Stoichiometric and Temperature Effects on Boiler Corrosion from High Chlorine and High Alkali CoalsResearch Group : Shrinivas Lokare, David Dunaway, Douglas Rogers, Marc Anderson, Larry Baxter, Dale Tree, Brigham Young University, Provo, UT- 84602.

ACERC 17th Annual Conference

February 20-21, 2003

University of Utah

Salt Lake City, Utah

Research Background• Increased corrosion problems due to increased use

of low rank or moderate to high chlorine coals for low NOx emissions.

• Alkali chlorides have demonstrated significant potential for the corrosion of heat transfer surfaces under the operating temperature range (400-550 oC).

Project Objectives

• To examine the results of reducing and oxidizing combustion on the ash deposition and consequent corrosion.

• Based on experiments, investigate the mechanisms of chlorine condensation on heat transfer surfaces.

Experimental Set-up

Reactor design (Multi-fuel Flow Reactor)

Premixed fuel burner

1.93 m

Auxiliary methane

Sample location

Cooling water

Inside diameter = 12 cm

Probe Designs

12 cm

6 cm

Fixed sleeve

Thermocouple Movable sleeve

Cooling air

Cross flow type deposit collection probe

Gas flow

Cooling fluid IN

Cooling fluid OUT

Thermocouple placement

6.5”

5”

3/8” O.D.

Refractory wall

Refractory wallReactor axis

Parallel flow type deposit collection probe

CoalIllinois #6

(Wet)

Illinois #6

(Dry)

Black Thunder

(Wet)

Black Thund

er (Dry)

% Moisture 11.29 0 21.3 0

% Ash 6.26 7.06 5.08 6.46

% C 68.95 77.7 55.01 69.9

% H 4.14 4.68 3.97 5.05

% O 6.36 7.17 13.45 17.1

% N 1.41 1.59 0.74 0.94

% S 1.59 1.79 0.38 0.48

% Cl N/A 0.45 0.06 0.08

Fuel analysis

Fuel analyses were performed at Commercial Testing & Engineering Co., Denver, CO 80239.

Results and Discussion

Operating conditions

• Sampling section temperature - 1000 oC.

• Sampling period = 30 minutes to 5 hrs.

• Deposit collection probe surface temperature = 90 - 450 oC.

At the probe surface temperatures of 300-450 oC, the absence of alkali chlorides or alkali sulfates under respective stoichiometric conditions is attributed to the fraction of alkali in fuel ash available to form chlorides and the extent of evaporation of these chlorides under given operating conditions.

Reducing test - Illinois #6 coal - 30 minutes.

aluminum

Oxidizing test – Illinois # 6 – 30 minutes

Oxidizing test - Illinois #6 - 5 hrs

Reducing test - Illinois #6 – 30 minutes

The co-existence of sulfur and chlorine in longer tests on parallel flow probe supports the hypothesis that sulfate formation is heterogeneous reaction between gas phase sulfur (SO2, SO3 or H2S) with solid alkali chloride layer on the heat transfer surface.

Tprobe = 91 oC Tprobe = 240 oC Tprobe = 350 oC

The dew point of the chlorides, and hence the temperature for chloride condensation varies with amount of chlorine and available alkali.

The alkali chlorides condense on heat transfer surfaces under both oxidizing and reducing conditions, however, under oxidizing conditions for longer time periods, the heterogeneous reaction starts to form sulfates from alkali chlorides or alkali silicates on the surface. The temperature dependence of chloride condensation is controlled by an additional factor, the chloride content of the fuel. Further investigation is needed for determining the correlation between these.

Conclusions

Chlorine maps at three different probe surface temperatures

Acknowledgements – Arun Mehta, Wate Bakker, Tony Facchiano, Electric Power Research Institute, Palo Alto, California - 94304