bluuebunny/crossref_metadata_2025 huggingface dataset:
Ukraine’s First Large-Scale CFB 200 MWe Anthracite Fired Starobeshevo Power Plant
Authors: Shevtchenko Victor A. , Franke Werner , Gummel Peter , Kotrus Marian , von Wedel George
Published: October 2008

JSC Donbassenergo, a major utility in the Ukraine, is operating power plants of approx. 3500 MW, mostly operated with their local fuel anthracite. As the existing facilities are reaching their age a strategy has been developed to apply state-of-the-art technology for revamping. On this basis the decision has been taken to replace boiler No. 4 of the Starobeshevo Power Plant with a boiler based on CFB technology. The unit is designed for 670 t/h of superheated and 538 t/h of reheated steam with 545 / 543 °C and 13.2 / 2.5 MPa temperature and pressure to account for the existing steam turbine which generates 200 MW electricity. Fuels used are a local anthracite and anthracite sludge left from coal washing and which is available in large quantities. Emissions are designed in accordance with European regulations allowing 200 mg/m3 (STP) for NOX and 200 mg/m3 (STP) for SO2. A basic description of the overall plant will be given. Details on the design of the CFB boiler which is equipped with Lurgi’s patented pant-leg and other design issues will be explained. Operating results from the commissioning and first commercial operation will be presented.
Biomass and Coal Co-Combustion in Utility Scale: Operating Experience of Alholmens Kraft
Authors: Kokko Ari , Nylund Marko
Published: October 2008

CFB technology has been scaled-up and demonstrated in the size range of around 250 MWe. One of the biggest advantages of CFB is it’s capability to burn different kind of fuels either at the same time or separately. The utilization of biomass alone or in co-combustion with coal has been demonstrated in this size scale in Alholmens Kraft CFB for three years now. Alholmens Kraft produces electricity for owners in Finland and in Sweden and also supplies process steam to the nearby UPM-Kymmene paper mill, and for district heating in town of Pietarsaari, Finland. The CFB boiler capacity is maximum 240 MWe. The Alholmens Kraft CFB boiler is a multi-fuel boiler, whose main fuels are bark, wood residue and peat, with coal as a support and back-up fuel. Bark and wood residue are low calorific, high moisture fuels with varying energy content and having also very heterogeneous physical properties. Peat is also low calorific fuel with high moisture content but with much more stable quality. Fuel consumption utilizing these fuel components is about 20 000 m3/d (700 000 ft3/d), which sets huge challenges to the whole logistic chain of fuel procurement. The maximization of CO2 neutral fuels is favoured, but some higher heating value and always available fuel, coal, is needed to ensure the high plant availability. Fuel mixture is variating all the time and it is optimized to fulfil operational, environmental and economical requirements. This paper describes the experience of using several fuel components in different operational situations during first three years of operation. The paper introduces also experiences of auxiliary system needed for reliable operation in co-combustion. The paper will also introduce the experience of the boiler controllability — changing load or fuel mixture — with this heterogeneous fuel combination. The co-combustion of biomass and coal is a real opportunity also in a large scale when including certain additional features in boiler and auxiliary equipment design. Interest towards co-combustion seems to be continuous-design considerations of a new boiler project of the same size is introduced in this paper.
Pore Structure of Coal-Chars Derived From Atmospheric and Pressurized Spouted Fluidized Bed Gasifiers
Authors: Duan Yufeng , Zhou Yi , Chen Xiaoping , Zhao Changsui , Wu Xin
Published: October 2008

Pore structure is one of the most important factors that dominate the reactivity of post-combustion of coal-chars derived from partial gasification process of atmospheric and pressurized spouted fluidized bed gasifiers. The influential factors on pore structure of coal-chars were analyzed in terms of the coal size feed, operational conditions, coal-char size and its components. It concluded that pyrolysis and devolatilization play a leading role in forming the pore structure of coal-chars in the partial gasification process. It is the reaction of coal-char with CO2 and H2O (steam) that plays a dominant positive impact on promoting enlargement and development of the coal-char pores at the elevated pressure gasification. There may exist an optimal coal-char size range that possesses abundant porosity and bigger pore specific surface area, which contributes to enhancing the gasification reactions in the atmospheric gasifier.
On Effect of Air-Separating Grid on Low-Grade Solid Fuels Combustion in a Fluidized Bed
Authors: Isemin Rafail L. , Kuzmin Sergey N. , Kondukov Nikolay B. , Mikhalev Alexsandr V. , Budkova Ekaterina V. , Konayahin Valentin V.
Published: October 2008

