Co-firing In Boilers Research Articles

Effects of Flue Gas Internal Recirculation on NOx and SOx Emissions in a Co-Firing Boiler

Volumetric combustion has been developed to realize a high substitution ratio of biomass in co-firing boilers, which features an intensive flue gas internal recirculation inside furnace. However, the characteristics of NOx and SOx emissions in large-scale boilers with volumetric combustion were not fully clear. In this paper, an Aspen Plus model of volumetric combustion system was built up based on a co-firing boiler. In order to characterize the reductions of NOx and SOx, three biomass substitution ratios were involved, namely, 100% biomass, 45% biomass with 55% coal, and 100% coal. The effects of flue gas recirculation ratio, air preheating temperature, oxygen concentration, and fuel types on pollutants emission in the volumetric combustion system were investigated. According to the results, it was concluded the higher substitution ratio of biomass in a co-firing boiler, the lower emissions of NOx and SOx. Moreover, flue gas internal recirculation is an effective pathway for NOx reduction and an increased recirculation ratio resulted in a significant decreasing of NOx emission; however, the SOx increased slightly. The influences of air preheating temperature and O2 concentration on NOx emission were getting weak with increasing of recirculation ratio. When 10% or even higher of flue gas was recycled, it was observed that almost no NOx formed thermodynamically under all studied conditions. Finally, to reach a low emission level of NOx, less energy would be consumed during biomass combustion than coal combustion process for internal recirculation of flue gas.

Solid Biofuels for Energy

Fossil fuels, widely used for electricity generation and heating, emit greenhouse gases which should be minimized according to the most recent environmental legislation. The utilization of solid fuels of biogenic origin could contribute, to some extent, towards the aim of reducing greenhouse gas emissions. Within this book, special attention has been given to biomass co-firing with coal as it has the highest potential for commercial application in large-scale units, whereas according to the author’s interpretation, combustion and gasification are more promising for units of small to medium scale. In chapter 1, key questions arising from biomass availability and supply are discussed. A detailed analysis of solid agricultural biomass feedstock in EU27 summarizes the relevant data, which influence the availability and future supply of this feedstock for energy and fuel production. The European Standards for the specifications of solid biofuels are presented in chapter 2. Chapter 3 provides an overview of all technical issues for biomass-coal cofiring in boilers designed exclusively for coal (mainly pulverized coal) combustion. Biomass-coal co-combustion represents a low-risk, low-cost, sustainable, renewable energy option that promises an effective near-term reduction in CO2, SOX, and often NOX emissions, as well as several societal benefits. A step ahead on co-firing development is covered in chapter 4 in which the co-utilization of solid recovered fuels (SRF) with coal is extensively reviewed. SRF are solid fuels prepared from high-calorific fractions of non-hazardous waste materials intended to be fired in existing coal power plants and industrial furnaces. The subject of chapter 5 deals with the biomass combustion characteristics. Unlike pulverized coal, biomass particles are neither small enough to neglect internal temperature gradients nor equate enough to model them as spheres. Experimental and theoretical investigations indicate particle shape and size influence on the biomass particle dynamics, including essentially all aspects of combustion such as drying, heating, and reaction. This chapter theoretically and experimentally illustrates how these effects impact particle conversion. Fluidized bed combustion (FBC) technology developed in the 1970s has recently expanded to the usage of biomass and other low-grade fuels as presented in chapter 6. The benefit of the FBC is the large amount of bed material compared to the mass of the fuel and, thus, the large heat capacity of the bed material that stabilizes the energy output caused by variations in fuel properties. Another thermochemical conversion technology for biomass is gasification which is examined in chapter 7. Gasification is a mature technology for energy production that permits an easier separation of CO2 for its storage. This chapter concentrates on syngas end uses, focusing on newly developed ones, such as gas turbines or engines in IGCC, synthesis of methanol, ethanol, and dimethyl ether, Fischer-Tropsch synthesis, and hydrogen production. Integrated schemes of micro-CHP and biofuels are very promising for decentralized applications. Renewable micro-CHP systems are a combination of micro-CHP technology and renewable energy technology, such as biomass gasification systems or solar concentrators. Chapter 8 discusses the state of the art of technological options in the field of renewable micro-CHP with biofuels with regard to technology, cost, and environmental impacts. It also presents a market survey concerning the possibility of future penetration of the technology in Europe. Chapter 9 provides an overview of the main ash formation and deposition Correspondence: Michael.Flamme@kit.edu Karlsruher Institut fur Technologie (KIT), Institut fur Technische Chemie ITC, Eggenstein-Leopoldshafen 76344, Germany Flamme Energy, Sustainability and Society 2012, 2:8 http://www.energsustainsoc.com/content/2/1/8

