Grass Biomass Energy Field Day Proceedings

Transcription

1 Grass Biomass Energy Field Day Proceedings September 13, 2012 Vermont Technical College Randolph Center, VT Sponsors

2 Agenda 9:30-10:00 Registration and Networking (Red School House) 10:00-10:45 Presentations Red School House Conference Room 10:45 11:20 Tour of Frohling pellet boiler/poster sessions 11:20 12:15 Tour of UVM Extension Warm Season Grass Trials 12:15 1:15 Lunch (VTC Cafeteria or on your own) 1:15 2:30 Grass Densification Demonstrations at the VTC Farm 2:30 3:15 Optional follow up and networking opportunities - RSH tour of Frohling boiler - Discussion of business opportunities at RSH - Discussion of VTC Projects and Curricula at RSH - Revisit grass plots 3:30 Adjourn Table of Contents Page Map of Vermont Tech with directions to Plots and Cafeteria 1 Plot Plan of Warm Season Grass Trial 2 Summary of Field Research Projects on Grass Energy in Vermont 3 Pelletizer Interim Assessment Report from Vermont Tech SOAR Program 11 Special Thanks 22 For More information about the Grass Energy Partnership contact: Sid Bosworth, (802) , sid.bosworth@uvm.edu Netaka White, (802) , netaka@vsjf.org Joan Richmond Hall,(802) JRichmond@vtc.vsc.edu A special thank you to U.S. Senators Patrick Leahy and Bernie Sanders and the U.S. Department of Energy for their generous support for ongoing renewable energy research and education. UVM Extension helps individuals and communities put research-based knowledge to work. University of Vermont Extension, and U.S. Department of Agriculture, cooperating, offers education and employment to everyone without regard to race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, and marital or familial status. If you require accommodations to participate in this program, please let Sid Bosworth, (802) , know by Sept. 4, 2012 so we may assist you.

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5 Using Perennial Grasses for Biomass Production in Vermont A Summary of Research Projects on Grass Energy in Vermont Sid Bosworth, Extension Agronomist, University of Vermont In developing the Vermont Grass Energy Partnership, several questions were raised concerning the potential of using perennial grasses for biomass production: What grasses and grass cultivars would work best for grass biomass in Vermont? What are the challenges for establishing these grasses? What are the production and sustainability concerns for managing these grasses? What are the harvest considerations for making biomass from grass? What are the economic considerations for growing, harvesting and processing grasses for biomass energy? What is the environmental impact (air quality) on using perennial grasses as a biomass source for heat energy? Over the past four years, the University of Vermont and UVM Extension has conducted field trials to address some of these questions. Starting in 2009, several field trials were established at various locations in Vermont. The following is a table showing the type of trial, the locations for these trials and the years conducted. Table 1 Title of Each Trial Warm Season Grass Specie and Cultivar Evaluation Cool Season Grass Specie and Cultivar Evaluation Switchgrass Seeding Rate Study Switchgrass Emergence Study Switchgrass Nitrogen Response Study Reed Canarygrass Nitrogen Response Study Years 2009 to to to to to to 2010 # failed due to major weed problems South Burlington Shelburne Locations Randolph Center East Randolph Alburg x x x # x x x x x x x x x 3 of 22

