GB2538789A

GB2538789A - Construction design and the method of construction of a silo or bin to store bulk material

Info

Publication number: GB2538789A
Application number: GB1509233.1A
Authority: GB
Inventors: Narasimhamurthy Prakashkumar
Original assignee: Individual
Current assignee: Individual
Priority date: 2015-05-29
Filing date: 2015-05-29
Publication date: 2016-11-30
Also published as: GB201509233D0

Abstract

A storage silo or bin 001 comprise at least two opposing vertical load bearing structures including inclined load bearing surfaces 003, 006 positioned at different levels. Preferably the silo is constructed from stacking together only vertically or both horizontally and vertically, plurality of modified shipping containers 002 or fabricated metal frame, panel as individual component, pre-fabricated modules or their combination thereof. At the base 009 of the silo there is a bulk material moving system such as a conveyor 010. There may be closable air vents 012 located in the vertical structures as well as a closable door 011.

Description

CONSTRUCTION DESIGN AND THE METHOD OF CONSTRUCTION OF A SILO OR BIN TO STORE BULK MATERIAL.

DESCRIPTION:

0001. Background:

A silo or bin (herein referred to as silo) is essential for safe and protective storage of bulk material. The taller the structure, the greater the storage capacity per square meter area. All prior art silos are known to have various issues in the handling of stored bulk materials. In summary, the few main issues are: irregular mass flow, uniform discharge efficiency, susceptibility to microbial activity, possible fire hazard, accidental risk to workers and consumption of electrical energy (for mechanical aeration, loading & unloading). These issues are more pronounced during storage of cohesive materials in bulk, bulk materials which do not have free flowing characteristics, bulk materials with higher moisture content and dry bulk materials with dust. In power, steel, cement and many other industry, the irregular mass flow of bulk material is a cause of concern and a challenge to engineers. In the agriculture industry, loss of material due to microbial activity and frequent accidental injuries and deaths to workers during 'grain walking' (to rectify the mass flow) within a silo have been reported. The cost of insuring and securing protection from the loss of bulk material is increasing. This is mainly due to accidents in silos and bins, resulting in human and material losses, as frequently reported from around the world.

0002. The enclosed structure of a silo protects stored bulk material from wind, rain, snow, rodents, insects etc. In order to prevent microbial activity and the loss of material, due to quality deterioration, there is a need for an improved aeration as well as facility to allow quick changeover from aerating to inert environment and back to aerating environment within the enclosed silo. Such improved environment control is achievable with improved natural aeration and with facility to introduce a carbon dioxide or nitrogen dominant environment within the enclosed silo, whenever the situation demands to restrict microbial activity. The microbial activity may be initiated when the bulk material is not dried or get wet before and during storage. After initiation, the microbes may thrive under aerating environment resulting in further quality deterioration, heat build-up in the bulk material and increase the fire hazard. In such circumstances, a temporary changeover to inert environment is necessary to secure the stored bulk material.

0003. It is a normal engineering practise to provide fire explosion vent panel to enclosed structures like silo. However, there have been many instances that heat build-up in the stored bulk materials within a silo has led to fire followed by explosion causing fatal injuries, deaths and destruction to silo, bulk material, surrounding environment, building, plant and machinery. Therefore, measures must be taken to prevent the causes of fire within a silo including the reason mentioned above in 002. Adequate ventilation and improved aeration to prevent heat and the following pressure buildup inside an enclosed silo is essential. Arrangement must be in place to sense the heat build-up (heat sensors) and activate quenching the heat build-up quickly, well before it develops to ignite a fire explosion. Such arrangement must also be useful to quickly extinguish any accidentally caused fire. A temporary changeover to inert environment within an enclosed silo (0002) is an essential part of such arrangement. This stops the oxidation from aeration and the resulting heat built up leading to combustion.

0004. The perimeter wall shape of a silo determines the storage capacity within an area of a footprint as required to accommodate its outer perimeter wall. For example, a square shape accommodate more capacity storage than a cylindrical shape. Condensation and formation of ice on the inner wall affect the quality of stored bulk material and demand insulation but this adds to the cost.

0005. In a prior art flat bottom silo of any perimeter wall shape, all stored bulk material near the bottom and around the exit is difficult to discharge. The non-moving material resting on the static flat base around the exit and the vertical load of the material above, forces the formation of arching, bridging, tunnel flow and rat holing, all of which cause irregular mass flow. In a hopper (conical) bottom silo, the converging inner wall surface leading to the neck of an exit, causes compression to the bulk material due to the vertical load of the material above and also increases friction on the converging inner wall surface, thus forcing the formation of arching, bridging, tunnel flow and rat holing, all of which cause irregular mass flow. Irregular mass flow is one of the major reasons for fatal injuries and deaths to people working inside the silo. For an improved first-in-first out bulk material management as well as worker safety, there is a need for a silo to prevent the formation of arching, bridging, tunnel flow, rat holing and facilitate efficient discharge of all the stored bulk material during unloading.

