The Rotary Compression Unit’s Usage In Anaerobic Digestion And Animal Wastes

The Rotary Compression Unit’s Usage In Anaerobic Digestion And Animal Wastes

Prepared by: Nancy Heimann

Enginuity Worldwide LLC scientists and engineers have invented a cost-effective process to upgrade annually renewable biomass feedstock and waste materials into either an engineered, energy-dense solid fuel for use in power generation facilities, a biochar for soil remediation, or a slow release fertilizer to be stored or transported before usage. Enginuity’s targeted biomass feedstock supply includes, but is not limited to, excess agricultural residues (corn stover or wheat straw), grasses from non-forage acreage (USDA designated CRP/WRP), purpose grown energy crops; consumer wastes including used pallets, coffee grounds, cellulosic wastes, food waste, food processing by-products and other landfill bound organic material and forest products including woody-waste, invasive and diseased wood. Fertilizer in this case is referred to as the processing of any manure-based or Anaerobic Digestion waste stream by the novel technology at less extreme conditions thus producing a fertilizer source that can easily be densified into those shapes named previously, stored in a long term manner with no microbial growth, or transported easily as the result of a much higher bulk density. These materials can include poultry litter, poultry manure, and Anaerobic Digestate.

The Enginuity facility is located at the Missouri Plant Science Center (MSPC) in Mexico, Missouri and has pilot fuel production capacity of 1-5 tons per hour. Enginuity’s engineered solid biomass fuel product formulated from US Midwestern grown agricultural wastes is known as eCARB™ (Environmentally Continuous Annually Renewable Biomass) fuel. This facility is currently producing engineered biomass solid eCARB™ fuel for performance and emissions evaluations. By using engineered biomass solid fuel in co-firing, the technology may bring new life to legacy coal fired power generation facilities for US GHG compliance and sustainable energy independence. Though the technology is currently used in the production of this eCARB™ material, the technology has been found to have many more applications that result in value added products other than those associated with the fuel industry. These applications include, but are not limited to, fertilizer production, biochar production, grain applications, and cellulosic ethanol applications. The highlighted technology is unique in that it produces a wide variety of products from an even wider variety of biomass sources.

The Enginuity technology provides a solution for many commonly acknowledged biomass issues including low bulk density, heterogeneity of materials, high and sometimes variable levels of moisture, handling logistics, and storage/flowability issues. The result of using Enginuity technology to process diverse biomass feedstocks is a fertilizer, soil remediater, or a solid engineered biofuel that is homogenous in nature, highly durable, high in bulk density, and ideal for long term storage or transport. Enginuity is focused on accessing best-in-world biomass resources to create new sources for biopower generation and agricultural fertilizers/soil remediating agents. From Canada to the Gulf of Mexico there exists a biomass corridor in America’s heartland that can produce and deliver these value added products and fuel sources.

Impending regulations are changing the way that waste streams such as poultry litter or Anaerobic Digestate may be used in agriculture. Traditional methods of disposing of this waste stream involves application on the field as a fertilizer or composting the waste stream. Application to the field is oftentimes in excess of the level of benefit as the result of poor transportation and storage capabilities of the materials. These shortcomings leave producers with no choice but local application to the field resulting in high levels of contamination in the form of runoff into water sources surrounding agricultural districts. Contaminants can include bacteria, nitrates, ammonia, and nutrients. High levels of nitrates have been shown to cause an increase in Blue Baby Syndrome as well as increases in certain cancers, respiratory illness, and livestock illness. High levels of other nutrients as well as off gassing of ammonia can lead to eutrophication of waters and contamination. In the interest of keeping shared waterways clean and uncontaminated, it is becoming increasingly important to mitigate these waste streams and provide alternative methods of disposal from the sources.


The drying of biomass requires an energy input to facilitate the process. Conventional dryers utilize a broad spectrum of fuels available to produce heat, even burning a portion of the biomass for energy. These methods drive off unbound moisture by creating a temperature-induced differential in vapor pressure, a simple process practiced for decades.
A novel process has emerged recently not requiring combustion of external fuel to produce heat as in conventional dryers. The process requires no external heat or steam source to treat material, only energy to power a motor. A Rotary Compression Unit, utilizing both friction and compression, generates steam from not only unbound water but also bound or cellular water to upgrade biomass. Since the machine can readily manage processing both below and above the autoignition temperature it can produce dried material or biochar readily, and may also be used to produce a form of “bio-coal”. The process converts biomass feedstock into engineered and upgraded biomass materials that are storage ready with a high heating value and energy density. These engineered biomass materials exhibit increased bulk density, and may also be densified to produce fuels (pellets, briquettes, or compacts) that are very dense, durable, and transportable. When engineered to fit the needs of the coal-fired power plant, these fuels have great potential as an effective alternative to coal that requires no changes in handling or combustion procedures/equipment.