Co-firing Solid Recovered Fuels (SRFs) with brown coal in large-scale pulverised fuel power plants – a simulation approach

The results of the numerical simulations performed in a pulverised fuel boiler co-firing coal and Solid Recovered Fuels (SRFs) are presented. SRFs are initially modelled as a mixture of two different fractions (biogenic and plastic) and further simplifications are proposed to save computational expenses. The SRF submodels are validated with available data obtained from a laboratory-scale combustion facility. The furnace of a 600 MWe brown coal plant is further simulated. The respective boundary conditions are obtained from a performed large-scale measurement campaign during an SRF co-firing demonstration in the specific boiler. The results of the baseline case are in good agreement with the available experimental data for the large-scale boiler. A number of fuel and process-related combustion parameters is further examined, including the co-firing thermal share, injection locations and the Particle Size Distribution (PSD) of SRF particles. Computational Fluid Dynamics (CFD) modelling in large-scale boilers can be a reliable and efficient tool towards predicting specific changes of the combustion behaviour. It is particularly valuable when the intended investigations cannot be easily realised on a large scale, such as increasing the co-firing thermal share or modifying the injection locations of alternative fuels.

Field test corrosion experiences when co-firing straw and coal: 10 year status within Elsam

In Denmark, straw is utilised for the generation of energy and district heating in power plants. Combustion of straw gives rise to high contents of potassium chloride and some sulphur dioxide in the flue gas. These compounds can lead to deposits with high content of potassium chloride and potassium sulphate on superheater tubes resulting in increased corrosion rates. From field experimental results this paper show, that by co-firing straw with coal, corrosion rates can be brought down to an acceptable level.This paper firstly deals with the results from a demonstration program co-firing coal and straw at the 150MW pulverized coal fired boiler Studstrup unit 1. Two exposure series lasting 3000 hours each were performed for co-firing 10 and 20% of straw (% energy basis) with coal. Using built in test tubes in the hot end of the actual superheaters and air/water cooled corrosion probes, the corrosion during these experiments was monitored. Various ferritic and austenitic materials were investigated at steam temperatures ranging from 520 to 580°C and flue gas temperatures ranging from 925 to 1100°C.The results obtained in the demonstration program led to the rebuilding of the 350MW pulverized coal fired boiler, Studstrup unit 4, into a co-firing boiler with straw in 2002. During the rebuilding, test tube sections of X20CrMoV12 1 and TP347H FG were built into the superheater and the reheater loops. The temperature ranges during these exposures was for the steam from 470 to 575°C and for the flue gas from 1025 to 1300°C. All these test tubes have been removed during the last three years at one year intervals for corrosion studies.The corrosion studies performed on all investigated tubes included measurements of the corrosion attack, light optical microscopy and scanning electron microscopy of the corrosion products.

Utilization of fly ash coming from a CFBC boiler co-firing coal and petroleum coke in Portland cement

Fly ash coming from a circulating fluidized bed combustion (CFBC) boiler co-firing coal and petroleum coke (CFBC fly ash) is very different from coal ash from traditional pulverized fuel firing due to many differences in their combustion processes, and thus they have different effects on the properties of Portland cement. The influences of CFBC fly ash on the strength, setting time, volume stability, water requirement for normal consistency, and hydration products of Portland cement were investigated. The results showed that CFBC fly ash had a little effect on the strength of the Portland cement when its content was below 20%, but the strength decreased significantly if the ash content was over 20%. The water requirement for normal consistency of cement increased from 1.8% to 3.2% (absolute increment value) with an addition of 10% CFBC fly ash; and the free lime (f-CaO) content of CFBC fly ash affected the value of increasing. The setting time decreased with an increase of CFBC fly ash content. The volume stability of the cement was qualified even when the content of SO3 and f-CaO reached 4.48% and 3.0% in cement, respectively. The main hydration productions of cement with CFBC fly ash were C–S–H (hydrated calcium silicate), AFt (ettringite), and portlandite.

