Koch, H. However, challenges do still exist concerning refractory corrosion and furnace life. It has been recognized that the high concentration of sodium species in an oxy-fuel fired furnace can lead to accelerated corrosion of the furnace crown. In this paper, the details of an operational campaign for an oxy-fuel fired container glass furnace are presented and discussed.
The furnace crown was constructed with a low lime silica brick 0. The furnace also employed ultra low-momentum. Wide Flame burners to help minimize volatilization from the melt surface. The experience from this furnace campaign indicates that the crown material and burners both met performance expectations and should be considered as part of a robust operating solution for container glass manufacturers. Although the concept of an all refractory, reverberatory furnace with continual operation has not changed, great strides have been made in the materials of construction, maintenance and operation of these systems.
One operational change which has greatly changed the operation and environmental footprint of glass production is the use of industrially pure oxygen in place of air. The conversion of typical air-fired glass furnaces to oxy-fuel firing has led to reductions in specific energy requirements, reduced emissions of air pollutants, increased specific pull rates, simplified furnace construction, and improved operational consistency and glass quality.
However, oxy-fuel technology has also forced glass makers to consider alternative materials of construction, creative construction, operational changes and robust maintenance programs to address the challenges of using industrially pure oxygen. The primary goal in optimizing the design, operation and maintenance of an oxy-fuel fired glass furnace has been extending the life of superstructure refractories, particularly the furnace crown.
Traditional air-fired furnaces utilize silica brick for crown construction due to its relatively low density, thermal conductivity, corrosion characteristics, and moderate cost. However, silica crown bricks applied to oxy-fuel furnaces sometimes experience accelerated corrosion, , varying greatly with system design e. The mechanism of this accelerated corrosion is based on the formation of an alkali containing silicate or calcium silicate slag which is highly dependent on the concentration of Na species in the furnace atmosphere [ 1 -5].
The corrosion process is highly dependent on the temperature, NaOH concentration in the vapor phase, water content, gas velocity and calcium content in the brick. However, these refractory materials are substantially heavier than traditional silica brick more steel infrastructure required and are approximately an order of magnitude greater in cost to install. One tactic to address the less than optimal performance of silica while maintaining the cost advantages over other alternatives, has been to slightly adjust the composition of silica brick to minimize the CaO concentration.
The presence of a CaO as a binder in the brick leads to the formation of a calcium silicate slag in which the calcium exacerbates the absorption of alkali species into the slag. The alkali results in further reduction in the melting point of the slag and a reduction in viscosity causing the slag to run. By reducing the CaO in the brick, this effect may be minimized, resulting in a larger, effective operating range e. Silica crown corrosion can be further controlled by using good construction practices to minimize joints and by the use of high quality materials to avoid joint expansion during the furnace campaign.
Also, a good insulation package on the crown is critical to maintain sufficient temperature and avoid Na species penetration. The combustion system and furnace design are also critical to reduce Na species volatilization from the glass melt. Volatilization of Na species from the melt is a function of temperature, gas velocity and gas composition near the surface. Thus, burners should be designed and positioned to result in low momentum flames while maintaining the proper temperature distribution throughout the furnace crown .
This paper reviews the performance of alternative materials, combustion technology and operational practices over the campaign lifetime of a modem, oxy-fuel fired container glass furnace. Gonzales et al. While these goals are mostly common sense and good operating practice, it is worthwhile to reevaluate these items during any major change to a furnace system.
This furnace was built to replace a smaller oxy-fuel glass melter. The furnace specifications are shown in Table 2. One of the major goals of this furnace design was to implement a potential improvement on typical silica crowns by utilizing a low lime silica brick which was specifically manufactured as a single production run for this furnace.
The reduced CaO content approximately 0. Table 3 shows a comparison of the basic properties of a conventional silica brick against the new, low-lime silica material used in Furnace Specific Energy : 3. The combustion system was also designed to minimize refractory corrosion. The furnace utilized six 6 Praxair Wide Flame burners in an opposed arrangement.
The burners were specifically designed to minimize gas momentum near the melt surface while maintaining good heat transfer characteristics and low NO x emissions. With this combination of materials and combustion system, Grupo Pavisa hoped to maintain proper furnace life while optimizing operating costs. The early results first 45 months of operation of this furnace have been previously described and the construction details outlined .
For business reasons, Grupo Pavisa made the decision to end the furnace campaign and complete a cold repair in April , after 9 years and 4 months of operation. A summary of this furnace campaign is presented below. Figure 1 illustrates the pull rate and cullet ratio of the furnace over a month period leading up to the shutdown and subsequent cold repair. The cullet ratio of the furnace also varied significantly over the furnace life, mainly due to the availability of external cullet. Furnace 14 Pull Rate and Cullet Ratio versus Month of Operation Furnace operating conditions were adjusted during the campaign to satisfy requirements from the production lines and to respond to process variables changes.
This included a general increase in electric boost during times of lower cullet input. Figure 2 illustrates the energy input via fuel and electric boost over the life of the furnace. The electric boost was used somewhat sporadically through the furnace campaign to handle changing operational needs.
