Seeking a new R&D path to clean coal1 December 2007
‘We need to rethink radically our approach to the R&D effort being put into clean coal technology’
Research is mostly a good thing. We learn something and people are employed. However, not all research yields equal value. Where coal power generation is concerned, current research involves the capture and storage of CO2 using high-cost and inefficient technology. Increases in atmospheric CO2 concentration and higher cost fuels, combined with the probability of treaties and legislation requiring reductions of greenhouse gas emissions, require R&D approaches that involve more risk and a long range definition of success.
It is clear that CO2 emissions need to be controlled. Worldwide, the level of CO2 concentration in the atmosphere is increasing. It is not necessary to wait for nations to reach consensus about the cause and effect of climate change impacts. The probability of bad things happening is more likely than good; and chemistry tells us there will be more acidification of air, land, water and humans. While we do not fully understand how the human body and the environment will react to higher pH levels, prudence dictates that we act now to determine ways to mitigate atmospheric CO2, and to understand the technologies and processes that will be required for mitigation to occur.
CO2 sources, especially from power generation, are easy targets for these efforts. They are very visible, stationary sources; the amount of CO2 produced in any given year is huge; and there are practical opportunities to capture some portion of the total. Power plant CO2 for 2005 was some 2.5 gigatons (billions of tons). In volume this is more than twice the amount of natural gas produced, pipelined and consumed in the US annually.
Current R&D programmes
The United States and most of the developed world have research and development programmes in place to reduce CO2 from coal power plants. Current clean coal projects pursue, in one way or another, the capture of carbon dioxide so it can be stored in carefully selected geological formations deep below ground. In the United States the Department of Energy is focused on FutureGen, which gasifies coal to hydrogen for power generation. FutureGen partners include international industrial and government organisations led by the US. Industry will cost-share at least 50% of the plant costs. Canada and the European Union are exploring oxygen-coal combustion and post-combustion flue gas processes to capture the CO2. In addition, there is a number of ‘commercial’ or niche market gasification projects being considered in North America, Europe, and Asia that may install CO2 capture capabilities.
CO2 is not easy to control. It is relatively inert chemically, requiring large amounts of heat to convert it into its elements or other less worrisome compounds. And the very, very large volumes of gas to be treated call for new thinking about solutions that fit the problem. The current solution involves brute force separation of the CO2 from mixed gas streams before it can be compressed into a liquid for pipeline transportation and injection at least 3000 feet deep where the pressure will maintain the liquid state of the CO2.
Economics driving R&D
There are plenty of carbon management R&D problems to solve (and fund) so choices are difficult. Let’s assume that the transportation by pipeline and even the injection and geological storage are technically sound. While these parts of the CO2 sequestration process have many public relations, legal and political hurdles, there really are few technical issues left to consider and solve. In addition, the transport and storage of CO2 is relatively inexpensive compared with the cost of separating it and compressing it to be ready for the pipeline.
For example, if the total sequestration cost is $60 per ton of CO2, the transportation and storage is perhaps $10 and the rest is for capture and compression. Unfortunately the $60 figure is outdated and too low. The September, 2005 Intergovernmental Panel on Climate Change (IPCC) report on capture and sequestration has capture costs including compression that range from $11 to $56 per metric ton depending on the coal technology, and from $33 to $57 for natural gas combined cycle power plants. These figures do not include transportation and storage. In addition, the references used in the report very likely made their calculations prior to the volatility which has characterised material and construction costs in the last few years.
It will be very interesting to see how the cost estimate treading for the FutureGen plant alters the thinking on CO2 capture costs. Original FutureGen plant estimates were on the order of $1 billion. The gasification plant has a 275 MW generating capacity. DOE is now forecasting $1.7 billion and even with its research function that is more than $6000 per kilowatt plant cost. Historically $1000 to $1500 per kW has been a widely sought goal for conventional pulverised coal and gasification combined cycle plants. $100 per ton of CO2 is not an unreasonable estimate for the cost to capture and compress the gas at a power plant.