6 In order to summarize results from these trials as well as observations that we have made over the years at these sites and other demonstration sites, I will again address each question one at a time. What grasses and grass cultivars work best for grass biomass in Vermont? Just about any type of plant material can be dried, densified and burned for energy. However, for a particular crop to be sustainable and economical for this purpose, it would need to be productive and persist over a long period. It would also need to meet minimum fuel quality characteristics. The focus of this research is on perennial grasses. They can persist for many years, they generally form a sod that helps to protect the soil from erosion and runoff, they can be very productive, and can be harvested using standard hay equipment that is readily available in Vermont. Up to six warm season grass species were evaluated at one to three locations including switchgrass, big bluestem, indinagrass, giant miscanthus, cordgrass and coastal panicgrass. There has also been four cool season grass species at one location including reed canarygrass, intermediate tall wheatgrass, tall wheatgrass and wild rye. For some of these grasses, several cultivars were also included in the trials. Below are some findings from our studies so far: In the seeding year in 2009 at UVM and Meach Cove Farm, only the switchgrass plots had enough growth at the end of the season to warrant a harvest (Figure 1) Yield at UVM and Meach Cove was quiet low in the seeding year (about 1 to 1.5 tons per acre), probably not enough to offset the cost to harvest (Figure 1). However, seeding year yields were higher at VTC due to excellent weed control and timely rainfall patterns. Even big bluestem and coastal panicgrass had yields over on ton per acre (Data not shown). Yields improved each year with the highest in the third and latest year of collecting data (Figure 1). There will be at least one more year to collect yield data. Of the switchgrass cultivars, Cave-N-Rock and Shawnee have been the most productive in biomass yield across all locations (Table 2 and Table 3). Kanlow, a lowland cultivar, has done well at UVM but poorly at the other two sites. Blackwell has done well at VTC, its only location. Sunburst yields less and consistently shows more leaf diseases. Bowmaster was killed out the first winter. Of the other grass species, Prairieview big bluestem has yielded well at the two locations where it is located. Niagara big bluestem has had moderate yields. The other grass species have not yielded as well. Ash content varied by location reflecting both soil fertility levels and water availability (Tables 2 and 3). Generally, the big bluestem cultivars were consistently lower in ash content than the switchgrass cultivars (Tables 2 and 3). 4 of 22

7 Figure 1. Biomass yield of switchgrass cultivars in the first three years of the stand. The first year is the seeding year (2009 at UVM and Meach Cove and 2010 at VTC). All harvests were made in October of each year. 5 of 22

8 Table 2. Average yields and ash content of three year old stands of warm season grasses plus reed canarygrass harvested in Table 3. Average yields and ash content of two year old stands of warm season grasses in Randolph Center (VTC Farm) harvested in of 22

9 Results so far (continued): Cordgrass also had very low ash content but yields are fairly low (Table 3). Lodging can be a problem. It seems to be worse with certain species particularly big bluestem and cordgrass (data not shown). Stand persistence is an issue considering long term sustainability. The most obvious treatment was Bowmaster switchgrass with died out the first winter. Another switchgrass cultivar that has been inconsistent across locations is Kanlow and the indiangrass cultivar has been inconsistent. Giant miscanthus, which had to be planted by rhizome cuttings since the seed is sterile, had winter kill of some of the plants especially at VTC and Shelburne. Its yield has varied greatly across locations (Table 2 and 3) and needs several more years of evaluation before being considered as a viable option in Vermont. One consideration would be to formulate polyculture mixtures of various species. Most compatible would be switchgrass with big bluestem and indiangrass. This would help spread the risk of failure due to some climatic or soil condition The polyculture mix in these trials were a mixture of Cave-N-Rock switchgrass and either Prairieview or Niagara big bluestem. This combination works well with the higher yields from the switchgrass and the lower ash content of the big bluestem (Tables 2 and 3). Cool season grasses yields have not been as good as some of the warm season grasses and their ash content is fairly high. There is also a lodging problem with many of the wheatgrasses and, other than reed canarygrass, their stands appeared to have declined by 2012 (Table 4). Table 4. Biomass yield, ash content and lodging of cool season grasses harvested in 2010 and 1022 in South Burlington. Planted on 8/18/2009. Adams sandy loam soil. 7 of 22