Late in the campaign, a loss of cooling water to the electrodes resulted in a major malfunction and the permanent loss of the electric boost system. Hot work also had to be performed in the electrode area of the tank to avoid glass leaks and guarantee continued operability. Furnace 14 Fuel Energy Input and Electric Boost versus Month of Operation Analysis of the energy efficiency of the furnace over time requires normalization to compensate for changes in pull rate, cullet ratio and electric boosting. It was also necessary to correct for an increment observed in the glass temperatures at higher loads.
Based on the operating experience from the full furnace campaign, the performance of the new refractory material met or exceeded these expectations. Bricks showed minimum deterioration after more than 9 years of operation with oxy-fuel firing. Zone A was in the vicinity of the batch charge area, Zone B was near the hot spot and Zone C was near the glass discharge point. The dotted line near the top of the figure represents the original brick height of 15 inches. Examining the measured height of the remaining brick reveals corrosion of bewtween This level of material loss or less was consistently observed throughout the crown.
The temperature of the furnace crown was monitored throughout the campaign, and the profile along the length of the furnace varied with pull rate. Figure 5 illustrates the average crown temperature profile along the length of the furnace at varying pull rates. As might be expected, higher pull rates resulted in higher crown temperatures. The only problem reported with the crown was in the expansion joint zones.
Furnace 14 had two expansion joint zones, one close to the charging end and the other close to the refining area. Immediately after the furnace startup, sealing problems were detected at the expansion joints. However, at that time, the magnitude of the furnace gas leakage was not considered important and the issue was not immediately corrected. After a period of operation, alkali vapors started to penetrate the joint, absorb into a slag layer attacking the crown and causing damage to the nearby bricks. Hot repairs had to be made in these areas to avoid losing parts of the superstructure.
No additional hot work was required after making this repair. Figure 6 and Figure 7 show images of the crown after cooling the furnace at the end of the campaign. The images illustrate consistent wear throughout the crown, and no significant points of deterioration. The operations team at Grupo Pavisa felt that the furnace could have operated for at least 2 additional years under these conditions. With the current global economic downturn, this was an ideal time to take a furnace outage.
Also, the tank refractory contained higher levels of chrome than desired for color requirements of certain product lines. Finally, the loss of electric boost resulted in an increase in furnace temperature due to increased gas firing, and the team felt it was important to restore electric boost capacity to properly balance furnace energy input. Figure 6. These burners were designed to be a simple and flexible piece of combustion equipment and Grupo Pavisa selected this burner due to its unique attributes.
In addition, the large, low velocity, luminous flame allows the burner to transfer heat more efficiently and prevent hot spots on the glass surface. Sufficiently high burner elevation together with low flame velocities and low momentum minimize alkali volatilization from the glass melt resulting in less furnace superstructure corrosion, longer furnace life, and reduced particulate formation. Figure 8 shows a schematic of the first generation burner.
In order to minimize NOx formation, oxygen is staged through a separate set of nozzles under the fuel nozzles. The burners were fired between 2. The new generation burner incorporates an evolution in Dilute Oxygen Combustion technology, including deeply staged oxygen injection and minimized gas velocities near the burner face.
The result is a robust and durable burner with all the positive characteristics of the previous generation as well as the benefits of advanced flame dynamics. Figure 9 illustrates a schematic view of the second generation burner. Total evaluation time was approximately 9 months 37 weeks. Figure 10 illustrates the installed view outside the furnace left and the burner in operation from the interior view of the furnace through a viewport right.
Figure The flame shape and heat transfer characteristics were consistent with the first generation design, making substitution a seamless process. Both burners were carefully inspected after the shut down. The results of the inspection revealed that the burners were in excellent condition with no sign of deterioration in the burner blocks or other parts. These results indicate that the burners should be able to operate without maintenance for a much longer period of time.
Grupo Pavisa was very pleased with the performance of the new burner design and plans to replace the existing burners with the new design in the near future. Another test of the next generation burner is currently underway on a container glass furnace at another site, with similar observations and results to date. The operating campaign of Furnace 14 at Grupo Pavisa demonstrates the potential for a new type of silica brick to limit crown corrosion. This low-lime silica brick contained relatively low levels of CaO The furnace also untilized low-momentum Wide Flame burners to reduce volatilization off the melt, while maintaining good heat transfer and emissions characteristics.
Allendorf and K. Brown, K. Wu, and H. Beerkens and O. Kobayashi, K. Wu, and W. Kobayashi and A. Drummond III. Velez, M. Karakus, X. Liang, W. Headrick, R. Moore, J. Hemrick, and J. Varner, T. Seward III, H. Spear and M. Brown, R. Spaulding, D. Whittemore, and H. Conference XV, Parma, Italy, , , Gonzalez R. Weilacher, M. Wu and H. Kobayashi and W. Snyder, K. Wu, and R. J, Snyder. Some of these include the type of charging system, the reliability and sensitivity of the level detector, the type of control logic loop and the stability of the process itself. This paper will only consider the various types glass level sensors and the pros and cons associated with each.
