Effects of air excess control in a heat storage solid fuel-fired household furnace

Due to a significant increase in electricity prices during the last decade and insufficient production capacity of the electric power industry in Serbia, many households that are currently using electric heat storage furnaces for heating have been forced to find an alternative solution for heating. A possible solution is replacing electric heating appliances with similar solid fuel-fired ones. Existing solid fuel-fired furnaces are often unsatisfactory with respect to their efficiencies and flue gas emissions. A prototype of a new concept of heat storage, solid fuel-fired furnace has been developed to meet these growing needs, providing electricity saving together with considerable environmental benefits. In order to examine furnace performance, efficiency and environmental aspects, and to assess the influence of air excess control in the furnace on the efficiency and flue gas emissions, numerous experimental tests were conducted. The amount of combustion air, the flue gas flow rate and the fuel feeding regime have been adjusted in order to keep the flue gas oxygen content in a relatively narrow range, thus obtaining controlled combustion conditions and, correspondingly, lower carbon monoxide emission and higher furnace efficiency. In this way, the furnace was made able to respond to the changes in heating needs, fuel quality and other parameters, which is considered to be advantageous in comparison with similar solid-fuel fired furnaces.     

Thermal and emission characteristics in a tangentially fired boiler model furnace

Tangentially fired furnaces are vortex‐combustion units and are intended for use as low NO formation furnaces. NO characteristics inside these furnaces depend on many parameters. The present study investigates numerically the problem of pollution in a real furnace of a 1699 MW tangentially fired boiler having 32 burners. NO formation contour maps in a tangentially fired furnace are presented. The study covered different combustion air temperature values, different fuel–air ratios and different cases of tripped burners. Available experimental measurements were used for validating the calculation procedure. The details of the temperature and NO fields were obtained from the solution of the conservation equations of mass, momentum and energy and transport equations for scalar variables in addition to the equations of the turbulence model. The equations governing the NO formation were solved to calculate the NO distribution. The simulation provided more insight on the correlation between the total NO concentration and the maximum furnace temperature and furnace average temperature. The results have shown that the furnace average temperature and NO concentration decrease as the excess air factor increases for a given air mass flow rate. As the combustion air temperature increases, furnace temperature increases and the thermal NO concentration increases sharply. The results show that the temperature distributions are significantly distorted by tripping any of the burners. The results show that tripping one or two burners either adjacent or opposite or tripping four results in regions of high temperature gases close to the walls. Heat absorptions in super‐heater and economizer are greatly influenced by combustion air temperature and excess air factor and are slightly influenced by burner tripping. Copyright © 2009 John Wiley & Sons, Ltd.     

工业炉窑节能的思考

从燃烧、传热的角度出发,依据热工的基本原理,对工业炉窑热量损失的各种途径进行了分析,系统地介绍了工业炉窑进行节能、改造的方法,对提高工业炉窑的热效率,节约能源,保护环境有一定的指导意义。     

Improving furnace energy efficiency through adjustment of damper angle

Numerous furnaces and boilers are extensively used in industrial and commercial facilities to generate thermal energy so that small improvements of the furnace thermal efficiency will amount to tremendous reduction of energy consumption and green gas emission. In this research, the furnace flue damper angle is adjusted to lower the pressure in the furnace for reducing the velocity of hot gas rising in the furnace. This allows more time for the heat to be transferred to the thermal flow that improves the furnace overall thermal efficiency. On the other hand, when the damper angle is adjusted from 45 to 39°, the pressure in the furnace rises from −14.7 to −9.3 mmH₂O, the average fuel volumetric flow rate reduces from 751 to 491 m³/h, and the average temperature lowers from 949 to 909 °C in the radiation section and from 756 to 798 °C in the conventional section. Hence, about 1.7 × 10⁶ m³ of fuel gas consumption can be saved, and 1.9 × 10³ ton of CO₂ emission can be reduced annually. The results confirm that simply by adjusting the flue damper angle of a furnace will achieve significant savings of energy and reduction of carbon dioxide emission.     

