INTERIM SECTION

Contents Subject To Change Pending Completion Of Source Testing Being Conducted

9.9.1 Grain Elevators And Processes

9.9.1.1 Process Description1-14

Grain elevators are facilities at which grains are received, stored, and then distributed for direct use, process manufacturing, or export. They can be classified as either "country" or "terminal" elevators, with terminal elevators further categorized as inland or export types. Operations other than storage, such as cleaning, drying, and blending, often are performed at elevators. The principal grains handled include wheat, corn, oats, rice, soybeans, and sorghum.

Country elevators are generally smaller elevators that receive grain by truck directly from farms during the harvest season. These elevators sometimes clean or dry grain before it is transported to terminal elevators or processors. Terminal elevators dry, clean, blend, and store grain before shipment to other terminals or processors, or for export. These elevators may receive grain by truck, rail, or barge, and they have significantly greater grain handling and storage capacities than do country elevators. Export elevators are terminal elevators that load grain primarily onto ships for export.

The first step at a grain elevator is the unloading of the incoming truck, railcar, or barge. A truck or railcar discharges its grain into a hopper, from which the grain is conveyed to the main part of the elevator. Barges are unloaded by a bucket elevator (marine leg) that is extended down into the barge hold. The main building at an elevator, where grain is elevated and distributed, is called the "headhouse". In the headhouse, grain is lifted on one of the elevator legs and is typically discharged onto the gallery belt, which conveys the grain to the storage bins. A "tripper" diverts grain off the belt and into the desired bin. Other modes of transfer include augers and screw conveyors. Grain is often cleaned, dried, and cooled for storage. Once in storage, grain may be transferred one or more times to different storage bins or may be emptied from a bin, treated or dried, and stored in the same or a different bin. For shipping, grain is discharged from bins onto the tunnel belt below, which conveys it to the scale garner and to the desired loadout location (possibly through a surge bin). Figures 9.9.1-1 and 9.9.1-2 illustrate the basic elements of an upright country elevator and an export terminal elevator, respectively.

The potential sources of emissions in grain elevators and their respective SCCs are as follows:

Operation	SCC

Receiving	3-02-005-05, 3-02-006-05, 3-02-031-05

Grain drying	3-02-005-04, 3-02-006-04, 3-02-031-04

--	Column

--	Rack

Internal handling

--	Cleaning	3-02-005-03, 3-02-006-03, 3-02-031-03

--	Tunnel belts	3-02-005-07, 3-02-006-07, 3-02-031-07

3-02-005-10, 3-02-006-10, 3-02-031-10

INTERIM SECTION

Contents Subject To Change Pending Completion Of Source Testing Being Conducted

--	Gallery belt	3-02-005-09, 3-02-006-09, 3-02-031-09

--	Headhouse	3-02-005-08, 3-02-006-08, 3-02-031-08

3-02-005-11, 3-02-006-11, 3-02-031-11

Bin vents

Grain shipping	3-02-005-06, 3-02-006-06, 3-02-031-06

A grain processing plant or mill receives grain from an elevator and performs various manufacturing steps that produce a finished food product. The grain receiving and handling operations at processing plants and mills are the same as at grain elevators. Examples of these plants are flour mills, rice mills, oat mills, dry corn mills and animal feed mills. The following paragraphs describe the processing of the principal grains. Figure 9.9.1-3 depicts these major grains.

9.9.1.1.1 Flour Milling2,5 -

Most flour mills produce wheat flour, but durum wheat and rye are also processed in flour mills. The wheat flour milling process consists of 5 main steps: (1) grain reception and storage; (2) grain cleaning; (3) tempering and conditioning; (4) milling the grain into flour and its byproducts; and (5) storage and/or shipment of finished product. Figure 9.9.1-4 presents a simplified diagram of a typical flour mill. Wheat arrives at a mill and, after preliminary cleaning, is conveyed to storage tanks. As grain is needed for milling, it is withdrawn and conveyed to the mill area for more cleaning. The wheat first enters a separator, where it passes through a vibrating screen. Next, an aspirator removes dust and lighter impurities. The stream of wheat then passes over a magnetic separator that removes iron and steel particles. From the magnetic separator, the wheat enters a disc separator designed to catch individual grains of wheat and reject larger or smaller material. The wheat is then directed to a stoner for removal of stones, sand, flints, and balls of caked earth or mud, which may be so close in size to the wheat grains that they cannot be adequately sifted out. The wheat then moves into a scourer which buffs each kernel and removes more dust and loose bran (hull or husk). Following the scouring step, the grain is sent to the tempering bins where water is added to raise the moisture of the wheat to make it easier to grind. When the grain reaches the proper moisture level (after 8 to 72 hours), it is passed through an Entoleter-scourer-aspirator as a final cleaning step, possibly after passing through a second magnetic separator. The wheat then flows into a grinding bin from which it is fed continuously into the mill itself.

The grain kernels are broken open in a system of breaks by sets of corrugated rolls, each set taking feed from the preceding one. After each break, the grain is sifted. The sifting system is a combination of sieving operations (plansifters) and air aspiration (purifiers). The flour from the plansifters still contains minute bran particles, which are removed by the purifier where air carries the bran away. The flour then passes through the smooth reducing rolls, which further reduce the flour-sized particles and facilitate the removal of the remaining bran and germ particles. Plansifters are used behind the reducing rolls to divide the stock into over-sized particles, which are sent back to the reducing rolls, and flour, which is removed from the milling system. Flour stock is transported from the milling system to bulk storage bins and subsequently packaged for shipment.