A summary table is provided at the end. When it comes to sensing changes in glass level, there are many different methods available from which to choose. They can be broken down into two basic categories, i. The contact types are oscillating probes, static conductivity probes and bubble pressure tubes. The non- contact types include nuclear, pneumatic, laser and optical. They vary in cost of installation and operation, frequency and cost of maintenance and system requirements. Since the various processes and glass compositions used in the industry have different requirements, this paper will look at the advantages and drawbacks of several techniques with the aim of helping you with the selection process.
This information was derived where ever possible from interviewing engineers who have hands-on experience with these pieces of equipment installed in their plants. The one pictured here is installed directly into the forehearth through the breastwall. Some plants will have a separate alcove off to the side of the refiner or forehearth but the principle is the same. The oscillator moves a platinum-tipped probe down until contact with the glass is made. This completes an electric circuit telling the batch charger to speed up or slow down depending on the glass level and tells the oscillator to raise the probe to start another cycle.
This process is very straightforward but not without its problems. The unit shown here has a ceramic tube having a platinum tip. The batch charger interpreted this as a high level reading and stopped charging. The level dropped a couple of inches before the effects were seen in the process downstream. Fortunately, this was corrected before the electrodes became exposed. The same unit in the sister plant has a water-cooled probe which has never drooped. To prevent this, the temperature in this zone should be monitored closely and the probe should be visually inspected periodically to make sure that no build up is occurring.
Fortunately, the maintenance required is not costly and it can be handled by plant personnel. As the glass level rises, the air pressure required to cause bubbles to form increases. Similarly when less of the end of the tube is covered, that is when the glass level falls, the air pressure is lower. One thing to be aware of with this system is that the response can change with glass temperature viscosity. A correctly damped system for normal melt rates can become a little erratic at low melt rates i.
The only maintenance required is maintaining a constant supply of air. If you lose the air to the probe, the end will fill with glass and it will have to be removed and cleaned out. Care must be taken to mark the exact position of the probe prior to pulling it out so that the immersion depth will be exactly the same when it goes back into the glass. These regulations are not burdensome however and should not deter you from considering one of these units.
To me, the unit with the fewest adjustments or moving parts is the most desirable. The conductivity probe illustrated here is as simple as it gets. A refractory holder rests on the forehearth sidewall and two platinum probes stick down into the glass. As the level rises or falls, the probes detect changes in the apparent conductivity of the glass due to greater or lesser surface contact. This probe is a little less sensitive to changes in temperature than the bubble probe is but the more stable the temperature, the better the readings.
There is no maintenance or cooling required other than periodic replacement due to the deterioration of the refractory in the forehearth atmosphere. In a standard Soda-Lime glass the probe will last for years but in a more aggressive environment, like a Fluoride Opal, a year is the most one can reasonably expect. The principle, on which these operate, is simply measuring the amount of radiation hitting the detector.
As the glass level goes up, more radiation is absorbed by the glass and as the level goes down more radiation reaches the sensor. The most important is being careful to maintain the cooling water to the detector as it houses all of the electronics. The second is to be aware that as the refractory in the forehearth erodes the reading will drift slightly. It may not be enough to bother your process depending what you are making but we typically have the units recalibrated every 5 years. Unfortunately, a service technician is needed for this job and chances are his travel expenses will be a large part of the service call.
Non - Contact Level Sensors: Pneumatic Probes water-cooled probes shown here are technically non-contact probes but the tips are over the glass so they are exposed to the heat and the atmosphere inside. Because of this exposure, one year is considered a reasonable life expectancy for the probe itself. Air is blown out of the tip and changes in pressure are sensed as the glass level rises or falls.
Although the unit has a bigger footprint than any of the other models, the ease of operation and low investment make this a practical choice for several segments of the glass industry, such as tableware. Non - Contact Level Sensors: Laser Level Detectors The development of lasers has revolutionized our approaches to everything from warfare to eye surgery. For our purposes, it is a simple matter, or at least it should be simple, to bounce a beam of light off the relatively smooth surface of glass flowing in a forehearth and then measure the amount of deflection.
This deflection can then be correlated to a rise or fall in glass level. A number of years ago, we trialed one of these units near the end of a furnace campaign ran into difficulties that were not the fault of the method but of the retro fit. The first problem was due to our having bubblers in our forehearth.
The waves caused by the bubbling action and the bubbles themselves caused scattering of the beam which gave a very erratic signal. I suspect that had we trialed this on one of our electric forehearths, our experience would have been very different. Non - Contact Level Sensors: Optical Level Detectors The latest method we have tried relies strictly on optics and the ability of a computer to sense changes in the pixels of an image being received by a camera mounted on the forehearth.
The camera is focused on an object in the forehearth, in our case a platinum thermocouple sticking through the crown into the glass, and the increase or decrease in the number of pixels between the glass and reference point are measured. The problem was that thermocouple and the distance to the camera were such that we were unable to focus the image properly even after trying a lens with a longer focal length.
