A new cold chain for Collect&Go
“We rethought a complete cold chain at Collect&Go and linked it to an IoT solution", project manager Peter De Bonte says. He emphasises the uniqueness of the project, not only for Colruyt Group but also for the broader retail sector.
Efficient and sustainable refrigerated transport
“We developed a solution ourselves for the transport of fresh and frozen products with regular trailers, without refrigerated trucks, implementing significant innovation and in a sustainable way.”
Londerzeel's Collect&Go distribution centre (DC) is gradually rolling out a new delivery system. It used to deliver fresh products with a cart that was transferred into the pickup point's refrigerator. Transferring is no longer necessary today. Ordered products are put directly from the DC's refrigerated warehouse into folding crates that are placed in pairs into a newly developed cool box.
Self-developed cooling plates there keep the contents cool. That filled cool box is then transported to one of Collect&Go's 210 collection points in Belgium. When customers pick up their orders there, a store co-worker reads the temperature data for that box.
Indeed, the pickup points are equipped with receivers that automatically display each box's sensor and temperature history. If everything meets the requirements, payment follows by the customer taking his filled folding crate. There are already 5,000 individual cool boxes for fresh products in use at Collect&Go. Moreover, the same concept is now being used for frozen food.
Smart cool box
The cool box concept was conceived by concept engineer Erik Cousaert, who took the initiative at R&D in 2016 to design a box with passive cooling. It might come in handy one day. The cool box (1,200 x 600 x 400 mm) is made of black expanded polypropylene (EPP). “EPP is very light and has a good insulation value. The material is easy to inject and equipped with a trap door.
In addition, the box is 100 % recyclable at end of life.” Each box can hold two folding crates side by side. At the top, stainless steel cooling plates slide in and out of the box on a rail. It took quite a lot of effort to get those welded. Not only was an accuracy of 0.2 mm required, but also a perfectly smooth surface. Additional challenge: the cooling plates contain water.
First, the corners of the preformed base plate are welded. Then the bottom is filled with a water-graphite mixture and the lid is welded shut. The added graphite increases the thermal conductivity coefficient of the water by a factor of 3. “Due to that better conductivity, the plate does not cool first on outer edges and corners but maintains the same (ice) temperature everywhere.”
The graphite also allows the plate to cool down three times faster. The application for frozen products requires a so-called phase changing material with a freezing point of
-26 °C. In this case, a salt solution. “None of these materials are harmful in the event of a possible leak. We can also fit the box with a thermally conductive aluminium liner and additional lambda vacuum insulation panels.”
In the fresh box we have vacuum insulation panels in the back wall, bottom and lid. For the freezer box, we have vacuum insulation panels all around. In contact with the cooling plates, the liner ensures better distribution of cold inside the box. “Without liner, the equilibrium temperature is 6 to 7 °C", Cousaert calculates. “This liner smoothly keeps the box 2 to 3 °C cooler for longer periods of time.”
The plate freezer or the "waffle iron’
Freezing of the cooling plate is done by contact cooling. This requires not only maximum contact with the plate above and below, but also a huge cooling capacity. “With glycol, that wasn't achievable", says Cousaert, who started looking for CO2 solutions. At a Danish machine builder for the fish and meat industry, he found a machine that ran on ammonia.
“We adapted it to our requirements.” The "waffle iron system" simultaneously cools eighteen plates. The aluminium contact cooling elements in the system are brought to -35 °C. The cooling elements are placed hydraulically on the plates. Above and below. The flatness of the cooling plates is crucial to ensure contact.
Efficiency and sustainability
Fairly early in the project, workshops were organised to determine Collect&Go's specific needs. Project Manager Peter De Bonte, who was assigned the project two years ago: “There has been a lot of tinkering with every component.” For example, locks and hinges, as well as the first refrigerated boxes, were redesigned to allow smooth stacking and unstacking and to keep the stack stable during transport.
“There is also ongoing work on the connectivity of the temperature sensor in the cooler that shares its results with the IoT platform via bluetooth. Our cooling elements have been developed according to a whole new concept. We worked together with the machine supplier for the engineering of the cooling circuit.” The focus was on rapid freezing. The plate freezer operates on CO2 in the cold stage.
“We easily evaporate to -38 °C there.” There are no ventilation losses. Cooling is done by compressors in a cascade system. Power can be controlled according to demand. The glycol circuit runs on propane chillers that also cool the rest of the building's refrigerated area. The photovoltaic panels on the roof provide the energy for it.
When the truck delivers fresh products to the pick-up point in the morning, it takes the used boxes back to the DC in Londerzeel. The operator puts the hot cassettes on a modular belt. ‘Air knives' ensure that the cassettes are blown dry in the conditioned room before sliding them into the freezing machine. The cooling plates are visually inspected.
The integrated checkweigher checks that all cassettes have the expected weight and are not leaky. “Our automation takes care of the transport to and handling in the freezer," says Sven Doms, who is in charge of the automation of the machinery and thus also the automatic transport of the cold chain. The cooling plates are frozen at -20 °C the day before delivery. Keeping moisture out of the machine was a challenge. “A dew point of -20 °C is ideal. There will be some frost ripening but minimal.”
The cooling plates then enter a 5.7 m high storage buffer that can hold up to 1,500 cooling plates. This all happens in a room 30 m by 7.5 m and 6.7 m high. The ambient temperature there is -7 °C. “The automation is completely done according to our own concept," Doms says. “We shifted to more robust, mechanical sensors that click off as the cooling plates pass through the freezer. With optical measurement, the risk of a miscount was too high.”
That count must be 'correct'. Always. Today, the freezer is still loaded and unloaded manually. Now engineers are working hard to automate that supply and removal. The plates will automatically be placed on a roller conveyor and enter and exit the plate freezer in groups of six. In a second phase, the loading and unloading of cool boxes will also be automated.
“We are proud that we were able to make this happen," says Doms, who points to the multidisciplinary nature of the project and the collaboration with external partners. “Covid added an extra exciting challenge. The uncertainty about the availability of materials, price fluctuations, delivery times etc. Remote engineering of a box is not obvious either. At some point it does require hands-on.”
This article previously appeared in Engineeringnet.
“We developed a solution with smart techniques, such as temperature monitoring, that was to be commercialised", concept engineer Erik Cousaert says. As with the previously developed 'liquid ice container'", which contains a frozen but liquid mixture of water and ethanol, Colruyt Group took out a patent on the whole concept of cool box and cooling plate but now also on the special freezing method of the stainless steel cooling plates. The first one has already been validated. The second one follows. There is also interest from companies outside Colruyt Group to use this particular technology under license.