Generally, durum wheat processing comprises the same steps as those used for wheat flour milling. However, in the milling of durum, middlings rather than flour are the desired product. Consequently, the break system, in which middlings are formed, is emphasized over the part of the reduction system in which flour is formed. Grain receiving, cleaning, and storage are essentially identical for durum and flour milling. The tempering step varies only slightly between the two

INTERIM SECTION

Contents Subject To Change Pending Completion Of Source Testing Being Conducted

processes. The tempering of durum uses the same equipment as wheat, but the holding times are shorter. Only the grain milling step differs significantly from the comparable flour milling step.

The break system in a durum mill generally has at least five sets of rolls for a gradual reduction of the stock to avoid producing large amounts of break flour. The rolls in the reduction system are used for sizing only, and not to produce flour. The sizing produces a uniform product for sale. The sifting system differs from that in a wheat flour mill in that it relies heavily on purifiers. In place of plansifters, conventional sieves are more common and are used to make rough separations ahead of the purifiers.

Rye milling and wheat flour milling are quite similar processes. The purpose of both processes is to make flour that is substantially free of bran and germ. The same basic machinery and process are employed. The flow through the cleaning and tempering portions of a rye mill is essentially the same as the flow through the wheat flour mill. However, because rye is more difficult to clean than wheat, this cleaning operation must be more carefully controlled.

In contrast to wheat milling, which is a process of gradual reduction with purification and classification, rye milling does not employ gradual reduction. Both the break and reduction roller mills in a rye mill are corrugated. Following grinding, the screening systems employ plansifters like those used in wheat flour mills. There is little evidence of purifier use in rye mills.

A basic difference between wheat milling and rye milling is the purpose of the break rolling system. In wheat flour milling, the intent is to produce as little flour as possible on the break rolls. In rye milling, the intent is to make as much rye flour as possible on the break rolls. Consequently, there are more break rolls in proportion to reduction rolls in a rye mill than in a wheat flour mill.

The potential sources of emissions in flour milling and their respective SCCs are as follows:

Operation	SCC

Receiving and storage	3-02-007-11, 3-02-007-21, 3-02-007-31

--	Unloading

--	Elevator legs

--	Garner/scale vents

--	Cleaners	3-02-007-12, 3-02-007-22, 3-02-007-32

--	Conveyor

Cleaning house	3-02-007-13, 3-02-007-23, 3-02-007-33

--	Separator

--	Aspirator

--	Disc separator

Mill house	3-02-007-14, 3-02-007-24, 3-02-007-34

--	Break rolls

--	Purifier

Product shipping

9.9.1.1.2 Oat Milling2,7 -

The milling process for oats consists of the following steps as illustrated in Figure 9.9.1-5: (1) reception, preliminary cleaning, and storage; (2) cleaning; (3) drying and cooling; (4) grading and hulling; (5) cutting; (6) steaming; and (7) flaking. The receiving and storage operations are comparable to those described for grain elevators and for the wheat flour milling process.

INTERIM SECTION

Contents Subject To Change Pending Completion Of Source Testing Being Conducted

Preliminary cleaning removes coarse field trash and objects that could damage conveying equipment and it removes dust, loose chaff, and other light impurities before storage. After the oats are removed from storage, they flow to a milling separator combining coarse and fine screening with an efficient aspiration. In the next sequence of specialized cleaning operations, the oats are first routed to a disk separator for stick removal, and then are classified into three size categories. Each size category is subjected to a variety of processes (mechanical and gravitational separation, aspiration, and magnetic separation) to remove impurities. Large and short hulled oats are processed separately until the last stages of milling.

The next step in the oat processing system is drying and cooling. Oats are dried using pan dryers, radiator column dryers, or rotary steam tube dryers. Oats typically reach a temperature of 88° to 98°C (190° to 200°F) here, and the moisture content is reduced from 12 percent to 7 to 10 percent. After drying and cooling, the oats are ready for hulling, which separates the hull from the grain. Hulled oats are called groats. Some mills are now hulling oats with no drying or conditioning, then drying the groats separately to develop the desired toasted flavor. Hulling efficiency can be improved by prior grading or sizing of the oats. The free hulls are light enough that aspirators remove them quite effectively.

Generally, the final step in the large oat system is the separation of the totally oat-free groats, which bypass the cutting operation and are directed to storage prior to flaking. The rejects are sent to the cutting plant. The cutting plant is designed to convert the groats into uniform pieces while producing a minimum of flour. The cut material is now ready for the flaking plant. First, the oats are conditioned by steaming to soften the groats thereby promoting flaking with a minimum of breakage. The steamed groats pass directly from the steamer into the flaking rolls. Shakers under the rolls remove fines and overcooked pieces are scalped off. The flakes generally pass through a dryer and cooler to quickly reduce moisture content and temperature which ensures acceptable shelf life. The cooled flakes are then conveyed to the packaging system. Additional information on the processing of oats and other grains can be found in AP-42 Section 9.9.2, Cereal Breakfast Food.

