Concrete Batch plants4 Particulate matter, consisting primarily of cement dust but including some aggregate and sand dust emissions, is the only pollutant of concern fiom concrete batch operations.

### All but one of the emission points are fugitive in nature. The only point source is the transfer of cement to the silo, and this is usually vented to a fabric filter or "sock." Fugitive sources include the transfer of sand and aggregate, truck loading, mixer loading, vehicle traffic, and wind erosion fiom sand and aggregate storagepiles. The amount of fugitive emissions generated duringthe transfer of sand and aggregate depends primarily on the surface moisture content of these materials. The extent of fugitive emission control varies widely fiom plant to plant. Types of controlsused may include water sprays, enclosures, hoods, curtains, shrouds, movable and telescoping chutes, and the like. 

### A major source ofpotential emissions, the movement ofheavy trucks overunpaved or dusty dams in and around the plant, 

### can be controlled by good maintenance and wetting ofthe road surface.

Hot Mix ~sphalt~

As with most sources in the mineral products industry, batch mix

### HMA plants have two major categories of emissions: ducted sources (thosevented to the atmosphere 

### through some 

### type of stack, vent, or pipe), and fugitive sources (those not confined to ducts and ventsbut emitted directly fiom the sourceto the ambient air). Ducted emissions 

### are usually collected and transported by a. industrialventilation systemhaving one or more fans or 

### air movers, eventually to 

### be emitted 

### to the atmosphere through some 

### type of 

### stack Fugitive emissionsredtfiom process and open sources and consist of a combination of gaseous pollutants and 

### PM.

The most significant ducted source of emissions from batch mix 

### HMA plants is the rotary 

### dnun dryer. Emissions fiom the 

### drum consist ofwater (as steam evaporated fiom the aggregate); PM; products of combustion (carbon dioxide [Ca], nitrogen oxides [NOx], and 

### sulfUroxides [S&]); carbon monoxide (CO); and small amounts oforganic compounds of various species (including volatile organic compounds [VOC], methane LC&], and hazardous air pollutants 

## @MI). The organic compound emissions result fiom incomplete combustionofthe fuel and from heating and mixing of the liquid asphalt cement insidethe 

### drum. The CO emissions result fiom incompletecombustion of the fuel. ProcessingofRAP materials may 

### increase organic compound emissionsbecause of an increase in mixing zone temperature duringprocessing, Once the organiccompounds cool after discharge fiom the process stack, some condense 

### to form a fine organic aerosol or "blue smoke"plume. Because liquid asphalt cement, aggregate, and sometimes 

### RAP, are mixed in a zone not in contact 

### with the hot exhaust gas 

### stream, counterflow 

### drum mix plants will likely have lower organic compound emissions

### than parallel flow 

### drum mix plants. Other potential process sourcesinclude the hot-side conveying, classifj.ing, and mixing equipment, which are vented to either the primary dust collector (along with the dryer gas) or to a separate dust collection system. The vents and enclosures that collect emissionsfiomthese
sources

### m commonly called "fugitive air" or "scavenger" systems. The scavengersystemmay or may not have its own separate air mover device, depending on the particular facility. The

NIUMProc TSD 6-14-02 Created on 6/38/20029:39:00AM 7