热管在油田加热炉上的应用研究

对热管元件应用于油田火筒式加热炉必须解决的技术关键问题进行了研究。根据传热学原理,给出了盈制热管工作温度的工程实用技术;针对油田加热炉改造问题,提出以热管流动阻力最小为目标函数的一种优化设计思想,用以限制烟气的流动阻力。通过40余台加热炉的改造实践证明,改造后加热炉的热效率平均提高8％左右,热管温度控制及烟气阻力控制是改造设计的关键。     

双级双向热底冷盖熔铝炉

介绍一种新型燃油熔铝炉。该炉是将大型熔铝炉分解成两组双级、双向炉,采用冷炉盖、热炉底连体结构以及预热炉料的烟气强迫循环系统,与４台普通单炉相比,可明显减少散热面和能量消耗。垂直炉料安装的整体烧嘴结构,能在整个熔炼周期内保持恒定均匀的供热强度,能将多品种、小批量合金组织在同一套熔炼设备中集中开炉,连续作业,是中小铝厂熔炼设备改造的理想炉型。     

订单生产对加热炉提出全新要求

对湘钢宽厚板加热炉进行了热平衡测试,其热效率为60.09%,可比单耗37.35kgce/t,在国内同类型加热炉能耗比较中处于中上水平。分析了订单化生产对加热炉经济指标造成的影响,湘钢宽厚板厂加热炉比国内先进同类型加热炉氧化烧损率高0.8%～0.9%,而炉底强度低300～600kg/(m2.h)。针对订单化生产对加热炉操作提出全新要求,湘钢需要不断优化生产组织,提高板坯质量,实施热送热装,完善加热炉操作控制。     

肝癌碘油栓塞后肝区平片所见碘油沉积量与疗效关系

本文分析了90例肝癌肝动脉灌注化疗碘油栓塞后,肝区平片所见碘油沉积量和疗效的关系。碘油沉积分为多,中,少三组,从ATP下降,肿瘤缩小率及一年生存率三方面比较。结果沉积多的与中等组三项都有显著差别;沉积中等的与少的组差别不明显。说明碘油沉积要达到一定的量后,疗效才会显著提高。同时分析了影响碘油沉积的几个因素。     

单元熔窑燃烧过程数值模拟

对单元熔窑燃烧空间内的流动,燃烧及辐射传热等过程进行数值模拟研究,比较燃烧布置方式对火焰形状及传热过程中的影响,结果表明,对于所研究的宽度为3．2m的窑炉,燃烧器的布置应采用错排方式。     

Unsteady‐state lumped heat capacity system design for tube furnace for continuous inline wire annealing process

A continuous annealing furnace is developed, which incorporates the principle of electric resistance heating for obtaining the desired temperature in the furnace. The concept of lumped heat capacity system is applied for the determination of annealing time of a continuously moving wire through the refractory tube. Also, the heat transfer inside the system and heat losses to the atmosphere are considered using the principles of conduction, convection, and radiation. The parameters related to the dynamics of moving wire are also designed. The designed furnace is fabricated and tested for its working, the observations of which show that 30 minutes are required to reach about 400°C furnace temperature and 30 seconds for annealing 1 m length of wire. The morphological testing of annealed and nonannealed wire is done to study the microstructure, which shows more traces of pearlite in annealed wires than in nonannealed wires. Thus, continuous annealing furnaces are more effective for inline annealing of wires; so as to relieve the internal stresses, induced by the step cold rolling process.     

高温空气燃烧技术的特点及其应用前景

高温空气燃烧技术（HTAC）是九十年代初在日本开发的一项新的燃烧技术,该项技术具有节约燃烧、低NOx排放、热利用率高和减设备尺寸等特点。分析了HTAC的火焰温度分布特征及其可降低NOx排放的原理。高炉煤气、焦炉煤气及94．5％高炉煤气与5．5％焦炉煤气的混合煤气应用于HTAC技术的理论计算结果表明,理论燃烧温度随着预热空气和燃气温度的升高而升高,因此HTAC技术可燃用传统燃烧方式不能使用的低热值燃气。此外,空气、燃气双预热可奖排烟温度将得更低,热利用率提高更高。最后,指出了在燃油、燃气锅炉及煤（或可燃固体废弃物）气化系统中采用HTAC技术的可能性。     

Efficiency analysis of radiative slab heating in a walking-beam-type reheating furnace

