In a statement, Paul Wurth said the the project included a reline of the granulation system and modernization of the cooling tower and hot water tank. The work was carried out during a seven-month period last year, and performance testing took place this winter. 

The system serves the the plant's No. 4 blast furnace and has a daily capacity of 1,600 metric tons of blast furnace slag sand and a maximum slag flow of up to 8 metric tons/minute.

“For the customer, it was crucial to minimize the loss of blast furnace slag sand to one month’s production only. Therefore, Paul Wurth came up with the idea to reline the complete cooling tower gradually during uninterrupted, regular production and to use the four granted stoppage weeks in August 2019 to modify the hot water tank with a new water recirculation concept,” Paul Wurth said in a statement. 

“The four-week stoppage in August was used to (replace) the lower part of the old hot water tank as well as the connected process water recirculation system with a new design. Additional work during that time included the reline of the cooling tower, modernization of the water pump reservoir and replacement of its clogged coke filters downstream of the said hot water tank.” 
You can read more about the project here.