10 What are the challenges for establishing biomass grasses? Many of the warm season grass species are very slow to establish. Their seed has innate dormancy mechanisms which can delay germination by many months and once germinated the seedlings are relatively slow to grow. Weed control is very critical since these grass seedlings are not very competitive. We conducted two different studies at two locations to assess the optimum seeding rate. The following is a summary of the findings from both the trials and field observations in establishing these grasses. A seeding rate of 8 to 10 pounds per acre of switchgrass (accounting for both % germination and % dormant seed found on the seed tag) seems adequate to achieve a productive stand (Table 5). Purchase seed that has a high germination and low dormancy if possible. Seed that is treated with fungicides can also help prevent seedling diseases. Seed should not be planted until the soil is warm enough to promote quick germination. This is usually within the first two weeks of June in Vermont. It is best to plant in a field with low weed pressures, particularly summer annual grasses like crabgrass or foxtails. To manage weeds, a stale seedbed approach can work affectively if weather allows. The field should be prepared one month to six weeks before planting and allowed to have a couple of weed flushes before planting. Emerging weed seedlings can be killed with blind cultivation using a flex tine weeder Set the tines for shallow tillage to avoid bringing up more weed seed form lower soil depths. The flush of weeds can also be killed with a herbicide like glyphosate before the warm season grass is planted. In this situation, the weeds should be allowed to emerge and grow some before spraying in order to get adequate foliage coverage. For fields with a history of heavy weed pressures, it may be best to rotate the field for a year or more with an annual forage crop such as sorghum-sudangrass that affectively suppresses weed emergence and growth. This can help reduce the weed seed bank before establishing the warm season grass. Table 5. Biomass, tiller population and tiller weight of four switchgrass cultivars harvested in autumn of 2010 from plots seeded at four different seeding rates in of 22

11 What are the production and sustainability concerns for managing these grasses? Once established, the major factors that will affect the life of the stand and sustained productivity include fertility management, weed control, diseases, and cutting management. Much research has shown that cool season grasses respond to nitrogen (N) fertilizer when managed for hay; however, less is known when managed for biomass. Nitrogen response trials were conducted on established stands of reed canarygrass ( Palaton ) and switchgrass ( Cave-N-Rock ) over a two to three year period to assess biomass productivity. The following is a summary of the findings for both grass trials and our observations in maintaining established stands. Summary of Reed Canarygrass N Response Trials: In a two year study, reed canarygrass did have a positive yield response to additional N fertilizer with the response being similar in both years. (Table 6) Linear regression analysis indicates that the optimum N application rate would be about 75 lbs. of N per acre (applied just as the grass is starting to grow in mid spring). There was visually significantly more lodging in the high nitrogen plots; however, the degree of lodging was mild enough that a normal mower or mower/conditioner should have been able to efficiently handle it if this had been a production field. Ash content as well as P and K content were lower with increased N fertilization rates which is desirable from a fuel quality perspective. Removal rates of P were about the same regardless of N fertilization; however, K removal was highest with the 100 lb./acre N rate. At 70 lbs of K removed per year, a producer would most likely need to supplement with either fertilizer or manure to sustain the field over a long period of time. Summary of Switchgrass N Response Trials This study was initiated on a four year old stand of Cave-In-Rock switchgrass located at the Borderview Farm in Alburgh, VT. In the first year, there was no difference in yield amongst the N treatments (Table 7). Switchgrass is very efficient at utilizing N from the soil. Studies in New York have found similar results in which switchgrass showed no response to additional N in the first four years of their study. However, by the next year, there was a significant response to N when treatments were applied to the same plots. There was visually significantly more lodging in the high nitrogen plots in the first year but not to the point of being a mowing problem (Table7). Ash content was not affected by N treatment (Table7). Neither phosphorus nor potassium levels were affected by nitrogen fertilizer applications at the rates applied (Table 8). With their low P content, there was relatively little of this mineral removed. However, the average removal of potassium was a little over 40 lbs. of K per acre. So, over a period of a few years, a producer would need to replace this K with either fertilizer or manure. 9 of 22

12 Table 6. Biomass yields, lodging, ash content and mineral removal of a four year old stand of Palaton reed canarygrass harvested August 27, Table 7. Biomass yields, lodging, and ash content of a four and five year old stand of Cave-N- Rock switchgrass in Alburg, VT. Treatments were repeated on same plots. Table 8. Biomass mineral content and removal of a four year old stand of Cave-N-Rock switchgrass harvested October 28, 2010 in Alburg, VT 10 of 22

