Decarbonise tile production with semi-wet granulation

Submitted through the COP31 Sustainable Transformation Awards · SKD Türkiye (WBCSD Global Network Partner)

The company is a porcelain and ceramic tile manufacturer with more than 1,000 employees and hosts the industrial pilot for this initiative at its Çanakkale operations.

Porcelain tile bodies are conventionally prepared by wet milling followed by spray drying, and that route concentrates the plant's resource use in a single step. Wet milling and spray drying together account for 34 per cent of total plant energy consumption and 95 per cent of water use.

The physics behind that is straightforward. Slip leaving the wet mills carries 35 to 40 per cent water, which must be evaporated in a spray dryer using gas at 550 °C to obtain granulated powder at 5 to 5.5 per cent moisture. That evaporation is responsible for 32 per cent of direct CO2 emissions.

The same route also constrains circularity. Wet milling makes it hard to return process waste, rheologically difficult raw materials and secondary raw materials to the body at high ratios, so recipes remain dependent on primary minerals. Among them is feldspar, classified as a critical raw material under European Union critical raw materials legislation, which leaves the sector exposed on supply as well as on energy.

The initiative, INNOVATILE, began in 2024 with co-funding from the European Union Interreg NEXT MED programme and is at industrial pilot stage inside the company. It builds on earlier conceptual and methodological validation of semi-wet granule preparation carried out between 2014 and 2016 with national research council support.

The company frames the work against four of the Sustainable Development Goals, covering clean energy, industry and infrastructure, responsible consumption and production, and climate action. Corporate disclosure follows the ISSB standards (IFRS S1-S2) and TCFD-aligned reporting.

Location of the initiative: Çanakkale, Türkiye, as the industrial pilot site of a consortium spanning Spain, Türkiye, Italy, Cyprus, Tunisia and Egypt

The technology changes how the body is prepared rather than what comes out of the kiln: not all raw materials are sent through wet milling.

Between 15 and 20 per cent of the raw materials, selected to include secondary raw materials and alternative fluxing minerals, are dry milled to a micronised powder with no water added. The wet-milled slip and the dry-milled micronised powder are then brought together in a high-speed mixer operating at 1,200 to 3,000 rpm until the mixture is homogeneous.

The first effect is thermal. Solids content of the slip fed to the spray dryer rises from 63 per cent to between 66 and 68.5 per cent in laboratory work, and to 69 per cent in the process specification, with slip density moving from 1,650 g/L to 1,750 g/L and above. Less water entering the dryer means less evaporation, and therefore less gas burned at 550 °C.

The second effect is on the recipe. Dry milling tolerates materials that wet milling handles poorly, which opens the body to ceramic waste, glass cullet and industrial by-products in place of feldspar and clay. A secondary raw material inventory catalogues the industrial wastes available as substitutes, and a parallel search identifies local and alternative minerals able to form the fluxing phase that alkaline feldspar currently provides.

Candidate materials are characterised before use: chemical composition by X-ray fluorescence, mineralogy by X-ray diffraction, particle size distribution and thermal behaviour, followed by body compatibility and equivalence testing that fixes the integration ratio for each material and by an assessment of how each behaves under dry milling and micronisation.

Within the consortium the company is positioned as the idea owner, end user and pilot operator, responsible for integrating laboratory outputs into real production lines.

Figure 1: Body preparation compared: in the semi-wet route 15 to 20 per cent of the raw materials are dry milled and then homogenised with the wet-milled slip in a high-speed mixer, which raises solids content and lowers the evaporation load at the spray dryer.

Figure 2: Comparative life cycle inventory per tonne of dried ceramic powder, conventional process against semi-wet process, on a logarithmic scale.

Sustainability Impact

Climate

The initiative targets Scope 1 emissions from natural gas combustion in the spray dryer, which is the point where the water carried by the slip is evaporated.

Comparative life cycle inventory work, carried out with the CML-IA baseline method on the basis of 1 tonne of dried ceramic powder, uses 2023 conventional processing as the baseline: slip at 1,650 g/L density and 63 to 64 per cent solids. Against that baseline the semi-wet route gives spray dryer natural gas consumption of 27.92 kg against 36.91 kg, a fall of 24.36 per cent; direct CO2 emissions of 76.36 kg against 101.54 kg, a fall of 24.80 per cent; dryer air demand of 2,095.02 kg against 2,763.68 kg, a fall of 24.20 per cent; released water vapour of 504.75 kg against 603.64 kg, a fall of 16.38 per cent; and slip mass entering the dryer of 1,418.69 kg against 1,493.78 kg, a fall of 5.02 per cent.

