Influence of Steam, Hydrogen Chloride, and Hydrogen Sulfide on the

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Influence of steam, hydrogen chloride and hydrogen sulphide on the release and condensation of cadmium in gasification Maria Benito Abascal, Marc Bläsing, Yoshihiko Ninomiya, and Michael Müller Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.5b02676 • Publication Date (Web): 28 Dec 2015 Downloaded from http://pubs.acs.org on January 3, 2016

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Energy & Fuels

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Influence of steam, hydrogen chloride and hydrogen sulphide on the release and condensation of cadmium

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in gasification

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Maria Benito Abascal a,*, Marc Bläsing a, Yoshihiko Ninomiya b, Michael Müller a

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a

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52425 Jülich, Germany

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b

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*

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E-mail address: [email protected]

Institute of Energy and Climate Research (IEK-2), Forschungszentrum Jülich GmbH, Leo-Brandt-Straße,

Department of Applied Chemistry, Chubu University, 1200 Matsumoto-Cho, Kasugai, Aichi 487-8501, Japan

Corresponding author. Tel: +49 246161 5710, Fax: +49 246161 3699

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ABSTRACT

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The development of more efficient clean up techniques in coal power plants is essential in order to reduce trace

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metals emissions into the atmosphere. However, the understanding of the behaviour of the trace metals during

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the gasification process is necessary for the optimisation of the hot gas cleaning systems. Thereby, in this work

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the influence of H2O, HCl and H2S on the release and condensation behaviour of Cd was experimentally

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investigated. The experiments were conducted in two different setups. The condensation behaviour (temperature

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and speciation) of the trace metal vapours was investigated in a heated flow channel reactor housed in a furnace

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with a gas cooling zone. Experiments on the release of the inorganic vapours were carried out in a heated flow

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channel reactor coupled to a Molecular Beam Mass Spectrometer (MBMS) in order to analyse the gas in-situ.

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The results of the experimental investigations were compared with Scheil-Gulliver Cooling calculations

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performed by FactSage 6.3. Furthermore, thermodynamic pseudo-equilibrium calculations were carried out to

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help understanding the condensation mechanisms of the trace metal cadmium and the global kinetics in the

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experiments. The experimental results showed that the main chemical species detected in the condensation and

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release experiments were Cd, CdO, CdCl2 and CdS. In general, the speciation as well as the temperatures at

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which the species condensed and were present in the gas phase in the release experiments had the same trend in

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the calculations and in the experimental results. Thus, the Scheil-Gulliver Cooling model was proved to be an

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excellent tool for the prediction of the release and condensation of cadmium. With this work, a better

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comprehension of the behaviour of cadmium under gasification conditions was obtained.

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Keywords: coal gasification, cadmium, hot gas chemistry, condensation, release

31 ACS Paragon Plus 1 Environment

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1. Introduction

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The International Energy Agency estimated a 37 % increase in the global energy demand from the year 2014 to

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2040. By the year 2040, the world’s energy supply mix will divide into four almost-equal parts: oil, gas, coal and

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low-carbon sources [1]. In the central scenario, growth in global demand slows markedly, from above 2 % per

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year over the last two decades to 1 % per year after 2025. This is a result of price and policy effects [1]. Coal is

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the world´s more abundant fossil fuel and its supply is relative secure. Global coal demand will grow by 15 % to

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2040 but almost two-thirds of the increase will occur over the next ten years [1]. However, coal contains trace

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metals of particular environmental concern, e.g. cadmium, that are released during gasification. These traces of

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heavy metals are emitted into the atmosphere, impacting the environment, human health and causing several

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technological problems in gasification plants [2]. These trace metals present in parts per million levels in coal

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give rise to several tons of these pollutants in the environment per year. Thus, the future use of coal is

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constrained by measures to tackle pollution and reduce CO2 emissions [1]. Therefore, the development of cleaner

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techniques in next generation coal power plants is of vital importance. A promising coal utilization process is the

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Integrated Gasification Combined Cycle (IGCC) with integrated hot gas purification and CO2 separation [3].

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IGCC technology has been proved to be reliable and commercially viable in Spain and the Netherlands [4]. An

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increased efficiency and a decreased amount of heavy metal species can be accomplished through hot fuel gas

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cleaning [5, 6]. However, in order to develop clean up techniques that reduce or remove heavy metal traces, it is

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necessary to understand their hot gas chemistry during the gasification process. Some studies have already

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determined that the chlorine, sulphur and moisture content of fuels have a significant influence on the behaviour

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of some trace metals [7-11]. To some extent, trace metal´s behaviour in combustion processes is already known

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[9-15]. Studies have shown that trace elements can be classified into three groups considering their partitioning

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in combustion processes [16-18]. The behaviour of trace elements varies between gasification processes.

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However, their behaviour may be similar to that in conventional power plants [18]. Cadmium is considered one

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of the elements of greatest concern with respect to coal utilization and its typical concentration in coal varies

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from 0.1 – 3 ppmv [19]. Due to its high volatility cadmium belongs to the group of elements which volatilise in

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the gasifier and condense downstream [18]. Finally, cadmium enriched particles may escape particulate control

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systems. In other words, it is of great importance to remove or reduce cadmium particles since they can impact

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the atmosphere, human health and cause technological problems in power plants. Thus, due to the lack of

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knowledge in the behaviour of trace metals during gasification and the importance of reducing cadmium

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emissions into the environment, it was decided to study the behaviour of cadmium under gasification conditions.

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Hereby, the influence of H2O, HCl and H2S on the release and condensation of Cd was experimentally

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investigated.

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2. Experimental setup and thermodynamic calculations

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2.1 Experimental setup

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Two different setups were used to carry out the experiments: An atmospheric flow channel reactor with a cooling

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zone for the condensation experiments and an atmospheric flow channel reactor coupled to an MBMS system for

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the release experiments.

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The content of trace elements in coal range from 0.1 to 300 ppm. An average concentration of the trace metal

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was considered in this study. The desired average concentration of cadmium in both experiments was 100 ppmv.

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The vaporisation temperature was calculated with FactSage 6.3 and the resulting cadmium concentration was

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experimentally proved. In order to vaporize 100 ppmv of Cd in the experiments, the sample boat containing the

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trace metal was placed at 370 °C. The exact concentration of Cd in each experiment was calculated from the

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weight loss of cadmium during the respective experimental runs.

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The initially considered atmospheric conditions were a producer gas composition of a coal gasifier and a gas

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composition before the water-gas shift reaction (WGSR) with a steam to CO ratio of 1.5 (see Table 1). However,

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due to the goal of avoiding the use of CO in the laboratory, the search of alternative atmospheric conditions was

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necessary. The so-called lab conditions should replace the use of CO for the use of Ar or He. For these more

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fundamental investigations a CO-free gas mixture was used having the same hydrogen content and oxygen

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partial pressure as after entrained flow gasification of coal and in the water-gas-shift reactor. These conditions

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were obtained by curve-fitting the oxygen partial pressure evolution of the real conditions in FactSage 6.3. In

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order to validate this simplification a set of equilibrium calculations with cadmium were carried out to see the

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influence of the CO-free conditions. In the equilibrium calculations the same species were found for the real and

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laboratory conditions. Therefore, the simplification was considered as valid and the so-called laboratory

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conditions without CO were taken as experimental conditions for all the experimental runs.

