Pre-Treatment of Lignocellulosic Biomass (PI: Kent Hoekman, DRI)

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1 4 th Quarterly Report NVREC Subtask Pre-Treatment of Lignocellulosic Biomass (PI: Kent Hoekman, DRI) The primary objectives of this subtask are to develop and utilize pre-treatment processes that will: (1) enable handling of non-homogeneous lignocellulosic biomass feedstocks having a variety of sizes, shapes, compositions, and densities and (2) increase the energy density of all feedstocks. The pre-treatment method we are exploring, called hydrothermal carbonization (HTC) or hydrothermal pretreatment (HTP) involves reacting raw biomass in hot, pressurized water. Under these conditions, the hemi-cellulose components of biomass are degraded, while the cellulose and lignin components remain largely intact. The resulting biochar is a blackcolored, friable solid that has higher energy content (BTU/lb) than the starting raw biomass. In this project, DRI will design and fabricate a laboratory-scale, semi-continuous HTC process unit. This unit will subsequently be used to treat a variety of Nevada-relevant biomass feedstocks. Gaseous, aqueous-phase, and solid products will be collected and characterized. Complete mass and energy balances will be conducted, and optimized pre-treatment conditions will be defined. Another task involves upgrading bio-oil through thermochemical reactions in a tube reactor. Optimized conditions will be defined in terms of H 2 yield and energy consumption. Accomplishments Task : Modify facilities and develop safety plan The small laboratory room described in previous quarterly reports has been used as the primary location for building and experimenting with a plastic model of the auger-based HTC reactor system. This space has proved adequate for these preliminary experiments. However, the final pressure-vessel reactor system will require more space -- and greater access to utilities -- than this small room provides. Therefore, under separate contract, DRI has begun a project that will involve construction of a Renewable Energy Experimental Facility (REEF). Part of the REEF will be a garage-like structure that will ultimately house the HTC process unit. The expected occupancy date for the REEF building is April, A draft laboratory safety plan has been completed, but will require modification once the HTC process unit is built and located in the REEF building. Task : Design pre-treatment reactor During the past quarter, DRI continued to experiment with the transparent, plastic, nonpressurized model of the HTC unit to investigate the behavior of different biomass types and learn to operate the augers for optimum conveyance of the biomass into and through the reactor system. Two DC motors (Dayton 90V permanent magnet gear motor) and variable speed DC controls (Dart controls) were used to operate the feed and reactor augers simultaneously, while feeding four different biomass materials: rice hulls, rice straw, pinion-juniper wood chips, and mixed Tahoe wood chips. Under all conditions tested (fast and slow auger speed, Y and T reactor configuration), the rice hulls and Tahoe Mix wood chips could be conveyed through the system quite easily, while pinion-juniper and rice straw could only be conveyed with great 1 Nevada Renewable Energy Consortium Quarterly Progress Report

2 difficulty. However, it is expected that in the hot, pressurized system, conveyance of all feedstocks will become somewhat easier, as the material begins to crumble in the HTC process. During actual HTC operation, we intend to sample both gaseous and liquid-phase products. A conceptual design for such sampling is shown in Figure 1-1. A draft design drawing of the reactor system mounted on a portable frame is shown in Figure 1-2. Pressure relief valve Motor T-configuration Y-configuration P Motor Make-up water T Solid container Ball valve Ball valve Screen Cooling water P Orifice T Canister Cooling water He Liquid container Gas container Figure 1-1. Gas, liquid, and solid sampling subsystems of hydrothermal carbonization (HTC) process unit. Figure 1-2. Schematic of HTC unit mounted on portable rack. 2 Nevada Renewable Energy Consortium Quarterly Progress Report

3 Task : Build and test pre-treatment reactor To better define optimum pre-treatment operating conditions for the HTC process unit, we continued to perform small-scale HTC experiments using Tahoe Mix feedstock in a 2-Liter, stirred Parr pressurized reactor. A schematic of this Parr reactor system is shown in Figure 1-3; a typical temperature and pressure profile plot is shown in Figure 1-4. Figure 1-3. Schematic of Parr Reactor system used for the HTC process. Temperature (ºC) A Time (min) Wall Temp. (C) Internal Temp.(C) Pressure (psi) B Pressure (PSIG) Figure 1-4. Temperature and pressure profile for HTC process of Tahoe Mix at 255ºC. Zone A = reactor heatup; Zone B = reactor hold time; Zone C = reactor cooling; Zone D = reactor venting. C D Steam Curve Press. (psi) A series of experiments was conducted in which the reactor temperature was varied from 215ºC to 295ºC while holding the reaction time constant at 30-minutes. A second set of experiments varied the reaction time from 5-min. to 60-min. while holding the temperature constant at 255ºC. The previous quarterly report gave preliminary results showing that as the reaction temperature increased, the production of gases (CO and CO 2 ) increased, while the amount of recovered biochar decreased. In this reporting period, it was demonstrated that increasing reaction time has a similar (though smaller) effect to increasing reaction temperature. The effects of reaction temperature and time upon the amount of biochar recovered, and the energy content of the biochar, are shown in Figure 1-5. As temperature or time increase, energy densification of the biochar also increases. Another way of depicting this is by means of a VanKrevelen Diagram, where atomic H/C ratio is plotted against atomic O/C ratio. This is a commonly used way of showing the relative energy contents of solid fuels. As can be seen in Figure 1-6, HTC treatment of raw biomass reduces both H/C and O/C values. With increasing HTC severity (higher temperature or longer time) the biochar increasingly resembles low-grade coal. These Parr reactor experiments have been very helpful in determining operating conditions to apply to the semi-continuous HTC process system. Once the process unit is built, we intend to begin operation of it over a temperature range of ºC, and a reaction time of 5-30 minutes. 3 Nevada Renewable Energy Consortium Quarterly Progress Report

