Design of an inventory management system in an agricultural supply chain considering the deterioration of the product: The case of small citrus producers in a developing country
Inventory management along the agrifood supply chain is a subject of great interest due to the constraints related with the perishable condition of product. Signifi cant problems like demand forecasting, inventory management and transportation was evidenced within the supply chain studied. Additionally, the management of perishables and their lifecycle are the most frequently issue in this kind of supply chain.An inventory management policy is defi ned taking in consideration the optimal quantity for an order and the time for ordering so as to ward off costs related with understock or overstock. This paper presents a mathematical model for inventory management in agricultural supply chains considering perishability. The supply chain studied involves a retailer, a producer and a supplier. The advantages of integrating inventory management along the supply chain are discussed and fi nally some recommendations and research opportunities set forth.
Citrus Inventory management along the agrifood supply chain is a subject of great interest due to the constraints related with the perishable condition of product. Significant problems like demand forecasting, inventory management and transportation was evidenced within the supply chain studied. Additionally, the management of perishables and their lifecycle are the most frequently issue in this kind of supply chain.An inventory management policy is defined taking in consideration the optimal quantity for an order and the time for ordering so as to ward off costs related with understock or overstock. This paper presents a mathematical model for inventory management in agricultural supply chains considering perishability. The supply chain studied involves a retailer, a producer and a supplier. The advantages of integrating inventory management along the supply chain are discussed and finally some recommendations and research opportunities set forth.
Radar level measurement improves inventory control for citrus processor
A Florida-based citrus grower and processor replaced manual tank level measurements inside a frozen warehouse with an automated system to cut costs, improve operations and enhance safety.
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Growing citrus has many challenges, as does processing the fruit. Nonetheless, in the state of Florida, it’s a $9 billion industry with 600,000 acres dedicated to citrus groves supporting about 74 million trees. Altogether, 76,000 people in the state are engaged in all phases of citrus production.
This population includes Southern Gardens Citrus, a grower/processor based in Clewiston, Florida. Southern Gardens Citrus is a worldwide supplier of premium, not-from-concentrate (NFC) Florida orange juice as well as orange by-products. The Southern Gardens Citrus processing plant was built in 1994 and is capable of processing up to 180 million pounds of oranges a year. The facility can store 56 million gallons aseptically, and ship and receive more than 100,000 tankers annually.
Like others in this industry segment, Southern Gardens Citrus must deal with problems such as citrus greening disease, international competition, and the inefficiencies that come with an aging plant, while staying as profitable as possible. Its facility in Clewiston — while still the newest of its kind in Florida — is 25 years old.
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Figure 1. Extracting juice is fully automated and the lines run continuously. Image courtesy of Southern Gardens Citrus.
Juice and more
Oranges and grapefruit are far more versatile fruits than most people realize. Juice is the primary product, but little of the whole fruit goes to waste. Once the juice is extracted (Figure 1), the peels are squeezed to produce a liquor, which can be made into citrus molasses for use in distilleries and even as cleaning products. The solids from the peel and pulp can also be dried, pelletized and sold as cattle feed. This article will focus on making orange juice concentrate.
To produce concentrate, fresh juice is put into an evaporator, where much of the water is removed until the specific gravity is raised to 65 °Brix, so it is very viscous. Storing the concentrate takes place in a special building within the facility where 16 tanks stand close together connected by catwalks (Figure 2). Each tank is 32 feet in diameter by 32 feet tall with a capacity of 186,514 gallons.
The building is a huge freezer. Florida is known for its heat and humidity, but the temperature inside this building is a frigid 16 °F (-9 °C), with a lot of internal air movement. Maintaining this environment allows the product to cool rapidly in the tanks, with no internal cooling coils or jackets required. And even with a product this viscous, foam can be created, so the product movement has to be handled carefully, with all filling and emptying processes from the bottom.
The tanks cycle through filling and emptying cycles one-by-one so there is activity in the freezer room on a daily basis. This is where all the concentrate inventory is stored, so it has to be monitored carefully to determine how much product is in each tank.
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Figure 2. Operators can walk around the freezer building above the tanks on a network of catwalks, but it is close to the air handling equipment and very cold. Image courtesy of Southern Gardens Citrus.
Monitoring concentrate inventory
When first built, Southern Gardens Citrus’ tanks were fitted with ultrasonic acoustic level instruments designed to determine the level in each tank reading from mounts on the tank roofs. These instruments proved to be temperamental and were removed from service. Operators had to check the tank levels on a daily basis by hand, using manual measuring devices. While the idea of going inside a freezer on a hot day in south Florida might have some appeal, the novelty wears off quickly when it takes up to 30 minutes to check just one tank while working in the bone-chilling temperatures.
