Supercritical Carbon Dioxide – A Plan to Eliminate 25% of Existing Power Plants

Duane M. Tilden, P.Eng                           October 26, 2018

Is it possible that we can drastically reduce the existing fleet of power plants by 25% or more? Yes, this does seem to be a rather extravagant claim considering how many power providers or utilities such an increase in energy efficiency in output will impact.  Examining the United States as our example:

As of December 31, 2017, there were about 8,652 power plants in the United States that have operational generators with a combined nameplate electricity generation capacity of at least 1 megawatt (MW). A power plant may have one or more generators, and some generators may use more than one type of fuel. (1)

So, reducing the existing fleet by 25% would enable us to decommission approximately 2,163 of these plants.  This plan would require the examination of the total supply chain to optimize these reductions whilst maintaining the integrity of the existing distribution network. A significant project having enormous impact on the economy and meeting carbon reduction strategies on a global scale.

Supercritical Carbon Dioxide (SCCD) Turbines

In previous posts I have discussed the technology of SCCD turbines for power production and how this system can be used for a wide variety of power production and energy extraction methods. A recent article published by Euan Mearns with commentary delves even deeper into this technology to discuss the global impacts of increased power production efficiency on reducing carbon emissions.

GHG’s, carbon, NOx, pollution, waste heat, entropy effects, and consumption of resources are all commensurately reduced when we systematically increase power production energy efficiency at the plant level. An improvement of energy efficiency at the system level has a profound impact in output capacity or input reduction. For example, if we can increase the efficiency by 10% from 30% to 40% in conversion, the output of the plant is improved by 4/3 or 33% or inversely, the input requirement will reduce by 3/4 or 25%.

Power Plant Energy Efficiency

To measure the energy efficiency of a thermo-electric power plant we use the heat rate. Depending on the quality of the fuel and the systems installed we convert heat energy into electrical energy using steam generators or boilers. We convert water into steam to drive turbines which are coupled to generators which convert mechanical motion into electricity.

Examination of data provided will be simplified using statistical averages. In 2017 the average heat rates and conversion efficiencies for thermal-electric power plants in the US (2) are given as follows:

  • Coal: 10465 Btu/Kw – 32.6%
  • Petroleum: 10834 Btu/Kw – 31.5%
  • Natural Gas: 7812 Btu/Kw – 43.7%
  • Nuclear: 10459 Btu/Kw – 32.6%

Examination of the US EIA data for 2017 shows us that currently Natural gas is 11.1% more efficient than Coal in producing electricity while consuming 25.4% less fuel for the same energy output.

So we already have proof that at a plant level, energy efficiency gains in consumption are leveraged by smaller improvements in the thermodynamic cycle. For natural gas power plants the current state of the art is to use a combined cycle combustion process which is not employed in other thermo-electric power plants.

HOW A COMBINED-CYCLE POWER PLANT PRODUCES ELECTRICITY (3)

This is how a combined-cycle plant works to produce electricity and captures waste heat from the gas turbine to increase efficiency and electrical output.

  1. Gas turbine burns fuel.

    • The gas turbine compresses air and mixes it with fuel that is heated to a very high temperature. The hot air-fuel mixture moves through the gas turbine blades, making them spin.
    • The fast-spinning turbine drives a generator that converts a portion of the spinning energy into electricity.
  2. Heat recovery system captures exhaust.

    • A Heat Recovery Steam Generator (HRSG) captures exhaust heat from the gas turbine that would otherwise escape through the exhaust stack.
    • The HRSG creates steam from the gas turbine exhaust heat and delivers it to the steam turbine.
  3. Steam turbine delivers additional electricity.

    • The steam turbine sends its energy to the generator drive shaft, where it is converted into additional electricity.

Image result for combined cycle power plant

Figure 1. Schematic of Combined Cycle Gas/Steam Turbine Power Plant with Heat Recovery (4)

Comparing Combined Cycle Gas Turbines with SCCD Turbines

The study of thermodynamic cycles is generally a domain studied and designed by engineers and physicists who employ advanced math and physics skills. The turbine is based on the Brayton cycle, while steam turbines operate on the Rankine cycle. The Rankine cycle uses a working fluid such as water, which undergoes a phase change from water to steam. The Brayton cycle is based on a single phase working fluid, in this case combusted natural gas.

