The Cross-ministerial Strategic Innovation Promotion Program (SIP) “Energy Carriers”, which aims development of hydrogen value chain, was conducted for five years from 2014. Research and development of ammonia combustion played an important role in the project, and significant outcomes related to utilization of ammonia as a carbon-free fuel were produced for gas turbines, internal combustion engines, industrial furnaces, co-firing of pulverized coal combustion, as well as feasibility study of ammonia combustion in large scale power plants. The project introduced renewed interest of ammonia combustion into international combustion community in terms of reducing greenhouse-gas emission from combustion in energy and industrial sectors. Ammonia combustion also has an impact not only on Japanese domestic policy for energy and environment but also on international energy agencies, which influence governments and industries of various nations.
AIST carried out demonstration tests with the aim to show the potential of ammonia-fired power plant. 50kW class turbine system firing kerosene is selected as a base model. A standard combustor is replaced by a prototype combustor which enables a bi-fuel supply of kerosene and fuel gas. The gas turbine started firing kerosene and increased its electric power output. After achievement of stable power output, ammonia gas was started to be supplied and its flow rate increased gradually. Ammonia combustion in the prototype bi-fuel combustor was enhanced by supplying hot combustion air and by modifying the air inlets. However, the exhaust gases from the ammonia flames had high NOx concentrations. NOx removal equipment using selective catalytic reduction can reduce NOx emission levels to below 10 ppm from more than 1,000 ppm (converted value of NOx to 16% O2) as already reported. However, downsizing of NOx removal equipment should be achieved for practical use. Therefore, a low NOx combustor was developed. We modified the combustor to the rich-lean burning method and found the condition that the NO emission can be reduced to less than half, but the NOx emission reduction was insufficient as compared with the small-scale flow test at the lab scale. Therefore, each part of the combustor was redesigned so that mixing of fuel and air improves uniformity. Low-NOx combustor (Step2) was designed using knowledge of Prototype bi-fuel combustor for ammonia (Step0) and Low-NOx combustor (Step1). As a result, we found a condition that the NO emission can be reduced to 200ppm or less as compared with before redesigning for rich-lean combustion.
To develop an ammonia/natural-gas co-fired gas-turbine which clears environmental regulations, power generation tests have been conducted using a 2 MW class gas-turbine. The test unit consists of an ammonia supply unit, a natural-gas compressor, a gas-turbine, and a NOx removal device. In the ammonia supply unit, ammonia is pressurized in liquid state by a pump and gasified with a hot water evaporator. The high-pressure ammonia gas is supplied to the gas turbine. For the gas turbine, IM270 gas-turbine manufactured by IHI Corporation is used. Only the combustor is modified for ammonia/natural-gas co-firing. In the NOx removal device, a catalyst which used in a natural-gas firing plant is applied. Low-pressure ammonia gas is supplied from the ammonia supply unit as a NOx reducing agent. As a result of the tests, the successful power generation of 2 MW has been demonstrated for the first time with ammonia mixing ratio of 20%LHV. It has further been confirmed that CO2 emissions can be reduced about 23%. Although the NOx concentration at the outlet of the turbine is higher than that of the natural-gas fired gas turbine, it has also been confirmed that the NOx removal device can reduce it to 7 ppm or less.
This paper describes research and future plan of ammonia cracking gas turbine system, which burns hydrogen decomposed from ammonia using exhaust heat of gas turbine. The system has two alternative configurations: a co-firing system which burns mixtures of natural gas and ammonia cracked gas, and a mono-firing system which burns ammonia cracked gas. The co-firing system has fewer development subjects, because heat necessary to crack ammonia is fed by steam branched from HRSG. The gross/net thermal efficiency of the mono-firing system was 102.4 % and 101.7 % of that of the natural gas fired GTCC, respectively, owing to the increase in the calorific value of the fuel during ammonia cracking and to the increase in the flow rate of the turbine working fluid. Among several known catalysts for cracking ammonia, a base metal catalyst and a noble metal catalyst which have high catalytic activity even under relatively low temperature conditions were selected and tested under at 5.2 MPa, which is the assumed operating condition of the system. Then, the rate equation as a function of temperature and pressure was derived from the measurement of ammonia cracking ratio. A laminar combustion burner which forms a flat plate flame was prepared and NOx concentration was measured. Also, NOx concentration was calculated by a one-dimensional laminar premixed flame calculation model combining the PREMIX code of CHEMKIN and the GRI 3.0 mechanism. These results indicate that the NOx concentration increases in proportion to the increase in the residual ammonia concentration. They also show that most of the residual ammonia in the fuel is converted into NOx.
