Progress 09/01/15 to 08/31/19
Outputs
Target Audience:The target audience reached by our efforts included individuals and groups in academia, state government agencies, industry, and disadvantaged communities. The relevant topics of discussion were related to biomass processing and utilization. Discussions with members of the California Biochar Association, Green Carbon Nexus, and companies Nexchar, Phoenix Energy, and Professional Traffic Solutions were performed. Some of the results and lessons learned in this project were utilized for applications related to wastewater treatment plants, where biochar activation techniques, developed in this project, were used in a project led by the California Association of Sanitary Agencies. In addition, the PI was invited to be part of Biochar Research Advisory Group for the Governor's Office of Planning and Research, where biochar utilization potential was analyzed. The interaction with low income communities has been performed in terms of outreach meetings and workshops organized together with Green Carbon Nexus. Some of the results obtained in this project were fundamental in obtaining additional funding to develop a mobile biochar production unit with the intent of reducing greenhouse gas emissions with the additional benefit of training and providing skills to members of low-income and disadvantaged communities. Changes/Problems:Although the results obtained for plasma activation are very encouraging by being able to get high fractions of microporosity even at relatively low steam temperatures (of the order of 400 oC), one of the main issues continues to be the scaling up of the process. This presented a challenge at the time of determining adsorption capabilities of the material. The PI is actively looking for additional funding to be able to produce plasma activated carbon at scales larger than the one utilized for laboratory experiments. What opportunities for training and professional development has the project provided?The opportunities for training and professional development were diverse and benefited several students at the graduate and undergraduate level. It is important to mention that five out of seven students that underwent training were from minority groups, which helps to expand the STEM workforce of the nation. - Undergraduate student Jose Rubalcava-Cruz and graduate student Sai Kiran Hota underwent training to use the scanning electron microscope (SEM) at the Imaging and Microscope Facility at UC Merced. SEM micrographs have been used to characterize the surface morphology/characteristics of the treated and untreated biochar and activated carbon samples. Graduate student Andres Munoz-Hernandez worked one-on-one with the PI in the design and testing of conventional physical activation process. In addition, he was mentored by the PI in developing a computational model to analyze charge and temperature distribution of carbonaceous material subject to an electric field. He also presented his work at technical conferences, which improved his communication skills. He attended a workshop about biochar organized by UC Merced. - Graduate student Viacheslav Plotnikov also received mentoring from the PI in the design, manufacturing and testing of the plasma reactor and required power supply, in order to perform plasma-activation tests. He also presented his work at technical conferences, which improved his communication skills. He also attended a workshop about biochar organized by UC Merced. - Graduate student Hector Gomez has been trained in the technique of Gas Chromatography and has been mentored by the PI in the analysis of results for both conventional and steam activation process. - Graduate student Maria Lozano was trained in performing conventional and plasma activation of biochar tests. - Undergraduate student Juan De Dios Mariscal was trained in manufacturing parts at the machine shop. How have the results been disseminated to communities of interest?The results of the project have been disseminated through peer-reviewed journal publications, technical conference presentations and proceedings, and presentations at workshops where members of academia, industry, state government agencies, and low-income communities have participated. Discussions with the California Biochar Association, the Governor's Office of Research and Development, and California Association of Sanitary Agencies have shared many of the results obtained in this work, especially for the use of biochar and activated carbon as a means of using it for soil amendment, filter material, and stable carbon capture. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
The main idea behind this project is to increase utilization of agricultural and forest waste in order to match the growing supply of biochar (produced from gasification) with the demand for activated carbon used in a variety of applications, such as wastewater treatment and air-pollution control. The project converts locally available biomass into biochar by means of a thermochemical process known as gasification. This is performed by our industrial partner at a facility that generates 500 kWe of electric power, where biochar is produced as a byproduct of the power-generation process. Biochar is post processed to make activated carbon, which can be used as a material for filters. Two radically different activation techniques have been tested, i.e., conventional steam activation and low steam-temperature plasma activation. Activated carbon is one of the most effective materials for removing a wide range of contaminants from industrial and municipal wastewater, agricultural drainage water, landfill leachate, and contaminated groundwater. The impact of the project has the potential of being significant. It is estimated that public utilities spend about 2 billion dollars per year purchasing activated carbon from imported coconut shells and anthracite-based coal. The project has shown that local biomass can be processed to produce a material with properties