UC Discovery /West Biofuels Project Research Plan. An Investigation of a Thermochemical Process for the Conversion of Biomass to Mixed Alcohol

Transcription

1 UC Discovery /West Biofuels Project Research Plan An Investigation of a Thermochemical Process for the Conversion of Biomass to Mixed Alcohol Principal Investigators: Prof. Robert Cattolica, University of California at San Diego, PI Prof. Bryan Jenkins, University of California at Davis, Co-PI Robert Dibble, University of California at Berkeley, Co-PI Status: A UC Discovery Pilot Grant (UCSD/UCB/UCD) funded: 6/1/2007-5/30/2009. Two year program: $3M (1.9M West Biofuels/$1.1M UC). Operating budget $1M/year Manpower: 9 Professors, 7 post doctoral researchers, 1 development engineer. Project Goals: Provide energy/mass balance and performance analysis for a thermochemical conversion process for the production of a mixed alcohol fuel from biomass. Develop and apply advanced controls for complex systems and advanced laser sensors to maximize the efficiency of the thermochemical conversion of biomass to alcohol. Determine internal combustion engine performance/emissions of mixed alcohol in gasoline blends in conventional/flex fuel engines for fuel qualification by the State of California. Develop computer engine simulation of mixed alcohol in gasoline blends for the prediction of engine performance and emissions to support internal combustion engine studies. Develop chemical mechanisms for the combustion characteristics/emissions of mixed alcohol fuel for use in computer engine simulation of engine performance and emissions. The purpose of this research is to investigate a thermochemical process for the conversion of biomass to a renewable mixed alcohol fuel (primarily ethanol with methanol, propanol, butanol, and pentanol). This conversion process has the potential to recycle the large biomass waste stream feedstocks in California. In this investigation the industrial partner, West Biofuels, LLC, will provide a biomass to mixed alcohol research reactor based on a three-step process that includes biomass gasification, reforming to a high quality syngas, and synthesis of the syngas into a mixed alcohol. These processes can include both proprietary and non-proprietary catalysts. Advances in the gasification, reforming, and synthesis technologies involved have occurred in other contexts. However, the integration of these technologies for the purpose of converting biomass to mixed alcohol fuel has only recently been considered. Critical to the successful integration and optimization of this three step chemical process is the development and application of advance controls engineering techniques for complex systems and advanced laser sensors for process monitoring. Research advances in these techniques not only provide insight into the performance of these processes but can be applied to future pilot and commercial scale biomass to mixed alcohol facilities based on this research. Thermochemical Conversion of Biomass to Mixed Alcohol: The thermochemcial conversion of biomass to a mixed alcohol is based on a three-step chemical process that includes: gasification of biomass to producer gas, reforming of producer gas into syngas, and synthesis of 1

2 syngas to produce the final product, a mixed alcohol fuel. A schematic diagram summarizing the thermochemical processes that are involved is presented in Fig. 1. Fig. 1 Schematic diagram of the thermochemical conversion of carbon in biomass to a mixed alcohol liquid fuel. Gasification Reactor: In the thermochemical conversion process the carbon from a biomass source is combined with water at higher temperature (steam) in a gasification reactor to generate producer gas which is composed of CO, H 2, CO 2, and CH 4. This process can be accomplished with a variety of techniques. Dual-fluidized bed gasification illustrated in Fig. 2 was chosen to eliminate the use of oxygen in biomass gasification and at the same time minimizing the nitrogen in the producer gas. Fig. 2 Schematic of dual-fluidized bed gasification process. In dual-bed gasification the biomass is introduced in a reactor with out the presence of oxygen or air. Volatiles and some fixed carbon are converted to product (producer) gas in the presence of steam in the gasification section of the dual-fluidize bed. The bed material in the gasifier carries the remaining fixed carbon (coke) to the combustion section of the dual-fluidized bed where air is introduced for combustion and energy is released to heat the bed, which is returned to the gasifier reactor through convective circulation of the bed material. 2

