Tank Truck and Rail Car Cleaning November 1994 Technical Disclaimer References to abatement equipment technologies are not intended to represent minimum or maximum levels of Best Available Control Technology (BACT). Determinations of BACT are made on a case-by-case basis as part of the New Source Review of permit applications. BACT determinations are always subject to adjustment in consideration of specific process requirements and recent developments in abatement technology. Additionally, specific health effect concerns may indicate stricter abatement than required by the BACT determination. The represented calculation methods are intended as an aid in the completion of acceptable permit submittals; alternative calculation methods may be equally acceptable if they are based on, and adequately demonstrate, sound engineering assumptions or data. These guidelines are applicable as of the date of this document, but are subject to revision during the permit application preparation and review period. It is the responsibility of the applicants to remain abreast of any guideline or regulation developments which may affect their industries. BACT Discussion There are several sources of emissions associated with a tank truck/rail car cleaning operation. These sources can include the control device handling the emissions captured by the vapor recovery system like a flare, thermal oxidizer, scrubber, carbon beds, etc., and emissions from uncontrolled tank truck/rail car cleaning, heel tanks, wastewater treatment system, fugitives from pipes, valves, flanges and boiler emissions. Some facilities use natural gas fired boilers for steam and/or hot water cleaning. For new construction permits and permit amendments, each of the above emission sources will be required to go through a BACT review. The following paragraphs will discuss some of the BACT criteria for tank truck/rail car cleaning facilities. BACT Guidelines Tank truck/rail car vessels handling material with a vapor pressure of 0.5 psia or greater at a temperature of 100F should be degassed to a control device prior to opening. After the degassing operations are complete, the vessel needs to be checked for presence of residual product or heel. All vessels handling and/or containing liquid material shall be deheeled prior to cleaning. There shall be no standing liquid inside the vessel when cleaning operations commence. Vessels handling materials with a maximum vapor pressure of 0.5 psia or greater at a temperature of 100F shall be connected to a vapor recovery system like a vacuum system which will maintain a negative pressure inside the vessel during the entire cleaning process. The discharge of the vacuum system shall be routed to a control device. Maintaining a vacuum on the vessel during the cleaning process will ensure that 100 percent of the emissions generated by the cleaning operation itself are collected and controlled. For vessels handling material with a maximum vapor pressure of less than 0.5 psia at a temperature of 100F, the emissions resulting from the cleaning operation can be vented to the atmosphere provided that the off-property impacts are acceptable. The destruction or removal efficiency of the control device used to control emissions from the cleaning operation itself depends upon the system being used. A flare should obtain a volatile organic compound destruction efficiency of ninety-eight percent. If the material is routed to a thermal oxidizer, the destruction efficiency should be 99.9 percent. If the oxidizer is followed by a scrubber for handling the by-products of halogenated combustion or if the scrubber is controlling emissions from inorganic acid tank trucks and/or rail cars, the scrubber should obtain a minimum removal efficiency of ninety-nine percent. It is very possible that some of the material handled by tank truck and/or rail car cleaning facilities will fall in the halogenated category. If this is the case, please be aware that by-products of combustion like hydrogen chloride, hydrogen bromide, hydrogen fluoride need to be estimated and possibly controlled. By-products of combustion for compounds containing sulfur (sulfur dioxide (SO2) emissions) and nitrogen (nitrogen oxide emissions) will also need to be estimated. If sulfur containing compounds are being combusted, the resulting SO2 emissions must meet the off-property impact concentrations as described in TRNCC Regulation II, Section 112.3. If a carbon adsorber is being used to control emissions from the cleaning operation, the emissions should be estimated on a case-by-case basis. BACT is three canisters in series with a continuous hydrocarbon analyzer located between the second and third canister to monitor for breakthrough. The breakthrough concentration will be determined on a case-by-case basis and will typically be less than 100 ppmv. The carbon adsorption system is typically considered an option for control of compounds not suitable for combustion. The used cleaning solution or wastewater is typically removed from the bottom of the cleaned vessel. The wastewater may either be loaded into another tank truck for removal off-site, routed to a wastewater storage tank prior to tank truck load out and removal off-site or routed to a wastewater treatment system. The primary settling tank of the wastewater treatment system, if applicable, should be an enclosed vessel. If emissions from the wastewater system exceed five tons per year (TPY), the applicant will need to investigate possible ways of controlling the wastewater emissions. For example, stripping or covering the rest of the treating system is one example of emissions control. The applicant may also be requested to control wastewater emissions with emission rates of less than five TPY if impact problems are indicated by the modeling exercise. Storage tanks, heel tanks and wastewater tanks should follow current BACT guidelines. A floating roof or vapor control system will be required if the vapor pressure of the material stored is 0.5 psia or greater at maximum temperature and the tank is larger than 25,000 gallons in capacity. Loading operations related to the removal of heel and wastewater, if applicable, from the cleaning facility will be subject to BACT. Possible control of heel tank truck loading may be required for a material with a vapor pressure of 0.5 psia or greater at maximum temperature, depending on the amount of material handled. Some TNRCC standardization packages specifically address some of the above mentioned control devices or operations. After the engineer reviewing the application has determined that BACT is applied and that the emissions are calculated correctly, dispersion modeling may be required to verify that the expected emission rates from the cleaning facility will not cause or contribute to an unacceptable odor or impact situation off-site.