that approximate the foreign product. Not only local producers could benefit from the sale of their biomass, but in the case of forest waste, the development of an industry that processes forest biomass could help in reducing the dead wood available in forests, which in many cases fuels devastating wild fires. In addition, the project allows to cut down in open burning of agricultural waste, which produces large amounts of air pollution, especially at low-income and disadvantaged communities. The accomplishments are summarized in connection to the project objectives as follows: - Biochar production from industrial gasification Production of biochar from two different local biomass types, i.e., woodchips and peach pits, was accomplished by Phoenix Energy, utilizing a 500 kW for woodchips and a 1 MW biomass gasifier, for peach pits. These two types of feedstock are locally available in the San Joaquin Valley of California and were chosen because they represents forest and agricultural biomass available in this region. - Conventional Steam Activation Conventional steam activation was accomplished for peach pits, almond shells, almond tree cuttings, and ponderosa pine biochar. BET surface area was analyzed for all samples produced and compared with the raw biochar obtained from the biomass gasification process. Raw biochar was measured to hav BET surface areas in the range between 1 to 20 m2/g with a low percentage (below 30%) of microporous surface. The very low surface area limits the capacity of biochar to be utilized as adsorption material in filters. A vertical tube furnace was utilized for the steam activation tests, where nitrogen gas was used to cool down the system upon completion of the experiments until a temperature low enough to avoid spontaneous combustion in the presence of air was achieved. This procedure was performed to prevent the thermochemical reactions to continue taking place inside the reactor after the steam activation process had been completed. Steam temperatures were varied between 750 and 850 Celsius degrees with steam flow rates between 0.8 g/min to 4 g/min and activation times between 15 and 45 min. A substantially larger BET surface area was obtained for the steam activated samples, which showed values in the range between 300 and 650 m2/g for most feedstock. A BET surface area of 730 m2/g was obtained for ponderosa pine steam activated samples, with microporosity of the order of 30%. Comparison with commercial activated carbon from coconut shells, which were measured at around 1000 m2/g with 95% micropore surface, shows that properties approximate the commercial product but do not match the same quality. It is noted that burn off ranged between 30% to 60% of the original biochar sample mass. - Plasma-enhanced steam activation Conventional activation of biochar utilizing steam at temperatures near 800 Celsius degrees consumes a very large amount of energy. Thus, this project intended to activate the biochar at a lower steam temperature, but in the presence of non-thermal plasma. A non-thermal plasma reactor was designed and constructed to be able to perform steam plasma activation of biochar samples. Due to the geometry of the reactor, it was determined that surface plasma was the best option for this particular process. The discharge is generated by inserting a steel coil inside the ceramic wall of the reactor. Nonthermal plasma is generated close to the surface of the coil and at ceramic walls, where carbonaceous material located in the spaces between the coil becomes in contact with plasma and steam. An input power of 100W showed the best results for the tests performed. The most interesting result is that, although BET surface areas in the range of 300 m2/g are low compared to commercial activated carbon, the micropore area obtained using plasma activation was of the order of 80 to 90% compared to a value around 30% of the conventional activation process. It is clear that plasma has a strong effect in increasing micropore area and a weak effect increasing BET surface area. The latter one can be increased by increasing steam temperature during the steam plasma activation process. If the purpose is to utilize the activated carbon for adsorption of pollutants, pesticides, pharmaceuticals, etc., the presence of plasma improves the fraction of micropore area to percentages near commercially available activated carbon. - Computational models Computational models were developed to explore the effects of Joule heating in carbonaceous materials. In addition, a hydrodynamic model has been developed for the detailed analysis of Joule heating with a two-carrier approach for the analysis of temperature increase, electron and hole density, and electric field distribution for graphite and graphene. The models have been published in peer reviewed journals and a PhD dissertation. The models also show the difference in electric field magnitude needed in order to reach temperature run-away conditions for biomass, biochar, and graphite. - Control schemes Temperature variations affect the properties of the steam activated sample. Although the furnace has a PID controller to maintain a fixed temperature at the heater, steam reforming reactions and the loss of mass during the activation process result in changes of temperature over time. This problem was solved by utilizing an intelligent learning control algorithm that learns the dynamics of the temperature inside the reactor and provides a control action to the heater to maintain the temperature at the sample constant. A couple of learning tests were needed to reduce temperature variation from 20 oC to +- 2 oC. In addition, control schemes were used to maintain plasma conditions during tests.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2017
Citation:
V. Plotnikov, G. Diaz, and E. Leal-Quiros. Elevated concentration of nitrate ions in water through direct treatment by dielectric barrier discharge. IEEE Transactions on Plasma Science , 45(12):3246-3251, December 2017.