We are going to continue to experiment with this method however as it appears to have potential. Regardless of how reliable or accurate any of these sensors may be there are still going to be upsets in the glass level from time to time. Obviously, if you are making wide-mouth jars, you will need tighter level control than someone making insulation fiberglass but many of the above methods should do just fine if it fits with your type of glass and forehearth design.
How you handle these upsets can be a bigger issue than the upset itself. Even though it is caught right away, it still takes 10 minutes to change it out and begin charging again. If you leave your controllers in automatic mode to recover the level this may cause more problems than the leak and level loss have already. Have they been properly trained in how to respond? Mistakes cost more than equipment. For more information on these devices contact: Oscillating probes - wvwv. Hoyle and Douglas H. Davis Toledo Engineering Co. The method of achieving these goals will first require an inventory of emissions, followed by the introduction of a cap and trade system, establishing a market for greenhouse gas emissions.
So what does this mean for the glass industry? The glass industry cannot continue to do what it has always done. To assess the challenge that lies ahead we must first establish where we are now.
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For the purpose here, this can also be considered as the national level. How does the U. In , the last year for which all the data is available, the U. In terms of the U. Although we represent only a small fraction of the total emissions, we are a concentrated and easily targeted source. If glass is to remain in common use, we will have to consider large changes in how it is produced. We will establish a base case, look at the requirements to meet HR , as well as some options to reduce carbon dioxide emissions and the cost implications of the cap and trade system.
These comparisons will be made at a micro, or plant level, and at the wider macro, or national level. In Table 1 the size, energy and utilities usage for the three furnace types are given. For completeness we include the electricity for the end port combustion air fans and the oxy-gas oxygen separation plant. We will calculate the carbon dioxide evolved from the construction, the glass and the fuel. All the comparisons will be shown as the emission per ton of glass produced. It is about 1. Figure 1 shows the carbon dioxide emissions for the three furnaces.
As the electricity is generated off site there is no carbon dioxide emissions associated with it.
The clear winner is the electric furnace. So what are the implications of HR for the glass manufacturer? Greenhouse gas emissions are expressed in metric tonnes of carbon dioxide equivalents. We can not confirm as to the value of greenhouse gas emissions under the cap and trade system that will be implemented in the U.
The purpose of the cap is to progressively reduce emissions over time, so whilst emissions can be traded, allowing plants which do not meet the targets to purchase additional emissions credits, the total amount of emissions is progressively reduced. The reductions will be implemented between now and , although the act does not specify if the reductions will be implemented at a cold repair or not.
Figure 2-shows the reductions required by HR It can also be safely assumed that as the reductions in the cap get larger the price of greenhouse gas emissions will rise, thus, making it more attractive to invest in a plant and equipment with a lower carbon dioxide emission or move to a location where they are not limited. There are a number of areas that can be attacked. In order of increasing capital cost, they are the batch and raw materials, furnace efficiency and melter type and design.
Taking the batch and raw materials, the simplest means of reducing carbon dioxide emissions is to increase the use of cullet. Most plants already recycle all the in house cullet generated by their own manufacturing processes, so increasing cullet use will necessitate the use of external cullet from downstream processes or post consumer recycling. Increasing cullet use also reduces energy consumption as we do not need to supply energy for the endothermic batch reactions.
Figure 3 shows the reduction in carbon dioxide emissions by increased cullet use. However, as is often the case, this is easier said than done. Using cullet at these levels will mean the quality of the cullet will have to closely match the glass composition of the product. Present methods of post consumer recycling will not deliver either the quantity or quality of cullet required. Some major investment will be required to improve current cullet recycling systems to the necessary level.
The other means of reducing carbon dioxide emissions from batch is to reduce or eliminate the use of carbonates. The use of burnt lime or dolomite is already proven, especially in textile fiberglass production, but both these materials are more costly and have handling problems that will require batch plant modifications. Soda ash can be replaced with sodium hydroxide, but again, this is more expensive and will also require batch plant modifications and increased maintenance due to its corrosive nature. The use of pelletized batch could eliminate some of these handling problems, but this may require major modifications to the batch plant.
However, applying both increased cullet use and eliminating carbonates from the batch will allow us to just about meet the emissions target. Improvements or changes in operation and furnace efficiency will also reduce greenhouse gas emissions. Improved furnace efficiency by increasing insulation, improvements in regeneration, improved port and burner design and better control and monitoring will all help but they will not significantly improve a modem, well designed and operating furnace.
One technically proven method of significantly improving energy efficiency for regenerative and oxy- gas furnaces is batch and cullet preheating. This is especially true for oxy-gas furnaces where a significant quantity of high grade energy is currently most often thrown away.
Up to now the return on investment of this technology has not been good, hence the very small number, less than ten, of installations worldwide. Including the price of carbon dioxide emissions may tip the balance in its favor. Figure 4 shows the effect batch and cullet preheating has on furnace efficiency. Another technically proven method of improving energy efficiency is to take advantage of the waste heat using a waste heat boiler that in turn drives a steam turbine.
It is also possible to use this energy more directly in any application where the heat can be used directly, such as preheating for other processes. It can also be used to provide cooling when used in conjunction with an absorption chiller. It should be noted that these forms of waste heat recovery have not generally proven to be economically feasible.
