Mercury Emissions during Fluidised Bed Combustion of different fuels

Transcription

1 Mercury Emissions during Fluidised Bed Combustion of different fuels D.Boavida, P.Abelha, T.Diall, H.Lopes & I.Gulyurtlu 43 rd IEA FBC Meeting Lisbon 22 nd November 2001

2 Abstract The aim of this work was to study the mercury emissions during the combustion of coals and the cocombustion of coals and waste materials. The effect of the sulphur content and temperature on the speciation of mercury was studied.

3 Introduction Mercury can be introduced into the combustion environment in many physical and chemical forms. The subsequent transformation and vaporisation depend on: the combustion environment the presence of chlorine and other species (reducing or oxidising) the nature of the species formed the presence of other species (activated carbon)

4 Introduction The mercury vapour cloud may pass through its dew point to form tiny nuclei or condense around existing particles. The mercury vapour cloud may be react chemically at or within the existing particles (Adsorption). The speciation of mercury in coal combustion and co-combustion with wastes flue gas is especially important for devising control strategies

5 Fuels Proximate analysis Colombian Coal South African Coal US Coal PPRF Sewage Sludge Moisture (a.r., Wt%) Ash, (d.b., Wt%) Volatile matter, (d.b., Wt%) Fixed carbon, (d.b., Wt%) Gross Calorific Value, (MJ/kg) Elemental analysis (d.b., Wt%) C H N S Cl O

6 Mercury content Mercury analysis Colombian Coal South African Coal US Coal PPRF Sewage Sludge Hg (mg/kg)

7 Experimental Apparatus HEAT EXCHANGER FUEL FEED ING UN DER GRAVITY 300 HEAT EXCHANGER POINT S OF INTRODUCTION OF STAGED AIR FUEL FEED ING UND ER GRAVITY POINT S OF INTRODUCTION OF STAGED AIR REC YCLING CYC LONE Air feeding system: 1º air - 2 ventilators 2º air - compressor Combustible feed system: screw feeder 1000 ASH REMOVAL AIR PNEUMATIC TRANSPORT OF FUEL RECIRC ULATION OF PARTICLES Bed temperature: cooling surfaces

8 Experimental Apparatus HEAT EXCHANGER FUEL FEED ING UN DER GRAVITY 300 HEAT EXCHANGER POINT S OF INTRODUCTION OF STAGED AIR FUEL FEED ING UND ER GRAVITY POINT S OF INTRODUCTION OF STAGED AIR REC YCLING CYC LONE Temperature monitoring: 19 thermocouples 10 type K 9 type T Pressure monitoring: 1000 AIR PNEUMATIC TRANSPORT OF FUEL RECIRC ULATION OF PARTICLES 20 points - water column ASH REMOVAL

9 Experimental Apparatus Gas sampling: HEAT EXCHANGER REC YCLING CYC LONE 3 lines in reactor body: 0.5m, 1.60m and 4.90m FUEL FEED ING UN DER GRAVITY HEAT EXCHANGER 300 POINT S OF INTRODUCTION OF STAGED AIR FUEL FEED ING UND ER GRAVITY POINT S OF INTRODUCTION OF STAGED AIR Species measured: 1 heated line at exit of the second cyclone 1000 AIR PNEUMATIC TRANSPORT OF FUEL RECIRC ULATION OF PARTICLES O 2, CO 2, CO, N 2 O, NO X and SO 2 ASH REMOVAL

10 Experimental 50%SS+ 35%SS + 40%PPRF + 100%SS 100%SS 50%C Coal100%C Coal100% US Coa 65%US Coal 100% SA Coal 60%SA Coal I II III IV V VI VII VIII Fuel Rate (kg/h) Air 2nd/1st Sand (Kg) Temperatures (ºC) Bed Temperature - 50 mm T exit 1st Cyclone T exit 2nd Cyclone Emissions O2 (%) CO2 (%) CO (ppm_6%o2) NOx(ppm_6%O2) SO2 (ppm_6%o2)

11 Sampling Train Set-up Nozzle Pilot Glass Probe Liner Thermometer Heated Area Glass Filter Holder Thermometer Check Valve Manometer Bath Silica Gel Orifice Bypass Valve Vacuum Gauge KCI HNO 3/H 2O 2 H 2 SO 4/KMnO 4 Main Valve Vacuum Line Dry Gas Meter Air Tight Pump

12 LECO Hg analyser No requirements for sample pretreatment Results are matrix independent Typical results in five minutes Liquid and solid samples PC control The AMA-254 Advanced Mercury Analyser is fully compliant with EPA Method 7473 (Mercury in Solids and Solutions by Thermal Decomposition, Amalgamation, and Atomic Absorption Spectrophotometry).

13 Concentration of Hg in the Ashes 100% 80% 60% 2nd Cyclone 1st Cyclone Bed 40% 20% 0% 100% SS - I 100% SS - II 50% SS + 50% C Coal 100% C Coal 100% US Coal 65%US Coal + 35% SS 100% SA Coal 60% SA Coal + 40% PPRF

14 Stack Hg Emissions µg/nm3 (11%O2) 60% SA Coal + 40% PPRF 100% SA Coal 65%US Coal + 35% SS [Cl]=60mg/ Nm3 [Cl]=49mg/ Nm3 [Cl]=30mg/ Nm3 100% US Coal [Cl]=35 mg/nm3 100% C Coal [Cl]=26,1 mg/nm3 [Cl]=94,0 mg/nm3 50% SS + 50% C Coal 100% SS - II 100% SS - I [Cl]=187,8 mg/nm

15 100% Distribution of Hg Species in Flue Gases 90% 80% 70% 60% 50% 40% Hg (part) Hg (II) Hg (o) 30% 20% 10% 0% 100%SS - I 100%SS - I I 100% C coal 50%SS+ 50% C coal 35%SS + 65%US coal

16 Conclusions From the mercury found in ashes, almost none was found in bed ashes due to its high temperature. Most of the Hg is capture in the 2nd cyclone.

17 Conclusions When a high sulphur content coal was added at relatively lower temperature more than 80% of the Hg in the flue gases was found in the particles. This could be a result of the reaction of SO 2 to H 2 SO 2 in the particles that reacts with elemental Hg and the condensation at lower temperatures.

18 Mercury Emissions during Fluidised Bed Combustion of different fuels D.Boavida, P.Abelha, T.Diall, H.Lopes & I.Gulyurtlu 43 rd IEA FBC Meeting Lisbon 22 nd November 2001