Sugar is a staple commodity in most countries worldwide. It is believed that the production of sugar dates back to 8000 B.C., produced from two primary sources namely, sugar cane and sugar beets. Presently, around 120 countries produce sugar, with 80% of sugar extracted from sugar cane and the remaining 20% from the sugar beet. In India, sugar cane is one of the dominant plantations, taking place in October, March, and July annually, depending on the location. India is the world’s largest consumer and producer of sugar, with sugar mills producing more than 305 lakh tons of sugar annually. Boilers in sugar industry play an imperative role in various process operations.
Sugar is available in various forms, and the most widely consumed among them is granulated sugar, also known as table sugar. Table sugar with large crystals is known as coarse sugar, and the one with smaller crystals is called superfine sugar. Other types of sugar consumed are brown sugar, powdered sugar, pearl sugar, muscovado sugar, turbinado-style sugar, and demerara-style sugar.
Process Stages in a Sugar Mill:
Sugar cane or sugar beet undergoes several stages of processing before sending it to markets and shops. The process stages in the sugar industry include:
Washing:
Once the sugar cane or sugar beet is transported from farms to sugar mills, it is washed before further process. Washing takes place on belts sprayed with water or flue gases containing water. The products are washed by rotating and removing dirt in a rotating drum sprayed with water. Sugar cane is crushed through rollers or swing-hammer shredders and then sprayed with hot water. On the other hand, sugar beet is sliced as small stripes called cossettes that are soaked in hot water to swell plant cells for the extraction process.
Extraction:
Extraction of juice from sugar cane takes place through milling, in which a series of mills crush the sugar cane fiber to separate the juice from the bagasse that can be used as a fuel source. The juice collected is dark green in color and acidic with the sugar concentration that is measured. In the case of sugar beets, the cossettes are filled in tanks of 10 to 20 meters in length that transport sugar beet upwards through a rotating shaft as the sugar is extracted.
Purifying Juice:
In this stage, the sugar cane juice extracted is further purified in a tall tower-like structure. The sulfur dioxide vapor at the bottom starts rising in a process termed sulfitation. Soluble non-sugar material is further separated from sugar juice by the process of carbonation that consists of calcium carbonate or calcium sulfite that assists in precipitation. The juice is heated to denature the protein properties and then mixed with calcium hydroxide. Carbon dioxide bubbles are administered to reduce the alkalinity and the sludge formation that requires filtration to purify the juice.
This process may take several hours, and the sludge is further filtered to remove the remaining sugar. The purified juice is later boiled in a series of evaporators till it reaches 50% to 65% of sugar concentration.
Crystallization:
Crystallization is a major process stage that relies on a steam boiler. In the crystallization process, a vacuum pan evaporates the syrup to saturate with sugar crystals through a process, termed seeding. This seed is pure sucrose suspended in alcohol and glycerin that is added to the syrup. The minute grains of sugar in the solution helps in extracting the sugar in the solution and forming it into crystals. With the boiling of the mixture in the vacuum pan, the crystals convert into a paste known as ‘massecuite’ that is a mixture of sugar crystal and syrup. The mixture is further processed in a large container named ‘crystallizer’ to continue crystallization by stirring and cooling the massecuite.
Centrifugation:
The massecuite is transferred to a high-speed centrifuge to separate sugar crystals and molasses. The centrifuge rotates at 1000 to 2800 revolutions per minute to remove the molasses and retain the sugar in the centrifuge basket. After the process of centrifugation, the sugar is washed with water.
Drying:
Large hot air dryers are used to dry damp sugar crystals and reduce their moisture content to as low as 0.02% and then pass it through hot air in a granulator. The dried crystals are later segregated as per their sizes and packed to transfer to the market.
Role of Steam Boilers in Sugar Processing:
Steam boilers are pivotal in the processing operations of crystallization and drying in sugar mills. Boilers in sugar industry primarily use bagasse, coal, and biomass as fuel. Boilers with traveling grates can ensure proper combustion with fuels like coal and biomass, thus saving excess fuel costs. Additionally, boilers in sugar industry also generate electricity through cogeneration plants.
For optimal performance of the steam boiler in sugar processing, it is advisable to reduce the excess air for the combustion of solid fuels. It helps in improving energy efficiency and reducing emissions. The excess air that reduces the boiler efficiency leads to carry over. Carryover causes erosion in equipment such as economizer, Induced Draft (ID) fan, etc., resulting in unexpected downtime.
It is also essential to monitor the fuel quality and modify the amount of air required for complete combustion and preventing unburned fuels and stack losses.
Rakhoh Boilers have manufactured and delivered efficient steam boilers for the sugar industry that are ideal for sugar processing and generating electricity. Our models such as Bi-Drum/D Type/Power X, Solid Fuel Bi-Drum, Combo X are preferred by our sugar process industry clients.