13 Pelletizer Interim Assessment A Report by the 2012 SOAR Interns: Adam Sprague Ben Cayer Blaine Conner Cole Predom James Blakely June of 22

14 Pelletizer Interim Assessment 24 July 2012 GOALS Vermont Tech sought to identify the process parameters of making biomass fuel pellets with a small-scale pellet mill. The 2012 SOAR team developed operational procedures needed to produce pellets with the Buskirk pellet mill and conducted pellet production experiments modifying the speed of the pellet die, feedstock type, and moisture content, mass flow rate of input material, and additives. Figure 1: Ben and Blaine running the Pelletizer. The 55HP Tractor was generously supplied by Roger Howes. RESEARCH We began research by conducting an internet search on biomass pellets. We found various sources suggesting that moisture content and lignin content of the feedstock have the most impact on biomass pellet quality (Pelheat.com and Biomass Energy Resource Center). Lignin is a naturally occurring chemical compound that acts as a binding agent when heated in the pelletizing process. It is general knowledge that attempts to make 100 percent grass pellets were typically unsuccessful because of low lignin content. The moisture content of the feedstock governs the ability of the pellet mill to melt the lignin and glassify the exterior of the pellet. If the moisture content is too high, the pellet mill is unable to evaporate the moisture and pellets are not produced. Too low, the heat transfer rate from the pellet mill die to the feedstock drops and the feedstock exits the mill as dust rather than cohesive pellets. Next we began research on the pellet mill itself. Using U.S. Department of Energy funds obtained with the help of Vermont Senator Bernie Sanders, Vermont Tech purchased a turn-key system manufactured by Buskirk Engineering of Ossian, IN. This system includes a hammer mill, blower, surge tank, pellet mill, water pump and cooling conveyor, all mounted on a 5 x 10 steel base. We mounted this self-contained system on a 7 x 16 trailer. Though the system was advertised as turnkey it was clear that this machine was complex and that a thorough investigation of the operating parameters was necessary before any laboratory experiments could be conducted. First, we analyzed each component of the system and became familiar its individual operating parameters. Documentation included with the system was sparse and required us to look up specific information from the manufacturer of each specific part or device. Once we understood how each component worked, we were able to look at the system as a whole and start developing operating procedures and key parameters. Summer of Applied Research July 2012 Page 4 of of 22

15 Pelletizer Interim Assessment 24 July 2012 COMMERCIAL PELLET MILL TOUR We were fortunate enough to take a tour of Vermont Wood Pellet Company in North Clarendon, Vermont on May 23. Although our pellet mill is much smaller than theirs, our Buskirk system replicated every step and process of their larger mill. Brian Pinsonault the maintenance manager reiterated the fact that lignin and moisture content of feedstock are major factors in the pellet making process. He also said that the type and depth of your die can be a factor in production. Vermont Wood Pellet uses a vertical-ring die where the rollers roll on the inside of the ring. Our system has a horizontal die in which the rollers rotate on top and force the material down through the die. The tour gave us firsthand knowledge about the process of making a wood pellet, and we were able to apply this knowledge directly to our own system. SAFETY As delivered, the pellet mill did not have all of the safety equipment in place that we felt Figure 1: Top view of Safety Platform with tractor on the right and trailer and pelletizer w/ safety deck on left is necessary. The biggest risk we identified with this pellet mill was the PTO (power take off) driven portion of the machine. We determined that a safety platform would need to be built to keep operator away from the PTO shaft. The safety platform also includes handrails and is only accessible from the left side of the trailer. The safety platform allows the person operating the electrical panel to oversee the entire machine during production and react quickly to any issues that may arise. The tractor cannot be operated from the safety platform; however an emergency cord was run from the fuel shutoff on the tractor to the platform so if a problem arises the tractor and PTO can be shut down quickly from the safety platform. Two or three people can observe the pellet mill during production from the platform. Figure 1 shows the safety platform as-built drawings. During production, eye and hearing protection are a must. We used clear safety glasses to protect our eyes. The hammer mill poses the greatest risk for eye injuries because when feedstock is fed into the Figure 3: Operation of hammer Summer of Applied Research July 2012 Page 5 of of 22

