Patent Grant
11634884
The invention encompasses methods, systems, and devices for dredging sediments from water reservoirs and wetlands while simultaneously burning the methane emissions and gases entrapped in the sediments, or through the use of an external gaseous fuel
The construction of dams and reservoirs over the last two centuries has led to the accumulation of sediments in large volumes estimated to be of the order of 7000 billion cubic meters on a world scale. The silting of reservoirs reduces the live storage capacity for water, and reduces the ability to produce hydro-electricity. Silted sediments provide an environment for fermentation of organic matter leading to emissions of methane, reaching 22% of the emissions from the earth causing green-house gases. Methane emissions are more dangerous than carbon dioxide emissions.
The internal combustion liquid piston pump engine was initially developed by Humphrey (1909). The engine operates on the explosion of a mixture of gaseous fuel and air, and uses an oscillating column as the momentum instead of a flywheel.
Abulnaga (1991) a developed a liquid piston engine that incorporated a constant rotation turbine such as a Savonius rotor or a Darrieus rotor between two cylinders operating in alternating stroke.
Dredging at great depths in excess of 50 m is often considered difficult and dangerous with electric submersible pumps in the presence of methane pockets entrapped in sediments.
Sediments accumulation in reservoirs constitute traps for the emission of methane (Maeck et al (2013)) They examined a number of reservoirs in Europe and noted an increase on the average from 0.23 mmol CH4/m2/day for freshwater bodies to 19.7 mmol CH4/m2/day in dams due to trapping by sediments. They estimated that dams therefore increase world emissions of methane by 7%.
Methane is produced in lakes and reservoirs from degradation of organic matter in sediments. Methanogenesis is the process of producing methane by microbes known as methanogens. The decomposition occurs in the absence of oxygen using the Carbon in organic matter under anoxic conditions. Archae cells (not to be confused with bacteria) obtain their energy by stoichiometric conversion of substrates such as H2+CO, formate, acetate, methanol, or methylamines to CH4 gas. DelSontro et al (2010) showed that extreme emissions of methane occurred in a hydropower reservoir in Switzerland, a country not considered tropical. Their work over a year indicated that the total methane emission from Lake Wohlen was on average larger than 150 mg CH4/m2/day, which is the highest ever documented for a midlatitude reservoir. The substantial temperature-dependent methane emissions discovered in this 90-year-old reservoir indicate that temperate water bodies can be an important but overlooked methane source.
In a paper “Tapping Freshwaters for Methane and Energy”, Bartosiewicz, Rzepka and Lehman (2021) indicated that levels of atmospheric methane CH4 have tripled over the last century from pre-industrial times. They estimated that methane was 80-100 times more potent in terms of greenhouse effects than CO2. They estimated that lakes and water reservoirs contribute to 92 to 142 Tg of CH4 per year or 20% world emissions of methane (1 Tg=1 million metric tonne). Rivers and wetlands contribute to 35% of the emissions of the Earth at 143 to 291 Tg/year of CH4.
Bartosiewicz et al point out that the emissions from reservoirs is only a fraction of the methane produced in the sediments, Therefore they estimated that the annual production of methane in reservoirs, lakes, wetlands and other freshwaters was around 469 and 865 Tg/year. If this amount of methane could be collected at 75% efficiency, the authors estimated that the global production of methane from fresh waters was equivalent to 50 to 100×1011 kWh. By considering that the worldwide production of electricity in 2018 reached 23×1012 kWh, the authors made the case that there could be sufficient methane to tap to cover as much as energy needed.
The authors also conducted a more conservative bottom-up calculations. They assumed a gross sedimentary efflux (by diffusion only) of 10 mmol/m2/day for rivers, lakes and reservoirs, and 250 mmol/m2/day for wet lands, and considering that the global surface area of freshwater was of the order of 1.75×107 km2, they calculated a total amount of CH4 released from freshwater sediments of the order of 190×1012 kWh/year. They also estimated that the rate of sedimentary CH4 production is bound to increase in the future as consequence of eutrophication, global warming and proliferation of anoxia.
