Analysis of ammonium bisulfate/sulfate generation and deposition characteristics as the by-product of SCR in coal-fired flue gas

Nitrogen oxide (NOx) emitted from boilers in coal-fired power plant may be reduced by 90 percent through the application of the selective catalytic reduction (SCR). However, the escaped ammonia from the SCR systems could react with sulfur oxides (SOx) in the flue gas to form ammonium bisulfate (ABS) in exhaust systems. The blockage and corrosion caused by ABS seriously impact the rotary air preheater (RAPH), which would not only increase operating cost on ash-blowing and cleaning but also lead to unplanned outage. To solve the problem, in this paper a novel preheater system is proposed. A single preheater is split into two sub-preheaters, between which the main flue gas flow is mixed with the recirculated flue gas from outlet of the lower-temperature preheater. After the mixing point, a reaction chamber and a precipitator are installed. A numerical finite difference method (FDM) is employed to model the RAPH and obtain the accurate temperature distribution of fluid and heat transfer elements. The initial formation temperatures of (NH4)2SO4 and ABS are 200 °C and 170 °C, respectively, according to the flue gas composition in this work. By calculation, this split design of the RAPH is believed to be effective in reducing deposition of ABS.

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The Causes Analysis of the Air Preheater and Performance Blocking Evaluation of the Measures on the SCR De-NOx Unit

E3S Web of Conferences ◽

10.1051/e3sconf/201911803056 ◽

2019 ◽

Vol 118 ◽

pp. 03056

Author(s):

Su Pan ◽

Pengfeng Yu ◽

Linbo Liu ◽

Jing Han ◽

Xiao Shen

Keyword(s):

Flue Gas ◽

Differential Pressure ◽

Control Measures ◽

Gas Temperature ◽

Air Preheater ◽

Environment Temperature ◽

Ammonium Bisulfate ◽

And Performance ◽

Exhaust Gas Temperature ◽

Ammonia Injection

In order to solve the problem of abnormal rise of the differential pressure of the revolving air preheater on 300MW unit, we analysed the causes of abnormal rise of the differential pressure of the air preheater and evaluated performances of control measures, through historical data mining and on-site inspection of the unit. The results show that, with the gradual decrease of environment temperature with the decrease of the exhaust gas temperature, the ashes in flue gas are bound by acid liquid produced by condensation of flue gas, and the adhesion areas of the ammonium bisulfate produced in the denitration process are enlarged. However the original set ash blowing pressure can no longer satisfy the requirements of the air preheater, giving rise to the differential pressure of the air preheater on both sides to rise. The reason of the higher differential pressure of the unilateral air preheater is that the large ammonia injection amount, leading to the increases of ammonia escape of the denitrification system. So the side of the air on preheater ammonium bisulfate type blockage is more serious. After the Measures of Adjusting distribution coefficient of ammonia supply valve on both sides, increasing the dust blowing frequency and pressure of the air preheater, the differential pressure of air preheater on both sides are close to the consistent. The decrease amplitude of the differential pressure of the air preheater on 280MW is about 300-500Pa.

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

Scientific Reports ◽

10.1038/s41598-021-90040-w ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Kunling Jiao ◽

Xiangyang Chen ◽

Xuan Bie ◽

Daokuan Liu ◽

Mingjie Qiu ◽

...

Keyword(s):

Flue Gas ◽

Negative Impact ◽

Dew Point ◽

Detection Methods ◽

Nox Removal ◽

Air Preheater ◽

Catalyst Life ◽

Ammonium Bisulfate ◽

The Impact ◽

Ammonia Injection

AbstractWhen 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.

