Thermodynamic Analysis of Air-Cooled Gas Turbine Plants

At present high temperature, internally cooled gas turbines form the basis for the development of highly efficient plants for utility and industrial markets. Minimizing irreversibility of processes in all components of a gas turbine plant leads to greater plant efficiency. Turbine cooling, like all real processes, is an irreversible process and results in lost opportunity for producing work. Traditional tools based on the first and second laws of thermodynamics enable performance parameters of a plant to be evaluated, but they give no way of separating the losses due to cooling from the overall losses. This limitation arises from the fact that the two processes, expansion and cooling, go on simultaneously in the turbine. Part of the cooling losses are conventionally attributed to the turbine losses. This study was intended for the direct determination of lost work due to cooling. To this end, a cooled gas turbine plant has been treated as a work-producing thermodynamic system consisting of two systems that exchange heat with one another. The concepts of availability and exergy have been used in the analysis of such a system. The proposed approach is applicable to gas turbines with various types of cooling: open-air, closed-steam, and open-steam cooling. The open-air cooling technology has found the most wide application in current gas turbines. Using this type of cooling as an example, the potential of the developed method is shown. Losses and destructions of exergy in the conversion of the fuel exergy into work are illustrated by the exergy flow diagram.

A Rotor Blade Cooling Improvement for Heavy Duty Gas Turbine Using Steam and Mixed Steam/Air Cooling

This paper proposes a theoretical study of steam cooling application for a typical rotor blade cooling system of heavy duty gas turbine. The steam cooling introduction is evaluated using open and closed loop configurations; the possible interaction of steam and air cooling is also studied; the simulation is realized with a family of modular codes developed by authors. The study is conducted with the characteristic cooling parameters (efficiency, effectiveness) analysis and by the evaluation of blade temperature distribution. The results show the possibility of a mass coolant reduction and/or, a maximum cycle temperature increase with the same cooling system used for standard air cooling. The best results are obtained with an innovative closed-open/steam-air cooling system.

The pollution profile of alcohol distilleries treating beet sugar molasses

Fermentation of molasses and refining the produced alcohol by distillation is a common agroindustrial activity. The wastewaters originating from the process, especially the spent mash, are highly concentrated and contain TDS of over 50,000 mg/l as well as organic matter. Character of wastewaters varies with production application which affects the treatability characteristics. In this study four alcohol distillery plants treating beet sugar molasses are investigated to assess production applications and wastewater characteristics. Process profiles for three major modes of operation are prepared. Use of open steam and recycle of spent mash was calculated to affect the wastewater volume up to 25%. COD load is found to be practically unchanged with recycle while TDS increased significantly. Nature of COD and treatability characteristics are also expected to vary with recycle.

Basic Reactions Occurring during Rubber Reclaiming. I. The Influence of Reclaiming Media, Antioxidant, and Defibering Agents on Vulcanized Natural Rubber at 195 Pounds Per Square Inch Gauge Pressure (196.6° C)

The influence of surrounding atmosphere, antioxidant, and defibering agents at 196.6° C on the hydrocarbon of rubber was studied by subjecting a laboratory prepared, pure-gum, natural rubber compound to reclaiming in the absence of any reclaiming oils or chemicals. Data obtained on the amount of acetone and chloroform extracts and on the unsaturation of the reclaims and the chloroform extracts could therefore be interpreted in terms of the effect of the factors mentioned above on the rubber hydrocarbon and not as the effect of any chemicals added to the rubber to promote reclaiming. It was found that the effect of the surrounding atmosphere during reclaiming is the predominant factor in the reaction. Acidic surrounding atmospheres result in a slow and rather uniform rate of molecular breakdown and in the formation of small amounts of oxidation products. Apparently no secondary oxidative attack occurs at the double bonds. An open steam atmosphere provides the greatest amount of oxidized products and also a high initial molecular breakdown, followed by a slow progressive increase in it as the reclaiming periods are lengthened. A decrease in the unsaturation value of the acetone extracted reclaim indicates that secondary oxidative attack at the double bonds occurs at long reclaiming intervals. Alkaline reclaiming atmospheres provide little if any oxidation products and result in a very high initial rate of molecular breakdown. Longer reclaiming periods do not change further the amount of molecular breakdown. The very small amounts of oxygen necessary to promote the reclaiming reactions, the dependence of the course of these reactions on the acidity or alkalinity of the surrounding reclaiming media, together with the high initial rate of molecular breakdown reactions under conditions where such rate would be speeded up, permit the tentative explanation of these reactions on the basis of hydroperoxidic chain reactions. Further experiments along this line are being carried out.

Properties of Hard Rubber. XIII. Experiments on Thermal Effects during Vulcanization

The characteristics and technical importance of the internal heating effect during the vulcanization of hard rubber, due to the exothermic reaction between rubber and sulfur, are recalled, and the conditions under which thermal instability may occur are outlined. The necessity of avoiding even slight increases in internal temperature when vulcanizing material for research purposes is emphasized. Experiments are described in which sheets of rubber-sulfur mixings of various thicknesses were vulcanized in a platen press at various temperatures, and the internal and surface temperatures were measured throughout the vulcanization period by means of thermocouples. The time-temperature curves are reproduced. The relations between internal temperature rise, platen temperature, and thickness of sheet are indicated. The choice of maximum safe thickness for a given platen temperature or of maximum safe platen temperature for a given thickness is shown to be very critical. The rise of temperature is greater in open steam vulcanization than in press-vulcanization, for a reason which is pointed out. It is important that these limiting factors in the use of high-grade rubber-sulfur materials should be taken into account in designing hard rubber articles.

THE DEHYDRATION OF PORK

Four preprocessing and three drying procedures for the dehydration of pork were studied. The best product resulted from cooking in an open steam-jacketed kettle, followed by mincing and tunnel–tray drying in four hours or less with a tray load of 2 lb. per square foot. Little difference in quality of the product was observed for air velocities of 700 to 1200 ft. per min. over the trays, or for initial stage temperatures between 70° and 80 °C. and final stage temperatures between 55° and 70 °C.Pork, when dried to a moisture content of 3 to 4% in less than four hours, still retained a high percentage of the thiamin present in the raw meat, showed no fat deterioration when assessed by peroxide oxygen determinations, and on reconstitution had a palatability rating approximately equal to that of the initial cooked material.

Tensile Tests of Plantation Rubber

The investigation which has just been described can be summarized as follows: (1) A technique for the commercial testing of plantation rubber has been developed which is simple and precise, and by means of which it is possible to reproduce control tests, a feature which is indispensable if rubber is to be sold on a basis of quality rather than superficial appearance. (2) The tentative specifications for testing rubber drawn up by the Crude Rubber Committee of the Division of Rubber Chemistry of the American Chemical Society have been found acceptable as a basis for this testing procedure. (3) It has been found necessary, however, to revise the specifications of the Crude Rubber Committee in some ways and to amplify them, so that they fulfill the three conditions described above and also conform to the particular working conditions of laboratories in the tropics. The revisions to the Crude Rubber Committee specifications include: (1) The use of an autoclave for vulcanizing in open steam. (2) A mill roll temperature of 65° C instead of 70° C. (3) A definite, fixed weight of batch, containing 200 grams of rubber, plus accessory ingredients. (4) A temperature of 25° to 30° C during testing. (5) The use of ring test-specimens instead of dumb-bell specimens.