H. Mätzing

Analyses of products formed by electron beam treatment of VOC/air mixtures

Abstract Butylacetate and xylene were irradiated with electron beam in the dose range of 0–10 kGy at ambient temperature and the removal efficiencies measured by FID and gas chromatography. Gaseous reaction products were measured by FT-IR spectroscopy and by wet sampling of the irradiated gas. Ion chromatographic analyses of the gaseous samples showed that formic, acetic, propionic and butyric acids were important products for the irradiation of butylacetate and xylene. Aerosols were only formed by irradiation of xylene. The overall composition of the aerosols at 10 kGy can be represented by the formula C 25 H 36 O 16 N. Mass balance of experiments for butylacetate and xylene was calculated on the basis of C-balance (mgC/Nm 3 ) and more than 80% recovery was obtained in all experiments. The reaction mechanism is discussed briefly.

Adsorption of PCDD/F on MWI fly ash

The removal of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) from waste incinerator off-gas is a costly task, because a considerable part of the PCDD/F may exist in the gas phase (often 50-100% around 200 degrees C). The volatile fraction passes the particle filter and the subsequent gas cleaning equipment, so that an additional unit is needed to remove the gaseous PCDD/F from the flue gas. Moreover, dioxins and furans can accumulate in some parts of the equipment in a way that they can act as a latent source. In this work, we investigate the possibility to adsorb the PCDD/F at the fly ash particles and to remove them during the filtration. The gas/particle partitioning of the PCDD/F depends on the temperature, the vapor pressure, the particle size, the particle number density and on the physical and chemical properties of the particle surface. These relationships are investigated by model calculations and by pilot scale experiments (500 Nm3/h) which employ one selected hexachlorinated dioxin congener. At room temperature, approx. 90% of the HxCDD are found in the particulate phase, while at 135 degrees C that portion is only 10%. This means that at ambient temperatures, the gas/particle partitioning of the dioxin corresponds well to the sublimation equilibrium. At higher temperatures, it is much different from the sublimation equilibrium and the apparent adsorption enthalpy is smaller than the enthalpy of sublimation. This observation is in agreement with literature data. From the above experiments and from similar literature data, the efficiency of fly ash particles as a sink for PCDD/F can be evaluated. The data suggest that the adsorption rate is not the limiting factor for the transfer into the particulate phase. The important factors appear to be the chemical composition of the fly ash and the temperature.

Electron beam induced decomposition of chlorinated aromatic compounds in waste incinerator offgas

Abstract Gaseous emissions of polychlorinated dibenzo-dioxins and -furanes (PCDD/F) in incinerator flue gas are decomposed to below 0,1 ng m N −3 by the irradiation with accelerated electrons. A mobile off gas cleaning plant (AGATE-M), equipped with a 200 keV electron accelerator (EB), was used to treat a flow of 1000 m N 3 h −1 of flue gas from a waste incinerator. Very high decomposition efficiencies were obtained at a dose of 5 – 10 kGy. A computer model (AGATE-code) was developed to analyze the gas phase chemistry of the process. The experimental and the theoretical results are reported and compared.

Removal of volatile organic compounds from industrial offgas by irradiation induced aerosol formation

Abstract Organic trace components can be removed efficiently from largevolumes of industrial offgas by irradiation with 300 keV electrons. The major reaction product is a sub μm aerosol besides CO and CO 2 . A complete carbon balance of the process was established. The energy efficiency of the process is significantly higher than for conventional technology.

