Technology About Gas

Gas and water: a new hybrid technology?

 By Robin Wylie
About gas

The waste geothermal heat from natural gas production could help to harness the ocean’s thermal energy, a new study suggests…

Ocean thermal energy conversion (OTEC) is a marine renewable energy technology which uses the temperature difference between warm surface water and cooler deep water to produce electricity via a heat engine. The technology has been available since the 1880s, however, the technology is not widely used, due largely to the high up-front costs. One proposed way to improve cost effectiveness of OTEC is by adding an external heat source to supplement the marine thermal energy, since the efficiency of the process is greatly increased by larger temperature differences. Researchers previously suggested adding solar collectors to OTEC systems, or incorporating the waste heat from nuclear power stations. But new research suggests that natural gas could also be a good candidate to give OTEC a helping hand.

Ocean thermal energy conversion diagram and applications (Wikimedia)

The natural gas extracted from deep reservoirs contains significant quantities of geothermal energy, with temperatures potentially exceeding 100 degrees centigrade (212 degrees Farenheit). This heat is often wasted during natural gas production. But according to a study published this April, waste geothermal heat from natural gas could give a much-needed boost to OTEC technology. In the study, researchers from the Malaysia-Japan International Institute of Technology in Kuala Lumpur proposed a new technology which uses a combination of OTEC and raw, geothermally-heated natural gas to generate electricity, which the authors call GeOTEC.

OTEC facility at Keahole Pointe (Wikimedia)

In the study, the researchers performed a numerical simulation to estimate the potential performance of a GeOTEC system, based on the natural gas output of an offshore gas production platform operating in Malaysia. The simulation involved using a geothermal water heating system to capture the geothermal heat energy of the extracted natural gas, before using it in combination with seawater to vaporize liquid ammonia—this would then be used to power a turbine, generating electricity.

The team’s analysis suggested that by incorporating the natural gas geothermal component to OTEC, the capital cost of the process could be as low as $4,489 per kW (based on a 32.6MW plant), which is approximately 2.5 times cheaper than a similarly-sized regular OTEC plant. Moreover, the predicted efficiency of the process was up to 4.6 percent, significantly higher than the 3 percent efficiency which is commonly practically achievable by OTEC systems. The researchers performed their analysis using production figures from an offshore gas production platform, however, they anticipate that the greatest potential exists in deep sea combined oil and gas production platforms.

SEE MORE: Fossils + Renewables, a viable option? by Amanda Saint

about the author
Robin Wylie
Freelance earth/space science journalist. Currently finishing off a PhD in volcanology at University College London.