Thermodynamics is the branch of Physics that deals with the relationship between all forms of energy. One aspect of the Second Law of Thermodynamics, simply stated in the work of Carnot, teaches “work equals heat”. Based on that principle, the Rotary Compression Unit’s only source of work is a prime mover such as an electric motor that continuously compresses biomass via a novel screw design. The general arrangement of the dryer is a compression screw within a barrel, belt driven by an electric motor, all in a horizontal plane. The material moves through a continually decreasing space sufficient to increase the surface friction, and results in increased bulk temperature. Removing moisture under “drying only” settings can readily lower moisture content (MC) from 30% MC by weight to 10% MC by weight with energy consumption efficiencies approaching 90% of theoretical evaporation energy. All biomass materials will readily dry in this process including both wood and non-woody.


As the biomass is processed through the Rotary Compression Unit, as detailed in Figure One, the materials passes through transitions of physiochemical states namely: feed /pre-compression, steam drying, followed by steam explosion as the material exits the dryer. The exit clearances of the screw/barrel can be adjusted to effect a variety of process conditions of increasing pressure and temperature. Under lower pressure conditions in the nozzle, simple drying can be effected. As the biomass is processed under “light roast” conditions through the Rotary Compression Unit and the maximum temperature of the material is held below the autoignition temperature of the raw material. This light roast condition can be used to process waste streams such as anaerobic digestate and poultry litter into a dry and dense fertilizer product that is storage ready. This upgrade under these conditions is important to disposal of agricultural waste streams that would otherwise be applied in excess to the field. The upgrade also allows the ease of transportation of the material to be used in another locality, reducing the amount used in a single location. Feedstock input moisture parameters ranges in moisture content from 10% to 60% by weight and output is as low as 5% MC by weight. The Rotary Compression Unit is unique in its ability to dry many various types of fibrous biomass with ease. Enginuity Worldwide has performed i

nitial processing tests with much success involving poultry litter and anaerobic digestate waste.

The resulting dried waste stream can be densified into puck, briquette, or log form. This densification after processing using the Rotary Compression Unit provides a higher bulk density value in the material which improves transportation and long term storage characteristics. Improved transportation characteristics allow the resulting dry fertilizer product to be transported to other locales for usage. This decreases the chance of over application to a single locale, resulting in eutrophication and contamination of waters. Long term storage conditions are also improved as the moisture content of the material decreases as a result of the RCU process. The Rotary Compression Unit is also responsible for the destruction of microbes in material as a result of the steam, temperature, and high pressure. This decrease in microbial growth allows for storage of material without degradation.

Another aspect of the Rotary Compression Unit is in the conditioning and/or conversion of raw biomass into engineered biomass solid biofuel with increased energy density (BTU per pound) by 25-40% and increased fixed carbon content. In some cases the fixed carbon content is almost doubled. A “dark roast” is readily accomplished by adjusting the annular gap to settings that significantly increase the pressure on the biomass. This condition operates above the autoignition temperatures of the process and is responsible for the thermal upgrading of raw biomass into a coal-like biofuel to be used in combustion for power generation. This dark roast condition produces a material so named Biocoal™.


Under the conditions shown in Figure Two, the material sees temperatures above the autoignition temperature and is believed to experience auto/acid hydrolysis, then a steam pyrolysis phase, immediately before the steam explosion into a closed section. The steam explosion mechanism is responsible for increasing the surface area and porosity of the material by 100%. Under these conditions, the so-named Biocoal™ material is explosively ejected from the barrel/screw interface. At this instant, it is believed the Biocoal™ material loses heat to the escaping gases. The Biocoal™ is transported to a reflux condenser while the volatiles are contained, then continuously reintroduced into the reflux condenser where they are absorbed by the Biocoal™. This reabsorption of high BTU value volatiles found in the bio oil of the biomass is unique to the Enginuity technology process. An aftercooler cools the new biofuel and it is discharged through a cyclone. Depending upon the process conditions and the raw material characteristics, the potential for any non-condensable gases may be mitigated through a thermal oxidizer prior to release.


