Molatek – 19 years of custom designs

By Ilana Koegelenberg

In 1998, HC Manufacturing first supplied Molatek with a world-first innovative solution for a problem of spontaneous combustion occurring in stacks of animal feed bags. Since then, HCM has supplied them with a total of nine refrigeration systems, each an improvement on the last.

THE INITIAL PROBLEM

In the past, gas forming in bags of feed stacked at Molatek’s Animal Food Division was accompanied by heat which had no way of escaping. This led to generating temperatures that resulted in spontaneous combustion destroying product, delivery trucks (both road and rail), stock, and warehouses.

Even after enlisting the assistance of the Council for Scientific and Industrial Research (CSIR) in researching the problem, no clear-cut solution could be found. In the meantime, the Molatek production team in Malelane continued evaluating the problem, looking for solutions.

The complex refrigeration system in the casing that had to be manufactured to fit into the plant structure. The switch panel housing electrics and PLC controls.Mike Schaefer (left), the design engineer, during commissioning with Molatek’s plant engineer. The original monitor.

Three factors that contributed towards the problem of spontaneous combustion — namely heat, moisture, and pressure — were identified. If one of these three factors were to be eliminated, the pressure/temperature generation cycle could be broken.

It would be almost impossible to solve the pressure problem as there was no other sensible way to store the feed bags other than by stacking them. There simply would not be enough space to store the feed in any other way.

Secondly, it was not feasible to reduce gassing by removing moisture from the product as this would lead to caking and hardening of the feed which would render it useless.

The only solution would be to cool down the feed itself thereby reducing the heat or energy in the stacks. The Molatek team, therefore, decided to pursue this line as the most likely route to a solution.

One indication that high temperatures could be controlled by cooling the feed was the fact that during the colder winter months there were fewer incidents of spontaneous combustion when compared to the warm summer months.

The cooling down of any molasses-based product was a huge challenge and no examples could be found of this type of technology being employed anywhere else in the world.

A team of engineers was appointed to investigate methods of cooling down the feed before it was bagged. After several tests using a pilot plant, a full-scale cooling unit was designed and manufactured in June 1997.

The cooling plant was operational by February 1998 and initial results were very positive.

Feed, fed through the cooling plant at a rate of seven tons per hour experienced  a drop in temperature from 40°C to below 20°C — in some cases even as low as 15°C.

The evaporative condensers after rigging with the roof sheeting removed.The evaporative condensers in the confined space.The finished product before delivery. The packaged unit being lifted into position.

SYSTEM DESCRIPTION

HCM’s main considerations in the design of this refrigeration system were as follows:

  • Functionality (considering various alternatives)
  • Cost-effectiveness
  • Availability of components
  • Site suitability (the initial plant had to be rigged through the roof!)
  • Design and manufacturing period.

The refrigeration system was designed to cool air from ambient temperature to a temperature of approximately 5°C. This air was directed into a rotating drum entering at one end of the drum and being brought into contact with the product (counter flow) before it exited at the other end of the drum.

The cooling plant   consisted of two evaporative condensers and a packaged refrigeration / air handling unit where air entered the air handling unit at the filter section where it was cleaned by two stages of air filters before entering the compressor section.

After the compressor section, air needed to be cooled by three stages of refrigeration before entering the fan section at the end of the last cooling stage. Here, a fan discharges the air into a supply air duct, which is connected to the drum product outlet end.

The duct is fitted with an opposed blade damper that maintains a constant airflow, depending on the dirty state of the filters and/or the wet state of the cooling coils. Due to the very corrosive atmosphere, the complete unit, including the cooling coils, is manufactured from high-grade stainless steel.

The three cooling stages are each independent refrigeration circuits. Two of these stages are connected to one evaporative condenser and one system is connected to the other evaporative condenser. The systems are connected to the condensers by means of treated copper tubing refrigerant lines.

The condensers draw in air from the surrounding building and discharge it through the roof.

The entire system is fully automatic and is controlled by a microprocessor-based control system that controls the electromechanical functions of the unit.

The total cooling capacity amounted to 372kW for this first system.

The initial casing was made from fibreglass but is now primarily constructed from first-grade stainless steel.Molatek as seen from above — it has grown considerably over the years. The original unit designed by HCM.Stephen Steyn of Robertec seen in the picture while commissioning the original system on site. The control panel of the latest unit.

A LASTING RELATIONSHIP

This project was featured in the November 1998 edition of what was then still Refrigeration and Airconditioning (now RACA Journal).

Since then, the Molatek Malelane operation has expanded significantly and they have continued their partnership with HCM — their cooling plants now totalling nine, as of 2017.

Not much has changed from the initial design, just a few tweaks to modernise it. The HCM team has had the opportunity to test the system over the nearly two decades they have been supplying Molatek, finding out what works and what does not.

Things like electronic expansion valves have been added and the casing has been changed, too. The initial casing was made from fibreglass, but now everything is done in stainless steel (as copper would not last six months with the amount of ammonia released into the atmosphere). This still leaves the challenge of the fans as these do not come in a stainless steel option, making them essentially a consumable item.

Molatek is very happy with HCM’s work, which is why they have continued the relationship. “HCM, as far as we know, was the only company at that stage that could design and build a cooling unit that suited our expectations and requirements,” explains Pieter Deacon, Molatek’s projects manager – Animal Feeds (Sugar and Milling Division). “After that, they gave us ongoing excellent service on the cooling system,” he says. “They are still giving us a good service.”

* Photos courtesy of HCM


 

Click below to read the January 2018 issue of RACA Journal

RACA JAN2018

 

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