Reduction characteristics of NOX emissions by optimal urea injection rate in a LPG steam boiler with urea-SCR reactor
The aim of this study is to develop the urea-SCR reactor aftertreatment system for reducing NOX emissions in a LPG steam boiler. The urea-SCR system utilizes ammonia converted from 17% aqueous urea solution injected in front of the SCR catalyst as a reducing agent for reducing NOX emissions. In this study, NOX emissions and exhaust gas temperatures according to boiler load were measured and compared with before and after urea injection in a LPG steam boiler with urea-SCR reactor. Also, the equivalence ratio, urea injection rate, ammonia slip and NOX conversion rate relative to boiler load were investigated. The equivalence ratio is different by changing the fuel consumption rate or intake air rate. In this experiment, the average equivalence ratio is calculated by changing only fuel consumption rate while the intake air rate is constantly fixed at 25,957.11 cm3/sec. The average equivalence ratios are 1.38, 1.11, 0.81 and 0.57 when boiler loads are 100, 80, 60 and 40%. In this experiment, NOX conversion rates are calculated by 89, 85, 77 and 79% in cases of the boiler loads of 100, 80, 60 and 40%. NOX conversion rate is raised with increasing urea injection rate, and NH3 slip is boosted at the same time. Consequently, the optimal urea injection rate for the respective boiler load should be determined by considering NOX conversion rate and NH3 slip simultaneously. In this study, the urea flow rates of 230, 235, 233 and 231 mg/min are injected at the boiler loads of 100, 80, 60 and 40%, and the final NH3 slips are measured by 8.48, 5.58, 11.97 and 11.34 ppm at the same conditions.
A Study on the Effect of Recirculated Exhaust Gas with Scrubber EGR System upon Exhaust Emissions in Diesel Engines
The effects of recirculated exhaust gas on the characteristics of and soot emissions under a wide range of engine load have been experimentally investigated by a water-cooled, four-cylinder, indirect injection, four cycle and marine diesel engine operating at two kinds of engine speeds. The simultaneous control of and soot emissions in diesel engines is targeted in this study. The EGR system is used to reduce emissions, and a novel diesel soot removal device with a cylinder-type scrubber for the experiment system which has 6 water injectors(A water injector has 144 nozzles in 1.0 mm diameter) is specially designed and manufactured to reduce the soot contents in the recirculated exhaust gas to intake system of the engines. The intake oxygen concentration and the mean equivalence ratio calculated by the intake air flow and fuel consumption rate, and the exhaust oxygen concentration measured are used to analyse and discuss the influences of EGR rate on and soot emissions. The experiments are performed at the fixed fuel injection timing of BTDC regardless of experimental conditions. It is found that emissions are decreased and soot emissions are increased owing to the drop of intake oxygen concentration and exhaust oxygen concentration, and the rise of equivalence ratio as the EGR rate rises.
Urea removal strategies for dialysate regeneration in a wearable artificial kidney.
The availability of a wearable artificial kidney (WAK) that provides dialysis outside the hospital would be an important advancement for dialysis patients. The concept of a WAK is based on regeneration of a small volume of dialysate in a closed-loop. Removal of urea, the primary waste product of nitrogen metabolism, is the major challenge for the realization of a WAK since it is a molecule with low reactivity that is difficult to adsorb while it is the waste solute with the highest daily molar production. Currently, no efficient urea removal technology is available that allows for miniaturization of the WAK to a size and weight that is acceptable for patients to carry. Several urea removal strategies have been explored, including enzymatic hydrolysis by urease, electro-oxidation and sorbent systems. However, thus far, these methods have toxic side effects, limited removal capacity or slow removal kinetics. This review discusses different urea removal strategies for application in a wearable dialysis device, from both a chemical and a medical perspective.