In furnaces and other types of fluidized bed reactors one can easily observe gas bubbles flow and fluid jet preferable rise zones where solid particles in form of fountains are carried away from the layer. Let us call these layers as zones of local flowing. We assume that in these zones of local flowing occurs the removal of unburned fuel particles from fluidized bed. It results in heat leakage up to 20–40% due to mechanical imperfection of fuel combustion in types of vessels with fluidized bed furnaces. We investigated particles with diameter of 2,5–3,0 mm motion and local flowing zones formation in a model column of 172 mm in diameter at room temperature. Experimental application of air-separating grid enabled to form at the layer input “flat” and “convex” air velocity line. At the “flat” line the air distributed uniformly on the input section of the device. When the line was “convex” the air velocity at the layer input in the device center was twice higher than at the device periphery. It was found out that at “flat” line when air velocity increases there appeared zones of local flowing in the layer. To eliminate these zones one should increase the height of stationary particles layer. At “convex” line of input air velocity elimination of local flowing zones is possible by stable increase of air velocity or by lowering the height of stationary particles layer. It was concluded that for small fluidized bed fireboxes it is better to apply air-separating grids forming “convex” input air velocity line. The grid under discussion was manufactured to be applied in experimental fluidized bed firebox. There was carried out a detailed study of ordinary anthracite combustion in a firebox. It was established that at “convex” input air velocity line fuel loss due to entrainment amounted 2,0–2,5%. According to experimental results there were designed water boilers with heating efficiency from 300 up to 800 kilowatt. In these water boilers there was applied the grid forming “convex” input air velocity line. During tests there was burned culm (particle size from 0 up to 6 mm, heating efficiency of 20,6 MJ/ kg, output of volatile matter up to 6%, zoning 26,2–31,1%). Efficiency factor of these water boilers is 83–85% (without entrainment return to the firebox).
Heat Transfer to Small Cylinders Immersed in a Fluidized Bed
Authors: Friedman Jacob , Koundakjian Polo , Rosero Dennis
Published: October 2008

Heat transfer to horizontal cylinders immersed in fluidized beds has been extensively studied, but mainly in the context of heat transfer to boiler tubes in coal-fired beds. As a result, most correlations in the literature have been derived for cylinders of 25–50mm diameter in vigorously fluidizing beds. In recent years, fluidized bed heat treating furnaces fired by natural gas have become increasingly popular, particularly in the steel wire manufacturing industry. These fluidized beds typically operate at relatively low fluidizing rates (G/Gmf < 5) and with small diameter wires (1–6mm). Nusselt number correlations developed based on boiler tube studies do not extrapolate down to these small size ranges and low fluidizing rates. In order to obtain reliable Nusselt number data for these size ranges, an experimental investigation has been undertaken using two heat treating fluidized beds; one a pilot-scale industrial unit and the other a lab-scale (300mm diameter) unit. Heat transfer measurements were obtained using resistively heated cylindrical samples ranging from 1.3 mm to 9.5 mm in diameter at fluidizing rates ranging from approximately 0.5 × Gmf (packed bed condition) to over 10 × Gmf using aluminum oxide sand particles ranging from dp = 145–330 μm (50 to 90 grit). It has been found that for all cylinder sizes tested, the Nusselt number reaches a maximum near 2 × Gmf, then remains relatively steady (± 5–10%) to the maximum fluidizing rate tested, typically 8–12 × Gmf. A correlation for maximum Nusselt number is developed.
Effect of Mineral Matters in Coal on Formation Behaviors of Particulate Matter and Alkali Metal Compounds During Coal Combustion
Authors: Takuwa Tsuyoshi , Naruse Ichiro
Published: October 2008

Combustion tests for 2 types of coal (SC and BT coals), which have similar combustion performance and main fraction in the ash compositions, were conducted, using an electrically heated drop tube furnace. The burning particles were sampled by the Low Pressure Impactor (LPI) and analyzed concentration of alkali metal in the collected particles. Furthermore, they were observed by a scanning electron microscope (SEM) to discuss formation behaviors of the fine particles during combustion. In order to elucidate the relationship between formation characteristics of fine particulates during combustion and coal types, analysis of included and excluded mineral particles in the raw coals was conducted by a Computer Controlled SEM (CCSEM). Additionally, the composition analysis of the mineral particles in the raw coal was also carried out, using an energy dispersive X-ray spectrometer (EDS). As a result, the particle size distribution of ash particulates formed was different each other for two types of coal. Especially for the fine particulates with the size of less than 1 μm, the result for SC coal showed much more fine particulates formation than those for BT coal. Sodium compounds were enriched in the fine particulates for both the coals. Shapes of the fine particles with the size less than 1 μm for both the coals were spherical. For the coarse particles, however, spherical particles were observed for only SC coal. This difference was due to difference of the characteristics of mineral particles in the raw coals. The CCSEM analysis indicated that the excluded mineral matters, which tended to fragment during combustion, were contained more in SC coal than those in BT coal. This is the reason why SC coal forms more fine particulates during combustion than BT coal. From the EDS analysis, moreover, content of sodium in the excluded minerals of SC coal was higher than that of BT coal. This result suggests that SC coal tends to form the spherical fine particulates, in which the sodium compounds are enriched, during combustion.
Retrofitting 25T/h Pulverized Coal-Fired Boiler Into 35T/h Circulating Fluidized Bed Boiler for Burning Mixture of Coal and Bagasse
Authors: Chen Han-Ping , Wang Xian-Hua , Zhang Shi-Hong , Liu De-Chang , Lai Yu-Hua , Tian Jian-Xin , Jiang Shao-You , Wei Shao-Peng , Liu Jian-Hui , Huang Ming-Ge
Published: October 2008