16 Pelletizer Interim Assessment 24 July 2012 mill, the machine tends to kick some particles back out through the hopper. The tractor, pellet mill, hammer mill and blower are the loudest components of the system and require hearing protection when they are running. During production runs, we used over-the-ear hearing protection with an NRR of 29. General-purpose nuisance dust masks are strongly recommended. We used leather safety gloves to protect our hands when feeding material into the hammer mill as seen in figure 2. INITIAL COMPONENT TESTING The primary focus of the first rounds of testing was to familiarize ourselves with the operation of the turn-key pellet mill. Though the manufacturer provided some specifications about the machine and its capacities, it was necessary to confirm these specifications and determine if correction factors needed to be included in any of our pre-production calculations. UNIVERSAL FRICTION CLUTCH The manufacture did not provide method of separating the pellet mill from the tractor. For safety purposes we installed a universal friction clutch (slip clutch) on the pellet mill side of the PTO. The slip clutch (Figure 4) protects the tractor and the machine in the event of the mill rollers locking. If the pellet mill locks, the torque spikes and the tractor slips the friction clutch, and the pellet mill isolates from the tractor. If the slip clutch was not in place, the tractor could shear the pellet mill shaft or break the PTO transmission. We adjusted the clutch springs to allow the clutch to spin during a lock up situation but hold during normal operation. Figure 4: Universal Slip Clutch HAMMER MILL The Hammer Mill utilizes a single phase VFD controlled 10 HP motor that spins a series of beater arms or knives at 3600 RPM. These beater arms are encircled by an 18 circular screen with perforations of a material specific size. Material is inputted through a Plexiglas hopper that incorporates a plate magnet to catch any metals that may be in the mix. The material is hammered with the beater arms against the circular screen which reduces the input material to the size of the perforations. The reduced material is then Figure 5: Inside hammer mill Summer of Applied Research July 2012 Page 6 of of 22

17 Pelletizer Interim Assessment 24 July 2012 transferred from the Hammer Mill to the Surge Tank via a pneumatic air system that draws the processed material from the bottom of the metal cabinet towards the front of the pelletizer unit. The air system draws air from both the hopper intake and a 4 drilled plate, and other parts of the pelletizer unit. FEED AUGER RATE The feed auger moves the feedstock from the surge tank through screw action into the pellet mill. It is electronically controlled by a variable frequency drive (VFD) connected to a Human Interface Module (HIM) located on the main power enclosure. The feed auger frequency, in hertz, is displayed on the HIM. The HIM allowed for on-the-fly adjustment of frequency, which in turn changed the speed of the auger motor. However, the module does not display the mass flow rate of the material being moved. Figure 6: Measuring Flow Rate During the initial testing of this component we realized that we needed to know delivery rate (mass flow rate) of the auger at different frequencies. It was important to determine this mass flow rate because we need to know how many gallons of water per unit Sample Moisture Content (%) Hertz Mass Flow Rate (lbs/hr) Farm Sawdust Farm Sawdust Farm Sawdust Farm Sawdust Farm Sawdust Kiln-Dried Shavings Kiln-Dried Shavings Kiln-Dried Shavings Table 1: Mass Flow Rate Results for the Farm Sawdust Figure 7: Surge mixers in surge tank time needed to be added to the feedstock mix to bring it up to the optimum moisture content for pellet production. To determine the mass flow rate of the auger at different motor speeds we collected several samples at various feed auger motor speeds and recorded the amount of time needed to deliver a specific volume. Figure 4 shows the feed auger and one gallon bucket used. These measurements allowed us to calculate a volume per unit time, or mass flow rate. It should be noted that the Summer of Applied Research July 2012 Page 7 of of 22