Low return on R&D
Assuming all the FutureGen and other systems undergoing R&D function, what will we get for our money? We get the promise of future plants that can make electric power and/or hydrogen and a stream of CO2 that can be transported and sequestered below ground. That’s the good part. The downside for taxpayers and investors is that the plants only operate at about 30% efficiency going from the coal energy to electric power; maybe somewhat more if fuel cells can replace the gas/hydrogen turbine.
This is not to single out the FutureGen project. The other publicised carbon management projects use equally inefficient technologies in designs that are limited variations of systems that work well in other commercial applications, but are not intended for or suited to process the large volume, low pressure (atmospheric) and contaminated flue gas from coal or the exhaust from natural gas power plants.
Too much of the current R&D efforts are focused on too short a time horizon and because of that, the technologies are too ‘commercial’ with combinations of well-tested components: gasifiers, syngas treatment processes and gas turbine power generation. Commonly the R&D plans call for testing any less mature technologies like fuel cells with smaller ‘slip-stream’ versions of the technology.
In Europe and Canada the focus on gasification may be less, but the low level of risk-taking is similar. Statoil currently recovers CO2 from natural gas turbine exhaust and stores it under the North Sea to avoid a carbon tax of $50 per ton. European and Canadian approaches include post-combustion separation of CO2 from pulverised coal plants and even natural gas-fired combustion turbines with chemical absorbents or the use of oxygen to substitute for air in the combustion process, which if properly implemented turns the flue gas into a highly concentrated steam of CO2 that can be compressed and made suitable for pipeline transport.
Working toward 60% to 70% efficiency
A high-efficiency generation process is needed, with a goal of 60 to 70% efficiency going from the energy in the coal to electricity leaving the plant.
High efficiency solves or mitigates many problems. If less coal is needed there is less CO2, solid and other waste to begin with, and this means there is much less that has to be cleaned up, treated or, for CO2, sent to sequestration. A 60% efficiency power plant would generate roughly half the wastes compared with the best planned ‘clean coal’ plant with CO2 capture from the flue gas or by separating it from a gasification syngas.
A second goal is to eliminate or minimise the steam cycle currently needed to make electric power. While it is reliable, robust and part of almost every medium to large power generation unit ever built, the subcritical steam cycle is relatively inefficient, and raising steam conditions to supercritical or
ultra-supercritical pressures significantly increases cost. Perhaps equally important today, the cycle of steam generation, expansion and condensing consumes large quantities of water for cooling. There are options to avoid wet cooling, but they are expensive to install and operate.
Can 60% plus efficiency be achieved?
Can a power plant achieve high efficiency and compete economically? There are concepts currently being explored, but none that would be ready to build at commercial scale for 10 years. Does that mean we give up on these concepts? No: it means we have lots of R&D to do and that this R&D will be much more meaningful, much higher risk, and perhaps more expensive than the work now going forward. Those are good things if you really want to advance the state of the art, and may be cost-effective in an absolute sense given trends in the amount of greenhouse gas emissions worldwide.
The zero emission coal alliance or ZECA is one example of conceptual engineering to explore highly efficient power generation with CO2 capture. ZECA was active from 2000 to about 2003. Some 20 international organisations co-operated to explore technical opportunities to successfully manage carbon. They did this not to create intellectual property or to construct plants, but to support the survival of their core businesses of coal production, power generation, equipment manufacturing, engineering and other operations. The alliance organisations saw the risk of carbon constraints early, and sought to explore new technologies and concepts that they could use in the future to protect their businesses. About $1.5 million was funded by the private companies in the alliance for engineering, and most importantly for assessments of roadblocks to employment of the technology. Many of the industrial participants are now involved with FutureGen. The ZECA concept actually resulted in a coal-to-electricity efficiency of nearly 70%, so the 60% target leaves room for flexibility and compromise often arising from R&D projects. There are other advanced concepts and many of the R&D needs for these processes are similar and well know by the energy community.
Projects worth the risks and costs
Since we are dealing with coal, the process would benefit from technologies to clean the hot coal gas, thereby limiting energy losses incurred by cooling the gas, as is now done, before cleaning. If a feasible hot cleanup process cannot be found, an alternative would be to make the power generator and other parts of the downstream system more tolerant of sulphur and other impurities in the hot gas.
