8 th U.S. National Combustion Meeting Organized by the Western States Section of the Combustion Institute And hosted by the University of Utah May 19-22, 213 Biomass Pyrolysis and Gasification of Different Biomass Fuels Eric Osgood, Yunye Shi, Tejasvi Sharma, Albert Ratner Mechanical & Industrial Engineering, University of Iowa, Seamans Center, Iowa City, IA 5224
Abstract This work explores the gasification and pyrolysis of various biomass fuels such as seed corn, wood chips, and paper sludge at temperatures between 4 C and 55 C. The gas evolution of hydrogen, carbon monoxide, and carbon dioxide of the biomass is measured. To achieve the desired accuracy, a custom experimental setup was constructed with a lab scale gasifier to obtain time varying gasification and pyrolysis data at high heating rates. Biomass is dropped into a flow of heated nitrogen where the biomass thermally breaks down and releases various gases. A gas chromatograph and a CO sensor measure the resulting species concentrations produced from the various biomass samples. The results show that pyrolysis occurs faster at higher temperatures and yields higher concentrations of CO, CO 2, and H 2, as expected. It was found that CO 2 and H 2 production increases with increasing temperature.
Contents 1 Introduction... 4 2 Setup & Materials... 8 3 Results & Discussion... 13 4 Conclusions & Future Work... 18 5 Acknowledgements... 18 6 References... 19
1 Introduction This work explores biomass gasification, which is a process that uses solid or liquid biomass to create energy through incomplete combustion. Since most of the world uses nonrenewable fossil fuels as energy sources focusing research on renewable energy sources is worthwhile. Fossil fuels, such as coal, emit carbon dioxide (CO 2 ) and sulfur (S) into the atmosphere. These gasses and many others released in energy production contribute to global warming and environmental damage. Biomass gasification uses biomass, material from living or recently living organisms, and converts it into carbon monoxide (CO), hydrogen (H 2 ), and methane (CH 4 ) which can later be converted into liquid biofuel through Fischer Tropsch processes or can be used to generate electrical energy. Through biomass gasification the CO 2 originally absorbed by the biomass when grown is released making it a carbon neutral process. A carbon neutral process is one in which no additional carbon is released. Biomass is also a cost effective solution in some applications. There are four main types of biomass gasifiers; they are updraft (counter-flow), downdraft (co-flow), crossdraft, and fluidized bed. They are fundamentally different in the way the air and synthesis gas flow through the system. An updraft gasifier has the air injected at the bottom while the biomass is injected at the top. The gasification products exit through the top. This is called a counter flow because the fuel flows opposite the air. A downdraft gasifier has the air and biomass injected at the top and the products of gasification exit at the bottom. This is called a co-flow gasifier because the air flows in the same direction as the biomass. A cross draft gasifier has air passing through the fuel from side to side. A fluidized bed gasifier has heated air flow up from the bottom suspending the biomass particles which creates fluid-like behavior. Each type of gasifier has different applications, advantages, and disadvantages. Biomass with a
low density should not be used in an updraft gasifier because of the high ash production associated low density biomass (Sadaka, 28). Gasifiers have different zones within them; the zones common to updraft, downdraft, and crossdraft gasifiers are the drying zone, the pyrolysis zone, the reduction zone, and the combustion zone. An updraft gasifier with the gasification zones are shown in Figure 1-1 (Verhoeven, 28). Figure 1-1. Updraft gasifier. The gasifier used in the Combustion Laboratory at the University of Iowa is considered a fluidized bed/updraft gasifier. Heated inert gas, nitrogen, flows up through the biomass which causes it to gasify. The gasifier at the Oakdale Combined Heat and Power Plant is a downdraft gasifier while the gasifier at the University of Iowa Main Power Plant is a fluidized bed gasifier.
