Furnace support

CO+ sensor


Experts in combustion technology agree that the spatial CO concentration close to the burner flames is the only suitable parameter to both:


  • Quantify the completeness of the combustion process and
  • Use as control parameter for manual or automatic burner control
  • Control near stoichiometric firing conditions, needed for low NOx production without the risk of too high CO levels and potential excessive refractory corrosion


CelSian’s CO+ sensor is the way to enable continuous monitoring of representative values for both the spatial CO and oxygen concentrations which are prerequisite for adequate burner control.

Moreover, in contrast to current sensors, CelSian’s in-line CO+ sensor involves non-invasive and non-extractive laser technology which protects the sensor from attack by the hot and corrosive flue gases. This safeguards the long-term and reliable operation of the sensor.

Besides energy and CO2 reduction the CO+ sensor is very useful to decrease furnace emissions. We have proven results of 20% decrease in NOx by lowering the oxygen levels in the furnace. SOx can be decreased by lowering the local and total CO levels in the furnace. Our CO+ sensor provides a very good insight in your combustion process with the ability to optimize it, including optimizing NOx and SOx emissions.

Benchmarking of energy usage and CO2 emissions


The first step of our energy reduction approach delivers

  • A determination & global ranking of the energy efficiency of your glass furnace(s)
  • An estimation of the realistic energy savings potential for your furnaces
  • A proposal and explanation of process based and/or technological solutions delivering energy saving


At the moment  our database contains energy and emission data of  more than 450 glass furnaces. You can compare the energy efficiency of your furnaces with the database. We take the following process conditions into account:

  • Cullet fraction
  • Ageing
  • Electric boosting
  • Pull rate


Based on normalized input data our database provides you with an apple to apple comparison. All data will be treated confidentially and anonymously.


Click here to learn more or register.

Energy balance measurements


We use energy balance measurements to determine the energy savings potential of your glass furnaces. Our calculations and conclusions used for implementation in optimized process conditions often result in 4 – 8 % energy reduction. To do this, we need to perform industrial measurements and collect process data. These measurements include the following:


  • Combustion air and flue gas temperature measurements with a suction pyrometer (before and after the regenerator or in the burner ports)
  • Combustion air and flue gas flow measurements (pitot-tube) and calculations from fuel consumption and flue gas compositions
  • Flue gas composition measurements before and after the regenerator (O2, CO2, CO,  H2O)
  • Gas composition measurements at different locations in the combustion space to determine infiltration of air
  • Measurements of batch humidity (including cullet)
  • Outer furnace wall temperature measurements with thermographic camera and thermocouples for calculation of the local energy losses through the walls, crown, and bottom of the furnace
  • Flow and temperature of cooling air/water


The results of these measurements and the collected process data form the necessary foundations to calculate the energy balance of your glass furnaces. From the measured data, accurate information on flue gas volumes, flue gas compositions, flue gas heat losses, heat fluxes through walls, cooling losses, melting reaction enthalpy and glass melt heat contents will be derived. For these calculations the CelSian Energy Balance Model will be used. The different energy flows in the furnace will be quantified and the efficiency of the glass furnace and regenerator will be determined.

The potential energy savings will be qualified and quantified. These measurements are based on potential reduction of energy losses that are a result of:


  • Cold air leakages by open joints, openings or bad sealing
  • Excess of combustion air or incomplete combustion
  • Optimized humidity of the batch
  • Cullet fraction and pull rate
  • Improving emissivity of flames
  • Cleaning of regenerators
  • Improved insulation
  • Cooling water or air


The end result for your glass furnace is a calculation of the most energy efficient situation and the energy saving potential (in TJ).

Energy Balance Model


Our proprietary Energy Balance Model (EBM) software uses actual process data as input to calculate the current energy balance of your glass furnace. Many of our customers had used a wide variety of different methods tracking the energy usage of their furnace fleet, with EBM you have all relevant data of your entire fleet instantly available. Using EBM has the following benefits:

  1. Visualization of the current energy flows around the melting tank and the regenerators;
  2. Visualization of the main energy carriers (fuel, preheated air, electric boosting);
  3. Trending of achievable and attained energy reductions with savings in MJ/ton and EUR/day
  4. Scenario calculator for modified process conditions. This engine will recalculate a hypothetical energy balance based on modified process settings and/or modified batch compositions.

EBM has proven to be a very powerful tool to compare multiple furnaces and reduce energy usage.

