Fulity of use of expander-generator sets at thermal power plants

Abstract

The so-called expander-generator sets (EGS) have found some application in Western Europe. Their operation is based on a drop in the pressure of natural gas (NG), which comes to a power-generating or industrial facility, and which used to be lost in choking devices of the gas distribution station (GDS) of these facilities. The capacity of such sets, e.g., in Germany, is limited to just tens to hundreds of kilowatts. The benefit for their owners lies in obtaining, according to the German law, markups to the cost of energy released to electricity consumers. However, the economic environment in place in Russia is somewhat different.According to the author, the limited number of EGS in Russia’s power industry, as well as cases of their decommissioning, are due to the lack of evidence of their thermodynamic or technical-economic efficiency, or even worsening economic conditions at facilities, where those were implemented. Besides, the facilities in question have to be provided with considerable specific conditions. These include a relatively high value of initial NG pressure at the input of EGS, its considerable flow rate and the possibility of NG heating at the input of EGS. This necessity to heat NG upstream the EGS is determined, on the one hand, by the intention to enhance the EGS capacity, and on the other hand, by having to comply with requirements imposed by the EGS manufacturer regarding the temperature values upstream and downstream the EGS. Without a required source of heat of relevant parameters at the facility, application of EGS turns out to be impossible, altogether. An interest in EGS in Russia arose due to construction and commissioning (first, at CHPP-21, and later at CHPP-23 of Mosenergo) of two power-generating centers, each equipped with two 5 MW EGS. Since then, a large number of articles have been published, and numerous theses have been defended based on the studies undertaken, mostly of analytical nature. Yet, those publications have not considered, for a real expander, matters of effects produced by the relation between the absolute electrical efficiency (ηe) of CPP and/or CHPP and the efficiency ratio of expander (ηer ), the NG expansion ratio (δ). Conditions, at which heating NG upstream the EGS is expedient, have not been established, either, whereas these are the factors crucial for economic feasibility of a TPP to be equipped with EGS.