Process simulation of oxy-fuel combustion for a 300 MW pulverized coal-fired power plant using Aspen Plus
Graphical abstract
This paper studied the combustion processes of pulverized coal in a 300 MW power plant using Aspen Plus software. The amount of each component in flue gas in coal-fired processes with air or O2/CO2 as oxidizer was obtained. The differences between the two processes were identified, and the parameter influences of temperature, excess oxygen ratio and molar fraction of O2/CO2 on the proportions of different components in flue gas were examined by sensitivity analysis.
Introduction
It is well known that CO2 is the main greenhouse gas. According to the published statistics by the international energy agency (IEA), the amount of global CO2 emissions is 31.6 billion tons in 2011 and over 40% of the total is attributed to the coal combustion [1]. Therefore, it is very important to reduce CO2 emissions from coal-fired power plant (CFPP). Oxy-fuel combustion is considered as one of the major options for CO2 capture for both new and existing CFPPs. Coal is burned with a mixture of oxygen and recycled flue gas to obtain a CO2 rich stream ready for sequestration. At the same time, the NOx emissions can also be reduced, so oxy-fuel combustion is a comprehensive measure in pollution control and a new clean combustion technology [2], [3], [4].
In recent years, lots of investigations on oxy-fuel combustion technology have been carried out relating to the characteristics of coal combustion. Wang et al. [5] studied the combustion of pulverized coal in O2/CO2 as well as in air atmosphere. Predictions using a one-dimensional computer code were compared with the experimental data from tests conducted by Battelle Columbus Laboratories. The results showed that the combustion of pulverized coal could be completed more thoroughly in O2/CO2 atmosphere over a range of CO2-to-O2 molar ratios between 2.23 and 3.65. Kimura et al. [6] studied the pulverized coal combustion in the O2/CO2 using a 1.2 MWt tunnel furnace with a coal feed rate of 150 kg/h. Payne et al. [7] studied the combustion of coal with oxygen and recycled flue gas. The feasibility of this process had been evaluated in a pilot scale test furnace. The results showed that flue gas recycle is a viable means of controlling combustion and heat transfer characteristics, and that recycle conditions exist at which performance changes are minimal from operation with air. Suda et al. [8] studied the flame propagation velocity in O2/CO2 atmosphere. Experiments were carried out in a spherical chamber with inner diameter of 200 mm. Micro-gravity condition was used in order to achieve uniform pulverized coal cloud in the chamber. Flame propagation velocity was measured from the photographic image of the flame front by using high speed camera. The results showed that the flame propagation velocity of pulverized coal cloud in O2/CO2 mixture gas decreased to about 1/3–1/5 of that in N2/O2 gas mixture at the same oxygen concentration.
The emission characteristics of coal oxy-fuel combustion were also studied. Okazaki and Ando [9] and Okawa et al. [10] found that the emission of NOx under O2/CO2 atmosphere is only about 25% of that in air atmosphere. Meng et al. [11] studied the effects of temperature and excess air ratio on NOx formation using a one-dimensional drop-tube furnace. The results showed that, the amount of NOx increases quickly with temperature in air, but very slowly in O2/CO2 atmosphere. The peak value of NOx increases with excess oxygen ratio in both air and O2/CO2 atmospheres. The combustion characteristics of a bituminous coal and an anthracite coal in O2/CO2 atmosphere were studied by Niu et al. [12]. The results showed that, the total conversion of the fuel-N to NO is strongly decreased in O2/CO2 atmosphere, and at 1473 K, the conversion is reduced by 28.99% for the bituminous coal and 22.54% for the anthracite coal, respectively. Sivaji and Sreenivas [13] studied NO formation in oxy-fuel combustion at high pressures showing that the peak NO concentration nearly doubles when the pressure increases from 1 atm to 30 atm. Zheng and Furimsky [14] considered that the SOx emissions are governed by O2 concentration in O2 + CO2 mixture. Pak et al. [15], Li et al. [16] and Salkuyeh and Mofarahi [17] studied the CO2 emission, capture and storage for the oxy-fuel combustion.
The combustion characteristics and emission characteristics of pulverized coal in O2/CO2 atmosphere have been studied by many researchers. However, few studies refer to the amounts and components of flue gas for the oxy-fuel combustion in a CFPP. The differences between air and O2/CO2 atmospheres in a CFPP are also needed to be identified. The purpose of this article is to analyze the components of flue gas in a 300 MW CFPP under the atmospheres of air and O2/CO2 mixture, in which Aspen Plus software is used to simulate the process.
Section snippets
Process description
The process of coal combustion to be modeled is based on the following assumptions: (1) the combustion process is divided into four sequential steps: pulverized coal drying, pyrolysis, burning and flue gas dust removal; (2) all the blocks are in stable operation states, the parameters could not be changed with time; (3) air and pulverized coal are homogeneously mixed in the reactor; (4) in the process of coal pyrolysis, elements of O, H, N and S are vapourised into gas phase, and C element is
Results and discussion
The simulation results are presented in Table 3. The major component of flue gas is CO2 with the highest mass fraction of 94.4% which occurs in stream GASES. In the final outlet of flue gas, the mass fraction of CO2 is 81.5%, H2O and O2 are 14.9% and 2.2%, respectively. Other gas contents in the flue gas are quite low. Due to the high concentration of CO2 content, the flue gas can be compressed directly to realize near zero emission of CO2 to the atmosphere.
Conclusions
The oxy-fuel combustion process in a 300 MW CFPP unit is simulated by the software Aspen Plus, according to the calculation and analysis results, the conclusions are as follows:
- (1)
Compared with combustion in the air, the flame temperature under 21%O2/79%CO2 atmosphere decreases by 394 °C, and the mass flow rate of flue gas produced reduces to 1/4 of that in the air. When the molar fraction of O2 increases to 30%, the flame temperature is similar with air atmosphere.
- (2)
The generation of NOx is
Acknowledgements
The authors gratefully acknowledge financial supports from the National Natural Science Foundation of China (NSFC, 51176009) and the Fundamental Research Funds for the Central Universities (2013YJS078, 2013YJS069) for this work.
References (22)
- et al.
Oxy-fuel combustion technology for coal-fired power generation
Progr Energy Combust Sci
(2005) - et al.
The characteristics of pulverized coal combustion in O2/CO2 mixtures for CO2 recovery
Energy Convers Manage
(1995) - et al.
Effect of carbon dioxide on flame propagation of pulverized coal clouds in O2/CO2 combustion
Fuel
(2007) - et al.
NOx reduction mechanism in coal combustion with recycled CO2
Energy
(1997) - et al.
Trial design for a CO2 recovery power plant by burning pulverized coal in O2/CO2
Energy Convers Manage
(1997) - et al.
CO2, NOx and SO2 emissions from the combustion of coal with high oxygen concentration gases
Fuel
(2000) - et al.
NOx and SO2 emissions from O2/CO2 recycle coal combustion
Fuel
(2001) - et al.
Comparison of pulverized coal combustion in air and in mixtures of O2/CO2
Fuel
(2005) - IEA. CO2 emissions from fuel combustion. International Energy Agency;...
- et al.
Research progress of oxy-fuel combustion for coal-fired utility boilers
Boiler Technol
(2012)
A review of recent developments in carbon capture utilizing oxy-fuel combustion in conventional and ion transport membrane systems
Int J Energy Res
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