Software Simulation


With our superior Computational Fluid Dynamics (CFD) simulation software (GTM-X), we are able to optimize furnace designs, maximize the furnace pull, minimize emissions and solve operational challenges of your furnace. As furnaces are running more and more at the edges of their capabilities, sophisticated models are needed to predict a stable and profitable operation during the lifetime of the furnace. We validate our models through lab analyses or process measurements in your furnace.

We model all kinds of furnaces like airfired regenerative, oxyfuel, full-electric and everything in between. Firing on CO2 neutral fuels like hydrogen and biogases is also possible.


Already during the design phase of the furnace, emissions can be taken into account. We have several validated cases where we have lowered emissions by making design changes. We have very good models on evaporating species like sodium, sulphur and boron. These emissions can all be optimized by our software during the furnace design phase.

During the furnace campaign it is also possible to model the furnace to see if emissions can be optimized. For instance, sometimes unstable combustion behavior is observed, resulting in increased emissions. CelSian’s CFD models show possible measures to get your furnace stable again.


We can further decrease energy consumption and CO2 emissions by making a detailed CFD model of your furnace. With this model we make variances in design, process settings or batch/glass composition to see what the effect is on energy consumption. To reduce CO2 emissions even further a feasibility study on electrification of your furnace can be performed with our software.


Our software is ready for future challenges with sophisticated batch flow, combustion and boosting models. Proper modelling of expected shear stresses, temperature profiles and flow patterns prevent severe and costly production problems during the lifetime of the furnace.


The model can also be used to create a MPC (Model Predictive Control) to control your furnace on the most critical aspects like crown, bottom and glass temperatures, excess oxygen and optimal distribution of gas and electricity.  Energy savings of a few percent are normally achievable.

Emission optimization


Our specialists can optimize emissions levels by tuning the furnace operating settings during a plant visit. Firstly we measure flue gas compositions at several positions in and around the furnace to determine the baseline. With CelSian’s thorough knowledge about process settings leading to emissions we can solve a lot of emissions problems by just changing some operating parameters without compromising glass quality. During the change we perform the same measurements to show the improvement. Furthermore we can give advice and additional support on prevention and emission control.

Process measurements


With our professional equipment CelSian can measure all kinds of process related issues like carry-over and evaporation of species from the glass melt. In combination with temperature measurements of the internal refractories the potency for corrosion in the furnace can be determined. Flue gas compositions in the furnace are measured to determine the combustion effectiveness locally.

These measurements can be very affected when severe corrosion issues are faced.

With the report of these measurements you will have a clear view how to make improvements in your furnace settings or furnace design to enhance furnace lifetime.

CelSian has performed many process measurements over the last 30 years on industrial carry-over and evaporation. Every glass manufacturer has to face the negative effects that carry-over of batch particles and/or evaporation of volatile (alkali) species can bring. Carry-over material (e.g. sand, dolomite, limestone, fine cullet) that is entrained in the combustion gases will interact with the refractory material of the superstructure, burner ports and top layers of the checker work in the regenerator to cause corrosion. Volatile species (e.g. NaOH) that evaporate from the glass melt/batch blanket also react with the superstructure of the furnace and cause corrosion of (for example) the crown. Furthermore, these volatile species (e.g. sodium, potassium) react with the sulfur during cooling of the flue gas to form salts that can both corrode the refractory materials used in the regenerator and block the flow of air/flue gas through the regenerator or flue gas channel. These effects reduce the lifetime of a furnace dramatically.


Carry-over of raw materials and powder depends among other things on:

  • Applied raw materials (e.g. grain-size distribution and decrepitating dolomite/limestone);
  • Doghouse construction and position of the doghouse;
  • Type of charging equipment (pushers, screw-feeders etc);
  • Combustion gas velocities;
  • Batch humidity;
  • Burner angle.


Evaporation rates from the glass melt and batch blanket depends among other things on:

  • Applied raw materials (e.g. chlorine can promote additional evaporation);
  • Combustion gas velocities;
  • Burner angle;
  • High glass melt surface temperatures;
  • High CO concentrations near batch blanket and/or glass melt.


CelSian will investigate the current evaporation and carry-over rates that are taking place inside the furnace and give advice on how to minimize those. Also critical locations where refractory corrosion is more likely to take place will be pointed out. If a new batch formulation is to be tested in the furnace process, CelSian can investigate the impact of the new composition on carry-over and evaporation rates.


Some examples for measuring locations can be:

  • Via peepholes in the combustion space;
  • In the top and bottom of the regenerator;
  • In the stack/flue gas channels;
  • Before and after preheating systems.


