Vent Condensersfor asphalt tanks

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Used to capture asphalt vapor emissions and return them to the storage tank in liquid form.

CEI asphalt tanks with vent condensers at a hot mix asphalt plant in British Columbia.

Finned pipe provides plentiful surface area for heat to dissipate.

Vent Condenser

Asphalt Tank

Asphalt vapors pass upward from the storage tank, into the vent condenser’s finned pipe.

Vent Condenser

Vent Condenser

Cooler ambient air circulates around the finned pipe, dis-sipating heat and cooling the asphalt vapors.

Vent Condenser

Asphalt vapors cool and re-turn to liquid state, dropping back down into the storage tank.

CEI extreme-duty vent condensers reduce exhaust temperatures below ambient air temperatures.

Refrigeration Unit

Finned pipe provides plentiful surface area for heat to dissipate.

Asphalt vapors pass upward from the storage tank, into the vent condenser’s finned pipe.

The refrigeration unit cools ambient air to below-ambient temperatures, and circulates the cooled air around the finned pipe.

Exhaust temperatures of well below 120° F are attainable.

Asphalt vapors cool and return to liquid state, dropping back down into the storage tank.

Vent Condensers reduce

asphalt fumes and visible “blue

smoke” emissions from AC

storage tanks.

Light ends that are present in

liquid asphalt become va-

pors when heated to elevated

temperatures. Condensing the

vapors back into a liquid form,

through a heat exchanging pro-

cess, returns these constituents

back into the AC tank instead

of allowing them to escape into

the atmosphere.

Vent condensers are effective,

simple to maintain devices that

are suitable for horizontal tanks

(stationary or portable), vertical

tanks, and even underground

storage tanks. Normally,

one vent condenser per tank

compartment is recommended.

However, multiple tanks (or

compartments) can be connect-

ed to a single vent condenser

through a common header

system.

ASPHALT TANK

VENT CONDENSERS

also need an additional source of

external cooling.

Heat Transfer Area

Removing heat is an equal and

opposite reaction to adding

heat. Expanding the total avail-

able surface reduces the number

of BTU’s transferred per unit

of area and increases efficiency.

The required heat transfer area

decreases with larger differential

temperatures (ambient to tank

temperature) and increases with

reduced differential tempera-

tures.

Time Pass a candle under your hand

and it will not burn. Hold it

there and time will manifest

itself. Any reaction requires an

element of time. Increasing the

differential temperature and

increasing the transfer area will

both reduce the time — to a

degree.

Multiple passes through a fixed

number of tubes increases the

time for heat transfer, provides a

reducing differential of tem-

perature per pass, and increases

efficiency without increasing the

total surface area. In addition, a

multiple pass design benefits by

the reduced velocities achieved

as vapors (and mass volume) are

reduced.

CEI vent condensers are

provided in standard sizes and

configurations that are most

commonly used in the industry.

For some applications, vent con-

densers are specifically designed

to meet local load requirements

and emission standards. High

ambient moisture contents

and low ambient temperatures

usually require multiple pass

designs. External cooling, as well

as exhaust temperature monitor-

ing are available options.

Specifications are subject to change without notice.

The simple design of a vent

condenser uses ambient airflow

to remove heat from exhaust

vapors as they pass through a

bundle of finned tubes. Single

pass designs have been the

industry standard. However,

more stringent regulations re-

quire the use of more efficient

designs.

Heat exchange technology

is relatively straightforward —

it’s a function of differential

temperature, heat transfer area

and time. For the highest level

of efficiency you simply maxi-

mize these three criteria.

Differential Temperature

If ambient air temperature at

a plant site is relatively low,

then the efficiency of a single

pass design is likely adequate.

If the ambient air temperature

is approaching triple-digits,

you most likely will require a

multiple pass design. You may

CEI ENTERPRISES,INC. an Astec Industries Company

245 WOODWARD RD, SE • ALBUQUERQUE, NM 87102 USA • 800.545.4034 • FAX 505.243.1422 • ceienterprises.com

Extreme-duty vent condenser reduces exhaust tem-peratures below ambient air temperatures.

Extreme-duty vent condenser with optional cartridge air-cleaning device to eliminate visible emissions.

Temperature indicator from extreme-duty vent condenser in operation.

CEI Extreme-Duty Vent Condensers are designed to handle maximum steam-volume flow rates. This occurs when the amount of vapors present in a tank are combined with the rapid rate of exhaust encountered when filling the tank with liquid asphalt.The actual tank volume has a minor impact on the required vent condenser size, as evacu-ation volumes (and velocities) are relatively low in a storage tank under decreasing or dor-mant stages.