In China, there are a large number of pulverized coal-fired industrial boilers, whose steam capacities are usually relatively small. These boilers can burn only high-grade coal and have low combustion efficiency. Furthermore, the combustion emissions, such as SO2 and NOx, pollute the environment severely. Therefore it is very important and urgent to adopt economically efficient and environmentally friendly technologies to retrofit these boilers. At the same time, there are many industrial wastes, such as bagasse, wood waste, rubbish, petroleum coke and so on, need burning disposal in China. Fluidized bed combustion technology is a kind of clear combustion technology, which has many advantages, such as excellence fuel flexibility, high combustion efficiency, low pollutant emission and good turndown capability etc. So, adopting fluidized bed combustion technology, retrofitting pulverized coal-fired boiler into fluidized bed boiler can realize pure burning various wastes or co-firing with coal, which should have great economic benefits and social benefits. And the application prospect of the method is also extensive. The State Key Laboratory of Coal Combustion has successfully retrofitted a 25t/h pulverized coal-fired boiler into circulating fluidized bed boiler with in-bed tubes and downward exhaust cyclone. The retrofitted boiler can burn mixture of coal and bagasse and the steam capacity reaches 35t/h. This paper presents the retrofitting measures and the operation status of the boiler after retrofitting.
A Novel Technique for “In-Situ” Characterization of Devolatilization Rate of Solid Fuels in Fluidized Beds
Authors: Solimene R. , Chirone R. , Marzocchella A. , Salatino P.
Published: October 2008

The characterization of volatile matter (VM) emission from solid fuel particles during fluidized bed combustion/gasification is relevant to reactor performance influencing the fate of VM as it results from competing phenomena of release, mixing/segregation and burn-out. The rate and the time-history of volatile matter release strongly affect axial segregation of fuel particles in the bed, favoring the establishment of the stratified combustion regime. On the other hand, the comparison between the devolatilization and radial solids mixing time scales affects the radial distribution of volatile matter across the reactor. Short devolatilization times determine VM release localized near feeding point. The knowledge of devolatilization kinetics, as determined by thermogravimetric analysis, does not take into account key process phenomena such as the effective time-temperature history of the devolatilizing particle. A novel and easy-to-use diagnostic technique for “in-situ” characterization of the devolatilization rate of fuel particles in gas fluidized beds is proposed in the present paper. It is based on the time-resolved measurement of pressure in a bench scale fluidized bed reactor equipped with a calibrated flow restriction at the exhaust. The procedure consists of the injection of a single fuel particle (or small batches of multiple particles) and continuous monitoring of the pressure in the reactor. The bed was kept at a constant temperature by external heating and fluidized with nitrogen. Gas pressure inside the reactor increases during devolatilization as a consequence of the increased flow rate, due to the emission of volatile matter, across the calibrated flow restriction at the exhaust. Experimental data are analyzed in the light of a model of the experiment based on the transient mass balance on the reactor volume referred to the fluidizing gas and to the volatile matter. The comparison between experimental pressure time series and model computations enables the characterization of the kinetic parameters of devolatilization rate for samples of different coals as well as of non-fossil solid fuels.
Experimental Study of HCl Emission and Removal on Incinerating of Typical MSW Components in Fluidized Bed
Authors: Jiang Xu-Guang , Yan Jian-Hua , Li Xiang-Pai , Liu Bing-Chi , Lu Sheng-Yong , Chi Yong , Cen Ke-Fa
Published: October 2008

As incineration is widely used in the disposal of municipal solid waste (MSW), the relation of harmful gas HCl, SOx, NOx, CO from incineration should not be neglected. In order to study the characteristics of HCl emission and removal during MSW incineration, several kinds of typical MSW components are selected for experiments in a Φ 150mm fluidized bed test rig. The effect of temperature on Cl → HCl conversion rate is discussed; the influence of HCl concentration on emission of NO, SO2 during incineration is analyzed. Finally the effect of Ca-based sorbents on dechlorination is also discussed. Results show that The Cl → HCl conversion rate varies obviously as temperature increases. With the increase of HCl concentration, the concentration of NO decreases, The inhibition of HCl to NOx is very obvious. At the temperature of 920 °C the capture of SO2 become more than at the temperature of 880°C. The type and amount of Ca-based sorbents can affect dechlorination rate.
Experimental Measurement on Bubble Parameters During Fluidized Bed Scaling
Authors: Wang Xin , Lu Junfu , Zhang Jiansheng , Yang Hairui , Zhang Hai , Yue Guangxi , Suda Toshiyuki , Sato Junichi
Published: October 2008

An experimental verification is reported on the bubble parameter similarity during fluidized bed scaling. Two bubbling fluidized beds were designed according to Horio’s scaling method, and bubble size and mean bubble rising velocity were measured and compared. It can be concluded from the results that with the increment of u/umf, the similarity between two beds increases with respect to the bubble diameter and rising velocity. The analysis of the experimental data confirms the applicability of Horio’s method on bubble fluidized bed. When given dynamic behavior prediction of a real boiler is desired, the Horio’s law is valid to establish a cold model and the analysis method introduced in the present paper can be used.
An Experimental Study on N2O Reduction Over Circulating Ashes of CFB Boilers
Authors: Zhang Hai , Lu Junfu , Chen Keyu , Yang Hairui , Yue Guangxi
Published: October 2008

