Reduction of NOx by use of a Multi functioning Catalyst and Diesel Oil – More than 80% NOx Reduction – with Increased Plant Efficiency
Injected Oil is converted to Heat – More than 90% Heat can be recovered – To be used for electricity or water production
Using the ADNOX System, the temperature after the Reactor is increased around 55 °C compared to reactor inlet temperature. I.e. the temperature at turbocharger turbine inlet after mixing with the bypassed air is increased. The surplus energy is bypassed using valve V3.
The introduction of the ADNOX System into the 2-Stroke diesel engine requires an Environmental Control System to control valve positions., supplied as part of the Control Unit.
1. ADNOX System Compared to urea-SCR
The until now most commonly used NOx reduction System is the Urea-SCR System. In the following, we will compare the ADNOX System to the urea-SCR as frequently used:
The main differences between the ADNOX- and the Urea-SCR system are:
The ADNOX System does not need an extra tank for reactant (”Urea tank”)
The ADNOX reactor including catalyst has a 40% lower weight than a reactor with extruded catalysts – corresponding to 1300 kg for an 2,500 kW diesel engine;
The ADNOX system does not need a long evaporation and mixing pipe, especially important for 2-Stroke diesel engines;
The ADNOX System does not have the potential problem of precipitation of urea on the pipe wall, blocking the catalysts when dropping of; Either Ammonium sulfate or ammonium bisul- fate can damage the catalyst system;
The ADNOX System produces heat. Therefore no increase in specific oil consumption is re- quired on 2-stroke engines;
The ADNOX System converts the injected oil to heat. In a standard ADNOX System up to 85% of the Lower heating Value can be recovered in an exhaust gas boiler, and used for produc- tion of steam, water or electricity; With an Oxidation catalyst installed up to 100% of the heating value of the injected diesel oil can be recovered – increasing the total plant efficiency
2. The ADNOX-NOx Reduction Process
The System starts injection of diesel oil, at an exhaust temperature of 350 °C . After a period of oper- ation, the ADNOX System can operate, at an exhaust inlet temperature of 320 °C, due to the heat formed.
In the exhaust, the oil evaporates and is evenly distributed in the exhaust, when reaching the first catalyst layer.
The ADNOX catalyst is a multi-functioning catalyst, having following main functions,
- NO oxidation;
- Heterogeneous NOx conversion and
- Homogeneous NOx conversion
3.0 The ADNOX – System
The standard scope of supply includes;
- SCR Reactor and Instruments;
- SCR Catalysts;
- Soot Blowing System;
- Pump and Dozing Unit;
- Injection Unit;
- Control and Safety System;
- NOx analyzer and sensor;
- Air compressor station;
- Heat recovery Boiler;
Other necessary items:
- Expansion bellows;
- Piping and cables between units;
A simplified arrangement drawing is shown on Fig. 2
3.1 SCR Reactor
One reactor per diesel engine up to 20 MW engines for 4-Stroke diesel engines, hereafter two reac- tor units per engine. Reactors have a circular cross section with inlet and outlet cones, all in black steel. The size for a 2.5 MW 4-stroke diesel engine is shown in Attachment 2.
The Reactor have two to three service openings through which the steel-boxed catalysts are inserted and removed. The steel cassettes are placed on steel structures.
Temperatures are measured at reactor inlet, at reactor outlet and between the two first service openings. Additionally, a temperature switch is installed at reactor outlet, causing a shut down if the reactor outlet temperature is above 520°C.
Pressure is measured at reactor inlet and reactor outlet. If the pressure difference exceeds the pres- sure difference limit, the interval between soot blowing is decreased and an alarm sounds.
For 4-stroke diesel engines, the Reactor can be integrated with a Silenser and a spark arrestor. Here- by, the total building length is reduced and the total pressure difference is reduced.
The catalyst powder is coated on corrugated ceramic blocks of 150mm x 150 mm in cross section area. The blocks are boxed in steel frames, collected in four parts per layer, easy to install and re- move.
The base material of the catalyst powder is Cu-ZSM5 with metals added. The expected lifetime is up to 20,000 diesel engine operating hours. If a NOx analyzing system is included, and a service agree- ment is entered, ADNOX A/S – via the Internet – will monitor the activity, and supply and exchange catalyst blocks as required.