Removal of butylacetate and xylene from air by electron beam a product study

Abstract VOC emissions from industrial processes can cause hazardous impacts on the environment through increased ozone and smog formation. Previously, it was demonstrated that the electron beam technology is a powerful tool to scrub small amounts of VOC from large volume flows at ambient temperature. In this paper, product analyses are presented for the removal of common aliphatic and aromatic hydrocarbons from air. Butylacetate and xylene were added to an air stream of 1000 Nm 3 /h at concentration levels close to 100 mg C/Nm 3 , and irradiated with 550 keV electrons at the AGATE-2 pilot plant of KfK. The removal efficiencies were measured by FID and GC in the dose range 0–10 kGy. The removal efficiency of xylene was found to be close to 90% at 10 kGy which is almost twice as high as that of butylacetate. Three types of products were measured quantitatively by wet chemical analysis, filtration, and FTIR: (i) organic acids (formic, acetic, propionic, butyric acid) (ii) aerosol (iii) inorganic products and by-products (CO, CO 2 , O 3 , NO X ) The major product obtained from xylene irradiation was a particulate matter with a molecular C/O ratio close to 1.5. No aerosol formation was observed in case of butylacetate, the major irradiation product of which was acetic acid. Less than 15% of the removed carbon were converted to CO and CO 2 in both cases. The total carbon balance was 95 ± 15% in all experiments. By model calculation with the AGATE-code, the removal efficiencies and product distributions can be interpreted starting from OH radical attack on the hydrocarbon molecules and subsequent mechanisms which are known from atmospheric chemistry.

Electron beam induced purification of dilute off gases from industrial processes and automobile tunnels

Abstract The electron beam process has proved to be an efficient method for the removal of inorganic pollutants from flue gas. Since it simulates natural processes which occur in the atmospheric photochemistry, it appeared attractive to investigate the potential of the e-beam process to clean off-gases which contain hydrocarbon and inorganic trace components. Such emissions arise from industrial processes and from automobile tunnels. Commercial solvents were vaporized in air and irradiated with energetic electrons (300 keV). CO, CO 2 and aerosol particles were found as products and were determined quantitatively. The aerosol particles can be collected by a gravel bed filter and can be removed by combustion or biological degradation. From experiments and model calculations it was found that the e-beam process is a very economic tool to remove hydrocarbons from large off-gas volumes at initial concentrations of 50–100 mg C/m 3 , and that NO x can be removed very efficiently from tunnel off-gas.

Chemistry of the electron beam process and its application to emission control

The irradiation of air-like gas mixtures with energetic electrons (300 - 800 keV) generates excited state species, ions and radicals. Only the radicals remain available for reactions with the trace components. Like in atmospheric chemistry, the most reactive radical is OH, hence the pollutants are degraded by oxidation preferentially. Industrial applications of the electron beam rocess are the removal of NO, and SO2 from power plant flue gas and the chlorinated hydrocarbons from contaminated groundwater and to remove VOC an8 NO, from automobile tunnel off-gas. removal of hy 8 rocarbons from cold off-gas. Further, the process can be used to de rade

Flue gas cleaning by multiple irradiation with electron beam

Abstract By electron beam treatment, NOx and SO2 can be reduced simultaneously from combustion flue gas. The efficiency of the process has been shown to improve by multiple irradiation. It appears most promising to perform the multiple irradiation with an intermediate gas scrubber. This paper reports experimental investigations on the efficiency of the intermediate filter.

A simple kinetic model of PCDD/F formation by de novo synthesis

A simple fixed-bed reactor model is used to describe experimental data about the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) from fly ash carbon. The heterogeneous oxidation of graphite-like carbon is represented by a reaction which is first order in carbon and one half order in oxygen. The same orders of reaction are assumed to be valid for PCDD/F formation, such that the oxidation of fly ash carbon would have three parallel channels leading to COx, PCDD and PCDF. In addition, PCDD/F degradation by oxygen is considered and appropriate rate constants were fitted to simulate the experimental data. The effects of water vapour and particulate copper on PCDD/F formation are included. As a result, an overall kinetic model of PCDD/F formation is obtained which describes most of the experimental data with reasonable accuracy. The main reaction channel, COx formation, needs to be understood more completely, in order to interpret PCDD/F reaction pathways better. The model can be extended to include other chlorinated aromatics and the gas/particle partitioning of the semivolatiles. It provides a basis for the qualitative and quantitative interpretation of fixed-bed and flow reactor results and it is hoped to be applicable to industrial installations like waste incinerators and metal smelters.

Electron beam processing of industrial off gas by the mobile irradiation plant agate-M

Abstract A mobile irradiation plant (AGATE-M) has been constructed for on-site demonstration of off-gas treatment by electron beam. AGATE-M has been designed for flow rates up to 1000 Nm 3 /h and is equipped with a pre-filter, a reaction chamber connected to a low energy (200 kV) accelerator, a product filter and measurement systems.