Over ten years ago Xella started to introduce a professional energy management system at its factories in order to identify and implement energy saving measures. Despite the effort involved in organization and logistics, this has been a worthwhile undertaking. Even considering the advances that have already been made, further potential for savings is consistently being uncovered. Making just small changes can often have a large impact.
Although we have managed to reduce direct energy consumption in 2013 by 13.74 percent compared to 2011, production at the building material business unit decreased by only 7.9 percent. This was achieved through a range of individual measures such as more efficient use of steam and better heat recovery during the production process. Investments made in energy-efficient machines and plant also paid off in this respect.
Eastern Europe in focus
The new European Energy Efficiency Directive adopted by the European Parliament stipulates binding energy saving targets for energy consumers in the Member States by 2020 and requires large corporations – including Xella – to conduct energy audits every four years. In other words, they must carry out a review of their energy status. This requirement is not yet binding because it must still be transposed into national legislation. In the meantime however, Xella has been performing its own audits. Initially the western European factories were inspected and their energy use optimized. Now the focus has shifted to Eastern Europe. Special energy assessment programs have been developed so that the sites can be subjected to a standardized energy efficiency audit. The result of this assessment – the energy status – is presented for each factory in the form of the Xella Energy Pass, specifically developed in-house for this purpose.
The modernized Xella factories include the Polish autoclaved aerated concrete factory in Milicz, where a new steam generating plant has been installed. During the course of its replacement it made sense to convert the plant from a coal to a natural gas-fired system. In addition to substantially lower fuel costs, natural gas is also much more efficient and therefore emits significantly less CO2. The results of this investment are clear to see: It has been possible to reduce the specific energy consumption of the factory by 66 percent and the CO2 emissions by as much as 80 percent. This saves the equivalent of some 10,000 tons of CO2 annually.
A roof that saves energy
Lightweight roofs also play their part in saving energy at Xella. Arched roofs have been installed at our Alzenau and Rotenburg sites following a suggestion by an employee. These roofs enable some 3,000 tons of demolished aerated concrete waste to be stored in dry conditions, protected from rain and snow. But their open construction brings even bigger benefits by allowing the sun and wind to reduce the residual moisture in the aerated concrete granulate. Our dryers now consume some 70 kilowatt-hours less energy per ton. This reduces costs by around five percent and protects the environment through lower CO2 emissions. It has also been possible to increase granulate production as a result of the dry raw material.
Multiple use of steam
Ytong and Silka blocks are hardened at temperatures of 190 degrees Celsius in hardening chambers (autoclaves). The steam necessary for this requires a large amount of energy to generate and is used multiple times by being directly channeled from autoclave to autoclave or temporarily stored for use as required. Furthermore, waste heat from the autoclaves is routed through heat exchangers and employed to heat the process water, thereby saving energy. If its energy level is no longer sufficient for production, the waste heat is used for indoor heating purposes. This allows us to save some three million kilowatt-hours of primary energy annually in Germany alone – equivalent to heating 100 single-family homes for one year. The reduced consumption of natural gas saves approximately 600 tons of CO2 emissions.
Feasibility of generating energy in-house
Xella is currently assessing the feasibility of generating energy in-house at four sites. However, the viability of this depends upon four different factors – including the cost of energy. We are completing calculations among others on the installation of three combined heat and power plants (CHP) and the feasibility study for the factory at Calbe is at a relatively advanced stage. There, the existing heat supply could be effectively supplemented by a CHP plant. The simultaneous generation of heat and electricity is particularly productive and environmentally friendly because of the higher overall efficiency achieved. Depending upon the size of the plant the efficiency of generating electricity in this way lies between 25 and 50 percent. By utilizing the waste heat close to where it is generated, combined heat and power plants can achieve savings in primary energy of up to 40 percent. We are also studying the feasibility of generating electricity using a micro gas turbine at a fourth site.