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The term Gas-to-Power (GTP) describes the process of converting natural gas, typically ethane and methane or other petroleum gasses, into power. Natural gas accounts for about 22.9 % of global energy consumption, of which approximately 8.7 % is supplied as LNG.
Although demand for fossil fuels has decreased during the COVID-19 pandemic and is predicted to decline in demand for years to come, natural gas has remained resilient, especially when compared to coal and oil. However, according to the EIA the long-term impacts on global energy demand and industry structures due to the pandemic are unknown. The world’s energy use is expected to double by 2040, led by regions with accelerating population or wealth growth, such as India, China and several African countries. Efficiency, flexibility, and reliability are required on the path to a zero-emission future, making GTP increasingly important in the energy transition.
Regasification
Converting liquid gas back into a gaseous state takes place at a regasification plant. This plant can either be entirely land-based, can be supplemented by floating terminal technology such as FSUs, or entirely floating such as FSRUs, which are an increasingly important part of LNG infrastructure in the future. A regasification facility normally uses sea water to convert the LNG back to its gaseous state, but air vaporizers can also be used. Air vaporizers utilize several large fans that push air through heat exchangers to vaporize the LNG, whereas submerged combustion vaporizers (SCV) burn some of the natural gas to drive the vaporization. In cases where sea water is used, the water is run through a heat exchanger with the natural gas, and high-pressure pumps pressurize the gas to a pressure level of 70-100 bar. In periods of high demand, regasification might also be processed using underwater burners running on natural gas. Once converted back into its gaseous state, natural gas is transported to a gas-fired power plant to generate electricity.
Transporting the gas to the power station is the next step. Electricity generation from gas can occur either at, or near, a reservoir source. This electricity then can be directed to its designated location via power lines, or it can be transported as a gas closer to the end user for conversion to electricity. The former alternative can be used to power offshore plants and infrastructure, while the latter is considered a more flexible and efficient solution, due to power losses during transmission over long distances, and as waste heat can be used in heating and for other industrial purposes.
How is natural gas used to generate power?
Transforming gas into electric power is made possible through the thermodynamic process of converting the chemical energy stored in the natural gas to thermal energy, via mechanical energy to electrical energy. A common GTP method utilizes gas turbine generators, either in simple cycle or combined cycle configurations. In a simple cycle gas plant, natural gas is fed into a combustion chamber where it is mixed with pressurised air from a compressor and ignited. Further, the hot air-fuel mixture from the combustion chamber is fed into a turbine which is connected to a crankshaft. The crankshaft connects to the compressor and a generator, which generates and then delivers electricity to a grid system.
This thermodynamic process is commonly referred to as a Brayton cycle; where a compressor, a mixing chamber (the combustion chamber) and an expander (the turbine) generate work. The Brayton cycle is based on the ratio between the exit temperature of the compressor to the atmospheric temperature.
Energy efficiency for a GTP system can be significantly increased by adding a steam bottoming cycle (SINTEF).
Alternatively, the Carnot efficiency is based on the ratio between the highest and lowest temperature in a heat engine cycle, therefore setting the boundary condition for a heat engine’s maximum efficiency which can be obtained. In terms of efficiency, even a fully idealized Brayton cycle would not be able to match a Carnot process.
The efficiency of simple cycle gas plants is typically around 35%, but overall efficiency can be increased by introducing a combined cycle, also known as a bottoming cycle. The combined cycle consists of a simple cycle with an attached steam bottoming cycle with a heat recovery steam generator (HRSG). The bottoming cycle utilizes excess heat from the single cycle gas turbine to generate steam which is used to generate electrical power through a second generator. In this way, the amount of waste heat and gas consumption is lowered, CO2 emissions are lowered by around 30 %, and the plant’s overall efficiency can increase to 60 %.
The term Gas-to-Power (GTP) describes the process of converting natural gas, typically ethane and methane or other petroleum gasses, into power. Natural gas accounts for about 22.9 % of global energy consumption, of which approximately 8.7 % is supplied as LNG.
What are the benefits of Gas-to-Power?
Historically, one of the most common issues with GTP has been the relative positions of the gas reserves and the end consumer, and the transportation methods to bring raw natural gas to treatment facilities. The shift from large scale to small scale LNG trade comes from discovery of relatively small gas reserves in remote locations, increasing power and fuel demand, new regulations and the modernisation of existing supply chains. The emergence of disruptive technology, which is able to substantially lower financial risks of projects and mobilise quickly on demand, is another reason why small-scale gas projects, LNG projects in particular, hold great future potential.
The global energy mix benefits from small-scale gas projects, as natural gas serves as an effective and reliable transition fuel on the path to a sustainable and green future. As many renewable energy sources, such as solar power and wind, are considered intermittent as they depend on weather conditions, gas-fired backup plants can provide system redundancy in case of power shortage. Most gas-fired power plants are flexible and effective in terms of readiness and can go from an idle state to being fully operational within minutes, unlike many coal and oil plants which require much longer time to generate output. Another way in which natural gas has proven its effectiveness is through its high heating value, which for methane and ethane are among the highest of all fuels, only beaten by hydrogen.
There are significant environmental benefits not to be overlooked with the use of LNG - a study commissioned by the Center for Liquefied Natural Gas (CLNG), found that existing US domestic coal power plants produce two and a half times more emissions on a life cycle basis than that of LNG; emissions from the average existing coal-fired power plants in the five LNG export markets studied were found to range between 139% and 148% greater than the High GHG case for LNG. This study accounts for the lifecycle analysis of natural gas and coal, from production to transmission.
Improving energy efficiency is one of the most cost-effective climate measures in terms of the direct relationship between investment and the reduction of emissions due to lowered energy use. Clever gas to power technology such as combined cycles is one example of how innovation can further improve value chain efficiencies.
What Gas-to-Power services and products does ECONNECT Energy support?
At ECONNECT Energy, we believe that new technology will shape the global energy systems of tomorrow. In recent years, floating marine technology and changes in the LNG market have enabled the value chain to be realised in the form of gas to power projects.
LNG is the first step in a cleaner energy journey - the technology is proven and there is global infrastructure to support its use, there are robust safety measures and regulations in place, LNG can seamlessly blend with renewable gases and the existing LNG infrastructure is easily adapted for zero carbon fuels such as ammonia. It is the lower carbon fuel that will take us to the adoption of zero carbon fuels.
Lastly, LNG trading and effective sales models expand the global reach of natural gas to power industries and support growth for developing nations with new energy infrastructure. We believe we have identified the bottlenecks of the value chain, and as a reliable supplier of technology and innovative solutions, we are set to prioritize our customers’ challenges to achieve results together.
With the jettyless IQuay, we provide flexible and adaptable GTP solutions for both onshore and offshore installations. Read more about our GTP-solutions.
This article was co-written by Magnus Eikens and Mats Møller
