Design and Performance Analysis of Air Pre heater for Water Tube Boiler to improve its Efficiency

Air preheater is a heat transfer surface in which air temperature is raised by transferring heat from other media such as flue gas which is coming from boiler exhaust. The paper presents the design of regenerative –air preheater to designed to meet specific performance requirements, using the software application CFD (Computational Fluid Dynamics) / CADD. An analytical study was planned to find out the various heat transfer performance parameters like outlet and inlet air temperature of the air preheater and the boiler, Pressure drop inside the Air preheater and the boiler heat transfer coefficients, heat transfer rate, overall heat transfer coefficient and Velocity of the air and flue gas also Conduction and convection modes of heat transfer were found. These heat transfer parameters are critical in designing and functioning of the air Preheater and to calculate the efficiency of the boiler.

Experimental Investigation of Ammonia and Sulfur Deposition Characteristics in Rotary Air Preheater

With the application of selective catalytic reduction (SCR) technology, the operation of rotary air preheaters is faced with a challenge, the fouling problem caused by ammonium bisulfate (ABS). In previous studies, within the operational temperature range of the preheater, the gaseous ammonia and sulfur trioxide (or H2SO4) in the flue gas can react to form ABS and ammonium sulfate (AS). The initial condensation temperature of ABS might be over predicted due to the effect of the formation of AS, which has a higher initial formation temperature than ABS. In this study, the effects of the deposition temperature, ammonia-sulfur molar ratio and molar product of inlet flue gas on the deposition characteristics of inducing ash deposition compounds were experimentally studied to provide guidance to prevent fouling and corrosion of rotary air preheaters. The results show that the main path to generate ABS is the reaction between H2SO4 and NH3. With the increase in the deposition temperature, the contents of NH4+ and SO42− in the sediments decrease continuously, and the proportion of AS deposition increases. On the contrary, with temperature decreasing, more ABS is deposited. When the molar ratio of ammo-sulfur in the inlet flue gas increases, the proportion of AS in the sediments increases, and the deposition rate also gradually increases. When the ammo-sulfur product in the inlet flue gas increases, the concentrations of both NH4+ and SO42− in the sediments increased in a nearly consistent trend. The variations of the ratio and deposition rates of the two ions in the sediments were not obvious. The ratio of NH4+ and SO42− remains at about 1.2, and the sediment is mainly ABS.

Data Driven Approach to Analyzing The Impact of Power Plant Cycling on Air Preheater Degradation and Remaining Useful Life

Due to the increased penetration of renewable energy generation sources, and fluctuations of the oil and gas prices, modern coal burning power plants deal with increased variability in the demand for power generation. These varying demands result in their intermittent under-capacity operation (cycling). Periodical ramping down and back up to follow the daily power demands causes damages to the plant components reducing its operational life. In this paper we analyze the impact of cycling on a rotary Ljungstrom air preheater (APH) unit installed at a coal fire power plant in the US. An inefficient air preheater can significantly impact boiler performance. Due to the repeated boiler’s hot-cold start, the APH experiences fluctuating operating conditions that result in accelerated degradation mechanisms, such as dew-point corrosion, fouling/deposition plugging, and air heater leakage. The analysis in this paper utilizes field data related to APH basket replacement, and the number of cycles experienced by the boiler to model the life expectancy of the baskets. The data-driven model enables preventive maintenance strategies for the APH by predicting how long the APH baskets will last in a probabilistic sense. The analysis showed that an increase in cycling for a fixed operation time can reduce the APH basket remaining useful life by about 30%.

Status and development for detection and control of ammonium bisulfate as a by-product of SCR denitrification

When denitrification technology using NH3 or urea as the reducing agent is applied to remove NOx from the flue gas, ammonium bisulfate (ABS) by-product will also be generated in the flue gas. ABS has an impact on catalyst life span, denitrification efficiency etc., air preheater and its downstream thermal equipment also have a significant negative impact due to its plugging and corrosion. The requirement for NOx removal efficiency is improved by ultra-low emissions in China. However, wide-load denitrification makes the flue gas composition and temperature changing more complicated. Increasing ammonia injection can improve the NOx removal effect, but too much ammonia injection will lead to the formation of ABS and the increase of deposition risk, the contradiction between these two aspects is amplified by ultra-low emissions and wide-load denitrification in many plants. Coordinating NOx control and reducing the impact of ABS on equipment are issues that the industry needs to solve urgently. In recent years, extensive research on ABS had been carried out deeply, consequently, there has been a relatively in-deepth knowledge foundation for ABS formation, formation temperature, deposition temperature, dew point temperature, decomposition behavior, etc., but the existing researches are insufficient to support the problem of ABS under full load denitrification completely resolved. Therefore, some analysis and detection methods related to ABS are reviewed in this paper, and the impact of ABS on SCR, air preheater and other equipment and the existing research results on reducing the impact of ABS are summarized also. It is hoped that this review will provide a reference for the industry to solve the problems of ABS that hinder wide-load denitrification and affect ultra-low emissions.

Effect of air combustion preheater on furnace efficiency by using refinery simulator

One of the basic crude oil refining steps is the heat up to high temperature about 3700 C, which is done in the furnace. The balance between fuel and air required to combustion provide an economical and efficient heating. In this research operating data of heating up the furnace are collected by using an interactive simulator of Drilling System Company (ORTIS) which gives a flexibility of operation cannot be obtained in real furnace, these data are related to find the operation paths under different control system of manual, automatic and working automatic without pre-heating are used . Using of combustion air preheater, by exchanging heat with the flue gases, leading to increase furnace heating efficiency from 85% to 93% also the fuel supplied to the burners is more less than working without preheater. As the simulator used in this research very closed to real operating system of furnace which cover all the variables of furnace inside temperatures, excess air analyzer, and fuel gas control and inside pressure control. The using of interactive simulator is very useful in stating the right operating conditions. The use of pre-heating of combustion air is best economical method to reach heating the crude oil to the required temperature with minimum fuel gas consumption, which directly affects the efficiencies of the furnace in each case.