William Thompson & Son turn landfill into stockpile with CDE Washing Plant

When most people look at an expanse of construction, demolition and excavation material they see only waste. Andrew Thompson, Director at William Thompson & Son, is able to see things differently with the introduction of a CDE C&D waste recycling plant, “This material which was once left unused can now be washed, screened and sorted into a range of valuable products.”

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William Thompson & Son have been in business since 1946 at their site in Dumbarton Glasgow. The company began in 1946 as a quarrying business. Now as they celebrate their 70^th year in business they offer a wide range of products for the construction sector. The most recent addition to the Group is Thompson's Recycling & Landfill which recycles construction, demolition and excavation waste in its 120 tonnes/hr wash plant, which was installed in January 2016.

William Thompson & Son are able to supply the C&D waste recycling plant using material exclusively from their landfill site as well as imported material. This was the original Rigangower quarry which was then used for disposal of construction and excavation waste. The C&D recycling plant will now be utilised to turn these waste materials into a range of products with a commercial value. Andrew Thompson, Director, commented, “We are able to recycle around 80% of the landfill material. “

William Thompson & Son who supply customers mainly within a 30 mile radius of their Glasgow quarry have a wide range of new products from their C&D waste. The smallest aggregate is suitable for pipe bedding, the mid-range aggregate is sold for closed drainage and the largest aggregates suit open drainage. The 0-4 grit is in high demand for block making, the company also produces 0-2 fine sand and a concrete sand.

Project Delivery

At the initial pre-sales stage, before any agreement is signed, CDE will always carry out detailed testing of the feed material and determine the capacity of the plant to ensure that the models and options included are those best suited to the site. In this case the feed material is very dirty given that it had been stored in a landfill for up to 25 years. In addition, it is very wet and sticky, making it more difficult to process.

After consultation with the team at CDE a fully integrated C&D plant was designed to suit the Thompson site’s specific output requirements. The plant comprises a R2500 Primary Screening Unit, an AggMax 153R Logwasher, M2500 mobile wash plant, an AquaCycle thickener, an Overhead Beam Filter Press and completed with four water storage and sludge buffer tanks.

Speaking about his first foray into wet processing, Andrew Thompson commented, “As our previous projects utilised dry crushing and screening we carried out a lot of research into all the possible options. Given the complexity of the equipment and the difficult feed material, we knew that working directly with the manufacturer was going to be essential. “

“We opted for CDE as I know that they are not just selling this equipment, they are the manufacturer and we see a lot of value in that: it means the same person who designed the plant can come to our site.”

As with all CDE projects William Thompson & Son were assigned a dedicated Project Manager to be a point of contact and ensure a successful installation and commissioning. Describing the design phase, Project Manager Ciaran Hegarty said, ‘We made use of a modular design which allows us to utilise our bespoke designs, which have been tried, tested and installed on many other projects worldwide. This also means that any spare parts are easily and readily available.”

The other benefit of the modular design is the quick installation time. Whilst the major plant items are modular in design, all the pipework and conveyors have been designed to interlink seamlessly within the agreed plant layout ensuring efficient transfer points and maximum material retention within the processing circuit

Ciaran Hegarty continued, ‘It is part of my role as Project Manager to assess the site and create solutions to ensure efficient delivery and ongoing operation. Every site has its own issues based on our strong experience we always find a solution.”

One of the first considerations was power supply as there were limited kilowatts available from the local transformer. Rather than incur extensive costs to upgrade the power supply the plant was designed to allow the control system to run from the mains connection while the generator would supply any shortfall.

Another issue on the site was a limited supply of fresh water to supply the plant. As the CDE modular systems are used across the world they are designed to have minimal water requirements and the plant was designed to maximise water recovery and recycling through the use of the Overhead Beam Filter Press.

With the efficient use and recycling of water along with the installation of a Filter Press CDE have been able to reduce the water requirement to below 15m³/hr. The alternative to a Filter Press would have been settling ponds; however this steep hillside site was not suitable and this would have reduced the amount of water which could be recycled quickly back into the system.

One of the key requirements for William Thompson & Son was that the primary screening unit would be suitable for the long term plans for the site. To facilitate this, the R2500 has been designed with extendable hopper sides to allow for larger loads in the future. Andrew Thompson said, “We had originally considered the R1500 but we went for the R2500 as our long term plan is that as the nearby stocks are exhausted we shall be able to tip directly from lorries into the hopper.“

Another request from William Thompson & Son was that all walkways would be interlinking, meaning once an operator has stepped onto any of the walkway he can access all parts of the plant. Ciaran Hegarty commented, “This was something which we were able to design into the plant which will save operator time climbing up and down stairs onto different parts of the plant, therefore increasing operational efficiencies when carrying out essential plant inspection and maintenance. Ultimately this will help ensure that the customer can meet production targets and customer supply by increasing the available production time.”