Payback for these types of projects currently can range from 6 to 20 years or more, depending on a large number of variables; however, they will become more attractive as energy and carbon credits become more valuable. Combining the use of increased cullet. So far the only proven method of meeting the target would be to convert to all electric melting, in addition to modified batch and high levels of cullet. Whilst this is feasible for some types of glasses, it certainly does not apply to all; the production of high quality float glass, for example, has up to now proved impossible with electric melting.
The aim of the bill is to reduce carbon dioxide emissions nationally, but looking nationally we have to include the production of electricity and pre-processing of raw materials. Merely shifting the emissions from one place to another does not help the nation advance towards the goal of carbon dioxide reductions. Figure 5 shows the generating mix for the U. Current DOE projections to , both for the U. Taking the electricity generation mix into account produces a very different picture and conclusion.
The average carbon dioxide emission based on the generating mix is 1. If we recalculate the carbon dioxide emissions, including the average emission for electricity generation, a very different picture emerges see Figures 9 through Glass manufacturers will have to be concerned about how their electricity is generated as this will have a big impact on their carbon emissions and hence operating costs. Electricity from renewable, nuclear and fossil fuel with carbon capture and sequestration CCS will dramatically lower carbon dioxide emissions.
The effect of HR will be to increase the price of electricity generated from fossil fuels, bringing closer the time when electricity generated from renewable or nuclear sources is equal or cheaper in price. This is a significant milestone of the renewable industry, i. However, to have a significant impact on national emissions, a massive investment in both renewable and fossil fuel with CCS technology will be necessary. Installed total generating capacity in the U.
There is a lot of discussion and research in progress on carbon capture and sequestration, seen by many in the coal industry as the white knight coming to the rescue of fossil fuel electricity generation. In principal, the carbon dioxide produced from burning fossil fuels is somehow separated from the waste gas stream and then pumped into an underground storage facility so that it cannot be released into the atmosphere.
However, we do not know if these technologies can become practicable nor can we know the long term viability or implications of storing vast quantities of carbon dioxide underground. To make CCS viable it has been estimated that the European carbon dioxide emissions trading price would have to increase by three to five times the current level. In any case, the effect of any legislated reduction in carbon emissions should aim to benefit the whole planet not merely move emissions from one place to another.
At the macro level an efficient air fuel regenerative furnace has the lowest carbon emission. In order to prepare for a carbon emission limit this is the technology of choice, particularly given the average furnace campaign is 10 to 12 years for containers, 15 to 20 years for float glass and spans more than one step change in carbon emissions, and that the currently predicted electricity generation mix will not significantly change. If the carbon cap and trade system does bring about a change in the generating mix away from fossil fuels, then the glass industry should focus now on developing electric melting technologies to produce better quality glass in larger quantities.
Under either scenario increased use of cullet will be necessary to reduce carbon dioxide emissions. Present post-consumer recycling systems are incapable of supplying the quantity and quality of cullet required. We need to address this problem urgently due to the time required to set up the infrastructure. If the use of burnt raw materials, sodium hydroxide and preheating is adopted more widely, batch pelletization will become more desirable to offset some of the problems associated with using these materials. Turner in , which is still valid in our days of global challenges.
Competition develops the powers of hard thinking, ingenuity and resourcefulness, and can thus be salutary. But there are many ways in life in which we can carry on competition and yet be helpful to one another.
There can, I feel sure, be many occasions, even in business, when mutual giving and mutual taking help both parties to the exchange. The International Commission is a body in which its distinguished members can talk with one another and be mutually helpful Wondraczek, Unlversltat Erlangen-Niimberg. University of Sao Canos. Brazil Nanomechanics TC09 M. Sheffield University. University de Paris. Hehlen, University Montpellier 2. Beerkens, TNO. Dunkl, Dunkl Consulting. Schott AG. Ptlkington European Technical Centre.
Rupertus, Schott AG. Impenal College. Marra, Savannah River Nat Lab.. Tanabe, Kyoto University. British Glass Manufacturers Confederation. Corning Museum. Reports on TC meetings. Furnace Design Dieiectrtc Megneiical tone. Different conditions were researched, such as natural gas, mixed and pure fuel oil fired furnaces and waste gas filters working at high and low temperature. The results are: Fine dust and coarser dust levels in the flue gas are reduced by the same degree by the filter system, the particle size distribution in raw and clean gas are measured to be very similar in nearly every case.
Only the total level is much lower in the clean gas. Electrostatic precipitators are therefore adequate to reduce homogeneously the fine dust for all relevant sizes observed. The chemical composition of the clean gas dust resembles the raw gas dust composition before injecting the absorption agent , but it is significantly different from that of the collected ESP dust.
Consequently, a big part of the dust slipping through the ESP system is un-absorbed raw gas dust, only a smaller fraction is coming from the fines of the scrubbing reagent. This indicates that an electrostatic precipitator is capable of reducing dust emissions for all particle sizes 75 Particle Size Measurements in the Flue Gas of Glass Melting Furnaces observed to comply with the emission limits and while doing so, does not preferentially remove any particular size of particles.
