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Condensation of water vapor and sulfuric acid in boiler flue gas.

机译:锅炉烟气中水蒸气和硫酸的冷凝。

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Condensation of vapors in flue gas is a complicated phenomenon since heat and mass transfer of water vapor and various acids simultaneously occur in the presence of non-condensable gases such as nitrogen and oxygen. Design of a condenser depends on the knowledge and understanding of the heat and mass transfer processes. A computer program for analytical modeling of water and sulfuric acid condensation in a flue gas condensing heat exchanger was developed using MATLAB. Governing equations based on mass and energy balances for water vapor condensation were derived to predict variables such as flue gas exit temperature, cooling water outlet temperature, mole fraction and condensation rates. The equations were solved using an iterative solution technique with calculations of heat and mass transfer coefficients and physical properties. An experimental study was carried out in order to yield data for validation of modeling results.;To evaluate the performance of a condensing heat exchanger, the term 'condensation efficiency' was defined as the ratio of total mass flow rate of condensed water from the heat exchangers to the incoming mass flow rate of water vapor on the flue gas inlet. Parametric studies for both modeling and experiments were performed to investigate the effects of parameters such as flue gas flow rate, cooling water flow rate, inlet cooling water temperature and tube configurations (bare and finned tubes) on condensation efficiency. Predicted results of water vapor condensation were compared with experimental data for model validation, and this showed agreement between experimental data and predictions to within a few percent. The most important parameters affecting performance of the condensing heat exchangers was the ratio of cooling water to flue gas flow rates, since this determines how much heat the cooling water can absorb.;Modeling results for prediction of sulfuric acid vapor concentration in the flue gas were compared with measured data obtained by the controlled condensation method. An analytical model for oil-firing showed two trends - steep reduction within high temperature HX and smooth reduction within lower temperature HX, which is in agreement with experimental data. An analytical modeling for coal-firing showed a larger discrepancy between predicted and measured sulfuric acid concentration in flue gas than the oil-firing analysis.;A full scale modeling developed for large scale condensing heat exchangers for application to a 625 MWe power plant in the range of m˙ c/m˙g,in from 0.5 to 1.0 with inlet cooling water temperature of 90 °F and heat transfer surface area of 50,000 ft 2 showed the condensation efficiency from 10.2 to 28.4 wt%. The investigation for effects of design parameters showed that the condensation efficiency was improved up to 15 %. The condensing heat exchanger had the largest effectiveness with a given heat transfer area when the flue gas flow rate was equal to the cooling water flow rate.
机译:烟气中蒸汽的冷凝是一个复杂的现象,因为在不可冷凝的气体(例如氮气和氧气)的存在下,水蒸汽和各种酸的传热和传质会同时发生。冷凝器的设计取决于对传热和传质过程的了解和理解。使用MATLAB开发了计算机程序,用于烟气冷凝热交换器中水和硫酸冷凝的分析建模。导出了基于质量和能量平衡的水蒸气冷凝控制方程式,以预测变量,例如烟气出口温度,冷却水出口温度,摩尔分数和冷凝率。使用迭代求解技术对方程进行求解,并计算了传热和传质系数以及物理性质。为了获得数据以进行建模结果验证,进行了实验研究。为了评估冷凝式换热器的性能,术语“冷凝效率”定义为冷凝水与热量的总质量流量之比。交换器将烟气入口上水蒸气的进入质量流率提高。进行了模型和实验的参数研究,以研究诸如烟道气流量,冷却水流量,入口冷却水温度和管道配置(裸管和翅片管)等参数对冷凝效率的影响。将水蒸气冷凝的预测结果与实验数据进行比较以进行模型验证,这表明实验数据与预测之间的一致性在百分之几以内。影响冷凝热交换器性能的最重要参数是冷却水与烟道气流量的比,因为这决定了冷却水可以吸收多少热量。预测烟道气中硫酸蒸气浓度的模型结果为与通过控制冷凝法获得的测量数据进行比较。烧油的分析模型显示了两个趋势-高温HX内的急剧降低和低温HX内的平稳降低,这与实验数据一致。燃煤的分析模型表明,烟气中预测和测量的硫酸浓度之间的差异比燃煤的分析更大;;为大型冷凝热交换器开发的全尺寸模型,用于625 MWe电厂点的范围入口冷却水温度为90°F,传热表面积为50,000 ft 2时,c / m·g,in在0.5至1.0之间,冷凝效率为10.2至28.4 wt%。对设计参数影响的研究表明,冷凝效率提高了15%。当烟气流量等于冷却水流量时,在给定的传热面积下,冷凝式热交换器的效率最高。

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