SYMPOSIUM O N APPLIED RESEARCH
Applied Research in Glass Melting J. 6. HAMILTON
Data gathering essential plus “hard-headed engineering”
omeone has defined applied research as the search
S for new knowledge directly applicable to a specific industrial problem and the application of all existing knowledge to the practical solution of that problem. We, in Owens-Illinois Engineering, do not necessarily call it that. We say it is simply the hard-headed, day-today, application of engineering and scientific principles to the solution of our problems. Perhaps the thing which I have been most associated with throughout my years in the glass industry is the glass melting process, and my subject is the use of applied research in glass melting. History of Data Gathering
When I started in this business in 1933, our engineering director had decided that we needed to accumulate a lot of recorded data and knowledge about the glass melting process, if we were to improve it. We needed facts upon which to base engineering decisions. We have continued gathering information without ceasing since 1932, and the information collected has served as the basis for nearly every scientific decision that has been made during the years concerning the process. As new knowledge in other disciplines became available, our accumulated information showed us how to apply that knowledge to assist in improving our melting process. As the background knowledge developed, it also served to indicate where our problems were and to help define them so that we could attempt satisfactory solutions. Many trends became evident quite early in our datalogging period and identified problems which we would have to face if we were to maintain a profitable process. One of the basic premises which developed and on which we have always worked, is “to melt a ton of usable glass with the least possible amount of fuel.” The lower the amount of fuel, the lower the melting cost, the lower the temperature, and the lower the destructive effect on the furnace itself; and the lower the temperature required, the greater the capacity of the furnace. 16
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
In the early days, we used many kinds of fuel, including heavy oil, light oil, soft coal producer gas, hard coal producer gas, natural gas, and city gas. Obviously, in our melting processes, there were wide variations in all of the practices used for combustion and combustion control. Temperature/Fuel Data Basic
I t soon became apparent through our data collection, that many factories were operating at temperatures widely variant from others for doing the same job. It quickly became evident that the application of temperature measurement techniques and adjustment of air fuel ratios to maintain predetermined temperatures at specific loads were absolutely necessary. Applied research in temperature measurement and instrumentation was one of our first projects. We began to utilize thermocouples and potentiometers for recording temperatures continuously. We began to use gas and oxygen analyzers and air infiltration control measures based on them. We learned the importance of maintaining and cleaning regenerator systems. We stopped stack leakage and paid much more attention to furnace pressures and damper control. As we continued in these efforts, our major premise was rewarded in that it began to take less and less fuel to melt a ton of glass. Figure 1 shows the tendency in the early years to reduce the amount of fuel required per ton of glass. These figures are averages and I do not intend to try to make comparisons over the thirty-five year period which has passed, but I will show certain sections of charts which tend to indicate the effect of applied research during those times. After a while it become apparent that it was not possible with some fuels to attain the same efficiencies as developed with other fuels. Obviously, there was a difference in the rate of heat transfer between one fuel
Figure 7 . Fuelper ton glass
Figure 2. Production improvement
and another and between opposing usages of fuel. By this time, many of our producer-gas and oil-fired furnaces had been changed to the use of natural gas which a t this time, was fired a t relatively high pressure-that is, 5-10 lb/sq in. a t the burner nozzle. At these nozzle pressures, the preheated air mixed quickly. T h e flame was short and bright, with very little luminosity. From our studies higher flame luminosity seemed to result in greater heat transfer. Gradually a new period of adjustment to burner nozzle pressures in the range of a few ounces was developed. This resulted in lazy, luminous flames with a far greater heat transfer to the glass surface. The following period, according to Figure 1, indicates that this was beneficial to our basic premise, and the amount of fuel per ton of glass melted continued to decrease. During the two periods mentioned previously, the requirements for improved process control in terms of furnace operation were becoming more demanding. Improvements in instrumentation such as thermocouples, radiation meters, level controls, automatic charging, oxygen, COZ analyzers, and automatic air-fuel-ratio controls, added to the complexity, and yet to the control of the process. This was indeed fortunate because it helped to get greater productivity out of existing furnaces. With the lower amount of fuel required, and the greater control of the process, the tonnage per unit of furnace area increased. This is indicated in Figure 2. The amount of glass produced in 1954 in 58 furnaces would have required 223 furnaces, if they were still operating a t the 1932 fuel and load efficiency.
