Farm fields landscape

Urban Fuel Coop Design & Analysis - Introduction

From Liquid Sun Energy web site

Complete report available here

Executive Summary

An Urban Fuel Cooperative (Co-Op) is described and analyzed for feasibility and efficiency. An Urban Fuel Co-Op differs from the more familiar Farm-based co-ops in several key ways:

  • Urban dwellers are assumed to have a "day job" that is outside of agricultural production. They are only available for fuel making on weekend days of the week.
  • Urban dwellers do not have land to grow feedstock. They must use waste material for feedstock for their fuel.

The concept of the Urban Fuel Co-Op is that Co-Op members collect stale bakery products that have become inedible and are destined to be discarded. Processing of this type of feedstock into ethanol was studied extensively by the author and two colleagues in 2012. We found that this feedstock could be processed into ethanol using one enzyme (gluco-amylase) that requires just one pH adjustment and can operate at low temperature (as low as 115 degrees F). The stale bakery waste is available year round. A highly resource-efficient model has been developed and analyzed for ethanol fuel production using this feedstock material. A concept model for an Integrated Bio-Refinery is described in this document that can reuse the energy recovered from distillation for processing the next batch of feedstock. The Integrated BioRefinery can also reuse stillage from distillation to greatly reduce water consumption. Fuel grade ethanol (near azeotrope) can be continuously produced using this Integrated Bio-Refinery model for an energy cost that is less than 20% of the energy in the ethanol fuel that is produced.

A 20 person Co-Op should be able to collect stale bakery waste from an average population of 107,000 people. The amount of waste collected is enough for the Co-Op to produce 20,000 gallons of fuel ethanol per year (50 week per year operation; 2 week per year preventive maintenance downtime). 20%, or 4,000 gallons, is dedicated to process energy, leaving 16,000 gallons, or 800 gallons per Co-Op member, for distribution. This is enough to fuel every member's car for the year. In exchange for this fuel, each Co-Op member is required to devote one weekend day every 5 weeks to either feedstock collection or feedstock processing.

The Urban Fuel Co-Op is theoretical at this time and is not without problems and issues. The largest single issue that has been uncovered is the time to collect feedstock from many small sources. Success of the Co-Op may depend upon finding points of concentration for the feedstock, such as food banks and other charities. Transportation and unattended operation are two additional issues, owing to the fact that Co-Op members do not reside and work at the processing facility.

This document presents a complete operational, thermodynamic, and flow analysis for the Urban Fuel Co-Op and the Integrated Bio-Refinery. The tools, concepts and issues presented herein may be useful to other small scale ethanol production models as well.

The next logical step would be development and operation of a pilot facility that would be used to flesh out the issues and validate the theoretical models that are documented herein.