It's no surprise that discussions about energy efficiency have extended to include glass tempering lines. Glass tempering, after all, isn’t typically seen as a "green process." Considering energy consumption is not only about environmental values and government subsidies but also about reducing operational costs.
However, this topic is often misunderstood in the industry. Manufacturers and processors frequently use terms without fully understanding their meanings and implications. We aim to shed light on your actual line energy consumption and how to minimize it. Whether you’re considering entering the business or already operating a tempering line, we believe this information will be beneficial.
Let's start by defining some key terms. To keep things simple, there are three main terms you need to understand:
Energy consumption
Installed power
Average process power (APP)
Energy consumption refers to the amount of kWh used to process a certain amount of glass. Note that the unit of energy consumption is kWh, not kW or kVA. It should always be expressed as a function of the produced glass per area, hence the unit should be kWh/m² (or ft²).
Installed power is the total power of all electrical components combined, and it doesn't directly relate to energy consumption. This figure alone is not particularly meaningful. However, the heating power indicates the tempering line’s capacity for high-production runs. When combined with information on how much power is used at various stages, it can help in sizing transformers. This is akin to focusing solely on engine size when buying a car without considering its fuel efficiency.
Average process power (APP) is the average power demand during one tempering cycle for a given product. APP is usually measured in kVA or kW and varies with glass type and thickness. It can be easily reduced by processing less glass. In essence, APP is higher when more glass is processed. For instance, a fast and efficient tempering line will have a higher APP. However, this doesn’t apply to energy consumption (kWh); a fast and efficient line will actually reduce the energy consumption per produced m².
Now, let's delve deeper into the energy consumption of the tempering line.
Understanding Energy Consumption in Different Sections
To identify which parts of the machine have the greatest impact, let's examine a glass tempering line processing different glass types. We will focus on the furnace and the quench, as loading and unloading conveyors have minimal overall energy consumption.
Energy Consumption in Heating
The furnace accounts for the largest share of total energy consumption in a glass tempering line. The majority of energy is used to heat the glass. The energy required to heat the glass remains constant due to the physical properties of float glass. Regardless of the technology, the energy required to heat the glass stays the same.
In an ideal scenario, only the theoretical minimum energy needed for glass heating would be required. However, in reality, there are losses:
Heat loss through walls: Some heat escapes through the furnace walls.
Heat loss due to convection compressed air: If compressed air is used for convection, the incoming air must exit the furnace, resulting in lost energy.
Energy for generating convection: This includes compressor power or motor power for circulated convection systems.
Energy Consumption in Quenching and Cooling
The quench also significantly contributes to the total energy consumption in the tempering process. For thinner glasses, it accounts for almost the same amount of total energy consumption as heating.
The main energy-consuming component in the quench is the blower motor(s), which create the air pressure to temper the glass. Factors affecting total energy consumption in the quench include:
Loading efficiency: Higher loading efficiency leads to lower energy consumption.
System for running the blower motor (e.g., inverters): Inverters allow the motor power to reduce between heating cycles in an oscillating furnace. The more the power can be reduced, the more energy can be saved.
Pressurized area in quenching: Running thin glass with lower loading efficiency can be offset by limiting the pressurized area in the quench.
Furnace capacity: Higher line capacity reduces blower idling time and power, lowering kWh/m². Even with inverters, blower motors consume some energy between loads.
By understanding and optimizing these factors, you can significantly reduce the energy consumption of your glass tempering line, contributing to both cost savings and a more environmentally friendly operation.
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