Refractory Research With the advent of higher loads, and higher temperatures (because of the increased total amount of heat used), we soon began having refractory problems and were launched into applied research of a very extensive VOL. 6 2
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nature in the testing and evaluation of refractories for glass melting usages. About 1954, refractory companies did very little in the way of refractory testing. Specifically, against glass melting conditions, we developed tests for the effect of glass corrosion on glass contact refractories, tests against carry-over and temperature for superstructure refractories, and for temperature and carry-over on regenerator refractories. These applications of applied research still continue on every new refractory and for every new glass which is developed. O u t of these tests have come refractory specifications for use in glass melting furnaces. These have resulted in the foundry up-grading of nearly all refractories. Out of this research also have come pictorial histories of individual blocks or shapes in individual furnaces. T h e performance of an individual piece of refractory can be checked and correlated with its installation conditions and judgment of its suitability based on actual service conditions. From these studies, it soon became apparent that not every portion of the furnace deteriorated in the same way a t the same time, like the one-horse shay. Therefore, it was decided that strategically used partial repairs would effect tremendous cost savings. Pictorial and written records of refractory performance and continued observation of specific trials soon led to replacement procedures which would utilize the full life of the refractory. Furnace l i f e Investigated
Since the price of refractories in general, and the use of more expensive refractories in certain areas have increased, the result is a more expensive furnace. Obviously new methods of furnace construction and maintenance must be developed to keep the average cost of producing a ton of glass within bounds. We have seen that we have been reducing the amount of fuel required per ton of glass melted, thus circumventing the increased cost of fuel, but the use of better refractories and their increased cost as well, definitely require improvement in the life of the furnace. Figure 3 illustrates a gradual trend in the improvement in furnace life until about 1957, but since that time there has been a drastic increase in the average life of furnaces. This last increase is the result of the applied research into refractories, and the use of strategic minor repairs, which I previously mentioned, and has resulted in improved costs of $3,000,000 to $5,000,000 per year for Owens-Illinois. T h e oldest furnace which Owens-Illinois has ever had was nine months old when I came to work in 1933. Today, the oldest furnace we have in our organization is 130 months. 18
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Figure 3. Furnace life
For 30 years we have been interested in insulation as a way to improve the thermal efficiency of a melting furnace. First efforts were directed to the regenerative system, since no glass containment problems were involved and no really serious refractory problems were anticipated. Later, we started insulating the main crown of the furnace and later still the side wall holding the glass. Since the average furnace holds about 300 tons of molten glass at 2700”F, and since failure of the refractory could result in the destruction of a factory, you might say we approached the project gingerly. After several years, and several near calamities, however, we did develop satisfactory methods of insulating caps and sidewalls, but one of the heat losses still plagued us-the loss through the bottom of the furnace. Perhaps this is one of the best illustrations of applied research in glass melting so I will go into the project in some detail. Refractory Materials
A brief review of the types of refractory materials which have been used to date for furnace bottoms, appears in order at this time. The first widely used material was clay “Flux,” a rammed or slip-cast highly siliceous refractory block that offered satisfactory results, but required heavy cooling, which meant high heat loss. Even with satisfactory cooling, the usable life of Flux in most cases was relatively short. I n some cases other areas of furnaces could be “hot repaired” to extend furnace life, but when a bottom in Flux became thin, it usually dictated that a furnace be shut down and the entire bottom replaced. The next material used as an improvement over Flux was “Super Flux.” This material was similar to Flux, but offered better service because of its lower silica and higher alumina content. Even though longer life could
TABLE I .