Both SCCD turbines and Gas Turbines operate on the Brayton cycle, however, they use different working fluids and requirements based on operating conditions. The gas fired turbine takes in air which is compressed by the inlet section of the turbine and natural gas is combined with the compressed air and ignited. The hot expanding gasses turn the turbine converting heat to mechanical energy. A jet engine operates on the Brayton cycle.

For a combined cycle gas turbine some of the waste heat is recovered by a heat exchange system in the flue stack, converted to steam to drive  a second turbine to produce more electricity and increase the overall energy efficiency of the system.

In the case of an SCCD the turbines working fluid is maintained in a closed loop, continually being heated through a heat exchanger from a source and run in piping through the turbine and a compressor. Secondary heat exchangers for recuperation and cooling may be employed. These are all emerging technologies undergoing serious R&D by the US DOE in partnership with industry and others.

Closed Loop SCO2 Recompression Brayton Cycle Flow Diagram

Figure 2. Closed Loop SCO2 Recompression Brayton Cycle Flow Diagram (NETL)

 

Technology Development for Supercritical Carbon Dioxide (SCO2) Based Power Cycles

The Advanced Turbines Program at NETL will conduct R&D for directly and indirectly heated supercritical carbon dioxide (CO2) based power cycles for fossil fuel applications. The focus will be on components for indirectly heated fossil fuel power cycles with turbine inlet temperature in the range of 1300 – 1400 ºF (700 – 760 ºC) and oxy-fuel combustion for directly heated supercritical CO2 based power cycles.

The supercritical carbon dioxide power cycle operates in a manner similar to other turbine cycles, but it uses CO2 as the working fluid in the turbomachinery. The cycle is operated above the critical point of CO2so that it does not change phases (from liquid to gas), but rather undergoes drastic density changes over small ranges of temperature and pressure. This allows a large amount of energy to be extracted at high temperature from equipment that is relatively small in size. SCO2 turbines will have a nominal gas path diameter an order of magnitude smaller than utility scale combustion turbines or steam turbines.

The cycle envisioned for the first fossil-based indirectly heated application is a non-condensing closed-loop Brayton cycle with heat addition and rejection on either side of the expander, like that in Figure 1. In this cycle, the CO2 is heated indirectly from a heat source through a heat exchanger, not unlike the way steam would be heated in a conventional boiler. Energy is extracted from the CO2 as it is expanded in the turbine. Remaining heat is extracted in one or more highly efficient heat recuperators to preheat the CO2 going back to the main heat source. These recuperators help increase the overall efficiency of the cycle by limiting heat rejection from the cycle. (4)

Commentary and Conclusion

We already are on the way to developing new systems that offer significant improvements to existing. Advancements in materials and technology, as well as other drivers including climate concerns and democratizing the energy supply. Every percentage of increase in performance reduces the consumption of fossil fuels, depletion of natural resources, generated waste products and potential impacts on climate.

SCCD systems offer a retrofit solution into existing power plants where these systems can be installed to replace existing steam turbines to reach energy efficiency levels of Combined Cycle Gas Turbines. This is a remarkable development in technology which can be enabled globally, in a very short time frame.

References:

  1. USEIA: How many power plants are there in the United States?
  2. USEIA: Average Operating Heat Rate for Selected Energy Sources
  3. GE: combined-cycle-power-plant-how-it-works
  4. https://www.netl.doe.gov/research/coal/energy-systems/turbines/supercritical-co2-turbomachinery

 

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Oldest Nuclear Power Plant in US to be Retired – The 60 Year Decommissioning Process

When a nuclear plant retires, it stops producing electricity and enters into the decommissioning phase. Decommissioning involves removing and safely storing spent nuclear fuel, decontaminating the plant to reduce residual radioactivity, dismantling plant structures, removing contaminated materials to disposal facilities, and then releasing the property for other uses once the NRC has determined the site is safe.

