據碳氫化合物工程4月26日消息，天然氣是美國最普遍的發電能源。在該國491吉瓦的天然氣發電容量中，超過一半（280吉瓦）是包括蒸汽輪機和燃燒式渦輪機的聯合循環系統。聯合循環系統的主要配置包括兩臺燃燒式渦輪機和一臺蒸汽輪機。

天然氣發電廠利用簡單循環或聯合循環能量轉換。簡單循環系統在單個轉換系統中消耗天然氣，例如燃燒式渦輪機、帶有蒸汽輪機的鍋爐或內燃機。在這些系統中，來自一次轉換排氣熱的能量會損失掉，并且不會發送到另一個渦輪機。聯合循環系統將燃燒式渦輪機排出的熱量輸送到熱回收蒸汽發生器，為一個或多個產生額外電力的蒸汽輪機加壓。

聯合循環系統在將單位天然氣轉換為單位電力方面往往更有效。由于效率的提高，聯合循環系統通常以比簡單循環系統更高的容量因數運行。因此，聯合循環系統通常服務于電網的基本和中間負荷，而簡單循環系統通常服務于峰值負荷。

EIA的電力年度調查收集了一個單元代碼標識符，將聯合循環部件分組到功率塊中。功率塊配置差異很大，包括多個燃燒式渦輪機支持一個或多個蒸汽輪機等配置。大多數聯合循環發電機組都有燃燒和蒸汽輪機部件，每個部件都與發電機相連。然而，13吉瓦的聯合循環容量是單軸系統，其中燃燒和蒸汽渦輪機在一根軸上驅動一個公共發電機。

就發電量而言，美國最大的天然氣聯合循環發電廠是佛羅里達電力與照明公司的西縣能源中心。西縣能源中心由三個3x1 發電機機組組成，或總共12個燃燒和蒸汽渦輪機。三個發電機組中的額定功率均為1259兆瓦，使該工廠的總裝機容量達到3777兆瓦。西縣能源中心2021 年發電量20.3太瓦；到2021年，只有5座核電廠和1座燃煤電廠發電量增加。

自2015年以來，聯合循環發電機組的平均容量有所增加，當時一種新型燃燒式渦輪機變得更加普遍。這些較新的燃燒式渦輪機允許聯合循環發電機組具有更大的容量和更高的效率。2x1發電機組的平均容量從2015年之前建造的500兆瓦增加到2015年之后建造的超過700兆瓦。

祝精燕 摘譯自 碳氫化合物工程

原文如下：

EIA: natural gas is the most prevalent energy source for electricity generation in the US

Natural gas is the most prevalent energy source used for electricity generation in the US. Of the 491 GW of natural gas-fired electric-generating capacity in the country, more than half (280 GW) are combined-cycle systems that include both steam turbines and combustion turbines. The predominant configuration for combined-cycle systems involves two combustion turbines and one steam turbine (2x1).

Natural gas-fired electric power plants utilise either simple-cycle or combined-cycle energy conversion. Simple-cycle systems consume natural gas in a single conversion system, such as a combustion turbine, boiler with a steam turbine, or internal combustion engine. In these systems, energy from the primary conversion exhaust heat is lost and not sent to another turbine. Combined-cycle systems send combustion turbine exhaust heat to a heat recovery steam generator, pressurising steam for one or more steam turbines that generate additional electric power.

Combined-cycle systems tend to be more efficient at converting a unit of natural gas (measured in Btu) to a unit of electricity (kWh). Combined-cycle systems have an average operating heat rate of 7146 Btu/kWh compared with simple-cycle systems, which consume approximately 10 000 Btu to generate 1 kWh, based on 2020 averages. Because of the efficiency gains, combined-cycle systems generally operate at higher capacity factors than simple-cycle systems. As a result, combined-cycle systems generally serve base and intermediate loads to the grid, while simple-cycle systems generally serve peak load.

The EIA's Electric Power Annual survey collected a unit code identifier to group combined-cycle components into power blocks. Power block configurations vary widely, including configurations such as multiple combustion turbines supporting one or more steam turbines. Most combined-cycle power blocks have combustion and steam turbine components each connected with a generator. However, 13 GW of combined-cycle capacity are single-shaft systems in which both the combustion and steam turbines drive a common generator on one shaft.

In terms of generating capacity, the largest natural gas combined-cycle power plant in the US is Florida Power & Light’s West County Energy Center. The West County Energy Center consists of three 3x1 power blocks, or a total of 12 combustion and steam turbines. Each of the three power blocks is rated at 1259 MW, giving the plant 3777 MW of total generating capacity. The West County Energy Center generated 20.3 TWh of electricity in 2021; only five nuclear power plants and one coal-fired plant generated more electricity in 2021.

Combined-cycle power blocks have increased in average capacity since 2015, when a new class of combustion turbines became more common. These newer combustion turbines allow combined-cycle power blocks to have larger capacities and improved efficiencies. The average capacity of a 2x1 power block increased from 500 MW for those built before 2015 to over 700 MW for those built after 2015.