Energy efficiency for glass wool production at Saint-Gobain ISOVER AB

Transcription

1 Energy efficiency for glass wool production at Saint-Gobain ISOVER AB Abstract Author: Björn Öhrstrand Department of Chemical Engineering, Lund University, Sweden Date: 27/ The Saint-Gobain ISOVER AB in Billesholm is a plant that is a part of the world-leading production companies of glass wool based insulation products. In the year 2007 a report covering energy mapping of the factory in Billesholm made by Morgens Johansson from Dansk Energi Analyse A/S was done. The energy mapping suggested a proposal on energy savings by preheating the glass/batch before the glass furnaces. [1] With a base in that proposal this master thesis aim is to investigate how preheating of the glass/bath before melting in the glass furnaces with waste energy from other places in the process could be done and if it is profitable. The thesis consist of an energy identification to show where there is a lot of potential energy savings in the production and a drying test because of the high moisture level in the crushed glass. The flows that have the most potential to be used is the flue gas and excess air from the, which has a power of 309 kw for T4 and 576 kw for T6 glass furnaces. The other flow of interest is the air flow to the glass furnaces filter, which has a power of 129 kw for T4 and 284 kw for T6 glass furnaces. A drying will give at least an energy saving for vaporization of all water in the crushed of 230 MWh for the T6 glass furnaces and 105 MWh for the T4 glass furnaces a year. The drying was confirmed in the drying test to work in theory but in the real process the drying temperature should be around 140 to 150. The power needed for the fan is approximately 4.3 MWh a year. This makes it profitable for the continually process for both lines, but most profitable for the T6 line. Keywords: Glass wool production, Energy identification, Crushed glass drying Introduction The production in Billesholm is done in two separated glass furnaces, T4 and T6. To the glass furnaces there is a flow of batch that contains chemicals, eco glass (external recycled glass), crushed glass (internal recycled glass) and oxymelt glass (remelted glass wool scrap). The melted glass is tempered in before it comes to the spinners for fiberisation in the different production lines. From the T4 glass furnaces there are three lines of production, which are T4, R5 and R4. From the T6 glass furnaces instead there are two lines of production, which are T6 and V2. The T-lines are producing glass fibre mat according to TEL technique, R-lines is production of pipe sections and V-line is production of white wool. At all lines except V2, the glass is mixed with binder and water after fiberisation and then cured in separated curing ovens. After the product is cured it is cooled, cut in to desired shape and packed. [2] In the year 2007 a report covering energy mapping of the factory in Billesholm by

2 Morgens Johansson for Dansk Energi Analyse A/S was done. The energy mapping was made from October 2006 to July 2007 covering the whole factory and it resulted in proposals for savings that could be done. One of the proposals is to preheat the glass/batch before the melting in the glass furnaces. In the proposal the crushed glass should be preheated to 200 before the glass furnaces, according to them this is going to give an energy saving of 3400 MWh/year. [1] Aim This master thesis aim is to investigate how preheating of the glass/bath before the melting in the glass furnaces with waste energy from other places in the process could be done and if it is profitable. Energy identification To get a good picture of where the energy is going to be taken from and if it is possible to preheat the crushed glass and/or batch before the glass furnace, an identification of the energy flows have been done. The identification has been separated into two main parts, the T4 and T6 glass furnaces. The delineation of the energy identification is made to only use the part of the process that is important and possible to use for preheating of the crushed glass and/or batch regarding to localization in reality. Because of this the energy identification is limited to the part of the process from the glass furnace to spinners. The energy identification gave a deficit of energy of 21.1% for T4 and 0.4% for T6, the energy flows characterized and size of them is summarized in table 1. This big difference in T4 energy identification can be because of inconsistencies when values has been taken, which means there might be a difference in what process parameters the process is operating under at different times. Table 1 Summary of the energy flows in and out of the T4 and T6 glass furnaces with following lines Line T4 (kw) T6 (kw) Oxymeltglas(T4)/ Crushed glass(t6) in Batch in Electric melting glass furnace Air to glass furnace filter Air from surrounding room Cooling of electrodes with water Melting Heat Radiation losses glass furnace crust Electric heating in primary feeder Extra cooling in - 40 primary feeder Natural gas heating Melting heat Flue gases and excess air Radiation losses Convection losses Glass outflow to spinners In-Out Deficit 21.1% 0.4% The main streams that is of interested for preheating and drying of the crushed glass is the flue gases and excess air from the and the air to the glass furnaces filter. Experimental design From the energy identification, as stated above, it was clear that the two energy flows that are most interesting to use for drying and preheating the crushed glass are the air that flows to the glass furnace filter and the flue gases and excess air from the. The aim

