MW CFB Boiler Research Articles

Research on the effect of the flue gas recirculation on the combustion and operating economy of circulating fluidized bed boiler

To meet the requirements of the power grid’s deep peak shaving, a 300MW CFB boiler in a power plant transformed the flue gas recirculation. After the transformation, it is found that after putting into the flue gas recirculation, the main parameters of the boiler such as environmental protection emission value, the boiler operating bed temperature, and the inlet temperature of the separator had changed. To analyze the changes, this paper was carried out by related thermal state tests during the start-up or the normal operation of the boiler. The operating data of the boiler was collected before and after putting into the flue gas recirculation, and the influence of the gas recirculation on the main parameters and economic indicators of the boiler is quantitatively analyzed and discussed. The result shows that the technology of the flue gas recirculation can reduce the oxygen content in the dense phase area of the furnace and increases the reducing gas atmosphere to reduce the generation of NOX emission during the start-up or in the normal operation of the boiler. This provides a technical reference that optimizes the operation mode of the flue gas recirculation during the deep peak shaving in the CFB boiler.

MP-PIC Simulation on Solid Dispersion in a 350 MW CFB Boiler

MP-PIC Simulation on Solid Dispersion in a 350 MW CFB Boiler

Analysis on “against the wind” of primary air fan in 300MW CFB boiler

When the primary air fan of a 300MW circulating fluidized bed boiler is operated at a variable frequency, there is a problem of “against the wind” under the condition that the fan is under low load and the air pressure is low. This paper aims at fixing the aforementioned problem and finding out the cause of the “against the wind” of the primary air fan, and proposing the solutions of adjusting the frequency conversion and the inlet diversion at the same time by analyzing the cold fluidization test, the combination test of the fan adjustment mode, the frequency and speed test of the frequency converter, etc. This method successfully avoids the “Agiainst the wind” situation during low load operation, which is important for the adjustment of low-load down-conversion operation of primary air fan of circulating fluidized bed boiler.

Mechanism analysis of gas solid flow non-uniformity problem of 330 MW CFB boiler

The bed inventory overturn in pant-leg CFB boilers and bed pressure wave in single air distributor CFB boilers were the two well-known non-uniformity problems in large scale CFB boilers. However, a special gas solid flow non-uniformity problem, bed pressure deviation, occurred in a single air distributor 330 MW CFB boiler. The bed pressure in one side was 2 kPa constantly higher than that in the other side and lasted for a long time, resulting to the local over temperature and endangering the boiler performance. Mechanism analysis showed that the primary air temperature deviation caused the serious primary air rate deviation, further forming a stable solid concentration deviation in the bottom bed and bed pressure deviation, which was totally different from above two non-uniformity problems. The similar phenomenon was replicated in a laboratory CFB test rig, validating the gas velocity deviation had a serious effect on the bed pressure deviation. To solve the problem, solutions, like increase the primary air ratio, were put forward. To solve the primary air non-uniform distribution, further study on optimizing air chamber and air distributor is urgent, so that other large scale CFB boilers can avoid such a problem.

An experimental study on the hydrodynamic performance of the water-wall system of a 600 MW supercritical CFB boiler

The temperature distribution on the backside of the water-wall tubes in the first 600 MW CFB boiler operating at 60%, 80% and 100% of the boiler Maximum Continuous Rating (MCR) loads was experimentally determined and the thermal-hydrodynamic performance of water-wall system based on the mass and energy equations using the measured temperature was calculated. The results showed that the temperature of the water-wall tubes increased as the furnace height increased, showing a positive response characteristic in the water-wall system. However, the temperature of the water-wall tubes in the upper furnace was obviously declined at the places where the superheaters and cyclone separator inlet-channels were arranged. This suggests that the arrangement of the heat-transfer surfaces in the upper furnace was significantly influenced the temperature distribution of the water-wall tubes. Meanwhile, the calculated total pressure-drop and mass flux in the water-wall system increased as the boiler’s load raised, showing an energy-efficiency for the vertical once-through boiler. In addition, the metal temperature was calculated to check the working condition of the water-wall tubes and the results showed the highest metal temperature of 426.3 °C of the water-wall tubes was found at the tip of the fin at 100% MCR. This temperature was far below the permissible temperature of the metal, implying that a safe working condition of the metal at three loads was guaranteed. Nonetheless, analysis into the heat-transfer characteristics of the water in the water-wall reflects that the water temperature in the water-wall at 80% MCR load was adjacent to the boundary of the large specific-heat region, implying that heat-transfer deterioration was more likely to occur at such condition. Therefore, the metal temperature of the water-wall tubes operating at 80% MCR load requires the most concern and monitor to avoid overheating of the water-wall tubes.