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{Table 1}

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An overview of the atmospheric conditions in the experiments is given in Table 2. The experiments were carried

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out with 0, 50 and 500 ppmv of HCl or H2S. This values were chosen in order to obtain comparable results to real


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power plants. In the release experiments, each experimental run was carried out at three different temperatures at

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the end of the reactor. In these experiments, argon was replaced by helium, since its low atomic mass leads to

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high signal intensities in the MBMS.

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{Table 2}

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2.1.1 Condensation experiments

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A schematic of the experimental setup for the condensation experiments and the temperature profile in the

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furnace are given in Figure 1 and in Figure 2. The reaction zone consisted of an inner tube and an outer tube. The

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inner tube was used for placing the cadmium source in the reaction zone and the introduction of the simulated

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gasification product gas (H2 and Ar) into the experiments. The outer tube, however, was necessary for

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introducing the steam and the trace gases HCl and H2S. The gas atmospheres considered were 14 % H2 / 17 %

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H2O / 69 % Ar and 28 % H2 / 3 % H2O / 69 % Ar. The total gas flow in the experiments was 650 ml/min and the

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duration of each experiment was 24 h.

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Both tubes were made of quartz glass. The outer tube had a total length of 210 cm. 75 cm of them corresponded

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to the reaction zone and 110 cm to the cooling zone. The inner diameter of the outer tube was 2.7 cm. The inner

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diameter of the inner tube was 1.4 cm and the total length was 77 cm. This tube also had a 5 cm gap in order to

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hold the sample boat for the introduction of the heavy metal. The sample boat was also made of quartz glass and

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had a total length of 4.5 cm. Each filter had a total length of 10 cm and was filled with quartz rings.

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A typical experimental run consisted of the following procedure. Eight quartz glass filters were placed at

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different positions along the cooling zone for the deposition of the metal compounds. The temperature and

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position of each filter in the cooling zone is shown in Figure 2.

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The metal species deposited in the filters and in the outer tube were firstly dissolved and afterwards determined

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by means of ion chromatography (IC) and inductively coupled plasma optical emission spectroscopy (ICP-OES).

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The relative error of the ICP-OES and IC analysis was ± 5 – 20 %. Furthermore, the relative error of the

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separation methods was approximately ± 0 – 20 %.The reason that part of the cadmium species condensed in the

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outer tube was a small gap between the filters and the tube. Thus, the fraction that condensed in the outer tube


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predominantly corresponded to fractions that condensed at the temperature ranges where the majority of the

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cadmium species condensed. In other words, the fraction condensed in the tube could be considered as a fraction

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that condensed at the filters where most species were deposited. CdCl2, CdO, CdS and Cd were dissolved in

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water, sulphuric acid (25 %), hydrochloric acid (25 %) and nitric acid (20 %), respectively. The amount of Cd2+

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was determined in each solution. The results of the analyses were compared with the weight gain of the filters

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during the experiments. Thus, the filters were weighed before, after the experiments and after dissolving the

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condensate. The relative variance between the elemental analysis and the gained weight of the filters during the

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experiments was determined in the range -16.5% - +5%.

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{Fig. 1}

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{Fig. 2}

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2.1.2 Release experiments

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The main aim of these experiments was to determine the species present in the gas phase and their behaviour

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under different experimental conditions. The experimental setup for the release experiments was very similar to

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the experimental setup for the condensation experiments. However, it only consisted of a reaction zone and did

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not include a cooling zone. Thus, at the end of the reaction zone the outer tube was coupled to a MBMS in order

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to analyse the gas in-situ. The total length of the outer tube was 900 mm and the inner diameter 27 mm. The

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inner tube had the same dimensions as the inner tube for the condensation experiments. The total gas flow in the

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release experiments was 4300 ml/min.

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In the release experiments, each experimental run was carried out at three different temperatures at the end of the

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reactor. The temperatures at which the experiments were carried out were 700, 900 and 1000 °C. In these

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experiments, argon was replaced by helium, since its low atomic mass leads to high signal intensities in the

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MBMS. Like in the condensation experiments, the concentration of HCl and H2S considered was 0, 50 and 500

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ppmv.

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2.2 Thermodynamic calculations

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2.2.1 Scheil-Gulliver cooling calculations


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Calculations were performed in order to evaluate the experimentally determined release and condensation data of

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cadmium under gasification-like conditions. The calculations were performed using the Scheil-Gulliver cooling

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model incorporated in the FactSage 6.3 Software. The non-equilibrium Scheil-Gulliver Cooling tool has been

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used and explained in detail in recent work [20, 21].

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With the Equilib module of FactSage 6.3 it is possible to calculate all equilibrium, or Scheil-Gulliver non

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equilibrium phase transitions as a mixture with different components is cooled [22, 23]. The Scheil-Gulliver

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cooling model is often utilized in metallurgy to predict the solid/liquid alloys composition during solidification.

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This model assumes a non-equilibrium solidification path calculating a sequence of equilibrium states. In the

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calculations the composition of the gas phase at high temperature is considered and then the temperature

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decreases stepwise. The equilibrium state is calculated at every temperature step. The elements that appear in the

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condensed phase are removed from the total mass balance and are not considered in the following calculations.

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The remaining phase is in the next incremental step cooled and the process is repeated. Thus, the initial

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composition of each calculation starts with a 100 % gaseous phase [20]. Using the Scheil-Gulliver cooling

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calculation model, results reasonably close to real conditions can be achieved [21].

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The calculations to determine the release and the condensation behaviour (temperature and speciation) of Cd

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were carried out at decreasing temperature steps of 25 °C starting from 1000 °C to 45 °C. The calculations were

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carried out at atmospheric pressure. As input data for the calculations the same atmospheric conditions as in the

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experiments were considered. Thus, the main aim was to evaluate the influence of H2O, HCl and H2S on the

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release of gaseous species and condensation behaviour of the condensable metal species. The results of the

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calculations are presented as the speciation of the gaseous and condensed phase versus temperature and were

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compared with the obtained experimental results.

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2.2.2 Thermodynamic pseudo-equilibrium model

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In order to understand the condensation mechanisms of metal vapour species during flue gas cooling, a

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thermodynamic pseudo-equilibrium model was developed by researchers from the University of Chubu using

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ChemApp linked with the FactSage 6.2 database (FACT, Fact 53, FToxid and FTsalt). This model is capable of

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predicting the condensation behaviour of metal vapours under the influence of cooling rate and chemical reaction


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control [9, 10, 24]. With this model a better understanding of the global kinetics in the condensation experiments

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was achieved. The schematic of the model is shown in Figure 3.