The SCC for overall particulate emissions from oat milling is 3-02-007-60. The potential sources of emissions in oat milling are as follows:

Operation

Receiving, storage, mixing

--	Unloading

--	Elevator legs

--	Garner/scale vents

--	Transfers

Cleaning

--	Aspirator

--	Receiving separator

--	Disc seperator

Drying

--	Pan dryer

--	Coolers

INTERIM SECTION

Contents Subject To Change Pending Completion Of Source Testing Being Conducted

Grading, hulling, finishing

--	Disc separators

--	Hullers, aspirators

--	Gravity tables

Cutting and flaking

--	Shaker

--	Disc separator

--	Aspirators

--	Streamers

--	Groat conditioners

--	Coolers

Shipping

9.9.1.1.3 Rice Milling2,8-10 -

The first step in rice processing after harvest is rice drying. Both fixed-bed and continuous-flow dryers are used to reduce the wet basis moisture content (MCwb) from 24 to 25 percent to 13 to 14 percent MCwb. After the rice is dried, it is stored and subsequently shipped to either conventional or parboil rice mills for further processing. There are three distinct stages in both mills: (1) rough rice receiving, cleaning, drying, and storage; (2) milling; and (3) milled rice and byproduct bagging, packaging, and shipping. Figure 9.9.1-6 shows the process flow for a conventional rice mill, which is the focus of this section. Differences for the parboil plant are identified in the discussion.

Grain is received primarily by truck and rail. The rough rice is then precleaned using combinations of scalpers, screens, aspirators, and magnetic separators. The rice then passes through a stoner, or gravity separator, to remove stones from the grain. The cleaned rice is transported to a disk huller where the rice is dehulled. The rice then passes through a sieve to remove bran and small brokens and to an aspirator to remove hulls. The unshelled rice grains (commonly called paddy) and brown rice are separated in a paddy separator. The unshelled paddy is then fed into another pair of shellers set closer together than the first set, and the process of shelling, aspiration, and separation is repeated.

From the paddy machines, the rice is conveyed to a sequence of milling machines called whitening cones, which scour off the outer bran coats and the germ from the rice kernels. Milling may be accomplished by a single pass through a mill or by consecutive passages through multiple whitening cones. The discharge from each stage is separated by a sieve. After the rice is milled, it passes through a polishing cone, which removes the inner bran layers and the proteinaceous aleurone layer. Because some of the kernels are broken during milling, a series of classifiers, known as trieurs, is used to separate the different size kernels. The rice may be sold at this point as polished, uncoated rice, or it may be conveyed to machines known as trumbels, in which the rice is coated with talc and glucose to give the surface a gloss.

INTERIM SECTION

Contents Subject To Change Pending Completion Of Source Testing Being Conducted

The potential sources of emissions in rice milling and their respective SCCs are as follows:

Operation	SCC

Receiving and storage	3-02-007-71, 3-02-007-72

--	Unloading

--	Elevator legs

--	Garner/scale vents

--	Transfers

--	Drying	3-02-007-73

Cleaning house	3-02-007-74

--	Precleaners

--	Scalpers

--	Screens

--	Disc huller

Mill house and loadout	3-02-007-74

--	Skellers

--	Paddy separator

--	Hullers

--	Whitening cones

In parboiling mills, the cleaned rough rice is steamed and dried prior to the milling operations. Pressure vessels are used for the steaming step, and steam tube dryers are used to dry the rice to 11 to 13 percent MCwb. Following the drying step, the rice is milled in conventional equipment to remove hull (bran), and germ.

9.9.1.1.4 Corn Dry Milling2,11-13 -

Corn is dry milled by either a degerming or a nondegerming system. Because the degerming system is the principal system used in the United States, it will be the focus of the dry corn milling process description here. Figure 9.9.1-7 shows a flow diagram for the degerming dry corn milling process, which is more accurately called the tempering degerminating (TD) system. The conventional degerming system involves the following steps after receiving the grain: (1) dry cleaning, and if necessary, wet cleaning; (2) tempering; (3) separation of hull, germ, and tip cap from the endosperm in the degerminator; (4) drying and cooling of degermer product; (5) multistep milling of degermer product through a series of roller mills, sifters, aspirators, and purifiers; (6) further drying of products, if necessary; (7) processing of germ fraction for recovery of crude corn oil; and (8) packaging and shipping of products.

Unloading and dry cleaning of corn is essentially the same as described for wheat. However, for corn, surface dirt and spores can best be removed by wet cleaning, which involves a washing-destoning unit followed by a mechanical dewatering unit. After cleaning, the corn is sent through the tempering or conditioning step, which raises the moisture content of the corn to 21 to 25 percent. After tempering, the corn is degermed, typically in a Beall degermer and corn huller. The Beall degermer is essentially an attrition device built in the form of a cone mill. The product exits in two streams, thru-stock and tail stock. Rotary steam-tube dryers are often used to dry the degermer product, because its moisture content must be in the 15 to 18 percent range for proper milling. After

INTERIM SECTION

Contents Subject To Change Pending Completion Of Source Testing Being Conducted

drying, the product is cooled to 32° to 37°C (90° to 100°F). After drying and cooling, the degermer stock is sifted or classified by particle size and is fed into the conventional milling system.

The milling section in a dry corn mill consists of sifting, classifying, milling, purifying, aspirating, and possibly, final drying operations. The feed to each pair of rolls consists of selected mill streams produced during the steps of sifting, aspirating, roller milling, and gravity table separating. For the production of specific products, various streams are withdrawn at appropriate points in the milling process. A number of process streams are often blended to produce a specific product. The finished products are stored temporarily in working bins, dried and cooled if necessary, and rebolted before packaging or shipping in bulk.

