Ethanol pipelines

Feb. 18, 2008
Many issues surround ethanol’s growing prevalence as a component of the US gasoline pool.

Many issues surround ethanol’s growing prevalence as a component of the US gasoline pool. These include subsidies for its production, the relative distillation efficiency of various source products, import tariffs, the effect on prices of various food products, and the potential overuse of groundwater supplies. The issues also include its efficient transport from sources of production to consuming centers.

The American Coalition for Ethanol placed 2007 US ethanol production at 6.8 billion gal and expects 9 billion gal to be produced this year. The Renewable Fuels Association counts 131 ethanol refineries operating as of November 2007, with 10 expansions and 72 newbuild plants in the works. Production expansion at this pace will require increasingly efficient transportation to market.

Pipeline problems

Ethanol’s tendency to separate from gasoline in the presence of water currently prevents gasoline-ethanol blends from being shipped through pipelines, causing ethanol to be transported primarily by rail at up to four times the cost of products shipped by pipeline. A water concentration of 1% will cause ethanol to separate from gasoline in E85 blends, while just 0.5% is sufficient in E10 gasoline.

The Association of Oil Pipelines is sponsoring three research and development projects to help address pipeline transport of ethanol. The Pipeline Research Council International will fund the projects, with research carried out by CC Technologies.

Research completed in early 2007 showed that different pipeline steels are vulnerable to stress corrosion cracking when transporting fuel-grade ethanol and that the presence of oxygen in ethanol is one of the most important factors determining a pipeline’s susceptibility to SCC. Research also showed that removing oxygen from fuel-grade ethanol with nitrogen or oxygen scavengers effectively mitigates internal SCC.

These results and other research suggest that a new multiproduct pipeline could be designed with ethanol compatible polymers in valves, gaskets, and seals, using steel specified to reduce the possibility of SCC. What still needs to be determined, however, is both whether a smaller diameter dedicated ethanol pipeline may still pose a better alternative by removing any transmix or product quality issue that might otherwise arise and the terms under which ethanol transport might be possible in current multiproduct lines.

Current research

Continuing AOPL projects include determining requirements for existing pipeline, tank, and terminal systems to transport ethanol without cracking (PRCI SCC 4-4), identifying environmental factors that produce SCC in existing ethanol pipelines and terminals (PRCI SCC 4-3), and determining requirements for new pipeline systems to transport ethanol without cracking by studying environmental stress factors (PRCI SCC 4-5).

AOPL expects full results from PRCI SCC 4-4 to be available as early as September and lists three major objectives of the research. The first of these is developing the data necessary to make engineering assessments of the feasibility of transporting fuel-grade ethanol and ethanol blend in existing pipelines; either dedicated or batched as part of a multiproduct line.

It also hopes to identify which ethanol blends can be transported in existing pipelines without significant modification, which would require significant modification, and which couldn’t be moved through existing systems but would instead require a specially designed line. Finally, SCC 4-4 seeks to characterize the time to initiation of SCC in a range of ethanol environments and identify safe operating and batching practices that prevent its initiation and growth.

SCC 4-4 also hopes to determine ethanol’s effect on drag reducing agents, including whether it will render DRA ineffective, change required injection rates, or alter the amount of DRA that can be injected without affecting fuel quality. It is also examining ethanol and ethanol-water’s effect on transmix reprocessing.

Key preliminary results from this work include finding that variances in quality of fuel-grade ethanol affect SCC development, decreasing the oxygen content of fuel-grade ethanol reduces SCC development, and that fuel-grade ethanol contains natural SCC inhibitors that degrade with time. CC Technologies is also testing identified means of mitigating SCC.

Beyond the AOPL-sponsored research, both Colonial Pipeline and Kinder Morgan Energy Partners LP are working to determine the terms under which fuel-grade ethanol can be transported through existing pipelines without inducing SCC. Both companies plan to conduct tests along parts of their respective operating clean products’ systems this year.

The cumulative results of these efforts will go some way toward determining the true feasibility of economically transporting ethanol via pipeline.