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{Fig. 3}

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In the model, the variable α is utilized to describe the proportion of a metallic vapour which does not condense

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on a cooling stage. In accordance with that, the metal vapours that condense in a specific cooling stage

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correspond to 1 – α. An alpha value of zero at a certain cooling stage means that all the species have reached the

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equilibrium and therefore, it does not exist super-cooling or thermodynamic reaction control. In agreement with

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the model, the flue gas quenching rate is decisive in terms of the condensation of a metallic vapour at a given

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temperature. That means, a rapid cooling of flue gas, “super-cooling”, can cause super-saturation of a vapour

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causing only a little deposition. Thus, the alpha value reflects the effect that super-cooling has on the

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condensation of the metal vapour species. Furthermore, super-cooling causes the condensation of the gaseous

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species at lower temperatures than the temperatures that are predicted by thermodynamic equilibrium modelling.

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In other words, it decreases the temperature at which the gaseous species condense. A detailed description of this

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model was given by Jiao et al. [9, 10].

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The value of alpha was optimized by curve-fitting the results of the condensation experiments. This was carried

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out for all the atmospheric conditions considered, to wit, H2O, HCl and H2S in the atmosphere. The flue gas

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compositions and the amount of inorganic vapours determined under the condensation experiments were the

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input for the modelling. The temperatures taken into account were an arithmetic mean of the temperature ranges

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of each filter. For the calculations, a temperature range from 1000 °C to 45 °C with an interval of 100 °C and

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atmospheric pressure was considered.

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3. Results

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3.1 Condensation of Cd species

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3.1.1 Condensation experiments

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Figure 4 shows the condensation distribution of cadmium in the filters and in the outer tube when the atmosphere

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contained H2O (g). The bars on the left for each temperature show the results obtained when the atmosphere

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contained 3 % volume H2O and the bars on the right the results with 17 % volume H2O. When the atmosphere


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only contained water vapour, cadmium condensed as metallic Cd at temperatures between 325 – 78 °C.

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Cadmium oxide was not found under these conditions. Under both experimental conditions, with 3 and 17 %

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volume water vapour, cadmium condensed in the fifth and sixth filters (325 – 78 °C). Furthermore, in both

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experiments, at least 68 % of the total cadmium condensed in the fifth filter. The results clearly show that an

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increase of the water vapour amount did not affect the condensation behaviour of cadmium under the present

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experimental conditions.

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{Fig. 4}

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Figure 5 shows a comparison between the condensation behaviour of cadmium when the atmosphere did not

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contain HCl and when it contained 50 and 500 ppmv HCl. In these experiments the amount of water did not vary

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and was 3 %vol. The bars on the left for every temperature show the results obtained when the atmosphere

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contained 0 ppmv HCl. The bars in the middle represent the results with 50 ppmv HCl and the bars on the right

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the results with 500 ppmv HCl. Cadmium condensed as a mixture of CdCl2 and metallic Cd in the presence of

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HCl. Cadmium condensed as metallic cadmium in the fifth (325 – 163 °C) and sixth filters (163 – 78 °C) when

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50 ppmv HCl was present in the atmosphere. Thus, Cd condensed at the same temperatures in the experiment

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with 0 and 50 ppmv HCl. However, with 500 ppmv HCl in the atmosphere cadmium started to condense

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preferably in the fourth filter (438 – 325 °C). CdCl2 condensed in the fourth (438 – 325 °C) and fifth filters (325

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– 163 °C) when the atmosphere contained 500 ppmv of HCl. The percentage condensed as CdCl2 in this

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experiment was 52.6 %. However, in the experiment containing only 50 ppmv of HCl just a small amount of

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cadmium (2.7 % of the total) condensed as CdCl2 and this also condensed in the fourth and fifth filter.

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In conclusion, both compounds, Cd and CdCl2 condensed at temperatures lower than 438 °C but CdCl2 deposits

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appeared at higher temperatures than the metallic Cd deposits. Larger amounts of HCl lead Cd to condense at

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slightly higher temperatures. However, no conclusions could be drawn about the influence of HCl on the

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condensation temperature of CdCl2 due to the small amount of cadmium that condensed as CdCl2 when only 50

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ppmv of HCl was available in the atmosphere. Nevertheless, it can be said that a higher amount of HCl caused

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the condensation of a larger amount of CdCl2.

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{Fig. 5}


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The condensation distribution of cadmium when the gas atmosphere contained the trace gas H2S is depicted in

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Figure 6. A comparison between the condensation behaviour of cadmium when the atmosphere did not contain

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H2S and when it contained 50 and 500 ppmv H2S is shown. As well as in the experiments with HCl, the amount

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of water considered was 3 %vol. Cadmium condensed as CdS and Cd when H2S was introduced into the outer

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tube. Cd condensed in both experiments at temperatures between 438 and 78 °C. In other words, Cd condensed

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in the fourth, fifth and sixth filters (438 – 78 °C), although mostly condensed in the last two ones. That is,

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between 325 and 78 °C. Cadmium condensed as CdS in both experiments at 438 – 163 °C, in other words, in the

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fourth and fifth filters. The main difference was the amount of cadmium condensed as CdS in both experiments.

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With 50 ppmv of H2S, 42.1 % of the total cadmium condensed as CdS. With 500 ppmv H2S, this amount

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increased to 66.3 %. In general, the condensation temperatures of Cd and CdS were not affected by the amount

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of H2S introduced into the atmosphere.

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{Fig. 6}

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3.1.2 Scheil-Gulliver cooling calculations for the solid phase

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The condensation calculations performed with the Scheil-Gulliver cooling model of FactSage 6.3 software are

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presented in Figure 7. The graphs show the molar amount of cadmium species that condensed at each

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temperature. As in the condensation experiments, the influence of H2O, HCl and H2S in the condensation

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behaviour of cadmium was studied.

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A comparison between the results with 3 % vol water and the results with 17 % vol water is presented in Figure

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7 a).

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{Fig. 7}

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The model calculations showed that cadmium condensed as metallic Cd at 310 – 150 °C independently of the

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water vapour amount considered. The results from both simulations overlapped, the program predicted for both

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atmospheric conditions the condensation of the same amount of metallic cadmium and at the same temperatures.


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Therefore, according to the cooling calculations, it can be considered that the amount of water vapour introduced

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in the atmosphere did not influence the condensation behaviour of cadmium.

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Figure 7 b) shows the results obtained from the Scheil-Gulliver cooling model when 50 and 500 ppmv of HCl

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were present in the atmosphere. In this case, the results obtained with 50 ppmv of HCl are depicted with a solid

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line and the results obtained when the atmosphere contained 500 ppmv of HCl are depicted with a dashed line.

