Miller Magazine Issue: 113 May 2019

48 COVER STORY MAY 2019 a diagram, you must have information and experience with grinding. Information at the new literature on the planning of a mill diagram is not enough and is often not based on industrial experience. As companies in the milling industries see the diagram as a competition element and consider as important in ter- ms of grinding economy, they do not publish the diagram. Researches at universities and research centers are limited because in commercial scale mills many variables have to be tried on a large scale. Commercial mills do not permit such researches. Some of the information in sources is eit- her old or limited. When industrial companies design mills, commercial concerns, and technical data are taken into consideration. Before industrial companies offer a tender to investors, in order to gather these data, they want investors to fill out a survey. Generally, technical data can be classified into two main subjects: general technical data and technical data related to grinding diagram. General technical data is the result of feasibility report on the weather conditions where the mill will be installed (temperature and moisture level), how much wheat will be taken at a time and which transportation vehicle will be used, how much it will be stored, wheat storage preferen- ces, building height, product packaging, storage duration and delivery method and loaded deliveries, milling auto- mation, preferences regarding to building type (hangar or multi-storey full closed). The technical data for the grinding diagram can be summarized as follows: • The capacity of the mill in 24 hours, • Variety of wheat available and its characteristics, • Product diversity, quality, and extraction rate. In terms of the available wheat diversity and characteristi- cs, the mills can be classified as specialized and multi-purpo- se mills. Specialized mills are designed for a single product (eg common flour, biscuit flour). In the multi-purpose mill, different types of wheat are milled separately, and the flours are blended, and various flours are obtained. This practice provides high added value. However, the requirement for investment, information, personnel, and technology are high as well. Based on the technical data related to the grin- ding diagram, the number of machines required in forming the diagram (such as unit grinding length, unit screening area and the use of semolina purifier) is calculated. The mill design starts with the flow diagram (grinding diagram). The preparation of the mill diagram is the selec- tion and design of order, types, number, and specification of grinding units by taking into account technical data that previously specified. The length of a flow sheet determine the flexibility of the miller has in making changes in flour yield and quality of flour produced to meet specific needs of different cus- tomers . Although it is complex to design a flow sheet, the analysis of the flow chart is similarly complex. However, the analysis of the flow chart can be easy by splitting into several subsystems. The flow sheet of the milling process can be divided into flour main subsystems: 1. Break System: The break system break and open the kernel and separate the endosperm as much as possible with minimum bran and flour. In this process, it pays special care to leave endosperm as big as possible. So, it gets ea- sier to separate this from bran at purifier. The break system consists of break roller mill corrugated and after each of these machines, there is sifting machinery. Based on the capacity of mills, there are 4-5 break stages in the break system. The final stages in mills with high capacity can be formed with two breaking machines with thin and coarse. After each stage, the material is sorted by sifting. Flour is separated at sifting. The material, which is coarse and con- sists of particles in which the bran and endosperm have not yet been separated, is sent to the next breaking machine. The medium size material is sent to the purification system of the plant for the separation of pure endosperm particles. These processes are repeated at each breaking stage and at the end of the last stage; the endosperm is removed with the residual bran. 2. Purification System: The purification system consists of machines called as purifier that separate bran, pure en- dosperm, and composite particles in midsized coming from the sifting of the break system based on size, air resistance, and specific weight. Bran are delivered to feed materials, and composite particles are sent to either breaking system or sizing system based on the capacity, and the endosperm particles are also classified and sent to the reduction rollers. The use of the purification system is reduced in modern mills due to cost efficiency and efficiency in other parts of the grinding process. 3. Sizing System: The duty of sizing system is to se- parate bran, endosperm, and germ from endosperm particles attached to the shell and came from the puri- fication system and to refine coarse semolina which is not very clean. Particles coming to the sizing system are cleaner than materials going to breaking system and