Environmental performance assessments of different methods of coal preparation for use in small-capacity boilers: experiment and theory

The purpose of this article is to receive environmental assessments of combustion of different types of coal fuel depending on the preparation(unscreened,size-graded,briquetted and heat-treated)in automated boilers and boilers with manual load-ing.The assessments were made on the basis of data obtained from experimental methods of coal preparation and calculated methods of determining the amount of pollutant and greenhouse gas emissions,as well as the mass of ash and slag waste.The main pollutants from coal combustion are calculated:particulate matter,benz(a)pyrene,nitrogen oxides,sulfur dioxide,carbon monoxide.Of the greenhouse gases carbon dioxide is calculated.As a result of conducted research it is shown that the simplest preliminary preparation(size-graded)of coal significantly improves combustion efficiency and environmental performance:emissions are reduced by 13%for hard coal and up to 20%for brown coal.The introduction of automated boil-ers with heat-treated coal in small boiler facilities allows to reduce emissions and ash and slag waste by 2-3 times.The best environmental indicators correspond to heat-treated lignite,which is characterized by the absence of sulfur dioxide emissions.

R&D and Demonstration of Large Domestic CFB Boilers

In order to develop large CFB boilers with independent intellectual property, Xi'an Thermal Power Research Institute (TPRI) established a laboratory with complete functions for the technical development of CFB boilers. This laboratory consists of a 1-MW and a 4-MW CFB combustion test facilities and a laboratory for limestone desulphurization performance evaluation. It carried out tests on CFB combustion and desulphurization for Chinese typical coals and limestone and research on heat-transfer characteristics and key parts, and developed the first home-made 100-MW CFB boiler. Based on the experience of R&D, the laboratory further researched key techniques for enlarging capacity systematically, and cooperating with Harbin Boiler Co. (HBC), developed the first domestic 210-MW CFB boiler with independent intellectual property and put it into engineering demonstration, laying a solid foundation for the development of CFB boilers of even larger capacity.

Smart Boilers: Grid Support Services from Non-Critical Loads

The aim of this paper is to present the concept of a simple and cheap upgrade for electric water boilers, allowing them to provide power quality services to the distribution grid. The upgrade requires only minimum additional hardware and it is easily installable. “Smart Boilers”, as the upgraded boilers are named, perform precise active and reactive power control, but most significantly mitigate line current harmonics. Αctive and reactive power control is implemented by appropriate regulation of the modulation sinewave amplitude and phase, respectively. This type of control is easily customizable in order to accommodate a variety of power quality targets, depending on the required level of services and available grid monitoring equipment. The method used for line current harmonic compensation is based on the injection of mirror harmonics created at the modulation stage of the converter. It is indifferent of harmonic source: it is equally successful at mitigating harmonics caused by the power electronic converter of the Smart Boiler, other sources of current harmonics or loads. The achieved grid services are clearly beyond the “on/off” operation of electric boilers, currently implemented by Demand Side Management (DSM) in order to shift load away from peak hours. It has been demonstrated through simulations, that Smart Boilers can assist voltage regulation at terminal buses, compensate reactive power and suppress harmonic currents at lines.

INTRODUCTION TO INCONEL ALLOY 740: AN ALLOY DESIGNED FOR SUPERHEATER TUBING IN COAL-FIRED ULTRA SUPERCRITICAL BOILERS

Chinese utilities as well as those worldwide are facing increased demand for additional electricity, reduced plant emissions and greater efficiency. To meet this challenge will require increasing boiler temperature, pressure and coal ash corrosion resistance of the materials of boiler construction of future coal-fired boilers. A new nickel-based tube alloy, INCONEL^R alloy 740, is described aiming at meeting this challenge. Emphasis will be on describing the alloy＇ s mechanical properties, coal-ash and steam corrosion resistance. Microstructural stability as a function of temperature and time is addressed as well as some of the early methodology em- ployed to arrive at the current chemical composition.