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The cooling calculations show that cadmium condensed as a mixture of CdCl2 and Cd when HCl was introduced

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into the atmosphere. With an atmosphere containing 50 ppmv of HCl, cadmium condensed as CdCl2 (340 – 200

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°C) and Cd (310 – 150 °C). An increase in the amount of HCl to 500 ppmv, induced the condensation of CdCl2 at

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temperatures between 390 and 300 °C. Furthermore, the amount of CdCl2 deposited under these conditions

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increased by 358 %. In this case, the program did not predict the deposition of metallic cadmium. In conclusion,

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according to the calculations, the increase in the HCl amount shifted the deposition of CdCl2 to higher

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temperatures. The amount of CdCl2 deposited also increased.

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The cooling calculations for 50 ppmv H2S and 500 ppmv H2S introduced into the atmosphere containing

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cadmium are shown in Figure 7 c). The Scheil-Gulliver cooling model predicted the condensation of cadmium as

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a mixture of metallic Cd and CdS when 50 ppmv H2S was in the atmosphere. Cd condensed at low temperatures

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(300 – 150 °C) and CdS at higher temperatures (480 – 350 °C). The amount deposited of both compounds was

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similar. When 500 ppmv of H2S was considered, only the species CdS condensed. Under these atmospheric

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conditions, CdS condensed at higher temperatures (530 – 400 °C) than in the simulation with only 50 ppmv of

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H2S. The amount of cadmium condensed as CdS increased by 78 %.

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Basically, an increase in the H2S amount considered shifted the condensation of CdS to higher temperatures. The

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amount of CdS deposited increased with the quantity of H2S introduced. Therefore, cadmium reacted with the

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available H2S to form CdS and no metallic cadmium was found in the deposits with 500 ppmv of H2S.

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3.1.3 Thermodynamic pseudo equilibrium model

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Figure 8 shows the comparison between the model calculations and the experimental results of the condensation

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of cadmium in an atmosphere containing H2O (3 and 17 % vol), HCl (50 and 500 ppmv) and H2S (50 and 500

308

ppmv).


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{Fig. 8}

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The curve-fitting of the experimental results indicated an alpha value of zero for all experimental conditions

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except for the experiments with 50 and 500 ppmv of H2S, where alpha values of 0.8 for the experiment with 50

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ppmv of H2S and 0.7 for the one with 500 ppmv of H2S fit nicely the experimental results. As it has been

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explained before, an alpha value of zero assumes that the species have reached the equilibrium and therefore

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there is not any reaction or cooling control. For this reason, the model assumes that the experiments containing

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H2O or HCl were in equilibrium and hereby, the model calculations predicted very well the experimental results.

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In the experiments with H2S the deposition fractions predicted by the model were far higher than the observed in

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the experimental results. Thus, the experiments did not reach the equilibrium and the condensation of the

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metallic vapours was affected by the flue gas cooling rate. That means, Cd and CdS vapours were possibly

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saturated and they condensed at lower temperatures than the temperatures predicted by the calculations.

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According to the model, the super-cooling effect can be offset by the chemical reaction of inorganic vapours

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when H2O and H2S are introduced into the atmosphere. Thus, in the experiments the alpha value decreased with

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the addition of a larger concentration of H2S. The alpha value was 0.7 with 500 ppmv of H2S and 0.8 with 50

325

ppmv of H2S. The formation of a higher amount of CdS compensated slightly the negative effect of super-cooling

326

and the condensation was shifted to higher temperatures.

327 328

3.2 Release of Cd species

329 330

The influence of water vapour, HCl and H2S on the gas phase speciation of cadmium was investigated by

331

MBMS. Experiments were conducted at 1000, 900 and 700 °C at the end of the furnace, because the Scheil-

332

Gulliver calculations predicted important variations in the behaviour of the cadmium species in this temperature

333

range. Due to the strong temperature gradient in the reaction zone of the furnace, the concentration of cadmium

334

in the gas phase varied from experiment to experiment. Therefore, only a qualitative study of the gas species

335

could be carried out. Thus, the main target of these experiments was the determination of the cadmium species in

336

the gas phase under different experimental conditions.

337 338

As the mass spectrometer only determines the gaseous ionized species based on their mass-to charge ratios

339

(m/z), it was necessary to carry out a calibration before starting the experiments. With this calibration it was


Energy & Fuels

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Page 12 of 32

340

possible to correlate the intensities of the isotopes present in the experiments with the trace metal vapour

341

concentration (ppmv) obtained. In the experiments the monitored species were

342

114

343

which lead to the overlapping of the spectra. However, in order to detect easily both species,

344

measured. Thus, m/z = 146 corresponded to a mixture of CdO2 and CdS. Therefore, examining the intensity peak

345

of m/z = 146 and knowing the relationship between CdO2 and CdS, it was possible to determine the relative

346

amounts of CdO2 and CdS in the gas phase. The ratio of the percentage of the peak intensity of the species with

347

m/z = 146 that corresponded to CdO2 and CdS was measured in experiments previous to the experimental runs.

348

Similarly,

349

114

350

experiments were compared with the results obtained with the Scheil-Gulliver calculations for the gas phase.

Cd35Cl2+ and

114

106

114

Cd+,

114

Cd16O+,

114

Cd16O2+,

Cd33S+. The main isotope of CdO2 and CdS had the same mass-to-charge ratio, namely 146, 139

CdS+ was also

Cd+ does not only originate from metallic Cd but can be a fragment of all Cd-compounds and

Cd16O+ can also be a fragment of CdOH. Like in the condensation experiments, the results of the gas phase

351 352

3.2.1 Release experiments

353 354

The results of the MBMS measurements are provided in Figure 9, Figure 10 and Figure 11. The graphs show an

355

overview of the relative concentrations of all the cadmium species detected in the gas phase at 1000, 900 and

356

700 °C. Cd (g) was generally the major species in all experiments. Its concentration in the gas phase during the

357

experiments was in most of the cases much higher than the amounts of the other Cd-species present in the gas

358

phase.

359 360

The release experiments showed that during the experiments with H2O, Cd and CdO were the only compounds

361

present in the gas phase as can be seen in Figure 9, Cd was the dominant species in in both 3%vol H2O and

362

17%vol H2O at 700, 900, and 1000 °C. It represented approximately 85 – 99 % of the total cadmium present in

363

the gas phase. The concentration of CdO in the experiments with 17 % vol increased with the temperature. In the

364

experiments with 3 % vol H2O, the concentration of CdO was very similar at 900 and 1000 °C. However, at 700

365

°C no CdO was present in the gas phase in both experiments. Furthermore, the concentration of CdO at 1000 °C

366

was considerably higher in the experiments with 17 % vol of H2O than in the experiments with 3 % vol of water.