HEAT LOSS
TABLE
(B tu/ftz/hr) Through 12-in. clay flux
1760
12-In. clay flux
Through insulated bottom
47 5 1285
Insulated
Thermal savings I
II. COST INSTALLED REFRACTORY BOTTOM PER SQUARE FOOT $19.90
27.91 8.17
Repair glass contact I
be obtained with Super Flux, the inherent shortcomings of Flux were still present. As a means of reducing furnace bottom erosion and corrosion, the next step was to use a paving material on top of either Flux or Super Flux. These paving materials were fusion-cast refractories, bonded refractories, or various ramming mixes. These paving materials greatly improved the erosion and corrosion resistance of furnace bottoms, but the heat loss factor was still present along with the high repair cost. Our original thinking for improving the performance of a glass furnace bottom included the idea of saving fuel by reducing the heat loss through the bottom, and at the same time having a practical and economical construction. Based on this premise, we established the following five desirable characteristics for a furnace bottom. 1. It should be a n excellent thermal transfer barrier 2. I t should provide a t least as good resistance to wear on the glass contact face as a n uninsulated bottom 3. The initial installation cost should be as low as possible 4. Future repairs should be held to a physical rninimum and a low dollar cost. 5 . T h e total thickness should be no more than necessary to produce minimum wear and obtain maximum insulation I n addition to these five items, the furnace containing such a bottom must be capable of making commercial quality glass of the necessary tonnage for a reasonable campaign life. O u r original efforts to develop a n insulated furnace bottom started approximately 14 years ago. I n the initial installations we encountered major unforeseen problems which resulted in partial or complete failures. Through extended applied research work, we have
AUTHOR J . C. Hamilton is Vice President (Administration),
Director of Engineering, Corporate Engineering Department, Owens-Illinois Co., Toledo, Ohio 43601. This paper was presented as part of the Symposium on Applied Research, Its Accomplishments and Futures, 151th National A C S Meeting, Minneapolis, Minn., April 13-18, 1969.
established a material combination and construction methods that encompass the five previously mentioned desirable characteristics for a furnace bottom. I n addition, the development required that we conduct extensive laboratory investigations in order to evolve the necessary procedures for improving the overall performance of the bottom construction and to avoid major operational problems. T h e developed combination of materials, treatments, and related procedures are patented by Owens-Illinois. The initial cost for installing this insulated bottom in a new furnace is higher than the cost of a flux or a paved bottom. This added cost is readily recovered through fuel savings during a normal campaign. T h e cost for incorporating this bottom construction into a n existing furnace is again higher because of necessary steel changes and other possible factors. The repair costs for the bottom are low. Experience has shown that the only replacement generally required is in portions of the glass contact layer whil: the filler and thermal barrier materials remain in place for future operations. The development work with this bottom was done with soda-lime glass because of the larger number of soda-lime furnaces operated by Owens-Illinois. T h e construction has been modified to perform satisfactorily in furnaces melting glasses other than soda-lime with no major problems. Before we can consider the cost savings on any furnace bottom, we need to establish some basis for comparison. T o measure the actual Btu loss through a furnace bottom is not practical; however, some assumptions can be made based on temperature measurements for calculation purposes (Table I). For the comparisons, we will assume that the average melter bottom hot face temperature is 2500" F and ambient air of 70" F on the cold face. Since experience has been common with 12-in. clay Flux bottom, we will use it as our standard. We will assume that there is no wear on either type of bottom during operation. I n reality, there is relatively little wear on the insulated bottom that would effect heat flow, while a clay Flux bottom on a flint furnace would have considerable wear early in the campaign. Approximately 40 thermocouples VOL. 6 2 NO.
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TABLE I I I.
I‘J”
placed in many locations in one of the insulated bottoms have confirmed our assumptions of the thermal gradients. The cost comparisons for installing an insulated bottom will be based on the data in Table 11. During the past 30 years, detailed records of fuel consumption have been kept and analyzed. From this experience, we have found that for every Btu put into the glass, it is necessary to furnish 1.5 Btu above the melt. Since the Btu loss from a furnace bottom must come from the glass, for every Btu saved through insulation, 1.5 Btu’s will not have to be supplied by the fuel. The saving, of course, is independent of the load or pull on the furnace. We have performance figures on furnaces equipped with insulated bottoms which have completed campaigns. Using the information previously shown, let’s look at the data from an operating unit (Table 111). Our data from Table I11 were in Btu/ft2/hr. Considering the age of the furnace and the cost of fuel during the campaign, we can compute the dollar savings due to the insulated bottom as in Table IV. This saving, of course, is based on the previously mentioned assumptions, but the savings can be substantiated by a review of the operational data for the full campaign. The best basis is to compare this campaign to the previous campaign where the furnace had a 12-in. clay Flux bottom. See Table V. The actual fuel saving, in dollars, for the first 37.25 months of Campaign No. 15 was computed as follows:
FURNACE COST
874 Ftz clay flux a t 19.90.
=
$17,392.60
874 Ftz insulated a t 27.91 = 24,393.34 Premium cost insulated
TABLE IV.