- Type:
Journal Articles
Status:
Accepted
Year Published:
2019
Citation:
V. Plotnikov, G. Diaz, and E. Leal-Quiros. Effects on temperature and velocity distribution due to application of pulsed corona discharges in liquid-phase ethanol. Accepted in Journal of Enhanced Heat Transfer.
- Type:
Journal Articles
Status:
Under Review
Year Published:
2019
Citation:
V. Plotnikov, G. Diaz. High-voltage pulsed plasma generation with frequency control for streamer initiation in liquid phase. Under review in IOP Plasma Research Express. (Revised version manuscript has been submitted.)
- Type:
Theses/Dissertations
Status:
Published
Year Published:
2018
Citation:
Andres Munoz Hernandez, Charge and Joule Heat Transport in Carbonaceous Materials and Activation of Biochar. Ph.D. Dissertation, Department of Mechanical Engineering, University of California Merced.
- Type:
Theses/Dissertations
Status:
Published
Year Published:
2019
Citation:
Viacheslav Plotnikov, Development of high-voltage systems for direct and surface plasma treatment of liquids in sustainable energy. Ph.D. Dissertation, Department of Mechanical Engineering, University of California Merced.
|
Progress 09/01/17 to 08/31/18
Outputs
Target Audience:The target audience reached by our efforts included individuals and groups in academia, industry, and State government institutions. The main area of interest of the audience consisted in biomass and biochar processing and utilization. Discussions with members of the California Biochar Association,California Association of Sanitary Agencies, and companies such as Heatech, West Biofuels, and Phoenix Energy were performed. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?The project has provided training and professional development to the following students: - Andres Munoz-Hernandez in the design and testing of conventional physical activation process. He is defending his dissertation based on this project at the end of November 2018. - Viacheslav Plotnikov in design, manufacturing and testing of the plasma reactor and required power supply - Hector Gomez in analysis of results for both conventional and steam activation process - Maria Lozano in performing conventional and plasma activation of biochar - Undergraduate student Juan De Dios Mariscal in training and manufacturing of parts at the machine shop. How have the results been disseminated to communities of interest?During this year, two journal articles and five conference and poster presentations have been generated with parts of the results obtained from this work. Discussions with the California Biochar Association, the Governor's Office of Research and Development, and the California Association of Sanitary Agencies have allows us to share many of the results obtained in this work, especially for the use of biochar and activated carbon as a means of filter material, and stable carbon capture What do you plan to do during the next reporting period to accomplish the goals?The project was granted a no-cost extension. The work planned to be performed work follows the timeline of tasks described in the proposed project. The next step and final to be completed is to analyze performance of produced activated carbon in adsorbing methylene blue. H2S adsroption might also be tested since this is an important byproduct of waste water treatment plants for which the California Association of Sanitary Agencies is interested in removing from their product gases.
Impacts
What was accomplished under these goals?
