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Novel Design of an Integrated Pulp Mill Biorefinery for the ...

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1 Introduction<br />

The global tr<strong>an</strong>sport sector uses approximately 70 to 90 EJ <strong>of</strong> energy per year[1]. In<br />

OECD countries, 97% <strong>of</strong> <strong>the</strong> tr<strong>an</strong>sport sector uses petroleum-based fuels. It is estimated that <strong>the</strong><br />

world has peaked in petroleum production, <strong>an</strong>d world petroleum consumption has outpaced newfound<br />

reserves. There<strong>for</strong>e, great ef<strong>for</strong>ts in research <strong>an</strong>d development have been made into new<br />

vehicle technology <strong>an</strong>d new fuels. A me<strong>an</strong>s <strong>of</strong> reducing or eliminating <strong>the</strong> dependency on<br />

petroleum is <strong>the</strong> use fuels derived from natural gas, biomass or coal. For this reason, meth<strong>an</strong>ol,<br />

eth<strong>an</strong>ol, dimethyl e<strong>the</strong>r, Fischer-Tropsch fuels, biodiesel, etc. are being researched as alternative<br />

fuels. Whatever fuel is to supplement or replace petroleum, it must address <strong>the</strong> following criteria:<br />

availability, economics, acceptability, environmental <strong>an</strong>d emissions, national security,<br />

technology, <strong>an</strong>d versatility[2].<br />

This report details a gasification-based production scheme to produce dimethyl e<strong>the</strong>r <strong>an</strong>d<br />

Fischer-Tropsch fuels as alternative fuels that could potentially replace petroleum-based fuels in<br />

terms <strong>of</strong> <strong>the</strong> availability, environmental <strong>an</strong>d emissions factors, <strong>an</strong>d technology. Attention is<br />

growing in research areas where alternative fuels are produced from biomass feedstocks based<br />

on <strong>the</strong> potential <strong>for</strong> CO2 reduction <strong>an</strong>d energy security.<br />

Fischer-Tropsch Diesel (FTD) is a promising fuel that c<strong>an</strong> be produced from gasified<br />

hydrocarbons, such as coal, natural gas <strong>an</strong>d biomass feed stocks. FTD is a high quality diesel<br />

fuel that c<strong>an</strong> be used at 100% concentration or blended with lower quality petroleum based fuel<br />

to improve per<strong>for</strong>m<strong>an</strong>ce [3]. The main adv<strong>an</strong>tage <strong>of</strong> large scale production <strong>of</strong> FTD is that no<br />

ch<strong>an</strong>ges or modifications are necessary to utilize it in current fill stations or vehicles.<br />

With social, political <strong>an</strong>d environmental dem<strong>an</strong>ds <strong>for</strong> eco-friendly renewable<br />

tr<strong>an</strong>sportation fuel, FTD produced from biomass should be considered. FTD does not have <strong>the</strong><br />

logistical problems <strong>of</strong> bio-diesel. FTD does not need to be blended with regular diesel fuel. It<br />

c<strong>an</strong> be run at a 100% concentration without vehicle modifications. FTD does not suffer from<br />

cold flow problems like bio-diesel[3].<br />

Fischer-Tropsch syn<strong>the</strong>sis (FTS) is a mature technology that has been commercially<br />

utilized to produce FTD by Sasol since 1955. Comp<strong>an</strong>y such as Shell, Chevron, ExxonMobil<br />

<strong>an</strong>d Rentech have been creating production facilities as FTD has become more economically<br />

feasible with <strong>the</strong> onset <strong>of</strong> high petroleum fuel costs.<br />

Production efficiency <strong>of</strong> FTD is lost to low selectivity <strong>of</strong> hydrocarbon chains during<br />

Fischer-Tropsch syn<strong>the</strong>sis. When creating FTD, middle distillates <strong>an</strong>d long chained wax are<br />

desired, but regardless naphtha <strong>an</strong>d light carbon chain gases are produced. Ekbom et al. created<br />

models showing Fischer-Tropsch products having a 65% biomass-to-fuel efficiency, with 43%<br />

being FTD <strong>an</strong>d 22% being naphtha [4]. In a compellation <strong>of</strong> previous works, Semelsberger et al.<br />

reported FTD to have a ~59% well-to-t<strong>an</strong>k efficiency, based on syngas produced by natural<br />

gas[5]. Production <strong>of</strong> FTD from coal c<strong>an</strong> be assumed to have similar trends in production<br />

efficiency since FTD syn<strong>the</strong>sis begins with gasification <strong>of</strong> a feed stock to create syngas.<br />

U.S. pulp <strong>an</strong>d paper mills have <strong>an</strong> opportunity to utilize biomass (as black liquor) <strong>an</strong>d<br />

coal gasification technologies to improve <strong>the</strong> industry’s economic <strong>an</strong>d energy efficiency<br />

per<strong>for</strong>m<strong>an</strong>ce with new value-added streams including liquid tr<strong>an</strong>sportation fuels from syn<strong>the</strong>sis<br />

gas. The black liquor pulping byproduct contains cooking chemicals <strong>an</strong>d calorific energy that<br />

should be optimally recovered through gasification.<br />

Although <strong>the</strong> heating value per ton <strong>of</strong> dried black liquor solids is relatively low, <strong>the</strong><br />

average Kraft mill represents <strong>an</strong> energy source <strong>of</strong> 250-500 MW [1,2]. Black liquor is<br />

7

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