TG-FTIR pyrolysis of coal and secondary biomass fuels: Determination of pyrolysis kinetic parameters for main species and NOx precursors

Co-firing of secondary biomass fuels with coal in coal-fired pulverized fuel boilers is facing increased application in large-scale power production. Fundamental knowledge on the thermochemical behavior of biomass and waste fuels is still lacking, especially regarding the release of the fuel bound nitrogen. Characterization of chicken litter (CL), biomass mix (BM) and meat and bone meal (MBM) and an HV coal blend was performed using TG-FTIR analysis. Three heating rate profiles were applied (10, 30 and 100 °C/min), with a final temperature of 900 °C. NH3 was found to be the major gaseous N-product, while HCN and HNCO were also released in substantial amounts. Kinetic parameters for the pyrolysis of biomass fuels were obtained using a model based on parallel first-order reactions with a Gaussian distribution of activation energies. Input files for the coal FG-DVC (functional group-devolatilization, vaporization, cross-linking) and FG-BioMass pyrolysis models were prepared. The fit of model parameters to TG-FTIR product-evolution data was found to be generally good, but the model-predicted yields for some species did not fit experimental data at all heating rates equally well. This problem can be overcome by improvements in the FG-BioMass model. The results of this study can be used to have an improved input of initial pyrolysis in CFD modeling of co-fired boilers.

Field test corrosion experiences when co-firing straw and coal: 10 year status within Elsam

In Denmark, straw is utilised for the generation of energy and district heating in power plants. Combustion of straw gives rise to high contents of potassium chloride and some sulphur dioxide in the flue gas. These compounds can lead to deposits with high content of potassium chloride and potassium sulphate on superheater tubes resulting in increased corrosion rates. From field experimental results this paper show, that by co-firing straw with coal, corrosion rates can be brought down to an acceptable level.This paper firstly deals with the results from a demonstration program co-firing coal and straw at the 150MW pulverized coal fired boiler Studstrup unit 1. Two exposure series lasting 3000 hours each were performed for co-firing 10 and 20% of straw (% energy basis) with coal. Using built in test tubes in the hot end of the actual superheaters and air/water cooled corrosion probes, the corrosion during these experiments was monitored. Various ferritic and austenitic materials were investigated at steam temperatures ranging from 520 to 580°C and flue gas temperatures ranging from 925 to 1100°C.The results obtained in the demonstration program led to the rebuilding of the 350MW pulverized coal fired boiler, Studstrup unit 4, into a co-firing boiler with straw in 2002. During the rebuilding, test tube sections of X20CrMoV12 1 and TP347H FG were built into the superheater and the reheater loops. The temperature ranges during these exposures was for the steam from 470 to 575°C and for the flue gas from 1025 to 1300°C. All these test tubes have been removed during the last three years at one year intervals for corrosion studies.The corrosion studies performed on all investigated tubes included measurements of the corrosion attack, light optical microscopy and scanning electron microscopy of the corrosion products.

Evolved gas analysis of some solid fuels by TG-FTIR

Co-firing of secondary biomass fuels with coal in coal-fired pulverized fuel boilers is facing increased application in large-scale power production. Fundamental knowledge on the thermochemical behavior of biomass and waste fuels is still lacking, especially regarding the release of the fuel bound nitrogen. Characterization of chicken litter (CL), biomass mix (BM) and meat and bone meal (MBM) and an HV coal blend was performed using TG-FTIR analysis. Three heating rate profiles were applied (10, 30 and 100 °C/min), with a final temperature of 900 °C. NH3 was found to be the major gaseous N-product, while HCN and HNCO were also released in substantial amounts. Kinetic parameters for the pyrolysis of biomass fuels were obtained using a model based on parallel first-order reactions with a Gaussian distribution of activation energies. Input files for the coal FG-DVC (functional group-devolatilization, vaporization, cross-linking) and FG-BioMass pyrolysis models were prepared. The fit of model parameters to TG-FTIR product-evolution data was found to be generally good, but the model-predicted yields for some species did not fit experimental data at all heating rates equally well. This problem can be overcome by improvements in the FG-BioMass model. The results of this study can be used to have an improved input of initial pyrolysis in CFD modeling of co-fired boilers.