367

Thus, with 3 % H2O only 1 % of the total Cd species in the gas corresponded to CdO and with 17 % H2O, the

368

concentration of CdO increased to 16 % at 1000 °C. It seemed that with a high amount of H2O, higher

369

concentrations of CdO were present in the gas phase at 1000 °C.


Page 13 of 32

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371

Energy & Fuels

{Fig. 9}

372 373

The release experiments with HCl showed that cadmium was in the gas phase as a mixture of Cd, CdCl2 and

374

CdO (see Figure 10). Cd was the major species in every experiment. The amount of CdO was generally low (the

375

maximum value was 14 % at 1000 °C and 500 ppmv HCl) and increased gently with the temperature. For

376

example, with 50 ppmv HCl, the concentration of CdO increased from 1 to 6 % at 900 and 1000 °C. In the

377

experiment with 500 ppmv HCl, the concentration of CdO increased from 10 to 14 % at 900 and 1000 °C. The

378

concentration of CdCl2 was higher than the concentration of CdO and it also increased with the temperature. For

379

example, in the experimental run with 500 ppmv HCl, the concentration of CdCl2 increased from 31 to 34 and 40

380

% at 700, 900 and 1000 °C, respectively. Furthermore, it could be noticed that the concentrations of both

381

species, CdO and CdCl2, were higher in the experiments with 500 ppmv HCl than in the experiments with only

382

50 ppmv HCl.

383 384

{Fig. 10}

385 386

The results of the release experiments with H2S are depicted in Figure 11. Cadmium was present in the gas phase

387

as a mixture of Cd, CdS and CdO. The major species in the gas phase was Cd. In the experiments with 50 ppmv

388

the concentration of Cd was constant. However, with 500 ppmv the concentration of Cd decreased with the

389

temperature. In general, the concentration of CdS and CdO was similar in every experiment except in the

390

experiment with 500 ppmv at 1000 °C. In this experiment the concentration of CdS (31 %) was higher than the

391

concentration of CdO (17 %). As it can be observed in the graph, only in the experiments with 500 ppmv H2S the

392

total concentrations of CdO and CdS were higher than 7 %. In the experiments with 50 ppmv H2S they

393

represented less than 7 % of the total Cd-species present in the gas phase.

394 395

{Fig. 11}

396 397

3.2.2 Scheil-Gulliver cooling calculations for the gas phase

398 399

The gas phase composition regarding cadmium species predicted by the Scheil-Gulliver cooling model is shown

400

in this section. The calculations show the speciation of the main inorganic gaseous species at temperatures

401

between 1000 °C and 0 °C under the influence of H2O, HCl and H2S.


Energy & Fuels

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402 403

The speciation of the gas phase predicted by the Scheil-Gulliver cooling calculations in an atmosphere

404

containing water vapour and cadmium is shown in Figure 12. The graph shows a comparison between the results

405

obtained with 3 and 17 % vol water vapour in the atmosphere. According to the calculations, Cd, CdOH and

406

CdO were present in the gas phase at temperatures between 1000 and 50 °C when the atmosphere only had water

407

vapour. The concentration of CdO was less than 1 ppb and therefore, out of the range considered in this study.

408

The concentration of Cd was 100 ppmv (log10(act) ≈ 10-4) at temperatures between 1000 – 300 °C. At

409

temperatures less than 300 °C the concentration of Cd decreased significantly. CdOH was in the gas phase at

410

concentrations considerably smaller than Cd. Besides, the concentration of CdOH increased with the temperature

411

and with the amount of water considered.

412 413

{Fig. 12}

414 415

The gas phase composition of cadmium when 50 and 500 ppmv of HCl were present in the atmosphere predicted

416

by the Scheil-Gulliver cooling model is depicted in Figure 13. The main inorganic species present in the gas

417

phase were Cd, CdOH, CdCl2 and CdO. However, CdO was present in concentrations smaller than those

418

addressed in this investigation. 100 ppmv of Cd was present at temperatures between 1000 and 350 °C. The

419

concentration of CdCl2 decreased with the temperature (at 320 – 1000 °C) and a higher concentration of the

420

species was in the gas phase with high amounts of HCl. At temperatures below 350 °C the concentration of

421

CdCl2 decreased abruptly. The concentration of CdOH increased with the temperature. However, the amount of

422

HCl did not influence the concentration of CdOH present in the gas phase at high temperatures.

423 424

{Fig. 13}

425 426

Figure 14 shows the release behaviour of cadmium predicted by FactSage when H2S was introduced into the

427

atmosphere. A comparison between the results with 50 ppmv H2S and 500 H2S is shown. According to the

428

calculations, Cd, CdOH, CdS and CdO were the cadmium-containing species present in the gas phase when H2S

429

was introduced into the atmosphere. Like in the calculations with H2O and HCl, the concentration of CdO was

430

out of the concentrations considered in this study. With 50 ppmv H2S, 100 ppm of Cd were in the gas phase at

431

temperatures between 1000 and 300 °C. However, in the calculation with 500 ppmv H2S, 100 ppm of Cd were

432

present in the gas phase only from 1000 to 550 °C. At temperatures lower than 550 °C the concentration of Cd


Page 14 of 32

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Energy & Fuels

433

decreased significantly. The concentrations of CdOH and CdS increased with the temperature and the amount of

434

H2S influenced their behaviour. Thus, the concentration of CdS between 500 and 1000 °C was higher with 500

435

ppmv of H2S than with 50 ppmv H2S. Furthermore, at temperatures between 250 – 500 °C, a higher concentration

436

of CdOH was found in the gas phase with 50 ppmv H2S than with 500 ppmv H2S.

437 438

{Fig. 14}

439 440

4. Summary and discussion

441 442

In this section a comparison of the experimental results with the results of the cooling calculations and the

443

thermodynamic pseudo-equilibrium model is given.

444 445

4.1 Condensation behaviour of cadmium

446 447

When the atmosphere contained water vapour, cadmium condensed as metallic Cd at 325 – 78 °C. An increase

448

of the water vapour amount did not affect the condensation behaviour of cadmium. The results of the cooling

449

calculations were in good agreement with the experimental results.

450 451

In the presence of HCl, cadmium condensed as a mixture of CdCl2 (438 – 163 °C) and Cd (325 – 78 °C). In

452

general larger amounts of HCl lead Cd to condense at slightly higher temperatures. The cooling calculations did

453

not match accurately with the experimental results. However, the speciation as well as the condensation

454

temperatures of the species matched perfectly.

455 456

In the experiments containing H2S, cadmium condensed as CdS (438 – 163 °C) and Cd (325 – 78 °C) regardless

457

of the amount of cadmium introduced. The cooling calculations predicted quite well the results with 50 ppmv of

458

H2S. However, some discrepancies were found between the calculations and the experimental results with

459

500 ppmv of H2S.