Because the initiative is at pilot stage, the wider figures are targets rather than achieved results. The project targets a fall of 30 to 35 per cent in total process energy and natural gas consumption against the conventional wet milling and atomisation system, and a fall of 30 to 35 per cent in direct stack CO2 emissions and total greenhouse gas footprint. The award submission also records commitments of more than 25 per cent for Scope 1 CO2 reduction and more than 20 per cent energy efficiency at the spray dryer, attributed to the lower evaporation load.

Environmental measurement is directed by an Italian university partner using life cycle assessment and carbon footprint calculation aligned with the GHG Protocol. Five metrics are tracked across the 36-month project timetable, from laboratory testing through to pilot production, with regular monitoring against the secondary raw material inventory and reporting to European Union project standards.

Nature

The resource case rests on displacing primary minerals with secondary ones. Feldspar, an alkaline flux classified as critical by the European Union, is the specific target: the project aims for a reduction of more than 40 per cent in feldspar consumption by substituting process waste and glass cullet, with alternative fluxing minerals screened to cover the remainder.

Fresh water and primary raw material consumption in the process are targeted to fall by 10 to 20 per cent, and water saving against the conventional process is stated as more than 25 per cent, reflecting the smaller volume of water that has to be introduced and then evaporated.

The systemic effect is on the value chain rather than on a single plant. The conventional chain runs linearly from feldspar and clay extraction through production to consumption; using by-products from the glass and ceramic industries as raw material avoids virgin extraction upstream and lowers waste disposal volumes and costs downstream.

The use rate of ceramic waste and secondary raw materials is itself one of the tracked metrics, so substitution is monitored as an outcome rather than assumed from recipe design.

Social

The initiative is delivered as a multi-country ecosystem rather than a single-site upgrade, which shapes its social contribution. Six Mediterranean countries take part, and knowledge is refined across an international network instead of remaining inside one organisation.

A regional technopark partner carries responsibility for transferring academic knowledge into industry in its region, which builds local technical capacity alongside the plant work and makes Çanakkale a reference point for international research and development projects.

The secondary raw material inventory and the green-collar employment goals developed within the project are intended as lasting shared value for local communities as well as for the wider industry.

Business Impact

Benefits

The direct commercial benefit is lower natural gas consumption at the single most gas-intensive step in body preparation, together with lower freshwater use. Because spray drying accounts for 34 per cent of plant energy and 95 per cent of water, a reduction of roughly a quarter in gas per tonne of powder moves a material share of plant operating cost.

Supply risk falls alongside cost. Reducing feldspar consumption cuts exposure to a mineral formally classified as critical by the European Union, and using ceramic waste, glass cullet and industrial by-products as inputs converts a disposal cost into a raw material.

Product quality is preserved rather than traded away, which is what makes the commercial case viable. Laboratory tablets pressed from semi-wet slip and fired at 1,180 °C gave firing shrinkage of 7.96 to 8.14 per cent and water absorption of 0.04 to 0.09 per cent, confirmed as fully meeting standard porcelain tile criteria.

The funding structure limits the company's own exposure: 89 per cent of the EUR 2.8 million total budget is secured by the European Union under the Interreg NEXT MED programme. A corporate policy of allocating 2 per cent of total revenue to research and development is intended to keep the method embedded in standard production processes after the project period ends.

Costs

The cost base is the capital and process change needed to run two milling routes in parallel: a dry milling and micronisation line for part of the raw material mix, and a high-speed mixer operating at 1,200 to 3,000 rpm to homogenise the dry powder with the wet-milled slip.

Process control effort rises. Raising solids content while keeping the slip pumpable required density, viscosity, sieve analysis and deflocculant optimisation work, and blend ratios between wet and dry fractions had to be tested across a range from 85 to 15 per cent. That control burden persists in operation rather than ending with commissioning.

Input variability is a dependency. Secondary raw materials and alternative fluxes have to be characterised for composition, mineralogy, particle size and thermal behaviour, and their dry millability assessed, before they can enter the body, which means a continuing analytical cost tied to supply.

