Regulations on nitrogen oxide (NOX) emissions from stationary gas turbines are being tightened around the world. In response to this fact, Kawasaki (Japan) developed a DLE combustion system that emits single digits NOX for use with its 8 MW gas turbine.
Kawasaki's 8 MW m7A-03D engine, designed to cut NOX emissions
Kawasaki has cut its NOX emissions to a new low. The guaranteed maximum NOX emissions of the Dry Low Emissions (DLE) system used together with the company's 8 MW m7A-03 gas turbine have been reduced from 15 ppm (parts per million). down to 9 ppm (converted to 15% O2). This is the first time in the world to achieve a guaranteed single-digit maximum NOX emissions in a DLE combustion system at this power level, according to Kawasaki.
The DLE combustor uses a premix combustion method to generate the high temperature smoke required for the turbine to run at high speeds. NOX is generated in the combustion of gas turbine fuel, however this amount of emissions mainly depends on the combustion temperature. The premix combustion technique reduces the burning temperature, no need to spray water or steam. By pre-mixing the fuel with air, NOX emissions are significantly reduced. Thanks to this feature, the DLE combustion chamber is widely used in combustion systems used in gas turbines.
However, the big problem with mixed combustion in the past has been stability, especially when used to reduce NOx emissions. Kawasaki has overcome a long stumbling block of technology to reduce NOX emissions from the DLE combustion chamber. The driving force behind the successful development of this new DLE system, with respectable combustion stability, is the innovative combustion engine owned exclusively by the company.
A distinctive feature of the Kawasaki combustion mechanism is the multi-stage combustion using the pilot burner, as well as main and additional burners. This latest technological breakthrough in NOX emission reduction builds on a solid foundation of ongoing DLE combustor research and development. Kawasaki has taken on the high technology level acquired over the years to replace all of its combustors with low emission pre-mix combustors.
Because NOX emissions can cause photochemical smog and acid rain, stationary gas turbines must comply with strict regulations around the world. NOX emission standards have been set at 25 ppm (or lower) in most countries, however more and more local governments are in the US and Europe, where public awareness of Air quality is even implementing stricter NOX emission standards, requiring a maximum emission level of 15 ppm, and 10 ppm in some regions.
To meet these increasingly stringent NOX emissions standards, Kawasaki is working to improve total gas turbine efficiency and develop new combustion technologies that will reduce gas turbine emissions. Kawasaki is looking for ways for new technology to serve global environmental benefits, with products with higher efficiency and less impact on the environment.
Achieve a single-digit emissions rate
In response to the requirement of NOX emissions lower than 15 ppm in many parts of the world, Kawasaki has set up a DLE combustion system that ensures NOX emissions <15 ppm (at 15% oxygen) for the m7A-03 gas turbine (class 8 MW) from 2009 and for the L20A gas turbine (18 MW) from 2010.
To meet new customer demand, Kawasaki completed the development of a DLE combustion system that emits NOX at a single digit. Their criteria are NOX <9 ppm and CO <25 ppm (at 15% oxygen) emissions. Kawasaki has adopted a single-digit NOX DLE combustion system for the m7A-03 gas turbine, one of Kawasaki's best-selling engines.
This single digit NOX DLE combustor was developed by improving the third generation 15 ppm NOX DLE combustor. The 15 ppm combustor system consists of pilot fuel burners, main fuel burners and supplemental fuel burners (see Figure 1).
The pilot fuel burners of this system are diffuse type, while the primary and complement fuel burners are pre-blended. The premix complementary fuel burner is applied for the first time to this combustor set. This burner has fuel injection holes between the slots, and a longer mixing length than that of a diffuser type supplemental fuel burner. By applying these technologies to enhance the blend of air and fuel to the add-on fuel burners, Kawasaki has ensured NOX emissions below 15 ppm in the load range from 50% to 100%.
In order to develop a single-digit NOx DLE combustor, a premixed fuel priming burner was applied for the first time. Although the premix burn is applied to the pilot burner, the performance of the pilot ignition and flame stability are still very important and should be comparable to that of the diffuser. Therefore, the fuel / air concentration was investigated using computational fluid dynamics (CFD), and investigated emissions, ignition and stability. flames by test and engine tests.
Figure 2 shows a cross section of the diffusion pilot burner of a DLE NOX 15 ppm, Figure 3 shows the fuel / air concentration at the output plane of the pilot burner obtained by CFD method. .
The purpose of using the premix combustion for the pilot fuel burner is to reduce NOx emissions. Figure 4 shows a single digit NOx emissions from the DLE burner vertical section of the fuel priming burner. This pilot burner has lots of air clearances and fuel injection holes placed between the gaps.
Fuel is injected perpendicular to the direction of the air flow. The tear force of the air increases the mixing efficiency between the air and the fuel. The direction of the gas mixture was pushed 90 ° away, so the mixture was thoroughly mixed due to turbulent movement.
Figure 5 shows the fuel / air concentration at the output plane of the pilot fuel burner obtained by the CFD method. The fuel / air concentration is homogeneous within the burner as well as on the output plane of the burner, except in a very small area around the center of the burner.
Testing on the staging is done at the air-to-fuel ratio (AFR) equivalent to the load range in the 50% to 100% range under actual engine conditions. Figure 6 shows the NOx emission performance in this test. In addition to the pilot fuel burner and the main fuel burner, an additional fuel burner is also used. This test demonstrates that NOX emissions are maintained at a low level in all air / fuel ratio regions.
Figure 7 shows the emission performance of the engine test. In all these tests, the NOX and CO emissions reached the set level (NOX <9 ppm, CO <25 ppm) in the load range 50% to 100%. At full load, the NOX level is the lowest, about 4 ppm. Confirmed that flame stability achieved high stability during load shedding tests.
Kawasaki has achieved extremely low emissions (NOX <9 ppm and CO <25 ppm in the load range 50% to 100%) on the m7A-03 gas turbine engine and began promoting this item. Kawasaki has also announced that it will then apply the technology to its other engines in a market that is increasingly interested in eco-friendly products and wants to further reduce the environmental burden. school.