Large volume tanks, such as bulk storage tanks used at asphalt terminals, do have large surface areas which must be considered in addition to displacement volumes. The required maximum exhaust temperature must also be taken into account along with the local allowable level of visible emissions.

EXTREME-DUTYVENT CONDENSERS

a relatively simple air condition-ing unit. Cooling the exhaust to below 120 degrees F still does not remove 100% of the light oils that cause visible emissions. When zero visible emissions are required, a cartridge air-cleaning device such as in the photo above can be employed to elimi-nate the blue smoke effect.

To optimize the efficiency of a vent condenser, you take into consideration tempera-ture differential and time. The highest efficiency is obtained by using multiple passes. As exhaust fumes exit each pass, the total volume decreases with the condensing process, and the following passes are subject to lower velocities and hence

longer dwell-time to allow temperature differential to be a more significant factor.Reducing visible emissions from asphalt storage tanks is not only a compliance issue with local codes, it is also a good neighbor policy. Most people believe that a “smoking stack” is bad health, even if that smok-ing stack is simple steam. In an asphalt tank application, the use of a vent condenser not only impacts the visual aspects of the plant, but condensing the light oils also helps reduce associated odor levels. With elevated prod-uct temperatures, such as those found in polymer-modified or rubber-modified asphalt ce-ments, the impact is even more pronounced.

Specifications are subject to change without notice.

A conventional vent con-denser will have an efficiency of 95% or more with ambient air. However, the exhaust tem-peratures will still be elevated above ambient temperatures, and there will be some light oil constituents escaping in the form of “blue smoke”.If local codes require lower exhaust temperatures, then an external cooling system is re-quired. Exhaust temperatures of below 120 degrees F are achievable with the addition of

©2008 CEI Enterprises, Inc.

CEI ENTERPRISES,INC. an Astec Industries Company

245 WOODWARD RD, SE • ALBUQUERQUE, NM 87102 USA • 800.545.4034 • FAX 505.243.1422 • ceienterprises.com

Additional Information

available on the Literature page at www.ceienterprises.com

Hopper

Auger

Mix Tank 1

Grinding Mill

Mix Tank 2

Holding Tank

CEI ENTERPRISES,INC. an Astec Industries Company

245 WOODWARD RD, SE • ALBUQUERQUE, NM 87102 USA • 800.545.4034 • FAX 505.243.1422 • ceienterprises.com

A typical system for blending SBS polymer includes a box-dumping hop-per, two mixing tanks mounted on load cells, a grinding mill to reduce the pellets in size and hasten the dissolving process and a pair of holding tanks for diluting to the final desired concentration.

The process requires elevated AC temperatures and finite control over the ratio of asphalt cement to SBS on a weight basis. The control panel is PLC-based to simplify the operation.

Due to the viscosity of the product, a large-diameter pumping system is desired to maintain production rates. Ver-tical tanks with mixers installed should be used for all polymer-handling applications.

SBS POLYMER BLENDING SYSTEM

Specifications are subject to change without notice.

An Auger is used to transport the SBS pellets from the hop-per and into the mixing tank. Asphalt cement is metered into the mixing can until a concen-tration of 12–15% is achieved. The mixing can is mounted on load cells to obtain an accurate measurement of each constitu-ent.

The mixer helps pull the pel-lets down into the liquid AC. This action “wets” the pellets and aids in dispersion prior to being circulated through the grinding mill at the bottom of the tank. The concentration level is maintained at a higher-than-use level to enhance the grinding efficiency.

The grinding mill shears the pellets into smaller pieces as they make multiple passes in a circulation loop. This speeds up the blending and dissolving process. The temperature of the mixture is normally 170 degrees C (340 degrees F) in the mixing tank.

Each batch of concentrate requires about 3 to 4 hours for processing. Therefore, it is nor-mal to have two parallel mixing tanks in the process to increase the system’s production rate. The two-batch process also lends itself to higher quality control.

The grinding mill provides three functions. First of all, it reduces the size of the pellets. In the grinding process, it adds heat to the mixture. Finally, it is used as the transfer pump to empty the mixing can into the holding tank.

The holding tank, or use tank, is fitted with a mixer to ensure that the polymer stays sus-pended. Virgin asphalt cement is metered into the holding tank to obtain a final mixture concentration of 3 to 4 percent polymer by weight. The hold-ing tank is maintained at 170 degrees C (340 degrees F) for 45 to 60 minutes prior to being ready for use.

© 2009 CEI Enterprises, Inc.

©2010 CEI Enterprises, Inc.