Trace element partitioning during the firing of washed and untreated power station coals

The effect of coal washing on trace element content and combustion behaviour of four world-traded coals has been studied at rig scale. The inputs and process outputs from a 1 MW combustion test facility, including coal, bottom ash, suspended fly ash, retained ash and flue gas, have been analysed for a standard suite of 17 trace elements. The results suggest that although coal cleaning significantly reduces the total ash content of the coal, the concentrations of individual trace elements are not reduced proportionately. Combustion of the washed coals resulted in increased concentrations of trace elements in the fly ash, although total fly ash loadings were reduced. Cleaning appeared to have little effect on concentrations of gaseous trace elements in the flue gas. The partitioning of the more volatile trace elements such as mercury and selenium between the vapour and solid phase was influenced by the amount of excess oxygen in the furnace, presumably affecting carbon-in-ash levels.The results suggest that the coal cleaning undertaken for these experiments did not significantly reduce the emissions to atmosphere of trace elements. The ultimate emissions will be determined by the efficiency of the dust capture systems.     

Thermodynamic equilibrium study of trace element transformation during underground coal gasification

In order to provide theoretical basis for gas cleaning and pollution control thermodynamic equilibrium calculations were performed to predict the partitioning of trace element species under special conditions for underground coal gasification, including both oxygen-steam gasification and air blown gasification under elevated pressures. The trace elements studied include As, Se, Pb, Ni, Cd, Cr, Sb. The results indicate, in the condition of large-section UCG process with oxygen-steam injection, all the elements studied present in the gas phase during gasification stage. Ni and Cr are hardly volatile and tend to condense below 1000 °C. Most of them will be enriched in bottom ash. As, Pb, Cd, Sb totally or partially occur in gas phase in underground gas cleaning system. In cold cleaning system, they exist in condensed phases and tend to be enriched in fly ash, which is beneficial to trace element removal. Se presents in gas phase in the form of H₂Se(g) even in ground cold gas cleaning system. The presence of potassium makes arsenic less volatile due to the formation of K₃AsO₄ and selenium is not affected. Also the amount of gaseous antimony chloride is reduced because of prior formation of alkali metal chloride. Pressure shows a remarkable effect on equilibrium partitioning of As, Se, Sb. With rising pressure, increasing quantities of hydrides of these trace elements are generated due to the enhancement of the reducing atmosphere. At the same time, the condensation points of all the trace elements sharply increase with pressure. It is found that for underground air blown gasification, the gaseous species of trace element sulfide can be easily formed, and the trace elements have lower condensation points than those for oxygen-steam gasification.     

Trace element evaporation during coal gasification based on a thermodynamic equilibrium calculation approach

Thermodynamic equilibrium calculations using the HSC-Chemistry program were performed to determine the distribution and mode of occurrence of potentially toxic and corrosive trace elements in gases from coal gasification processes. The influence of temperature, pressure and gas atmospheres on equilibrium composition was evaluated. In these reducing conditions, the behaviour of the trace elements is complex, but some form of organization can be attempted. Elements were classified into three groups. Group A includes those elements that, according to thermodynamic data at equilibrium, could probably be condensed in coal gasification. Mn is classified in this group. Group B contains those elements that could be totally or partially in gas phase in gas cleaning conditions, and can be divided into two subgroups, depending on whether the cleaning conditions are hot or cold. Co, Be, Sb, As, Cd, Pb, Zn, Ni, V, Cr are elements in this group. Group C contains those elements that could be totally in gas phase in all the possible conditions, including flue gas emissions. Se, Hg and B are the elements that make up this group.     

Porous Permeable Ceramics for Filter Elements Cleaning Hot Gases from Dust

The filtering characteristics (air permeability, efficiency) of porous permeable ceramic materials with different microstructures are determined. The requirements on ceramic filter elements are formulated; specifications for a module-type plant with ceramic filter elements are prepared. The use of these elements for cleaning hot gases from dust, apart from the ecological effect, yield an economic effect manifested as additional energy produced due to recovery of waste gas heat. __________ Translated from Steklo i Keramika, No. 5, pp. 14 – 18, May, 2005.     

卷式纳滤膜的气液两相流清洗特性

引言 膜分离技术在化工、食品、医药、石油、环境等领域已有广泛应用.其中卷式纳滤膜因装填密度大、膜元件更换方便、适用面广等优点,在各行业已大规模进人工业应用,但膜污染问题是制约其发展的主要因素.工业上通常采用化学清洗方法,但清洗时间长,清洗用水和清洗剂消耗量大,同时产生大量清洗废水,且难以保证清洗效果.     

