Decarbonising glass manufacturing: which hot-end investments should come first?

The hot end will be critical to decarbonising glass plants. Decarbonising a glass plant does not begin and end with the melting furnace. The furnace remains the main energy user, but investment plans often overlook what happens between the gob feeder and the annealing lehr. Yet the hot end has a decisive influence on production stability, reject rates and the energy consumed for every bottle that actually reaches the customer.

The cheapest energy is the energy you do not waste on rejects.

A hot-end review can take place before a glass plant commits to a furnace rebuild. In its container glass decarbonisation material, updated in 2026, the European Container Glass Federation, FEVE, links CO2 reductions to electrification, fuel switching, higher cullet content and more efficient operations. An energy strategy therefore needs to cover the glass’s entire journey, from the furnace through forming to annealing. Assessing each stage in isolation risks simply moving part of the problem a few metres down the line.

Worth knowing: Assessing melting, forming, annealing and cullet reuse together gives a more accurate picture. Looking at individual stages in isolation can simply shift energy consumption from one process to another.

Where emissions arise — and why the hot end is often overlooked

The melting furnace remains the largest contributor to energy use and emissions in glass manufacturing. The European Commission’s 2013 Best Available Techniques Reference Document for the Manufacture of Glass describes melting as a heat-intensive process whose emissions are closely linked to the fuel used. It remains a useful technical reference, but the rest of the plant should not be buried under a vague heading of “auxiliary energy” and then ignored.

The hot end covers molten glass feeding, gob formation, container forming, mould cooling, handling, conveying and transfer into the annealing lehr. An individual section (IS) forming machine may use Blow and Blow (BB), Press and Blow (PB) or Narrow Neck Press and Blow (NNPB) processes. The forming process influences container weight, glass distribution and the precision required from every movement.

Electric drives: These consume energy to operate machine movements, convey products and control downstream equipment.
Compressed air: This places a load on the compressor house. Leaks, unnecessarily high pressure and worn pneumatic components can all push consumption up.
Cooling and ventilation: These maintain the conditions required for moulds, equipment and the working environment.
Annealing: This requires a temperature profile matched to line speed, container size and belt loading.

The problem often starts with cost allocation. Electricity used by the compressor house or cooling circuit may not be allocated to a particular line. Management then has no clear view of the actual kWh or normal cubic metres (Nm³) of compressed air consumed per 1,000 bottles.

The hot end’s carbon footprint cannot therefore be calculated from equipment power ratings alone. Line availability, start-up cullet, product changeover times, reject rates and the amount of glass returned as cullet all belong in the picture. Cullet can be remelted, but the energy already used to melt, form and cool it cannot be recovered.

Watch out: A machine’s power rating alone does not tell you how much energy each saleable product requires. Include the compressor house, cooling, start-up losses and rejects in your measurements.

Changes to melting technology, fuel or energy infrastructure need to align with the long-term capital investment plan. Air leak surveys, drive checks, temperature profile analysis and reject monitoring, however, can begin during normal production. The result should be more than another spreadsheet: it should provide an emissions map and a basis for calculating equipment total cost of ownership.

More efficient machines can cut consumption ahead of major investment

Conventional IS machines use pneumatics for many operating movements. Compressed air is easy to distribute, but producing it consumes electricity. Every leak therefore creates extra work for the compressor house. Pressure conditions, valve condition and component wear also affect the accuracy and repeatability of each movement.

Full-servo control replaces pneumatic movements with electrically controlled axes wherever the process allows. The benefit is not simply a matter of counting servomotors. What matters is which air demands are eliminated, how precisely motion profiles can be set and whether those settings can be reproduced on every cycle. Reducing reliance on pneumatics can therefore benefit energy performance, maintenance and process stability.

This is clear even at the gob-forming stage. The plunger meters the molten glass, the rotating tube controls its flow and the shear mechanism cuts the gob at the right moment. Their synchronisation determines gob weight, length and shape. A small deviation at the start travels downstream into the blank mould, final mould, cooling and product inspection.

A defect that starts with the gob rarely stays there.

More consistent gobs reduce the need for corrective adjustments. During a product changeover, they can shorten the time needed to establish a stable operating window and reduce start-up cullet — provided the recipes and mechanical components have been prepared correctly.

Electricity: Track kWh per 1,000 saleable bottles, not just total consumption per shift.
Air: Compare Nm³ per 1,000 bottles for the same product and line speed, using consistent reference conditions.
Start-up losses: Record rejects after product changeovers or shutdowns.
Stability: Separate normal production from periods when settings are still being fine-tuned.

