GLIAS VISIT TO TUNNEL REFINERIES
28TH June 1996
By Bruce Blissett
The GLIAS group assembled in the training centre where we were welcomed by the Environmental and Safety Manager, Mr. Turner who started by emphasising the company’s respect for the local environment. He said that the company had set out a garden area and created a riverside walkway. He added that the smell about which local residents had complained was due to the processing of maize, which had just ceased. The group was told that the company generated all its own steam, compressed air and electricity of which any surplus was sold to the national grid.
The company processes all waste water from the factory. At present, the waste water is made suitable for discharge to sewers but a new aerobic waste water treatment plant is being commissioned for producing an effluent suitable for direct discharge into the Thames.
Mr. Turner outlined the sources of raw materials, me company’s products and the methods by which they were manufactured. In summary, products manufactured on the Greenwich site include animal foodstuffs, starch. Vital Wheat gluten, glucose syrup, dextrose monohydrate, fermentation syrups containing maltose and blended syrups containing combinations of glucose, fructose, maltose, maltotriose and higher sugars.
Potable alcohol is also produced by the fermentation and distillation of a low grade glucose syrup which would otherwise be unsuitable for sale as a foodstuff ingredient. By-products, rich in vegetable protein, are also sold for animal feed.
Glucose, fructose and maltose etc, arc made from the same starting material, namely, starch. Starch is obtainable from many crops but the source exploited by Tunnel Refineries is milled wheat grain and until recently, maize.
Maize was formerly shipped from France and unloaded from the jetty into large silos. After cleaning, the maize was transferred to large stirred cylindrical tanks where it was treated with water containing sulphur dioxide and, after a few days. The seeds were soft enough to be mechanically broken open to allow the starch to be extracted using demineralised water.
Wheat is milled at the company’s Marston Mill in East Anglia. The wheat germ is removed and sold to make cooking oil while the remaining flour is supplied to Tunnel Refineries in road tankers.
Starch is converted into glucose syrup by either of two methods. Glucose is formed when a starch solution is sprayed into a fast moving stream of steam or it may be produced by Heating the starch solution with an enzyme (presumably diastase) and acid hydrolysis using dilute hydrochloric or sulphuric acid. Maltose and fructose are produced by enzyme processing.
Pure starch is used as a thickener in soups, gravies and sauces etc while modified starches are used in paper manufacture.
Finally the group was shown, on a map of the site which parts of the works would be visited.
The Works Tour.
In the subsequent tour of the site, the group was shown the waste water treatment plant which uses an anaerobic process to produce an effluent fit for discharge into sewers. Also visible was the new aerobic processor for producing an effluent suitable for direct discharge into the Thames. It was pointed out where the maize was formerly cleaned and our tour took us past Greenwich Distillers where potable grade ethyl alcohol was recovered from processed low-grade glucose syrup.
It was evident that the company is in a state of continual change and heavy investment is being made in rearranging the site as a result of the discontinued use of maize as a raw material.
The group was shown where the maize was formerly soaked in demineralised water and treated with sulphur dioxide to soften and sterilise it. Sulphur dioxide for this was generated from two small burners; each contained in a metal box about 18 inches cube from which the gas was pumped from a chimney from the top of the box. Softened maize was then transferred to mechanical disintegrators where the seeds would be broken open to allow the starch to be extracted with heated demineralised water. Extraction was complete after a few days from this point; the process was similar whether the starch was extracted from wheat or maize. Animal feed and gluten are separated from the starch and the starch is either recovered and dried 01 further processed to produce the various sugar syrups. Likewise, the gluten is dried and sold as Vital Wheat Gluten, which is used to strengthen flour to produce bread of lighter texture and improved moisture retention. Vital Wheat Gluten also enables soft European wheat as grown in Britain to be used in bread making instead of the formerly used American hard wheat.
The group was taken round the plant making and refining the glucose syrup. Refining involves decolourising. filtering and demineralising the syrup. The syrup is decolourised and filtered using one of two methods. The older method is the normal industrial method of mixing the product with diatomaceous earth and charcoal before pumping it through normal vertical plates, industrial filler presses but in the newer process, the syrup is filtered under vacuum. Instead of draping the filter cloth over metal plates as in a conventional tiller press, it is stretched over and attached to a rotating cylinder. The cloth is coated with a thick layer of diatomaceous earth and the charcoal laden syrup is drawn though the filter under vacuum. A knife spanning the length of the cylinder scrapes spent charcoal from the outside of the cylinder. The spent charcoal is rich in vegetable protein and is used as an additive for animal feed.
Other parts of our works tour included a small works laboratory where osmometers were being used to measure the sugar content of syrups, the control room from where pumps and valves etc. arc remotely controlled from computer screens, the boiler room, the gas turbine generators and finally the equipment used to crystallise dextrose monohydrate from glucose syrup.
The tour ended with a brief discussion about the company, a short video about the Amylum group of companies and Marston Mill and Tunnel Refineries in particular. After thanking Mr. Turner for such an excellent and informative tour of the site, he directed us to the works canteen where most of us enjoyed an excellent lunch. During the lunch, I met one of the firm’s electricians who is a personal acquaintance of mine and he described further, the way the various pumps and valves are remotely controlled and the way density and volume could be measured by transducers and other electronic sensing devices in the various reaction and blending vessels around the production plant.
A Little Background Chemistry.
Glucose belongs to a large class of compounds known as the saccharides. It shares with fructose, the empirical formula C6H1206, and both these sugars are classed as monosaccharides and hexoses because there are six carbon atoms in the molecule. The structural formula of glucose may be written as: CH2OH.(CHOH)4CHO which includes the aldehyde group -C1H0 and means that glucose is reducing agent. Similarly, the structure of fructose may be represented as CH2(CHOH)4CO.CH2OH in which the ketone group, CO may be seen Ketones are also reducing agents thus glucose and fructose are termed reducing sugars.
Starch (amylum) has been extracted industrially from wheat, maize, rice, horse-chestnuts, potatoes and the pith of the sago palm. The true starch, amylose. is found in the interior of the starch cells. Starch is a polysaccharide and was thought to consist of glucose units joined to form a polymer.
Maltose is a disaccharide having the empirical formula C12H22011 and is made industrially by the action of the enzyme diastase on starch. Diastase is formed in wheat when it germinates and produces malt. Both maltose and starch can be hydrolyzed with dilute mineral acid to form glucose alone. During the acid hydrolysis of starch, a gummy soluble mixture known as dextrin is initially formed. Dextrin however, is manufactured by healing starch alone or with a small amount of nitric acid to a temperature of 110″C.
The molecular structure of the glucose referred to in this article may be represented as:-
Each of the middle four carbon atoms has a different group or atom attached to each valency link and as such can change the plane of plane polarised light passing through the substance. Compounds changing the plane of plane polarised light in a clockwise direction are described as dextro rotator while in the reverse case they are known as laevo rotatory. A small d written as a prefix to a chemical’s name means that the compound is a dextro compound while the prefix l means that it is the laevo compound. The glucose referred to in this article is the dextro form and hence the name dextrose. Strictly speaking, I should have written d-glucose throughout this text because 1-glucose is known together with - and -glucoses, which are non-reducing sugars with a cyclic structure.
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