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New degreening rooms for Sundays River Valley

By Jacques Mouton, Project Manager, Refrigeration at Coldfact Projects | All image credits © Coldfact Projects

The Sundays River Citrus Company (SRCC) manages approximately 9 million cartons of citrus for export, and a further 2.5 million pockets of oranges for the local market each season.

From their humble beginnings way back in 1924, the SRCC has grown into the largest grower, packer, and exporter of South African citrus. Respected internationally as a trusted supplier, their strategy continues as a reliable provider to both local and international markets of excellent quality fruit. The SRCC is proudly owned by their growers that produce:

  • Clementines (mandarin family)
  • Nadorcotts (mandarin family)
  • Novas (mandarin family)
  • Lemons
  • Navel oranges
  • Cara oranges
  • Valencia oranges
  • Star ruby grapefruit

All citrus fruit processed is exclusively grown in the famous Sundays River Valley that is said to be exceptionally blessed in beauty and has everything needed to produce the finest tasting citrus. They further state that the very best lemons in the world are produced in the Sundays River Valley.

Phase one of this project was the supply and installation of 10 de-greening rooms, with a further four rooms to be added in future. The projected commenced on 1 March 2021 and was completed on 30 April 2021. It was completed according to schedule through good planning and management of the work required, while also having to negotiate the installation around other contractors working on site.

De-greening is an international practice in the process of removing the green colouring (known as chlorophyll) from the skin of citrus fruit. This is achieved by introducing measured amounts of ethylene gas into a temperature and humidity-controlled environment. It is important to note that only mature fruit is suitable for de-greening.

The facility at the start of the construction process.

The facility at the start of the construction process.

It is absolutely critical that immature fruit is not harvested and de-greened. Immature fruit will have very high acid levels and low sugar levels and will generally not meet minimum standards, but immature dark green fruit will also not successfully de-green. Ethylene treatment only helps with the breakdown of the green colour in the skin. The process using ethylene does not ripen fruit. The levels of sugars and acids are not affected by de-greening and therefore when de-greening fruit, it is critical to apply the process in mature fruit based on particular colour. The correct de-greening process also assists in the shelf life of the product.

Degreening is necessary for several reasons, including that consumers associate green citrus fruit with immaturity and thus poor quality while the fruit colour is due to the interaction of chlorophyll (green) and carotenoid (red – yellow) pigments. Colour change in the field is especially stimulated when night-time temperatures drop below a specific value.

Room design

Each room has a chilled water (110kW) and hot water (80kW) coil with two evaporator fans.

Temperature control is achieved with two-way modulating valves to control the room temperature between 19°C and 22°C depending on the citrus cultivar being de-greened.

Each room has a water spray nozzle to maintain the humidity in the rooms at 98% relative humidity (RH). Control in this element is with dry bulb and wet bulb sensors for accurate measurement and spark-proof solenoids. Ethylene classification will be changed to flammable gas and thus the spark-proof solenoids were selected as a precaution.

Each room is fitted with a CO₂ extract fan to control the CO₂ levels below
5 000PPM. The rooms also each have an ethylene supply which again is controlled with a spark-proof solenoid. Ethylene is introduced into the room only when the room temperature and RH are at the set values and kick-starts the de-greening process. Each room, with a 480-bin capacity of citrus, will be de-greened over a 72-hour cycle. This is an industry norm but can be achieved in a shorter time if required.

Each room is controlled via a PLC, connected to the Eliwell Telivis monitoring system and an HMI installed in front of each room. Each room can be controlled and monitored from the Telivis or the HMI. A history on the performance of each room can also be downloaded from the Telivis BMS system.

Chilled water is maintained at 6°C. Hot water is maintained at 45°C.

Equipment used in the project

Two Daikin water cooled chillers, with a cooling capacity of 519kW each, were installed for the cooling requirements.

Two IWC cooling towers were installed for each of the chillers with a THR of 675kW each.

Two 10 000 litre insulated plastic buffer tanks were installed as hot and cold well storage tanks for the chilled water.
Two secondary chilled water pumps were installed for the water distribution to the chilled water coils. The pumps are controlled with variable speed drives (VSD) to maintain constant water flow.

Two Daikin heat pumps were also installed with a heating capacity of 300kW each for the hot water requirements.

Two 5 500 litre Sirac hot water buffer tanks were installed as hot and cold well storage tanks for the hot water element of the project.

Two secondary hot water pumps were also installed for the water distribution to the hot water coils. Again, the pumps are controlled via VSD’s to maintain a constant water flow.

Two primary pumps controlled on pressure, were installed to supply water at 5 Bar to the humidification spray nozzles in each room. Class-12 HDPE pipe, with fusion welded fittings was selected for the installation in the chilled water and hot water elements to the 10 rooms.

Class 12-PVC piping with stainless steel headers was installed in the plant room. All piping is insulated with 40mm polyurethane sections and vapour sealed with fibreglass wool, resin, and hardener. With the high humidity conditions, mould growth on standard foster/calico insulation will be difficult to remove or treat. With fibreglass it can be washed and sterilised as required and was thus selected for the installation.

Elements of difficulty

As with many steel supplies, a nationwide shortage of HDPE and PVC pipe and fittings was a notable struggle to get stock on for this project due to a shortage of raw material.

A shortage of ethylene flow meters and flame proof solenoids was also a challenge and had to be specially imported for the project.

Energy efficiency

The chillers have stepless screw compressors for capacity control, operating with R134a refrigerant and a COP of 5.2. The global warming potential (GWP) of the refrigerant is 1300.

Heat pumps have high efficiency scroll compressors operating with R32 refrigerant with a COP of 3.2 and GWP of 675.
Circulation pumps controlled via VSDs allow optimal energy efficiency of these elements. Control valves are controlled via modulating 0-10VDC inputs for exceptional precision control.

With an 80kW heating requirement for each room, hot water used for heating is not generated via mechanical heater elements.

List of Professionals:

Project Name SRCC Addo
Owner Sundays River Citrus Company
Designer GPB Consulting and Planners
Project manager GPB Consulting and Planners
Consulting Engineer Jeff Wedgwood Consulting Engineers
Contractor Coldfact Projects CC
Product Suppliers Daikin SA Water cooled chillers (CUWD150CSY1)
Daikin SA Heat pumps (300kW)
IWC Cooling Towers Cooling Towers
Thermocoil Hot and cold water coils
Donkin Fans Evaporator fans
Calpeda Pumps Pumps
Keystar Eliwell Controls PLC controls and Telivis BMS
Carel Controlli two-way valves and actuators
Cape Instruments Ethylene flow meters
Hydraquip Sparkproof solenoid for ethylene and water
AMS CO₂ extract fans
Electromechanica Electrical switchgear and variable speed drives
West Coast Power Solution Distribution board enclosures