Batch and Cullet Preheating

Batch and cullet are normally introduced cold to the furnace. By using the residual heat from the furnace – applicable only for the fossil-fuel fired furnaces – significant energy savings can be achieved. In addition to energy savings, this technique can give an increase in furnace capacity of 10 – 15 % without compromising the furnace life. Investment in equipment and infrastructure downstream of the furnace will be required in order to be able to utilise any increase in pull capacity. Costs, in particular related to increased machine capacity, could be significant.(IPTS/EC, 2013. p. 319-320).

As of 2008, cullet preheaters were only found in container furnaces. Preheating of cullet is easier than batch preheating, as clumping of incoming materials can affect the product quality and melter efficiency (Worrell et al., 2008. p.68). Preheating temperatures should not be lower than 270 °C and should not exceed 500 – 550 °C. In practice, most preheaters operate at batch temperatures between 275 to 325 °C (IPTS/EC, 2013. p. 318). In theory, any system with over 50% cullet in the batch can install preheaters. Batch-only preheaters are not considered proven technology (Worrell et al., 2008. p.68).

Direct, indirect, and hybrid systems are the three types of preheaters used. 

In the direct preheater, the cullet is in direct contact with the flue gas in a cross–flow arrangement, and is heated to about 300 °C and could go up to 400 °C (IPTS/EC, 2013. p. 318). A bypass is available in case the preheater cannot be used (Worrell et al., 2008. p.68).

The indirect preheater is a cross-flow plate heat exchanger. The cullet moves through the heat exchangers that preheat the cullet to a temperature of approximately 300 °C (Worrell et al., 2008. p.68);

A hybrid system combining dust removal with preheating is offered by Prexair Edmeston electrified granulate bed (EGB) filter system, which combines an electrostatic precipitator for dust removal and a direct cullet preheater. This system can heat the cullet and the dust from the furnace to around 400 °C (Worrell et al., 2008. p.68).

In preheating, problems can occur with very fine cullet, which can bind under heat and pressure from the cullet bed and form lumps that restrict flow. Slow cullet flow can also cause problems in the build up of fines, restricting the flow of waste gas. A control system may be able to adjust the flow to avoid this problem (Worrell et al., 2008. p.69)

 

Development Status Products
Commercial

Batch and Cullet PreheatingCosts & Benefits

Parent Process: Melting and Refining
Energy Savings Potential

Specific energy savings of between 10 and 20 % can be achieved (IPTS/EC, 2013. p. 319)

EU flag By installing a cullet/batch preheating heat exchanger, a packaging glass company in Netherlands was able to raise the temperature of cullet to 277 °C, which reduced electric boosting by 60 (or 90 kWh/t) and natural gas usage by 8% (or by 0.32 GJ/t) (Worrell et al., 2008. p.68).

CO2 Emission Reduction Potential
Costs

EU flag For a 350 tonnes/day cross-fired regenerative furnace, the additional investment cost associated with the use of the preheater is about € 2.5 million, including some adaptations in the batch-charging machinery. The annual operational cost savings are about € 820 000 per year, assuming a fuel price of € 9.4 per GJ gross combustion value. The average cost savings during the furnace campaign are estimated at € 3 per tonne molten glass, calculated on the basis of 2013 energy prices (IPTS/EC, 2013. p.320).

EU flag The application of batch/cullet preheating to a 450 tonne/day furnace allows for an increase in pull capacity from 450 to 500 tonnes/day and for saving energy. The investment costs are € 3.4 million and cost savings (based on a 500 tonne/day capacity) are € 1.1 million per year. In this case, the payback time is three years. The total cost savings are equivalent to € 5 – 6 per tonne glass, partly due to the increased melting capacity of the furnace without the need of enlarging its structure (IPTS/EC, 2013. p.320).

EU flag Installation of a cullet/batch preheating heat exchanger in a a packaging glass company in Netherlands in 1996 costed $ 1.4. The project had a payback time of 2.6 years, based on natural gas prices of $4.11/GJ and electricity prices of $0.05/kWh (Worrell et al., 2008. p.68).

Batch and Cullet Preheating Publications

Page Number: 

67-69

Batch and Cullet Preheating Reference Documents

Best Available Techniques (BAT) Reference Document for the Manufacture of Glass

As a reference of the EU Industrial Emissions Directive (2010/75 EU) this new version provides extensive information on Best Available Techniques (BATs) applicable to European Glass Manufacturing Industry for reducing environmental impact. The document is prepared by the  Institute for the Prospective Technological Studies of European Commission's Joint Research Center. 

Page Number: 

318-322