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Article # 0050

AIR QUALITY PERMITTING OF A FUEL ETHANOL DISTRIBUTION FACILITY

  By Jack L. Bullard, P.E.

Introduction

This article describes various considerations when applying for an environmental air quality permit for operation of an ethanol distribution facility in the State of Texas.  Specifically this article identifies various sources of ethanol emissions that must be considered when preparing an air permit application for an ethanol distribution terminal.  The purpose of the air quality permitting process is to ensure that the operation of the facility will not cause a condition of air pollution that causes an adverse effect on the surrounding environment which includes considerations of the health effects on people, vegetation, and the general quality of life. This article addresses “changing the service” of an existing petroleum-based fuel (e.g., gasoline, diesel, etc.) distribution terminal to handle ethanol a renewable fuel. 

Background on Ethanol Production, Transport, and Use

Most of the ethanol (or ethyl alcohol) in the United States is produced by one of two processes: wet milling or dry milling. In dry milling, the entire kernel or grain is first ground into meal and processed without separating out the components of the grain. The meal is then mixed with water and enzymes are added to convert the starch contained in the grain meal to dextrose. This mixture is referred to as mash.  Ammonia is added to the mash to control pH and as a nutrient to the yeast.   The mash is then “cooked” at high temperature to reduce bacteria levels that may impact the next process which is fermentation. More yeast is added to the mash and the dextrose starts changing to ethanol during fermentation.  The fermented mixture is distilled in distillation columns to separate out the pure ethanol. The ethanol is further processed to remove all water to a very pure ethanol known as anhydrous ethanol.  The pure ethanol is then blended with a denaturant to render it unsuitable for consumption and to designate it as fuel ethanol. One of the most common denaturants is methanol and is typically added to five percent volume.

Most fuel ethanol is transferred long distances from production site to distribution terminals by rail car rather than by pipeline like petroleum based fuels.  This is because ethanol can form an azeotrope with water which can cause the ethanol to be rendered useless as a fuel component.  This is especially a problem over long pipeline distances wherein more moisture contact is possible.

Most gasoline currently sold in the United States contains up to ten percent ethanol. The ethanol distribution terminal to be “permitted” and the potential sources of ethanol emissions to the atmosphere are discussed in the process description below.  The fictional city where the terminal is located is called “Anycity” and assumed to be located in Texas.  The facility is being evaluated for an air permit-by-rule under the Texas Administrative Code (TAC).

Process Description and Emission Point Identification

The purpose of this permit-by-rule (PBR) claim is to register the storage and distribution of ethanol at an existing fuel storage and distribution terminal in Anycity, Texas.  It has been determined that the terminal can meet the general PBR under 30 TAC 106.261 and/or 106.262.  The terminal is currently authorized to handle gasoline(s), petroleum distillates, and fuel additives under an existing State New Source Review (NSR) Air Permit.  The PBR registration will cover the operation of the facility when it handles ethanol.

The ethanol will be received at the terminal by a short pipeline (less than 1000 feet) that connects a local railcar spur to the terminal.  The ethanol is offloaded from railcars through a piping manifold at the spur and traverses the short distance by pipe from the spur into existing above-ground storage tanks located at the distribution terminal. The equipment at the rail spur and the piping that connects the railcar offload manifold to the terminal are a separate entity from the terminal.  This equipment would be evaluated for a PBR separate from the terminal since it is owned and operated by the rail company and not the terminal itself. The emissions from the terminal are all sources located within the terminal’s property boundary that are owned and controlled by the terminal.  The terminal equipment or potential ethanol emission sources is discussed below.

The three storage tanks located at the terminal are potential sources of ethanol emissions due to the potential of leaks from the tank seals, fittings, and covers and from displacement of vapor during tank filling.  The storage tanks will be assigned Emission Point Numbers (EPN) TANK1, TANK2, and TANK3.

Independently owned tanker trucks will arrive at the terminal, be filled with ethanol, and then transport the ethanol to off-property fuel blending sites located throughout Anycity.  The ethanol is blended with gasoline at these sites and then the gasoline/ethanol mixture is transferred to local gasoline retailers.  In some cases the tanker trucks will arrive at the terminal partially filled with gasoline and ethanol - up to a volume of ten percent - will be added to the gasoline in the tanker truck.  This gasoline and ethanol mixture is then transferred directly to local retailers.

The ethanol at the ethanol distribution terminal is loaded into the tanker trucks at the terminals covered loading rack.  Loading arms at the rack are attached to the tanker trucks. The trucks are bottom-filled with ethanol that can be pumped from TANK1, TANK2, and/or TANK3.  The loading rack equipment consists of valves, pumps, and connections that are potential sources of emissions (for example a leaking valve) of ethanol.  The loading rack equipment leaks will be assigned EPN RACK.

All tanker trucks will be connected to the existing vapor collection system when loaded with ethanol. The vapor collection system collects the vapor that is displaced from the tanker truck as it is filled with ethanol and routes the vapor (a mixture of air and ethanol) to the existing Vapor Combustion Unit (VCU). The VCU combusts the vapor displaced from the truck with a destruction efficiency of approximately 99%, the remaining 1% leaves the VCU as ethanol emissions.  The VCU also forms nitrogen oxides, carbon monoxide and a small amount of sulfur dioxide as combustion products. The Vapor Combustion Unit will be assigned (EPN VCU). 

The wastewater sump (EPN SUMP) or oil/water separator will collect any water, oily leaks from trucks, or minor ethanol drips through floor drains in the loading rack area.  The contents of the sump will be periodically pumped into a vacuum truck and taken off-site for recycling.  The sump has emissions through the evaporation of ethanol from the sumps contents to the atmosphere.

New minor process equipment (e.g., valves, pumps, non-welded connectors) source counts will be added throughout the facility to accommodate the new piping configurations to handle the ethanol process.  These equipment counts will be added to the existing minor process equipment counts under existing EPN FUG that is identified in the existing new source review air permit. All minor process equipment emission estimates assume 100% ethanol service.

Various maintenance activities are necessary to “change the service” of the terminal from petroleum-based fuels to ethanol.  These activities were performed under 30 TAC 106.263 Routine Maintenance, Start-up and Shutdown of Facilities, and Temporary Maintenance Facilities.  These activities include the addition of a fire prevention foam system for ethanol storage tanks to address fire safety issues when storing ethanol, changes to storage tank roof types to accept the foam and/or to remove damaged or worn roofs and to prevent water from entering the ethanol (ethanol is soluble in water and external floating roofs are more apt to leak rainwater - that pools on top of the roof - into the tank contents), and the replacement of tank seals to remove worn or damaged seals and guard against the corrosive effects of ethanol on the existing seal types. 

Summary

An ethanol storage and distribution facility will have multiple sources of air emissions for equipment such as storage tanks, loading facilities, vapor combustion devices, wastewater (sumps), and minor and miscellaneous process equipment throughout the site. Ethanol fuel handling must consider the added problems of water forming azeotropes and ethanol corroding tank seals.  There are also fire safety issues when storing ethanol that will require addition of fire prevention foam systems.

Biography

Jack L. Bullard, P.E. is an Engineering Partner of Bullard Environmental Consulting, Inc. He has over 19 years experience in environmental engineering, compliance, and permitting. Jack has a Bachelors of Science Degree in Chemical Engineering from the University of Texas at Austin.

Jack L. Bullard, P.E. No. 83547

Final Edition Completed December 27, 2009 using Previously Composed Material. 

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