New Dry Process for Separating HCl from Flue Gases by Adsorption on MgO

Fossil fuels are still the most important source for supplying the world's energy and heating needs. The growing demands of more stringent pollution control regulations make it necessary to develop new flue gas cleaning processes. Up to now there is no known process that allows the dry separation of hydrogen chloride from flue gases with ready adsorbent regeneration. The well known BF-Uhde process cannot be applied to flue gases containing hydrogen chloride. Our aim was to develop a process for dry separation of hydrogen chloride from flue gases that can be used in combination with the BF-Uhde process. The new process is based on a gas-solid reaction between active magnesia and hydrogen chloride at temperatures of about 120 °C. The new process performed well in experiments conducted under industrial conditions. The adsorbent can be regenerated at temperatures of about 450 °C. Hydrogen fluoride is the only known flue gas component that interferes with the regeneration capability of the adsorbent.     

Innovative material technology removes dioxins from flue gases

Adiox™ is an innovative material for removing toxic dioxins from combustion gases, making it an ideal absorbing material for tower packings and demisters in wet scrubbers. Adiox can also be used as a police filter to reduce the memory effect, as well as the primary dioxin removal technology. Sven Andersson, Siegfried Kreisz and Hans Hunsinger discuss this novel technology for the cleaning of flue gases.     

Efficiency of reduction of nitrogen oxides in ceramic filters

Calculated results and experimental data on the efficiency of the processes of reduction of nitrogen oxides in the channels of ceramic packings of high-temperature filters are presented. A method for evaluating the quality of cleaning of flue gases of nitrogen oxides in a temperature range of 600–900°C for different perforation densities in ceramic filter packings is described. The possible limits of control over the cleaning coefficient in the deposition of refractory catalytic coatings on the surface of the channels of filter packings and rational structural and regime characteristics of the filters that make it possible to attain a cleaning coefficient as high as 40 – 45% are established.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 6, pp. 21 – 23, June, 1996.     

Verfahren zur Entschwefelung von Rauchgas

Processes for flue gas desulphurization . The continuous high emission of sulphur dioxide from the combustion of fossil fuels is causing increasing damage not only to nature but also to buildings and machinery, especially in industrialized countries. It is possible by desulphurization of the flue gases to reduce the emission of sulphur dioxide by as much as 90%. This can be achieved industrially by dry absorption using activated charcoal or addition of limestone, and by wet processes employing soda, limestone, calcium hydroxide or ammonia as absorbents. The characteristic features of each of the different processes are described. The main residues obtained from these desulphurization processes are gypsum, sulphur, or fertilizer salts, most of which can be recycled. The running costs for such flue gas cleaning processes amount to between DM 0.007 and DM 0.018/kWh depending on location and requirements.     

Modelling of thermal desorption of active coke loaded with sulphuric acid and ammonium sulphate

The BF-Uhde-Mitsui Process uses active coke for SO₂- and NO_x-removal from flue gases in the temperature range between 100 and 190 °C, Experimental methods of thermal regeneration were applied to the evaluation of the state of the adsorbent after use in flue gas cleaning and of the parameters for disrober design. A reaction model was derived from experiments carried out in differential and back-mix reactors. The parameters were evaluated by adaptation of the model to the adsorption spectra. The model was successfully applied to the regeneration of active coke in a fluidized bed reactor.     

炭素生产中煅烧炉烟气余热的利用

对烟气余热回收利用原理及在有机热载体锅炉上应用进行介绍,对烟气余热回收利用系统的节能效果进行分析。     

Preliminary analysis of process flow sheet modifications for energy efficient CO2 capture from flue gases using chemical absorption

The energy penalty associated with solvent based capture of CO₂ from power station flue gases can be reduced by incorporating process flow sheet modifications into the standard process. A review of modifications suggested in the open and patent literature identified several options, primarily intended for use in the gas processing industry. It was not immediately clear whether these options would have the same benefits when applied to CO₂ capture from near atmospheric pressure combustion flue gases. Process flow sheet modifications, including split flow, rich split, vapour recompression, and inter-stage cooling, were therefore modelled using a commercial rate-based simulation package. The models were completed for a Queensland (Australia) based pilot plant running on 30% MEA as the solvent. The preliminary modelling results showed considerable benefits in reducing the energy penalty of capturing CO₂ from combustion flue gases. Further work will focus on optimising and validating the most relevant process flow sheet modifications in a pilot plant.     

