The following section presents brief characteristics of the emission control technologies available for stationary sources. The following NOx control options for boilers and furnaces:
1. Combustion modification (CM)
2. Selective catalytic reduction (SCR)-( Exhaust Gas Treatment (After treatment)
3. Selective non-catalytic reduction (SNCR)
4. Combined measures (combustion modification and SCR or SNCR)
EXHAUST GAS TREATMENT (AFTER TREATMENT)
The Selective Catalytic Reduction of Nox (SCR) is widely using NH3 as reducing agent in the diesel engines. Urea is used as a source of NH3 in the SCR technique. Urea has been increasingly used in place of anhydrous NH3, as it is safer to store and handle. In this process, first the hydrolysis of urea is done over a catalyst which produces NH3 and CO2. Then NH3 reacts with NOx in the exhaust to convert it to N2.
The Urea concentration of around 35 to 40% in water solution is usually used . During vehicle operation on road, concentration of NOx in the exhaust gases varies all the time requiring continuous variation in the urea injection rate. Nox in diesel engines consist of around 10% NO2. Based on stochiometric conditions for 90% conversion of NOx, the urea / NOx molar ratio of 0.9 is required. The Nox could be reduced by injecting NH3 – water solution before SCR catalyst.
The experiment was conducted in a light duty stationary single cylinder, 4 stroke, water cooled, direct injection Kirloskar Engine as shown in the fig.(1) The engine was connected to an eddy current dynamometer. The torque can be varied from the control panel. Water cooling system was used for cooling the engine with a separate water cooling pump.
Methodology of experimental
Before starting the engine, urea solution should be prepared for different concentration varying from 5% to 25% by weight in the order of 5%. By adjusting the 3 way control valve and selecting the needle the flow rate of urea solution should be fixed and maintained constant for a set of experiment.
Initially the engine was started and allowed the engine with constant speed for some period of time. The engine was loaded gradually in the order of 20%, 40%, 60%, 80%, and 100% of full load. For every loading the fuel flow rate, emission of HC, CO, CO2, O2,NOX.
Fig. 2 to 5 indicates variations of various engine parameters with respect to brake power for various concentration of urea from 10% to 40% with varying flow rate of urea solution.
From the investigations it was concluded thet urea injection with titanium di oxide as SCR in the exhaust gives a reduction of about 82% of NOx. Thus this method was found to be an effective method for controlling NOx from Diesel Engines.