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Study on Formation, Deposition and Fouling Prediction of Ammonium Bisulfate (ABS) at Air Preheater in Utility Boiler

ASME 2020 Power Conference ◽

10.1115/power2020-16708 ◽

2020 ◽

Author(s):

Liping Pang ◽

Qiyuan Liang ◽

Liqiang Duan

Keyword(s):

Flue Gas ◽

Time Data ◽

Concentration Data ◽

Air Preheater ◽

Iterative Computation ◽

Ammonia Slip ◽

Actual Operation ◽

The Finite Difference Method ◽

Ammonium Bisulfate ◽

Physical And Mathematical Models

Abstract The ammonium bisulfate (ABS) widely exists at air preheater. The ABS may deposit and foul at the heating elements of air preheater because of the chemical reaction between SO3 at flue gas side and ammonia slip from SCR excess injection. The heat transfer equation between flue gas side and air side is constructed and simplified using physical and mathematical models accordingly. The finite difference method is applied to solve numerically by means of iterative computation. Based on the NH3 and SO3 concentration data from the real time data in the actual operation and the discrete calculation of the temperature field, the Radian number (Ra) is used to evaluate the possibility of ABS fouling and the developing trend of heating elements at the air preheater. A 1000MW ultra supercritical boiler is selected as example. The ABS deposit area is simulated under different working conditions 100%BMCR, 75% BMCR and 50% BMCR. The possible ABS deposition and fouling is analyzed for operators to evaluate the risk of cold-end and hot-end heating elements plate at air preheater. As the working load decreases lower than 50%BMCR, the deposition and fouling position could extend to the hot-end area of heating elements at air preheater.

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Locomotive Boiler Flue Gas Analysis*

Scientific American ◽

10.1038/scientificamerican09071912-159supp ◽

1912 ◽

Vol 74 (1914supp) ◽

pp. 159-160

Author(s):

Lawford H. Fry

Keyword(s):

Flue Gas ◽

Gas Analysis

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Flue-gas desulphurisation—Drax: the first UK retrofit

Power Engineering Journal ◽

10.1049/pe:19890033 ◽

1989 ◽

Vol 3 (4) ◽

pp. 185 ◽

Cited By ~ 1

Author(s):

F.G. Hage

Keyword(s):

Flue Gas

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Could biomass-fueled boilers be operated at higher steam temperatures? Part 3: Initial analysis of costs and benefits

TAPPI Journal ◽

10.32964/tj13.8.65 ◽

2014 ◽

Vol 13 (8) ◽

pp. 65-78 ◽

Cited By ~ 3

Author(s):

W.B.A. (SANDY) SHARP ◽

W.J. JIM FREDERICK ◽

JAMES R. KEISER ◽

DOUGLAS L. SINGBEIL

Keyword(s):

Flue Gas ◽

Power Plants ◽

Superheated Steam ◽

Black Liquor ◽

Simulation Software ◽

Operating Conditions ◽

Costs And Benefits ◽

Steam Generation ◽

Fireside Corrosion ◽

Corrosion Resistant

The efficiencies of biomass-fueled power plants are much lower than those of coal-fueled plants because they restrict their exit steam temperatures to inhibit fireside corrosion of superheater tubes. However, restricting the temperature of a given mass of steam produced by a biomass boiler decreases the amount of power that can be generated from this steam in the turbine generator. This paper examines the relationship between the temperature of superheated steam produced by a boiler and the quantity of power that it can generate. The thermodynamic basis for this relationship is presented, and the value of the additional power that could be generated by operating with higher superheated steam temperatures is estimated. Calculations are presented for five plants that produce both steam and power. Two are powered by black liquor recovery boilers and three by wood-fired boilers. Steam generation parameters for these plants were supplied by industrial partners. Calculations using thermodynamics-based plant simulation software show that the value of the increased power that could be generated in these units by increasing superheated steam temperatures 100°C above current operating conditions ranges between US$2,410,000 and US$11,180,000 per year. The costs and benefits of achieving higher superheated steam conditions in an individual boiler depend on local plant conditions and the price of power. However, the magnitude of the increased power that can be generated by increasing superheated steam temperatures is so great that it appears to justify the cost of corrosion-mitigation methods such as installing corrosion-resistant materials costing far more than current superheater alloys; redesigning biomassfueled boilers to remove the superheater from the flue gas path; or adding chemicals to remove corrosive constituents from the flue gas. The most economic pathways to higher steam temperatures will very likely involve combinations of these methods. Particularly attractive approaches include installing more corrosion-resistant alloys in the hottest superheater locations, and relocating the superheater from the flue gas path to an externally-fired location or to the loop seal of a circulating fluidized bed boiler.

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