Altanlagen – Sanierung nach TA Luft durch Kombination von Verbrennung und Absorption

A waste-gas cleaning system was constructed for a group of drug production plants. The chemical – synthetic processes taking place there are characterized by inevitable emissions, mainly of vapours of organic solvents. Their concentrations vary within a wide range and at any given moment in principle remain unknown. This paper describes the initial situation and the requirements for the waste gas cleaning process, including the calculation of the gas volume flow capacity. The polluting substances were divided into two groups; for critical substances only thermal oxidation was found to be adequate, whereas for non-critical, water-soluble material, water-fed absorption columns were chosen; on one hand to avoid full exhaustion of the capacity of the thermal waste-gas system and on the other hand to offer additional possibilities in the case that this system should be out of action. The criteria for this decision as well as for the combination of one central with several decentralised cleaning units are discussed in detail. The equipment of the waste-gas emitting plants for feeding the cleaning units and the technical details thereof are described as well as the safety design. At last, experience gaine during preparation of the systems and considerations concerning further use of the thermal cleaning system are discussed.     

Production of synthetic natural gas (SNG) from coal and dry biomass - A technology review from 1950 to 2009

SNG production from coal or biomass is considered again due to rising prices for natural gas, the wish for less dependency from natural gas imports and the opportunity of reducing green house gases by CO₂ capture and sequestration. Coal and solid dry biomass (e.g., wood and straw) have to be converted to SNG by thermo-chemical processes (gasification followed by gas cleaning, conditioning, methanation of the producer gas and subsequent gas upgrading). During the 1970s, a number of methanation processes have been developed comprising both fixed bed and fluidised bed methanation. Meanwhile several new processes are under development, especially with a focus on the conversion of biomass. While coal based systems usually involve high pressure cold gas cleaning steps, biomass based systems require, due to the smaller unit size, different gas cleaning strategies. Moreover, the ethylene content of a few percent, typical for methane-rich producer gas from biomass gasifiers, is a challenge for the long-term catalyst stability in adiabatic fixed bed methanation due to the inherent high temperatures.This paper reviews the processes developed for the production of SNG from coal during the sixties and seventies and the recent developments for SNG production from coal and from dry biomass.     

Predicting Hg emissions rates from utility gas cleaning systems

This study validates the Hg emissions rates from NEA’s MercuRator™ with field test data for 25 full-scale utility gas cleaning systems that emphasize SCR/ESP/FGD combinations and activated carbon injection (ACI). Validations of the extents of Hg⁰ oxidation across SCRs and of Hg retention in wet FGDs gave correlation coefficients greater than 0.9 for both units. The validations for ACI applications yielded the first quantitative interpretations for different saturation levels of Hg capture for the highest ACI rates. When all the reaction mechanisms were combined to simulate Hg transformations along complete gas cleaning systems, the predicted Hg emissions rates were correctly rank ordered for nine of ten stations with SCR/CESP/FGD combinations, and for all six ACI test sites.     

Experimental study on the nozzle effect of the pulse cleaning for the ceramic filter candle

The effects of the nozzle size and its shape for the pulse cleaning of a ceramic filter candle were observed experimentally in the hot and cold bench units using commercial filter elements. The traces of the transient pressure, temperature, and overpressure in the filter cavity were measured to estimate the pulse cleaning effects. At the given pulse cleaning system, the pulse cleaning was optimized by the reciprocal effect of the nozzle size, which increases the primary pulse gas mass and reduces the secondary pulse mass as its size increases. The convergent nozzle showed a higher pulse effect than the straight one due to its concentrating effect, which leads to high pressure of the gas leaving the pulse nozzle.     

Systeme zur Abgasreinigung bei dezentralen Rückstandsverbrennungen in der chemischen Industrie

Gas Cleaning Systems of Decentralized Hazardous Waste Incinerators in the Chemical Industry In the chemical industry wet gas cleaning systems are frequently employed for the treatment of exhaust gases emerging from decentralized hazardous waste incinerators. With respect to the extremely high pollutant emissions, multistage gas cleaning processes are used that consist in most cases of a quench, one or more wet scrubbers and an optional aerosol separation stage. In order to select a suitable design of the gas cleaning process and equipment, beside the specific technical performance of each apparatus, particularly economic criteria have to be considered, like maintenance as well as investment costs. Additionally, the choice of the suitable material of construction plays a major role, especially at the transition section of dry to wetted gas in the quench. The present comparison of different process and equipment alternatives indicates that only the consideration of all relevant parameters yields to an optimal solution.     

Liquid phase residence time distribution for gas–liquid flow in Kenics static mixer

The residence time distribution (RTD) of the liquid phase for co-current gas–liquid upflow in a Kenics static mixer (KSM) with air/water and air/non-Newtonian fluid systems was investigated. The effect of liquid and gas superficial velocities on liquid holdup and Peclet number was studied. Experiments were conducted in three KSMs of diameter 2.54 cm with 16 elements and 5.08 cm diameter with 8 and 16 elements, respectively, of constant L_e/D_e = 1.5 for different liquid and gas velocities. A correlation was developed for Peclet number, in terms of generalized liquid Reynolds number, gas Froude number and liquid Galileo number, where as for liquid holdup, a correlation was developed as a function of gas Reynolds number. The axial dispersion model was found to be in good agreement with the experimental data.     