Soot Blowing System
The soot blowing system includes a pressure vessel and rapid opening solenoid valves keeping up- stream surfaces clean. The soot blowing system is operating, whenever the diesel engine is operating. The blowing takes place with fixed intervals set by the control unit.
The air is supplied from the on-board service air system. The air supply has to be in operation when- ever the engine is running.
3.2 Oil Pump and Dozing Unit
The Oil Pump and Dozing Unit is located near the diesel oil tank. It pumps oil from the tank to the Oil Injection Unit located upstream the Reactor and injected via air controlled nozzles. The oil pressure is fixed. The air pressure controls the oil amount injected and the Control Unit regulates the air pres- sure as function of Diesel Engine Load.
The main components are an electric motor driven oil pump upstream of which a filter is installed. From the pump, surplus oil flows back to the diesel oil tank via a return pipe. A flowmeter measures the injected oil and a pressure gauge measures the oil pressure. Hereafter, the oil line is split into two lines, each with a solenoid valve, supplying oil to the injection unit.
In addition to the oil line, an air-line is included in the Pump and Dozing Unit. After an air pressure gauge, the air-line is split into two lines. On each air- line, control valves controlling the air-pressure of the injection nozzles.
A removable steel cover encloses the Pump and Dozing Unit. If an oil leak happens, the oil is flowing to the oil leak detector, which gives an alarm. The leaked oil ends up in the waste oil tank.
The Pump and dozing unit can be placed as a stand-alone unit or supported by a tank wall
3.3 Oil Injection Unit
Oil is injected into the exhaust through a number of air-controlled nozzles. The Control Unit controls the injected oil amount as function of the diesel engine load by regulating the air pressure to the nozzles.
Each oil nozzle is placed at the end of a lance. Each lance is enclosed in a protection pipe. The lance is flanged to the protection pipe, and the flange is enclosed in a steel box. Leaked oil – should any occur – is piped to the Pump and Dozing Unit, as part of the oil leak detection system.
When oil injection is stopped, dump valves are opened and service air is removing remaining oil in the nozzle and lance to the waste oil tank. After the removing of oil, the dump valves are closed and a small amount of service air flows through the nozzles until the engine stops.
3.4 Control Unit
The Control Unit controls the ADNOX System. When in RUN Mode the System starts automatically when the Diesel engine starts – and stops when the engine stops.
In addition to the PLC based system, a hardwired safety system is included, ensuring the system is safely closed, in case of a power loss or a PLC failure.
The injection of oil is controlled as a function of the diesel engine load. The Control Unit also controls the soot-blowing system.
The PLC system is controlled from a touch screen. The PLC is enclosed in a cabinet, where all cables are entered. The Cabinet is placed close to the Reactor.
4.0 Operation Conditions
Under normal conditions, the pressure loss over the ADNOX Reactor is max 12 mbar at 100% diesel engine load.
The maximum temperature from the diesel engine is expected to be 450°C. The oil injection starts at a temperature of 350 °C. After a running in period the ADNOX System can operate, at an exhaust temperature down to 320°C.
Diesel oil consumption
We assume diesel engine operates in accordance with IMO TIER II conditions (See Attachment Figs. A1.1 and A1.2). By including the ADNOX System, the IMO TIER III can be obtained. At 75% engine load, said reduction requires an oil amount of 15 L oil/MWh (around 7% of the oil used by the diesel engine).
Air quality, pressurized Air
The service air supplied for the ADNOX system must be dry and clean. According to the specifications in ISO 8573, purity class 3 with respect to particles, purity class 2 with respect to oil and purity class 5 with respect to water.
5.0 ADNOX for 2-Stroke diesel engines
On 2-Stroke diesel engines, the ADNOX reactor has to be installed between exhaust gas receiver and turbocharger turbine inlet, to reach a temperature closer to the required operating temperature for the ADNOX System (See Fig. 3). Due to the location, the ADNOX system is an integrated part of the diesel engine. The extra installed heat capacity means the ADNOX Reactor shall be bypassed, during start and stop of the diesel engine.
Furthermore, due to the low exhaust temperature, at lower engine loads air from the air receiver has to be bypassed to the turbocharger turbine inlet (Valve CBW on Fig. 3). Due to the reduced air amount, the exhaust temperature is increased up to the level required by the ADNOX System.