By Louis Wibberley
Leader, DICE Development Program, CSIRO
The power plants serving tomorrow’s electricity grid must overcome challenges that include higher penetration of renewables, and thus a need for increased flexibility, lower emissions, and water constraints. Even as these challenges are met, electricity will need to remain affordable. While DICE (direct injection carbon engine) is unlikely to displace ultra-supercritical baseload generation, the technology presents a very real chance to use coal to follow dramatic load changes in markets with high renewables penetration and to add smaller electricity generation in remote areas without reliable grid access.
THE DICE OPPORTUNITY
DICE combines the superior thermal efficiency, flexibility, and lower capital cost of the diesel engine with the low cost and availability of coal.1 The technology dates back to the development of the diesel engine by Rudolf Diesel in 1892, which was originally intended to use pulverized brown coal as fuel, but then the inventor turned to peanut oil after difficulties with the injection equipment. The modern variant of DICE uses finely ground low-ash carbons (e.g., coal, lignite, and biomass) slurried with water—a fuel called micronized refined carbon (MRC). MRC is a liquid fuel (similar in consistency to acrylic paint), which can be used in diesel engines that have been adapted with a slurry fuel injection system and hardened cylinder components. The DICE fuel cycle is depicted in Figure 1.
DICE is based on using adapted diesel engines, which are a mature power generation technology. Such engines play a minor role in baseload power production in today’s market due to the high cost of diesel fuel, higher maintenance costs, and, in the past, the relatively small unit size. Currently, the largest diesel engine in commercial production is 76 MW—a size used principally for large ships. If larger capacity engines were required, the manufacturer MAN B&W have a K108 engine design, which in its 18-cylinder form would generate around 120 MW. MAN B&W believes that engines up to 150 MW are technically feasible using current engine and manufacturing technologies.2 In addition, there are a range of options to optimize large marine engines for land-based power generation to reduce both capital and operating costs.
However, in contrast to conventional coal-fired power plants, which gain economy of scale via increased unit capacity, diesel (and gas) reciprocating engines obtain economy via modularity and multiple units (e.g., a 1000-MW reciprocating gas-engine power plant has been constructed near Salvador using 120 medium-size gas engines). It is anticipated that the same modular approach could apply for DICE.
Regarding fuel for DICE power plants, MRC fuel could become a new global commodity for low-emissions power, given that MRC is nonflammable, environmentally benign, and can be safely transported and stored. This option is being actively considered in Victoria, Australia, with the potential to efficiently convert vast reserves of brown coal to export MRC, at around one third of the cost of LNG. In Australia, MRC fuel also costs less than fuel oil and most gas, and could reduce power generation costs for remote or decentralized generators. This would also enable lower cost electricity for off-grid communities (especially in developing countries) and assist sustainable mining development by providing cost-effective power for mines and communities.
Like other reciprocating engines (gas or diesel), DICE power plants could be modular and can be ramped relatively quickly, and can thus be used for load following and even baseload generation in some circumstances.
Development of DICE faltered historically largely because the
intended purpose was to use coal as a substitute for oil in shortages that did not materialize. However, today, DICE is being pursued not to replace oil, but as a unique high-efficiency, low-emissions (HELE) coal technology that can support a grid with increased renewables and water constraints, and with decreased emissions.
DICE as a HELE Coal Technology
DICE could play a role in the transition to a lower emissions energy sector as it is a cost-competitive, lower emissions technology in its own right. See Figure 2 for an example based on Victoria, Australia, showing the cumulative effects of an integrated carbon management scheme.
DICE provides a higher efficiency coal-based generation technology, with a step reduction in CO2 emissions of 20–35% for black coals and 30–50% for brown coals (ranges based on new DICE and new ultra-supercritical pulverized coal–new DICE and an old subcritical coal-fired power plant in Australia). Greater emissions reductions can be achieved if MRC composed of a coal/biomass blend is used, where the biomass is likely to be in the form of a char. However, coal must make up some of the MRC for DICE as it improves the combustion characteristics.
Further reductions in CO2 emissions could be achieved by providing backup and load-following power to enable the cost-effective and increased use of intermittent renewables without the loss in efficiency incurred from load following by conventional thermal power plants. DICE also could assist in the uptake of carbon capture and storage (CCS), delivering a 30–40% cost advantage (in terms of $/t CO2 abated)A compared to CCS on conventional coal-fired power generation through increased efficiency and the ability for waste engine heat to provide at least 65% of the CO2 stripper heat requirement.
Flexibility: An Increasing Challenge
Increased flexibility is a challenge for grids—one that is growing in magnitude with the ever-higher penetration of intermittent renewable generation in response to policy initiatives. Continued growth of renewables over the long term will further exacerbate the need to provide more flexible and distributed generation capacity.