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Also the emission levels of particulate matter of stationary sources is controlled by national regulations in all EU member states. The limit values always refer to.. Gaogla Aerodynamically smaller particles are flushed away with the gas flow. From stage to stage, the impacted particles are smaller and smaller.
The last stage of the impactor is a quartz fiber filter with high filtration efficiency, absorbing also the very finest particles quantitatively. The upper and lower particle size limits of the given impactor are controlled by the choice of the right entrance nozzle and the drawing velocity of the gas pump. Also the waste gas temperature, humidity and density have to be taken into account.
The time needed for one measurement may vary largely, from 15 minutes in a raw i. The following table 1 shows an example for the raw results such a measurement in clean gas. Table 1: Example for a raw measuring result, size intervals and collected masses Stage Size interval d l. It calculates a 40 point size distribution curve, taking into account the kind of impactor apparently the program is used for other impactor types as well , the masses impacted on the different stages, the pump rate, the entrance nozzle diameter, the gas density and the gas temperature.
But the results are also qualitatively plausible, i. Particle size distribution is given on the basis of differential mass. In every point, the measurement was carried out three times, but we never found significant differences comparing successive measurements. It becomes clear that indeed mainly fine dust is emitted lists besides diagrams also in the clean gas.
In the example, the removal rate of the ESP is very high: The following figure 4 compares both curves in the same scales, the clean gas result is marked in red, because otherwise it would be invisible. Numbers from 1 to 8 signify different production lines with different operating conditions, as mentioned above; in every line, a series of measurements were taken, and the average values obtained are represented in the diagrams of figure 5.
The publication will be filed in Autumn this year The chemical analysis done by microanalysis, see example of figure 6 of the particles absorbed on the different stages of the impactor instrument is - within the precision of the EDX used - the same, but with different scrubbing reagents we find different compositions. Additionally, the chemical analyses of clean gas dust sampled following VDI , and the collected ESP dust appear to be significantly different. Obviously, the clean gas dust mainly consists of unabated primary raw gas dust the primary dust already contains ca. Fine dust and coarser dust in the flue gas are reduced by the same degree comparing the flue gas upstream of the scrubber with the flue gas downstream the ESP, the particle size distribution shapes in raw and clean gas are very similar in nearly every case.
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The chemical composition of the clean gas dust resembles the raw gas dust, but it is significantly different from that of the collected ESP dust in our cases float gas furnaces, using both bi-carbonate and hydrated lime dry-scrubbing. This mechanism is very important for the abatement of fine and finest particles. The biggest part of the dust passing through the ESP is un-absorbed raw gas dust, only a little fraction is coming from the fines of the scrubbing reagent.
The pollutants in glass furnace off gases are dust particles, oxides of sulphur and oxides of nitrogen. Well established techniques exist for treating these pollutants, either individually or in combination notably electro-static precipitators, fabric filters and Selective Catalytic Reduction SCR. Each technique has its limitations to effectively and economically clean up the mixture of pollutants present in the gas stream.
An emerging technology for glass furnace off gas clean up is the employment of low density ceramic filter elements. Ceramic filter elements are extremely efficient and work well in combination with a dry scrubbing agent for acid gas removal. Furthermore the filtration temperature can be maintained at a suitable level for catalytic treatment of NOx. The Clear Edge catalytic ceramic filter element, registered trade name Cerafil TopKat, offers deNOx functionality as well as efficient particulate and acid gas removal. Thus the major pollutants emitted by a glass filmace can be treated in a single piece of equipment.
The technology, apart from major environmental performance benefits, offers the possibility of substantial savings both in monetary terms and space utilisation. The issue of available space is of paramount importance for many existing glass manufacturing sites. The use of ceramic filter technology also offers the potential for phased implementation of pollution abatement equipment and the ability to meet abatement requirements without unnecessary or premature expense.
The product was initially developed in the mid 's in response to the need to clean hot dirty gas from coal gasifiers down to levels of particulate matter sufficiently low provide a clean fuel gas to a turbine. The earliest commercial applications for the product were rather specialised but application soon broadened out to a wide variety of duties where the benefits of the product could be exploited.
The benefits of ceramic filters are focussed on the need to filter gas, either process or off gas, at a high or variable temperature while delivering high particulate removal efficiency. Key applications therefore include waste incineration and gasification, metals processing, mineral processing and glass melting. The majority of duties are air pollution control APC however there is also now an increasing uptake of ceramic filters for process filtration and product recovery duties. These trends have precipitated an ongoing development program aimed at providing a range of ceramic elements tailored to meet the demands of industrial end users.
Cerafil TopKat patent granted represents a revolutionary development in the technology. The larger sizes can be employed like fabric bags in new equipment and can also be retrofitted into existing plant. Ceramic elements are manufactured from ceramic or mineral fibres, which are bonded together with a combination of organic and inorganic binders. Elements are formed into a shape which incorporates an integral mounting flange resulting in a rigid, self supporting structure. Ceramic elements take the benefits of fabric bag filtration a stage further by offering excellent filtration efficiency coupled with the ability to operate at elevated temperatures.