The potential sources of emissions in dry corn milling and their respective SCCs are as follows:

Operation	SCC

Receiving, cleaning, storage	3-02-007-41, 3-02-007-43

--	Unloading

--	Elevator legs

--	Garner/scale vents

--	Transfers

--	Dryer	3-02-007-42

Cleaning house	3-02-007-44

--	Separator

--	Aspirator

--	Disc separator

--	Scourer

Degerming	3-02-007-45

--	Degerminator

--	Dryers/coolers

--	Aspirators

Milling	3-02-007-45

--	Roller mills

--	Purifiers

--	Aspirators

--	Dryers/coolers

Byproducts and shipping

--	Hammermills

--	Oil extraction

--	Bulk loading

Oil is recovered from the germ fraction either by mechanical screw presses or by a combination of screw presses and solvent extraction. A more detailed discussion of the corn oil extraction process is included in AP-42 Section 9.11.1, Vegetable Oil Processing.

INTERIM SECTION

Contents Subject To Change Pending Completion Of Source Testing Being Conducted

9.9.1.1.5 Animal Feed Mills2,14

As shown in Figure 9.9.1-8, the manufacture of feed begins with receiving of ingredients at the mill. Over 200 ingredients may be used in feed manufacture, including grain, byproducts (e. g., meat meal, bone meal, beet and tomato pulp), and medicinals, vitamins, and minerals (used in very small portions). Grain is usually received at the mill by truck, rail, or possibly barge. Most mills pass selected feed ingredients, primarily grains, through cleaning equipment prior to storage. Cleaning equipment includes scalpers to remove coarse materials before they reach the mixer. Separators, which perform a similar function, often consist of reciprocating sieves that separate grains of different sizes and textures. Magnets are installed ahead of the grinders and at other critical locations in the mill system to remove tramp iron, bits of wire, and other foreign metallic matter, which could harm machinery and contaminate the finished feed. From the cleaning operation, the ingredients are directed to storage.

Upon removal from storage, the grain is transferred to the grinding area, where selected whole grains are ground prior to mixing with other feed components. The hammermill is the most widely used grinding device. The pulverized material is forced out of the mill chamber when it is ground finely enough to pass through the perforations in the mill screen.

Mixing is the most important process in feed milling and is normally a batch process. Ingredients are weighed on bench or hopper scales before mixing. Mixers may be horizontal or vertical type, using either screws or paddles to move the ingredients. The material leaving the mixer is meal, or mash, and may be marketed in this form. If pellets are to be made, the meal is conditioned with steam prior to being pelleted.

Pellet making is an extrusion process in which the conditioned meal is forced through dies. Pellets are usually 3.2 to 19 mm (1/8 to 3/4 in.) in diameter. After extrusion, pellets are dried and cooled in pellet coolers. If pellets are to be reduced in size, they are passed through a crumbler, or granulator. This machine is a roller mill with corrugated rolls. Crumbles must be screened to remove fines and oversized materials. The product is sent to storage bins and then bagged or shipped in bulk.

INTERIM SECTION

Contents Subject To Change Pending Completion Of Source Testing Being Conducted

The potential sources of emissions from animal feed mills and their respective SCCs are shown in the following listing. Not all of the potential sources apply to smaller capacity animal feed mills located at cattle feedlots.

Operation	SCC

Receiving and storage

--	Unloading	3-02-008-02

--	Elevator legs	3-02-008-04

--	Transfers	3-02-008-04

--	Garner/scale vent

--	Scalper

--	Bin vents

Preparation/milling	3-02-008-05, 3-02-008-15

--	Grinder

--	Flaker

--	Cracker

--	Screen/aspirators

--	Crimper

--	Mixer

--	Mesh cleaner

--	Transfers

Pelleting

--	Mills

--	Pellet cooler	3-02-008-06, 3-02-008-16

Shipping	3-02-008-03

9.9.1.2 Emissions And Controls2-5,15-17

The primary pollutant emitted in significant quantities from grain elevators and processing operations is particulate matter (PM) (including particles ≤ 10 micrometers in aerodynamic diameter, PM-10). Exposure to these grain-derived particles, which contain a variety of proteinaceous constituents, mold, and pollens above levels permitted by current federal regulations, provokes allergic responses in some workers. Organic emissions (e. g., hexane from certain operations at corn oil extraction facilities) may also be significant. These organic emissions (and related emissions from soybean and peanut processing) are discussed in AP-42 Section 9.11.1, Vegetable Oil Processing. Also, direct-fired grain drying operations and product dryers in grain processing plants may emit small quantities of volatile organic compounds (VOC) and other combustion products. The following discussion focuses primarily on PM/PM-10 sources at grain elevators and grain milling/processing facilities. However, potential sources of VOC and sulfur dioxide (SO2) are also identified, even though no data are available to quantify the emissions of these pollutants. Table 9.9.1-1 provides a summary of the major potential emission points discussed earlier.

In addition to criteria pollutants, various gas-phase hazardous air pollutants were identified at grain elevators resulting from the use of fumigants. Phosphine is legally registered as a fumigant, and is the predominant fumigant used by the industry.