According to a 2019 article in Glass Worldwide, the full-servo ISX IS machine is designed to deliver energy savings of up to 50% compared with conventional IS technology. That is not an automatic outcome for every installation. Actual savings must be verified against a measured baseline, using the same product, BB, PB or NNPB process, line speed and measurement boundary.

A stable annealing lehr prepares the line for fuel switching

The annealing lehr relieves internal stress through controlled heating and cooling of glass containers. An uneven temperature profile can create differences between the edges and centre of the belt. Operators may then respond by adjusting speed, heat input and cooling. Production becomes less stable, making the underlying causes of defects harder to identify.

The lehr must maintain a stable profile as line speed, product size and belt loading change. Heavier containers or more densely loaded belts impose a different thermal load from lighter products. Without sufficient operating headroom, a change in the production schedule can trigger further adjustments or force a reduction in line output.

The AL 25-03 annealing lehr uses 300 mm-thick insulation. Its heating zones operate at up to 600 °C, cooling zones at up to 450 °C and discharge section at up to 200 °C. These specifications define the conditions for controlling the annealing curve, but do not, on their own, determine consumption on a particular line. Belt width, loading, speed and the temperature of incoming containers also affect energy demand.

An audit should examine temperatures across the belt, control zone response, insulation condition, sealing and integration with the conveyors. Greater cooling capacity and a precise temperature profile provide headroom for changes in product or output — provided they do not mean running continuously at unnecessarily high power.

Preparing for a change in heat source is not just a matter for the melting furnace. The ISX feeder and the annealing lehr can be engineered for natural gas firing, electric heating or hydrogen firing. Hydrogen, however, is not a straightforward like-for-like burner replacement.

Combustion: Check fuel properties, burner suitability and flue gas arrangements.
Safety: Assess leak detection, ventilation, hazardous area classification and operating procedures. This includes reviewing the risks under the applicable national regulations on explosive atmospheres.
Controls and materials: Verify the compatibility of control components, pipework and equipment.
Infrastructure: Include fuel or electricity availability, supply connections and distribution capacity.

Tip: Define energy flexibility in the technical specification from the outset. Being ready does not mean installing every heat source at once. It means allowing the space, capacity and safe upgrade route to add alternatives later.

Audit the hot end before setting investment priorities

The first step should be an independent hot-end audit based on operating data. A list of installed power ratings is not enough. Measurements must capture actual operation and distinguish stable production from start-ups, product changeovers and downtime.

Set the measurement boundary: Include electricity, compressed air, cooling, annealing and other line-related consumption.
Record the context: Link consumption to the product, BB, PB or NNPB process, line speed and measurement period.
Link energy to performance: Track availability, product changeover times, start-up losses, defects and temperature stability.
Normalise the results: Express consumption and losses per 1,000 saleable bottles.

Decisions can be grouped into three tiers. The first covers immediate measures, such as fixing leaks and adjusting controls. The second involves retrofitting a specific part of the process, such as the feeder or a section of the annealing lehr. Only the third involves strategic replacement of a machine or complete furnace, or a change in the plant’s energy strategy.

Every option needs to be assessed on the same basis. Alongside capital expenditure (CAPEX) and operating expenditure (OPEX), the assessment should cover effects on the production schedule, shutdown duration, spare parts, service support risks and the remaining life of connected equipment. Total cost of ownership (TCO) must also account for rejects, maintenance labour, utilities and lost production.

Request a compatibility assessment before placing an order. A new feeder must integrate with the glass supply and line controls. A servo system needs suitable electrical infrastructure, a safety control architecture and sufficient space. The annealing lehr must match the conveyor, line speed, product range and factory layout. Changing the heat source also requires a separate assessment of supply connections and operating requirements.

For a new plant, energy flexibility is determined at the design stage. Space allowances, electrical capacity, utility routes, ventilation, hazardous areas and the control architecture are difficult and expensive to change later. Readiness does not mean installing every option. It means keeping future options open.

Good decisions start with measurement and the right sequence of work

Glass plant decarbonisation will be shaped by melting technology, the energy mix and access to low-carbon fuels. But the hot end offers measures that can be tested before a major capital commitment. More consistent feeding, less reliance on pneumatics, controlled annealing and lower reject rates reduce the energy used for each saleable product.

Measure first. Then prioritise investment.

The practical next step for glass plant management is straightforward. Commission a combined performance baseline covering kWh and Nm³ of compressed air per 1,000 saleable bottles, together with line availability and reject data. Then rank interventions by TCO, production risk and the shutdown window that can realistically be accommodated. The result is a plan that connects CO2 emissions with margins, capacity and the plant’s technical readiness.