Optimization of Load Assignment to Boilers in Industrial Boiler Plants

Along with the increasing importance of sustainable energy, the optimization of load assignment to boilers in an industrial boiler plant becomes one of the major projects for the optimal operation of boiler plants. Optimal load assignment for power systems has been a long-lasting subject, while it is quite new for industrial boiler plants. The existing methods of optimal load assignment for boiler plants are explained and analyzed briefly in the paper. They all need the fuel cost curves of boilers. Thanks to some special features of the curves for industrial boilers, a new model referred to as minimized departure model (MDM) of optimization of load assignment for boiler plants is developed and proposed in the paper. It merely relies upon the accessible data of two typical working conditions to build the model, viz. the working conditions with the highest efficiency of a boiler and with no-load. Explanation of the algorithm of computer program is given, and effort is made so as to determine in advance how many and which boilers are going to work. Comparison between the results using MDM and the results reported in references is carried out, which proves that MDM is preferable and practicable.

Fault Diagnostics on Steam Boilers and Forecasting System Based on Hybrid Fuzzy Clustering and Artificial Neural Networks in Early Detection of Chamber Slagging/Fouling

The slagging/fouling due to the accession of fireside deposits on the steam boilers decreases boiler efficiency and availability which leads to unexpected shut-downs. Since it is inevitably associated with the three major factors namely the fuel characteristics, boiler operating conditions and ash behavior, this serious slagging/fouling may be reduced by varying the above three factors. The research develops a generic slagging/fouling prediction tool based on hybrid fuzzy clustering and Artificial Neural Networks (FCANN). The FCANN model presents a good accuracy of 99.85% which makes this model fast in response and easy to be updated with lesser time when compared to single ANN. The comparison between predictions and observations is found to be satisfactory with less input parameters. This should be capable of giving relatively quick responses while being easily implemented for various furnace types.

Correlating furnace characteristics of utility boilers with coal characteristics

1.IntroductionCoal is listed in China’s energy policy as the predominant fuelto be used for thermal power generation.It includes nearly the wholespectrum of coals that China has,ranging from anthracite to browncoal.This poses a situation to China’s utility boiler manufacturers thattheir products have to cope with all kinds of coal available.China is now producing a full range of utility boilers with ca-pacities from 35 t/h through 2000 t/h.They have successfully burnedanthracities with volatile matter greater than 7% and low grade coalswith high moisture and high ash contents.They burn bituminouscoals and lignites with satisfactory efficacy.

Development and Installation of High Pressure Boilers for Co-Generation Plant in Sugar Industries

The sugar cane containing minimum 30% fiber was referred as bagasse and used the generation of power required for the operation of sugar mill. The bagasse is fired in the boiler for producing steam at high pressure, which is extracted through various single high capacity turbines and used in the process. The installation of high pressure boilers and high pressure turbo-generators has provision for the operation of co-generation plant during the off-season also that enhances the power generation from 9MW to 23MW. The annual monetary benefits achieved are Rs. 204.13 million and this was based on cost of power sold to the grid @ Rs 2.548 per unit, sugar season of 219 days and off season of 52 days. This required an investment of Rs 820.6 million. The investment had an attractive simple payback period of 48 months.

Development of 600 MW Class Coal Fired Boilers in China

This article introduces the present status anddevelopment of 600 MW class boilers in China. The statisticaldata indicate that most 600 MW generating units experiencedrelatively length" growing up" period. In this period, unitscould not operate stably , their unplanned outage times weremany and durations long, and availabilities low. On the basis oftesting and research and the summing-up of practice, it wasindicated slagging in the furnace, deviation of tine gas energy atthe exit of furnace, and overheating bursting of superheater andreheater etc, endangering the safety and economics ofoperation,main problems could be completely alleviated oravoided through design and type selection of boiler furnace andburners, coal characteristics and coal handling management,and optimization management of operation conditions etc.

Combustion and Self-Desulfurization Characterization of Blended Low-Rank Coals for Improved Resource Utilization in Fluidized Bed Boilers

