Milling Journal - Q2 2008 - (Page 44) Filters in Mill Pneumatic Systems The right filters keep the mill running. Technical Manager Rami Flamer has been milling at the “Shalom” Flour MIll in Petach Tikva, Israel since 1982. In this article, he discusses the role of filters in pneumatic systems. This article was submitted by Flamer and edited by Milling Journal. 2 and 30 seconds. The duration of the pulse is between 50 and 90 milliseconds. Normally, the air-to-cloth ratio in modern types of filters for mill pneumatics is 4m3/min : 1m2. It can reach to 6m3/min : 1m2 but then the time between cleaning or changing the sleeves will be very short. If the filter is working well, the sleeves will be changed once each year. In mills where there is a milling of soft wheat or rye, the air-to-cloth ratio can be 3m3/min per 1m2. The pneumatic conveying system of a flour mill is a complex system that is comprised of many air/material conveying lines that take air and material from grinding machines to sifters and then to cyclones and filters that separate materials from the conveying air. The filter has two main functions: Rami Flamer • Produce very clean air for discharge to the atmosphere. The filter must be able to meet today’s strict environmental regulations. Shalom’s Special Filter • Reclaim the dust and add it to the flour, a very important At the “Shalom” Flour Mill, one of our lines mills soft wheat. function from a commercial point of view. To enlarge the time between sleeve changes, and to operate the mill without Filter Types a long disruption, a special filter called There are three types of filters commonly circular bag-type filter was installed in used in the milling industry. In all the types, 1982. the sleeves are dressed on special sleeve Originally, this circular bag-type filter cages, and the pressure of the cleaning air (see illustration) was developed by blast is on the open top of the sleeves. The Baumgarten of Germany for feed mills. The sleeves are closed on the bottom. application for flour mill pneumatic systems The dust is collected outside the sleeves was made in cooperation between and the cleaned air flows from outside to Baumgarten and Shalom Flour Mill inside of the sleeves. In the low pressure Air with dust enters tangentially. The reverse jet filter, the air is blown into each bags are mounted on special frames (G). of the sleeves at a pressure of 0.04 to 0.06 The cleaning air is produced by a blower bar by blast nozzles on the ends of the ro(0.1 to 0.2 bar) that enters the gear-driven tating manifolds. slit nozzle that continuously rotates (M). In the medium pressure reverse jet filThe velocity of the rotation can be ter, the pressure of the cleaning air blast is changed electronically according to need. 0.4 to 0.8 bar. The pressure is produced by The bags are cleaned when the slit a blower. Above each sleeve is a nozzle from nozzle comes in front of the open side of the compressed air reservoir that directs the bag. the blast of cleaning air into the open top The advantages of this type of filter are: of the sleeve. • The time between changes of cleanThe third type is the high pressure pulse ing bags is very long. We have used the jet filter where the pressure of the cleaning same bags since 1997 without changair blast is between 6 and 7 bar, sometimes ing or cleaning them (More than 10 8.5. years!). The compressed air is produced by a com• A big filtering surface in a small pressor. The sleeves are arranged in rows and housing. A cylinder with a diameter of above each row is a blow tube with nozzle 200 cm and height of 100 cm contains orifices directly above the open top of each filter bags with an area of 50 square sleeve. meters, 80% more area than in a conEach row of sleeves is cleaned in seventional filter. quence. The sequence is controlled elec• Low filter maintenance as there are tronically. The time between pulses is between no diaphragm solenoid valves. 44 Second Quarter 2008 MILLING JOURNAL
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.