The competitiveness of coal relies on its wide availability and stability in supply and cost. Coal contributes to 39 % of worldwide electricity generation and plays an important role in global energy supply. For coal to serve as a source of the global energy supply, the greenhouse gases that are emitted from its utilization must be reduced. Oxy-fuel combustion technology is an emerging approach to capture post combustion CO2. In this technique, coal is burned using a mixture of high-purity oxygen and recycled flue gas. Oxy-fuel combustion has some other advantages over conventional coal-air combustion, such as lower NOx and unburnt hydrocarbon emissions as well as easier CO2 removal. Char gasification in mixtures of O2 and CO2 is also discussed in this paper. A sufficient active site, mainly consisting of catalyst in this study, was important not only to enhance char gasification reactions but also to prevent competitive reactions between char-O2 and CO2 gasification.
This paper introduces the concept of chemical looping clean coal technologies, included the type of carriers, base reactions, process components and analysis result. This paper also reviews the development situation of chemical looping clean coal technology projects in the world and the recent motion for development of chemical looping clean coal technology in Japan.
Lignin and cellulose chemicals were used as artificial biomass components to make-up a simulated biomass. Alkali and alkaline earth metal (AAEM) as well as volatile matter contents in these chemicals were much different from each other. Co-gasification of coal with simulated biomass shows improved conversion characteristics in comparison to the average calculated from separate conversion of coal and simulated biomass. Two conversion synergetic peaks were observed whereby the first peak occurred around 400 °C while the second one occurred above 800 °C. Although co-gasification of coal with lignin that has high AAEM content also shows two synergy peaks, the one at higher temperature is dominant. Co-gasification of coal with cellulose shows only a single synergy peak around 400 °C indicating that synergy at low temperature is related with interaction of volatiles. Investigation of morphology changes during gasification of lignin and coal, suggests that their low reactivity is associated with their solid shape maintained even at high temperature.
Humid air turbine systems that are regenerative cycle using humidified air can achieve higher thermal efficiency than gas turbine combined cycle (GTCC) power plant even though they do not require steam turbine, high combustion temperature, or high pressure ratio. In particular, the advanced humid air turbine (AHAT) system appears to be highly suitable for practical use because its composition is simpler than that of other systems. Moreover, the difference in thermal efficiency between AHAT and GTCC is greater for small and medium-size gas turbines. To verify the system concept and the cycle performance of the AHAT system, a 3 MW-class pilot plant was constructed. As a result of an operation test, the planned power output of 3.6 MW was achieved, so that it was confirmed the feasibility of the AHAT as a power-generating system. Moreover, the 40 MW-class AHAT test facility was developed and confirmed practicability of the AHAT system with a heavy-duty gas turbine for industrial use. In these AHAT systems, a cluster nozzle burner configuration, which has many coaxial jet streams of fuel and air, was adapted to cope with both flame stability and NOx reduction problems. From the test results, NOx emission is expected to be less than 10ppm for the future commercial AHAT system.
It is projected that the long-term global demand for gas turbine combined cycle (GTCC) engine is going to expand as a clean and economical electrical power plant. In order to improve the thermal efficiency of the cycle, the development of 1700 °C class gas turbine is carried out in national projects. A part of the results of the national projects has already been applied to the development of 1600 °C J-type gas turbine. In the national projects, Exhaust Gas Recirculation (EGR) system has been investigated as a high temperature combustion technology in order to reduce NOx emission. In the high pressure EGR combustion test to the full-scale combustor, NOx has decreased remarkably and become lower than development target 50 ppm on 1700 °C condition. In addition, OH-PLIF measurement was applied to the full-scale combustor of gas turbine engine as a technique to estimate the flame instability. It was found that flame fluctuation and pressure fluctuation have a strong correlation on the flame holding point which locates between main nozzle and pilot nozzle. In order to suppress the pressure fluctuation, investigation of the mechanism which causes the flame fluctuation is important.