At these locations the following parameters can be measured:

  • The carry-over rates (concentrations of e.g. Si, Ca, Mg);
  • The evaporation rates (concentrations of e.g. Na, K, S);
  • The chloride (Cl) and/or fluoride (F) concentrations;
  • The dust composition (concentrations of e.g. MgO, CaO, SiO2, Na2O, Al2O3);
  • The gaseous components (concentrations of O2, CO2, CO, NOx, SOx);
  • Inner wall temperatures (to derive critical corrosion temperatures).


On the customer’s request it is also possible to perform thermodynamic calculations (based on the measured concentrations) to predict reaction mechanisms between flue gases and refractory materials.

Based on the results, advices on how to minimize carry-over and/or evaporation rates, as well as other possible process optimization steps will be provided in a written CelSian report.

Furnace inspections


One of the most important aspects of increasing lifetime of a furnace is maintaining the refractories of the furnace at a high level. CelSian has a clear vision how and when to inspect your furnace throughout the lifetime to prevent sudden process interruptions, like glass leakage, to happen. Furthermore refractory issues or corrosion problems will be identified in an early stage resulting in better (and cheaper) planning of proper maintenance ahead. CelSian offers three kinds of inspection:

  • A visual inspection of the exterior of your furnace including approximately 250 temperature measurements of the refractories. These inspections are normally performed each quarter when the furnace is in its critical last phase of the lifetime.
  • An annual inspection including the above extended by pictures of the internal refractories of the furnace. Doing this every year gives a very good insight in refractory wear and corrosion.
  • And a full inspection including the above and extended by measurements of the flue gas in the furnace, carry over, evaporation (process measurements) and energy. Normally we perform this kind of inspection once each 5 to 7 years (depending on furnace and glass type) starting with a zero measurement just after start-up of the furnace. This inspection determines thermal efficiencies, potencies for corrosion and risk on refractory wear to fully understand the furnace set-up.


All inspections are including a full report concluded with clear recommendations how to improve the furnace in terms of furnace lifetime, energy consumption and emissions. Support to implement the improvements can be supplied by CelSian as well.


The table below indicatively shows a scheme for inspections. The exact timing depends e.g. on furnace type, glass type and operational settings/performance of the furnace. This example is for an End Port Fired Container glass furnace.

The full inspection in year 0 can also be used as an independent Site Acceptance Test (SAT) for the glass furnace supplier.


Quarterly inspections typically start at the moment when the furnace is reaching its critical lifetime. CelSian uses a scorecard whereby all essential parts of the furnace will be evaluated and rated. This will result in a total final score. Depending on this final score and detailed discussions with the customer, the condition of the furnace will be identified as critical or not.


Annual inspection

The annual inspection is performed to obtain insight in more gradually progressing refractory wear issues at the interior of the furnace. The weak spots of the furnace will be identified by making pictures/videos with an endoscope and comparing these with the images taken the previous year. In this way, accurate and precise recommendations can be given on locations where a repair has to be carried out and at what time interval. By doing this inspection every year a track record is created and this gives a very good insight in degradation of the furnace.


During an annual inspection the following activities will be carried out:

  • The quarterly inspection;
  • Endoscopic pictures of the interior of the furnace (internal refractories);
  • Temperatures of the internal refractories (superstructure, crown, burner port).


The pictures and measurements will be reported and discussed with the people involved. This will include recommendations on short and long terms necessary furnace repairs to ensure the furnace lifetime.


In case corrosion issues are identified the inspection can be extended by carry-over and/or evaporation measurements (see full inspection).


Full inspection

During the full inspection the furnace will be inspected thoroughly on refractory, emissions and process parameters. This inspection should take place a few times during the furnace’s lifetime to ensure that process parameters are optimal to achieve the expected lifetime with low energy costs and emission levels.

Carry-over and evaporation may lead to severe corrosion of refractories and/or increased emissions while unexpected energy leaks will lead to increased operational costs and CO2 emissions. Therefore it is important to fully understand the operations of the furnace to obtain the most optimal process settings.

The first full inspection should take place a few weeks after the startup of the furnace in order to obtain a good baseline and to ensure that the process settings are correct right from the start. The full inspection should be repeated after a few years to ensure a healthy operation.


The inspection will include:

  • The annual inspection;
  • Carry-over measurements;
  • Flue gas composition in the furnace (evaporation);
  • Thermographic pictures of the external refractories;
  • Energy balance model.


The energy balance model enables to show all the energy flows (energy input, heat losses/leaks, combustion efficiency and regenerator efficiency) in the furnace. The inspection comes with a report with recommendations to optimize the furnace on lifetime (corrosion of refractories), emissions and energy (CO2 emissions).  CelSian also supports with implementations of the improvements.