The challenge

Despite being an essential element of Faxe Kalk’s production, the kiln had become difficult to operate continuously, resulting in significant disruptions to the company’s operations. The kiln’s problem was centred on the instability of its gas analyser.


The kiln’s design meant operators were forced to control it by using the exit gas analyser. Kiln oxygen levels had to be kept at a high combustion level to avoid creating explosive gasses, such as CO. Downstream from the filter, the oxygen level was a relatively high 10% vol, resulting in 4% vol oxygen in the kiln. This created a need to add – and heat – a large amount of excess air, increasing energy consumption to unacceptable levels.


Kiln operators also had to deal with dust build-up in the probe, which required more than four hours of maintenance every week.


An important objective for Faxe Kalk was to reduce emissions of harmful substances, such as NOX in order to minimise any negative impact on the environment and in accordance with local legislation. However, the existing kiln set-up did not allow the accurate measurement of NOX which made it difficult to optimise settings to reduce emissions.


As a result of these challenges and objectives, it was decided to upgrade the kiln analysis capabilities to provide greater control over fuel consumption and greater stability to kiln operations. Specifically, greater control was required over lime quality parameters, such as reactivity and calcination efficiency.

Analysis of alternatives

Faxe Kalk Process Specialist, Thomas Koudal Maul, was responsible for evaluating and purchasing a gas analysis system that would allow the company to meet its objectives. 

Systems were evaluated based on their technical capabilities, price, documentation, and after-sales service.


  • Better reliability
  • Less maintenance
  • Lower emissions

Thomas and his team considered several options, including a simple, non-cooled probe. However, such probes can become blocked with dust and, in order to unblock the probe, the kiln must be shut down. The team saw this type of conventional gas analysis system as unsuitable because it would not help them to minimise downtime.


The team contacted FLSmidth to establish whether the recently released KilnLoq#3 kiln iinlet analyser was a viable option.


FLSmidth’s gas analysis system is based on a straightforward, patented One-Pipe design that can handle the hot (up to 1,400 degrees Celsius), highly corrosive, dust-filled process, and it can be installed on a wide range of kiln inlet processes. Cleaning the pipe takes no more than a few minutes.


Thomas and his colleagues were impressed with what they discovered.

We saw FLSmidth’s KilnLoq #3 solution as all in all the best solution for Faxe Kalk.

Thomas Koudal MaulFaxe Kalk Process Specialist

He highlights the probe cleaning system as particularly important and better than competitive systems: “The probe cleaning system appeared to be well designed, and the automatic probe extraction system provided good access to the probe and filter.”


Other key reasons for choosing the FLSmidth KilnLoq included its modular design, enabling it to be configured specifically to Faxe Kalk’s kiln. Faxe Kalk was also impressed by FLSmidth’s complete engineering capabilities and outstanding experience in kiln technology.


Once the decision was made to implement the FLSmidth KilnLoq #3, a kiln shutdown period, which allowed ample time for installation, was planned.


Thomas Maul talks about the installation process, which began in August 2015: “Installation involved upgrading the area around the new KilnLoq with a new platform. The frame and extraction unit is quite large, so we needed to make sure it would fit the available space. The KilnLoq was modified with new and longer support legs, the top covers were lifted to allow hot air to escape, and we added heat shell plates at the front end to lower radiation heat.”


Following the successful installation of KilnLoq, the system was put into action in October 2015.

Implementation went well and proceeded according to plan. It only took a couple of days to start up the KilnLoq and train our staff, which is exactly what we had expected when we placed the order.

Thomas Koudal MaulFaxe Kalk Process Specialist


The implementation of the KilnLoq gas analysis system delivered immediate benefits.


By being able to continuously measure O2, NO and CO at the kiln inlet, Faxe Kalk has reduced the kiln inlet level to 1-1.5% vol, which minimises excess air and lowers total fuel consumption. It also significantly reduces the risk of explosive CO being formed, thus improving the safety of the entire system.


The solution provides accurate NO measurements, which is a convenient way of monitoring NOX emissions. Such accurate measurements allow the operator to react and make necessary adjustments when excessive levels of NO are detected.


While installing the KilnLoq system, Faxe Kalk revamped seals in the kiln, dry crusher, preheater and separator. Faxe Kalk is now able to run a stable process with more constant excess air in the kiln and less leakage air intake at the preheater system. This has a positive impact on total flue gas flow and O2 concentration at the outlet (downstream from the filter) without jeopardising the safety of the ESP filter and other process components. The stable process conditions also enable additional process optimisation initiatives.


Faxe Kalk can now accurately and continuously monitor important parameters, including lime reactivity and calcination efficiency, throughout kiln production, which allows a constant focus on stable quality. Every kiln adjustment performed has an impact on energy consumption, so it is essential to be able to control the process and balance heat consumption.


The kiln inlet measurement enabled by the KilnLoq solution is an essential part of maintaining this balance.

Minimum maintenance

One of the most noticeable benefits to Faxe Kalk is that there is no need to clean the probe. The hours of maintenance previously required have been removed, and continuous measurement is now possible. To ensure the KilnLoq solution is operating well, staff perform a quick inspection each shift. This also keeps the staff familiar and confident with the system.


Emissions reporting

Faxe Kalk also decided to implement an emissions data reporting system that could include power consumption and product storage.


Thomas Maul explains: “Our old Excel-based system was not easy to use, and we could only access it from the kiln control room. Also, we didn’t have a QAL3 tool.”


Here, too, the choice fell on an FLSmidth solution. Thomas Maul and his team chose FLSmidth’s ReportLoq system, which could combine all emissions data together with useful process and production data. It also provided full accessibility to all data from anywhere in the plant. With the successful implementation of the KilnLoq gas analysis solution and ReportLoq data reporting system, Faxe Kalk has continued its core operations of lime processing with a reduced environmental footprint and more stable operating conditions.

About the customer

Lhoist is one of the world’s largest producers of lime, dolime and minerals. With headquarters in Belgium, Lhoist has locations in 25 countries and more than 90 facilities around the globe.

Lhoist differentiates its business by being close to its customers, understanding their needs and providing them with the high-quality products their activities require.

Faxe Kalk A/S is a subsidiary of Lhoist in Denmark delivering limestone-based products to the Nordic market. Lhoist in Denmark has a wide range of limestone-based products for different industrial applications, including environment, glass, chemical, building/construction and agriculture.

Lhoist Faxe Kalk A/S produces lime, based on limestone from the Faxe quarry, in a rotary kiln installed by FLSmidth in 1968. The lime produced can be sold directly or processed further at the plant’s milling or hydration installations.

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