Ron Zevenhoven

Cement manufacturing using alternative fuels and the advantages of process modelling

Energy costs and environmental standards encouraged cement manufacturers world-wide to evaluate to what extent conventional fuels can be replaced by alternative fuels, i.e., processed waste materials. Clinker burning is well suited for various alternative fuels. In order select a suitable alternative fuel, a commercial modelling tool (ASPEN PLUS®) is used to model the four-stage pre-heater kiln system of a full-scale cement plant (clinker production ∼2900 tons/day), using petcoke as fuel. The goal is to optimise process control and alternative fuel consumption, while maintaining clinker product quality. Calculations with varying amounts of different fuels are compared with a reference case. The dependence of process performance on the amount of combustion air is clearly demonstrated and the energy demand of the process could be predicted for varying fuel mixes.

Arsenic in soil and groundwater: an overview

Contamination of the environment with arsenic (As) from both anthropogenic and natural sources has occurred in many parts of the world and is recognized as a global problem. Principal anthropogenic sources of As include base metal smelters, gold mines, power plants that burn As-rich coals or treated lumber, disposal sites for wastes from As-processing plants, as well as industrial and municipal dump sites. In many areas, the levels of As in the environment have become one of concern and epidemiological studies have documented various adverse health effects on local populations. Arsenic poisoning episodes from exposure to industrial sources have been reported all over the world; for instance, in Japan, where cases have been associated with pollution around As mines and pollution of groundwater around As-using industries and industrial waste burial sites. Other examples of contaminated environments with increased risk for As poisoning include agricultural lands treated with arsenical pesticides, urban areas, war zones defoliated or sprayed with As compounds, and the superfund sites in the United States and other countries. Although a lot of people get exposed, most often, however, it is not possible to associate the exposure to elevated As levels with adverse human health effects. Nevertheless, long-term cumulative exposure to As in these contaminated environments should be a matter of public health concern and scientific interest.

The reactivity of chars from coal, peat and wood towards NO, with and without CO

The reduction of NO by chemical reaction with chars prepared from bituminous coal, peat and wood was studied, with and without CO present in the gas. Chars were prepared in pure nitrogen at the same temperatures as for the NO reduction: 750, 850 and 950°C. Tests were conducted in a quartz fixed bed reactor with gas analysis for NO, CO and the product gas CO2. The bulk gas was nitrogen; since no oxygen was present N2O was not considered. Eleven different solid fuel qualities were studied. Chars from peat and lignite appeared more reactive with respect to NO than chars from bituminous coal or wood. This trend was different from char gasification reactivities of these fuels, which increased with increasing fuel volatility. Activation energies were in the range 28–131 kJ mol−1 for the NO reduction with CO, catalysed by the char, against 29−95 kJ mol−1 for the NO reduction by char. For peat, the reduction of NO was found to be faster without CO than with CO present in the gas. Correlations between NO reduction capacity and char composition were made, which showed the catalytic effect of calcium, magnesium and potassium. The role of iron appeared unclear.

Kinetics studies on wet and dry gas–solid carbonation of MgO and Mg(OH)2 for CO2 sequestration

Mineral carbonation is a carbon dioxide capture and storage (CCS) route that warrants further investigation. Although most of the CCS research to date has been concerned with underground storage in liquefied form, mineral carbonation is the only method that disposes CO2 in a permanent and inherently safe manner. Here, we consider the gas–solid conversion of both MgO and Mg(OH)2 with CO2 in the presence and absence of steam in an attempt to model and predict the optimum conditions for rapid and complete carbonation. Results from pressurised thermogravimetric analysers (PTGA) and a laboratory scale pressurised fluidised bed (PFB) are presented. The results show that the carbonation of Mg(OH)2 is much faster (∼50% in 4 min) in a PFB than the carbonation of comparatively fine MgO ( 10%) accelerates the carbonation considerably. However, in the case of Mg(OH)2, the addition of steam to the CO2 is less important as it is provided intrinsically, as a result of the dehydroxylation of Mg(OH)2 at elevated temperatures. Still, humidifying the gas stream can help control dehydroxylation, thereby sustaining carbonation, which typically levels out short of completion. A careful control of the carbonation conditions (temperature, pressure, fluidising velocity, gas composition) and particle properties should allow for close to complete carbonation (>90%) without compromising the carbonation kinetics. Because the PFB carbonation step considered here is part of a larger CCS process (Mg extraction from a natural and abundant mineral followed by production of MgCO3), the precipitation stage [Mg(OH)2 formation] may be tailored to obtain the necessary particle properties (surface area, porosity).