Parkas and gloves are the uniform, and none of the operators necessarily like getting tasked with the job. It is also clear that checking 16 tanks daily required eight hours, so the plant spent as much as 56 man-hours per week on nothing but checking inventory in these concentrate tanks. Considering that plant operators are in short supply nationwide, telling a prospective employee that he or she will spend many hours in a freezer makes the job even more challenging to attract and retain operators.
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Figure 3. The new radar instrument bolted in place using the existing flanged spuds. Image courtesy of Southern Gardens Citrus.
Southern Gardens Citrus is a highly automated plant, so the notion of having to perform this routine level measurement task manually every day seemed a wasteful misuse of human resources. Unfortunately, the negative experience with the earlier measurement technology left an impression that meant any new solution would have to prove itself capable of solving several critical challenges including:
Deliver continuous readings that are precise enough at all product levels to satisfy production and financial planners
Perform flawlessly in the constant low-temperature environment of the freezer building
See through any layer of foam to determine the true product level
Eliminate any reason for operators to enter the freezer building related to level measurement
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Figure 4. The Rosemount 5402 is a two-wire, non-contact radar level instrument. Courtesy of Emerson Automation Solutions
Finding the solution
After studying Southern Gardens Citrus’ application, Emerson engineers suggested the Rosemount 5402 Non-Contact Radar Level Instrument (Figure 3). On paper it had the right specifications for measurement precision and maximum distance, and the electronic elements were rated for temperatures down to -40 °F (-40 °C). It could even be mounted using the flanged spuds on top of the tanks originally designed for the earlier ultrasonic instruments, so no tank modifications would be necessary. But, one question would have to be answered: Would it work as well in real life as the specs promised?
The first question related to foam. The concentrate coming out of the evaporators is viscous, but still flows easily prior to cooling. It is also prone to foaming. As a result, all connections to the concentrate tanks are from the bottom to eliminate any splashing. Still, there can be a layer of foam on top that forms during filling and tends to freeze. The foam surface is capable of reflecting the radar pulse, causing the instrument to deliver a false reading.
However, if the pulse is strong enough, the actual liquid surface can send a second reflection, and the measuring software can capture it as the true reading. The suggested non-contact radar level measurement instrument uses an approach called dual-port technology, which creates a stronger radar pulse for just this type of multiple echo application. This can be a much better approach for these and other similar applications than single-port configurations where the pulse is sent out and returns through the same port. This causes some of the energy to be diverted in both directions and results in lower usable power for the reading.
With dual-port technology, the pulse leaves through one port and returns through another, so far-less energy is lost. The result can be a 75% increase in reading power compared to conventional designs. This improves the quality of readings where there is potential for multiple echoes from multiple levels, and the one on top is not necessarily the most important.
Although Southern Gardens Citrus had challenges with measuring tank levels, other aspects of the application were favorable:
The tanks have no agitators, cooling coils or other internal obstructions
The inlet and outlet are on the bottom, so no product is pumped in from the side or top, which could disrupt the reading
The instrument is in a good location
The liquid surface, despite the product’s viscosity, settles flat so there are no mountains or gullies to confuse the radar image
Testing the concept
The plant made an initial test installation on one tank and found the instrument had no problem with the temperature. That was good news, considering how cable from the instrument’s transmitter runs to a controller located outside the freezer room, and since it is a two-wire device, it carries both the signal and power.
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Figure 5. Using Emerson’s Radar-Master software, workers can easily see how much concentrate is in each tank. Courtesy of Southern Gardens Citrus
The unit is also configurable via HART, so once the instrument was bolted in place (Figure 3) in the freezer room, it was possible to handle the settings and adjustments from outside using a handheld communicator, and to check diagnostic information to assess the instrument’s operational status.
The initial success provided all the proof necessary to issue the order to outfit all 16 concentrate tanks, and now data from all the new instruments is captured, presented and analyzed using Emerson’s Radar-Master (Figure 5) software. Southern Gardens Citrus has realized several important benefits, including how:
Operators can see exactly what is in each tank as they move product in and out of storage
Planners and accountants have a continuous live picture of concentrate inventory available at any time, not just once each day
Operators are freed from a cold and tedious task for more important duties
Plant managers can control output and
profitability on this important product stream thanks to high-confidence production data
Best of all for the operators, the new solutions mean no more gloves and parka-laden trips into the freezer to take inventory measurements.
