More ways to recover energy in sugar refineries
Pre-heating at melting stage offers opportunity to reduce energy consumption
Author: Jean-Marc Reichling
For more than 30 years, indirect heat transfer using vertical plate technology has been accepted as a proven and effective method for cooling granulated solids such as sugar crystals before storage and packaging. Solex Thermal Science first pioneered its moving bed heat exchanger technology in the late 1980s within the Western Canadian fertilizer industry, later developing additional applications within numerous food and industrial sectors.
In 2000, our Calgary, Alberta-headquartered company commissioned its first sugar installation in Europe. Since then, Solex has installed its proprietary cooling technology in sugar plants around the world such as France, Germany, Portugal, Mexico, Poland, Russia and the United States.
|Pictured left, a refined sugar cooler for 65 tph. Pictured right, a raw sugar cooler in Colombia.|
Until 2015, most of these installations were focused on cooling refined sugar. In 2014, however, Solex successfully launched a solution to also cool raw and amorphous sugar, leading to installations in key sugar-refining countries such as Peru, Brazil and Colombia.
Today, the types of plants utilizing Solex’s indirect cooling technology covers all spectrums of the sugar industry, ranging from sugar beets and cane to refineries and producers of starch and derivate sugars (e.g. Maltose and Sorbitol). The technology can also be installed either as a primary or a secondary cooler, and is readily adaptable to plant retrofits due to its small footprint (typically two metres by two metres).
The cooling technology used by Solex consists of banks of vertical, closely spaced, hollow, stainless-steel plates, commonly known as pillow plates. Sugar flows slowly by gravity through the channels while a cooling fluid (e.g. water) passes counter-currently within the plates, resulting in high thermal efficiency. The cooling occurs by heat transfer through the sugar particles, and is based exclusively on thermal conduction.
A vibrating feeder is commonly used as the discharge device, which guarantees uniform velocity of the product (mass flow) at any position within the heat exchanger.
In sugar refineries, Solex’s technology can also pre-heat the crystals by recovering low-grade energy from elsewhere in the plant that is otherwise wasted. The unique design of Solex’s heat exchangers provide a high-density heat transfer area within a compact unit that allows for efficient utilization of the recovered energy. The narrow channels provided by the pillow plates make this possible by maintaining high velocities of the working fluid in the channels, which is essential to high rates of heat transfer.
Solex has already successfully installed several pre-heaters in the oilseeds crush industry to warm up seeds (e.g. rapeseed, soybean and sunflower seeds) before the oil extraction step (e.g. cookers and press screw). The low-grade energy used in these applications is typically either condensate or hot water coming from the gas treatment of the oil extraction process.
The first step in the sugar refining process (or second if an affination step takes place) consists of melting the raw sugar into a stirred tank called a melter. (See figure on left). To melt the sugar, direct steam injection into the melter is often needed for the solution to reach 70 to 85°C.
If the temperature is too high, it could negatively impact the final product (e.g., darkening or yellowing the sugar). This can then lead to higher ICUMSA scores (the grading scale is a type of yellowness index from the International Commission for Uniform Methods of Sugar Analysis). Higher ICUMSA scores for refined sugar means a lower-value product.
The objective of the melter is to produce a melt liquor around 70 Brix at 75°C.
By installing a vertical indirect heat exchanger before the melter and utilizing the available, low-grade waste heat such as hot water coming from condensate or fume treatment, operators can pre-heat the sugar crystals. Doing so reduces the amount of steam that needs to be injected and, in turn, overall energy consumption.
The payback period for this type of project will depend on conditions such as the cost to produce steam and the amount of pre-heating that is needed. For example, in cold climates, the incoming raw sugar can be below freezing ambient temperatures. A pre-heating step in these situations will significantly reduce the energy needs of the melter.
In some cases, government subsidies are also available to encourage investments in energy-efficiency improvements. Comparatively, several models have shown that, at the cooling stage, indirect heat transfer technology can reduce energy consumption by four to 10 times as compared to alternative technologies used in sugar plants such as rotary drums or fluid beds.
Learn more about how Solex uses indirect heat transfer technology to pre-heat and cool sugar.
About the author: Jean-Marc Reichling is a Global Sales Director with Solex Thermal Science who has more than 20 years of experience in developing heat transfer solutions for sugar beet, cane and refining applications.
This entry was last updated on 2021-6-9
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