Lightweight foamed filler in granular form from raw kaolin

Conclusions The technological parameters were determined for the production by the foam method of a lightweight granulated filler of apparent density 0.5–0.7 g/cm³ from raw kaolin without the addition of a nonplastic material to the batch.When the operations are carried out separately, the duration of the production cycle is 2.5–3 h, which includes the firing of the porous lump material by passing flue gases through a layer up to 500 mm in depth and demonstrates that in principle it is possible to set up a line for the production of foam-kaolin filler by the new method. The filler can be used, e.g., with good results as aggregate for heat-insulation concrete.Translated from Ogneupory, No. 1, pp. 46–52, January, 1977.     

Using coke-battery flue gas to dry coal batch before coking

The utilization of heat from coke-battery flue gases and other potential secondary energy resources in drying coal batch prior to coking is considered. The main factors that influence the thermal potential of the flue gases as a drying agent are identified. The reduction in moisture content of the coal batch prior to coking thanks to the coke-battery flue gases is calculated for different battery operating conditions. Technological principles for combining the drying of coal batch with its preparation by selective crushing and pneumomechanical separation are considered.     

Modelling of a fluidized bed carbonator reactor to capture CO2 from a combustion flue gas

In recent years several processes incorporating a carbonation-calcination loop in an interconnected fluidized bed reactor have been proposed as a way to capture CO₂ from flue gases. This paper is a first approximation to the modelling of a fluidized bed carbonator reactor. In this reactor the flue gas comes into contact with an active bed composed of particles with very different activities, depending on their residence time in the bed and in the carbonation-calcination loop. The model combines the residence time distribution functions with existing knowledge about sorbent deactivation rates and sorbent reactivity. The fluid dynamics of the solids (CSTR) and gases (PF) in the carbonator are based on simple assumptions. The carbonation rates are modelled defining a characteristic time for the transition between a fast reaction regime to a regime with a zero reaction rate. On the basis of these assumptions the model is able to predict the CO₂ capture efficiency for the flue gas depending on the operating and design conditions. Operating windows with high capture efficiencies are discussed, as well as those conditions where only modest capture efficiencies are possible.     

Computational screening of porous metal‐organic frameworks and zeolites for the removal of SO2 and NOx from flue gases

Sulfur oxides (SO₂) and nitrogen oxides (NO_x) are principal pollutants in the atmosphere due to their harmful impact on human health and environment. We use molecular simulations to study different adsorbents to remove SO₂ and NO_x from flue gases. Twelve representative porous materials were selected as possible candidates, including metal‐organic frameworks, zeolitic imidazolate frameworks, and all‐silica zeolites. Grand canonical Monte Carlo simulations were performed to predict the (mixture) adsorption isotherms to evaluate these selected materials. Both Cu‐BTC and MIL‐47 were identified to perform best for the removal of SO₂ from the flue gases mixture. For the removal of NO_x, Cu‐BTC was shown to be the best adsorbent. Additionally, concerning the simultaneous removal of SO₂, NO_x, and CO₂, Mg‐MOF‐74 gave the best performance. The results and insights obtained may be helpful to the adsorbents selection in the separation of SO₂ and NO_x and carbon capture. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2314–2323, 2014     

Recent developments in novel sorbents for flue gas clean up

Coal combustion is one of the most important energy sources for electricity generation, but also produces airborne pollutants. The amount of SO₂ and NO_x for example, is in the order of hundreds to thousands of ppm, and tens to hundreds of ppm, respectively, while Hg in flue gases could be up to tens to hundreds of ppb. Flue gas desulphurization technology is already in place for SO₂ removal, and new sorbents such as zeolites are being investigated for such an application. NO_x can be removed by selective catalytic reduction with various catalysts. Mercury is the hardest to remove due to its persistent nature and relatively low concentration in flue gases. New sorbents have also been developed for mercury removal applications. A current trend in flue gas emission control is to remove Hg, NO_x and SO₂ simultaneously. Various catalytic sorbents have been investigated to remove two or more of these pollutants concurrently. This article reviews recent developments made for emission control of coal-fired power plant flue gases using novel sorbents to target individual or multiple pollutants.     