9.9.1.2.1 Grain Elevators -

Particulate emissions occur whenever quantities of grain are set into motion during loading, conveying, transfer, drying, or cleaning operations at a grain elevator. The emission rate can be

INTERIM SECTION

Contents Subject To Change Pending Completion Of Source Testing Being Conducted

affected by the quantity of foreign material in the grain (dirt, seeds, sticks, stones, etc., known as "dockage") and by the type of grain. While it is difficult to quantify the effect of dockage, observations indicate that oats, sorghum, corn, and soybean are usually very dusty, whereas wheat and rice are comparatively clean. Interim total PM and PM-10 emission factors for the principal operations at grain elevators are presented in Table 9.9.1-2. The emission factors in Table 9.9.1-2 are considered to be interim values for all types of grain elevators because particulate emission testing is currently being conducted at country and terminal elevators. After the testing has been completed and the test reports reviewed and evaluated, these emission factors will be adjusted to reflect the new data. The emission factors for internal operations consider only transfer of the received grain to a storage bin and then transfer from the bin for shipping. They do not consider any internal transfer of grain. In elevators, grains may be transferred from one storage bin to another or may be emptied from one storage bin, treated or dried, and then transferred to another storage bin. These types of internal transfers have not been considered in the emission factor, because the numbers of times grain is transferred internally varies considerably from one elevator to another.

Test data are often provided in the literature for a single type of grain, which complicates comparison of emissions between grain types. In an attempt to alleviate this problem, interim relative dustiness factors were estimated for various types of grain so comparison of test results can be made for different grain types. These relative factors are to be considered interim because testing is currently being conducted to develop new data for the relative dustiness of selected types of grain. Research reports were reviewed for data on dust generation for various types of grain. Six reports provided data on the weight of dust generated from corn, soybeans, wheat, and milo (sorghum).15,17,23,27-28,32 From these data, wheat was selected as the baseline grain because it generated the lowest relative quantity of dust. Dustiness ratios relative to wheat were calculated for all reported data for each of the other grains. For each grain, the relative dustiness factors were compiled, the highest and lowest factor excluded, and the remaining factors averaged. The calculated average ratio of dust generated by soybeans, corn, or milo, relative to wheat, is as follows:

Grain	Relative dustiness

Wheat	1 .0

Soybeans	2 .5

Corn	2 .5

Milo (Sorghum)	1 .75

Mixed	1 .95

Since particulate emission data are sometimes presented for "mixed" grains, an average of the relative dustiness factors for the 4 grains was calculated (1.95) and this average was assigned as the relative dustiness factor for mixed grains. It should be noted that while the average relative dustiness factors for soybeans and corn are 2.5, individual ratios for soybeans ranged from 1.0 to 4.1 and individual ratios for corn ranged from 1.5 to 5.6. After exclusion of the highest and lowest ratio, the average ratio for milo was based on 3 individual ratios, which showed a very narrow range.

In Table 9.9.1-2, the interim total particulate emission factors for receiving by truck or rail represent an average of the results for unloading wheat from trucks at 3 country elevators.21,28,30 Since hopper cars are the exclusive method for rail transportation of grain, dust emissions from rail unloading was assumed to be no greater than emissions from truck unloading. More specifically, unloading from hopper cars occurs predominantly in a choke condition whereas truck unloading may occur in either a choke condition or free flowing from straight bed trucks. The interim emission

INTERIM SECTION

Contents Subject To Change Pending Completion Of Source Testing Being Conducted

factor for barge unloading is the factor shown for unloading at country elevators in the previous AP-42 section, Grain Elevators and Processing Plants.4

For grain drying, the interim emission factor for column dryers is based on the average of 2 data points for corn at country elevators adjusted to wheat based on the relative grain dustiness values for corn (0.22/2.5).30 The interim factor for rack drying is also based on 2 data points for corn at country elevators and adjusted to wheat based on the relative dustiness value (3.0/2.5).30

The interim emission factor for internal handling is comprised of factors from 4 emission sources: tunnel belts, gallery belts, grain cleaning, and headhouse emissions. Interim factors were derived for each of these 4 sources and then summed to provide an overall interim factor for internal handling. The interim factor for tunnel belts (0.72) was derived from data for mixed grains at a terminal elevator adjusted to wheat using the relative dustiness factor (1.4/1.95).32 Similarly, the interim factor for gallery belts (0.06) was obtained for mixed grains in the same report and adjusted to wheat (0.11/1.95). For the grain cleaning interim factor (0.82), 6 data points were obtained for mixed grains from test reports at 5 country elevators.29,31-32,38,40 The 6 data points were averaged and adjusted to wheat (1.6/1.95). An interim emission factor for the headhouse was developed using 4 data points for wheat from 2 reports for country elevators.27-28 The average of the 4 data points (0.87) was doubled to represent the in/out movement of grain through the headhouse (1.74). The sum of the interim emission factors for the 4 sources comprising internal handling is 3.34 lb per ton. A 1994 test report for studies at country elevators showed that total particulate measurements for gallery belt transfers ranged from 10 to 26 times less than the emission factor of 0.11 lb/ton for gallery belts presented in a 1974 report, which were obtained by testing upstream of a control system.16,32 Since all of the emission factors for internal handling were obtained using upstream testing, the interim emission factor for internal handling was assumed to be 10 times smaller than the sum of the 4 sources (3.34/10). This interim emission factor for internal handling (0.33 lb per ton) will be reevaluated as additional test results become available.

