تجزیه و تحلیل حساسیت بر روی حداکثر مقاومت گنجشک از نظر ترکیب و غلظت آب گاز

Fly ash resistivity is one of the critical factors influencing its collection efficiency of electrostatic precipitators (ESPs). This paper discusses the resistivity in terms of ash compositions and water concentration and evaluates available resistivity models with over 120 groups of ashes. The analysis shows that the available models hardly match each other for predicating the resistivity. With regard to ash compositions, only Li2O plus Na2O and Fe2O3 have obvious effects on the maximum resistivity. A new simplifying model is proposed for approximating the maximum ash resistivity in terms of the ash compositions and the water concentration, which is used to size ESPs and to predicate the collection efficiency.

Today, electrostatic precipitators (ESPs) have been widely applied in industries, and a number of ESPs need to be upgraded for matching the latest emission standards. Our knowledge for predicating ESP performances, however, is still poor because of lack of reliable ESP models. Many factors do influence ESP performance, such as flue gas velocity, gaseous temperature and compositions, electrical power sources, ESP configuration and fly ash characteristics [1], [2], [3], [4] and [5]. Ash resistivity is one of the critical parameters to affect ESP’s collection efficiency and power consumption. For higher than 1012 Ω cm and smaller than 104 Ω cm ashes, ESP performance significantly deteriorates due to ash reentrainment. A small value of resistivity leads collected ash too fast losing its charge. A higher value, however, hardly leads to discharge its charges but to the so-called back corona [1] and [6]. As a result, ash reentrainment occurs in such cases. Many investigations have been performed to limit the reentrainment and/or back corona by optimizing electrode rapping [7], electrode construction [8], flue gas conditioning [9] and [10] and upgrading the power sources [11] and [12] for energy saving and emission reduction. Ash resistivity models have been very useful for selecting and/or blending coals and sizing ESPs in order to achieve a better ESP performance. Ash and gaseous compositions, electric field strength and temperature play key roles for determining its value. As a pioneer, R.E. Bicklhaupt proposed one analytical model to derive the resistivity in terms of ash compositions, electric field and gaseous temperature [13]. V. Arrondel and G. Bacchiega recently reported a comprehensive ESP model and also developed the so-called ORCHIDEE, by which the ash resistivity and the particle grade collection efficiencies can be evaluated in terms of coal characteristics and ESP specifications [14]. After Bicklhaupt’s model, Chandra proposed a revised one with new coefficients according to Indian utilities [15]. These three empirical models present the state of the art of theoretical investigations on the ash resistivity. Unfortunately, those models hardly match each other when considering ash effects on the resistivity. As part of our investigations on fine particle collection [19] and [20], this paper discusses those models and also proposes a new one by considering sensitivity analysis on the maximum resistivity with over 120 types of Chinese ashes. Its final objective is to develop an industrial ESP model for upgrading ESPs to control fine particle emissions.

Based on our analysis with over 120 groups of ashes, we give the following remarks on coal-fired fly ash resistivity: 1. Present available resistivity models hardly match each other when evaluating effects of ash compositions and gaseous temperature. 2. Based on the proposed normalization method, the maximum resistivity shows a simple relation with Li2O, Na2O, Fe2O3 and water concentration. Other ash compositions such as aluminum, potassium, calcium plus magnesia and sulphur show ignorable effects on the maximum resistivity.