Conventional Steam Activation: A number of conventional steam activation tests were performed for peach pits, almond shells, almond tree cuttings, and ponderosa pine biochar. BET surface area for the raw biochar was measured and values remained below 20 m2/g with some samples showing surface areas near 1 m2/g, and most of them showed a low percentage (below 30%) of microporous surface. The very low surface area limits the capacity of biochar to be utilized as adsorption material in filters. Steam activation tests were performed using the vertical tube furnace described in our previous progress report. Steam temperatures were varied between 750 oC and 850 oC with steam flow rates between 0.8 g/min to 4 g/min and activation times between 15 and 45 min. BET surface areas of steam activated samples showed significant increase with respect to the raw biochar. Surface areas between 300 and 650 m2/g for most feedstock and BET surface areas higher than 730 m2/g were obtained for ponderosa pine activated samples, with microporosity of the order of 30%. This BET surface area compares well with respect to commercial activated carbon from coconut shells which were measured at around 1000 m2/g with 95% micropore surface. It is noted that burn off ranged between 30% to 60% of the original biochar sample mass. Thus, a balance between maximizing BET surface area and minimizing burn off needs to be defined. Temperate variations affect the properties of the steam activated sample significantly. Although the furnace has a PID controller to maintain a fixed temperature at the heater, steam reforming reactions and the loss of mass during the activation process result in a change of temperature inside the reaction which can reach between 10 to 20 degrees C. This problem was solved by utilizing an intelligent learning control algorithm that learns the dynamics of the temperature inside the reactor and provides a control action to the heater to maintain the temperature at the sample constant. A couple of learning tests were needed to reduce temperature variation from 20 oC to +- 2 oC. Plasma-enhanced steam activation: A non-thermal plasma reactor was designed and constructed to be able to perform steam plasma activation of biochar samples. After testing standard dielectric barrier discharge plasma, it was determined that unsymmetrical conditions were likely to lead to formation of arcs which is un undesirable effect for the plasma activation process. The main goal of the study is to perform activation with steam at lower temperatures (around 400 oC) than standard physical activation (750 to 1000 oC) but in the presence of non-thermal plasma. Thermal arcs will generate temperatures of the order of 200 to 3000 degrees Celsius at localized spots of the carbonaceous material, yielding a nonuniform treated surface. Due to the geometry of the reactor, it was determined that surface plasma was the best option for this particular process. The discharge is generated by inserting a steel coil inside the ceramic wall of the reactor. Nonthermal plasma is generated close to the surface of the coil and at ceramic walls. Approximately 300 mg of ponderosa pine biochar were introduced inside the reactor for each test. Steam was generated at temperatures of 150 oC, 300 oC , and 400 oC, while activation times were kept between 10 and 15 minutes, with plasma power set at 50 and 100 Watts. One test was performed without plasma in order to obtain a baseline of comparison. As expected, the low operating temperature increased the BET surface area moderately to values between 200 to 318 m2/g. Increased in steam temperature resulted in increase in BET surface. It was also observed that plasma increase in plasma power also had an effect in increasing BET surface area of the treated sample. An input power of 100W showed the best results for the tests performed. The most interesting result is that, although BET surface areas in the range of 300 m2/g are low compared to commercial activated carbon, the micropore area obtained using plasma was of the order of 80 to 90% compared with a value around 30% of the conventional activation process. It is clear that plasma has a strong effect in increasing micropore area and a weak effect increasing BET surface area. The latter one can be increased by increasing steam temperature during the steam plasma activation process. If the purpose is to utilize the activated carbon for adsorption of pollutants, pesticides, pharmaceuticals, etc., the presence of plasma improves the fraction of micropore area to percentages near commercially available activated carbon. Computational models Computational models have been that explore the effects of Joule heating in carbonaceous materials have been explored with the development of an electric-thermal model that allows for simulation of heating due to the addition of electric fields in a number of materials, including biomass, biochar, graphite. In addition, a hydrodynamic model has been developed for the detailed analysis of Joule heating with a two-carrier approach for the analysis of temperature increase, electron and hole density, and electric field distribution for graphite and graphene. These models have been validated against published works. Control schemes: Control schemes to maintain uniform plasma conditions have been developed. Voltages can be varied between 5000 V to 25000V and frequencies can be changes from 1kHz to 10kHz. Current is obtained based on the settings of the voltage and frequency, as well as the impedance of the sample being treated.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2018
Citation:
A. Munoz-Hernandez G. Diaz. Modeling of thermal runaway of carbonaceous materials: graphite, biochar, and wood. AIP Advances , 8(095312):1-15, 2018.
- Type:
Journal Articles
Status:
Published
Year Published:
2017
Citation:
A. Munoz-Hernandez, G. Diaz, W. Calder_on-Mu~noz, and E. Leal-Quiros. Thermal-electric modeling of graphite: Analysis of charge carrier densities and joule heating of intrinsic graphite rods. Journal of Applied Physics , 122(245107):1-12, 2017.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2018
Citation:
A. Munoz-Hernandez, S. Dehghan, and G. Diaz. Physical (steam) activation of post-gasification biochar derived from peach pits. In Proceedings of ASME IMECE 2018, Paper # IMECE2018-88386 , Pittsburgh, PA, November 2018.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2018
Citation:
Poster: V. Plotnikov, H. Gomez, Andres Munoz-Hernandez, and G. Diaz. Non-thermal plasma-assisted steam activation of ponderosa pine biochar. In Biochar Field Day, Russell Ranch Sustainable Agriculture Facility, Winters, CA, June 2018. CDFA and UC Davis.