The interim emission factor for internal handling can be summarized as follows:

Emission source	Emission factor

Tunnel belts	0 .72

Gallery belts	0 .06

Grain cleaning	0 .82

Headhouse	1 .74

TOTAL	3 .34

INTERIM EMISSION FACTOR = 3.34/10 = 0.33 lb/ton

For bin vents, the interim emission factor is based on emission data for wheat at country elevators.27

In Table 9.9.1-2, the interim total particulate emission factors for shipping by truck or rail are based on the results from truck loading of wheat at a country elevator.21 Since hopper cars are the sole method of grain transportation by rail, the emission factor for rail loading was assumed to be the same as for truck loading. The barge shipping, the interim total particulate emission factor was developed from 6 data points for mixed grain at terminal elevators.19,32-33 Terminal elevators are the most common location for shipping grain by barge. The average of the 6 data points was adjusted to a wheat basis using the relative dustiness factor (0.31/1.95). The interim total particulate emission

INTERIM SECTION

Contents Subject To Change Pending Completion Of Source Testing Being Conducted

factor for ships is based on an average of 2 emission data points for shipping of wheat at 2 terminal and export elevators.32-33

All of the previous discussion of interim emission factors in Table 9.9.1-2 have addressed total particulate emissions. A 1994 test report of studies at country elevators showed that PM-10 was 24.5 percent and 25.3 percent of the total particulate for milo and corn, respectively.16 In Table 9.9.1-2, the interim emissions factors for PM-10 were obtained by assuming the factors were 25 percent of the interim total particulate emission factors.

Several methods are available to reduce or control dust emissions at grain elevators. Since most emissions are generated when air passes swiftly through a mass of grain, measures that slow down grain transfer (conveying) rates or that reduce free fall distances will reduce emissions. Bulk grain, especially when falling through the air, should be protected from significant air currents or wind sources. Many operations at elevators are partially or totally enclosed (e. g., screw conveyors, drag conveyors, elevator legs) to isolate generated dust from the atmosphere. Hooding in the vicinity of some operations (e. g., grain unloading, conveyor transfer points) collects generated dust by creating a negative pressure area (through suction or air aspiration) near the center of activity and then ducting the dusty air to a control device. Recent developments in the control of ship and barge loading operations include the use of "dead boxes" and tent controls. The dead box is a baffled attachment on the loading spout that serves to reduce the speed of the falling grain before it reaches the open air and strikes the grain pile. Aspiration to a control device often accompanies the use of the dead box. Large flexible covers connected to the loading spout and aspiration ducting, called tents, are used to cover the holds of ships during most of the loading operation. The tent must be removed during topping off (usually about 25 percent of the total loading), allowing essentially uncontrolled emissions during those periods.

The emission control methods described above rely on either process modifications to reduce dust generation or capture systems to collect dusts after they are generated. An alternative control measure that has developed over the last 10 years is dust suppression with food-grade oils, generally either white mineral oil, soybean oil, or other vegetable oils. Currently the U.S. Food And Drug Administration restricts application rates of mineral oil to 0.02 percent by weight. The oil is applied to the grain by a spray system at the end of the transfer belt from the receiving pit to the elevator boot or on the boot feed chute.

The driving force behind most of these dust suppression systems has been grain elevator explosion control rather than emission control. Consequently, few data have been published on the amount of emission reduction achieved by such systems. A 1994 study conducted at a country elevator showed that a mineral oil dust suppression system operating under typical conditions (i. e., 25 psi oil spray pressure) controlled, on average, approximately 60 percent of both total particulate emissions and PM-10 emissions from the gallery belt transfer of milo (sorghum).16 For the transfer of corn, under the same operating conditions, the results showed 69 percent and 48 percent control of PM-10 and total particulate, respectively. Internal elevator dust concentration reductions of 80 to 90 percent have also been reported for oil applications in the range of 0.01 to 0.03 percent by weight. Furthermore, these reductions are maintained when the grain is stored for 30 days after application. These limited data suggest that appreciable emission reductions may be obtained from handling and storage operations using this dust suppression approach.

Most elevators use PM control devices on at least some of their operations. The traditional form of control at elevators has been mechanical collectors, or cyclones. Cyclones collect particles larger than about 10 micrometers, but because they offer only 85 to 95 percent control efficiency,

INTERIM SECTION

Contents Subject To Change Pending Completion Of Source Testing Being Conducted

they often allow visible emissions. Hence, fabric filters are usually selected in areas having more stringent control requirements. Well-operated fabric filters typically exceed 99 percent efficiency and allow no visible emissions. The air aspirated from enclosed equipment and hoods is ducted to a fabric filter or, in some cases, one or more cyclones. Other PM control devices, such as wet scrubbers and electrostatic precipitators, are rarely applied at elevators.

Grain dryers present a different sort of control problem because of the large volumes of warm, moist air exhausted. Most dryers are enclosed with a continuously vacuumed polyester or stainless steel screening to collect PM; the air is usually discharged through a cyclone. Two principal dryer configurations, rack and column, are used. The majority of dryers manufactured today are of the column type, which has considerably lower emissions.