In a recent study, J. Harrison et al (2021), scientists from Washington State University and University of Quebec at Montreal. showed per-area greenhouse gas emissions from the world's water reservoirs were around 29% higher than suggested by previous studies. They attributed the increase to methane degassing, a process where methane passes through a dam and bubbles up downstream.
Decomposing plant matter near the bottom of reservoirs fuels the production of methane, a greenhouse gas that is 25 to 34 times more potent than carbon dioxide over the course of a century and comparable to rice paddies or biomass burning in terms of overall emissions.
Harrison and colleagues found methane degassing accounts for roughly 40% of emissions from water reservoirs. This large increase in previously unaccounted for emissions was partly offset by a projected lower amount of methane diffusing off the surface of reservoirs, according to the analysis. Carbon dioxide emissions were similar to those reported in past work.
The idea of using CH4 extracted from deep reservoirs is not new. A deep stratified lake, Kivu Lake, one of the great lakes of Africa, is approximately 90 km (56 mi) long and 50 km (31 mi) at its widest. It covers an approximate surface area of 2,700 km2. Gas is extracted from deep waters (>260 m to 300 m), collected and scrubbed. It is estimated to have 60 billion cubic meters of methane and 300 billion cubic meters of carbon dioxide. These harmful gases were expected to saturate the lake in 50 to 200 years causing gas eruption threats to surrounding populations on the shores A plant was built in 2016 to produce 26 MW, and is being upgraded to produce 34 MW, with plans to install a further 75 MW plant. The first phase consisted of an investment of $142 million and the second phase was budgeted for $180 million. The first phase plant consisted of a 750 ft floating barge integrating a gas extraction and treatment facility (Power Technology)
The bottom of lake Tanganyika in Tanzania, is also estimated to store 23 Tg of CH4. Shema Power Lake Kivu (2021) is also developing a new 56MW Methane Gas to Power Generation plant in the Ribavu district of Rwanda.
The development of technologies to harvest methane in the USA has been limited to recovery from landfills or wastewater treatment plants. Therefore, there is no commercial project at present to recover from hydropower reservoirs. Bartosiewicz et al (2021) propose that adsorption-based technologies be developed as they would be less capital intensive than compression or liquefaction approaches. A hydrophobic gas-liquid membrane contactor (GLMC) is therefore proposed. The membrane allows gas molecules to pass while preventing water to flow. They state that microporous polymer-based membranes have successfully employed in large-scale methane recovery from anaerobic effluent upon biogas upgrading and have been tested for large wastewater treatment plants. One type, called hollow fibers ultrafiltration achieves 53% separation efficiency on digestion of sludge from urban wastewater to 98% on synthetic CH4 rich wastewater streams. The authors suggest that membrane manufactured from polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF) would be of particular interest to recover methane from freshwater sources, because of their high resistance to wetting and their particularly high CH4 flux rate or mass transfer rate.
It is therefore my belief that technologies are needed for capturing methane emissions from wet lands and water reservoirs, but considering the large accumulation of sediments behind dams, the fuel should be used directly towards dredging the very same sediments that entrap the methane. Our invention focuses on the combustion of the methane in an internal combustion liquid piston engine with capabilities to dredge.
About 65% of the reservoirs of water in the United States are not producers of hydro-electricity. Many are close to natural gas pipelines. Therefore, the invention can be operated on natural gas.
There are many deep reservoirs where electric submersibles do not perform well and must be removed in the presence of a methane pocket. Methane also causes cavitation of centrifugal pumps, while our proposed invention would not suffer from such a problem.
The invention consists of a submersible system that can be sunk at great depth to dredge sediments from reservoirs. The invention features a dredging cutter, operated by a turbine immersed in an oscillating column of dredged slurry whose oscillation is induced by the periodic explosion of a mixture of compressed air and a gaseous fuel such as natural gas provided from shore or methane emissions collected in the reservoir.
| Number | Name | Date | Kind |
|---|---|---|---|
| 1214791 | Humphrey | Feb 1917 | A |
| 1272269 | Humphrey | Jul 1918 | A |
| 20220205384 | Abulnaga | Jun 2022 | A1 |
