Steel silos are widely used in grain processing and transportation due to their high land utilization rate, high degree of automation, short construction period and low investment cost. With the need of economic development, the obvious trend in the use of steel silos at present is that the single silo capacity is increasing. With the gradual increase of the storage capacity, how to ensure the smooth discharge of materials has become a key issue to be considered in the design and use of steel silos. In some cases, it even becomes the decisive factor for whether or not a project can be launched. This paper introduces and discusses the commonly used discharging methods in grain steel silos, so that customers have a general understanding of the advantages and disadvantages and their respective applicable scopes, so that they can make choices in engineering projects according to the actual situation.
1.1 Full cone bottom self-gravity discharging
There are two types: concrete foundation (concrete hopper) and full steel support. The advantages of this discharging method are: smooth material discharging and basically no residual material in the silo; using the material’s self-gravity to discharge, the process is simple and no auxiliary equipment is needed, the operation is convenient; the silo capacity can be fully utilized, and there is no loss of silo capacity; the full cone bottom itself can also effectively increase the silo capacity; the construction period of using steel support is short. The disadvantage is that the height of the cone bottom itself is relatively high, resulting in a higher silo foundation and higher civil engineering cost. If the diameter of the silo is too large, the civil engineering cost will even exceed the cost of the steel silo itself. Therefore, this discharging method is generally not suitable for large-diameter silos.
1.2 Half cone bottom combined with silo backfilling discharging
Its advantages are: basically no residual material in the silo; using the material’s self-gravity to discharge, no auxiliary equipment is needed; the silo foundation is lower than the full cone bottom self-gravity discharging method. The disadvantage is that backfilling occupies part of the silo capacity, resulting in actual silo capacity reduction. If the diameter of the silo is too large, the loss of silo capacity will be very considerable. Therefore, this discharging method is generally only suitable for small and medium diameter silos.
1.3 Flat bottom multi-point discharging
On the silo foundation plate, multiple discharge holes are opened at a certain interval (generally an odd number). The advantages of flat bottom multi-point discharging are: no backfilling in the silo, and all silo capacity can be utilized. The disadvantage is that the material in the silo cannot be self-discharged, and other means need to be used to assist in clearing the silo.
Generally, the commonly used auxiliary silo cleaning methods are: sweep silo machine cleaning and loader cleaning. In some places with relatively cheap labor costs, direct manual cleaning is also used. At present, the price of sweep silo machine is relatively high and it is more troublesome to use. When there are many silos, the cost of using sweep silo machine is high. If the loader cleaning method is to be adopted, the problem to be solved is to open a large enough hole in the silo wall for the sweep silo machine to pass through. The 3×2.8m large door that has been developed has effectively solved the problem of the sweep silo machine entering and leaving the silo. This form has been used in many units such as Nanjing Port Authority, Qingdao Port Group Co., Ltd. and Guangzhou Port Group Co., Ltd. with good results. Therefore, it is feasible to adopt this discharging method for silos with larger diameters. In order to facilitate the loader entering and leaving the silo, the silo foundation is generally recommended to adopt the landing type, so the ground ditch must be made under the silo to install the discharging equipment. In most cases, there is no problem with this design, but in some places with high groundwater level, due to the waterproof problem, the construction requirements for this method are high. At this time, the civil engineering foundation still needs to adopt the silo support structure.
1.4 Multi-point discharging combined with silo backfilling
Its advantages are: basically no residual material in the silo, using the material’s self-gravity to discharge, no auxiliary equipment is needed; the backfilling amount is small, and the loss of silo capacity is small. The disadvantage is that there is still a part of the silo capacity loss, and the backfilling process is complex and the construction difficulty is large.
The scheme of multi-point discharging combined with silo backfilling is proposed to solve the problem of silo cleaning of multi-point discharging. This scheme can be regarded as a combination of half cone bottom combined with silo backfilling and flat bottom multi-point discharging. This scheme still uses the material’s self-gravity to discharge, but because of the use of multiple symmetrically arranged discharge holes (commonly used “ten” shape arrangement), the backfilling amount is greatly reduced. In the case that sweep silo machine