The thermal efficiency of a reheating furnace was predicted by considering radiative heat transfer to the slabs and the furnace wall. The entire furnace was divided into fourteen sub-zones, and each sub-zone was assumed to be homogeneous in temperature distribution with one medium temperature and wall temperature, which were computed on the basis of the overall heat balance for all of the sub-zones. The thermal energy inflow, thermal energy outflow, heat generation by fuel combustion, heat loss by the skid system, and heat loss by radiation through the boundary of each sub-zone were considered to give the two temperatures of each sub-zone. The radiative heat transfer was solved by the FVM radiation method, and a blocked-off procedure was applied to the treatment of the slabs. The temperature field of a slab was calculated by solving the transient heat conduction equation with the boundary condition of impinging radiation heat flux from the hot combustion gas and furnace wall. Additionally, the slab heating characteristics and thermal behavior of the furnace were analyzed for various fuel feed conditions.     

An evaluation on rice husks and pulverized coal blends using a drop tube furnace and a thermogravimetric analyzer for application to a blast furnace

To evaluate the potential of pulverized coals partially replaced by rice husks used in blast furnaces, thermal behavior of blends of rice husks and an anthracite coal before and after passing through a drop tube furnace (DTF) was investigated by using a thermogravimetry (TG). For the blends of the raw materials in the TG, fuel reaction with increasing temperature could be partitioned into three stages. When the rice husks were contained in the fuel, a double-peak distribution in the first stage was observed, as a consequence of thermal decompositions of hemicellulose, cellulose and lignin. A linear relationship between the char yield and the biomass blending ratio (BBR) developed, reflecting that synergistic effects in the pyrolytic processes were absent. This further reveals that the coal and the rice husks can be blended and consumed in blast furnaces in accordance with the requirement of volatile matter contained in the fuel. After the fuels underwent rapid heating (i.e. the DTF), a linear relationship from the thermogravimetric analyses of the unburned chars was not found. Therefore, the synergistic effects were observed and they could be described by second order polynomials. When the BBR was less than 50%, varying the ratio had a slight effect on the thermal behavior of the unburned chars. In addition, the thermal reactions of the feeding fuels and of the formed unburned chars behaved like a fingerprint.     

Modeling of thermal characteristics for a furnace of a 500 MW boiler fired with high-ash coal

An advanced zonal computational method has been used to determine the temperature and heat flux profiles and other thermal characteristics for a furnace of the 500 MW boiler fired with high-ash, medium-volatile Ekibastuz coal. The predicted temperature profiles for a 100% boiler load and different methods of fuel distribution through the burner tiers were compared with respective data obtained in experimental tests. The effects of the fuel dust fineness and excess air on the furnace temperature pattern were studied. The cases associated with the reduced boiler loads were considered as well. The lower limit for the boiler load has been established, based on the predicted results.     

Utilization of combustible waste gas as a supplementary fuel in coal‐fired boilers

A system is proposed to use the combustible waste gas as a supplementary fuel in coal‐fired boilers. The combustion air can be partially or fully substituted by ventilation air methane or diluted combustible waste gases. The recommended volume fraction of combustible waste gas in combustion air is no more than 1.0%. The effect of waste gas introduction on thermodynamic parameters of boiler is evaluated through thermal calculation based on material balance, heat balance, and heat transfer principles. A case study is conducted by referring to a 600 MW supercritical pressure boiler. The results show that no retrofit of boiler is required. The operation of boiler is scarcely influenced, and the original forced and induced draft fans can meet the requirement. With increasing volume fraction of combustible waste gas, the flue gas temperature at the furnace exit decreases monotonically, resulting in an increment of heat absorption in furnace and a decrement of heat transferred in convective heating surfaces. When 1.0% volume fraction of hydrocarbon gas is introduced, the thermal efficiency of boiler is increased by 0.5%, and the coal consumption rate is reduced by 25.4%. The cost analysis of the proposed system is conducted, and break‐even curves are given as references for the utilization of waste gas as a supplementary fuel. The economic velocity of the combustion air is suggested to be 18.2 m s^?1.     

