Technical Papers
Dynamic Characteristic of a Two-Stroke Slow Speed Diesel Engine with De-NOx System*
Osamu Motomura**, Kenichi Maeda**, Junji Kondo**, Katsuhiko Tatsumi**, Masahiko Okabe, Yuji Oda**
In the 2-stroke diesel engine power plant, application of SCR (Selective Catalytic Reduction System) in between engine's cylinder exhaust gas outlet and the turbo-charger is one solution to get higher NOx reduction rate.
In this case well know phenomena is unstable engine operation due to rather large heat mass of the SCR, specially during engine load up and down program.
This paper shows that this phenomena is soluble by installing exhaust gas extract valve and adequate active valve control, also shows the outline of mathematical analytic evaluation model and the test results on the actual power plant.
1. Preface
In the circumstances that worldwide electric power demand increases and electric power companies look for various sources of electric power, the diesel engine having more than 50% thermal efficiency by engine itself is in existence and many diesel generating plants have been constructed as their own electric power generation equipment in power demand side. As well, the adoption of large normal diesel generating plant of 10 to 50 MW class increases as electric power supply to developing countries.
On the other hand, reflecting the mounting concern over the global issue of reducing the NOx emissions, more and more of diesel generating plants installed in dispersed locations have come to employ the selective catalytic reduction (SCR) system to remove NOx from the dynamo engine exhaust gases. When the two-stroke-cycle diesel engine is employed as dynamo engine, however, the generally followed practice of installing the SCR system between the engine exhaust outlet and associated exhaust turbocharger gas inlet for efficient NOx removal can lead to the problem of SCR system, being large in heat capacity, upsetting the plant heat cycle to the detriment of plant dynamic characteristics especially in the process of bringing down the plant output power.
In this report, it is described that the authors investigated by numerical simulation the mechanism and preventive measures for the problem of SCR system provided in the above mentioned plant configuration due to the disorder in plant dynamic characteristic, confirmed the effectivitiy on the preventive measures in the actual plant, and developed a low cost diesel generating plant which has excellent in dynamic characteristic and as low in NOx emission level as the gas-turbine plant.
Besides, the nomenclatures used in this report as follows.
Tm : SCR temperature
Tg :gas temperature
γm : SCR specific weight
γm : Gas specific weight
Vm : SCR volume
Vg : gas volume
λ : excess air ratio
ηcomb : combustion efficiency
Cm : SCR heat capacity
QHL : SCR heat loss
Cm : SCR specific heat
Cp : gas mean specific heat at constant pressure
Cm : SCR specific heat
Cp : gas mean specific heat at constant pressure
ug : gas flow velocity
Gs : gas weight
α : heat conductivity
A : heating surface area
F : SCR internal gas passage cross sectional data
dx : SCR longitudinal unit length
dt : unit calculation time
2. Dynamic Characteristics of Diesel Generating Plant Fitted with SCR System of NOx Emission Control
2-1. Plant Configuration
The diesel generating plant configuration employing the two-stroke-cycle diesel engine as dynamo engine and with the SCR system installed between the engine exhaust manifold and exhaust turbocharger is shown in Fig. 1, which represents what the authors addressed by numerical simulation.
Also, the plant dynamo engine and SCR system specifications are shown, respectively, in Table 1 and 2.
* Translated from Journal of MESJ Vol. 34, No. 1 (Manuscript received Oct. 28, 1998) Lectured May 13, 1998
** Mitsubishi Heavy Industries, Ltd. (Hyogo-ku, Kobe city)
