Chemical Vapors Control Gains Importance

Sept. 1, 2000
CONTROL and recovery of gasoline vapors at bulk chemical storage and terminal facilities continue to have a high profile in the United States, Asia, and

CONTROL and recovery of gasoline vapors at bulk chemical storage and terminal facilities continue to have a high profile in the United States, Asia, and Europe, said Gordon Croudace of ChemVec Pty Ltd, Sydney, Australia.

"The introduction of more stringent regulations for the control of atmospheric emissions, an increasing awareness of the potential health risks associated with exposure to certain vapors, and the need to continually strive for higher levels of plant safety are all factors dictating effective capture and control of emissions," said Croudace.

Croudace discussed the subject at the Independent Liquid Terminals Association meeting June 12 in Houston, Texas.

The variety that exists of chemicals, storage tanks, tank trucks, rail cars, drums, ships, and barges must be considered in order to have an appropriately integrated vapor collection facility and processing plant. The optimum must be obtained in simplicity; storage flexibility; product integrity; multiple vapors; and system performance, reliability, safety, and cost, he said.

"The necessity for the capture and control of simultaneous emissions from a large variety of chemicals places unique demands on vapor emissions control system technology," he said.

The work necessary for the selection and application of appropriate vapor collection and vapor processing plant is extensive and requires a scoping study, he said. Detail engineering, procurement, installation, commissioning, and operator training also are high priority considerations.

Initial attention should be given to implementing cost effective vapor emission minimization techniques to conserve product and reduce the overall size of the plant.

"It is important to appreciate that there is no one single approach to address all likely emission control needs of a bulk chemical storage terminal," he said. "Technology utilized for gasoline recovery is generally not suitable for the recovery of a broader range of chemicals."

The vapor emissions control system technology chosen should be able to address the broadest range of chemicals likely to be stored at the terminal.

To insure safe and effective operation, both the vapor collection facility and the vapor processing technology must be appropriately integrated. The vapor control system should be designed to have as little impact as possible on storage tank design and storage tank flexibility. Preference should be given to passive technologies to insure the highest level of operational safety.

To secure the most cost effective and efficient overall approach, terminal operators need to devise a medium- to long-term emission control strategy, satisfying both existing and anticipated regulations.

"With such a strategy in place, it is generally far more cost effective to apply vapor emissions control system technology with the capability to simultaneously address a range of chemical vapors as opposed to installing many individual dedicated units over a period of time," he said.

The installation of a series of dedicated units will ultimately impact upon both the operating economies and storage flexibility of the terminal. The logistics of effectively operating and maintaining a number of smaller dedicated units, without compromising safety, also becomes considerably more difficult.

The work necessary for the selection and application of an appropriate vapor collection and control plant can be extensive. The organization engaged should have a demonstrated ability to ascertain and define emissions, assess options, and to apply the optimum solution.

Various aspects of an operation must be taken into account, including transfer rates, product throughput, chemical properties, storage temperature, ambient conditions, pressure vent settings, terminal layout, rules and regulations, statutory requirements, and utilities available.

Various technologies are available to remove emissions. They include adsorption, absorption (scrubbers), absorption, vapor condensing, membranes, biofiltration, thermal oxidation, and flares.

"The selection of the appropriate technology largely depends upon the need to either address one single volatile organic compound or a mixture of the compounds," he said. "Most are somewhat limited in their ability to safely address the variety of chemical vapors requiring simultaneous control."

Although no one emission control technology can be applied to address all products, it is generally far more cost effective to apply technology with the capacity to address a variety of chemical vapors, he said.

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