An experimental study on nitrous oxide (N2O) reduction with circulating ashes of circulating fluidized bed (CFB) boilers was conducted for the development of an effective and economical technology to reduce the N2O emission from CFB boilers. The experiments were conducted with three kinds of circulating ashes, by using a fixed bed reactor with a diameter of 25mm, under various conditions of different operational temperatures, initial N2O concentrations, NH3 additions and O2 concentrations. The effects on N2O reduction were compared that with quartz sand. The experimental results showed that circulating ashes may possess remarkable catalytic effect on N2O reduction and the intensity of the catalytic effect strongly depends on operational parameters such as reaction temperature and O2 concentration. It was also found nitric oxide (NO) was produced during the process of N2O reduction and its concentration also strongly affected by reaction temperature and O2 concentration. The mechanisms of N2O reduction were discussed. The study confirmed the feasibility of injecting NH3 at the cyclone entrance of CFB boiler to form a selective catalytic reduction (SCR) process for N2O emission without using extra catalyst and provided some guidance to choose the operational parameters for N2O reduction with circulating ashes.
Experimental Study on Characteristics of Pyrolysis, Ignition and Combustion of Blends of Petroleum Coke and Coal in CFB
Authors: Zhao Changsui , Chen Chuanmin , Chen Xiaoping , Wang Fengjun , Wang Wenxuan , Zhu Aiqiang , Wu Xin
Published: October 2008

It is a common understanding that co-firing of petroleum coke and coal in circulating fluidized bed (CFB) is an efficient, economical and environment-friendly way to utilize petroleum coke with medium or high sulfur content. Experimental investigations on characteristics of pyrolysis, ignition and combustion of petroleum coke, coal and their blends with different mixing ratios were conducted on a thermogravimetric analyzer and a pilot CFB combustor systematically. Ignition temperature and burnout temperature were also acquired. The effects of several parameters in terms of the fuel category, the heating rate, the coal/coke mass flow ratio, the CO2 partial pressure, and the Ca/S molar ratio on the ignition and burnout characteristics of the petroleum coke and the blends of the petroleum coke and coal were verified. The results show that the ignition temperature and the burnout temperature of the petroleum coke are between those of bituminous coal and anthracite, which implies that its combustion characteristic is between bituminous coal and anthracite, but is more closer to the bituminous. The pyrolysis process of blends of petroleum coke and coal accords with mechanism model (1−α)1.5 well, and the combustion process accords with mechanism model w1.5 well. Although the ignition temperature of the blended fuels keeps the same when the heating rate, or the CO2 partial pressure or the Ca/S molar ratio increases, the burnout temperature decreases gradually. With decrease in the coal/coke mass flow ratio, the ignition temperature and the burnout temperature of the blends rise.
Measurement of Heat Transfer in a 465t/h Circulating Fluidized Bed Boiler
Authors: Wang Yu , Lu Junfu , Yang Hairui , Zhao Xinmu , Yue Guangxi
Published: October 2008

The study of heat transfer and thermal boundary layer in the combustor of a circulating fluidized bed (CFB) is important to the boiler design and operation. Both heat transfer coefficient between the solid-gas flow and the water-wall and the thickness of thermal boundary layer are key data to determine the amount and layout of the tube walls in a CFB furnace. A series of experiments was conducted on a 465t/h commercial CFB boiler, which operated at bed temperature between 850 and 900°C, and at superficial gas velocity between 5.2 to 5.9m/s. Local bed to water wall heat transfer coefficients and temperature profiles near the wall were measured at a set of test ports at different heights of the sidewall. In the same time, the local solid bulk density near the wall was also measured. Special tools such as heat flux probe, solid bulk density sampling probe and temperature probe were developed for the experiments and their structures were introduced. The experimental results were compared with the data from previous studies. Theoretical analysis of the factors that play important role in heat transfer in a CFB boiler was also performed. The relationship between heat transfer and thermal boundary layer was also discussed. Furthermore, a simple model correlating the local heat transfer coefficients with bulk density was developed.
The Design and Operation of a New Clapboard-Type Internal Circulating Fluidized-Bed Gasifier
Authors: Wu Zhengshun , Zhu Chuanfang , Ma Long-Long , Wu Chuangzhi
Published: October 2008

The design and operation of a new clapboard-type Internal Circulating Fluidized-Bed gasifier is introduced in this paper. By setting clapboard in the middle of gasifier, bed layer in gasifier is divided into two regions that have different fluidization velocity, the incompletely reacted fuel or carbon in the high velocity region flows to the low velocity region companying with bed medium, and gasification reaction takes place in this region; still incompletely reacted fuel or carbon returns to the high velocity region in the bottom of gasifier, then gasification reaction further occurs. By this way, internal circulation in the gasifier was formed, gasification reaction time and efficiency increased. The experimental results indicate that gas yield (1.6 ∼ 1.9Nm3/kg fuel), gas heat values (5340kJ/Nm3 for wood chip fuel and 4880kJ/m3 for rice husk), and gasification efficiency (70%) can be obtained using this kind of gasifier in the optimal operational temperature range of 790∼850°C.
Investigation on Co-Combustion Characteristic of Paper Mill Waste and Coal in Circulating Fluidized Bed
Authors: Zhao Changsui , Sun Xin , Chen Xiaoping , Gu Lifeng , Li Yongwang , Yuan Ke
Published: October 2008

