Beet sugar factory
A beet sugar factory, or sugar factory, is a type of production facility that produces sugar from sugar beets or alternative plants to sugarcane in making refined sugar. These factories process the beets to produce refined sugar, similar to sugarcane in other regions. The process involves several steps, including washing, slicing, and extracting the sugar content through diffusion. Nowadays, most sugar factories also act as sugar refineries. The first beet sugar factory was built in 1802.
Sugar mill, factory and refinery
Beet sugar factories can differ in the extent of the processing:- Most process sugar beet into white sugar and brown sugar.
- Some process beets only as far as an intermediate stage to be refined elsewhere.
- A few process beets and also process raw sugar from cane in their refining section.
When the first facilities to produce sugar from sugar beets were built, these facilities were mostly called manufactories or just factories, simply because they were buildings where something was manufactured. These first sugar factories were modest affairs driven by animals, wind, or waterpower. Like the sugar mills, sugar factories sold most of their raw sugar to sugar refineries. In time, most beet sugar factories began to refine their own production, but this did not lead to them being called refineries. In 2005, all sugar factories in the United States produced only refined sugar, but this was not universal practice.
In the tropics, the introduction of the steam engine put an end to the clear definitions of mill, factory, and refinery. The creation of large separate steam-powered facilities to produce raw sugar led to the separation of the manufacturing of raw sugar from the occupations of the planter. These buildings were also called sugar factories. Nowadays, the distinction between a sugar mill and a sugar factory is in whether it refines the raw sugar that it produces or sells it. This explains why in India EID Parry refers to sugar factories.
It is important to note that the distinction between a sugar mill and a sugar factory lies in whether it refines the raw sugar it produces or sells. The processing steps involve the purification of sugary liquid extracted from beets, including carbonatation and crystallization, which are integral to sugar refining processes.
Sugar beet processing
In the 1960s, beet sugar processing was described as consisting of eight steps, but these can be further divided into smaller steps. Transport could be considered the first step although it was not considered a direct part of production. However, transport cost was very important for the scale at which processing could take place. Storage was an important separate step as well. Purification of the sugary liquid extracted from the beet, including carbonatation and crystallization, are not specific to sugar beet processing, and similar steps are used in the production of sugar from sugarcane. Therefore, these were the primary part of the Sugar refining process.Transport
After they are harvested, beets are transported to a factory. In the United Kingdom, beets are transported by a hauler, or by a tractor and a trailer by local farmers. In Ireland, some beets were carried by rail, until the complete shutdown of Irish Sugar beet production in 2006.In areas with good navigable inland waterways, transport by boat used to be prevalent. See e.g. the media related to boat transport to Halfweg sugar factory in the Netherlands. In time, it was replaced by road transport, but due to the increased cost, traffic congestion and environmental concerns, boat transport came into use again for longer distances in 2021.
A mode of transport that has almost disappeared is the transport of raw juice by pipeline. The concept is that one or more râperies first extract the raw juice from the sugar beet. The juice is then transported by pipeline to a central sugar factory. The Râperie de Longchamps in Belgium is the last remaining râperie in Europe.
Reception
On arrival at the factory, each load is weighed and sampled at the tare-house. The beet sample is checked for:
- soil tare – the amount of soil and other detritus from harvesting that is included in the load;
- crown tare – the amount of beet that forms the crown of the root. This has a lower sugar content than the rest of the root and has less value to the operator;
- sugar content – a measurement of the amount of sucrose in the crop;
- nitrogen content – for recommending future fertilizer use to the farmer.