The co-combustion of low-rank coals through fluidized bed boiler(CFB)is an effective approach to enhance the level of resource utilization.To date,there has been a lack of investigation concerning the co-combustion kinetics and self-desulfurization characteristics of coal slime,coal gangue,and raw coal.In this study,we adopted multiple model-free and model-fitting methods to comparatively analyze co-combustion kinetics of blended coals on the basis of thermogravimetric data.Then,the sulfur balance and self-desulfurization of blended coals in the co-combustion were intensively investigated using a tube furnace set-up.The results reveal that in the presence of coal gangue in blended coals,the average activation energy(E_(a))falls within the range of 65.7 kJ/mol to 100.4 kJ/mol,as determined by four model-free methods.Conversely,in the absence of coal gangue,only the Flynn-Wall-Ozawa(FWO)and Friedman(FM)methods are deemed appropriate for calculating the average E_(a),yielding a value of 77.3 kJ/mol.The first order reaction model is confirmed to be reliable for analyzing the co-combustion kinetics of low-rank blended coals.Irrespective of the specific composition of the blended coal,a significant linear correlation exists between the Ea and the natural logarithm of the pre-exponential factor(lnA)within an extensive range of parameters.Moreover,the addition of coal gangue to the blended coal substantially enhances the self-desulfurization level,resulting in an increase from 25.7%to60.7%at 1073 K.The self-desulfurization efficiency exhibits a good linear relationship with both the mass ratio of coal gangue to coal slime and the molar ratio of calcium to sulfur.In a practical implementation,the optimal addition ratio of coal gangue is a trade-off between the self-desulfurization efficiency and the ignition capacity.

Comparative investigation of coal-and oil-fired boilers based on emission factors,ozone and secondary organic aerosol formation potentials of VOCs

Volatile organic compounds(VOCs)are the important precursors of the tropospheric ozone(O3)and secondary organic aerosols(SOA),both of which are known to harm human health and disrupt the earth’s climate system.In this study,VOC emission factors,O3 and SOA formation potentials were estimated for two types of industrial boilers:coal-fired boilers(n=3)and oil-fired boilers(n=3).Results showed that EVOCs concentrations were more than nine times higher for oil-fire d boilers compared to those for coal-fired boilers.Emission factors ofΣVOCs were found to be higher for oil-fired boilers(9.26-32.83 mg-VOC/kg)than for coal-fired boilers(1.57-4.13 mg-VOC/kg).Alkanes and aromatics were obtained as the most abundant groups in coal-fired boilers,while oxygenated organics and aromatics were the most contributing groups in oil-fired boilers.Benzene,n-hexane and o-ethyl toluene were the abundant VOC species in coal-fired boiler emissions,whereas toluene was the most abundant VOC species emitted from oil-fired boilers.O3 and SOA formation potentials were found 12 and 18 times,respectively,higher for oil-fired than for coal-fired boilers.Total OFP ranged from 3.99 to 11.39 mg-O3/kg for coal-fired boilers.For oil-fired boilers,total OFP ranged from 36.16 to 131.93 mg-O3/kg.Moreover,total secondary organic aerosol potential(SOAP)ranged from 65.4 to 122.5 mg-SOA/kg and 779.9 to 2252.5 mg-SOA/kg for the coal-fired and oil-fired boilers,respectively.

PARTICULATE CONCENTRATION ENRICHMENT OF PRIMARY AIR IN PULVERIZED COAL BOILERS

Particulate concentration enrichment (PCE) of primary air favors flame ignition and stabilization, and the reduction of NOx emission in pulverized coal combustion. The methods used for PCE are summarized in five categories: Cyclone PCE, Elbow PCE, Blunt-body PCE, Hydrodynamic PCE and Swirling PCE. Practice of each PCE method is il- lustrated with typical burners and the associated pros and cons are discussed. It is found that the same principle prevails in all PCE methods, that is, due to inertial difference, solid particles preferentially decelerate and separate from the gas stream when the main flow deviates in flow orientation. From analysis of various P-C burners, PCE design is deemed to yet comprise “rule of thumb” practice. Somediscussions regarding PCE application are given.

Theoretical analysis for sound wave scattering by parallel cylindrical tubes in boilers

Although the sonic soot cleaning techniques have been applied in boilers in power plants, petrochemical works and general industries world wide, most of the correlated basic problems have not been well solved yet. By using Helmholtz integral equation, sound wave scattered by heat-exchanger tubes is numerically calculated. Sound field distribution characteristics on the tube surfaces and around the tube group is obtained. The results can be applied to the development of sonic soot cleaning techniques in boilers.