460 461

According to the results of the thermodynamic pseudo-equilibrium model, all experiments were in equilibrium

462

except the experiments with H2S. Alpha values of 0.8 and 0.7 fit the experimental results nicely. The model

463

assumed that the experiments containing water and HCl were in equilibrium and hereby, the calculations with an


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

464

alpha value of zero predicted well the experimental results. In the experiments with H2S, Cd and CdS were

465

probably saturated and condensed at lower temperatures than the predictions. Alpha decreased with larger

466

concentrations of H2S, which means that a larger formation of CdS compensated the super-cooling effect and the

467

condensation was slightly shifted to higher temperatures. In this way, the model confirmed the importance of the

468

chemical reactions in the condensation behaviour of cadmium.

469 470

4.2 Release behaviour of cadmium

471 472

Due to the strong temperature gradient in the reaction zone of the furnace, the vaporization of the exact same

473

amount of cadmium in every experiment was not achieved. Therefore, only a qualitative analysis could be done.

474

The main target of these experiments was the determination of the cadmium-species in the gas phase and their

475

behaviour under different experimental conditions. The results of the MBMS measurements showed that Cd (g)

476

was generally the major species in all experiments.

477 478

The release experiments showed that during the experiments with H2O, Cd and CdO were the only species

479

present in the gas phase. The results of the Scheil-Gulliver calculations predicted the existence of high

480

concentrations of Cd and CdOH in the gas phase. The concentration of CdO was lower than 1 ppb. However, in

481

the experiments the concentration of CdO was at ppm level. Besides, no CdOH was detected in the gas phase. In

482

conclusion, the speciation as well as the behaviour of some species were slightly different in the calculations and

483

in the experiments. However, the calculations could predict appropriately the behaviour of Cd and CdO.

484 485

The experiments with HCl showed that cadmium was in the gas phase as a mixture of Cd, CdCl2 and CdO. The

486

amount of CdO and CdCl2 increased gently with the temperature. Besides, the concentration of CdCl2 was higher

487

than the concentration of CdO. The calculations predicted the existence of Cd, CdOH, CdCl2 and CdO. CdO was

488

present in the gas phase in concentrations smaller than those addressed in this investigation (1 ppb). The major

489

species in the experiments and in the calculations concurred. Furthermore, their behaviour was similar. However,

490

in the experiments the concentration of CdO was appreciable and no CdOH was detected. Thus, although some

491

differences were found between the calculations and the experimental results, the Scheil-Gulliver calculations

492

presented a similar tendency as observed in the experiments.

493


Page 16 of 32

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Energy & Fuels

494

The results of the experiments with H2S showed that cadmium was present in the gas phase as a mixture of Cd,

495

CdS and CdO. The concentrations of CdO and CdS increased with the temperature and the concentration of CdS

496

was higher than the concentration of CdO. According to the Scheil-Gulliver calculations, Cd, CdOH, CdS and

497

CdO were the species present in the gas phase. The behaviour of CdO and CdS in the calculations and in the

498

experiments was found to be similar. However, in the experiments the concentration of CdO was higher than in

499

the calculations. Although in the experiments no CdOH was found in the gas phase and some discrepancies were

500

found between the experimental results and the calculations, it could be concluded that the Scheil-Gulliver

501

model predicted quite good the experimental results obtained.

502 503 504

In general, a good agreement between the cooling calculations and the experimental results was found. The

505

speciation as well as the temperatures at which the species condensed under the influence of H2O, HCl and H2S

506

had the same trend in the calculations as in the experimental results. In the condensation experiments with HCl

507

and H2S some differences were observed between the calculations and the experimental results. These

508

differences could be explained by the difficulty of evaporating the same amount of cadmium (ppmv) in each

509

experiment and by the error associated to the analytical methods used for determining the species present in the

510

filters and outer tube of the cooling zone. The Scheil-Gulliver calculations for the gas phase predicted the

511

experimental results acceptably. Although for some species the behaviour in the calculations and in the

512

experiments showed the same trend, the model predicted the existence of species that were not found in the gas

513

phase during the experimental runs. However, the behaviour of the main species in the gas phase was predicted

514

nicely. To sum up, the Scheil-Gulliver calculations could be considered a good tool for the prediction of the

515

condensation and release behaviour of cadmium.

516 517

4.3 Practical implications

518 519

The present results confirm earlier findings that Cd species are relatively volatile and will condense at relatively

520

low temperatures [18, 19]. Accordingly, Cd will be exclusively present as gaseous compounds in the gasifier

521

itself and condense in downstream parts of the plant operated at temperatures below 400 °C depending on the

522

concentration of Cd itself and other gas phase constituents like HCl and H2S. Therefore, if high Cd concentration

523

in a specific fuel is an issue, special attention has to be given to deposits and ashes collected from colder parts of

524

the plant. Ashes directly collected from the gasifier should contain relatively low amount of Cd compounds. If a


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

525

hot gas cleaning system for Cd shall be designed, the temperature range above 400 °C should be considered

526

since Cd is exclusively present in the gas phase at these temperatures.

527 528

5. Conclusions

529 530

The purpose of this work was to assess the influence of H2O, HCl and H2S on the condensation and release of

531

cadmium. The condensation behaviour (temperature and speciation) of the cadmium vapours was investigated in

532

a heated flow channel reactor housed in a furnace with a gas cooling zone. Glass filters were placed on different

533

stages along the cooling zone for the deposition of the metal compounds. The metal species deposited in the

534

filters were dissolved and determined by means of ion chromatography (IC) and inductively coupled plasma

535

optical emission spectroscopy (ICP-OES). Experiments on the release of the inorganic vapours were carried out

536

in a heated flow channel reactor coupled to a molecular beam mass spectrometer (MBMS) in order to analyse the

537

gas in-situ. The experiments were carried out under two typical gasification conditions (H2/H2O/He or Ar) and

538

atmospheric pressure with different concentrations of HCl and H2S. Concentrations of 50 and 500 ppmv of the

539

trace gases in the experiments were considered. Hot gas analysis was done by MBMS at 700, 900 and 1000 °C.

540 541

With this work a better understanding of the release and condensation mechanisms of cadmium was achieved.

542

The speciation as well as the behaviour of cadmium under the influence of different concentrations of H2O, HCl

543

and H2S was determined. The key inorganic species detected during the condensation experiments were Cd,

544

CdCl2 and CdS. The species found in the gas phase were Cd, CdO, CdCl2 and CdS. The release and

545

condensation of cadmium-species were strongly influenced by steam, HCl and H2S. The experimental results

546

were compared with Scheil-Gulliver cooling calculations (solid and gas phase) carried out with FactSage 6.3 and

547

with the results obtained with the thermodynamic pseudo-equilibrium model developed by researchers of Chubu

548

University (Japan). The global kinetics in the experiments were clarified through the pseudo thermodynamic

549

model. The Scheil-Gulliver Cooling model was proved to be an excellent tool for the prediction of the release

550

and condensation of Cd. The speciation as well as the temperatures at which the species condensed and were

551

present in the gas phase under the influence of H2O, HCl and H2S had the same trend in the calculations as in the

552

experimental results. Although in this study the model was only applied for some atmospheric conditions and the

553

calculations were only compared with laboratory results, the model could be applied for wider conditions and

554

bigger systems typical in gasification processes. Thus, predictions of the behaviour of cadmium under

555

gasification conditions that combine the trace gases HCl and H2S simultaneously, could be carried out with the


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Energy & Fuels

556

cooling model. Good and reliable predictions of the release and condensation of cadmium under other

557

atmospheric conditions not considered in this work could be done by the model.