Storage
The load is then tipped onto the reception area, typically a flat concrete pad. From there, the beets are moved into large heaps. When it is time to process them, the beets are moved into a central channel or gulley and are washed towards the processing plant.Washing and scrubbing
The next step of the production process is washing and scrubbing. This is done by moving the beet around in washing and scrubbing tanks not unlike a washing machine. However, the actual washing is caused by the friction of the sugar beets against each other. This removes sand and stones and other objects.Slicing
The cleaned beets are then mechanically sliced into fine "v" cross-section strips, called cossettes. The V-shape maximizes the area of the slice while maintaining some rigidity to the cossette so it is not completely broken up in the diffuser.Diffusion
The cossettes are then passed to a machine called a diffuser. Here hot water permeates them to extract the sugar content into a water solution, a process known as leaching. The diffusion process ends with two products: raw juice and beet pulp.Diffusers are long vessels of many meters in which the beet slices go in one direction while the hot water goes in the opposite direction. The movement may either be caused by a rotating screw moving the cossettes or the whole unit rotating in which case the water and cossettes move through internal chambers of the drum. The three common designs of diffuser are the horizontal rotating "RT", inclined screw "DDS", or vertical screw "Tower". Modern tower extraction plants have a processing capacity of up to per day. A less-common design uses a moving belt that carries the cossettes over a series of tanks. Water is pumped onto the top of the belt and passes through the cossettes into the tank below which it is pumped over the next section. In all cases, the flow rates of cossettes and water are in the ratio one to two. Typically, cossettes take about 90 minutes to pass through the diffuser, the water only 45 minutes. These countercurrent exchange methods extract more sugar from the cossettes using less water than if they merely sat in a hot water tank. The liquid exiting the diffuser is called "raw juice". The color of raw juice varies from black to a dark red depending on the amount of oxidation, which is itself dependent on diffuser design.
The used cossettes, now called beet pulp, exit the diffuser at about 95% moisture, but low sucrose content. Using screw presses, the wet pulp is then pressed down to 75% moisture. This recovers additional sucrose in the liquid pressed out of the pulp, and reduces the energy needed to dry the pulp. The liquid pressed out of the pulp is combined with the raw juice, or more often introduced into the diffuser at the appropriate point in the countercurrent process. The final byproduct, vinasse, is used as fertilizer or growth substrate for yeast cultures.
During diffusion, a portion of the sucrose breaks down into invert sugars. These can undergo further breakdown into acids. These breakdown products are not only losses of sucrose, but also have knock-on effects reducing the final output of processed sugar from the factory. To limit bacterial action, the feed water may be dosed with formaldehyde and control of the feed water pH is also practiced. Attempts at operating diffusion under alkaline conditions have been made, but the process has proven problematic. The improved sucrose extraction in the diffuser is offset by processing problems in the next stages.
The products of the diffusion step are beet pulp and raw juice. The beet pulp is generally used as livestock feed. It can be sold directly as "wet pulp", but wet pulp has high moisture and soon develops mold. Dried pulp has higher value whether sold as shreds or pelleted. Pulp can also be mixed with molasses during the drying process for higher nutrient content. The raw juice moves to the next processing stages for removal of impurities and conversion to solid sugar.
Sugar refining
The production of white sugar from the beet extract is similar in some parts to the production of sugar from raw sugar derived from sugar cane but adapted to the particular circumstances of beet.Purification
The raw juice first undergoes purification to remove impurities which affect white sugar recovery quantity and quality. The steps commonly used for beet are carbonatation and sulphonation. Carbonatation uses milk of lime, an alkaline liquid produced from calcium hydroxide, together with carbon dioxide to precipitate impurities into a form that can be removed from the raw juice.In the carbonation step, proteins are coagulated, and the calcium carbonate forms solid particles which incorporate the coagulated materials, pieces of vegetable matter, and absorb some soluble impurities. The high alkalinity destroys monosaccharides and other compounds which are thermally unstable and would breakdown in subsequent processing steps. The precipitate is removed by gravitation and filtration to leave a clear, lighter colored alkaline liquid known as thin juice. Flocculants may be used in the process to speed separation of precipitate.
Thin juice may then undergo a sulphonation step, in which sulfur dioxide is used to bleach this juice.
The addition of milk of lime and carbon dioxide may be in sequential steps with pre-liming and primary and secondary carbonatation steps separated by filtration of precipitates or in a process where juice is continuous cycling through primary and secondary steps to build particle size with a clarifier and rotary filters to remove precipitate.