Overall thermal efficiency

Biomass whether trees, plants, grasses, algae, or water plants, has a heating value of 15.1 X 10 J/dry t, and is converted in integrated biomass planting, harvesting, and conversion systems to SNG at an overall thermal efficiency of 50%. 

Synthetic jet fuel derived from coal is even more difficult and expensive, since the best of the conversion processes produces a fuel very high in aromatics. With hydrogenation, overall thermal efficiency is only 50%. Without additional hydrogenation, the gas turbine fuels would contain 60—70% aromatics. 

Efficiency. Since only 35 to 50% of fired duty is absorbed in the radiant section, the flue gas leaving the radiant chamber contains considerable energy that can be extracted efficiently in the convection section of the furnace. In the convection section, the feed is preheated along with dilution steam to the desired crossover temperature. Residual heat is recovered by generating steam. The overall thermal efficiency of modem furnaces exceeds 93%, and a value of 95% is not uncommon. 

Employing wood chips, Cowan s drying studies indicated that the volumetric heat-transfer coefficient obtainable in a spouted bed is at least twice that in a direct-heat rotaiy diyer. By using 20- to 30-mesh Ottawa sand, fluidized and spouted beds were compared. The volumetric coefficients in the fluid bed were 4 times those obtained in a spouted bed. Mathur dried wheat continuously in a 12-in-diameter spouted bed, followed by a 9-in-diameter spouted-bed cooler. A diy-ing rate of roughly 100 Ib/h of water was obtained by using 450 K inlet air. Six hundred pounds per hour of wheat was reduced from 16 to 26 percent to 4 percent moisture. Evaporation occurred also in the cooler by using sensible heat present in the wheat. The maximum diy-ing-bed temperature was 118°F, and the overall thermal efficiency of the system was roughly 65 percent. Some aspec ts of the spouted-bed technique are covered by patent (U.S. Patent 2,786,280). 

A comparison of the effect of the various cycles on the overall thermal efficiency is shown in Fig. 29-40. The most effective cycle is the Brayton-Ranidne (combined) cycle. This cycle has tremendous potential in power plants and in the process industries where steam turbines are in use in many areas. The initial cost of the combined cycle is between 800- 1200 per kW while that of a simple cycle is about 300- 600 per kW. Repowering of existing steam plants by adding gas turbines can improve tne over plant efficiency of an existing steam turbine plant by as much as 3 to 4 percentage points. 

To obtain a more accurate relationship between the overall thermal efficiency and the inlet turbine temperatures, overall pressure ratios, and output work, consider the following relationships. For maximum overall thermal cycle efficiency, the following equation gives the optimum pressure ratio for fixed inlet temperatures and efficiencies to the compressor and turbine ... 

The cycle leads to an increase in output work and an increase in overall thermal efficiency. 

The results of a set of computer calculations for a CBT plant with single-step cooling (i.e. of the first stage nozzle guide vanes) are illustrated in Fig. 5.2, in the form of (arbitrary) overall thermal efficiency (tjq) against pressure ratio (r) with the combustion temperature T. oi as a parameter, and in Fig. 5.3 as tjq against with r as a parameter. 

Newby et al. found that increasing the PO turbine pressure resulted in higher steam flow (for a given pinch point temperature difference in the HRSG), increased PO turbine power and overall plant efficiency. However, at the highest pressure of 100 bar attempts to increase the steam flow further resulted in incomplete combustion in the main combustor and the overall thermal efficiency did not increase substantially at this pressure level. 

Another method of increasing the overall cycle efficiency is to use the waste heat energy in the exhaust air to heat process fluids as depicted in Figure 16-10. This is a direct savings in fuel gas that would otherwise be consumed in direct-fired heaters. Overall thermal efficiencies can be as high as 50 to 60% in this type of installation. 

Hie best overall efficiency of a turbine can be ensured by maintaining tile efficiency of the air compressor section. Conversely, allowing the air compressor efficiency to deteriorate will deteriorate the overall thermal efficiency of the turbine. Air compressor efficiency can be draslically reduced in a very short time when dirt, salt water mist, or similar air con-... 

Large power stations use complex feed heating systems before the boiler feed pumps (LP) and after the boiler feed pumps (HP), which can give high overall thermal efficiencies of 39 per cent. However, for the smaller machine, it becomes uneconomic to consider multiple bleeds from the turbine, and the final choice is dictated by the extra cost for the additional complexity against lower running costs due to increased efficiency. As a minimum, a contact type de-aerator is often employed which would extract a small bleed of around 2-3bar from the turbine. 

Percent of nominal rating, R Percent overall thermal efficiency, E... 

Fluidised bed combustors are now common-place for large-scale operations and are extensively used in large electricity generating stations. More recently, smaller scale units have been developed for use by individual industrial concerns and in operating, as combined heat and power units, can give overall thermal efficiencies of up to 80 per cent. 

Legislative restrictions on pollutant emissions have motivated the combustion community to seek new low-emission combustion techniques that are practical industrial energy sources. However, to meet the needs in most industrial applications, a combustion source needs to be able to maintain low-emission output over a range of heat release rates, occupy minimal volume, and have low operating costs per unit energy produced. One would like to maximize the turn-down ratio, volumetric heat release, and overall thermal efficiency while minimizing NOa , CO, and hydrocarbon emission levels. The ultra-low NO, emission performance of the CSC has been previously documented by the authors and its... 

The suitability of a cycle for hydrogen production depends upon the overall thermal efficiency and operational feasibility. A highly endothermic reaction step is required in a cycle to achieve effective heat-to-chemical energy conversion. For efficient mass and momentum transfer a fluid based system is preferred [96] and, ultimately, for large-scale hydrogen production other factors such as environmental effects and cost effectiveness must also be considered. 

The reversible potential for the sulfur dioxide electrolysis is only 0.17 V, less than 10% that of water electrolysis (minimum of 1.23V at 298K and 1 bar) [65,69]. However corrosion problems in the electrolysis step are severe due to the presence of high concentration (about 50%) sulfuric acid. The overall thermal efficiency of the process, considering both thermal and electrical energy input derived from the same heat source, is estimated as 48.8% [116]. However, in terms of economics and process complexity the hybrid cycles face tough competition from advanced water electrolyzers. 

Heat exchange from reactor effluent to the pressurised feed is the major feature that increases the overall thermal efficiency of SCWO over other oxidation processes for... 

Basic specifications on the process are the total heat release (102.86 MBtu/hr), overall thermal efficiency (75%), excess air (25%), the fraction of the heat release that is absorbed in the radiant section (75%), and the heat flux (10,000 Btu/(hr)(sqft). 

Tabic 3 shows the effect of the second methanation stage on product calorific value. While consumption of LI G is minimized, the capital cost is increased and Ihe overall thermal efficiency is slightly reduced. 

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