Feasibility Analysis of Coupling Hydrogen-Derived Fuel on a Coal-Fired Boiler for Power Generation

Abstract

As an alternative to hydrogen, hydrogen-derived fuel (NH3, CH3OH, or CH3OCH3) is considered to be an ideal secondary energy source. The effects of coupling hydrogen-derived fuels with coal on the thermodynamic parameters of a boiler are analyzed through thermal calculations according to the principles of mass and energy conservation. A 300 MW tangentially fired boiler is selected for a case study. The results show that the variations of boiler thermodynamic parameters depend on the properties of hydrogen-derived fuels and coupling mass percentage. After the coupling, the furnace exit flue gas temperature changes, which results in alterations in heat distribution of radiation and convection for the water-cooled walls and the convective heating surfaces. The furnace exit flue gas temperature drops for coupling H2 or NH3 but rises for coupling CH3OH or CH3OCH3 with the growth of the coupling mass percentage. The variations of boiler thermal efficiency with different coupling mass percentages under BMCR load are 0.55% to 0.90% for H2, −0.32% to −1.16% for NH3, −0.22% to −2.03% for CH3OH, and −0.08% to −0.59% for CH3OCH3. The acid dew point rises and then drops as the coupling mass percentage grows. The flow rate of the total flue gas increases at the outlet of the air preheater. Thus, the current forced draft fan could not meet the requirements, and its retrofit should be performed. After the large proportion of cofiring, the coal consumption rate drops. The annual emissions reductions of CO2 are up to 0.734 million tons for H2, 0.231 million tons for NH3, 0.062 million tons for CH3OH, and 0.101 million tons for CH3OCH3 under BMCR load at a 20% coupling mass percentage. The lifecycle CO2 reduction potential should be considered for better illustrating the benefits of cocombustion in future studies.

The Influence of Co-Firing Coal with Biomass Syngas on the Thermodynamic Parameters of a Boiler

“…Finally, it is of vital importance to note that iterative calculations are required until the discrepancy between the estimated and fictitious exhaust gas temperatures of the boiler falls within a suitable range (±1 • C in this study). Based on the above procedures, a calculation program was proposed by our group [24]. The accuracy of the program can be verified since it has been applied in lots of manufacturers and research institutes [23,24].…”

“…Based on the above procedures, a calculation program was proposed by our group [24]. The accuracy of the program can be verified since it has been applied in lots of manufacturers and research institutes [23,24]. The calculation methods of thermodynamic parameters described below are based on 1 kg of coal and the corresponding volume of biomass syngas, represented by x (m 3 kg −1 ), which is correlated to the volume fraction of biomass syngas and the fuel compositions under the standard condition.…”

“…Heat conservation, which is the balance between the heat entering and leaving the boiler envelope, is calculated to obtain the coal consumption rate and thermal efficiency of boilers [23,24,28]. The coal consumption rate B (kg s −1 ) is defined as…”

“…where m t0 (t) is the CO 2 annual emission under the boiler maximum continuous rating (BMCR), and m t (t) is the CO 2 annual emission, which is calculated by [24].…”

“…The CO 2 annual emission is the product of CO 2 emission intensity (M i , g kW −1 h −1 ) and generation capacity (W, kW h). M i can be calculated by [24].…”