This latter benefit is utilised across a broad spectrum of industrial applications where there is a requirement to filter gases which are at a high or variable temperature or where temperature surges can occur. An otherwise stable operation can suffer from temperature surges, which can be very damaging to conventional fabric media. When such events occur it is not just the cost of the media which has to be taken into account; the costs associated with an unscheduled filter plant shutdown can also be high.
These benefits can be directly applied to the glass furnace operator to realise a more forgiving reliable and robust pollution control system as well as a more efficient and better performing system. Ceramic elements are employed on duties where the benefits, described earlier, of the medium can be effectively utilised. This is typically duties where high capture efficiency is required in combination with temperature resistance. However it is worthwhile stressing that ceramic elements are not simply a "hot gas filter".
Although ceramic elements can be and are applied in high temperature filtration duties they are equally applicable where the filtration temperature regime is variable or subject to surges which could damage conventional fabric media. The filter element incorporates an integrated catalyst formulated to oxidise dioxins and reduce NOx, the latter in combination with ammonia or urea injection.
The catalyst material is a proprietary mixture of oxides which is incorporated into the body of a filter element in such a way as to ensure even distribution. Catalyst efficiency is further enhanced by virtue of the fine nano sized particles of the material employed. This application of nano technology ensures that the diffusion restrictions associated with conventional catalyst technology are eliminated thus ensuring optimal removal efficiencies. High filtration efficiency is a key benefit associated with ceramic filter elements.
This results from the development, during the early stages of operation, of a protective dust layer on the element surface which promotes cake filtration. Cake filtration is essential to long term performance of a barrier filter medium. Even after cleaning with a pulse of air there is a residual dust cake on the surface of the element ensuring continuity of filtration efficiency and acid gas treatment. The catalyst particles can be clearly seen as needle like particles bonded into the fibre matrix 4. As these species increasingly become the focus of environmental legislation technically and economically effective means of controlling them need to be developed.
70th Conference on Glass Problems: Ceramic Engineering and Science Proceedings, Volume 31, Issue 1
Selective catalytic reduction SCR can be employed for glass furnace off gas NOx reduction, particularly where primary controls are unable to meet local legislative requirements. The technology is effective but there are drawbacks. SCR catalysts can be poisoned by particulate matter carried over from upstream abatement plant. The use of catalytic filter elements is a potential solution providing the necessary removal efficiency through a filter plant with the minimum of ancillary components.
The dust poisons are prevented from contacting the catalyst particles and the dust collected accumulates on the surface of the filter. This leaves a cleaned gas to pass through the filter element ensuring close and intimate contact with the catalyst. The catalytic reaction is enhanced compared with standard SCR technology, as the contact time is not reduced by diffusion of gases in and out of the catalyst pores. This diffusion slows the reaction and can lead to slippage of untreated gases with SCR systems. Dry acid scrubbing requires a sorbent such as sodium bicarbonate and the destruction of NOx requires the addition of ammonia or urea and the catalyst acts to break down NOx at relatively low temperatures to form nitrogen and water.
Where particulates are the only pollutant to be controlled then electrostatic precipitators or bag filters have been widely applied in Europe. The filtration mechanism exhibited by ceramic filters is essentially a surface filtration phenomenon. This results from the development, during the early stages of operation, of a dust layer on the element surface which promotes cake filtration. The dust layer is a mixture of dust from the furnace and sorbent added to react with and control acid gas emissions. This ensures a high removal efficiency of acid gases as well as extremely low particulate emissions.
Dry scrubbing of acid gases is widely applied across many industry sectors and is an effective way to remove gaseous acids converting them into a solid by-product that can then be easily collected by the filtration system. Clearly barrier filtration systems such as bags and ceramic filters have an advantage here over electrostatic precipitators as efficiency of removal is very high and consumption of sorbent is kept to a minimum.
Sodium bicarbonate or lime are the common sorbents used. Often an extra stage of equipment is needed and a scrubbing tower is inserted into the equipment line ahead of the precipitator to ensure intimate mixing of acids and sorbent and this is not necessary with barrier filters. Dry scrubbing has an advantage over wet scrubbing technology as the by-product is collected dry and requires no further treatment before disposal.
Bag filters are efficient enough 90 - 70th Conference on Glass Problems Ceramic Filter Elements for Emission Control on Glass Furnaces to remove this threat of catalyst poisoning but at the low temperatures enforced on the filtration system by the limitations of the fabric itself then a re-heat of the flue gases is needed to increase the temperature to that where the SCR catalyst can work efficiently. It can be seen that the ceramic filter option is an elegant solution to these technical issues.
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The filter and the catalyst can comfortably and efficiently operate at the same temperature and of course the dry scrubbing operation can also be accommodated therefore removing the need to cool gas and reheat. An added advantage is that the catalyst is buried within the filter element and allied with the highly effective surface filter the catalyst is protected from poisoning which will enhance both the effectiveness and the lifetime of the catalyst. Ceramic filters offer the potential for phased implementation of pollution abatement equipment.
