asphalt plant level ii january of module asphalt … plant 2/04 - module...asphalt plant level ii...

Asphalt Plant Level II – January 2009 of 18 Module 4 – Asphalt Supply Systems

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Module 4

Asphalt Supply Systems

ConstructionTrainingQualification Program

Asphalt Plant

Level 2

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Module 4What you will learn….

• Asphalt storage tank systems• FDOT requirements for all AC systems• Asphalt tank heating systems• BMPs to maintain asphalt cement temperature• BMPs to maintaining asphalt cement integrity• Equipment for crumb rubber asphalt• BMPs for polymer modified cement• Fiber additives for 337 mixes• BMPs for Multiple Tank Installations

In this module different types of asphalt storage tanks will be covered, as well as department requirements for all AC systems. Asphalt tank heating systems will be reviewed, along with Best Management Practices for maintaining asphalt cement temperature and integrity. Equipment and requirements for batch mixing Crumb Rubber Modified asphalt cement will be reviewed, along with requirements for fiber injection systems for 337 mixes.

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The information presented in this section is found …

• “Hot Mix Asphalt Production Facilities”(NHI Course 131044)

• Module 4, pages 4-2 to 4-23• “Hot Mix Paving Handbook 2000”

• Section 7, page 66

The information presented in this section is found in Module 4 (pages 4-2 to 4-23) in NHI Course 131044 “Hot Mix Asphalt Production Facilities,” and in Section 7 (page 66) in the “Hot Mix Paving Handbook 2000.”


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RequirementAC Storage Tanks

• Requirements for AC systems for all plantsincluded this module

• Specific requirements AC systems on batch plants – Batch Plant Appendix

• Specific requirements AC systems on drum plants – Drum Mix Section

Department specifications for all AC storage systems for all plants are included in this module. There are several specifications relating specifically to batch style plants. These are covered in the appendix dedicated to batch plant production. The specifications that are related specifically to drum style plants that are covered in the section dedicated to drum-mix production.

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January 2009 4 - 5Tanks Can be Either Horizontal or Vertical

Asphalt tanks can either be horizontal or vertical. Most tanks found in the field are horizontal, but many of the new tanks are vertical. Vertical tanks take up less space and are more easily designed with agitation equipment for modified binders.

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320-2.3Must be capable of heating liquid asphalt to the required temperature

This general specification ensures that the storage tank must be capable of heating liquid to the required temperature, which also implies keeping it stored at the proper temperature (320-2.3).


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Tanks typically have hot oil heating coils, but some are heated electrically or directly with burner.

Tanks are typically heated with coils installed in the bottom of the tanks. These coils either have hot oil passing through them, or have electric heating elements installed in them.

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Fossil Fuel Fired Hot Oil Heater

If hot oil is used to heat the tanks, then the heat transfer oil must, of course, be heated. This illustration shows the inner workings of a fossil fuel fired hot oil heater. Fossil fuel heaters can be fired on oil, propane, natural gas, liquefied natural gas, or butane. The hot oil is circulated through pipes surrounding the combustion chamber, and the exhaust stack. The hot oil is then pumped through the asphalt tanks.

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Fossil Fuel Fired Hot Oil Heater This photograph shows the same fossil fuel fired hot oil heater in the field. Notice the hot oil pumping system in the foreground. The hot oil reservoir is located over the burner.


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320-2.3 No flame must come into contact with tank

The flame in the storage tank, if it is direct fired, must not come directly in contact with the tank (320-2.3).

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Electrically Heated AC Tank

January 2009

Electric heating elements can also be installed directly in the asphalt tanks. Electric heating elements are enclosed in these tubes. The tubes get hot and heat the asphalt tank.

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Portable AC Tank with Heater Mounted in Tank

HEATER

Fossil fuel fired heaters can also be installed directly in the tank. The combustion chamber and exhaust stack are mounted inside this type of tank and heat the asphalt as the hot gases exit the combustion area. There is metal heat jacketing around the combustion chamber and stack to keep the hot steel from coming in direct contact with the liquid. This protects the quality of the asphalt, by keeping the material from coking against the combustion area.


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320-2.3 Keep circulating during production

Asphalt must be kept in circulation during production (320-2.3). There are natural convective currents in an asphalt tank, but these are typically not sufficient to keep modified binders homogenous. Asphalt rubber binders must be circulated or else the crumb rubber materials can settle.

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The simplest method for keeping modified binders homogenous is to keep them circulating through the tank. The same pump used to off-load asphalt from a tanker can be valved to accomplish this task.