0006. The mechanised aeration, unloading and loading of bulk material into silo consumes electricity. Normally silos are built as tall structures. Locating wind turbines on top of silos, at such height, exploits the advantage of increasing wind speed with increase in altitude. Their pillar and foundation support can add to the overall structural strength of the silo if such pillar is fastened along the wall of the silo. A single ladder would access both the top of silo as well as the wind turbine for maintenance. Unlike habitable buildings, silo walls do not require window openings. Therefore, the normally large outer wall surface area is ideal to mount solar panels to harness solar energy. Such designed silos can generate its own required electricity (renewable) and export excess to the grid. Generally, silos are located in an industrial complex or a farm land away from townships. This scenario will be ideal to exploit and harness wind and solar energy within a smaller foot print. This will also bring an additional income to the owner of the silo.

0007. Preferred embodiment: The preferred embodiment is a method to construct a silo that will provide: improvement in protection, fire safety, worker safety, natural aeration, environment control as necessary, regularity in mass flow and uniform discharge efficiency of the bulk materials in comparison to a prior art flat bottom or hopper bottom silo. It resolves all issues related to storage of all types of bulk materials, with different characteristics, as mentioned in 0001. Furthermore, its design facilitates and encourages installation of wind turbine and solar panels.

0008. The cross section, as shown in figure 1, comprises of two opposite facing vertical load bearing structures with inclined surfaces, each located at different level, which together, significantly reduces the vertical load of the bulk material on the base. It will also reduce the velocity of the mass flow. This will allow manual unloading of the bulk material, for example using a JCB front bucket loader through a closable door fixed to the structure's side wall. The manual unloading is more suitable for bulk materials which do not have free flowing characteristics and may benefit small scale operation.

0009. For mechanical unloading, adding a bulk material conveyor system such as moving floor planks, screw, belt or chain conveyor on to the base, will allow a more controlled and uniform discharge velocity of the stored bulk material. If required, the mass flow and discharge control efficiency is augmented by adding a conveyor system or any other form of mechanical agitation to push and move the material on top of the inclined surfaces of the two vertical load bearing structures.

0010. The bulk material is loaded from the top and will naturally take the shape of inner contour of the wall surface, as shown in the cross-sectional drawing in figure 1. The opposite facing inner side walls of the structure are parallel to each other, as in a flat bottom silo, from eave height (normally in case of cylindrical shape silo) or the roof top height to base, thus allowing mass flow of the material due to gravity (vertical load bearing weight) and causing less friction on all inner wall surfaces. Towards the bottom end, the mass flow velocity of the material is restricted by the opposite facing vertical load bearing structures with inclined surfaces. Then the bulk material flows down to the base due to gravity, which can be boosted by fitting an optional conveyor or mechanical agitation system (0009) to the inclined surfaces. The structure of prior art static flat bottom silos cause bulk material to become immobile at the bottom around the exit. The immobility is more pronounced as the vertical load above it increases. The construction design of the preferred embodiment resolves this issue; the immobility of bulk material on the static flat bottom base is avoided. It also avoids converging of the inner wall surfaces, unlike prior art hopper bottom silo. The parallel opposite facing walls across the flow of bulk material, until the bulk material reaches the base (that is free from the impact of the vertical load above), causes less friction on the inner walls and will have lesser compression compared to bulk material within the converging inner walls of a prior art hopper bottom silo. The inclined surfaces of the structural supports will have less friction during bulk material movement compared to the friction on the converging inner walls surface of a hopper bottom silo. Therefore, the forces causing formation of arching, bridging, tunnel flow, rat holing etc. in prior art silos (0005) are reduced or eliminated in the preferred embodiment. This will result in improved mass flow and discharge efficiency of the bulk material.

0011. A door is located on the silo wall to access bulk material for manual unloading. When the door is closed, it simply acts like a dam or barrier to stop the flow of the bulk material and there will be less load bearing impact on the door. This is because there is less or no impact on the base from of all the vertical load inside the preferred embodiment. This facilitates safe and easier manual unloading of bulk material through the opened door using for example, a JCB front bucket loader. The unloading can be automated by adding conveyor system as mentioned above in 0009 which will also facilitate controlling the uniform discharge velocity of the bulk material. In this case, the bulk material can be moved horizontally on a flat base surface applying, for example, moving floor planks or conveyor belts system. Screw conveyor running perpendicular to them can pick up and exit the bulk material out of the preferred embodiment. Alternatively, the wall surrounding the base combined with an inclined base is converged into a conveyor system. This will allow all the bulk material to fall into such conveyor system. In both methods described above, it is possible to mechanically discharge all the bulk material from the preferred embodiment.

