BAAQMD Is Requiring Air Pollution Control Of Vacuum Truck Processes
Bay Area Air Quality Management District (BAAQMD) Executive Officer/APCO Jack P Broadbent announces that BAAQMD is the “first in the country specifically addressing vacuum truck emissions”. BAAQMD Rule 8 regulation 53 governing vacuum truck fugitive emissions became effective April 1, 2013.
EXCERPT FROM BAAQMD STAFF REPORT:
Prepared by Mr. William Saltz BAAQMD Air Quality Specialist
“Carbon Adsorption Systems
A carbon adsorption system is a system that is composed of a tank or vessel containing a specific amount of activated carbon onto which organic gases or vapors molecularly adhere as they flow through the particles. Activated carbon is a form of carbon that has been processed to make extremely porous. Its porosity results in a very large internal surface which enables it to adsorb gases within its structure. The degree to which activated carbon adsorbs organic vapors is affected by the temperature, humidity, flow-rate, concentration, and molecular structure of the gas. High vacuum truck blower discharge temperatures may actually release previously adsorbed compounds, thus allowing emissions to vent into the ambient air. According to various industry sources, it may take anywhere from 2 to 10 pounds of carbon to control 1 pound of TOC…
Internal Combustion Engines
“Internal combustion engine technology is currently available to control organic vapor emissions.
The equipment contains the vacuum source and vapor control device in one unit mounted on a truck. Internal combustion engines that are utilized to control organic vapors from vacuum trucks have a large cubic inch displacement and are able to run on compressed gas such as propane. When an internal combustion engine is used to control organic vapor emissions, it initially runs on propane and then switches to the incoming organic vapors as the primary fuel source. In some applications, the engines can power a refrigerated condenser (or “chiller”) to condense a portion of the organic vapor stream back to liquid.
In a Southern California demonstration observed by District staff, the refrigerated condenser was powered by the truck’s engine using the extracted organic vapors as the primary fuel source. Emissions were monitored from the control device’s exhaust with a portable engine analyzer that was previously source-tested, as required by the South Coast Air Quality Management District (SCAQMD), to confirm the accuracy of the instrument readings. While loading transmix (a material blend containing primarily gasoline and diesel fuels) into a vacuum truck, emissions were reduced by over 99.6%. The engine/chiller vapor control equipment abated approximately 33 lbs. of potential organic vapor emissions for this 10 minute loading event.5 Figure 8 is a diagram of an engine/chiller combination unit integrated into a vacuum truck.
The small reddish-orange circles depict the flow of organic vapors as they flow from right to left in the vacuum truck’s barrel. Some of the vapors are captured by the chiller (see #3 in the diagram) while the majority of the remaining vapors are combusted by the internal combustion engine (see #4 in the diagram below).”
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Although shown as an option in BAAQMD Staff Report,
carbon adsorption alone should not be used for vacuum truck vapor abatement, explained as follows:
EXCERPT FROM SAGE WHITE PAPER:
1. Vacuum Truck Controls
Issue: The TCEQ stated that several refineries proposed to utilize carbon adsorbers to control VOC emissions from vacuum trucks. The TCEQ stated that carbon adsorption is Tier I BACT for filling vacuum trucks if the liquid has a VOC vapor pressure >0.5 psia.
Analysis: For refinery vacuum truck operations, carbon canisters are utilized primarily on an as-needed basis to control emissions of specific compounds, either for odor control or for safety purposes (e.g., to minimize benzene exposure). However, carbon adsorption has not been demonstrated as an effective control for general VOC emissions from vacuum truck operations. Carbon adsorption is not BACT for the following key reasons:
a) The direct service cost for obtaining and reactivating (regenerating) the carbon canisters is estimated to be over $40,000 per ton. This does not include associated labor costs or costs for certifying the carbon, which is required for the carbon to be reactivated. Carbon reactivation is an energy-intensive process that will probably generate more total air pollutant emissions than the VOC that was adsorbed onto the carbon. As an alternative to reactivating the carbon, carbon disposal costs have not be evaluated but are expected to be high given that each ton of VOC removed will generate at least 24 cubic yards and 9.3 tons of spent carbon.
b) Although carbon has a relatively high affinity for benzene and certain other compounds, many organic compounds will pass through a carbon bed with minimal removal. Therefore, a study would be required to determine what overall VOC reduction efficiency is likely to be achieved with carbon. As an example, 90% mass removal of total VOC will probably not be possible for all materials managed in vacuum trucks.
c) Refineries typically have sufficient process knowledge to characterize the vapor pressure of MSS-related materials that are managed in vacuum trucks. However, it would not be practical or appropriate to collect samples of materials to support the determination that VOC vapor pressure is below 0.5 psia. MSS-related liquids should be transferred into controlled management systems by vacuum truck as quickly as possible and without the delays inherent in collecting and analyzing samples to verify control requirements.
d) If carbon adsorption were required for vacuum trucks, then some form of monitoring would probably be required to determine when VOC breakthrough occurs. The costs of installing and maintaining continuous VOC detection systems would add to the >$40,000/ton control cost discussed above. Furthermore, the primary responsibility of vacuum truck operators during transfer is to monitor the liquid transfer process to prevent leaks, spills and other releases. Manually checking for VOC breakthrough will distract the operators from their primary responsibility and may slow the process of getting MSS-related materials transferred into controlled management systems.
e) Another safety concern is that activated carbon is known to heat rapidly when adsorbing some organic compounds at higher rates and associated fires have been documented. Continuously monitoring the carbon temperature is impractical for the same reasons noted above. Unsafe control technologies cannot be considered BACT.
Conclusions: Carbon adsorption is not BACT for VOC emissions from vacuum trucks because the control cost is unreasonable, associated environmental problems outweigh the benefits, compliance demonstration is not practical, and there are safety concerns. BACT should consist of observing the transfer lines during transfers for visible/audible/olfactory indications of leaks, minimizing air intake into the fill line, verifying that all hatches/openings are sealed, and transfer via submerged fill.