Experimental research on co-combustion of paper mill waste and coal was conducted in a pilot circulating fluidized bed combustor with a cross section of 0.23×0.23m2. Mixed waste of paper mill sludge and process residue from a paper company and bituminous coal were used in the experiments. The temperature distribution in the combustor was measured. The bottom ash and fly ash were sampled and analyzed. Six gas components were analyzed with a gas analyzer. The effects of some parameters, such as waste variety, fluidization velocity, secondary air rate, excess air, on the combustion characteristics and the emission of SO2 and NOx were clarified. The experimental results indicate that the incinerator temperature decreases with increase in secondary air rate and waste/coal mass ratio for the waste/coal mass ratios tested. When the excess air ratio increases, the dense bed temperature increases, but the temperature in the dilute phase region first increases, and then it decreases with further increase in the excess air ratio. The combustion efficiency increases with increase in the secondary air rate and decrease in the waste/coal mass ratio. With increase in the excess air ratio, the combustion efficiency first increases, then it reaches a peak and finally decreases. For the waste/coal mass ratio of 1.0, the highest combustion efficiency corresponds to the excess air ratio of 1.25. Higher desulfurization efficiency can be obtained with higher excess air, proper incinerator temperature and lower secondary air rate. The NO emission increases with increase in excess air ratio and decrease in the secondary air rate. Higher temperature, stronger staged air injection and lower excess air ratio are beneficial to suppressing N2O emission from incineration. The emission can be reduced by decreasing excess air ratio, increasing incinerator temperature and secondary air rate.
Trace Organic Pollutants Emission From Large-Scale Circulating Fluidized Bed Incinerators of Co-Firing Chinese MSW and Coal
Authors: Yan Jian-Hua , Lu Sheng-Yong , Gu Yue-Ling , Jiang Xu-Guang , Li Xiao-Dong , Cen Ke-Fa
Published: October 2008

Complex components, high moisture and low caloric value of raw Chinese MSW (Municipal Solid Waste) lead to the difficulties of keeping stable burning and low pollutant emission. Differential Density Circulated Fluidized Bed (DDCFB) incinerator was first developed by Zhejiang University to overcome such difficulties. The research of organic pollutants, especially dioxins and polycyclic aromatic hydrocarbons emission and control from MSW incinerators has been carried out in ITPE since 1998. The aim of this paper is to provide the scheme of a new co-firing CFB incineration technology, and useful data for environmental evaluation of trace organic pollutants emission from incinerators. The art of co-firing CFB is presented briefly in the first part of this paper. The dioxin content in original Chinese MSW is estimated to be 10 pg I-TEQ/g based on the data from Abad et al. Several test runs are conducted in a real-scale (150ton/day) incinerator co-firing MSW and coal to investigate dioxins and polycyclic aromatic hydrocarbons emission to ambient air. Test results show that dioxins input into the incinerator is estimated around 300∼600 mg I-TEQ/y, dioxins output is estimated 3∼100 mg I-TEQ/y, and dioxins emitted to ambient air is around 0.1∼15mg I-TEQ/y. It seemed that most of dioxins in original waste are decomposed by incineration process. For seventeen priority PAHs, its emission to ambient air is around 200∼4160g/y for co-firing runs, which is much more than 80g/y for coal combustion only. This suggests that PAHs emission to ambient air needed to be more concerned than dioxins. That is to say, PAHs emission regulatory should be proposed as soon as possible to restrict all incinerators. Several new incinerators (200 tons/day per unit and 300 tons/day per unit) were built by using new Co-firing CFB technology in past few years. From the environmental evaluation report, dioxins emission in stack gas is in range of 0.0025∼0.06 ng I-TEQ/Nm3, which seemed far below the European limit. The annual dioxin emission to air for 200ton/day or 300 t/d units is around 3∼6 mg I-TEQ. It shows that co-firing CFB incinerator is capable of reducing dioxin emission effectively. Based on industrial demonstration experience of new co-firing CFB incineration technology, it has been proven environmental friendly method for thermal treatment of MSW in developing countries. Some reasons for low dioxin emission of co-firing processes are discussed in this paper.
Co-Firing of Steam Coal With High Sulfur Content Lignite in a Bubbling Fluidized Bed Combustor
Authors: Selc¸uk Nevin , Gogebakan Yusuf , Altindag Hakan
Published: October 2008

Combustion and emission behavior of 100 % steam coal (SET 1) and a mixture of 80 % by weight steam coal and 20 % by weight local lignite, characterized by high sulfur and ash contents, (SET 2) were investigated in the 0.3 MWt Middle East Technical University (METU) Atmospheric Bubbling Fluidized Bed Combustor (ABFBC) Test Rig. Experiments were performed with limestone addition at various Ca/S molar ratios with fines recycle. In both sets of experiments, parameters other than Ca/S molar ratio were held as nearly constant as possible. On-line measurements of O2, CO2, CO, SO2, NOx emissions were carried out. Comparisons between the emissions show that lower NOx and SO2 emissions are obtained from combustion of steam coal/lignite mixture compared to those from steam coal only despite higher sulfur and almost equal nitrogen contents of the mixture. Calculated combustion efficiencies were found to be around 98 and 96 % for SET 1 and SET 2, respectively. As for the sulfur retention efficiencies, up to three times higher efficiencies were achieved when steam coal is co-fired with high sulfur lignite.
Study on Pollutants Emission Characteristic of Coal Gasification in a Fluidized Bed Test Rig
Authors: Zhong Zhaoping , Jin Baosheng , Huang Yaji , Zhou Hongcang , Ross Davide , Horio Masayuki
Published: October 2008

