Lean operations

An oxygen storage component stores oxygen under lean operating conditions, ie, fuel-poor/air-rich, and releases it under fuel-rich, air-poor... 

The NOxTrap can be assimilated to a three-way catalyst7 complemented by a NOz storage function. This system contains two types of precious metals the first one, dedicated to NO, HC and CO oxidation in lean operating mode, will generally consist of platinum or palladium. The second one, dedicated to NOx reduction in rich operating mode, is typically rhodium. Rhodium price spectacularly increases, with a multiplication by three of its value in 2006 (see Figure 7.13)8. 

Lean operations in production and related processes companies need to be flexible and cost-efficient - this ever-true statement is especially important in the resource-intensive production processes for specialties (batch production and related manual handling). 

To achieve the sustainable continuous improvements of truly lean operations, companies need to execute holistic programs. They have to give their organizations clear visions for operational excellence and the ability to identify and execute on situation-specific targets, but also individual approaches to address the soft side of change - capability building and changes in mindsets and behaviors. The journey is difficult, but the rewards are still fast and very considerable. 

Operational Improvement - the Bar Is Rising 227 Making Lean Operations Happen in Chemicals 230 Defining Relevant Aspects of Successful and Sustainable Operational Transformations 231 Making Transformation Happen - Front-end Loading with Content 233... 

The steady-state characteristics of practical significance for a lean-burning jet combustor intended to control pollutant emissions are its lean operating limits for eflBcient, stable combustion i.e., the minimum operating equivalence ratios that yield acceptable levels of CO and un-bumed HC emissions. Those operating points that also yield acceptable... 

The lean operating boundary shown in Figure 1 (to its interception of the lean limit line) represents the line of constant turbine inlet gas temperature (1407 K or 2073°F) typically required for cruise power. This boundary line shows that there is a minimum allowable premixed equivalence ratio that satisfies power requirements. But, since air-film cooling and perhaps secondary air injection for temperature pattern factor adjustment (at the turbine inlet) will be required in an engine combustor, the useful lean boundary will lie possibly 20-30% to the right of that shown. Cooling requirements should be much reduced from current practice because of the ultralean (cooler) burning zone. 

Although the pnmary dnving force in autocatalyst development is performance, cost is, of course, also a major consideration. Early oxidation catalysts used platinum and palladium, since both are good oxidation catalysts under lean operating conditions. When... 

Control of HC and CO under lean operating conditions should be straightforward, but the reduction of NOx under these strongly oxidizing conditions is not. Nevertheless, especially in Europe, NOx emissions are a major concern, and legislative proposals now being discussed will require the removal of some NO from lean-bum engines. So far, three approaches have been tried, two of these have met with some level of success... 

All these systems use lean operation to achieve the improved fuel consumption. However as NOx emission standards are lowered to meet environmental concerns this presents a challenge to the conventional 3 way catalyst technology used on gasoline engines and to the technologies described above for diesel engines. 

Lean operation of any internal combustion engine is advantageous in terms of oxides of nitrogen emissions and fuel economy. 

For hydrocarbon engines, lean operation also leads to lower emissions of carbon monoxide and unburned hydrocarbons. As more oxygen is available than required to combust the fuel, the excess oxygen oxidizes more carbon monoxide into carbon dioxide, a less harmful emission. The excess oxygen also helps to complete the combustion, decreasing the amount of unburned hydrocarbons. 

As with hydrogen, the drawback of lean operation with hydrocarbon fuels is a reduced power output. Lean operation of hydrocarbon engines has additional drawbacks. Lean mixtures are hard to ignite, despite the mixture being above the LFL of the fuel. This results in misfire, which increases unburned hydrocarbon emissions, reduces performance and wastes fuel. Another disadvantage is the reduced conversion efficiency of 3-way catalytic converters, resulting in more harmful emissions. 

Modern engine concepts (fuel cut, lean operation, etc.) require catalysts operating with leaner mixtures, i.e., with regard to NO conversions an extension into the lean range is desirable. 

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