Ammonia is expected as a potential fuel to substitute fossil fuels, because it does not discharge carbon dioxide and is easily handled by liquefaction. One of the possible applications for the direct use of ammonia as a fuel is the combustion use in thermal power plants. In particular, co-firing of ammonia in coal-fired power plants seems to have a relatively great advantage on the suppression of greenhouse gases, because coal is one of the main emission source of carbon dioxide. On the other hand, it is concerned that concentration of nitrogen oxides (NOx), which is one of the typical atmospheric pollutant, in the flue gas would considerably increase due to the oxidation of ammonia. In this study, we examined the influence of ammonia co-firing with coal on NOx emissions and investigated the methods to reduce NOx emissions using two coal combustion test furnaces, a single-burner test furnace and a multi-burner test furnace. When the ammonia co-firing rate was increased up to 20% of the low heat value (LHV), there was no significant increase in NOx concentration at the furnace exit. In the case of injecting ammonia into the pulverized coal combustion flame through the side port of the furnace wall using a single-burner test furnace, NOx concentration could be reduced at the appropriate location of ammonia injection. As a result of examining the effect of changing the burner stage for injecting ammonia using a multi-burner test furnace, it became clear that NOx concentration could be reduced by injecting ammonia concentrated in the lower burner rather than injecting ammonia evenly throughout all of burners.
This paper informs the achievements of the research activity related to the direct combustion of ammonia for the coal fired power plant. There are some technical issues expected in the ammonia utilization for the coal fired power plant. One is the increase of the NO concentration in the exhaust gas. Another is the inflection of the local heat flux on the boiler wall. The first issue related to the NO concentration was solved by the experimental approach with the 10 MW thermal input test facility. NO generation was under controlled by injecting the ammonia into the strong reduction zone, that is created by the coal combustion. Ammonia was well decomposed into the nitrogen and hydrogen in such a strong reduction zone. By this experiment, it was proved that the ammonia can be safely co-fired with coal by 20% in the calorific base. The second issue related to the heat flux on the boiler wall was discussed by the numerical analysis. The size of the boiler in this discussion was 1000 MW which is the biggest size in the present market. Although the gas temperature in the ammonia co-firing is a slightly lower than that in the coal firing, there is not largely different in the local heat flux nor total heat flux between coal firing and ammonia co-firing conditions. For the next step to penetrate this technology into the society, the demonstration in the commercial scale boiler is demanded.
The Co-firing tests were conducted using a fuel mixture which consists of ammonia gas and coal in the boiler at Mizushima thermal power station. As a result of tests, it was confirmed that there is no problem with the equipment while the mixture (the rate of ammonia gas against coal is 0.6 wt% or 0.8 wt%) is burned in the boiler. Furthermore, it was estimated that CO2 emission is reduced by using ammonia gas.
The reduction of greenhouse gas such as CO2 has been strongly desired to prevent global warming. The reduction of GHG has become the urgent issue to be addressed in the maritime sector as well. For the GHG reduction from internal combustion engines (diesel engines), which most ships have, the use of alternative fuels such as natural gas, biomass fuels, and hydrogen (H2) is considered to be promising and the research to use such fuels is actively conducted. Among such fuels, we chose ammonia (NH3), because it is carbon free, has higher energy density per unit volume than hydrogen, and is liquefied below 240K at atmospheric pressure or above 0.857MPa at atmospheric temperature. We have proposed a mixed combustion system, in which ammonia is mixed into the intake air and liquid fuel is injected into the air-ammonia mixture to burn it in the cylinder. Such system can be retrofitted easily. The issues to be solved in this system are a) ammonia's low ignition performance and b) the high NOx emission due to nitrogen contained in the ammonia. To solve these issues, we conducted experiments and simulations. In this paper, we report the experimental results obtained through tests using a single cylinder engine and simulation results relating to the experiments. In the experiments, we found that the increase of the temperature was effective to decrease the leak of unburned ammonia due to the low ignition performance. In addition, pre-injection of the liquid fuel is found to be also effective to reduce the leak ammonia. These effects have also been observed in the simulation.
