel facility for rendering

Wood dust II fly ash, which was generated after boiler retrofit (implementation of low-NOx burners combined with over-fire air), apparently is an enhanced quality for rendering. This is attributed to the mineral phases formed, an increase in the amount of free lime, and performance test results. After accelerated aging tests, the wood dust II fly ash showed no visible occurrence of cracks or detachment of the render base coat from the substrate. Tensile strength values met the applicable limit requirement of 8 MPa. The results contribute to a sustainable ash management for wood fly ash from pulverized fuel facilities.

Numerical study of a large-scale pulverized coal-fired boiler operation using CFD modeling based on the probability density function method

The paper presents results of numerical modeling of pulverized coal combustion process in the front wall coal-fired boiler. The developed numerical model of the coal combustion process included particle heating, devolatilization, char combustion, as well as turbulent flow and radiative heat transfer. In gas phase combustion process modeling, the mixture fraction approach with PDF was used. Presented modeling results were carried out using the Open Source CFD code – Code_Saturne, and were used to study the pulverized coal combustion in a 225 MWe power plant unit. The input data and boundary conditions were defined based on the collected data about boiler operating conditions and Rosin-Rammler law was used to calculate coal particle distribution. The behavior of pulverized coal and air flow through the burners, as well as the three-dimensional flue gas path through the combustion chamber, was analyzed. Results in form of velocity, temperature, unburned coal and combustion products distribution were presented to show places inside the boiler with high erosion hazard and place where intensive particle deposition may occur, as well as to show the impact of coal particle diameters on Unburned Carbon (UBC) content. Calculation results confirm proper locations of Over-Fire Air (OFA) nozzles and allowing continuing of combustion process at the furnace outlet using only OFA II and OFA III nozzles set. Based on the obtained results is possible to increase the understanding and conduction detailed investigation of boiler operation. The results have been validated with data collected from the power station measurement system and were analyzed in order to find an answer for operational questions regarding optimization of combustion characteristics.

Comparative investigation of a co-firing scheme in a lignite-fired boiler at very low thermal-load operation using either pre-dried lignite or biomass as supporting fuel

This work presents an investigation of an indirect firing scheme using biomass (cardoon) as supporting fuel for a pulverized-lignite boiler during its operation at a thermal load of 35%, lower than the current minimum one. Results are compared with an alternative indirect firing scheme which employs pre-dried lignite (PDL) as supporting fuel. The numerical investigation of the boiler has been conducted using the commercial software ANSYS Fluent® v15.0, supported by in-house built functions for the combustion rate of the fuels and the drag force exerted on biomass particles. The simulation and the comparison of the combustion of two different fuel blends in a co-firing strategy is important in order to evaluate technically the available possibilities and select among them the optimal firing concept (number and position of the operating injection ports) and the ideal fuel blend for the operation of the unit at lower than technical minimum thermal loads, in order to attain reduction of emissions and improvement of the boiler flexibility. Due to the implementation of a two-stage over-fire air (OFA) system and the consideration of sub-stoichiometric conditions exhibited at the nominal load, this work also takes into consideration the modeling of the boiler convective section, following the porous media analysis provided by the available Macro Heat Exchanger Model, ANSYS Fluent®. The validation of the applied models has been performed in previous works of the same group of authors, while the combustion results regarding crucial combustion parameters have been compared against corresponding values derived by a suitably-developed thermodynamic model. The agreement between these two models is good, since the maximum percentage deviation is calculated to be in the range of approximately 10%. Based on the numerical results, it can be concluded, that the utilization of both types of supporting fuel can ensure the stable operation of the boiler at thermal loads, lower than the technical minimum of the unit, promoting its flexibility. Between the two different supporting fuels, it is observed, that biomass ensures higher combustion efficiency compared to pre-dried lignite. However, it is also indicated, that the reduction of NOx emissions and the intensity of the induced thermal loading on the membrane walls with the utilization of biomass is more dependent on the firing strategy compared to lignite, proving the key role that this parameter plays to the operation of a boiler using this specific fuel blend.

Application of eccentric-swirl-secondary-air combustion technology for high-efficiency and low-NOx performance on a large-scale down-fired boiler with swirl burners

A 300-MWe anthracite and down-fired boiler equipped with swirl burners, which was retrofitted with the previously proposed deep-air-staging combustion technology to reduce particularly high NOx emissions, still suffered from high carbon content in fly ash (despite this content being slightly lower than that before retrofit) on basis of significant NOx reduction. To comprehensively produce a high-burnout and low-NOx setting, a novel combustion technology was proposed in which relative to the axis of the primary air duct, the axes of the inner and outer secondary air ducts of the swirl burner shift away from the furnace center, and this technology is called an eccentric-swirl-secondary-air combustion technology. The coaxial symmetrical arrangements of primary and secondary air ducts for traditional swirl burners are broken. Full-scale industrial measurements under original, deep-air-staging and eccentric-swirl-secondary-air combustion technologies with respect to different loads (i.e., 180, 250, and 300 MWe) were carried out to compare and analyze the validity of and improvement offered by the eccentric-swirl-secondary-air combustion technology. Under different boiler loads, especially at low and middle loads, compared with original and deep-air-staging combustion technologies, eccentric-swirl-secondary-air combustion technology markedly extends the penetration depth of coal/air flow and recirculation regions below arches. The thermal resistance between primary coal/air flow and high-temperature flue gas at the furnace center is reduced further, and the ignition of pulverized coal is timelier. The heating gradient in the burner outlet zone is maintained throughout, and the flame fullness in the primary combustion zone increases. The above three aspects contribute to pulverized coal burnout. Similar to deep-air-staging combustion technology, a low-oxygen and strong reducing atmosphere was formed in the primary combustion zone to reduce NOx formation due to the introduction of overfire air. Compared with deep-air-staging combustion technology, for the eccentric-swirl-secondary-air combustion technology, the air staged combustion in the furnace is improved further, and pulverized coal combustion in the primary combustion zone is more well distributed, which is beneficial to further reducing NOx emissions. The results of low-NOx and high-efficiency performance show that compared with the original boiler, NOx emissions and carbon content in fly ash for the boiler with the eccentric-swirl-secondary-air combustion technology are significantly reduced by above 42% and 32.5 to 20.7% at loads of 180, 250 and 300 MWe, respectively.