Experimental research of heat transfer uniformity for fluidized bed heat exchangers in a 300 MW CFB boiler

In order to investigate the heat transfer uniformity of fluidized bed heat exchangers (FBHEs), a series of experimental tests were carried out in a commercial 300 MW CFB boiler. The test results indicate that there is a good linear correspondence between the FBHEs conical valve openings and circulating ash flow rate, the average heat transfer coefficient of different heat exchangers takes on a monotonically increasing trend with the increase of the boiler loads. Moreover, there is a non-uniform heat transfer process between the different measuring points under the same load as well as the different loads for the same measuring points, the heat absorption proportion of two FBHEs (71# and 72#) on the left side is larger than that of two FBHEs (73# and 74#) on the right side of the furnace, there is a non-uniform heat transfer phenomena in the symmetrical arrangement of four FBHEs, the heating surface arrangement in the FBHEs must be adjusted from snake tube perpendicular to the ash flow direction to parallel to ash flow direction, the test results can provide a good reference for the optimized design and operation of 600 MW supercritical CFB boiler with the FBHEs in the future.

Effect of furnace pressure drop on heat transfer in a 135 MW CFB boiler

The effect of the pressure drop across the furnace on heat transfer inside large scale CFB boilers was investigated with a 1-D CFB combustion model developed at Tsinghua University. The results from the 1-D model agree well with the field test data carried out in a 135MWe CFB boiler. It was found that, at a certain load and with fixed size distribution of the coal particles fed to the boiler, a decrease in furnace pressure drop yields an increase in furnace temperature and reduced heat transfer coefficient. According to the heat balance, when the pressure drop decreases by 1kPa, the heat transfer coefficient is expected to decrease approximately by 2%. The increase in temperature with decreasing pressure drop is less steep, when the boiler load increases or smaller sized coal particles are fed to the boiler. In both cases, more fine particles are carried to the upper parts of the furnace which results in a more uniform solid volume fraction distribution along the furnace height. The influence of the pressure drop on heat transfer by changing the solid suspension density weakens. Operation of the bed at relatively low pressure drop by reducing the size of coal particles will ensure adequate heat transfer.

Field test of coal type adaptability on a 300 MW CFB boiler

Coal type adaptability for CFB boilers is of great importance because it influences whether the unit can operate safely, economically and environmentally when the coal type is changed. Research is carried out on a 300MW CFB boiler located in Longyan power plant, Fujian province by burning three types of coal, i.e. Fujian anthracite, Shenhua bituminous coal and Indonesia lignite. The results show that all the three coals are capable to meet the basic requirement of bed temperature. But the fly ash carbon content and exhaust gas temperature depend on the coal type. Compared with Fujian anthracite, Shenhua bituminous coal and Indonesia lignite tend to possess lower fly ash carbon content and lower exhaust gas temperature under high boiler load, which helps to increase the boiler efficiency. The auxiliary power consumption rates under all the three types of coal are all lower than 4.3% with the successful utilization of lower energy consumption technology based on state specification design theory. Besides, when the fuel is changed from Fujian anthracite to Shenhua bituminous coal and Indonesia lignite, SO2 emission and dust emission decreases, while the NOx emission increases.

The Experimental Study of SO<sub>2</sub> Removal by Atomized Ammonia Injection in the Tail Flue of a 300 MW CFB Boiler

An experimental study on the desulfurization system by atomized ammonia injection was conducted in the tail flue of a 300MW CFB boiler. The tests was going under the unit load ranges from 229.5MW to 267MW with ammonia concentration of 5.2~9% and flow at 3.7~9.0 t/h, the gas temperature at 145~149°C, the maximum final desulfurization efficiency is 55.6%, the average removal efficiency at 21% ~ 26%. The ammonia also has an activation function to the CaO in fly ash, which counts 15.7% to 29.8% of the total amount CaO in fly ash.

The Industrial Test of Coal Type Adaptability for 300MW CFB Boiler

The CFB boilers located in Longyan and Jinjiang in the province of Fujian, was originally designed to burn anthracite. Recently, a research was carried out to study the adaptability of coal type by burning Shenhua bituminous coal in this unit. It showed that the temperature of bed and exhaust gas would not change signally after the change of coal type. Both of the coals share similar ash characteristics. But the use of Shenhua bituminous coal can reduce the carbon content in the fly ash and the auxiliary power rate, thus improving the economic operation of boiler. As for the pollutant, Shenhua bituminous coal brought less dust emission and more NOx. On the whole, change of the coal type is beneficial to the economic operation of the plant. The study can provide valuable references for similar type units on how to expand coal sourcing channels and reduce plant cost.