|
Progress 09/01/16 to 08/31/17
Outputs
Target Audience:The target audience reached by our efforts included individuals and groups in academia and industry related to biomass processing and utilization. Discussions with members of the California Biochar Association and companies Nexchar and Phoenix Energy were performed. Two conference papers, two poster presentations, and an invited talk were presented during this period. Changes/Problems:No problems have been encountered during this project. What opportunities for training and professional development has the project provided?Undergraduate student Jose Rubalcava-Cruz underwent training to use the scanning electron microscope (SEM) at the Imaging and Microscope Facility at UC Merced. SEM micrographs have been used to characterize the surface morphology/characteristics of the treated and untreated biochar samples. How have the results been disseminated to communities of interest?After completing the design and installation of the conventional steam activation test stand, a number of tests have been generated some of which are still being analyzed. Also, computational models for the Joule heating of biochar and pyrolytic graphite have been developed. Some of these results have been presented at the ASTFE conference in 2017, at the HEENAC conference, and at a forum organized together with the California Biochar Association where members from academia, industry, and government agencies, assisted. A poster was also presented at the Latin American Workshop for Plasma Physics. What do you plan to do during the next reporting period to accomplish the goals?The performed work follows the timeline of tasks described in the proposed project. The next steps that need to be completed are (a) Finalize construction of the plasma-enhanced steam activation reactor in order to carry out the tests for activation of biochar under the presence of plasma discharges, and (b) Finalize the development of the control scheme required to optimize power delivery during plasma steam activation of biochar. (c) Analyze performance of produced activated carbon in adsorbing methylene blue.
Impacts
What was accomplished under these goals?
Conventional steam activation: The test stand for conventional steam activation of biochar has been completed and used to perform physical activation of both materials proposed in this project, i.e., biochar from peach pits and from wood chips. A vertical tube furnace with a maximum operating temperature of 1200 Celsius degrees, and 24 in. of heated length is utilized for the tests. The stainless steel work-tube features an internal coil made with 3 mm OD 310S stainless steel used to increase the resident time of the working fluid inside the furnace. The coil connects to a 2 in. OD reactor, where the biochar is placed during the activation process. A type-K thermocouple is inserted insider the reactor to measure the actual temperature near the biochar. The gases coming out from the activation process are flared at the end of the exhaust pipe. In addition, the water line that connects to the bottom of the furnace is fed by a high-pressure low-flow water pump that allows flow rates in the range between 0.8 and 6 ml/min. Deionized water is used for the experiments, and nitrogen from a tank is fed to the reactor once the test is over, in order to stop the steam reforming reactions and to cool down the contents inside the reactor. For the sample preparation, biochar is sieved in the range between 0.6mm and 2.38 mm. The biochar is then placed on a crucible and dried in an oven for 8 hours at 105 C. A sample of twenty grams of the sieved, dried biochar is used for each activation run. Activation times range between 30 and 75 minutes. Porosity analysis has been performed for several samples: wood chips biochar, peach pits biochar, and activated peach pits. Wood chips biochar had a BET surface area of 39.4 m2/g, a mean pore size of 29.7 Angstroms, (A), and a total pore volume of 0.029 cm3/g. The peach pits biochar had a BET surface area lower than 1 m2/g, a mean pore size of 52 A, and a total pore volume of 0.001 cm3/g. Activated peach pit for (30 minutes at about 780 C under a steam flow rate of 0.83 g/min) had a BET surface area of 514.1 m2/g, a mean pore size of 20.7 A, a total pore volume of 0.27, and a mass loss of 30.3 %. A second peach pit sample, activated for 30 minutes at about 800 C under a steam flow rate of 3.7 g/min, had a BET surface area of 379.1 m2/g, a mean pore size of 21.8 A, a total pore volume of 0.21 cm3/g, and a mass loss of 37.4%. Several more samples have been activated and sent for analysis. The porosity analysis will be available in the next few months. Plasma generation: A design of a plasma reactor for biochar treatment has been accomplished. The plasma treatment is based on the principle of surface dielectric barrier discharge. The material under treatment, biochar, remains stationary in the reactor. Biochar is treated by a combination of superheated steam and non-thermal plasma that is generated on the surface of an energized spring electrode. The outer electrode is connected to ground, and has a cylindrical shape. Both electrodes in the reactor are separated by an alumina ceramic insulator. They are connected to the previously designed and assembled AC high-voltage power supply with a frequency of operation close to 15 kHz. The voltage magnitude is variable and can be regulated up to 30 kV peak-to-peak. Superheated steam with the temperature up to 250 oC enters the inlet and passes through the active plasma region. The walls of the plasma region are preheated by an external heat gun to prevent