Emission factors, ozone and secondary organic aerosol formation potential of volatile organic compounds emitted from industrial biomass boilers

To evaluate the potential benefits of biomass use for air pollution control, this paper identified and quantified the emissions of major reactive organic compounds anticipated from biomass-fired industrial boilers. Wood pellets(WP) and straw pellets(SP) were burned to determine the volatile organic compound emission profiles for each biomass-boiler combination. More than 100 types of volatile organic compounds(VOCs) were measured from the two biomass boilers. The measured VOC species included alkanes, alkenes and acetylenes, aromatics, halocarbons and carbonyls. A single coal-fired boiler(CB) was also studied to provide a basis for comparison. Biomass boiler 1(BB1) emitted relatively high proportions of alkanes(28.9%–38.1% by mass) and alkenes and acetylenes(23.4%–40.8%),while biomass boiler 2(BB2) emitted relatively high proportions of aromatics(27.9%–29.2%)and oxygenated VOCs(33.0%–44.8%). The total VOC(TVOC) emission factors from BB1(128.59–146.16 mg/kg) were higher than those from BB2(41.26–85.29 mg/kg). The total ozone formation potential(OFP) ranged from 6.26 to 81.75 mg/m^3 with an average of 33.66 mg/m^3 for the two biomass boilers. The total secondary organic aerosol potential(SOAP) ranged from 61.56 to 211.67 mg/m^3 with an average of 142.27 mg/m^3 for the two biomass boilers.The emission factors(EFs) of TVOCs from biomass boilers in this study were similar to those for industrial coal-fired boilers with the same thermal power. These data can supplement existing VOC emission factors for biomass combustion and thus enrich the VOC emission inventory.

Heat and power load dispatching considering energy storage of district heating system and electric boilers

As one of promising clean and low-emission energy, wind power is being rapidly developed in China.However, it faces serious problem of wind curtailment,particularly in northeast China, where combined heat and power(CHP) units cover a large proportion of the district heat supply. Due to the inherent strong coupling between the power and the heat load, the operational flexibility of CHP units is severely restricted in winter to meet the heat supply demand, which imparts considerable stress on the wind power connection to the grid. To promote the integration of wind power and enhance the flexibility of CHP units, this paper presented a method of heat and power load dispatching by exploring the energy storage ability of electric heating boilers and district heating systems. The optimization results indicate that the proposed method can integrate additional wind power into the grid and reduce the coal consumption of CHP units over the optimized period. Furthermore, the thermal inertia of a district heating system is found to contribute more to the reduction of coal consumption, whereas the electric heating boilers contribute to lower wind curtailment.

Accommodation of Curtailed Wind Power by Electric Boilers Equipped in Different Locations of Heat-supply Network for Power System with CHPs

Electric boilers (EBs) provide an alternative method to deal with the accommodation of curtailed wind power. To pursue the minimum coal consumption in the system, a dispatching model integrating combined-heat-and-power (CHP) plants and EBs in different locations is developed, and the penalty of wind power curtailment and cost of EB employment are also incorporated in the model. The transmission loss and transportation lag of heat-supply network as well as the elasticity of heat load are considered in this paper. A kind of constrained programming with stochastic and fuzzy parameters is applied to deal with the uncertainties. A case in East Inner Mongolia in China demonstrates that the EBs are able to absorb curtailed wind power and supply the heat. The results indicate that the utility of EBs in the primary or secondary heat-supply network to accommodate curtailed wind power is mainly related to the efficiency of heat transmission and the elasticity of heat load.

Characteristics of particulate-bound polycyclic aromatic hydrocarbons emitted from industrial grade biomass boilers

Polycyclic aromatic hydrocarbons（PAHs） are carcinogenic or mutagenic and are important toxic pollutants in the flue gas of boilers. Two industrial grade biomass boilers were selected to investigate the characteristics of particulate-bound PAHs： one biomass boiler retro-fitted from an oil boiler（BB1） and one specially designed（BB2） biomass boiler. One coal-fired boiler was also selected for comparison. By using a dilution tunnel system, particulate samples from boilers were collected and 10 PAH species were analyzed by gas chromatography–mass spectrometry（GC–MS）. The total emission factors（EFs） of PAHs ranged from 0.0064 to0.0380 mg/kg, with an average of 0.0225 mg/kg, for the biomass boiler emission samples. The total PAH EFs for the tested coal-fired boiler were 1.8 times lower than the average value of the biomass boilers. The PAH diagnostic ratios for wood pellets and straw pellets were similar.The ratio of indeno（1,2,3-cd）pyrene/[indeno（1,2,3-cd）pyrene ＋ benzo（g,h,i）perylene] for the two biomass boilers was lower than those of the reference data for other burning devices, which can probably be used as an indicator to distinguish the emission of biomass boilers from that of industrial coal-fired boilers and residential stoves. The toxic potential of the emission from wood pellet burning was higher than that from straw pellet burning, however both of them were much lower than residential stove exhausts.