0012. Furthermore, the air vents in the body of the silo wall and the inclined surfaces, as illustrated in figure 1, facilitates improved natural aeration to the stored bulk material. In the preferred embodiment, air vents on the inclined surfaces (compared to a horizontal surface), provide a larger surface area for air distribution into the silo, therefore improving aeration to the stored bulk material. Also the embodiment exploits the thermodynamics of air moving from a warmer region, i.e. inside insulated enclosed silo to the colder region i.e. the atmosphere outside the silo. The air inside gets warmer due to heat resulting from transpiration and from the friction caused by movement in the stored bulk material. The warmer air rises and exits into colder outside atmosphere via the vents located at the higher level. The colder air from outside moves into the silo via vents located at lower levels to replace the outgoing warmer air, resulting in improved natural aeration. The aeration also keeps the immediate layer of the bulk material above the air vented inclined surfaces dry, causing lesser friction when the material move on its surface. This, combined with the uniform discharging of the bulk material across the entire space between the opposite facing parallel inner walls of the structure (0011), further assist in preventing the formation of arching, bridging, tunnel flow and rat holing. It eliminates the need for workers entering into a silo for example to 'walk the grain' and therefore the resulting fatalities that normally occur in the prior art silo.

0013. The above features can be incorporated into any shape of the outer wall perimeter of the silo structure i.e. cylindrical, square, rectangle etc. However, the much preferred perimeter shape of the preferred embodiment is a rectangle. This preference is due to additional storage capacity within available footprint compared to the cylindrical shape and also due to the possibility of using new (modified) or used (modified) shipping containers as standard module to build a structurally strong large preferred embodiment silo. This can be cost effectively built to safely withstand high wind speed, hurricane, flood, tsunami and seismic hazard. Using reefer shipping containers takes the advantage of its thick insulated wall. This in particular reduces the possibility of condensation and ice formation on the inner wall surface. The rectangular or square shape provide a generally flat roof and a flat wall surface which is advantageous to exploit and harness wind and solar renewable energy.

0014. A plurality of shipping containers are stacked together only vertically or both horizontally and vertically, left mostly hollow inside within the outer wall except for reinforcement that hold them together as shown in figure 1. This will be sufficient to facilitate mass flow of bulk material due to gravity without much obstruction caused by reinforcements. Fabricated reinforcements will hold all the stacked shipping containers together and the containers in the base are firmly fixed to the ground. This will be an ideal and cost effective silo when fabricated as a standard size module, comprising parts of the preferred embodiment's features. All such modules can be stacked only vertically or horizontally and vertically to make one large silo.

0015. The other method is to fabricate plurality of metal frames, panels as individual components, pre-fabricated modules and assemble them on site of installation, as normally practised in prior art silo especially with cylindrical shape outer perimeter wall. A combination of modified shipping containers and fabricated metal frames, panels as individual components, pre-fabricated modules is another alternative. In the construction method mentioned above, the perimeter of the silo i.e. the wall can be insulated and the inside of the wall perimeter is mostly left hollow comprising of: metal reinforcements (0014), load bearing structures with inclined surface (0008), the optional mechanical bulk material moving and agitation system (0009).

0016. Description of drawing:

0017. Figure 1: The cross section of the preferred embodiment shows a method to construct a silo or bin (001) made from stacking together only vertically or both horizontally and vertically, plurality of modified shipping containers or fabricated metal frame, panel as individual component, pre-fabricated modules or their combination thereof (002) comprising a load bearing structure (003) with an inclined surface (004). This (003) will bear most of the vertical load of the bulk material (015) resting above it in a section (005) of the (001). It will also guide the flow of the (015) down on to its opposite facing, another load bearing structure (006) with an inclined surface (007), which is located at a lower level to (003). This (006) will bear most of the vertical load of the (015) resting above it in the remaining section (008) of the (001). It will also guide the flow of the (015) down on to the base (009) of the (001) or to a mechanically operated bulk material moving system (010) that is fitted to (009). The (010) will move and discharge (015) out of the (001). In the absence of (010), the (015) can also be unloaded from the (009) of the (001) for example, using a JCB front bucket loader. The JCB front bucket loader can access the (015) resting above (009) which has flowed down from (006), through a closable opening (011) on the side wall of the (001). The other purposes of the two vertical load bearing structures (003), (006) and their corresponding inclined surfaces (004), (007) are: to reduce the gravitational flow velocity of the bulk material, deflect all the vertical load of the (015) above them in their corresponding silo sections (005), (008), prevent all the vertical load resting onto (009) or (010), facilitate reduced friction to the parts of (010) and allow safe and easy unloading of bulk material (if necessary) from (009) using for example, a JCB front bucket loader.