According to Exelon, Oyster Creek will undergo a six-step decommissioning process. The typical decommissioning period for a nuclear power plant is about 60 years, so parts of the Oyster Creek plant structure could remain in place until 2075. (1.)

retired nuclear power plants and nuclear power plants that have announced retirement

Since 2013, six commercial nuclear reactors in the United States have shut down, and an additional eight reactors have announced plans to retire by 2025. The retirement process for nuclear power plants involves disposing of nuclear waste and decontaminating equipment and facilities to reduce residual radioactivity, making it much more expensive and time consuming than retiring other power plants. As of 2017, a total of 10 commercial nuclear reactors in the United States have been successfully decommissioned, and another 20 U.S. nuclear reactors are currently in different stages of the decommissioning process.

To fully decommission a power plant, the facility must be deconstructed and the site returned to greenfield status (meaning the site is safe for reuse for purposes such as housing, farming, or industrial use). Nuclear reactor operators must safely dispose of any onsite nuclear waste and remove or contain any radioactive material, including nuclear fuel as well as irradiated equipment and buildings. (2.)

References:

  1. America’s oldest operating nuclear power plant to retire on Monday
  2. Decommissioning nuclear reactors is a long-term and costly process

Japan Set to Restart First Nuclear Reactor Since Industry Shut-Down After Fukushima Disaster

Japan is due to switch on a nuclear reactor for the first time in nearly two years on Tuesday, as Prime Minister Shinzo Abe seeks to reassure a nervous public that tougher standards mean the sector is

Sourced through Scoop.it from: www.reuters.com

>” […] Abe and much of Japanese industry want reactors to be restarted to cut fuel imports, but opinion polls show a majority of the public oppose the move after the nuclear crisis triggered by the earthquake and tsunami in March 2011.

In the worst nuclear disaster since Chernobyl 25 years earlier, the meltdowns at the Fukushima Daiichi plant caused a release of radioactive material and forced 160,000 from their homes, with many never to return.

The crisis transfixed the world as the government and the Fukushima operator, Tokyo Electric Power (Tepco), fumbled their response and took two months to confirm that the reactors had undergone meltdowns.

Kyushu Electric Power said it aimed to restart its No. 1 reactor at its Sendai plant at 0130 GMT on Tuesday (2130 ET on Monday).

The plant on the west coast of Kyushu island is the furthest away of Japan’s reactors from Tokyo, where protesters regularly gather outside Abe’s official residence to oppose atomic energy.

At nearly 1,000 km (600 miles) from the capital, Sendai is closer to Shanghai or Seoul.

A successful restart would mark the culmination of a process whereby reactors had to be relicensed, refitted and vetted under tougher standards that were introduced following the disaster.

While two reactors were allowed to restart for one fuelling cycle in 2012, the whole sector has been shut down since September 2013, forcing Japan to import record amounts of expensive liquefied natural gas.

As well as cutting energy costs, showing it can reboot the industry safely is crucial for Abe’s plans to export nuclear technology, said Malcolm Grimston, a senior research fellow at Imperial College in London.

“Japan also has to rehabilitate itself with the rest of the world’s nuclear industry,” said Grimston.

At the Sendai plant, Kyushu Electric expects to have power supply flowing within a few days if all goes to plan. It aims to start the station’s No. 2 unit in October.

The head of Japan’s atomic watchdog said that the new safety regime meant a repeat of the Fukushima disaster would not happen, but protesters outside the Sendai plant are not convinced.

“You will need to change where you evacuate to depending on the direction of the wind. The current evacuation plan is nonsense,” said Shouhei Nomura, a 79-year-old former worker at a nuclear plant equipment maker, who now opposes atomic energy and is living in a protest camp near the plant.

Of Japan’s 25 reactors at 15 plants for which operators have applied for permission to restart, only five at three plants have been cleared for restart. […]”<

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Cover-up: Fukushima Nuclear Meltdown a Time Bomb Which Cannot be Defused

epa02660905 A handout picture provided by Air Photo Service on 30 March 2011 shows an aerial photo taken by a small unmanned drone of the damaged units of Tokyo Electric Power Co (TEPCO) Fukushima Daiichi nuclear power plant in the town of Okuma, Futaba district, Fukushima prefecture, Japan, 24 March 2011. TEPCO Chairman Tsunehisa Katsumata announced on 30 March it will be more than a few weeks to fix the Fukushima Daiichi nuclear power plant. EPA/AIR PHOTO SERVICE / HO EDITORIAL USE ONLY +++(c) dpa - Bildfunk+++