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If simply pumping the modified asphalt through the tank is not adequate for storage requirements, mechanical agitators can be installed in the tanks. This illustration shows mechanical agitators installed in a vertical tank. Mechanical agitators can also be installed in horizontal tanks.


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Liquid Asphalt Storage Tanks Equipped with Agitators

This set of photographs shows several different asphalt tanks equipped with agitators. Both vertical and horizontal tanks can be fitted with agitators, but horizontal tanks require at least two. These are available on new tanks or available as kits so they can be retrofitted to existing tanks.

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320-2.3Use heated jacketed lines to prevent heat loss

Heat jacketed lines must be used to prevent heat loss (320-2.3).

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Hot Oil Heated Asphalt Lines

(HEATER)

This photograph shows the heated asphalt lines and valves at a typical plant. Notice the hot oil heater in the background, and the hot oil piping also running to the hot mix storage silo.


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320-2.3 Provide thermometer in tank or AC Feed line to plant (200-400°F)

A thermometer must be fitted to the tank or the feed line to the plant to verify the temperature of the asphalt cement is being maintained within tolerance (320-2.3).

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320-2.3 Locate a sampling device in the discharge piping exiting the storage tank (or at a location approved by the Engineer)

A sampling device must be fitted to the discharge piping exiting the storage tank, or at a location approved by the Engineer (320-2.3).

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When sampling at a plant the same sampling directions apply as sampling from a transport, including wearing proper protective gear. Use a clean can. Use caution when opening valve. Draw off some material prior to fill can. Remember, cans get hot when filling. Cover cans with lids to avoid contamination. Properly identify the material on the can.


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330- 4 Preparation of Asphalt Cement– Temperature Requirements not to exceed

370°F – Equip the transport tankers with sampling

and temperature devices (300-3.2)– Maintain the asphalt cement from 230°F to

370°F – Maintain constant heating within these

limits– Do not allow wide temperature fluctuations

Asphalt cement must be delivered to the plant in a temperature range not to exceed 370°F, maintained at a temperature between 230°F and 370°F, and heated in such a fashion as to not allow wide temperature swings within these ranges. In addition to the storage tanks, transport tankers are to be equipped with sampling and temperature devices.

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Typical AC Delivery Ticket

Ticket Information• Supplier• Grade of Asphalt• Modifier Added• % Antistrip Added• Net Tons/Gallons• (QPL numbers)

This photograph shows a typical asphalt cement delivery ticket. It contains information on the supplier, grade of asphalt, modifiers added, percent anti-strip added, net weight and gallons, and QPL numbers of the asphalt product and antistrip (starting shortly).

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Best Management PracticesMaintaining AC Temperature

• Critical to proper coating of the aggregate• Critical for proper placement and compaction• Critical for a quality paving product

The reason it is so critical to maintain temperature of the liquid asphalt cement in the tank and the lines is that adequate coating, adequate placement, and adequate compaction is all dependent on a proper product temperature. Cooling asphalt cement impacts the quality of the entire construction operation.


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Best Management PracticesMaintaining AC Temperature

• Must be managed by monitoring temperature in each tank and the feed line into the plant

• Must be managed by adequately heating the asphalt lines feeding plant

• Why?– There is no material test that ensures that the

asphalt cement was at the required temperature– The temperature of the AC binder affects the

coating characteristics and quality of the mix

The only way to ensure that the asphalt is being stored at the right temperature is to monitor the temperatures in each tank, inspect visually that heating of the asphalt lines is occurring, and monitor the temperature of the asphalt cement in the plant line. This sounds like a “method spec” approach and not an “end result” approach, but is necessary because there is no material test that can be performed in the lab that ensures that the asphalt cement was at the required temperature, and the temperature of the binder dramatically affects the coating characteristics and the quality of the mix.

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Hot Oil Heat Also Used for Other Plant Components

– AC pumps– AC lines– AC Valves– Hot Mix Silos– Pugmills– AC Weigh Hopper– Etc.

Hot oil is used to heat various other components on the plant, in addition to the asphalt tanks. These include the AC pumps, AC lines, AC valves, hot mix silos, batch plant pugmills, and batch plant AC weigh hoppers, etc.


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Electric Hot Oil Heater

The hot oil can also be heated electrically. This is an illustration of an electric hot oil heater. The hot oil circulates around electric heating elements encased in pipe and mounted in the horizontal cylinder below the unit. The hot oil pumping system is located at the rear of the unit. The hot oil is pumped through the asphalt tanks.