3 Research Issue: The biomass gasifier is based on a well established design that has been used successfully for the production of producer gas for electric power. For the production of alcohol fuels this design requires research to maximize the syngas component (H 2,CO) of the producer gas from the gasifier. This can be accomplished with the use of catalytic additives and advanced adaptive controls techniques using new laser/sensors for process monitoring. Energy, mass balance and performance analysis of the system is required as well as modeling to scale the gasifier. Reformer Reactor: The reformer reactor is a key new element in the process and is based on a proprietary design from West Biofuels, LLC. The purpose of the reformer reactor is to convert the producer gas to syngas with the highest possible concentration of H 2 and CO and minimizing the CO 2 and CH 4. Typically a catalyst is used to perform the conversion. The reforming method to be used is based on a double trickle bed design with direct-contact between the reforming catalyst and alternately both the syngas and hot-exhaust gases for thermal regeneration as depicted in Fig. 3. Characterization of the catalytic material to be used in the reformer reactor will be accomplished in separate research studies in a flow reactor at UCSD. Fig. 3 Schematic diagram of gasifier and reformer stages of the 1 ton/day biomass dry (100 lbs/hr wet) to mixed alcohol research reactor to be provided by West Biofuels. Research Issue: The function of the reforming reactor is to shift the methane and carbon dioxide in producer gas to syngas (H 2 and CO). Conventional steam reforming requires a 3 to 1 ratio of H 2 O (steam) to CO 2 on a mass basis for this process. In the proposed reformer a proprietary catalysts with regeneration using the combustion gas stream from the gasifier will be used. The goal of the research on the reformer is to reduce the H 2 O (steam) to CO 2 ratio to 0.5 to 1, increasing the efficiency of the reforming process by 600% and increasing the overall yield of syngas. This approach requires advanced adaptive controls engineering methods using new laser/sensors for process monitoring. Energy, mass balance, and performance analysis of the reforming is required for modeling to scale the process. 3

4 Synthesis Reactor: The conversion of syngas to a mixed alcohol is based on the modern extension of the first synthesis process develop by Fischer-Tropsch over Fe catalysts in More recently, process and catalyst improvements were developed and patented by both Dow Chemical and by Union Carbide during the 1980's with continued improvements by other commercial sources. An example of the patent from Dow Chemical that is now in the public domain and can be used in the synthesis reactor to be integrated in the overall biomass to alcohol process is presented in table I. The synthesis catalyst is composed of a mixture of MoS 2, CoS 2, and K 2 CO 3 in ratio of (3:2:1.5) on mass basis. The Dow Chemical original catalyst patent is based on the process used to manufacture the compound, in this case by a co-precipitation method. This patent expired in 2006 and is available for use in the thermochemical process for the conversion of biomass to mixed alcohol. Other suppliers of this type of synthesis catalyst with proprietary catalyst manufacturing patents are available. West Biofuels will provide the synthesis reactor as an in kind match to the research. At present the selection of the catalyst is to be determined. Although the Dow Chemical process is without license restrictions, other proprietary catalyst manufacturers may provide their formulations to this research for evaluation in the context of biomass derived syngas. US Patent: Dow Chemical Company Mixed Alcohols from Syngas Date of Patent: 5/16/1989 Catalyst A B C D E F G MoS % 64.3% 57.1% 64.3% Haldor 64.3% 64.3% CoS 2 0.0% 21.4% 28.6% 21.4% Topsoe NiS % FeS % K 2 CO % 14.3% 14.3% 14.3% Denmark 14.3% 14.3% preparation mixed mixed precipitated precipitated precipitated precipitated Temperature (C) CO coversion 33.1% 10.3% 39.0% 29.2% 12.7% 33.1% 27.1% mass conversion Ethanol % % % % % % % Methanol % % % % % % % Propanol % % % % % % % Butanol % % % % % % % Pentanol % % % % % % % total alcohol 73.6% 82.8% 75.7% 80.8% 65.5% 71.4% 63.7% H % 1.4% 1.8% 2.3% 4.6% 1.9% 6.7% Table I. Summary of Dow Chemical Co. patent for the production of mixed alcohol from syngas. Research Issue: A variety of potential commercial catalysts to convert syngas into mixed alcohol are available, including the Dow Patent (Table I) which is in the public domain. The objective of the synthesis reactor research is to evaluate potential catalysts and maximize the mixed alcohol yield using advanced adaptive controls engineering. Energy, mass balance, performance analysis, and system modeling is required to scale the synthesis reactor. Mixed Alcohol Fuel: The mixed alcohol fuel produced by the synthesis of syngas based on the Dow Chemical catalyst "D" in table I or similar proprietary catalyst has been granted registration by the US Environmental Protection Agency allowing it to be used as a blending agent in gasoline or diesel. This unique authorization was granted under the original registration in 1980's under the name Octamix TM and more recently in 2002 Ecalene TM. The basic mixture composition is given in Table II using a MoS 2 based catalyst described in the Dow Chemical patent. The baseline composition contains 30% methanol. Since methanol raises the Reid Vapor 4

