Batch Preparation

Batch preparation stage involves weighing fine-ground raw materials – that include formers, fluxes, stabilizers and sometimes colorants – according to recipe required for the final product and their subsequent mixing to achieve a homogenous composition. Approximate compositions used for different glass products are given in table below:

Approximate Compositions Used for Different Glass Products (Worrell et al., 2008. p.9)
Constituent Container Glass Flat Glass Fiber Glass Laboratory Ware
  (in terms of weight percentage)
SiO2 73 72 54 80
B2O3     10 10
Al2O3 1.5 0.3 14 3
CaO 10 9 17.5 1
MgO 0.1 4 4.5 1
Na2O 14 14   5
K2O 0.6      

Although most raw materials are already received in ground form, some of them may need to be ground on site. Grinding is an inherently inefficient process and grinding to very fine particle sizes may be energy intensive (Worrell et al., 2008. p. 53).

Creating a properly homogenized feed to the melting process is of critical importance for product quality and for energy consumption. Depending on whether the manufacturing process is operated continuously or in batches, mixing, storage and feeding systems may show variations (EC IPTS, 2012. p. 39). In larger plants, with computer controlled weighing equipment, materials are generally weighed directly onto a conveyor belt, which feeds into a solids mixer. Non-automated mixing, which mostly occurs at smaller plants is the most inefficient method (Worrell et al., 2008. p. 53).

Due to its abrasive nature and larger particle size, cullet is usually handled separately from the primary batch materials and may be fed to the furnace in measured quantities by a separate system (EC IPTS, 2012. p. 39).

Electricity is used in batch preparation for bucket elevators, (pneumatic) conveyors, batch mixers, and agglomeration of materials, with the the batch mixer having the greatest share of in this process step. Total electricity use for batch preparation varies and estimated at 80 kWh/ton for flat glass, 155 kWh/ton for container glass, and up to 337 kWh/ton for glass fiber (Worrell et al., 2008. p. 56). In general, around 4% of a glass plant's total energy demand is used for batch preparation (Worrell et al., 2008. p. 53)

Batch PreparationTechnologies & Measures

Technology or MeasureEnergy Savings PotentialCO2 Emission Reduction Potential Based on LiteratureCostsDevelopment Status
Using Lithium Compounds as Fluxing Agents

Recent estimates suggest that adding lithium to glass batches can reduce furnace energy consumption by as much as 5-10% (Worrell et al., 2008. p.54).

Quantitative information not available. 

Quantitative information not available. 

Commercial
Selective Batching

Early findings suggest that the melting time can be reduced by 50%, resulting in fuel savings of 20-33% (Worrell et al., 2008. p.54).

Research
Cullet Separation and Grinding

Increased availability of suitable cullet helps reduce energy consumption. 

In one plant, recycling rate for internally produced cullet has been increased from 30% to 75% with the installation of a cullet crusher (Worrell et al., 2008. p.56). 

Installation of a crusher enabled increasing the recycling rate of internally produced cullet from 30% to 75%, resulting in US $190 000 [1997 dollars] cost savings due to reduced waste handling and material purchases. Payback time was 3 weeks (Worrell et al., 2008. p.56). 

Commercial
Reduced Rotational Speed in Grinding

Quantitative information not available. 

Quantitative information not available. 

Quantitative information not available. 

Commercial
Optimizing mixing

While intensive mixing can consume 50 kWh/t or more, screw orbit and ribbon mixers consume around 10 kWh/t and ring through and rotating pan mixers typically consume about 20 kWh/t. Tests in Netherlands revealed that rotating pan mixers resulted in least variability in composition at the shortest mixing period (Worrell et al., 2008. p.53).

Quantitative information not available. 

Quantitative information not available. 

Commercial
Optimizing Batch Wetting

A reduction of the moisture content of the batch by one percent will result in fuel savings in the furnace of 0.5% - depending on the share of cullet (Worrell, et al., 2008. p.54)

Quantitative information not available. 

Quantitative information not available. 

Commercial
Use and Optimization of Conveyor Belts

Use of ASDs in conveyor belt systems typically reduce energy consumption by 8 _ 15%, with actual amounts differing from application to application (Worrell et al., 2008. p.54)

Quantitative information not available. 

Quantitative information not available. 

Commercial

Batch Preparation Publications

Page Number: 

9

Batch Preparation 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: 

39