Solvent selection for CO<Subscript>2</Subscript> capture from gases with high carbon dioxide concentration

Amine absorption processes are widely used to purify both refinery and process gases and natural gas. Recently, amine absorption has also been considered for application to CO₂ removal from flue gases. It has a number of advantages, but there is one major disadvantage-high energy consumption. This can be solved by using an appropriate solvent. From a group of several dozen solutions, seven amine solvents based on primary amine, tertiary amine and sterically hindered amine were selected. For the selected solutions research was conducted on CO₂ absorption capacity, an absorption rate and finally a solvent vapor pressure. Furthermore, tests on an absorber-desorber system were also performed. In this study the most appropriate solvent for capturing CO₂ from flue gases with higher carbon dioxide concentrations was selected.     

Effect of fuel properties on biomass combustion. Part II. Modelling approach—identification of the controlling factors

Biomass fuels come from many varieties of sources resulting in a wide range of physical and chemical properties. In this work, mathematical models of a packed bed system were employed to simulate the effects of four fuel properties on the burning characteristics in terms of burning rate, combustion stoichiometry, flue gas composition and solid-phase temperature. Numerical calculations were carried out and results were compared with measurements wherever possible. It was found that burning rate is mostly influenced by fuel size and smaller fuels result in higher combustion rate due to increased reacting surface area and enhanced gas-phase mixing in the bed; combustion stoichiometry is equally influenced by fuel LCV and size as a consequence of variation in burning rate as well as the mass ratio of combustible elements to the oxygen in the fuel; for the solid-phase temperature, material density has the strongest influence and a denser material has a higher maximum bed temperature as it results in a less fuel-rich combustion condition; while CO concentration in the flue gases is mostly affected by both fuel calorific value and size, CH₄ in the exiting flow is greatly affected by material density due to change in reaction zone thickness.     

On-line monitoring of fuel moisture-content in biomass-fired furnaces by measuring relative humidity of the flue gases

Combustion of biomass for heat and power production is continuously growing in importance, because of incentives for replacing fossil energy resources with renewable ones. In biomass combustion, the moisture content of the fuel is an essential operation parameter, which often fluctuates for biomass fuels. Variation in moisture content complicates the operation of the furnaces and results in an uncertainty in the energy content of the fuel delivered to a plant. The fuel moisture-content in a furnace may be determined either by direct measurement on the entering fuel or by measuring the moisture and oxygen contents of the flue gases deriving the moisture content of the fuel. However, reliable methods of a motivated cost for the small to medium-scale furnaces are today not available. An exception is if the furnace is equipped with flue-gas condenser, which can be used to estimate the moisture content of the flue gases. A limitation of this method is, though, that not all furnaces have flue-gas condensers and that the measured signal has an inherent time delay.In this work, measurement of the relative humidity (RH) of the flue gases from a furnace is investigated as the central component in the on-line monitoring of the moisture content of the fuel in a furnace. The method was analysed with humid air in a laboratory environment and tested for accuracy and dynamical behaviour in two biomass-fired heat-production units, one circulating fluidised-bed boiler (CFB) and one grate furnace. The results show that the method, which is easy to calibrate on site, can be used to predict the moisture content of the biomass fuel in the grate furnace with very good precision (<4% error). Furthermore, the method detects variations in moisture content of the furnace flue gases due to changes in the moisture content of the combusted fuel within the order of seconds. Since the transport time of the flue gases from the furnace to the measurement position is of the same order of magnitude, the total time for detection of a change in the moisture content of the fuel is small enough for the signal to be used to control both the fuel feed and the combustion air in a grate furnace.     