18 Pelletizer Interim Assessment 24 July 2012 mass flow rate is dependent on the density of the feedstock and its moisture content. These rates are only applicable for the materials tested and must be determined for any feedstock used to make pellets. WATER PUMP FLOW RATE The second parameter tested was the water pump flow rate metered by a King C-04 inline flow gauge measures in gallons per hour (GPH). As described on the manufacture s website, the meter has an accuracy of ±6% of full scale flow, or ±.72 GPH. We repeated the method used to determine the auger mass flow rate and found that the gauge was inaccurate and required a correction factor. Table II shows the percent error of the meter at different gauge readings with an average error of 25%. Gauge Reading (gal/hr) Actual Output (gal/hr) Percent Error % % % % % % % % Table 2: Water Meter Actual Output COOLING CONVEYOR The Buskirk pellet mill has a cooling conveyor that is used to cool down the hot pellets coming out of the die and to suck out the fines that made it through the pellet mill (Figure 9). The blower that is hooked up to the conveyor sucks out the fines to be reused in the surge tank. The fines become very dry after exiting the die and are blown back into the surge tank; this caused some problems with our moisture content. We also noticed that the pellets were coming out warm even after Figure 9: Cooling Conveyor exiting the conveyor. We decided to slow down Figure 8: Pellets entering Cooling Conveyor the cooling conveyor speed from 60 Hz to 30 Hz to give the pellets more time to cool and more time for the fines to be removed. Summer of Applied Research July 2012 Page 8 of of 22

19 Pelletizer Interim Assessment 24 July 2012 DIE THERMOCOUPLE Buskirk Engineering specified a normal operating temperature for the pellet mill die of between degrees F. Buskirk did not provide a method of measuring this temperature so we installed a thermocouple to one of the mounting Figure 10: Thermocouple Lead bolts on the die. This thermocouple is attached to a multi meter that displays the temperature of the die. We mounted the multi-meter next to all of our other controls and included the die temperature in the data collected during a production run (Figures 10 & 11). We found that a die temperature of ±170 F contributed to a durable pellet. Figure 11: Black Bolt where Thermocouple is Mounted Moisture Analysis & Feedstock Before we started to make pellets we needed to identify a good test feedstock that would allow us to determine optimal moisture content for pellet production. Our research told us that lignin holds the pellets together and is a chemical compound of wood and found in plants and algae. We had a few materials like feedstock from the farm and commercial bedding sawdust which were easy to get. Samples before pelletizing Moisture Content Dry sawdust from the farm 19.47% Wet sawdust from the farm 46.70% Pre-hammer mill Control sample 48.10% Post hammer mill sample 41.70% Central Supply Commercial bedding sawdust 9.70% Round bale of switch grass 13.50% 50/50 mix switch grass and sawdust 25.80% We used an oven and electronic Table 3: Feedstock Moisture Contents balance to determine the actual moisture content, and then we tried to duplicate those results using a microwave. We concluded that the tests were very similar and that we could use the microwave oven, saving time while completing our moisture testing. The first material that we tested was sawdust from the Vermont Tech farm which is used for bedding. The sawdust appeared very moist in the middle of the pile and drier on the outside so we Summer of Applied Research July 2012 Page 9 of of 22

