How Swiss Roll Combustors Mitigate Methane Emissions
Methane emissions are one of the most pressing environmental challenges facing the oil and gas industry. Oil and gas operations release large amounts of methane, a potent greenhouse gas, either by accident through fugitive emissions, design and systems upsets in venting or process inefficacy, known as methane slip.
As shown in Figure 1, Methane emissions occur in all segments of the natural gas industry, from production, through processing and transmission, to distribution. Recent federal and state regulations have forced industry to adopt newer technologies to mitigate methane emissions.
One of the methane mitigation techniques involves combustion/flaring of methane and other gaseous hydrocarbons using combustion control devices, such as flares and enclosed combustors. However, current devices are bulky and lose the methane destruction efficiency with changes in flow rate and gas composition.
With funding from the Department of Energy, Department of Defense, and ARPA-E program, ACT has advanced the Swiss Roll Combustor for Methane Emissions’ technology to address these shortcomings and provide a technologically and economically viable option for methane mitigation challenges in the oil and gas industry.
What is a Swiss Roll Combustor?
Our Swiss Roll combustor is based on the concept of a heat-recirculating combustor, an animation of which is shown in Figure 2.
The design was modified to prevent flashback risks. Instead of injecting fuel and air at the inlet, fuel is now introduced near the combustion zone. This allows sufficient time for mixing but prevents auto-ignition, which could occur if fluctuations in flare gas flow created a strong mixture in the inlet channels.
As shown in Figure 3A, air and gas mix near the center before entering the reaction zone where combustion occurs. The hot products then flow out from the core through the adjacent outlet channel. This design utilizes a spiral heat exchanger, transferring heat from the hotter outlet channel to the cooler inlet channel. This heat transfer significantly increases the temperature of incoming reactants, boosting combustion temperature and reaction rates. It also extends the flammability range of various fuels and promotes complete combustion, resulting in high destruction efficiency of methane and other hydrocarbons. Previous experiments have demonstrated that this Swiss roll combustor design can achieve very low NOx emissions, between 0-1 ppm.
Features of the Swiss Roll Combustor for Methane Emissions
- Near 100% methane and VOCs destruction efficiency over a wide operating range due to the ability of operating at high combustion temperatures.
- Compact combustor, with portable trailer mounted option, for rapid deployment at hard-to mitigate, remote, and intermittent sources of methane emissions. (Figure 4)
- A fully enclosed combustion – operating environment has minimal effect on combustion efficiency. Low thermal radiation for operator safety and site compliance. Deployable in dense, urban areas
- Fully automated with integrated low-cost sensors, continuous flame monitoring, and combustion controls to minimize NOx, and enable emissions monitoring and reporting
- Cost –effective solution (compared to vapor recovery units) for small, distributed, intermittent vents
Typical Applications of Swiss Roll Combustor
- Methane Sources at Compressor Stations
- Liquid storage tanks
- Glycol dehydrator (regenerators/reboilers and flash tanks)
- Centrifugal compressor seals
- Reciprocating compressor rod packing vent/drain
- Venting during Blowdown Events
- Midstream transmission pipelines
- Gas utility Distribution pipeline
- Underground Storage Facilities
- Tanks
- Dehydrators
- Marginal or Seasonally Producing Wells
Siliconized Silicon Carbide
Siliconized Silicon Carbide (Si/SiC), a new ceramometallic material, is used to create a Swiss roll combustor for high-temperature use. The complex shape is made through a multi-step 3D printing process:
- A binder-jet machine creates the initial shape using SiC powder and a special binder, creating something called the “green” part, formed by not yet fully processed.
- The “green” part is heated to turn the binder into carbon.
- Liquid silicon is added, filling gaps and reacting with carbon to form new SiC.
The result is a Si/SiC composite. Figure 5 shows the finished Swiss roll combustor.
Final Performance Results
ACT tested a smaller version of the combustor that could handle up to 4 MSCFD, a thousand standard cubic feet per day. In these lab tests, the sub-scale version combusted almost all the methane in the gas mixtures, similar to what would be seen at an on-site station of facility. Figure 6 shows the experimental results. Figure 7 shows a computer simulation that validated the experimental results and proves most of the methane is burned in the swiss roll. The Si/SiC material was also durability tested for high temperature, providing valuable feedback for design optimization.