Experimental investigation and model validation of the heat flux profile in a 300MW CFB boiler

In this paper, systematic experimental investigation on the heat flux distribution inside the furnace of a 300 MW CFB boiler was presented. Detailed experimental setup and measurement techniques were presented and a finite element method approach was applied to determine the heat flux. The heat flux profile on the rear wall along the horizontal direction shows a significant imbalance at different boiler loads. As a result of the non-uniform layout of the heating surfaces, which is the essential reason, as well as the imbalance and deviation of the temperature field, solid suspension density and solid flow rate, the central section of the furnace possesses higher heat flux distribution compared to the side sections. The heat flux is also found to increase with the increasing boiler load and decrease as the height increases. Heat flux near the roof, where the solid suspension density is rather small, is found to decrease remarkably revealing less heat absorption in this area. In addition, an empirical model of heat transfer coefficient is revised using the average data at different boiler loads. A mechanism heat transfer model based on the membrane water-wall configuration is proposed and validated with the heat flux profile obtained from the measurement. The model provides good accuracy for correlating 85% of the data within ± 10%.

The Optimization to Control System of Desulfurization in Furnace of 300MW CFB Boiler

This paper contraposes 300MW CFB boiler of Shanxi certain coal-fired power plant, then optimize the control system of desulfurization and remake limestone transmission system. Collect the signal to establish knowledge base for judging starting or stalling control of feeding machine through lots of experiments. Adopt feedback control strategy to adjust the speed of feeding machine. Achieve the purpose of automatically controling the starting or stalling of feeding machine and the speed of feeding machine finally.

The thermal-hydraulic calculation and analysis of the medium temperature platen superheater in a 300 MWe CFB boiler

Abstract The characteristics of outlet steam temperature and the metal temperature of the medium temperature platen superheater at different boiler loads was obtained in a 300 MWCFB boiler, the result shows that the imbalance rate of tube mass flux is determined by the structure of header and tube. Generally Z type arrangement is one of the reasonable types arrangement.

Prediction of Bed Agglomeration Propensity Directly from Solid Biofuels: A Look Behind Fuel Indicators

Determination of ash-forming elements directly from solid biofuels is essential in the prediction and prevention of ash-related problems like slagging, fouling, agglomeration, and corrosion in FB-boilers. In this contribution, we report the characterization of reed canary grass, straw, pine and spruce needles, as well as two peat samples by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and scanning electron microscope energy dispersive spectroscopy (SEM-EDS). For comparison, their ash-forming elements have been determined by inductively coupled plasma optical emission spectrometry (ICP-OES) after digesting in a microwave oven or, in case of chlorine, after leaching with tetramethyl ammonium hydroxide. The analytical data are in agreement with those recorded previously for the ash of the biofuels in question and are consistent with their relative slagging, fouling, and agglomeration propensities. The prediction of the onset of ash-related problems is facilitated by use of fuel indicators that are conventionally based on bulk analytical data. The extension of the use of these indicators by considering the compositional distribution of discrete particles in the fuel by SEM-EDS and LA-ICP-MS provides more detailed understanding of the properties of different fuels and their mixtures upon combustion. In addition to laboratory tests, fuel and bed samples were received from a full-scale 315 MW CFB boiler during its normal operation using a mixture containing 60% of peat, 20% of woodchips and sawdust, and 20% of forest residue as fuel. While the operation of the boiler was unproblematic, occasional formation of coating layers on the bed particles has been reported. This behavior can be explained by the distribution of numerical values of selected fuel indicators.

MODELLING OF AN INTEGRATED SUPERHEATER BASED ON A WIENER APPROACH

This paper considers identification of a multiple-input single-output Wiener model of a new type of superheater integrated to a CFB boiler. The static part is based on energy- and mass balances. Simultaneous estimation of model parameters in both static and dynamic parts was based on the industrial data from an 80 MW CFB boiler. The results indicate that the approach can be satisfactorily used to capture and describe the steam temperature in a wide range of variation in the input variables.