Pressure cycling for purging of dead spaces in high‐purity gas delivery systems

The purging of stagnant or dead volumes in gas distribution systems is an important method for removing impurities and maintaining cleanliness. A combination of experimental investigation and computational process modeling is used to study the dynamics of impurity removal under variety of purge conditions. The controlled cycling of pressure during purge is found to enhance the cleaning process significantly, particularly in dead spaces. The process simulator was used to develop and analyze a pressure‐cyclic purge (PCP) method and understand the conditions that would make PCP advantageous over steady‐state purge (SSP). In particular, the effect of geometric factors, impurity surface interactions, flow rate, and cycle characteristics on PCP and its comparison with SSP was studied. The advantage of the PCP method, in terms of both purge time and gas usage, becomes more pronounced in systems with larger number and size of dead spaces and impurities that interact strongly with the surfaces. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3973–3980, 2015     

Research progress of hot gas filtration,desulphurization and HCl removal in coal-derived fuel gas: A review

The present review paper highlighted on the recent progress of hot gas filtration, desulphurization and HCl removal in coal-derived fuel gas for combined cycle power generation (IGCC) or molten carbonate fuel cells (MCFC) technologies. As a critical process in the gasification system, hot gas filtration in the particulate control device (PCD) was introduced with enhanced understanding of equipment and operation, filter element and failsafe material properties, and gasification ash characteristics. The issues associated with the commercialization of hot gas filtration were also addressed, and some novel systems and methods were also discussed. The hot gas desulphurization in coal-derived fuel gas has concentrated on developing regenerable sorbents including the single and composite oxides of Zn, Fe, Cu, Mn and other species, and the reduction of metal oxides in the highly reducing atmosphere followed by vaporization of elements can be a problem for reactivity and regeneration. With regard to the removal of HCl, the studies have indicated sorbents prepared by pelletizing the powders of naturally available alkali metal and alkali earth metal substances can rapidly react with HCl vapor and reduce the HCl vapor concentration to less than 1 ppmv, and some sorbents lab-made have very high chlorine capacity. The sorbents based hot gas cleaning also has some challenges. Kinetics studies showed that unreacted shrinking core (USC) can be applied to the modeling of H₂S and HCl removal by sorbents at high temperature, and the surface chemical reaction and reactant diffusion by product layers between solid sorbents and gases were very important mechanisms. The paper also proposed and discussed a rational concept for the simultaneous removal of multiple contaminants including ash, H₂S and HCl, which will offer a possible cost reduction by two or more processes in a single vessel for hot gas cleaning.     

Consequences of high transitory airflows generated by segmented pulse-jet cleaning of dust collector filter bags

Baghouse dust collectors are commonly used in industry for removing solid particles from dust-laden gas. Baghouse filter media need to be periodically cleaned in order to remove collected particles from the filter surface. Pulse-jet cleaning is the most commonly used method but the detachment forces involved always affect downstream particle emission adversely. Although it is possible to find information about the mechanisms and the factors that cause particle emission, no link has been made between the distribution of the dirty airflow via the filter elements and the increase in released downstream particles after the bag cleaning.Innovative instrumentation of a pulse-jet-cleaned pilot dust collector allowed measuring the variation in the individual airflows which pass through each filter bag during clogging and cleaning cycles. The way in which segmented pulse-jet cleaning influences total dirty airflow distribution amongst filter elements was investigated. The consequences on bag airflow resistance and downstream particle emission were studied. Filtration cycles can be related to a succession of segmented pulse-jet cleaning, leading to imbalanced bag airflow resistances, and clogging. This in turn leads to compensations between bag resistances as a function of dust-laden individual bag airflow values. Airflow resistance variations are caused by two complementary phenomena: permeation of high transitory airflows on the first bags cleaned and the re-suspension of detached particles after a pulse-jet cleaning.During a cleaning sequence, strong airflow increases on the first cleaned bags are mainly prejudicial to dust collector downstream particle concentration.     

