Mercury Southdown Power Station
History
The Mercury Southdown Power Station was commisioned in 1996, as a natural gas-fired combined cycle gas turbine cogeneration power station. Located in a southern suburb of Auckland it was New Zealands nothernmost power station with capacity exceeding 50 MW. Once the site was upgraded to contain 3 LM6000 gas turbines and one steam it produced 170MW of power. In 2015 Mercury announced it was decommissioning the site in line with their commitment to green energy. In May 2022 Ward Demolition began the task of demolishing the structure, sitting on 2.2 hectares of land set to be completely cleared and later sold.
Stage 1
Demolition commenced 2nd of May 2022, kicking off what was set to be a highly technical job with extremely high risk hazards. Stage 1 reached completion mid June, consisting of deconstructing a wet surface air condenser (cooling tower) nestled in amongst an extremely high voltage, live site. With 11,000 Volt cables suspended on trays only 3 meters from the structure, this job was anything but ordinary. We ran the risk of a news worthy event if we were to merely create excessive dust or vibrations. As we operated in close proximity to a high voltage major switch yard and kiwi rail transformer, that was connected to a large percentage of Aucklands powersupply and transport network.
At this stage the site was still connected by earth grid meaning we were limited to above ground excavations only. Additionally the site contained multiple underground reservoir tanks that we had to be extremely mindful not to track over incase of collapse. This posed a high risk not only to the machine but any team member in or around it. We worked closely with the Murcury team to ensure every team member was thuroughly aware of all hazards. Every morning Mercury attended our prestarts adding their extensive knowledge of hidden hazards to our plans and processes.
This was especially helpful when we had to separate all the pipework that ran underneath the live 11V cables and connected to the structure. We would have regular walk throughs where we discussed what needed to be cut and they would ensure each pipe was completely isolated and explain to us the thickness and material of each so that we could proceed safely and well prepared for the task ahead. Some pipes were up to 80 mm thick (photo provided). Needless to say these were extremely challenging to cut.
Minimizing dust and vibrations was crucial on this job as a major switch yard was located no further than 100 meters from operations and was extremely sensitive to both. Heavy vibrations or dust could result in a fault shutting down the grid connected from Henderson to Otahuhu, a major chunk of the city. Dust can contain iron particles that result in a track that can short the equipment out and shut down the grid, so we heavily relied on our 7500 Dust Fighter to minimise this hazard. Fortunately we’re in our winter months that contain high rain fall that aided our efforts. On the flip side the weather posed further risk to our team as electrical storms posed extremely high risk of lightening strike. We played close attention to weather reports and had to shut down during electrical storms to eliminate the lightening hazard.
Further added precautions on this high risk job included compulsory PPE of 11CAL Fire resistant overalls and rubber gloves for any manual handling, above the standard Steel caps, high viz and helmet. Our health and safety officer was a regular presence onsite constantly ensuring all safety measures were applied.
Recycling
The structure mainly consists of concrete and various metals, we are confident we can obtain a recycling rate in the high 90% range. All of the concrete will be crushed and put into the foundations of the site so that 100% of it is directly recycled. All of the metal is being trucked to the scrap metalists located only 5 minutes from site, with our yard being of similar distance we’re pleased this also means for lower carbon emmisions.
Method
Our method for demolishing stage 1 included, firstly fully isolating the structure from its suroundings, then seperating structure A and B from each other and the high tensile steel pipe that ran between them. Once completed we were able to proceed with two 50 tonne and two 20 tonne diggers. We demolished structure A first, processing the materials as we went. The large wet sacks were particularly challenging due to their weight and quantity of steel, they required two 50 tonne diggers to move them around site, followed by a full day of cutting with the 50 tonnes shear attachment.
Once structure A was completed this provided room for us to continue processing materials while structure B was being dismantled. As structure B was extremly close to the 11,000 Volt cables we left the outside wall in place to provide a barrier, protecting these cables from the machines. This will remain intact until the site is fully isolated in August. Lastly we broke out the foundations of the large pipe and pushed it off it’s perch so that we could cut it up. Due to the magnitude of the large pipe it worked as an amplifier of the sound and vibrations and set off our monitors when we atempted to cut it with shears. This meant we had to stop and adjust our method before proceeding to cut the entire piece down by hand.
Stage 2
Our Team have moved onto chillers and auxiliary boilers next. Where stage 1 was has become a lay down area for the remainder of the demolition. We will proceed by isolating each section at a time an continuing to uphold our high level of health and safety practices in everything we do. As we get closer to the large powerline and grid we will tackle the additional hazard of minimum approach distance by ensuring all our machines are sufficiently earthed.
Team members
Site supervisor Tyler Ward, although only 23 years of age has lived and breathed Demolition since birth and is an extremely capable operator. Alongside him was lead operator Francis better known as Fridae, who is coming up to his 20 year anniversary of working with us at Ward Demolition. I myself, Bayleigh Ward, worked alonside the men operating these machines. Being a female I believe I’m more prone to taking care and operating with a gentle precision which the job definitely required. As well as my brother I too have been raised by Demolition. Our highly capable ground team consited of Bruce Bond and Dan Pryor to begin with who completed the daunting job of seperating each building with extreme caution resulting in zero incidents or injuries. Later the team has been joined by Jay and Temple as we proceed onto stage 2.