Reduction of CO2 Emissions from steel plants by using steelmaking slags for production of marketable calcium carbonate

By carbon dioxide mineralization, CO2 can be stored safely and leakage-free for very long times. Owing to their high calcium content, steelmaking slags are suitable for mineral carbonation. In a country like Finland, where no suitable geological formations for CO2 storage seem to exist, steelmaking slag carbonation offers an important CO2 emissions reduction option for steel plants. If calcium could be extracted selectively from the slags prior to carbonation, a pure, and possibly marketable, calcium carbonate may be produced. This could replace some of the natural and synthetic CaCO3 used in industry, combining savings in natural resources with CO2 emissions reduction. Development work on the production of pure calcium carbonate from steelmaking slags by carbonation is presented in this study. Selective extraction of calcium from steelmaking slags was investigated using various solvents. Precipitation of CaCO3 from dissolved calcium at atmospheric pressure was also investigated. Amongst the various tested solvents ammonium salt solutions (NH4Cl, CH3COONH4, NH4NO3) were found to be the most promising for selectively extracting calcium from steel converter slag. These solvents dissolved calcium efficiently also from desulphurization slag, while extraction of calcium from two other types of slag was poor. CaCO3 was successfully precipitated from the solution containing ammonium salt and dissolved steel converter slag.

Activation of serpentine for CO2 mineralization by flux extraction of soluble magnesium salts using ammonium sulfate

This paper concerns the growing role of cheap and potentially recyclable ammonium salts in CO2 mineralization. The powerful hyphenated technique TG-FTIR, along with XRD and ICP-AES, were used to shed light on the underlying chemistry and measure the efficiency of magnesium ion extraction from a Finnish serpentinite in contact with molten ammonium sulfate above 300 °C. From micro- and gram-scale tests, flux extraction as epsomite [MgSO4·7H2O] proceeds via the intermediacy of Tutton salts, NH4/Mg double sulfates increasingly rich in Mg. Extraction is effected through the agency of acidic derivatives, principally ammonium bisulfate and sulfamic acid, which are created sequentially from ammonium sulfate in situ. However, sulfamic acid volatilizes and/or decomposes at a significant rate by 400 °C. This loss mechanism is primarily responsible for the modest recovery of Mg (50–60%). An improved process would operate below 400 °C where Mg extraction as efremovite [(NH4)2Mg2(SO4)3] is effective. Future experiments evaluating the use of humid air to stabilize the bisulfate and impede the loss of flux are recommended.

Combustion and Gasification Properties of Plastics Particles

The combustion and gasification behavior of the most common plastics is studied and compared with conventional fuels such as coal, peat, and wood. The aim is to give background data for finding the optimum conditions for co-combustion or co-gasification of a conventional fuel with a certain amount of plastic-derived fuel. Atmospheric or pressurized fluidized bed co-combustion of conventional fuels and plastics are considered to be promising future options. The plastics investigated were poly(ethylene) (PE), poly(propylene) (PP), poly(styrene) (PS), and poly(vinyl chloride) (PVC). Some of the samples had a print or color. The reference fuels were Polish bituminous coal, Finnish peat, and Finnish pine wood. PE, PP, and PS were found to burn like oil. The particles shrank to a droplet and burned completely during the pyrolysis stage, leaving no char. Printing and coloring left a small portion of ash. PVC was the only plastic that produced a carbonaceous residue, and its timescales for heating, devolatilization, and char burning were of the same order as those for peat and wood, and much shorter for the other plastics studied. An important result is that char from PVC contains less than 1% chlorine,99% hydrocarbon. The gasification rate of PVC char (at 1 bar and 25 bar) was of the same order as that of char from coal. Peat-char and wood-char were gasified an order of magnitude faster.