Evaluation of a wood waste burner and heat recovery system—I. Operation,thermal efficiency and particulate emissions

In order to effect a substantial saving in fuel costs, Kakabeka Timber Co. has installed a novel system to heat air for the drying of lumber. This system, which replaces a propane fired heater, burns waste wood and uses an air-to-air heat exchanger to heat air for kiln-drying lumber. This paper presents an evaluation of the operation of, thermal efficiency of and particulate emissions from the furnace-heat exchanger unit.The furnace was fed with a mixture of sawdust and wood shavings, averaging about 12% moisture, at a rate of 95–150 kg/h. The heat output of the furnace varied from ≈0.3 to 0.45 MW with an average thermal efficiency of 53% based on the higher heating value of the fuel. The efficiency was found on the higher heating value of the fuel. The efficiency was found to decrease when the heat exchanger was heavily fouled with fly-ash, when the furnace was fed intermittently or fed at a rate exceeding 0.73 MW.The maximum emission rate of particulates from the stack was found to be ≈0.3 g/s when the furnace was fed intermittently. Decreasing the average feed rate and feeding continuously were found to decrease the emissions substantially.     

Performance of secondary aluminum melting: Thermodynamic analysis and plant-site experiments

This paper presents the results of plant-site experiments conducted on several natural-gas-fired, reverberatory aluminum furnaces to evaluate overall energy efficiency and to analyze major sources of heat loss, providing an overall picture of current aluminum melting furnaces in the US aluminum industry. Thermodynamic analyses were done for energy utilization according to energy balance and compared with the measured data. Our experimental results indicate that the effective energy efficiency in most melting furnaces measured is around 26–29%, and the major heat loss through flue gas is between 35% and 50%. The energy availability concept is introduced to predict the maximum energy potential and minimum flue gas heat loss in this type of aluminum furnace. Pollutant formation and control of nitrogen oxides and greenhouse gas are discussed. Methods that may improve energy efficiency and reduce pollutant emissions from melting operations are also addressed.     

陶瓷管少氧化加热炉节能的潜力

通过对炉子的热效率的研究,推出了研究加热设备节能潜力的数学方法,运用该法对陶瓷管少氧化加热炉(简称CT炉)节能潜力进行了评定。进而根据CT炉热平衡试验和对节能因素原则的分析提出了提高CT炉节能潜力的措施。     

Identifying and quantifying energy savings on fired plant using low cost modelling techniques

Combustion in fired heaters, boilers and furnaces often accounts for the major energy consumption on industrial processes. Small improvements in efficiency can result in large reductions in energy consumption, CO₂ emissions, and operating costs. This paper will describe some useful low cost modelling techniques based on the zone method to help identify energy saving opportunities on high temperature fuel-fired process plant.The zone method has for many decades, been successfully applied to small batch furnaces through to large steel-reheating furnaces, glass tanks, boilers and fired heaters on petrochemical plant. Zone models can simulate both steady-state furnace operation and more complex transient operation typical of a production environment. These models can be used to predict thermal efficiency and performance, and more importantly, to assist in identifying and predicting energy saving opportunities from such measures as:

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Improving air/fuel ratio and temperature controls.

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Improved insulation.

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Use of oxygen or oxygen enrichment.

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Air preheating via flue gas heat recovery.

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Modification to furnace geometry and hearth loading.

There is also increasing interest in the application of refractory coatings for increasing surface radiation in fired plant. All of the techniques can yield savings ranging from a few percent upwards and can deliver rapid financial payback, but their evaluation often requires robust and reliable models in order to increase confidence in making financial investment decisions. This paper gives examples of how low cost modelling techniques can be applied to improve confidence in implementing energy efficiency improvements whilst safeguarding manufacturing output and quality.     

Fracture prediction of electromagnetic silicon steel in reheating furnace

This article proposes the use of strain energy density (SED) for the prediction of fracturing in silicon steel slabs undergoing reheating in a furnace. Reheating is commonly used to soften steel before hot rolling into ultra-thin silicon steel sheets referred to as electromagnetic steel. High heating rates are required to reduce the time spent in the reheating furnace to increase the efficiency of producing ultra-thin electromagnetic steel sheets and decrease fuel consumption. However, an excessive increase in heating rates may induce fracturing due to the comparatively brittle nature of the silicon used in electromagnetic steel slabs to enhance the electromagnetic properties. In this study, the authors used finite element numerical calculation to elucidate the fracture mechanism of electromagnetic steel slabs undergoing heating. The authors then used SED as a criterion by which to optimize the heating rates without inducing fracturing in electromagnetic steel. The proposed model could be used as a guide to shorten the time required for heating various types of steel in reheating furnaces.