(215c) Technoeconomic Assessment of Two-Step Process for Upgrading and Utilizing Used Railroad Ties in an Integrated Biorefinery

Authors: 
Aboulmoumine, N., University of Tennessee
Houston, R., University of Tennessee
In the USA, over 21 million wood railroad ties are produced per year to replace the approximately 20 million used ties that have provided excellent primary service in railroad track over 40 years. Due to the presence of carcinogenic preservatives, these used ties will primarily be either landfilled or incinerated as they do not meet U.S. Environmental Protection Agency (U.S. EPA) stringent requirements. Consequently, a two-step pyrolysis process was developed to upgrade used ties by first extracting wood preservatives (Step One) and converting upgraded used ties into biofuels, bioproducts, power, and heat (Step Two). This study evaluates the techno-economic viability of the proposed two-step process embedded in integrated pyrolysis biorefinery with liquid fuel, power and recovered preservatives as product streams.

The technoeconomic analysis assumed 2.33 million metric tons of used railroad ties are available yearly according to statistics by the Railroad tie association. This analysis considers 3 plants spread across the U.S. to minimize transportation cost with 2358 tons/day throughput each. The rail road ties biorefinery consists of eight areas including preprocessing (A100), thermal desorption (A200) and fast pyrolysis and vapor quenching (A300), hydroprocessing (A400), hydrogen generation (A500), power generation (A600), cooling and other utilities (A700) and waste management (A800). The minimum selling prices as well as sensitivity analyses were performed to determine the impact of thermal desorption conditions on the overall economic.