558 559

Acknowledgement

560

The work described in this paper was supported by Bundesministerium für Witschaft und Technologie in the

561

framework of the HotVeGas-EM project (FZK 0327773C) and by Deutsche Forschungsgemeinschaft (DFG)

562

with Grant No. BL 1363/1-1.

563 564

REFERENCES

565 566

[1]

OECD/IEA.World energy outlook. Paris: International Energy Agency; 2014.

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[2]

Wate B. High temperature corrosion in gasifiers. Materials Research 2004; 7: 53-59.

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[3]

Joshi M.M and Lee S. Integrated gasification combined cycle. A review of IGCC technology. Energy

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Sources 1996; 18: 537-568. [4]

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development needs for clean coal deployment. IEA Clean Coal Centre 2008. [5]

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[6]

[7]

Frandsen F, Dam-Johansen K and Rasmussen P. Trace elements from combustion and gasification of coal—An equilibrium approach. Progress in Energy and Combustion Science 1994; 20: 115-138.

[8]

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Descamps C, Bouallou C and Kanniche M. Efficiency of an integrated gasification combined cycle (IGCC) power plant including CO2 removal. Energy 2008; 33: 874-881.

577 578

Müller M. Integration of hot gas cleaning at temperatures above the ash melting point in IGCC. Fuel 2013; 108 : 37-41.

575 576

Kather A, Raifailidis S, Hermsdorf C, Kostermann M, Maschmann A, Mieske K et al. Research and

Miller B, Dugwell D.R and Kandiyoti R. The Influence of injected HCl and SO2 on the behavior of trace elements during wood-bark combustion. Energy & Fuels 2003; 17: 1382-1391.

[9]

Jiao F, Cheng Y, Zhang L, Yamada N, Sato A and Ninomiya Y. Effects of HCl, SO2 and H2O in flue

581

gas on the condensation behavior of Pb and Cd vapors in the cooling section of municipal solid waste

582

incineration. Proceedings of the Combustion Institute 2011; 33: 2787-2793.

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[10]

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Jiao F, Zhang L, Yamada N, Sato A and Ninomiya Y. Effect of HCl, SO2 and H2O on the condensation of heavy metal vapors in flue gas cooling section. Fuel Processing Technology 2013; 105: 181-187.

[11]

Song et al. Condensation behavior of heavy metals during oxy-fuel combustion: Deposition, species distribution, and their particle characteristics. Energy Fuels 2013; 27 (10): 5640-5652.


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high-temperature processing. Powder Technology 2008; 180: 210-215. [13]

590 591

Querol X, Fernández-Turiel J and López-Soler A. Trace elements in coal and their behaviour during combustion in a large power station. Fuel 1995; 74: 331-343.

[14]

592 593

Sekine Y, Sakajiri K, Kikuchi E and Matsukata M. Release behavior of trace elements from coal during

Mojtahedi W. Trace Metals volatilisation in fluidised-bed combustion and gasification of coal. Combustion Science and Technology 1989; 63: 209-227.

[15]

Reddy M.S, Basha S, Joshi H.V and Jha B. Evaluation of the emission characteristics of trace metals

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from coal and fuel oil fired power plants and their fate during combustion. Journal of Hazardous

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Materials 2005; 123: 242-249.

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[16]

Germani M.S and Zoller W.H. Vapor-phase concentrations of arsenic, selenium, bromine, iodine, and

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mercury in the stack of a coal-fired power plant. Environmental Science Technology 1988; 22: 1079-

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1085.

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desulphurisation facility. Kema Scientific & Technical Reports 1989; 7: 267-292. [18]

602 603

Clarke L.B. The fate of trace elements during coal combustion and gasification: an overview. Fuel 1993; 72: Start Page: 731.

[19]

604 605

Meij R. Tracking trace elements at a coal-fired power plant equipped with a wet flue-gas

Díaz Somoano M and Martinez Tarazona M.R. High-temperature removal of cadmium from a gasification flue gas using solid sorbents. Fuel 2005; 84 (6): 717-721.

[20]

Froment K, Defoort F, Bertrand C, Seiler J.M, Berjonneau J and Poirier J. Thermodynamic equilibrium

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calculations of the volatilization and condensation of inorganics during wood gasification. Fuel 2013;

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Gheribi A.E, Audet C, Le Digabel S, Bélisle E, Bale C.W and Pelton A.D. Calculating optimal

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conditions for alloy and process design using thermodynamic and property databases, the factSage

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software and the mesh adaptive direct search algorithm. Calphad 2012; 36: 135-143.

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Bale C.W et al. FactSage thermochemical software and databases — recent developments. Calphad 2009; 33: 295-311.

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Bale C.W et al. FactSage thermochemical software and databases. Calphad 2002; 26: 189-228.

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Jiao F, Zhang L, Song W, Meng Y, Yamada N, Sato A and Ninomiya Y. Effect of inorganic

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618

Energy & Fuels

Figures

619 620

Fig. 1 – Schematic of the experimental setup for the condensation experiments.

621

Fig. 2 – Temperature profile in the condensation experiments.

622

Fig. 3 – Schematic of the thermodynamic pseudo-equilibrium model [9].

623

Fig. 4 – Condensation distribution of cadmium in the outer tube and in the filters placed along the cooling zone

624

in an atmosphere containing 3 % vol water vapour (left bar) and 17 % vol water vapour (right bar).

625


626

in an atmosphere containing 0 ppm HCl (left bar), 50 ppm HCl (middle bar) and 500 ppm HCl (right

627

bar).

628


629

in an atmosphere containing 0 ppm H2S (left bar), 50 ppm H2S (middle bar) and 500 ppm H2S (right

630

bar).

631

Fig. 7 Speciation of the condensed phase during cooling from 1000 to 0 °C predicted by the Scheil-Gulliver

632

cooling model in an atmosphere containing: a) 3 % vol water vapour (solid line) and 17 % vol water vapour

633

(dashed line); b) 50 ppmv HCl (solid line) and 500 ppmv HCl (dashed line); c) 50 ppmv H2S (solid line) and 500

634

ppmv H2S (dashed line).

635

Fig. 8 – Comparison between the calculated and the experimental results of the condensation of cadmium

636

vapours in the presence of H2O (3 – 17 % vol), HCl (50 – 500 ppm) and H2S (50 – 500 ppm).

