Abstract
Low-speed marine diesel flue gas denitrification is in great demand in the ship transport industry. This research proposes an ammonia supply system which can be used for flue gas denitrification of low-speed marine diesel. In this proposed ammonia supply system, ammonium bicarbonate is selected as the ammonia carrier to produce ammonia and carbon dioxide by thermal decomposition. The diesel engine exhaust heat is used as the heating source for ammonium bicarbonate decomposition and ammonia gas desorption. As the ammonium bicarbonate decomposition is critical to the proper operation of this system, effects have been observed to reveal the performance of the thermal decomposition chamber in this paper. A visualization experiment for determination of the single-tube heat transfer coefficient and simulation of flow and heat transfer in two structures is conducted; the decomposition of ammonium bicarbonate is simulated by ASPEN PLUS. The results show that the single-tube heat transfer coefficient is 1052 W m2 °C−1; the thermal decomposition chamber fork-type structure gets a higher heat transfer compared with the row-type. With regard to the simulation of ammonium bicarbonate thermal decomposition, the ammonia production is significantly affected by the reaction temperature and the mass flow rate of the ammonium bicarbonate input.
Highlights
The marine diesel engine is competitive in large ships because of its high fuel efficiency and power output
The ammonium bicarbonate is decomposed by absorption of heat from the hot oil, and the gases carbon dioxide, ammonia and some water vapour are produced by the ammonium bicarbonate thermal decomposition
An ammonia supply system for flue gas denitrification of low-speed marine diesel is proposed, and ammonium bicarbonate is selected as the denitrification agent
Summary
The marine diesel engine is competitive in large ships because of its high fuel efficiency and power output. For the SNCR technology, the reducing agent is directly sprayed into the diesel flue gas, with the denitrification reaction temperature at 900–1100°C. Three kinds of reducing agents, which contain ammonia, are commonly used in power plants for flue gas denitrification: ammonia, ammonia–water mixture with a concentration at 20–30% [10] and urea [11,12]. Their application on shipboard is quite a different matter due to the safety concern on the transportation and storage of reducing agents, as well as requirement of the limited bulk size of the ammonia supply system. The thermal decomposition of ammonium bicarbonate in the ammonia supply system was simulated by ASPEN PLUS; the effects of ammonium bicarbonate concentration and the reaction temperature of thermal decomposition on the ammonia production were analysed
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