Topic of the Month in September: Significant Increase of Productivity in the Glass Melting Process

COROX®-CGM Convective Glass Melting:

Significant Increase of Productivity in the Glass Melting Process

Linde AG, Linde Gas Division, together with The BOC Group has reached a license agreement on marketing of the BOC Convective Glass Melting (CGM) technology. The letters CGM are a trade-mark of The BOC Group. Linde will offer this new technology with the registered trade-mark COROX®-CGM to the glass industry world-wide.

COROX®-CGM oxy-fuel burners are located in the crown of a glass melting furnace such that burners are installed with a vertical, as opposed to the conventional horizontal orientation, as shown in figures 1 and 2.

Figure 1: Conventional Burner installation - horizontal





Figure 2: COROX®-CGM Burner installation - vertical

The effective heat is transferred by the sum of both the radiative and convective mechanism (1).

The heat transfer by radiation and convection can be described by the well known Stefan-Boltzmann law (2) and Newton's law of cooling (3) respectively (3).

The convective heat transfer coefficient (a) is a function of Nusselt number (Nu) which again is a function of the Reynold's (Re) and Prandtl (Pr) numbers (4,5).

Because the gas velocity for horizontal burners close to the batch/glass surface is very small and the gas velocity for COROX®-CGM burners is higher (6), the Reynold's number for COROX®-CGM flames are also higher (7) resulting in a significantly greater heat transfer coefficient (8).

The COROX®-CGM burners are designed such that an intense flame is formed flowing over the surface of the glass bath or batch beneath the burner. This results in extremely high temperatures in the proximity of the surface, a factor that further drives both the convective and radiative mechanisms. The convective mechanism is enhanced through increasing the DT between gas and surface, and by the exothermic recombination of dissociated species on the relatively cool bath surface. The radiative mechanism is enhanced locally by the reduced distance over which attenuation takes place by the furnace atmosphere. It has been observed that as a combination of the enhanced convective and radiative heat transfer mechanisms that the effective heat transfer with COROX®-CGM burners is about twice compared with conventional burners as shown in Figure 3.

Figure3: Heat transfer to the batch from impinging CGM flame

This enhanced heat transfer in addition to the normal radiant heat transfer from the furnace atmosphere and walls means, that more energy is transferred into the glass melt.

Because of the changed burner orientation the number of burners are not restricted by breastwall space limitations.

This leads to a significantly increased melting capacity and/or improved glass quality compared with conventional oxy-fuel burners and air-fuel burners anyway.

The objectives (and the implementation) of COROX®-CGM melting technology are:

Objective

Höhere Increase pull rate

Implemetation
Apply CGM oxy-fuel boost in addition to air-fuel energy
Observe regress of batch line
Increase pull to obtain original batch line

Objective
Improved product quality

Implemetation

Apply CGM oxy-fuel boost in addition to air-fuel energy
Allow regress of batch line for increase in refining area

Objective

Extend furnace life
due to regenerator plugging
by preventing regenerators from plugging

Implemetation

Apply CGM oxy-fuel boost
Reduce air-fuel energy on a global basis by 1.3 x oxy-fuel energy
Permit temperature profile to change slightly

The CGM technology has successfully been implemented in 20 furnaces (float, container and specialty glass). It has been demonstrated that air-fuel furnaces as well as oxy-fuel-furnaces can be further optimized by the implementation of COROX®-CGM technology.

Source: OGIS GmbH, glassglobal.com
in cooperation with: Linde AG, Linde Gas Division, Unterschleissheim (Germany)

Authors: Hans Mahrenholtz; Linde AG, Linde Gas Division, Unterschleissheim (Germany)
Richard Marshall and Andrew Richardson; The BOC Group, Murray Hill (USA)