Final Report: Converting Campus Waste Streams into Locally Used Energy Products through Steam Hydrogasification and Methane ReformationEPA Grant Number: SU834709
Title: Converting Campus Waste Streams into Locally Used Energy Products through Steam Hydrogasification and Methane Reformation
Investigators: Norbeck, Joseph , Bagtang, Michael , Brendecke, Phillip , Duchon, Alex , Duchon, Douglas , Park, Chan Seung , Pichette, Joseph , Stasiuk, Stephanie , Tam, Kawai
Institution: University of California - Riverside
EPA Project Officer: Nolt-Helms, Cynthia
Project Period: August 15, 2010 through August 14, 2011
Project Amount: $9,999
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2010) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Energy , P3 Challenge Area - Materials & Chemicals , P3 Awards , Sustainability
All University of California campuses have been mandated to divert campus waste from landfills, and must meet certain requirements: 75% diversion must be accomplished by 2012, with full diversion by 2020. Ultimately, the University of California is trying to create a zero-waste campus system. The process used in the proposed project will not only help create a zero-waste campus and a sustainable source of energy, but it also has the potential to eliminate the necessity of landfills and other waste-treating facilities. In an effort to help meet these requirements, the team investigated the potential of steam hydrogasification (SHG) to convert campus carbonaceous waste (agricultural, paper, and food) into fuel. The waste-to-fuel transformation includes three main reaction steps: SHG, steam methane reformation (SMR), and the Fischer-Tropsch (FT) reaction. The product gases from the steam hydrogasification reactor (SHR) (CH4, CO, CO2) are further reacted in SMR to form syngas (CO and H2). Syngas is then reacted in the Fischer-Tropsch reactor to form longer chain hydrocarbons, which are characterized in terms of volume and composition. The obtained data was used in simulation and economic analysis programs, such as Aspen, to determine the potential yield of biodiesel and the economic feasibility of the project. Since extensive research has already been done on the last two stages of the process, the proposed project will primarily focus was on the SHR and the constituents going into, and out of, this reactor. Thus, testing focuses on the characterization of the SHR with a complex feedstock representative of campus waste. Pine wood is used to simulate agricultural waste, paper to simulate paper waste, and Gerber baby food to simulate food waste.
In particular, three important questions are addressed in the work:
- Given the agricultural, paper, and food feedstock supplied to the SHG, what would be the profile of gases coming out?
- How much carbon would be converted to gases?
- Could the process be done in the same reactor, with similar H2O:C ratios, similar H2:C ratios, and the same testing parameters (temperature, pressure, duration) as done before with conventional feedstocks (wood and coal)?
At a temperature of 800°C, a water to carbon ratio of 2:1, and a hydrogen to carbon ratio of 1:1, each of the feedstocks was individually reacted in the SHR for thirty minutes. A commingled waste of paper, wood, and baby food in a ratio of 40:45:15, respectively, to match the campus waste profile, was also tested. Experiments were run in triplicate at each condition. The output of the reactor was fed into a mass spectrometer to determine the gas profile in terms of the composition of the major products. The major products were CH4, CO, and CO2, and their respective ratios for each test in weight percent are as follows: 40:28:32 for paper only, 58:17:25 for wood only, 65:14:21 for baby food only, and 54:19:27 for the mixture. Additionally, the carbon conversion for the wood and paper feedstock was about 85%, while the commingled feedstock had a carbon conversion of about 75%. The carbon conversion data for baby food was variable and difficult to quantify due to the resultant viscous nature of the baby food after SHG. At the bench-scale, the sensitivity of the measurement technique for the carbon conversion calculation was not suitable for a viscous product. Using Aspen modeling and previously collected data to simulate the final Fischer-Tropsch reactor, the final yield of energy products in weight percent is as follows: diesel (C9-C21) comprised 26%, (C5-C8) comprised 9%, volatiles (C1-C4) comprised 38% and waxes (C22+) comprised 26%. Given an input of 3.5 dry tons of waste per day there is an output of 386 gallons per day. At this capacity and based on findings obtained from the bench-scale, the economic analysis indicated an unattractive payback period of 24 years. However, with economies of scale, this could be greatly improved by rising diesel prices and an increase in waste input. Through a sensitivity analysis, a 2.74 factor increase in waste conversion rate (tons/year) or if diesel prices rise to a likely value of $5 per gallon, the payback period could be reduced further to 10 years. More accurate kinetic data obtained from a pilot scale study would be beneficial in the economic analyses as proposed in Phase II.
For the first time, commingled wastes representative of a typical college campus have been steam hydrogasified using the patented CE-CERT process. The results show successful conversion. Each of the different tests showed that CH4 dominates the output gas profile, which also contained CO and CO2. The commingled feedstock produced a gas profile that appears to be midrange on the spectrum of individually reacted feedstocks. The conversions of 85% for the paper/wood test and 75% for the commingled test showed that a significant amount of carbon was converted from waste to gas for use as energy, while the error in baby food testing is expected to lessen as the scale of the project is increased and equipment modifications are made. Improved sorting methods, increased encatchment radii for waste feedstock, and soaring diesel prices would improve the economics of the process and contribute towards waste reduction to landfills, as well as a cleaner environment.