The main steps in biomass gasification include preprocessing, gasification, gas clean-up and reforming, and gas utilization (Kumar, 29). The gasification process can further be split into three stages as follows: 1 Pre-heating and drying 2 Pyrolysis 3 Char oxidation and gasification The pyrolysis stage is the main focus of this work. The goal of this work is to characterize the instantaneous gas concentrations. The gas concentrations in particular of CO, CO 2, CH 4, and H 2 were closely examined for different materials such as corn kernels, oat hulls, wet and dry paper sludge, and wood chips at gasification temperatures from 4-55 C. The combustion equation uses a carbon-based fuel reacting with oxygen in the presence of heat to form by-products, as shown in Equation 1.1. (1.1) In the case of biomass gasification, the amount of oxygen present is not enough to fully combust the fuel resulting in different products. The gasification reaction with the biomass fuel in the form of CH x O y N z is shown in Equation 1.2 (Gautam, 29). ( )
( ) (1.2) The temperature ranges are directly related to the chemical reactions that take place. At higher temperatures (6-8 C), Equations 1.3 and 1.4, the rate of steam reforming and dry reforming reactions, respectively, are dominant and increase the production of CO and H 2 whilst breaking down heavy hydrocarbons such as CH 4 and CO 2. (1.3) (1.4) Equations 1.5 and 1.6, the boundary and primary water-gas reactions, contribute to the increase of CO and H2 at higher temperatures. (1.5) (1.6) From the understanding of these previous equations and prior experience it is known that through the pyrolysis process H 2 and CO are produced in higher concentrations at higher temperatures. However, increasing temperature is not the only factor that affects the product gas.
Several other aspects that affect the product gas are equivalence ratio, heating rate, residence time, and biomass type. 2 Setup & Materials i. Materials This work investigated seed corn, wood, and paper sludge. Corn is quite abundant in many Midwestern states and is already being used as a renewable energy source in ethanol. Treated seed corn is considered toxic and must be stored under 18 inches of earth in an isolated area far from water sources (Ohio State University). The corn is considered toxic because pesticides and fungicides are applied to the corn before it is planted. Because of this reason thousands of bushels of corn are wasted every year. If these toxic additives could be removed then this unused corn could be used as a biomass fuel. Extensive research on how to remove these chemicals must be conducted before treated seed corn is a feasible energy source. However, untreated seed corn and corn stover are widely available in Iowa and the Midwest as a biomass source. The paper sludge is a byproduct of Weyerhaeuser out of Cedar Rapids, Iowa. Weyerhaeuser produces the sludge from recycling cardboard and creating cardboard pallets. They are a company focused on green manufacturing of paper related products. Paper sludge contains small strands of paper, sand, and a small amount of a plastic contaminant. Weyerhaeuser creates about 62, tons per year of paper sludge at 5% moisture content. The wood is classified as B12 fine grind wood and has the highest carbon content of all the materials investigated in this work.
By understanding the chemical formulation of the materials it is much easier to predict the volatile products formed by gasification. The ultimate and proximate analysis of the materials can be seen in Table 2-1 and Table 2-2. By examining the ultimate and proximate analysis it can be predicted that higher levels of CO and CO 2 production are the result of using a fuel with higher carbon content. It can also be predicted that the majority of the permanent gasses are a result of high carbon and oxygen in the material. A very small amount of hydrogen is expected since a small amount is present in the fuel. Table 2-1. Material ultimate analysis (Ratner, 212). Seed Corn Wood Paper sludge Moisture 11.59% 1.6% 46.99% Carbon 39.13% 44.32% 22.97% Hydrogen 5.5% 5.23% 2.88% Nitrogen 1.28%.8%.5% Chlorine.4%.1%.1% Sulfur.1%.1%.7% Oxygen 41.53% 39.5% 2% Ash.83%.71% 7.3% Total 1% 1% 1%
Table 2-2. Material proximate analysis (Ratner, 212). Seed Corn Wood Paper Sludge Moisture 12.91% 1.6% 46.99% Volatile Matter 74.42% 77.85% 44.99% Fixed Carbon 7.46% 1.84%.99% Ash 5.21%.71% 7.3% Total 1% 1% 1% HV [BTU/lb] 8,91 7,629 3,556 ii. Experimental Configuration The experimental setup for this work which shows the main components is shown in Figure 2-1 andfigure 2-2. Figure 2-1 is a schematic of the experimental setup which shows the main components such as the industrial heater, torch system, thermocouples, flow controllers, and the gasifier. Figure 2-2 shows a picture of the experimental setup that was used for this work. Important components not seen in the schematic include particulate filter, gas chromatograph, CO sensor, and the working environment. A list of the components in their entirety can be seen in Table 2-3. A torch and an electric heater were used to jointly heat the reaction chamber to the desired temperature. The electric heater heated the system to approximately 25 C and the torch provided additional necessary heating for the reaction chamber. The ratio of O 2 and CH 4 flow rates for the torch was set to approximately 2.5 2.9 to ensure any excess O 2 not burned through combustion can be accounted for.