5 pressure of gasoline it is limited by regulation to a 3% fraction in gasoline. That restriction limits the blending level of the baseline composition of the mixed alcohol to be no more than 10% in gasoline. However, mixed alcohol can be used as an E85 blend with no increase in the Reid Vapor pressure. Since the synthesis catalyst is based on building higher order alcohols starting with methanol, the recycling of methanol through the catalyst will produce higher ethanol and more of the higher order alcohols as listed in Table II. Alcohol Mixed Alcohol Baseline Composition Mixed Alcohol with Methanol recycle Ethanol 50 % 75% Methanol 28 % - Propanol 16 % 11% Butanol 4 % 8% Pentanol 2% 6% Table II Mixed alcohol composition for MoS based catalyst "D" and composition with methanol recycle. The baseline mixed alcohol fuel in Table II that can be produced from the thermochemical process has been approved by the US Environmental Protection Agency for use as a blending agent in gasoline. However, acceptance in California will require separate evaluation and certification of this new fuel by the California EPA and Air Resources Board. To determine the combustion characteristics and pollutant emissions of this new mixed alcohol fuel, both basic and applied combustion research on the fuel is required. Research Issue: The combustion characteristics, performance, and emissions of the mixed alcohol fuel must be understood for acceptance by regulatory agencies. The current inclusion of ethanol (the primary constituent of the mixed alcohol fuel) in gasoline is well understood, the higher alcohol components of the mixed alcohol (propanol, butanol, and pentanol) are not well documented. Both fuel characterization in internal combustion engines and basic research on the combustion chemical kinetics of the higher order alcohols are necessary to provide a full understanding of this new mixed alcohol fuel. Research Design Summary The organization and design of the Biomass to Mixed Alcohol Research is summarized in Fig. 4 which is a chart showing the personnel and coordinated research activities to be accomplished in this project. The leadership for the project is provided by Professors Robert Cattolica (PI) UC San Diego, Bryan Jenkins (Co-PI) UC Davis, and Robert Dibble (Co-PI) UC Berkeley. The research is organized under system, applied, and basic research tasks. In addition to the PI and Co-PIs six additional Professors (Herz, Krstic, Buckley, Chen, Seshadri, and Williams) and seven post doctoral researchers, and a development engineer will perform the research tasks outlined in detail in Tasks 1.0 to 6.0. System research directly supports the three chemical reactors provided by the industrial sponsor, West Biofuels, and is divided between research tasks on analysis and modeling (1.0), advanced controls (2.0), and laser/senor monitoring (3.0). Applied research is complementary to the research on the performance of the biomass to alcohol reactors with flow reactor studies on the 5

6 reforming catalyst (4.0) directly supporting the reforming reactor and fuel/engine research (5.0) providing data and analysis required for qualification of the fuel for approval of by regulatory agencies such as the California EPA and Air Resources Board. Basic research (6.0) will provide fuel/combustion properties and fuel/chemical mechanisms for interpretation of the applied fuel/engine research for fuel qualifications. This basic research is particularly import because of the introduction of propanol, butanol, and pentanol along with ethanol in gasoline blends with this new mixed alcohol fuel. Figure 4. Organization Chart for Biomass to Alcohol Research Personnel and Research Tasks. Task 1.0 Biomass to Mixed Alcohol Research Reactor Energy and Mass Balance and Performance Research: Research to evaluate the performance of the mixed alcohol research reactor consists of instrumenting each of the three process reactors (gasifier, reformer, and synthesis) to obtain mass flow rates, composition, and temperature of the process streams. The data will be collected locally on the research reactor and mirrored to a data center at UCSD for analysis using energy and mass balances models and also used for the development of advanced control engineering methods described in Task

