Energy efficiency and improved maintenance with new 2-stage Lime Kiln Cooler

Energy efficiency and mechanical durability are crucial in lime kiln design as the kiln is an integral part of chemical recovery process in pulp mills. One key driver for lime kiln’s energy efficiency is the cooling process where the heat in the hot burned lime is recuperated and heats-up the combustion air.

For decades, lime kiln coolers were based on satellite-based coolers design where the hot burnt lime is transported through cooler satellite tubes uphill on the periphery on the kiln shell. This was and is a simple design with its benefits and limitations.

Since the 1990’s Valmet has offered a more efficient cooler today known as Valmet Rotary Cooler, which has several benefits compared to the satellite based cooler design, e.g. improved heat recovery, low noise and less maintenance.

New design to meet customer needs

“While visiting customer sites, I had received constructive feedback about the challenges of our smaller technically very efficient Rotary Cooler. I started gradually developing ideas to tackle the issues. We were also developing ideas for developing a Rotary Cooler especially for retrofits,” tells Per Brix, Senior Design Engineer from Valmet’s Lime Kiln technology team.

Valmet’s Senior Design Engineer Per Brix showing 2-sage cooler design drawings by his desk at the Copenhagen office.

In 2019, Södra Cell Mörrum contacted Valmet to discuss the option of replacing the cooler in one of their existing lime kilns.

“It was an excellent opportunity to put our ideas into practice. We didn’t just send the sales team to discuss with customer but included, product development, engineering and project management right from the start. Additionally, we only had a couple of weeks to put together the successful proposal,” explains Claus Jensen-Holm, Director for Valmet’s Lime Kiln technology unit.

Valmet was awarded the project in April 2019. During the following six months the team worked intensively to finalize the design, do the detailed engineering and manufacture the equipment. The work was done in close cooperation with both the customer and also Valmet’s suppliers. Valmet started the erection works in mid-October and start-up was done in November 2019.

The result of the customer driven development work was a new cooler design named Valmet 2-stage Rotary Cooler, which is based on Valmet’s standard 3-stage Rotary Cooler, building on the same benefits but especially addressing the easier maintenance access in the smaller size range.

The intense installation works were supervised by Valmet’s Commission Manager Charles Brooks-Wind and Installation Manager Anders Jensen.

Installation works for a new lime kiln cooler  were completed in November 2019 at the Södra Cell Mörrum pulp mill in Sweden.

Success in many ways

With a new product design, tight delivery schedule and turn-key delivery, there are always several risk for successful project execution.

“We identified the risks right in the beginning. With a dedicated team, very good cooperation with the customer and tight involvement of contractors, we were able to manage the risks and deliver the project on-time and on-budget,” tells Jørgen Jantzen, Valmet’s Senior Project Manager.

After the first months of operation the new lime kiln cooler has performed very well. It has proven that the operation and cooling efficiency is significantly better compared to the original cooler installed.

Securing safety for own and contractor employees is essential to both Valmet and Södra. A safety workshop was arranged at the mill before the construction works started in order to train the subcontractors on safety mindset and policies. The participants included Södra’s representatives, Valmet’s supervisors, and subcontractors from SKS and Megamet. The project was completed safely without any accidents or near misses.

The new cooler has been operating at the mill for almost a year and has performed very well.

Perfect solution for retrofits

The new 2-stage cooler compliments Valmet’s portfolio of lime kiln coolers ensuring that Valmet has the most cost competitive cooler solutions for small, medium and large coolers. The 2-stage cooler is expected to have only slightly less cooling efficiency compared to the 3-stage cooler, but in addition offers a light weight solution, which is easy to retrofit into existing kiln installations without the need for major modifications. In addition, the 2-stage cooler provides easier access to monitor and maintain kiln shell compared to the traditional satellite based cooler design.

Due to its smaller size the 2-stage cooler is easy to retrofit into existing kiln installations without the need for major modification e.g. in crushers and conveyors.

“We are very happy to see that the cooling capacity is proven to be per design and the cooling efficiency and thereby reduction in fuel consumption is as good as, or even better than, projected. This means that Valmet has a new proven light-weight cooler speciallly designed to replace satellite-based coolers,” Jensen-Holm summarizes.