3 of this experiment is to see how the drying process of the crushed glass functions. To do this a smaller scaled test was done. The experimental setup is a five times reduction according to the dimensions (diameter and height) of the crushed glass silo that is used in the real production, with a fan that makes the air flow from the glass furnaces to the filter instead go through the crushed glass silo. The air flow that goes to the glass furnaces filter on T6 line was measured to approximately 7000 m 3 /h in the energy identification, which gave that the down scaled flow should be around 280 m 3 /h with a temperature around 148 as the most exact point for the air. In the experiment the air that was used was taken from chimney on V2 feeder with the fan through the crushed glass silo according to figure 1. In the experiments the temperature was going to be logged continuously with a type K thermocouple coupled to a data acquisition of type Agilent 34970A, with the thermocouples placed according to figure 1 marked as TI. The moisture and flow measurements was checked with equal time interval during the run, in the setup according to figure 1 marked as MI and FI. Working procedure The working procedure during the tests was to first check the temperature and flow into the silo. When it is as desired the flow was let into the silo and the temperature changing in the glass was logged and flow and moisture were checked before the silo to know if there were any drastic changes with time. The test run continuously until the temperature in the top of the silo was approximately the same as the rest of the silo. The silo was then emptied of the glass. To get an idea of how much water that has been dried during the experiment a sample of the same volume was taken before and after the test. The samples was weighted and then fully dried in a oven before being weighted again, the differences in weight was assumed to be the moisture level. This procedure should be done three to five times to get a good idea on the behavior of the glass when it is heated. Figure 1 A schematic figure over the experimental setup, with the indicators temperature marked as TI, moisture as MI and for flow FI Result and Discussion In the study four tests were preformed where result for the temperature and moisture level in the crushed glass measurement for the tests was measured against time. The incoming temperature was in test four about 90 instead of 70 as it was in test one and two. In figure 2 and 3 shows that the time for the first level to peak to the incoming temperature is about 43 minutes from the start of the fan, which comparing to the test at 70 is about 67 minutes, se figure 4. This is a decrease in time by 36 %. That the time is long before the peak to the incoming temperature and the instability in temperature of level one, two and three is due to problems with the inconsistency in the flow through the crushed glass bed. The result in the end part is misleading because it says that it takes equal amount of time with a higher incoming temperature, this should not be the result if the flow had been consistent. To make the drying possible in full scale there has

4 to be a higher incoming temperature of the air flow, more around the temperatures that was suggested in the experimental setup, about Figure 4 Temperature change at the inlet of the silo and at level 1, 2 and 3 of the silo against time for test two, the start and stop of the fan is marked with the vertical lines Conclusion Figure 2 Temperature change at the inlet of the silo and at level 1, 2 and 3 of the silo against time for test four, the start and stop of the fan is marked with the vertical lines Figure 3 Moisture level of the crushed glass change with time at the bottom and top of the silo for test four, the start and stop of the fan is marked with the vertical lines An Energy identification has been performed and the conclusion is that there is a lot of potential energy savings in the production. The flows that have the most potential to be used are the flue gas and excess air from the and the air flow to the glass furnaces filter. The crushed glass that is melted in the glass furnaces has a moisture level of approximately 2 % for T6 and 4 % for the T4 line. A good idea is to dry this before and this is why drying experiments were performed. From the tests it was clear that there is a possibility to dry the crushed glass in a silo, but with the incoming temperature that was tested 60, 70 and 90 it was clear that the drying took too long time. At a full scale the incoming temperature has to be higher to make the drying process in a good time for keep up with the outflow of crushed glass, approximately 140 to 150. The suggestion on how to use this in the real process is to use the air flow that goes to the glass furnaces filter instead go through the crushed glass silo like in the experimental setup but instead on the side so it could have an out flow of crushed glass. The drying will

5 give at least an energy saving for the vaporization of water of 230 MWh for the T6 glass furnaces and 105 MWh for the T4 glass furnaces a year. Where the power needed for the fan is approximately 4.3 MWh a year. This makes it profitable for the continually process for both lines, but most profitable for the T6 line. The flue gases and the excess air from the could possibly be used to heat up water that could be used in the curing step further down in the process line. References [1] Dansk energi analyse A/S, "Energikartläggning for Saint-Gobain Isover Billesholm," Mogens Johansson, Frederiksberg, [2] Saint-Gobain Isover AB in Billesholm, "Om Isover," Available: [Accessed 16 October 2012].