There are sever issues on increasing amount of CO2 emission in the world. Many studies are devoted on alternative fuels. One potential candidate is the utilization of hydrogen energy which can realize a low-carbon and hydrogen-based society. Ammonia, which is zero emission of CO2 and useful for hydrogen energy, might play an important role as a clean energy carrier and also can be burned directly as a fuel. For direct combustion of ammonia in industrial furnaces, there were three issues which were low burning velocity, weaker radiative heat flux and a huge amount of NOX emission compared with the combustion of methane. In this review, we introduce those solutions in our studies to overcome these three disadvantages of ammonia direct combustion in an industrial furnace. Firstly, the laminar burning velocity of ammonia, which is about 8 cm/s originally, could be improved with the increase of O2 concentration [1, 2]. Secondly, radiative heat flux under the condition of the oxygen enriched (30 vol.%) ammonia non-premixed flame formed in a 10 kW test furnace was improved more than that of the methane/air non-premixed flame . Thirdly, Air staged combustion could reduce the NOx emissions due to generated unburned-ammonia intentionally in the upstream of the furnace which played an important role in reduction action.
Ammonia has been expected as a hydrogen energy carrier to prevent global warming because hydrogen has no carbon and it means CO2 free combustion. However, there are some challenges to burn ammonia. The reasons are its low combustion intensity, low radiation intensity and high NOx emission. This paper shows the potential of a burner using ammonia fuel in an industrial furnace. Burner itself should be developed to burn ammonia fuel which is mixed in natural gas. Several types of burner design and several ratios of ammonia volume in natural gas were evaluated. Arrangement of burners in an industrial furnace is also important to get uniform heating on a steel sheet because dirt and oil on the steel sheet should be burned for degreasing. Distance of burners in one line and distance of lines were decided with evaluating uniformity of heating. Minimal capacity of furnace which has a developed impinge jet burner with optimal arrangement was installed in a continuous galvanizing line which produces galvanized steel sheets being supplied to automotive industry, appliance industry and construction industry. The developed impinge jet burners performed as expected ability in the industrial furnace.
The purpose of this article is to review the possibilities provided by the Laser Induced Plasma Spectroscopy measurement technique to get insights into gaseous or spray reacting systems under different working pressure. After a brief review and an overall presentation the requirements of the laser source and the detection systems are described. The processing of the spectral information is discussed before showing typical applications in gaseous, sprays and high-pressure environments. Finally, the potential of LI3PS (LIPS & Ignition & Interferometry) is presented and future directions for developments are given.
Indirect fire extinguishment was carried out by causing water droplets of a size of a few millimeter order to collide with a heated solid plate. We focused on the difference in the surface roughness of the heated plate and investigated the fire extinguishing characteristics experimentally. The evaporation characteristics of the droplet is related to the flame extinguishing probability. The coarser the solid surface roughness, the higher the Leidenfrost point moved to the higher temperature side, and the nucleate boiling region expanded. As a result, even when the solid surface temperature was high, steam and mist were sufficiently generated and fire extinguishment became possible. The spreading width of water vapor and mist was smaller as the solid surface roughness was coarser. In addition, the direction of its movement changed from the horizontal direction to the vertical direction as the solid surface roughness became coarse. This was related to the spreading behavior of the liquid film on the solid surface after droplet collision.
To develop a lean premixed with secondary NH3 injection (LPSI) for NH3/natural gas co-fired gas-turbine, characteristics of NOx and unburnt NH3 emission are studied numerically by applying a reactor-network model consisting of perfectly stirred reactors with a detailed chemistry. In the calculations, the equivalence ratio in NH3 injection region downstream of the primary natural gas/air burning region, φNI, is used as a parameter. Calculations for lean premixed (LP) combustion and rich lean (RL) combustion, in which NH3 and natural gas burn simultaneously, are also performed and compared with that for the LPSI combustion. Results show that in the LPSI combustion, low NO, NO2, N2O and unburnt NH3 concentrations are achieved by local RL combustion realized due to NH3 rich combustion in the NH3 injection region followed by air dilution region. It is also shown that, by the LPSI combustion, NO concentration decreases with decrease of equivalence ratio in the primary natural gas/air burning region. The mechanisms are discussed based on dilution with natural gas/air burnt gas and local equivalence ratio of NH3 as well as flame temperature, and it was confirmed that the parameter φNI proposed in this study can be used successfully for the LPSI combustion research. Furthermore, NO concentration of the LPSI combustion is minimized at lower φNI compared to that of the RL combustion. It can be explained by feature of H, O and OH radical productions from natural gas/air combustion. In the RL combustion, productions of these radicals are enhanced in the rich burning condition and promote the formation of NO and the consumption of unburned NH3. On the other hand, in the LPSI combustion, influences of these radical productions are weaker than those in the RL combustion because the NH3 burning region and the natural gas burning region are isolated.