637

Fig. 9 – Concentration of gaseous cadmium species (%) at 1000, 900 and 700 °C when the atmosphere contained

638

3 % vol water vapour (left bar) and 17 % vol water vapour (right bar).

639

Fig. 10 – Concentration of gaseous cadmium species (%) at 1000, 900 and 700 °C when the atmosphere

640

contained 50 ppmv HCl (left bar) and 500 ppmv HCl (right bar).

641

Fig. 11 – Concentration of gaseous cadmium species (%) at 1000, 900 and 700 °C when the atmosphere

642

contained 50 ppmv H2S (left bar) and 500 ppmv H2S (right bar).

643

Fig. 12 – Gaseous cadmium-containing species versus temperature in an atmosphere containing 3 % vol water

644

vapour (solid line) and 17 % vol of water vapour (dashed line) calculated by the Scheil-Gulliver cooling model.

645

Fig. 13 – Gaseous cadmium-containing species versus temperature in an atmosphere containing 50 ppmv HCl

646

(solid line) and 500 ppmv HCl (dashed line) calculated by the Scheil-Gulliver cooling model.

647

Fig. 14 – Gaseous cadmium-containing species versus temperature in an atmosphere containing 50 ppmv H2S

648

(solid line) and 500 ppmv H2S (dashed line) calculated by the Scheil-Gulliver cooling model.


Energy & Fuels

649

650 651

Fig. 1. Schematic of the experimental setup for the condensation experiments.

652 1200 1100 Reaction zone

1000

Cooling zone

900

Temperature (°C )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 32

Filter 1

800 700

Filter 2

600 Filter 3

500 Filter 4

400 Cadmium source (370 °C)

300

Filter 5

200

Filter 6 Filter 7

100

Filter 8

0 0

653 654

10

20

30

40

50

60

70

80

90

100 110 120 130 140 150 160 170 180

Length of reactor (cm) Fig. 2. Temperature profile in the condensation experiments.

655 656 657 658


Page 23 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

659 660

Energy & Fuels

Fig. 3. Schematic of the thermodynamic pseudo-equilibrium model [9].

661 662

663 664

Fig. 4. Condensation distribution of cadmium in the outer tube and in the filters placed along the cooling zone in

665

an atmosphere containing 3 % vol water vapour (left bar) and 17 % vol water vapour (right bar).

666


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

667 668


669

an atmosphere containing 0 ppmv HCl (left bar), 50 ppmv HCl (middle bar) and 500 ppmv HCl (right bar).

670 671 672 673 674 675 676


Page 24 of 32

Page 25 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

677 678


679

an atmosphere containing 0 ppmv H2S (left bar), 50 ppmv H2S (middle bar) and 500 ppmv H2S (right bar).

680 681 682 683 684 685 686


Energy & Fuels

6E-3

a)

–––– 3 % H2O – – – 17 % H2O

5E-3

Cd(s)

mol

4E-3

3E-3

2E-3

1E-3

0E0 0

100

200

300

400

500

T (°C)

600

700

800

900

1000

6E-3

CdCl 2(s)

b)

–––– 50 ppm HCl – – – 500 ppm HCl

5E-3

Cd(s)

mol

4E-3

3E-3

2E-3

CdCl 2(s) 1E-3

0E0 0

100

200

300

400

500

T (°C)

600

700

800

900

1000

6E-3

c)

–––– 50 ppm H2S – – – 500 ppm H2S

CdS(s)

5E-3

4E-3

Cd(s)

mol

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 32

3E-3

CdS(s)

2E-3

1E-3

0E0 0

100

200

300

400

500

T (°C)

600

700

800

900

1000

687

Fig. 7. Speciation of the condensed phase during cooling from 1000 to 0 °C predicted by the Scheil-Gulliver

688

cooling model in an atmosphere containing: a) 3 % vol water vapour (solid line) and 17 % vol water vapour


Page 27 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

689

(dashed line); b) 50 ppmv HCl (solid line) and 500 ppmv HCl (dashed line); c) 50 ppmv H2S (solid line) and 500

690

ppmv H2S (dashed line).

691

692 693

Fig. 8. Comparison between the calculated and the experimental results of the condensation of cadmium vapours

694

in the presence of H2O (3 – 17 % vol), HCl (50 – 500 ppmv) and H2S (50 – 500 ppmv ).

695 696 697


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

698 699

Fig. 9. Concentration of gaseous cadmium species (%) at 1000, 900 and 700 °C when the atmosphere contained

700

3 % vol water vapour (left bar) and 17 % vol water vapour (right bar).

701


Page 28 of 32

Page 29 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

702 703


704

50 ppmv HCl (left bar) and 500 ppmv HCl (right bar).

705


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

706 707


708

50 ppmv H2S (left bar) and 500 ppmv H2S (right bar).

709 710

711 712

Fig. 12. Gaseous cadmium-containing species versus temperature in an atmosphere containing 3 % vol H2O

713

(solid line) and 17 % vol H2O (dashed line) calculated by the Scheil-Gulliver cooling model.


Page 30 of 32

Page 31 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

714

715 716

Fig. 13. Gaseous cadmium-containing species versus temperature in an atmosphere containing 50 ppmv HCl

717

(solid line) and 500 ppmv HCl (dashed line) calculated by the Scheil-Gulliver cooling model.

718

719 720

Fig. 14. Gaseous cadmium-containing species versus temperature in an atmosphere containing 50 ppmv H2S

721

(solid line) and 500 ppmv H2S (dashed line) calculated by the Scheil-Gulliver cooling model.

722 723 724 725 726 ACS Paragon Plus 31 Environment

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 32

727

Tables

728

Table 1 – Overview of the experimental conditions that most closely correspond to the real conditions.

729

Table 2 – Overview of the experimental conditions in the condensation and release experiments.

730 731

Table 1. Overview of the experimental conditions that most closely correspond to the real conditions. Atmosphere

H2 (%)

H2O (%)

CO (%)

CO2 (%)

Ar (%)

Water-gas-shift (real)

15

51

34

Gasification (real)

29

2

66

Water-gas-shift (lab)

14

17

69

Gasification (lab)

28

3

69

3

732 733

Table 2. Overview of the experimental conditions in the condensation and release experiments. Experimental run

Atmosphere

H2 (%)

H2O (%)

Ar (%)

HCl (ppm)

H2S (ppm)

Influence of H2O

Water-gas-shift

14

17

69

0

0

Influence of H2O

Gasification

28

3

69

0

0

Influence of HCl

Gasification

28

3

69

50

0

Influence of HCl

Gasification

28

3

69

500

0

Influence of H2S

Gasification

28

3

69

0

50

Influence of H2S

Gasification

28

3

69

0

500

734 735


Influence of Steam, Hydrogen Chloride, and Hydrogen Sulfide on the

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