After more than 25 years’ experience in the sector and extensive demolition work on chemical plants, industrial buildings and civil works, Lezama Demoliciones faced a new challenge: the demolition of the old Foix Thermal Power Plant, located in Cubelles, Barcelona.
The project, which started in 2017, consisted of the complete dismantling and demolition of the plant, which had been closed for almost two years.
Significant elements included the demolition of the 175 m (574 ft) high chimney stack, the turbine of the generator unit and its building and concrete bedplate, and the complete demolition of the boiler.
Lezama also performed the preliminar y cleaning and management of the waste from the operation of the plant, as well as removing other hazardous waste, including asbestos.
Preliminar y cleaning had to be approved before proceeding to demolition.
The turbine-generator was disassembled avoiding the use of cranes, which reduced risk. For the demolition of the building, the use of heavy machiner y in the removal of the bedplate enabled rapid execution and the complete separation of materials. It was carried out under stringent dust and noise emission control measures.
LONG -ARM MACHINERY
To fulfil the deadlines set for the project, the project management team used innovative equipment, machiner y and techniques. Remote controlled robots and long-arm machiner y were used to demolish the chimney stack, in addition to combining manual and mechanical demolition methods in the metal and concrete structures.
“From a safety standpoint, we reduced the number of crane manoeuvres significantly using different long-arm excavators of various sizes, the largest having a reach of 35 m (114 m),” said David Peral, technical site manager of Lezama Demoliciones.
Using robots and long-arm machiner y reduced the number of man-hours of risky work while enabling the complete segregation of waste from an environmental standpoint, removal of asbestos seals in the chimney stack and the interior refractor y brick and the concrete from the shaft.
The impossibility of blasting was also an important conditioning factor for the project, as it required the work to be carried out using manual or mechanical means. This impediment was due to the proximity of a railway line, roads and the nearby urban area.
“Apart from the chimney stack, the boiler was nearly 55 m (180 ft), and the turbine and ancillar y buildings exceeded 25 m (82 ft),” added David Peral.
“Wind control (both in the chimney stack and on the ground) was stringent, requiring stopping certain work at height for safety reasons on many occasions. Monitoring was performed in real time>
ADAPTED PL ANNING
From the environmental standpoint, Lezama even had to adapt to peregrine falcon nesting periods.
This was achieved by adapted planning, avoiding dust-generating work on windier days, for example. Neither did noise-related incidents occur, with 100% of positive results in the controls carried out.
After the successful demolition of the Foix Thermal Power Plant, Lezama embarked on another long-term project.
This was the Anllares Thermal Power Plant, located in Páramo de Sil (Leon) and started in June 2019.
The significant experience acquired at Foix served as a basis for executing this new project successfully, as well as providing an example of implementing improvements in demolition work in terms of quality, environment and work safety.
In this case, Lezama worked with a new company, Naturgy. It was the first demolition project executed for the energy company, which was followed by La Robla and Narcea thermal power plant projects, located in Leon and Asturias, respectively. The Anllares Thermal Power Plant, closed in December 2018, and had a single 365.2 MW thermal generator, jointly owned by Endesa and Naturgy.
The plant’s characteristics included a series of elements that represented a major demolition challenge. First, the slender chimney stack and large cooling tower, 150 and 110 m (492 and 360 ft) high, were demolished using explosives.
Next, the boiler, 50 m (164 ft) high and an apparent volume of 177,500 cubic metres (6.2 million cu ft), which was composed of such different materials such as fibrecement, insulation and various metals like iron, stainless steel and copper. This disparity of composition represented a major challenge for the demolition works, since it is essential to separate these materials to make proper use of the waste for recycling.
Lastly, the hopper shed building, with a height of 50 m, had to be dismantled with large-scale machines.
Additionally, dismantling work was carried out on the turbine of the generator set and the concrete bedplate, the building that housed it and the metal structures that connected all these elements to the thermal power plant.
All this work was carried out through the principle of selective demolition – separating the materials at source to minimise the production of waste deposited at landfills.
As a result, the preliminar y cleaning of the plant was initially carried out, removing potentially polluting materials such as fuel, diesel, ashes and other power plant products. Furthermore, hazardous waste was extracted, especially asbestos, contained particularly in locations such as the boiler, the inner chimney stack seals or the cooling tower.
In terms of safety, the demolition of the Anllares Thermal Power Plant represented a major step for ward for Lezama. Unlike Foix Thermal Power Plant, where no blasting with explosives took place, in this power plant demolition in Leon there were up to four blasts – silos, chimney stack, cooling tower and boiler – which eliminated the need for work at height and, using the appropriate procedures and ensuring the safety distance, the risk for workers was highly reduced.
Moreover, the use of long-reach and large-scale machines also guaranteed that workers were not exposed to work at very great heights. This was achieved due to the KMC 1200S long-arm excavator, by Japanese manufacturer Hitachi.
In the second half of the project period, Lezama acquired 3D vision equipment and a virtual platform from the company Ludus Global. This tool enables the persons in charge of site safety to provide workers with safety training, creating an immersive and very realistic experience with potential accidents in projects.
David Peral: “Blasting represented a major improvement process, since it offered greater performance both in terms of demolition and in the recover y of materials, and also reduced the risk for workers during the demolition of high-rise structures.”
The chimney stack had a diameter at the base of 13 m (42 m) and 7.35 m (24 ft) at the crown. It was made of reinforced concrete and internally lined with refractor y brick distributed in 12 trommels, with asbestos seals, leaving an air chamber between the concrete wall and refractor y brick wall.
Dismantling the refractor y brick lining turned out to be a major challenge from a safety standpoint, and had to be completed before blasting.
Horizontal reinforcements were cut on the outer blast side. Then horizontal cuts were made to reduce the resistance at the rear of the chimney and prevent it from impeding the directional fall. Lastly, the gelatinous dynamite was placed along two-thirds of the perimeter of the chimney, forming a rupture wedge of decreasing height from 2.65 m (8 ft) to 0.6 m (2 ft).
To cushion the fall of the chimney stack, a sand bed was placed on the fall position and water pools with explosives were also prepared, making it possible to trap the dust that raised during the falling process.
Thanks to this technique, the company was able to recover 3,500 t of concrete. ■