Sequential supplementary firing in natural gas combined cycle plants with carbon capture for enhanced oil recovery

摘要

The rapid electrification through natural gas in Mexico, the interest of the country to mitigate\udthe effects of climate change, and the opportunity for rolling out Enhanced Oil Recovery at\udnational level requires an important R&D effort to develop nationally relevant CCS\udtechnology in natural gas combined cycle power plants. Post-combustion carbon dioxide\ud(CO2) capture at gas-fired power plant is identified and proposed as an effective way to\udreduce CO2 emissions generated by the electricity sector in Mexico. In particular, gas-fired\udpower plants with carbon dioxide capture and the sequential combustion of supplementary\udnatural gas in the heat recovery steam generator can favourably increase the production of\udcarbon dioxide, compared to a conventional configuration. This could be attractive in places\udwith favourable conditions for enhanced oil recovery and where affordable natural gas prices\udwill continue to exist, such as Mexico and North America.\udSequential combustion makes use of the excess oxygen in gas turbine exhaust gas to\udgenerate additional CO2. But, unlike in conventional supplementary firing, allows keeping\udgas temperatures in the heat recovery steam generator below 820°C, avoiding a step change\udin capital costs. It marginally decreases relative energy requirements for solvent regeneration\udand amine degradation.\udPower plant models integrated with capture and compression process models of Sequential\udSupplementary Firing Combined Cycle (SSFCC) gas-fired units show that the efficiency\udpenalty is 8.2% points LHV compared to a conventional natural gas combined cycle power\udplant with capture. The marginal thermal efficiency of natural gas firing in the heat recovery\udsteam generator can increase with supercritical steam generation to reduce the efficiency\udpenalty to 5.7% points LHV. Although the efficiency is lower than the conventional\udconfiguration, the increment in the power output of the combined steam cycle leads a\udreduction of the number of gas turbines, at a similar power output to that of a conventional\udnatural gas combined cycle. This has a positive impact on the number of absorbers and the\udcapital costs of the post combustion capture plant by reducing the total volume of flue gas by\udhalf on a normalised basis. The relative reduction of overall capital costs is, respectively, 9.1\ud% and 15.3% for the supercritical and the subcritical combined cycle configurations with\udcapture compared to a conventional configuration. The total revenue requirement, a metric\udcombining levelised cost of electricity and revenue from EOR, shows that, at gas prices of 2\ud$/MMBTU and for CO2 selling price from 0 to 50 $/tonneCO2, subcritical and supercritical\udsequential supplementary firing presents favourably at 47.3-26 $/MWh and 44.6-25 $/MWh,\udrespectively, compared with a conventional NGCC at 49.5-31.7 $/MWh.\udWhen operated at part-load, these configurations show greater operational flexibility by\udutilising the additional degree of freedom associated with the combustion of natural gas in\udthe HRSG to change power output according to electricity demand and to ensure continuity\udof CO2 supply when exposed to variation in electricity prices. The optimisation of steady\udstate part-load performance shows that reducing output by adjusting supplementary fuel\udkeeps the gas turbine operating at full load and maximum efficiency when the net power\udplant output is reduced from 100% to 50%. For both subcritical and supercritical combined\udcycles, the thermal efficiency at part-load is optimised, in terms of efficiency, with sliding\udpressure operation of the heat recovery steam generator. Fixed pressure operation is\udproposed as an alternative for supercritical combined cycles to minimise capital costs and\udprovide fast response rates with acceptable performance levels.