Hybrid Exhaust Systems

An interesting and novel use of a soHd desiccant, the reduction of cold condensate corrosion in automotive exhaust systems, illustrates a hybrid closed—open system. Internal corrosion occurs in mufflers when the water vapor in the exhaust condenses after the engine is turned off and the muffler cools. Carbon dioxide dissolves in the condensate to form an acidic soup. In an essentially closed static drying step, an acid- and heat-resistant desiccant located in the muffler adsorbs water vapor from the exhaust gas as it cools to prevent formation of corrosive acidic condensate. When the engine is restarted, the system becomes open, and the desiccant is regenerated by the hot exhaust gas to be ready for the next cooldown step (19). 

Certain types of fume hoods and exhaust sources, such as perchloric acid hoods, should not be manifolded with other types of fume hood exhausts. In large buildings where the designer wishes to take advantage of the benefits of manifolded exhaust systems but wishes to isolate a few exhaust streams, a combination, or hybrid, of these two types of systems is usually the most prudent and cost-effective alternative. 

Hu H. Stover Th. (2007) Hybrid catalyst system for exhaust emissions reduction. Patent US 7213395 B2 (8 May 2007)... 

Mok, Y.S. and Huh, Y.J. (2005) Simultaneous removal of nitrogen oxides and particulate matters from diesel engine exhaust using dielectric barrier discharge and catalysis hybrid system, Plasma Chem. Plasma Process. 25, 625-39. 

There can be many different cycle configurations for the hybrid fuel cell/turbine plant. In the topping mode described above, the fuel cell serves as the combustor for the gas turbine, while the gas turbine is the balance of plant for the fuel cell, with some generation. In the bottoming mode, the fuel cell uses the gas turbine exhaust as air supply, while the gas turbine is the balance of plant. In indirect systems, high-temperature heat exchangers are used. 

In conclusion, it would seem that either recuperated case would always be preferred. However, the cost of a recuperator can be significant. Also, the analyses performed fixed the turbine inlet temperatures at fairly low values. Typically with larger heavy-duty turbines the temperature is pushed to material limits and heat recuperation from the turbine exhaust is done in a combined cycle (steam bottoming cycle). Such a system can achieve close to 60% LHV efficiency on natural gas. Section 8.4 will consider whether a steam bottoming cycle is potentially appropriate for a hybrid system. A steam cycle is generally not economical for smaller systems. 

In this examination, the cathode recycle case will have no recuperator and the recuperator case will have no cathode recycle. However, it is quite possible that a hybrid system could use both. The anode exhaust is combusted at the turbine inlet in all cases. This could be done in other locations, such as the recycle loop, which would reduce the recycle required. It is apparent that a number of other configurations could be imagined (such as intercooling) however, each will likely be a modification of one of the base configurations given here. 

In order to avoid a social shock when the global energy system should transfer from fossil system to the CO2 recycling system using renewable energy, a hybridization between fossil and solar energy should be also discussed. That is, there are various kind of energy sources (solar, fossil fuels and their complex sources), and of carbon sources (CO2 from flue gas of combustion, CO2 from exhaust gas of fossil fuel chemical conversion, and carbon of fossil fuel itself). 

A major challenge even for advanced diesel engines is the array of impending U.S. federal Tier 2 and California LEV II emissions standards. Work is ongoing to achieve these standards and to ensure that the exhaust after-treatment devices required will meet the necessary durability standards. Two things are certain Diesel fuel quality must improve dramatically, at least to the 2006 ultra low sulfur diesel requirements and preferably well beyond, and the cost of a Tier 2 Bin 5 or LEV II compliant diesel system will be substantial, rivaling the cost of hybrid electric gasoline fueled vehicle systems. 

Although it does not exhaust the entire range of porous materials, the list attempts to cover those that can be described in terms of extended porous structures and whose electrochemistry has been extensively studied. In addition, since 1990 there has been a growing interest in the preparation of nanostructures of metal and metal oxides with controlled interior nanospace, whereas a variety of nanoscopic poro-gens such as dendrimers, cross-linked and core-corona nanoparticles, hybrid copolymers, and cage supramolecules are currently under intensive research (Zhao, 2006). Several of such nanostructured systems will be treated along the text, although, for reasons of extension, the study in extenso of their electrochemistry should be treated elsewhere. 

Electrical generators capable of high conversion efficiencies and extremely low exhaust emissions will no doubt power advanced hybrid vehicles and stationary power systems. Fuel cells are generally considered to be ideal devices for these applications... 

Spectroelectrochemistry [99] Is a hybrid technique resulting from the association of electrochemistry with spectroscopy via the use of cells with optically transparent electrodes [100-103]. The potential of this technique lies in the possibility of Identifying both the type and the amount of the species generated In an electrochemical step. The Intrinsic characteristics of spectroelectrochemistry require the use of fast measuring systems —spectroscopic image detectors in most cases [104-107]— and the consequent acquisition of the large number of data provided by the detection system In a short time by means of an oscilloscope or, even better, of a computer also allowing the subsequent exhaustive treatment of the raw data. 

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