H-Silo Problems.pptx homo silo and cf silo

Homo silo and cf silo

1. Homogenizing Silos

2. Operation Problems Of Continuous Homogenizing Silos The most important problems appearing in the continuous homogenizing silos are a sudden or a gradual decrease of the homogenizing efficiency or a disturbance of the raw meal extraction. The three main reasons for these disturbances are: Moisture, Aeration and Silo stops . Problems can be prevented by a regular control of the silo, but when difficulties have appeared usually, the silo must be emptied and cleaned.   During emptying such a silo nearly always it can be observed that material is remaining in some parts.

3. The following figure shows a typical case:

4. Raw meal with a too great moisture content has the tendency to stick together and loose the flow ability. Therefore it remains in some parts of the silo where the aeration is too weak for a transport of this material. Furthermore wet material blocks the aeration elements 1 Moisture

5. The upper limit for the raw material moisture fixed by the silo suppliers is 1 %. Often this limit is exceeded because the raw meal drying was not sufficient. Especially dangerous are cases where during longer time intervals (e.g. wet season) too wet raw meal is produced. An error in the raw meal moisture should be prevented by a regular control. However, when problems once have appeared the silo must be emptied and cleaned. 1-1 Raw Material Moisture

6. In the past it has been observed that after a certain time after erection of the silo the homogenizing efficiency decreases. Responsible in this case is often a too poor drying of the silo after the construction. In this case the silo should be emptied and cleaned 1-2 Moisture from the wall

7. It can happen that water enters into the silo through cracks and especially through leaky roofs, if the feed installation is not properly sealed. When this happens the causes must be eliminated as well as the silo emptied and cleaned. 1-3 Water penetrating from outside into the silo

8. 2 Aeration Problems The aeration of the raw meal by the bottom elements is very important thereby the air distribution as well as the quantity and the pressure must be correct. The order of magnitude is for the pressure at the inlet of the aeration per m 2 , elements 0.6 – 0.8 bar and for the air quantity between 1.0 and 2.0 m 3 /min per m 2 of aeration elements. In case that e.g. the air pressure is insufficient the raw material is aerated sufficiently, remains on the same place over long periods, gets compact because of influences like raw material pressure from the superimposed layers, moisture, etc.

9. 2 Aeration Problems  The aeration systems should be controlled regularly, whereby the pressure in the ducts is the main indication for a disturbance. If the pressure is too low e.g. the compressors can not work properly or somewhere is a leak in the system. In case of too high pressure it is possible that ducts, valves, air distributors, etc. are blocked. The following problems can occur:

10. The aeration of the whole silo bottom or of parts of it (e.g. one sector) can be too weak. A regular control and maintenance should prevent a long operation with such a system and therefore a great disturbance of the silo. Some possibilities of such a disturbance are presented in the following. 2-1 Weak Aeration

11. 2-1-1 Compressor Problem A compressor can work with a reduced pressure and/or a reduced mass flow. 2-1-2 Air Leak Leaks in the air distribution system, in sealing, etc. can reduce the air quantity as well as the pressure at the outlet of the aeration systems 2.1.3 Disadvantageous Air Distribution In correct adjustment or plugging of the air distribution valves, blocked or damaged aeration pads, etc. often cause a disadvantageous air distribution in the silo. Dangerous is particularly the case where too little air is conducted to the outer parts of the aeration systems. In such a case the raw meal can remain over long time intervals in this zone. As a rule of thumb it can be stated that the air volume per surface unit should be constant

12. An aeration system is divided into 3 segments. The air quantity given to each segment can be adjusted. Example The ratio of the surface area is: Al : A2 : A3 = 1 : 3 : 5

13. Therefore the air volume should be distributed with the same ratio. That means 5/9 of the total air volume should be conducted to segment 3 . Normally there is no indication of the air quantity. The only indication is the valve position. In case of doubt the air should be preferably distributed to the outer aeration elements.

14. 2.1.4 Extraction Frequency The frequency of withdrawing raw meal from the individual extraction points can be adjusted. This valve has above all an influence on the homogenizing efficiency of the silo but usually does not produce operation problems. An exception is a total shut down of the frequency control and therefore an extraction from only one silo area .

15. 3 Silo Stops During a silo stop the raw meal remains underrated in the silo and gets gradually compacted. Therefore during longer stops the silo should be aerated regularly

16. Emptying of the Silo   There is no standard procedure to empty a silo since practical execution depends on  the distribution of the remaining material in the silo compacting degree of the remaining material Possibilities of access to the silo (latterly by man hole or top).   In any case emptying a silo should be made with the highest possible safety factor and in this connection it is above all very important that the personal entering into the silo has always a sure escape possibility.