00/03549 Influence of air-staging on the concentration profiles of NH 3 and HCN in the combustion chamber of a CFB boiler burning coal

The characterisation of the concentration profiles of NH3 and HCN are of great importance for increasing the knowledge of the formation and destruction pathways of NO and N2O in a fluidized bed boiler. Further improvements of the sampling methods for the determination of both NH3 and HCN in the combustion chamber in full-scale CFB boilers are also needed. A gas-sampling probe connected to a Fourier Transform Infra Red (FTIR) instrument and a gas-quenching (GQ) probe in which the sample is quenched directly in the probe tip by a circulating trapper solution were used. The FTIR technique is based on analysis of hot combustion gases, whereas the trapper solutions from the GQ probe were analysed by means of wet chemistry. The tests were performed during coal combustion in a 12 MW CFB boiler, which was operated at three air-staging cases with the addition of limestone for sulphur capture. The concentration profiles of NH3 and HCN in the combustion chamber showed a different pattern concerning the influence of air-staging. The highest levels of NH3 were observed during reducing conditions (severe air-staging), and the lowest were found under oxidising conditions (no air-staging). The levels of HCN were much lower than those measured for NH3. The highest levels of HCN were observed for reversed air-staging and severe air-staging showed almost no HCN. The potential reactions involving NH3 and HCN in the combustion chamber as well as the potential measurement errors in each sampling technique are discussed for the three air-staging cases.

Gas Concentrations in the Lower Part of the Combustion Chamber of a Circulating Fluidized Bed Boiler: Influence of Bed Height

The effect of the height of the bottom bed on the conditions in the lower part of a 12 MW CFB boiler was studied. Pressure measurements along the furnace height were made together with gas (CO, hydrocarbons, O 2 , NO, and SO 2 ) and zirconia-cell probe measurements in the splash zone. The operation in the exploding bubble regime causes the particulate phase to be under reducing conditions. However, as the height of the bottom is decreased the conditions become more oxidizing. Additionally, the concentrations of NO and SO 2 in the splash zone are significantly affected by the height of the bottom bed. Thus, the gas flow phenomena in the bottom bed are of great importance for the understanding of processes related to combustion, for instance formation and reduction of pollutants.

98/02247 First year of operation of Provence SOPROLIF 250 MW CFB boiler

In this paper we determine the fundamental relation between global performance and flow configuration (constructal design) in the case of steam power generation with superheater and reheater placed in parallel in the same stream of hot gases of combustion. The superheater heats the steam for the high pressure turbine, and the reheater supplies steam to the low pressure turbine. Both turbines operate irreversibly. We consider superheaters and reheaters with balanced counter flows and unbalanced counter flows. The total heat transfer area (or the overall number of heat transfer units) is finite. We show that the heat transfer area can be allocated to the superheater and reheater such that the overall power output is maximum. The optimal area allocation ratio is reported for two scenarios: designs with and without a maximum allowable steam temperature.

Ash behaviour in a CFB boiler during combustion of coal, peat or wood

This paper presents selected results from an extensive on-site measurement campaign where the ash behaviour in a 12 MW CFB boiler was studied during firing of coal, peat and wood. Samples were taken from all in-going (bed material, fuel) and out-going solid material streams (secondary cyclone and bag filter) as well as from the bed and the return leg. Deposit samples were further collected from the cyclone inlet and from two different locations in the convective path. In addition, the boiler operation was monitored, including collection of operational data, flue gas temperature profiles and emissions. The paper discusses the differences in the ash chemistry that were detected between the three different combustion cases and draws conclusions on the impact of the chemistry on the bed agglomeration and fouling tendency for each fuel.

Fluid-dynamic boundary layers in CFB boilers

The characteristics of the fluid-dynamic boundary layer (FBL) were studied in the 12 MW circulating fluidized bed boiler at Chalmers University of Technology. For a comparison, some additional measurements were made in a 165 MW CFB boiler. The FBL consists mainly of the falling film of particles at the furnace wall. The distance from the wall to the zero net particle flux position is used as a measure of the thickness of the layer. Horizontal profiles of particle flux, velocity and concentration were measured in the transport zone of the furnace. It was found that the FBL thickness varies only slightly or not at all with particle concentration, gas velocity and height in the furnace. An estimation of the thickness is given as a function of the horizontal bed dimension. The particle falling velocity inside the FBL is about 0.9–1.6 m/s depending on location. There is a sharp increase in particle concentration in the FBL all the way towards the wall. The disparity between the particle flux profile normal to a plain refractory-lined wall and the corresponding profile normal to a membrane-tube wall can be compensated for by taking the fin-tube configuration into account. From this point of view, the particle redistribution mechanism at the membrane-tube wall is discussed.