4 % of Starting Dry Feedstock 75% 70% 65% 60% 55% 50% 45% 60 min 60 min 5 min 5 min Feedstock HTP Reactor Temperature Figure 1-5. Effects of reaction temperature and hold time on mass recovery and energy content of biochar from HTC of Tahoe Mix. (Hold time = 30 minutes, except where otherwise indicated.) Energy Content (MJ/kg) Atomic H/C Ratio Biomass Peat 215 Lignite 235 Feedstock min Coal 60 min Anthracite Atomic O/C Ratio Figure 1-6. Van Krevelen Diagram of Biochar from HTC of Tahoe Mix. Hold time = 30 min. except where indicated. Temperature at 255ºC for indicated hold times. Task : Refine raw and pre-treated bio-oil using bench-top tube reactor This new task started in December 2010 as a component of the NVREC-10 Subtask 1.1. The bench-top tube reactor has been acquired and set up in DRI s Aerosol Application Lab. The reactor is interfaced to a nebulizing system. The size distribution of bio-oil droplets from the nebulizing system is being investigated. Task : Project management and reporting Project planning and review meetings are continuing to be held at DRI on an as-needed basis. On December 6-7, 2010, our subcontractor, the Gas Technology Institute (GTI), visited DRI in Reno, NV for a second time. During this visit, we reviewed the performance of the plastic model system and developed improved concepts for design of the pressurized, semi-continuous HTC reactor system. Cost Status Project expenses to-date have been below what was expected at this stage of the project, due to delays in fabricating the HTC process unit. Accelerated expenses are anticipated during the next reporting period, as hardware is purchased and the process unit is fabricated. We anticipate completing the project within budget. Schedule Status Our progress in designing and building the HTC process unit has been slower than anticipated at this stage of the project. The chart below reflects the revised schedule. Once the HTC unit has been fabricated, we will immediately utilize it in a follow-on project under NVREC. 4 Nevada Renewable Energy Consortium Quarterly Progress Report

5 NVREC Subtask 1.1 Project Schedule Months from Contract Initiation Activity Task 1: Modify facilities and develop safety plan Task 2: Design pre-treatment reactor system Task 3: Build and operate pre-treatment reactor Task 4: Bio-oil refinement in tube reactor Task 5: Project management and reporting Deliverables* Q Q Q Q *Deliverables: Q = Quarterly report; D = Draft Report; F = Final Report Changes in Approach or Aims Design and fabrication of the continuous HTC process unit is anticipated to require the entire 12- month project period. This will leave relatively little time for actual operation and optimization of the HTC unit. Because of this, we have conducted preliminary HTC pre-treatment experiments using a 2-Liter, Parr pressure reactor. While this approach does not accurately simulate the conveyance of feedstock into and out of the reaction zone, it is a good way to explore important reaction parameters especially temperature. The knowledge we gain from the Parr reactor experiments will be immediately transferred to the continuous process system, thereby reducing the learning time needed to operate this system. Actual or Anticipated Problems The conveyance of biomass feedstocks into and through the HTC process unit has proven to be considerably more difficult than expected. This has necessitated re-design and more extensive experimentation of the auger system than originally planned. Also, because of complexities (and high expenses) of incorporating water recycle under hot, pressurized conditions, we have decided to build the semi-continuous HTC process unit without recycle capability. Absence or Changes in Key Personnel Dr. Antony Chen has been added to the project to manage the Task 4 activities. Products and Technology Transfer During the past quarter, DRI prepared and submitted a manuscript for publication in the journal, Energy and Fuels: Hydrothermal Pre-Treatment (HTP) of Lignocellulosic Biomass. This paper describes the experimental HTC work conducted using Tahoe Mix feedstock in the 2-Liter Parr pressure reactor. 5 Nevada Renewable Energy Consortium Quarterly Progress Report