Thermodynamic and economic analysis of a gas turbine set coupled with a turboexpander in a hierarchical gas-gas system

Thermodynamic and Economic Analysis of Trigeneration System Comprising a Hierarchical Gas-Gas Engine for Production of Electricity, Heat and Cold

“…In the analyzed trigeneration system, as in the systems in [1], it is beneficial to install a turboexpander and a low-pressure compressor in a single installation and on a common shaft, which is presented by symbols in Figures 1-3 using dashed squares, identically, as is the case for the turbine part and gas turbine compressor. Such a solution reduces the necessary investment in a gas-gas engine.…”

“…On the basis of the analysis of the performance of the hierarchical, trigeneration gas-gas system, it is also reasonable to find the answer to the question: to what extent does the use of heat regeneration in the turboexpander- Figure 4-as well as in the gas turbine [1] increase its capacity, i.e., electric, thermal and cooling power. A significant increase in any of them would be converted into greater economic feasibility of their operation.…”

“…The energy and economic efficiency of two alternatives involving an innovative, hierarchical two-cycle gas-gas engine operation were analyzed in [1]. In this design, two Joule circulations were combined and implemented, i.e., a high-temperature Joule cycle of a gas turbine and a low-temperature Joule turboexpander cycle.…”

“…As a consequence, the ratio of the power of the turboexpander to the one of the gas turbine N TE /N GT in a gas-gas system for the case of production of only electricity in both systems is even more than three times smaller than the ratio of steam turbine power to gas turbine power N ST /N GT in a gas-steam system. In the case of operation of both systems in a combined cycle, the ratio N TE /N GT is about two times smaller than N ST /N GT [1]. Higher electricity production in the gas-steam system results from the built-in heat recovery steam generator, which makes it possible to apply the low-temperature enthalpy of exhaust gases from the turbine throughout the year for steam production applied to feed the steam turbine [2].…”

“…The temperature of the gas extracted from the heat-recovery steam generator and released the environment, both for the combined cycle and the purely condensing operation of the gas-steam system, is low all year, as it is in the range from 70 to 90 • C, whereas in the gas-gas system the temperature of the exhaust gas to the environment is relatively high. In the case of a system applied for the production of only electricity (this system does not contain the heat exchanger (HE) in Figures 1 and 2), the temperature of the exhaust gas fed into the stack is in the range of about 180 to 250 • C (this temperature depends on the temperature of the gas entering the gas turbine [1]), and in the case of combined operation in the heating season in the range of about 130 to 160 • C, and in the non-heating season in the range of about 170 to 240 • C [1]. Of course, these are then the flue gas temperatures behind the heat exchanger (HE), Figures 1 and 2.…”