cooling of the superheated steam and its subsequent condensation. An extra ceramic tube surrounds the flow of air from the heat gun to prevent heat losses to the ambient air. Thus, biochar is prevented from absorbing condensed water while being treated by superheated steam and dielectric barrier discharge plasma. Controls: The purpose of the control system design is to ensure optimal performance of both, conventional and plasma-activation processes. The first step is to characterize the conditions that need to be maintained through the process that results in the most desirable product. Then control system is designed to ensure reaching those conditions and maintaining them to achieve them and to optimize the process in terms of time and energy consumption. The conventional steam activation system is now completely developed and a series of experiments for characterization of the optimal treatment conditions are been performed. The reactor is located inside a furnace for which its temperature is controlled using an embedded PID scheme that accurately tracks a given temperature profile. From controls point of view, the challenge is to reach and maintain the desired temperature at the reactor, noting that the reactor temperature considerably deviates from the furnace temperature (considering the dynamics of the heat transfer from furnace to reactor and also heat loss to steam flow and through the insulation). Since the input temperature profile is set in the beginning of each batch treatment and there is no control over it during the process, an Iterative Learning Control (ILC) method for batch processes is implemented. This method allows for designing an input profile, which will result in the desired set point temperature in the reactor. The learning filter is then designed by obtaining a feed forward transfer function using Zero Phase Error Tracking Control method (ZPETC). In order to apply the mentioned tracking method, an estimated model of the system is required. Several experiments have been conducted, treating biochar at different temperatures, with different flow rates of seam, and for different lengths of time. The desired input temperature profile and the reactor temperature have been recorded for each experiment and the input output data are used to obtain an estimated model for the system, using system identification techniques. The model is still in need of refinement considering the nonlinearities due to wide range of change in temperature (from room temperature to around 800 oC). The proposed control method addresses optimality issue by reaching the desired condition in the minimum possible time to cut the waste of time and energy. The plasma activation reactor is still under design and development. In this novel method biochar will be treated with Dielectric Barrier Discharge (DBD) plasma in presence of superheated steam flow through a cylindrical reactor. Steam flow rate, steam (reactor) temperature, and electrical properties of the DBD plasma such as frequency and voltage are the parameters influencing the process. The main challenge in plasma activation is dealing with the variability in the discharge in presence of the biochar particles and steam, influencing the plasma behavior. Therefore, the main objective of control system design is to sustain the plasma discharge and to avoid any sort of spark or arc formation and to ensure optimization of power delivery. Arcs and sparks are avoided by implementing saturation thresholds on drawn current. Then, to address the optimality issue, a "self-optimizing" adaptive control strategy is being explored utilizing well-known strategies such as extremum seeking control (ESC) and Maximum Power Point Tracking (MPPT). The steam generator system, up-stream of the plasma reactor, includes a pump and a control valve responsible for modulating the delivery of water to a gas sampling bomb rapped with a heating element working as boiler, and a metal tube located downstream of the gas sampling bomb rapped with another heating element to deliver superheated steam to the plasma reactor. The steam flow rate is limited to the heating element's power rapped around the boiler and experiments show that it reaches around 4 ml/min at maximum power (150 Watts). The superheated steam temperature is limited to the heating element's power when rapped around the metal tube. Experiments show that the temperature reaches to more than 200 Celsius degrees at the maximum power (300 Watts).
Publications
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2017
Citation:
A. Munoz-Hernandez, G. Diaz, Heat transfer analysis of graphite rods subject to joule heating using a modified semiconductor formulation, Proceedings of the 2nd Thermal and Fluids Engineering Conference, 4th International Workshop on Heat Transfer, April 2-5, 2017, Las Vegas, Nevada, USA.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2017
Citation:
V. Plotnikov, G. Diaz, and E. Leal-Quiros. Temperature increase in liquids due to high-voltage plasma discharges. In Proceedings of TFEC-IWHT, Paper # TFEC-IWHT2017-18242, Las Vegas, NV, April 2017. ASTFE, Received a Travel Award from ASTFE.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2017
Citation:
Poster: V. Plotnikov, E. Leal-Quiros, and G. Diaz. Pulsed corona plasma in glycerin for fuel gas generation. In 16th Latin American Workshop for Plasma Physics, Mexico City, Mexico, September 2017.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2016
Citation:
Poster: A. Munoz-Hernandez, S. Dehghan, V. Plotnikov, G. Diaz, and Y. Chen, Exploring plasma activation of biochar for enhanced properties, HENAAC Conference, 2016.
