Abstract
Abstract The low reactivity of natural gas leads to a sudden increase of carbon monoxide (CO) and unburned hydrocarbons (UHC) emissions below a certain load level, which limits the part load operation range of current utility gas turbines in combined cycle power plants (CCPP). The feasibility of catalytic autothermal syngas generation directly upstream of gas turbine burners to improve burn-out at low flame temperatures is studied in this paper. The adiabatic reformer is supplied with a mixture of natural gas, air and water and generates syngas with high reactivity, which results in better low-temperature combustion performance. Substitution of part of the natural gas by syngas provides the opportunity of lowering overall equivalence ratio in the combustion chamber and of extending the operation range towards lower minimum power output without violating emission limits. A generic gas turbine with a syngas generator is modelled by analytic equations to identify the possible operating window of a fuel processor constrained by pressure loss, low and high temperature limits and carbon formation. A kinetic study shows good conversion of methane to syngas with a high hydrogen share. A calculation of the one-dimensional laminar burning velocity of mixtures of syngas and methane and the assessment of the corresponding Damköhler number show the potential for lowering the minimum equivalence ratio with full burn-out by fuel processing. The study shows that such a fuel processor has a possible operating range despite the before mentioned constraints and it has potential to reduce the lowest possible load of gas turbines in terms of thermal power by 20%.
Highlights
Conventional power plants must compensate fluctuations in the power supply because of an increasing amount of volatile renewable energy sources such as wind and solar power
The solution scheme calculates all variables until the steam temperature change becomes smaller than 1 K and the pressure loss changes less than 100 Pa
According to the considered generic gas turbine, the total natural gas mass flow for part load is 11.9 kg/s, assuming a reduced air intake to 70% of full load intake and an equivalence ratio φCH4 = 0.5
Summary
Conventional power plants must compensate fluctuations in the power supply because of an increasing amount of volatile renewable energy sources such as wind and solar power. This demands more flexible conventional power plants. Gas turbine power plants adjust total power output quickly but CO and UHC emissions limit the part load regime to about 60% of the full load. This study focuses on the operational range extension of gas turbines in a combined cycle power plant to lower loads. The basic idea to accomplish this goal is to increase the reactivity of the fuel and to reduce the possible overall equivalence. The desired increase of reactivity is achieved by converting methane to hydrogen
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