SYSTEM 5oo FOREHEARTH
The System 5oo forehearth was specifically designed to achieve the best glass thermal homogeneity over the widest operating range with optimum fuel efficiency and with more than 5oo worldwide installations to date its ability to achieve these objectives is well proven.
- Direct, hot face longitudinal cooling maximises the cooling efficiency and cooling capacity of the forehearth.
- The single piece profile design roof block separates the cooling and combustion functions within the forehearth.
- Separate, automatically controlled, combustion and cooling dampers allow separate exhausting of combustion products and cooling air.
- Automatic control of the dampers and cooling air inlet volume ensures a positive internal forehearth temperature is maintained.
- The PSR sub-zoning concept maximises the cooling capacity of the forehearth.
- Based on the operating details provided, we design our systems to the optimal configuration and then provide guarantees of the glass thermal homogeneity, temperature stability and fuel consumption which will be achieved.
The roof block geometry used in the System 5oo technology effectively divides the forehearth into three lateral chambers. The central chamber is used as a conduit for a longitudinal, forced convection cooling system in which cooling air is injected into the forehearth chamber at the start of each cooling zone and exhausted through a central flue at the end of the zone. The cooling air flow rate and the position of the exhaust damper are automatically controlled. This allows the forehearth to ensure that a positive internal forehearth pressure is maintained.
In addition the forehearth is configured with side flues which, when operating in cooling mode, allow the combustion gases to exhaust from the forehearth without entering the central cooling section. These exhausts are also fitted with automatically controlled damper blocks.
By containing the cooling in the central chamber of the forehearth and the heating in the side chambers of the forehearth we can target the heating and cooling functions where they are required therefore cooling the central hot stream of glass and heating the cooler streams of glass at the sides of the forehearth to overcome the heat losses through the channel side walls. Additionally by ensuring that the cooling and combustion functions remain separate inside the forehearth we can maximise the combustion and cooling efficiency.
When the system is operating in heating mode, the cooling air control valve and side dampers are closed automatically. This forces the combustion gases into the centre of the forehearth to exhaust through a small notch in the central cooling damper block therefore inputting heat into the glass across the entire forehearth width and allowing the forehearth to react to any changes in operating conditions. However, the profile design of the roof block re-radiates heat from the burners back towards the channel side walls, and the closure of the combustion dampers prevents any heat loss to atmosphere, allowing preferential heating of the side streams of glass.
The PSR concept of sub-zoning also works to maximise the effect of the cooling system. By introducing two cooling air inlets and two cooling air exhausts in each cooling zone, we halve the path length of the cooling air within the forehearth, optimising the use of the cooling air volumes and minimising the possibility of overcooling the glass surface at the cooling air inlet point.
The distributor is a vital component of the glass conditioning process. The achievement of good glass thermal homogeneity before the glass enters the forehearth reduces the reliance on forehearth conditioning and improves the flexibility and production efficiency of the whole glass conditioning system.
Tansverse Pressurised Radiation Cooling
- By employing the same System 5oo technology on the distributor, we start the glass conditioning process as soon as the glass leaves the furnace.
- Low superstructure configuration reduces fuel consumption and improves glass temperature control.
- Transverse, pressurised radiation cooling can be used to maximise heat loss where required.
- Triple Jet longitudinal cooling provides high cooling rates without the intense cooling effect of radiation cooling.
Triple Jet Longitudinal Cooling
Many distributors or working ends still use construction techniques, combustion, cooling and temperature control systems based on furnace technology, with high arched superstructures and nozzle mix type burners in the working-end breast walls. These systems do not apply any significant conditioning to the glass and are very inefficient.
By viewing the distributor as an extension of the forehearth, not the furnace, we can provide all the advantages of the System 5oo forehearth throughout the glass conditioning process.
If required higher cooling rates can be achieved with the installation of ‘Transverse Pressurised Radiation Cooling’ over the throat riser and ‘Triple Jet Longitudinal Cooling’ in adjacent cooling zones.
‘Pressurised Radiation Cooling’ is used over the throat riser area. As cooling is required the radiation cooling dampers move to the open position and cooling air is introduced automatically from side entry flue blocks. The glass surface radiates directly to atmosphere and is further cooled by radiation to the underside of the roof blocks. The cooling air also maintains the internal pressure inside the distributor.
‘Triple jet longitudinal Cooling’ is used in zones adjacent to the throat riser section. As cooling is required the dampers move to the open position and cooling air is introduced through 3 outlet holes in a special vented mantle block. The cooling air cools the underside of the roof blocks across their entire width, enabling the glass surface to be cooled right across the distributor width. This ensures fast cooling rates without the intense cooling effect of radiation cooling to atmosphere.