00/00954 Ash chemistry aspects of straw and coal-straw cofiring in utility boilers

Deposits formed in straw-fired grate-boilers showed significant amounts of KCl (40--80% (w/w)) and KCl-coated Ca-Si-rich particles. CFB co-firing of straw and coal caused deposits in the convective pass containing predominantly K{sub 2}SO{sub 4} (50--60% (w/w)) with small amounts of KCl close to the metal surface. In pulverized coal-straw co-fired boilers, deposits almost free of KCl were found. Most of the potassium in these deposits is derived from K-Al-Si-rich fly ash particles and the rest occurs as K{sub 2}SO{sub 4}. The presence of K-Al-Si-rich fly ash particles indicates that solid residue quality and reuse of fly ash in cement and concrete production rather than deposit formation may be of concern when utilizing straw in pulverized fuel boilers. This paper provides a review of Danish experiences with high-temperature ash deposit formation in the following full-scale utility boilers: Slagelse CHP (31 MWth), Haslev CHP (23 MWth) and Rudkoebing CHP (10.7 MWth), all straw-fired grate-boilers; Grenaa CHP (80 MWth), a coal-straw co-fired Circulating Fluidized Bed (CFB) boiler; and the Midtkraft-Studstrup Power Station, Unit 1 (380 MWth), a coal-straw co-fired PF-boiler.

99/01617 Health effects of indoor fluoride pollution from coal burning in China : Ando, M. et al. Environ. Health Perspect., 1998, 106, (5), 239–244

Even though ratio of air to fuel is the major factor in determining the thermal efficiency of a boiler, how to optimize the ratio in the real operation is still more like art than science, especially for a gas/solid multi-fuel combustion system. This study, taking operation data from a real gas/solid fuels co-firing boiler, is aimed to develop the thermal efficiency model. To cope with the complexity of combustion mechanism in a co-firing boiler, this study proposed a two-tier approach to modeling thermal efficiency. The first tier is to transform the plant input variables into the derived variables, which are physically and statistically meaningful to the model-building. In the second tier, this study proposed an adaptive modeling approach by employing nonnegative garrote variable selection and auto-regression integrated moving average correction. Both approaches are first time proposed in building the thermal efficiency model for boilers. The prediction error of boiler thermal efficiency made by the acquired model reaches less than 0.03%. The high accuracy of the proposed modeling approaches makes the implementation of the model-based control of ratio of air to fuel for improving boiler’s efficiency readily practicable.

Erosion-Oxidation of Carbon Steel in the Convection Section of an Industrial Boiler Cofiring Coal–Water Fuel and Natural Gas

Walsh et al. (1994) reported measurements of erosion of carbon steel by fly ash and unburned char particles in the convective heat transfer section of an industrial boiler cofiring coal–water fuel and natural gas. Erosion was enhanced by directing a small jet of nitrogen, air, or oxygen toward the surface of a test coupon mounted on an air-cooled tube. Ash and char particles that entered the jet from the surrounding flue gas were accelerated toward the surface of the specimen. Samples were exposed for 2 hours with metal temperature at 450, 550, and 650 K (350, 530, and 710°F). Changes in shape of the surface were measured using a surface profiler. Time-averaged maximum erosion rates were obtained from the differences between the original surface height and the lowest points in the profiles. Erosion was slowest at the lowest metal temperature, regardless of the jet gas composition. When the oxygen partial pressure at the sample surface was very small, under the nitrogen jet, erosion increased with increasing temperature over the range of temperatures investigated. At the intermediate oxygen level, in the air jet, erosion was most rapid at the intermediate temperature. In the presence of the pure oxygen jet erosion was slow at all three temperatures. A model was developed by Xie (1995) to describe wastage of tube material in the presence of the erosion by particle impacts and oxidation of the metal. The observed changes in erosion rate with temperature and oxygen concentration were consistent with a mechanism based upon the following assumptions: (1) Metal was eroded as a ductile material, at a rate that increased with increasing temperature. (2) Oxide was eroded as a brittle material, at a rate independent of temperature. (3) The oxide scale was strongly attached to the metal. (4) The erosion resistance of metal and scale was a linear combination of the resistances of the individual components. (5) Oxide formed according to the parabolic rate law, with a rate coefficient proportional to the square root of the oxygen partial pressure. (6) Erosion resistance from particles sticking to, or embedded in, the surface was negligible. Using the model and rate coefficients for metal and oxide erosion derived from the measurements, estimates were made of the erosion rate of a boiler tube as functions of impaction angle and gas velocity. Under the conditions of metal temperature, gas composition, particle size, particle concentration, and particle composition investigated, erosion of carbon steel is expected to be slower than 0.05 μm/h when the gas velocity in the convection section is less than approximately 8 m/s.

オイルコークスボイラの操業経験

This is a introduction of a petroleum coke co-firing boiler which was converted from heavy oil-fired boiler. This petroleum coke co-firing boiler is located in Futatsuka works Toyama prefecture, and being operated since December 1984.This converted boiler had some probrems in burner and draft at the initial few months.However, these problems were solved through new trials and now this boiler has been operating very well in these years.