Costs are contained by the funding structure and by the sequencing. With 89 per cent of the EUR 2.8 million budget met by European Union co-funding, the company's share is limited to the pilot integration work, and laboratory and pre-assessment stages were completed with partner laboratories before industrial commitment.

The main open cost item is scale-up. Results to date are laboratory and pre-assessment figures expressed per tonne of dried powder over a 36-month project window; converting them into permanent plant-level performance is the work still in progress.

Impact Beyond Sustainability And Business

Co-benefits

The secondary raw material inventory built with the partner university is reusable beyond the plant that created it, because it describes candidate industrial wastes against ceramic body requirements rather than against one recipe.

Transfer routes are built into the delivery model. Once validated at pilot scale, the technology is intended to reach other countries and producers through the partner technopark and partner universities, so the result is designed for replication rather than retrofitted for it.

Glass and ceramic producers upstream of the tile plant also benefit, since by-products that would carry a disposal cost acquire a use, which shifts stakeholder behaviour towards circular practice across more than one industry.

Potential side-effects

The initiative is not complete. Verified results exist at laboratory and pre-assessment level per tonne of dried powder; the process energy, emission and raw material figures quoted as project outcomes are targets for the 36-month programme, not achieved plant performance, and should be read as such.

Higher solids content makes the slip harder to handle. Moving from 62.5 to 64 per cent solids in the conventional slip to 66 to 68.5 per cent in the semi-wet slip, with density rising from 1.63 to 1.65 g/cm³ up to 1.73 to 1.75 g/cm³, brings rheological risk that has to be managed with deflocculant and viscosity control rather than avoided.

Adding a dry milling route introduces a dry powder handling operation where none existed, which changes dust containment and occupational exposure requirements at the body preparation stage.

Substituting secondary raw materials for a controlled primary mineral also transfers variability into the body. Colour and thermal behaviour depend on the incoming waste, so equivalence testing has to be repeated when the supply changes rather than performed once.

Typical Business Profile

The model suits porcelain and ceramic tile manufacturers that prepare bodies by wet milling and spray drying, since the saving comes from reducing the evaporation load at the dryer and only exists where that step is present.

It fits producers with an in-house research and development capability able to characterise materials and reformulate bodies, because the recipe work, not the equipment, determines how far substitution can go.

Access to ceramic waste, glass cullet and industrial by-products within economic transport distance is a practical precondition, which is why Mediterranean basin producers are the first target group before wider application to porcelain tile plants elsewhere.

Approach

1. Quantify where energy and water go in body preparation: establish the share of plant energy and water consumed by wet milling and spray drying, and the slip water content and dryer gas temperature behind it, so that the evaporation load is identified as the target rather than the kiln.

2. Build a secondary raw material inventory: identify industrial wastes and secondary materials that could substitute for raw materials in tile bodies and record them as a catalogue against body requirements rather than as an ad hoc list of available wastes.

3. Screen alternative fluxing minerals: search local and alternative mineral sources capable of forming a fluxing phase within the body, specifically to lower the proportion of alkaline feldspar classified as critical.

4. Characterise every candidate material before recipe work: analyse chemical composition by X-ray fluorescence, mineralogy by X-ray diffraction, particle size distribution and thermal behaviour in the laboratory, so that integration decisions rest on measured properties.

5. Split the raw materials into wet and dry milling groups: assign 15 to 20 per cent of the mix, including the secondary raw materials and alternative fluxes, to dry milling, complete the dry milling to the target particle size distribution, and design semi-wet recipes around that split.

6. Optimise the combined slip: blend wet-milled slip and dry-milled micronised powder at ratios across an 85 to 15 per cent range in a high-speed mixer at 1,200 to 3,000 rpm, and run density, viscosity, sieve analysis and deflocculant optimisation to raise solids content while preserving flow.

7. Press and fire laboratory tablets under industrial conditions: form tablets from the semi-wet slip and fire them at 1,180 °C, then measure water absorption, firing shrinkage and surface colour to confirm compliance with standard porcelain tile criteria.

8. Cross-check results independently and run a comparative life cycle assessment: verify slip rheology and physico-chemical test results against independent laboratory analysis, then compare conventional and semi-wet processes with the CML-IA baseline method based on 1 tonne of dried powder.