Throughout the project William Thompson & Son have shown a commitment to finishing the installation to the highest standard. This is shown in the approach they took to the civil requirements where they went beyond the basic requirement of concrete pads and installed a raised concrete plinth on which the entire plant could be placed. This investment will have long term benefits aiding operator efficiency, improving access to the machines for maintenance and ensuring a safe working environment which will all result in increased plant availability.

The Process

The material is transported the short distance from the stockpile to the hopper of the R2500 primary screening unit by shovel loader but the larger extended feed bin shall allow for the long term plan to feed by the lorry load. The primary screening unit scalps off all the oversized +100mm material at this stage. The R2500 incorporates the latest screening technology in the Infinity P2 75R. The patented design includes huck bolt construction removing the need for welds and Trilogy side wall construction reducing the weight resulting in a stronger, lighter screen requiring less power.

The -100mm material then travels by conveyor to the M2500 mobile wash plant where it passes an overband magnet on the feed conveyor (to remove any metals) and then onto the Infinity screen for washing, sizing and sorting. The top deck contains all the +40mm material which is stockpiled as oversize. The bottom deck contains all material sized 4-40mm which is then transferred by conveyor to the AggMax modular logwasher.

Once in the AggMax the clay bound material is scrubbed clean and split into three washed products sized 4-10mm, 10-20mm and 20-40mm. The trash and lightweight organic materials are floated off the rear of the AggMax and dewatered and discharged into a skip. Filtrates from the trash screen and sizing screen are then pumped back to the M2500 where it is processed through the EvoWash section to produce two sands, 0-4mm and 0-1 mm fine sand.

The waste water and silts from the cyclone feeds into the AquaCycle thickener where flocculent is added to aid the separation of the silts from the water, with the clean water recycled into the Aquastore and the slits pumped into the sludge buffer tanks ready to be processed through the Filter Press.

The plant incorporates four 100m³ capacity steel tanks which have several applications. Two of the tanks are used as sludge buffer tanks to feed the Filter Press, allowing the wash plant to run at capacity whilst the tanks can buffer the quantity of sludge being produced thereby removing the filter press as a major bottle neck in the processing capacity of the complete plant. Another tank is used as the main water recirculation tank, storing all the water recovered from other parts of processing ready to supply the plant when needed. The final tank is a water storage buffer tank which enables William Thompson & Son to keep up with the necessary water top-up requirements even though fresh water availability is limited.

The Overhead Beam Filter Press is fed from the buffer tanks. This model comprises 183 plates measuring 1.5m x 1.5m. The plates fill with sludge and are set on a press cycle to produce a dried out cake material which can be shovelled away. Utilising a filter press also enables another 5% of the water to be recycled back into the washing plant.

Customer for Life

It is integral to the CDE values that customers are supported beyond the initial installation phase to ensure the plant is maintained in proper working order and to allow customers to receive the greatest benefits from the plant.

Ciaran Hegarty says, “For CDE it is very important to maintain contact with our customers after the installation and really encourage setting up an ongoing maintenance schedule to ensure the plant can perform at its maximum effectiveness and to extend the life span of the plant.”

William Thompson & Son are subscribers to this idea and have signed up for a two year Preventative Maintenance contract which shall see a member of the CustomCare team visit every quarter to carry out a review of the site, advising on any wear parts nearing the end of their life and ensuring the plant is running at optimum levels of productivity.

Andrew Thompson added, “The regular direct contact with CDE is something we really value, it gives us the confidence that we have everything in place to ensure the ongoing efficiency of the plant.”

Conclusion

William Thompson & Son have grown from a small operation to a large, dynamic business which they have achieved through constantly developing new markets and re-investing in the available technology. They have once again secured their position as an industry leader with the installation of the largest CDE C&D recycling washing plant in the UK.

Giving his final thought on the plant Andrew Thompson remarked, “We have had the installation completed and we are now going through a commissioning phase since January 2016 and we have been producing clean high quality material that we are able to move very quickly. There is a growing acceptance of recycled products and with the systems we have in place we are able to produce a large range of high quality products.”