Precombustion

FluidiZed-Bed Combustion. Fluidized-bed combustors are able to bum coal particles effectively in the range of 1.5 mm to 6 mm in size, which are floating in place in an expanded bed (40). Coal and limestone for SO2 capture can be fed to the combustion zone, and ash can be removed from it, by pneumatic transfer. Very Htfle precombustion processing is needed to prepare either the coal or the sorbent for entry into the furnace (41). 

In recent years, each power head is fitted with a bolt-in precombustion chamber, which allows the engine to bum a very lean mixture, resulting in very bw exhaust emissbns... 

Vor-untersuchung,/. preliminary investigation, -iirteil, n. prejudice, bias, -vakuum, n. preliminary vacuum, -verbrenmmg, /. precombustion. -verdampfer, m. pre-evaporator. 

Reduction of exhaust emissions is being tackled in two ways by engineers, including precombustion and postcombustion technology. One of the most effective methods now being researched and adopted includes use of synthetic fuel made from natural gas. This fuel is crystal clear, and just like water, it has no aromatics, contains no sulfur or heavy metals, and when used with a postcombustion device such as a catalytic converter any remaining NO, or other emissions can be drastically reduced. Estimates currently place the cost of this fuel at 1.50 per gallon, with availability in 2004 to meet the next round of stiff EPA exhaust emission standards. 

Smith, S.R. and Gordon, A.S., Precombustion reactions in hydrocarbon diffusion flames The paraffin candle flame, /. Chem. Phys., 22, 1150,1954. 

Desulfurization of fossil fuels was the subject of an authoritative review by J. B. Hyne (Alberta Sulphur Research Institute). This is a topic of increasing importance as Canada relies more and more on sulfur-containing fuels such as tar sands and heavy oils. Hyne reviewed the present state of the chemistry and technology for both precombustion desulfurization of natural gas and crude oils and postcombustion tailgas clean up of coals and cokes. He clearly identified areas of possible future research such as the high temperature-high pressure chemistry pertaining to in-situ desulfurization processes. 

The first major attempt at precombustion desulphurisation was in the coal gas industry and a number of efficient and effective techniques for removal of H2S, COS, CS2, mercaptans and other volatile sulphur containing products of the gasification process were developed. Many of these techniques found application in the subsequent development of sour natural gas processing where large volumes of hydrogen sulphide had to be removed from the hydrocarbon component. 

As costs of precombustion hydrodesulphurisation and post combustion flue gas clean-up have escalated and as environmental regulations have further limited the sulphur dioxide emission rates, there has been a growing interest in technology designed to effect fuel desulphurisation during the combustion process. Desulphurisation during fluidised bed combustion of coal has been a leading technique in these developments. 

The German COORETEC CO2 Reduction Technologies) concept favours coal gasification with precombustion capture to introduce COj capture into coal fired power plants. The same capture process is suited to produce hydrogen from coal in an environmentally-friendly way. This technical option is outlined in the recently drawn up national vision on hydrogen technologies. The first projects in this area are to be funded in the near future. 

Knock resistance has also been correlated with other preflame reaction properties such as the rate of pressure development during adiabatic compression (17), the temperature coefficient of preflame reactions (202), and the pressure developed prior to firing (34). Estrad re (59) made a correlation between the temperature of initial exothermic oxidation in a tube and knock. No quantitative connection exists between apparent activation energy (160) or the total heat (179) of the precombustion reactions and knock. 

Mention has already been made of the relatively small reactivity of allyl peroxy radicals compared with other alkyl peroxy radicals. Jost (88, 96) has reasoned that paraffins react by a small number of long chains, whereas olefins oxidize by a large number of short chains. Olefins are thus attacked more readily than paraffins but form less reactive allyl radicals. In addition, during oxidation chain transfer occurs in which alkyl radicals are replaced by allyl radicals. Shorter chains would then be expected. Comparison of the precombustion products of iso-octane and diisobutylene (154) indicates that marked self-inhibition of reaction chains was occurring in the latter case. 

Although the influence of products enters as a perturbating factor in precombustion reactions, marked differences have been found in initial rates of reaction among isomers (63). Neither chain length nor product effects can therefore explain all the facts. 

Figure 2. Relationship between fuel octane number and extent of precombustion reactions as measured by work equivalent of the reactions...

The actual energy required for ignition of a fuel decreases rapidly as the temperature and pressure of the fuel is increased (51). This results, in part, from sensitization of a fuel to ignition by precombustion reactions (58). 

In the development of the Diesel engine (117) the design of the combustion system has played an important role. Several combustion chamber shapes are presently in use. These include the open chamber (38, 54, 68, 82), the precombustion chamber (24, 32, 92, 108), the turbulence or air-swirl chamber (32), the air cell, and the energy cell (32). In all of these fuel is vaporized by transferring heat from the air charge to the fuel. In a recently developed combustion system (87) the fuel is sprayed on a hot surface which... 

Power Plant and combustion byproducts Scotia) 1126 (precombustion mill rejects, mostly pyrite) 39 (bottom ash) 766 (flyash) and Crandlemire (1996)... 

Automotive Valve plate in common rail systems Glow plugs for diesel engines and additional car heating Fuel injector parts, valves, valve train components, rocker arm pads, tappet disks, cam follower roller, turbocharger rotors tappet shim precombustion chambers... 

Schematic of a simple, singe-shaft gas turbine process (1) inlet, (2) comprssed state, precombustion, (3) post-combustion, pre-compressor, (4) post-turbine to exhaust.

State-of-the-art precombustion C02 capture technology in an IGCC plant employs amine-absorption treatment of the syngas however, even when optimized, this... 

The following example illustrates the potential of membrane-separation processes for precombustion carbon capture in an IGCC. This approach avoids using an expensive air-separation unit (asu) or a difficult-to-implement high-temperature mixed-ion conducting membrane process however, it still enables capture of C02 at purities suitable for commercial use or sequestration. 

Figure 9.1 Basic schematic diagram of (a) postcombustion capture, (b) precombustion decarbonization, and (c) oxy-fuel processes.

Air (compression not necessary) co + h2 Partial oxidation of natural gas in precombustion... 

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