Figure 2-1. Schematic of experimental setup.
Figure 2-2. Actual experimental setup. Table 2-3. Equipment list. Agilent 49 Micro Gas Chromatograph Biomass Injection Valve Biomass Samples Chromalox Industrial Heater Computer with LabView Computer with ChemStation Exhaust Fan and System Gas Chromatograph Gas sampling bags (1) High Precision Scale High Tempurate Insulation Ice Bath In-line 7 micron filter Equipment List IR CO Sensor Lighter Nitrogen Tank NI USB-9162 DAQ Card Omega FMA-54 Flow Controller Omega FMA-A249 Flow Controller Oxy-acetylene torch Oxygen Tank Particle/moisture Filter Quartz Tube Screen Packet Stainless Steel Mesh Tubing and Fittings Type K Thermocouples (2)
iii. Procedure When the reaction chamber reached the desired temperature the compressed air was shut off and the N 2 was turned on, this was to prevent waste of bottled nitrogen. Then a baseline sample was collected in one gas sampling bag. This was so the nitrogen and oxygen contents can be subtracted and the pure synthesis gas content can be known. The ratio of O 2 to CH 4 for this work was similar for all samples and temperatures. The ratio was approximately 2.9 for 4 C and 2.5 for 55 C. Samples were taken at varying temperatures from 4-55 C for seed corn kernels, wood chips, and dry paper sludge. For each sample a baseline condition was collected in a gas sampling bag so the oxygen and nitrogen content could be examined. Then five gas sampling bags were filled for each biomass sample. These samples were then tested in the GC and analyzed in ChemStation. The data gathered from the GC is compared to the CO sensor s result. 3 Results & Discussion The gas evolution for corn kernels, paper, and wood chips was examined at 4 C and 55 C. It was found that higher temperatures yielded higher amounts of H 2, CO 2, and CO and consumed more O 2, as expected. These trends were more evident at higher temperatures. This phenomenon is explained by Equations 1.5 and 1.6, shown above. The results from the GC are plotted in Figures 3.1-3.6.
Percent Percent Percent Percent Percent Percent Corn 4 C Corn 55 C 8 7 6 5 4 3 2 1 O2 H2 CO CO2 1 2 3 4 5 6 7 8 9 1 GC Run # 16 14 12 1 8 6 4 2 1 2 3 4 5 6 7 8 9 1 11 12 GC Run # O2 H2 CO CO2 Paper 4 C Paper 55 C 7 6 5 4 3 2 1 1 2 3 4 5 6 7 8 GC Run # O2 H2 CO CO2 16 14 12 1 8 6 4 2 1 2 3 4 5 6 7 8 GC Run # O2 H2 CO CO2 Wood 4 C Wood 55 C 8 7 6 5 4 3 2 1 1 2 3 4 5 6 7 8 9 1 GC Run # O2 H2 CO CO2 14 12 1 8 6 4 2 O2 H2 CO 1 2 3 4 5 6 7 8 CO2 9 1 GC Run # Figure 3-1 3.6. Gas evolution for corn kernels at 4 C (upper left), corn kernels at 55 C (upper right), paper sludge at 4 C (middle left), paper sludge at 55 C (middle right), wood chips at 4 C (lower left), wood chips at 55 C (lower right).
