Objective
The objective of this project was to demonstrate a fully automated and portable waste to energy system for eventual use at forward operating bases of the U.S. Military. The system uses an inclined rotary gasification system which converts both solid and liquid waste into electricity.
The demonstration took place at military training Camp Buckner, located on the United States Military Academy in West Point, New York. The rotary gasification system was to demonstrate the following:
- Conversion of non-hazardous waste into electricity for a period of six months
- Ability to convert camp generated waste into a gaseous fuel and fully burned densified ash
- Reduce the amount of liquid fuel required for electrical power generation at the generator by at least 50%
- Process consumes all fluids
- Ash is non-hazardous
- Meets required federal and state emissions requirements
Items 2, 3, and 5 were successfully demonstrated. Item 1 was not fully demonstrated as planned and is explained in subsequent sections. Item 4 was demonstrated successfully, but enhancements will be required on future systems to operate at higher temperatures to prevent the formation of condensate. Item 6 was demonstrated, but requires more testing due to the variable content of waste.
Technology Description
Solid and liquid wastes are converted to a flammable synthetic gas (syngas) using a unique patented (U.S. Patents #10,760,016 and #11,939,545) inclined rotary gasifier. The reactor is simple (no mechanical seals), lightweight (no refractory lining), rugged, and safe for soldier use. The process can handle a wide variety of wet mixed wastes without the need of pre-drying or sorting. A slow speed shredder grinds waste to < 3” inch chunks, which pass through the feedstock handling system without the need for segregation. Inert items pass through the gasifier and discharge with the ash. A waste volume reduction greater than 95% is possible by producing a fully burned and densified ash. The gasifier operates “non-slagging” and self-grinds clinkers, but is equipped with an automated dump door to periodically to pass large items (metals, stone, glass, etc.).
Waste converts to a flammable syngas using simple thermal devolatilization process as shown on Figure 3. A wet scrubbing system cleans the gas prior to co-fueling a 60 kW advanced medium-sized mobile power source (AMMPS) generator (MEP-1070A). The inclined rotary gasifier (IRG) both dries the waste and gasifies in one step. Moisture evaporates into the syngas, passes through the engine at temperatures well above the saturation dew point, and discharges as invisible superheated steam in the diesel exhaust. The only emissions from this process are diesel engine exhaust and a highly densified ash.
Demonstration Results
The system operates as proposed and is able to reliably consume significant amounts of waste. The waste consumption varies proportionally with syngas production. Syngas consumption at the generator varies with the electrical load and percentage of gaseous co-fueling. The Cummins QSB 4.5 engine used in the 60 kW AMMPS exceeded expectations by operating on a wide range of syngas composition without the need to modify the engine, fueling system, or electronic control module (ECM).
Waste consumption varies with generator power output and the percentage of gaseous fueling. The Cummins Industrial Engine Family (QSB) 4.5 engine used in the 60 kW AMMPS generator is tolerant of co-fueling with syngas, with no modifications required to the engine or electronic control module. A 50% liquid fuel savings is easily obtainable at any generator load. Liquid fuel savings exceeding 75% are possible with careful regulation of syngas flow relative to electrical load. Syngas displaces engine combustion air and was found to compromise diesel particulate matter (DPM) exhaust emissions when generating at electrical loads over 30 kW. Emissions can be mitigated by use of an electrically regenerating DPM filter and post diesel exhaust catalyst.
Implementation Issues
The primary challenge with this project was the AMMPS generator exceeded performance and efficiency expectations, providing insufficient exhaust heat to the IRG to effectively process wet waste. These challenges were resolved by modifying the gaseous fueling system to the engine and adding a syngas fueled proprietary swirl burner (PSB) to double the temperature of the engine exhaust supplied to the gasifier, providing sufficient heat to dry wet waste.
Another primary challenge with this project was the AMMPS generator operates at significantly lower engine intake manifold (EIM) pressure than planned, reducing the anticipated combustion airflow thru the engine by over 40%. Insufficient airflow created significant visible DPM emissions when co-fueling (over 50%) on syngas, with risk of public complaint when operating the generator over 30 kW. This was resolved at the end of the demonstration by feeding pressurized syngas directly into the intake manifold, causing the turbo charger (TC) to spool up and increase the EIM pressure by 33%. This allows the use of the engine air filter, Holset TC, charge air cooler, and charge air piping that comes standard with the generator and provides the ability to field modify any 60 kW AMMPS to operate dual fueled on IRG syngas. This arrangement was found to naturally force the TC to provide the additional air to self-compensate for syngas displacement.