Natural gas combined-cycle and conventional coal-fired power plants can follow load demand, although their efficiency decreases at lower loads and maintenance requirements increase due to thermal swings. In addition, due to their large unit size, which helps to optimize efficiency, most conventional coal-fired power plants have low ramp rates on the order of about 1%/min, although some plants in Europe have reported ramp rates of about 4%/min. In comparison, DICE provides superior flexibility with ramp rates of 10%/min.
The flexibility of DICE is not limited to load following. The technology provides an option for customers seeking new power generation capacity at various sizes. DICE is modular (in 10–100-MW increments). In addition, for cash-strapped customers that need immediate capacity, DICE requires half the capital investment (US$1.1 million/MW for four-stroke DICE and US$1.6–2 million/MW for low-speed two-stroke marine engines; 2015 estimate) of conventional coal-fired power plants.
DICE could also provide users of natural gas with the option of installing multi-fuel gas engines and retrofitting with a DICE conversion kit in the future if natural gas prices become uneconomic. This approach could prevent stranded assets. Such a conversion is not possible for gas turbines, regardless of mineral content of the MRC fuel, due to intolerance to alkalis.
The Water–CO2 Nexus
Cooling water (for noncoastal installations) has become a serious issue for Rankine cycle thermal plants in many parts of the world. Taking coal-fired power plants as example, at the lowest cost and highest efficiency such plants use 2000 L of water for condenser cooling for every MWh generated. This level of water consumption is becoming intolerable in some locations (e.g., Australia, India, South Africa, and China), requiring the use of dry cooling. Although this reduces water consumption to around 300 L/MWh, dry cooling increases plant costs, delivered electricity cost, and CO2 intensity—the last by up to 5%. Thus, dry cooling can result in an additional 1000 kg CO2 being emitted for each 30 tonnes of water saved.
DICE is much easier to dry cool because the temperature at which heat is rejected is much higher. This enables much lower cost dry-cooling (radiator) systems and completely avoids the need for cooling water. Water is needed for MRC fuel production, but this is at a rate similar to that for a dry-cooled conventional coal-fired power plant. Notably, fuel preparation for DICE can be located remotely from the power plant (i.e., fuel preparation can be co-located with reliable and abundant sources of water).
NATURAL GAS VERSUS DICE
Although natural gas-based generation can be considered an easy option for reducing CO2 intensity, to compete with coal for baseload electricity natural gas must be a sufficiently low price (without excessive volatility), and have security of supply. The “dash for gas” in Europe has abated due to gas price increases, with recent mothballing of gas generation capacity (both combined and open cycle) in some countries. As examples, GDF Suez has closed gas power plants with a combined capacity of over 7 GW; in the UK, the Keadby 750-MW power station (commissioned in 1996) was mothballed last year; and RWE is closing its Claus C plant in the Netherlands, just two years after it was commissioned.
Based on the availability of unconventional natural gas, the U.S. has expanded natural gas-based generation, although price volatility remains an issue (particularly in winter). As an extreme example, the price in New England in January and February 2014 rose to $17/GJ, whereas the average gas price for the U.S. for the same period was US$7.4/GJ, and the average coal price was US$2.3/GJ (data from U.S. EIA Electric Power Monthly).
Overall, considering fuel options that can respond to demand should provide new opportunities for coal—providing the technology is highly efficient, highly flexible, and CCS ready. DICE potentially has all of these attributes, and is well suited to balance the additions of intermittent renewables to the grid, but does not suffer from the high prices and/or price volatility often associated with natural gas.
Despite the many potential advantages, the use of coal in DICE has required addressing a number of technological issues (especially injector nozzle and piston ring wear), which were essentially solved for smaller engines (i.e., <5 MW) in a comprehensive U.S. Department of Energy (DOE) program (1978–1992).3–5 Since the DOE program ended, a number of significant technology developments have occurred in both coal processing and engine design and materials. These, combined with the use of larger, lower speed engines (and many new drivers), are expected to significantly increase both the technical and the economic viability of DICE.6
In past programs, the cost of coal processing reduced the cost advantage of DICE, and, together with falling oil prices, was a key factor in the termination of the DOE program. Fuel production now has the advantage of large and efficient mills for micronization (e.g., IsaMill™) and improvements in fine-coal cleaning.7 These technological advances provide a step reduction in processing cost and also allow cost-effective recovery of MRC from tailings. Thus, in Australia, MRC is now estimated to cost AUD$2–3/GJ (US$1.4–2.2/GJ) for Victorian brown coal and AUD$4–6/GJ (US$2.9–4.3/GJ) based on bituminous coal. Economic assessments have shown that the increased cost of coal processing is more than offset by increased grade recovery, lower capital cost, and reduced fuel rate of DICE (together with a range of environmental benefits).8
The largest challenge facing the development of DICE may be a non-technical one. There is no clear owner or champion for the technology, but many interested parties, including the coal industry, technology providers, engine producers, and power producers. Although DICE needs considerable development and demonstration, it has an enormous advantage via the ability to carry out a near-commercial-scale demonstration at a relatively small size (around 10 MW), both quickly and at relatively low cost. This should enable DICE to leapfrog the usual technology development steps, resulting in a time to first commercial deployment of five years, and as low as US$70 million, including fuel processing and logistics. An international umbrella organization, DICEnet (www.dice-net.org), has been established to help coordinate efforts, and a staged, integrated DICE development program has been devised for both black and brown coals with a goal of a large-scale demonstration after 2020.
