Characteristics of particle emissions and their atmospheric dilution during co-combustion of coal and wood pellets in a large combined heat and power plant

Figures & data

Table 1. Properties of coal and industrial pellets (Mylläri et al. 2017).

Properties	Unit	Industrial pellet	Coal
Moisture	%	6.7	11.0–11.3
Ash	%	0.8	10.5–11.4
Volatiles	%	78.1	32.8–33.1
Heating value	GJ/t	17.7	24.6–24.9
C	%	47.4	62.3–63.1
H	%	5.6	4.1–4.2
N	%	0.1	1.8–2
O	%	39.4	0
S	mg/kg dry	180	3100–4600
Cl	mg/kg dry	39	236
Ca	mg/kg dry	2300	4300–4800
Mg	mg/kg dry	280	1700–1900
Na	mg/kg dry	69	1400–1600
K	mg/kg dry	760	2500–2900
Fe	mg/kg dry	140	4800–5700
Al	mg/kg dry	130	14,200–15,000
Ti	mg/kg dry	8.8	600–640
Ba	mg/kg dry	26	270–280
B	mg/kg dry	<40	210–230
Ag	mg/kg dry	<0.5	<0.5
As	mg/kg dry	<0.5	4.9–14
Be	mg/kg dry	<0.5	<0.5
Bi	mg/kg dry	<0.7	<0.7
Cd	mg/kg dry	0.2	0.1
Co	mg/kg dry	<0.5	1.4–2.1
Cr	mg/kg dry	1.2	9.7–11
Cu	mg/kg dry	1.6	7.8–8.5
Li	mg/kg dry	<0.5	9.3–10
Mn	mg/kg dry	140	38–66
Mo	mg/kg dry	<0.5	1.1–1.3
Ni	mg/kg dry	<0.5	4.1–6.6
Pb	mg/kg dry	<0.5	3.4–4.1
Rb	mg/kg dry	2.5	5.2–9.0
Sb	mg/kg dry	<0.5	<0.5
Se	mg/kg dry	<0.7	<0.7–1.1
Sr	mg/kg dry	5.5	150–170
Th	mg/kg dry	<0.5	1.2–1.3
Tl	mg/kg dry	<0.5	<0.5
U	mg/kg dry	<0.5	<0.5–0.6
V	mg/kg dry	<0.5	13–15
Zn	mg/kg dry	30	11–18

Figure 1. (a) Measurement setup used in stack measurements. (b) Measurement setup installed in the helicopter.

Table 2. Flue-gas concentrations of CO₂, SO₂, NO_x, O₂, and CO, total particle number (N_{tot, >2.5 nm}), dust, flue-gas flow rate, and temperature in the stack during the measurements. Mean values (± standard deviation) are presented for both flue-gas cleaning situations (“FGD+FF off” and “FGD+FF on”) for coal + 10.5% industrial pellets. Emission factors for BC_PM1 (EF_BC, ng MJ⁻¹) and emission factors for particle number and mass (MJ⁻¹ and μg MJ⁻¹) are shown for the co-combustion situation and coal combustion situation. See Supplementary Table SI1 for CO₂, SO₂, NO_x, N_>2.5 nm, and dust concentrations in (mg Nm⁻³ or m⁻³) when reduced to 6% O_2.

	Coal + 10.5% pellets FGD+FF off	Coal + 10.5% pellets FGD+FF on
CO2 (%)	10.6 ± 0.13	10.3 ± 0.16
SO2 (ppb)	256,000 ± 61,400	59,900 ± 7200
NOx (ppm)	260 ± 8.1	260 ± 8.1
O2 (%)	5.9 ± 0.2	5.9 ± 0.12
CO (ppm)	33 ± 31	2.4 ± 8
N>2.5 nm (cm^−3)	(738 ± 70) × 10^3	354 ± 623
EFN>2.5 nm (1 MJ^−1)	4.4 × 10^11	1.7 × 10^8
Dust (mg Nm^−3)	110 ± 13	5 ± 2
EFPM (mg MJ^−1)	50	2
Temperature (°C)	129 ± 5	77 ± 7
Flow (Nm^3 hr^−1)	(461 ± 4.2) × 10^3	(457 ± 9.6) × 10^3
EFBC (880 nm) ng MJ^−1	11,470	14

Figure 2. (a) Particle number size distribution of solid particles measured at the stack in “FGD+FF on/off” situations with ELPI and SMPS. (b) Particle volume size distribution calculated from SMPS and ELPI results. (c, d) TEM images of particles collected on TEM grids in (c) “FGD+FF off” and (d) “FGD+FF on” situations. A mixture of industrial pellets and coal was used as a fuel in the experiment.

Figure 3. Concentration of CO₂ (black line, ppm, y-axis on the left), concentration of SO₂ (blue line, ppb, y-axis on the left), and ΔN_tot (red line, 1 cm⁻³, y-axis on the right) in flue-gas plume diluting in the atmosphere as a function of flue-gas plume age after the emission from stack. ΔN_tot is the particle number concentration in the flue-gas plume after subtracting the background particle number concentration from measured values. The gray vertical lines present the 2-km distance from the stack. A mixture of 10.5% industrial pellets and coal was used as a fuel in the experiment.

Figure 4. Median particle number size distribution measured from the atmosphere with a helicopter in “FGD+FF off/on” (upper/ lower) situations. The measurement data were classified to 5-sec time intervals based on the plume age. Measurements were made with EEPS. The mixture of industrial pellets and coal was used as a fuel during the experiment.

Mylläri, F., P. Karjalainen, R. Taipale, P. Aalto, A. Häyrinen, J. Rautiainen, L. Pirjola, R. Hillamo, J. Keskinen, and T. Rönkkö. 2017. Physical and chemical characteristics of flue-gas particles in a large pulverized fuel-fired power plant boiler during co-combustion of coal and wood pellets. Combust. Flame 176. doi:10.1016/j.combustflame.2016.10.027.

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