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Storing & UsingModified Asphalts

• Typically blended at terminal

• Need to be kept in circulation

• Asphalt rubber can be blended at the hot mix plant (several equipment options exist)

Modified asphalt frequently requires additional storage management. Additives in modified asphalts are typically in chemical solution or physical suspension in the liquid. The additives can come out of solution or suspension if they are not kept moving. This negatively impacts the quality of the mix. Modified asphalts are typically blended at the terminal, but asphalt rubber can be blended at the plant. Several equipment options exist for blending and storing these materials.

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Asphalt Rubber (Section 336)

• Used as binder for 337 FC type mixes.

• Typically terminal blended

• Can be blended at the HMA Plant

Asphalt rubber is used extensively in Florida, primarily as a modifier for 337 type mixes. This can be terminal blended or plant blended.


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Asphalt Rubber Blended at Plant

This photograph shows a typical blending system installed at a plant. The crumb rubber is loaded into the hopper at the left, then conveyed to the batching tank where it is mixed with a pre-determined quantity of asphalt cement. The hot oil heater seen in the middle of the photograph is dedicated to this batching system. Mechanical agitators are installed in the tank to aid in blending. Most blending operations require some retention time in the tank. When the modified asphalt is completed, it is pumped to the plant storage tank, and another batch is prepared in the batching tank.

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RequirementAsphalt Rubber Blending Equipment

336-4Use blending equipment designed for asphalt rubber

Certify accuracy of meter used in blending with scale technician every 6 months

Blending equipment used is to be designed for blending asphalt rubber. The accuracy of the meter(s) being used to blend the rubber and asphalt are to be certified for accuracy with a scale technician every six months.


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RequirementAsphalt Rubber Testing / Certification

336-5.2 Blending at Terminal(Keep Certificates with Data)

336-5.1 Blending at Project Site(Keep Rubber Weights & AC Gallons Used)

Certificates with data are to be collected for review by the Engineer with terminal blended asphalt rubber, and if produced at the project site, the rubber weights and AC gallons used are to be collected for review.

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RequirementAsphalt Rubber QC Records

336-5.3 Maintaining Records for Review• Project Number• Shipping Date• Customer Name• Asphalt Rubber Binder Grade• Asphalt Rubber Binder Producer

(more…)

Records are to be maintained for review with the following information recorded: •Project Number •Shipping Date •Customer Name •Asphalt Rubber Binder Grade •Asphalt Rubber Binder Producer •Asphalt Binder Quantity in Gallons (liters) •Ground Tire Rubber Producer and Lot Number •Ground Tire Rubber Quantity in Pounds (kg) •Viscosity Results

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RequirementAsphalt Rubber QC Records

336-5.3 Maintaining Records for Review• Asphalt Binder Qty in Gallons [liters]• Ground Tire Rubber Producer & Lot Number• Ground Tire Rubber Qty in Pounds [kg]• Viscosity Results


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BMP for Polymer Modified Binder

• Follow BMPs for asphalt cement, plus• Follow binder manufacturers

recommendations for storage temperature• Avoid cross contamination with other binders• Don’t mix different source polymer binders• Agitation is helpful. • Polymer balls

Best management practices for storage and handling of polymer modified asphalt include: 1. Follow BMPs for asphalt cement, plus 2. Follow binder manufacturers recommendations for storage temperature 3. Avoid cross contamination with other binders 4. Don’t mix different source polymer binders 5. Agitation is helpful. 6. If visible balls of polymer show up in the completed mix, take all steps necessary to eliminate them. The supplier should be notified.

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Fiber Injection Systems

Used for 337 FC-5 mixes.

Mineral or Cellulose fibers can be used.

Added to the mix at the plant.

Fiber injection systems are used for 337 Friction Courses (FC-5). These fibers are added at the plant. Several equipment options are possible.


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RequirementFiber systems for 337 FC -5 mixes

337-9.1 All plants

• Separate feed system• Accurately proportion• Interlock to aggregate quantity• ± 10 % accuracy• No-flow = plant shutdown

Specifications require that the equipment used for fiber additive is a separate feed system, that it accurately proportions the fibers, that the fiber injection is interlocked to the aggregate quantity, and for no-flow plant shutdown. The tolerance level for the equipment is ± 10 % of the fiber target (337-9.1).

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Clockwise from top left shows fiber bale being prepared, fiber machine side view, fiber hopper being raised to dump bale into hopper, and bale being fluffed by augers prior to being blown pneumatically to the drum.

