Mechanical aeration materials

Where materials are stored in bulk, to reduce the risk of mould formation or fermentation it is advisable to store them in aerated rooms or containers using natural or mechanical aeration and ventilation. These areas should also be equipped in such a way as to protect against the entry of insects or animals, especially rodents. Effective measures should be taken to limit the spread of animals and microorganisms brought in with the plant material and to prevent cross-contamination. 

In many countries (including the United States), regulations require mine operators to comply with specific limitations relating to effluents. In order to meet these lequiranents, the following treatments are typically anployed (1) addition of alkaline material, such as Ume or sodium hydroxide, (2) natural or mechanical aeration, and (3) settling. When the pH is raised to 7 or 8 and settling has occurred, most drainage waters will meet the standards for iron content and suspended solids. 

This process, according to the manufacturer,54 has been developed in such a way that space requirements are kept to a minimum. A BIOPAQ IC reactor is used as the initial step in the treatment process. The name of this anaerobic reactor is derived from the gas-lift driven internal circulation that is generated within a tall, cylindrical vessel. These reactors have been operational in the paper industry since 1996. The second step in the purification process is a mechanically mixed and aerated tank. The aerating injectors can be cleaned in a simple way without the need to empty the aeration tank. Potential scaling materials are combined into removable fine particles. At the same time, the materials that may cause an odor nuisance are oxidized into odorless components. The process can be completed by a third and a fourth step. The third step focuses on suspended solids recovery and removal. The fourth step is an additional water-softening step with lamella separation and continuous sand filters in order to produce fresh water substitute. The benefits claimed by the manufacturer are as follows54 ... 

Minimize drop height. Drop height serves to aerate the material, induce dust, and increase momentum of the material as it hits the pile, increasing the tendency for each of the three segregation mechanisms described earlier. 

It has already been pointed out that experiments in differently scaled models are inevitable if physical properties cannot be changed and therefore one has to use the same material system (Example 8 Mechanical foam breaker, section 6.1). The same is true if the acceleration due to gravity is influencing the process under investigation. However, as we all know, gravity cannot be varied on Earth (Example Surface aeration, section 10.3.2). 

Oil acts as a heat transfer medium during the frying process which rapidly heats, cooks, and sometimes puffs, dehydrates, or forms a crust around the product. The mechanics of deep fat frying are shown in Fig. 34.32.173 The entering material carries oxygen that temporarily aerates the hot oil, and water that forms steam, with both rapidly swept out... 

Dust generation and fluidization of the material should be minimized during material movement. Dust can be controlled by way of socks or sleeves, to contain the material as it drops from the blender to the bin, for example. Some devices are commercially available. An example of this is a solids decelerator shown in Figure 11. Drop heights should be minimal, as they aerate the material, induce dust, and increase momentum of the material as it hits the pile, all of which can increase the tendency for each of the three segregation mechanisms to occur. Valves should be operated correctly. Butterfly valves should be operated in the full open position, not throttled to restrict flow. 

Figure 8.2 is a schematic of an in-vessel, static-pile composting device. In mechanically agitated, in-vessel composting, contaminated material is aerated and blended with carbon-source materials in a mechanical composter. These devices have been used at municipal sewage treatment facilities and applied to explosives waste. 

Much contaminated debris is incompatible with flail-type windrow aeration equipment used for composting due to its large size. Physical size reduction is an effective option for preparing the debris for compatibility with the windrow equipment. Crushing is a standard method to reduce the particle size of rock materials. The size-reduced debris would be returned to the composting system to reduce the explosives concentrations to the remedial action objective levels. The crushing process will use mechanical size reduction equipment to crush the large debris. 

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