Abstract: The multi-temperature joint distribution (MTJD) vehicles equipped with different temperature cold boxes, replacing specialized refrigeration power with eutectic plates, not only effectively reduce energy consumption and carbon emissions and fully utilize vehicle capacity, but also achieve packaging material savings through the circulation of cold boxes. At the same time, the cold box can maintain a constant temperature throughout the entire vehicle service process for more than 8 hours, ensuring that the quality of cold chain products is not affected by sudden situations such as frequent door opening and road congestion. Therefore, the transformation from mechanical refrigeration mode to cold accumulation mode is not only a requirement for the development of green, low-carbon, intensive, and efficient cold chain distribution but also an inevitable requirement for the development of new quality productivity. This article takes an MTJD vehicle routing problem as the research object, where a refrigerated distribution center (DC) uses ordinary vans with the same specifications to carry different colored cold boxes (less than one box of goods is distributed as a whole box) loading cold seafood (0oC to +7 oC), chilled seafood (-2 oC to +2 oC), frozen seafood (below -18 oC) to customers and pick up the last unloaded cold box within a specified time window considering carbon emissions. The objective function is to minimize the total cost, including vehicle cost, fuel cost, cold box cost, penalty cost for violating the time window, and carbon emission cost, through constructing an MTJD optimization model. In solving the model, a mixed pheromone update strategy is adopted based on an improved ant colony algorithm. The effectiveness of the model construction and algorithm was verified through practical examples of JIAJIAYUE sales stores. The contribution of this article lies in: firstly, it not only considers the differences in customer demand (unloading volume) and the combination of "insulation box+ eutectic plate" used for loading different temperature range seafoods but also increases the impact of the recovery volume of the cold box on the vehicle load capacity, making the transportation cost and carbon emission cost of the vehicle more in line with the reality of the cold chain. Secondly, from the life cycle of insulation boxes and eutectic plates, considering the impact of the usage cost and their carbon emission cost on vehicle routing optimization can better guide the production and operation practice of MTJD. Thirdly, considering the carbon emission cost generated by the whole refrigeration process of the eutectic plates (after the vehicle arrives at the customer, the unloaded cold box can be used for the customer continuously, and the insulation box and the eutectic plate that has been released will be retrieved by the delivery vehicle next time), rather than the carbon emission cost based on transportation time and service duration, is more in line with the actual operation of the MTJD.

Key words: Low carbon delivery, MTJD, vehicle delivery and cold box pickup, VRP