If the plant uses oxygen for gasification, the commercial cryogenic air separation process has to be improved or replaced by better technology. In the ZECA model, oxygen was avoided by recycling hydrogen from the coal gasification step and using this as the thermal energy carrier to make the gasification reactions go forward.
The gasifier operates at an elevated pressure of about 900 lb/in2 in ZECA’s case. The rest of the plant should run at high pressure too so that the pressurised CO2 is captured and most of the costs for compression to pipeline specifications (in the order of 2000 psi) are avoided.
All the concepts require a separation step that removes the CO2 from fuel gas, and finally there has to be an efficient way to convert the fuel to electric power.
These are just a few, broad R&D recommendations. Other ideas certainly warrant investigation so long as they enhance the objective of generating power at high efficiency and capturingthe CO2.
High temperature fuel cells
High temperature (probably solid oxide) fuel cells are prime candidates for the power generation step and as a path to avoid steam cycle inefficiencies. The cells can operate at pressure and at high temperature, but the current versions are too costly to make competitive electric power. Today’s fuel cells also lack sufficient tolerance to impurities in coal-derived feedstocks. This reinforces the need for R&D to produce more robust and less expensive high temperature fuel cells combined with more effective hot gas cleaning.
Fuel cells also greatly mitigate the water consumption problem when their high quality process heat is used in chemical reactions that replace the steam cycle for power production. The ZECA concept had an elegant method, using most of the heat to regenerate and recycle the material that was used to capture the CO2.
Currently, there is some R&D being conducted to make fuel cells more coal compatible and scale them up in size to be economical for large power plants, but much more needs to be done. Most importantly, the question of how to integrate fuel cells with other plant components requires a parallel R&D path to focus on the high efficiency and CO2 capture objectives.
Revolution, not evolution.
Until very recently, efficiency was not a major issue for power generation. It was considered good to save some fuel with a more efficient design, but only if the equipment did not cost too much compared with a less expensive, less efficient alternative. The main reason for not ‘chasing Btus’ to improve performance was the low cost of fuel. Whether the plant used coal or natural gas, fuel was cheap and it did not require much capital expense to out-weigh the benefits of greater efficiency.
And for corporate decision-makers with accounting or legal backgrounds the increased capital costs were clear and certain, but the improved efficiency and future savings were risky and uncertain. The regulated utility structure helped ensure a low business priority for efficiency and since the plant people were interested in making electricity with the simplest and most reliable, proven technology this left a few engineers and academics wandering in the wilderness doing studies ‘chasing Btus’.
The relationship of capital costs to efficiency changed somewhat with increasing fuel costs, and perhaps even more from the shock of price volatility in coal and natural gas. However, even higher fuel costs have not moved the industry and government away from the lower risk R&D options.
A “typical” 500 MW coal power plant operating at 30% efficiency will generate about 2.8 million tons per year of CO2. If the CO2 cost or tax is $60 per ton, this equals $168 million per year. For perspective, the plant will use about 1.7 million tons per year of coal for fuel. At a fuel price of $50 per ton or about $2.30 per million Btu, the annual fuel cost is $85 million or roughly half the cost of the CO2 sequestration. These figures do account for the lost generating capacity that results from installing CO2 capture technologies.
While one cannot recommend any single future power generation technology with CO2 capture and sequestration components at this stage of the R&D path, one can certainly question the current direction of our carbon management R&D. We have failed to properly define the problem and have wandered from the R&D path best suited to find solutions. High efficiency coal systems with CO2 capture can be developed, but too much R&D money is being spent on near-commercial technologies that have little promise of advancing to the point where their performance and economics make practical sense to anyone other than regulators and special interest groups. The research actually being done on more efficient, higher risk technologies is inadequate given the scope of the problem.
There are as many reasons for our current R&D path as there are interest groups and government agencies, but as taxpayers, electric power consumers and workers we owe it to ourselves to ask what we are going to get from the R&D when it is successfully completed. It is not too late for this dialogue to begin and reroute the research toward highly efficient power generation with CO2 capture.