20 Pelletizer Interim Assessment 24 July 2012 decided to take samples from each part of the pile for testing. We found that the average dry sawdust moisture content was about 19.47% and the wet sample had about 46.7% moisture. Both values seemed relatively high given that we a wanted a moisture content of 10%-15% going into the die to produce good pellets. We then decided to test moisture content after the sawdust was processed through the hammer mill and blown into the surge tank. We found the sample to be about 7% drier after going through the Hammer Mill. This meant that we would have a lower moisture content going into the die, but that moisture content would still be high enough so that no water would need to be added. The next material we tested was commercial bedding sawdust from Central Supply; a much drier material. We tested the moisture content of the bedding sawdust and found it to be about 9.7%. Because this material was drier, we needed to add water to bring it up to a moisture content of about 15% for production. Our third biomass sample was switchgrass. Switchgrass is native to the United States and has a lower ash content than other grasses which makes it a promising biomass crop. Switchgrass, as a C4 species, has greater photosynthetic, water and N use efficiencies compared to C3 species. (Jerry H. Cherney) Switch grass has high productivity, high moisture content and nutrient use efficiency that adapts to marginal soils. The switchgrass we used came from one of Sid Bosworth s test fields in Shelburne Vermont. We used a bale chopper to chop the grass into smaller pieces for the hammer mill. We found that the moisture content of the switchgrass was about 13.50%. PELLETIZING TRIALS & RESULTS In order to learn about this system and see how it actually worked we ran it several times and focused more on our safety and getting used to running it than on pellet production. We couldn t see the sense in doing experiments with this system before we could run it in a somewhat flawless way. In these first trial runs we had some success, and after running the machine several times we had a system down, but the production rate and pellet quality was poor. We consulted with Buskirk and they suggested that we adjust the distance between the rollers and the pellet Figure 12: Inside the Pellet Mill die. Buskirk said that the rollers in the pellet mill could be spaced too far away from the die, therefore not making enough contact to push the material through the die. We tightened the large bolt on top of the roller shaft that you can see in Figure 11. We immediately saw improvements in our next experiment, when we were able to make some pellets out of Pine shavings from our local supply store. We noticed that the pellet production rate Summer of Applied Research July 2012 Page 10 of of 22

21 Pelletizer Interim Assessment 24 July 2012 was much faster. This small adjustment made the pellet mill work the way that it is supposed to. For two days we experimented with the commercial feedstock from the supply store and the sawdust that the college farm uses for bedding. We were able to make consistently good pellets by dialing in the right amount of water, feeding the stock into the mill at the right rate and monitoring the speed of the PTO. Moisture content and relative humidity seem to be the factors with the most influence on our pellet production rate. Our data demonstrates that humidity does not affect the pellet quality, but they significantly lower the rate of pellet production. In one of our experiments, relative humidity was low and we had great quality pellets out of feedstock that had a moisture content of 46%. We saw that the pellet mill would go through a cycle when we were making these pellets. This was a lag period which would spin for about 10 seconds without pushing pellets out, and then send them out for about 4-5 seconds. We came to the conclusion that as the feedstock material sat and the rollers continued to spin, the feedstock was losing a large amount of the moisture, until it was at an optimum moisture Moisture Content Moisture Cont. Feedstock (%) Moisture Cont. Finished Pellet (%) Graph 1: Moisture Content of Feedstock and Finished Pellets content that would allow for pellet production. In fact, the process was evaporating roughly 40% of the moisture, because the finished pellets from those experiments consisted of 6-7% moisture. The optimal temperature has been anywhere between F. Once we achieved some success with wood feedstock, we moved on to switchgrass. We used a bale chopper to roughly chop up about half of a round bale of switchgrass that was grown on the college farm last year. We were finally ready to start making pellets with grass. We didn t want to start with 100% grass because we had read about how challenging grass pellets could be, so we started with a 50/50 (w/w) mixture of wood sawdust from the farm, and switchgrass, Panicum virgatum. We mixed the two together and ran the mixture through the hammer mill and into the surge tank. We knew the moisture content of the wood and the switchgrass, but wanted to confirm that addition of water was not needed. The moisture content of the wood/grass mixture was 25.8%, so we proceeded to make pellets without additional water. We used old pellets to warm up the die to about 165 F. We fed the wood/ grass mix in at 40 Hz and immediately pellets started coming out at a very fast rate. The temperature climbed into the F range, and we continued the pellet making process for Summer of Applied Research July 2012 Page 11 of of 22

