improved HEAt Recovery in clay roof Tiles an bricks production

PROJECT DESCRIPTION

BACKGROUND

The terracotta building materials industry uses mainly natural gas to dry and fire clay to make roof tiles and bricks. The gas combustion in dryers and kilns is responsible for 70% of the sectors CO2 emissions. The sector also uses large quantities of water for humidifying the clay and is responsible for greenhouse gas emissions of sulphur, chlorine and fluorine. The volatile compounds may be present in certain types of clay and can be freed into the environment depending on the type of firing.

In a typical modernclay tile manufacturing plant, equipped with classical recovery systems: 90% of the thermal consumption of the dryer is lost in fumes and returned into the atmosphere; 20% of the warm air recovered in the kilns during cooling of the products is used in the dryer, or the pre-oven; and 45% of the thermal consumption of the kiln is lost in fumes and returns into the atmosphere. The recovery of these losses is one of the main areas in which energy efficiencies in the terracotta manufacturing process can be achieved.

OBJECTIVES

The projects overall objective was to demonstrate the feasibility of a thermal recovery system for the clay and roof tile industry that combines a low temperature and corrosion resistant heat exchanger (on the kiln fumes) and an industrial ammonia heat pump (on the dryer fumes). The pilot system would be installed in a roof tile factory in south-west France.

The recovered heat would pre-heat the air inflow into the dryer. The water condensed by the heat pump would be reused to moisturise clay for the shaping of the products in place of the use of more water. The heat exchanger on the kiln fumes would clean these fumes from their volatile pollutants (fluorine, sulphur, chlorine) by producing acid concentrates that would be neutralised.

The project aimed to show that a significant part of the thermal losses of a clay brick or roof tile production unit could be recovered and reused in the process; an that the new recovery system could be retrofitted easily and safely into an existing clay brick or roof tile factory.

Other specific goals included:

Recovery of water by condensing steam for reuse in the clay process, thereby significantly reducing water consumption;

Purification of the kiln fumesof volatile pollutants; and

A new standard for clay brick and roof tile technology.

Expected results: For the demonstration production unit, the target was to reduce by around 25% the consumption of natural gas and the associated CO2 emissions, and by 90% the consumption of water, compared to 2011 figures under normal activity.

Specific estimates were:

A reduction of natural gas consumption by 17 GWh HCV/yr (- 27%);

An increase in power consumption by + 3.7 GWh/yr (to operate the heat pump, the ventilators and the heat transfer fluid circuit);

A reduction of direct CO2 emissions by 3 170 tonnes/yr (- 23%);

An increase of indirect CO2 emissions by + 210 tonnes/yr, taking into account the French emissions factor for electricity; and

A reduction in water consumption by 10 000 m3/yr (- 90%).

The system would also clean the fumes with data measured during the project and an additional benefit will be the ease of installation of the system to existing factories.

In order to disseminate its results, the beneficiary would prepare a user guide, a pre-dimensioning tool and a test bench to measure how the fumes will be cleaned by the heat exchanger.

RESULTS

Due to corrosion problems that destroyed the HEART equipment, the project could not achieve the foreseen objectives and did not lead to sustainable direct benefits. Still, it has innovation value and could lead to environmental and socio-economic benefits in the future.