9.9.1.2.2 Grain Processing Plants -

Several grain milling operations, such as receiving, conveying, cleaning, and drying, are similar to those at grain elevators. In addition, applications of various types of grinding operations to the grain, grain products, or byproducts are further sources of emissions. The hammermill is the most widely used grinding device at feed mills. Some product is recovered from the hammermill with a cyclone collector, which can be a major source of dust emissions. Mills, similar to elevators, use a combination of cyclones and fabric filters to conserve product and to control emissions. Several types of dryers are used in mills, including the traditional rack or column dryers, fluidized bed dryers (soybean processing), and flash-fired or direct-fired dryers (corn milling). These newer dryer types might have lower emissions, but data are insufficient at this time to quantify the difference. The grain precleaning often performed before drying also likely serves to reduce emissions. Interim emission factors for various grain milling and other processing operations are presented in Table 9.9.1-3. In this interim section, it has been assumed that PM-10 emissions from cyclones used in animal feed mills are 50 percent of the total particulate emissions from that cyclone. These emission factors may change based on receipt of new emission test data.

Because of the operational similarities, emission control methods used in grain milling and processing plants are similar to those in grain elevators. Cyclones or fabric filters are often used to control emissions from the grain handling operations (e. g., unloading, legs, cleaners, etc.) and also from other processing operations. Fabric filters are used extensively in flour mills. However, certain operations within milling operations are not amenable to the use of these devices and alternatives are needed. Wet scrubbers, for example, are applied where the effluent gas stream has a high moisture content. A few operations have been found to be difficult to control by any method. Various emission control systems have been applied to operations within the grain milling and processing industry.2

Grain processing facilities also have the potential to emit gaseous pollutants. Natural gas-fired dryers and boilers are potential sources of combustion byproducts and VOC. The production of various modified starches has the potential for emissions of hydrochloric acid or ethylene oxide. However, no data are available to confirm or quantify the presence of these potential emissions. Neither are there any data available concerning the control of these potential emissions.

INTERIM SECTION

Contents Subject To Change Pending Completion Of Source Testing Being Conducted

References For Section 9.9.1

1.	Draft Emission Factor Documentation For AP-42 Section 9.9.1, Grain Elevators And Processing Plants, Contract No. 68-D1-0115, Midwest Research Institute, Cary, NC, May 1994.

2.	L. J. Shannon, et al., Emissions Control In The Grain And Feed Industry, Volume I— Engineering And Cost Study, EPA-450/3-73-003a, U. S. Environmental Protection Agency, Research Triangle Park, NC, December 1973.

3.	V. Ramanthan and D. Wallace, Review Of Compliance Monitoring Programs With Respect To Gain Elevators, Final Report, EPA Contract 68-01-4139, Tasks 12 and 14, Midwest Research Institute, March 1980.

4.	G. A. LaFlam, Emission Factor Documentation For AP-42 Section 6.9.1, Grain Elevators And Processing Plants, Pacific Environmental Services Inc., Durham, NC, September 1987.

5.	D. Wallace, Grain Handling And Processing, Part of Chapter 13, "Food And Agricultural Industry", in Air Pollution Engineering Manual, Van Nostrand Reinhold, NY, 1992.

6.	Letter from Thomas C. O'Connor, National Grain and Feed Association, to Dallas Safriet, U. S. Environmental Protection Agency, Research Triangle Park, NC. November 24, 1993.

7.	Francis H. Webster, Oats: Chemistry And Technology, American Association Of Cereal Chemists, St. Paul, MN, 1986.

8.	Bienvenido O. Juliano, Rice Chemistry And Technology, American Association Of Cereal Chemists, St. Paul, MN, 1985.

9.	Bor S. Luk, Rice, Volume I, Production, Second Edition, Van Nostrand Reinhold, New York, NY, 1991.

10.	Bor S. Luk, Rice, Volume II, Utilization, Second Edition, Van Nostrand Reinhold, New York, NY, 1991.

11.	Samuel R. Aldrich, Walter O. Scott, and Robert G. Hoeft, Modern Corn Production, Third Edition, A. & L. Publications, Champaign, IL, 1986.

12.	G. F. Spraque and J. W. Dudgley, Corn And Corn Improvement, Third Edition, American Society Of Agronomy, Inc., Crop Science Society Of America, Inc., and Soil Science Society Of America, Inc., Madison, WI, 1988.

13.	S. A. Watson and P. E. Ramstad, Corn Chemistry And Technology, American Association Of Cereal Chemists, Inc., St. Paul, MN, 1987.

14.	R. R. McElhiney, Feed Manufacturing Technology III, American Feed Manufacturers Association, Arlington, VA, 1985.

INTERIM SECTION

Contents Subject To Change Pending Completion Of Source Testing Being Conducted

15.	Health and Hygiene, Inc., Worker Exposure To Dust In The Grain Industry, Unpublished report for the National Grain And Feed Association, Washington, DC, September 1991.

16.	Tests Of Oil Suppression Of PM-10 At Grain Elevators, Test Report, Midwest Research Institute, Kansas City, MO, November 1994.

17.	F. S. Lai, et al., Examining The Use Of Additives To Control Grain Dust, Final Report To The National Grain And Feed Association, Washington, DC, June 1982.

18.	Written communication from Paul Luther, Purina Mills, Inc., St. Louis, MO, to Greg LaFlam, Pacific Environmental Service Inc., Durham, NC, March 11 and August 28, 1987.

19.	GCA/Technology Division, Emission Factor Development For Ship And Barge Loading Of Grain, Revised Draft Final Report, EPA Contract No. 68-02-3510, Work Assignment No. 46, U. S. Environmental Protection Agency, Research Triangle Park, NC, October 1984.

