A REVIEW OF INDUSTRIAL FLUE GAS CLEANING
T. Golesworthy (pages 23-33)
Environmental awareness has grown significantly in the last 10 to 20 years. The general public and green eco-groups have swayed public opinion through the media such that the legislators have put increasingly stringent emission limits on many industrial processes and activities. The US Environmental Protection Agency has led the way with many countries following its lead. The Environmental Protection Act in the UK is an example of new legislation that seeks to protect our environment from all known industrial pollution hazards whilst acknowledging the need for industry to remain economically viable. A necessary part of industrial activity is generating electricity, in part through the combustion of fossil fuels, managing its wastes, using processes such as incineration, and transporting materials, using fossil fuel based transport systems. Emissions to air from these activities involve a wide range of materials that can include particulate matter, oxides of nitrogen and sulphur, hydrogen chloride, volatile organic compounds, polychlorinated bi-phenyls/di-benzo furans (dioxins) and heavy metals.
A range of mature and emergent control technologies exist for the control of these pollutants including inertial separation, filtration, electrostatic separation, wet and dry scrubbing and catalysis/conversion processes. These techniques are reviewed as well as current state of the art composite gas cleaning plant for total solutions to the emission of currently prescribed pollutants
METAL SCAVENGING PURIFICATION TECHNOLOGY FOR THE PHARMACEUTICAL AND FINE CHEMICAL INDUSTRY
K. Treacher (pages 33-38)
The manufacture of pharmaceuticals in modern-day industry is becoming an ever more involved process as the chemical complexity of active ingredients increases, driven by more intelligent and intricate design. Consequently the range of synthetic techniques required is constantly expanding, with an increasing reliance on metal-based catalysis, which can deliver more efficient, selective and cleaner processes.
FILTER MEDIA PORE SIZE COMPARISON BETWEEN POROMETRY AND GLASS BEAD CHALLENGE TESTING G. Rideal and E. Mayer (pages 38-41)
The accuracy of pore size measurement by porometry has been found to be dependent on the instrument and operator. Similarly, challenge testing using ISO test dusts is dependent on both the precision of the particle analysis of the irregular shaped particles and the laboratory protocols. To overcome the ambiguity of shape, a much simpler challenge method has been developed using NIST certified, narrow particle size distribution glass beads. The new high-speed method determines the filter efficiency (cut-point) using a novel dry sonic device for pore sizes above 20 μm and a wet suspension method for pore sizes below 20 μm. This paper will compare porometry values obtained for a number of porometers after cross-validation with the new microsphere challenge test method.
A NEW CONCEPT FOR SIMULTANEOUS REDUCTION OF ALKALINITY, OIL AND UNDESIRABLE GASES SUCH AS CO2 AND H2S
J. Chen and D. Douglas (pages 42-45)
In a steam assisted gravity drain (SAGD) application to extract oil from the reservoir, lime softening is often utilized to reduce the hardness and silica concentration to meet feed water quality requirements for ‘wet steam generators’. Produced water is normally treated for recycle and reuse as feed water to the steam generator. When the produced water contains a high alkalinity concentration, the lime softening reaction will produce excessive volume of ‘wet’ sludge resulting in large capital cost for sludge dewatering, handling and disposal. This paper presents a method to reduce alkalinity concentration in produced water without excessive sludge production and discusses stripping CO2 produced from the chemical reaction. Free oil removal by induced gas flotation (IGF) is well documented, so no discussion of oil removal is presented here since the new concept focuses on the improvement of IGF to achieve the above mentioned objectives.
HOT GAS FILTRATION – A CASE STUDY HIGHLIGHTING SUCCESSFUL DIOXIN CONTROL
R. Williams (pages 45-47)
In February 2007, R Williams Consultants assisted in the commissioning of Chinook Sciences’ proprietary Air Pollution Control (APC) system which exclusively serves the RODECS® system. The RODECS® is an industrial pyrolysis system that utilizes a novel active pyrolysis concept, and is used for the full gasification of organic material from metal and industrial waste, and municipal solid waste (MSW). In this application, the RODECS® system was processing secondary aluminium painted scrap, heavily contaminated with PVC.
THE IMPACT OF ULTRAFINE BYPASS FILTRATION ON EXTENDED DRAIN INTERVALS
R. Russell and T. Gilbert (pages 48-51)
The ability of a Cleantechnics International Inc. high capacity ultrafine fluid bypass filtration system to extend lube oil and hydraulic fluid service levels was studied. Test results show a four- to six- fold increase in filter change intervals and a more than fifteen fold increase in oil change intervals. Results of installations on Class 8 trucks, heavy duty work trucks and off-road heavy equipment are presented. These results include a review of oil analysis reports from an independent oil analysis laboratory of samples taken during normal service intervals on both control and test vehicles over extended time periods. In addition to the review of oil quality, calculations reporting long term cost savings and environmental benefits of the bypass filtration system as the result of extended drain intervals and reductions in oil change related expenses (oil costs, filters, labour, equipment downtime and waste disposal) are cited.