In the first instance a filter based around standard filter elements can be installed. This phase provides particulate abatement, acid gas removal with a sorbent and sufficient temperature for future NOx control. At the point when NOx control is required the end user has the choice to opt for selective catalytic reduction SCR technology or retrofit the ceramic filter with Cerafil TopKat catalytic filter elements. The most appropriate choice can be made on the basis of economic and technical considerations. The attractions of phased introduction are the ability to meet abatement requirements without unnecessary or premature expense.
The trials ran for several months and data was collected under different operating conditions to establish to optimum operation of the plant. The filtration temperature was controlled by the addition of quench air. Volume flow through the plant was adjusted by means of a frequency inverter on the fan which in mm was controlled by the orifice plate flow measurement. The SOx removal efficiency was also measured. The pilot trial used a slipstream of gases from a producing furnace and demonstrated very clearly the effectiveness and the potential for the application of this technology within the glass industry.
The effectiveness of gas acid scrubbing was excellent and deNOx was achieved by the addition of ammonia solution upstream of the filter plant. Pilot unit details Element type TopK. Both are for full sized units, one for a float glass line and the other for a container glass furnace. The first plant was commissioned in early September and the second is scheduled for November The principal benefits of ceramic elements are high filtration efficiency and high temperature capability now allied with a catalyst capable of removing NOx.
These benefits can most effectively be utilised to treat the gases associated with glass furnaces. Cerafil TopKat represents a revolutionary advance in ceramic filter technology. This system offers the highest efficiency for particulate removal even with very fine particles and the new catalytic element extends ceramic filter capability by incorporating an integral catalyst for dioxin, NOx and VOC removal.
The product has already exhibited excellent NOx removal ability both in pilot and full scale plants. Empirical data collected to date has demonstrated that it is possible to effectively combine filtration capability with catalytic activity. Following the successful trials at two major glass companies in Europe two orders were received for this new catalytic filter element system. The latest reference document BREF generally gives information on a specific industrial sector in the EU, techniques and processes used in this sector, current emission and consumption levels, techniques to consider in the determination of BAT, the best available techniques BAT and some emerging techniques.
Ceramic filters are very efficient for the separation of dust and will work well in combination with a dry scrubbing stage for acid gas removal. Furthermore given the refractory nature of the filter medium and the favourable filtration temperature the catalytic reduction of NOx emissions is possible with this technique by applying catalytic ceramic filters where the catalyst is incorporated into the ceramic filter elements.
In the first phase a filter based on standard filter elements can be installed for particulate abatement and acid gas removal maintaining sufficient temperature for future NOx control. In a second stage the filter may be retrofitted with catalytic filter elements for NOx reduction or a SCR system can be installed. The phased introduction would avoid unnecessary or premature expenses. The initial costs of the catalytic ceramic filter can be substantially lower than traditional alternatives.
Maguin design and build filtration systems under the Cercat name, utilizing Cerafil Topkat, and ran the pilot tests detailed in this article. Ganjoo, L. McCamy and M. Since the cell efficiencies and performance of a solar harvesting device are directly related to the number of absorbed photons, the first and foremost demand for glass to be used in solar application is to have a very high transmission in the visible region of the electromagnetic spectrum. This makes the glass composition a very critical parameter as various additives to normal clear glass, which act as absorbing centers for photons in the visible region, need to be taken out of the glass compositions.
In addition, one of the biggest requirements for solar glass is its chemical durability. The glass needs to be durable to withstand sudden and drastic changes in temperature and humidity among other things for prolonged and effective use. Furthermore, the glass needs to be mechanically strong as it is exposed to harsh weather conditions, which include, rain, snow, sleet, hail, etc.
In this paper, we will take a look at the various issues facing the glass selection in various solar related applications and will discuss the importance of glass composition in addressing these issues. The predicted growth of the solar energy industry is one such area, which has taken on even more importance with the recent concern with global warming from green house gas GHG emissions . The requirements for glass compositions for solar applications vary depending on the end use, which can range from arrays of roof-top photovoltaic PV panels and concentrated photovoltaic CPV devices to massive solar power plants SPP generating up to MW of electricity annually.
Other growing markets include the use of glass in building integrated photovoltaic BIPV devices. Flat glass products for use in solar industry applications are manufactured today basically in only two forms for economic reasons to provide either improved solar light transmission or aesthetics.
These include pattern glass used mainly as cover plates for photovoltaic solar cells, and float glass commonly used in new thin film photovoltaic applications, often in combination with transparent conductive oxide TCO coatings, antireflective AR coatings or mirror coatings on glass substrates.
Several flat glass producers have investigated methods to further improve light transmittance , Innovative technical approaches are currently being explored to identify potential solutions when making float glass for solar applications. Lezersrecensies Beoordeel zelf slecht matig voldoende goed zeer goed. Lezersrecensie van '70th Conference on Glass Problems' Wat vindt u van dit boek? Algemene beoordeling slecht matig voldoende goed zeer goed.
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