|
Progress 09/01/15 to 08/31/16
Outputs
Target Audience:The target audience reached by our efforts include individuals and groups in academia and industry related to biomass processing and utilization. Discussions with members of the almond industry were performed and a poster was presented at the 2016 Biochar conference. Researchers from industry and academia were reached during the conference. Changes/Problems:No problems have been encountered during this project. What opportunities for training and professional development has the project provided?Graduate Student Andres Munoz Hernandez underwent training to use the scanning electron microscope (SEM) at the Imaging and Microscope Facility at UC Merced. SEM micrographs will be used to characterize the surface morphology/characteristics of the treated and untreated biochar samples. How have the results been disseminated to communities of interest?Since this is the first year of the project, only preliminary results have been disseminated by means of a poster presented at the 2016 Biochar conference in Oregon. However, two manuscripts describing the computational modeling of Joule heating in pyrolytic graphite are currently under development, and one manuscript related to the development of the Dielectric Barrier Discharge plasma generator that will be utilized in the plasma-enhanced steam activation is also being generated. An abstract related to Joule heating analysis in carbonaceous materials has been accepted in ASTFE 2017. What do you plan to do during the next reporting period to accomplish the goals?The work is being systematically carried out following the timeline of tasks described in the proposed project. The next steps that need to be completed are (a) perform conventional steam activation at optimal temperatures around 830 oC, (b) complete design and construction of the plasma-enhanced steam activation reactor in order to carry out the tests for activation of biochar under the presence of plasma discharges, and (c) Complete the development of the control scheme required to optimize power delivery during plasma steam activation of biochar.
Impacts
What was accomplished under these goals?
The project is being developed following the timeline of the proposed tasks. Biochar production from a 500kW biomass gasification plant, operated by Phoenix Energy, has been accomplished, and preliminary tests of conventional steam activation of biochar have been performed. Development of a DBD plasma discharge generator has been finalized and preliminary tests of biochar exposed to plasma have been carried out with air as the surrounding atmosphere. The dynamical model of dielectric breakdown and thermal runaway in pyrolytic graphite is currently under development. In addition, initial measurements of plasma characteristics have been obtained with the intension of developing the control system for the plasma-enhanced steam activation process. Overall, the project is on time and within the requested budget. The following paragraphs describe some of the performed tasks in more detail. Conventional steam activation: A test stand for biochar steam activation was designed, built and tested. A configuration containing two immersion heaters in series was utilized to quantify temperature and flow rate characteristics of the test stand. Nitrogen gas was used to cool down the system upon completion of the experiments until a temperature. This procedure was performed to prevent the thermochemical reactions to continue taking place inside the reactor after the steam activation process had been completed. Hydrogen and carbon monoxide are produced during steam activation and the reduction in temperature is also utilized, to avoid autoignition of gases, in case of accidental contact of product gases with air. Successful production of biochar obtained from two different local biomass types, i.e., woodchips and peach pits, was achieved by Phoenix Energy, utilizing a 500 kW and a 1 MW biomass gasifier, respectively. The samples investigated were: Peach pits: Ten grams of peach pits biochar, with particle sizes ranging from mesh #4 (4760 μm ) to mesh #30 (600 μm). Processed with superheated steam for 90 minutes at temperatures ranging from 426 to 461 °C. Wood chips: Ten grams of wood chips biochar, with particle sizes ranging from mesh #8 (2360 μm) to mesh #30 (600 μm). Processed with steam for 90 minutes at temperatures ranging from 434 to 540 °C. The treated biochar samples were sent out for testing to obtain porosity and BET surface area measurements to EMSL Analytical, Inc. In addition, scanning electron microscope (SEM) images were taken at the Imaging and Microscopy Facility at UC Merced. Based on the SEM images, the peach pits' structure showed a rather rough surface compared to wood chips which showed various unidirectional channels aligned together, but with very smooth surfaces, making it less likely to be a good candidate for activated carbon, based on the physical structure. The reported values for BET surface area for untreated wood chips was 14.86 m2/g, while for the steam processed samples, the BET surface area was 31.74 m2/g. The reported values for BET surface area for untreated peach pits was 