The title ‘cement plant with the lowest emissions in the world’ is not awarded every day. However, Kirchdorfer Zement spares no effort in the search for the best environmental protection. Here, it presents the development of emissions abatement systems at the plant, with a focus on the recent commissioning of a DeCONOx system from Scheuch GmbH.
Cement has been produced in Kirchdorf Zement for 127 years. For many decades the management has taken numerous steps to reduce the plant’s impact on the environment to a minimum. One of the reasons in the early days was its immediate proximity to the city centre of Kirchdorf an der Krems, which is just 600m away.
Over the years, this careful and considerate approach to the environment and its resources became second-nature. A summary of major milestones is shown overleaf. In 2010 the management and the owner announced a new vision for the Kirchdorfer Zementwerk, namely to become the most resource-efficient cement plant with the lowest emissions and highest safety standards in Europe.
DeCONOx system launch
Now, with the help of a sophisticated and award-winning DeCONOx installation from Scheuch GmbH, a globally-unique facility has been installed to further purify the plant’s exhaust and enhance the use of waste heat. The system uses the energy from exhaust air to break down NOx and volatile organic compounds. The residual energy is then recycled in the production process and de-coupled through heat recovery. Thus, waste heat of about 20GWh/yr can be fed into the district heating grid of EnergieAG Wärme Upper Austria to supply more than 1000 households in Kirchdorf and the surrounding area.
The facility was officially opened on 29 September 2016. At the event Upper Austria’s Economic Secretary Dr Michael Strugl, said, “With this pioneering facility for air purification and heat recovery, the Kirchdorfer Zementwerk clearly reflects the new focus of Upper Austrian energy policy. With this new facility the Kirchdorfer Zementwerk implements innovative technology in order to protect resources and the environment. I can only congratulate the company on the realisation of a cement works with the lowest emissions in the world.” Managing director Mag Erich Frommwald said, “Over the past 15 years we have already invested more than Euro23m in environmental protection. The DeCONOx facility is the highlight in a series of measures.”
The DeCONOx system
‘DeCONOx’ stands for the reduction of (De) CO (carbon monoxide) and NOx (nitrogen oxide). The process combines regenerative thermal oxidation (RTO) with low dust selective catalytic reduction (SCR), in a single system to fulfil two totally different tasks in exhaust gas purification.
The combination of RTO and SCR systems makes it possible to reduce organic carbon compounds and CO, while minimising odours. The installation of catalysts also enables a reduction in NOx emissions. The DeCONOx system will run autothermally, meaning that the combustion process feeds itself. The fuels (CO, organic material) are present in the crude gas. This reduces the energy demand. The flue gas entering the system will have a CO concentration of 6500mg/Nm³.
Structure and function of the facility
The DeCONOx system consists of five towers. Two are pressurised with crude gas from prior to the reaction / combustion and two are pressurised with clean gas from after the reaction / combustion. The fifth tower is rinsed with clean gas in order to avoid peaks of crude gas concentrations (during switch over cycles) and thus reduce the half-hourly mean
Organic hydrocarbons and CO are converted in the combustion chamber at above 850°C. In order to guarantee complete oxidation, the combustion chamber is set to 860°C. During start-up (heat-up) and non-autothermal operation the temperature in the combustion chamber is regulated by burners or gas lances.
|Parameter||Warm side||Cold side|
|Thermal output (kW)||5300||-|
|Mass flux (kg/hr of water)||156176||116407|
|Inlet temperature (°C)||106||65|
|Outlet temperature (°C)||77||104|
Above - Table 1: Heat recovery technical data.
|Regenerator and catalyst weight:||215t|
|Hoisting of ammonia tank:||500t crane|
|Total installation time:||~25,000hr|
Above - Table 2: Project data.
The special burners used only need natural gas during operation, not during standstill. With a combustion chamber temperature above 750°C the temperature can also be regulated with gas lances. These enable the temperature to be fine-tuned and do not need any burner air, thus reducing the energy demand even further. The clean gas leaving the DeCONOx is 25 - 35°C hotter than the crude gas.
Before start-up, the chamber is heated up with natural gas and fresh air. This takes 6 - 12hr. A maximum heat-up rate of 6°C/min should not be exceeded because of material stress. As soon as the temperature of the catalyst reaches 250°C and the temperature in the combustion chamber is beyond 850°C, the facility can be pressurised with flue gas. During standstill periods and maintenance work the plant must be rinsed with fresh air for about 30 minutes.
Regenerators serve to transfer the heat. During the cycles they are alternately heated up and cooled down by the flue gas. The catalysts are installed between the regenerators. The geometric set-up of the catalysts basically corresponds with the set-up of the regenerators. Thus, the catalysts work as regenerators and replace parts of the regenerators. The catalyst must not be damaged in the course of permanent switching procedures and the temperature changes involved. The switch over is carried out every 50 – 120 seconds, during which the gas absorbs heat with the upward flow and releases the heat with the downward flow. In the bottom regenerator the crude gas reaches the necessary catalyst inlet temperature of at least 240°C, depending on the SO2/SO3 content. The ammonia injection and the catalyst layer is then followed by a second regenerator layer that raises the flue gas to combustion chamber temperature.
“This new technology enables to operate temporarily without any fossil energy carriers and to save valuable raw material through the use of suitable recycling material such as waste sand or brick chippings. As a traditional enterprise, we feel obliged to act responsibly towards the next generations. We are proud that the facility went into operation without any problems and that it will set new standards in the cement production,” concludes Erich Frommwald.
Kirchdorfer Zement’s Milestones so far
1958: First electrical filter almost completely eliminates dust emissions.
1984: Installation of the first waste heat recovery (WHR) system for cooling of the clinker cooler exhaust. This has so far fed 250,000MWh of industrial waste heat into the Kirchdorf municipal heating system.
1998: Installation of the world’s first pilot selective catalytic reduction (SCR) facility.
2006: Measures against noise pollution, including high-quality mufflers, reduce noise impact in and around the plant.
2007: Selective non-catalytic reduction (SNCR) system installed to reduce NOx emissions.
2008 - 13: Installation of several waste gas
purification pilot facilities, with a view to the future development of the new DeCONOx-technology.
2010: Installation of a new kiln filter.
2011: Energy-efficient clinker cooler fitted.
2014: Implementation of an ISO 50001 energy management system.
2015: Erection of large-scale DeCONOx plant and WHR system.
2016: Opening of the DeCONOx-facility.