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Lower CO2 emissions with Type 8 Cruciforms - Industrial feedback
October 05th, 2020
In the Glass International October 2020 issue, S.Schaller, E.Lopez, I.Cabodi*, Dr.M.Gaubil and M.Allen-Larut** discuss a type of Cruciform which can substantially increase energy efficiency.
SEFPRO offers a complete range of checkers for regenerators and more specifically the fused alumina material (ER 5312 RX) Type 8 which can increase refractory surface area at the top of the packing. The thermal measurements performed on one furnace equipped with Type 8 Cruciforms show a strong correlation between numerical predictions and actual performance, and an increase in energy efficiency compared to standard solutions.
Introduction
The glass industry faces a challenge to reduce the environmental footprint of its glass furnaces, to meet environmental regulations concerning the reduction of CO2 and NOx/SOx emissions. Energy consumption reduction and furnace efficiency are key in the pursuit of competitiveness and environmental friendly glassmaking. Regenerative furnaces are the most efficient solution for the glass industry to recover lost energy contained in the furnace’s exhaust gases.
Checker design
The main phenomena driving heat exchanges in the regenerator are radiation, free convection, and forced convection – with their respective intensity varying along the height of the chamber. Therefore, the shapes, materials, and flue dimensions of the checker pack should vary accordingly to maximise thermal efficiency and ensure longer performance. In regenerative furnaces, checker packs design is the key to maximise regenerators’ thermal efficiency and reduce CO2 and NOx emissions. A significant part of the exhaust gases energy can be recovered, allowing decreased fuel consumption. Using a large-scale high temperature experimental setup and specific numerical models, SEFPRO developed a simulation tool able to predict local heat exchange rates and temperatures in the regenerator chambers. Combining the numerical approach with a range of fused cast checkers offering different materials, shapes (Fig. 1), and adjustable flue dimensions can help maximse regenerators efficiency and sustainability. Type 8 checkers were developed as a solution to increase energy recovery in the top part of a regenerator chamber. Made from fused alumina material (ER 5312 RX), Type 8 Cruciforms exhibit a high corrosion resistance to chemical aggression caused by alkaline vapors and carryover particles at high temperature. Their particular shape (Fig. 2) can increase refractory surface area of the packing resulting in higher heat transfer rates. In addition, the corrugated shape of Type 8 Cruciforms generates turbulences in air cycle, increasing heat exchanges in the top portion of the chamber. In recent years, Type 8 Cruciforms have been installed in many furnaces.
Industrial application
Type 8 Cruciforms were installed in the regenerator chambers of an end-fired furnace for STOELZLE Masnières, France (Fig. 4). STOELZLE’s furnace was rebuilt in 2013 and produces 54 metric tons per day of extra-clear glass for the perfume containers market. SEFPRO provides a service of industrial measurements using various devices and methods to monitor regenerators’ ageing and performance. In May 2019, gas temperature measurements and endoscopy of the chambers were performed at STOELZLE to assess the thermal performances of the checkerpacks and evaluate the ageing of materials inside the regenerator chambers after six years of operation. Gas temperatures were measured by aspiration pyrometers, at the top and bottom of the chambers simultaneously (Fig. 3). The performances measured on site are similar to the results of the simulation with a variation of 0.2% in thermal efficiency and 0.6% regarding energetic efficiency (Table 2). Energetic efficiency of the regenerator is above 70% for both chambers and air outlet temperatures are around 1330°C. According to the glassmaker, the comparison of the 2013- 2019 period with the previous campaign shows a 22.9% increase of the average pull rate while decreasing specific fuel consumption by 0.5%. Table 1 presents the simulation results for STOELZLE’s Type 8 solution compared with SEFPRO’s standard cruciforms design (Type 3 / Type 4, Fig. 4).
Considering a fixed fuel consumption, simulation shows a difference of 2.8% in energetic efficiency between the solutions, due to a diminution of air outlet temperature from 1332°C to 1300°C. Additional simulations show that, to maintain the energy input to the furnace, the use of a standard Type 3 / Type 4 Cruciforms solution would require a 470 Nm3/h gas consumption increase (representing a 2.2% increase).
With the Type 8 Cruciforms solution, the CO2 emissions avoided thanks to fuel savings during the campaign are estimated at 40,436 tonnes, corresponding to the emissions from 4,666 homes’ energy use for one year(3). One of the concerns associated with the use of smaller flues in regenerator chambers is the risk of additional clogging. Clogging of the checker packs is generally due to the accumulation of dust carried by the exhaust gases and condensation of alkaline species as they cool in the chamber (between 1150°C and 880°C for sodium sulphates). SEFPRO recommends the use of Type 8 Cruciforms up to 5 courses in a packing. Every layer added can increase regenerator’s performance while maintaining Type 8. Cruciforms outside of the condensation area. Endoscopic observation of the top of the chambers and pictures taken below the rider arches revealed unclogged channels after the six-year period. In addition to Type 8 Cruciforms, Type 6 Cruciforms with larger flues (Fig. 1) were used in the condensation area to prevent clogging and reduce maintenance costs during the campaign. The packing density of STOELZLE’s Type 8 / Type 6 Cruciforms solution (742 kg/m3) is therefore similar to the density of the standard Type 3 / Type 4 Cruciforms solution (744 kg/ m3) while maintaining higher energetic efficiency. The redistribution of checkers’ density along packing height can maximise refractory presence in areas with high heat exchange potential for an almost constant overall weight of the checkerpack thus optimising efficiency and investment costs.
Conclusions
Efficient regeneration is a key factor to reduce fuel consumption in a furnace’s lifetime and a step towards greener glassmaking. Checkerpacks’ design is crucial to maximising the energy recovery of regenerators and substantially reduce the carbon footprint of glass products. Thanks to the versatility of the Cruciforms checkers product range, SEFPRO offers tailor made solutions to glassmakers to address their specific needs. The use of Type 6 Cruciforms prevents clogging issues in the condensation areas of the checkerpacks while Type 8 Cruciforms intensify heat exchanges at the top of the packings. In addition to the fuel savings due to better energy recovery (estimated at 2.2%), the prevention of clogging reduces maintenance costs during the campaign. SEFPRO proprietary numerical tool, developed using a large scale high temperature experimental setup and validated with industrial measurements (0.6% variation), accurately predicts the thermal behaviour of regenerator during operations. The combination of predictive simulation and flexible product range allows the design of tailormade and optimised solutions for glass furnaces’ regenerators targeting long lasting energy savings.
Acknowledgements
Laurent Derigny, Raw Materials & Melting Process Manager, STOELZLE Masnières Parfumerie, France.
References
1 D. Lechevalier, A. Pinto, V. Domingues, O. Citti, M. Gaubil, Glass International, vol. 35 (8), pp.33-36 (2012)
2 D. Lechevalier, O. Citti, S. Bourdonnais, Proceedings of International Congress on Glass (2010)
3 EPA Greenhouse Gases Equivalencies – Calculations and References, epa.gov (2019)
*Saint-Gobain Research, Provence, France
**SEFPRO, France
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