Methane Gas Cofiring Effects on Combustion and NO x Emission in 550 MW Tangentially Fired Pulverized-Coal Boiler.

A shift from coal to liquefied natural gas for electricity generation can mitigate CO2 emissions and respond to the intermittent and variable characteristics of renewable energy. With this objective, numerical simulation was performed in this study to determine the optimal position of the methane injector and evaluate the achievable reduction in NO x emissions before applying methane cofiring to an existing 550 MW tangentially fired pulverized-coal boiler (Boryeong Unit 3). The combustion and NO x reduction in the furnace were intensively analyzed based on the methane cofiring rate (up to 40%). The optimal position of the methane injector was found to be inside the oil port based on the spatial distribution of NO x and the stoichiometric ratio along the furnace height. The NO x reduction rate was logarithmically proportional to the methane cofiring rate, and compared to the base case, a 69.8% reduction was achieved at the 40% cofiring rate. In addition, the fraction of unburned char at the boiler outlet was equivalent to that of the existing boiler as the increase in the flow rates of the close-coupled and separated overfire air improved fuel and air mixing. Simultaneously, methane cofiring led to a reduction in the total fuel loss and CO emissions. Finally, this study showed that the recommended optimum cofiring rate was 20% based on the furnace exit gas temperature. Under the 20% methane cofiring condition, the boiler achieved a 57.3% reduction in NO x emissions and a 7.4% improvement in fuel loss.

Development of Subair Technique for Combustibility Enhancement and NOx Reduction in a Pulverized Coal-Fired Boiler.

In this work, subair injection was proposed to improve the combustibility and NOx emission in a 500 MW tangentially fired coal boiler. The location of injection ports was determined based on the coal particle trajectory and its effect was investigated numerically. The flow rate of subair was set to 0, 5, and 10% of the total combustion air. The secondary air flow rate was decreased appropriately to ensure that the total quantity of combustion air remained constant. The over-fire air was not adjusted to retain the effect of an air-staged combustion. The simulation results showed that the subair improved the combustibility of coal particles originating from burners A and B in the lower part of the furnace. Particles from other burners were not affected significantly. In addition, this method achieved reduction of NOx by 6.3 and 13.2% when the subair accounted for 5 and 10% of the combustion air, respectively. This reduction was attributed to the decrease in the peak temperature as a result of a wider combustion region. The proposed subair technique improved the coal combustibility and reduced the NOx emissions successfully in the furnace.

Surgical correction of whistle deformity using cross-muscle flap in secondary cleft lip.

BACKGROUND: The whistle deformity is one of the common sequelae of secondary cleft lip deformities. Santos reported using a crossed-denuded flap for primary cleft lip repair to prevent a vermilion notching. The authors modified this technique to correct the whistle deformity, calling their version the cross-muscle flap. METHODS: From May 2005 to January 2011, 14 secondary unilateral cleft lip patients were treated. All suffered from a whistle deformity, which is characterized by the deficiency of the central tubercle, notching in the upper lip, and bulging on the lateral segment. The mean age of the patients was 13.8 years and the mean follow-up period was 21.8 weeks. After elevation from the lateral vermilion and medial tubercle, two muscle flaps were crossed and turned over. The authors measured the three vertical heights and compared the two height ratios before and after surgery for evaluation of the postoperative results. RESULTS: None of the patients had any notable complications and the whistle deformity was corrected in all cases. The vertical height ratios at the midline on the upper lip and the affected Cupid's bow point were increased (P<0.05). The motion of the upper lip was acceptable. CONCLUSIONS: A cross muscle flap is simple and it leaves a minimal scar on the lip. We were able to reconstruct the whistle deformity in secondary unilateral cleft lip patients with a single state procedure using a cross-muscle flap.