大机组油路的清洗

详细介绍了合成氨装置大机组公用油系统油路存在的问题、清洗方法、步骤。清洗后，各机组运转平稳，油过滤器滤芯使用寿命大大延长。     

Minimierung von Abgasemissionen aus diskontinuierlichen Produktionsanlagen der chemischen Industrie

Minimising Waste Gas Emissions from Batch-Operated Production Plant in the Chemical Industry. In fulfilling legal obligations to limit waste gas emissions, the strategy of avoidance and reduction has to take precendence over waste gas cleaning. Fundamental disadvantages and limited possibilities of waste gas cleanning systems create a necessity to minimize waste gas emissions by substitution of process materials, or by better encapsulation of process systems. Reduction of process gas emissions is shown by the examples of gas feedback, avoidance of gas pressure cushions, and encapsulating of stirring systems as well as centrifuges. The problem of diffuse emissions from gaskets in separatable connections and from fitting casings is discussed. An example of chemical reaction in a strictly closed system is given. With regard to the reduction of exhaust volumes from open sources, bulk materials feed and sampling are discussed; centrifuges, pressure filters and continuous belt filters are shown as examples of closed systems in solid-liquid-separation.     

A lab-scale study on the humidity conditioning of flue gas for improving fabric filter performance

A centrifugal separator was constructed to examine the effect of flue gas humidity on the adhesional force between fabric and collected dust. A lab-scale fabric filter sampling system (FFSS) was also manufactured by using a piece of flat fabric as a sample of bag material. In addition, an automatic control system for gas humidity was devised and installed in the FFSS, and, then, the following effects were studied: (i) the influence of gas humidity on the adhesional force between fabric and dust particles; (ii) the influence of gas humidity on the performance of fabric filter in terms of pressure drop, ΔP, dust removal efficiency, η, and specific cake resistance, K′₂; (iii) the variations in the composite-performance indices with gas humidity; and (iv) the influence of gas humidity on cleaning of dust-cake in terms of effective residual pressure drop. The main objectives were to determine the minimum and maximum values for the gas humidity range and to find the appropriate conditions for dust cleaning in terms of the critical value of effective residual pressure drop.     

Modelling pressure drop evolution on high temperature filters

A high temperature high pressure filtration facility is available at the ETSI-University of Seville, which allows testing different elements and cleaning reverse-flow pulse strategies using real coal ash under diverse operating conditions. The facility is capable of processing 850 Nm³/h gas flow rate at maximum temperature and pressure of 550 °C and 7.5 barg respectively. An extensive testing campaigns have been carried out with the aim of evaluating alternatives for hot gas filtration technologies and optimising the performance of commercial filtering elements.In this framework, this paper focuses on a semi-empirical model developed for predicting the rise of the pressure drop with time. The model is based on theoretical considerations and the application of the experimental data generated using four filtering elements (PTFE and 3MFB700 bag filters, DSN1020 and CS1150 rigid filters). Nonlinear regression has been used to estimate and validate the coefficient of the model (specific dust cake coefficient) with arbitraries relations between independent and dependent parameters, by using iterative estimation algorithms. This is a valuable tool to select the best filtration options and optimum cleaning strategies in high temperature applications. Investigations about the factors affecting the specific dust cake resistance coefficient (filtration velocity, temperature, filter medium) are also presented.     

Gas cleaning at high temperatures and high pressures: A review

This is a review of gas cleaning methods to be used for particulate removal from the gases emerging from pressurized coal gasifiers or fluid bed combustors at high temperature and high pressure. References are given (collected in tables) for the emissions of these processes, the inlet requirements if the hot gas is to pass a turbine and all cleaning methods that have been proposed in this context, including the removal of gaseous alkalis.

The design feasibility and available performance data for high temperature, high pressure applications of cyclones, electrostatic precipitators, barrier filters (using fibre, felt and sintered filter elements) and various types of granular bed filters, are discussed in some detail and suggestions are made for the further research and development. The theory of capture mechanisms is reviewed in so far as relevant in the present context. Turbulent flow, electrostatic forces, and re-entrainment are the phenomena that require special attention in almost all applications.     

陶瓷过滤器脉冲反吹用喷嘴优化设计

The experimental study was carried out to optimize the nozzle shape and dimension for the pulse cleaning of a ceramic filter candle. A bench scale unit of ceramic filter consisting of four commercial filter elements was used to measure the traces of the transient pressure around the nozzle and the overpressure in the filter cavity during the pulse-jet injection of pulse gas. Overpressure in the filter cavity is related to the pulse cleaning force. Nozzle design is concerned to increase the overpressure at the open end of filter element of pulse cleaning inlet, as well as to minimize the consumption of pulse gas. Convergent nozzle induces more secondary flow and generates higher pulse cleaning effect than straight nozzle. Nozzles of different convergent ratio （ratio of outlet to inlet diameter of nozzle） by changing the convergent angle and height were tested. The outlet diameter of convergent nozzle seriously influences the cleaning effect. The optimum convergent ratio increases with the increase of pulse gas pressure The nozzle position （distance of nozzle tip from the open end of filter inlet） is also important to decide the nozzle dimension. Nozzle of large outlet diameter accepts high pressure of pulse gas to provide large overpressure in the filter cavity of top position by applying long distance.