9. Move to industrial pilot and monitor against project standards: integrate the validated laboratory output into the production line, track the five agreed metrics through the 36-month timetable, and report against the secondary raw material inventory to European Union project reporting standards.

Stakeholders Involved

• Project leads: The company research and development centre coordinates the initiative and carries out industrial applicability validation. Within the consortium the company holds the combined role of idea owner, end user and pilot operator, which makes it accountable for moving laboratory outputs onto real production lines rather than only for hosting trials. Senior management owns the technological step directly, as part of the corporate sustainability vision and its carbon neutral objectives, and the initiative sits at the centre of the company's research and development strategy rather than at its periphery.

• Company functions: Technology design sits with the company's own research and development centre, which originated the semi-wet preparation concept. Pilot testing on the production site, optimisation decisions and scale-up are carried out by the company itself rather than by partners, so process decisions stay with the team that operates the line. Laboratory work on raw material grouping, recipe design, dry milling, slip optimisation, tablet pressing, firing and fired-product performance analysis runs through the same research and development function, which keeps recipe development and plant integration on one decision path.

• Main providers: Academic know-how for validating the industrial prototype is directed by a Spanish university partner. Environmental impact analysis and the feedback loops around it are managed with scientific metrics by an Italian university partner. Laboratory and pre-assessment work supporting technical and environmental feasibility was carried out in the company's own laboratories together with a Spanish ceramic technology institute. A regional technopark partner takes on regional knowledge transfer and the movement of academic knowledge into industry. Earlier conceptual and methodological validation of semi-wet granule preparation, between 2014 and 2016, was supported by the national research council.

• Other: The consortium spans six Mediterranean countries (Spain, Türkiye, Italy, Cyprus, Tunisia and Egypt) and includes a Cypriot partner organisation, a Tunisian university and an Egyptian development agency alongside the technical partners. Co-funding comes from the European Union through the Interreg NEXT MED programme, which covers 89 per cent of the EUR 2.8 million budget and provides the medium to long term financial basis for the work. The collaboration is structured so that findings are refined across the international network rather than held by one institution, with the secondary raw material inventory and green-collar employment goals as the shared outputs.

Key Parameters To Consider

The initiative is at industrial pilot stage within a 36-month project timetable that runs from laboratory testing to pilot production. Figures should be read against that stage: laboratory and pre-assessment results are measured, programme-level energy, emission and raw material figures are targets.

The comparison basis matters. Results are expressed per 1 tonne of dried ceramic powder against a 2023 baseline of conventional processing at 1,650 g/L slip density and 63 to 64 per cent solids, using the CML-IA baseline method, so they describe body preparation and not the full tile life cycle.

The technical envelope is set by rheology. Solids content can be raised from 63 per cent to the 66 to 68.5 per cent range, and to 69 per cent in the process specification, only as far as viscosity and flow remain manageable with deflocculant optimisation.

Financial continuity rests on two structures: 89 per cent European Union co-funding of the EUR 2.8 million budget during the project, and a corporate policy of allocating 2 per cent of total revenue to research and development to carry the method into standard production afterwards.

Implementation And Operations Tips

Attack the evaporation load, not the dryer. The gain comes from putting less water into the slip in the first place, which is why the solids content of the feed is the controlling variable rather than dryer efficiency.

Use the dry milling branch to solve two problems at once. It lowers the water in the mix and simultaneously admits materials that wet milling handles poorly, so the energy case and the circularity case are delivered by the same change rather than by two separate projects.

Prove fired properties before claiming the process. Water absorption and firing shrinkage measured on tablets fired under industrial conditions are what establish that the substitution has not been paid for in product quality.

Build the material inventory before the recipe. Characterising candidate wastes for composition, mineralogy, particle size, thermal behaviour and dry milling ability first avoids reformulating around a material that cannot be milled dry.

Cross-check the analysis externally. Rheology and physico-chemical results verified against independent laboratory analysis carry more weight with both partners and regulators than single-laboratory data, particularly in a multi-country project.

Separate targets from results in reporting. Where a programme is mid-delivery, stating measured per-tonne inventory results alongside clearly labelled programme targets avoids overstating performance that has not yet been demonstrated at plant scale.

External Links

• TSRS-aligned sustainability report 2024

• Group sustainability report 2024

• INNOVATILE project page on Interreg NEXT MED