Field and CFD Study of Fuel Distribution in Pulverized Fuel(PF)Boilers

The article presents both field and CFD results of a new concept of a mechanical pulverized fuel(PF)distributor.The goal of the study was to improve the pulverized coal-air mixture separation in PF boilers where the fuel preparation and feeding system was operated in a combined coal and biomass grinding conditions.The numerical analysis was preceded after a field study,where measurements were carried out in a pulverized coal-fired(PC)boiler equipped with a technology of NOx reduction by means of primary methods.Proper distribution of a pulverized coal-air mixture to the individual burners is one of the fundamental tasks of the combustion systems where the primary methods are implemented to control the NOx emission.Problems maintaining the proper distribution of fuel to the burners related primarily to the boilers where the coal and biomass co-grinding is used.Changing the load of coal-mills and fuel type at the same time(i.e.,different types of biomass)could result in less effective separation of pulverized fuel particles in PF distributors.Selection of an appropriate construction of a distributor will allow the better control of the combustion process which results in decreased NOx emission while keeping the proper combustion efficiency,i.e.,less unburned carbon(UBC)in the fly ash.The results of the field measurements made it possible to create a CFD distribution base model,which was used for the analysis of a new splitter construction to be used in a PF distributor.Subsequent analysis of the numerical splitter enables precise analysis of its construction,including the efficiency of separation and the prediction of conveying of the coal and biomass particles.

Modelling and analyzing the impact of hydrogen enriched natural gas on domestic gas boilers in a decarbonization perspective

Decarbonization of energy economy is nowadays a topical theme,and several pathways are under discussion.Gaseous fuels have a fundamental role for this transition,and the production of low carbon-impact fuels is necessary to deal with this challenge.The generation of renewable hydrogen is a trusted solution since this energy vector can be promptly produced from electricity and injected into the existing natural gas infrastructure,granting storage capacity and easy transportation.This scenario will lead,in the near future,to hydrogen enrichment of natural gas,whose impact on the infrastructures is being actively studied.The effect on end-user devices such as domestic gas boilers,instead,is still little analyzed and tested,but is fundamental to be assessed.The aim of this research is to generate knowledge on the effect of hydrogen enrichment on the widely used premixed boilers:the investigations include pollutant emissions,efficiency,flashback and explosion hazard,control system and materials selection.A model for calculating several parameters related to combustion of hydrogen enriched natural gas is presented.Guidelines for the design of new components are provided,and an insight is given on the maximum hydrogen blending bearable by the current boilers.

PM10 emissions from industrial coal-fired chain-grate boilers

Industrial coal-fired boiler is an important air pollutant emission source in China. The chain-grate boiler is the most extensively used type of industrial coal-fired boiler. An electrical low-pressure impactor, and a Dekati？ Low Pressure Impactor were applied to determine mass and number size distributions of PM10 at the inlet and the outlet of the particulate emission control devices at six coalfired chain-grate boilers. The mass size distribution of PM10 generated from coal-fired chain-grate boilers generally displays a bimodal distribution that contains a submicron mode and a coarse mode. The PM in the submicron mode for burning with raw coal contributes to 33% ± 10 % of PM10 emissions, much higher than those for pulverized boilers. And the PM in the submicron mode for burning with briquette contributes up to 86 % of PM10 emissions. Multiclones and scrubbers are not efficient for controlling PM10 emission. Their average collection efficiencies for sub-micron particle and super-micron particle are 34% and 78%, respectively. Operating conditions of industrial steam boilers have influence on PM generation. Peak of the submicron mode during normal operation period is larger than the start-up period.