The fuel produced using the Rotary Compression Unit combined with a follow-on densification process results in a low moisture, high energy, weather resistant fuel with high durability and bulk density. This remedies logistics problems normally experienced when handling biomass. The material conditioning, densification and potential weather resistant characteristics makes the fuel ideal for travelling, handling, and long term storage.The resulting product is unique in every aspect including BTU content, fixed carbon content, friability and flow ability. What nature took millions of years to produce, the Rotary Compression Dryer can perform in minutes without cobalt, cadmium, selenium, mercury, boron, chromium, or lead.


Recent data and research has suggested that the RCU can be used not only for processing solid Anaerobic Digester waste into fuel or biochar but also to produce biochar that could improve the efficiency and function of the Anaerobic Digester when producing biogas. Most recently, fresh poultry droppings and fresh Anaerobic Digester offal from a cattle feedlot were processed using the RCU. The poultry droppings were obtained from a confined egg production facility and the anaerobic digester offal was obtained from a confined feeding facility after processing through a screw press to dewater. After processing through the RCU, the moisture content of the poultry droppings (Figure 3) decreased from 50% to 21.5% and the final heating value reached 18MJ/kg. The moisture content of the Anaerobic Digester offal decreased from 69.49% to approximately 11.79% moisture and the heating value increased from 17.9 MJ/kg to 22.4 MJ/kg.


The RCU is capable of producing a very porous, carbon-rich biochar that can be used in soil remediation efforts. Biochar has been researched extensively for decades since the discovery of the Terra Preta soils of the Amazon Basin. The addition of biochar to soils provides a stable and resilient source of carbon for plants as well as recovers carbon that would otherwise be released as a greenhouse gas. Biochar also improves moisture and nutrient retention of soils, increases the cation exchange of soils, and provides a habitat and carbon source of a healthy soil flora. These characteristics combined with the PKN inherently present in the animal manures and Anaerobic Digestion waste provide a well-rounded biochar product. The RCU process can also be operated under full carbonization conditions in order to produce a Salt & Pepper™ (Figure 4), or partially carbonized, product. This partially carbonized product provides a dose of carbon for the soil that also adsorbs the volatile content associated with off gassing ammonia and nuisance odors from animal wastes.


Biochars and carbons are important tools in water remediation of pollutants and excess nutrients. According to a report by the EPA (2000), the porous nature of carbon makes it ideal for adsorbing compounds like nitrates, pharmaceuticals, heavy metals, chlorine and ammonia. Because of its reactive surface area and adsorptive characteristics, recent literature also suggests that the addition of biochars can increase the production of biogas when added to anaerobic reactors in small amounts. Biochars (Figure 5) are capable of adsorbing compounds toxic to the flora of the digester, allowing the bacteria to reach optimum growth potential. Mumme et al (2014) found that an addition of 2 g of biochar to an anaerobic reactor had the ability to increase methane yield by 32%. Older studies have shown the addition of surface active materials like charcoal and coals can increase gas yields 15-30% (Geeta, 1986). In 2013, it is suggested that the addition of char could increase the methane production of a reactor 1.6 times as the result of hydrogenotrophic methanogens found on the char consuming hydrogen at increased levels (Watanabe, 2013). At a symposium in 2015 it was presented that the symbiotic relationship between bacteria and the hydrogenotrophic methanogens found on carbonaceous materials is responsible for the decreased levels of propionate which results in an increased methane production (Tada, 2015). Ongoing projects for Enginuity Worldwide include a project analyzing the effect biochar produced by the RCU has on an Anaerobic Digestion system, measured by gas production. This study will monitor the reduction of compounds toxic to bacterium as well as the bacterial health of the Anaerobic Digestion system.


Geeta, G.S; Raghevendra, S.; Reddy, T.K.R. 1986. Increase in biogas production from bovine excreta by addition of various inert materials. Agricultural Wastes 17 (2): 153-156.

Mumme, Jan; Srocke, Franziska; Heeg, Kathrin; Werner, Maja. 2014. Use of biochars in anaerobic digestion. Bioresource Technology 164: 189-197.

Tada, Chika; Takashi, Suzuki; Watanabe, Ryoya; Nakai, Yutaka. 2015. Carbon materials promote propionate acid degradation during anaerobic digestion of organic waste. Third International Symposium on Energy Challenges and Mechanics. Presented 7-9 July 2015 in Aberdeen, Scotland, UK.

Watanabe, Ryoya; Tada, Chika; Baba, Yasunori; Fukuda, Yasuhiro; Nakai, Yutaka. 2013. Enhancing methane production during the anaerobic digestion of crude glycerol using Japanese cedar charcoal. Bioresource Technology 150: 387-392.

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