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Fiber Addition Photo on left shows hose leaving hopper (fibers blown) and photo on right shows hose entering drum where fibers are deposited.


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RequirementFiber systems for 337 FC -5 mixes

337-9.1 Batch plants• Add fiber to weigh hopper or as engineer

approves• Increase dry mix cycle 8-12 seconds or as

engineer approves• Fibers must be uniformly distributed before

AC is injected

For batching plants, the Engineer must approve the fiber injection system, and the dry mix cycle must be increased 8-12 seconds or as indicated by the Engineer (337-9.1). Fibers must also be uniformly distributed before the AC is injected (337-9.1).

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RequirementFiber systems for 337 (FC-5) mixes

337-9.1 Drum plants

• Uniformly distribute before AC is injected

• Must not be entrained in air stream

In addition to this general spec, as with hydrated lime, the fibers must be distributed before the AC is injected and not be entrained in the air stream.

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Best Management PracticesMultiple Storage Tanks

Multiple storage tanks are often found at modern hot mix plants. They offer mix flexibility to the producer, but create management issues as well.


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Best Management PracticesMultiple Tank Installations

• Don’t mix asphalt types (affects asphalt binder properties)

• Care should be exercised when switching valves to direct asphalt storage (can contaminate asphalt)

• Tanks should be “pulled down” or emptied before a new type binder is stored

It is important that different types of asphalts are not mixed in the storage tanks. This will negatively affect the properties of the binder and the mix. Care should also be taken when switching valves. It is easy to contaminate asphalt when changing valves at the plant. Tanks should always be emptied as much as possible before storing a new type of asphalt in a tank.

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Screen capture from ASTEC TCII Total Control Continuous Feed System Software showing tank farm and controls screen.

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Best Management PracticesMultiple Tank Installations

On putting another grade on that “last little amount” in the tank…..(the real world)

• Use discretion, it could affect the next binder if a large quantity exists

• Consult District Bituminous Engineer if concerned for final decision

Real world conditions prohibit asphalt tanks from being completely emptied when storing a new type of cement. Discretion for contamination must be used. If a sufficient quantity of another type of binder is suspected in the tank to be used, the District Bituminous Engineer should be consulted for the final decision on storing the new liquid.


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Safety IssuesAsphalt Storage Tanks

• Condensation in empty tanks is very dangerous. Moisture turns to steam when charging tank with hot asphalt.

• Never look inside a tank being charged with asphalt.

• Better to use suction pumps connected to tanks for off-loading tankers (safer).

• CAUTION when loading, unloading, sampling. Asphalt is HOT.

There are several safety issues when pumping and storing liquid asphalt. Dangerous steam can be created when hot liquid asphalt is introduced into a tank that has been empty and has accumulated moisture from condensation. A person should never look inside a tank when it is being charged. The steam and the hydrocarbon vapor can both be dangerous to personal health and safety. Pumps hard-piped to storage tanks using suction to off-load tankers offer additional safety over pumps mounted on transport tankers that “push” asphalt into storage tanks, in case flexible lines rupture or become disconnected. Asphalt is also HOT! CAUTION should always be used when loading, unloading, sampling, and dealing with asphalt cement.

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InspectionAsphalt Storage

• Heated in tanks to correct temperature (320-2.3)?• Heat jacketed lines (320-2.3)?• Kept in circulation during production (320-2.3)?• Temperature readout and sampling provisions(320-2.3)?• Fiber injection systems comply with specs (337-9.1)?• Asphalt Rubber Binder systems comply with specs

(336-4 and 5)?

(Testing AC content in mix covered later.)

Inspection guidelines for asphalt storage fall into only a few categories. Inspection for asphalt content in the mix will all be covered later. When inspecting for storage, focus on: •Is the asphalt properly heated to the proper temperature (320-2.3)? •Is there heat jacketing on the lines (320-2.3)? •Are there temperature readouts and sampling provisions (320-2.3)? •Do any required fiber injection systems comply with the requirements (337-9.1)? •Do any required asphalt rubber binder systems comply with the requirements (336-4 and 5)?


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Module 4What we covered….

• Asphalt storage tank systems• FDOT requirements for all AC systems• Asphalt tank heating systems• BMPs to maintain asphalt cement temperature• BMPs to maintaining asphalt cement integrity• Equipment for crumb rubber asphalt• BMPs for polymer modified cement• Fiber additives for 337 mixes• BMPs for Multiple Tank Installations

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QUESTIONS ?

Any Questions?

asphalt plant level ii january of module asphalt … plant 2/04 - module...asphalt plant level ii...

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