(192g) Experimental Study of so2 Emissions and Desulfurization of Oxy-Coal Combustion in a Pressurized Fluidized Bed Combustor

Experimental
study of SO₂ emissions and desulfurization of oxy-coal combustion in
a 30 kW_th pressurized fluidized bed
combustor

Lei Pang¹, Yingjuan Shao^1,*, Wenqi
Zhong[1]

1.      Key
Laboratory of Energy Thermal Conversion and Control of Ministry of Education,
School of Energy and Environment, Southeast University, Nanjing 210096, P.R.
China

Oxy-fuel
combustion has been widely accepted as a highly-effective CO₂ capture and storage (CCS)
technology. A combination of this technology and fluidized bed combustion
technology, i.e., oxy-fuel-based fluidized bed combustion, had attracted
attention from researches during last decade due to its advantages in terms of
fuel flexibility, furnace desulfurization and low NO_x emission. Among
these studies of oxy-fuel combustion, SO₂ emission is a major
concern because it leads to not only the corrosion of the tube and device but
also acid rain. In addition, the high SO₂ concentration in flue gas also
has negative impacts on CO₂ compression and purification. Although oxy-fuel
combustion has shown advantages and potentials in both combustion and CO₂
capture processes, the biggest obstacle to its application is the net
efficiency loss associated with the cost of the air separation unit (ASU) and
compression purification unit (CPU). It is estimated that the net efficiency
can be reduced by more than 10% when a conventional air-fired coal power plant
is converted to oxy-firing. In order to improve the efficiency, the pressurized
oxy-fuel combustion (POFC) technology has been proposed, and many economic
system analyses have proved that an increase in combustion pressure can bring
economic benefits as it is helpful to recover more thermal energy from the flue
gas and reduce the energy cost of CO₂ compression work. However,
there are few experimental researches about POFC technology, and studies of SO₂
emissions and desulfurization under POFC conditions are even less.

This study presents the SO₂
emission behaviors under both air and oxy-coal combustion in a 30 kW_th fluidized bed combustor with different
pressures, and the effects of combustion atmosphere, pressure and temperature
on the desulfurization of limestones were investigated carefully. The results
showed that the SO₂ emission in air was 15-20% less than that in
oxy-30 atmosphere as more sulfur sunk in ashes, while the increase of
combustion pressure from 0.1 MPa to 0.4 MPa had no effect on SO₂
emissions. Combustion temperature can affect the desulfurization of limestones
in both atmospheric and pressurized oxy-coal combustion conditions
significantly, and the desulfurization efficiency increased by more than 30%
when the bed temperature increased from 850 ^oC
to about 950 ^oC. Although the indirect
desulfurization of limestones cannot occur under 0.4 MPa and oxy-30 combustion
condition with a bed temperature of 950 ^oC,
its desulfurization efficiency reached about 80% which was close to the value
of conventional atmospheric air combustion.

Figure 1. Schematic of the
pressurized oxy-coal fluidized bed combustion system

Figure 2. Temperature profiles and
gas concentrations at the outlet of the combustor without limestone

Figure 3. Thermodynamic
equilibrium curve of CaCO₃ calcination

Figure 4. Effect
of temperature on desulphurization efficiency