Optimum cleaning cycles for heat transfer equipment undergoing fouling and ageing

Complete elimination of fouling in heat transfer equipment is rarely achieved in practice, so cleaning of fouled units is a regular task in the process industries. Algorithms for scheduling cleaning have, to date, minimized the net losses due to fouling by focusing on when and which units to clean. In contrast, this paper focuses on when and how to clean a unit, when more than one cleaning method is available.The model formulation is approached by idealizing a foulant deposit as consisting of two layers, soft (fresh) and hard (aged). The hard material is formed through the ageing of the soft material. Hard deposits are more difficult to remove and require time- and cost-intensive cleaning methods (such as mechanical cleaning). Soft deposits are removed through less time- and cost-intensive methods such as chemical cleaning by recirculation of solvents. The hard deposit usually consists of more thermally conductive material and hence, for a given thickness, has a lower thermal resistance compared to the soft deposit.This work introduces a new methodology to identify optimum cleaning cycles (OCCs) under the presence of both soft and hard deposit, when two cleaning methods (solvent and mechanical cleaning) are available. The analysis of OCCs is extended and a new concept called the ‘cleaning supercycle’ is elaborated, which can be related to the optimal time between plant shutdowns.     

A novel continuous reactor for catalytic reduction of NOx—fixed bed simulations

A novel dual‐zone fluidized bed reactor was proposed for the continuous adsorption and reduction of NO_x from combustion flue gases. The adsorption and reaction behaviour of such a reactor has been simulated in a fixed bed reactor using Fe/ZSM‐5 catalyst and propylene reductant with model flue gases. Fe/ZSM‐5 exhibited acceptable activity at T = 350°C and GHSV = 5000 h^?1 when O₂ concentration was controlled at levels lower than 1% with a HC to NO molar ratio of about 2:1. XPS and BET surface area measurement revealed the nature of the deactivation of the catalyst. Those performance data demonstrated the feasibility of a continuous dual‐zone fluidized bed reactor for catalytic reduction of NO_x under lean operating conditions.     

A Single Stage Membrane Process for CO2 Capture from Flue Gas by a Facilitated Transport Membrane

Carbon dioxide is the most important anthropogenic greenhouse gas and it accounts for about 80% of all greenhouse gases (GHG). The global atmospheric CO₂ concentrations have been increased significantly and have become the major source responsible for global warming; the greatest environmental challenge the world is facing now. The efforts to control the GHG emissions include the recovery of CO₂ from flue gas. In this work, feasibility analysis, based on a single stage membrane process, has been carried out with an in-house membrane program interfaced within process simulation program (AspenHysys) to investigate the influence of process parameters on the energy demand and flue gas processing cost. A novel CO₂-selective membrane with the facilitated transport mechanism has been employed to capture CO₂ from the flue gas mixtures. The results show that a membrane process using the facilitated transport membrane can also be considered as an alternative CO₂ capture process and it is possible to achieve more than 90% CO₂ recovery and 90% CO₂ purity in the permeate with reasonable energy consumption compared to amine absorption and other capture techniques.     

Catalytic Flue Gas Treatment from Nitriding Processes

Efficient control and minimization of emissions from technical processes is of major concern in industrial development and process operation. The technical process in the focus of the present contribution is the nitriding process of metallic specimen. The ammonia content in nitriding process flue gases reaches up to 618 g·m^–3 (80 vol.‐%) and needs to be reduced to less than 30 mg·m^–3 (40 ppm) to fulfill present regulations. Exhaust gases from nitriding processes today are burnt in flares without emission control where fuels need to be added that produce additional exhaust gas components. The objective of this investigation is to develop an alternative gas cleaning route for nitriding processes based on catalytic dissociation of ammonia. The decomposition was studied for different catalysts at varying process conditions. With these results a dissociation pilot plant was successfully tested in a technical‐scale nitriding process.     

烟气中SO2及NOx污染防治新进展

综述８０年代后期以来国内外防治烟气中ＳＯ２及ＮＯｘ污染的概况以及防治技术，简要介绍一些正在开发的新过程及高新技术，包括膜技术，电化学技术及结合化学反应的高能辐射技术，这些新方法可提高经济效益弥补传统方法的不足。