TS-85
Onboard Ammonia Production Unit for De-NOx
Yasuo SAKAI*
ABSTRACT
A new on-board ammonia production unit for Selective Catalytic Reduction of NOx (SCR) with ammonia is introduced in this report. Ammonia is synthesized with highly active ruthenium catalyst without feed-stocks or utilities other than air, water and fuel. Operating pressure and temperature are about 1 MPa[gauge] and 350℃, which are extremely lower than the conventional ammonia synthesis technologies which are operated at 15 to 30 MPa[gauge] and about 500℃. Ammonia is produced as aqueous ammonia which can be utilized for SCR by spraying into the exhaust gas stream from engines at the inlet of the SCR reactors. No harmful effluents are discharged from this unit.
KEY WORDS: Diesel Engine, SCR, De-NOx, Catalyst, Ruthenium, Ammonia, Electrolysis, PSA
1. INTRODUCTION
It is estimated that NOx emissions from ships are about 13 percent of from ships all over the world and 37 percent within and around Japan. [1] This is because almost no ships of which exhaust gases contain more than about 1,000ppm of NOx are equipped with NOx reduction facilities though many on shore stationary facilities of which exhaust gases contain about 60 - 300 ppm are equipped with SCR, from refuse incineration plants of about 20,000m3N/h to power plants of more than 3,000,000m3N/h. Ammonia is most widely utilized as reductant in these SCR facilities.
Many kinds of technologies to reduce NOx emissions from marine diesel engines are developed or being developed such as engine tuning, EGR, water injection, NOx reduction by hydrocarbons and SCR. SCR with ammonia is the most effective and reliable technology among them. It is applied to almost all kinds stationary facilities such as boilers, heating furnaces, sintering machines, nitric acid plants and refuse incineration plants. De-NOx efficiency by engine tuning, EGR and water injection is much lower than that of SCR. Reduction of NOx by hydrocarbons had been researched many years before SCR research for stationary facilities, but quite a few facilities by hydrocarbon reduction are installed because of poor selectivity and low efficiency of NOx reduction which results in high running cost. SCR is the most reliable and practical method to reduce NOx in the gas from engines on ships as well as that for stationary sources.
This new ammonia production unit will be very useful for SCR for ships and can produce ammonia on demand on-board. Details are reported in the following.
2. EXPERIMENTAL DEVICE AND METHOD
2.1 Catalyst Selection
Three kinds of catalysts which contain ruthenium for ammonia synthesis as the active component and three different promoters of alkali metals are prepared for testing. That is Ru(A), Ru(B) and Ru(C). Catalyst activity is tested and analyzed at 1.0MPa[gauge] and 315℃ - 400℃ utilizing a 3/4" tubular rector packed with catalyst of 10g. The most active was Ru(A) as shown on Fig. 1, with which a concentration of ammonia of about 5.4 percent is obtained at 1.0MPa[gauge], 350℃ and 4,800h-1 of space velocity. Ru(A) of 300 grams is used in the following experiments.
2.2 Flow Diagram
The ammonia synthesis experiment was performed with ammonia separation and process gas recycling systems with a bench scale experimental device. Fig. 2 is a flow diagram of the experiment.
Fig. 1 Ammonia Conversion vs. Space Velocity
