Replacing gas with a hot water heating system for a ceramic tile manufacturing plant

A step towards a greener process

A ceramic tile manufacturer in Spain enlisted the expert engineering services of Operational to help them reduce their greenhouse gas emissions and energy bills. Here’s how our waste energy recovery system saves the site €720,000 in gas per year and reduces its annual carbon footprint by 3,300 tonnes.

Capturing waste energy

The client had already installed a ductwork system that allows a proportion of hot gases from two kilns to heat spray dryers in an adjacent building. However, the manufacturer needed assistance to identify what else could be done with the remaining waste energy. After surveying the entire factory process, we planned a solution whereby even more waste energy could be recovered from all five of the kilns and re-used to heat the tile dryers

Replacing reliance on gas

To prepare tiles for firing in the kilns they need to be dried after forming. Tiles require perfect conditions whilst they are drying to avoid cracking or other damage. This takes place in semi-continuous horizontal tile dryers each fitted with 14 recirculation zones and gas burners – operating within specific temperature profiles to ensure tile quality and integrity.

Quality, precision and an understanding of the site’s unique manufacturing processes were essential when calculating the amount of energy that could potentially be recovered.

A closed-loop medium pressure industrial hot water system

Operational designed and installed a closed-loop, medium pressure hot water system that recovers energy from the kilns exhaust air. The hot water is delivered to 30 new heat exchangers fitted to a number of the dryers recirculation circuits. This system enables recirculated air to be heated by hot water, replacing the dryer’s reliance on gas burners.

Each of the five kiln exhausts are fitted with robust and cleanable heat exchangers. A bypass damper system was also incorporated into the design to prevent production issues in the event of any faults occurring. The dryer air temperatures are lifted from 90 C up to 120 C by the medium pressure hot water system which significantly reduces the load on the gas burners during heating of the recirculated drying air. These exchangers were tailor-made to fit inside the existing recirculation ducts due to space restrictions.


Return on investment:

  • Energy recovered from arc furnaces & reused in boilers = 18,000 megawatt-hour (MWh) per year of natural gas.
  •  Reduction in CO2 emissions of ≈3700 tonnes/year & savings** = €360,000 per year
  • Total savings = €720,000 per year
  • Return on investment = Based on gas price of €40/MWh*, CO2 savings & 25% grant = 1.5 years

Notes: *Gas price used = €40/MWh. Actual @ 24/02/22 and futures (2023) price = €120 and €60/MWh respectively – source ref; **Carbon price@ 24/02/22 = €95/T & savings/MWh nat. gas = €17.4/MWh – ref. excluded from savings; All prices & ROI best estimates but fluctuating.


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