7 Task 2.0 Controls Engineering Advanced Controls for Biomass to Mixed Alcohol Research Reactor: The control problems arising in gasifier, reformer, and alcohol synthesis technologies are difficult to model and are not tractable using standard linear control methods for systems modeled from first principles like linear optimal control. Control of this complex integrated chemical process system can be accomplished with modern real-time optimization techniques for hard-to-model nonlinear uncertain systems. These techniques, known as Extremum Seeking, have been under intense development at UCSD for nearly a decade and have been applied in gas turbine and automotive engine industries. The project will entail three real-time optimization tasks and a final task to monitor the adaptability of this optimization control method: Task 3.0 Multiplexed Tunable Diode Laser Sensor for Gas monitoring Conventional gas monitoring of the producer and syngas in the biomass to mixed alcohol process requires gas composition measurements using gas sampling with heated stainless steel sampling lines to bring the samples to conventional chemical analysis system. In situ laser-based optical methods provide a solution to the sampling problems in conventional composition measurement and can provide rapid measurements for use in control systems. The current UCSD Wavelength Modulated Spectrocospy (WMS) system can measure temperature, H 2 O, CO 2, CO, CH 4, NH 3, and H 2 S simultaneously, in real-time and high sensitivity. WMS has provided dramatic improvement in signal-to-noise (S/N) over traditional direct absorption methods; the measurement is essentially baseline-free, and the use of lock-in detection with modulation frequencies on the order of 10 khz moves the sensing signal far from the frequencies of noise in a typical gasifier (< 1 khz), with an overall improvement in S/N of 2-3 orders of magnitude over traditional direct absorption methods. The WMS technique will be applied to the gas phase composition measurements of the gasifier and reformer reactors in the biomass to mixed alcohol fuel process. Task 4.0 Flow Reactor Reforming Catalyst Research The function of the reforming reactor is to shift CH 4 and CO 2 in producer gas to syngas (H 2 and CO). Conventional steam reforming using a NiO catalyst requires a 3 to 1 ratio of H 2 O (steam) to CO 2 on a mass basis. In the proposed reformer a proprietary catalysts with regeneration using the combustion gas stream from the gasifier will be used. The goal of the research on the reformer is to reduce the H 2 O (steam) to CO 2 ratio to 0.5 to 1, increasing the efficiency of the reforming process by 600% and increasing the overall yield of syngas. Flow reactor studies will be conducted to evaluate the performance of selective catalysts to determine efficiencies, lifetimes, and regeneration parameters to guide the operation of the reforming stage of the biomass to mixed alcohol research reactor. Task 5.0 Mixed Alcohol Fuel Engine Research Mixed Alcohol Fuel/Engine Studies: To provide the octane, engine performance and emissions characteristics for eventual fuel qualification of the proposed mixed alcohol fuel, fuel/engine applied research consisting of engine experiments and advanced engine modeling with the mixed alcohol fuel and fuel blends with gasoline will be conducted. Applied research will be conducted in the standard engine for octane rating, the single cylinder CFR engineat the Combustion Analysis Laboratory (CAL) at UC Berkeley. The performance (torque, power, vs rpm) and 7

8 emission characteristics of the combustion of biofuels requires calibration of the engine on the traditional fuels (octane number=100) and n-heptane (octane number = 0). These calibrations are required for mixed alcohol fuel octane characterization. A dynamometer and emission monitoring measurements at CAL laboratory will be performed to quantify NOx, CO, CO 2, O 2, and unburned hydrocarbons (HC) in both conventional and flex fuel engines. Advanced Engine Modeling: Research on advanced engines using mixtures of fuels derived from biomass can be greatly accelerated by simulations using KIVA and realistic chemistry. KIVA allows a realistic description of engine geometry including piston and cylinder head shapes, intake and exhaust ports, and valve lifts. Research on advanced engines using mixtures of fuels derived from biomass can be greatly accelerated by simulations using KIVA and realistic chemistry. Advanced engine modeling of the CFR engine will be compared to the fuels with known octane number containing isooctane and n-heptane. For fuel mixtures with various alcohol components, a reduced chemical kinetic model will be used based on the detailed chemical mechanisms developed at UCSD. Simulations using KIVA with reduced chemistry will be used to help to interpret the engine performances measurements. Task 6.0 Fuel/Combustion Properties and Fuel Chemical Kinetic Research Fundamental Combustion Experiments and Chemical Mechanism Evaluation: Fundamental flame characterization experiments will be conducted in the counter flowing burner configurations with controlled strain rates. Experiments will be conducted at a pressure of 1 atm, and will consider laminar non-premixed flows. Numerical calculations will be performed using detailed chemical-kinetic mechanisms, in particular the San Diego Mechanism. Studies will be performed for surrogate gasoline (n-heptane and iso-octane) alcohol fuels (methanol, ethanol, propanol, and butanol) and blends of alcohol fuel. Two types of configuration, the condensed fuel configuration and the prevaporized fuel configuration will be employed in the experimental study. For alcohol fuels and mixtures conditions of extinction will be measured as a function of the strain rate. In autoignition experiments as a function of strain rate will provide data for comparison with chemical kinetic mechanisms for the higher order alcohols and associated blends. Chemical kinetic mechanisms for the combustion of higher alcohols. Detailed and reduced chemical kinetic mechanisms for the combustion of higher alcohols will be developed. These mechanisms are important in evaluating the combustion properties and pollutant emissions associated with the utilization of mixed alcohol fuel. Chemical-kinetic descriptions for propanol, butanol, and petanol do not exist. The approach will be based on a detailed chemical-kinetic mechanism for combustion that has been developed at UCSD in recent years and that is refer to as San Diego Mech, to distinguish it from other mechanisms that are available in the literature. 8