In 1998, TVA undertook the implementation of Selective Catalytic Reduction systems at the Paradise Generating Station. The station has three fossil-fired cyclone boilers totaling 2515 Mw of power generation which have been online since the early 1960s for Paradise Units 1 and 2, and since 1970 for Unit 3. Design efforts started late 1998 with Paradise Unit 2, a 704 Mw cyclone-fired unit that went into operation for the May 2000 ozone season. This was followed by Paradise Unit 1, an identical 704 Mw unit that went into operation for the May 2001 ozone season. Paradise Unit 3, an 1107 Mw unit, is currently in manufacture and erection for placement into service for the 2003 ozone season. The Paradise Units 1 & 2 SCR modules are among the largest single modules in service for treating the entire flue gas path. The system design considered the operation of the boiler without overfire air NOx control, where the emission of NOx would be 688.5 g/GJ (1.6 lb/MMBtu) and with overfire air NOx emission of 370 g/GJ (0.86 lb/MMBtu). Paradise Units 1 & 2 are fitted with scrubbers and burn a high sulfur fuel. Paradise 3, not currently fitted with a scrubber, fires a blend of PRB and Utah bituminous coal. The SCR is configured with two modules. The SCR project guarantees are 90% NOx reduction, 2-ppm ammonia slip and a catalyst life of 20,000 hours. Each of the cyclone units retained their tubular air heaters. Each unit required the erection of either temporary or new ductwork from the air heater to the downstream equipment to allow the demolition of equipment that had been part of the gas path but is no longer in service. The old equipment had to be removed to permit the building of the SCRs. Each SCR unit is equipped with a full flow bypass and man-safe dampers. These man-safe dampers permitted the construction and maintenance of the SCR while the boiler was in operation. Paradise Unit 2’s SCR was fitted with steam soot blowers. Sonic horns were tested on a section of Unit 2 and based on the results, Paradise Unit 1 was fitted only with sonic horns for catalyst cleaning. The anhydrous ammonia unloading and storage facility is more than a mile from the ammonia vaporizers that are located at grade adjacent to their respective SCR unit. The monthly ammonia consumption under full power conditions for Paradise Units 1 & 2 and 90% NOx reduction is 1,703.3 m 3 (450,000 gallons) per month with the overfire air system in service. This paper addresses the issues and decisions related to integration of the SCR systems and the experiences of manufacturing and erecting each of the SCR units.

The combustion phenomena of vaporizing spray in a catalyst and a post-catalyst flame were studied experimentally. This study is a part of the development of a catalytic combustor for a ceramic gas turbine engine. A palladium catalyst supported on the cordierite honeycomb monolith was used as a combustion catalyst. A premixture of air and kerosene vapor was introduced into the catalyst. The parabolic shaped flame, called a thermal combustion flame, which was supported on the catalyst, was formed even when the equivalence ratio of the mixture was less than stoichiometry. Intermediate products in the exhaust gas after the catalyst honeycomb were investigated using an ion probe. When the thermal flame appeared, ions were detected in the exhaust gas between the honeycomb and the flame. It was indicated that some reactive species were included in the exhaust gas. Even when the thermal flame did not appear, the ions were slightly detected in the exhaust gas. The concentration of the ions rapidly decreased a slight distance away from the honeycomb surface and increased in front of the thermal flame. When the equivalence ratio was increased, the ion concentration at the honeycomb surface increased. Furthermore, in order to investigate the effect of the mixing behavior of the vaporized fuel on post-catalytic combustion, the length of the mixing tube was changed. When the mixing of fuel was insufficient, the thermal flame appeared at a lower equivalence ratio than the more homogeneous mixing condition. However, regardless of the mixing length and equivalence ratios, the concentration of ions near the honeycomb surface was almost constantly at the onset conditions of the thermal combustion flames.

In this paper, wastepaper gasification with steam and carbon dioxide was tested in the presence of molten carbonate salt catalysts. Reactions with steam or carbon dioxide were first compared. Hydrogen was mainly produced by gasification with steam, but no carbon monoxide was generated. For the case where carbon dioxide was used as a reactant instead of steam, generation of carbon monoxide greatly increased via the Boudouard reaction. Different ratios of mixtures of lithium, sodium and potassium carbonates were examined. Lithium was found to play a critical role in the various catalyst combinations. The reaction rate with respect to carbon conversion was approximately first order for low carbon conversions. The rate constants were investigated at different temperatures (923–1023K) and the activation energies were determined. In addition, the flexibility of this technique was examined with three different types of wastepaper. These results suggest the applicability of this process for the effective use of wastepaper and recovery of carbon dioxide.

Environmental regulations are very stringent in the U.S., requiring very low emissions of nitrogen oxides (NOx) from combined cycle power plants. Selective Catalytic Reduction (SCR) systems utilizing vanadium pentoxide (V 2 O 5 ) as the active material in the catalyst are a proven method of reducing NOx emissions in the exhaust stack of gas turbines with heat recovery steam generators (HRSG) to 2–4 ppmvd. These low NOx emissions levels require an increase of SCR removal efficiency to the level of 90 + % with limited ammonia slip. The distribution of flow velocities, temperature, and NOx mass flow at the inlet of the SCR are critical to minimizing NOx and ammonia (NH 3 ) concentrations in HRSG stack. The short distance between the ammonia injection grid and the catalyst in the HRSG complicates the achievement of homogeneous NH 3 and NOx mixture. To better understand the influence of the above factors on overall SCR system performance, field testing of combined cycle power plants with an SCR installed in the HRSG has been conducted. Uniformity of exhaust flow, temperature and NOx emissions upstream and downstream of the SCR were examined and the results served as a basis for SCR system tuning in order to increase its efficiency. NOx mass flow profiles upstream and downstream of the SCR were used to assess ammonia distribution enhancement. Ammonia flow adjustments within a cross section of the exhaust gas duct yielded significantly improved NOx mass flow uniformity after the SCR while reducing ammonia consumption. Based on field experience, a procedure for ammonia distribution grid tuning was developed and recommendations for SCR performance improvement were generated.