Trigeneration units on carbon dioxide with two-time overheating with installation of turbo detainder and recovery boiler

A program that allows modeling, thermodynamically optimizing and performing exergetic analysis of more than a hundred different variations of the schemes of trigeneration turbine units based on low-boiling working fluids. With the aid of the program that had been developed, an exergetic analysis of six schemes of trigeneration turbine units on the organic Rankine cycle was performed, viz. on an overheated steam with a steam compression refrigeration unit; with an intermediate overheating of the working fluid and a steam compression refrigeration unit; on an overheated steam with a refrigeration unit with carbon dioxide production; with an intermediate overheating of the working fluid and a refrigeration unit with carbon dioxide production; on an overheated steam with a refrigeration unit with production carbon dioxide and cooling of the turbine condenser with liquid carbon dioxide; with intermediate overheating of the working fluid, a refrigeration unit with carbon dioxide production and cooling of the turbine unit condenser with liquid carbon dioxide. A gas turbine unit was used as an energy source for the above-mentioned schemes. The possibility of using the resulting liquid carbon dioxide to cool the condenser of a turbine unit on an organic Rankine cycle has been studied. A comparative analysis of two methods of obtaining cold (using a steam compression refrigeration unit and a refrigeration unit with carbon dioxide production) for use in trigeneration schemes has been carried out. The research was based on the method of exergetic analysis, the results of which are presented in the form of enlarged Grassmann – Shargut diagrams. A technical and economic analysis of the use of intermediate overheating in the organic Rankine cycle has been carried out, ozone-safe freon R245FA was used as the working fluid. Recommendations for the application of the studied trigeneration schemes on the organic Rankine cycle are formulated.

Section: Introductionunclassified

Trigeneration Turbine Units Based on Low Boiling Working Fluids

Ovsyannik

Kliuchinski

2022

Turbo-Expander Units on Low Boiling Working Fluids

Ovsyannik

Kliuchinski

2021

The article examines the possibility of increasing the efficiency of the turbo-expander cycles on low-boiling working fluids using those methods that are used for steam turbines, viz. increasing the parameters of the working fluid before the turbo-expander and using secondary overheating. Thus, four schemes of the turbo-expander cycle are considered: the one without overheating of the low-boiling working fluid, the one with single overheating of low-boiling fluid, the one with double overheating and the one with double overheating at supercritical parameters. All the studied cycles were considered with a heat exchanger at the outlet of the turbo expander, designed to heat the condensate of a low-boiling working fluid formed in the condenser of the turbo expander unit. Cycles in P–h coordinates were built for the studied schemes. The method of thermodynamic analysis of the studied cycles based on the exergetic efficiency has been developed. The results of the research are presented in the form of Grassman-Shargut diagrams, which show exergy losses in the elements of the studied cycles on a scale, and also show the positive effect of the operation of the turbo-expander cycle in the form of electrical power. The analysis of the obtained results showed that the main losses that have a significant impact on the exergy efficiency are the losses of exergy in the recovery boiler. The increase of parameters of low-boiling working body, and the use of intermediate superheating reduce losses in the waste heat boiler and, consequently, increases exergetic efficiency of turbo-expander cycle. The turbo-expander cycle with double overheating at supercritical parameters of the low-boiling fluid is of the largest exergetic efficiency out of the schemes that have been examined.

Thermodynamic Analysis and Optimization of Secondary Overheating Parameters in Turbo-Expander Plants on Low Boiling Working Fluids

Овсянник

Ключинский

2021

The paper presents a thermodynamic analysis of secondary overheating in turbo-expander plants on low-boiling working fluids. The possibility of optimizing the parameters of the working fluid in a secondary stem superheater has been studied. The research was carried out for two typical turbo-expander cycles: with a heat exchanger at the outlet of the turbo-expander, intended for cooling an overheated low-boiling working fluid, and without a heat exchanger. Cycles in T–s coordinates were constructed for the studied schemes. The influence of pressure and temperature in the intermediate superheater on the exergetic efficiency of the turbo-expander unit was studied. Thus, the dependences of the exergetic efficiency and losses on the elements of the turbo-expander cycle are obtained when the temperature of the working fluid changes and pressure of the working fluid not changes in the intermediate superheater, and when the pressure changes and the temperature does not change. As a low-boiling working fluid, the ozone-safe freon R236EA is considered, which has a “dry” saturation line characteristic, zero ozone layer destruction potential, and a global warming potential equal to 1370. It has been determined that increasing the parameters of the low-boiling working fluid in front of the low-pressure turbo expander (regardless of the scheme of the turbo expander cycle) does not always cause an increase in the exergetic efficiency. Thus, overheating of the working fluid at a pressure exceeding the critical pressure causes a positive exergetic effect, but for each temperature there is an optimal pressure at which the efficiency will be maximum. At a pressure below the critical pressure, overheating leads to a decrease in the exergetic efficiency, and the maximum exergetic effect is achieved in the absence of a secondary steam superheater. All other things being equal, a turbo-expander cycle with a heat exchanger is more efficient than without it over the entire temperature range and pressure of the low-boiling working fluid under study.