This paper presents the results of coal gasification in a fluidized bed test rig of Xuzhou bituminous coal. The diameter of the fluidized bed combustor is 0.1m and the height is 4.22m. The bed temperature is maintained by a method of high temperature flue gas interline heating to overcome high heat losses associated with a oil burner. Test results are reported for variations in the bed temperature, air to coal, steam to coal and Ca to S ratio and their influence on gas yields and desulphurization efficiency. The distribution of polycyclic aromatic hydrocarbons (PAHs) and heavy metal trace elements into the char and syngas are also presented. The molar contents for CH4 and H2 in the coal syngas are found to decrease with increasing air to coal feed ratio from 2.5 to 5, while the content of CO shows little variation. Increasing the steam to coal feed ratio from 0.4 to 0.65 results in all three of the main gas components measured to form a local maximum content at a steam/coal feed ratio of 0.55. The efficiency of desulphurization improves as the ratio of Ca to S, air to coal and the bed temperature are increased, while decreasing with increasing steam to coal feed ratios. The volatile trace element species in decreasing order of relative mass ratio released into the gas phase are Hg, Se, As, Co, Cr, Cd, Cu, and Zn. Besides Hg, Se, and As, for all other trace heavy metals the majority of their mass distribution remains within the char with the proportion contained within char always greater than their combined yields in the coal syngas and slag. The total PAHs in the coal syngas is greater than that contained in the original coal and this indicates that PAHs are formed during the coal gasification process.
Phosphorous in Ash From Co-Combustion of Municipal Sewage Sludge With Wood in a CFB Boiler: A Comparison of Experimental Data With Predictions by a Thermodynamic Equilibrium Model
Authors: Elled AnnaLena , A˚mand Lars-Erik , Andersson Bengt-A˚ke , Leckner Bo
Published: October 2008

Combustion tests have been carried out in a circulating fluidised bed (CFB) boiler co-firing wood and municipal, digested and mechanical dewatered sewage sludge from two Swedish wastewater treatment plants, using either iron sulphate or aluminum sulphate as precipitating chemicals. Experimental data on the concentration of various phosphorous compounds in the ashes are compared with theoretical equilibrium predictions. A clear relationship is not found between the employed precipitation chemical and the formation of phosphorous compounds in the ash. Hematite (Fe2O3(s)) is predicted to be the stable iron compound, and even in the sludge precipitated by iron sulphate, the aluminium content is sufficient to form aluminium phosphate (AlPO4(s)) in similar amounts as in the sludge precipitated by aluminium sulphate. Lime addition to the bed gives a decreased formation of AlPO4(s) in favour of calcium orthophosphate (Ca3(PO4)2(s)), which interferes with the sulphur capture efficiency of lime.
The Kinetics of Oxidation of Chars From Three Different Coals, as Measured in Fluidized Beds
Authors: Fennell P. S. , Hayhurst A. N. , Dennis J. S. , Kadchha S. , Lee H.-Y.
Published: October 2008

There is substantial disagreement over the order of the reaction between a coal char and O2. This is chiefly because of the difficulties of making good measurements when burning is kinetically controlled; thus heat and mass transfer can often obscure the true kinetics of the reaction. Consequently, a fluidized bed is an attractive reactor in which to measure the rate of this reaction. Chars from three different coals (of high, medium and low ranks) were prepared. The rate of oxidation of a char was measured by adding a small mass (∼ 3 mg) of tiny particles (sieved to 106–150 μm) of the char to a fluidized bed of silica sand (90–126 μm), which was electrically heated to a fixed temperature between 700 and 950°C. The fluidizing gas was a mixture of O2 and N2 at 1 bar; its composition varied between 0 and 100% O2. The concentrations of CO and CO2 were continuously measured in the off-gases from the bed, using i.r. analysers, thus enabling the rate of oxidation of the added batch of char to be measured. Interestingly, it was found necessary to modify the quartz cylinder housing the fluidized bed to prevent backmixing of ambient air into the freeboard. The char particles were sufficiently small that mass transfer to their exteriors did not control the rate of reaction. Furthermore, the rapid rates of heat transfer from the bed to the particles of char ensured that the char burned at the temperature of the bed. Likewise, the mass of added char was small enough for the rate of burning not to be controlled by inter-phase mass transfer. The maximum rate of oxidation was taken to be the initial rate, which could, at least in principle, be correlated with the initial properties of a char, such as its BET area, pore diameters, etc. The char of the low-rank coal burned with kinetics which were zeroth order in O2 and with a negligible activation energy. The other two coals had orders of reaction which were 0.7–0.8 at 700°C, but 0.2–0.25 at 950°C. These orders are discussed in detail.
Reactivation of FBC Ash as Sulphur Sorbent: Hydration and Sulphation Studies
Authors: Wang Jinsheng , Wu Yinghai , Anthony Ben
Published: October 2008