20.	Source Category Survey: Animal Feed Dryers, EPA-450/3-81-017, U. S. Environmental Protection Agency, Research Triangle Park, NC, December 1981.

21.	P. Kenkel and R. Noyes, "Grain Elevator Dust Emission Study", Oklahoma State University, Stillwater, OK, October 21, 1994 and "Clarifying Response To MRI Report On OSU Dust Emission Study", Oklahoma State University, Stillwater, OK, February 13, 1995.

22.	H. J. Taback, et al., Fine Particle Emissions From Stationary And Miscellaneous Sources In The South Coast Air Basin, Final Report, PB-293-923, California Air Resources Board, Sacramento, CA, February 1979.

23.	F. J. Wade, et al., "Investigation To Determine Dust Concentration And Characteristics Inside Enclosed Work Areas And Equipment At Large Grain Terminals", U. S. Department Of Agriculture, Federal Grain Inspection Service, Kansas City, MO, 1979.

24.	Report Of Particulate Emissions Tests For Stockton Hay And Grain Company, Environmental Research Group, Inc., Emeryville, CA, September 1983.

25.	P. Lonnes, Results Of Particulate Emission Compliance Testing At The Peavey Company In Valley City, North Dakota, Conducted March 16-18, 1977, Interpoll Inc., St. Paul, MN, April 15, 1977.

26.	Report Of Particulate Emissions Tests For Wayne Farms Laurel Feed Mill, Environmental Monitoring Laboratories, Ridgeland, MS, August 29 and September 20, 1994.

27.	W. H. Maxwell, Stationary Source Testing Of A Country Grain Elevator At The Great Bend Cooperative Association Elevator B, Great Bend, Kansas, Final Report, Contract No. 68-92-1403, Task 19, Midwest Research Institute, Kansas City, MO, April 29, 1976.

28.	W. H. Maxwell, Stationary Source Testing Of A Country Elevator-Overbrook, Kansas, Final Report, EPA Contract No. 68-02-1403, Tasks 15 and 18, Midwest Research Institute, Kansas City, MO, February 19, 1976.

INTERIM SECTION

Contents Subject To Change Pending Completion Of Source Testing Being Conducted

29.	A. L. Trowbridge, Particulate Emissions Testing, ERC Report No. 4-7683, Environmental Research Corporation, St. Paul, MN, January 16, 1976.

30.	J. M. Willenberg, et al., Air Pollution Emissions From Eastern Washington Grain Elevators, Annual Meeting Of The Pacific Northwest International Section Of The Air Pollution Control Association, Seattle, WA, November 19-21, 1975.

31.	C. S. Hulburt, Particulate Emissions Evaluation And Performance Test Of The Dust Control Systems At Farmers Coop Elevator In Enderlin, North Dakota, Pollution Curbs Inc., St. Paul, MN, October 23, 1974.

32.	P. G. Gorman, Potential Dust Emissions From A Grain Elevator In Kansas City, Missouri, Final Report, EPA Contract No. 68-02-0228, Task No. 24, Midwest Research Institute, Kansas City, MO, May 1974.

33.	Valentine, Fisher, and Tomlinson, Air Pollution Emission Test, Cargill, Inc., Seattle, Washington, EMB Test No. 73-GRN-8, U. S. Environmental Protection Agency, Research Triangle Park, NC, January 1974.

34.	Particulate Emission Testing For Wayne Farms, Air Systems Testing, Inc., Marietta, GA, September 1-2, 1992.

35.	L. J. Shannon et al., Emissions Control In The Grain And Feed Industry, Volume I: Engineering And Cost Study, EPA-450/3-73-003a, U. S. Environmental Protection Agency, Research Triangle Park, NC, December 1973.

36.	W. D. Snowden, Atmospheric Emission Evaluation, Mayflower Farms Grain And Feed Milling Plant, Portland, Oregon, Test No. 72-C1-34(GRN), U. S. Environmental Protection Agency, Research Triangle Park, NC, February 8, 1973.

37.	R. W. Gerstle and R. S. Amick, Test Number 73-GRN-1, Ralston Purina Company, Louisville, Kentucky, Final Report, EPA Contract No. 68-02-0237, Task 17, U. S. Environmental Protection Agency, Research Triangle Park, NC, 1972.

38.	F. J. Belgea, Grain Handling Dust Collection Systems Evaluation For Farmer's Elevator Company, Minot, North Dakota, Pollution Curbs Inc., St. Paul, MN, August 28, 1972.

39.	Environmental Engineering Inc., Source Test Report On Measurement Of Emissions From Cargill, Inc., Sioux City, Iowa, Test No. 72-Cl-28(GRN), U. S. Environmental Protection Agency, Research Triangle Park, NC, 1972.

40.	F. J. Belgea, Cyclone Emissions And Efficiency Evaluation, Pollution Curbs Inc., St. Paul, MN, March 10, 1972.

41.	Thomas Rooney, Emission Performance Testing Of A Rice Mill, Western Environmental Services, Redondo Beach, CA, March 1992.

INTERIM SECTION

Contents Subject To Change Pending Completion Of Source Testing Being Conducted

42.	Written communication from W. James Wagoner, Butte County Air Pollution Control Agency, Durham, CA, to Dallas Safriet, U. S. Environmental Protection Agency, Research Triangle Park, NC, October 11, 1993.