# Feasibility Study of Using Carbide Slag as In-Bed Desulfurizer in Circulating Fluidized Bed Boiler
## 2 Experimental Design
### Brief Introduction of 1 MW\({}_{\text{th}}\) Pilot Boiler and 690 t-h\({}^{-1}\) CFB Boiler  
In order to better study the feasibility of using carbide slag as the alternative desulfurizer in a CFB furnace, experiments were carried out on a 1 MW\({}_{\text{th}}\) pilot-scale boiler and a 690 t-h\({}^{-1}\) industrial boiler, respectively. The influence of different operating parameters, including bed temperature, types of desulfurizer, Ca/S mole ratio of limestone, and carbide slag on the desulfurization reactions in furnace are discussed in detail.  
The schematic diagram of a 1 MW\({}_{\text{th}}\) pilot CFB boiler is shown as Figure 2. The height of the furnace was 23 m, which was close to the typical height of the industrial CFB furnaces, ensuring the sufficient burn-out time of fuel particles. The cross-section of the air distributor was 0.175 m \(\times\) 0.351 m, whereas the cross size of dilute phase zone was 0.351 m \(\times\) 0.351 m. There were some groups of additional water-cooled tubes on the top of the dilute phase zone. The temperature of each zone in the furnace could be effectively controlled by adjusting the flow rate of cooling water in heating surfaces. A total of 43 thermocouples and 32 pressure or differential pressure measuring points were arranged in the system to monitor its operating conditions.  
In this experiment, the flue gas sampling point was arranged at the outlet of the cyclone. A PMA-10 oxygen sensor (M&C GmbH, Germany) was used to monitor the O\({}_{2}\) concentration in the flue gas, with a resolution of 0.05%. The Rosemount(tm) NGA 2000 gas analyzer (Emerson Electric Co, USA), which has a good resolution (\(\sim\)1 ppm) for the target gases, was used for the measurements of CO, NO, and SO\({}_{2}\).  
The industrial-scale tests were carried out on a 690 t-h\({}^{-1}\) CFB boiler, whose structure is shown in Figure 3, to verify whether the conclusions obtained from the pilot bench could be applied to larger industrial boilers. This boiler was manufactured by Shanghai Boiler Works, Ltd. The outlet pressure of superheat steam was 13.73 MPa, whereas the outlet temperatures of superheat and reheat steams were all 540 \({}^{\circ}\)C. Three cyclones were used in the boiler, and the furnace size was 37.5 m \(\times\) 22.74 m \(\times\) 7.845 m. The fluidization velocity was around 5 m-s\({}^{-1}\) under the boiler maximum continuous rating (BMCR) condition and the ratio of primary to secondary air was about 6:4.  
Figure 1: Particle size distribution (PSD) of limestone and carbide slag.  
Figure 2: Schematic diagram of 1 MW\({}_{\text{th}}\) pilot CFB boiler system. 1. Feed water pump, 2. cooling water tank, 3. fuel crusher, 4. screw conveyor, 5. coal silo, 6. limestone silo, 7. motor hoist, 8. blowing cooling tower, 9. cooling water tank at high level, 10. cyclone, 11. furnace, 12. water cooling surface, 13. air heater, 14. first economizer, 15. second economizer, 16. dust collector I, 17. dust collector II, 18. chimney, 19. U-type loop seal, 20. starting burner, 21. circulating ash pipe, 22. bottom ash discharge pipe, 23. windbox, 24. air blower, 25. roots blower, and 26. induced draft fan.