June 19, 2015

Future hotter and more efficient coal plants

The hotter coal (or any thermal plant - natural gas and nuclear) can run then the more efficient they can be.

Upgrading existing plants and building new high-efficiency, low-emissions (HELE) coal-fired power plants addresses climate change concerns in two important ways. In the near term, emissions can be reduced by upgrading existing plants or building new HELE plants. Such plants emit almost 20% less CO2 than a subcritical unit operating at a similar load. Over the longer term, HELE plants can further facilitate emission reductions because coal-fired plants operating at the highest efficiencies are also the most appropriate option for CCS retrofit.

The best new coal plants in China are in the Ultra-supercritical 44-46% efficiency range.

Developments in AUSC steam cycles are expected to continue this trend. AUSC coal-fired plants are designed with an inlet steam temperature to the turbine of 700–760°C. Average metal temperatures of the final superheater and final reheater could be higher, up to about 815°C. Nickel-based alloy materials are needed to meet this demanding requirement. Various research programs are underway to develop AUSC plants. If successful, a commercial AUSC-based plant would be expected to achieve efficiencies in the range of 45–52% (LHV [net], hard coal). A plant operating at 48% efficiency (HHV) would emit up to 28% less CO2 than a subcritical plant, and up to 10% less than a corresponding USC plant. Commercial AUSC plants could be widely available by 2025, with the first units coming online in the near future.

Ultracritical coal reactor turbines in China

China is the premier example of a country benefitting from an actively pursued HELE upgrade policy. By utilizing state-of-the-art USC plants for new and replacement capacity, and with the retirement of older, less efficient units, CO2 emissions are projected to rise less steeply than the increase in demand for coal-based electricity; emissions are projected to reach 6136 Mt in 2040. If China continues to adopt the best technology and retire older units on a roughly 25-year timescale, a largely AUSC-based coal fleet would see projected CO2 emissions actually fall between 2035 and 2040; in this case the CO2 emissions are projected to be 5153 Mt in 2040 (a 16% reduction over the base case scenario), despite a continuing increase in demand. If the most effective CO2 abatement pathway is followed (25-year plant retirement, AUSC upgrades after 2025, CCS installation) emissions could fall to 750 Mt in 2040. Although the analysis presented here does not incorporate China’s recent announcement to peak coal utilization by 2020, such a policy approach would certainly require continued aggressive deployment of HELE coal-fired power plants.

On July 23, 2010, the Chinese National Energy Administration announced the establishment of a “National Innovation Union of 700°C Ultra-supercritical Coal-fired Power Generation Technology,” formally launching China’s 700°C ultra-supercritical technology development plan. This plan is mainly focused on research related to the optimal design of unit systems and major equipment as well as the development of the necessary thermally resistant alloys. Construction of the 700°C steam temperature demonstration project is expected to begin in 2018; the targeted demonstration completion date is approximately 2020

Carbon capture and storage should be technically feasible but will need

* massive investment
* a cross country pipeline network to run CO2 from plants to underground storage
* it will also cost energy which reduces plant efficiency by 10% or more

The USA has older coal plants and is looking at tweaking efficiency to go from 32% efficient to about 37% efficient.

Natural gas is close to double the CO2 efficiency versus Coal

The data below is for average heat rates for US steam-electric generators in 2013 using those fuels.
Each could get about 50% better with the best technology that could be available in 10-20 years.
They each can be about 30% better with the best technology in the world today.

Natural gas plants are pushing towards 65% efficiency.

SOURCES - Cornerstone, IEA, FAS

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