CHE.10 – Turning Manure into Money: Converting Cow Manure into Compressed Natural Gas

• Lila Aryadwita
• Yazeed Kawaleet
• Sarah Pabilic
• Salem Saeed
• Daniel Sendroiu

Animal manure is typically stored in large pits or lagoons on a farm where it will eventually be transported to be further treated to use as fertilizer or bedding. However, manure pits are prone to spills as they are often uncovered and there are many cases where the spills reach water ways. Additionally, since manure pits are uncovered, the manure can decompose and produce hazardous gases such as hydrogen sulfide and methane when left long enough. Along with being a very potent greenhouse gas, methane is also a primary component of natural gas. The largest source of greenhouse emissions is from transportation. To lower greenhouse emissions, biogas can be utilized as it creates a lower carbon emission when burned. As a result, to kill two birds with one stone, our group has developed a process to utilize the excess manure that farms have trouble handling to produce Compressed Natural Gas. Two process pathways were considered to produce methane: thermochemical and biochemical. With thermochemical, gasification of the manure to methanation was considered. Compared to biomass combustion, gasification syngas is economically better, easier to clean, and more environmentally friendly due to the method of carbon dioxide capture. However, gasification can be a high risk, low yield process as many plants have trouble maintaining energy required to remain in business as well as problems with controlling pollution. Through the biochemical pathway, microorganisms break down organic matter into biogas and digestate which can be used in a variety of ways. To reduce the carbon footprint of natural gas, the team has chosen to utilize a biochemical process with the help of methanogenic bacteria that can produce a Renewable Natural Gas alternative (methane) out of consumed manure from Holstein cows. This process will occur in a two-stage linear vortex Plug Flow Reactor (PFR) Anaerobic Digester that is 35.7% efficient at converting the manure to biogas. The influent slurry, consisting of water and manure, enters the reactor at a temperature of 35°C, pressure of 55 bar, and a biome set at a pH of 7. This entire process will have a residence time of 20 days then two exit streams will come out of the reactor. One of the streams is the effluent slurry that wasn’t reacted, which is sent to a separation operating unit that will separate the water from the manure for recycling purposes, leaving the dry manure to be sterilized for bedding purposes. The other exit stream is the raw biogas product which consists of 60% CH₄, 39% CO₂, 0.8% H₂S, and 0.2% H₂O. The biogas then goes through an absorber that utilizes Monoethanolamine (MEA), for absorbing CO₂ and H₂S to separate them from a 90% pure methane stream that is the product. The CO₂, H₂S, and MEA rich stream is then sent to a stripper that extracts the two gases from the MEA for capturing purposes.