Steam jet equipment manufacturer Applied Vacuum has supplied a KwaZulu-Natal sugar mill with two steam jet thermocompressors to replace the mill’s mechanical vapour recompressor (MVR).
Applied Vacuum was approached by the sugar mill to supply an alternative to the MVR, which often broke down. The mill needed technology that would not only use high-pressure steam to compress low-pressure steam, but also keep it running uninterruptedly.
“The sugar industry generates steam for its plants, either by burning coal or by using bagasse. As coal is expensive, these plants generally use bagasse, but if it is in short supply or the bagasse runs out, they have to use coal,” says Applied Vacuum MD Geoff Levy.
He mentions that, although the steam jet thermocompressor ejector is not as efficient as the MVR it has replaced, it offers greater operating reliability.
“The installation of the thermocompressors are more of a cost-saving exercise, as the mill is now burning less coal, which is an expensive input material,” says Geoff Levy.
Applied Vacuum project manager Lael Levy points out that he has discussed the advantages of the steam jet ejectors and their cost advantages with KwaZulu-Natal sugar mills and refineries.
In addition to steam jet ejectors, liquid ring pumps are also used in the sugar industry.
A liquid ring pump is a rotating positive displacement pump and is typically used as a vacuum pump but can also be used as a gas compressor. Its function is similar to that of a rotary vane pump. The difference is that the vanes are an integral part of the rotor and churn a rotating ring of liquid to form the compression chamber seal.
It is an inherently low-friction design, with the rotor being the only moving part. Sliding friction is limited to the shaft seals.
By contrast, a steam jet ejector is a type of pump that uses the Venturi effect of a converging-diverging nozzle to convert the pressure energy of a motive fluid into velocity energy.
It then creates a low-pressure zone that draws and entrains a suction fluid. After passing through the throat of the injector, the mixed fluid expands. The velocity is reduced, which recompresses the mixed fluids by converting velocity energy back into pressure energy.
“Liquid ring pumps are more efficient on paper. They use less energy than steam pumps but the cost of repairing one liquid pump every year is the same as buying a brand-new steam jet ejector,” says Geoff Levy.
“This is a well-proven technology and we’re the only people in the country who produce it. “In Germany, there are only two companies producing this technology and, in the whole world, there might be 30 or 40,” he adds.
Applied Vacuum has produced equipment for various sectors in South Africa and has expanded into the sugar industry to promote the use of steam jet ejectors, which are used in most sugar producing countries in North, South and Central America. Steam ejectors have become items of choice in other countries because they require minimal maintenance.
In addition to the steam jet ejector, the company has also provided other equipment for the sugar mill industry. It has designed and manufactured a line of steam desuperheaters, including the steam atomising type, which has a large turndown capability.
This is used as the driving force to create a fine spray with the cooling water to maximise the surface contact area between the steam and water, thereby increasing the rate of water evaporation.
Another Applied Vacuum product is the steam-injection heater nozzle, which has been successfully used in sugar remelting tanks.