Low quality carbon resource is hydrocarbons containing moisture and ashes at high density, which is disposed as waste. Those materials have not been considered as the energy resources for a long time, because of low heating value and difficulty in use. However, it is very important to use those hydrocarbons as the alternative fossil fuels in the aspect of environment and energy security in Japan. There are so many problems and issues in utilization of low quality carbon materials. Therefore, this article explains the present situation and current challenges in the utilization of low quality carbon fuels and introduces new energy utilization techniques of those materials, especially in sludge treatment and utilization.
The effects of the air-fuel injection velocity ratio on the emission characteristics of the rapidly mixed tubular flame have been experimentally investigated. The NOx and CO emissions were examined for three tubular flame burners of which injection velocity ratios were αst = 1.0, 0.5 and 0.25. Results showed that the NOx and CO emissions of the rapidly mixed tubular flame could be drastically reduced for fuel lean conditions of the αst = 0.25 burner due to the rich-lean combustion. As the injection velocity ratio was enough less than unity, a super-rich mixture could be formed around the injection part even under the fuel lean condition, and thus, the NOx formation was suppressed in the upstream region. A large amount of CO could be formed in the region, however, the CO was reduced by reacting with the excess O2 which was not consumed in the upstream region.
The effects of elevated-pressure on rotating counterflow twin flame were numerically investigated. The range of pressure is from 1 to 8 atm. We performed numerical simulations with and without radiative heat loss. The loss was evaluated by using an optically thin model, which does not consider reabsorption of radiative energy. Without radiation, the leanest extinction limits reached ultralean conditions; the higher the pressure is, the leaner the extinction limits are. On the other hand, with radiative heat loss, the leanest extinction limits are shifted to richer condition as the pressure becomes higher; above 2 atm, the leanest extinction limits cannot reach ultralean condition. The response curves of the flame temperature to the equivalence ratio are distorted when radiative heat loss is considered. Under high pressure, the flame thickness is thinner and the heat release rate is enhanced mainly because of the increase of gaseous density in the both cases of with and without radiation heat loss. However, the temperature behind the flame zone much decreases due to the radiative heat loss in the high pressure case. This is because of increments of partial pressures of the radiative species and the length of the residence time of fluid in the backflow region of burned gas.
An experimental study has been conducted to obtain knowledge on a new heating technique with use of the inner hot gas region of tubular flames. Two kinds of tubular flame burners of non-swirl type and swirl type have been made, and the flame appearances and the stable flame regions have been mapped as a function of the mixture flow rate and the equivalence ratio. An air to be heated has been introduced into the inner hot gas region of the tubular flame and the radial as well as the axial temperature distributions have been determined. Results show that in contrast to the non-swirl type burner, the swirl type burner gives a better axisymmetric tubular flame and a wider stable flame range, and in addition, the swirl type burner gives a faster temperature rise than the non-swirl type burner. The temperature rise becomes more rapid as the swirl number of the burner is increased. A simple analysis demonstrates that the enhanced temperature rise can be explained through an increase of the heat transfer area between the air stream to be heated and the hot burned gas of the tubular flame; the air to be heated is involved into the swirling hot burned gas, resulting in a rapid temperature rise in the heating process.
An experimental study was performed to evaluate measurement of temperature development behavior for autoignition process in Rapid Compression Machine simulating a HCCI engine. In the experiments, n-heptane was used as the fuel and the charge mixture was compressed in homogeneous manner with varying compression ratio. Infrared emission method was used to capture the temperature distribution and CO2 gas was used as the emission medium, as CO2 has strong emission band near 4.3-4.5μm. The emitted radiation was recorded by a high speed infrared camera. The relationship between the emitted energy and the medium temperature was calculated with RADCAL code, and the database for different pressures and temperatures within relevant ranges to engine combustion was prepared in advance. The obtained results show that the temperatures in the cylinder were not uniform due to a roll-up vortex right after the compression. The difference in the temperature distribution behavior at different equivalence ratio during the ignition delay was successfully captured. The developed technique could be applied for detecting the slight temperature change due the low temperature reaction and the motion of the charge.