Communication of industry knowledge, best practices, and lessons learned in the space of cellulosic biofuels plant design, project development and execution and operations. Task 1 report

Abstract

Most pioneer cellulosic biofuel plants worldwide failed to achieve designproduction capacity, and many have shut down. The major causes of failure to achieve the design throughput include: (i) feedstock logistics causing significant variability of the properties of raw biomass delivered to the plants, (ii) inability of the plants to handle the variability in biomass properties, which leads to low feedstock throughput and low product yield, (iii) integration of feedstock preprocessing unit operations with downstream conversion processes at the plants, which leads to unreliable operation as operating difficulties in one area can cause process upset or shutdown of the other.ExxonMobil Research and Engineering Company, via a technical services agreement, engages Idaho National Laboratory (INL) to provide general industry knowledge, best practices, and lessons learned in cellulosic ethanol plant design, project execution, and operations. INL will also assess publicly proposed cellulosic plant designs. The scope of work will be accomplished in three tasks: Task 1, Communicate industry knowledge; Task 2, Present high-level lessons learned; Task 3, Provide an engineering assessment of publicly proposed ethanol plant designs.This Task 1 report provides a high-level summary of general industry knowledge, best practice, and lessons learned in biomass feedstock logistics and integration with bioconversion processes. Based on INL's more than 15 years of research and development (R&D) in biomass feedstock preprocessing and the author's more than 40 years of R&D, engineering design and cellulosic ethanol plant operating experience and published research results related to biomass harvest, collection, transportation, and storage, the following observations can be drawn:

Identification of Critical Process Parameters for Knife Milling and Alternative Communication Strategies

“…Preprocessing of biomass feedstocks involves a number of unit operations that involve mechanical operations that can result in wear of components [11]. These operations include bale processing (deconstruction/shredding of corn stover bound up into square/rectangular, or round bales weighing approximately ½ ton), and size reduction operations to yield loose, free flowing biomass that can be readily treated by downstream pretreatment and conversion/digestion processes.…”

“…The functional heads that perform the shredding can be sawed-tooth shaped as illustrated in Figure 4, narrow hammers, augers, or tines. Care must be taken to select heads that avoid breaking bales into large flakes that often cause surging of flow and plugging of downstream operations [11].…”

“…However, issues related to poor operation with high moisture feedstock, generation of fines, and poor control of the biomass size is raising concerns about the ability of hammer milling to meet efficiency and productivity goals and has fallen out-of-favor, leaving knife milling and/or rotary-shear milling as the primary technologies for sizereduction. While knife mills and rotary shear mills may have lower throughput, they are not as sensitive to moisture, generate less fines, and produce product with a narrower size distribution [11].…”