22 Pelletizer Interim Assessment 24 July 2012 about an hour until we ran out of material. This mix of grass and wood made a very durable pellet at an increased production rate. There was no lag time as there had been with the wood feedstock. Our next step was to try a mix that was 75% grass / 25% wood. We created the mixture as described above, with the moisture content of the mixture being 20.5%. We fed the 75 / 25 mixture into the pellet mill at 40Hz, when the die was about 160 F. Pellets began forming soon after we started the feed auger. The pellets were not the quality of the ones that we made in the previous experiment, but they were not the worst pellets we had made either. We saw some signs of insufficient lignin in this mixture, as some of the pellets began to fall apart as they cooled. The final experiment of our three-week pelletizing project was to make 100% grass pellets. We knew that we would have to add a small amount of water because the moisture content of the switchgrass was 13.8%. We started the process when the die was about 160 F, and did not add water. The initial result without addition of water was that the pellet mill was pushing out fines, but no pellets. We started to add water, and nothing seemed to happen. We then added vegetable oil, which acts as binder. We added small amounts of the oil and began to make pellets. We kept adding about 2 gallons per hour of water, and stopped adding the oil, and the mill continued to make pellets for the remainder of the batch. We think that the oil helped bind the grass long enough to plug the holes in the die and slow down the material as it passed through the die. We did a standard PFI (Pellet Fuel Institute) durability test on all of the pellets we had produced. All pellets passed the durability test, in which means they are placed in the durability testing apparatus for 10 min at 50 RPM (See Figure 13). We determined the mass of pellets after removing fines in a 1/8 sieve before and after durability testing. If the Pellet Durability Index number is above 96.5 then the pellets are considered premium grade, and all of our pellets were graded as premium. PDI Pellet Durability Index Figure 13: Pellet Durability Tester Graph 2: Heat Content of Pellets Summer of Applied Research July 2012 Page 12 of of 22

23 Pelletizer Interim Assessment 24 July 2012 NEXT STEPS The SOAR research funded by this grant identified the operating parameters of the pelletizing process for this PTO and electricity powered Buskirk mill. Our results are promising, but more work needs to be done to further define the factors required for successful processing and to develop a recipe for pelletizing success. First, we need to determine what blends of wood and grass produce a durable pellet, and what additives, if any, could be introduced to create a stronger pellet. Alongside this, we should develop a reliable method to quickly determine the moisture content of the feedstock. The microwave test worked well but still took about 30 minutes to test the feedstock so we had to wait on production until the test was complete. Secondly we have only been able to consistently produce pellets at about 60 lbs/hr, though the Buskirk system is said to be capable of producing 800 lbs/hr. A next step would include identifying the characteristics that constrain pellet production rate. Preliminary testing shows a strong correlation between moisture content and production rate. BTU/lb BTU Comparison of Finished Pellets Graph 3: Heat content of finished pellets Lastly we will continue to test these pellets for their heat content with the Parr 1341 Bomb Calorimeter. The standard operating procedures for the bomb calorimeter are attached in the appendix section of this report. Graph 3 shows that our grass pellets have slightly lower heat content than wood ones. These results are approximate, because we were only able to test 1-2 samples of each type of pellet. As we do more tests we will be able to compare different types of feedstock and different pellets. Taking these steps will allow us to more clearly refine the pellet production process. Wood and grass blends could help create a niche market for these types of pellets. Further research into increasing production rates could make this particular unit feasible as a mobile pellet production facility. If production could be increased with this unit, it could be used similar to the way that some people use mobile sawmills. Someone could have some land that they are logging off, and rather than sell the logs they could have you come in with a pellet mill and means of chipping up the logs and make pellets for them for their home. Summer of Applied Research July 2012 Page 13 of of 22

24 A special thanks to the many collaborators and advisors in this project: John Abley, owner, Meach Cove Farm Trust, Shelburne, VT Chris Davis, manager, Meach Cove Farm Trust, Shelburne, VT Roger Rainville, Borderview Farm, Alburgh, VT Sam Lincoln, Lincoln AgriSource LLC, Randolph Center, VT Sosten Lungu, Vermont Technical College, Randolph Center, VT Paul Salon, USDA-NRCS Plant Materials Station, Corning, NY Jerry Cherney, Extension Forage Specialist, Cornell University 22 of 22