0.12 m2/g, while the treated samples had a value of 1.17 m2/g. Although there is an increase in surface area for both samples, the absolute values are one to three orders of magnitude lower than common reported values (>~1000 m2/g). In addition, samples previously tested by Phoenix Energy using butane activity, showed surface areas of untreated peach pits to be of the order of 202 m2/g, which are very typical of values found in the literature. Additional tests will be conducted with different grain sizes and with more typical steam activation temperatures of around 800 oC to compare results with lower operating temperatures. Plasma generation: A high voltage power supply with maximum output power 150 watt was assembled for the purpose of generation of direct current (DC) corona and spark plasma discharge. A linear programmable power supply unit was utilized to control the amplitude of DC potential difference on the input of a zero-volt switching Royer-Mazzilli oscillator. The oscillator switched two metal-oxide field effect transistors (MOSFET) by the use of a resonant LC tank. The switching mechanism produced an alternating current (AC) signal with voltages up to 30 volt RMS. The signal was put through the primary winding of a high voltage cathode ray tube (CRT) transformer. The built-in rectification of the transformer produced a DC potential difference on the output high voltage line up to 32 kilovolt, which was measured by the high voltage probe Tektronix P6015a and oscilloscope GW Instek 1052u. One of the dangers of operating non-thermal discharge is its transition into an arc plasma discharge. Such a phenomenon can cause electromagnetic interference, increased power consumption, high voltage transients and electrode destruction. Furthermore, the material under treatment becomes significantly heated, which leads to its irrevocable transformation or destruction. Therefore, mechanisms to prevent formation of an arc were developed: voltage divider based sensing control and power sensing mechanism. The former relies on capturing the transition to an arc through repetitive check of potential difference across the load. A dramatic drop of potential difference across the load (for example, from 20-30 kilovolt to 2-3 kilovolt) signifies of transition into an arc. This is accompanied by a noticeable increase in current. In addition, overall power consumption increases when transition into an arc occurs. The programmable power supply unit is then controlled to limit current on the primary winding of the CRT transformer. An arc cannot be sustained and the discharge returns to corona regime after a short delay. Experimentally, it was verified that spark discharge and, especially, arc discharge draw significantly more power than corona discharge. Constant monitoring of power consumption was performed through a programmable power supply. Preliminary tests have been carried out in which positive corona plasma was utilized to treat peach pits. The material was put on the grounded plate, and was treated by the corona plasma that originated from the positive pin electrode. Adjustment of electrode distance was necessary to maximize the region of plasma. AC or pulsed DC plasma have the advantage of being used in a dielectric barrier discharge (DBD) configuration. This type of a setup allows plasma to be generated even if the material under treatment completely blocks the path between a cathode and an anode. In addition, DBD configuration has such benefits as uniform plasma region distribution throughout the treated material, and simpler prevention of an arc formation compared to a continuous DC plasma. Therefore, steps have been taken to carry out design and assembly of a reactor for biochar steam activation with both high voltage AC and pulsed DC generation systems. Control In the developed test platform, the plasma discharge is generated between a pin and a plate by transforming a low voltage DC (up to 30 volts) from the power supply to a high voltage DC (up to 32 kilovolts according to measurements). While the measurements on the low voltage side provide data on the whole system power consumption and electrical characteristics, high voltage measurements over plasma discharge provide more information about the discharge itself. The high voltage probe Tektronix P6015a was utilized along with oscilloscope GW Instek 1052u to measure voltage characteristics. Voltage drop over a 12 Ohm shunt resistor in series with the plasma discharge was measured, and current was calculated. Preliminary tests showed waveforms from the high-voltage-side current and voltage, where current showed noticeable peaks during the times that spark occurred. Identification methods to obtain the dynamics of the plasma system in order to develop control techniques such as Maximum Power Point Tracking (MPPT) with the purpose of maximizing power efficiency.
Publications
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2016
Citation:
A. Munoz-Hernandez, S. Dehghan, V. Plotnikov, G. Diaz, and Y. Chen, Exploring plasma activation of biochar for enhanced properties. Poster Presentation in Biochar 2016, Corvallis, Oregon. Aug. 22-25. 2016
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