The efficiency of limestone utilization for in situ sulphur capture in fluidized bed combustors is low due to incomplete sulphation of CaO. Reutilization of the partially sulphated limestone sorbent for SO2 emission control is highly desirable both on economic and environmental grounds. Hydration of the FBC ash can reactivate the spent limestone so that the hydrated ash will take up SO2 effectively when reinjected into the combustors as SO2 sorbent. In this work hydration of ashes from a large fluidized bed combustor was studied with special focus on the hydration rate. Factors, which affect the rate and efficiency of the reactivation process, such as temperature, particle size, and hydration time, were examined and the effect of hydration on sulphation was also discussed.
2nd Generation PFB Plant With W501G Gas Turbine
Authors: Robertson A. , Fan Zhen , Goldstein H. , Horazak D. , Newby R. , Bose A. C.
Published: October 2008

Research has been conducted under United States Department of Energy (USDOE) Contract DE-AC21-86MC21023 to develop a new type of coal-fired, combined cycle, gas turbine-steam turbine plant for electric power generation. This new type of plant — called a 2nd Generation or Advanced Pressurized Fluidized Bed Combustion (APFB) plant — offers the promise of efficiencies greater than 48 percent (HHV) with both emissions and a cost of electricity that are significantly lower than those of conventional pulverized-coal-fired plants with scrubbers. In the 2nd Generation PFB plant coal is partially gasified in a pressurized fluidized bed reactor to produce a coal derived syngas and a char residue. The syngas fuels the gas turbine and the char fuels a pressurized circulating fluidized bed (PCFB) boiler that powers the steam turbine and supplies hot vitiated air for the combustion of the syngas. A conceptual design and an economic analysis was previously prepared for this plant, all based on the use of a Siemens Westinghouse W501F gas turbine with projected gasifier, PCFB boiler, and gas turbine topping combustor performance data. Having tested these components at a pilot plant scale and observed better than expected performance, the referenced conceptual design has been updated to reflect that test experience and to incorporate more advanced turbines e.g. a Siemens Westinghouse W501G gas turbine and a 2400 psig/1050°F/1050°F/2-1/2 in. Hg steam turbine. This paper presents the performance and economics of the updated plant design along with data on some alternative plant arrangements.
Preparation and Pumping Characteristics of Coal Water Paste Fired Into PFBC
Authors: Lu Ping , Xu Shengrong , Zhang Mingyao
Published: October 2008

Water seepage properties of coal water paste (CWP) under pressure are studied experimentally; the influences of particle size distribution, water content and limestone on the pumping properties of CWP are analyzed. By analyzing the pile pattern of coal particles and flowing properties of CWP in pipe, a novel method for evaluation coal water paste pumpability based on combination of the slump index and the amount of water seepage under pressure is proposed. It is found that the optimum mass ratio of coarse coal powders to the fines is 60:40 for Xuzhou coal of 0∼6 mm, coal water paste pumpability can be described by two indices, namely the slump index and the total water seepage quantity under pressure. The CWP with a good pumpability has a slump in the range of 80∼240mm. The corresponding relative water seepage rate and water seepage quantity are S10 ≤ 40% and V = 70∼110 ml, respectively.
A Novel Approach Towards Waste Treatment in FBC
Authors: Eldabbagh Fadi , Rink Karl K. , Kozinski Janusz A.
Published: October 2008

Waste combustion has the potential to play an important role in the energy production despite its contribution to heavy metals emissions. A new multi-zone temperature combustion technique, known as a Low-High-Low (LHL) temperature method, was developed to reduce pollutant emissions, particularly heavy metals, from FBCs. This paper focuses on the environmental impacts of biowaste combustion at different FBC conditions with emphasis on gas and solid emissions. The biowaste (de-inking sludge) studied contained 15% moisture, 27% carbon, 18% oxygen, and 35% ash. Ash elemental analysis shows a dominance of SiO2, Al2O3 and CaO (38%, 28% and 19%, respectively) with selected alkalis Na2O and K2O (0.3% and 0.2%, respectively). The used biowaste material had a heating value of 10,000 kJ/kg, which indicates that its combustion may be used to treat a portion of the total solid waste produced, while generating energy. The paper reports the following results of LHL vs. Classical FBC: (1) average axial profiles of gas concentrations (NO, NOx, and CO2) as well as their final averages at the exhaust, (2) final heavy metals leachability from generated fly ash. During the multi-temperature combustion experiments (LHL), the final average gas measurements for NO, NOx, and CO2 were 91 ppm, 175 ppm, and 6.1%, respectively. As for the classical FBC experiments, the final average gas measurements were similar (94 ppm, 141 ppm and 5.9% for NO, NOx and CO2, respectively). The final fly ash sample had leachability rates of 0.14 ppm and 0.061 ppm for Cd and Cr, respectively. Such low leachability rates are due to the LHL’s ability to form dense and compact final fly ash structures. On the contrary, 30.7 ppm and 14.3 ppm of Cd and Cr leached out of the porous no-LHL final fly ash structures, respectively. These results confirm that the LHL combustion could be considered as an effective waste-to-energy approach.
Biomass Combustion With Emphasis on Interactions Between Metals and Inorganic Particulate
Authors: Eldabbagh Fadi , Ramesh Appadurai , Rink Karl K. , Kozinski Janusz A.
Published: October 2008

