Asphalt batching

A mobile source of air pollution can be defined as one capable of moving from one place to another under its own power. According to this definition, an automobile is a mobile source and a portable asphalt batching plant is not. Generally, mobile sources imply transportation, but sources such as construction equipment, gasoUne-powered lawn mowers, and gasoline-powered tools are included in this category. 

Many industries operated throughout the world do not fall into the previous categories. Some of these are universal, such as asphalt batching plants, whereas others are regional, such as bagasse-fired boilers. Each has its own emission and control problems and requires knowledgeable analysis and engineering. Some of the more widely used processes are examined in this section. 

Stone aggregate ordinarily used to make asphalt concrete. Asphalt-batching processes are characterized as either hot mix or cold mix. Each type of process is briefly described below. 

Cold-mix asphalt batching occurs at ambient temperature. The ambient temperature has two effects. First, the product cannot be made or applied when the ambient temperature is below 0°C (32°F). Second, volatile compounds remain in the mixture, in contrast to the hot-mix process. Large proportions of VOCs can soften the final product. Leaching of these VOCs from the final product may also be a concern. 

Cold-mix asphalt batching may be subject to state regulations. For example, those regulations may limit the concentrations of contaminants in the feed, the materials used for the asphalt, the properties of the product, and the conditions under which the asphalt can be placed. 

Limitations. In addition to the regulatory restrictions already described, the following factors may limit the application of asphalt batching ... 

Stones or debris larger than 5 to 8 cm (2 to 3 in.) in diameter must be screened out of the soil before asphalt-batching. 

The Arizona State Plan applies to all public and private sector places of employment in the State, with the exception of Federal employees, the United States Postal Service (USPS), private sector maritime, employment on Indian Lands, areas of exclusive Federal jmisdiction copper smelters, and concrete and asphalt batch plants that are physically located within mine property, which are subject to Federal jurisdiction. See 29 CFR 1952.355. 

Air-blown asphalts, more resistant to weather and changes ia temperature than the types mentioned previously are produced by batch and continuous methods. Air-blown asphalts, of diverse viscosities and flow properties with added fillers, polymers, solvents, and ia water emulsions, provide products for many appHcations ia the roofing industry. 

Preparation is accompHshed by simple blending of the diluent into the hot base asphalt. This is generally accompHshed in tanks equipped with coils for air agitation or with a mechanical stirrer or a vortex mixer. Line blending in a batch circulation system or in a continuous fashion (40) is used where the volume produced justifies the extra faciUties. A continuous, line-blending system is appHcable to the manufacture of cutback asphalts and asphalt cements (Fig. 8). 

Two types of asphaltic concrete plants are in common use, batch mix plants and continuous mix plants. Figure 30-5 shows a batch mix asphalt... 

Fig. 30-5. Batch mix asphalt plant P, denotes fugitive particulate matter emissions. Source Ref. (16),...

This is a batch-type process in which the rates of flow of the solvent, the asphaltic material, the sulfonating agent, and the neutralizing agent and the... 

Asphalt feedstock (flux) is contacted with hot air at 200-280°C (400-550°F) to obtain desirable asphalt product. Both batch and continuous processes are in operation at present, but the batch process is more prevalent because of its versatihty. Nonrecoverable catalytic compounds include copper sulfate, zinc chloride, ferric chloride, aluminum chloride, phosphorus pentoxide, and others. The catalyst does not normally contaminate the process water effluent. 

SAS mixtures using batch-type asphalt hot mix facilities. 

One and one-half miles (2.4 km) of existing asphaltic concrete pavement on Loop 1604 were overlaid with an inch (25.4 mm) thick Sulphlex mixture The Sulphlex hot-mix was produced in a three ton (2.7 tonne) batch plant, and hauled approximately five miles (8.05 km) in open trucks to the construction site. 

Processing. Early asphaltic crudes, such as Panuco (Mexican) and Heavy Californian, yielded up to 65% asphalt (4), and were fairly readily processed in horizontal, direct-fired batch stills as shown in Figure 2. Usually steam was introduced to assist in the vaporization of the volatile constituents. The temperature at the termination of the process varied between 600° and 750° F., and the time of distillation was between 12 and 36 hours. These batch stills were replaced by continuous stills of similar construction. The oil flows from one still to another, with each still producing a predetermined grade of distillate. 

Fluidized bed dryers, for example, are operated as batch or continuous, for pharmaceuticals or asphalt, at rates of hundreds or many thousands of pounds per hour. 

Test Strips. Larger batches of direct-substituted sulfur-asphalt paving mixtures were prepared with type IVb aggregate materials. Mixtures containing 0-, 15-, 25-, and 35-vol % sulfur in the asphalt binder were... 

Sulfur Dispersion in Asphalt Plants. Sulfur-extended binder and Thermopave mixes were prepared in several batch type commercial hot-mix plants to verify the effectiveness of aggregate shear on sulfur dispersion during mixing in the pugmill. The influence of the following variables on the dispersion of sulfur was assessed. 

Thermopave mix (medium sand)—asphalt content, 6 wt % sulfur content, 13 wt % Plant, Cedarapids capacity, 6000 lb (2722 kg) batch batch size evaluated, 5000 lb (2268 kg) mixing time, 25 sec with sulfur. 

Figure 2. Appearance of sulfur particles dispersed throughout asphalt phase of sulfur-extended binder mix after 15 sec mixing in Cedarapias pugmill. Batch size 7000 lb.

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