CO2 Mineralization—Bridge Between Storage and Utilization of CO2

CO2 mineralization comprises a chemical reaction between suitable minerals and the greenhouse gas carbon dioxide. The CO2 is effectively sequestered as a carbonate, which is stable on geological timescales. In addition, the variety of materials that can be produced through mineralization could find applications in the marketplace, which makes implementation of the technology more attractive. In this article, we review recent developments and assess the current status of the CO2 mineralization field. In an outlook, we briefly describe a few mineralization routes, which upon further development have the potential to be implemented on a large scale.

Mercury emissions from industrial sources in India and its effects in the environment

This study describes the atmospheric mercury (Hg) emissions from industrial sources in India for the years 2000 to 2004. In India emission inventories of Hg and other trace elements from anthropogenic sources have been largely neglected, although the GDP (Gross Domestic Products growth) has touched 9.6% at the beginning of the 21st century. In coal production India is the third largest in the world, whereas Indian cement and brick production have reached second place in the world. With increased industrial development, acute pollution problems have been identified in the subcontinent. There is no consistent earlier information for Hg emissions to the environment for any sectors of industry. This paper may be the first road map in which we have tried to find out the total emission of Hg from a wide range of sources, e.g. from coal combustion to clinical thermometers broken during production or packing. There is a lack of basic data and in an attempt to correct this, emission factors suitable for Asian countries have been selected to complete this study. Before this document, there were some efforts in Europe to develop emission inventories for Hg from coal combustion or chlor-alkali plants for India. In this study it was found that total atmospheric emission from industrial sources has decreased from 321 Mg in 2000 to 253 Mg in 2004 due to a switch for the membrane cell process in the chlor-alkali industry. In 2004 the largest part of the Hg emissions stemmed from coal combustion in thermal power plants. Hg-cell technology had been used earlier in chlorine and sodium hydroxide production, as a result of which Hg concentration in terrestrial and aquatic species are nowadays quite high in coastal areas. India can thus be referred to as a mercury “hot spot”. We have received limited information on emissions of Hg from industrial sources in India. Estimates are based on emission factors and the values taken from the literature. Against a background of limited data and information, this paper gives an overview of Hg emissions in India and of the recent steps undertaken by authorities to curb the emissions of Hg and its subsequent trans-boundary movement in the global environment.

Mechanisms of serpentine–ammonium sulfate reactions: towards higher efficiencies in flux recovery and Mg extraction for CO2 mineral sequestration

There is a growing research interest in CO2 mineral sequestration methods that follow an intermediate Mg extraction step (from Mg-silicates, especially serpentinite rock) by fluxing with ammonium sulfate (AS) or ammonium bisulfate (ABS). This study reports the use of thermogravimetry (TG) combined with differential scanning calorimetry (DSC), mass spectrometry (MS) and/or Fourier-transform infrared spectrometry (FTIR), to explore the serpentinite/flux [(S)/AS and S/ABS] reaction chemistry in more detail and identify conditions under which flux losses are restricted. TG-DSC-MS results show that AS decomposition proceeds through a series of reactions leading to the formation of ammonium pyrosulfate [(NH4)2S2O7, APS] via an ABS intermediate. That APS is the key intermediate is attested by the fact that the analogous potassium salt is a well-known flux for metal oxides. As expected the mechanisms for S/AS reaction are more complex than those of thermal decomposition of pure AS or ABS compounds. Two likely possibilities were identified with S/AS thermolysis: formation of APS or sulfamic acid (SA) precursors that extract Mg/Fe cations from serpentinite above 400 °C. A sulfur dioxide peak was detected on the ensemble spectra at 280 °C. This indicates a loss of ABS through sublimation rather than a complete degradation of AS or ABS reagents. At a fast heating rate of 40 K min−1, tests on S/AS resulted in a significantly lower weight loss (ΔW) than at 10 K min−1 (46% vs. 54%), implying better retention of flux and higher extraction efficiency. From TG-FTIR tests, the presence of humidity has a suppressive effect on SA volatilization, stabilizing the hydrated intermediate APS and/or ABS. It also inhibits mineral transformation to the less reactive forsterite (Mg2SiO4). Extraction of magnesium is primarily dependent on serpentine particle size, but it can be increased significantly in the presence of humidity.