Looking ahead, Southern Gardens Citrus hopes to duplicate this success on other troublesome applications in the facility. For instance, working with solid materials such as quicklime in Florida’s heat and humidity can present a variety of challenges. Quicklime is used as part of the cattle feed manufacturing process to reduce the acidity of the pressed peels and dried pulp. One of the company’s targets is finding a better way to monitor quicklime inventory and consumption.
Mecalux has equipped the 4th range food warehouse of Grupo Alimentario Citrus’s (GAC) production centre in Ribarroja (Valencia) with Movirack mobile pallet racking, push-back racks with rollers and live preload channels. Input and output pallet conveyors were also installed in the finished products warehouse. The combination of these solutions helps optimise the available space, to achieve a >1,500 pallet storage capacity and to organise goods according to their features and rotation.
About Grupo Alimentario Citrus (GAC)
GAC is a company which specialises in fresh product making. Among its main customers, Mercadona stands out, the leading supermarket chain in Spain.
The company carries a wide variety of fresh and healthy, on-the-go packaged foods, which it updates continually launching new products like green smoothies, different ready-to-eat salad varieties, spiralised courgette or quinoa salads, among others.
Needs of GAC
Grupo Alimentario Citrus focuses its business strategy on developing cutting-edge products, as well as diversifying popular ready-to-eat salad bowls.
It had to reorganise operations of the 4th range food processing plant’s warehouse in Ribaroja de Túria (just 20 km from Valencia) to handle business growth. The company, which maintains a close relationship with Mecalux for many years running, once again requested its collaboration to expand the warehouse and mould it to the storage requirements.
GAC knew more storage capacity was a must, with products sorted as per their characteristics and rotation. Likewise, by dealing with perishable products, it would have to pay special attention to preserving the cold chain in all processes, aiming to ensure the foods’ maximum quality and optimal freshness.
Pau Pérez - GAC’s project engineer
“The automated warehouse for the 4th range plant in Ribarroja has solidified our decision to go with efficiency and quality service that the system gives our installations. We enjoy greater versatility and speed in our dispatches, while at the same time we have improved workplace safety for our workers.”
The installation –which runs at a steady 4 ºC–is split into four different zones, each one allocated to a specific operation and product type. These zones are separated via vertical doors that block cold air from escaping.
Mecalux has supplied a quadruple storage solution:
Movirack mobile pallet racking
Live preload channels
Push-back pallet racking
Finished product warehouse
This warehouse holds processed goods waiting to be shipped out. It contains eight double Movirack mobile pallet racks, each 8 m high with three storage levels, placed on laterally sliding mobile bases.
It operates straightforwardly: the operator gives the automatic open order to the base selected via a remote control device and, then, enters the desired aisle, where they slot or pick goods with the help of a reach truck.
The system is equipped with several safety devices whose role is to protect the operators and the stored goods. Among these are:
External sensors: stop everything in motion if a person enters the aisle.
Internal sensors: detect the presence of objects inside the aisle that would prevent the system from operating properly.
Proximity sensors: ensure a safe, smooth stop.
Mecalux has also installed input and output conveyors for the goods in this warehouse. The conveyors –with rollers for inputs and chains for outputs– mean pallets can accumulate on the belt and this facilitates quick product retrieval.
Consumer goods warehouse
High consumption products (i.e. consumer goods) are set in two specific distribution centre zones.
Both are comprised of push-back racks with rollers, a solution that secures high space-purposing density and reduces handling times of the goods.
Access to the goods is done from a single working aisle. The first pallet is placed in the level’s first slot (closest the aisle). By inserting the second pallet, it pushes the first, and so on, until the channel is full. The racks are inclined, meaning the front is slightly lower to encourage the unit loads to advance through gravity to the first position when a pallet is removed.
Picking is also done in one of these two zones. To do so, 7.5 m high pallet racks were set up, whose direct access to the merchandise provides direct order picking off lower levels.
The warehouse has a huge preloads staging area with twelve live channels that are each eleven pallets deep.
Roller channels are slightly inclined so that pallets slide via gravity from the highest to the lowest point (which faces the docks). The channel’s split-roller outlet allows unloading via pallet truck.
Pallets are grouped according to if they correspond to a particular order or route, aiming to speed up subsequent distribution vehicle loading which minimises wait times.
Advantages for Grupo Alimentario Citrus (GAC)
Efficient organisation: each product is slotted in the most suited storage system taking their characteristics and rotation into account.
Storage capacity: the combination of different storage systems provides a 1,531 pallet capacity.
High productivity: all installations are organised to dispatch the goods at a fast pace.