As shown in the above figures the gasification experiments performed at higher temperatures yielded clearer trends. Paper sludge and corn at 55 C yielded the highest concentrations of H 2. Paper sludge at 55 C consumed the most oxygen. Corn at 55 C yielded the highest amount of CO 2. The data points in these plots are time averaged because of the synthesis gas being mixed in the gas sampling bags over time. This disrupts the peaks in the data which is why an instantaneous CO sensor was used. Figures 3.7-3.9 show the plots of the CO gas evolution for corn, paper and wood chips.
CO Evolution [g CO/g Paper/s] CO Evolution [g CO/g Wood/s] CO Evolution [g CO/ g Corn /s].1.9.8.7.6.5.4.3.2.1 Corn CO Evolution 4C 55C 5 1 15 Time [sec] Paper CO Evolution Wood CO Evolution.7.6.5.4.3.2.1 4C 55C 5 1 15.2.15.1.5 4C 55C 5 1 15 Time [sec] Time [sec] Figure 3.7-3.9. CO evolution from CO sensor for corn at 4 C and 55 C (uppermost), paper sludge at 4 C and 55 C (lower left), wood chips at 4 C and 55 C (lower right).
Axis Title CO Production [g CO/ g Corn] CO PRoduction [g CO/g Paper] The materials at higher temperatures had CO evolution curves that reached higher maximums but had shorter duration. Corn CO Production Paper CO Production.4.12.3.1.8.2.1 4C 55C.6.4.2 4C 55C 5 1 15 5 1 15 Time [sec] Time [sec] Wood CO Production.3.25.2.15.1.5 5 1 15 Axis Title 4C 55C Figure 3-1-3.12. CO production from CO sensor for corn at 4 C and 55 C (upper left), paper sludge at 4 C and 55 C (upper right), wood chips at 4 C and 55 C (lower). To determine the total CO yield, each fuel and temperature series was integrated to find the total CO production. As shown in the above figures, corn at 4 C yielded the largest CO concentration and paper sludge at 55 C yielded the lowest amount of CO. This was unexpected and could be due to the fact that pyrolysis was slower but more complete. This trend was similar
for paper sludge but not for wood. For both temperatures, 4 C and 55 C, paper sludge produced the smallest amount of total CO. This could be due to the amount of moisture in the paper sludge. This moisture required more energy to dry the fuel therefore less energy dense gas was released. The materials gasified at lower temperatures had longer solid residence times than the higher temperature gasification experiments. When the results from the CO sensor are compared to the results from the GC, it is seen that the data is quite similar and yielded the same trends thus providing further validation for the results. 4 Conclusions & Future Work The goal of this work was to identify the gas evolution of various biomass fuels in a gas chromatograph. The results were validated against a CO sensor which showed similar trends in the data. Corn at 4 C yielded the highest amount of CO, which was unexpected. However, gasifying at higher temperatures produced more H 2 and CO 2 signifying that the higher temperature equations were dominating. Suggested future work includes performing more gasification experiments at higher temperatures to further validate these trends. Gasifying several more local fuels would also be beneficial. 5 Acknowledgements The author would like to thank Yunye Shi, Tejasvi Sharma, and Albert Ratner for their help in the lab.
6 References Gautam G, Adhikari S, Bhavnani S: Estimation of Biomass Synthesis Gas Composition using Equilibrium Modeling. Energy and Fuels 29, 24, 2692-2698. Kumar A, Jones D D, Hanna M A: Thermochemical Biomass Gasification: A Review of the Current Status of the Technology. Energies 29, 2 (3), 556-581. The Ohio State University: Seed Treatment. Bulletin Ratner: Measurement of Biomass Gasification and Combustion Characteristics in an Upgraded Lab- Scale Gasification System. 212 Sadaka S: Pyrolysis Sungrant Bioweb. Sungrant Initive, 15 Nov. 28. Web.