0018. In the prior art hopper bottom silo, all the bulk material, when flowing down the converging inner walls leading to the narrow neck of an exit at the base, are compressed due to the impact of the vertical load (gravity) above. This causes increased friction on the converging inner walls, which forces formation of arching, bridging, tunnel flow, rat holing and affect the mass flow. Contrary to this, in the preferred embodiment, the bulk material flow continues between parallel inner walls until it reaches the exit in the base (009), causing less friction on the surface of the parallel inner walls. Therefore, this prevents the compression (due to the impact of vertical load) of bulk material in the base before the exit, friction on inner walls and the resulting formation of arching, bridging, tunnel flow, rat holing that affect the mass flow. The base in a preferred embodiment can have inclined base surface (020), to guide the flow of all the bulk material into the conveyor system. As an option, the inclined base surface (020) is fitted with a conveyor or some form of agitation system (not shown in the drawing). Therefore, all the bulk material is discharged. In this case, there is no impact of entire vertical load on the conveyor system (010) and all the bulk material flows freely into the conveyor system (010).

0019. Closable air passage vents (012) and (013) through the body of the (001), in combination with the constructed air passages (014) on the inclined surfaces (004), (007) of the two vertical load bearing structures (003), (006) facilitates improved natural aeration to (015) during storage within an enclosed body of the (001) built to fully protect stored (015). Aeration may be further improved for example by using a mechanically operated blower which is fitted to (012) to draw the air from outside the (001) and blow it through (014) into the stored (015). At least one closable opening on top (016) of the (001) will facilitate loading of the (015) into (001). The top of the inclined surfaces (004), (007) may be fitted with mechanically operated conveyor or some form of agitation system (not shown in drawing) to improve the control over discharge of (015) out of (001).

0020. In cylindrical, square or a rectangular shaped outer perimeter wall structure of the (001) is insulated (017). In a square or rectangular shaped perimeter of a silo, the inside is left mostly hollow only exposing the structural metal frame and the reinforcement (018) that holds them together. The drawing shows the air flow (019) entering via (012) and exiting (001) via (013). Exposed to normally colder environment outside the (001), the temperature of the non-insulated metal sheet (020) is normally colder than the temperature of air (019) exiting (001). The colder inner surface of (020) thermodynamically attracts the normally warmer moist air (019). Therefore (020) serves a dual purpose in providing a rain guard whilst also improving the thermodynamics of the air flow from within the normally warmer fully insulated (017) inside of the (001). It must be noted that the free flowing air (019) will gain some heat and moisture from the transpiration and friction caused by movement of the stored bulk material (015). This combined with insulation (017) to the body of the silo (001) helps maintain temperature difference in air inside and outside (001), thereby causing continuous and improved natural aeration within (015) due to thermodynamics. This continuous natural air flow caused due to temperature difference between inside and outside (001) prevents the microbial activity and the resulting temperature increase within the stored pile of bulk material. However, some type of bulk material, its condition and moisture content before storage may initiate a microbial activity when stored in (001). In such a case, continuous aeration may assist further growth of microbial activity and therefore require a dominant inert environment inside (001) at least for a short period to curb the microbial activity, heat build-up and the resulting fire hazard.

0021. Insulated tanks containing fire extinguishers (not shown in the drawing), such as liquid carbon dioxide and liquid nitrogen, may be located in the space (020) within the load bearing structures (003) and (006). In the event the temperature sensors (not shown in drawing) sense temperature increase than normal within (015) and in the event of an accidental fire, the air vents (012) are shut, and the fire extinguishers are activated. The microbial growth supporting as well as combustible air within (001) is quickly replaced by non-combustible, cooler and inert gas. After a brief period, the vents (013) are shut to minimise the consumption of inert gas. This process will curb the microbial activity, quench the heat build-up and extinguish fire. Heat sensors inside (001) can automatically activate the fire extinguishing process, preventing the possible ignition of fire as well as curbing the microbial activity. This saves the stored bulk material from fire accident and microbial activity.

0022. The preferred embodiment facilitates a proper first-in-first-out bulk material management because it is possible to discharge all the stored bulk material (015) from (001), either by manually unloading via opening (011) or by mechanically unloading using conveyor system (010) when (011) is shut.

0023. Figure 2: Shows the cross section of only the base part of the preferred embodiment (001) having any outer perimeter wall shape such as cylindrical, square, rectangle etc. The inner wall surface around (009) is converged and the base surface is inclined (020) leading to a conveyor system (010) to guide all the (015) into (010) and discharge the material out of (001). There is no static flat base surface for (015) to rest or the vertical load impact from above on (015). This results in improved discharge efficiency of (015) from (001). If necessary, the inclined base surface (020) is fitted with a conveyor or some form of agitation system (not shown in the drawing).