Currently, a number of groups are investigating the DICE fuel cycle in Australia, Europe, China, Japan, the U.S., and South Africa. MAN Diesel and Turbo have engaged with a number of MRC proponents, and are considered the industry leaders in DICE development. MAN has established a staged development program with a specially adapted low-speed 1-MW single-cylinder test engine at Mitsui in Japan. Development efforts will also benefit from recent experience from firing engines with bitumen slurries and residual fuel oils (e.g., Orimulsion and MSAR®).9–11
Combining the superior thermal efficiency, flexibility, and lower capital cost of the diesel engine with the low cost and availability of coal provides an innovative step change technology that could markedly increase the competitiveness and reduce the environmental footprint of coal-based power generation. Australian R&D over the last five years has focused on “derisking” the fuel cycle, and confirmed the potential of this alternative technology for coal and other carbons. Internationally there are many opportunities for DICE, including:
- Incremental replacement of less efficient coal generation plants—175 GW of smaller/older capacity identified (e.g., below 300 MW and older than 40 years)
- Smaller incremental capacity for developing nations
- A cost-effective/CO2-equivalent technology for replacing open-cycle natural gas turbines used for load following and backup duty
- New capacity for ancillary services to underpin growth in renewables
- A replacement technology for high-cost diesel generation in remote mining sites and communities, especially in developing countries
- Replacement capacity for uneconomic gas generation
Recent technology assessments have shown no major technical barriers in developing DICE to a commercial scale. Some further development work is required to optimize for a range of coal types and engine technologies, but the development-to-deployment time scale could be as short as five years based on an assessment by MAN Diesel & Turbo.B The costs to commercialization (from R&D to demonstration and first commercial plant) would be comparatively low (i.e., estimate of US$70 million).
Development and deployment of DICE provide an opportunity for the coal industry, the electricity generation sector, and governments to support a breakthrough technology—for the combined benefit of coal and renewables-based electricity systems.
A. Based on personal communications with, among others, Barry Hooper of CO2CRC in May 2013, regarding CO2CRC‘s calculations on the use of the UNO MK3 capture system for DICE.
B. This information is taken from a series of conversations with Larry Silva, Managing Director, MAN Diesel & Turbo Australia—especially those based on an internal report (#LDF1-20120014), “A first plan for the development of a stationary low-speed two-stroke engine to be operated on coal water slurries,” issued by MAN Diesel & Turbo on 29 June 2012.
- Jha, C.M., Smit, F.J., Shields, G.L., & Moro, N. (Undated). Pre-mium fuel development, Contract No. DE-AC22-92PC92208. U.S. Department of Energy, National Energy Technology Laboratory, www.netl.doe.gov/publications/proceedings/97/97cl/jha.pdf
- Van Dyck, P. (2005). The big one from MAN B&W. Motor Ship, 86(1013), 8–9.
- Hsu, B. (1992, July). Coal-fueled diesel engine development update at GE Transportation Systems. Journal of Engineering for Gas Turbines and Power, 114(3).
- Ryan, T. (1994, October). Coal-fueled diesel development: A technical review. Journal of Engineering for Gas Turbines and Power, 116(4), 740-748.
- Arthur D. Little, Inc. (1995, October). Coal-fuelled diesel system for stationary power applications – Technology development. Final Report March 1988–June 1994. Topical Report Contract DE-AC21-88MC25124, For U.S. Department of Energy, Office of Fossil Energy, www.netl.doe.gov/File%20Library/Research/Coal/major%20demonstrations/cctdp/Round5/M96000600.pdf
- Nicol, K. (2014). The direct injection carbon engine. International Energy Agency Clean Coal Centre. Available at www.iea-coal.org/site/2010/publications-section/reports
- IsaMill. (2015). IsaMillTM breaking the boundaries, www.isamill.com/EN/Pages/default.aspx
- Wibberley, L., & Osborne, D. (2015). Premium coal fuels with advanced coal beneficiation. Presented at Clearwater Clean Coal Conference, Clearwater, FL, 31 May–4 June. Available at jamesoncell.com/EN/Downloads/Pages/TechnicalPapers.aspx
- Modern Power Systems. (2000, 21 July). Optimism about Orimulsion?, www.modernpowersystems.com/news/newsoptimism-about-orimulsion-
- Wärtsilä. (2005). Annual report ‘05 sustainability report, www.euroland.com/arinhtml/sf-wrt/2005/bu_eng_2005/index.htm
- Quadrise Canada Corporation. (2015). Low cost alternative fuel, www.quadrisecanada.com/fcs-low-cost.php
The author can be reached at email@example.com
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