Biomass is clean, stored solar energy. Not only is it a plentiful fuel, but its use also reestablishes the natural carbon cycle helping mitigate greenhouse gas emissions. This renewable energy source is nearly CO2 neutral. Overall, it is possible to achieve a 93% reduction in net CO2 emissions per unit heating value by switching from coal to biomass and a 84% reduction by switching from natural gas-fired cogeneration to biomass. Due to inherent advantages of the biomass in substituting fossil fuels, and increasing legislative pressures against CO2 emissions (Kyoto Protocol), biomass-based power is genuinely considered. It seems practically impossible to meet Kyoto requirements by replacing fossil fuels combustion with nuclear energy, hydropower or fuel cells. Simply, there is not enough time. In this context, there exists a niche for the biomass-based power generation. This paper compares interactions between metals and solid particles evolving from biomass during the classical Fluidized Bed Combustion (FBC) and a new Low-High-Low temperature (LHL) combustion. Experiments, conducted at a pilot-scale, reveal a clear pattern of surface predominance of light metals (Ca, K) and core predominance of heavy metals (Cd, Cr) within the LHL-generated particles. No such behavior was induced by the classical FBC approach. Metals migration is linked to the evolution of inorganic particles. A composite picture of the metals rearrangements in the particles was obtained by the combination of independent analytical techniques including electron probe microanalysis, field emission scanning electron microscopy, inductively-coupled plasma spectrometry and X-ray diffractometry. It is suggested that the combination of (i) the high-temperature region in the LHL and (ii) changes in the surface free energy of the particles is the driving force for the metal-particle behavior. Important practical implications of the observed phenomena are proposed including removal of hazardous submicron particulate and reduction in fouling/slagging during biomass combustion. These findings may contribute to redesigning currently operating FBC units in order to generate non-hazardous, non-leachable, re-usable particles where heavy metals are immobilized while environmental and technological problems reduced.
An Investigation on Low-Temperature Fluidized Combustion of Liquid Fuels
Authors: Ferrante Lorenzo , Miccio Michele , Solimene Roberto , Miccio Francesco
Published: October 2008

Presently, the combustion at low temperature is receiving a great deal of interest because emissions of micro- and nano-pollutants are expected to be greatly reduced. Following previous studies on the low temperature combustion behavior, the authors report results and discussion of steady-state experiments on an atmospheric, pre-pilot scale, 140 mm ID, FB reactor, equipped with an under-bed, air-assisted, liquid-fuel injector. The experimental program was focused on the operation at temperatures lower than the classical value for FBC of solid fuels (i.e., 850°C). The data series taken into consideration are the concentrations of the main unburned species in the splash zone, those of oxygen measured in the bed and in the splash zone as well as the freeboard pressure. The interpretation of the results is mainly based on the statistical analysis in the time domain. The combustion pattern of bio-diesel is compared to that of the diesel fuel under varying operating conditions (e.g., bed temperature, dispersion air velocity at the fuel nozzle, injector height in the bed). Conclusions that were previously published on the base of lab-scale results are checked against new data obtained on the pilot scale. An innovative technique for the analysis of the micro-explosive regime is presented. It consists in the comparison of oxygen concentration measured by the zirconia-based probes at different heights in the bed and in the splash region, pressure signals measured in the freeboard and purposely filtered, and video-recordings of the bed surface phenomena.
Alternative Bed Materials for High Alkali Fuels
Authors: Almark Matts , Hiltunen Matti
Published: October 2008

Fluidized bed combustion of high alkali fuels may cause agglomeration and defluidization of the bed as sodium and potassium react with quartz particles in the bed, forming alkali-silicate layers causing the particles to stick together. In certain cases the use of quartz free bed materials has been shown successful, like “Ofita” in the combustion of the residues from olive oil production in Spain. There are alternatives available to be used as quartz-free bed materials but some of them may be more expensive compared to natural sand. They are not always found in suitable form or particle sizes. Furthermore, the knowledge of the alternatives, and when it would beneficial to use them, is limited. The economics are not always favorable to using the alternative, effective but expensive bed materials since the build-up of harmful elements in bed usually can be avoided with sufficient make-up sand addition. A minimum level of make-up material addition is in any case necessary when combusting fuels with ashes that do not maintain the bed inventory. A study of minerals and materials available in Finland and elsewhere as possible bed make-up materials was carried out. The differences between these materials compared to quartz as a reference are investigated. The economics of the use of the alternative bed materials are discussed.
Combined Heat and Power Burning Coal Waste in ICFB
Authors: Virr Michael J.
Published: October 2008

The problem of burning coal waste to low emissions has existed for some time, although the larger boiler suppliers have installed successful designs for some years typically in the range of 40–80 MW’s. The author has been developing small automated fluid bed boiler plants for some 25 years, which can be successfully applied in the range of 10,000–140,000 lbs/hr of steam.
Bed Agglomeration During the Fluidized Bed Combustion of Olive Husk
Authors: Cammarota Antonio , Chirone Riccardo , Scala Fabrizio
Published: October 2008

The fluidized bed combustion of a biomass residue (olive husk) common in the Mediterranean area has been investigated in a bench scale reactor. The focus of the study was the high propensity of this fuel to give rise to bed agglomeration problems during combustion, as a consequence of the high alkali content of the ash. Bed agglomeration characteristic times as well as temperature and pressure gradients were measured at different operating conditions. In addition, a diagnostic tool based on the measurement of the dynamic pressure signal inside the bed was tested for its capability to predict the bed agglomeration onset.