$ 7,000.74
THEORETICAL L L J ”FURNACE SAV I NGS
Savings/ftZ
=
1185 Btu
Size
=
874 ftz
Age
-
cost
= $ 0.465 mm Btu
Input us. loss
=
53 mos.
1.5
1 X 2 X 3 X 4 X 5, = $28,027.91
-
TABLE V.
COMPARATIVE DATA
Campazgn Camjaign Age M m Btu/ton Fuel cost/mm Btu Total tons melted Melting rate
A’o. 15
No. 14
Camjatgn N o . 15
37 25
37 25
53 25
total
6 831
6 217
6 374
0 440
0 464
0 465
143,724
142,406
204,278
6 4
6 4
6 4
r
1 TABLE VI.
ADDITIONAL SAVINGS-EXTRA
LIFE
Final 12 mos. No. 14 = 7.716 m m Btu/ton
-
Final 16 mos. No. I 5 = 7.459 mm Btu/ton 0.257 mm Btu/ton
0.257 m m Btu/ton X $0.466 X 55,872 tons = $6691.34
InBtu’s/ton = 6.831
- 6.217
= 0.614
In dollars = 0.614 mm Btu X
[email protected]/nimBtu X 142.406 tons = $640.570 There were additional savings due to the additional 16 months of operation (Table V I ) . The loads for the periods above were comparable to Campaign No. 14 at 76.0pZ and Campaign No. 15 at 76.8yo. Thus, the total fuel saving is : Comparable life $40,570.80 Extra 16 mos. life 6,691.34 $47,262.14 The total actual saving on fuel is far in excess of the $28,027.91 we theoretically attributed to the insulated bottom. This indicates that we are not making excess claims for this construction at the expense of other operating features. As mentioned previously, the minimum amount of repair required, before the bottom can be reused, constitutes an additional savings. I n the case of “J” furnace, only 35y0of the glass contact surface, had to be repaired. No other repairs to the bottom were necessary. During the development of the insulated bottom, we had to deal with such things as expansion, corrosion re-
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x
Figure 4. Cost comparison
Figure 5. Unitfuel cost us. total fuel costper ton
Figure 6. Annual cost savings by year over 7956 eflciency
sistance, structural strengths, and structural stability of the materials used. Here we found that transferring theoretical data and laboratory tests results to a functional unit was beset with pitfalls and problems. Interpretation and construction errors were made and there were failures in experimental trials before obtaining the present workable combination. What we now have is a unique combination of materials and procedures which provides maximum insulation without increasing the corrosion and wear on the glass contact refractories. I n summary, the insulation practices described have served to reduce the fuel consumption which in turn has increased furnace life and lowered the cost of the glass being produced. Figure 4 represents how our total cost to melt a ton of glass has been held to an increase of less than 20%, in spite of the very large increases in labor, refractories, and fuel. I t is our belief that the use of applied research, or good hard-headed engineering, is responsible for our ability to maintain these costs. Our actual fuel cost per ton melted has increased even though our fuel per ton has decreased. This is primarily the result of the huge unit fuel cost increases (Figure 5). In spite of this, we have continued to make sizable fuel savings, as indicated in Figure 6, which shows that if we had melted all the glass required from 1957 to 1967 a t the efficiencies of 1956, our fuel cost would have been $5,186,000 higher. In the next phase of our applied research, we are searching for control techniques which will take advantage of the vast ability of computers to handle processes. We already have two such systems operating with some decided advantages, although we still have not been able to develop, in their entirety, the mathematical models essential to this kind of control. We are also looking to fundamental research and basic research to come u p with practicable changes in our processing which can result in future ability to combat increases in operating cost. So far, we have been talking about essentially the same glass melting process used 30 years ago. We believed some alterations to that process are due and possible, and it will be u p to us to see that they are properly applied to the process for the most gain. Use of electric power both as a primary source of energy and as a booster to fossil fuel firing offers the possibility of both new processes and improvements to our existing process. Owens-Illinois is actively pursuing both approaches. Possibly ideas encountered in solving pollution problems may offer impetus to further developments. We are of the opinion that almost any process can be 90% efficient with fair ease, but it is that last 10% that requires the constant use of applied research. VOL. 6 2
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