CHANGING WASTEWATER SLUDGE CHARACTERISTICS AFFECTING THE FOULING OF A SINGLE STAGE MECHANICAL DEWATERING AND THERMAL DRYING PROCESS
B. Peeters, L. Vernimmen and W. Meeusen (pages 52-62)
At the Monsanto Europe site in Antwerp, Belgium, wastewater sludge is mechanically dewatered and thermally dried in a single compact machine. Over the years, the biosolids throughput was limited by two main bottlenecks, namely (1) high vibrations of the solid bowl decanter centrifuge, and (2) periods of daily fouling around the centrifuge cake outlet or somewhat further in the flash drier. In that case, sludge feed towards the centrifuge has to be stopped to remove product build-up by flushing.
The vibrations of the centrifuge were reduced by simply reducing the centrifuge bowl speed from historical 3165 rpm to 2880 rpm. But the fouling issue was harder to resolve. Through research over the years, it was shown that the fouling frequency was higher for sludge comprised of higher inorganic fractions. The inorganic fraction varied significantly over time for this particular wastewater treatment plant (WWTP) as a result of varying calcium concentrations in the wastewater. Periods of 15% inorganic fractions are followed by periods with more than 30% inorganics in the sludge flocs. Sludge settleability varied in accordance with these changes in inorganic fractions, with a higher inorganic fraction resulting in a heavier floc and a better settling ability. Spin tube tests executed in the lab, simulating cake compaction in the field, have shown that the inorganic fraction of the sludge flocs has a significant impact on cake dryness, with a higher inorganic fraction yielding a drier cake. Taking into account the fact that activated sludge goes through a sticky phase while being dried (somewhere in the range around 40-50 %DS), this implies that the centrifuge cake dryness determines timing and place in the system where the sludge is going through the sticky phase. The hypothesis is that a ‘too dry’ centrifuge cake goes through the sticky phase at an earlier stage in the next drier system where it seems to be more susceptible to product build up, for example at the point where the cake particles are leaving the centrifuge with high velocity and hit the centrifuge casing for the first time.
In that case, in periods of sludge characterised by a higher inorganic fraction, centrifugation conditions in the field have been adjusted to make the centrifuge cake again less compact and less dry. This resulted in a significantly higher capacity of the system by reducing the fouling issue
PERFORMANCE OF FILTERS WHEN LOADED WITH NaCl AND KCl PARTICLES IN LOW RELATIVE HUMIDITY ENVIRONMENTS
T.-C. Hsiao and D.-R. Chen (pages 62-71)
In this study two low efficiency cellulose filters were loaded with sodium chloride (NaCl) and potassium chloride (KCl) particles of super-micron sizes in low relative humidity (RH) environments (RH < 30%). As NaCl and KCl particles have similar material properties, such as density and crystal structure, it was believed that no difference would be observed in the filter loading curves (pressure drop vs. the loaded particle mass/volume) of particles of the same size in such low RH environments. It is shown that at 30% RH the initial penetration and the loading curves of filters loaded with NaCl and KCl particles are nearly the same. However, as the RH decreased to 15% so the loading curve of NaCl particles deviated from that of KCl. The curve of NaCl particles moved to the right of the KCl curves. In other words, with the same pressure drop, the filter can be loaded with a greater volume of NaCl particles than KCl particles. Furthermore, the influence of filter structure and particle size on the shifting of the loading curve was investigated by performing the same loading test with two different particle sizes. It was found that the observed RH effect on the loading curve was more significant for low efficiency filters loaded with large super-micron particles. SEM examination showed that the morphology of the test particles is different when RH is varied. It was concluded that a possible reason for the dissimilarity of the NaCl particle loading curve at 15% RH is the difference in the particle morphology.
CFD BASED DEVELOPMENT OF INERTIAL SEPARATORS IN OIL MIST REMOVAL FROM CRANKCASE EMISSIONS
S. Schütz, K. Kissling, G. Gorbach, A. Zink and M. Piesche (pages 71-80)
For passenger cars and heavy duty vehicles, the current tightening in exhaust gas legislation is the driving force for new developments of oil mist separators to clean blowby gases in crankcase ventilation systems. One important aspect is the limited installation space for the oil droplet separation systems, hence the development of small-scale separators is a challenging task. As there are only a few design rules for small-scale separators, computational fluid dynamics (CFD) was used for the development of two types of centrifugal separators, small cyclone separators and disc stack centrifuges.
With CFD calculations based on high quality numerical meshes, the separation efficiency, grade efficiency and pressure drop can be predicted for non-standardized, small-scale cyclone separators. Though the pressure drop should not exceed about 40 mbar with a blowby volume flow of 80 l min-1, oil droplets in the sub-micron scale can be separated partially. Concerning the disc stack centrifuge, the CFD results show that there is a non-homogeneous volume flow distribution across the different separator gaps. Depending on the operational conditions the volume flow distribution is oscillating due to flow instabilities in the outer annular gap of the disc stack centrifuge. So there exist different grade efficiency characteristics dependent on the gap position but the separation behaviour of the whole apparatus can be described by a mean grade efficiency curve. As a further result of the CFD simulations the separation characteristics of disc stack centrifuges can be described with a universal grade efficiency curve for a wide range of geometrical and operational data.
Experimental investigations on the droplet size distributions in the raw and the clean gas volume flow show a good accordance with the simulation results. Two droplet size measuring systems, a cascade impactor and a three wavelength laser spectrometer, were used to determine droplet size distributions in an experimental setup