Four years after the Fukushima nuclear disaster which has caused incredible an ongoing destruction, in the meantime authorities have tried to cover up the serious consequences…

Image source: http://www.theasiasun.com/

Sourced through Scoop.it from: oilprice.com

>” […] Fukushima will likely go down in history as the biggest cover-up of the 21st Century. Governments and corporations are not leveling with citizens about the risks and dangers; similarly, truth itself, as an ethical standard, is at risk of going to shambles as the glue that holds together the trust and belief in society’s institutions. Ultimately, this is an example of how societies fail.

Tens of thousands of Fukushima residents remain in temporary housing more than four years after the horrific disaster of March 2011. Some areas on the outskirts of Fukushima have officially reopened to former residents, but many of those former residents are reluctant to return home because of widespread distrust of government claims that it is okay and safe. […]

According to Japan Times as of March 11, 2015: “There have been quite a few accidents and problems at the Fukushima plant in the past year, and we need to face the reality that they are causing anxiety and anger among people in Fukushima, as explained by Shunichi Tanaka at the Nuclear Regulation Authority. Furthermore, Mr. Tanaka said, there are numerous risks that could cause various accidents and problems.”

Even more ominously, Seiichi Mizuno, a former member of Japan’s House of Councillors (Upper House of Parliament, 1995-2001) in March 2015 said: “The biggest problem is the melt-through of reactor cores… We have groundwater contamination… The idea that the contaminated water is somehow blocked in the harbor is especially absurd. It is leaking directly into the ocean. There’s evidence of more than 40 known hotspot areas where extremely contaminated water is flowing directly into the ocean… We face huge problems with no prospect of solution.”

At Fukushima, each reactor required one million gallons of water per minute for cooling, but when the tsunami hit, the backup diesel generators were drowned. Units 1, 2, and 3 had meltdowns within days. There were four hydrogen explosions. Thereafter, the melting cores burrowed into the container vessels, maybe into the earth. […]

Following the meltdown, the Japanese government did not inform people of the ambient levels of radiation that blew back onto the island. Unfortunately and mistakenly, people fled away from the reactors to the highest radiation levels on the island at the time.

As the disaster happened, enormous levels of radiation hit Tokyo. The highest radiation detected in the Tokyo Metro area was in Saitama with cesium radiation levels detected at 919,000 becquerel (Bq) per square meter, a level almost twice as high as Chernobyl’s “permanent dead zone evacuation limit of 500,000 Bq” (source: Radiation Defense Project). For that reason, Dr. Caldicott strongly advises against travel to Japan and recommends avoiding Japanese food.

Even so, post the Fukushima disaster, Secretary of State Hillary Clinton signed an agreement with Japan that the U.S. would continue importing Japanese foodstuff. Therefore, Dr. Caldicott suggests people not vote for Hillary Clinton. One reckless dangerous precedent is enough for her. […]

Mari Yamaguchi, Associated Press (AP), June 12, 2015: “Four years after an earthquake and tsunami destroyed Japan’s Fukushima nuclear power plant, the road ahead remains riddled with unknowns… Experts have yet to pinpoint the exact location of the melted fuel inside the three reactors and study it, and still need to develop robots capable of working safely in such highly radioactive conditions. And then there’s the question of what to do with the waste… serious doubts about whether the cleanup can be completed within 40 years.” […]

According to the Smithsonian, April 30, 2015: “Birds Are in a Tailspin Four Years After Fukushima: Bird species are in sharp decline, and it is getting worse over time… Where it’s much, much hotter, it’s dead silent. You’ll see one or two birds if you’re lucky.” Developmental abnormalities of birds include cataracts, tumors, and asymmetries. Birds are spotted with strange white patches on their feathers.

Maya Moore, a former NHK news anchor, authored a book about the disaster:The Rose Garden of Fukushima (Tankobon, 2014), about the roses of Mr. Katsuhide Okada. Today, the garden has perished: “It’s just poisoned wasteland. The last time Mr. Okada actually went back there, he found baby crows that could not fly, that were blind. Mutations have begun with animals, with birds.” […] “<

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